Basic knowledge of the heating furnace section

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1. What is the function and working principle of a flame arrester? Answer: The function of a flame arrester is to prevent the open flame from lamps or continuously burning lights from entering the fuel gas system, thereby avoiding combustion and explosion accidents. Its working principle is as follows: when the flame passes through a narrow aperture, the sudden increase in heat loss prevents further combustion, causing the flame to go out. 2. Why is an explosion-proof door needed in a heating furnace? Answer: Before the heating furnace is ignited, if its furnace chamber is filled with flammable gases, an explosion can occur upon contact with an open flame or static electricity. In such cases, the explosion-proof door opens, allowing the pressure inside the furnace to be released rapidly and preventing damage to the furnace itself. It can be seen that the purpose of installing explosion-proof doors in heating furnaces is to prevent excessive damage in the event of an explosion in the furnace. 3. What is the function of the damper? Answer: The flame combustion is adjusted by regulating the amount of air entering the furnace through the dampers. 4. What is the function of the flue damper? Answer: Adjusting the amount of air entering and leaving the heating furnace allows for the regulation of the negative pressure inside the furnace, thereby controlling the combustion of the flame. 5. Why is it necessary to maintain a certain negative pressure in the heating furnace? Answer: Fuel needs a certain amount of air to burn. Only by maintaining a certain negative pressure, with the pressure inside the furnace being lower than that outside, can air from outside enter the furnace. If the negative pressure inside the furnace is very low, the amount of air drawn in is minimal, resulting in incomplete combustion of the fuel. This leads to a decrease in the furnace’s thermal efficiency, black smoke being emitted from the chimney, a dim interior of the furnace, and even flames shooting out, which can disrupt the proper operation of the system. 6. How is the negative pressure in the heating furnace generated? Answer: The difference in density between the flue gases inside the furnace and air creates a suction force, aided by a tall chimney. Under the action of this suction force, a negative pressure is created inside the furnace. 7. What is the impact of the negative pressure in the heating furnace on operation? Answer: The negative pressure in the heating furnace has a significant impact on its operation. If the negative pressure is too high, the amount of excess air in the flue gas increases, which leads to an increase in the heat carried away. This reduces the furnace’s thermal efficiency; at the same time, it also accelerates the oxidation of the furnace tubes ； Too low negative pressure leads to incomplete combustion, which also reduces the furnace’s thermal efficiency. 8. What are the reasons for the increase in pressure inside the furnace? What should be the appropriate negative pressure value? Answer: (1) The dampers are opened too wide, resulting in excessive excess air. (2) The flue dampers are not adjusted properly, the flue gas exhaust fans are faulty, and there is severe ash accumulation in the convection tubes or air preheaters, which leads to an increase in pressure drop inside the furnace. Generally, the negative pressure in the furnace should be maintained at -5 to -10 mmH2O; if increasing the opening of the flue dampers does not enhance the exhaust force, then the fuel supply should be reduced and the load on the heater should be lowered. 9. What is furnace temperature? Answer: Furnace temperature generally refers to the temperature of the flue gas as it leaves the radiation chamber. Furnace temperature is an important process parameter in operating a heating furnace. Inside the furnace, the heat generated by fuel combustion is transferred to the furnace tubes through two modes of heat transfer: radiation and convection. The amount of heat transferred depends on the furnace temperature and the tube wall temperature. 10. How to understand the flow rate and pressure drop of materials in the furnace tube? Answer: If the flow rate of the material within the furnace tube is too low, the residence time of the oil in the tube increases, which makes coking more likely to occur. The flow rate within the furnace tube is generally expressed as the flow rate of cold oil, that is, the flow rate of the oil at 15°C. It is sometimes also expressed as the weight flow rate, which is the mass of oil passing through each square meter of the furnace tube’s cross-sectional area per second (kg/m2s). The pressure drop in the furnace tubes is an important indicator to determine whether coking has occurred in them. If the flow rate of the cold oil remains constant but the pressure drop increases, it is a sign of coking in the furnace tubes; as coking occurs, the inner diameter of the tubes decreases, the actual flow rate of the oil increases, and as a result, the pressure drop rises.