What are the characteristics of FDI-type burners?

The outlet flow of a direct-flow burner is a straight jet, characterized by a small diffusion angle and a long range. For a single jet alone, it has less surrounding suction effect compared to a swirl-flow burner, and there is no central recirculation flow, which is unfavorable for ignition. However, the DC burner uses a four-corner arrangement with tangential combustion; the airflow within the furnace is created by the four jets from the corner burners, which together form a rotating airflow. The coal powder stream ejected by the burner transforms into highly heated flue gas as it passes through the central area of the combustion chamber; part of this gas is directly added to the base of the jet from the adjacent burner, thereby raising its temperature and triggering combustion there. The self-suction of the jet and the characteristic of mutual ignition between adjacent jets enable the four-corner arrangement and tangential combustion mode of DC burners to exhibit excellent ignition performance. Another advantage of DC burners is the way in which the secondary air is supplied. Since the secondary air inlets are relatively independent of the primary air inlets and can be arranged freely, various configurations are possible. This allows control over the timing of mixing between the secondary and primary air, meeting the different mixing requirements of various fuels and thereby improving the ignition performance. Furthermore, due to the slow attenuation of the primary air and the strengthening effect of the secondary air, mixing of the coal powder airflow occurs intensively in the later stages. Coupled with the airflow rotation within the furnace, the coal powder rises spirally upward, covering a long distance; as a result, the tangential combustion mode of direct-flow burners also features good burnout efficiency. The main difference among various direct-flow burners lies in the arrangement of their primary and secondary air inlets. A brief introduction to the air inlet arrangements of several types of direct-current burners. I. The primary and secondary air are arranged at intervals; after ignition, the secondary air mixes in quickly, which meets the requirement of coal with high volatile content for timely mixing of secondary air. I. The distance between the primary and secondary air inlets can be determined based on the properties of the coal type; for high-quality bituminous coal, this distance can be set to zero. This burner is a typical bituminous coal burner. DC burner with perimeter wind. Its characteristic is that the primary air is relatively concentrated, thereby increasing the local concentration of coal powder; the distance between the primary and secondary airs is large, resulting in delayed mixing, which helps to improve the ignition performance. The primary air inlet is rectangular in shape, giving the coal powder airflow a longer perimeter in contact with the flame, which is favorable for ignition. Surrounding the primary air inlet is peripheral air, but this air has a low volume flow rate yet a high wind speed, serving to cool the primary air nozzles. There are 2 upper secondary air inlets, which allow for graded air distribution and facilitate adjustment. This burner is used to burn anthracite, taking into account its characteristics of low volatility, difficulty in ignition, high degree of carbonization, and difficulty in complete combustion. When a DC burner is arranged at the four corners for circular combustion, the optimal cross-section for the combustion chamber is square. However, due to reasons related to the boiler’s structural design, a rectangular cross-section is often used as well; in such cases, the ratio of width to depth is close to 1, generally not exceeding 1.2. The diameter of the hypothetical cut circle should be determined by taking into account both the ignition properties and the slagging properties of the fuel. When the diameter of the tangent circle is large, the flame at the center of the furnace rotates intensely; the flame that rushes in is close to the base of the air inlet, and this may even cause the airflow to stick to the wall, with the flame hitting the water-cooled walls and leading to slag formation. If the diameter of the tangent circle is too small, the flame at the center of the combustion chamber becomes smaller, which is not favorable for combustion.

The outlet flow of a direct-flow burner (FDI type burner) is a straight jet, characterized by a small diffusion angle and a long range. For a single jet alone, it has less surrounding suction effect compared to a swirl burner, and there is no central recirculation flow, which is unfavorable for ignition. However, the DC burner uses a four-corner arrangement with tangential combustion; the airflow within the furnace is created by the four jets from the corner burners, which together form a rotating airflow.