Optimization Of Coal Char Chemical Looping Gasification System And Study Of Oxygen Carrier

The chemical looping gasification combined with coal pyrolysis coupled system is a solid fuel chemical looping gasification coupling process based on the the solid heat carriers coal pyrolysis technology.It can be used to product tar and syngas.In this system,the oxygen carriers can provide heat for coal pyrolysis process.And coal pyrolysis process can provide char and phenolic wastewater which can be used as the raw materials and gasification agents for chemical looping gasification.This system realizes the cascade conversion of coal and the efficient use of energy.The coal char chemical looping gasification process is the core of the coupling system.This paper investigated the coal char chemical looping gasification process from three aspects,that is,thermodynamic feasibility analysis,optimization of process conditions and preparation and test of Fe-based composite oxygen carrier.（1）The simulation and analysis of the Fe₂O₃ oxygen carrier coal char chemical looping gasification system were carried out by using thermodynamic software.The results showed that the optimum parameters were:a gasification temperature of 900℃,steam to carbon ratio of 0.2:1,oxygen to carbon ratio of 1:1.According to the results of heat balance,the load of inert carrier Al₂O₃ in the oxygen carrier was adjusted to 74%;（2）Optimization of process parameters（oxygen to carbon ratio,gasification temperature and steam flow）of coal char chemical chain gasification process and exploration of its gasification mechanism were carried out by using fixed bed experiment.The experimental results showed that the coal char chemical-looping gasification reaction obtained higher carbon conversion and synthesis gas selectivity,respectively 93.42%and 85.48%,when the conditions were oxygen to carbon ratio 1:1,steam flow rate 0.03 m L/min,temperature900℃.The increase in steam and oxygen carrier content could promote the carbon conversion rate of coal char.However,it consumed synthesis gas at the same time,resulting in the reduction of synthesis gas selectivity.Improving the gasification temperature could promote the degree of coal char gasification reaction,in which increased CO and H₂ yield.However,the high temperature might cause the sintering problem of the oxygen carrier.Furthermore,the interaction between coal char,oxygen carrier and steam changed with the progress of gasification reaction.（3）The effects of metal promoters including species and load on the activity of Fe-based composite oxygen carriers were studied by using fixed bed experiment.The results showed that the metal promoters could improve the reactivity of the oxygen carrier.However,the highly active oxygen carrier could deeply oxidize the synthesis gas,reducing the selectivity of the synthesis gas.Among the six Fe-Ni composite oxygen carriers,the oxygen carrier with a Ni-based load of 15%had the best gasification performance,with a carbon conversion rate of 95.65%and a synthesis gas selectivity of 85.81%.And then among the six Fe-Cu composite oxygen carriers,the oxygen carrier with a Cu-based load of 10%had the best gasification performance,with a carbon conversion rate of 96.07%and a synthesis gas selectivity of 84.06%.In addition,both complex oxygen carriers did not show significant sintering and agglomeration phenomena before and after the coal char gasification reaction,the oxygen-carrying exhibited good cycle stability.