New Technology Simplifies the Measurement of Hydrocarbon Dew Point

Improved hydrocarbon dew point (HCdp) measurement in natural gas processing

Since 1987, Michell Instruments has led the development of advanced hydrocarbon dew-point measurement devices, and we understand the importance of HCdp measurement for the safe, efficient and profitable operation of natural gas processing, pipeline and energy generation systems. We also realize how difficult it can be, even for experienced engineers, to achieve accurate and consistent measurement. That’s why we’ve launched a new generation of hydrocarbon dew-point analyzers, which offer simplicity of use, precision and full traceability.

The complexity of measuring hydrocarbon dew point

Hydrocarbon dew point occurs when the temperature of the gas, at a given pressure, reaches the level at which hydrocarbons begin to condense. Unlike moisture dew point, where there is essentially a simple compound formed of just two elements, a hydrocarbon gas can contain multiple complex hydrocarbon compounds, plus varying impurities that include water, nitrogen, sulphides and carbon dioxide.

This makes precise HCdp detection challenging, as different hydrocarbon compounds condense at different temperatures at given pressures. For example, heavier hydrocarbons such as propane and butane will condense at higher temperatures but leave lighter compounds entrained in the gas vapor.

Typical phase envelopes for natural gas through stages of processing

To learn more about hydrocarbon dew point, take a look at our in-depth blog post.

Safety, efficiency and contractual compliance

It is essential that hydrocarbon dew point is measured accurately, at different stages in the process of natural gas extraction, processing, distribution and combustion, for operational efficiency, reliability and equipment safety to be maintained.

For example, the formation of hydrocarbon condensates, or natural gas liquids, in pipelines can restrict gas flow and potentially damage pipeline compressors. Similarly, in natural gas-fired power stations, it is necessary to maintain the temperature of the fuel gas by at least 10°C (50°F) differential above hydrocarbon dew point or water dew point (whichever is higher), to avoid the risk of condensates forming as the gas pressure drops from pipeline to burner inlet pressure; failure to do this can lead to an increase in NOx emissions and possibly result in flashback from the ignition nozzle to the mixing chamber, causing major turbine damage.

Measuring hydrocarbon dew point is also part of the contractual obligations for producers, processors and pipeline operators, to ensure that the quality of the gas they supply meets the required specifications.

Dew-point testers, gas chromatographs and chilled mirrors

Traditionally, hydrocarbon dew point has been measured manually using a portable cooled mirror instrument, such as a Bureau of Mines Dew Point Tester. These devices have been in use for many years, but are complex and time consuming, offer only a spot check and, more importantly, rely on the skill and judgement of the operator to produce accurate results.

An alternative option is a gas chromatograph, using an equation-of-state analysis method. Gas chromatographs are widely used in the natural gas sector and, while capable of producing accurate results, are limited in terms of their suitability for precise hydrocarbon dew-point measurements. Sampling is again based on spot checks, analysis methods are indirect, and compounds such as benzine and toluene can produce large measurement errors.

A third, and increasingly popular, technique, is to use an automatic, on-line, continuous measurement system. These have been available for some years and use a proven cooled mirror detection technique, where a cooled stainless-steel optical sensor with a central conical-shaped depression is used as the surface on which hydrocarbon condensate can form. A collimated red light is then directed onto this depression and the reflected light captured by an optical detector, where the difference between the dry and condensate conditions is measured. This method is extremely accurate, fast, reproducible and ideal for detecting levels of condensate below traditional manual inspection methods. The system also allows the nature of the condensate, and thus the gas, to be easily characterized.

Innovative sensor technology

The CD603 Dew-Point Analyzer extends this capability. Using a new detection technology, it measures both hydrocarbon and water dew points (Wdp) through its cooled mirror system. This new model builds upon proven measurement techniques while adding enhanced features and specifications. A single cooled-mirror sensor cell with greater than 65 ˚C (149 °F) measurement depression range with automated HCdp and Wdp measurement modes provides superior sensitivity to the previous generation of HCdp analysis products.

The high-contrast capacitive button-operated, color LCD presents all measured data to the user in a clear and understandable format. The main display incorporates a real-time trend graph and alarm indicators based on the NAMUR 102 standard. A powerful and intuitive HMI makes control, logging and configuration of analyzer parameters easy.

The analyzer provides two user-configurable analog outputs, and Modbus RTU/TCP communications, allowing it to interface with a SCADA DCS system, or by a computer using the dedicated application software. A set of four adjustable volt-free alarm contacts allows the CD603 to be used for direct process control.

CD603 Condumax Dew-Point Analyzer

This new system has the potential to enhance efficiency and productivity across the natural gas sector, with even higher levels of accuracy, simplicity of use, low maintenance requirements and full traceability.

We are the world’s leading experts in moisture monitoring and measurement. We have eight different technologies covering all moisture applications, backed by unrivalled technical and customer support. To learn more, talk to one of our application specialists today.