CO2 emission reduction from natural gas power stations using a precipitating solvent absorption process

Abstract

There has been a rapid increase in the use of natural gas for power generation based on gas turbine technology which elevates the importance of carbon dioxide (CO2) capture technology to reduce CO2 emissions from gas turbine based power stations. The low content of CO2 in the gas turbine exhaust results in low rates of CO2 absorption and larger absorption equipment when compared to studies done on coal fired power stations. Furthermore the high oxygen (O2) content in the exhaust gas adversely affects the solvent stability, particularly for the traditional amine based solvents. This paper describes how exhaust gas recirculation (EGR) along with CO2CRC's low cost “UNO MK 3” precipitating potassium carbonate (K2CO3) process can overcome the challenges of CO2 capture from gas turbine power stations. To further bring down the energy requirements of the capture process, heat integration of the UNO MK 3 process with power generation process is carried out. An economic analysis of the various retrofit options is performed.The current study shows that in the case of retrofitting the UNO MK 3 process to a natural gas combined cycle (NGCC), the use of EGR can reduce the energy penalty of CO2 capture by 15%, whilst a reduction of up to 25% can be achieved with the heat integration strategies described.Significantly the study shows that converting an existing open cycle gas turbine (OCGT) to a combined cycle with steam generation along with retrofitting CO2 capture presents a different steam cycle design for the maximum power output from the combined cycle with CO2 capture. Such a conversion actually produces more power and offers an alternative low emission retrofit pathway for gas fired power.Cost analysis shows that inclusion of the UNO MK 3 CO2 capture process with EGR to an existing NGCC is expected to increase the cost of electricity (COE) by 20%. However, retrofit/repowering of an underutilised or peaking OCGT station with the inclusion of CO2 capture can reduce the COE as well as produce low emission power. This is achieved by increasing the load factor and incorporating a purpose built steam generation cycle.