Straw Pellet Fuel Cold Molding By Compression: Experimental Study And Numerical Simulation

The pellet fuel cold molding discipline of different crops straws is studied detailed in this thesis,under the background of developing biomass utilization technology as a kind of energy resource.It starts a new way for biomass solid pellet fuel to be used as renewable energy substituting for coal.It is listed in a sub project of Chinese National '863 Project' "Agriculture Waste FB Gasifying Pretreatment Technology" and the project of the Natural Science Foundation of Henan Province project "Study of Agriculture Waste Cold Molding Mechanism".The main research contents are in the following,experiments are done from five aspects including pressing speed,moisture ratio,variety of the material,length diameter ratio of the die and split taper by universal stuff experimental equipment.According to the feature of straw pellet cold moling,using large deform elastic and plastic theory as the method for finite element computation,it adopts the software ANSYS to simulate the molding process.The stress and strain distribution chart,fluid deform chart and equivalent plastic strain in the molding process are obtained.And simulations on various ratios of length and diameter and split taper are done.Detailed influence on molding is analyzed from four aspects, biology structure,physical property,chemical property and dynamic property.The stick mechanism is obtained.And the micro structure changes are studied by SEM under different molding conditions.According to the molding mechanism,pilot pellet equipment is designed. And a series of experiments on molding rate and electricity consume rate are done under different pressing condition.From the study work above,the optimal molding conditions and technological parameters obtained by different means have good consistency.This provides scientific evidence for the exploration of molding discipline.The main conclusions are in the following:(1)At the condition of speed 40mm/min,moisture ratio 16%,ratio of length and diameter 5.2 and taper 45°with wheat straw,the best results can be obtained.The molding process can be divided into four stages,loose,interim,pressing and lapse.The loose and pressing stages fit linear equations.And the interim stage fits exponential equation.The lapse stage fit Maxwell Model.These conclusions provide evidence for the selection of pressing conditions and parameters.(2)The friction force and the taper are the main reasons why the deforming near the split is delayed.And optimal ratio of length and diameter and split taper are accordant with the experiment results.It's proved that the simulation fits well with experiment study.This provides theoretical evidence for the selection of die parameter and control of the pellet equipment.(3)The micro connecting mode is put forward from straw cold molding by compression. In the cross section,the structure of the biomass is destroyed seriously and connected by joint form.And in the lengthwise section,little destroy appeared,so they connect by chimeric form. This provides evidence for the exploration of the common regulations on pellet molding.(4)The molding rate is sound under swoop angle 45~0 and ratio of die and roller diameter 0.585.The molding rate of wheat is better than rice straw,the worst is corn straw.The electricity consumption is the lowest under granularity 6mm,moisture ratio 16%,ratio of length and diameter of the die 5.2.This conclusion proves the correctness of the experiment study and computation simulation.And the best molding condition and parameter has universal significance,guiding the design of pellet mill for industry use.