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1. What is the purpose of a pipe lifting ring? The pipe lifting ring on the chimney of a cylindrical furnace is used to lift pipes. When the furnace was first installed, the furnace tubes were lifted using cranes or other methods. It is only used with the upper suspension ring during production maintenance to replace individual furnace tubes. Because it cannot bear too much weight, only two radiation tubes can be lifted at a time. 2. What are the different types of chimney baffles? What materials are used? There are two types of chimney baffles: sealed and unsealed. Before 1980, the baffles used in the chimneys of petroleum chemical plant heaters were basically non-sealed; later, due to energy-saving needs, sealed baffles were designed. Currently, newly designed or modified heating furnaces mostly use sealed baffles. Sealed chimney baffles are available in single-axis, double-axis, three-axis, and four-axis types; these baffles have been standardized and can be selected and ordered directly. The materials for the baffles of the above types are as follows: (1) Carbon steel is used when the maximum flue gas temperature is ≤450°C. (2) When the maximum flue gas temperature is greater than 450°C and less than 750°C, 18Cr-8Ni shall be used. (3) When the maximum flue gas temperature is greater than 750°C and less than 950°C, 25Cr-12Ni is used. 3. What are the common types of adjustment mechanisms used for chimney dampers? What are their advantages and disadvantages? For chimney dampers in tubular heating furnaces, 75kgf manual winches, ground-based adjustment mechanisms, and ZSL-type pneumatic long-stroke actuators are commonly used for adjustment. Before 1980, the dampers on the heating furnaces in petrochemical plants were generally adjusted using 75kgf manual winches, as such mechanisms are small in size, light in weight, simple in structure, easy to manufacture, and inexpensive. Moreover, they offer great flexibility in adjusting dampers on chimneys with a diameter of less than ϕ500mm; therefore, they are still used on small chimneys today. However, adjustment on baffles with a diameter of over ϕ600mm is not very flexible. For this reason, after 1980, a new ground adjustment mechanism was designed; this mechanism allows for more flexible adjustment on baffles with a diameter of under ϕ800mm, but is less flexible for those with a diameter of over ϕ900mm. The greatest advantage of the ZSL control mechanism is its high degree of flexibility in operation, which makes it very popular among furnace operators; however, its price is higher than that of the two control mechanisms mentioned above. Based on the above, when selecting a control mechanism, furnace designers should make a decision through comparison according to the specific circumstances. However, the most important factor is ease of operation; if it is not easy to operate, then a low price is of no use. 4. Where should the adjustment of the chimney baffle be made? To ensure the normal operation of the furnace, it is essential to adjust the opening degree of the chimney damper in a timely manner according to the magnitude of the furnace’s negative pressure. Therefore, in addition to using negative pressure at the inlet of the furnace’s convection chamber to automatically (or manually) control the opening degree of the baffles, the adjustment of the chimney baffles (via a 75-kilogram manual winch or an on-ground adjustment mechanism) should be carried out on the floor beneath the furnace. The adjusting mechanism should be effortless and flexible, and should be equipped with an opening indication mark and a locking mechanism. If the adjustment mechanism is placed at the furnace top baffle, it is inconvenient to move it up and down during normal operation ； On the other hand, when a rupture accident occurs in the furnace tube and a fire breaks out inside, requiring all the baffles to be opened, going to the upper part of the furnace to do so poses an even greater risk. XI. Steel Structures and Their Accessories 5. What regulations must be followed in the design of steel structures and their accessories? The design of steel structures and their accessories shall comply with the relevant provisions of the **current ‘Code for Loads on Building Structures’, ‘Code for Seismic Design of Buildings’, and ‘Code for Design of Steel Structures’. For tubular furnaces in areas with seismic fortification degrees of 6 to 9, they shall also comply with the current \"Code for Seismic Design of Petrochemical Equipment\" issued by Sinopec Group. 6. What should be included in the design loads for steel structures? The design loads for steel structures should include permanent loads, live loads, wind loads, snow loads, all loads generated by furnace tubes and elbows, seismic effects, and temperature effects. 7. What regulations should be followed regarding the selection of steel structures and their accompanying materials? The selection of steel structures and their accompanying materials shall comply with the following regulations: (1) Steel structures are generally fabricated from steel grades such as Q235-A, Q235-A, F, or 16Mn. When the average monthly minimum temperature in the coldest month of the site where the plant is to be built is equal to or below -20°C, calm steel should be used for the main load-bearing components. (2) The metal design temperature for steel structures and their associated materials shall be determined as the metal calculation temperature plus 50°C. The calculated temperature of the metal is determined based on the highest temperature under various operating conditions, with no wind and an ambient temperature of 30°C. 8. What requirements must be met in the design of steel structures and their accessories? The design of steel structures and their accessories shall meet the following requirements: (1) Consideration must be given to the space required for extracting and inserting horizontal furnace tubes, as well as the lifting measures and necessary site area for vertical furnace tubes. (2) The distance between the bottom plate of the bottom-fired tubular furnace and the ground beneath the furnace must meet the requirements for the operation and maintenance of the burners, and shall not be less than 2.2 m. (3) An inspection and maintenance space with a height of not less than 800 mm should generally be provided at the upper part of the convection tube ； For small furnaces, the space height must not be less than 600 mm. (4) When the length of the convection chamber is greater than 10 m, two or more chimneys or flue gas outlets should be provided. (5) When the elbows or collector pipes of a horizontal tubular furnace are located inside the furnace chamber, a removable movable plate should be installed on the side wall. (6) The wall panels of the tube furnace shall be seam-welded. (7) Drainage facilities should be provided for all components, the furnace top, and the platform surface. (8) The elbow box should be well sealed. The minimum distance between the lining surface on the box door of the elbow and the elbow itself shall meet the thermal expansion requirements of the furnace tubes, and shall not be less than 50 mm. (9) A fireproof layer should be provided on the columns at the lower part of the steel structure of the furnace bottom in bottom-fired tubular furnaces. 9. What requirements must be met for the installation of platforms and ladders? The installation of platforms and ladders must comply with the following requirements: (1) The platform decking should be made of checkered steel plate thicker than 4 mm or anti-slip-treated steel plate. (2) Platforms or straight ladders shall be provided at the following locations where operations cannot be performed from the ground. ①At the burner and its control mechanism. ②Areas at both ends of the convection chamber that require regular maintenance. ③Maintenance areas for the baffle and soot blower. ④All at the fire doors and manhole covers. ⑤At the opening of the gauge. ⑥At the fans, drive units, and air preheaters. (3) Except for single platforms with a cylinder furnace diameter of less than 6 m or straight-section platforms with a length of less than 6 m, each operating platform shall be equipped with two upper and lower openings. (4) A spiral staircase should be provided when the radiation elevation of the cylindrical furnace is greater than 10 m. (5) When the diameter of the shell of a cylindrical furnace is greater than 3 m, a full-circle platform and an inclined ladder should be provided on the furnace bottom plane ； When the shell diameter is 3 m or less, a straight ladder and platform can be provided separately at each manway. (6) When using a horizontal coil with a plug-type elbow, the platform on the side of the elbow shall meet the requirements for installation and maintenance. 10. What are the structural requirements that must be met in the design of steel structures and their accessories? The structural requirements for the design of steel structures and their accessories are as follows: (1) The minimum thickness of the steel plates in the following areas of steel structures: furnace walls and elbow boxes: 4 mm. Top and bottom of furnace: 6mm. (2) Structural design of cylindrical furnaces: ① When the diameter of the cylinder is less than 4m, a columnless cylindrical structure can be used ； When it is 4m or greater, a cylindrical structure with columns is recommended. The number of columns should be even, and the arc length between adjacent columns should be 1.6 to 2.5 meters. ②The vertical spacing between the upper and lower simple ring beams should not be less than 2.5 m. (3) Steel structure of vertical furnaces and box furnaces: ① The joints within the plane of the column frame should be connected in a rigid manner. ②At both ends of the lateral column array, diagonal braces between adjacent columns should be properly arranged. When there is a chimney on the furnace top, diagonal braces should be installed between the columns supporting the chimney. The angle between the diagonal brace and the main column should be 30º to 60º. ③The distance between adjacent columns in a lateral column array should be less than 4.5 m. ④The vertical spacing between the lateral beams should be 3 to 6 meters.