Main control failure of the hottest supercritical

2022-08-02
  • Detail

Cause analysis and Countermeasures of main control failure and boiler turnover of supercritical CFB boiler. The boiler is composed of three parts: main circulation circuit, shaft flue and tail flue, which are arranged symmetrically on the left and right and supported on the boiler steel frame. The external heat exchanger is used to adjust the furnace bed temperature and reheat steam temperature, and the high-temperature cooling cyclone separator is used for gas-solid separation. The boiler is provided with 4 coal feeding lines, each of which is provided with a weighing belt coal feeder and a scraper coal feeder, and each scraper coal feeder is provided with 3 coal drop openings. The 12 coal feeding ports are respectively set on the 6 Return legs of the reclaimer and the 6 Return ash channels of the external bed of the boiler (as shown in Figure 1)

1 phenomenon overview

on a certain day in February 2015, the unit load was 330MW, and the C coal feeding belt was overhauled. 11: During the maintenance, the C coal feeding belt was started locally for trial operation. At 11:01, the coal quantity control tripped to manual, and the boiler master control tripped to manual. 11: 02 the total coal quantity, coal quality correction coefficient and boiler calorific value become bad points, and the boiler master control fails. 11: 05 the primary air control valve and the primary air fan inlet baffle switch from automatic to manual, the primary air volume deviation on the left and right sides increases, the bed pressure deviation on the left and right sides of the furnace increases rapidly, the boiler starts turning over, and the unit bed temperature, steam temperature and other parameters fluctuate greatly. The operator shall immediately manually adjust the primary air volume and air pressure to control the bed pressure deviation to continue to expand. When the deviation is the largest, the primary air volume on the left is 432knm3/h, the primary air volume on the right is 116knm3/h, the bed pressure on the left is 9.5kpa, and the bed pressure on the right is 24kpa. After adjustment, the deviation of air volume and bed pressure gradually decreases. At 11:20, the primary air volume, the bed pressure returns to normal, and the unit parameters gradually return to normal

2 cause analysis of boiler calorific value deterioration point and boiler master control failure

under normal circumstances, when the coal feeding belt is powered off for maintenance, the coal feeding instruction is 0 and the coal feeding flow feedback output is a bad point. When the feedback is a bad point, the flow signal of the coal feeding line will be automatically switched to the coal feeding command value as the signal output. When line C is shut down, its coal feed command is 0, and the flow feedback output of the coal feed line is also 0. Therefore, the maintenance of the coal supply line by power failure at ordinary times will not cause the calculation error of the boiler's real-time total coal supply, and the relevant control logic (as shown in Figure 2)

at 11:00 of that day, when the C coal feeding line was overhauled for local test run, the feedback display after the C coal feeding belt was powered on was 0, which was a bad point. At this time, the coal feeding output was switched to the command value of the C belt coal feeder, i.e. 0t/h. After starting line C, the coal feeding command will automatically change to 10t/h as the initial command. At this time, the coal feeding output of line C is 10t/h, which is involved in the coal feeding calculation of the boiler

5 s after the C feeding belt is started, the coal feeding command value decreases from 10t/h to 0 and becomes a bad point. At this time, the C feeding line command and feedback become bad points. The most common type of coal feeding quantity command signal of coal feeder C is that the so-called "crawling" has no quality judgment and is directly output after becoming a bad point to participate in the calculation of coal feeding quantity

this leads to errors in the calculation of coal feeding amount of CD coal feeding line. The main control of CD coal feeding line changes from automatic to manual, and the main control of boiler also changes to manual. At 11:02, the total coal quantity of the boiler also became a bad point. The monitoring of total coal quantity of boiler loses accuracy. 11:05 the operator removes the automatic of AB coal feeding line and manually adjusts the coal feeding amount of AB and CD lines to ensure the accuracy of coal feeding

when the main control of AB and CD coal feeding lines are manual, the boiler calorific value is switched from the current load command calculation value to the total coal quantity calculation value. At this time, the total coal quantity of the boiler is a bad point, which makes the calorific value output of the boiler become a bad point. The boiler calorific value is directly involved in the automatic control of the flow of the primary air control valve. Therefore, the automatic control of the two primary air valves fails after 4S, and it jumps to manual control, and the air volume and bed pressure on both sides begin to deviate

from the above analysis, it can be seen that the coal feeding command value of coal feeding line C becomes a bad point, which is transferred to the higher-level logic operations such as the total coal quantity and boiler calorific value of the boiler layer by layer, and participates in the calculation of the total coal quantity and boiler calorific value, making the total coal quantity and boiler calorific value become bad points, which leads to the failure of the main control of the boiler and the failure of the automatic control of the primary air regulator

3 analysis of boiler bed turning

before the failure of boiler master control, the automatic control of primary air volume regulating valve was put into good operation. The bed pressure on the left side of the furnace is 14kpa, the air volume is 245knm3/h, and the air volume on the right side is 16kpa, the air volume is 246knm3/h. The two primary air volume control valves on the left and right sides of the furnace automatically control the stability of the bed pressure and air volume on both sides of the boiler

when the boiler calorific value becomes a bad point, the left and right primary air valves jump to manual control, the bed pressure and air volume on both sides lose the ability of automatic balance, the left furnace bed pressure is low, the relative resistance is small, and the air volume gradually increases, making the bed material blow to the right. This further increases the pressure difference between the beds on both sides, which makes the air volume on the left rapidly increase and the air volume on the right decrease. The cross fluctuation of bed pressure at both sides will cause the boiler to turn over, and the operating parameters such as bed temperature and steam temperature of the unit will fluctuate greatly

when the deviation between the left and right sides of the boiler is maximum, the primary air volume on the left side is 432knm3/h, the bed pressure is 9.5kpa, and the bed pressure on the right side is 116knm3/h, 24kpa. After the boiler bed turnover occurs, the operator shall immediately manually increase the primary air pressure, reduce the primary air volume on the left, increase the primary air volume on the right, strengthen parameter control, and control the bed pressure deviation on both sides. After treatment, the air volume and bed pressure deviation on both sides gradually decreased and returned to normal. During the regulation process, the maximum primary air pressure reaches 25.5kpa. From import to production, customers close to any industry will benefit from Altair's deep-rooted composite material design knowledge in products and the closely integrated fan rated pressure head with Optistruct and multiscale designer

4 optimization measures and Countermeasures

optimize the calculation logic of coal feeding line, increase the quality judgment of measuring points, and shield the bad points of coal feeding quantity from participating in the logical calculation of coal quantity and boiler calorific value. In the optimized calculation logic of coal feeding quantity, if the feedback and instruction of coal feeding quantity become bad points, the output value of coal feeding quantity of the coal feeding line will be switched to the instruction value of coal feeding quantity at the previous time. Avoid other consequences caused by the failure of the boiler master control due to the participation of the measurement bad point of a coal feeding line in the boiler calorific value calculation. The coal feeding control logic after optimization and transformation is shown in Figure 3

in case of similar situations, if the primary air volume control valve jumps to manual

control, the operator must closely monitor the change trend of air volume and bed pressure on both sides of the furnace. If the deviation expands, it should be manually adjusted immediately to increase the primary air pressure in time to prevent the divergence and expansion of air volume and bed pressure deviation from causing the boiler to turn over. During the treatment process, the inspection of air duct expansion joint shall be strengthened, the monitoring of furnace bed temperature shall be strengthened, and the adjustment of intermediate point superheat and steam temperature shall be strengthened to prevent furnace coking and overheating of heating surface metal

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