(91e) Analyses of Hot/warm CO2 Capture for Igcc Processes

There is growing concern that the buildup of anthropogenic CO2 and other greenhouse gases in the atmosphere is contributing to climate change with undetermined consequences. To address this problem, the U.S. Department of Energy's Carbon Sequestration Program has been developing technologies that will allow coal, our most abundant fossil fuel, to be burned in power plants with very low emissions of CO2. One promising approach is pre-combustion CO2 capture from an Integrated Gasification Combined Cycle (IGCC) power plant. One current state-of-the-art CO2 capture technology for high-pressure IGCC power plants is SelexolTM scrubbing. Coal is gasified in a high-pressure, high-efficiency gasifier to produce a high-pressure syngas stream. The H2 and CO2 concentrations are maximized by converting CO to CO2 and H2 in a water-gas shift (WGS) reactor and then cooled to around 100oF before entering into a two-stage SelexolTM acid gas removal process. The H2S is removed in the first stage and sent to a Claus sulfur plant; while the CO2 is recovered in the second stage and compressed to supercritical conditions in preparation for pipeline transport. The hydrogen-rich fuel gas is reheated and combusted in a gas turbine (GT) topping cycle to produce power.

The process of cooling and reheating the syngas before and after the acid-gas removal (AGR) process decreases the efficiency to the overall power cycle. A CO2 removal process operating at a temperature between WGS reaction and gas turbine inlet temperatures can eliminate extra cooling/heating of the syngas and thus improve the thermal efficiency and economic performance of an IGCC process. However, an adsorption/absorption based capture process which operates at a higher temperature will require stronger chemical interaction (larger heat of reaction) between CO2 and the sorbent/solvent and thus result in higher energy consumption. Such an increase in heat of reaction is not an issue for trace contaminants but could be critical to bulk gas such as CO2 due to its large quantity.

Detailed engineering analyses on different types of hot/warm gas CO2 capture removal technologies have been performed to analyze the energy requirement of an adsorption/absorption based hot/warm CO2 capture process. In addition, thermodynamic analyses of the hot/warm separation processes were also conducted to obtain a relationship between required reaction heat (heat of adsorption/absorption) and CO2 capture temperature.