THE EFFECTS OF CO₂ CONCENTRATION ON LIMESTONE DESULFURIZATION DURING O₂/CO₂ COMBUSTION

Experimental studies on the decomposition and desulfurization of CaC0₃ have been performed at a TGA-FTIR analyzer and a combustion test furnace under 0₂/C0₂ conditions and conventional combustion environment. The effects of C0₂ concentration on limestone decomposition, desulfurization product properties, limestone desulfurization efficiency were investigated. The desulfurization reaction mechanism was analyzed. Decomposition temperature of CaC0₃ under 0₂/C0₂ environment is higher than that under air environment. The presented C0₂ constrains the decomposition of CaC0₃. At a given temperature, CaC0₃ decomposition ratio decreased as C0₂ increase. Moreover, the initial decomposition temperature increased. The reactive surface area of CaC0₃ decomposition samples in high C0₂ environment was larger than that in conventional conditions. Two-stage reaction mechanism of limestone desulfurization during pulverized coal combustion in 0₂/C0₂ atmosphere was obtained. At low temperature, the reaction is: CaC0₃+S0₂→CaS0₄. CaC0₃ having lower reactivity than CaO reacts with S0₂ directly results in lower desulfurization efficiency compared with air atmosphere. At high temperature, the reaction is: CaC0₃→ CaO+C0₂, CaO+S0₂→CaS0₄. Higher reactivity CaO under 0₂/C0₂ than air environment reacts with S0₂ and formed CaS0₄ reduction reaction at high temperature is restrained under 0₂/C0₂ resulted in higher desulfurization efficiency.