Experimental Study On Drying Characteristics Of Cut Tobacco And Drum Dryer

The quality of cigarettes is inseparable from the physical and chemical properties and mechanical characteristics of cut tobacco.In the processing of cut tobacco,different drying process parameters,such as the temperature of cylinder wall and hot air,have different effects on the physical and chemical properties including moisture content,whole silk rate and filling value.Therefore,the regulation and optimization of the drying process is very important for the quality control of finished tobacco.The research on the drying characteristics of cut tobacco during the drying process is of great significance to deeply analyze the state change of cut tobacco and the heat transfer phenomenon during the processing of cut tobacco,and optimization of cigarette processing parameters.However,due to the high temperature rotation of the inner cylinder of the drum dryer currently used in the industry,it is difficult to measure the environment in the cylinder and the state of the cut tobacco during the drying process.In order to solve this problem,this paper designed a small-scale electric heating drum dryer by investigating the isothermal drying characteristics of cut tobacco.According to the test structure built in the drum dryer,the temperature and humidity changes in the drum could be effectively measured.It could also provide theoretical and practical guidance for the research on the changes of humidity and physicochemical properties after drying of cut tobacco under different processing parameters by studying the changes of temperature and humidity in the cylinder under different processing parameters.The research content of the dissertation primarily covers the following points:(1)Based on the halogen moisture meter,the isothermal drying kinetics of three typical cut tobaccos in a tobacco factory was studied,to discuss the effects of different drying temperatures and initial moisture contents on the drying characteristics of cut tobacco.Results showed that the isothermal drying process of cut tobacco could be divided into the speed-up stage,the first speed-down stage and the second speed-down stage,while the speed-down drying occupied the main part of this process.The results of the moisture diffusivity and activation energy of the three kinds of cut tobacco indicated that the moisture diffusivity of the cut tobacco increased gradually with temperature at 70℃～100℃,and decreased with the initial moisture content of cut tobacco.The activation energy of the three kinds of cut tobacco were 13.85 kJ/mol,22.12 kJ/mol and 14.92 kJ/mol.At the same time,9 common thin-layer drying models were used to perform nonlinear fitting on the experimental results.The fitting results found that the three types of cut tobacco had the best fitting effect of Midilli model at different temperatures.(2)According to the drying characteristics of the cut tobacco and the features of the steam drum dryer of the production line,the electric heating small-scale drum dryer was developed.The diameter of the inner cylinder was 0.3 m,the length was 1.5 m,and the production capacity was 0 kg/h-50 kg/h.The main components included the inner drum,the feeding and discharging structure,the supporting structure,the temperature and humidity test structure of the environment inside the cylinder,etc.The test adjustment of the small-scale drum dryer was carried out,and the adjustment range of each parameter could meet the requirements of subsequent test.(3)The drying experiment of cut tobacco was carried out on the developed small-scale drum dryer,and it was found that the ambient humidity in the drum could be divided into constant speed section,speed-up section and speed-down section along the length of the drum when the cut tobacco was dried in the drum.The overall trend of the ambient humidity and the maximum humidification rate at each position in the cylinder decreased with the increase of airflow temperature,airflow velocity,and cylinder wall temperature,and increased with the increase of flow rate.The law of influence was not significant.The moisture content of cut tobacco after drying decreased with the increase of airflow temperature,airflow velocity and cylinder wall temperature,and raised with the increase of flow rate,rotation speed and inclination angle.The changing trend of the filling value under different process conditions was generally opposite to that of the moisture content of cut tobacco after drying,and there was no obvious regularity in the percentage of whole and shredded tobacco under different process conditions.According to the principle of heat and mass exchange between the cut tobacco and the environment in the cylinder,the change of the humidity of the cut tobacco was inferred by analyzing the change of the temperature and humidity in the cylinder,and the dynamic change characteristics of the cut tobacco in the cylinder with the airflow temperature and the temperature of the cylinder wall were grasped.(4)According to the structure of the drum dryer,the model was designed and meshed,and the appropriate calculation model was debugged to simulate the temperature and humidity field inside the drum by fluent.The simulation results were generally the same as the experimental data.Based on the simulation results,the structure of the drum dryer was changed,the number of plates in the drum was doubled and two annular baffles were installed.The same calculation model was used to compare the simulation results before and after the variable structure.The temperature and humidity field distribution in the cylinder is more uniform,which enhanced the heat and mass transfer degree of the cut tobacco in the cylinder.