Study On The Effect And Mechanism Of Circulating Pyrolysis System On Gas Production From Sludge-rice Husk Co-pyrolysi

Sewage sludge（SS）is a by-product of municipal sewage treatment plants and currently sludge pyrolysis has become one of the most promising ways for sludge disposal.To improve the efficiency of sludge pyrolysis,the addition of different substances to co-pyrolyze with sludge is a common method.However,the effects and mechanisms of N,S and Cl contained in organic particles in the additions on the release of polluting gases from the pyrolysis products are unclear.In this study,SS-rice husk（RH）co-pyrolysis was used as the experimental group,and SS-biochar（BC）and SS-coal ash（CA）were used as the control group.The release characteristics of condensable/non-condensable gases during the pyrolysis of RH and SS were analyzed by thermogravimetric-mass spectrometry（TG-MS）and pyrolysis-gas chromatography/mass spectrometry（Py-GC/MS）techniques to elucidate the effect of RH as a co-pyrolysis substance on sludge pyrolysis products.In addition,this study developed a novel cyclic catalytic integrated pyrolysis system（hereinafter referred to as the circulating pyrolysis system）.In response to the challenges of short pyrolysis steam residence time,low syngas yield,low calorific value,and high tar yield,this system promotes tar reforming to syngas through catalytic pyrolysis steam circulation to improve the yield and quality of pyrolysis syngas.SS and RH were used as biomass feedstocks.The process parameters of the circulating pyrolysis system,such as the SS and RH mixing ratio,pyrolysis steam cycle rate,and catalyst dosing,were optimized to improve syngas yield and lower heating value（LHV）.The specific results were obtained as follows:（1）The addition of RH promoted the generation of C/H/O-containing gases during pyrolysis.In terms of the release of pollutants,the addition of RH increased the release of NH₃,the addition of CA increased the production of H₂S and COS,and the addition of RH decreased the release of Cl₂ and CH₃Cl.The three different substances did not noticeably promote or inhibit the release of S-containing pollutants during sludge pyrolysis.Several reaction kinetic models fitted using the Coats–Redfern method have shown that the addition of BC and CA had a certain catalytic effect on sludge pyrolysis,reducing the activation energy（Ea）.By comprehensively comparing and analyzing the reaction mechanism of three different substances in sludge pyrolysis and their influence on the pyrolysis products,it provides a theoretical basis for future research on the co-pyrolysis of SS with different substances.（2）The mixing ratio of SS,RH and cycle rate of pyrolysis steam are crucial to driving syngas generation,while the cycle rate is a key factor for tar reduction.And the catalyst addition mainly changed the syngas fraction and promoted the hydrogen-rich syngas generation.By optimizing the circulating pyrolysis system,the liquid phase product yield was reduced by 6 wt%and the gas product yield was increased by 27 wt%compared to the normal pyrolysis system SS pyrolysis,in which the yields of H2,CH4,CO and CO2 were increased by 131.51 vol%,87.80 vol%,223.57 vol%and 210.45 vol%,respectively.In terms of energy recovery,the LHV of syngas increased from 7.99 MJ/Nm³ to 11.31 MJ/Nm³ by41.55%through synergistic optimization.In this study,based on the CCIP system,co-pyrolysis of SS and RH and promotion of pyrolysis tar reforming through pyrolysis steam circulation effectively improved the yield and LHV of syngas,and achieved high quality recovery of syngas.