Utilization of lime mud from paper mill as CO2 sorbent in calcium looping process

Lime mud (LM), a solid waste that results from the causticization reaction in alkali recycling process of paper manufacture industry, was utilized as CO2 sorbent in calcium looping process in this study. The carbonation behavior of LM in the calcination/carbonation cycles was investigated in a dual fixed-bed reactor and a thermo-gravimetric analyzer. The results show that the carbonation conversions of LM are lower than those of limestone at the same reaction conditions. It attributes to the high chlorine content in LM which leads to more pronounced sintering and decreases the CO2 capture performance of LM. A pre-wash process was employed to decrease the chlorine content in LM. Based on an overall consideration of various factors, the pre-wash process is effective enough if the Cl/Ca molar ratio in LM is smaller than 1:100. Pre-washed lime mud (PLM) achieves higher carbonation rates and carbonation conversions, compared with LM. When calcined at 850 °C and carbonated at 700 °C, the carbonation conversion of PLM maintains at 36% after 100 cycles, which is 1.8 and 4.8 times as high as LM and limestone after the same number of cycles, respectively. The pore volume and surface area of calcined PLM were greater than those of calcined LM after the same number of cycles, especially the volume of the pores in the range of 10–100 nm in diameter. That is the reason why PLM exhibits higher CO2 capture capacity than LM in the multiple calcination/carbonation cycles. The carbonation conversions of LM and PLM are further enhanced by hydration of their calcines.

The cyclic carbonation conversion of lime mud (LM) is relatively lower than that of limestone in the previous 10 cycles. The carbonation conversion of LM is higher than that of limestone after 15 cycles. The cyclic carbonation conversions of LM are greatly improved after pre-wash treatment. The carbonation conversion of pre-washed lime mud (PLM) maintains at 36% after 100 cycles which is 1.8 and 4.8 times as great as LM and limestone after the same number of cycles, respectively.Figure optionsDownload as PowerPoint slideHighlights
► Carbonation conversions of lime mud are low due to high chlorine content.
► Pre-wash treatment decreases chlorine content in lime mud.
► Pre-washed lime mud exhibits higher CO2 capture capacity.
► Microstructure of calcined lime mud after pre-wash treatment is improved.
► Pre-washed lime mud can be used in calcium looping technology for CO2 capture.