Study On Hybrid Combustion Mechanism Of Biomass,Plastics And Coal

Coal is the most important energy in China.Biomass is renewable,but its utilization rate is low.Plastic waste is increasing rapidly,which is extremely difficult to degrade and easy to produce white pollution.In order to solve the shortage of fossil energy and enhance the efficient utilization of biomass and plastics,the experimental study on the mixed combustion of cornstalk,polyethylene and anthracite coal was carried out.The combustion characteristics of the mixed samples were studied by thermogravimetric combined with Fourier transform infrared（TG-FTIR）,fixed bed combustion furnace and ash melting point tester.Based on Thermogravimetric analyzer,the effects of heating rate and mixing ratio on combustion characteristics and combustion dynamics of cornstalk,polyethylene and anthracite were obtained.It was found that there were two stages of the combustion of cornstalk,namely volatile matter precipitation and combustion and fixed carbon combustion.The maximum reaction rate of volatile matter precipitation and combustion（-7.82%/min）was higher than that of fixed carbon combustion（-4.28%/min）,and the weight loss rate of the whole combustion stage was 86.94%,of which the weight loss of volatile matter combustion was 61.55%.The main combustion zone is the combustion zone of volatile matter precipitation and combustion.The combustion of polyethylene and anthracite has only one combustion stage which was the combustion of fixed carbon.There are four stages in the combustion of mixed samples.The TG and DTG curves are located between the combustion curves of cornstalk and anthracite.With the increase of heating rate,the ignition point,maximum reaction rate and burnout temperature of the sample increase.Calculating curves of mixed samples converted proportionally based on the experimental curves of individual combustion of samples is different from the experiment curves,and there are synergistic effects among the samples in the combustion process of mixed samples.The calculation and analysis of sample combustion kinetics showed that the activation energy of cornstalk was the smallest and divided into two stages.The activation energy of volatilization analysis was38.03 kJ·mol^-1 in the volatile matter combustion stage and 54.63 kJ·mol^-1 in the fixed carbon combustion stage.The activation energy of polyethylene is the most,which is 134.60 kJ·mol^-1.The activation energy of anthracite is 118.64 kJ·mol^-1 between cornstalk and polyethylene.The activation energy of the mixed samples in each stage of combustion is less than that of the single combustion of polyethylene and anthracite,and the mixing of the samples promotes the combustion reaction.The first stage activation energy of the mixed samples ranged from30.7 to 53.38 kJ·mol^-1,which was dominated by the combustion of cornstalk.In the range of reaction temperature of polyethylene,the activation energy of mixed samples is between10.16-94.61 kJ·mol^-1,which is much lower than that of polyethylene.The activation energy of the mixed sample in the range of anthracite combustion temperature is also far less than that of anthracite.Synergistic effects are produced in the combustion process of samples.According to the results of Fourier transform infrared spectrometer,the mixture of samples has no effect on the types of gas products.CO,CO₂,CH₂ and C=O are the main products in the combustion process.The appearance,change and disappearance of different absorption peaks in combustion process show the beginning and end of different reaction processes.The combustion experiments of samples with different mixing ratios at different final temperatures in a fixed bed reactor reflect the effects of mixing ratios and reaction temperatures on the emission process of flue gas.The increase of reaction temperature promoted the conversion of nitrogen-containing products to NO,reduced the peak value of CO formation,and made the sample burn more fully.Sample mixing reduces the production of SO₂.The four ash melting characteristic temperatures of anthracite are all over 1500℃,and the biomass characteristic temperatures are between 1200℃ and 1300℃.After sample mixing,the ash melting point of anthracite decreases relative to the ash melting point of anthracite,increases relative to the cornstalk,and the softening temperatures are all over1400℃,so no special consideration should be given to fuel slagging when burning in boilers.