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[Keywords of the paper] Boiler, fan, operation methods. The combustion in a boiler relies on its air system, which includes the secondary air system, the primary air system, the scanning cooling air system, and the roof sealing air system. The air for each system is supplied by corresponding fans. Taking the smoke and air system of Boiler No. 4 in the 2-300MW unit project of a certain thermoelectric company as an example, the installation procedures for the AN axial flow suction fan, the FAF axial flow supply fan, and the centrifugal fan are described separately. The installation of the smoke and air system for Boiler #4 in the 2×300MW unit project of this thermoelectric company is designed based on balanced ventilation, ensuring that the primary fan, supply fan, and exhaust fan can operate on one side when the boiler is operating at low load or when one of the fans fails. Isolation valves are installed on the smoke and air ducts at both the inlet and outlet of the air preheater. Two axial flow fans with adjustable vanes and 50% capacity are used as the supply fans, two axial flow fans with adjustable stator vanes are used as the suction fans, and two fixed-speed single-suction centrifugal fans with 50% capacity are used as the primary fans. The grinding system adopts a positive-pressure direct-blowing type with a medium-speed mill and a cold primary fan. Its sealing system employs a master-tube sealed air system, with 2 centrifugal seal fans installed for each furnace – one in operation and one as a backup. According to the requirements of the construction drawings, the supply fans, exhaust fans, primary fans, and seal fans for the coal mills are all located on the zero-meter level of the boiler room. The supply fans are arranged symmetrically on both sides of the furnace frame, in the areas where the cold air from the preheater is stored; their center lines are perpendicular to the longitudinal center line of the boiler. The lifting equipment used for installation should be HB36B construction tower cranes on the expansion side, and KH180 crawler cranes on the fixed side ； The exhaust fans are arranged symmetrically behind the electrostatic precipitator, with their center lines parallel to the longitudinal center line of the boiler; the lifting equipment used is a KH180 crawler crane ； The primary fans are symmetrically arranged below the horizontal flue at the preheater outlet, and their lifting equipment is a KH180 crawler crane ； The seal fan is installed below the air duct at the inlet of the furnace preheater, with a winch used to assist with its installation. I. Specific steps in the construction process (1) Operation method for AN axial flow suction fans The general principle for installing such fans is to use the assembly of the fan casing (the rear guide vanes and the impeller housing) as a reference point and fixed end ； Its intake box, collector, and guide vanes are the thermal expansion sliding ends facing forward (toward the motor), while its diffuser and diffuser core tube are the thermal expansion sliding ends facing backward (away from the motor). The specific installation sequence, steps, and requirements are as follows: 1. Place all components near the foundation, remove debris and burrs, and prepare the lifting equipment. 2. Clean the foundation thoroughly, and check the elevation of each part of the foundation as well as the dimensions of each foundation hole ； After connecting the shims, base plates, and legs together, place them in position. Level the base plate and check the elevation. 3. Assemble the casing (rear vane assembly and impeller housing assembly) together, connect them, lift them to the designated position, and insert the foundation bolts. Use a frame level to check the verticality and levelness of the casing assembly. At the same time, keep the casing axis aligned with the fan’s inlet and outlet pipes. 4. After rough alignment, the bases of the rear guide vane assembly and the impeller casing assembly can be grouted once. After the cement reaches the specified hardness, recheck the condition ； After verification, tighten the anchor bolts to the required torque. 5. After assembling the lower half of the diffuser housing, lift it to the designated position; on one side, connect it to the flange bolts of the rear guide vane housing, and on the other side, spot-weld the arc-shaped plate of the leg to the leg and the junction point of the diffuser housing to ensure a secure connection. 6. Connect the small collector, the guide vane assembly, the large collector, and the lower halves of the various components of the air intake box in sequence. Note: Sealant material must be added between the flanges as required, and after the legs of the air intake box and the arcs have been positioned correctly, they should be welded firmly. It is important to ensure strict verticality of the casing assembly before spot-welding the front and rear leg supports, in order to prevent excessive external gravitational forces, tilting, and loosening of the foundation bolts used for the casing assembly. If it is not possible to carry out spot-welding of the legs promptly upon lifting and positioning them, they should be secured using sleepers and jacks to ensure safety. 7. Install the intake box sliding legs and the diffuser sliding legs in accordance with the assembly drawing requirements. Make sure to appropriately lengthen the exposed part of the bolt head; a sliding pressure plate will need to be added later (as shown in the assembly diagram). When welding the legs and the arc plates of the legs, pay attention to welding them in symmetrical sections to reduce welding deformation. 8. Install the main bearing housing, add anti-loosening washers as required, and tighten the connection bolts to the specified torque ； After tightening, install the radial temperature sensor as shown in the diagram. Install the front and rear cold air shields as well as the axial temperature sensing elements according to the diagram, with the upper part of the conical cold air shield being installed last. 9. Lift the impeller, tighten the gland bolts to the specified torque, rotate the shaft to check the axial clearance between the hub and the rear guide vane cylinder, as well as the radial clearance between the blade tips and the inner wall of the casing. 10. The impeller side half coupling (Form03) is connected to the impeller; tighten the bolts to the specified torque. 11. Install the motor end coupling (Form01) as shown in the diagram, and roughly position the motor at the desired location. 12. Lift the torque-transmitting intermediate shaft; its tightening torque should meet the required values. It is recommended to prepare a gantry at the motor end before lifting; after its axis is connected to the impeller end, the other end should be lifted using pulleys within the gantry, and once the height is adjusted, it should be connected to the coupling at the motor end as soon as possible. Note: During the lifting process, once the impeller end is connected, the offset distance at the other end must not exceed 5 mm. Otherwise, it will have an adverse effect on the elastic properties of the diaphragm coupling, and may even cause damage to the coupling. 13. According to the schematic diagram of the alignment principle for the shafting of AN series axial flow fans: alignment is carried out by taking the horizontal position of the impeller-end coupling and the motor spindle as a reference. It is necessary to ensure adequate thermal expansion compensation for the position of the main bearing seat in the rear guide vane assembly at the impeller end, that is, an appropriate upward adjustment of the motor’s horizontal position (specific values are given in the assembly diagram). It should be ensured by the opening value between the diaphragms of the two couplings, and the magnitude of this opening value can be determined through calculation ； According to standard ratios, a opening value of around 0.20 mm is sufficient (as the flue gas temperature is also kept within a certain range). 14. Perform secondary grouting for the motor foundation, intake box foundation, and diffuser foundation; once the specified hardness is achieved, tighten the foot bolts and recheck the gap measurements. 15. Assemble the diffuser core cylinder, torque-transmitting intermediate shaft guard tube, shaft seal cylinder, etc. 16. Assemble the cold air duct protective sleeve, install the cold air ducts, and install the oil pipes. 17. Installed on the upper part such as the intake box, large collector, guide vanes, small collector, and the upper part of the diffuser. Note that sealing material must be installed between each flange; no additional sealing material is required outside the circular flanges and mating plates that require on-site welding (see the fan assembly diagram). 18. Before adjustment, the opening degree of the guide vanes should remain basically consistent; it is recommended to carry out the adjustment and inspection at 0 degrees (i.e., when the blades of the front guide vanes are parallel to the centerline of the main shaft). 19. Install the pilot vane actuator, being careful to open the vane; the indications on the actuator outside the casing should be consistent. 20. Install the cooling fan, fueling device, on-site temperature and vibration measurement devices, anti-surge alarm device (if any), etc., in accordance with the requirements of the drawings (see the respective assembly drawings for details). 21. Install inlet and outlet expansion joints as well as internal and external insulation layers, and connect the entire fan to the piping system. (II) Adjustment of axial pre-tension Since these types of fans operate under hot conditions, with high flue gas temperatures and relatively long shafts for torque transmission, their shafts experience significant thermal expansion (approximately 5–10 MM). Therefore, during installation in a cold state, the installation clearance of a single coupling should be increased by 2.5~5 MM compared to its natural clearance. 1. Equipment inventory and inspection. Once the equipment arrives, conduct an inventory check of it. 2. For basic marking and shim placement, the deviation of the longitudinal and transverse center lines from the boiler’s center line shall not exceed 20 mm. The elevation error of the anchor bolt box shall not exceed 10 mm, and the relative error between them shall not exceed 2 mm. 3. Bearing assembly installation. The bearing set shall be installed in place with the following requirements: a center distance error of 5 mm, an elevation error of 10 mm, and a horizontality tolerance of 0.1 mm/m for the center line of the bearing set. Adjust the leveling bolts and tighten the foot bolts. 4. Installation of the intake chamber and diffuser. The intake chamber and diffuser are in place; the foundation bolts have been installed, and shims are used to align them with the main bearing ducts. The allowable elevation deviation is 0 to -10 mm, while the levelness deviation should not exceed 3 mm. The clearance between the two and the main bearing air duct is 20 mm as specified in the drawings. 5. Motor alignment and coupling installation. The coaxiality tolerance for the axes of the fan and motor is 0.05 mm. The gap between the coupling ends should be even, with a deviation from this value not exceeding 0.08 mm. 6. Lubrication of the fan (1) During the installation of the oil station and oil pipelines, strict adherence to the technical requirements specified by the manufacturer of the oil supply equipment is necessary. Apply the lubricant or grease specified in the drawings or instructions to all areas that require lubrication. (2) The pipeline installation should be arranged in a logical manner with an aesthetically pleasing layout; the return pipe must have an inclination of 3.5 degrees. Inspect and clean the fuel tank and its accessories; conduct a leakage test on the fuel tank using kerosene. Perform a hydrostatic test on the cold oil cooler at 1.25 times its operating pressure. After cleaning the accessories, restore the fuel injection function. (3) Perform oil flushing on the oil pipeline system; it can be ready for trial operation only after the flushing test is successful. II. Operating Methods for Centrifugal Fans （I）Equipment Inspection and Maintenance 1. Check that the rotation direction of the impeller, the bending direction of the blades, and the angle of the air outlet on the casing are in accordance with the drawings (pay special attention to whether the impeller rotates clockwise or counterclockwise) ； 2. The casing and rotor should be free of defects such as cracks, sand holes, and missed welds ； The wear-resistant lining inside the casing should be firm, flat, and free from any looseness ； 3. The inlet control damper doors must be complete in parts, free from deformation or damage, and operate smoothly and synchronously while being firmly fixed in place ； 4. The hydraulic pressure test for the bearing cooling water chamber must be carried out tightly without any leaks, using a pressure level 1.25 times that of the operating pressure ； The impeller and shaft must be assembled correctly, without any looseness ； The bearing model and clearance should comply with the design, and each clearance should be checked using the fuse-pressing method ； The thrust clearance of the fan bearings should be between 0.3 and 0.4 mm; this should be checked using a compression fuse, while the expansion clearance must comply with the specifications given in the drawings ； During installation, the lateral and longitudinal centering deviation of the bearing should be =10mm, and the axis levelness deviation should be =0.1mm/m ； 5. The removed parts should be stored properly, numbered in order, and placed in a clean area to avoid contamination by foreign substances, and they must not be damaged. (II) Installation method of centrifugal fans 1. First, check the external dimensions of the foundation as well as the center dimensions of each reserved cavity ； The dimensional deviation of the foundation base should be within ±20 mm, while the dimensional deviation of the center of each reserved cavity should be between ±10 mm ； For the basic marking, using the building reference point of the main plant or the longitudinal and transverse center lines of the boiler as a basis, the deviation of the main longitudinal and transverse center lines of the foundation should be within ±10 mm, the deviation in the distance between the center lines should be within ±3 mm, and the foundation elevation should be within ±5 mm ； 2. Level the foundation, install foot bolts, and arrange shims. A shim set typically consists of 2 flat shims, 1 inclined shim, and 3 additional shims; the thicker shims should be placed at the bottom, while the inclined shims should be used in pairs ； and extend about 20mm from the frame ； After alignment, it must be welded firmly; there should be no looseness ； Shims should be placed on the main load-bearing plates of the equipment, at the vertical ribs of the frame, or on either side of the foundation bolts; they should be as close as possible to the foundation bolt holes, as long as this does not interfere with the secondary grouting ； 3. Rough positioning of the lower half of the casing: Pay attention to the manufacturer’s installation markings; usually, each unit corresponds to mark B. Before positioning, be sure to consider the relationship with the inlet and outlet air ducts as well as the rotation direction of the impeller ； 4. After inserting the collector flared end into the impeller and securing it with wire, lift the entire rotating assembly to the predetermined position ； Install the foot bolts; the bending degree of these bolts should be ≤ L/100 (where L is the length of the foot bolt), and the bottom end of the foot bolts must not touch the bottom or walls of the hole. The foundation bolts should be subjected to even stress, with 2–3 threads of the bolt exposed ； Then loosen the wire and fix the lower part of the collector to the lower half of the housing with bolts, in order to initially adjust the gap between the impeller and the flared opening. 5. Leveling and alignment of the fan’s rotating assembly: The verticality between the fan’s main shaft and the bearing housing is adjusted using the following method: Attach a magnetic base to the main shaft, and point the dial indicator at the outer ring of the bearing or at the surface of the bearing housing’s elastic mounting surface (i.e., the surface processed on the upper cover) ； At this point, it is sufficient that the reading on the pointer does not exceed 0.15 mm after rotating the main shaft by more than one full turn; this reading indicates the degree of perpendicularity between the bearing housing and the main shaft. 6. Motor leveling and alignment: Adjust the coaxiality between the fan and the motor shaft (i.e., align the coupling). Use three dial indicators for alignment: two axially and one radially ； Rotate each shaft by 90 degrees, record the data, measure the readings in the up, down, left, and right directions, and adjust the coaxiality so that the error is ≤0.05mm ； There should also be a 10mm gap between the two backrest wheels. After alignment, recheck parameters such as the shaft center height and take proper records. 7. After aligning the fan, install the upper cover of the casing as well as the collector in place; asbestos rope should be placed between the two casings ； Tighten the connection bolts; the bolts on all four sides should be under even stress ； Using the impeller as a reference, adjust the gap between the impeller and the flared mouth again. 8. Install the air intake box, the inlet control damper doors, and the remaining parts of the fan. Ensure that the control dampers rotate smoothly; if not, apply lubricant to facilitate rotation until they move smoothly before proceeding with installation ； During installation, the vanes should be securely fixed, with sufficient expansion clearance from the housing ； The control operating device should be flexible and accurate, with consistent actions, and the opening indication markers should match the actual value ； Pay attention to the installation direction; it must not be installed backwards, with the air intake direction being the same as the rotation direction of the impeller. 9. The layout of cooling water and lubricating oil pipelines shall meet the requirements of the drawings, be properly and aesthetically arranged, and the pipelines must not contain any debris.