Thread Content
1. What are the accessories and components of a heating furnace? The accessories of a heating furnace refer to ordered parts that are not manufactured on-site. Mainly include: burners, soot blowers, dampers, floor adjustment mechanisms, duct butterfly valves, return bends, sharp-radius elbows, studded tubes, finned tubes, tube supports, furnace tube pull hooks, furnace tube suspension hooks, cast convection tube sheets, cast doors (including explosion-proof doors and inspection doors), spring hangers, etc. The components of a heating furnace refer to parts that can be manufactured on-site. Mainly include: positioning pipes, guide pipes, pressure measurement pipes, thermocouple sleeves, flue gas sampling pipes, drain pipes, etc. 2. What are the classifications and representation methods of elbows? (1) Elbows are divided into plug-type expansion or welding elbows, as well as sharp-angle elbow bends. (2) Representation method: ① Sharp bend elbow. When the bending angle of a sharp bend pipe is 90º, the outer diameter and wall thickness of the furnace tube are φ152×10 mm, and the center-to-center distance between pipes is 152 mm, it is denoted as: 90º–φ152×10–152. When the bending angle of a sharply curved pipe is 180º, the outer diameter and wall thickness of the furnace pipe are φ 152×10 mm, and the center-to-center distance between the pipes is 304 mm, its notation is: 180º－φ 152×10－304. ②Plug-type expansion joint or welded elbow. When the bending angle of the elbow is 180º, the outer diameter and wall thickness of the furnace tube are φ 152×10 mm, the pipe center distance is 304 mm, and the nominal pressure is 2.45 MPa (25 kgf/cm²), its notation is: 2.45(25)–180º–φ152X10–304. When two pipes of different diameters are connected, an eccentric elbow is used. For example, when the bending angle of the elbow is 180º, the outer diameters of the furnace tubes are φ 152 mm and φ 219 mm respectively, the tube center distance is 372 mm, and the nominal pressure is 2.45 MPa (25 kef/cm²), the notation method is: 2.45 (25) – 180º – φ 219/φ 152 – 372. 3. What are the requirements for selecting elbow bends with sharp turns, plug-type expansion joints, or welded elbow bends? The selection of elbow bends with sharp turns, plug-type expansion joints, or welded elbow bends must comply with the following rules: (1) The material of the elbow bend with a sharp turn should be the same as that of the furnace tube it is connected to. Its thickness shall not be less than the wall thickness of the furnace tube. (2) The design pressure of the plug-type elbow should be the same as that of the furnace tube it is connected to, and its design temperature should be equal to the temperature of the medium being heated inside the tube plus 30°C. (3) When a plug-type elbow is used and mechanical methods are required to remove coking and scale inside the pipe, a dual-hole plug type should be employed. When using elbow fittings with plugs in a vertical furnace, the upper part of the coil should feature a two-hole plug design, while the lower part can use a single-hole plug design. (4) For coiled tubes connected by sharp bends, if it is necessary to inspect the interior of the furnace tube or drain it during maintenance, a plug-type elbow can be installed at an appropriate location. (5) The typical pipe center distance for 180º sharp bends and elbows should be selected according to Tables 3–6. 4. What type of pipe is used to manufacture elbows with sharp bends? Elbows with sharp bends used in heating furnaces are made from furnace pipes; other types of pipes cannot be used for this purpose. 5. Where are sharp-bend pipes used? Before the 1980s, sharp-bend pipes were mainly used in the convection section of heating furnaces and on the transfer lines from convection to radiation sections; a certain amount were also used in the radiation section. When a socketed tube is used for the radiant furnace tube, an elbow is employed in the upper part of the furnace tube ； When suspended tubes are used for radiant furnace tubes, sharply bent tubes are employed at the lower part of the furnace tubes. The radiant coils of heating furnaces designed after the 1980s use sharp bends at both the top and bottom; for example, the radiant coils of the atmospheric-pressure furnace at Wuhan Petrochemical Plant employ suspension pipes, with 180º sharp bends at both the upper and lower sections of these pipes. Since their installation in June 1981, they have been functioning properly without any issues. 6. Which two types of tube sheets are commonly used in the convection chambers of current heating furnaces? At present, the tube sheets used at both ends of the convection chambers of heating furnaces are usually fabricated on-site from Q235-A.F ； The tube sheet used in the middle of the convection chamber is a cast tube sheet. 7. What principles should the structural design of tube sheets follow? The structural design of tube sheets should adhere to the following principles: (1) The segmentation of the end tube sheets and the intermediate tube sheet in the convection section should remain the same. (2) The difference between the inner diameter of the tube sleeve on the tube sheets at both ends and the outer diameter of the bare tube, nail head, or finned tube must not be less than 8 mm. (3) The design of the tube sheet shall prevent mechanical damage to the expanded surface tubes, and facilitate the removal and insertion of the furnace tubes. (4) The rows of stud heads located on the tube sheet should be no less than 3 ； The fins located on the tube sheet should have no fewer than 5 turns. (5) The structure and fixation of the tube sheet should take into account its own thermal expansion and contraction. (6) A refractory and insulating layer shall be provided on the flue gas side of the tube sheets at both ends. When lightweight heat-resistant concrete is used as insulation, its thickness shall be no less than 75 mm for convective tube sheets ； The radiant tube plate shall not be less than 125 mm. The fire-resistant and thermal insulation layer shall be fixed with insulation nails. 8. How is the position of the furnace tube hook determined? For vertical-type heating furnaces, furnace tube hooks should be installed on all radiant tubes. The position of these hooks is determined as follows: (1) When the radiant tubes are socketed tubes, the distance from the hook to the upper end of the furnace tube is 1/3 to 1/4 of the total length of the furnace tube. (2) When the radiant tube is a suspended tube, the distance from the position of the furnace tube pull hook to the lower end of the furnace tube is approximately 1/3 of the total length of the furnace tube. 9. What is the purpose of the flame view window? The purpose of the flame view window is to observe the color, shape, and length of the flame from the burner inside the radiation chamber ； Additionally, it is used to inspect furnace tubes, elbows, pull hooks, lifting hooks, thermocouples, furnace walls, furnace roof linings, furnace bottom linings, firebox bricks, etc., to check for any abnormalities such as burning or deformation during operation. 10. What conditions must the number and location of the viewing ports meet? The number and location of the viewing ports should allow for an overview of the burning condition of all burners, as well as enable comprehensive inspection of all furnace tubes, elbows, hooks, lifting hooks, thermocouples, furnace walls, furnace top linings, furnace bottom linings, and burner bricks during operation.