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1. How to prevent backfire in gas burners? To prevent backfire in gas burners, it is necessary to ensure that the flow rate of the air-gas mixture is greater than the flame propagation speed. When there is an adequate supply of gas, adjusting the damper on the burner or the butterfly valve in the air duct can make the flow rate of the air-gas mixture greater than the flame propagation speed, thereby preventing backflow. 2. How to prevent flashback in gas burners? To prevent flashback in gas burners, it is necessary to avoid excessive exit flow velocity of the gas mixture; when flashback occurs, the supply of gas and air should be reduced. 3. How to make full use of low-pressure gas? If the low-pressure gas coming from the top of normal-pressure columns and vacuum distillation columns is not utilized, a significant amount of energy will be lost. However, the pressure of this gas is too low; it cannot be injected into the furnace to burn on its own. Therefore, steam is generally ejected through small holes, and a Venturi tube is used to draw in low-pressure gas, so that the steam and the low-pressure gas mix together and are injected into the furnace for combustion. In this way, it is also possible to prevent the flame from drifting and make it more powerful. 4. What is the relationship between the angle at which oil is sprayed from the nozzle and the length of the flame? Once the amount of oil used by the nozzle is determined, different nozzle opening angles can be designed as needed to achieve various flame lengths. During bottom combustion, the length of the flame is related to the height of the radiant furnace tube; generally, it is required that the length of the flame in the radiant chamber be 50% to 60% of the length of the vertical tube. For common oil-gas combined burners, the orifice angles of the oil nozzles range from 30º, 40º, 50º, to 60º; the smaller the angle, the longer the flame. As a rough estimate, the number corresponding to the opening angle can be used to divide the amount of fuel burned by the nozzle, and the resulting value gives the length of the flame in meters. For example: if the opening angle of the nozzle is 40º, then for every 40 kg of oil burned, the flame will be 1 meter long ； When 400 kg of oil is burned, the flame length is estimated to be (400/40) × 10 meters. The common opening angle for oil nozzles is 40º. When the nozzle angle is changed, the dimensions of the furnace bricks also need to be adjusted accordingly. If the dimensions of the furnace bricks are not changed and only the opening angle of the nozzle is reduced, it will result in poor mixing of fuel and air ； If the nozzle angle is increased, it will cause the fuel to spray onto the flame path and lead to coking. 5. Is the practice of using multiple nozzles with short flames correct? In the past, the requirement for furnace operation was to use multiple nozzles with short flames; this requirement was put in place to address issues such as uneven heat distribution and flames licking the tubes. However, the furnaces used in the past were box furnaces or inclined-roof furnaces, with dimensions such as length, width, and height that were all relatively small. If the flame was too long, it could touch the tubes or reflect off the fire wall, causing localized overheating; therefore, it is appropriate to use multiple burners with short flames in box furnaces or inclined-roof furnaces. However, in some bottom-fired cylindrical furnaces or other vertical tube heating furnaces, multiple nozzles with short flames are not suitable. The burners of these heating furnaces are located at the bottom of the furnace, so it is not possible to have many of them. Additionally, short flames cause uneven heat transfer up and down the furnace tubes; therefore, short nozzles with long flames are required. Currently, in foreign countries, there are heating furnaces that use only one forced-air large burner, with the flame length required to be 70% of the length of the furnace tube. The quality of heating furnace design and operation depends primarily on whether the relationship between the furnace tubes and the flame is handled properly; different conditions require different approaches, as there is no one-size-fits-all solution. 6. What issues should be considered when installing bottom-fired oil-gas combined burners? For the oil-gas combined burners commonly used in heating furnaces in petrochemical plants, the following points should be taken into account during installation: (1) The oil gun should be vertical, without any tilt, and at an appropriate height. (2) Do not reverse the oil and vapor positions at the connection port at the lower part of the oil gun. (3) The gas pipe with nozzles should be vertical, and the center of the nozzle opening of each nozzle should be aligned with the center of the burner. (4) The inner and outer fire channel bricks and the burner must be concentric, and the joints of the outer fire channel bricks should be offset from those of the gas nozzles. The gap between firebrick tiles must be kept under 2 mm; otherwise, serious consequences will occur. In mild cases, the furnace bottom plate near the burner gets deformed due to heating ； In severe cases, the furnace bottom plate becomes severely distorted, causing the burner to sag and become unusable. (5) The damper must have good sealing properties as well as flexible rotation. (6) The interiors of the fuel oil pipes and gas pipes, as well as the oil nozzles and gas nozzles, must be thoroughly cleaned, and all connections must be secure to prevent leaks. 7. Why does the oil nozzle leak or drip oil? During the operation of a heating furnace, it is common for the oil nozzle to leak or drip oil. The reasons for this are: first, the seal at the connection point of the oil gun is not proper ； Secondly, at the start of operation, due to the low temperatures of the flame channel bricks and the furnace chamber, there is cold oil in the oil pipes that is difficult to atomize, or water present in the steam ； Third, the fuel oil temperature is low, the oil pressure increases, or the atomization steam pressure drops suddenly. Ways to prevent oil leaks or drips from the nozzle are: (1) using a well-sealed connection structure. (2) Before starting up and igniting, the condensate water in the steam pipe should be drained. (3) During operation, it is necessary to maintain the temperature of the fuel oil ； The oil pressure and steam pressure must be stable, with the oil pressure required to be 98 kPa lower than the steam pressure ； It is necessary to adjust the oil-to-gas ratio properly in order to shape and stabilize the flame ； Control the damper to keep the flame color orange-yellow. (4) After shutting down, the oil remaining in the oil gun and the fuel oil branch pipes must be purged completely. 8. What are the causes of abnormal burner flame combustion and what are the solutions? During the operation of heating furnaces, it is common to encounter situations where the burner flame does not burn properly, such as sparks appearing in the flame, the flame turning black, instability in the flame, pulsations, and popping sounds. The reason for the above phenomenon is: (1) the viscosity of the fuel oil is too high ； Insufficient amount of atomized steam or inadequate superheat, as well as an excessive amount of water or fuel oil, or an incorrect connection of the atomized steam line, can all lead to poor atomization, resulting in sparks or black smoke coming from the chimney. (2) Fuel oil contains mechanical impurities, asphalt deposits, nozzle coking, etc.; in particular, the presence of such impurities in pipelines that have just started operation can cause the spray nozzles to become blocked, leading to abnormal flame behavior. (3) If fuel oil contains a high amount of water or if fuels with many light components are preheated excessively, vaporization will occur, disrupting the uniformity of the fuel oil flow and causing flame pulsations and knocking. Ways to prevent abnormal combustion of the burner flame are: (1) The viscosity of the fuel oil must be less than 0.025 Pa•s ； The amount of vaporized steam and its temperature meet the requirements ； The oil-to-gas ratio should be appropriate ； The oil pressure and steam pressure meet the operational specifications ； The steam pressure must not be lower than that of the fuel oil. (2) The connection of the fuel oil pipes and steam pipelines must be correct. (3) For pipelines that have just started operation, before installing the burner, the impurities in the oil pipes, steam pipes, and gas pipes must be purged first, and then they can be connected to the burner. (4) Before entering the burner, fuel oil must be dehydrated and filtered to remove water and impurities from it. (5) Too light fuels, such as kerosene, should not be used for fuel oil. 9. What preparations are required for a heating furnace before ignition? Before igniting a heating furnace, the following tasks must be completed: (1) The furnace tubes that have been overhauled must be checked to ensure they are in good condition and free from leaks. (2) Check whether the tube sheet, hooks, and pull hooks are secure ； Check whether the furnace walls and linings have fallen off, and whether there are any debris inside the furnace chamber and flue. (3) Check whether the chimney dampers, adjustment mechanisms, soot blowers, pressure gauges, thermocouples, burner air control valves, and air duct butterfly valves are flexible and functional. (4) Check whether the explosion-proof doors and observation doors are flexible and functional, and whether their sealing is good. (5) Check whether the fire extinguishing steam pipes and other fire protection facilities are in good working condition. (6) No leaks were detected during the pressure test for the fuel oil pipelines, steam pipelines, high and low pressure gas pipelines, and heat mixing lines. (7) Use steam to check each burner to ensure it is functioning properly, and verify that the primary and secondary air valves of the burner are flexible. (8) Open the baffle on the chimney to 1/3 position. (9) Blow steam into the furnace for 5–10 minutes, until steam is visible in the chimney, in order to disperse any flammable gases inside the furnace. (10) Clean up debris and flammable materials in the furnace area. (11) Prepare tools such as ignition rods, matches, and diesel. (12) After the above tasks are completed, fuel can be introduced into the furnace area. If fuel oil is being used, open the vent valve to see the oil, and turn on the heating coil in the fuel oil pipeline. 10. How to determine the quality of furnace operation? The quality of furnace operation can be assessed based on the following aspects: (1) The temperature at the total outlet of the medium is within the specified technical range. (2) The flow rates and temperatures of various media must be uniform. (3) The furnace tubes are heated evenly, and no coking occurs inside the tubes. (4) Low fuel consumption and high thermal efficiency. (5) The furnace temperature is within the specified range for the process. (6) The negative pressure at the outlet of the radiation chamber is between -20 and -40 Pa. (7) The flame is orange-yellow in color, and its shape remains stable. (8) The chimney of the furnace does not emit black smoke.