COSWEET~(TM) : Deep COS removal from natural gas compatible with all H2S/CO2 specifications

摘要

Natural gases, when collected from production wells, are commonly polluted with many contaminants. Among these contaminants are sulfur compounds such as H2S and COS and unwanted molecules like CO2. Throughout the oil and gas treatment chain, various steps are used to separate most of the undesired compounds from the profitable part of natural gas. Amine solvents are very often used for this step, as they can be adapted to various specifications and to a wide range of feed gas compositions. However, the amine processes do not provide attractive compromises between investment and operational costs when they target tight COS specifications from gas with large amounts of COS as, for example, (i) When total CO2 removal is required, conventional amine processes can be adapted to remove COS down to very low levels in treated gas, but this is generally achieved by increasing the solvent flowrate along with expensive absorber arrangements (ii) To achieve selective removal of H2S, MDEA is required, but since the reaction between MDEA and COS is very slow, the MDEA is not capable of achieving deep COS removal. IFPEN and PROSERNAT have developed the COSWEET? process for the removal of COS from natural gases down to 1 ppmv COS or lower. COSWEET? process is based on a combination of deacidification with an amine solution and of COS destruction on a metal based catalyst. It reaches nearly 100% COS conversion even at low temperature. The COSWEET? reactor handles most of the COS removal independently of the amine process scheme. Coupled to the adapted solvent, it is possible to tailor the amine scheme for any specifications of acid gas removal, or for selective removal of H2S. Reduced investment for the deacidification section and positive consequences of the quality of acid gas on the design of the sulfur recovery facilities improve the AGRU + SRU processing scheme. This paper presents the results obtained on COS conversion, the model and simulation tool, and case studies showing the advantages of coupling COSWEET? to amine based solvent. In particular, emphasis is made on the performance of COSWEET? at low temperature and subsequent thermal integration, as well as on the reduced investment and operating costs compared to conventional amine processes (including formulated MDEA units and the quality of acid gas to the Sulfur Recovery) designed to reach the same COS specification. The impact on the SRU chain is therefore evaluated in the case studies.