Fan is the customary abbreviation for gas compression and gas conveying machinery, commonly referred to as fans include: ventilators, blowers, and wind generators. Gas compression and gas conveying machinery is a machine that converts rotating mechanical energy into gas pressure energy and kinetic energy and transports gas out. In this special topic, I will introduce in detail the characteristics of various types of fans, fan models, fan principles and other fan knowledge.
1 What is a fan
A fan is a machine that increases gas pressure and discharges gas by inputting mechanical energy. It is a driven fluid machine . Fans are widely used in ventilation, dust removal and cooling in factories, mines, tunnels, cooling towers, vehicles, ships and buildings, ventilation and induced draft in boilers and industrial furnaces; cooling and ventilation in air conditioning equipment and household appliances ; Drying and selection of grain, air source of wind tunnel and inflation and propulsion of hovercraft, etc.
2 Types and characteristics of fans
1. Advantages of centrifugal compressors
1. The centrifugal compressor has the advantages of large air volume, simple and compact structure, light weight, small unit size and small footprint.
2. Balanced operation, reliable operation, high operation rate, less friction parts, less spare parts required, less maintenance cost and less personnel.
3. In the chemical process, the centrifugal compressor can achieve an absolutely oil-free compression process for the chemical medium.
4. Centrifugal compressor is a rotary motion machine, which is suitable for direct driving of industrial steam turbine or gas turbine. For general large-scale chemical plants, by-product steam is often used to drive industrial steam turbines as power, which provides the possibility for comprehensive utilization of thermal energy. However, centrifugal compressors also have some disadvantages.
Second, the performance characteristics of axial compressors
High efficiency, single machine efficiency can reach 86%～92%, which is higher than The centrifugal compressor is 5% to 10% higher, has a large flow capacity per unit area, and a small radial size. It is suitable for occasions where the flow rate is greater than 1500m3/min. The single-stage pressure is relatively low, and the single-cylinder multi-stage pressure ratio can reach 11. Compared with the compressor, the stable working area of the stationary vane non-debuggable axial flow compressor is narrower, and at a constant speed, the flow rate changes relatively little, and the pressure change is large. In addition, the structure is relatively simple and maintenance is convenient. Therefore, the axial flow compressor is ideal for medium, low pressure, large flow, and the load is basically unchanged. The fully static vane adjustable axial flow compressor can expand the stable working area of the compressor, make up for the deficiencies of the static vane non-adjustable axial flow compressor, and can improve the efficiency of the compressor and reduce the starting power. At present, the oil refinery mainly uses the axial flow compressor with full vane adjustable.
3. Advantages of reciprocating compressors
1. High thermal efficiency and low unit power consumption
2. Easy processing, low material requirements, low cost
3. Simple device system
4. Early design and production, mature manufacturing technology
5. Wide range of applications
Fourth, performance characteristics of centrifugal blower
This series of blowers has high efficiency, low noise, stable operation, absolute No pulse, wide stable area, clean, dry and oil-free gas, few wearing parts and easy installation, operation and maintenance.
V. Performance characteristics of Roots blower
The biggest feature is that the flow rate is adjusted when the pressure is within the allowable range. The change is very small, the pressure selection range is very wide, and it has the characteristics of forced gas transmission. The medium does not contain oil when conveying. Simple structure, convenient maintenance, long service life and small vibration of the whole machine. The conveying medium of the Roots blower is clean air, clean coal gas, sulfur dioxide and other inert gases, the first choice for special gas industries (gas, natural gas, biogas, carbon dioxide, sulfur dioxide, etc.) and high-pressure conditions. In view of the above characteristics, it can be widely used in metallurgy, chemical industry, fertilizer, petrochemical, instrument and building materials industries.
3 The working principle of the fan
1. Centrifugal fan
The airflow enters the rotating blade channel, and under the action of centrifugal force The gas is compressed and flows radially.
Centrifugal fans are based on the principle of converting kinetic energy into potential energy, using a high-speed rotating impeller to accelerate the gas, then decelerate and change the flow direction to convert kinetic energy into potential energy. In a single-stage centrifugal fan, the gas enters the impeller from the axial direction, the gas changes to the radial direction as it flows through the impeller, and then enters the diffuser. In a diffuser, the gas changes the direction of flow causing a deceleration, which converts kinetic energy into pressure energy. The pressure increase occurs mainly in the impeller, and secondly in the diffusion process. In a multi-stage centrifugal fan, a recirculator is used to move the airflow to the next impeller, creating a higher pressure.
2. Axial flow fan
After the air enters the fan impeller axially, it flows along the axial direction in the flow channel of the rotating blade fan. Compared with centrifugal fans, axial flow fans have the characteristics of large flow, small volume and low pressure head, so attention should be paid to the occasions with dust and corrosive gases.
When the impeller rotates, the gas enters the impeller axially from the air inlet, and is pushed by the blades on the impeller to increase the energy of the gas, and then flows into the guide vane. The guide vanes turn the deflected airflow into an axial flow, and at the same time guide the gas into the diffuser, further convert the kinetic energy of the gas into pressure energy, and finally introduce it into the working pipeline.
3. Diagonal flow (mixed flow) fan
In the impeller of the fan, the direction of the airflow is in the axial flow direction. During the time, it flows approximately along the cone, so it can be called an oblique flow (mixed flow) fan. The pressure coefficient of this fan is higher than that of the axial fan, and the flow coefficient is higher than that of the centrifugal fan.
When the impeller rotates, the gas enters the impeller axially from the air inlet, and the Bailey beam is pushed by the blades on the impeller to increase the energy of the gas, and then flows into the guide vane. The guide vanes turn the deflected airflow into an axial flow, and at the same time guide the gas into the diffuser, further convert the kinetic energy of the gas into pressure energy, and finally introduce it into the working pipeline.
4 Models of fans
Meaning of centrifugal fan models: It consists of basic models and supplementary models. If the basic model of the fan is the same, but the purpose is different, for the convenience of distinction, a symbol such as “G” or “Y” is added before the basic model. “G” means a blower (blower) “Y” means an induced draft fan. The supplementary model number consists of two digits. The first digit indicates the suction type of the fan inlet, represented by “0”, “1”, “2”, where “0” represents a double suction fan; “1” represents a single suction fan; “2” represents a two-stage series fan. The second digit represents the design serial number. The complete representation method of the fan model includes: name, model, machine number, transmission mode, rotation direction, outlet position and other parts.
Axial flow fan model 200FZY4-D: 200 is the model of the fan (generally refers to the diameter of the fan blade), F-fan in YZFZ, Z – Axial flow fan, Y-cylinder type. 4- The serial number of the motor’s performance parameters (generally refers to the speed of the motor) is also what we often call a 4-pole motor.
5 Fan impeller wear prevention and repair
(1) To reduce the dust and corrosive gas entering the fan, the fan operation system must be transformed.
(2) Try to make the local wear tend to be uniform, which requires improving the wear resistance of the impeller. If the wear resistance of the impeller can be improved, materials with high hardness and good wear resistance can be used, which will not only bring difficulties to the impeller manufacturing process, but also is unreasonable from an economic point of view.
(3) The material used for the fan impeller can be replaced. In order to prolong the life of the rotor, in addition to considering the physical and mechanical properties of the material, attention should also be paid to its chemical properties. The material of the fan impeller is stainless steel. When the chromium content exceeds 12%, the corrosion resistance is extremely strong.
(4) Use Soleil industrial polymer carbon nano-polymer material for repair and protection, and bond and combine special fibers, ceramics, silicon steel and other materials through polymerization technology, so that they not only have ultra-high strength And hardness, but also has good corrosion resistance, so that it can also show unimaginable results in the harshest dry grinding environment. The effect of the repaired fan rotor is very significant. The corrosion and wear problem of the gas fan rotor has been basically solved, which ensures the normal operation of the unit, and thus achieves good economic and social benefits.
