Overcoming Challenges to Reduce H2S Content in Sales Gas Transmission Pipelines

摘要

This paper presents a case study highlighting actual implementation of technology advancements for removal of H2S (slipped from upstream gas plants) from sales gas pipeline at remote locations. GASCO’s pipeline network is designed for sour service (250 ppmv H2S). The guidelines for design of sour service pipelines as stated in ISO 15156 have been complied with. One of the pipelines which supplies sales gas to major power plants on a continuous basis is of 48" (of Consumer) and is designed for sweet service. This consumer is normally supplied sales gas by another gas Supplier A. GASCO is required to supply sales gas to power plants during the emergency requirement / outage scenario of regular gas supplier A. Indeed, slippage of H2S due to upsets in upstream plant facilities may cause several technical problems for instance, corrosion. Therefore, initial study focused on defining the corrosion implications of operating the 48" Pipeline with GASCO gas supply with up to 250 ppmv H2S.The main corrosion threat to the Pipeline is the risk of sulphide stress corrosion cracking (SSC). Study of the Gas Supplier A of Consumer Pipeline records indicates that the pipeline is not exposed to H2S partial pressure of 0.05 psi (a) as required by ISO 15156. The online H2S trends were reviewed for GASCO sales gas to assess the actual time of exposure. Starting 2014 to Target 48" Pipeline Integrity, Process Safety (PS), enhancement in HSE and performance monitoring, GASCO embarked on an ambitious Project installing state of the art H2S Scrubbers systems to mitigate H2S slippage into the pipeline. FEED was conducted to select the optimum Technology for H2S removal. The H2S removal technology selected was Non-Regenerative type, metal oxide based absorbent catalyst for removal of H2S from the sales gas. These catalysts have to be replaced after a fixed duration of service life estimated based on inlet H2S content and flow conditions. Owing to the size of the pipeline and the H2S content in the gas, the selected process of Non Regenerative technology has distinct technical and economic advantages over conventional regenerative processes. By virtue of the selected lead lag arrangement, multiple (three) train options and high SIL rated H2S analyzers, the usage of the catalyst is optimized and the overall system reliability, availability, maintainability and integrity is ensured for continuous operation without affecting the existing facilities. The process is unique and one of its kind on major pipeline within GASCO sales gas network.