Study On Physical Properties And Combustion Characteristics Of Straw Stalk Solid Fuel

The millet,which is the first of the "grains," is an important crop in Shanxi’s characteristic small grains.The planting area in Shanxi is stable at about 200,000 hm2,accounting for about 21%of the country’s total milled area,ranking second in the country.In the large-scale planting,straw treatment after harvesting has gradually become a common concern.Traditionally,the traditional treatment method is silage,rot and fertilizer,etc.With the enhancement of environmental protection and energy awareness,it become a trend that used as a solid fuel.Biomass solid fuels have many advantages such as high density,high calorific value,ease of transportation,and storage.Hot compression molding technologies for agricultural and forestry waste such as corn stover,wheat straw,Chinese fir,and Caragana korshinskii have been studied at home and abroad.However,the study on the energy utilization of millet solid fuel has not been reported yet.For this reason,this dissertation focused on the research of the forming mechanism,physical properties and combustion characteristics of solid fuel in millet stalks,and mainly explored the moisture content,particle size,pressure,temperature and other factors on the effect of fuel forming.And we try to quantify the molding mechanism of several micro-adhesion force,establish a force model between particles,analyze the impact of forming factors on the interparticle force,then study the slagging characteristics and combustion characteristics of millet straw solid fuels,establish combustion dynamic model,which could provide the basis for the design of related processing and utilization equipment.The main contents and conclusions are as follows:(1)Though the univariate analysis performed on the physical properties and influencing factors of the solid fuel of millet stalk,the curve and relationship of each factor and fuel density,durability,and resistance to crushing were obtained,and a reasonable range of molding parameters was determined.The results show that the density of fuel increases with the decrease of particles in the experimental test range,and it also increases first and then increases slowly with the increase of pressure,but it increases first and then decreases with increasing temperature and moisture content.Combining the changes in durability and resistance to crushing,it was found that the moisture content of the solid molded fuel with good molding quality was between 8%and 10%,the molding temperature was between 80 and 110℃,and the optimal pressure was between 90 and 110MPa.(2)The order of influence of the moisture content,particle size,pressure,and temperature on the effect of fuel formation(density)was studied.Orthogonal test method was used to analyze the contribution rate and the primary and secondary influence of the response factors on the four impact factors of millet stalk solid fuel.The test results show that the contribution rates of moisture content,particle size,pressure and temperature are 19.83%,46.11%,17.52%and 16.55%,respectively.(3)The minimum Mahalanobis distance method was used to optimize the analysis of the density,durability,and crush resistance of millet solid fuel,and the best treatment solution(ie,optimal process parameters)for each response variable was obtained.The water content was 10.7.%,temperature 97℃,pressure 107 MPa,density,durability and resistance to crushing under these conditions reached 1.18 g/cm3,99.75%and 99.77%,respectively.(4)From the microscopic and microcosmic perspectives,the interaction forces of the grain fuel of the millet stalk were studied to establish a mechanical model between the solid fuel particles.At the same time,the laser particle size analyzer,contact angle analyzer,and micro-electrophoresis apparatus were used to analyze the compression molding.Effects of temperature,pressure,particle size,and moisture content on contact angle and Zeta potential.The results show that the van der Waals force,mechanical friction force,electrostatic attraction force and liquid bridge force between the particles in the molding process play a key role in the establishment of the solid fuel strength of the millet stalk,and different compression conditions affect the relevant physical quantities of the interparticle forces—The contact angle and Zeta potential also have significant effects,establishing the relationship between the macroscopic test conditions and the bonding mechanism.(5)The thermal analysis method was used to study the melting characteristics,combustion characteristics and combustion dynamics of millet straw fuel.The combustion kinetics equations were solved and the slagging characteristics of millet stalks were analyzed.The results show that the solid fuel of millet stalk has a lower ignition temperature,easy ignition and high burnout rate,but the bottom ash is easy to slag.The conclusions of the study provide a reference for energy utilization of the form of solid fuel in millet stalks,which has guiding significance for actual production.