| Chemical looping technology is an advanced developing direction based on zero emission concept,with complete change in energy utilization route.The process allows energy with different levels following staged utilization,and has high exergy efficiency.Cyanobacteria is one kind of biomass with abundant resources.Chemical looping combustion of cyanobacteria is one kind of negative carbon technology,while its process of chemical looping gasification can obtain high grade syngas.However,compared with other solid fuels(coal),cyanobacteria has the characteristics of high volatility and good reaction activity,but the problems of high water content and low calorific value restrict its large-scale utilization.Therefore,from the perspective of large-scale utilization and disposal of energy,the densification of cyanobacteria and its briquette fuel are important research directions of cyanobacteria chemical looping utilization technology.The paper proposed a technique route suitable for cyanobacteria fueled chemical looping combustion/gasification.Base on the key concerns of the route,that is:cyanobacteria densification parameters and the physical and chemical evolution behavior during chemical looping process;reaction kinetics with oxygen carrier;conversion behavior in case of using a mixed cyanobacteria/coal as fuel,the related detailed investigations were performed in this paper.Biomass densification technology has important research value for improving the energy density of cyanobacteria and reducing the storage and utilization cost of cyanobacteria.The influence of moisture content,molding rate and relaxation density on cyanobacteria densification was evaluated,and the densification parameters were optimized.Based on fluidized bed reactor and iron ore oxygen carrier,the chemical looping behavior of pelletized cyanobacteria was primary detected.The process was divided into four stages as:cyanobacteria powder densification,dehydration,devolatilization and remaining char conversion.The optimum moisture content of single cyanobacteria was 10%.In the dehydration process,regardless of the moisture content and heating rate,the molding rate and relaxation density of the dehydrated residual samples increased with the increase of compression load.The higher the heating rate in the dehydration process,the more severe the dehydration process and the more serious the internal structure damage,which was not conducive to the mechanical strength of the pelletized cyanobacterial after dehydration.In the process of cyanobacterial chemical looping with hematite as oxygen carrier,the carbon conversion efficiency of the pelletized cyanobacterial was significantly improved due to the presence of hematite.In the 10 redox cycles,hematite showed good continuous reactivity.In order to explore the dynamics of cyanobacterial chemical looping reaction,a high loading rate thermogravimetric analysis device with movable furnace body was built to meet the requirements of cyanobacterial shaped fuel.The effects of temperature,compression load and oxygen carrier on the dynamics of cyanobacterial chemical looping reaction were studied.Based on the experiments,the chemical looping reaction kinetics of using cyanobacteria powder or its single pellet were obtained.By fitting the experimental data,the chemical looping reaction kinetic model of cyanobacteria powder is dX/dt=72.626 exp(-75.217/8.314T)(1-X)2,and the chemical looping reaction kinetic model of cyanobacteria pellet is dX/dt=10358×104 exp(-125.042/8.314T)(1-X)5.According to kinetic model calculation,the activation energy of 49.825kJ/mol was needed to overcome internal transfer residence for the pelletized cyanobacterial.Considering that red mud is a large amount of solid waste and can be used as a new type of oxygen carrier material with good reaction activity,the chemical looping gasification and combustion characteristics of cyanobacteria shaped fuel were studied in this paper.The influence mechanism of red mud oxygen carrier on the pyrolysis,gasification and combustion process of cyanobacteria was revealed,and the phase migration and distribution law of red mud oxygen carrier in the chemical looping thermal conversion process was clarified.The presence of oxygen carrier had remarkably positive effect on the pelletized cyanobacteria pyrolysis and gasification processes.It improved the pressure gradient caused by the pelletized cyanobacteria devolatilization.Consequently,the volatiles could be released gradually through the relatively developed channels.During chemical looping gasification process,the H2 content in the syngas has the highest concentration with its value higher than 45%,followed by CO2,CH4 and CO.The increase of the reaction temperature or oxygen carrier to fuel ratio led to the increase of carbon conversion.When the reaction temperature increased from 750℃ to 950℃,the ratio of H2/CO in the syngas decreases from 7.26 to 4.83.Meanwhile,with the increasing oxygen carrier to fuel ratio,the ratio of H2/CO first increased and then decreased,and the peak was 5.6 with the value of the oxygen carrier to fuel ratio as 0.5.Due to the high water content and low calorific value of cyanobacteria,there are still many problems in the industrial chemical looping combustion process.Coal is still one of the main energy sources in China,and the high calorific value is also the first choice for the mixed combustion of many biomass fuels.Therefore,taking high sodium Zhundong coal and cyanobacteria as mixed fuel,the study on the chemical looping synergistic combustion characteristics of coal and cyanobacteria mixed fuel was carried out.The differences of combustion characteristics under different ratios and pressure intensities were investigated,and the phase migration laws of oxygen carriers in the chemical chain thermal conversion process of mixed fuel were obtained.When the mass ratio of cyanobacteria to coal was 4:1,the highest average gasification rate(26.39%/min),average carbon conversion rate(9.24%/min)and the shortest reaction time(8.7 min)were obtained,and the conversion rate was lower than that of pure cyanobacteria but higher than that of pure coal.With the increase of reaction temperature,the concentration of CO2 at the outlet of the reactor first decreased and then increased slowly.The concentration of H2 gradually increased at 750-900℃ and then decreases at 950℃.The concentration of CH4 gradually decreased and the concentration of CO changed slightly.In the mixed fuel,only relying on the internal water of cyanobacteria itself had limited ability to ensure the conversion of mixed fuel.The introduction of additional water vapor ensured the gasification of coke and promoted the conversion of mixed fuel.The results showed that the composition of fuel had little effect on the distribution of elements on the surface of oxygen carrier in red mud;when the temperature increased,the oxygen content on the surface of oxygen carrier increased;in the process of chemical looping combustion,the Fe atoms of oxygen carrier tended to migrate to the surface,and with the increase of coal proportion,the migration tendency of Fe atoms on the surface increased. |
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