Cause analysis and solution of abnormal combustion

2022-08-11
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Analysis of the causes of abnormal combustion in the baking furnace and solutions

1 overview the baking furnace of Thomson Foshan color kinescope Co., Ltd. was shut down for a long time. Before resuming production, we entrusted our company to inspect and repair the combustion system of the baking furnace. The baking furnace combustion system is divided into ten working areas, each of which is composed of furnace front pipes, combustion devices and combustion monitoring devices. A group of pressure regulators are set in the pipeline in front of the boiler in each area, and the fuel gas is distributed to the burners in this area through the pressure regulator shop and the pipeline in front of the boiler in the re channel. During the inspection and commissioning test process, we found that the following abnormal working conditions exist in the combustion system of the roaster. In three of the ten working areas, the flame is soft and short, and the furnace temperature is low. 2 problem analysis 2.1 reasons for low temperature of baking furnace baking furnace production process requirements: furnace temperature 330 ℃, flame hard, 2 meters long, inspection found that the actual furnace temperature is 280 ℃, flame soft and short, less than 1 meter long, combustion characteristics can not meet the production process requirements. According to the combustion characteristics of gas-fired industrial furnaces, the factors causing low furnace temperature are: (1) the heat load of burners is small; (2) Unreasonable burner layout; (3) Burner nozzle is blocked; (4) The gas pressure in front of the furnace decreases; (5) The burner head is damaged and the combustion condition is deteriorated; (6) Insufficient or excess air supply; Since the roaster can operate normally before, the two factors (1) and (2) can be excluded. After checking the burner, the burner is an injection low-pressure burner with normal structure. The second factor (3) and (5) can be excluded. Therefore, the causes of abnormal working conditions of the combustion system can be analyzed from two points (4) and (6), so as to find a solution to the problem. 2.2 influence of gas pressure in front of the furnace on flame and furnace temperature the burner of the roasting furnace is a low-pressure injection burner. According to the principle and momentum theorem of gas ejecting air in "gas combustion and application", continuity and energy conservation law; When the gas pressure in front of the furnace decreases, the amount of air Ma injected by the gas decreases. According to the "gas combustion and application", the gas flow VP at the outlet of the fire hole is: LG (1 + US) vp=----------------- FP LG = 0.0035ud2 √ H/S. in the formula, LG - flow rate of the circular nozzle (m3/h) u = ma/Mg - mass injection coefficient; When the fuel gas volume and pressure decrease, Ma decreases and u decreases. FP -- fire hole area (when the burner is selected for vacuum gold plating on the section, FP is certain) m -- nozzle flow coefficient h -- gas pressure (PA) s -- relative density of gas (air = 1) when the gas pressure in front of the furnace decreases and the gas supply is insufficient, LG decreases, u decreases, and the gas flow velocity VP decreases. According to the characteristics of gas combustion, the value of VP directly affects the length of flame and the combustion intensity of burner, and the combustion intensity directly affects the furnace temperature. Figure 1 shows the variation relationship between the gas flow velocity of diffusion burner and the working condition of combustion flame length. It can be seen from Figure 1 that when V, increases, the speed of oxygen diffusion to the flame surface remains basically unchanged, which makes the contraction point of the flame surface farther and farther away from the nozzle, and the flame length continues to increase. At this time, the surface area of the flame increases, and the fuel gas combustion in the unit hour increases, so the combustion intensity in the furnace increases. When the gas flow velocity further increases and the gas flow state changes from laminar flow to turbulent flow, the turbulent flame becomes shorter, but because the mixing of gas and air is greatly strengthened, the combustion process is strengthened, and the flame appears hard. The relationship between the air flow velocity VP and the combustion intensity provided by the burner can also be expressed by the following formula: q = FP · QP and H1 × VP qp=------- (1 x a'v0) where QP - - the thermal strength of the fire hole (kW/mm2) H1 - - the low calorific value of the gas (kJ/N meter) A'-- the primary air coefficient V0 - - the theoretical air demand (nnl') VP - - the gas flow velocity at the flame outlet (M/s) can be obtained from the above formula. The combustion intensity of the burner increases with the increase of the gas outlet flow velocity VP. We can know from the above prayer. The gas pressure in front of the furnace decreases, which reduces the gas flow velocity at the burner outlet, shortens and softens the flame, and reduces the combustion heat intensity. Therefore, the decrease of gas pressure in front of the furnace is one of the reasons for the low furnace temperature. 2.2 influence of air supply on furnace temperature the amount of air supply will also affect the furnace temperature. It can be seen from the necessary conditions for gas combustion reaction that an appropriate amount of oxygen needs to be supplied for gas combustion. The amount of air required for complete combustion of each standard cubic meter of gas according to the combustion reaction metering equation is called the theoretical air demand v0. When gas and air are mixed for combustion, due to the heterogeneity, the actual air volume required for complete combustion of gas is V, and the ratio of the actual air volume V supplied to the theoretical air volume V0 is called the excess air coefficient a, that is, a = V/v0. During the combustion process. The value of has a direct impact on the thermal efficiency of combustion equipment.. Too small, the chemical heat of gas combustion can not be brought into full play; A is too large, the volume of flue gas increases, the furnace temperature decreases, the heat loss of flue gas increases, and the thermal efficiency of burner decreases. As a result, the furnace temperature decreases. The split sleeve design of shoulder end sample tooling accelerates the progress of production field experiment. The relationship between furnace thermal efficiency, excess air coefficient and exhaust gas temperature can be visually shown in Figure 2. From the above analysis and Figure 2, it can be seen that insufficient or excessive air supply will reduce the thermal efficiency of the furnace body and the furnace temperature. 3. To sum up, there are two reasons for the soft and short flame and low furnace temperature of the roasting furnace. One is the low gas pressure in front of the furnace; Second, the clamping force of the gas combustion sample will change with wear, and the gas supply is unreasonable. To improve the furnace temperature, we can adjust the gas pressure regulator in front of the furnace, increase the pressure in front of the furnace, and adjust the air supply to cooperate with it, so that the gas can be fully burned, the combustion intensity can be increased, and the heat supplied to the furnace can be increased, so as to improve the temperature of the furnace hall to meet the requirements of the production process. It is very important for theory to guide practice in practical work. By adjusting the gas pressure in front of the roaster and allocating the amount of air entering, the problems of soft and short flame and low temperature of the roaster have been satisfactorily solved

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