Heat Duty Evaluation for Solid Acid Catalyst-Aided CO2 Desorption in Amine-Based Post combustion CO2 Capture and Option for Integration of Process with a Coal-Based Electricity Generating Power Plants
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This research introduces a novel idea for CO2 absorption technology used in post combustion capture in coal based electricity generations. It has as its objective the reduction of the energy requirement for the regeneration of amine solvents with the aid of solid acid catalysts. The work included two major components: laboratory experiments and process simulations of the integration of the CO2 capture process with a coal fired power plant. The experiments were performed in a bench scale CO2 capture apparatus. The absorber and desorber were stainless steel pipes with inside diameter of 0.05 m and height of 1.50 m. The desorber was loaded with varying amounts of each solid acid catalyst (γ-Al2O3 or HZSM-5) and operated at average bed temperatures of 75, 85, and 95˚C. The solvents tested were both single primary amines and mixtures of primary and tertiary amines, namely 5 M MEA, 5 M MEA:2 M MDEA, and 5 M MEA:1.25 M DEAB. Simulated flue gas, 15% CO2 in N2, was used at a total flow rate of 15 SLPM. The results showed that cyclic capacity and absorption efficiency increased while heat duty decreased when the catalyst quantity was increased. The increase in absorption efficiency was found to be in the order of 5 M MEA:γ-Al2O3 < 5 M MEA:HZSM-5 < 5 M MEA:2 M MDEA:γ-Al2O3 < 5 M MEA:2 M MDEA:HZSM-5 < 5 M MEA:1.25 M DEAB:γ-Al2O3 < 5 M MEA:1.25 M DEAB:HZSM-5. The relative reduction in heat duty of the system was found to be in the order of 5 M MEA:1.25 M DEAB:HZSM-5 < 5 M MEA:2 M MDEA:HZSM-5 < 5 M MEA:1.25 M DEAB:γ-Al2O3 < 5 M MEA:2 M MDEA:γ-Al2O3 < 5 M MEA:HZSM-5 < 5 M MEA:γ-Al2O3. The results demonstrate improvements due to the addition of the tertiary amine, with DEAB providing the superior performance with the two catalysts. The performance of HZSM-5 was better than that of γ-Al2O3 for all conditions. In order to evaluate the energy saving of the amine absorption process with a catalytic desorber, a process simulation was undertaken. A supercritical coal fired power plant of 130 MW gross electricity output integrated with a CO2 capture plant was modeled in PROMAX®. For the CO2 capture island, two amine solvents (5 M MEA and 5 M MEA:2 M MDEA) and two different CO2 capture configurations – conventional CO2 capture process and CO2 capture process with catalytic desorber – were selected for the comparison. For the power production island, supercritical main steam at 25 MPa/600˚C and reheat steam at 3.5 MPa/620˚C were used to drive the turbine set. The comparison was made between the conventional CO2 capture process withdrawing steam from between the intermediate and low pressure turbines at 0.9MPa/406˚C and the catalytic desorption process using steam at 0.3 MPa/ 266˚C. It was found that the energy penalty was 30.32% for 5 M MEA and 25.06% for 5 M MEA:2 M MDEA when operating with the conventional CO2 capture process and 27.77% and 16.02% with the catalytic process. In addition, if the energy from flue gas cooler was recovered for use in the catalytic desorption process, the energy penalty was reduced to 23.60% for 5 M MEA and 12.01% for 5 M MEA:2 M MDEA.