A Novel Power Generation System Utilizing Un-treated Sour Gas Fuel

Abstract

A significant portion of natural gas reserves around the world contain large quantities of sulfur species and carbon dioxide, which are often referred to as sour gas reservoirs. The IEA reports that more than 40% of the world's gas reserves are sour, with the number increasing to 60% for Middle Eastern gas reserves. Sulfur species, such as hydrogen sulfide (H2S), are highly corrosive when mixed with water and toxic to biological organisms. Compounds such as SO2 and SO3, which are derived from direct sour gas combustion, are also highly corrosive when mixed with water at the condensation temperature of sulfuric acid. Therefore, removal of H2S to trace levels from natural gas is typically considered as the first step of the utilization of sour gas for power generation. This paper presents a novel method which enables sour natural gas to be directly burned for power generation without pretreatment. Oxidized sulfur compounds are captured by limestone in the combustion process to eliminate downstream sulfur corrosion. The desulfurized flue gas then goes through a solids removal process before entering a gas turbine or a turbine expander for power generation. A steam cycle is used for waste heat recuperation from both the turbine exhaust stream and the solids stream to improve the cycle performance. Both air-combustion and oxy-combustion configurations were investigated and modeled using Aspen Plus. The design conditions of each cycle are within the operating envelope of commercially available equipment, including compressors, turbines and heat exchangers, enabling near-term deployment of the presented system. Aspen modeling results show the range of efficiency percentages for different cycles is from the low 40's to the low 50's on a Lower Heating Value (LHV) basis. Without pretreatment, the heating value of sulfur in the sour gas and the heat released from the limestone scrubbing process can be fully utilized for power generation, thus improving the cycle performance. Economic analyses estimate that the baseline air-combustion sour gas system with a conservative estimated Capex ($2142/kW) is 41% cheaper than NGCC in 2011, and is about 28% cheaper than advanced NGCC in 2022 on a simplified Levelized Cost of Electricity (LCOE) basis. The LCOE of the oxy-combustion sour gas system is estimated to be 53% lower than advanced NGCC in 2022 when the revenue from CO2 and Argon sales is taken into account. Therefore, the novel untreated sour gas combustion system presented in this paper enables the petroleum and power industries to use sour gas for power generation more efficiently and cost effectively, even with full carbon capture.