HC1 Removal Performance Of Cycled Carbide Slag From Calcium Looping Process For CO₂ Capture

The CO2 and HCl emissions from the power generation process of chlorine-containing fuels such as biomass and refuse-derived fuels (RDFs) have adverse effects on the surrounding environment. The calcium looping process, namely the carbonation/calcination cycles of CaO, is considered to be one of the most promising technologies for large-scale CO2 capture. The cycled carbide slag from calcium looping process for CO2 capture was proposed to remove HCl originating from the combustion of chlorine-containing fuels in this paper. This novel method can utilize the carbide slag experienced carbonation/calcination cycles, which has low carbonation reactivity, for HCl absorption. Consequently, the waste recycling and HCl removal can be realized.The HCl removal characteristics of the calcined carbide slag were investigated in this work and the microstructures of the carbide slag in calcination and chlorination reactions were discussed to reveal the reaction mechanism. The results show that the chlorination product of the calcined carbide slag after 60min HCl absorption is CaClOH and 700℃ is the optimum temperature for HCl removal of calcined carbide slag. The calcined carbide slag exhibits better HCl removal capacities than the calcined limestone in the chlorination temperature range of 650-900℃ and has more advantages at high temperatures. The calcined carbide slag possesses more pores than the calcined limestone, especially in the range of 2-10nm, which is beneficial to HCl removal.The carbide slag experienced the carbonation/calcination cycles for CO2 capture was proposed to remove HCl and the HCl removal characteristics of the cycled carbide slag were studied. The cycled carbide slag from calcium looping process achieves the highest HCl removal performance at 700℃ and the feasible temperature window for HCl removal of the cycled carbide slag narrows with the number of the carbonation/calcination cycles. The carbide slag experienced 1 cycle exhibits the highest HCl removal performance with increasing the cycle number from 0 to 50. The chlorination conversions of the carbide slag experienced 1 and 50 cycles are approximately 0.32 and 0.1 mol/mol, respectively. The carbide slag experienced 1 cycle possesses more pores in the range of 20-100nm, which are more favorable for HCl diffusion in the sorbent.In order to improve the HCl removal performance of the cycled carbide slag from calcium looping process, the aluminum-modified carbide slag was prepared from carbide slag, Al(NO3)3·9H2O and glycerin by the combustion synthesis method. The CO2 capture behavior of the aluminum-modified carbide slag during calcium looping process was investigated and the HC1 removal characteristics of the cycled aluminum-modified carbide slag experienced the carbonation/calcination cycles were discussed. The main components of the aluminum-modified carbide slag are CaO and Ca3Al2O6. Ca3Al2O6 is an inert substance, but can stabilize the pore structure of the sorbent, which facilitates the HCl absorption of CaO. The cycled aluminum-modified carbide slag shows high HCl removal capacities in a wide chlorination temperature window of 600-800℃ and the optimum temperature for HCl removal of cycled aluminum-modified carbide slag is 700℃ . With increasing the cycle number from 0 to 50, the aluminum-modified carbide slag experienced 5 cycle exhibits the greatest HCl removal capacity. The aluminum-modified carbide slag after 5 cycles has the largest surface area and pore volume and possesses more pores in 30-100 nm in diameter, which is conductive to HCl removal. The cycled aluminum-modified carbide slag exhibits better HCl removal behavior than the cycled carbide slag from the calcium looping process. The HCl absorption capacities of the aluminum-modified carbide slag after 20 and 50 cycles were 2.3 and 2.6 times as high as those of the carbide slag after the same number of cycles, respectively.