Intelligent Heat Transfer For Green Energy And Application To Tobacco Curing

In agricultural production of flue-cured tobacco,the curing of the tobacco leaves requires a high concentration of heat,which consumes a high quantity of fuel.Coal fuel is traditionally used to provide curing heat for tobacco leaves in China.Approximately 3–4 million tons of coal are consumed each year,which produces a large quantity of CO₂,fly ash,and toxic gases.In recent years,with the increasing demand for environmental protection worldwide and the frequent occurrence of haze in some areas of China,air pollution caused by coal-fired heating for tobacco curing is becoming increasing noticeable.However,as an important economic crop,tobacco plays an important role in the development of China's economy and alleviation of poverty for farmers in remote mountain areas.Tobacco planting can not be banned in the current economic climate;therefore,it is necessary for green and clean energy to replace coal heating for tobacco curing to achieve sustainable development of tobacco agriculture.After reviewing heating equipment both in China and worldwide,we chose four types of clean energy to include in this study biomass fuel,alcohol-based liquid fuel,natural gas,and solar energy in consideration of China's availability of clean energy technology.By using the effective space at the bottom of the heating chamber of the bulk curing barn,in compliance with Document No.418 by the National Tobacco Monopoly of China,a variety of heating equipment of clean energy for tobacco curing was designed and manufactured,and the original intelligent control system was optimized by adding different chip modules and up grades.?1?Based on the combustion laws for biomass briquettes and firewood,the traditional coal fuel direct-fired combustion furnace was redesigned and modified into an integrated furnace with two separate areas for the combustion of solid fuel and gases.With a 4-3-4 array from left to right,the heat exchanger structure had three columns with a total of 11 flues.To control the combustion and gasification rate of solid biomass fuel in an orderly way,the combustion air,controlled by the automatic controller,entered the air inlet gate on the new dovice with a rotation of 0–90°.On the left side of the new equipment,a display showed the spatial distribution of the continuous temperature change during the combustion of the biomass fuel.There were two regions with the highest temperature,the solid fuel area and the gas combustion area.?2?A shuttle-drum shaped furnace for tobacco curing was designed based on the shape of the combustion flame of the alcohol-based fuel.A mesh structure of gridded high-temperature resistant metal was installed at the rear of the furnace.The mesh promoted the combustion of the residual gasified liquid fuel with the mixed air touching the mesh.The row structure of the heat exchanger utilized three horizontal sections with a 6-6-1 array installed top to bottom,including one large-diameter and 12 small-diameter flues.The burner was composed of a light oil combustion machine which was retrofitted with a configuration of two nozzles rated at3.64 kg/h and 9.09 kg/h.A 55 W centrifugal fan was installed with an opening 2/3 the size of the combustion air inlet on the base of the burner to complete the spray,atomization,and combustion of the alcohol-based fuel under automatic control.The automatic control system switched the working power of the two nozzles according to the reqirements of the tobacco curing.During heat generation,the temperature distribution of the radiator rose from the end of the shuttle-drum shaped furnace and decreased toward the chimney outlet.The temperature of the six flues connected to the lower cabinet for heat shunting reached the highest temperature,exceeding 540°C.?3?A convex-shaped combustion furnace for a natural gas fuel integrated heat exchanger was developed according to the spray shape of the flat-shaped air outlet duct.The heat exchanger adopted a 6-6-6 array top to bottom in three rows with a total of 18 flue pipes structure.There was one high-temperature region during fuel combustion,which appeared between the front and back part of the convex-shaped combustion furnace and the front part of the heat pipes in the low shed.In the interface between the furnace and the gas burner,and the interface of the tail end of the heat exchanger and the chimney there were two low temperature regions?86.53-168.65°C?.The power of the turbine centrifugal fan for gas fuel burning was 60 W?air pressure?hPa?:32/40,air volume?m³/min?:6.5/7.8?.?4?The form of hot air of solar energy in the flat-plate solar collector that was built on the roof of the bulk curing barn is designed.Cool air was transported to the flat-plate solar collector during the tobacco curing process,the heated air in the flat-plate solar collector was then piped to the heating chamber of the barn with small centrifugal fan?380 V,0.55 kW,2900 rpm,1247–2250 m³/h and 901–937 Pa?installed in the heating chamber.And then the heated air was transported to the loading chamber of the barn owing to a large axial to provide the curing heat.The collection efficiency of hot air of the flat-plate solar collector designed by this study was 63.93%,and 16.38%fuel consumption can be saved by conversion which combinated with the heat pump.The highest temperature of the hot air in the flat-plate solar collector was over 120°C,which could provide heat for the entire tobacco curing process.To compared the traditional heating coal-fuel direct burning to the new clean energy heating equipment for tobacco curing,the experimental verification was carried out in eleven tobacco-planting areas involving seven provinces from 2013 to 2017 in China.?5?A comparison was made between the target and actual dry-bulb temperature in the loading chamber of the barn during the curing process.The actual dry-bulb temperature controlled by all of the fuel heating equipments were not strictly in accordance with the target dry-bulb temperature—the temperature curve fluctuated up and down around the target temperature.The volatility of each system was:biomass fuel,±0.8°C;alcohol-based fuel,±0.5°C;natural gas,±0.5°C;solar energy with heat pump heating,±0.5°C;the coal fuel control,±1.5°C.?6?According to the economic parameters of the curing process,biomass fuel,alcohol-based fuel and natural gas can improve the efficiency of the bulk curing barn by 8.10–14.05%.In the exhaust gas exiting the chimney of the alcohol-based fuel and natural gas,CO,NOx and SO2 were lower than 2%of the coal combustion.Considering the price difference between the different fuels,a comprehensive economic analysis demonstrated that the cost/kg to dry tobacco was from lowest to highest:heat pump,biomass fuel,coal fuel,alcohol-based fuel and natural gas.?7?The clean energy heating for tobacco curing,compared to coal,increased the proportion of yellow orange leaf,and improved the tobacco inner chemical composition,neutral aroma constituents,and smoking quality.A comparative test was conducted to evaluate the curing performance of the different heating equipment designed and manufactured in this study.?8?The analysis of the equipment investment and curing cost showed that total operating cost from least to greatest was:biomass fuel heating,coal-fired heating,alcohol-based fuel heating,natural gas heating,heat pump.Under the premise of ensuring the quality of the tobacco during the curing process,the solar the flat-plate solar collector is profitable in terms of its life expectancy compared with the investment for coal fuel heating equipment.Therefore,a combination of heating methods should be promoted first.