Simulation Of Flue Gas CO₂ Capture Form Natural Gas-fired Power Plan

Fossil fuel power plants are one of the major sources of electricity generation, although invariably release green house gases. Due to international treaties and countries regulations, CO₂ emissions reduction is increasingly becoming key in the generators’ economics. The relatively low carbon content in natural gas compared to coal and oil as well as the low investment cost for natural gas combined cycles（NGCC） along with their high efficiencies assures that NGCC will have an important role in the future power generation mix.Currently, NGCC constitute a worldwide used generation technology, NGCC combined heat and power（CHP） can save more energy than the former. If future CO₂ abatement policies require that owners of NGCC-CHP units reduce CO₂ emissions, the feasibility associated with installing large-scale carbon capture to NGCC plants will be particularly relevant. The near term implementation of CO₂ capture in terms of an absorption and stripping process has been a topic extensively investigated the last couple of years. However, CO₂ capture from NGCC through a post-combustion and monoethanolamine（MEA） absorption option constitutes a technological challenge due to the low concentration of pollutants in the flue gas and the high energy requirements of the capture process.An analysis of the large-scale CO₂ capture process based on aqueous MEA solution for a 350 MW NGCC-CHP was carried out using process simulation. There economic indicators, namely, amine flow rate, thermal energy consumption in the reboiler and the cooling utilities were considered. Firstly, the modeling of capture system process was performed using Aspen Plus with RadFrac. The effects of CO₂ removal efficiency, absorbent concentration, lean solvent loading, flue gas and lean solution temperature, stripper operating pressure, rich solvent temperature at the stripper inlet on economic indicators were investigated and studied. Secondly, the design specification and sensitivity analysis function in Aspen Plus were used to optimize process parameters of the capture system. The best operating conditions of the CO₂ capture process with rich solvent temperature of 110 oC was determined. A minimum thermal energy requirement was found at a lean MEA loading of 0.3, using a 35 wt.% MEA solution and a stripper operation pressure of 2 bar, resulting in a thermal energy requirement of 3.55 GJ/t CO₂. Finally, an alternative configuration of desorption spliting was investigated, aimed at further reducing the overall energy requirement. With 17.5% of cold, rich solvent directly into the stripper, the thermal energy reduced to 3.20 GJ/t CO₂, relatively about 10% lower than the optimized result within the traditional capture process.Furthermore, the heat-economy analysis of the NGCC with CO₂ capture including desorption split configuration was carried out. The results showed the whole consumption of low-pressure steam for solvent regeneration accounted to 41% of the available and that the total efficiency penalty 6.34%-points in the power generating mode（reduced from 59.14%（LHV） to 52.80%）, while 20.20%-points in thermoelectric mode（reduced from 88.14% to 67.94%）, among which the efficiency loss with thermal supplying and power was 17.17%-points and 3.03%-points, respectively. It was also pointed out at the end, that the further research direction of CO₂ capture from NGCC.