The Need for an In-Line Oil-In-Water Monitor

A.W. Jamieson
Shell U.K. Exploration and Production, Aberdeen

Summary

In-line oil-in-water monitors have long been wanted for monitoring overboard discharges from oil and gas producing facilities, or for controlling water handling systems. In general their performance has fallen far below operational requirements. New techniques and steadily increasing demands for better measurement capabilities mean that systems are becoming available with the potential to give good performance. A review is given of oil-in-water measurement in Shell, application areas, and the difficulties in implementing the technology.

1. Introduction

As part of the production of oil and gas, large quantities of water are also produced. Whether on land or at sea, it is generally accepted that produced water should be processed sufficiently that the quantities and concentrations of potentially harmful components are reduced to levels that are known or are deemed to be harmless to the environment in which the water is discharged. In the North Sea, the current protocol limits the content of discharged water to 40 parts per million (ppm) averaged over a calendar month. Over the years the relative quantity of water has increased as oil fields have watered out. North Sea water production is approaching one hundred million tonnes per annum, and consequently the current legislation permits some four thousand tonnes of oil per annum to be discharged from oil production facilities. This situation is replicated in most offshore facilities world wide. It is generally accepted that discharge of too much oil represents a global threat to sensitive marine environments, but there is not a clear consensus on what is "too much". Around the world, environmental and legislative bodies are trying to establish meaningful limits.

The situation is further complicated by the difficulty of measuring oil-in-water to part-per-million levels on continuously operating facilities in a hostile environment, where it is considered essential to keep operational costs, and hence manning levels, to a minimum.

What is "oil" in this context? Is it dissolved or dispersed? Are there particles coated with oil present? The current methods for detection and measurement of oil-in-water, namely chemical analysis of intermittent samples, or monitoring bypass sample lines by a variety of optical techniques such as fluorescence, absorption or scattering, respond in significantly different ways. Tests have shown that no single instrument gives a satisfactory solution for dealing with water disposal from current facilities.

Future facilities in the North Sea may require disposal of water from unmanned facilities, subsea facilities or even downhole. Oil-in-water measurement systems will have to operate at high temperature and pressure, and for other reasons than pollution monitoring. Active control of de-oiling systems is a clear example where there is no suitable instrumentation at present.

In this paper I attempt to set oil-in-water measurement in the general context of the measurements required for oil and gas production systems. I give a review of oil-in-water measurement as I have seen it over the last twenty years. I then discuss the needs for-oil-in water measurement, the variety of applications and the difficulties of implementing satisfactory solutions. I conclude by attempting to give an outlook for oil-in-water measurement.

2. Oil-In-Water as a Multiphase Fluid

Oil-in-water measurement is but one of the many measurements required in oil and gas production. Traditionally these measurements have been treated separately, and mostly without regard to the interactions with other parts of the production process. The development of multiphase technologies to transport and meter unseparated hydrocarbon streams allows and indeed forces one to take a more integrated view of the whole production process.

Figure 1: Multiphase Composition Triangle

The 'Multiphase Composition Triangle' shown in Figure 1 can be used to indicate conditions under which any measurement in the oil and gas production processes is made. We find single phase oil, water and gas at the vertices of the triangle; two phase fluids, oil/gas, water/gas and oil/water along the sides of the triangle; and the vast range of three phase fluids occupy the interior of the triangle. I have also shown a transition region, where the liquid part of the multiphase mixture may be either water-in-oil or oil-in-water, making measurements difficult for instruments using electrical properties of the fluid.

It is now easy to see that any oil and gas production process takes a particular multiphase mixture and performs a sufficiently good separation into marketable oil and gas streams and a waste water stream. How well these streams approximate to single phase flow depends on the process and how it reflects the specification of the oil and gas in the supply contracts and the environmental constraints for the waste water stream.

If we now focus on the waste water stream, we can immediately see that oil in water monitors may be required to control the water handling process as well as monitor the quality of the final discharge stream. Thus the Multiphase Composition Triangle is also useful in indicating where we have inadequate measurements and where we should direct our attention in developing new instruments.

3. Oil-In-Water Measurement Over the Last 20 Years

I have been associated directly and indirectly with oil-in-water measurement since the late 1970s and I thought it was worth giving my view of how oil-in-water measurement has changed over that time. This is not an exhaustive review of oil-in-water measurement, but simply a personal account of how and where I have been involved. Others may then be able to set that experience alongside their own, and hopefully may be able to take a better approach, or at least avoid repeating unsuccessful approaches.

In the late 1970s it was recognised that continuous monitoring of oil in water was desirable, but colleagues working with fluorescence based instruments could not get acceptable performance. Most of Shell Expro's offshore platforms had concrete storage bases, where most of the oil and water separation took place. With long residence times it was not difficult to achieve good water quality, and twice daily manual determination of oil content was adequate.

I spent most of the 1980's in the Production Measurements group at KSEPL, the then Shell E&P laboratory in Holland. We worked extensively on oil-in-water measurement for applications throughout the Shell Group, both onshore and offshore. We examined a wide range of equipment, for example automated chemical extraction and IR absorption systems, an Attenuated Total Reflection (ATR) system, various optical scattering systems, and particle counting systems. Of these, the automated chemical extraction system and the scattering systems worked best, but none of the systems was suitable for long-term unattended low-maintenance operation.

Interest in oil-in-water measurement waxes and wanes; new legislation in one part of the world results in demands for better equipment; lower oil prices tends to lead to delays in development or implementation. Without the stimulus of specific application needs and constraints it is difficult to provide practical equipment for field use.

Towards the end of the 1980s Expro wanted to develop the Eider platform as an unmanned satellite of North Cormorant, but were required to monitor continuously the oil content of the overboard water discharge, as twice-daily manual measurements were clearly impractical. A fluorescence based system operating on a bypass stream was considered best bet, but after very extensive evaluation it became clear that although it might make a reasonable thermometer, it could not even approach the target specification for oil-in-water measurement. We considered ways of automating sample collection as a possible approach to Eider's needs, but when it became clear that it was impractical to operate Eider as a completely unmanned facility the immediate need for a continuous monitor faded.

In 1990 the OWTC (Orkney Water Test Centre) carried out extensive tests of commercial oil in water monitors. The best performing systems were based on scattering, but after a detailed evaluation of the results KSEPL concluded that they could only be used reliably on unattended facilities as a coarse alarm at about 300 ppm. Interest at KSEPL then focused on improving scattering and IR transmission/absorption systems to the extent that they would be suitable for Shell requirements. A commercially available instrument has come out of that work, but it utilises a bypass sampling loop and cannot perform well at high temperatures.

In 1990 I was back in Expro and became aware of work being done by Heriot Watt University to develop photoacoustic instrumentation. In this approach pulsed focused infra red light is directed at a substance. The illuminated substance absorbs the radiation, heats up, expands and generates a pressure wave which is detected as an ultrasonic pulse. Water has a low photoacoustic response whereas oil has a large photoacoustic response. The immediately attractive features of this approach were that it would be possible to get a reasonably straightforward measurement from a sensor mounted directly in the discharge line, eliminating hard-to-maintain sampling systems. In addition, the response of the system should be sufficiently different to dissolved and dispersed oil to allow them to be satisfactorily discriminated.

Development of the photoacoustic system has proceeded to the point where Expro is ready to evaluate the system in the field. In 1996 there was pressure on several of our facilities to improve the quality of their overboard discharges. My advice was that the scattering systems that came out best in the 1990 OWTC tests and the fluorescence based system that performed well in subsequent OWTC tests would prove to be too difficult to keep working to specification, and that we should try to accelerate the development of the photoacoustic system. While the advice on the scattering and fluorescence systems has proved correct, the accelerated development of the photoacoustic system has not been without problems. It is fair to say that the measurement principle has been thoroughly verified - in the laboratory from 3 ppm to over 2% oil-in-water; at the OWTC in the environmental range of concentrations; and in simulated field conditions up to several thousand ppm. Nonetheless, there is not yet an ex-certifiable sensor with sufficient sensitivity that can be deployed offshore, nor have two sensors been made with closely similar performance. There is however good reason to believe that these difficulties can be resolved.

4. The Needs

Why do we really need oil-in-water monitors? The answer from a responsible oil and gas operator and from a responsible government is that too much oil released into sensitive marine environments will result in significant, even irreparable damage. But there is a major difficulty in knowing what is "too much", or indeed which components of the oil cause most damage.

How much do we really want oil-in-water monitors? If we have steady production and good separation capability, then manual measurements twice a day are easily good enough to keep track of things. But if, as has happened, the freons used in the manual extraction measurement are banned, and the replacements are more toxic, what then? If production is not steady and it has become necessary to have an operator take many more manual samples to get a better idea of what is happening in the process, then there is much more interest in a continuous monitor.

How much hassle are we prepared to accept from a continuous monitor? The answer to that one is fairly easy - not a lot. If a continuous oil-in-water monitor cannot give reasonably accurate, highly repeatable measurements of what is deemed to be oil (dispersed and/or dissolved) and at the same time be highly immune to contamination, suspended particles gas bubbles etc, we are unlikely to be interested in installing it.

As someone who has tried to stimulate development of continuous oil in water monitoring systems through several cycles of interest and lack of interest, the main requirements have emerged as follows.

• The measurement should be based on sound physical principles.
• It should be possible to make the measurement directly in the discharge, as we have had most problems with the sampling parts of oil-in-water measurement systems.
• Any surfaces involved in the measurement process should not be subject to contamination, or the measurement should not be affected by such contamination.
• It should be possible to operate at high temperatures. As our fields produce more water, the discharge water temperature has risen, and is about 100°C in one case.
• It should in principle be able to work at pressures above atmospheric.
• For environmental measurements, the system should be able to measure in the range 0 - 100 ppm with a relative accuracy of 10% and a resolution of 4 ppm. It should be able to discriminate between dissolved and dispersed oil.
• The technique should be capable of further development. Too many of the oil-in-water systems commercially available have already reached their technical limits.

I believe that a system that can comply with the above should be compatible with any reasonable standard that is likely to be adopted for oil-in-water measurement, and may even be a de facto standard itself. I further believe that in the photoacoustic approach that there is at least one approach with a good chance of satisfying the above criteria.

5. The Applications

In line with what I have said above, the safest approach, and I think the best one, is to treat each application on its own merits. The simplest applications are for fields where the oil comes from one reservoir, temperatures are modest, and the produced water has no peculiar properties. Several on-line systems may give reasonable performance in these circumstances. Let us complicate matters a little, and introduce a second reservoir. The oils are different. Scattering, fluorescence and photoacoustic systems all respond differently to different oils. Indeed, how well does the standard extraction method cope with different oils? How does one calibrate the system to read accurately when only one of the reservoirs is producing? The produced waters are different. Does scale form, resulting in particles (or worse) that affect the measurement? What does one do on a facility where there are multiple tie backs, when one can expect that there will be significant differences between the fluids?

Let us consider the produced water from gas fields and gas condensate fields, where there tend to be higher concentrations of aromatic compounds dissolved in the water. Many on-line systems do not respond to dissolved oil. The photoacoustic system responds strongly to the anthracenes present in crude oil. These anthracenes are absent in condensates, so the photoacoustic system will have to look for other components if it is to be used successfully for condensate in water.

Let us complicate things still further. We want to operate subsea or even downhole, and do all the above remotely at high temperature and pressure.

We would like to be able to control water handling processes better, for example hydrocyclones or tank drainage, so we must have oil-in-water monitors that can operate up to say, 5000 ppm oil-in-water reliably. A notoriously difficult problem is to measure the few percent of oil in wells at the ends of their lives. A direct measurement of oil-in-water up to say 5% would be valuable for optimising production from old fields. I would argue that the oil industry should be far keener to develop instrumentation for these applications as these can really save money. Oil-in-water monitors at the discharge point can only tell you to shut down your facilities if you exceed the permitted limits: oil-in-water monitors at critical points in the process can prevent the excess discharges happening.

I have not attempted to give a classification of types of applications, but have rather tried to show where we can use high performance in-line oil in water monitors to improve our production operations. I believe that it is now possible to develop such equipment.

6. Implementation - The Difficulties

It has been my experience that implementing new measurement techniques successfully in the oil and gas industry is in practice fraught with difficulty. Let us assume that the early hurdles of turning a good idea into a working prototype instrument have been successfully overcome. Several years will have passed, and perhaps some £250,000 in total will have been invested. Let us further assume that there has been at least active interest by an oil company and an equipment manufacturer so that the prototype equipment is compatible with oilfield installation requirements. Nevertheless, a field evaluation of a new instrument will probably cost more than the whole development to date, and may take over a year to organise.

In my experience if a field evaluation is to give useful data the, the staff on the installation on which the evaluation is to be carried out must be able to see direct benefit to them if the evaluation is successful. In these days of minimal manning, if there is no direct benefit to the people who have to support the evaluation, they are unlikely to devote adequate time, especially when things go wrong. A further consequence of minimal manning is that for field evaluations today, it is almost essential to provide means of getting the data onshore so that the evaluation can be monitored remotely.

After satisfactory field evaluation, one is then faced by the difficulties of turning working prototypes into fully commercial instruments. In the case of oil-in-water monitors, one really requires considerable feed back from instruments operating in the field to confirm that the instrument performs correctly. Conditions in the field are quite different to those one can simulate in a test loop. It is often stated that operating platforms are not places on which to conduct R&D projects. Nevertheless, if one wants to gain the benefits that better measurements can undoubtedly bring, one cannot exclude operating facilities from the R&D process.

In saying the above, I am not making excuses for why we do not yet have satisfactory oil-in-water measurement systems, but I am trying to point out that many groups of people, academics, industrial researchers, government departments for environmental matters and also those for stimulating development, manufacturers, engineers and operators in oil companies and their contractors must somehow form an extended team for about ten years if a successful conclusion is to be reached. In my experience, such teams are not put together. They simply happen because those who decide to be members recognise that they need to be involved. I continue to be surprised at how effective such extended teams can be at getting things done while they can work together. It is at the implementation stage, when large amounts of money must be spent, that these extended teams are most likely to break up. If there is no longer a clear need expressed by a keen prospective user and that user's active involvement, there is virtually no incentive to continue. Development languishes until another potential user expresses enthusiasm, and all one can do is hope that earlier work has not been wasted.

7. The Outlook

Oil and gas producing companies have wanted cost effective continuous oil-in-water monitors for many years in order to have good knowledge of the quality of their produced water discharges. The systems available to date have not shown good performance, and require intensive maintenance. Most systems are operating close to their technical limits so it is very unlikely that they can be improved sufficiently even if large sums of money were spent in further development.

In recent years the photoacoustic approach appears not only to have the potential for measuring accurately in the environmental range, say 0 - 100 ppm, but also up to several percent, so that that approach could be used for control of compact water treatment systems, or even for monitoring the oil content of high watercut oil streams, potentially allowing better optimisation of production facilities at the end of their lives. This particular technology is in its infancy, but, in my opinion, can already outperform most other oil-in-water systems from a measurement point of view. However, there is a long way to go before there will be assured operational performance.

In the North Sea of the relatively near future there will be many different types of facilities; the early large fixed platforms, minimum topsides facilities, floating production systems, subsea production systems and even complete downhole separation facilities. These will require a wide range of oil-in-water measuring devices to cope with the very different installation requirements and the different physical and chemical properties of the produced water. For example, subsea and downhole systems will probably have to contend with high pressures and temperatures.

I think that there is a large potential market for cost effective oil-in-water measurement systems, with several on each facility for monitoring and control applications. This worldwide market is far bigger than can be serviced by one manufacturer, or indeed one measurement technique. However, for this market to develop there needs to be consistent confirmation from users and society as a whole that increased use of better monitors brings worthwhile benefits.

Comparing oil-in-water measurement Varying government regulations and measurement methods call for standardization Colin C. Tyrie, and Dan D. Caudle - There are several instrumental methods for measuring oil in produced water. None of them measure all the organic compounds in the water. Comparing what the commercially available methods actually measure will illustrate the problem of interpreting oil in water (OIW) analysis. From worldoil.

Humidity Sensors for Industrial Applications

It could be argued that humidity plays a part in every industrial production process. The very fact that our own atmosphere contains water vapour bears witness to this fact even if it is only that the end product is likely to be stored and eventually used in our environment; therefore, the product’s potential performance under varying conditions of humidity must be known. The extent to which humidity plays a part in any given production process may vary but in many cases it is essential that, at the very least, it is monitored and, in most cases, controlled. It may also be said that humidity is a more difficult property to define and measure than associated parameters such as temperature and pressure. Indeed, it is a truly analytical measurement in which the sensor must contact the process environment, in contrast to pressure and temperature sensors, which are invariably insulated from the process by a thermowell and a diaphragm respectively. This of course has implications for contamination and degradation of the sensor to varying degrees depending on the nature of the environment.

This paper reviews various humidity sensor technologies and their typical applications in context of the measurement ranges to which they are best suited. The effects of contamination, highly significant in view of the analytical nature of the measurement, are briefly assessed. In conclusion, it is suggested that, if initial cost is not the prime consideration, the chilled mirror, optical dew point hygrometer offer the most accurate, repeatable and reliable method of humidity measurement with the widest possible range.

Humidity Measurement Applications in a Range of Industries

Table 1 shows an A to Z of industries where humidity measurement plays a part. Whilst the list is by no means exhaustive, it does serve to illustrate the extremely wide range of applications with which a supplier of humidity instrumentation may be confronted. Indeed, these applications cover six orders of magnitude when considered in terms of Parts Per Million (PPM) by volume of water vapour, equivalent to an overall range of -85 to +100°C dew point. It is of course very unlikely that one measurement technique can cover the entire range but, if initial cost is not the prime consideration, the chilled mirror, optical dew point hygrometer can probably be said to come closest to achieving this.

In practice, a variety of commercial and technical criteria will dictate which measurement technology is used for any particular application. Table 2 shows the most common humidity measurement parameters used within the industries referenced, depending on application, and Table 3 illustrates how certain sensor technologies are associated with specific industries as dictated by the commercial pressures and technical demands of the measurement. These aspects are themselves invariably influenced by the criticality of the measurement.

Two important points to note are that different units are used for different parts of the measurement range and that the measurement units an industry uses are very often a good indicator as to the type of sensor technology they should be employing. Humidity measurement determines the amount of water vapour present in a gas. This gas can be a mixture, such as air, or it can be a pure gas, such as nitrogen or argon. While there are many measurement techniques, the most common parameters are Relative Humidity (RH), Dew/Frostpoint (D/F PT) and Parts Per Million (PPM).

Relative Humidity Measurement (RH)

An RH measurement is the ratio of the partial pressure of water vapour present in the gas to the saturation vapour pressure of the gas at a given temperature. Thus, RH is a function of temperature. The measurement is expressed as a percentage.

The human body is sensitive to, and can experience varying RH in terms of the contrast between a dry and a muggy Summer day.

Dew/Frost Point Measurements (D/F PT)

Dewpoint is the temperature (above 0°C) at which the water vapour in a gas condenses to liquid water. Frost point is the temperature (below 0°C) at which the vapour crystallises to ice. D/F PT is a function of the pressure of the gas but is independent of temperature and is therefore defined as fundamental.

We can all observe the dew point phenomenon in our bathrooms. On a cold day, when the temperature of the surface of a mirror or a polished metal surface such a tap, is below that of dew point of the atmosphere, a dew or condensation layer will form on its surface.

Parts Per Million (PPM)

Expression of water vapour content by volume fraction (PPMv) or, if multiplied by the ratio of the molecular weight of water to that of air, as PPMw.

This parameter is more difficult to conceive as it is beyond the ability of the human body to detect changes of this magnitude in the atmosphere. However a practical example of its application in an industry is that of medical gases: those gases such as nitrous oxide, carbon dioxide and oxygen when used in surgical operations should have a moisture content lower than 60ppm and are regulated in this regard.

The Consideration of some Sensor types and their Application

As previously stated, the wide range of humidity measurement required by the various industries described in Table 1 precludes any one sensor technology from being suitable for all applications. In view of this, and the subject matter constraints on this paper, what follows is a summary of some of the sensor technologies typically used in the industries referenced.

Relative Humidity Measurement Techniques

Relative humidity measurements can be made by psychrometry, displacement, resistive, capacitive and liquid adsorption sensors. Some of these techniques are described below.

Wet Bulb/Dry Bulb Psychrometer

Psychrometry has long been a popular method for monitoring humidity, primarily due to its simplicity and inherent low cost. A typical industrial psychrometer consists of a pair of matched electrical thermometers, one of which is in a wetted condition. In operation, water evaporation cools the wetted thermometer, resulting in a measurable difference between it and the ambient, or dry bulb measurement. When the wet bulb reaches its maximum temperature depression, the humidity is determined by comparing the wet bulb/dry bulb temperatures on a psychrometric chart.

Whilst the psychrometer provides high accuracy at near saturation (100% RH) conditions and is simple to use and repair, its accuracy at lower relative humidities (below 20%) is poor and maintenance requirements are intensive. It cannot be used at temperatures below 0°C and, because the psychrometer is itself a source of moisture, it cannot be used in small, closed volumes.

Psychrometers are typically used to control climatic/environmental chambers.

Displacement Sensors

Perhaps the oldest type of RH sensor still in common use is the displacement sensor. These devices use a strain gauge or other mechanism to measure expansion or contraction of a material in proportion to changes in relative humidity. The most common materials in use are hair, nylon and cellulose. The advantages of this type of sensor are that it is inexpensive to manufacture and highly immune to contamination. Disadvantages are a tendency to drift over time and hysteresis effects are significant.

Bulk Polymer Resistive Sensor

These electrical sensors provide a direct, secondary measurement of relative humidity. They are comprised of an insulating ceramic substrate on which a grid of interdigitated electrodes is deposited. These electrodes are coated with a humidity sensitive salt imbedded in a polymer resin. The resin is then covered by a protective coating that is permeable to water vapour. As water permeates the coating, the polymer is ionised and the ions become mobile within the resin. When the electrodes are excited with an alternating current, the impedance of the sensor is measured and used to derive the percent relative humidity (%RH).

By virtue of their structure, bulk polymer resistive sensors are relatively immune to surface contamination. Although surface build up does not affect the accuracy of the sensor, it does have an adverse effect on the response time. Due to the extremely high resistance at RH values of less than 20%, this sensor is generally better suited to the higher RH ranges.

Capacitive Sensor

The capacitive sensor (organic polymer capacitive) is usually designed with parallel plates with porous electrodes or with interdigitated fingers on a substrate. The dielectric material absorbs or desorbs water vapour from the environment with changes in humidity. The resultant change in the dielectric constant causes a capacitance variation which, in turn, provides an impedance that varies in relation to humidity. A dielectric constant change of approximately 30% corresponds to a 0-100% variation in RH.

The sensor material is made very thin to achieve a large signal change with humidity. This permits the water to enter and leave easily and also allows for fast drying and easy calibration of the sensor.

The measurement is made from a large base capacitance; thus the 0% capacitance readings are made at a finite and measurable RH capacitance level.

This sensor type is ideally suited for use in high temperature environments because the temperature coefficient is low and the polymer dielectric can withstand high temperature. Capacitive sensors are also suitable for applications requiring a high degree of sensitivity at low humidity levels, where they will provide a relatively fast response. At RH values over 85% however, the sensor has a tendency to saturate and become non-linear.

Typical applications for the polymer resistive and polymer capacitive sensors are: -

• HVAC energy management.
• Computer room / Clean room control.
• Handheld devices.
• Environmental and meteorological monitoring.

Relative Humidity computed from Dew Point & Temperature

For example, an optical dew point transmitter with a temperature measurement facility could be used to provide a high accuracy RH value. This would represent a relatively expensive ‘secondary’ output from a primary measurement.

Devices typically used for Dew/Frost Point (D/F PT) Measurements

The saturated salt lithium chloride sensor, the aluminium oxide sensor and the optical chilled mirror sensor are all used to measure D/F PT directly. These sensors provide a wide measurement range in terms of dew or frost point.

Saturated Salt Lithium Chloride Sensor

The saturated salt lithium chloride sensor has been one of the most widely used dew point sensors. Its popularity stems from its simplicity, low cost, durability, and the fact that it provides a fundamental measurement.

The sensor consists of a bobbin covered with an absorbent fabric and a bifilar winding of inert electrodes. The bobbin is coated with a dilute solution of lithium chloride. An alternating current is passed through the winding and the salt solution causing resistive heating. As the bobbin heats, water evaporates from the salt at a rate which is controlled by the vapour pressure of water in the surrounding air. As the bobbin begins to dry out, the resistance of the salt solution increases causing less current to flow through the winding and allowing the bobbin to cool. This heating and cooling of the bobbin reaches an equilibrium point where it neither takes on nor gives off water. This equilibrium temperature is directly proportional to the water vapour pressure or dew point of the surrounding air. This value is measured using a platinum resistance thermometer (PRT) and output directly as a D/F PT.

If a saturated salt sensor becomes contaminated, it can easily be cleaned and recharged with lithium chloride. The limitations of the technology are a relatively slow response time and a lower limit of the measurement range which is imposed by the nature of the lithium chloride . The sensor cannot be used to measure dew points when the vapour pressure of water is below the saturation vapour pressure of lithium chloride, which occurs at about 11% RH.

Saturated salt sensors are an attractive proposition when a low cost, rugged, slow responding and moderately accurate sensor is required. They are typically used for the following applications:

• Refrigeration controls
• Dryers
• Dehumidifiers
• Air line monitoring
• Pill coaters

For applications requiring greater accuracy and/or a wider range of measurement, condensation-type, electrolytic, or oxide sensors should be considered.

Aluminium Oxide Dew Point Sensors

The aluminium oxide dew point instrument and its derivatives, such as ceramic or silicon based sensors, are secondary measurement devices that infer the D/F PT value from the way in which the capacitance measurement is affected by the humidity environment in which it is situated. They are available in a variety of types, from low-cost, single point systems, including portable battery operated models, to multi-point, microprocessor based systems with the capability to compute and display humidity information in different parameters.

A typical aluminium oxide sensor is a capacitor, formed by depositing a layer of porous aluminium oxide on a conductive substrate and then coating the oxide with a thin film of gold. The conductive base and the gold layer form the capacitor’s electrodes. Water vapour penetrates the gold layer and is absorbed by the porous oxide. The number of water molecules absorbed determines the electrical impedance of the capacitor, which is in turn proportional to the water vapour pressure.

Oxide sensors are small in size and lend themselves to in-situ use. They are suitable for low frost point measurement (-100?C) and can operate over a relatively wide span encompassing high pressure applications. They can also be used to measure moisture in liquids and, due to low power usage, are suitable for intrinsically safe and explosion proof installations.

Aluminium oxide sensors are frequently used in the petrochemical and power industries where low dew points are to be monitored “in line” with economical multiple sensor arrangements.

The main disadvantage associated with these sensors is that they are secondary measurement devices and must be frequently recalibrated to accommodate ageing effects, hysteresis and contamination.

Chilled Mirror (Optical Condensation) Hygrometer

The chilled mirror hygrometer is widely considered to be the most precise method for dew point measurement. It is a primary measurement, measuring as its name suggests, the actual condensation point of the ambient gas and can easily made traceable to international calibration standards such as UKAS & NIST. The sensor contains a small metallic mirror, the surface of which is chilled until water condenses out of the sample gas onto the mirror surface.

The mirror is illuminated by a light source and the reflection is detected by a phototransistor. At the occurrence of condensation, the reflected light is scattered and, therefore, reduced at the detector. A control system keeps the temperature of the mirror at the point where a thin film of condensation is maintained. A PRT embedded in the mirror measures its temperature and therefore, the D/F PT temperature.

Accuracies of +/- 0.2°C are possible with chilled mirror hygrometry. Multi-stages of peltier cooling supplemented in some cases with either additional air or water cooling can provide an overall measurement range of -85 to almost 100°C dew point. Response times are fast and operation is relatively drift free. Inert construction and minimal maintenance requirements (the two features are intrinsically linked) also considered, the chilled mirror hygrometer is an excellent choice of sensor for demanding applications where the cost can be justified.

It is true to say that you will find an optical dew point hygrometer at the end of most calibration chains and the more robust designs are equally well suited to controlling a critical industrial process as they are to providing the reference standard in a calibration laboratory. Some systems have a fairly sophisticated method of addressing contamination but this issue will be dealt with in more depth within another section of this paper.

Typical applications for the Optical Condensation Hygrometer:-

• Medical air lines
• Liquid cooled electronics
• Cooled computers
• Heat treating furnaces
• Smelting furnaces
• Clean room controls
• Dryers
• Humidity calibration standards
• Engine test beds

Devices typically used for PPM Measurements

Electrolytic, piezo-resonance and multi-stage chilled mirror sensors are used to measure water vapour in the low PPM region. When making measurements in this range and using sample systems as opposed to in-situ measurement techniques (sometimes process conditions (high temperature, pressure, corrosive gases) and/or the type of sensor technology being used will preclude an in-situ measurement) it is vital to ensure all fittings are gas tight, non-hygroscopic materials (i.e. stainless steel) are used, and, when initiating the measurement, adequate time is allowed for the system to dry down and equilibrate.

Electrolytic Hygrometer

The electrolytic hygrometer is usually used in dry gas measurements as it provides reliable performance for long periods in the low PPM range. Typically, the electrolytic sensor requires that the gas being measured must be clean and should not react with a phosphoric acid solution, although recent developments in the sensor cell technology and sample conditioning systems allow more hostile applications, such as moisture in chlorine to be addressed.

The electrolytic sensor utilises a cell coated with a thin film of phosphorous pentoxide (P2O5), which absorbs water from the gas under measurement. When an electrical current is applied to the electrodes, the water vapour absorbed by the P2O5 is dissociated into hydrogen and oxygen molecules. The amount of current required to dissociate the water is proportional to the number of water molecules present in the sample. This number, along with the flow rate and temperature is used to determine the parts per million by volume (PPMv) concentration of the water vapour.

The electrolytic sensor is used in very dry applications up to a maximum of 1000 PPMv. and is well suited for use in industrial processes such as ultra pure gas, specialist catalyst, fine chemicals and integrated circuit production. In each of these cases, the success of the production process is dependent on the maintenance of inert blanket conditions. This means that very often a continuous supply of either nitrogen or argon is used to purge the production environment. As well as maintaining the purity of the gas, the water vapour content should also be kept very low and the electrolytic hygrometer is ideally suited to providing dependable measurements in just such an environment.

Other typical applications for this sensor include: -

• Ozone generators
• Dry air lines
• Nitrogen transfer systems
• Inert gas welding

In summary, whilst the electrolytic hygrometer can provide a primary, reliable measurement at low moisture, the accuracy of the device is dependent on maintaining a controlled and monitored sample flow. Applications must be selected carefully as certain gases will corrode and/or contaminate the sensor.

Piezo-Resonance Sensor

The piezo-resonance sensor operates on the principle of RH equilibrium where the sorption of water increases the mass, which directly affects the resonant frequency of the crystal.

The sensor has a humidity sensitive coating placed on a resonating crystal surface. The crystal resonant frequency changes as the humidity sensitive coating either absorbs or desorbs water vapour in response to changes in the ambient humidity levels. This resonant frequency is compared to a similar measurement in a dry gas or to a reference frequency that has been calibrated for % RH.

Optical Condensation Hygrometer with maximum cooling capability

As previously stated under the Dew/Frost PT measurement section, an optical condensation hygrometer with multi-stages of peltier cooling, supplemented in some cases with either additional air or glycol/water cooling, can provide a dew point measurements at the lower end down to -85°C, which is less than 0.25 PPMv of water at 1 atmosphere pressure.

The Problems of Contamination

In order to understand the significance of the potential effects of contamination on a humidity sensor it is appropriate at this stage to refer back to a statement made within the introduction to this paper:

‘Humidity is a truly analytical measurement in which the sensor must contact the process environment, in contrast to pressure and temperature sensors, which are invariably insulated from the process by a thermowell and a diaphragm respectively. This of course has implications for contamination and degradation of the sensor to varying degrees depending on the nature of the environment’.

Very little contamination should exist in pure gas stream, dew point or PPM level monitoring; however, in most industrial processes there is a high potential for contamination either by direct, process gas borne particulates or by soluble contaminants contained within the very moisture content which it is necessary to measure.

All the sensors referenced in this paper are affected by both soluble and insoluble contaminants. Unfortunately, many of the sensors when contaminated will not appear to be so but will be seen to be providing a very logical measurement value to the humidity control system. Without periodic checking and recalibration the only evidence that the sensor has “gone to sleep” will be derived from the gradual appearance of inferior product in some form or other; therefore, with the majority of humidity sensors it is essential that periodic maintenance should include checks of response and accuracy.

This may be done with humidity calibration systems, which include saturated and unsaturated salts, relative humidity and dew point generators.

Two approaches are adopted to try to accommodate contamination affects: one approach is to devise a sensor where the detrimental effect of contamination is reduced thereby prolonging the active life of the sensor. This may be inherent in the sensor design itself (this is the concept behind the bulk polymer, resistive RH sensor) or may be effected by introducing some form or filter or sheath into the system. The more physical barriers you put between the sensor and the environment however, the more problems you encounter in trying to make a viable and accurate measurement. Once contaminated and blocked, a filter may have the effect of creating an unrepresentative microenvironment between itself and the sensor. The measurement is therefore limited in terms of accuracy and response time and the filter will only intercept particulate contamination. Alternatively, the second approach is to accept that contamination will take place and therefore devise a way in which it can be monitored and, if possible, compensated for.

One measurement technique that falls into the latter category is the optical dew point hygrometer, which can incorporate a self-checking feature, which may be operated either manually or automatically (in the case of the most sophisticated designs), within the electronic control unit. Since the optical hygrometer provides a continuous, live measurement of the dewpoint or humidity value in that the optical control system is continually viewing the mirror’s surface and, therefore, the dew or frost layer formed upon it, it will react to contamination that deposits itself on the mirror either through solid particulate or salts contained within the water vapour being monitored.

When the dewpoint sensor is first put into operation and the mirror is clean, a perfect layer of condensation may be maintained on its surface and high accuracy and repeatability will result. As the sensor continues to operate, however, sometimes for weeks or even months contaminants are gradually dropped out of the sample stream being measured on to the mirror. These contaminants can cause two types of error as follows.

Solid Particulate Contaminants

Just as a dew layer decreases the quantity of light reflected from the mirror to the light detector so to does the increasing build up of non-water soluble contamination. If this were allowed to continue indefinitely the system would go out of control and read out a large dewpoint error. Prior to this occurrence, however, the mirror must be cleaned; in all industrial applications for dewpoint sensors it is recommended that the sensor mirror be cleaned before process measurement commences.

Water Soluble Contaminants

There are often water soluble contaminants occurring in the sample, usually in the form of natural salts. These salts go into solution with the pure water on the mirror surface and cause the vapour pressure to be lowered. This can result in an excess build up of water on the mirror (deliquescence) at the true dewpoint. The servo control loop detects the resulting loss of received light then raises the mirror temperature to compensate i.e. it evaporates some of the excess water. A positive error of several degrees may result from this effect and this phenomenon is called the Raoult effect since it is defined by Raoult’s Law.

Several contaminant error correction techniques have been developed over time for the optical dewpoint hygrometer. Early systems simply used a manual balance technique, which was then developed as an automatic balance control (ABC). Later twin beam/twin mirror and continuous balance systems evolved. All these methods involved re-balancing or upsetting the optical sensor bridge in order to compensate for the accumulated contamination error on the mirror. These techniques are effective in correcting only the particulate contamination described above; they will not correct contamination errors arising through the Raoult effect because the automatic servoloop is incapable of differentiating between an excessively thick dew layer due to a increase in actual dewpoint or an excessively thick dew layer caused by salt contamination on the mirror. In both cases the servoloop will make a positive temperature correction and evaporate some of the dew layer; it will correct in the first place but will cause a readout error in the second. This error can be of the order of several degrees.

An error correction technique called PACER (Programmable Automatic Contaminant Error Reduction) was developed by General Eastern as an effective way of reducing errors due to the Raoult effect. The PACER correction cycle starts with a coalescence period, that is the mirror temperature is intentionally cooled below the dewpoint of the sample, condensing out a large amount of water. This excess water dissolves any water soluble contamination. The mirror is then heated exactly as with an automatic balance system. The large puddles of water gradually evaporate carrying increasingly heavy concentrations of contaminants until finally, when all the water has been evaporated, dry islands of crystallised contaminants are left on the mirror.

Now 80 to 85% of the surface is clean and reflective where before the entire surface was covered with contaminant. The system then proceeds to grow a new dew layer in the clean areas on the mirror surface and a further period of error free operation follows.

Eventually, of course, the system will have to be shut down for cleaning but when that point is reached the instrument will advise the user by a visual alarm or by electronic means on a control panel. During the periodic PACER cycle, which typically last a few minute, the analogue output and digital display remain at the dewpoint level prevailing immediately before the occurrence; therefore, the actual process control value is maintained. At the end of the PACER cycle real time dewpoint information is once again displayed and a bumpless transfer occurs to any new dew or frost point value now measured.

Another type of optical device that merits reference at this point is the Cycling Chilled Mirror (CCM) hygrometer. This hygrometer employs a different method of addressing contamination in that it has no error reduction circuitry as such but simply limits the amount of time the mirror surface spends in the wet state. Cooling of the mirror to the prevailing dew point is performed on a cyclic basis. Once the dew point has been detected and reported, the mirror heats to a temperature slightly above ambient and then ‘waits’ in the dry condition. The measurement cycle then repeats. As the mirror is wet for a relatively small amount of time, the potential for contaminants to fall out of the gas stream into the dew is reduced.

In summary, all humidity sensors are affected by the environment they are monitoring which can lead to contamination, causing eventual insensitivity to a changing process humidity condition. The General Eastern PACER cycle, automatic balance control or manual balance adjustment available with chilled mirror optical dewpoint hygrometers not only enables the process operator to check whether the sensor is becoming contaminated but also allows adjustment either automatically or manually to compensate up to a limit when maintenance in the form of mirror cleaning is required. As a result, optical dewpoint hygrometers can generally operate continuously and unattended for longer periods of time than most other humidity measurement systems and provide what is probably the most accurate, repeatable and reliable humidity measurement available for process industry humidity monitoring, particularly in heavily contaminated atmospheres. Some devices such as the Cycling Chilled Mirror (CCM) hygrometers simply attempt to limit the affects of contamination by reducing the amount of time the mirror spends in the ‘wet’ state. The sensor cools to the prevailing dew point on a cyclic basis and therefore reduces the potential for contaminants to be deposited in the dew on the mirror surface. It should be recognised however that this is not a ‘live’ dew point measurement technology and is not suitable for applications where process conditions are subject to rapid change.

Conclusion

Having reviewed a wide range of industrial humidity measurement sensors it is clear that no one measurement technique is suitable for all applications; also, whatever the technique used the process environment will eventually contaminate the humidity sensor. The question which normally arises is, at what point did the sensor become so contaminated that it was no longer able to give a reliable and accurate measurement?

The phrase often heard in the humidity measurement industry is that the sensor has ”gone to sleep”, i.e. it appears to be measuring a very logical humidity value but has become totally insensitive to process humidity changes. In most cases only removal of the sensor from the process for periodic checking and recalibration can overcome this problem. Sometimes the sensor is so badly contaminated that it has to be replaced.

The one measurement technique, however, which can overcome this problem to a great degree is the chilled mirror optical dewpoint hygrometer. If initial cost is not the governing factor in any given humidity measurement application, then the chilled mirror optical dewpoint hygrometer would appear to provide the most versatile method of humidity measurement, having built in features which allow it to monitor the degree of contamination occurring and adjust its performance to compensate. When this adjustment, which can be manual or automatic, reaches its limit the instrument will advise the user by an operational indication or by an alarm thus allowing in-situ cleaning of the sensor and re-standardising to put it back into operation.

The optical chilled mirror hygrometer, therefore, not only provides what is considered to be the most accurate method of measurement with a wide measurement range, facilitated by using sensors with varying depression capabilities, but also the most repeatable and reliable measurement due to its self checking capability. Being a primary measurement technique, it is also accepted as a traceable, continuous, on line measurement, which is particularly relevant where traceable production quality is required. It is only the relatively higher initial cost of this type of hygrometer that prevents it from being used more widely, perhaps, to solve industrial humidity measurement problems.

Analyser Sample Systems

Analyser Sample Systems require experienced design engineering in order to achieve a representative, conditioned sample for analysis. Engineering design requires careful selection of materials, temperature and pressure conditioning along with correct process data. Don't forget, it is generally accepted that analyser sample systems are the victims of the Pareto principle (i.e., 20% of a system consumes 80% of the resources) since they are responsible for 80% of analyser system problems. 

The Haldatec product line includes;

• Enpro - Hot Loop Sample Probe Conditioning System specially designed for moisture analysers on Triethylene glycol dehydration units.
• Enpro - Pneumatic Sample Collection proportional-to-flow and timed controllers. LPG sample cylinders residue and spun styles.
• hot loop sample probe conditioning system specially designed for moisture analysers on Triethylene glycol dehydration units.
• Enpro - Odorant systems - wick, bypass and direct injection.
• Pressure Tech - High pressure, hydraulic, back pressure and heated instrument regulators.
• Phoenix - Manifolds, Gauge and Monflange Valves.
• SmartWatch - Leak Detection - Relief and shut-off valve leakage monitoring systems - wired RS-485 and RF included.

Go to Specific Subject: Analyser Sampling System Technical Resources | Analyser Sample Systems - The Basics | Analyser Sample Systems Design | Samplers | Sampling System Standards | Sampling System Applications | Forums and Organisations | NeSSI Modular Sampling System | Sampling Cylinders |

Analyser Sampling System Technical Resources from Haldatec

Eliminating Guesswork - Predicting Gas Temperatures for Analysers - Industry now has available prediction techniques for calculating the temperature of pipeline gas that is being presented to on-line analysers. Thus the risk has been taken out of having a liquid laden sample or a non representative sample, that can damage analysers or not make the analysis meaningful.

Instrument Filters - These filters are used extensively for removing contaminates that include dust, aerosols and water from the gas before it is used for such duties as gas supply to pneumatic instruments, valve actuators, and analysers.

Pressure Regulators for Analyser Applications - Pressure regulators are self contained devices that are often defined by their application. Hence similar regulators are described as Instrument or Analyser or High/Low Pressure. Whether the regulator is a liquid or gas regulator they all work in the same way. Porting may be different. Sizing is of course different with flow being constrained by the physical size of the regulator and it's flow configuration.

Self Contained Pressure Regulator - Sizing - This technical paper gives a technical introduction on self contained pressure regulators, capacity sizing, turndown and relief sizing.

Oil Sampling - This technical paper details the considerations to be addressed in order to obtain a representative sample.

Analyzer Liquid Shutoff and Eliminator Membrane Filter - The Liquid Eliminator is designed to protect analyzers from damage and contamination by removing liquids and particulates in gas samples. The gas sample enters the housing and flows through the membrane, effectively eliminating any free liquids from entering the analyzer columns.

Natural Gas Sampling - This technical information sheet gives details on sample probe positioning, sample transportation, liquid elimination measures for on-line analysers, sample cylinder materials of construction and more. These are essential requirements in achieving a repeatable and representative sample.

Taking the Guesswork out of Gas Temperatures - Predicting Gas Temperatures for Analysers - Industry now has available prediction techniques for calculating the temperature of pipeline gas that is being presented to on-line analysers. Thus the risk has been taken out of having a liquid laden sample or a non representative sample that can damage analysers or not make the analysis meaningful. Proprietary programmes have been developed specifically for use with insertion regulators and heated regulators. 

Sampling System Applications

Hot Loop Sample Probe Conditioning System specially designed for Moisture Analysers on Triethylene Glycol Dehydration Units - This unit is designed to gather a representative sample to remove free liquids and deliver a low pressure gas sample to a analyser.

Analyser Sample Systems - The Basics

The Basics of Analyzer Sample Systems

Written by Ian Verhappen

Included in this article are two spreadsheets for calculating pressure drops:

Pressure drops in a liquid line

Pressure drops in a vapour line

Analyser Sample Systems Design

Process Analyser Sample Conditioning System Technology Book

This book provides both novice and experienced technologist with the technical background necessary to choose sample conditioning system components that will allow the process analyzer system to function reliably with minimal maintenance.

The conditioned process sample presented to the process analyzer should be of similar quality to the calibration material used to zero and span the analyzer. Filling a long-standing void in the process field, this book addresses the system concept of Process Analyzer Sample-Conditioning Technology in light of the critical importance of delivering a representative sample of the process stream to the process analyzer. Offering detailed descriptions of the equipment necessary to prepare process samples, and listings of two or more vendors (when available) for equipment reviewed, Process Analyzer Sample-Conditioning System Technology discusses:

• The importance of a "truly representative sample"
• Sample probes, transfer lines, coolers, and pumps
• Sample transfer flow calculations for sizing of lines and system components
• Particulate filters, gas-liquid and liquid-liquid separation devices
• Sample pressure measurement and control
• Enclosures and walk-in shelters, their electrical hazard ratings and climate control systems

Practical Considerations of Gas Sampling, Gas Sampling Systems and Standards - David J Fish - The need to be able to take a representative sample of a hydrocarbon product is necessary to ensure proper accounting for transactions and efficient product processing. The various sampling methods that are available and the options and limitations of these methods are investigated; the most appropriate equipment to use; the reasons for its use and correct installation of the equipment are also addressed - from Welker.

Spot and Composite Sampling for BTU Analysis - Determination and Natural Gas Physical Properties - David J. Fish - The amount of hydrocarbon product that is transported between producer, processor, distributor and user is significant. To be able to verify the exact composition of the product is important from an economic and product treatment standpoint. A small percentage savings made by correctly determining composition will quickly recoup the investment made in the purchase of a system designed to obtain an optimum sample. In addition, if the best sampling procedures are followed, the potential for disputes between supplier and customer will be greatly reduced. The importance of properly determining hydrocarbon gas composition benefits all parties involved and will achieve greater significance as this resource becomes more expensive and plays a larger role in our energy needs worldwide - from Welker.

Flow Conditioner - This flow conditioner is designed to protect analytical instruments from liquids. Welker has taken two of it’s products and combined them into one great product. The “Guardian” is quick and easy to install. The “Guardian” is equipped with a shut-off ball that floats on the free liquid and moves up to shut off the flow of liquid slugs that would flood the analyzer. This design is to help protect analyzers from damage and contamination by removing liquids and particulates while sampling from Haldatec.

How to Manage Vaporization in an Analytical System - D Nordstrom and T Waters - When done properly, this process ensures that all compounds vaporize at the same time, preserving the sample’s composition - from Swagelok and Hydrocarbon Processing.

Verify Fluid Flow to Your Analyzer and Keep Your Plant Running - Sam Kresch - No matter how sophisticated a fluid analyzer system may be, it will be ineffective if a sample flow fails to reach the analyzer sensor or if the sample is contaminated or stale. The most advanced systems in the world cannot provide accurate results without a valid fluid sample. Gas chromatographs (GCs), mass spectrometers, optical spectrometers and photometers are a few examples of analyzer technologies applied in process and plant systems that need sample flow assurance. It is an accepted industry best practice that sampling systems have some type of flow monitor to assure valid samples and analysis - from Fluid Components.

How to use a Regulator to Reduce Time Delay in an Analytical System - Doug Nordstrom and Mike Adkins - Process measurements are instantaneous but analyser responses never are. From the tap to the analyser, there is always a time delay. Unfortunately, this delay is often underestimated or misunderstood - from www.chemicalprocessing.com.

Designing On-line Chromatograph systems for Liquid Fractionation Facilities - Murray Fraser - Liquid fractionation plants can optimize their operations by installing on-line gas chromatograph systems that have been properly designed to provide reliable, fast, accurate results. One of the most important, but overlooked, facets of designing an on-line analytical system for gas processing facilities is the sample conditioning system (SCS). The sample delivered to the Gas Chromatograph (GC) must truly represent the process media if the measurement is to be accurate - or even meaningful. Samples may be transported to the GC in either gas or liquid phase, but they will ultimately be analysed in the gas phase only. Selection of sample location and careful attention to sample phase (liquid or gas) is required to ensure optimum system performance. Discussed in this paper are: typical process conditions, GC location, sample transport systems, and details of both vapour- and liquid-phase sample conditioning - from Daniel Measurement and Control.

Breathe Easy - Darrell Leetham - For many organisations today, one aspect of the manufacturing process that needs to be monitored and controlled, for both efficiency and environmental benefit, is gaseous emissions - Plants are constantly looking for means to increase production and decrease costs. Increases in production are generally associated with an increase in fuel consumed and, in turn, a subsequent increase in emissions generated. In addition, regulatory entities are increasingly implementing standards and setting requirements for monitoring and reporting data on plant emissions. In order to improve efficiency throughout a manufacturing process and at the same time meet the needs of sustainable development goals, industry is finding an increased need for robust, reliable and accurate gas analysis methods. To meet the needs of this demand, different technologies for gaseous emissions sampling and analysis have been developed over the years. One particular technique is to extract a gas sample and dilute that sample prior to analysis. This article explains some advantages of the dilution extractive method. From Thermo Fisher Scientific and processonline.com.au.

The Integrity And Reliability Of On Line Process Analyzers is Crucially Related To The Design Of The Supporting Sample Handling System - Ronald A. Downie - Although a considerable amount of attention is normally given to the selection of the most suitable type of analyzer to perform the desired analytical task, a similar amount of attention is all too often not extended to the sample conditioning system. This may be due to a lack of understanding of the importance of this part of the complete system. A well-designed, properly applied measuring system can do no better than give a correct analysis of the sample being supplied to it. If the sample is not representative of the process, there is nothing an analyzer can do to correct the situation, and the analytical data can not be used for control purposes. The results of poorly designed sample conditioning vary from the analyzer not operating at all to an analyzer operating only with extremely high maintenance requirements and/or giving erroneous or poor data - from Teledyne Analytical Instruments.

Techniques of Composite Sampling - Kris Kimmel - Since a gas sampling system can be referred to as a “cash register” it is very important that the correct sampling method be selected and the appropriate industry standard be followed. Methods reviewed by this paper will include spot sampling, composite sampling, and on-line chromatography. In addition, Gas Processors Association (GPA) 2166-86 and American Petroleum Institute (API) 14.1 will be described - from YZ Systems, Inc and intellisitesuite.com.

Grab Sampling Systems: Maintaining Quality and Safety - The need for representative samples plays a critical role in ensuring product verification. Yet sampling directly from the process often includes the risks of exposure to the operator as well as contamination and pollution to the environment. The DOPAK^® sampling method reduces such risks with its patented design and simple method of operation. Thanks to Dopak.

A whole swag of Useful Sampling and Conditioning Papers from the NGS Tech 2011 Conference. All the papers are on a single pdf, just scroll down using the index - Paper subjects are;

• The Chemistry and Physics of Natural Gas Sampling and Conditioning - Dr. Darin George
• The Standards Pertaining to Sampling and Conditioning of Natural Gas - Fred Van Orsdol
• Spot and Composite Sampling for BTU Analysis Determination and Natural Gas Physical Properties - David Fish
• Sample System Design Considerations for “Online” BTU Analysis - Matthew Kinsey Modular Sample Conditioning Systems for Natural Gas Analysis - Jay St. Amant
• Measurement of Water Vapor in Natural Gas by Automated and Manual Water Dew Point Measurement Methods - Dan Potter
• Sampling and Conditioning Natural Gas for H2S and CO2 Analysis - Sam Miller
• Sampling Wet Natural Gas for BTU and Moisture Analysis - Shannon Bromley
• Sampling and Conditioning During Loading, Unloading, and Storage of LNG - Jim Witte
• Benefits of Training Measurement Technicians in the Science of Sample Conditioning and Analysis - Brad Massey
• Are company sampling procedures in line with current standards? - Matt Holmes

Sampling and Conditioning Papers from the NGS Tech 2014 Conference - All the papers are on a single pdf, just scroll down using the index- Paper subjects are;

• Basic Chemistry and Physics for Sample Conditioning - Jim Witte
• Economics of Compositional and Quality Determination - David Wofford
• Basics for New Engineer/Project Manager - Brad Massey
• API Wet Gas AdHoc Committee Update - David Fish
• New Techniques for Liquid Calibration Standards - Dan Bartel
• Lessons Learned from Sampling in Eagle Ford - Royce Miller
• Wet Gas Sampling - Jay St Amant
• Training New Employees and the Importance/Impact of Baby Boomer Retirement - Gary Hines
• Compressed Natural Gas (CNG) Sampling - Darin George
• New Techniques in LNG Sampling - Ken Thompson
• Improving the Speed and accuracy of Water Vapour and H²S Measurements by Optimising the Sample Transport System - Phil Harris
• Natural Gas Liquid (NGL) Sampling - Eric Estrada
• Injection of Chemicals and the Impact on Sampling - Brad Massey

The following technical information is from Jiskoot:

• What are the most important steps to consider when Designing or Specifying a Sampling System? - In a typical sampling application, the volume analysed is between 1 and 300 billionth of the total batch. When the custody transfer and batch quality is determined by such a small sample it is vital that it is representative of the fluids being sampled. The standards defines a number of steps that need following to ensure successful sampling.
• Why do the Standards Demand that Pipeline Contents must be Homogenous? - A sample is taken from a single point in the pipeline. Water and oil do not mix and therefore it is vital that the point of sampling is representative of a cross section of the pipeline. This can only be achieved by mixing. Natural mixing can be provided by valves, elbows and natural turbulence generated by the flow.
• IP Petroleum Measurement - Mark A. Jiskoot The interest in sampling accurately has led to a plethora of studies and the generation of the standards we now use. Much of the original content was based upon what was then known, bolstered with, one hopes, educated guesses. The testing of systems designed within practical/cost limitations has allowed us to accept or reject certain conceptions and better learn the envelope in which we should operate. This paper outlines some of the problems to be addressed and some of the discoveries made.
• Sampling Systems - The Options - What is the accuracy of different sampling systems and which is best for your application? There are two main types of sampling systems, probe based systems and bypass loop sampling systems.
• What is a Representative Sample? - How do you know if I have a representative sampler?
• Sample Receivers - Which type of sample receivers should you use? Once a representative sample has been extracted from the pipeline, it must remain representative in the sample receiver and when analysed in the laboratory. The standards recommend the use of either fixed or variable volume depending on the properties of the fluids being sampled.
• Jet Mixing - A New Approach to Pipeline Conditioning - M.A. Jiskoot - Accurate sampling from a flowing pipeline requires that the point from which the sample is drawn is representative of the average (quality) of the whole cross section.

Sampling System Standards

The following technical information is from Jiskoot:

• What International Standards Govern Sampling System Selection, Design, Installation and Operation? - There are four major standards that govern 'Sampling liquid hydrocarbons in pipelines'. They are ISO 3171, IP 6.2, API 8.2 and ASTM D4177.
• Sampler Control Systems - What type of control system is recommended by the standards? The primary function of the control system is to operate the sampling device in a time or flow proportional manner. This normally requires that the controller have a real-time operating system. The system should allow the operator to enter the batch size and should determine the necessary sampling rate to achieve the correct volume of sample.
• Sampling System Proving - How can you guarantee, prove and certify that a sampling system complies with the standards? A sampling system needs proving once installed. Only then can you certify that a system performs as specified. The only way to prove beyond doubt that an installed sampling system complies with the standards is to prove the system by water injection. The procedure is defined in the standards.
• Crude Oil Sampling - Crude oil sampling for custody transfer, fiscal, allocation or quality measurement purposes should be performed in accordance with sampling standards of ISO 3171, ASTM D 4177, API 8.2 and IP 6.2. These standards dictate a number of key design issues and steps that must be considered to ensure a system fully complies with the standards.

Sampling System Applications

The following technical information is from Jiskoot:

How can you decide which type of Mixing System is Best Suited to your Application? - Selection of the correct mixer as with any process conditioning depends greatly on the application. There are two main types of pipeline mixing systems available.

Crude Oil Sampling

The following technical information is from Jiskoot:

• The “Art” of Crude Oil Sampling - Mark Jiskoot - Crude oil is sampled to establish the composition quality, density and water content. The quality is normally known when the oil is purchased, as is the approximate density, for a cargo there is "expected" water content but receipt terminals can often be surprised by a water content that is far higher than the "bill of lading" as stated by the loading port. Depending on how the purchase contracts are written, discovery of more water may give rise to a claim first on the shipper and then on the supplier.
• Crude Oil and Condensate Sampling, Water in Oil and Density Measurement - What is the uncertainty of your quality measurement system? - Mark A. Jiskoot - The various standards applicable to sampling, density and on-line water content measurement have been developed and updated over many years but the most significant advances have happened over the last 20 years. While sampling systems have always been a feature of the metering process, many metering systems installed have been modified to incorporate density compensation (to yield total mass) water-in-oil monitors (OWD or On-line Water in petroleum Devices) or both. Integrated systems are now titled QMS or “Quality Measurement Systems”. Unfortunately, and to their cost (at least that of their company), many loss controllers pay the price for poor measurement by way of claims so there is a strong commercial reason to get measurement “right”.
• Crude Oil Quality Measurement - Loss Reduction Through Technology - Jon Moreau & Mark Jiskoot - Quality measurement system design and laboratory equipment, handling techniques and analysis methods have improved significantly over the last 20 years. Simultaneously, suppliers and users have worked together to develop/validate and improve measurement performance. One of the most significant steps in achieving this has been the collation and evaluation of water injection "proving" tests. This large (often independently validated) and rapidly growing data set enables a comparative evaluation of the performance of custody transfer sampling/on-line measurement systems. Proving the accuracy of an installed quality-measurement system is a challenge, even more so than proving a metering system. It requires adjustment of a physical property (in this case water content) and validating that the system accurately measures that change. However, unless an installed system has been proved and certified as compliant with the standards, its use to arbitrate claims or for custody transfer becomes questionable.
• Increased Profitability through Effective Measurement - Mark A. Jiskoot & Jon Moreau - The measurement of a Crude Oil shipment at an import terminal forms the basic measure of profit performance.Accurate techniques for measurement of flow are well documented and understood. The factor that is often overlooked is the accurate measurement of actual water, density and composition. Crude oil and water do not mix and therefore it is fundamental that any measurement of water content not only considers carefully how a sample is extracted but also how it is handled and tested. Typical errors in poor sampling techniques result in payment of oil prices both to transport and to process water. While the percentage errors between sampling methodologies may appear insignificant (of the order of 0.05- 0.15%) the volumes of crude traded make the losses significant and can easily justify the installation of an accurate sampling system that both the seller and purchaser can be confident in. The International standards of ISO 3171 clearly define standards which meet the requirement of accurate sampling of liquid hydrocarbons in pipelines.
• How Accurate is your Receiving Metering System? - Mark A. Jiskoot - Errors in terminal receipts due to poor sampling designs and procedures can result in huge losses. When receiving crude shipments via tanker, there is some doubt on the quantity of product unloaded. Many errors can be attributed to discrepancies in sampling and metering results. Oil quality measurement methods are under continual review. How much water are you actually purchasing in the latest receipt? An answer is determined by what methods are used to get product densities and the accuracy of laboratory analysis. Should physical sampling methods be replaced with online devices? These are just a few of the issues that refiners must consider as they try to improve the operation of their terminal metering systems.

Fuel Oil Sampling

Fuel Oil (Bunker) Sampling Break the link between Politics and Quality - Mark A. Jiskoot - The objective of sampling is to determine to the highest degree of accuracy possible, the properties of the fluid sampled.This proves beneficial to all parties as it can, if properly executed, ensure fair transactions. As the value of product increases or, as in the case of fuel oil, the potential for claims increase, it is necessary to assure all parties of the properties of the transaction both at the time of sale and in case of dispute later. In reading bunker related press it also becomes obvious that aside of the issue of a "fair deal" assurance of quality can have significant impact on the prevention of engine failure and the consequent disasters and claims than ensue. PSA and DNV have both made serious attempts to assure certain sampling procedures but it is the belief of the author that these are not yet enough. This paper is to outline the basis on which an accurate sample should be taken, sampling techniques which if used will serve to both improve the overall quality of the trade and to determine unintended quality problems which need resolution - from Jiskoot.

Natural Gas Sampling

Natural Gas Sampling - An Overview - Robert J. J. Jiskoot - Once a by-product of oil production discarded and flared off, Natural Gas has become an increasingly valuable energy source. The ability to verify the composition of the hydrocarbon gas is critical to the determination of its commercial value, be this in gathering, transportation or loading systems. Accurate and reliable sampling allows both buyer and seller to be confident of a fair transaction. The investment associated with the purchase and installation of a composite gas sampling system, correctly designed to provide a representative sample, will be quickly recouped. This paper attempts to outline the correct procedures and considerations that are necessary to obtain a representative gas sample - from Jiskoot.

Advances in Natural Gas Sampling Technology - Donald Mayeaux - The monetary value of natural gas is based on its energy content and volume. The energy content and physical constants utilized in determining its volume are computed from analysis. Therefore correct assessment of the value of natural gas is dependent to a large extent on overall analytical accuracy. The largest source of analytical error in natural gas is distortion of the composition during sampling. Sampling clean, dry natural gas, which is well above its Hydrocarbon Dew Point (HCDP) temperature is a relatively simple task. However, sampling natural gas that is at, near, or below its HCDP temperature is challenging. For these reasons, much attention is being focused on proper methods for sampling natural gas which have a high HCDP temperature. This presentation will address problems associated with sampling natural gas which is at, near, or below its HCDP temperature. Various approaches for solving these problems will also be discussed - from A+ Corporation and intellisitesuite.com

Spot Sampling of Natural Gas - Jerry Bernos - In 1978 the United States Congress passed the Natural Gas Policy Act. This legislation required that natural gas be priced according to its energy content rather than by volume alone. At the same time, the economics of the natural gas industry caused natural gas prices to soar. These two factors resulted in a vast increase in the demand for accurate analyses of natural gas systems. Since it was not economically feasible to place analytical instruments at each and every location requiring BTU determinations, a corresponding increase occurred in the need to obtain "spot" samples of these systems. This paper is intended to present the problems that arise in "spot" sampling and to introduce the industry accepted methods, which can overcome these problems.

Techniques of Gas Spot Sampling - George L. Bell, Sr - A natural gas sample may collected as a spot, composite, or as a continuous sample connected to a chromatograph. The most important things in taking a sample are where and how the sample is taken - From PGI International and intellisitesuite.com.

Wet Gas Sampling

Wet Gas Metering / Sampling - New Method to Determine the Liquid Content of a Wet Gas Stream and Provide a Sample of the Liquid Phase for Compositional Analysis.- Mark A. Jiskoot and Ken Payne - There is currently no other method available that is capable of accurate measurement of the liquid mass of a wet gas stream. Jiskoot has, in conjunction with AMEC, developed a wet gas sampling methodology that can determine the liquid/gas mass ratio as well as providing a compositional sample to allow laboratory determination of the chemical composition of condensates, methanol and water.

Samplers

The following excellent technical references are from Welker;

• Light Liquid Hydrocarbon Sampling - In the sampling of light liquid hydrocarbons, the liquid state of the sample must be maintained at all times. To accomplish this, the equipment and operating features detailed in this technical list should be employed.
• Gas Sampling Applications - Gas Sampling usually takes three forms, spot, continuous or representative, this technical bulletin gives information on this.
• Liquid Sampling Applications - Sampling liquids usually takes two forms, spot or representative. Spot samples are taken at one time at one point, normally via a pitot tube inserted in the process or pipeline. The sample is collected in a sample cylinder and taken to a laboratory for analysis. This form of sampling will only give a sample that is representative at one point in time only. Alternatively, Representative samples of light oil or condensate are collected using a by-pass sampler mounted adjacent to the pipe or mounted directly on the pipe. Grab samples are then collected in a sample cylinder over a period, for later analysis in a laboratory. For heavier oils such as Crude Oil or oils with contaminates in them, the by-pass method is not favoured, a direct mounted insertion type sampler is used. This type of sampler will take a representative sample from the centre of the pipe. The oil should first be thoroughly mixed using an upstream static mixer to ensure the best homogeneous sample is taken.
• Collection and Safe Transportation of Hydrocarbon Samples - David A Dobbs and David J Fish - This paper discusses the various types of collection methods and collection devices as well as the importance of proper collection cylinder construction, benefits of constant pressure sampling together with comparison of results from various sampling methods. Transporting samples for analysis remote from the collection point is often necessary and presents problems in selecting the appropriate container and mode of transport. Safe transportation is critical and subject to regulation, as well the integrity of the sample needs to be maintained. The various regulations and transport options are also detailed.

Analytical Sampling System Forums and Organisations

Center for Process Analytical Chemistry - CPAC, established at the University of Washington in 1984, is a consortium of Industrial, National Laboratory and Government Agency Sponsors addressing multidisciplinary challenges in Process Analytical Technology (PAT) and Process Control through fundamental and directed academic research. The present CPAC program can be summarized by two main components;

1. new measurement approaches including the miniaturisation of traditional instrumentation and the development of new sensors and non-traditional instruments.
2. mechanisms for interaction, collaboration, and communication of center activities, research programs, and information related to process analytical technology (PAT) among sponsors, other universities and academic departments, government agencies, and the general measurement and control community. CPAC has an established track record in fostering academic/industrial/national laboratory interactions, which aim at bridging the gap between basic research and full-scale process/product development.

ISA Analysis Division - Membership to the Analysis Division provides you with access to a network of knowledge and opportunity to develop your own expertise and share this with fellow professionals. Whether you are already a member or thinking about membership, ISA provides a wealth of industry knowledge at your fingertips and will ensure you are on the cutting edge of technology and developments. In the Analysis Division, we enable our members to do their jobs better and help their organizations strategically use technology so that they, in turn, make the world a better, just, and equitable place. Membership in the ISA entitles you to one free "Automation & Technology" divisional membership. Simply check off "Analysis Division" when you register for your annual ISA membership. You then have access to the finest collection of process analyzer professionals in the world for the price of belonging to the ISA. Don't miss out on this opportunity to be an Analysis Division Member.

NeSSI Modular Sampling System

CT76 Modular Substrate and Component System - This bulletin from Circor describes why this is "State of the Art" for modular systems.

Modular Substrate Sampling System (µMS³™) - from Circor.

Rethink Sample System Automation - NeSSI provides new tools to tackle the challenges and improve performance - By Robert N. Dubois, consulting analytical specialist - Thanks to chemicalprocessing.com.

NeSSI™ Generation II Specification - A Conceptual and Functional Specification Describing the Use of Miniature, Modular Electrical Components for adaptation to the ANSI/ISA SP76 Substrate in Electrically Hazardous Environments - This functional and conceptual specification is based on the use of the miniaturized, modular analytical systems designed to the ANSI/ISA SP76.00.02-2002 standard substrate. This 2nd generation specification deals chiefly with integrating electrical components such as sensors and actuators (collectively referred to as transducers) onto the substrate in a manner suitable for use in electrically hazardous areas commonly found in petrochemical, refining and chemical facilities - Thanks to CPAC.

NeSSI Keeps Chipping Away - The Plucky Sampling Sensor Initiative and Its Advocates Keep On Encouraging Users to Gain the Many Benefits That Its Standardized Hardware, Communications and Microanalytic Specifications Can Bring to Process Analytical Systems - Launched in 2000 by the Center for Process Analytical Chemistry at the University of Washington, Seattle, NeSSI's Generation I specification for its modular, compact, mechanical substrate and other hardware evolved from the ISA SP 76 standard. Next, CPAC and NeSSI's supporters released its Generation II specification for automation and communications in 2004 and more recently, its Generation III specification for microanalytical devices, which is NeSSI's ultimate goal - from Control Global.

The following articles are from www.chemicalprocessing.com:

• NeSSI’s Success should be a Lock - Mark Rosenzweig - The New Sampling/Sensor Initiative or NeSSI that replaces tubing, fittings and other hardware in a sampling system with miniature modular components makes sense. Enhancements now in the works should assure its success.
• Intrinsically Safe NeSSI Nears - An emerging bus standard promises to spur application in hazardous environments - Rick Ales - The New Sampling/Sensor Initiative (NeSSI) has provided the basis for modular miniaturized process sampling systems that offer ease of assembly and flexibility while cutting cost of ownership. Not surprisingly, plant acceptance of such NeSSI systems is growing. A group of analyzer specialists now is working to enable NeSSI to be used in hazardous environments. They envision an analytical system with smart transducers that would be capable of being field mounted at the sample point in a potentially explosive atmosphere and would be easily integrated into the analyzer control system.
• Smaller, Smarter Systems Streamline Sampling - Mike Spear - An emerging miniaturized, modular approach for sampling systems provides substantial savings in both capital and operating costs - Faced with ever increasing competition on price for their products, chemical companies are constantly searching for ways to cut costs across their operations. This, in turn, puts persistent pressure on engineers to reduce both capital and operating expenditures - without compromising their plants’ reliability and performance in any way. Easier said than done, perhaps, but this is precisely what a new approach to the task of delivering process samples to analyzers actually delivers, claim its proponents. Since coming into being some five years ago, the New Sampling/Sensor Initiative (NeSSI) has become the driving force behind the move to modularize and miniaturize process sampling systems. Now operating under the sponsorship and umbrella of the Center for Process Analytical Chemistry (CPAC) at the University of Washington, Seattle, NeSSI first surfaced as an ad hoc group of people drawn both from equipment manufacturers, keen to adopt the modular approach, and operating companies prepared to put the vendors’ prototype products to the test on their plants.
• Streamline Your Sampling System - Selecting the right stream selection assembly can improve performance - John Wawrowski, Doug Nordstrom and Joel Feldman.

Sampling Cylinders

Constant Pressure Sample Cylinders with Additional Special Purpose Standard Cylinders - Constant Pressure Cylinders are being increasingly used to address the problem of fugitive emissions in spot sampling situations and have been used for many years in continuous sampling applications. They have minimal dead space, eliminating or minimising the need to purge, are safe to transport, easily cleaned and maintained. 

Other Useful Information on Sampling Systems

Sampling Technical Papers - Some super technical information on sampling from Jiskoot International.

Humidity Measurement and Instrumentation

General Humidity Measurement Technology

A Technical article on General Humidity - Humidity Definitions, Details on Relative or Absolute Humidity, Practical Requirements of Humidy Measurement, State of the Technology and functional principles - from Vereta.

Notes on Relative Humidity - from the University of Illinois.

Atmospheric Moisture - Sample chapter from the textbook Meteorology Today by C. Donald Ahrens. (PDF 1.5MB 22 pages) - Thanks to www.novalynx.co.

Humidity Sensors for Industrial Applications - This paper reviews various humidity sensor technologies and their typical applications in context of the measurement ranges to which they are best suited. The effects of contamination, highly significant in view of the analytical nature of the measurement, are briefly assessed. In conclusion, it is suggested that, if initial cost is not the prime consideration, the chilled mirror, optical dew point hygrometer offer the most accurate, repeatable and reliable method of humidity measurement with the widest possible range - from Able Instruments and Controls - from Michell Instruments.

Cooled Mirror Sensor Technology - The optical condensation principle of dew point measurement has been established for centuries as the most fundamental method of determining the moisture content of a gas. The dewpoint temperature (that is, the temperature at which water vapour begins to condense to liquid or ice as the gas is cooled) describes precisely the moisture concentration of the gas. The major uncertainties in this measurement are related to the instantaneous detection of the on-set of condensation and the accuracy to which the temperature of the condensing surface can be measured. Early manual dew-point hygrometers suffered inaccuracies due to their cyclical nature, being cooled by an external coolant such as carbon dioxide or by the evaporation of a solvent, and also because of the time taken to produce an observable layer of condensate, often leading to an underestimation of the moisture content. The modern, automatic cooled mirror sensor addresses these deficiencies and also provides an instrument that is rugged and reliable enough to be applied to process control measurement as well as laboratory use - from Michell Instruments.

Moisture Sensor for the Measurement of Absolute Humidity in Process Air and Gases - This latest generation impedance dewpoint sensor combines fast response and high repeatability with long-term stability and resistance to contamination - from Michell Instruments.

Humidity Sensors - Humidity Sensors for Industrial Applications - It could be argued that humidity plays a part in every industrial production process. The very fact that our own atmosphere contains water vapour bears witness to this fact even if it is only that the end product is likely to be stored and eventually used in our environment; therefore, the product’s potential performance under varying conditions of humidity must be known. The extent to which humidity plays a part in any given production process may vary but in many cases it is essential that, at the very least, it is monitored and, in most cases, controlled. It may also be said that humidity is a more difficult property to define and measure than associated parameters such as temperature and pressure. Indeed, it is a truly analytical measurement in which the sensor must contact the process environment, in contrast to pressure and temperature sensors, which are invariably insulated from the process by a thermowell and a diaphragm respectively. This of course has implications for contamination and degradation of the sensor to varying degrees depending on the nature of the environment. This paper reviews various humidity sensor technologies and their typical applications in context of the measurement ranges to which they are best suited. The effects of contamination, highly significant in view of the analytical nature of the measurement, are briefly assessed. In conclusion, it is suggested that, if initial cost is not the prime consideration, the chilled mirror, optical dew point hygrometer offer the most accurate, repeatable and reliable method of humidity measurement with the widest possible range - from Able Instruments and Controls.

Metrology Humidity Technical Papers

The following technical papers are from gesensing:

• An Intercomparison of a Two-Pressure/Two-Temperature Frost Point Generator and Chilled Mirror Condensation Hygrometer
• Humilab Benchtop Humidity calibration system
• The Theory and Operation of Optical Chilled Mirror Hygrometers for Humidity Calibration
• Condensation Hygrometers as Humidity Transfer Standards
• A comparison of chilled mirror hygrometers
• Development of a Bench-Top Time Proportional Humidity Generator with Chilled Mirror Hygrometer Reference Standard
• The State of Pressure Uncertainty by Ken Kolb
• Differential Pressure Primary Standard - Technical Aspects
• Dew Point Measurement in Metal Heat Treatment
• The Effect of Air Laden Soluble Salts on Dew Point Measurement Using Condensation Hygrometers

Humidity Analysers - Theory and information of Condensation Chilled Mirror Hygrometers - from Able Instruments and Controls.

Moisture Analysers and Analysis

The following papers are from gesensing:

• Achieving Reliable Parts-Per-Billion Calibration of Moisture Analyzers
• Care of Grain: Guide to Professional Grainstore Management
• Dampness Measurement in Concrete Floors
• Ventilation, damp, mould & condensation feature article from "Housing Association Building and Maintenance"
• Online Moisture Analysis in Materials Handling - Graeme McGown - Moisture analysis during materials handling and processing presents a number of challenges that can be solved with appropriate use of online techniques - from Intalysis and www.processonline.com.au.

Natural Gas Moisture Measurement

Hydrocarbon Dew Point Technology - The condensation temperature of heavy hydrocarbon components in gas - commonly known as the hydrocarbon dew point - is a complex and difficult parameter to measure. Traditionally this measurement has been made using a manual optical technique based on the cooling of a mirrored surface in contact with the hydrocarbon gas mixture. Whilst it is possible, with experience and application, to obtain repeatable results with a manual dew-point hygrometer, the subjective nature of this technique yields it ever less applicable in today's de-regulated gas markets where continuous and precise measurement of this critical parameter are demanded - from Michell Instruments.

The following papers are from gesensing:

The War against Water - Ken Soleyn - Water even in small concentrations, poses large problems for the distribution of natural gas. Natural gas is dehydrated and treated prior to transportation and use, at considerable cost to the supplier and consumer. However attempts to reduce dehydration results in a reduction of 'gas quality' and an increase in maintenance costs and transportation, as well as potential safety issues. Consequently, to strike the right balance it is important that the water component of natural gas is measured precisely and reliably. A new instrument that utilises a tuneable diode laser is now available to continuously monitor the water concentration in natural gas and offers considerable advantages over traditional instrument technology.

Moisture Measurement in Natural Gas - Priya Rajesh - This article focuses on the basics of natural gas, why moisture measurement in natural gas is important and the various types of moisture measurement instruments.

The following technical articles are from Michell Instruments:

Moisture Measurement in Natural Gas - Thanks to Rolf Kolass, Michell Instruments GmbH, Friedrichsdorf Germany - Chris Parker, Michell Instruments Ltd, Cambridge, UK.

Hydrocarbon dew point of gas - Redeveloping Instrumentation to reduce the cost of ownership -Thanks to Jon Severn.

Hydrocarbon Dew-point - A Key Natural Gas Quality Parameter.

Moisture and Hydrocarbon Dew-point Measurement in Natural Gas

Pharmaceutical Humidity Measurement

Development of a Bench-Top Time Proportional Humidity Generator with Chilled Mirror Hygrometer Reference Standard - from gesensing.

Ultra High Purity Semiconductor Gases Moisture Measurements

Trace Moisture Measurement in Inert, Reactive and Corrosive Ultra High Purity Semiconductor Gases - from Able Instruments and Controls.

Moisture Behavior in Ultra-High Purity Gas Distribution Systems - The purpose of this Application Note is to familiarise users of CQC systems with the difficulty of making ultra-trace level moisture measurements, to set a practical expectation for moisture analyzer performance and to establish guidelines for the proper use of these analysers in controlling and monitoring moisture in UHP gases - from Delta F.

Detecting Single-Digit parts per billion Levels of Moisture in Ammonia Gas - Andrew O. Wright, Clayton D. Wood, Kimberly J. Reynolds and Mark L. Malczewski - An increasingly important chemical used in the manufacture of electronic devices such as high-intensity light-emitting diodes (LEDs) is ultrahigh-purity (UHP) anhydrous ammonia. However, the presence of residual trace moisture iUHP ammonia is a matter of concern. Especially in blue and white LEDs, there is a strong correlation between device performance and moisture content in the process ammonia used during manufacturing. In addition, increasing chemical consumption is forcing many facilities to use bulk storage tanks as a single supply source instead of cylinders as supply sources for individual tools. In light of these trends, it is imperative to have a robust, continuous process instrument with a single-digit parts-per-billion detection limit that can measure moisture in ammonia.

Humidity Tables - Humidity Charts - Humidity Calculator

Relative Humidity Tables - from the National Weather Forecast Centre.

Humidity Calculator - from the Australian Government Bureau of Meteorology.

Humidity Charts - from the Old Farmers Almanac.

Dew Point Temperature Table (Fahrenheit) - Also includes equations for calculating dew point temperature - from the University of Nebraska-Lincoln.

Humidity Calculator for Conversion of Humidity Measurements - The humidity calculator from E+E Elektronik is used for the rapid conversion of humidity measurements. Uniquely, the humidity calculator also includes measurement uncertainties in the calculation. This is helpful for obtaining realistic and reliable overall uncertainties based on the specification of the measuring device.

Thermal Processes using Electrolytic Hygrometers

Humidity Analysers - Product quality improvement with correct moisture measurement in thermal processes using electrolytic hygrometers - from Able Instruments and Controls. 

pH Measurement and Instrumentation

pH Measurement - A sample chapter from the title Practical Analytical Instrumentation in On-Line Applications - This chapter shows the need for pH measurement, Describes the properties of water, Defines pH, Demonstrates the principle of both the measuring and reference electrodes and their relationship to each other, Explains the Nernst equation and its dependence on temperature, Lists the various sources of error in the measurement of pH and shows how calibration is carried out - Thanks to IDC.

Guide to pH Measurement - the Theory and Practice of pH Applications - The aim of this book is to give a representative description of pH measurement in the process industries. The actual sensor, the pH electrode, is therefore the main focus of the text. Correct sensor use is fundamental for a meaningful pH measurement. Accordingly, both practical and theoretical requirements are discussed in depth so that the measuring principle is understood and an accurate measurement made possible - from Mettler - Toledo AG.

pH Measurement - Some super information thanks to Cole Palmer.

Typical Problems in Industrial pH Measurement & Control - Tips and solutions to Industrial pH problems from EUTECH Instruments.

The Easy Guide to pH Measurement - Thanks to ABB Automation.

The ABB Guide to Fast pH Measurement - Used for a host of applications across a variety of industries, getting the best from pH equipment requires consideration of a range of factors to achieve optimum efficiency and cost effectiveness.

pH Theory and Practice 

pH Measurement Basics

The following articles are compliments of Digital Analysis Corporation:

pH Probe Architecture - A description of how a pH electrode functions. Sample calibration procedures are also included in this discussion.

pH Probe Calibrations - Fundamental procedure for cleaning and calibrating the most common pH electrodes used in industry today which are also the most common probes that we use on our systems.

pH Adjustment, a Primer - A review of the meaning of pH, covering the pH scale, acids and bases, acidity and alkalinity, and the definition of pH. Also covered are the two basic system designs used in industry Continuous Batch (Flow Through) and Batch pH adjustment systems. Also discussed, but only briefly, is a proprietary design known as "Optimized Batch" pH adjustment / neutralization systems.

Limestone for pH Adjustment - This article clears up many misgivings regarding the use of limestone of for pH Adjustment. So you are thinking about using limestone? Better read this article first.

Chemicals used for pH Adjustment - The various choices for acid and base neutralizing chemicals are discussed here. If you are wondering which acid or base you should use as a neutralization agent then this discussion may be of help.

The following technical papers are from Emerson Process Management:

Theory and Practice of pH Measurement - An excellent 43 page handbook.

Theory of pH Measurement - pH is a measure of the acidity or alkalinity of a water solution. The acidity or alkalinity of a water solution is determined by the relative number of hydrogen ions (H+) or hydroxyl ions (OH-) present. Acidic solutions have a higher relative number of hydrogen ions, while alkaline (also called basic) solutions have a higher relative number of hydroxyl ions. Acids are substances which either dissociate (split apart) to release hydrogen ions or react with water to form hydrogen ions. Bases are substances that dissociate to release hydroxyl ions or react with water to form hydroxyl ions.

pH made Easy, Reliable - Jonas Berge - Water and wastewater treatment plants, as well as other industries, use several types of liquid analyzers to monitor quality in terms of many different properties. The pH meter is one of the most important. Analyzers communicate digitally using protocols such as HART^®, Foundation^® fieldbus, and WirelessHART. Maintaining this mix of analyzers can be a challenge. This is a result of analyzer probes being in direct contact with the process and subject to various different problems depending on the process conditions. However, modern pH analyzers diagnose themselves, the glass, and reference electrodes in the sensor, as well as the temperature sensor. This allows for more effective maintenance schemes that help keep the loop and plant running with minimum downtime. Recent enhancements to the EDDL (Electronic Device Description Language) IEC 61804-3 standards have helped improve calibration and advanced diagnosis of high-end pH analysers.

Advances in pH Modeling and Control - Gregory K. McMillan (Emerson) and Mark S. Sowell (Solutia Inc) - Many chemical and biological processes have pH control loops. Good pH control can be important for product quality as well as environmental compliance. The extraordinary rangeability and sensitivity of pH as a concentration measurement poses exceptional challenges in many aspects of pH design and implementation.

Virtual Control of Real pH - Virtual Design reduces the hassles of pH control.

Smart pH loops for Plug-n-Play Installation Reduce Calibration Time - Linda Meyers - New technology enhances pH sensors usage because of the Smart software that's implemented in advanced pH sensors and instruments. Never before has it been so easy to calibrate, plug-n-play, and evaluate pH monitoring. Before the Smart technology emerged, the only way to calibrate the pH sensor was to carry all of the calibration equipment into the field. In many facilities, this meant carrying at least two buffer solution bottles, two beakers and one rinse bottle to the various installation sites. Then, the calibration was done on-site at a location closest to the sensor installation. So come rain or shine, sleet or snow, hot or cold weather conditions, the technician had to maintain the sensor in even the worst environmental conditions.Smart technology changes all that. Smart pH sensors have a memory which holds calibration information, so there is no need to carry equipment to field - from PaceToday.

Bringing pH Measurement Systems Up to Date - George Pence and Richard Baril - Improvements in sensor life and range of applications can move liquid analysis from one of the most “cursed” functions in the plant, to one that requires only modest attention - Thanks to ISA and InTech.

pH Instrumentation Maintenance

pH Sensors: Know whether to Calibrate the Sensor, Clean the Sensor, Perform a Calibration Check or ...? - Fred Kohlmann - This paper addresses knowing when to do a pH sensor calibration versus a calibration check, how to properly clean a pH sensor, how to perform a pH sensor calibration and a decision tree for step by step guidance - from the ISA and Endress+Hauser.

pH Probe Maintenance - from the Digital Analysis Corporation.

Probe Cleaning

A common issue with pH meters is contamination and fouling of the probe, the following links provide some good information on cleaners available, including ultrasonic, bushing, chemical and self cleaning methods.

http://www.analyticon.com/analyticon/products/process/pH_cleaningdevices_immersionhc7.htm
http://www.wq.hii.horiba.com/pdf/k8.pdf
http://www.endress.com/eh/home.nsf/?Open&DirectURL=4E3EC3004B14A5F5C1256D4A002C6B7B

Other pH Instrumentation Accessories

Redundant probes

http://www.phneutralizing.com/products/redundant_probe.htm

Oxygen Analyser

Oxygen Measurement for Combustion Optimisation - Combustion optimisation for boilers and other combustion processes has long been an important issue with increasing fuel prices. There are many end users in Australia with fuel bills inexcess of one million dollars. With typical costs of combustion optimisationsystems, and possible fuel savings in excess of 5%, pay-back periods can be veryshort. This economy is based primarily on the measurement of oxygen in the fluegas - from processonline.com.au.

Paramagnetic oxygen measurement - Thanks to DragerSafety.

The following technical references are from Delta F Analysers:

• Paramagnetic Principles
• Zirconium Oxide
• Galvanic Fuel Cell
• Polarographic
• Delta F Non-Depleting Coulometric

Polarographic Oxygen Measurement For Cost-efficient, In-situ Operation - For the measurement of oxygen in continuous process analysis, several technologies are available. Because they differ widely in terms of application coverage, field performance and ease of use, the right technology has to be carefully chosen. In this white paper, we review the possibilities offered by measurement systems based on polarographic sensing technology - from Mettler-Toledo AG Process Analytics.

Oil in Water Analyser

The need for an In-Line Oil in Water Monitor - A.W. Jamieson Shell U.K. Exploration and Production, Aberdeen.

The following technical papers and application case studies are compliments of Jorin Ltd:

On-line determination of particle size and concentration (solids and oil) using ViPA Analyser - A way forward to control sub sea separators - A paper by Dr. Kami Nezhati, Senior Development Engineer, Merpro Ltd, Nick Roth, Technical Director, Jorin Ltd and Rick Gaskin, Marketing Director, Jorin Ltd.

Produced Water, Process Problem or Process Control - Nick Roth, Technical Director, Jorin Ltd and Rick Gaskin, Marketing Director, Jorin Ltd.

The ViPA Particulate Monitoring System - A Technical description from Jorin.

Oil in Water Analyser Application Case Studies

• Hydrocyclone Efficiency
• Separator Optimisation
• Desalter Optimisation
• Degasser Performance Study

Other Useful Links

Produced Water from Production of Crude Oil, Natural Gas and Coal Bed Methane - An 87 page White Paper from the US Department of Energy.