The Competitive Mechanism Of Sulfur Andchlorine On The Migration And Transformation Of Alkali During Biomass And Coal Co-Combustion

The technique of co-combustion of biomass and coal is widely concerned because of reducing the emission of CO2, NOx, SO2 and heavy metals. But biomass contains high amounts of volatile alkali metals and chlorine, which can cause deposition, corrosion and agglomeration during combustion. Meanwhile the migration and transformation of alkali metals can be influenced by sulfur and chlorine during biomass and coal co-combustion. It can choose rational methods to relieve relevant problem of alkali metals, if the study can fond the competition mechanism of sulfur and chlorine on alkali metals. This study was discussed in detail based on the combination theoretical and experimental method, and analytical methods of XRD, SEM, et al.The paper predicted the effects of temperature and additives of sulfur and chlorine on thermodynamic equilibrium state of alkali metals during rice straw and Tiefa coal co-combustion. The results show that with the rise of temperature, the volatilization of alkali chloride was more obvious, and KCl （g）, NaCl （g） were forms of existence; Sulfur fixation of alkali metals was more marked in the form of K₂SO₄, Na₂SO₄; Chlorine volatilization of alkali metals was weakened between 0.05-0.3mol of sulfur molar weight; As sulfur molar weight was greater than 0.1mol, alkali metals were captured in bottom ash in the form of K₂SO₄ and Na₂SO₄.On the base of chemical thermal equilibrium calculation, the competition mechanism of sulfur and chlorine on alkali metals was studied on the tube furnace by controlling temperature, molar ratio and proportion of mixture when rice straw, corn straw and wheat straw with coal co-combustion. The results show that with the rise of temperature, the volatile amounts of alkali metals and chlorine increased, and they separated out in the form of alkali chloride. Sulfur and chlorine affected on the condensation of alkali metals, and exisiting forms maybe KCl, NaCl, K₂SO₄, and Na₂SO₄. The action of capture and migration was more significant of sulfur on alkali metals, and the mostly alkali metal salts were K₂SO₄ and Na₂SO₄. 20% was optimal proportion when wheat straw with Yiyang coal co-combustion.At last, the rate of alkali metals precipitation was analyzed by gray association degree theory in different molar ratio. The results show that Cl/K molar ratio is the most important element.