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Application And Research Of Air Source Heat Pump Technology In Grain Drying

Posted on:2021-02-18Degree:MasterType:Thesis
Country:ChinaCandidate:W J WuFull Text:PDF
GTID:2381330602475335Subject:Heating, Gas Supply, Ventilation and Air Conditioning Engineering
Abstract/Summary:PDF Full Text Request
Grain is an important material foundation for human life activities.Grain drying is a key link to improve grain quality and ensure safe storage of grain.Ensuring efficient,safe and economic drying of grain will have a profound impact on Chinese grain security meaning.The traditional grain drying technology not only consumes a lot of energy,but also causes serious pollution and emissions,and puts more pressure on energy conservation and environmental protection.In recent years,heat pump technology has gradually been applied in the field of drying due to its unique drying principle,efficient energy efficiency and environmental protection.The application of air source heat pump drying technology to grain drying not only reduces the cost of grain drying,but also has no pollution to the environment and the materials being dried.In this paper,the experimental research and numerical simulation of the operation characteristics of air source heat pump technology in grain drying are carried out,and the economics and feasibility of exhaust heat recovery in the drying process are analyzed.In terms of experimental research,taking the heat source reconstruction project of a grain drying center as an example,the open and semi-open heat pump drying systems were tested experimentally.The influence of the inlet air temperature and humidity on the performance of the semi-open heat pump drying system was discussed.The effect of heat recovery on the operating characteristics of the system.The results show that the semi-open system adopts exhaust air heat recovery,and its inlet air temperature and humidity are higher than the open system,so that the supply air temperature can basically reach the set temperature,and the system COP value and average unit energy consumption dehumidification are higher than the open system,which can save energy while ensuring the drying quality.Exhaust heat recovery affects the temperature and humidity of the inlet air of the semi-open heat pump drying system.If the return air ratio in the inlet air is too large,the inlet air temperature is too high and the moisture content is too large,which is not conducive to drying effect.When the ambient temperature is too low,the supply air temperature cannot meet the requirements due to the low inlet air temperature.Therefore,the opening of the window should be adjusted according to the level of the ambient temperature,and the exhaust heat of the exhaust air should be reasonably used to maintain the inlet air temperature at 22℃-26℃ in autumn,so that the supply air temperature can meet the set requirements and ensure the quality of grain drying.In addition,the energy saving and economic benefit of the grain drying center transforming the coal-fired hot air furnace drying system into an air source heat pump drying system were analyzed.The results show that the grain drying center transforms the coal-fired hot air furnace drying into an air source heat pump drying,which not only achieves zero pollution drying,but also saves 76%of the equivalent standard coal a day while converting the equivalent standard coal while ensuring the drying quality of grain can save 31%,and can save about 1200 yuan in drying cost per day,saving energy and considerable economic benefit while ensuring the quality of grain drying.In terms of numerical simulation,a mathematical model for drying heat and mass transfer of grain was established,used COMSOL Multiphysics software to solve the equation,and studied the effects of some parameters,such as drying medium temperature,drying medium flow rate,drying-slowing time ratio and initial moisture content on the drying process of grain.The results show that the temperature of the drying medium has a greater impact on the reduction of the moisture content of grain drying.The higher the temperature of the drying medium,the faster the drying rate and the shorter the drying time.However,the temperature of the drying medium should not be too high,otherwise the burst rate of grain will increase.The drying medium flow rate has little effect on the moisture migration process of grain drying.It mainly affects the speed at which the grain reaches equilibrium temperature during the drying process.Increasing the drying medium flow rate helps the grain to reach the equilibrium temperature faster.The effect of drying-slowing time ratio on grain drying is mainly in the early stage of drying.The larger the drying-slowing time ratio,the faster the drying rate of grain and the shorter the drying time of the grain.However,the excessive drying-slowing ratio leads to uneven temperature and moisture distribution in the grain,which increases the burst rate.The effect of initial moisture content on grain drying is mainly in the early stage of drying.The higher the initial moisture content,the faster the grain drying rate,but the longer it takes for the grain to reach equilibrium moisture content.This paper aims to explore the economics and feasibility of exhaust heat recovery and utilization in air source heat pump grain drying technology,with a view to providing theoretical guidance for the promotion and application of this technology in the "two reductions,six governances and three enhancements" action in Jiangsu Province.
Keywords/Search Tags:Grain, Heat pump drying system, Semi-open system, Drying model, Energy saving
PDF Full Text Request
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