1 stream burner
There are two situations in which the outlet airflow of the swirling burner is a rotating jet airflow, one is that both the primary air powder airflow and the secondary air are rotating, and the other is that the secondary air is rotating and the primary air is direct current. According to the form of the swirl parts that promote the rotation of the airflow, there are generally two types: the volute type swirl burner and the vane type swirl burner. The volute swirl burner can be divided into double volute swirl burner and single volute swirl burner
1.1 Double volute swirl burner
The primary and secondary air of the double volute swirl burner are both generated by the flow in the volute to generate rotation, and the rotation directions of the two jets are the same. The large volute is the secondary air, and the small volute is the primary air. There is a central pipe in the center of the burner, and an oil nozzle can be arranged in the pipe. A tongue-shaped baffle is installed at the secondary air inlet to adjust the swirl intensity of the secondary air. Since the primary and secondary air are both swirling airflows, they diffuse into a hollow cone annular airflow after entering the combustion chamber. Under the action of air entrainment, the inner and outer surfaces of the hollow cone will be heated by high-temperature flue gas. The adjustment range of the swirl intensity of this kind of burner is small, and when the coal type changes, it may be easy to slagging due to the poor adjustment of the flame position. In addition, the resistance of the primary and secondary air is large, and the distribution of pulverized coal in the primary air flow is uneven, which is also the shortcoming of this burner.
1.2 Single volute swirl burner
The primary air of the single volute swirl burner is direct current, and the secondary air flow is generated by the volute and enters the combustion chamber along the annular passage. The primary air enters the combustion chamber from the central air duct, and a mushroom-shaped diffuser cone is installed at the outlet of the primary air. The diffusion cone can be moved back and forth by the hand wheel and the pull rod, thereby changing the diffusion angle of the primary air powder airflow, but the diffusion cone is located in the high-temperature flue gas recirculation area, which is easy to slagging or burn out.
1.3 vane type swirl burner
Axially movable vane type swirl burner. Its primary wind is direct current and the secondary wind is rotating. There is a central air pipe in the center of the burner, and the primary air annular passage is outside the central air pipe, and an oil nozzle can be arranged in the central air pipe. When the secondary air flow passes through the secondary air impeller, it is guided by the axial blades and rotates. The secondary air impeller can move axially through the adjustment mechanism, thereby adjusting the swirl intensity of the secondary air. The secondary air channel is a ring-conical sleeve, and the secondary air impeller is also a ring-conical impeller installed in the sleeve. The radial gap between the impeller and the ring-shaped channel can be changed by moving the impeller axially with the pull rod on the impeller. The air flow flowing through the radial gap of the annular channel is a non-rotating direct air flow, so adjusting the position of the impeller can change the ratio of the rotating air flow to the direct air flow, thereby achieving the purpose of adjusting the swirl intensity of the secondary air flow. Although the primary air is direct current, it can be adjusted by the tongue-shaped baffle installed on the primary air shell, so that the air flow at the outlet of the primary air can be expanded to a certain extent. The characteristic of the swirl burner is that the expansion angle of the airflow is large, and the recirculation zone in the center can entrain the high-temperature flue gas from the depth of the combustion chamber and heat the root of the pulverized coal airflow, which is beneficial to ignition; but on the other hand, The distance between the secondary air and the primary air is very close, and the mixing of the primary and secondary air is earlier, which increases the heat required for the fire to heat up and is unfavorable to the fire. The swirling effect of the swirling jet disappears quickly, and the maximum axial airflow velocity decays quickly, so for coals with low volatile content or medium volatile content and high ash content, the early mixing of the swirling flow burner appears to be early, while the late The mixing is not strong enough, so it is easy to cause unstable fire or difficult embers. The range of the swirling burner is small, the flame is thick and short, and the cross-sectional shape of the combustion chamber is not required to be square or close to a square, and it can be flat and long. The combustion chamber with a rectangular cross-section has a small depth, which is conducive to the arrangement of auxiliary equipment such as air preheaters and blowers at the rear of the boiler. The common layout of swirl burners: front wall layout and front and rear wall hedge or staggered layout. On large-capacity boilers, they are often arranged in multiple rows and multiple layers.
2 once-through burners
The outlet airflow of the once-through burner is a straight jet, which is characterized by a small diffusion angle and a long range. As far as the single jet is concerned, it has a smaller entrainment effect than the swirling burner and has no central backflow, which is very important for ignition. unfavorable. However, the once-through burner adopts a four-corner arrangement and a tangential circular combustion method. The air flow in the furnace is jointly formed by the four jets of the four-corner burner, which generally forms a rotating air flow. The pulverized coal flow from the burner passes through the middle area of the combustion chamber and becomes intensely combusted high-temperature flue gas, a part of which is directly supplemented to the root of the adjacent burner jet, so that the temperature of the adjacent burner can be ignited. The entrainment of the jet itself and the mutual ignition of adjacent corners make the four-corner arrangement of the once-through burner and the tangential circle combustion method have good ignition performance.
Another feature of the once-through burner is that the way the secondary air is fed is that the secondary air port and the primary air port are relatively independent and freely arranged with each other, and can be arranged in various forms to control the mixing of the secondary air and the primary air. Sooner or later, meet the different requirements of different fuels for mixing, and improve the ignition performance. In addition, due to the slow attenuation of the primary wind and the strengthening effect of the secondary wind.
Another feature of the once-through burner is the feeding method of the secondary air. Since the secondary air port and the primary air port are relatively independent and arranged freely with each other, various forms can be changed in the arrangement to control the mixing of the secondary air and the primary air. Sooner or later, it can meet the different requirements of different fuels for mixing and improve the ignition performance. In addition, due to the slow attenuation of the primary air and the strengthening effect of the secondary air, the late mixing of the pulverized coal airflow is strong. In addition, the airflow in the furnace rotates, and the pulverized coal spirals up in the furnace, and the passing distance is long. Round combustion has the characteristics of good embers. The main difference between various once-through burners lies in the arrangement of the primary and secondary air outlets. Briefly introduce the tuyere layout of several once-through burners. First, the secondary air is arranged at intervals, and the secondary air mixes in quickly after a fire, which is suitable for the high volatile coal type to the timely mixing of the secondary air. The distance between the primary and secondary air outlets can be determined according to the nature of the coal type, and the distance for high-quality bituminous coal can be designed to be zero. This burner is a typical bituminous coal burner. Once through burners with perimeter air. Its characteristics are that the primary air is relatively concentrated, which increases the local pulverized coal concentration; the distance between the primary and secondary air is large, and the mixing is delayed to improve the ignition performance; the primary air outlet is narrow and rectangular, and the perimeter of the pulverized coal airflow is long. It is good for fire; there is peripheral wind around the primary air outlet, but the peripheral air volume is not large and the wind speed is high, which has the effect of cooling the primary air nozzle. There are 2 upper and secondary air outlets, which can carry out graded air distribution, which is conducive to adjustment. This burner is used to burn anthracite to adapt to the characteristics of anthracite with low volatile content, difficulty in ignition, high degree of carbonization, and difficulty in burning out. When the once-through burner is arranged with four corners for tangential combustion, the best cross-section of the combustion chamber is a square, but in fact, due to the structural design of the boiler, a rectangular cross-section is often used, but the ratio of its width to depth is close to 1, generally No more than 1.2. The diameter of the imaginary tangent circle should be considered comprehensively in combination with the ignition performance and slagging performance of the fuel. When the diameter of the tangent circle is large, the flame in the center of the furnace rotates strongly, and the washed flame is close to the root of the tuyere, which may even cause the airflow to stick to the wall, and the flame rushes to the water wall to cause slagging; the diameter of the tangent circle will make the flame in the center of the combustion chamber smaller , which is not good for combustion.