Applications Of Transportable Water Dew-Point Analyzers

Interview conducted by G.P. ThomasAug 8 2013

Andy Benton, Technical Consultant at Michell Instruments Limited, talks to AZoM about the benefits and key applications of the new Condumax II transportable hydrocarbon and water dew-point analyzer.

Michell Instruments has recently developed a transportable version of its Condumax II hydrocarbon and water dew-point analyzer. Could you briefly explain the theory behind this instrument and how it utilises the ‘Dark Spot’ measurement principle?

The ‘Dark Spot’ principle for measuring hydrocarbon dew point is a variation of the fundamental chilled-mirror principle of measuring water dew point. Both technologies measure the actual formation of condensate on a temperature-controlled surface by reading changes in a beam of light which is reflected from it. It is this direct measurement of the actual dew point formation which makes the technologies so reliable, accurate and free from calibration drift.

The Condumax II technology is called ‘Dark Spot’ because the light reflecting off the shiny hydrocarbon condensates on the concave sensor surface forms a circle with a ‘dark spot’ in the centre when the dew point temperature has been reached.

Due to popular demand, the Condumax II is a transportable analyser – what are the inherent benefits of this compared to the on-line version, and have there had to be any compromises?

The Condumax II Transportable is not a replacement for the online version, but it enables flexibility for engineers to make reliable hydrocarbon dew point measurements in the field wherever needed. It can be used to help find faults in pipelines or to verify online measurements made by other hydrocarbon dew point analyzers.

No compromise has been made with the sensing unit, which is exactly the same on the transportable as with the online version of the Condumax II. The main difference is the sampling system. The transportable version has been designed to fit in the transportable case and is relatively simple. Online sampling systems can be designed to meet specific needs, and can be much larger and include extras such as heating or cooling elements, as required for permanent, continuous-operation analyser systems.

One main application area of the Condumax II is the quality determination of natural gas. In what situations is it important to be able to quickly and accurately measure this quality?

A classic example of where natural gas quality is important is at points of custody transfer - where the gas goes from one pipeline operator to another, but for this the online Condumax II is most appropriate.

The transportable version is most useful for troubleshooting – for example investigating the performance of hydrocarbon reduction processing or making spot-checks of gas quality at different points in a pipeline. Because it is transportable it can be brought into action quickly and at any point in the process.

Could you also explain how the hydrocarbon content and water dew-point of a gas act as a quality indicator? At what threshold is the gas seen as ‘poor’ quality’?

The quality of the natural gas is about ensuring that it is an efficient fuel and will not cause damage to the systems using it – whether these are domestic heating systems or power stations. High levels of heavy hydrocarbons – such as isobutene or pentane – mean that the natural gas is not an efficient fuel.

These heavy hydrocarbons also condense at higher temperatures and this condensate may damage systems and equipment. In a similar way, high levels of moisture makes the gas a much less efficient fuel.

Condensation of water in pipelines or transmission systems also creates the risk of corrosion – in cold climates it can freeze causing blockages. Hydrates – solid crystalline masses – may also form where there is a high level of moisture. These restrict pipeline flow capacity and carry the risk of impact damage to downstream pipeline infrastructure. To avoid these risks, transmission pipeline natural gas needs to conform to strictly enforced gas quality standards.

Such standards set maximum limits for HC and water dew point temperature. Specifications vary around the world, dependant on prevailing climatic temperature conditions, for example the EASEE-gas Common Business Practice for the EU countries limits the maximum permitted HC dew point to less than -2°C at any pressure and water dew point below -8°C at full line pressure.

What are the key similarities and differences between the Condumax II Transportable and the online version?

As mentioned before, the transportable version and the online version both use exactly the same sensing unit, with the same basic sample conditioning.

The main difference is the transportable sampling system has been designed to fit in a robust carrying case, while the online version offers a wide range of sampling options – such as heating or air conditioning so the unit can operate at the optimum temperature at all times whether sited in arctic or desert conditions.

Are there any further benefits to using a transportable analyser, such as cost or environmental considerations?

The main benefit of using the transportable version is ease of use and fast response: it can be set up to make measurements in almost any location. This is something that is just not possible with an online analyzer in such a swift timeframe.

The transportable version is also available to rent from Michell. This allows companies to verify their online analyzers quickly and at a fraction of the cost of purchasing and installing a new online analyzer. In environmental terms, enabling gas companies to find faults and make repairs faster can only help the environment.

Is the Condumax II suitable for use in harsh or extreme environments?

Absolutely – we have installed Condumax II systems in very extreme situations, where it can operate in temperatures from -20°C to +50°C. As mentioned before, Michell’s sampling systems can be designed with additional cooling or heating to enable operation in even more demanding situations.

The transportable version’s housing is designed to allow the unit to be moved from place to place in a pick-up truck, however, the sampling system doesn’t have the same heating or cooling options as the online version. Because of this, the ambient air temperature must be at least 5°C above both the hydrocarbon dew-point temperature and the water dew-point temperature at line pressure.

Are there any other important applications of the Condumax II?

The natural gas industry is in a phase of change at the present time, with alternative gas sources being developed to supplement traditional natural gas from geological sources. Such supplemental gases include bio-methane from anaerobic digestion of organic matter as well as hydrogen produced as a means to extract energy at times of excess electricity generation from wind or tide projects.

As these gases have extremely low HC dew point, as single component gases which traces of higher order hydrocarbons, these additions effectively reduce the HC dew point of the recipient natural gas. This can be of net benefit to a producer of natural gas in reducing the need to process the core natural gas to control HC dew point, but to gain such benefit it is essential to now the aggregate HC dew point of the gas blend. For this reason in-process on-line measurement is essential to ensure that gas quality is maintained.

How do you see the use of these transportable instruments progressing in the future?

Until the advent of the Condumax II Transportable, the gas industry has been reliant upon antiquated manual, visual dew-point measurement apparatus (referred to as Bureau of Mines) to perform spot-check measurements at gas sites, requiring specialist operator skill and cumbersome ancillary equipment such as coolant gas cylinders.

Michell Instruments now have the task of creating awareness that such spot check measurements can at last be easily fulfilled at any location by a self-contained automatic measurement system, free from the subjective interpretation, and therefore poor repeatability, explicit in manual cooled-mirror methods.

About Andy Benton

Andy Benton joined Michell Instruments in 1983, initially in the R&D section. Throughout his career he has specialised in devising innovative solutions to applications for online process gas and liquid analysis.

In the natural gas industry, he has advised best practice for water and hydrocarbon dew-point control and measurement to producers, pipeline operators and large-scale end users covering six continents.