Example interpretation of the control method of the temperature difference of the steam drum wall after the boiler is shut down

Abstract: An example interpretation of the control method of the temperature difference of the steam drum wall after the boiler is shut down is provided by the excellent flowmeter and flowmeter manufacturers and quotation manufacturers. Guangzhou Yuancun Thermal Power Co., Ltd. has three HG220/9.8-YM10 boiler drums with an outer diameter of 1800mm, a wall thickness of 100mm, a barrel length of about 11m, and a material of 19Mn6. After the boiler is shut down, according to the operating regulations, natural ventilation can be performed after 6 hours of fire off, and induced draft fan can be turned on for forced ventilation after 10 hours of fire off. The article details of the control method of the wall temperature difference of the rear steam drum. Guangzhou Yuancun Thermal Power 3 sets of HG220/9.8-YM10 boilers have an outer diameter of 1800mm, a wall thickness of 100mm, a barrel length of about 11m, and a material of 19Mn6. It is stipulated that natural ventilation can be performed after 6 hours of flameout, and induced draft fans can be turned on for forced ventilation after 10h of flameout (8h if overhauled); the main steam pressure is reduced to 0.5MPa and transferred to heating maintenance, and the main steam pressure is reduced to 0.2MPa to open each superheater. Air door. When performing relevant operations after furnace shutdown, the temperature difference of the boiler drum wall is often greater than 40°C, or even as high as 100°C, which seriously threatens the safety of the steam drum operation. For the statistics of the largest steam drum wall temperature difference after the furnace shutdown, see Table 1. 1. Analysis of the reasons for the large temperature difference of the steam drum wall after the shutdown of the boiler 1.1 Internal reasons (1) The steam drum pressure and steam temperature drop At the same time, due to the fact that each air door of the air and smoke system is generally not tightly closed, and there are different degrees of air leakage in each fire viewing hole, coke hole, manhole door and slag removal system, so that the boiler smoke air system has a certain degree of ventilation. The system is cooled to make the temperature gradually drop, and the steam pressure decreases accordingly. (2) The heat dissipation conditions of the upper and lower parts of the steam drum are quite different. Insulation, coupled with large heat capacity, makes the wall temperature of the steam drum gradually higher than the water vapor temperature in the steam drum. Part of the heat in the upper part of the steam drum is dissipated to the outside of the furnace, part of the heat is dissipated to the inside of the steam drum, and part of the heat is dissipated to the lower half of the steam drum , and part of the heat of the lower part of the drum body is dissipated to the outside of the furnace, part of the heat is dissipated to the inside of the drum, and at the same time, it also accepts the heat transferred from the upper half. , the natural convection heat transfer coefficient of water is (200～1000) W/(m2·℃), while the thermal conductivity of slightly superheated steam is (0.02～0.05) W/(m·℃), the thermal conductivity of the drum insulation layer is 0.061W/(m·°C) or so. After the steam temperature in the steam drum is lowered, the heat dissipation condition of the lower part of the steam drum is much better than that of the upper part, and the temperature of the lower wall is lower than that of the upper wall. In this way, the upper half of the steam drum dissipates heat through the lower half, and the thermal conductivity of the cylinder is (40-50) W/(m·℃), according to the normal value of the drum water level (-50 ~ 50) mm, the thermal conductivity thickness of the cylinder is (1.2 ~ 1.3) m, and the simplified heat transfer coefficient is (30 ~ 40) W/(m2·°C). Therefore, the lower part of the steam drum is mainly dissipated by natural convection through the saturated water in the steam drum, and the heat transfer coefficient is (200-1000) W/(m2·℃); the upper part of the drum body mainly dissipates heat from the lower part through the drum body in a heat-conducting manner, and the heat transfer coefficient is (30-40) W/(m2·℃), the heat dissipation conditions are quite different, which inevitably causes the temperature difference between the upper and lower walls of the steam drum after the furnace is shut down. 1.2 External reasons (1) After the furnace is stopped, the pressure of the steam-water system drops too fast. After the furnace is stopped, ventilate according to the regulations, the pressure of the steam-water system of the boiler will drop rapidly, the pressure in the steam drum will drop synchronously, and the saturated temperature of the steam-water in the steam drum will also follow the decline. Due to the difference in heat dissipation conditions between the upper and lower parts of the steam drum, it is inevitable that the temperature difference of the steam drum wall is too large after the furnace is shut down. Moreover, the lower the steam pressure, the faster the saturation temperature declines, and the faster the formation of the temperature difference between the walls of the steam drum. (2) A large temperature difference between the upper and lower walls of the steam drum has been formed before the shutdown of the sliding parameter. During the gradual decline of the steam pressure during the shutdown of the sliding parameter, the saturated pressure and saturation temperature of the steam drum also gradually decrease, and the upper and lower walls of the steam drum are gradually reduced. Although there is a certain convective heat transfer in the half part, the convective heat transfer coefficient of steam is much smaller than that of saturated water, which will inevitably form a certain temperature difference between the upper and lower walls of the steam drum. , The formation speed of the temperature difference of the lower wall is also accelerated, so that a large wall temperature difference has been formed before the boiler is extinguished, and it exceeds 40 °C in severe cases. After the furnace is stopped, the temperature difference of the drum wall is larger.

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