Experimental Studies On Effect Of Combustion Desulfurization And Denitrification By Nano-additives

The nanometer TiO₂ prepared by sol-gel method as additive for combustion was studied. The effects of combustion, desulfurization and denitrification by nanometer TiO₂ addition, Ca/S molar ratio, and combustion temperature were experimental investigated. The reaction products were analyzed by X-ray diffraction (XRD), Infrared spectrographic (IR), Scanning electron microscopy (SEM) and Ion chromatography(IC) analysis. The mechanisms of combustion, desulfurization and denitrification catalysis by nanometer TiO₂ addition were discussed. The issues of desulfurization, denitrification and fusibility during the coal combustion by the nano-additive addition were analyzed through the chemical and instrument methods. The results may be used to provide a useful basis for further applying nano-TiO₂ additive in circular fluidized bed boilers. It is helpful to the development of combustion desulfurization and denitrification technology simultaneously. The study was significant to look through the boundary and scale effects of nano-materials and to promote the removal of SO₂ and fuel NO in CFB boilers and to save the coal.The results show that desulfurization and denitrification efficiency were 87.8% and 36.0% when nano-titanium oxide dosage is 8%, Ca/S 2, temperature 850℃; it was 13.4% and 36.0% higher than that without nano-titanium oxide addition. The ignition temperature of coal decreased, its calorie value, and fuse temperature of coal ash can be effectively improved by nano-TiO₂ with CaO addition.The pore diameter and surface area of coal ashes with nano-TiO₂ addition increased. In the presence of nano-TiO₂, which serves as a catalytic active center, the gas (oxygen)-solid (catalyst)-solid (carbon and CaO) catalytic burning reaction takes place. In the burning of the coal, many holes and grooves on the surface of the coal particles are formed because the carbons around the catalytic active center burn faster than those away from the catalytic active center. The controlling course of the reaction changes from outer oxygen to inner oxygen. SO₂ and NO diffusion to the inner surface speed up. Finally, the accelerating effects of nano-TiO₂ on the burning and desulfurization of the coal are observed; the accelerating effects of reduction reaction of coal char, CO and NO were obvious by the addition of nano-TiO₂.The desulfurization and denitrification reactions are first order in SO₂ and NO concentration, respectively. The desulfurization reaction is zero order in O₂ concentration. The reactions include two zones—surface reaction zone and the product layer diffusion zone. In the desulfurization and denitrification reactions the product layer diffusion and surface-reaction showed the slow rate, respectively. The apparent activation energy of combustion with nano-TiO₂ addition with and without CaO decreased than that of without nano-TiO₂ addition simultaneously. The unreacted shrinking reaction core model was used to investigate the reaction kinetics.It is shown that this model can describe the courses of desulfurization and denitrification. This agrees with the experimental results.