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New air blowing technology for gas generator file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image1.wmf 0 Introduction In recent years, nitrogen fertilizer companies have made a lot of technical transformation work on the equipment in the gas generation process, such as furnace diameter expansion, waste heat recovery of three gases, sensible heat recovery of semi-water gas, increasing the temperature of steam entering the furnace, transformation of pipelines and valves, etc. At the same time, optimized operating methods have also been proposed, but the air entering the gas furnace has never changed. Considering that many low-temperature waste heats in nitrogen fertilizer companies are not utilized, the author proposed a process of blowing hot air into the furnace. 1 Existing blowing process In nitrogen fertilizer enterprises, when the gasifier produces semi-water gas, the operation process generally includes five stages: blowing, upward blowing, downward blowing, secondary upward blowing, and blowing. In these five working stages, blowing and cleaning are to blow air into the gas generator. The method is:: Blower - → Air main pipe - → Air branch pipe - → Gas generator 2. The hot air blowing process adds a heater to the existing fan main pipe to heat the air to 100~150°C before entering the gas generator. The way is: Blower - → Heater - → Air main pipe - → Air branch pipe - → Gas generator When designing the hot air blowing system, the following principles should be followed: ①Ensure safe and stable operation. ②Make sure the system resistance is within a reasonable range. After the hot air heater is installed, the system resistance increases by about 30mmH2O (0.294kPa). The newly increased resistance is completely within the resistance range that the blower can overcome. ③Impact on gas generators. Heating the air to 100~150℃ will not affect the normal gas production of the gas generator. 3 Several heating forms of air heaters 3.1 Blowing air heater During the gas production process of the gas generator, during the blowing stage, 300-400°C blowing air will be discharged from the gas generator. Some manufacturers will put part of the blowing air into the three-waste combustion furnace for combustion and recover the remaining heat. Some manufacturers will discharge this part of the blowing air directly into the air, which causes a waste of energy and pollutes the environment. In manufacturers that do not have blower air waste heat recovery, this waste heat can be used as the heat source of the air heater to heat the air from the blower to 100-150°C and then enter the gas generator for combustion (see Figure 1). file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image2.jpg Features of this air heater: 3.1.1 The working principle of this air heater is air-gas heat exchange. In order to improve the heat exchange efficiency of the air heater, the heat exchange tube uses a fin tube. 3.1.2 Fins should be added to the heat exchange surfaces of both blowing air and air media. It is difficult to add fins on both sides of the heat exchange tube in ordinary heat exchange tubes, and heat pipes can solve this problem well. 3.1.3 Working Principle of Heat Pipe A heat pipe consists of a tube shell and a working medium. Its working principle is to use a vacuum in a closed tube, and use the boiling heat absorption and condensation heat release of the working medium to complete the heat exchange process (see Figure 2). file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image3.jpg Characteristics of heat pipes: (1) The heat transfer amount is large. Fins can be installed in both the heating section and the condensation section to expand the heat transfer area and avoid mutual leakage and contamination between hot and cold fluids. (2) The heat flow density is adjustable. By changing the area ratio of the evaporation section and the condensation section, the heat flow density can be adjusted to avoid dew point corrosion. (3) The working medium circulation does not require power consumption. 3.2 Hot water heater In the nitrogen fertilizer industry, some manufacturers have many sections that need water for cooling and produce hot water. The hot water needs to be dissipated through the water drying tower. This part of the heat in the hot water is wasted. This air heater can recover the heat in the hot water and generate hot air. Features of this air heater: 3.2.1 The working principle of this air heater is air-water heat exchange, and its heat exchange efficiency is higher than that of the air heater. 3.2.2 The structure of the hot water heater adopts the structure of water flowing inside the pipe and air flowing outside. 3.2.3 In order to improve the heat exchange efficiency on the air side, the heat exchange tube uses needle-shaped fin tubes to improve the heat exchange efficiency of the equipment (see Figure 3). file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image4.jpg Features of needle tubes (1) The needle tube enhanced heat transfer element is a new three-dimensional enhanced heat transfer element. (2) Whether the air washes the tube bundle laterally or longitudinally, all needle-shaped expansion surfaces are washed by the transverse flow of air. The airflow forms a symmetrical steady-state vortex and reflow zone on the cylindrical back of the needle rib, and the thermal boundary layer is continuously destroyed and re-formed. (3) The needle-shaped tube rib is a cantilever structure. Under the impact of the air flow, the needle rib vibrates, causing the air to continuously change the flow pattern and improve the heat transfer effect. (4) The needle-shaped tube has high heat transfer efficiency, and the hot air heater produced by it has a compact structure and low metal consumption per unit of heat exchange. 3.3 Steam Heater In the nitrogen fertilizer industry, some manufacturers have their own power plants. The steam generated by the boiler in the power plant is turned into low-pressure spent steam after being generated by a steam turbine. The heat of this steam can be used as a heat source for the air heater to generate hot air (see Figure 4). file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image5.jpg Features of this air heater: (1) This air heater is a steam-gas heat exchange equipment, and its heat exchange efficiency is higher than the first two air heaters. (2) The structure of the steam heater can use steam inside the tube and air outside the tube. (3) The condensation heat transfer coefficient of steam is thousands of times that of air. In order to improve the heat transfer efficiency of the air heater, the heat exchange tube is made of rolled aluminum sheet steel pipe to increase the heat transfer coefficient on the air side. (4) Compared with the previous two types of air heaters, this air heater is smaller in size, has less equipment resistance, and has the best heat exchange effect. 4 Economic benefit analysis takes the D500 fan commonly used in nitrogen fertilizer plants as an example: 4.1 Fan air volume: N=30000Nm3/h, the air is heated from normal temperature T1=20℃ to T2=150℃. The specific heat of air r=0.312kCal/m3·℃ (1.3kJ/m3·℃) The coal used in the gas generator is Datong coal, and the calorific value of coal r2=6511kCal/kg (27.24MJ/kg) 4.2 Air recovery heat port Q=N×r×(T2-T1)=30000×0.312×(150-20)=1216800kCal/h (5086.22MJ/h) 4.3 Heater coal saving D1 D1=Q/r2=1216800/6511=186.8kg Calculated based on 330 days in a year and 24 hours a day, the annual coal saving is D = 330 × 24 × D1 = 330 × 24 × 186.8 = 1479456kg 4.4 Economic Benefits The price of Datong lump coal entering the furnace is calculated as 0.8 yuan/kg, and the annual savings are:: 1479456kg×0.8=1.18 million yuan. In theory, the economic benefits generated by a D500 fan equipped with an air heater can be more than 1 million yuan. The actual coal consumption of the gas generator may deviate from the theoretical coal saving amount, but we can see that the economic benefits brought by the air heater to the unit enterprise are certain. 5 Issues that should be paid attention to in this system 5.1 The air heater should be installed as close as possible to the gas generator when installed on the main air pipe. This can reduce the heat loss of the pipe and the workload of pipe insulation. 5.2 After the air passes through the air heater and is heated to 150°C, the volume of the air will increase to 1.5 times, so the diameter of the air main pipe and each branch pipe behind the air heater must also be appropriately increased. 5.3 Several types of air heaters introduced in this article have not been used in nitrogen fertilizer companies, but there have been precedents of using semi-water gas to heat air, and the manufacturers have indeed produced economic benefits. However, due to the unsafe factors of using semi-water gas to heat air, it has not been recognized by the majority of nitrogen fertilizer companies. However, the air heater introduced in this article does not have unsafe factors. The author hopes that through the introduction of this article, it can create new economic benefits for nitrogen fertilizer companies.