Piston screw scroll centrifuge compressor characteristics analysis

Piston screw scroll centrifuge compressor characteristics analysis

1. Semi-closed piston compressor
Principle: Rely on the reciprocating motion of the piston to compress the gas in the cylinder. Usually through the crank connecting rod mechanism, the rotary motion of the prime mover is transformed into the reciprocating motion of the piston. The work completed by the crankshaft every revolution can be divided into the suction process and the compression and exhaust process.
Structure: including the body, crankshaft, connecting rod assembly, piston assembly, valve cylinder liner assembly, etc.
Advantages of semi-closed piston compressor:
1. In the general pressure range, the requirements for materials are low, and ordinary steel materials are mostly used. The processing is easier and the cost is lower;
2. The thermal efficiency is high, and the thermal insulation efficiency of general large and medium-sized units can reach about 0.7 ~ 0.85;
3. The gravity and characteristics of the gas have little effect on the working performance of the compressor. The same compressor can be used for different gases;
4. Piston compressor is relatively mature in technology, and has accumulated rich experience in production and use;
5. When the air volume is adjusted, the adaptability is strong, that is, the exhaust range is wide, and it is not affected by the pressure level, and it can adapt to a wider pressure range and cooling capacity requirements;
Disadvantages of semi-closed piston compressor:
1. The structure is complicated and heavy, there are many wearing parts, and the maintenance workload is large;
2. Vibration during machine operation;
3. The exhaust is discontinuous and the airflow has pulsation, which is easy to cause pipeline vibration. In severe cases, the pipeline network or machine parts are often damaged due to pulsation and resonance of the airflow;
4. The power loss is large, and the efficiency is reduced during partial load operation;
5. When a large factory uses multiple compressor units, there are many operators or work intensity.

2. Screw compressor
Principle: Through the mutual immersion of the yin and yang rotors, and the space contact line continuously moves from the suction end to the exhaust end, the volume of the element changes periodically, thereby completing the continuous suction and pressure transmission and exhaust process.
Structure: composed of casing, screw (or rotor), bearing, energy adjustment device, etc.
Advantages of screw compressor:
1. Fewer parts, less wearing parts and high reliability;
2. Convenient operation and maintenance;
3. No unbalanced inertial force. Stable and safe operation, low vibration;
4. With the characteristics of forced gas delivery, the exhaust volume is almost not affected by the exhaust pressure;
5. The rotor tooth surface of the screw compressor actually has a gap. Therefore, it is not sensitive to wet travel and can withstand liquid shock;
6. The exhaust temperature is low, and it can be operated under a higher pressure ratio;
7. It can realize stepless adjustment of cooling condition, adopt slide valve mechanism, so that the cooling capacity can be adjusted steplessly from 15% to 100%, saving operating costs;
Disadvantages of screw compressors:
1. The rotor tooth surface is a space curved surface, which needs special tools to be processed on expensive equipment. The machining accuracy of body parts also has high requirements, and high-precision equipment must be used;
2. The compressor noise is high;
3. The screw compressor can only be used in the medium and low pressure range, not in high pressure occasions;
4. The oil injection volume is large and the oil treatment system is complicated, so there are many auxiliary equipment of the unit;
5. The screw compressor relies on the gap to seal the gas and does not have superior performance in a small volume range.

3. Scroll compressor
Principle: The vortex shape of the moving plate and the static plate are the same, but the phase difference is 180 ° to engage to form a series of closed spaces; the static plate does not move, the moving plate moves around the center of the fixed plate, and makes an orbital motion with the radius of eccentricity. When the orbiting disk revolves, it engages in sequence, making the crescent-shaped area continuously compressed and reduced, so that the gas is continuously infused and finally discharged from the central hole of the static disk.
Structure: moving disk (vortex rotor), static disk (vortex stator), bracket, cross coupling ring, back pressure cavity, eccentric shaft.
Advantages of scroll compressor:
1. The eccentric shaft driving the movable scroll can rotate at high speed, and the scroll compressor is small in size and light in weight;
2. The force change of moving parts such as movable scroll and main shaft is small, and the vibration of the whole machine is small;
3. Adapt to variable speed movement and frequency conversion speed regulation technology;
4. The noise of the scroll compressor is very low;
5. The scroll compressor has reliable and effective sealing, and its refrigeration coefficient does not decrease with the increase of operating time, but slightly improves;
6. Scroll compressor has good working characteristics. In the heat pump type air conditioning system, it is particularly manifested in high heating performance, good stability and high safety;
7. The scroll compressor has no clearance volume and can maintain high volume efficiency operation;
8. Small torque change, high balance, small vibration and stable operation, so it is easy to operate and easy to realize automation;
9. Few moving parts, no reciprocating mechanism, simple structure, small size, light weight, few parts, high reliability, life span is more than 20 years.
Scroll compressor shortcomings:
1. The surfaces of moving parts are mostly curved surfaces. The processing and inspection of these curved surfaces are more complicated. Manufacturing requires high-precision processing equipment and precise self-aligning assembly technology, so the manufacturing cost is higher.
2. Between moving parts or between moving parts and fixed parts, a certain movement gap is often used to achieve the seal, and the gas will inevitably cause leakage through the gap, which limits the difficulty of the rotary compressor to achieve greater compression. Than, therefore, most rotary compressors are more used in air conditioning conditions.

4. Centrifugal compressor
Principle: When the compressor impeller rotates, the refrigerant vapor enters the impeller flow path from the suction chamber through the inlet guide vane, and the gas rotates with the impeller under the impeller. Due to the centrifugal force, the gas flows radially along the impeller channel and leaves the impeller.
Structure: The single-stage compressor is mainly composed of suction chamber, impeller (working wheel), pressure regulator, volute chamber (volute) and seal. For multi-stage compression, there are also components such as bends and recirculators.

Advantages of centrifugal compressor:
1. The centrifugal compressor has large air volume, simple and compact structure, light weight, small unit size and small footprint. Compared with the piston compressor, when the cooling capacity is the same, the weight is 5 to 8 times lighter than the piston compressor.
2. Because it has no wearing parts such as steam valve piston ring, and no crank connecting rod mechanism, it has balanced operation, reliable operation, high operating rate, and few friction parts. Therefore, it requires less spare parts, less maintenance costs and fewer personnel.
3. There is no friction between the working wheel and the casing, and no lubrication is needed. 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 drag of industrial steam turbine or gas turbine. For general large chemical plants, by-product steam is often used to drive industrial steam turbines as power, which provides the possibility of comprehensive utilization of thermal energy.
Disadvantages of centrifugal compressors:
1. Centrifugal compressors are currently not suitable for occasions where the air volume is too small and the pressure ratio is too high, and because it is suitable to use a refrigerant with a relatively large molecular weight, it is only suitable for large refrigeration capacity, generally in the range of 25-30 million kcal / Hour or more.
2. The stable working area of the centrifugal compressor is narrow. Although the air volume adjustment is more convenient, it is less economical.
3. Generally, a speed-increasing gear is used for transmission, which has a relatively high speed and high requirements on the sealing of the shaft end. These all increase the manufacturing difficulty and structural complexity.
4. "Surge" is prone to occur at low load.