Coal-fired power plants, as the main part of my country's power supply sources, have caused serious air pollution problems. Under the background of energy conservation and emission reduction, major coal-fired power plants in my country have adopted various measures to reduce the emission indicators of nitrogen oxides. Among them, the most widely used is the low nitrogen retrofit burner. In this paper, the impact of low-nitrogen burner transformation on boiler operation is analyzed, and targeted solutions are given.
Under the requirements of environmental protection policies, the industry is now also attaching great importance to energy-saving and emission-reduction measures. Low-nitrogen combustion technology has certain advantages in environmental protection, but at the same time it also has a certain impact on the operation of boilers. Therefore, when new environmental protection technologies cause problems In terms of treatment measures, further strengthen and strive for the largest environmental protection mechanism for the sustainable development of the industry. This article discusses the relevant content, which has certain practical significance.
1. Analysis of the connotation of the burner
The burner is the main combustion equipment of the boiler in the fuel-fired power plant, and the burner is located on the four corners of the boiler furnace or on the wall. The burner will spray all kinds of fuel and air necessary for combustion into the furnace through a certain method, and the fuel and air will be fully mixed in the furnace, and will ignite rapidly and maintain stable combustion under a certain airflow structure . The burners used today are electromechanical equipment with a relatively high degree of automation. The burners mainly have five systems: air supply, ignition, monitoring, fuel and electronic control systems.
According to the type of fuel, burners can be divided into pulverized coal burners, gas burners and oil burners. Among them, the pulverized coal burner uses primary air and secondary air to inject pulverized coal fuel into the furnace, and forms a special airflow structure while uniformly mixing fuel and air, so that the fuel can be stably ignited and completely burned in the furnace. The ignitable characteristics of pulverized coal flow are enhanced by utilizing the swirling jet of secondary air to form a recirculation zone that is favorable for ignition, and the strong mixing in the swirling jet and between the swirling jet and the surrounding medium. A tongue-shaped baffle is installed at the entrance of the secondary air volute to adjust the swirling strength of the airflow. The volute pulverized coal burner has a simple structure and has a good effect on burning bituminous coal and lignite, and can also be used for burning lean coal.
2. Analysis of the impact of low nitrogen burner transformation on boilers
2.1 Influence of Combustion Stability
The stability of the boiler is reflected in many aspects, the most important of which is the stability of the temperature and the stability during operation. The low-nitrogen burner is equipped with a combination of thick and light at the primary air outlet, and uses technologies such as heat reflux relay combustion. During the combustion process, it is designed according to the principle of thermal and dynamic asymmetry, so that the pulverized coal at the nozzle is pyrolyzed and recombined with the center of the boiler. The jet flow and large vortex are connected, and the higher reflux rate of the heat return carbon powder makes the residence time longer, which increases the heat generated by combustion in the ring vortex, and the temperature rise affects the operation of the boiler.
The low-nitrogen transformation of the boiler also controls the amount of oxygen. During the combustion process, oxygen needs to meet the combustion conditions to generate heat. Since the amount of oxygen is controlled, the generation of heat is also inhibited, which affects the operation of the boiler. The existence of the two operating modes affects the stable operation of the boiler.
2.2 Environmental influence inside the boiler
The nozzle in the low-nitrogen burner is lower than that of the traditional burner. Therefore, the flame generated by the fuel also moves during the operation of the boiler. The reduction of the combustion area will make the boiler less accepting of the temperature, and the inside of the boiler The resulting pressure situation has also changed, and there will be some incongruous phenomena. The transformation of low nitrogen burner equipment has also changed the components of the boiler, and different conditions will occur in operation. The transformation of the low-nitrogen burner has affected the amount of oxygen inside the boiler to a certain extent. Usually, there will be a maximum operating oxygen amount and a minimum operating oxygen amount. Changes and changes in the degree of combustion cause changes in the internal and external pressure of the boiler, changing the internal environment, and making relevant personnel need to adjust and control the amount of oxygen, which directly causes the air supply work to be unable to be adjusted in time, and the boiler cannot continue to operate stably.
2.3 Influence on boiler reheating air temperature
After the transformation of the low-nitrogen burner, the elevation of the original burner is moved down, which has a great impact on the reheating temperature. After the transformation of the low-nitrogen burner, due to the slow coordination of the unit, the tracking and adjustment of the boiler pressure cannot keep up, which is easy to cause The phenomenon of overshoot makes the variation of temperature larger. The modified low-nitrogen burner has a set of oscillating burners. When the nozzles swing up, the temperature of the steam will rise, and when the nozzles swing down, the temperature will drop. However, because there is only one set of oscillating burners, the temperature adjustment speed is limited, and the adjustment time Too long plus the air ratio is controlled by low oxygen conditions, affecting the efficiency of the machine. In order to ensure that the boiler outlet temperature is within the specified range and the load is low, it is necessary to use a pulverizing system, which will cause the temperature of the heating surface to be too high, and it is difficult to keep the outlet temperature within the specified range without overheating, which affects the boiler. running.
2.4 Influence on furnace coking
Although measures such as horizontal double zones, vertical grading, wall-adhering wind and upwind jet flow were adopted during the transformation of the low-nitrogen burner to control the coking of the heating surface, coking can still be found at the burner nozzle during operation , especially when starting the lower pulverizing system, it will significantly affect the negative pressure, indicating that the combustion zone is not in good condition, and because the main combustion zone is anoxic, there will be coking on the cold wall near the burner, and it is serious. Moreover, coke loss often occurs during load reduction, which deteriorates the main combustion zone and affects the operation of the boiler.
2.5 Impact on slag combustibles
The modified low-nitrogen burner, although the output of NO has been reduced, but also increased slag combustibles. The low-nitrogen combustion technology uses low-temperature and low-oxygen combustion. The more the temperature in the combustion zone drops, the greater the impact on the pulverized coal fire. The lower the oxygen content in the combustion zone, the lower the burnout ability of the pulverized coal, and the longer the combustion process. In order to increase the slag combustibles, and the change of the nozzle area of some burners delays the mixed air, which is not conducive to the air flow of the pulverized coal in the boiler, so that the combustion is incomplete and increases the slag combustibles. The continuous increase of the slag combustibles will wear the tail of the boiler increase, thereby reducing the service life of the boiler.
3. Analysis of specific transformation measures for low nitrogen burners
3.1 Transformation design of primary wind
1) In this renovation, the primary winds of A, B, C, D and E floors are all replaced, and the upper and lower parts are arranged in the form of jets with different shades.
2) The thick-thin separation adopts the primary air elbow inertial separation combined with the shutter separation device of the pulverized coal air chamber.
3) Add a corrugated stable combustion body to the nozzle of the primary air, and increase the return flow of the flue gas. The side of the blunt body facing the fire adopts a special electrode surfacing process to achieve high temperature resistance and wear resistance.
4) Renovate and design the elbow of the primary air: reset and replace all the elbows of the primary air, and use low-resistance space steel plates and elbows with ceramic inner walls to match the original pulverized coal fuel pipeline flanges connect.
3.2 Transformation design of secondary air
1) The secondary air nozzle in the main combustion area is smaller than before the transformation, and an included angle of 3° is maintained between the jet flow direction and the primary air.
2) The secondary air is still taken from the original wind box.
3) Connect the original upper and lower large air boxes in the main combustion area.
3.3 Retrofit design of overburned air
The transformation of the overburning air is mainly to add four layers of overburning air equipment to the upper part of the main burner and at a distance of about 6.99m from the previous wind scale. On the top of the big wind box, the blown wind box is redesigned and installed on the walls on both sides, and the connection method is changed to the same connection method as the big wind box of the main burner.
The bellows pipe of the overfired air is extended to the elevation of the overfired air bellows, the air duct is connected with the baffle bellows of the overfired air through the overburned air, and the overburned air is controlled by the expansion joint made of additional anti-wear lining stainless steel. The thermal expansion of the expansion joint is compensated for expansion, and the wall thickness of the stainless steel expansion joint must exceed fifteen millimeters.
The nozzles of the overburning air are arranged in the form of multiple nozzles, and the overburning air nozzles in the form of vertical and horizontal multi-directional swings are used. For the control method, the swinging in the vertical direction should be controlled in the form of remote control, and the horizontal swinging direction should be controlled manually on the spot. .
Renovation of the overburning air fixing device: the modification of the overburning air fixing device adopts the same link fixing method as the original burner.
Renovation in heat preservation: The transformation of the heat preservation method of the overfired air is the same as the heat preservation method adopted by the main burner. That is, the newly added overfire air wind box and the connected air duct are wrapped with aluminum silicate plates, and corrugated plates are installed outside.
epilogue
To sum up, when the boiler is in operation, its performance will be affected by many factors. Although the transformation of the low-nitrogen burner has a certain impact on the operation of the boiler, in order to make the energy clean and reduce the harm to the environment, it is still necessary to It is necessary to optimize the transformation of low-nitrogen burners in combination with the actual situation. It is also possible to standardize the transformation process of low-nitrogen burners to improve the reliability of boiler operation and improve the transformation technology of low-nitrogen burners as a whole.
Coal-fired power plants, as the main part of my country's power supply sources, have caused serious air pollution problems. Under the background of energy conservation and emission reduction, major coal-fired power plants in my country have adopted various measures to reduce the emission indicators of nitrogen oxides. Among them, the most widely used is the low nitrogen retrofit burner. In this paper, the impact of low-nitrogen burner transformation on boiler operation is analyzed, and targeted solutions are given.
Under the requirements of environmental protection policies, the industry is now also attaching great importance to energy-saving and emission-reduction measures. Low-nitrogen combustion technology has certain advantages in environmental protection, but at the same time it also has a certain impact on the operation of boilers. Therefore, when new environmental protection technologies cause problems In terms of treatment measures, further strengthen and strive for the largest environmental protection mechanism for the sustainable development of the industry. This article discusses the relevant content, which has certain practical significance.
1. Analysis of the connotation of the burner
The burner is the main combustion equipment of the boiler in the fuel-fired power plant, and the burner is located on the four corners of the boiler furnace or on the wall. The burner will spray all kinds of fuel and air necessary for combustion into the furnace through a certain method, and the fuel and air will be fully mixed in the furnace, and will ignite rapidly and maintain stable combustion under a certain airflow structure . The burners used today are electromechanical equipment with a relatively high degree of automation. The burners mainly have five systems: air supply, ignition, monitoring, fuel and electronic control systems.
According to the type of fuel, burners can be divided into pulverized coal burners, gas burners and oil burners. Among them, the pulverized coal burner uses primary air and secondary air to inject pulverized coal fuel into the furnace, and forms a special airflow structure while uniformly mixing fuel and air, so that the fuel can be stably ignited and completely burned in the furnace. The ignitable characteristics of pulverized coal flow are enhanced by utilizing the swirling jet of secondary air to form a recirculation zone that is favorable for ignition, and the strong mixing in the swirling jet and between the swirling jet and the surrounding medium. A tongue-shaped baffle is installed at the entrance of the secondary air volute to adjust the swirling strength of the airflow. The volute pulverized coal burner has a simple structure and has a good effect on burning bituminous coal and lignite, and can also be used for burning lean coal.
2. Analysis of the impact of low nitrogen burner transformation on boilers
2.1 Influence of Combustion Stability
The stability of the boiler is reflected in many aspects, the most important of which is the stability of the temperature and the stability during operation. The low-nitrogen burner is equipped with a combination of thick and light at the primary air outlet, and uses technologies such as heat reflux relay combustion. During the combustion process, it is designed according to the principle of thermal and dynamic asymmetry, so that the pulverized coal at the nozzle is pyrolyzed and recombined with the center of the boiler. The jet flow and large vortex are connected, and the higher reflux rate of the heat return carbon powder makes the residence time longer, which increases the heat generated by combustion in the ring vortex, and the temperature rise affects the operation of the boiler.
The low-nitrogen transformation of the boiler also controls the amount of oxygen. During the combustion process, oxygen needs to meet the combustion conditions to generate heat. Since the amount of oxygen is controlled, the generation of heat is also inhibited, which affects the operation of the boiler. The existence of the two operating modes affects the stable operation of the boiler.
2.2 Environmental influence inside the boiler
The nozzle in the low-nitrogen burner is lower than that of the traditional burner. Therefore, the flame generated by the fuel also moves during the operation of the boiler. The reduction of the combustion area will make the boiler less accepting of the temperature, and the inside of the boiler The resulting pressure situation has also changed, and there will be some incongruous phenomena. The transformation of low nitrogen burner equipment has also changed the components of the boiler, and different conditions will occur in operation. The transformation of the low-nitrogen burner has affected the amount of oxygen inside the boiler to a certain extent. Usually, there will be a maximum operating oxygen amount and a minimum operating oxygen amount. Changes and changes in the degree of combustion cause changes in the internal and external pressure of the boiler, changing the internal environment, and making relevant personnel need to adjust and control the amount of oxygen, which directly causes the air supply work to be unable to be adjusted in time, and the boiler cannot continue to operate stably.
2.3 Influence on boiler reheating air temperature
After the transformation of the low-nitrogen burner, the elevation of the original burner is moved down, which has a great impact on the reheating temperature. After the transformation of the low-nitrogen burner, due to the slow coordination of the unit, the tracking and adjustment of the boiler pressure cannot keep up, which is easy to cause The phenomenon of overshoot makes the variation of temperature larger. The modified low-nitrogen burner has a set of oscillating burners. When the nozzles swing up, the temperature of the steam will rise, and when the nozzles swing down, the temperature will drop. However, because there is only one set of oscillating burners, the temperature adjustment speed is limited, and the adjustment time Too long plus the air ratio is controlled by low oxygen conditions, affecting the efficiency of the machine. In order to ensure that the boiler outlet temperature is within the specified range and the load is low, it is necessary to use a pulverizing system, which will cause the temperature of the heating surface to be too high, and it is difficult to keep the outlet temperature within the specified range without overheating, which affects the boiler. running.
2.4 Influence on furnace coking
Although measures such as horizontal double zones, vertical grading, wall-adhering wind and upwind jet flow were adopted during the transformation of the low-nitrogen burner to control the coking of the heating surface, coking can still be found at the burner nozzle during operation , especially when starting the lower pulverizing system, it will significantly affect the negative pressure, indicating that the combustion zone is not in good condition, and because the main combustion zone is anoxic, there will be coking on the cold wall near the burner, and it is serious. Moreover, coke loss often occurs during load reduction, which deteriorates the main combustion zone and affects the operation of the boiler.
2.5 Impact on slag combustibles
The modified low-nitrogen burner, although the output of NO has been reduced, but also increased slag combustibles. The low-nitrogen combustion technology uses low-temperature and low-oxygen combustion. The more the temperature in the combustion zone drops, the greater the impact on the pulverized coal fire. The lower the oxygen content in the combustion zone, the lower the burnout ability of the pulverized coal, and the longer the combustion process. In order to increase the slag combustibles, and the change of the nozzle area of some burners delays the mixed air, which is not conducive to the air flow of the pulverized coal in the boiler, so that the combustion is incomplete and increases the slag combustibles. The continuous increase of the slag combustibles will wear the tail of the boiler increase, thereby reducing the service life of the boiler.
3. Analysis of specific transformation measures for low nitrogen burners
3.1 Transformation design of primary wind
1) In this renovation, the primary winds of A, B, C, D and E floors are all replaced, and the upper and lower parts are arranged in the form of jets with different shades.
2) The thick-thin separation adopts the primary air elbow inertial separation combined with the shutter separation device of the pulverized coal air chamber.
3) Add a corrugated stable combustion body to the nozzle of the primary air, and increase the return flow of the flue gas. The side of the blunt body facing the fire adopts a special electrode surfacing process to achieve high temperature resistance and wear resistance.
4) Renovate and design the elbow of the primary air: reset and replace all the elbows of the primary air, and use low-resistance space steel plates and elbows with ceramic inner walls to match the original pulverized coal fuel pipeline flanges connect.
3.2 Transformation design of secondary air
1) The secondary air nozzle in the main combustion area is smaller than before the transformation, and an included angle of 3° is maintained between the jet flow direction and the primary air.
2) The secondary air is still taken from the original wind box.
3) Connect the original upper and lower large air boxes in the main combustion area.
3.3 Retrofit design of overburned air
The transformation of the overburning air is mainly to add four layers of overburning air equipment to the upper part of the main burner and at a distance of about 6.99m from the previous wind scale. On the top of the big wind box, the blown wind box is redesigned and installed on the walls on both sides, and the connection method is changed to the same connection method as the big wind box of the main burner.
The bellows pipe of the overfired air is extended to the elevation of the overfired air bellows, the air duct is connected with the baffle bellows of the overfired air through the overburned air, and the overburned air is controlled by the expansion joint made of additional anti-wear lining stainless steel. The thermal expansion of the expansion joint is compensated for expansion, and the wall thickness of the stainless steel expansion joint must exceed fifteen millimeters.
The nozzles of the overburning air are arranged in the form of multiple nozzles, and the overburning air nozzles in the form of vertical and horizontal multi-directional swings are used. For the control method, the swinging in the vertical direction should be controlled in the form of remote control, and the horizontal swinging direction should be controlled manually on the spot. .
Renovation of the overburning air fixing device: the modification of the overburning air fixing device adopts the same link fixing method as the original burner.
Renovation in heat preservation: The transformation of the heat preservation method of the overfired air is the same as the heat preservation method adopted by the main burner. That is, the newly added overfire air wind box and the connected air duct are wrapped with aluminum silicate plates, and corrugated plates are installed outside.
epilogue
To sum up, when the boiler is in operation, its performance will be affected by many factors. Although the transformation of the low-nitrogen burner has a certain impact on the operation of the boiler, in order to make the energy clean and reduce the harm to the environment, it is still necessary to It is necessary to optimize the transformation of low-nitrogen burners in combination with the actual situation. It is also possible to standardize the transformation process of low-nitrogen burners to improve the reliability of boiler operation and improve the transformation technology of low-nitrogen burners as a whole.