Source: Boiler Man
The influence of boiler parameters on the operation of the unit
What are the boiler burners?
Will it be burned from the end
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In fact, the main daily task of the boiler operation attendant is to monitor the parameters related to the boiler system, of course, there will be a lot of parameters, you can experience it once you read the meter, not to mention the one time you read it once an hour (the meter reading is soft). But the main parameters are as follows, as long as you carefully observe their changes, you will also become a small expert in burning boilers.
Main steam pressure, main steam temperature
The materials of boiler equipment (boiler body and pipes) have certain temperature and pressure limits, and exceeding a certain temperature and pressure will reduce the service life of the equipment, accelerate the creep of the metal, and even cause damage to the equipment.
If the steam pressure is too low, the enthalpy drop will be reduced, the functional force will be reduced, and the circulating thermal efficiency of the unit will be reduced. Too low steam temperature will not only reduce the circulating thermal efficiency of the unit, but also increase the steam humidity in the last few stages of the steam turbine, resulting in blade erosion and water shock in severe cases.
Drum water level
The water level of the steam drum is generally 0 water level is the normal water level (don't think that the dry pot is dry when you see the water level is 0), the water level protection will alarm when the value is high 1 or 2 and the value is low 1 or 2, and the high 3 and low 3 values are the action value of stopping the furnace protection.
The high water level will cause difficulties in separating the steam-water drum, the steam will carry water, the salt will increase, and the heat transfer effect will be worse due to the scaling of the heating surface. Steam carrying water can also cause a sharp drop in the temperature of superheated steam, which threatens the safety of the steam turbine.
If the water level is too low, it will cause the descending pipe to carry steam, destroy the normal water circulation, stagnate or reverse the water circulation, cause the furnace pipe to be overheated without cooling, and cause the pipe burst in serious cases.
One air temperature
Increasing the primary air temperature can reduce the ignition heat, advance the ignition position, and stabilize combustion at low loads. Increasing the primary air temperature is one of the necessary measures to improve the ignition speed and ignition stability of pulverized coal.
However, when the air temperature is too high and exceeds the regulations of pulverized coal transportation, it may cause the pulverized coal to burn in advance before entering the furnace, and even cause fire, explosion and other accidents.
Too low a primary air temperature is also not good for the boiler operation: delayed ignition, unstable combustion and reduced combustion efficiency.
Primary air volume
The larger the primary air volume, the more heat required for the pulverized coal gas flow to be heated to ignition, the slower the ignition speed, and the longer the ignition position, the total stroke of the flame in the furnace is shortened, that is, the effective combustion time of the fuel in the furnace is reduced, resulting in incomplete combustion. The flue gas temperature of the furnace will also increase, which may not only cause slag formation on the heating surface of the furnace outlet, but also cause a series of problems such as overheating of the superheater or reheater, which will seriously affect the safe and economical operation of the boiler.
For different fuels, the required primary air volume is also different due to their different ignition characteristics. On the premise of ensuring that the pulverized coal pipeline does not deposit pulverized coal, the primary air volume should be reduced as much as possible.
Primary wind speed
If it is too high, it will delay the ignition, cause instability of combustion, and even extinguish the fire. After any fuel is ignited, it has a certain flame propagation velocity when the oxygen concentration and temperature are constant. When the primary wind speed is too high, greater than the flame propagation speed, it will blow out the flame or cause "de-fire". The coarser pulverized coal has a large inertia and is easy to pass through the intense combustion zone and fall, forming incomplete combustion. In some cases, the pulverized coal gas flow can rush straight to the opposite furnace wall, causing slag formation.
If it is too low, it is also unfavorable to the temperature combustion and the prevention of slag formation: the rigidity of pulverized coal is weakened, the cutting structure is not good, the disturbance is not strong, and the combustion is slow. Ignition delay. When the wind speed is less than the flame propagation velocity, the phenomenon of "backfire" may occur, or the nozzle may burn out because the ignition location is too close to the nozzle. It is easy to cause pulverized coal deposition and pipe blockage.
Negative pressure in the furnace
The negative pressure of the furnace is too large, which increases the air leakage volume, which leads to the increase of the electric consumption of the induced draft fan, and the increase of the heat loss of combustion and exhaust gas, which may cause unstable combustion and deterioration of combustion to extinguish the boiler.
When the negative pressure of the furnace is small or even becomes positive, the flame and fly ash will come out through the poor place of the furnace, which will deteriorate the working environment and even endanger the safety of personnel and equipment.
Exhaust gas temperature
The higher the heat loss, the greater the heat loss of the exhaust flue, indicating that the heat absorption of the tail flue is insufficient.
If it is too low, the natural climbing height of the smoke will not be enough, and the smoke and dust diffusion area will be small, which will increase the air pollution in the local area. At the same time, due to the low temperature of the flue gas, the moisture in the flue gas will condense on the tail heating surface and the chimney wall, because these moisture contains sulfur dioxide left after coal combustion, etc., the tail heating surface and the inner wall of the chimney will be corroded, affecting the service life of the tail heating surface and the chimney.
Oxygen content
Too high indicates that the air volume is too large, the fan output is large, the economy is poor, and there may be air leakage, which will also cause an increase in NOx emissions and a decrease in environmental performance.
If the oxygen content is too low, it indicates that the combustion of pulverized coal is insufficient, resulting in an increase in the carbon content of fly ash.
Wall temperature
The high-temperature section prevents the metal from overheating, resulting in plastic deformation, and will also accelerate the oxidation of the pipe and reduce the thickness of the pipe wall. Serious overtemperature can cause accidents such as pipe bursts.
The low temperature section prevents the metal wall temperature from falling below the flue gas dew point temperature, forming condensate corrosion metal and sticky ash blockage.
Layer
For circulating fluidized bed boilers, it is also necessary to monitor the thickness of the material layer and the amount of material returned.
The material layer is too thick, in order to ensure the excess air coefficient, it is necessary to increase the primary air and the secondary air, the heat in the bed will be taken away by the wind, and the burned out materials in the bed will also absorb the heat of the material that is releasing heat, which will affect the output of the boiler, and the primary air volume is not well adjusted and easy to cause low-temperature coking.
The material layer is too small, the air volume is not well adjusted, the excess air coefficient is too large, the boiler output is reduced, and the flue gas flow rate is too fast to increase the wear of the heating surface. The bed surface has poor heat storage capacity, poor adjustment ability, and the adjustment time is shortened when the material is unstable or the coal is broken.
I remember that the New Year's wish of a little friend who burns a boiler is that the circulating fluidized bed boiler can be fully automatic, look at the beautiful photos of the inspection robot below, everything is possible~