What is the ideal way to measure Hydrocarbon dew point?

There might not be an ideal way to measure Hydrocarbon dew point as it is not an easy parameter to accurately determine due to several factors that may affect the measurement process.  

Direct measurement by fundamental chilled mirror analysis, and equation of state calculation from gas composition using a process gas chromatograph, are techniques that are  commonly used across different applications to measure Hydrocarbon dew point (HCDP).

While some techniques have proven to be more efficient than others, the final approach to be used for the measurement of HCDP may be dependent on the application as results in most methods have shown that a true value of hydrocarbon dew point is difficult to measure and define.

A report by the National Physical Laboratory compares several methods for measuring hydrocarbon dew point of natural gas to determine whether gas can be transported safely through national and international pipelines in the UK to ensure the final product meet quality standards.

The report outlined the results of a study that compared the conduct of direct and indirect methods for determining the hydrocarbon dew point of real and synthetic natural gases.

Results for the study were obtained from six samples using one automatic chilled mirror instrument (ACMI), one manual chilled mirror instrument (MCMI), two laboratory gas chromatographs (GCs), and two process gas chromatographs (GCs).

The study found that the dew point measured by the ACMI is greater than that measured by the MCMI. When compared with process gas chromatograph, the study also found that the dew points measured by the ACMI samples are greater than those from process GCs.

However, the study claimed that the results from the samples could have been influenced by factors such as the complex nature of the real mixtures which actual state is difficult to be determined by gas chromatography. It is suggested that hydrocarbon species (components) could be under-measured, not detected, or misidentified, which has a significant effect on the calculated hydrocarbon dew point.

     

Other factors such as cooling rate, trigger point, and cell construction directly related to the operation of MCMI and ACMI could also affect HCDP measurement.

In conclusion, the measured dew point is dependent on the analytical method, and it is suggested that any reported dew point should therefore be appended with the information on the analytical method used.

What techniques are used to measure hydrocarbon dew point, and which is ideal?

As stated above, fundamental chilled mirror analysis, and equation of state calculation from composition using a process gas chromatograph (often used in labs), are the commonly used techniques or methods that are widely accepted to measure hydrocarbon dew point (HCDP) or hydrocarbon liquid drop-out.

Fundamental chilled mirror (manual chilled mirror instruments):

The term dew point is most applied to the temperature at which  water vapour condenses when atmospheric air is cooled; dew or frost forms and becomes visible at this temperature.  In the case of HCDP in natural gas, the heaviest molecular weight trace components in the composition condense to form a liquid film when the gas is cooled.

The fundamental chilled mirror technique relies on a process of cooling a mirrored surface in contact with gas stream. The temperature of the mirror at the point where condensate is first observed is referred to as the dew point. In this process, thousands of manual ‘dewscopes’ are used to determine the hydrocarbon dew point of natural gas.

This technique is limited by the ability of the operator because it thoroughly relies on individual’s judgment to record the dew point temperature accurately.

    

Analysis of gas composition using a process gas chromatograph:

This technique requires a process gas chromatograph providing a detailed gas composition analysis including heaviest trace hydrocarbons in combination with a calculation dependent on the equations of state,  which predicts the resultant hydrocarbon dew-point temperature.

The measurement of potential hydrocarbon liquid content (PHLC):

PHLC is the least used technique within the industry. The method measures the amount of hydrocarbon liquid in milligrams per cubic meter, which will condense out of a natural gas stream at a particular operating temperature. This method is a parallel measurement to hydrocarbon dew-point temperature., which is applied by some pipeline operators as a laboratory reference method to define and harmonise the measurement sensitivity of on-line, automatic chilled mirror analyzers operating across their networks.

   

What are the benefits of measuring hydrocarbon dew point?

    

Hydrocarbon dew point in natural gas is often measured to control the risk of liquid condensate forming in the pipeline. These condensates jeopardize operational reliability and safety and may also prevent producers and transporters from meeting international quality standards.

What are the recommended analyzers to measure hydrocarbon dew point?

In most non-lab applications, the chilled mirror method is preferred.

We offer two instruments (See Below)

Dew Point instrument

The Michell Instruments' Condumax II Hydrocarbon Dew-Point Analyzer can deliver fully automatic on-line analysis, 0.5 °C hydrocarbon dew-point accuracy, it can self-clean, does not require a purge or cooling gas, and certified by IECEx, ATEX, UKCA, cQPSus, and GOST Ex.

The instrument is built on the fundamental chilled mirror principle. It uses a variation of the chilled mirror dew-point sensor referred to as the Dark Spot technique to determine the true measurements of hydrocarbon dew point.

Dew Point

Michell Instrument's CDP301 Condumax Dew Point Tester uses high-definition video to display condensate formation on a screen, reducing the reliance on operators. This analyzer makes it easy for operators to determine the exact dew-point temperature and record a video to report all measurements for further analysis accurately.

It features, high-definition color LC display, visual identification of both water and hydrocarbon dew point, 100 barg operating pressure rating, an automatic mirror cooling rate control according to ISO 6327 and ASTM D1142 test methods for natural-gas dew-point measurements, it is self-contained, rechargeable battery-powered, and Exd certified IECEx ATEX UKCA cQPSus Zone 1 IIB+H2 T3.

It can also measure greater than 60˚C measurement mirror cooling depression range (up to 100 barg pressure), and it is better than +/-0.5˚C accuracy of mirror surface measurement.

Watch the video below for more details:



Where to get hydrocarbon dew point analyzers (instruments)?

At PST, we have over 45 years of experience with moisture and hydrocarbon dew-point measurement.

We understand that making a final decision on the suitable hydrocarbon dew point analyzers for your process may be difficult. That is why we are available to support you through your decision-making process.

We are a multinational brand, and we are ready to support you regardless of your location.

    

Click here to see our global locations

  

Find further support

Please get in touch with us if you have any comments to make on this article or would like to discuss it further.  Contact US

You may also like to read our blog What is Hydrocarbon Dew Point and how is it measured? which highlights some of the factors you should know that may affect the process of measuring hydrocarbon dew point.

   

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