Numerical Simulation And Optimization Of Small Rapeseed Layered Bed Typed Drying Equipment With Biomass Energy

As a primary oil-bearing crop of China, rape is widely planted in central and southern areas. Drying and stockpiling of rapeseed is an important step in whole processing links. From farmers’ perspective, the drying equipment with low cost, low energy consumption and high efficiency is desired. Directed to these purposes, a kind of small layered and bed-typed drying equipment is processed. The equipment has a biomass semi-gasification combustion furnace which burn straw and firewood as the heat supply. Moreover, the equipment heats the air by using a heat exchanger and drying rapeseed by the exchange of ventilation of heated air.The thesis takes this equipment as a research object, makes a study of physical property of rapeseed and desiccation effects of the equipment by conducting several experiments. By using CFD(Computational Fluid Dynamics) and porous-media model, the distribution of single-phase flow field in desiccation chamber is analyzed. By studying desiccation uniformity of the equipment, an optimization of the distribution patterns of the internal flow field in airflow is given to improve the desiccation uniformity. Under the condition of high wind velocity, by applying Euler Model, the numerical simulation analysis on gas-solid two-phase flowing of rapeseed in desiccation chamber is made and the volume-fraction distribution of rapeseed during desiccation process. Moreover, we study the consumption rates of biomass fuels by using different fuels as heat supply. The main conclusions are as follows.(1) The real density of rapeseed is studied by using the method of pycnometry with toluene, and the bulk density is determined by volume weight method. In result, the density of rapeseed is increased along with the increase of moisture content. According to the experimental data the porosity of rapeseed bed is obtained, and the porosity is e=0.392. The particle size distribution of rapeseed is obtained by using sieving method, and the average particle size is.Dp =mm81. The regression analysis show that the moisture content and temperature of rapeseed have significant effects on its specific heat capacity and thermal conductivity, and it has a positive correlation between moisture content, temperature, specific heat capacity and thermal conductivity. Two-dimensional regression equations are also set up. Due to the input of numerical simulation is generally constant, the parameters of rapeseed which the initial moisture is 25.7% are considered as the reference of simulation.(2) After processing rapeseed drying test on the equipment, it is found that it can achieve the requirement of desiccation and has higher throughput. It takes about fifteen hours for the machine to lower moisture content to fewer than 9 %. For desiccation effect, the top and bottom beds are better than other beds of the equipment, and the central area is better than corners.(3) By using FLUENT under ANSYS Workbench, numerical simulation and optimization for flow-field model are building to predict the air flow in drying chamber under the inlet velocity at 2m/s and 5m/s. From velocity and pressure dropping contours, we find when single longitudinal ventilation is processed, distribution of vertical wind velocity changes significantly, distribution of the horizontal wind velocity is uniform, and a low velocity in intermediate material bed may lead to non-uniform desiccation. These phenomenons are consistent with the experimental results. After increasing the ventilation duct and transverse ventilation layer, the drying efficiency of middle layer increases and the entire distribution of flow in the drying chamber are uniform. By using two-way alternate ventilation the problem of drying uniformity can be effectively solved.(4) The critical fluidization velocity of rapeseed has been analyzed. Under the condition of larger input of wind velocity, rapeseed is blown in the drying chamber, and in this way, the gas-solid flow is formed. Based on the two-phase flow and experimental data, the fluidized state of rapeseed in drying chamber has been simulated. By analyzing the gas-solid flow state, the volume fraction distribution of particle at different time and sections are build. In result, the good fluidized state of rapeseed increase the contact area and contact time between air and rapeseed. In this way, the drying quality, uniformity and efficiency are improved.(5) In order to analyze the consumption rate and cost of biomass fuels, different biomass fuels as BMF, camphor branch, cotton straw and rape straw have been used to do the fuel consumption experiment in the biomass semi-gasification combustion furnace. The result shows that using BMF, camphor branch, cotton straw and rape straw the consumption rates respectively are 1.55kg/h, 2.41kg/h, 3.07kg/h, and 3.42kg/h. The cost by using BMF is 1.47 yuan per hour, and the other biomass fuels are basically flat at 1yuan per hour. In result, using biomass semi-gasification combustion furnace and heat exchanger can improve the economical efficiency and energy-saving, and can reduce the gas emission to protect the environment.By using CFD method, numerical simulation and optimization are conducted for biomass rapeseed layered and bed-typed drying equipment. The desiccation uniformity and efficiency are improved. The use of biomass energy reduces costs and energy consumption, which meet the farmers’ demands and reduce environmental pollution. The conclusion can be used as a future reference of rapeseed drying and optimization of drying equipment.