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Application of multifunctional temperature inspection and control device in the fire protection system of boiler room in power plant

abstract the problems existing in the fire protection system of Mitsubishi unit boiler room are analyzed, and the improvement measures are put forward. By applying the multi-functional temperature inspection and control device to the steam heat tracing system of fire pipeline, the problem of automatic control of water temperature in fire pipeline in winter is solved

keywords fire protection system steam tracing temperature control

0 introduction

Hejin Power Plant Phase I project 2 × 350 MW units are imported from Mitsubishi Corporation of Japan The boiler room is arranged in the open air, with a height of 63 5 m。 The fire-fighting system of boiler room adopts pressurized water fire-fighting system, and the normal pressure of the system is maintained at 0,8 MPa. A fire water ring header is designed at the bottom of the boiler room, and a dn 150 fire water supply pipe from bottom to top is designed at the four corners of the boiler room. According to the height of the maintenance platform of the boiler room, connect the universal testing machine on each floor of the maintenance platform. If there is an accident, immediately terminate the experiment with 7 fire hydrants of DN 65. According to the climatic characteristics of the local average temperature of - 10 ~ - 20 ℃ in winter, Mitsubishi company designed a double circuit steam tracing system on the fire pipe of the boiler room, and used rock wool and aluminum sheet for insulation outside the fire pipe. The heat tracing steam of the fire pipe is taken from the low-temperature auxiliary steam header of the unit, and the steam parameter is p= 0, 6 MPa, t=150 ℃. Since the 1 #, 2 # units were put into operation successively in 2000, due to the deficiencies in the design of the fire protection system of the boiler room, frequent leakage faults occurred in the pipeline of the fire protection system, which seriously affected the normal operation of the system. By analyzing and studying the problems existing in the original fire protection system, the author puts forward corresponding improvement measures. Among them, the self-developed multi-channel temperature inspection and control device has successfully solved the problem of automatic control of steam tracing temperature of fire pipe in boiler room, and achieved good operation results

1 problems existing in the original fire-fighting system

the boiler room fire-fighting system designed by Mitsubishi company mainly has the following problems: ① the number of isolation valves on the fire-fighting system pipeline of the boiler room is small, resulting in the need for large-scale isolation and drainage work in case of maintenance work of the fire-fighting system, which not only prolongs the maintenance time, but also is detrimental to fire safety; ② According to the requirements of China's fire protection design code, the fire pipes in the boiler room are connected by flanges, and the rubber seal ring connected by flanges is easy to age and fail, causing the leakage fault caused by flange connection; ③ There are no U-shaped expansion bends and elastic supports and hangers designed on the pipes of the fire protection system, which makes the pipes unable to expand freely when the heat tracing system of the fire protection pipeline is put into operation in winter, and has caused the cracking and leakage of the weld joint of the pipe elbow for many times; ④ The heat tracing steam of the fire pipeline is manually controlled. Because the temperature of the heat tracing steam is too high, the water temperature in the fire pipeline cannot be monitored, which brings great difficulties to the operation of operators. If the steam tracing system operates for a long time, the water temperature in the fire pipe will be heated to 80~90 ℃; If the exit time is too long, the fire pipeline will have frost crack leakage fault. Due to the above problems, the fire protection system of the boiler room has been unable to operate normally in winter, which has seriously affected the fire safety work and increased the overhaul and maintenance workload of the overhaul personnel

2 technical transformation measures

in view of the problems existing in the fire-fighting system of the boiler room, the following technical transformation measures are mainly adopted: ① isolation valves are installed on the fire-fighting water supply main pipe of the 1 #, 2 # boiler room and the fire-fighting water supply riser at the four corners of the boiler room respectively, so that the fire-fighting system of the 1 #, 2 # boiler becomes a unit system design, reducing the system isolation operation and drainage time in the maintenance work; ② Replace the rubber gasket between the flanges of fire pipes with steel wire wound gasket to improve the tightness and reliability of flange joint; ③ Four U-shaped expansion bends are installed on the fire water supply main pipe of 1 #, 2 # boiler room respectively, and two U-shaped expansion bends are installed on each fire water supply riser of the boiler room to absorb the stress changes caused by the thermal expansion and cold contraction of the fire pipe; ④ A set of multifunctional temperature inspection and control device suitable for the steam tracing temperature control of several fire-fighting pipelines has been developed by ourselves, which realizes the automatic detection and control function of the water temperature in the fire-fighting pipelines, so that the water temperature of the fire-fighting system in the boiler room is maintained between 10~40 ℃ during winter operation. This technical transformation measure provides successful experience for solving the problem that the fire protection system of boiler room in power plants in northern China can not operate normally. The following focuses on the working principle and application effect of the multi-channel temperature inspection and control device

3 multi channel temperature inspection and control device

3 1 working principle

according to the operation requirements of the fire protection system in the boiler room of the power plant, the normal operation of the whole fire protection system can be guaranteed as long as the water temperature in the fire protection pipeline is not lower than 5 ℃ in winter. As the boiler room of the power plant is generally arranged outdoors, the water temperature in the fire pipeline is greatly affected by different wind directions in winter, so it is impossible to keep the water temperature of the whole fire protection system constant, and the temperature can only be controlled within a reasonable range. According to the above characteristics, two thermocouple measuring points and two local thermometers are installed on each fire water supply riser at the four corners of the boiler room to monitor the water temperature changes in each fire pipe. The thermocouple and the local thermometer are respectively installed at 12 5 m and 47 m positions are convenient for patrol inspection and maintenance. An electric shut-off valve is installed behind the manual shut-off valve of the heat tracing steam of the fire pipe in the boiler room to automatically open and cut off the heat tracing steam of the fire pipe. A dn 50 fire water ring connecting pipe is installed on the 47m platform of the boiler room, and the principles of heat balance and microcirculation are applied to reduce the temperature difference of each fire water supply riser due to different installation positions and the influence of wind direction. A set of multifunctional automatic temperature inspection and control device is installed on the 12.5m maintenance platform of 1# boiler room to automatically inspect and control the water temperature in the fire pipe of the boiler room. According to the actual use effect of the multifunctional automatic temperature inspection and control device in Hejin Power Plant, in order to reduce the influence of wire resistance on the measurement signal in the process of temperature signal transmission, the maximum service radius of the wooden device should not exceed 500m. When the temperature of a measuring point reaches 5 ℃, the multi-functional automatic temperature inspection and control device sends out a control command, automatically opens the electric shutoff valve of the heat tracing steam of the fire pipeline, and the steam tracing system of the fire pipeline is put into operation to start to improve the water temperature in the fire pipeline; When the temperature of a measuring point reaches 45 ℃, the multi-functional automatic temperature inspection and control device sends out a control command, closes the electric shut-off valve of the heat tracing steam of the fire pipeline, the steam heat tracing system of the fire pipeline stops running, and the fire water in the fire pipeline enters the stage of insulation and heat microcirculation. When the temperature of a measuring point is lower than 5 ℃ or higher than 45 ℃, the multifunctional automatic temperature inspection and control device will send an alarm signal to remind the operator to take corresponding treatment measures. Figure 1 shows the working principle of the multifunctional automatic temperature inspection and control device

3.2 operation effect

the operation practice in the past two years shows that the device operates stably, the detection and control functions are reliable, the operation of operators is greatly reduced, and good actual operation effect is achieved. According to the operation records of the fire-fighting system in the boiler room, the steam heat tracing system of the fire-fighting pipeline is put into operation for an average of 2-4 times per person in winter, and each time it is put into operation for 2.5-3.5 hours. The water temperature in the fire-fighting pipeline of the whole boiler room is generally maintained between 5-45 ℃, and there is no pipeline frost crack or thermal expansion leakage fault, which significantly reduces the overhaul and maintenance workload of the fire-fighting system in the boiler room