Boiler unit combustion regulation mode and its significance
1. Adjustment of fuel quantity
The adjustment of fuel quantity is an important part of combustion regulation. Different combustion equipment and different fuel types, the adjustment method of the fuel amount is also different.
1. For boilers equipped with intermediate storage pulverizing system
One of the characteristics of the intermediate storage bin type pulverizing system is that there is no direct relationship between the change in the operating conditions of the pulverizing system and the boiler load. When the load (output) of the boiler changes, it is necessary to adjust the amount of fuel entering the furnace. It is done by putting (or stopping) the number of burners or changing the number of revolutions of the powder machine and adjusting the opening of the powder baffle under the powder machine. Achieved.
When the boiler load change is small, it is only necessary to change the speed of the powder feeder to achieve the purpose of adjustment; changing the number of revolutions of the powder feeder is done through the addition and subtraction of the flat controller. When the load of the boiler changes greatly, changing the rotation speed of the powder feeder can not meet the requirements of the adjustment range, and without prejudice to the internal combustion operating conditions, the number of powder feeders can be adjusted first, and then adjusted. Adjust the number of revolutions of the powder machine to make up for the contradiction of large adjustment range. If the above measures still can not meet the adjustment needs, you can use the method of adjusting the opening of the baffle of the powder machine to assist adjustment.
Due to the different arrangement and type of burner, the operation mode of the burner (corresponding powder feeder) is adjusted differently. When you need to put in a spare burner and powder feeder, you should first open the air door to the required opening and purge the primary air pipe; when the wind pressure is normal, start the powder feeder and start the burner Combustion-supporting secondary air, observe whether the fire is normal. Conversely, when the burner is deactivated, the powder feeder is first stopped and the secondary air is turned off. After the primary air is purged for several minutes, it is turned off again to prevent the deposition of coal in the primary air pipe. In order to prevent the burned burner from being burned out by heat, sometimes the proper opening of the primary and secondary air doors is maintained to cool the nozzle.
The adjustment range of the revolution of the powder feeder should not be too large. If it is adjusted too high, it will not only block the primary air pipe due to the excessive concentration of coal powder, but also easily overload the powder feeder and cause incomplete combustion of the coal powder. If the number of revolutions is adjusted to be too low, when the temperature of the furnace is not too high, due to insufficient coal powder concentration, the fire is unstable and the furnace fire is likely to occur.
When only increasing the number of revolutions of the powder feeder, the number of revolutions of the powder feeder should be increased first, so that each powder feeder strives for balance; when reducing the number of revolutions of the powder feeder, the number of high revolutions should be reduced first.
For the boiler with the burner arranged on the side wall, the burner in the middle position can be added to powder first. For the burner boiler arranged in the four corners, the number of revolutions of the powder machine needs to be increased symmetrically.
To adjust the combustion by putting or stopping the operation of the burner, the influence on the temperature needs to be considered. When the temperature is low, use the burner or the upper row of burners against the back wall of the furnace. When the temperature is too high, the burner or the upper row burner near the back of the furnace will be disabled.
Due to the different types of burner structure, it is difficult to make specific regulations on the burner on-off method. Generally, the following principles can be referred to:
(1). Dropping the row and stopping the upper row of burners can reduce the flame center and help burn out.
(2) The combustion method arranged in four corners should be deactivated in layers or diagonally, and no corner operation is allowed.
(3) The principle of starting and stopping the burner is to ensure the boiler load, operating parameters and boiler safety, and then consider the economic indicators.
Judgment of the amount of powder coming from the burner (or powder feeder):
(1) The amount of powder can be judged from the current of the powder machine. If the current of the powder feeder is large, there will be more powder coming; if the current is small, there will be less powder coming; [
(2) The amount of incoming powder can also be judged from the indication of primary wind pressure. For example, if the measuring point of the wind pressure gauge is taken under the powder pipe of the powder feeder, and the primary wind pressure is small, then the amount of powder will be large; the primary wind pressure Big comes with little powder.
(3) From the burner, you can directly observe the amount of powder at the fire hole. If the concentration of air-powder mixture at the burner outlet is large, it means that there is a lot of incoming powder; when the pulverized coal in the air-powder mixture is sparse, there is little incoming powder; when there is too much incoming powder, dark red appears at the burner outlet; Then sporadic Mars appears.
Sometimes due to the accumulation of pulverized coal at the dead corner of the pulverized coal bunker or the self-flow of pulverized coal and other reasons, it will bring certain difficulties to the adjustment of the amount of powder to the individual powder machine. At this time, the adjustment of the amount of incoming powder will be a meticulous and cumbersome task. This requires repeatedly opening and stopping the powder feeder, or opening and closing the powder baffle of the powder feeder, knocking with a wooden hammer, and vibrating the upper space of the powder feeder to promote the flow of the coal powder deposited in the coal powder silo or force a larger flow Of pulverized coal deposited. This adjustment operation is awkward and heavy, but it can meet the adjustment requirements.
2. Adjustment of fuel quantity
The adjustment method of fuel quantity is related to the type of fuel system and the atomization method of the fuel nozzle. For the adjustment of oil quantity, the current fuel oil boiler generally adopts a system that uses oil inlet or oil return to adjust.
The adjustment method using the oil inlet adjustment system is: when the load changes, usually change the oil inlet pressure to achieve the purpose of changing the oil inlet. When the load decreases greatly, the oil inlet pressure needs to be greatly reduced in order to reduce the oil inlet. This will affect the atomization quality of the incoming oil due to the low oil pressure. In this case, the oil pressure cannot be reduced blindly, but the method of disabling part of the oil nozzle needs to be taken to meet the needs of reducing the load.
The system that uses oil return to adjust is to control the amount of oil returned to adjust the amount of oil that enters the furnace. The oil return forms include internal oil return and external oil return. The internal oil return system has strong adaptability to the load, and can adapt to 70% of the load change. However, at low loads, the axial velocity at the nozzle decreases and the tangential velocity does not change, resulting in a corresponding increase in the atomization angle, which can easily lead to slagging or burnout at the burner expansion hole. Although the atomization angle of the external oil return system can be basically unchanged when the load changes, the quality of low-load atomization will decline, and the processing requirements of this nozzle are relatively high, so it is rarely used in China at present.
2. Adjustment of boiler air volume
When the external load changes and the boiler output needs to be adjusted, as the fuel quantity changes, the boiler air volume also needs to be adjusted accordingly.
In actual operation, from the economic aspect of operation, within a certain range, with the increase of the excess air coefficient in the furnace, the contact and mixing of fuel and air can be changed, which is conducive to complete combustion and loss of chemical incomplete combustion And the loss of incomplete combustion of machinery is reduced. However, when the excess air coefficient is too large, the furnace temperature decreases and the combustion time is shortened (due to the accelerated flue gas flow rate), which may increase the incomplete combustion loss. The heat loss carried by the exhaust gas always increases with the increase of the excess air coefficient, so when the excess air is too large, the total heat loss will increase.
In addition, as the excess air coefficient in the furnace increases, the flue gas volume also increases accordingly, and the flue gas flow rate also increases, thus increasing the power consumption of the blower and induced draft fan.
From the perspective of the safety of the boiler, if the excess air coefficient in the furnace is too small, it will cause the fuel to burn incompletely, causing the flue gas to contain more combustible gases such as carbon monoxide, reducing the melting point of ash and causing slagging of the water wall . This will cause the boiler operation to deteriorate, and in severe cases it will be forced to shut down. If the air volume is insufficient in the oil-fired boiler, it will cause secondary combustion.
Because the amount of fly ash wear on the heating surface is proportional to the cubic power of the flue gas flow rate, when the excess air coefficient is too large, the wear on the heating surface pipe and the fan blade will increase, affecting the service life of the equipment. In addition, when the excess air coefficient is increased, due to the corresponding increase in the amount of excess oxygen, the sulfur content in the fuel is likely to form sulfur trioxide, and the flue gas dew point temperature response is increased, thereby corroding the air preheater of the tail flue .
In short, too large or too small air volume will adversely affect the safe and economic operation of the boiler.
The air volume control of the boiler is regulated by the inlet guide baffle of the blower. After adjustment, the air volume sent by the blower can be better met by the adjustment of the primary and secondary air. The air volume distribution of the primary and secondary air should be adjusted according to their role. The primary air volume should meet the needs of the combustion of the volatile matter of the powder mixture entering the furnace and the oxidation of solid coke particles.
The secondary air volume not only meets the needs of combustion, but also supplements the insufficient air volume at the end of the primary air. More importantly, the secondary air can be mixed with the combustibles that have just entered the furnace. This requires a higher secondary air speed to ensure high It acts as a stirrer in the flame. The better the mixing, the faster and more complete the combustion.
The primary and secondary air can also adjust the deviation of the air volume of each burner due to the different resistance of the coal powder pipe or burner, and the air volume required due to the deviation of the fuel concentration in the coal powder pipe or burner. In addition, the deflection of the flame in the furnace, the deviation of the flue gas temperature, the position of the flame center, etc. need to be adjusted by adjusting the air volume.
3. Adjustment of the wind speed and rate of the burner outlet
1. Purpose of adjustment and air distribution conditions
Maintaining the proper outlet speed and air rate of the first, second, and third air of the burner outlet is a necessary condition for establishing a normal aerodynamic field in the furnace and stable combustion.
If the primary air velocity is too high, the ignition time will be delayed; if it is too low, the burner outlet pipe will be burned, and the coal powder deposits in the primary air pipe may always block the pipe. If the secondary air speed is too high or too low, it may destroy the normal mixing and stirring of the airflow and fuel, thereby reducing the stability and economy of combustion.
The size and flow rate of the burner outlet cross section determine the percentage of the first, second and third air volume. The change of the air rate will also have a great influence on the combustion conditions. When the primary air rate is too large, the amount of heat required to reach the ignition temperature of the wind powder mixture will be more, so the time required to reach the ignition will be extended. . This is very detrimental to the ignition of low-volatile coal-fired coal, such as lower primary air temperature is even more unfavorable. For coal with high volatile content, it is easy to catch fire. After the fire, it is necessary to ensure that the volatile content is burned out in time. Therefore, a higher primary air rate is required.
2. The adjustment method of the wind speed and rate of the burner outlet
(1) DC burner adjustment at four corners
The DC burners arranged in four corners are based on the requirements of coal quality for combustion, and there are many structural arrangements. Generally, bituminous coal is used for burning. The burner of lignite mostly adopts higher primary air rate and wind speed, and the distance between the primary and secondary air nozzles is closer, so that the coal powder can be mixed with the air required for combustion in time to make Burn completely. For burners that burn coal with low volatile matter, in order to facilitate the ignition of the primary air powder mixture, in addition to using a lower primary air rate and injection speed, the primary and secondary air will not be mixed too early, in addition The primary air concentration scheme is often adopted to ensure the stability of combustion. The air outlet of the primary and secondary air of the DC burner is often made to swing up and down, which is used to adjust the position of the combustion center, which is convenient for the adaptation of the coal type and the need for the adjustment of the superheated temperature.
Due to the large layout characteristics of the four-corner DC burner and the wide selection and adjustment range of wind speed, the following methods can generally be used to adjust the speed of the primary and secondary air outlets:
Change the percentage of the primary and secondary air rates; â‘¡ Change the air volume distribution of each layer of burners, for example, you can change the primary air volume and wind speed of the corresponding upper and lower two layers of burners, or change the air volume and wind speed of the secondary air of the upper, middle and lower layers . Under normal circumstances, reducing the secondary air volume in the lower row and increasing the secondary air volume in the upper row can move the flame center down; otherwise, the flame center can be raised. â‘¢ For the DC burner with adjustable secondary air baffle, the wind speed can be adjusted by changing the position of the wind speed baffle.
The criteria for judging whether the wind speed and wind rate are appropriate are firstly the stability of combustion, the rationality of the furnace temperature, and the influence on the superheated steam temperature; secondly, the comparison of economic indicators.
4. Control of furnace negative pressure and adjustment of induced draft
1. Monitoring and controlling the furnace air pressure is an important parameter that reflects the stability of combustion conditions and judges the accident.
If the negative pressure of the furnace is maintained too large, it will increase the air leakage of the furnace and the flue, cause the combustion to deteriorate, and cause fire extinguishing. On the contrary, if the wind pressure in the furnace becomes positive, high-temperature flames and soot will rise outwards, which will not only affect the health, burn the equipment, but also cause personal accidents.
When the combustion conditions in the furnace change or the heating surface of the furnace leaks or blasts, it will immediately cause changes in the furnace air pressure. The actual operation shows that when an abnormal situation or failure occurs in the combustion system of the boiler, the first reflection is the change of the furnace air pressure. For example, the fire extinguishing of the boiler, the first reflected phenomenon from the instrument panel is that the indication of the furnace air pressure gauge fluctuates sharply and swings to the bottom, and then the changes in the indication of water level and steam flow. When blasting occurs on the heated surface of the furnace, its negative pressure gauge indicates that it is swinging forward.
Therefore, it is necessary to monitor the negative pressure of the furnace during the operation of the boiler, and make correct judgments according to different changes, and then make necessary adjustments and treatments in time according to this. [
2. Changes in furnace air pressure and flue negative pressure
In the operation of the boiler, the flue gas generated by the combustion must be discharged into the atmosphere in time by the induced draft fan. If the amount of flue gas discharged from the furnace is equal to the amount of flue gas generated by combustion, the material entering and leaving the furnace will remain in balance, and the furnace air pressure will change. On the contrary, when the amount of suction air does not increase, increasing the amount of air supply will cause positive pressure in the furnace.
During operation, even when the opening of the baffle for adjusting the air supply and the draft is kept constant, because there is always a small change in the combustion conditions, the furnace air pressure is always pulsating, which is reflected in the furnace air pressure gauge. The pointer often shakes slightly around the control.
When the combustion is unstable, the furnace wind pressure will produce a strong pulsation, and the pointer of the furnace air pressure gauge will correspondingly shake violently. The appearance of this phenomenon is often a sign of fire fighting. At this time, we must strengthen the monitoring of meter changes and check the combustion situation in the furnace, analyze the reasons, and make appropriate adjustments and treatments in a timely manner.
When the flue gas flows through the flue and various heating surfaces, various resistances will be generated. These resistances are overcome by the pressure head of the induced draft fan; at the same time, because the heating surface and the flue are on the inlet side of the induced draft fan, Therefore, the negative pressure in the flue along the flue gas flow is gradually increasing.
The resistance generated when the flue gas flows is proportional to the drag coefficient and the flue gas severity, and to the square of the flue gas flow rate. Therefore, the negative pressure in the flue along the flue gas flow is gradually increasing.
The resistance generated when the flue gas flows is proportional to the drag coefficient and the flue gas severity, and to the square of the flue gas flow rate. Therefore, when the boiler load, fuel and air volume change, as the flue gas flow rate changes, the negative pressure also changes accordingly. Therefore, under different loads, the flue gas pressure in the flue of each part of the boiler is different. As the boiler load increases, the negative pressure in each part of the flue increases accordingly; otherwise, the negative pressure in each part decreases accordingly.
When slagging and ash accumulation occur on the heating surface tube bundles and cause partial clogging, the flue gas flow rate increases due to the decrease of the channel, so that the resistance of the flue gas flow through this part of the tube bundles is greater, so the negative pressure value and the pressure difference Increase accordingly.
Therefore, to monitor the working conditions of the flue, it is necessary not only to give the necessary attention to the flue gas temperature, but also to the negative pressure changes in the flue gas everywhere.
Under normal circumstances, the furnace wind pressure and the negative pressure of each part of the flue have a broad range of changes. Therefore, if there is any abnormal change in their indication value during operation, it should be analyzed to check the reason for timely treatment.
3. Adjustment of induced draft fan
The measurement point of the furnace air pressure gauge is usually set at the upper part of the furnace close to the outlet of the furnace roof. For negative pressure combustion boilers, the negative pressure is required to maintain 20-30Pa during normal operation. In order to maintain the normal negative pressure of the boiler, it is necessary to adjust the induced air.
The adjustment method of the induced wind is basically adjusted by changing the opening of the inlet baffle of the induced draft fan through the electric transmission device.
For the operation mode of the induced draft fan, its rationality should be considered according to the size of the boiler load and the working characteristics of the fan. In order to ensure personal safety, when the operating personnel are performing ash removal, soot blowing, cleaning coke slag or observing the combustion situation in the furnace, the negative pressure of the furnace chamber should be kept higher than the normal value.
Hengstar designed item Industrial Stretched Bar series LCD Display customized for different display resolutions, it is especially for industrial application, provide high quality image, the structure solid, rugged 15mm Aluminum front frame,3mm Aluminum chassis, strengthen the organic board protection, can be easily mounted touch screen, tempered glass display surface box, avoid dust, waterproof, avoid vibration.
Stretched Display,Digital Signage Display,Digital Display Board,Digital Advertising Screen
Shenzhen Hengstar Technology Co., Ltd. , https://www.angeltondal.com