Techno-economic analysis of sour gas oxy-fuel combustion power cycles for carbon capture and sequestration

Abstract

The world's growing energy demand coupled with the problem of global warming have led us to investigate new energy sources that can be utilized in a way to reduce carbon dioxide emissions than traditional fossil fuel power plants. One of these unconventional fuels is sour gas. Sour gas consists of mainly methane, containing large concentrations of hydrogen sulfide and carbon dioxide. Over 30% of the world's natural gas reserves are considered sour. However this unusual fuel poses many challenges due to the toxic and corrosive nature of the combustion products. One of the most promising technologies for carbon capture and sequestration is oxy-fuel combustion. This involves separating the nitrogen from air prior to the combustion itself. Then, after combustion, we separate the water and other substances and can use the resulting carbon dioxide stream for enhanced oil recovery representing an added economic benefit of this system. Firing temperatures for pure oxygen combustion can reach values up to 2500° C, which is well above what the combustor can handle. Therefore a diluent has to be added to reduce the temperature back to appropriate levels, but the key question is how this impacts the efficiency and performance of the entire cycle. Hence, if feasible, the use of sour gas in an oxy-fuel power plant could potentially allow us to harness the economic and environmental potential of this unconventional fuel. Depending on the cycle configuration, water or carbon dioxide can be used as diluents to control the flame temperature in the combustion process. All of these cycle types were modeled and the cycles' performances and emissions were studied. When the working fluid condenses in the cycle, sulfuric acid is formed due the presence of SO, compounds, which causes corrosion and can damage power plant components. Therefore, either expensive acid resistant materials should be used, or a redesign of the cycle is required to overcome this challenge. Different options were explored for each of the cycle types mentioned to help in the visualization and performance prediction of possible sour gas oxy-fuel power cycle configurations. A cost analysis of the proposed systems was also conducted in order to provide preliminary levelized cost of electricity estimates.