Thread Content
1. What are the advantages of switching from a naturally ventilated burner to a forced-air burner? A naturally ventilated burner draws in air by utilizing the pressure difference between the furnace interior and the atmosphere. The external atmosphere is at constant pressure, while there is generally a negative pressure of around 98 hPa at the burner; this pressure difference is sufficient to overcome the resistance loss as air passes through the burner and to supply the air required for combustion. When forced air supply is adopted, if this type of natural ventilation burner is still used, although pressurized air can be supplied to increase the amount of air, since other conditions remain unchanged, the air intake of the burner only needs to maintain the normal pressure under natural ventilation conditions to meet the air demand. Supplying too much air is not only unnecessary but also reduces the thermal efficiency of the heating furnace ； If the damper is reduced, the air pressure can increase, but this only results in a waste of energy without any benefit to combustion. As can be seen from the above, if the structure and energy of the naturally ventilated burner remain unchanged and natural ventilation is replaced by forced air supply, it can achieve certain positive effects in terms of controlling noise, reducing the impact of wind on the flame, and adjusting the excess air. To fully utilize the advantages of forced air supply, the burner flame gate should be reduced in size, along with the use of appropriate air regulators. 2. What are the advantages of forced-air burners compared to naturally ventilated burners? (1) The air flow rate into the burner is high, allowing for good mixing with the fuel, resulting in a low excess air coefficient. The wind speed at the throat of a forced-air flue is high, ranging from 30 to 60 m/s, whereas the wind speed at the throat of a naturally ventilated flue is only 10 to 15 m/s. (2) The small number of burners facilitates the use of flame control and safety protection systems. (3) It is easy to control the flame shape and improve heat transfer. (4) It has a wind shield that helps reduce noise; the noise level of a burner with natural ventilation is 100–110 dB, while that of one with forced air supply is below 85 dB. 3. What are the disadvantages of forced-air combustion burners? Forced-air combustion burners require a certain level of air pressure to ensure proper combustion; therefore, in the event of a failure in the fan or motor, it becomes impossible for the burner to operate at full capacity. Hence, it is very important to maintain the fans and motors properly to ensure the long-term operation of the heating furnace. When air preheating is used, the increase in air temperature is also the increase in the maximum flame temperature. An increase in combustion temperature leads to an increase in the amount of nitrogen oxides at the combustion center, thereby exacerbating pollution; currently, burners that utilize nitrogen oxides are already being used abroad. 4. Why are high-pressure steam atomization burners commonly used? Most of the burners used in tubular heating furnaces are internal mixing steam atomization burners. During natural ventilation, the maximum oil burning rate of this burner is 500 kg/h. The operating parameters of the high-pressure steam atomization burner are as follows: fuel oil pressure: 0.69～0.88 Mpa (7～9 kgf/cm2) ； Fuel oil viscosity: <0.025Pa•s ； Vaporization steam pressure: 0.78～0.98 MPa (8～10 kgf/cm2). The disadvantages of this burner are high noise levels and high steam consumption, but its advantages are: (1) good atomization. (2) The flame shape is stable, straight, and powerful. (3) It has a strong suction force, so forced air supply is not required. (4) Wide load regulation range. (5) Can burn heavy residue oil. Since these advantages precisely meet the requirements of tubular heating furnaces, the vast majority of such furnaces use this type of burner. IX. Soot Blowers 5. What are the common soot blowers used in heating furnaces, and what are their advantages and disadvantages? There are two types of soot blowing methods: one is the electrically driven, fixed-rotation type soot blower (see Figure 9-1) ； Another type is the long telescopic soot blower (see Figure 9-2). file:///C:\Users\Blackfox\AppData\Local\Temp\ksohtml\wpsA39E.tmp.jpg file:///C:\Users\Blackfox\AppData\Local\Temp\ksohtml\wpsA39F.tmp.jpg file:///C:\Users\Blackfox\AppData\Local\Temp\ksohtml\wpsA3A0.tmp.jpg (1) Electrically driven fixed-rotation soot blower: The soot blowing tube of this type of blower (see Figure 9-3) remains inside the furnace; steam nozzles are arranged along its length. Using steam as the medium, the tube rotates under the drive of a motor, and the steam ejected from these nozzles cleans the ash accumulated on the outer surface of the convection tubes in the heating furnace. This soot blower is small in size, light in weight, relatively simple to manufacture, and low in cost. The disadvantage is that the soot blowing tube is always located inside the furnace, and it is prone to being damaged or deformed, which can affect normal operation. It is generally best to use it in areas where the flue gas temperature is below 600°C. (2) Long telescopic soot blower: This type of soot blower is characterized by a soot blowing tube that can extend and retract, extending into the furnace during soot blowing. The tip of the soot-blowing tube is equipped with a nozzle; it rotates and blows soot as it moves forward, and after completing the soot-blowing process it retracts outside the furnace, which prevents the soot-blowing tube from being damaged or deformed. Its disadvantages are: complex structure, high cost, and the need for long guide rails and platforms outside the furnace. It is generally suitable for use in areas where the flue gas temperature is above 600°C. 6. Under what circumstances is it necessary to install soot blowers in the convection chamber? Soot blowers are not required when the furnace tubes in the convection chamber of a heating furnace are plain tubes ； When the convection tube is a nail-head tube or a finned tube, the convection chamber must be equipped with soot blowers, regardless of the fuel used in the burner. 7. How to choose between long-telescopic soot blowers and electric fixed-rotation soot blowers based on flue gas temperature? Major foreign companies generally select the type of soot blower based on the flue gas temperature at the location where the soot blower is installed. UOP Company (USA): When the flue gas temperature is >649°C, a long-telescoping soot blower should be used. : When the flue gas temperature is ≤649°C, an electric fixed-rotation soot blower should be used. ExxonMobil (USA): When the flue gas temperature is >593°C, a long-telescoping soot blower should be used. When the flue gas temperature is ≤593°C, an electric fixed-rotation soot blower should be used. Luchi Company (former West Germany): For flue gas temperatures >550°C, long-telescopic soot blowers should be used. When the flue gas temperature is ≤550°C, an electric fixed-rotation soot blower should be used. For the fuel oils commonly used in our country, it is reasonable to take a flue gas temperature of 600°C at the location where the soot blower pipes are installed as the dividing point. If the fuel oil is particularly dirty and there is severe ash accumulation, a long telescopic soot blower can also be used starting from 500°C. 8. What is the soot-blowing distance of a long-telescopic soot blower? Based on the conditions in China, the soot-blowing distance for such blowers can be recommended as follows: vertically, 4 rows of stud tubes or fin tubes each above and below. Horizontal direction: The effective soot-blowing radius is generally not greater than 1.3 m. 9. What is the soot-blowing distance for electric fixed-rotation soot blowers? When the steam pressure used for soot blowing is between 0.78 and 1.47 MPa (8–15 kgf/cm2), taking into account the arrangement of the tubes inside the furnace, it is recommended that the soot-blowing distance for electric fixed-rotation soot blowers be as follows: in the vertical direction, 3 rows of stud tubes or finned tubes above and below. Horizontal direction: The effective soot-blowing radius is 0.75–1.2 m. 10. What are the components of an electrically driven, fixed-rotation soot blower? This type of soot blower consists of two main parts: an external drive mechanism and a soot blowing tube that extends into the furnace (see Figures 9–1). The off-furnace drive section is a standard component that has been standardized. The main specifications are as follows: soot blower shaft speed: 1.28 r/min ； Motor model: 0.4kW, 1400r/min ； Weight: Approximately 85 kg. The soot-blowing tubes extending into the furnace should be designed based on the specific conditions of the furnace (such as the diameter and arrangement of the convection tubes).