Abstract
Power plants are a major source of CO2 emissions in the environment, which cause global warming; due to this issue, CO2 capture from hydrocarbon fuels is one of the key technology options to reduce greenhouse gases. Pre-combustion capture of CO2 in the combined gas and steam turbine cycle has been investigated in this paper. The first step in the pre-combustion method is to react the fuel with oxygen, which comes from the air separation unit and produces a mixture of hydrogen and carbon monoxide. The CO is converted to CO2 in a water-shift reactor, and a physical absorbent removes the CO2; a hydrogen-rich fuel is produced, which can be burnt in a gas turbine with minimal CO2 emissions. This paper presents a thermodynamic cycle analysis, where pre-combustion CO2 capture is applied in a combined cycle where the main goal is to reduce the CO2 emission into the atmosphere. The main parameters are varied to examine the influence on cycle performance. The cycle performance results for the combined cycle with CH4 as fuel are presented and compared to the combined cycle with precombustion CO2 capture, both with and without Nitrogen injection into the compressor. An exergy analysis is carried out to determine which case has more exergy destruction. The results indicate that at 45 oC the combined cycle efficiency is raised by around 3 % when the pre-combustion CO2 capture without Nitrogen injection into the compressor is used, and the power output has been increased by 29 %. The performance of combined cycle with CO2 capture can be further enhanced by the N2 acquired from the air separation process and injected into the compressor’s middle stage. The results demonstrate a good improvement in the performance; the power output increases by 48 % and efficiency by 4.2 %. However, exergy destruction is increased when the CO2 capture, both with and without N2 injection into the compressor is used. Nevertheless, pre-combustion capture requires large monetary investment for a new-build plant where also the CO2 emission is reduced by 100 %.