Study Of The Energy Saving Mechanism And Technology Of Hot Air Drying Condensation Increasing Efficiency Of Grain

During the 14^th Five-Year Plan period,China embarked on a new journey to fully build a modern socialist country.China has taken clean and low-carbon energy development as the leading direction and is promoting green energy production and consumption,accelerating institutional reform for promoting ecological progress,and advocating that“lucid waters and lush mountains are invaluable assets”,“win the battle against the blue sky”,and“build China into a country with a good environment”.Hot air drying is still the key operational link of grain postproduction security in China;it is the key link of energy consumption in agricultural production and is related to the country's food security strategy and the high-quality adevelopment of agriculture.China's three northeastern provinces have produced more than 110 million tons of corn.According to the current northeast corn mechanized drying level of 80%calculation,mechanically drying88 million tons of corn will consume 6.16 million tons of standard coal.According to the current pollutant emission coefficient of fossil energy in China,China will consume 6.16million tons of standard coal and emit 16.5846 million tons of CO₂,45,000 tons of SO₂,47,400 tons of NO_X and 17,100 tons of smoke dust.In the implementation of“the battle against the blue sky”,the grain drying industry is required to complete the replacement of fossil energy as soon as possible.It can be seen that the research of clean and energy saving drying technology and equipment is the urgent need of grain drying industry.Based on an analysis of the hot air drying process,heat source,model,control technology and equipment of grain at home and abroad,this paper analyses and condenses the exising model of the hot air drying operation,and demonstrates the possibility and feasibility that these are condensation increasing efficiency enery-saving mode.Then,the mechanism,technology and automation equipment of grain condensation increasing efficiency energy saving drying were studied by theoretical analysis,numerical simulations,process testing and application testing.(1)Possibility analysis of the new energy saving mode of clean hot air drying:In view of the exiting hot air drying process,heat source,model and control technology and equipment of grain at home and abroad,from material flow,the material and heat medium coupling mode,the heat medium exhaust utilization mode and so on,the main modes and energy consumption characteristics of hot air drying of grain were analyzed,and the theory of heat and mass transfer,water potential and exergy were used to further analyse the possibility of new energy saving modes.(2)Study on energy saving mode and mechanism of hot air drying condensation increasing efficiency of grain:We performed a comparative analysis of the energy transfer principle between open ordinary hot air and condensation increasing efficiency gain drying,an analysis of the state parameters changes of drying medium in the process of drying system,an analysis of the numerical model between the state parameters changes of grain and drying medium in the process of system operation,and an analysis of water potential and the exergy method guiding the control process.In addition,taking circulating and continuous condensation increasing efficiency drying as an example,the method and steps of deriving process parameters from known parameters in the operation process were analysed,and a reasoning basis of the condensation intensity and condensation ratio acquired by the auxillary control of the condensation process was obtained.(3)Experimental study on static energy saving technology of hot air drying condensation increasing efficiency drying mode:A comparison test,single factor test and response surface orthogonal test of open ordinary hot air drying and condensation increasing efficiency drying were carried out by taking air temperature,air velocity and condensation ratio as factors and specific heat consumption and drying rate as inexes.Experiments show that the condensation increasing efficiency drying method has 32-56%energy saving potential compared with the open common hot air drying method,and the regression equations of specific heat consumption and drying rate with air temperature,air velocity and condensation ratio were obtained.The influence of air temperature and air velocity on specific heat consumption models is extremely significant.Air temperature and the interaction term of air temperature and condensation ratio has significant effect on drying rate models.(4)Study on measurement and control method and system of hot air drying condensation increasing efficiency mode of grain:Based on an analysis of the condensation increasing efficiency drying process parameters and process flow,the graphic control method of hot air drying condensation increasing efficiency mode of grain based on water potential and exergy principle was studied,and the hardware and software system of graphical control was developed.Grain flow,drying medium flow and spray water circulation can be real-time dynamic monitored,cooling medium flow and grain flow can be automatically controlled,the basic parameters of the drying process and the microenvironment of the drying system can be real-time graphically displayed,and the drying process can be controlled by man-machine interaction.(5)Application experimental study on hot air drying condensation increasing efficiency mode of grain:A drying test of corn was carried out by a 50 ton circulating condensation increasing efficiency drying system,and the application effect of condensation increasing efficiency drying technology in an actual dryer was verified.The results showed that specific heat consumption of electric heating source of corn drying in March in northeast China was3913 k J/kg,if large-scale thermal power combined with cogeneration efficiency of 70%calculation,it is equivalent to 5590.5 k J/kg of specific heat consumption of ordinary coal-fired hot blast stove,it was significantly lower than the common open hot air drying,the specific heat consumption ratio was 74.5%compared with the standard value of specific heat consummption?7500 k J/kg in T/CAMDA 6-2019 Acceptance Technical Specification for grain drying Center.No SO₂?CO₂?NO_X emissions occurred during the drying process,the dust concentration was 4.4 mg/m³,far lower than the standard value that 8 mg/m³in the indoor in the group standard T/CAMDA 6-2019.The average energy efficiency of drying process was 64.4%,and the average exergy efficiency was 55.2%.Considering that electric energy is the secondery energy,the gas treatment of thermal power plant is more strengthened than that of hot blast stove,so the environmental benefit of electric heating grain drying is more significant than that of coal buring hot blast stove.The experimental study of corn drying by 3.4 t/d continuous condensation increasing efficieny grain drying system showed that for the constant temperature drying process,the drying temperature above 110°C can improve the exergy efficiency and sustainability index of the drying process,for the variable temperature drying process,considering specific heat consumption,energy efficiency,exergy efficiency,sustainability index and absolute water potential difference between hot air and grain,the variable temperature drying process with gradually increasing temperature from top to bottom is better than the drying process with gradually decreasing temperature.