Experimental Studies On Carbon Dioxide Absorption Into Aqueous Ammonia

The global warming caused by increasing emission of carbon dioxide isone of the most serious environmental problems, carbon dioxide emission hasbecome the focus of world. The fossil fuel power plant is the main stationarysources of the CO₂emission, therefore, removal of carbon dioxide from fossilfuel power plant flue gases is a key measure to reduce CO₂emission.In recent years, post-combustion capture has been recognized bygovernment and industry as a potential technique to reduce CO₂emissionsince it is simpler and can be used on existing power plants. There are varioustechnologies used to capture CO₂from flue gas, including chemical solventabsorption method, adsorption method, membrane separation and cryogenicmethod. Among the above techniques, chemical solvent absorption method isconsidered as a reliable and relatively competitive method for reducing CO₂emission from fossil fuel power plants. The researches of chemical solventabsorption method are mainly focus on the selection of absorbent, theresearch of the reaction mechanism, the selection of reactor, theascertainment of the operating conditions and so on. Due to high CO₂absorption capacity, low equipment corrosion rate and low cost, someresearchers found that aqueous ammonia seems to be an alternative andpromising absorbent for removing CO₂from flue gas.In order to obtain the kinetics of CO₂absorption into ammonia, theexperiments of the absorption of CO₂into aqueous ammonia in a wetted wallcolumn were carried out. The experimental results show that the reactionbetween aqueous ammonia and carbon dioxide is a second-order reaction withfirst-order for CO₂and NH3respectively, the kinetic rate constants forCO₂-ammonia, k2, can be described in terms of temperature as ln（k2）=22.3-4646.08/T, and the reaction activation energy is38.64kJ/mol.The performance of the packed column and the spray column wasevaluated experimentally under various conditions to reveal effects of process parameters, including CO₂partial pressure in gas phase, gas flow rate, liquidflow rate, concentration of ammonia and temperature. Experimental resultsshow that the removal efficiency of carbon dioxide exceeds95%under certainoperating conditions. The concentration of ammonia is a key parameter andplays an important role on CO₂removal efficiency, the CO₂removalefficiency increases with the concentration of aqueous ammonia. Althoughthe CO₂absorption rate increases with the liquid flow rate and the gas flowrate, the CO₂removal efficiency decreases with them. Experimental resultsalso suggest that the temperature plays an important role in CO₂absorptioninto aqueous ammonia, the suitable operated temperatures are40℃and35℃for the spray column and the packed reactor respectively. Compared withspray column, the packed reactor for CO₂absorption into aqueous ammoniashows superior performance.