Research On Process Characteristics And Parameter Optimization Of Combined Drying Of Kitchen Waste Based On Hot Air And Microwave

Kitchen waste generally refers to perishable organic waste such as raw meal,leftovers or fruits and vegetables discarded in daily cooking at home.At present,the treatment volume and production of kitchen waste is in a serious imbalance.Therefore,the reduction and recycling of kitchen waste are of great significance to the sustainable development of human society.The volume reduction effect of incineration treatment of kitchen waste is obvious,and the most effective way to deal with most urban kitchen waste is drying.It is an effective way to realize the utilization of waste resources.However,the moisture content of kitchen waste will greatly reduce the combustion calorific value of the waste and affect the incineration efficiency.Therefore,it is necessary to dry the kitchen waste before incineration.The use of drying treatment to reduce the moisture content can directly and effectively increase the calorific value of the kitchen waste with less environmental pollution.Common waste drying methods include hot air drying,microwave drying,and biological drying technology.The hot air drying method has high efficiency,but it consumes a lot of energy and is easy to operate.The microwave drying method has a high drying rate and a short time,but it is easy to cause uneven heating and easy zooming of the material.The biological drying time period is long and the process is complicated.In order to overcome the shortcomings of a single method,this paper uses the hot air microwave combined drying technology to dry kitchen waste.The hot air microwave combined drying technology has been widely used in crops,fruits and vegetables,but it is rarely used in the treatment of kitchen waste.In order to realize the reduction and resource utilization of kitchen waste,this paper carried out an experimental study on the combined drying of kitchen waste with hot air and microwave,and explored the influencing factors and drying characteristics of the combined drying technology of hot air and microwave on the drying process of kitchen waste.From a scientific point of view,the migration law of moisture in the process of combined hot air and microwave drying of kitchen waste is studied and analyzed,and the single factor experiment was carried out to optimize the combined drying process of hot air and microwave,which provided a theoretical basis for the design of the subsequent treatment process of kitchen waste.The main findings are as follows:（1）Through research and analysis,the drying effect of three drying methods and the combined drying characteristics of three different proportions of kitchen waste are analyzed.The results show that among the three drying methods,combined drying can obtain better drying effect.The drying time is shortened with the increase of the hot air temperature.When the temperature is 160℃and 20 min,the combined drying effect of kitchen waste is better and the speed is the largest;when the microwave power is P50,the drying time is the shortest and the effect is the best;when the converted moisture content is 60%,the drying time is the shortest and the efficiency is the greatest;the thickness of the material has a greater impact on the kitchen waste with high initial moisture content,and the thinner it is,the better it is for dehydration.The average calorific value of kitchen waste treated by hot air microwave combined drying technology is 24.64 MJ/Kg,which can be burnt independently,which has the advantages of improving drying quality and drying efficiency.（2）When kitchen waste is dried under the conditions of hot air temperature,microwave power and material thickness,the moisture migration characteristics of kitchen waste in the combined drying process of microwave and hot air are analyzed,and the optimal model is obtained.The results show that the effective water diffusion coefficient varies with the hot air.The temperature and microwave power increased with the increase of the temperature and the microwave power.The effective moisture diffusion coefficient D_effvalues of the three different proportions of kitchen waste in the hot air drying stage ranged from 5.071-8.114×10^-9m²·s,and the effective moisture diffusion in microwave drying stage the range of the coefficient D_effis0.811-12.070×10-8 m²·s;the average activation energy range in the hot air drying stage is 15.13 KJ/mol,and the average activation energy in microwave drying stage is44.28 J/mol;in seven thin-layer drying models among them,the Midilli model fits the experimental data of samples 1 and 3 the best,and the Logarithmic model fits the experimental data of sample 2 the best.（3）In order to study the kitchen waste hot air microwave combined drying process and determine the optimal drying process parameters of the combined drying,the response surface test was carried out according to the response surface method.The drying time and average drying intensity have the most significant effects on the drying process;the optimal process parameters of the optimized combined drying are:sample 1:hot air temperature 159.02°C,microwave power 493.08 W,conversion moisture content 58.97%;sample 2:hot air temperature 159.73℃,microwave power528.57 W,conversion moisture content 44.94%;sample 3:hot air temperature159.71℃,microwave power 466.97 W,conversion moisture content 59.79%.Under this condition,the drying time was 34.69 min,39.91 min,and 30.60 min,respectively,and the average drying strengths were 0.064 g/（g·min）,0.103 g/（g·min）,and 0.065g/（g·min）,respectively.The test results in this paper can provide a reference for the study of the process design based on hot air microwave combined with dry kitchen waste.