A technical and economic evaluation of CO2 separation from power plant flue gases with reclaimed Mg(OH)2

A method of inexpensively and reliably separating CO2 from flue gases by means of using magnesium hydroxide (Mg(OH)2) has been studied. Mg(OH)2 may be easily reclaimed from power plants using magnesium enhanced flue gas desulfurization systems (ME-FGD). The CO2 scrubbing system may be operated as either a oncethrough system which produces magnesium carbonate for sequestration of carbon, or as a regenerable system where a concentrated CO2 gas stream is created for further processing. The experimental results indicate that CO2 is absorbed into solutions containing reclaimed Mg(OH)2 by mean of a first order reaction, where the activation energy of this reaction was measured to be 7.7 kcal/mol. Continuous flow experiments were performed in a bubble reactor with simulated flue gas containing 15%V CO2 in contact with a solution of Mg(OH)2. Experiments have shown that up to 70% of CO2 separation may be achieved in this system. For a system based on a typical 500 MW power plant and reclaiming the magnesium hydroxide from a ME-FGD, experiments have shown that from 7-17% of the CO2 from the gas stream may be continuously removed through the regenerable system. The energy requirements for CO2 separation were also evaluated for a regenerable system based on equilibrium data in the liquid phase. A liquid solution equilibrium solver, MINEQL+, was used to determine the equilibrium values. The economic evaluation is based on a 500-MW power plant burning a high sulfur coal. The calculation considered up to a 22 °C temperature difference between the absorption step and the regeneration system. These calculations show that approximately 40 to 68 MW of energy are required to separate 7% of the CO2 from the flue gas stream. The energy required depends on the temperature and pH difference between the absorption and desorption step, and the liquid-to-gas ratio in the absorber. The details of the energy calculations are given in the paper. © Springer-Verlag 2003.