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A plan by Saudi Aramco to increase Saudi Arabia's crude processing capacity includes grassroots facilities for processing approximately 2,500 MMsft3d of feed gas from various offshore fields. As part of this development, two NGL fractionation trains will be constructed to process propane plus (C3+) NGL feed streams and produce propane, butane and natural gasoline products that adhere to Saudi Aramco product specifications. At a later stage of the project, a higher content of carbonyl sulfide (COS) was found to be present in the feed gas. If left untreated, high COS in feed will cause the propane stream to fail product specification requirements.
This article discusses Saudi Aramco's methodical approach to address this challenge during the design stage. It includes an analysis to shortlist the technologies available to remove COS and an explanation of the technology that provides the most optimum solution. This article also highlights key issues to be considered during the design stage and the technology selection approach to ensure that overall plant operability is not jeopardized.
Project scope. The NGL fractionation trains will receive a C3+ stream from the demethanizer bottoms and a C3+ stream from the condensate stripper bottoms feed from the plant. The NGL fractionation train will fractionate the C3+ NGL feeds into propane, butane, pentane, natural gasoline and color body products.
The composition of contaminants, particularly sulfur species for both feed streams, is summarized in TABLE 1. The simplified flow diagram for the NGL fractionation trains is shown in FIG. 1. The fractionated products will be stored onsite for domestic use or for export.
Propane and butane products are treated through a typical caustic-based process for mercaptans removal. The treated stream is then routed to a liquid dehydrator to meet a company water specification of 0.1 ppmv. Both treated liquid propane and butane products are then routed to their respective storage for either domestic consumption or export use.
One of the major challenges is the presence of COS that arrives in the feed fluids to the gas processing plant. COS contained in the inlet gas will tend to concentrate in the propane product stream. After fractionation of the treated gas, approximately 89% of the COS ends up in the C3 stream, while 5% and 6% remain in the C2 and...