| Under the background of my country's grain industry advocating green grain storage,various new technologies,new processes,and new products for green grain storage have emerged at the historic moment.Among them,room-type silo circulation uniform temperature and phosphine closed loop fumigation and insecticide are the current domestic conventional technical processes.This study adopts a combination of numerical simulation and experiment.First,it studies and analyzes the change law of the temperature field during the temperature uniformity of the room-type silo.By simulating the temperature uniformity process of the room-type silo under different working conditions,the average temperature of the room-type silo is given.Optimal temperature ventilation process plan.Secondly,based on the optimized circulating temperature equalization equipment technology,carry out the simulation optimization research of the phosphine closed loop fumigation technology in the room-type warehouse,and explore the phosphine fumigation under the working conditions of different amounts of aluminum phosphide(fumigant).Diffusion law and concentration distribution of deliquescent phosphine gas from aluminum phosphide tablets during insect pests in the grain pile,so as to obtain the best phosphine fumigation and insecticidal process parameters,in order to provide a scientific basis for the prevention and control of stored-grain pests.The specific work content is as follows:First,a numerical simulation study on the effect of grain temperature homogenization in the room-type silo's closed loop ventilation and closed loop fumigation process is carried out and compared with the actual silo test data.The research contents of this part mainly include:(1)Based on the principles of conservation of dose,momentum,and energy,the establishment of a room-type silo circulation temperature uniformity and circulation closed loop fumigation control model.(2)Use the Fluent software to evaluate and optimize the numerical simulation of the room-type silo's temperature uniformity process under three ventilation rates,and obtain the internal temperature distribution law and grain temperature uniformity of the grain pile when the silo's airflow downwards the circulation temperature uniformity process.Analyze and compare the actual warehouse test data to verify the mathematical model;(3)In addition,the numerical simulation study of the upward airflow circulation temperature uniformity process in the warehouse is also carried out to analyze the interior of the grain pile during the upward airflow circulation temperature uniformity process in the warehouse.The temperature distribution law and the effect of grain temperature homogenization,theoretical analysis of the uniformity of the internal temperature of the grain pile and the risk of condensation.Secondly,the numerical simulation of the phosphine fumigation ventilation process in the room-type warehouse and the optimization of the process parameters were carried out.(1)Using small-scale experiments to verify the deliquescent model of aluminum phosphide tablets,establish a fumigant(phosphine gas)convective diffusion model for the circulation ventilation of the room-style warehouse,which is the phosphine fumigation and insecticide of the room-style warehouse.The numerical simulation of the process lays the foundation.(2)Use the method of combining numerical simulation and experiment to explore the ventilation of the room-type warehouse closed loop fumigation system and the law of phosphine diffusion during the fumigation process.In the numerical simulation method,the diffusion process of phosphine and the influence of phosphine concentration during the grain fumigation process in the room-type silo are considered in the numerical simulation method.Analyzed and compared the distribution of phosphine gas in the process of phosphine fumigation and ventilation in the room-type warehouse when different fumigation dosages were used,and obtained the optimal design scheme of closed loop ventilation and closed loop fumigation system.The study came to the following conclusions:1.Based on the numerical simulation method of setting the built-in momentum source term in the circulating flow field,the temperature distribution law of the granary in the process of circulating temperature uniformity and ventilation of the room-type silo with downward airflow in the silo is obtained,and the simulated data is in good agreement with the actual silo test data.In addition,the downward airflow uniform temperature ventilation in the silo has a good effect on reducing the temperature of the upper air area of the silo and the surface of the grain pile.When the air flow in the warehouse is 800m~3/h,the air area temperature will drop from 30°C to23.6°C,and the surface area will drop from 27°C to 23°C when the air volume is800m~3/h.2.After 24 days,the airflow upward circulating uniform temperature and ventilation in the warehouse can reduce the maximum temperature(27?)of the top layer of the grain pile area to 26°C,which cannot meet the requirements of cooling and ventilation and energy saving and consumption reduction standards,and the bottom of the grain pile has a very high temperature.Condensation risk analysis may cause the grain pile to be heated and moldy.Therefore,it is not recommended to use this ventilation method for circulating uniform temperature ventilation.3.The most important factors affecting the effect of circulating temperature equalization(the total time of circulating temperature equalization and ventilation,ventilation energy consumption)are the air tightness of the granary and the unit ventilation volume.The poor airtightness of the granary will cause the total ventilation time and energy consumption to far exceed the working conditions of good airtightness of the granary;the different unit ventilation rate also affects the total ventilation time and ventilation energy consumption,and the same when airtightness is not considered After 8.3 days of circulating uniform temperature and ventilation,when the ventilation air volume is 1600m~3/h,the maximum temperature of the grain pile is reduced to 20?(the ventilation volume is 1200m~3/h to 21?),and the top grain temperature is reduced to 10?(1200m~3/h is reduced to 11?),and the temperature in the grain pile area is more uniform when the air volume is 1600m~3/h.From the perspective of the cooling effect alone,an air volume of 1600m~3/h is better,but from the perspective of saving energy and reducing costs,the two working conditions have reached the uniform temperature effect and meet the safe grain storage standards,and the energy consumption is more selected.The low plan is more in line with my country's sustainable development strategy.4.Closed loop fumigation is mainly divided into two processes:tablet deliquescent and internal circulation.After 3 days,the natural deliquescence of aluminum phosphide tablets ends.The phosphine concentration above the warehouse reaches 700ppm.After 2 days of forced convection through the circulation fan,the inside of the grain pile is approximately uniform.(600ppm),the gas leakage caused by poor airtightness of the granary,the fumigant concentration dropped to 200ppm after 14 days,so improving the airtightness of the granary is an important measure for my country to further increase grain production capacity.In addition,when the air tightness cannot be changed,some granaries can adopt the method of fumigation under the film,which can effectively reduce the leakage of phosphine gas.5.Different fumigant dosages in the room-type silo closed loop fumigation process lead to different distributions of phosphine gas.For every 1 m~3of grain storage,1.5 pieces of aluminum chloride(4.5g)are needed to obtain the required phosphine gas.The closed loop fumigation grain pile is at the requirement that the effective fumigation concentration(100ppm)is greater than 14 days,and every 1 m~3of storage requires 1 piece of aluminum chloride(3g)to obtain the required fumigant dose cannot meet the fumigation requirements,so 1 m~3The storage capacity requires1.5 aluminum chloride tablets as the standard for the selection of the aluminum phosphide dosage in the room-type warehouse. |
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