Experimental Study On The Ammonia Adsorption Of Coal Ashes

The consumption of energy in China is increasing rapidly with the great development of economy. Coal is the most important energy source in China, the reduction of sulfur dioxide will be offset by the rapid increase of nitrogen oxides, which makes environment problems more and more serious. SNCR (Selective Non-catalytic Reduction) and SCR (Selective Catalytic Reduction) could decrease NOx emission to the regulation emission standard, but the ammonia slip in the flue gas may lead to ash blocking or corrosion in the air pre-heater. Some experience in power plants had shown that ammonia or ammonium salt would be adsorbed by fly ash, which would hinder the secondary utilization of ash. So this paper had studied the ammonia adsorption in ash using some testing and characterization methods in order to provide theoretical guidance for the practical operations in power plants.First, Using XRD(X-Ray diffraction)and SEM(scanning electron microscope) to characterize coal ashes of Ximeng lignite and Yangquan anthracite, which were made under different conditions, NH3Temperature-programmed Desorption (NH3-TPD) was utilized to study ammonia adsorption in ashes. The results showed that Ximeng ash would adsorb more ammonia than Yangquan ash because of different Al content and Si/Al ratio; rapid cooling would increase the amount of amorphous phase in the ash and facilitate the ammonia adsorption, so the ashes cooled in liquid nitrogen would adsorb much more ammonia than those ashes cooled in the atmosphere; the reduction atmosphere could promote the generation of low-temperature eutectoid which would enhance the adsorption capacity; the residual carbon had more surface area, surface acidic functional group would increase the amount of ammonia adsorption in ashes, especially for Ximeng ashes.Then, using laser particle size analyzer and specific surface area analyzers to test features of Ximeng ashes and Yangquan ashes, the laboratory table was set up to make ammonia adsorbed in ashes and the amount of ammonia adsorbed was measured by ammonium-gas-sensitive electrodes. The results showed that the ammonia adsorption of Yangquan ashes decreased as the ignition temperature increased, but the adsorption of Ximeng ashes had been basically unchanged; the adsorption balance could be reached in a short time for Ximeng ashes and Yangquan ashes, but the later needed more time; the increasing NH3concentration in air flow would lead to more adsorption in Yangquan ashes, but it had little or no effect on Ximeng ashes; the ammonia adsorption of Yangquan ashes would decrease as the adsorption temperature increased, but the adsorption of Ximeng ashes would increase firstly and then decrease.