Modelling and Simulation of Transient Performance of the Semi-Closed O₂/CO₂ Gas Turbine Cycle for CO₂-Capture

One of the concepts proposed for capture of CO₂ in power production from gaseous fossil fuels is the semi-closed O₂/CO₂ gas turbine cycle. The semi-closed O₂/CO₂ gas turbine cycle has a near to stoichiometric combustion with oxygen, producing CO₂ and water vapor as the combustion products. The water vapor is condensed and removed from the process, the remaining gas, primarily CO₂, is mainly recycled to keep turbine inlet temperature at a permissible level. A model for predicting transient behavior of the semi-closed O₂/CO₂ gas turbine cycle is presented. The model is implemented in the simulation tool gPROMS (Process System Enterprise Ltd.), and simulations are performed to investigate two different issues. The first issue is to see how different cycle performance variables interact during transient behavior; the second is to investigate how cycle calculations are affected when including the gas constant and the specific heat ratio in compressor characteristics. The simulations show that the near to stoichiometric combustion and the working fluid recycle introduce a high interaction between the different cycle components and variables. This makes it very difficult to analytically predict the cycle performance during a transient event, i.e. simulations are necessary. It is also found that, except for the shaft speed calculation, the introduction of gas constant and specific heat ratio dependence on the compressor performance map will have only a minor influence on the process performance.