Oxygen Enrichment in Sulphur Plants to Reduce the Life Cycle Costs of New-Build, Large Gas Plants

Abstract

Abstract Oxygen enrichment is a well-known economic and reliable method of debottlenecking existing Sulphur Recovery Units (SRU) with minimal capital investment. It can also eliminate the need for fuel gas co-firing in the reaction furnace, required to maintain the correct temperature for contaminant destruction, for example for destruction of benzene, toluene and xylenes (BTX) in the acid gas. The concept of oxygen enrichment is simple: by replacing air with enriched air or pure oxygen the volumetric flow through the SRU decreases allowing more acid gas to be fed to the system – resulting in increased sulphur production capacity without the need for significant modifications to existing equipment or major changes to the process plant pressure profile. This paper specifically considers the application of oxygen enrichment to the design of new-build large gas plants where the feed acid gas is lean (has low H2S content) and contains BTX. Such plants typically require feed gas and/or combustion air preheating and the use of fuel gas co-firing and have not, historically, been considered for oxygen enriched operation. The effects of oxygen enrichment in such cases are presented and the resulting benefits in capital cost and operating cost reductions. An important part of the economic assessment is the supply of oxygen and the paper will provide guidance on the selection of the oxygen production technology - including cost indications depending on required oxygen volumes and oxygen-enrichment levels to be applied in the desulfurization process. The analysis focuses on a number of areas which include: –Equipment size: due to the smaller volumetric gas flowrate processed in oxygen enriched plants SRU and Tail Gas Treatment Unit (TGTU) equipment will be smaller compared to conventional air design and in the case of multiple trains it can even reduce the number of trains required.–Oxygen supply: The additional cost of the oxygen production; oxygen supply costs are considered as OPEX being supplied by industrial gas company, thus not requiring CAPEX.–Fuel Gas consumption: When fuel gas co-firing is required in the Reaction Furnace for contaminant destruction, the use of oxygen enrichment reduces or eliminates co-firing requirements. There are also savings in fuel gas consumption in the thermal oxidiser downstream of the TGTU.–Power consumption: this is reduced due to the smaller equipment required for the same sulphur capacity. Savings are also seen due to the reduced air demand and size of the combustion air blower.