- Puraspec 100 process for natural gas purification.
One of the current challenges facing gas and oil producers in Southeast Asia is the successful development of small gas fields (around 100 mcf/d) in remote locations. If the composition of the gas meets pipeline specification, it can be piped to a local industry or fed into a major distribution network. However, if processing is required, the cost of equipment coupled with the need to provide skilled operating staff means that these gasfields are not worth developing.
Recent technological advances are starting to give interesting options for the development of such gasfields. If the gas is at a reasonable pressure - say, above 70bar - and there are only modest amounts of CO2 and H2S to be removed, it is possible to build a gas processing plant with no rotating equipment and no liquid systems which will allow the pipeline specification to be met for CO2, H2O, H2S and Hg.
The absence of rotating plant and liquid systems means that there is no requirement for services and, more important, no need for continuous manning. These plants are built using a semipermeable membrane coupled with fixed bed absorbents. The membrane's role is to remove water and part of the CO2 and H2S whilst the fixed bed absorbents control precisely the level of H2S and Hg.
Units which use ICI Katalco's Puraspec technology are already in service in remote locations in Australia and Pakistan and are being considered for use offshore and onshore Indonesia. They can also be constructed in skid mounted form as early production units which are again of interest in Indonesia for the development of complex offshore gasfields.
A typical process flow is shown in the diagram. The raw gas is passed through a filter to remove dust and polycyclic aromatics. It is then contacted with the membrane which allows the diffusion of CO2, H2S and H2O to give a CO2-rich permeate stream which is flared or may be used for local heating. The product stream is then contacted with Puraspec reactors which contain fixed bed absorbents for the precise removal of H2S and Hg.
Typical process conditions are those of the Sagasco Resources plant at Beharra Springs 400 km north of Perth which has been in service since November 1993. The produced gas rate is about 25 mcf/d and is delivered at 70bar and 40C with the following composition:
An additional attraction of this type of plant is the extreme flexibility to changing gas rate and level of impurities to be removed. The spent absorbents are recycled through the metal recovery industry.
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