Study On Reaction Mechanism Of Coal With Fe₂O₃-based Oxygen Carrier Under Catalytic Activation Condition

The large-scale consumption of fossil fuels will lead to a large number of CO₂ emissions,and CO₂ is the main cause of environmental problems such as Greenhouse Effect.Controlling and reducing CO₂ emission is one of the important measures to mitigate global warming.China is a big energy consumption country in the world,and its energy consumption structure is mainly coal.Therefore,it is of great significance to study coal based CO₂ emission reduction technology in China to alleviate the pressure of carbon emission in China.Chemical looping combustion is a new type of flameless combustion technology,which can realize the separation and capture of CO₂ with high efficiency and low cost.The comprehensive performance of oxygen carrier is one of the key factors that restrict the chemical looping combustion technology.Iron-based oxygen carrier has many advantages,such as good thermal stability,low price,wide source,environmental friendly and so on.Therefore,it is of great significance to study the iron-based chemical looping combustion technology which directly uses coal as fuel to achieve the goal of carbon emission reduction in China.In the process of chemical looping combustion which directly uses coal as fuel,the gasification rate of coal char is the speed limiting step,which plays a very important role in the full conversion of coal,the utilization of oxygen carrier and the effective separation and capture of CO₂ in the process of coal combustion.In order to promote the efficient and clean utilization of coal and the effective capture of CO₂ generated by combustion in the process of chemical looping combustion,the effect of K₂CO₃ catalyst on Fe₂O₃ based chemical looping combustion reaction was explored.The effects of different catalyst loading paths on the chemical looping combustion process of coal and Fe₂O₃-based oxygen carrier were further studied from two aspects of K₂CO₃ catalytic activation of coal and alkali metal activation of Fe₂O₃ oxygen carrier Furthermore,the catalytic mechanism of K₂CO₃ was explored.The main research contents and results are as follows:Coal pyrolysis is the first step in the process of coal conversion,which has an important impact on the subsequent coal conversion.The addition of K₂CO₃ catalyst can significantly reduce the activation energy of coal pyrolysis reaction,and promote the pyrolysis reaction to the low temperature zone;K₂CO₃ has different catalytic effect on the pyrolysis process of different rank coal,and the catalytic effect on NX coal is the most obvious.During the pyrolysis process,K₂CO₃ reacts with coal to form C-O-K structure precursor on the surface of coal.NX anthracite tends to form Cn K like clusters with K₂CO₃ to prevent K from volatilizing.In the coal gasification reaction,the addition of K₂CO₃ can significantly accelerate the gasification reaction rate of three kinds of coal chars,and significantly shorten the gasification time of coal char;the formation rate of CO,H₂,CO₂ is significantly accelerated,K₂CO₃ catalyst has no obvious catalytic effect on CH₄;the effect of K₂CO₃ catalyst on the coal gasification process may be that the precursor of K-O structure on the surface of coal char is easier to react with H₂O The combination of O in the catalyst promotes the gasification reaction;The reaction process of coal with Fe₂O₃ based oxygen carrier can be accelerated by two kinds of K₂CO₃ catalytic activation paths.After adding K₂CO₃,the reaction rate of coal with Fe₂O₃ based oxygen carrier is obviously increased;Among them,the increase of reaction rate of modified oxygen carrier is more obvious,which may be because the modified iron-based oxygen carrier contains K₂Fe₂₂O₃₄.The K⁺in K₂Fe₂₂O₃₄ is easier to migrate to the surface of coal char to form an intermediate active structure containing C-O-K,and it is easier to react with H₂O,which greatly speeds up the gasification reaction rate of coal char and greatly shortens the whole reaction time,The overall reaction effect was improved.The XRD results show that K₂Fe₂₂O₃₄ still exists in the product after the reaction of modified Fe₂O₃ based oxygen carrier,which indicates that the existence of potassium polyferrite can reduce the loss of K⁺in the reaction process.In a word,this paper takes the deashing coal of three different coal ranks as the research object,starting with the whole process of the reaction between coal particles and oxygen carrier,and from the two angles of K₂CO₃ catalytic activation of coal and alkali metal activation of Fe₂O₃ oxygen carrier,studying the reaction characteristics of coal and Fe₂O₃-based oxygen carrier under the condition of K₂CO₃ catalytic activation,which has certain reference significance for promoting the application and popularization of iron-based chemical looping combustion technology directly using coal as fuel.