Application
C4-68 and Y4-68 centrifugal fans and induced draft fans are suitable for ventilation and induced draft of steam boilers below 230/h in large-scale power generation. C4-68 can also be used for mine ventilation and general ventilation when there are no other special requirements. The medium conveyed by the centrifugal ventilator is air, and the maximum temperature does not exceed 80℃; the medium conveyed by the induced draft centrifugal fan is flue gas. The maximum temperature does not exceed 250℃. A dust removal device with a dust removal efficiency of not less than 85% must be installed in front of the induced draft fan to reduce the dust content of the flue gas entering the centrifugal fan and increase the service life of the centrifugal blower.
Type
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Both the centrifugal ventilator and induced draft centrifugal fan are made into single suction, with 7 machine numbers from Na.8 to Na.16.
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Each centrifugal fan can be made into two types: right-hand rotation or left-hand rotation. When looking at the centrifugal blower from the motor end, the fan with the impeller rotating clockwise is called a right-hand fan, represented by "right"; the centrifugal fan with the impeller rotating counterclockwise is called a left-hand fan, represented by "left".
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The outlet position of the centrifugal fan is indicated by the outlet angle of the casing. Both right-hand and left-hand fans can be made into six angles: 0°, 45°, 90°, 135°, 180°, and 225°.
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The centrifugal blower's transmission mode is D type, and the motor and centrifugal fan are directly connected using an elastic coupling.
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Product type example: G/Y 4-68No.8D right 90°, where G and Y represent boiler ventilator and boiler induced draft centrifugal fan respectively.
Structural features
The centrifugal fan is mainly composed of an impeller, a casing, an air inlet, an adjusting door, and a transmission part.
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Impeller: It consists of 12 backward-inclined wing-shaped blades welded between the arc-shaped wheel cover and the flat wheel disc. The use of wing-shaped blades ensures high efficiency, low noise, and high strength of the centrifugal fan. The impeller is calibrated for static and dynamic balance and runs smoothly. The impeller structure of the induced draft centrifugal fan and the induced draft centrifugal blower of the same machine number is the same.
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Casing: Ordinary steel plates are welded into a volute body, and the centrifugal fan casing is made into an integral structure. For the induced draft centrifugal fan, a dust cleaning door is opened on the volute plate, and it is appropriately thickened to prevent soot wear and extend its service life.
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Air Inlet: To converge the streamlined overall structure, it is fixed to the inlet side of the casing with bolts.
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Adjusting Door: A device used to adjust the centrifugal fan flow rate. N.8-12.5 consists of 11 petal-shaped blades, and No.14-16 consists of 13 petal-shaped blades, all of which are axially installed in front of the air inlet. Due to the use of an external transmission structure, the rotation is flexible and convenient. The adjustment range is from 90° (fully closed) to 0° (fully open). The position of the lever of the regulating door is on the right side when viewed from the air inlet. For a right-handed centrifugal fan, the lever is pushed from bottom to top from fully closed to fully open; for a left-handed centrifugal fan, the lever is pulled from top to bottom from fully closed to fully open. In order for all parts of the regulating door to work properly, they must be well lubricated. For the regulating door of the centrifugal fan, calcium-sodium based grease is used for lubrication. For the induced draft centrifugal fan, due to the high gas temperature, the grease uses molybdenum disulfide high temperature (260℃) grease, which can ensure lubrication during high temperature operation.
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Transmission Part: The transmission mode is D type. It consists of a main shaft, bearing box, coupling, etc. The main shaft is made of high-quality steel. The rolling bearing water-cooled integral bearing box is adopted, so a water pipe needs to be installed. The water consumption varies with the ambient temperature, generally 0.5-1m³/h. The bearing box is equipped with a thermometer and an oil level indicator. The lubricating oil adopts the full loss system oil L-AN46, and the amount of oil added is in accordance with the requirements of the oil level mark.
Performance and Selection
Here we only give the dimensionless performance table and dimensionless performance curve of the two types of centrifugal fans Na 10 prototypes. From the dimensionless performance table and curve, the dimensional performance parameters of the centrifugal fans are calculated.
Treatment when the flow is too much or too little: During use, the flow is often too much or too little. There are many reasons for this phenomenon. If it occurs during use, it is mainly due to the resistance in the pipe network being large or small, or the centrifugal fan working in the flying area. If it gradually decreases over a long period of time during use, or suddenly decreases in a short period of time, it is mainly due to pipe network blockage.
After the centrifugal fan is newly installed, excessive or insufficient flow occurs during operation. The main reasons are as follows:
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The actual value of the pipe network resistance is too different from the calculated value. From the general pipe network characteristic equation p=Kq² (K is the resistance coefficient), it can be seen that if the actual value K is less than the calculated value K, the flow rate increases; if the actual value K is greater than the calculated value K, the flow rate decreases.
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The influence of the centrifugal fan's total pressure deviation ∆p was not considered during selection. When the centrifugal fan's total pressure has a positive deviation, the flow rate increases; when the total pressure has a negative deviation, the flow rate decreases.
When the centrifugal fan starts to operate after being newly installed, or when the flow rate is too large or too small during use, one of the following methods can be used to eliminate it:
① Use the opening and closing degree of the regulating door to adjust the flow rate;
② Change the speed of the centrifugal fan to adjust the flow rate;
③ Change the centrifugal fan with higher or lower pressure to adjust the flow;
④ Change the pipe network resistance coefficient to adjust the flow rate.
It must be pointed out that throttling devices are generally used to adjust the flow rate. However, when the actual flow rate is much larger than the required flow rate, this method wastes too much electricity and is very uneconomical. If conditions permit, it is usually necessary to reduce the centrifugal fan speed or replace the centrifugal fan with a lower pressure. When the regulating door is fully opened, the flow rate is still too small. At this time, the pipe network should be changed to reduce the resistance coefficient to increase the flow rate. It is also possible to increase the centrifugal fan speed and replace the centrifugal fan with a higher pressure, but the maximum speed of the centrifugal fan cannot exceed the maximum speed on the performance table.
The performance of a centrifugal fan generally refers to the performance of conveying air under standard conditions. The specified state of a centrifugal ventilator is Pa=101300Pa, gas temperature t₀=20℃, gas density Po=1.2kg/m³; the specified state of an induced draft centrifugal fan is Pa₀=101300Pa, gas temperature t₀=140℃, gas density ρ₀=0.85kg/m³. The performance in the performance table refers to when the blades are fully opened to 0°. The performance table shall prevail when ordering. When the actual use state does not match the above specified state, the performance of the actual use state must be converted to the performance of the specified state, and then the centrifugal fan is selected according to the converted performance.
