Improvement And Experimental Research Of Biochar-based Fertilizer Forming Machine

Biochar-based fertilizer is a new type of slow-released fertilizer made by blending biochar as a carrier and traditional fertilizer.It is widely used in crop production,soil improvement and pollution control.Biochar-based fertilizers are usually prepared by agglomeration,extrusion,melting,spraying,fluidization and the like.In the early stage,a new biochar-based fertilizer forming machine was developed.Compared with the traditional forming machine,the forming machine integrates conveying,extrusion,forming and pelletizing.The produced carbon-based fertilizer particles have high strength and are basically satisfied with the national standards for fertilizers.So the machine is stable,reliable,and applicable.However,through experiments it was found that the temperature rise of the forming equipment was obvious,which easily caused the problem of high energy consumption and low molding rate.This paper analyzed the temperature rise law of forming equipment,and improved it from two aspects: material forming process and forming machine structure: on the one hand,the combination of optimal process parameters was obtained by single factor test and response surface test by material extrusion forming test.On the other hand,the screw parameters were optimized by numerical simulation,the corresponding cooling system was designed,and the improved forming equipment was manufactured.Finally,a comparative experiment was carried out to verify the improvement effect.The main contents and conclusions of this paper are summarized as follows:Firstly,exploring the temperature rise mechanism of forming equipment.The temperature rise is mainly caused by the deformation heat and friction heat during material forming process.The calculation formula of friction heat and deformation heat is deduced by the micro-element method and the basic theory of screw.The temperature rise is affected by the screw structure,material compression characteristics and screw speed.When the material formulation and the structure of the forming machine are determined,the screw speed is a key factor in determining the temperature rise of the equipment.Secondly,the temperature field analysis model of the forming process was established,and the temperature rise law of the molding machine was actually measured and compared with the simulation results.According to the simulation results,the internal temperature of the barrel increases with the increase of the rotational speed,and the highest temperature is located in the area close to the screw,and the temperature distribution decreases from the inside to the outside.In actual production,the temperature of the material inside the barrel experiences a slow growth phase,a rapid growth phase,and finally tends to be gentle and the temperature distribution shows a gradient change.The closer the screw is,the higher temperature.As the speed increases,the maximum temperature inside the barrel first increases and eventually falls back.The temperature change trend of the barrel surface is similar to the inside of the barrel,but numerically there is a large gap,and the temperature distribution is uneven,the closer to the discharge port,the higher temperature.The error between the actual measured temperature and the simulation result is between 8% and 15%,indicating that the analytical model has certain rationality.Thirdly,the material extrusion forming tests were carried out.Through the single factor test and the four-factor three-level response surface test,the influence of the four factors including the speed,aspect ratio,moisture content and ratio of slow-release materials and fertilizer on indicators including energy consumption and compressive strength were discussed.Regression models of specific energy consumption and compressive strength were established and predicted.The results of response surface test show that the effect of various factors on the energy consumption are as follows: aspect ratio > moisture content > speed > ratio of slow-release materials and fertilizer;the interaction between aspect ratio and moisture content has a significant effect on energy consumption.The effects of various factors on the compressive strength are as follows: moisture content > ratio of slow-release materials and fertilizer > speed > aspect ratio;the interaction between moisture content and ratio of slow-release materials and fertilizer has a significant effect on the compressive strength.Under the conditions of minimum specific energy consumption and maximum compressive strength,the optimal combination of process parameters is obtained: speed is 50 mm/min,aspect ratio is 3.5,moisture content is 14.16%,and ratio of slow-release materials and fertilizer is 4.The specific energy consumption produced under this condition is 20.541 kJ/kg.The compressive strength is 35.013 N,and the predicted average relative error are 3.3% and 2.3%,indicating that the regression models have higher reliability.Lastly,with the help of FLUENT,the pressure field distribution in the barrel of different screw parameters was analyzed,and the screw parameter were optimized.When the compression ratio is 1.8,the groove depth is 17.5 mm,and the width of the screw edge is 5 mm.The forming effect of the material is better.According to the law of temperature rise,the corresponding cooling system was designed,and the rationality of the design was verified by calculation,and the corresponding fittings were properly selected.A new prototype was re-manufactured.After the improvement,the temperature rise of materials decreases by 15.4%,and the temperature rise of the barrel surface decreases by 28.8%.The product yield and molding rate are significantly improved,with an average increase of 51.1% in production and an average increase of 37.6% in forming rate,while maintaining high particle strength,indicating that the improvements are more reasonable.