35t/h, 75t/h circulating fluidized bed boiler ventilation and induced draft fan

1. Overview
Circulating fluidized bed boilers, as a new type of high-efficiency, energy-saving, and clean combustion boiler, have been widely used both domestically and internationally, and have rapidly developed towards large-scale production. They have achieved significant social and economic benefits, especially in the field of environmental protection. In order to meet the current development needs of circulating fluidized bed boilers in China, our company has successfully developed dedicated fans for 35t/h and 75t/h circulating fluidized bed boilers, and jointly developed the XG (Y) series dedicated fans for circulating fluidized bed boilers with Xi'an Thermal Power Research Institute.
This series of fans is developed based on the introduction of advanced foreign technology by our company, combined with the characteristics of fans used in circulating fluidized bed boilers. The primary and secondary fans have two types of blades (forward bending type and backward type); The efficiency and regulation performance of backward curved blades are higher than those of forward curved blades, but forward curved blades have smaller structural dimensions, lighter weight, smaller volume, and lower cost compared to backward curved blades. We recommend prioritizing the use of backward blade fans. Although the initial investment may be higher, this fan has low operating costs and good energy-saving effects. The impellers of this series of induced draft fans all use single plate blades, which overcome the disadvantage of hollow blades easily worn through and entering dust, causing rotor imbalance. At the same time, wear-resistant measures such as spray welding, overlay welding, and adding wear-resistant plates can be taken according to user requirements to improve the service life of the fan.
2. The purpose of the fan
The CGXG (Y) series circulating fluidized bed boiler dedicated fan is mainly used for the primary and secondary air supply fans and boiler flue gas induced draft of 300MW unit circulating fluidized bed boilers. It can also be used for other similar working conditions of air supply and induced draft systems, such as blast furnace combustion assistance air supply, blast furnace flue gas induced draft dust removal, etc. Circulating fluidized bed boiler blower (or primary fan, secondary fan), induced draft fan, slag cooler fluidization fan, and reflux valve fan are specialized fans for various tonnage circulating fluidized bed boilers. The medium conveyed by the induced draft fan is flue gas, with a maximum temperature not exceeding 250 ℃.
3. Form of fan
This series of fans has two transmission modes: D transmission and F transmission. It depends on the user's needs and the size of the fan. For primary and secondary fans with fan numbers above No.16, F transmission is recommended. For induced draft fans with fan numbers above No.20, F transmission is recommended. The stability and reliability of F transmission are better than D transmission (of course, the price and cost are higher). The angle of use of the fan is determined according to the user's needs.
4. Specification and model of centrifugal blower for circulating fluidized bed boiler
Performance range of fluidized bed boiler induced draft fan
Blower pressure: 7000 24000Pa t=20 ℃

5. Structural characteristics
Host: The fan is mainly composed of impeller, casing, air inlet, intake box, regulating valve, transmission group, bearing seat and other parts.
1) Impeller: It consists of backward curved blades (for CGXG-19, CGXG-26, and CGXG-28, it is a forward curved type), a conical front plate, and a flat rear plate. The blades are made of high-strength alloy steel plates (for induced draft fans, wear-resistant welding rods are used to weld wear-resistant layers near the disc where the blades are prone to wear, with a hardness of HRC48 or higher, which improves the service life of the impeller). After static and dynamic balance correction, the dynamic balance accuracy level is G4 level (special requirements can reach G2.5 level), with good air performance, high efficiency and low noise, and smooth operation.
(2) The casing and intake box (not available for F transmission, D transmission): The casing and intake box adopt a split structure for easy installation, debugging, and maintenance. The design of the fan enhances the strength of the casing and intake chamber. The exterior of the casing and intake chamber is welded with a well shaped grid plate of appropriate height, and the interior is welded with hollow tube support, thus eliminating vibration caused by insufficient rigidity of the casing.
(3) Air inlet: made as a whole, installed on the side of the fan, with a curved cross-section parallel to the axial direction, which can allow gas to enter the impeller smoothly with minimal loss.
(4) Adjustment door: This device is installed in front of the fan inlet chamber (or air inlet) to control the inlet flow of the fan. The adjustment door is equipped with five wing shaped blade adjustment dampers to adjust the characteristics of the fan and improve its adjustment efficiency. The support of the adjustment blades is equipped with a rolling bearing, which is a single row ball bearing. It is lubricated with grease, rotates flexibly, and is reliable to use. The blade adjustment range can be adjusted from O ° to 90 °, that is, from fully closed to fully open. The operation and control of the device are achieved by electric actuators. In this way, micro adjustment of fan flow can be achieved.
(5) Bearing seat: Water cooled bearing seat is used, and the bearing lubrication method adopts immersion lubrication. Rolling bearings are used (Swedish SKF bearings can be matched according to requirements). The water-cooled bearing seat requires the installation of a water supply pipe, and the water consumption varies depending on the ambient temperature. Generally considered at a rate of 0.5-/h, with a water pressure of ≤ 0.37MPa, the bearing box is equipped with a dual gold thermometer (remote control using platinum resistance thermometer) and an oil level indicator, and the lubricating oil uses mechanical oil N68. The bearing seat is connected to the bearing seat bottom plate for easy installation and maintenance.
(6) Spindle: Made of 40Cr alloy structural steel, which has undergone quenching and tempering treatment and precision machining. The main shaft is designed with a non-contact spiral seal extending from the bearing seat, ensuring reliable sealing without oil leakage or the need to replace seals (this structure belongs to our company's proprietary technology).
Electric motor: The electric motor adopts products from well-known domestic manufacturers, with insulation level F and protection level IP54. The motor is equipped with bearing temperature and vibration measuring elements and embedded with temperature measuring elements (platinum thermistor) on the stator. It is equipped with a motor base plate and anchor bolts for easy installation and maintenance.
The fan is equipped with a local low-voltage control cabinet according to user needs: it is equipped with a switch for local and remote control of the fan, a switch for adjusting the opening of the fan inlet air door, and indicator instruments for displaying the temperature and vibration of the fan and motor bearings, the temperature of the motor stator winding, and the motor current. At the same time, the control cabinet has sufficient input and output interfaces to achieve remote transmission and control of signals such as fan bearing temperature, fan operation, shutdown, and faults (i.e. equipped with DCS system interfaces).
Import and export expansion joints: Non metallic expansion joints are used to eliminate the impact of thermal expansion caused by temperature changes on the fan.
Muffler (used in primary and secondary fans): It is an impedance composite noise reduction structure, made of ultra-fine glass wool and perforated plate materials, with good noise reduction effect and low resistance loss.
The overall lifespan of the fan is 30 years, the service life of the bearings is 35000 hours, and the service life of the impellers for the primary and secondary fans is 35000 hours. When the dust content of the induced draft fan is 80-100mg/h, the service life of the impeller is 10000-15000 hours. When the dust content is around 50mg/, the service life of the impeller is 30000 hours.