Experimental study on adsorption of potassium vapor in flue gas by coal ash

Potassium removal from biomass combustion flue gas is important in power engineering because potassium may cause serious problems such as the agglomeration, contamination, corrosion and deposition of heating surfaces. It is feasible to capture potassium vapor in flue gas by solid adsorbents. Experiments were performed to study the reaction characteristics and mechanism of the potassium adsorption by coal ashes with KCl as the alkali model compound. The influences of adsorption temperature, alkali metal concentration and adsorption atmosphere on potassium removal were analyzed. The experimental results confirm that coal ash has a good ability of potassium adsorption. The potassium adsorption amount by coal ash in initial 2 h increases roughly linearly with the increase of alkali metal concentration. Potassium adsorption by Guizhou coal ash during the fixed adsorption period increases with the increasing temperature in the range of 650–900 °C; while the reaction temperature is over 900 °C, potassium adsorption by Guizhou coal ash begins to decline. The potassium adsorption under the conditions even with a little water vapor content is larger than that under the conditions without water vapor. However the effect of high water vapor content on the alkali adsorption capacity is not obvious. The alkali adsorption by coal ash sorbent at a given period is the highest in reducing atmosphere, the second in the conventional flue gas atmosphere and the lowest in the oxyfuel combustion flue gas. The present experimental results will provide the references for the development of economical efficient sorbent of alkali metal to reduce the harm of the alkali in the biomass combustion or gasification process.