The article designs a biomass-fired hot air oven for grain drying, which improves the thermal efficiency of the hot air oven, improves the combustion efficiency of biomass particles, saves fuel consumption, and then achieves the purpose of energy saving and consumption reduction in the hot air oven for grain drying through the utilization of residual heat recycling technology, supplemented by flue gas purification, air flow field analysis, and combustion analysis and other technologies.

At present, the general practice of grain drying is to heat the air through the hot air furnace (coal-fired, oil-fired, biomass-fired, etc.), the output of a stable temperature of the hot air into the dryer, the grain drying. China's current energy situation, generally coal-fired hot air furnace is the main, and year by year to reduce the fuel oil or biomass-fueled hot air furnace instead of the most widely used is the tube and tubeless hot air furnace. The vast majority of users in the hot air furnace exhaust is not equipped with desulfurization, denitrogenation and dust removal equipment, coal combustion dust, sulfur dioxide, nitrogen oxides and other pollutants directly into the atmosphere, resulting in environmental pollution. After the implementation of the new environmental protection law, many areas will be coal-fired hot air furnace into a biomass-fired hot air furnace, but simply replace coal with biomass pellet fuel, due to the lack of industry standards and norms, the prevalence of biomass combustion is not sufficient, low thermal efficiency, low degree of automation and other issues. In the unswerving implementation of the basic national policy of saving resources and protecting the environment, "green mountains are golden mountains" in the context of the development of "green mountains are golden mountains", to accelerate the elimination of old agricultural equipment, the promotion of agricultural energy-saving equipment, to enhance the cleanliness of rural energy use.

1 Biomass hot air furnace energy saving optimization impact factor

1.1 High temperature flue gas

　　The higher the temperature of the flue gas discharged from the hot air furnace, the more heat it takes away, which is the main reason for the heat loss of the hot air furnace. How to recover and utilize the waste heat of flue gas is one of the effective methods of energy-saving design of hot air furnace.

　　1.2 Thermal efficiency

　　The thermal efficiency of different structures of hot air furnace varies greatly, the thermal efficiency of high up to 75% ~ 80%, low less than 40%, the average thermal efficiency of 55%. Through the optimization of the internal structure of the design can be more substantial increase in the range of thermal efficiency.

　　1.3 Biomass combustion efficiency

　　Biomass is a complex polymer composed of cellulose, hemicellulose, lignin, different fineness, different raw materials, different molding density of biomass particles have different combustion characteristics, and also determines the calorific value of biomass particles and combustion efficiency.

　　1.4 Furnace heat dissipation

Manufacturers for cost considerations, generally welded with angle steel hot stove skeleton, rock wool and other insulation materials as filler insulation, the appearance of the shell with a steel plate. Such heat preservation furnace body heat loss is still as high as 15% to 20%.

2 hot air furnace working principle and structure

　　According to the existing hot air furnace problems, combined with the hot air furnace energy saving optimization impact factor, this paper proposes a new type of energy saving and environmental protection biomass hot air furnace. The overall structure is shown in Figure 1, the body cavity is set up with sequentially connected hearth, heat exchange tube group, cyclone dust removal barrel and bag dust removal group.

The inlet of the furnace chamber is connected to the hopper (biomass pellet material) through the automatic feeding device, the air outlet and air inlet are provided on both sides of the body, and the first dust collection box, the second dust collection box and the third dust collection box are provided correspondingly under the heat exchange tube group, the cyclone dust collection bucket and the bag dust collection group, respectively. The advantages of this hot air furnace are sufficient dust removal, energy saving and environmental protection.

　　2.1 Furnace chamber

　　The furnace chamber is made of thick steel plate rolled round and welded, and the outer wall is equipped with a number of heat-conducting sheets, which are arranged at intervals from bottom to top. The bottom of the combustion chamber of the hearth is tilted downward in the shape of a cone, and the lowest part of the bottom is equipped with a grate, and the hearth is also equipped with a combustion chamber and an oxygen supply channel outside the body, so that the combustion efficiency of the biomass pellets can be automatically adjusted according to the output temperature of the hot air.

　　2.2 Heat exchange tube group

　　The heat exchange tube group includes a number of vertical heat exchanger tube groups, which are divided into downward heat exchanger tube groups and upward heat exchanger tube groups according to the direction of air traveling. The smoke inlet at the upper end of the downward heat exchanger group is connected to the smoke outlet of the furnace chamber as described above, the lower ends of the downward heat exchanger group and the upward heat exchanger group are connected through the first dust collection box, and the smoke outlet at the upper end of the upward heat exchanger group is connected to the smoke inlet of the upper part of the cyclone dust remover barrel.

　　2.3 Cyclone dust removal barrel

　　The cyclone dust removing barrel is conical in shape and large at the top and small at the bottom, and the dust removing barrel is connected to the smoke inlet at the upper end of the bag dust removing group through the smoke pipe. There is a second fan inside the pipe, and one end of the pipe is set vertically downward in the cyclone dust removal barrel, and the smoke inlet at the end of the pipe is lower than the smoke inlet of the cyclone dust removal barrel.

　　2.4 Bag filter group

　　The dust bag group includes a plurality of vertically installed dust and high temperature resistant bags, which are connected up and down, and the hot air is blown out through the gap of the bags, and the dust is blocked in the bags and falls into the third dust collection box.

2.5 Air inlet and outlet

　　The air outlet is provided on the left side of the body, and the first fan is provided at the air outlet. The body has a side and is located in the cyclone dust barrel and bag dust group before and after the surface are equipped with louvered windows, the opening of the louvered windows that is the air inlet.

This hot air furnace work process is: hopper biomass pellets through the automatic feeding device into the furnace combustion chamber combustion, combustion of hot flue gas produced from the combustion chamber exhaust into the heat exchange pipe group of the downstream heat exchanger group, the first dust collection box, the upstream heat exchanger group in turn. In this process, some heavy dust will fall into the first dust collection box. Then the hot flue gas enters into the cyclone dust removal barrel. Since the port of the flue pipe is lower than the smoke inlet of the cyclone dust removal barrel, the flue gas will be quickly sucked into the cyclone dust removal barrel under the action of the second fan to rotate and fall down, and then sucked into the flue pipe. In this process, part of the dust will fall into the second dust collection box directly, and part of the lighter quality dust will adhere to the inner wall of the cyclone dust removal barrel and slowly slide down into the second dust collection box. Then the flue gas from the pipe into the bag filter group, through the high-temperature dust bag filtering small dust and then from the bag pores into the body of the inner cavity, in the first fan suction, and from the shutters into the room temperature air mixing, from right to left in turn by the cyclone dust barrel, heat exchange tube group and the furnace on the heat conduction sheet heated from the air outlet, into the grain dryer.

3 Conclusion

　　Combustion of biomass grain drying hot air furnace through the waste heat recovery and utilization technology, supplemented by flue gas purification, air flow field analysis and combustion analysis and other technologies, to improve the thermal efficiency of the hot air furnace, improve the combustion efficiency of biomass particles, saving fuel consumption, to achieve the purpose of energy saving and reduction of energy consumption of grain drying hot air furnace.