Effect Of Coal Ash On Oxygen Carriers In Chemical Looping Gasification Of Coal

The increase in CO₂ and other greenhouse gas emissions has caused many environmental problems such as the greenhouse effect.As a new type of CO₂ capture technology,Chemical looping combustion technology has broad application prospects.In the coal chemical looping combustion technology,coal ash will inevitably react with oxygen carriers.Therefore,the mechanism and influence of coal ash and its components on the oxygen carriers in the chemical chain process become a key issue.In this paper,the interaction of coal ash with manganese ore and Fe4Al6 oxygen carrier in the chemical chain gasification process was studied.The key factors such as the types of coal ash,different coal ash content,oxides in coal ash,and cyclic reactions are explored experimentally.The main research content of the thesis includes the following 3 parts:(1)Coal ash was prepared from three coal types:anthracite,bituminous coal,and lignite,and the influence of the type of coal ash and the content of coal ash on the gasification process was explored.For the manganese ore oxygen carrier gasification process,both bituminous coal ash and anthracite ash increase the carbon conversion rate when the content of 0-15%is added,but both reduce the synthesis gas production;the addition of 5%lignite ash slightly increases the synthesis gas production.For the Fe4Al6 oxygen carrier gasification process,when the ash content of anthracite is 0-10%,the carbon conversion rate is improved.The carbon conversion rate of bituminous coal ash increased the most when 5%was added,and then began to decline.The same two types of coal ash reduce the production of syngas.After adding lignite ash,the carbon conversion rate decreases with the increase of coal ash content,and the synthesis gas output increases.For both oxygen carriers,excessive coal ash will reduce the carbon conversion rate and synthesis gas production.(2)The coal ash was simulated with oxide configuration,and the mechanism of action of the various components in the coal ash on the oxygen carrier was investigated.The results showed that the addition of Fe₂O₃ significantly increased the carbon conversion rate,synthesis gas production and low calorific value,and improved the pore structure of the manganese ore,the pores become smaller and more,and the active sites become more.After adding Ca O,the gasification process of the two oxygen carriers did not increase the carbon conversion rate,but reduced the CO₂ content,increased the synthesis gas production and low calorific value,and the structure of the oxygen carrier remained basically unchanged.After the addition of Mg O,the carbon conversion rate,synthesis gas production,and synthesis gas concentration during the gasification of the two oxygen carriers were greatly reduced,and serious sintering occurred.Ca O and Mg O have the greatest influence when they exist at the same time,and serious sintering and agglomeration occurred in the oxygen carrier.After adding Si O₂,the carbon conversion rate and synthesis gas production decreased slightly,and the oxygen carrier slightly sintered..(3)The influence of coal ash on the cycle performance of the oxygen carrier was investigated.Through 10 cycles of experiments and micro-characterization,it was found that when no coal ash was added,the carbon conversion rate and synthesis gas production remained stable during the cycle.Oxygen carrier still has good reducing ability.The oxygen carrier has excellent performance,the pore structure is still good,and sintering blockage has not occurred;After the addition of coal ash,the carbon conversion rate and syngas production decline trend is more significant,and the oxygen carrier reduction ability is significantly reduced.Manganese-based oxygen carriers produce Ca₂Si O₄,Mg₂Si O₄ and other low-melting eutectics,and iron-based oxygen carriers also produce silicates and low-melting eutectics.These substances consume the active components of the oxygen carrier,cause sintering,block the pore structure of the oxygen carrier,and deactivate the oxygen carrier.