Keeping gas flowing
24 Jun 2006
Undersea pipelines and the import of liquefied natural gas (LNG) are now seen as key to meeting UK fuel demand in future. However, these new sources of gas must be tested for many contaminants, not least moisture, which can cause problems in the pipelines and during processing.
One of the first stages of gas processing is dehydration as gas from the wellhead is saturated with water and liquid hydrocarbons. This is carried out by desiccant drying using liquid glycol injection in contactor towers.
If the gas is still not sufficiently 'dry', it can corrode pipelines or risk hydrate formation - the combination of hydrocarbon condensates with water to form solid crystalline hydrates. These can line the inner pipe wall, reducing flow capacity, or even break off into the gas flow risking damage to process valves, filtration and compression stations, and potentially blocking the pipeline.
LNG processing requires even less water content in the gas, as moisture can freeze inside the cryogenic processes involved, reducing production capacity and eventually causing blockage. Water vapour content must be kept at levels of around 0.01 ppmV, which equates to a dew point of around -100°C.
Devices for measuring moisture levels in such conditions must also present no risk of a spark as natural gas is highly flammable.
Among those tackling this problem, Cambridge-based Michell Instruments has developed the Promet EExd analyser. The unit, it claims, is the world's first purpose-designed, EExd flameproof-certified, process moisture analyser and meets all the requirements of clients needing an installed solution in hazardous areas.
Promet EExd features EExd flameproof ATEX and CSA certification, complete zone 1 or 2 installation, and a remote interface option for mounting in a safe area if required. The analyser also offers single- and dual-channel moisture control capability, with integrated electronic pressure measurements, within the same single, field-installed, flameproof housing.
Each analyser communicates with a remote interface through the Modbus RTU, so transferring all of the functionality of the main unit to an indoor safe environment.
