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1. How should the material of the soot blower tube be selected? The material of the soot blower tube is determined by the flue gas temperature at the location where it is installed. When the flue gas temperature is ≤450°C, the soot-blowing tube is made of boiler carbon steel pipe. When the flue gas temperature is ≤600°C, the soot-blowing tube material is 18-8. When the flue gas temperature is >600°C, the soot-blowing tube material is Cr25Ni20. 2. What specifications are commonly used for soot blowing pipes? To prevent the pipes from bending due to prolonged exposure to flue gases, careful consideration should be given to their diameter and thickness. Japan typically uses three sizes of soot blowing pipes: ϕ 48 × 5mm, ϕ 60 × 5mm, and ϕ 64 × 7mm. Given the conditions in our country, it is generally recommended to use pipes with a diameter of ϕ 50x5mm. 3. What is the typical span of soot blowing pipes? The span of soot blowing pipes must be taken seriously during design and use; otherwise, it can lead to deformation of the pipes, severely affecting the soot blowing process. The span of the soot blowing pipe is usually taken as 1.2 to 1.4 m. 4. What precautions should be taken when installing an electric fixed-rotation soot blower? (1) Ensure smooth drainage. The soot blower is operated at most once per shift, so there is often condensate water throughout the entire steam delivery pipeline. If this water enters the soot-blowing tubes, it will cause severe damage to the furnace tubes and the lining of the convection chamber walls. If the flue gas contains a high amount of sulfur, it will also cause severe corrosion. Therefore, the pipeline must have an appropriate slope, with no horizontal sections, to ensure smooth drainage. (2) The loads and thermal expansion of the pipeline itself should be handled by the pipeline itself, and not borne by the soot blower, to avoid distortion of the soot blower itself and affect its operation. (3) Special attention should be paid to the relative positions of the nozzles on the soot-blowing pipe and the furnace tubes. After the soot blower tubes are installed, the position of the nozzles should be checked through the inspection holes to ensure it meets the requirements specified in the design drawings; any nozzles that are not in the correct position must be adjusted accordingly. X. Chimneys and baffles 5. What are the different types of chimneys? What are their characteristics? Chimneys can be classified by material into three types: brick chimneys, reinforced concrete chimneys, and steel chimneys. Brick chimneys are cheaper, generally not exceeding 50m in height. Bricks have poor thermal conductivity, thick walls, and a large temperature difference between the inner and outer walls; improper design or construction can lead to cracks, which affect smoke exhaust. Furthermore, brick chimneys should not be used in areas with high seismic intensity. Reinforced concrete chimneys have strong adaptability to thermal stress, and such chimneys can reach heights of over 150 meters. The greatest advantage of steel chimneys is their light weight and good seismic resistance. When the chimney height is 30 m or less, it can be placed directly above the convection chamber of the heating furnace, resulting in a compact structure ； The disadvantage of steel chimneys is that they are susceptible to corrosion by flue gases. Steel chimneys come in two types: lined and unlined. The flue gas temperature should be as low as possible, below 500°C; otherwise, the required lining will be too thick, or it will exceed the operating temperature range of the steel shell. In the tubular heating furnaces of petrochemical plants, lined chimneys are the most commonly used. The lining not only reduces the wall temperature of the steel chimney but also prevents corrosion of the chimney’s inner walls by flue gases; moreover, it protects the steel structure from overheating in cases of backdraft. The surface of the steel chimney is also coated with a heat-resistant paint to protect it from corrosion by the condensed acidic substances present in the flue gases. When several furnaces share one chimney, it is usually supported on the ground; in such cases, brick chimneys or reinforced concrete chimneys can be considered. A heating furnace does not necessarily have only one chimney; for example, large vertical furnaces use two or several chimneys in order to prevent the smoke from drifting off in an uneven manner. 6. What is the purpose of a chimney? The chimney of a heating furnace serves two purposes: one is to exhaust smoke into the upper atmosphere, thereby reducing pollution at ground level ； Secondly, when the heating furnace uses a naturally ventilated burner, the draft created by the chimney is utilized to draw in external air into the furnace for fuel combustion. 7. Why is there a suction force in chimneys? The suction force in chimneys exists because the temperature of the smoke inside the chimney is much higher than that of the outside air; in other words, the density of the smoke is lower than that of the air. Thus, just like a hydrogen balloon, the smoke inside the chimney rises naturally. As the smoke rises inside the chimney, a negative pressure (suction) is created at the lower part. Since the pressure of the outside air is higher than that inside the furnace, air is drawn into the furnace. The radiation and convection chambers through which the flue gas flows upward are not chimneys per se, but they are filled with hot flue gas, and they serve the same purpose as chimneys. 8. What factors are related to the draft force of a chimney? The draft force of a chimney is influenced by the height of the chimney, the density and temperature of the hot gases inside the chimney, as well as the density and temperature of the outside atmosphere. This can be expressed using the following formula: Δp = 9.8h(ρ_out – ρ_in), where Δp represents the draft force of the chimney, in Pa ； h – height of the chimney, m ； ρout – Density of the atmosphere outside the chimney, kg/m3 ； ρ_in – Density of the flue gas inside the chimney, kg/m3. As can be seen from the above formula, the suction force Δp of a chimney is proportional to the height of the chimney and the density difference of the gases; the higher the chimney, the greater the suction force ； The greater the difference in gas density, the greater the suction force. Under standard conditions (Δp equal to one atmosphere), the density of air is 1.293 kg/m3; therefore, the draft force in a chimney can be expressed in terms of absolute temperature: Δp = 12.67/h (273/T_out – 273/T_in), where T_out is the absolute temperature of the atmosphere outside the chimney, in K ； T_in – Absolute temperature of the flue gas inside the chimney, K. As can be seen from the above formula, when the height of the chimney remains constant, the greater the temperature difference between the gas inside and outside the chimney, the greater the draft force. Due to limitations in the process conditions, the flue gas temperature does not change significantly. Atmospheric temperature varies with seasonal climate; high temperatures in summer are unfavorable for chimney draft, while low temperatures in winter are favorable for it. When designing a chimney, its height should be determined based on the most extreme summer conditions. When the process conditions remain unchanged, the chimney dampers should be opened more in summer and closed more in winter. 9. What are the conditions for installing a suspension ring on the chimney of a cylindrical furnace? In petrochemical plants, some cylindrical furnaces have suspension rings on their chimneys, while others do not; this is determined by the length of the radiant tubes. When the length of the radiation tube is over 9 meters, a suspension ring should be installed on the chimney ； When the length of the radiation tube is 9 m or less, no suspension ring is installed on the chimney. 10. How should the diameter of the suspension tube ring be selected? The diameter of the suspension tube ring should generally be equal to the pitch circle diameter of the radial coil.