In asphalt mixers, the combustion equipment for drying aggregates generally uses mature products. Whether the heavy oil burns completely in the drying cylinder has a lot to do with the adjustment of the combustion process.
The debugging of the combustion system and the quality of the working conditions are ultimately reflected and determined by a series of intuitive features such as the color, brightness, and shape of the flame. For industrial, mining, and engineering construction site equipment, the judgment of whether the combustion system is working normally and whether it needs to be adjusted can only be carried out by observing the flame, which is the most concise and effective way.
When the fuel burns in the drying cylinder, the flame seen through the observation hole at the front of the cylinder should be: the center of the flame is in the middle of the drying cylinder, the flame is evenly distributed around and does not touch the cylinder wall, the filling degree is high, and the distance between the ignition point and the tuyere (nozzle) is appropriate (Do not burn the nozzle); the length of the flame is about 1/3 of the length of the drying cylinder, basically filling the entire combustion area, not too short to affect the efficiency of copying materials, and not too long to directly touch the material curtain to cause burnt paste; flame The center is pale orange, white and bright evenly, the entire flame outline is clear, there is no snowflake spark in the outer ring, the smoke outside the flame is transparent, and the material plate of the tube wall is clearly visible; the flame in the tube chamber is stable, white-orange, and generally has a "rumbling" sound , the flame has no beating or abnormal noise.
Flame adjustment mainly adjusts the position of ignition point, flame shape, color (complete combustion), etc.
1 Adjustment of ignition point
The ignition point of the oil mist should be close to the nozzle and there should be no flashback. The closeness of the ignition point is conducive to the complete combustion and stability of the oil mist, but it is easy to burn the nozzle if it is too close.
Bore temperature, oil type, atomization quality, air volume, wind speed, and heavy oil temperature will all affect the distance of the ignition point. When adjusting, it is necessary to analyze and determine the cause of improper ignition point, and take targeted measures to adjust the parameters. When the oil product, pressure, temperature are stable, and there is no obvious change in the atomization quality, the position of the ignition point is mainly determined by the wind speed and air distribution, that is, the position of the deflector; pushing in will reduce the air speed of the nozzle and make the ignition point front; otherwise , will delay the ignition point. When the oil pressure and oil temperature are too low or the aperture of the atomizing sheet is too large (worn or improperly selected), poor oil atomization will also delay the ignition point. Generally speaking, when the system works normally, the ideal ignition point can be obtained by adjusting the position of the deflector in a small range, that is, the position of the recirculation zone moves with the deflector.
2 Blast volume adjustment
Increasing the blast volume within a certain range can improve the mixing degree of oil mist and air, which is beneficial to combustion. However, too much air volume will reduce the temperature of the barrel, increase incomplete combustion loss and exhaust heat loss; insufficient air volume will cause incomplete combustion, resulting in dark red flames and increased carbon deposits.
Generally, road construction sites judge whether the air volume is suitable or not and whether adjustment is required based on the flame situation. If the combustion condition is not good or the atomizer with a different aperture has been replaced, the minimum opening of the damper of the air duct should be adjusted to achieve normal combustion. The corresponding relationship of air-oil ratio can be properly corrected. The usual method is to adjust the small fire damper to make it fit properly, and then adjust the height of each screw accordingly to form a smooth curve (equivalent to the cam principle); or adjust it first The damper of the minimum fire and the maximum fire, and then adjust the height of all the screw rods in the middle accordingly to form a smooth curve. This can generally ensure that different flame sizes have a more suitable air volume.
The feeding amount, rotation direction and rotation intensity of the wind at the root of the flame are all controlled by the deflector. The main function of the deflector is to strengthen the mixing of oil mist and air before ignition to form a suitable high-temperature recirculation zone to ensure smooth ignition of oil mist. Each vane of the deflector is inclined at a certain angle, so when the airflow passes through, a swirling airflow is formed, and the rotation of the airflow increases the expansion angle of the jet oil flow, and at the same time strengthens the mixing of oil and gas. The size and position of the high-temperature recirculation zone should be appropriate. If it is too large, it will extend to the nozzle, which is not only easy to burn the nozzle, but also unfavorable for early oil and gas mixing; if it is too small or the position is too late, the ignition will be delayed and the flame will be elongated. The wind passing through the deflector plays the role of supplying air to the root of the flame (primary air). Adjust the position of the deflector to control the appropriate airflow rotation intensity. Too strong or too weak corresponds to too large or too small of the recirculation zone. not suitable. The size and location of the recirculation zone play a decisive role in the location of the ignition point. When the number of deflector blades is reduced, the recirculation area will be reduced due to the poor flow guiding effect of the blades and the weakening of the airflow rotation, and the combustion situation will deteriorate. Therefore, it is very important to clean up the coking and restore the deformation of the deflector in time.
The deflector can strengthen the airflow turbulence at the burner outlet, which plays a big role in the ease of ignition and the appropriate position. However, this disturbance area is small and disappears quickly. The fundamental measure to strengthen the entire flame mixing is to increase the air velocity. On the one hand, the function of the deflector is to rotate the wind passing through the blades, so that a small part of the airflow at the root of the flame and the center generates a confluence area, and promotes the mixing of the root wind (primary wind) and oil mist; The wind in the circular passage between the pipe and the airflow (most of the airflow of the blower is direct-flow air), uses the characteristics of slow attenuation of the direct-flow wind speed to strengthen the mixing of oil and gas in the later stage, so that the oil and gas can be strongly mixed during the entire combustion process to achieve low-oxygen and complete combustion.
After passing through the deflector, the air duct has a flaring opening, which plays a role in guiding the airflow to a certain extent. The flaring angle also has an influence on the size of the confluence area, and the maximum diameter of the confluence area increases correspondingly when the flaring angle increases. Generally the flaring angle should not exceed 30°, it depends on the shape of the flame.
The air volume of the blower is distributed by the deflector, that is, it is divided into the swirl wind (primary wind or root wind) flowing through the deflector and the straight air (secondary wind) that does not pass through the deflector. The flow rate ratio of the two air streams depends entirely on the structural size of the deflector, which has been designed when the equipment leaves the factory, and generally cannot be changed arbitrarily. When the position of the deflector is at the flaring part of the air duct, what affects the distribution of air volume is the ratio of the diameter of the deflector at the section where the inlet of the deflector is located to the diameter of the air duct. decreases, the swirling wind increases, and the confluence area becomes larger. The function of the center hole of the deflector is to send a small amount of central axial air volume so that the confluence area is not close to the vicinity of the deflector, preventing the flame from burning the deflector and the nozzle. The outlet of the deflector vane is concave inward, which can prevent the end from being polluted, and the adjustment room of the nozzle position is also large, which is conducive to the mixing of air and oil.
When the outlet plane of the deflector is equal to the tuyere, the flame will roll back, and the smoke in the chamber will be turbid, causing the flame detection element to malfunction. As the deflector retracts, the flame becomes shorter and the curling phenomenon is gradually reduced. Generally, the distance between the deflector and the tuyere is about 0.1-0.2 times of the radius, which is more appropriate. When the nozzle is flush with the deflector, the flame also wraps back. When the nozzle is gradually retracted, the curling flame decreases, the flame becomes whiter and brighter, and the length becomes shorter. But when it is too retracted, the root of the flame will be dark, and the smoke in the chamber will be cloudy.
Under normal combustion conditions, the air volume should be reduced as much as possible to achieve low-oxygen combustion to promote complete combustion of heavy oil and reduce corrosion.
3 Induced air regulation
The induced air volume is adjusted according to the change of the fuel injection volume and the air blast volume. When the load changes, the fuel oil volume, air blast volume, and stone dust volume entering the drying cylinder will all change, and the smoke volume produced by combustion will also change. At this time, the air induction must be adjusted so that the drying cylinder chamber still maintains a good negative pressure combustion environment. For example, the combustion system of Marini MAP series asphalt mixer adopts a slight negative pressure combustion environment, and generally requires the negative pressure of the barrel to be kept between 8-15Psi. When the negative pressure is too large, on the one hand, the heat loss of the exhaust gas will be increased, which is very harmful to the prevention of low-temperature corrosion and the formation of carbon deposits, and the flame will be broken; if the negative pressure is too small or positive pressure occurs, the flame and smoke in the barrel will Reverse spraying may even cause equipment burnout and personal accidents. Generally speaking, when the load changes and the air volume needs to be adjusted, in order to avoid positive pressure or lack of oxygen and wind in the barrel chamber, the induced air volume is usually increased first when the load increases, and then the blast volume and fuel volume are increased; otherwise, the load increases. When reducing, reduce the amount of fuel and blowing air first, and then reduce the amount of induced air. The adjustment of the induced air volume is realized by controlling the opening of the induced air damper baffle through the servo motor.
4 Air-oil ratio adjustment
The amount of fuel fed into the combustion system of Marini MAP series asphalt mixers is linked to the blowing air volume. degree curve) increase or decrease synchronously, thereby controlling the size of the flame. It is realized by the synchronous control of the damper damper and the fuel saving valve by the servo motor on the burner, the drive cam and the connecting rod. The opening of the air door is controlled by a set of adjustable jack screws, and the position of the cam controls the opening of the fuel throttle valve. When working, the servo motor drives the cam to rotate through the transmission mechanism of the reducer (changing the opening of the fuel-saving valve), and the cam drives the damper connecting rod (the opening of the damper). As the rotation angle of the cam changes, the opening of the throttle valve and damper changes at the same time, thereby synchronously controlling the blast and fuel supply, and realizing the control of the size of the flame. The temperature change signal is fed back to the blower servo to control the size of the flame, and the wind pressure change signal is fed back to the induced air servo to control the induced air damper to ensure the negative pressure of the cylinder chamber. By weakening or strengthening combustion, the control of negative pressure and temperature is realized accordingly. In order to ensure complete combustion, you can adjust the throttle rod curve or change the initial opening of the throttle valve, or both at the same time to achieve the best air-fuel ratio. Proper coordination of the air-oil ratio is an important condition for realizing low-oxygen combustion. If the damper is too large, the air volume and wind speed will extinguish the flame, making it difficult to burn, and even lead to tar deposition, and there will be a foul smell in the cylinder; too small damper will cause combustion. Insufficient, and even lead to waste, equipment and personal accidents.
5 atomization quality
Good atomization is an important condition for the complete combustion of heavy oil. The appropriate type of fuel should be selected according to the requirements of the atomizer, and the working condition of the atomizer should be checked regularly. The pressure of the oil pump is also the key to affect the atomization. Always pay attention to whether the indication of the oil pressure gauge is within the appropriate pressure range.
In short, there are many factors that affect the combustion conditions of asphalt mixers, but for the combustion system of Marini MAP series asphalt mixers, there are three key links: atomization quality, air volume and deflector position. Inspection and analysis based on specific phenomena in actual work, and targeted measures can generally ensure good combustion.
In asphalt mixers, the combustion equipment for drying aggregates generally uses mature products. Whether the heavy oil burns completely in the drying cylinder has a lot to do with the adjustment of the combustion process.
The debugging of the combustion system and the quality of the working conditions are ultimately reflected and determined by a series of intuitive features such as the color, brightness, and shape of the flame. For industrial, mining, and engineering construction site equipment, the judgment of whether the combustion system is working normally and whether it needs to be adjusted can only be carried out by observing the flame, which is the most concise and effective way.
When the fuel burns in the drying cylinder, the flame seen through the observation hole at the front of the cylinder should be: the center of the flame is in the middle of the drying cylinder, the flame is evenly distributed around and does not touch the cylinder wall, the filling degree is high, and the distance between the ignition point and the tuyere (nozzle) is appropriate (Do not burn the nozzle); the length of the flame is about 1/3 of the length of the drying cylinder, basically filling the entire combustion area, not too short to affect the efficiency of copying materials, and not too long to directly touch the material curtain to cause burnt paste; flame The center is pale orange, white and bright evenly, the entire flame outline is clear, there is no snowflake spark in the outer ring, the smoke outside the flame is transparent, and the material plate of the tube wall is clearly visible; the flame in the tube chamber is stable, white-orange, and generally has a "rumbling" sound , the flame has no beating or abnormal noise.
Flame adjustment mainly adjusts the position of ignition point, flame shape, color (complete combustion), etc.
1 Adjustment of ignition point
The ignition point of the oil mist should be close to the nozzle and there should be no flashback. The closeness of the ignition point is conducive to the complete combustion and stability of the oil mist, but it is easy to burn the nozzle if it is too close.
Bore temperature, oil type, atomization quality, air volume, wind speed, and heavy oil temperature will all affect the distance of the ignition point. When adjusting, it is necessary to analyze and determine the cause of improper ignition point, and take targeted measures to adjust the parameters. When the oil product, pressure, temperature are stable, and there is no obvious change in the atomization quality, the position of the ignition point is mainly determined by the wind speed and air distribution, that is, the position of the deflector; pushing in will reduce the air speed of the nozzle and make the ignition point front; otherwise , will delay the ignition point. When the oil pressure and oil temperature are too low or the aperture of the atomizing sheet is too large (worn or improperly selected), poor oil atomization will also delay the ignition point. Generally speaking, when the system works normally, the ideal ignition point can be obtained by adjusting the position of the deflector in a small range, that is, the position of the recirculation zone moves with the deflector.
2 Blast volume adjustment
Increasing the blast volume within a certain range can improve the mixing degree of oil mist and air, which is beneficial to combustion. However, too much air volume will reduce the temperature of the barrel, increase incomplete combustion loss and exhaust heat loss; insufficient air volume will cause incomplete combustion, resulting in dark red flames and increased carbon deposits.
Generally, road construction sites judge whether the air volume is suitable or not and whether adjustment is required based on the flame situation. If the combustion condition is not good or the atomizer with a different aperture has been replaced, the minimum opening of the damper of the air duct should be adjusted to achieve normal combustion. The corresponding relationship of air-oil ratio can be properly corrected. The usual method is to adjust the small fire damper to make it fit properly, and then adjust the height of each screw accordingly to form a smooth curve (equivalent to the cam principle); or adjust it first The damper of the minimum fire and the maximum fire, and then adjust the height of all the screw rods in the middle accordingly to form a smooth curve. This can generally ensure that different flame sizes have a more suitable air volume.
The feeding amount, rotation direction and rotation intensity of the wind at the root of the flame are all controlled by the deflector. The main function of the deflector is to strengthen the mixing of oil mist and air before ignition to form a suitable high-temperature recirculation zone to ensure smooth ignition of oil mist. Each vane of the deflector is inclined at a certain angle, so when the airflow passes through, a swirling airflow is formed, and the rotation of the airflow increases the expansion angle of the jet oil flow, and at the same time strengthens the mixing of oil and gas. The size and position of the high-temperature recirculation zone should be appropriate. If it is too large, it will extend to the nozzle, which is not only easy to burn the nozzle, but also unfavorable for early oil and gas mixing; if it is too small or the position is too late, the ignition will be delayed and the flame will be elongated. The wind passing through the deflector plays the role of supplying air to the root of the flame (primary air). Adjust the position of the deflector to control the appropriate airflow rotation intensity. Too strong or too weak corresponds to too large or too small of the recirculation zone. not suitable. The size and location of the recirculation zone play a decisive role in the location of the ignition point. When the number of deflector blades is reduced, the recirculation area will be reduced due to the poor flow guiding effect of the blades and the weakening of the airflow rotation, and the combustion situation will deteriorate. Therefore, it is very important to clean up the coking and restore the deformation of the deflector in time.
The deflector can strengthen the airflow turbulence at the burner outlet, which plays a big role in the ease of ignition and the appropriate position. However, this disturbance area is small and disappears quickly. The fundamental measure to strengthen the entire flame mixing is to increase the air velocity. On the one hand, the function of the deflector is to rotate the wind passing through the blades, so that a small part of the airflow at the root of the flame and the center generates a confluence area, and promotes the mixing of the root wind (primary wind) and oil mist; The wind in the circular passage between the pipe and the airflow (most of the airflow of the blower is direct-flow air), uses the characteristics of slow attenuation of the direct-flow wind speed to strengthen the mixing of oil and gas in the later stage, so that the oil and gas can be strongly mixed during the entire combustion process to achieve low-oxygen and complete combustion.
After passing through the deflector, the air duct has a flaring opening, which plays a role in guiding the airflow to a certain extent. The flaring angle also has an influence on the size of the confluence area, and the maximum diameter of the confluence area increases correspondingly when the flaring angle increases. Generally the flaring angle should not exceed 30°, it depends on the shape of the flame.
The air volume of the blower is distributed by the deflector, that is, it is divided into the swirl wind (primary wind or root wind) flowing through the deflector and the straight air (secondary wind) that does not pass through the deflector. The flow rate ratio of the two air streams depends entirely on the structural size of the deflector, which has been designed when the equipment leaves the factory, and generally cannot be changed arbitrarily. When the position of the deflector is at the flaring part of the air duct, what affects the distribution of air volume is the ratio of the diameter of the deflector at the section where the inlet of the deflector is located to the diameter of the air duct. decreases, the swirling wind increases, and the confluence area becomes larger. The function of the center hole of the deflector is to send a small amount of central axial air volume so that the confluence area is not close to the vicinity of the deflector, preventing the flame from burning the deflector and the nozzle. The outlet of the deflector vane is concave inward, which can prevent the end from being polluted, and the adjustment room of the nozzle position is also large, which is conducive to the mixing of air and oil.
When the outlet plane of the deflector is equal to the tuyere, the flame will roll back, and the smoke in the chamber will be turbid, causing the flame detection element to malfunction. As the deflector retracts, the flame becomes shorter and the curling phenomenon is gradually reduced. Generally, the distance between the deflector and the tuyere is about 0.1-0.2 times of the radius, which is more appropriate. When the nozzle is flush with the deflector, the flame also wraps back. When the nozzle is gradually retracted, the curling flame decreases, the flame becomes whiter and brighter, and the length becomes shorter. But when it is too retracted, the root of the flame will be dark, and the smoke in the chamber will be cloudy.
Under normal combustion conditions, the air volume should be reduced as much as possible to achieve low-oxygen combustion to promote complete combustion of heavy oil and reduce corrosion.
3 Induced air regulation
The induced air volume is adjusted according to the change of the fuel injection volume and the air blast volume. When the load changes, the fuel oil volume, air blast volume, and stone dust volume entering the drying cylinder will all change, and the smoke volume produced by combustion will also change. At this time, the air induction must be adjusted so that the drying cylinder chamber still maintains a good negative pressure combustion environment. For example, the combustion system of Marini MAP series asphalt mixer adopts a slight negative pressure combustion environment, and generally requires the negative pressure of the barrel to be kept between 8-15Psi. When the negative pressure is too large, on the one hand, the heat loss of the exhaust gas will be increased, which is very harmful to the prevention of low-temperature corrosion and the formation of carbon deposits, and the flame will be broken; if the negative pressure is too small or positive pressure occurs, the flame and smoke in the barrel will Reverse spraying may even cause equipment burnout and personal accidents. Generally speaking, when the load changes and the air volume needs to be adjusted, in order to avoid positive pressure or lack of oxygen and wind in the barrel chamber, the induced air volume is usually increased first when the load increases, and then the blast volume and fuel volume are increased; otherwise, the load increases. When reducing, reduce the amount of fuel and blowing air first, and then reduce the amount of induced air. The adjustment of the induced air volume is realized by controlling the opening of the induced air damper baffle through the servo motor.
4 Air-oil ratio adjustment
The amount of fuel fed into the combustion system of Marini MAP series asphalt mixers is linked to the blowing air volume. degree curve) increase or decrease synchronously, thereby controlling the size of the flame. It is realized by the synchronous control of the damper damper and the fuel saving valve by the servo motor on the burner, the drive cam and the connecting rod. The opening of the air door is controlled by a set of adjustable jack screws, and the position of the cam controls the opening of the fuel throttle valve. When working, the servo motor drives the cam to rotate through the transmission mechanism of the reducer (changing the opening of the fuel-saving valve), and the cam drives the damper connecting rod (the opening of the damper). As the rotation angle of the cam changes, the opening of the throttle valve and damper changes at the same time, thereby synchronously controlling the blast and fuel supply, and realizing the control of the size of the flame. The temperature change signal is fed back to the blower servo to control the size of the flame, and the wind pressure change signal is fed back to the induced air servo to control the induced air damper to ensure the negative pressure of the cylinder chamber. By weakening or strengthening combustion, the control of negative pressure and temperature is realized accordingly. In order to ensure complete combustion, you can adjust the throttle rod curve or change the initial opening of the throttle valve, or both at the same time to achieve the best air-fuel ratio. Proper coordination of the air-oil ratio is an important condition for realizing low-oxygen combustion. If the damper is too large, the air volume and wind speed will extinguish the flame, making it difficult to burn, and even lead to tar deposition, and there will be a foul smell in the cylinder; too small damper will cause combustion. Insufficient, and even lead to waste, equipment and personal accidents.
5 atomization quality
Good atomization is an important condition for the complete combustion of heavy oil. The appropriate type of fuel should be selected according to the requirements of the atomizer, and the working condition of the atomizer should be checked regularly. The pressure of the oil pump is also the key to affect the atomization. Always pay attention to whether the indication of the oil pressure gauge is within the appropriate pressure range.
In short, there are many factors that affect the combustion conditions of asphalt mixers, but for the combustion system of Marini MAP series asphalt mixers, there are three key links: atomization quality, air volume and deflector position. Inspection and analysis based on specific phenomena in actual work, and targeted measures can generally ensure good combustion.