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Part I: Pre-Accident Conditions
1. Time 16:02 load 300MW, DEB mode, ADS input.
2. The main steam pressure is 164MPa, reheat steam pressure 34mpa, drum water level 53mm, coal volume 1263t h, the main steam flow rate is 8668t h, manual reference value 872%, the main steam temperature on the furnace side is 5378. The reheat steam temperature on the side of the furnace is 5398℃。
3. The negative pressure of the furnace is -112Pa, the secondary air volume is 883t h, the total air volume is 985t h, the air volume of 31 blower is 446t h, the air volume of 32 blower is 432t h, and the opening of 31 and 32 air supply motor blades is 667%, and the current is 526a, oxygen is 184%, 31, 32 induced draft fan inlet adjustment baffle opening is 372%。
Part II: How the accident happened
1. Time 16:03 The air volume of the 32 blower suddenly decreases from 439t h to 352t h, the air volume of the 31 blower increases from 453t h to 516t h, the total secondary air volume decreases from 894t h to 841t h, and the current of the 32nd blower is 536A is reduced to 47A, and the current of the 31 blower is reduced to 536a to 557a, see figure below.
2. Time 16:03:41 seconds 31, 32 air supply motor blade opening 90%, at this time, the air volume of 32 blower is reduced to 0t h, the air volume of 31 blower is increased to 681t h, the total secondary air volume is 657t h, and the current of 31 blower is raised to 84A (rated current is 66.)5A) During the period, the current fluctuates to 101A, the current of the 32 blower drops to 43A, and the current of the 32 blower also fluctuates at the lowest of 26A, and the highest is 639A, the negative pressure of the furnace has been reduced to -575Pa, and the inlet adjustment baffle of the two induced draft fans is closed to 327%, at which point the load is 300MW. See diagram below
3. Time 16:03 minutes and 58 seconds, the operator manually closes the 32 air supply motor blades from 90% to 10%, in this process the moving blade command has a short pause at the 65% position, the feedback of the two induced draft fan inlet adjustment baffles is 30%, the negative pressure of the furnace is -172Pa, the negative pressure has been basically stable, when the 32 air supply motor blades command to 10%, the two induced draft fan inlet adjustment baffle instructions directly from 302% is reduced to 8%, when the command of the 32 supply motor blades is 65%, the command of the inlet adjustment baffle of the two induced draft fans is 22%, and the negative pressure adjustment is still automatic at this time, and the current of the 31 supply fan is 84A and the power is 300MW. See diagram below
4. Since the two inlet adjustment baffles of the inlet of the induced draft fan are closed to 8% (the opening of the coupler of the two induced draft fans has not changed by 65%, because the amount of coal has not changed), the negative pressure has begun, due to the fast speed of negative pressure, and the opening of the inlet adjustment baffle and coupler of the two induced draft fans has not changed, resulting in the air volume of the 31 blower also began to decrease, and the current also decreased, when the negative pressure was 1637pa, the air volume of the 31 blower was reduced to 354t h, and the opening of the moving blades was 90% unchanged.
5. Time 16:04:9 seconds furnace negative pressure high high 1 and negative pressure high high 3 switch action, at this time the furnace outlet negative pressure 4 is up to 2239pa, and the remaining 3 points are 1177pa, 1177pa, 1126pa, 16:04 minutes 12 seconds (negative pressure high high three take two action delay 3 seconds mft) mft action, action preload 300mw. See diagram below
Part 3 Causes of Accidents and Treatment
1. Should be familiar with the feedforward effect of automatic adjustment, due to the 32 air supply motor blade opening directly from 90% to 10% in the accident, resulting in the two inlet draft fan inlet adjustment baffle instructions directly from 30% to 8%, this is the feedforward effect of the air supply motor blade opening on the inlet adjustment baffle of the induced draft fan, which is also the direct cause of MFT action, if the accident is mastered before the feed-in, there will be no negative pressure high MFT action, and there are many feedforward effects that the operating personnel do not know in operationIt is recommended that the thermal worker give a lecture to the operator.
2. In the process of reducing the air volume of the 32 blower from 439t h to 0t h, the blower did not send a surge alarm, which is also the main reason why the operator did not find the surge of the 32 blower in time.
3. Negative pressure fluctuations have repeatedly appeared after the commissioning of the No. 3 machine, and the department has also taken corresponding measures, I personally think that if the negative pressure automatic adjustment begins to diverge and the divergence is getting bigger and bigger, the manual adjustment should be decisively solved, and the timing of the manual adjustment should be grasped well, according to the operation experience, the corresponding air supply volume corresponds to the corresponding induced draft fan inlet to adjust the opening of the baffle, and the inlet adjustment of the induced draft fan is small or large. If necessary, add the adjustment of the induced draft fan coupler, but should avoid long-term operation at 45% of the coupler position, if the negative pressure still fluctuates greatly due to the fluctuation of the air supply volume after the negative pressure is released, the blower should be automatically released in time.
4. It is found that the blower stalls, the air volume decreases, the negative pressure of the furnace is reduced, the load of the unit is reduced, the guide and the conveyor are relieved, the induced air motor blade is appropriately reduced, the negative pressure of the furnace is adjusted to normal, the air volume is low and the protection action is low, and then the stall air supply motor blade is reduced to the opening before the stall (if the other is overcurrent, the other moving blade is lowered at the same time in the process of reducing the stall fan), and the stall fan is incorporated into the system.