Abstract: Chemical-looping combustion( CLC) has become a promising solid fuel combustion technology due to its inherent advantages of high concentration of CO_2,easy separation and low cost of CO_2 reduction. At present,CLC technology includes in-situ gasification CLC( i G-CLC) and oxygen uncoupling( CLOU) of solid fuel chemical-looping combustion.When solid fuel is used for combustion,the pollution elements will be released into the atmosphere or doped into the target gas of CO_2 in the form of gas,which will bring environmental and operational problems.In this paper,two technologies and related principles of i G-CLC and CLOU for chemical looping combustion of solid fuel were introduced,the research status at home and abroad was briefly described,and the properties,advantages and disadvantages of the two technologies were analyzed.At the same time,the pollution elements and their release rules in the process of solid fuel chemical chain combustion were summarized and analyzed.Most of the S elements in the solid fuel will eventually be transferred to the gas phase and released in the form of H2 S and SO_2( i G-CLC) or single SO_2( CLOU),a small portion of which will be fixed in the ashes or combined with the oxygen carrier.In terms of emission ratio,with the increase of fuel reactor temperature,the content of sulfur gas at the outlet of fuel reactor increases,while the content of sulfur gas at the source of air reactor decreases.For the solid fuel,all the N elements will be transferred to the gas phase and released in the form of N2 and NO in both technologies.The difference is that in CLOU technology,the formation of NO is more due to the oxygen release of oxygen carrier.At the same time,the change of nitrogen content and temperature at the outlet of fuel reactor and air reactor is consistent with that of S.The Hg elements in the solid fuel will be mainly presented in the gas in the form of Hg0 and Hg2+,and mainly in the form of Hg0 in the fuel reactor,and in the form of Hg2+in the air reactor,and a considerable part of the Hg( 42.5%) in the CLOU technology will be retained in the combustion ash.The release of Hg in the fuel reactor will increase with the increase of the temperature of the fuel reactor,and the release of Hg in the air reactor will decrease.The volatile matter in the chemical chain combustion process of solid fuel,as a pollutant,also needs to be paid attention to in the aspect of emission.The results show that the type of fuel seems to have a decisive effect on the amount of tar in the outlet gas of the fuel reactor.At present,tar emission is only found in the i G-CLC of biomass with high volatile content,while in CLOU technology,the tar compounds are completely burned due to the presence of gaseous oxygen in the fuel reactor.Finally,combined with the properties of pollution elements and the release law in the two chemical chain combustion technologies,some suggestions are put forward for the process development and design by the raw material treatment and process improvement to reduce the emission of pollutants.