Adsorption Process For CO₂ Capture From Flue Gas Of Coal-fire Power Plant

The emission of carbon dioxide into the atmosphere due to the combustion of fossil fuels has emerged as a significant environmental problem. The solution of this problem can be achieved by a combination of several strategies including increased energy efficiency, and use of renewable sources for energy production. One suggested combination of secure energy supply and environmental protection can be achieved by CO2 capture and storage, CCS. There are several techniques that can be employed to remove CO2 from different industrial streams: adsorption, absorption, membranes, cryogenic separations, etc. Capture of CO2 by adsorption from flue gases of power stations was considered recently in some works. This technique can present operating flexibility, low capital investment and energy efficiency. In this work, zeolite 5A was employed as the selective adsorbents, and different adsorption processes were investigated both experimentally and theoretically for CO2 capture from flue gas. The main contents include two parts as follows:(1) Fundamental research of CO2/N2 adsorption. The adsorption equilibrium of CO2 and N2 on zeolite 5A was measured in a magnetic suspension balance. The adsorbent is much more selective to CO2. Fixed bed breakthrough and desorption experiments were used to study the adsorption kinetics of CO2/N2 on zeolite 5A. Mathematical models were used to describe the equilibrium and dynamic of the adsorption on zeolite 5A. A classic Skarstrom-type vacuum swing adsorption (VSA) cycle was studied for CO2 separation from CO2/N2 stream. And the influence of the operating parameters, such as feed flowrate, CO2 concentration, feed pressure and vacuum pressure, to the performances were studied by experiments and simulations. A modelling framework for multiple beds VSA process was developed, and simulations of multi-bed VSA and two-stage VSA were carried out for CO2/N2 separation. Also a 6-step combined vacuum and temperature swing adsorption (VTSA) process was proposed for CO2 capture. With a two-stage VSA unit, the overall performance was:CO2 recovery:91.1%, CO2 purity:96.1%. While the VTSA process can provide the product contains 93.4% CO2 with a CO2 recovery of 95.4% with desorption at 10kPa and 423K.(2) CO2 capture from flue gas. The feasibility and efficiency of adsorption technology were evaluated experimentally and theoretically for CO2 capture from the flue gas.A3-bed 8-step unit was established in Shanghai Shenneng Xinghuo Coal-Fire Power Plant. The amount of zeolite 5A was 282 kg. The simulation results were validated with the onsite experiment results and the model can be used for further scale-up. The energy consumption for CO2 capture, which was compared with the reference on VPSA processes, was much lower than the absorption and can be further reduced in the larger-scale case.In conclusion, zeolite 5A provided high CO2 capacity and selectivity.Different adsorption processes can be developed to obtain good performance. From a 3-bed 8-step VSA process, 79% CO2 was captured with a purity of 85% from the flue gas with a flowrate of 46.0 Nm3/h. And the energy consumption was 2.37 MJ/kgCO2.With the development of the adsorbent and further optimization of the processes, the adsorption technology can be a promising CO2 capture technology.