Study On CO₂ Capture Performance And Synergistic NO_x Reduction Of CaO-based Sorbents Doped With Biomass

The global warming is getting worse and worse due to the emission of greenhouse gas CO₂.CO₂ capture,utilization and storage（CCUS）has become one of the important strategies to stop the global warming.Calcium looping technology is a CO₂ emission reduction technology with good industrial application prospects.However,the major challenge for the technology involves the loss of sorbents activity and serious attrition,due to sintering in multiple cycles.To address the above issue,sorbents were developed by doping with biomass to promote the carbonation performance.The NO_x reduction performance of the novel sorbents was investigated under the carbonation conditions.Performance of NO_x reduction of the novel sorbents during the carbonation process was also investigated.The specific research results are as follows:Biomass was utilized to enhance the CO₂ capture performance of calcium-based sorbents together with cement.The preparation of the sorbents was explored via extrusion-spheronization method.The influence of parameters,such as biomass types,addition,pretreatments,precursors,and cement amounts on CO₂ capture performance of sorbents were determined.The results showed that the sorbents doped with biomass achieved increased carbonation conversion compared with that of the original limestone.The sorbents with biomass after acetic acid solutions washing exhibited higher carbonation conversion.An increase of 36.5%enhancement in initial carbonation conversion was achieved for sorbents doped with pretreated biomass（X₁=0.71）compared with that without any pretreatment（X₁=0.52）.It was observed that the sorbents derived from dolomite doped with pretreated biomass exhibited higher carbonation conversion than those derived from limestone.The addition of cement slowed down the decay in conversion of sorbents during the multiple cycles.However,the cement did not contribute to CO₂ uptakes.The addition of 10wt.%cement in sorbents would be a better option based on above results.The excellent sorbents doped with coconut shell（L-A10-CS50-AC and D-A10-CS50-AC）presented wonderful CO₂ capture capacity as well as improved sintering resistant during the multiple cycles.The result of N₂ physisorption/desorption showed that the release of volatiles and pyrolysis of biomass char in sorbents are the main causes for microstructure improvement for sorbents.The result of situ-X-ray diffraction（XRD）showed that the formations of Ca Al₂O₄,Ca Al₄O₇ and Ca₁₂Al₁₄O₃₃ in sorbents during the carbonation/calcination cycles account for the enhancement of the sorbents’sintering resistant.The NO_x reduction of the novel sorbents during the carbonation process was investigated.The NO reduction was mainly developed in the study.Ca O presented catalytic effect on NO reduction by CO.It was attributed to the fact that NO can be absorbed to the active sites of Ca O which promotes its decomposition.The NO reduction of the sorbents doping with different biomass was different.The main factors that affect NO reduction performance were the content of volatile and the content of nitrogen.The increase of CO concentration did not significantly enhance NO reduction,indicating that CO was not the leading factor promoting NO reduction under these conditions（700℃,15vol.%CO₂,500ppm NO）.With the increase of O₂concentration from 0wt.%to 4wt.%,NO reduction rate firstly increased and then decreased,and the maximum reduction rate were achieved with O₂ concentration of0-1vol.%.With 5wt.%Fe doping in the sorbents,NO reduction rate was increased by34.7%.The biomass coke in sorbents was beneficial to NO reduction,and NO reduction was promoted by Ca O with biomass coke.The interaction between the carbonation and NO_x reduction for sorbents doped with biomass was investigated during the carbonation process.The presence of CO₂inhibit NO reduction for sorbents L-A10-CS50-AC and L-A10-CS50-AC.The increase of CO₂ concentration reduced the production of reducing gas.Meanwhile,CO₂ can react with Ca O and form Ca CO₃,which inhibited the catalytic effect of Ca O.NO reduction rate decreased with the increase of NO concentration.NO had little effect on the carbonation performance of sorbent L-A10-CS50-AC,but inhibited the carbonation performance of sorbent L-A10-CSC50-AC.NO occupied the active site on the surface of the sorbent and inhibited carbonation.The NO reduction rate firstly increased and then decreased with the increase of water vapor concentration,and the optimal concentration was 10 vol.%.A certain amount of water vapor could improve the microstructure of the sorbent and enhance CO₂ capture ability.When the water vapor concentration is too high,the sintering effect on Ca CO₃ will increase and the CO₂ absorption will decrease.