Study On Preparation And Combustion Behavior Of Biomass Molding Fuel

Biomass energy is rich in reserves in the word and a kind of renewable energy with the potential to replace fossil energy.Straw agricultural waste is one of the most common raw materials of biomass energy,but its low energy density leads to high transportation cost,so compression molding is one of the main pre-treatment methods.However,the characteristics of different types of biomass are quite different,resulting in the uneven quality of formed fuel.Moreover,the current biomass molding process requires high temperature（120-300℃）and pressure（40-100 MPa）,which makes the high molding energy consumption.Studying the influence of molding process parameters on the quality of molding fuel,optimizing molding process,and reducing costs are great significance for the application of molding fuel.Based on this,on the basis of previous work,this study first analyzes the molding conditions of typical agricultural wastes,and investigates the influence of molding conditions on the key indicators of forming fuel;and develops a molding binder to further reduce the molding pressure and temperature,and improve the quality of forming fuel;finally,the combustion and ash formation behavior of biomass fuel is investigated.Firstly,cotton straw and corn straw were selected as raw materials,with a fixed molding pressure of 12.5 MPa,for different temperatures（20℃,50℃,80℃）,moisture addition（7.5%,10%,12.5%）,and particle size（20-40 mesh,40-60 mesh,60-80 mesh）to conduct a detailed investigation to discuss its influence on the performance such as the drop strength and relaxed density of the molded fuel.As a result,it was found that the higher the molding temperature and the smaller the crushed particle size,the higher the two performance indexes of the molded fuel.With the increase of water content,the relaxed density of the molded fuel increases first,and then remains unchanged,but the drop strength increases first and then decreases.The results of orthogonal experiment shows that the drop strength and relaxed density of cotton straw are the highest when the temperature is 80℃,the crushed particle size is 60-80mesh and the moisture content is 10-12.5%.The prepared molding fuel meets the current molding fuel（drop strength industry standard>85%,relaxed density range0.7-1.2 g/cm³）index requirements,and the energy consumption of the optimized molding process preparation is significantly reduced.However,due to the influence of the physical properties of the raw materials,it is less likely to further improve the mechanical strength of the molded fuel under mild conditions.Therefore,it is considered to prepare a binder to solve the above problems.In this part,by-product kaolin and oil sludge from the petroleum industry are selected as the main components to prepare a solid powder composite binder.Oil sludge contains a large number of organic components（cycloalkane,aromatic hydrocarbons,colloids and asphaltenes,etc.）,which can play a role of binder in compression molding and improve the mechanical strength of molding fuel.The addition of kaolin can alleviate the problem of fouling during biomass combustion.However,due to the high viscosity of the sludge,it is not easy to mix with the raw materials,so a preparation method of solid powder composite binder is proposed,which is very easy to mix with the raw materials.The experimental results show that with the increase of binder ratio,the drop strength and relaxed density increases first and then decreases.According to the comprehensive analysis,the suitable proportion of binder is 5 wt.%.Finally,the combustion and ash formation behavior of briquette fuel with add binder were investigated.The results show that the ash melting temperature of the molding fuel with 5 wt.%binder is obviously increased,the combustion time is slightly increased,the maximum combustion rate is slightly reduced,and the comprehensive combustion performance has no obvious change.Compared with the combustion of biomass raw materials at the same combustion temperature,the content of K in the ash of biomass briquette fuel is higher,it may be that the biomass molding process inhibits the release of KCl and K₂CO₃during the combustion process;The content of K in the biomass molding fuel ash which add binder is further increased,because Si and Al in the kaolin combine with K from biomass to form high melting temperature KAl Si₃O₈during the combustion process,thus increasing the melting temperature.It shows that the addition of composite binder can inhibit the release of K during the combustion of biomass molding fuel,and thus can alleviate the tendency of combustion fouling and particulate matter release.Therefore,In this paper,through the investigation and optimization of biomass molding process parameters,the preparation of solid powder composite binder,the combustion of molding fuel and the more detailed investigation of the ash formation behavior,it further promotes the practical application of biomass molding fuel.