The Influnce Of Sulfur On The Migration Characteristic Of Alkali During Biomass And Coal Co-Combustion

The technique of co-combustion of biomass and coal is an efficient way to use biomass energy at low cost and wide scope, which can be widely applied in the future. But biomass contains high amounts of volatile alkali metals and chlorine, which can cause deposition, corrosion and agglomeration during combustion. Meanwhile coal contains a certain amount of sulfur that produces serious environmental pollution following combustion The sulfur of coal is apt to react with alkali metals to form alkali sulphate. Combination of alkali metals and sulfur will greatly alleviate pollution and corrosion problems. The migration characteristic of alkali metals and the effects of sulfur on the migration of alkali metals during biomass and coal co-combustion were discussed in detail based on the combination theoretical and experimental method and test methods analysis of XRD, SEM, etc.The pathway of alkali transformation during rice straw and Tiefa coal cofiring was studied by employing Gibbs free energy criterion. The effects of temperature and amounts of sulfur on the chemical morphology and distribution of alkali metals during rice straw and Tiefa coal co-combustion were studied based on the chemical thermal equilibrium calculation. The results show that lowering the temperature has positive effects on inhibiting the emission of potassium chlorine, and the amounts of potassium sulfate increase with the increase of sulfur content. When the mole quantity of sulfur is up to 0.4 mol, the amounts of potassium sulfate remain unchanged.The reaction mechanism of FeS2 and KCl was studied by employing Gibbs free energy criterion and the effect of mol ratio of sulfur and potassium on the reaction of FeS2 and KCl was experimentally investigated by using TG-DTA system. The results show that the optimum mol ratio of sulfur and potassium is 2 when model compound FeS2 reacts with KCl.On the base of chemical thermal equilibrium calculation, the effects of temperature and sulfur content on the transformation of alkali metals were studied on the tube furnace. The results show that the amounts of potassium and sodium in the gas phase and condensed phase rise and the effect of sulfation of alkali metal chlorine weakens with the increase of temperature. When the mole ration of sulfur to potassium is below 2, the amounts of potassium sulfate grow in number with the increase of ration. As the mole ration greater than 2, the sulfation of alkali metal chlorine keeps constant basically and has a slight downward trend. Meantime the transformation of alkali metals during rice straw, corn straw, and wheat straw combustion with Tiefa coal separately which contains low sulfur and rice straw combustion with Yiyang coal that contains high sulfur were studied on the tube furnace. The results show that when co-combustion with Tiefa coal, the proportion of rice straw and corn straw are 80 percent and 100 percent respectively, the amounts of potassium sulfate in the condensed phase and water-soluble solid-phase are the most. When the proportion of wheat straw is 50 percent and 80 percent, the amounts of potassium sulfate in the condensed phase and water-soluble solid-phase are the most respectively. The amounts of potassium sulfate in the condensed phase and water-soluble solid-phase are the most at the 80 percent of rice straw during rice straw and Yiyang coal co-combustion.