Study On The Chemical Looping Combustion Characteristics Of Coal And Biomass Based On Iron-based Oxygen Carriers

The lignite resources and biomass energy in the process of conversion and utilization,a large amount of greenhouse gases CO₂,and other pollutants SO₂、NO_x will be released.SO₂,NO_x and other harmful gases will cause acid rain and photochemical smog,which will do great harm to the environment and human body.The emission of a large amount of CO₂will make the global environment warm and pose a threat to the life system of animals and plants.In order to ensure that China’s carbon dioxide emissions will decrease year by year from the peak level after 2030,it is urgent to find efficient carbon dioxide capture technology.Chemical looping combustion technology is a new type of combustion technology which combines the clean and efficient combustion of coal,the green utilization of biomass energy and the efficient and low consumption capture of CO₂.Based on this,the chemical looping combustion characteristics of coal and biomass based on iron-based oxygen carrier were studied,the key factors affecting the chemical looping combustion of solid fuel were investigated,and the release law of nitrogen oxides in the process of chemical looping combustion of coal was deeply explored.First,a series of iron-based composite oxygen carriers were prepared with co-precipitation method,and the oxygen carriers were characterized and analyzed.It is verified that the use of nitrate as the precursor and the release of a large amount of gas during the calcination to prepare the oxygen carrier can make the pores of the oxygen carrier more abundant;Al₂O₃ as the inert oxygen carrier can improve the mechanical strength and wear resistance of the oxygen carrier Damaging.The Fe₂O₃/Al₂O₃ oxygen carrier modified with Cu O as the active component will generate Cu Fe₂O₄spinel at high temperature,which can improve the high-temperature sintering phenomenon of the iron-based oxygen carrier.Then,chemical looping combustion experiments were carried out with Ximeng lignite and salix as fuel.Based on a batch fluidized bed reactor,the effects of the reaction temperature,the structure of the solid fuel,and the number of cycles,the addition active components Mg O and Cu O in the oxygen carrier on the chemical looping combustion characteristics of the solid fuel were investigated.The study found that the increase of the reaction temperature can obtain a higher carbon conversion rate in a shorter period of time.The carbon conversion rate of coal char and biochar as fuel is higher than the carbon conversion rate of the original pellets,and the time to reach the peak is earlier than the original.The results of 15 cycles of experiments showed that after multiple cycles of experiments,the iron-based oxygen carrier modified by 5%Mg O still remained better reactivity.After adding Cu O active components to the oxygen carrier,the carbon conversion rate of the fuel is improved under the same temperature conditions,and in multiple cycles of experiments,the fuel carbon bricking rate has been maintained at a high level,all at 80%The above shows that the Cu O-Fe₂O₃/Al₂O₃ oxygen carrier can maintain stable activity in chemical looping combustion.Final,the release of nitrogen oxides during coal chemical looping combustion was investigated in a fixed bed reactor.The results show that the peak value of no release rate in the conventional combustion process at 900℃is 0.0013 mmol/min,which is much higher than that in the chemical looping combustion process;when the reactor temperature is 900℃and the atmosphere is ar,the maximum value of no release rate is 0.000228 mmol/min.The experimental results of Ar and CO₂ mixture show that CO₂ in gasification medium can increase the production of NO.With the increase of reaction temperature,the ratio of fuel nitrogen to no increases.In addition,when Cu O is added into the oxygen carrier,the gasification medium and reaction temperature have little effect on the no release rate and no formation rate.