Experimental Study On The Combustion Characteristics Of Mangcanthus Briquette Molding

China’s energy structure is dominated by coal.Every year,a large number of coal is burned directly without washing,forming and other processing,which not only pollutes the ecological environment,but also reduces the use efficiency of coal,resulting in a huge waste of energy.The biomass Chinese Miscanthus has the advantages of good combustion characteristics,strong environmental adaptability,low planting cost and high yield,and can absorb harmful gases and other harmful substances in the atmosphere and soil,with good economic and environmental benefits.However,in the vast rural areas of China,the conventional treatment of Miscanthus is incineration and landfill,which not only causes a lot of waste of resources,but also pollures the environment.In this paper,miscanthus and anthracite were used as the research object,mixed and crushed in a certain proportion,and a small amount of binder carboxymethyl cellulose was added,which was pressed into miscanthus brique-shaped coal by cold pressing.In this paper,the basic fuel characteristics of test raw materials,physical properties of miscanthus briquette,test raw materials and briquette microstructure,briquette combustion process,briquette combustion performance and other aspects are analyzed and studied.The main conclusions are as follows:（1）Miscanthus has the characteristics of high volatile content,easy ignition,low carbon（C）element content,low calorific value,low ash content but soluble,etc.Anthracite is characterized by low volatile content,difficult ignition,high content of C element,high calorific value,low ash content and insolubility,etc.Carboxymethyl cellulose has the characteristics of high C content,medium volatile content,high ash content and medium solubility.The contents of nitrogen（N）and sulfur（S）in Miscanthus,carboxymethyl cellulose and anthracite are low.Therefore,the mixture of Miscanthus and anthracite combines the advantages of rapid ignition and long combustion time,which is favorable to the combustion process.（2）The miscanthus type coal the best molding parameters combination of cold pressing molding is miscanthus accounted for 30%,105 kn forming pressure,carboxy methyl cellulose content 2%,miscanthus size 0-0.5 mm.Under this forming process,the relaxation density of Chinese straw briquette is 1.189g/cm³,the compressive strength is 96kN,and the drop strength is0.992.（3）Due to the high degree of coalification and high density of anthracite,its microstructure is characterized by relatively smooth surface;The binder carboxymethyl cellulose is a typical fibrous structure,the surface is smooth and smooth,but easy to form small particles;The surface of Miscanthus grass is rough and irregular due to the distribution of a lot of conduit cells,and there are relatively many pore structures.There are mesoporous and large pores produced by mass transfer in the growth process of the plant,and these pores provide a way for oxygen to enter during combustion.When the external pressure is imposed,the binder carboxymethyl cellulose will enter the pores of anthracite,resulting in strong bonding force.At the same time,the fiber in the biomass Chinese miscanthus can also play a certain"bridge"auxiliary role,the scattered anthracite and Chinese miscanthus mixed connection produced a certain mechanical meshing structure,so that the combination of Chinese miscanthus and Anthracite is more closely.Therefore,the preparation of miscanthus coal fuel requires the right pressure and the right binder.（4）According to the analysis of combustion curve during the combustion process,it is shown that the four stages of common precipitation of water,common precipitation of volatile matter,fixed carbon combustion and volatilizing analysis of anthracite,fixed carbon combustion and burning out of anthracite constitute the whole combustion process of Miscanthus briquette.When the heating rate increases,the combustion curves（TG,DTG and DSC）of single component and briquette samples in the combustion process all have a certain thermal hysteresis phenomenon and tend to shift to the high temperature region,and the corresponding peak value and peak width of the curve increase accordingly.When the blending proportion of Chinese miscanthus increases,it is helpful to reduce the ignition temperature of Chinese miscanthus briquette in the initial combustion process,and reduce the residual mass of Chinese miscanthus briquette after combustion,indicating that the incorporation of Chinese miscanthus has a relatively obvious improvement effect on the combustion process of anthracite.When the heating rate increases,the ignition temperature and burnout temperature of Miscanthus briquette increase,but the flammability index and combustion characteristic index both increase,indicating that the increase of heating rate is helpful to improve the combustion rate of Miscanthus briquette.Therefore,the increase of miscanthus blending ratio and heating rate can promote the combustion of miscanthus briquette and help to improve the stability of combustion process.（5）The test meets that the briquette forming parameters are 30%of awn grass,the forming pressure is 90kN,the combustion condition parameters are furnace temperature 1000℃and excess air coefficient 2.1.At this time,the relative combustion rate of awn grass briquette is the best,and the result of relative combustion rate is 55.012%.The industrial analysis results of Miscanthus briquette have little difference from the proportional conversion values of Miscanthus,carboxymethyl cellulose and anthracite,while the calorific value measured is about900kj/kg less than that.The addition of Miscanthus and carboxymethyl cellulose reduces the ash melting point of anthracite,and with the increase of Miscanthus,the ash melting point of Miscanthus briquette shows a downward trend,which is easy to cause ash accumulation and slagging in combustion.Through infrared spectrum analysis and X-ray diffraction analysis,it is found that the reason for the decrease in the combustion process of Miscanthus briquette may be that the elements such as Ca and Al contained in anthracite and Miscanthus will also form low-temperature eutectic with carbonate,so as to reduce the ash melting point of briquette to a certain extent,and a new sulfate substance Ca₂SO₄H₂O appears at the same time.Therefore,in the actual industrial utilization of mangcao briquette,attention should be paid to avoid the problems of ash accumulation and slagging on the heating surface and grate of industrial boiler,so as to ensure the normal operation of industrial boiler.（6）In the industrial use of Chinese straw briquette,the influence of forming pressure on the combustion rate of briquette is greater than the influence of forming,and the physical properties of briquette with forming pressure of 90kN are little different from those of 105kN.Therefore,considering all factors,when brique-forming parameters are Miscanthus 30%,molding pressure90kN,carboxymethyl cellulose 2%,Miscanthus particle size 0-0.5mm,moisture content 10%,anthracite particle size<0.2mm,combustion condition parameters are furnace temperature1000℃,excess air coefficient 2.1,The physical properties and combustion efficiency of Miscanthus briquette are the best.The industrial analysis results of briquette prepared under the optimum technological conditions are as follows:water content 5.13%,ash 11.42%,volatile matter 29.28%,fixed carbon 54.17%,calorific value 21653k J/kg,ignition temperature 302.5℃,burnout temperature 776.1℃,ash melting point 1388℃.