Influence of gas turbine exhaust CO₂ concentration on the performance of post combustion carbon capture plant

As a result of increased concern over Greenhouse Gas emissions, capture of CO₂ from stationary power sources is a topic under discussion throughout the world. The most developed technology for the application is post combustion carbon capture using liquid solvents. However, due to very low concentration of CO₂ in the gas turbine emitted flue gas, energy penalty caused by the capture process is relatively high. One of the methods to increase CO₂ concentration is the recycling of flue gas (also termed as EGR) in which part of the flue gas is sent back to join the air stream entering the compressor. This paper presents results of an experimental campaign carried out at the Pilot Scale Advanced Capture Technology (PACT) facilities of the UK Carbon Capture and Storage Research Centre (UKCCSRC). A Turbec T100 microturbine of 100kWe is integrated with a post combustion carbon capture plant of 1TPD (Ton per day) CO₂ capture capacity. The microturbine is very lean combustion system and produces a flue gas having only 1.5% CO₂. Therefore, in order to simulate EGR on industrial gas turbines which produce around 4-5% CO₂ in the exhaust stream, CO₂ from a cryogenic storage tank was injected into the slip stream of the gas turbine exhaust. The impact of different CO₂ concentrations (representing EGR) on the post combustion carbon capture process is experimentally evaluated. It is observed that the energy penalty caused by the capture process is considerably reduced at higher CO₂ concentration in the absorber inlet flue gas stream. EGR also has a negative impact on the produced power from the gas turbine as well as the combustion process. However, it has positive impact on the power output from steam turbine. Optimum recycle ratio for maximum power output from combined cycle gas turbine is discussed. Performance of the absorption column as indicated by rich and lean solvent CO₂ loadings is discussed. Moreover, emissions of solvent and some of the degradation products with the exhaust gas from the capture plant are monitored and reported.