Lowering the Energy Cost of Carbon Dioxide Capture using Ejectors for Waste Heat Upgrading

The largest technical challenge to full-scale post-combustion carbon capture in power plants is the enormous energy consumption for solvent regeneration. If legislative requirements impose CO2 capture, chemical absorption/desorption using amine solvent solutions is the most mature commercial technology available. The use of ejectors to upgrade external waste heat has recently been shown to significantly reduce the amount of valuable turbine steam required to regenerate the solvent. Using the Aspen Plus chemical process simulator, this study considers three different liquid sources for producing the ejector secondary steam in a waste heat supplied flash tank. In each case the goal is to minimize the sum of the heat duty of the ejector primary steam generator and the stripping tower reboiler. A base case 20 wt% MEA absorption/desorption CO2 capture process was modeled, with flue gas data from a 400 MW net power coal-fired electric plant. Using stripping column condensate or lean solution to create the ejector secondary steam were found to be viable options for reducing valuable turbine steam consumption, with respective reductions of 14% and 23% shown for the completed simulations. With ejectors, lower temperature waste heat can be used to partially replace valuable turbine steam normally required in the reboiler for solvent regeneration in CO2 capture.