Frequently asked questions about the operation of

FAQ of boiler operation

Q: when the combustion is unstable, put oil in, and exit the oil gun when the negative pressure becomes positive. Can you avoid the impact of large positive pressure? Why

answer: No; Because the negative pressure of the furnace becomes positive, it means that part of the extinguished pulverized coal is ignited, and the impact force generated by igniting part of the extinguished pulverized coal will not be reduced by stopping the oil gun. The consequence of returning the oil gun is that it is possible to extinguish the fire again. Q: the automatic pressure of steam injection pressure is high, the powder feeder stays at low speed, and the oxygen content is high. Should fire extinguishing be avoided

answer: first put in oil to stabilize the combustion, and then remove the automatic steam pressure. According to the situation, increase the speed of the operating powder feeder and shut down 1 ~ 2 powder feeders. If necessary, reduce the air supply, so that the oxygen content and steam pressure can quickly return to normal. The speed of the lowest row of powder feeder is ≮ 800 rpm. Q: what measures should be taken by the pulverizing system to prevent the boiler from extinguishing the fire when dealing with the failure of the coal feeder in a short time during operation

answer: turn down the inlet baffle of the pulverizer and control the current of the pulverizer to be 1~1 lower than the operating current. 5A, fully open the circulating valve and control the mill outlet temperature to operate at about 80 ℃. If the combustion is difficult to stabilize, ask the stoker to stop the operation of the pulverizing system. Q: why should we reduce the air supply and turn off the small secondary air after putting out the fire and before the ignition

answer: after extinguishing the fire, the furnace temperature is low. Too much lower secondary air and too much air supply will make the root air of the oil gun too large, and it is difficult to ignite the oil nozzle, or make the ignition point of the oil move back, blow out the burning oil nozzle, and affect the resumption of ignition

ask: when will the load reduction be notified after the boiler is extinguished? How should the magnitude and speed of load reduction be controlled

answer: after extinguishing the fire, when the steam pressure begins to drop, immediately notify the load reduction. The speed and amplitude of load reduction shall not cause the boiler to overpressure and open steam exhaust, and the load reduction value shall be determined according to the decrease amplitude of steam pressure and steam temperature and the ignition recovery time after fire extinguishing. According to experience, the normal fire extinguishing load of 220t/h boiler is reduced to 20MW, and the normal fire extinguishing load of 400t/h boiler is reduced to 40mW; Q: why should we maintain a slightly lower oxygen level when running at low load without affecting safety

answer: during low load operation, the furnace temperature is relatively low, the ignition of pulverized coal flow is difficult, and the combustion stability is relatively poor. Maintaining high oxygen operation will further reduce the furnace temperature, reduce the combustion concentration of pulverized coal in the furnace, reduce the anti-interference ability of combustion, and lead to the occurrence of fire extinguishing

ask: why should the boiler be equipped with explosion-proof doors

reduce the loss of life and property answer: when the furnace explosion occurs, the pressure relief is automatically turned on to reduce the impact and destructive force of the explosion on the boiler and avoid the damage of the furnace water wall, furnace wall and flue

ask: why should the moisture absorption pipe of the powder bin be opened during operation

answer: eliminate the moisture in the powder bin and the powder conveyor to prevent the pulverized coal in the powder bin from being wet and caking, affecting its fluidity, and maintain the temperature in the powder bin at an appropriate value due to the discharge of moisture, so as to prevent the spontaneous combustion and explosion of pulverized coal

ask: why should the recirculation valve of the economizer be opened when the water inlet is stopped

answer: if the economizer is still heated when the boiler stops feeding water, the water circulates between the economizer and the steam drum through the circulating pipe to protect the safety of the economizer

Q: what is the effect of hot water immersion backwashing of superheater

answer: the silicate and other salts that are easily soluble in water deposited in the superheater pipe can be soaked and dissolved, and then separated from the pipe wall after being softened, and then back washed by the superheater to the steam drum for discharge, so as to prevent serious scaling of the superheater and scaling of the flow passage part of the turbine

ask: why should the outlet temperature of the coal mill be controlled

answer: ensure the drying output of the pulverizing system; Avoid blocking the system due to low outlet temperature, increased moisture content of pulverized coal and poor fluidity; To prevent the spontaneous combustion and explosion of pulverized coal due to high temperature

Q: fire extinguishing protection conditions for the flame extinction of the whole furnace? Conditions for extinguishing layer flame

answer: three layers of flame go out; 3/4 corner flame goes out

ask: sometimes the superheater tube wall temperature is not found to be over temperature, but the tube explosion still occurs. What is the reason

answer: 1

because the number of installed measuring points for pipe wall temperature is limited and the representativeness of the measuring points is poor, it cannot reflect the true value of all pipe wall temperatures. Therefore, the pipe wall without measuring points may have overheated in actual operation, but the wall temperature does not show its overheating

2. The installed tube wall temperature measuring point is the outer wall temperature of the furnace, which has a temperature difference with the inner wall of the furnace. The inner wall temperature of some tubes may greatly exceed the controlled wall temperature difference, resulting in overtemperature tube explosion; 3.

the primary element error of the installed pipe wall temperature is large or the secondary instrument is inaccurate, and the wall temperature indication is wrong, misleading the operator

ask: the boiler is seriously full of water, and the steam temperature will drop sharply, but why do you have to shut down the boiler in an emergency

answer: 1 After the boiler flameout, the pressure will be reduced rapidly to improve the superheat of steam and reduce the harm to the steam turbine; 2. The boiler water shrinks rapidly after flameout. In a short time, the water level of steam drum will be sharply reduced to reduce the steam carrying water; 3.

after flameout, due to the sharp reduction of heat load, the evaporation capacity and the carrying capacity of steam, the water in steam will be reduced

ask: why does the rapid fire and pressure rise cause the superheater to overheat and burst

answer: rapid fire and pressure increase, that is, the thermal load of the boiler increases sharply, so that the flue gas flow and steam temperature through the superheater tube wall increase sharply, but the amount of steam produced by the water-cooled wall tube is later than the growth of the thermal load, the steam flow in the superheater cannot increase synchronously, the cooling condition of the superheater tube wall deteriorates, and the superheater or reheater tube wall temperature rises sharply in a short time, resulting in overtemperature tube explosion; In addition, the temperature of superheated steam will rise sharply due to rapid fire and pressure rise, and the adjustment of steam temperature often cannot keep up with the change of steam temperature, which is easy to cause steam temperature overheating and pipe explosion due to poor cooling of pipe wall; Q: when the steam temperature drops sharply and the safety of the steam turbine is in danger, what is the effect of opening on air exhaust

answer: the function of open air exhaust is to reduce steam pressure and increase steam superheat; Another side effect is to create conditions for increasing heat load and temperature after pressure reduction, but the first one is main; Depressurization reduces the steam flow, reduces the ability of steam to carry water droplets in the steam drum, and reduces the steam load, which can reduce the harm to the steam turbine

ask: how to protect superheaters and reheaters during boiler startup

answer: in the low-pressure stage, due to the less steam flow through the heating surface, the cooling condition of the pipe wall is poor. It is mainly used to control the flue gas temperature to be lower than the bearing temperature of the heating surface pipe to protect the superheater and reheater; When the pressure reaches a certain value, it is mainly by adjusting the amount of steam flowing through the superheater and reheater, that is, opening the air exhaust, primary and secondary bypass, superheater drainage, etc., so that there is enough steam to cool the heating surface and protect the safety of the pipe wall; In the start-up stage, the temperature rise and pressure rise shall be carried out in strict accordance with the relevant provisions of the temperature rise and pressure rise curve and technical standards, so as to avoid the overheating of the pipe wall caused by the sharp increase of thermal load; Q: why is there serious combustion instability in the boiler, and whether the fire extinguishing protection does not act? Can you put oil into the boiler to stabilize the combustion

answer: according to the action setting of fire-extinguishing protection, local fire-extinguishing or unstable combustion in the furnace will be close to the edge of fire-extinguishing. The signal of loss of flame in the whole furnace may not act, and the negative pressure pipe of fire-extinguishing protection may be blocked. If the negative pressure signal cannot feel the occurrence of unstable combustion and local fire-extinguishing, the fire-extinguishing protection will not act, so the consequence of serious unstable combustion and oil injection is deflagration, Cause large positive pressure impact or high furnace pressure signal action to extinguish the fire; Q: what is the purpose of turning down the inlet baffle of the pulverizer and turning up the recirculation valve of the pulverizing system

answer: because the temperature of the tertiary air is low, the wind speed is high, and the air volume is large, it will have a great impact on the combustion stability of the boiler. Turning down the inlet baffle of the pulverized coal exhauster can reduce the interference of the tertiary air to the combustion, stabilize the combustion, and avoid the occurrence of fire extinguishing. The main purpose of this operation is to increase the ventilation volume of the system so as to increase the output of the pulverizing system, so as not to significantly reduce the output by turning down the exhaust inlet baffle, and at the same time, reduce the tertiary air volume under the same ventilation volume of the system to maintain stable combustion. Q: what are the general measures for stabilizing combustion

answer: generally, the conventional measures for stabilizing combustion include reducing the air supply, turning down the primary air of the stopped pulverized coal feeder, reducing the primary air pressure and primary air speed, turning down the lower secondary air valve and the intermediate secondary air (#5 - #6 furnaces), and maintaining a slightly lower excess air coefficient and a higher rotating speed of the pulverized coal feeder without affecting safety

ask: why is it forbidden to turn down the powder baffle under the powder feeder to control the amount of powder during operation

answer: turning down the lower powder baffle to control the amount of powder will lead to uneven powder feeding of the powder feeder. When the powder level is high, the amount of powder feeding of the powder feeder will be greatly reduced, and the concentration of pulverized coal in the primary air will be reduced, which may lead to the occurrence of boiler fire extinguishing

ask: under what circumstances can oil be injected to stabilize combustion, and under what circumstances is oil injection prohibited from deflagration

answer: if the boiler has signs of unstable combustion, such as a sharp increase in oxygen content, an increase in negative pressure swing, a decrease in steam pressure, and individual flame indicators for fire protection flash or go out, oil should be added in time to stabilize combustion or other measures for stable combustion should be taken quickly. If the combustion instability is serious, and the negative pressure indication is negative to - 200Pa or below, the flame indicator light with one or more layers of fire extinguishing protection is extinguished, that is, when the boiler has serious combustion instability (the fire extinguishing protection has not been activated), it is strictly prohibited to throw oil for deflagration. Q: how much should the deviation of powder level not exceed during operation? What is the significance of controlling powder level deviation

answer: the level difference between the two sides should not exceed 0.5m; Controlling the powder level deviation can reduce the uneven powder feeding between the powder feeders, avoid the occurrence of excessive powder feeding or sudden rise and fall of the powder feeder on the low side of the powder level, and the reduction of the powder feeding of the powder feeder on the high side of the powder level, so as to maintain the stability of combustion and avoid the occurrence of fire extinguishing

ask: what measures should be taken to stabilize the combustion in addition to adding oil during the failure and shutdown of the lower discharge pulverized coal feeder

answer: we should strengthen the monitoring and adjustment of combustion. We can take measures to stabilize combustion, such as removing the automatic operation of the powder feeder at the shutdown angle, increasing the output of other powder feeders at this angle, turning down the primary air of the shutdown nozzle, improving the temperature level of the downstream nozzle area, and maintaining a slightly lower oxygen content within the safe range. And timely notify the maintenance personnel to eliminate defects. Q: what is the phenomenon of bad powder feeding in the powder feeder? What is the phenomenon of powder feeding interruption

answer: the phenomenon of bad powder: the primary wind pressure and wind speed fluctuate sharply; The steam pressure and temperature fluctuate greatly; The swing amplitude of furnace negative pressure increases, and the oxygen content is unstable, which may affect the unstable combustion or boiler fire extinguishing. Phenomenon of pulverized coal feeding interruption: the unit load and steam pressure and steam temperature decrease, the oxygen content increases, the furnace negative pressure becomes negative, the primary air pressure decreases, the primary air speed increases, the temperature of the short pulverized coal pipe under the pulverized coal feeder decreases, and there is no pulverized coal at the corresponding nozzle. When the combustion is unstable and serious, fire extinguishing can occur

ask: what measures can be taken to reduce the tube wall temperature of the right rear screen of the 400t/h furnace

answer: 1 Increase the input of the right side powder feeder and reduce the input of the left side powder feeder; 2. Turn up the left primary desuperheating water and reduce the outlet temperature of the left primary desuperheater; 3.

take measures to reduce the flue gas temperature at the inlet of the right platen superheater, turn up the opening of the right tertiary air or primary and secondary air valve baffle, and turn down the left tertiary air and primary and secondary air; 4. Increase steam pressure and temperature and reduce steam consumption; 5.

if the high-pressure heater is not put into operation, the steam turbine is required to put the high-pressure heater into operation

ask: what are the symbols of unstable boiler combustion

answer: 1 The negative pressure in the chamber fluctuates greatly or goes negative