1. Reciprocating compressor
working principle:
The reciprocating compressor mainly compresses gas through the reciprocating motion of the piston in the cylinder. The piston is driven by the crankshaft connecting rod mechanism. When the piston moves downward, the volume inside the cylinder increases, and the associated gas enters the cylinder through the intake valve; When the piston moves upward, the cylinder volume decreases, the gas is compressed, the pressure increases, and then discharged through the exhaust valve.
For example, in a double acting reciprocating compressor, both sides of the piston can perform intake and exhaust operations, thereby improving compression efficiency.
advantage:
It has a wide pressure range and can adapt to various pressure conditions from low pressure to high pressure. The maximum discharge pressure can reach tens of megapascals, making it suitable for high-pressure compression of associated gas.
High efficiency, under appropriate working conditions, it can effectively compress the associated gas to the required pressure, and its isentropic efficiency can reach about 70% to 90%.
Disadvantages:
The flow rate is relatively small because it compresses gas through the reciprocating motion of the piston, so the gas flow rate per unit time is limited.
The structure is complex, with many moving parts such as pistons, connecting rods, crankshafts, etc., which leads to high maintenance costs. Moreover, these moving parts generate significant vibration and noise during high-speed operation.
Applicable scenarios:
Suitable for the recovery of associated gas with low gas volume and high pressure requirements, such as in some small oil wells or wellhead situations where the associated gas needs to be compressed to a higher pressure for transportation.
2. Centrifugal compressor
working principle:
Centrifugal compressors mainly rely on high-speed rotating impellers to do work on gases. After the associated gas enters the impeller, as the impeller rotates, the gas is accelerated under the action of centrifugal force, and the pressure and velocity of the gas are increased. Then, the high-speed gas passes through components such as the diffuser, reducing its velocity and further increasing its pressure.
For example, a multi-stage centrifugal compressor can achieve higher pressure increase by connecting multiple impellers in series.
advantage:
Large flow, capable of handling a large amount of associated gas, suitable for large-scale associated gas recovery. Its flow range can range from small flow to very large flow, and the flow of some large centrifugal compressors can reach hundreds of thousands of cubic meters per hour.
The structure is relatively simple with few moving parts, mainly consisting of impellers and shafts, resulting in smooth operation and relatively low vibration and noise.
Disadvantages:
The ability to increase pressure is relatively limited and is generally suitable for compression in the medium and low pressure range. The pressure ratio of single-stage centrifugal compressors is usually around 1.1 and 1.3, and the maximum discharge pressure of multi-stage centrifugal compressors is generally below 10MPa.
The quality requirements for gas are high, and impurities in the gas may cause damage to components such as impellers, so pre-treatment equipment such as filters are usually installed at the inlet.
Applicable scenarios:
Commonly used in large oil and gas fields with high associated gas production and moderate pressure, such as in large natural gas processing plants, where a large amount of associated gas is subjected to centralized compression treatment.
3. Screw compressor
working principle:
A screw compressor compresses gas through a pair of interlocking male and female rotors. When the associated gas enters the suction port of the compressor, it is gradually compressed between the teeth of the anode and cathode rotors. As the rotor rotates, the volume between the teeth decreases continuously, the gas is compressed, and finally discharged from the exhaust port.
For example, in a twin-screw compressor, the two screw rotors rotate in opposite directions, and gas is compressed in the meshing space between them.
advantage:
It has good continuous intake and exhaust characteristics, stable flow rate, and can maintain high efficiency over a wide range of operating conditions.
Compact structure, relatively small volume, easy installation, and it has a certain tolerance to impurities in the intake, which can to some extent handle associated gas containing small amounts of impurities.
Disadvantages:
The pressure ratio is generally not very high, and the pressure ratio of a single-stage screw compressor is usually around 7-10. Moreover, as the pressure ratio increases, its efficiency will decrease.
Due to the gap between the rotors, there may be some gas leakage, which to some extent affects the compression efficiency.
Applicable scenarios:
Suitable for the recovery of associated gas with medium flow and pressure requirements, such as compressing the associated gas in the medium pressure range in some medium-sized oil wells or oil and gas processing stations.
Comparison between them:
1. In terms of traffic
Reciprocating compressor: relatively small flow rate. Its working principle determines that it gradually compresses gas through the reciprocating motion of the piston, and the intake and exhaust volume per unit time is limited. Usually used to handle associated gas with smaller flow rates, such as associated gas recovery from small oil wells, the flow range may be between a few cubic meters per hour and several hundred cubic meters per hour.
Centrifugal compressor: Its significant advantage is its high flow rate. It relies on the high-speed rotation of the impeller to push the gas and can process a large amount of associated gas in a unit of time. It can meet the large-scale associated gas recovery needs of large oil and gas fields or natural gas processing plants, with flow rates ranging from several thousand cubic meters per hour to several hundred thousand cubic meters per hour.
Screw compressor: flow rate between reciprocating and centrifugal. Its intake and exhaust processes are relatively continuous and stable, with a flow range generally ranging from tens of cubic meters per hour to several thousand cubic meters per hour. It is suitable for medium flow associated gas recovery scenarios, such as medium-sized oil wells or oil and gas processing stations.
2. In terms of pressure range
Reciprocating compressor: With a wide pressure range, it can produce high compression ratios. Capable of compressing associated gas from low pressure to high pressure, with a maximum discharge pressure of several tens of megapascals, suitable for high-pressure compression of associated gas to meet the requirements of long-distance transportation or specific high-pressure processes.
Centrifugal compressor: generally suitable for the medium and low pressure range. The pressure ratio of a single-stage centrifugal compressor is usually around 1.1 to 1.3. Although the pressure can be increased through multi-stage series connection, the maximum discharge pressure is generally below 10MPa, mainly used for medium and low pressure compression of associated gas.
Screw compressor: The pressure ratio is relatively limited. The pressure ratio of a single-stage screw compressor is usually around 7-10. As the pressure ratio increases, its efficiency decreases, making it suitable for compression of associated gas in the medium pressure range.
3. Efficiency aspect
Reciprocating compressor: Under appropriate operating conditions, its efficiency is relatively high, and its isentropic efficiency can reach around 70% to 90%. However, its efficiency is greatly affected by factors such as friction between the piston ring and the cylinder wall, resistance from the valve, and may decrease at high flow rates.
Centrifugal compressor: The efficiency is also considerable under design conditions, especially when dealing with high flow gases, it can perform well. But its efficiency is sensitive to changes in intake flow rate and pressure, and may decrease significantly when deviating from design conditions.
Screw compressor: It can maintain high efficiency over a wide range of operating conditions because its intake and exhaust are continuous processes, reducing the impact of pressure fluctuations on efficiency. However, as the pressure ratio increases and the leakage rate increases, the efficiency will also be affected to some extent.
4. In terms of structure and maintenance
Reciprocating compressor: It has a complex structure and many moving parts, such as pistons, connecting rods, crankshafts, etc. The friction and wear between these components require regular maintenance, and due to the inertia force of moving parts, significant vibrations and noise are generated during operation. The maintenance cost is relatively high, requiring regular replacement of vulnerable components such as piston rings and air valves.
Centrifugal compressor: The structure is relatively simple, and the main moving parts are the impeller and shaft. It runs smoothly with low vibration and noise. Daily maintenance mainly focuses on cleaning the impeller and maintaining the bearings, making maintenance relatively simple. But if key components such as impellers are damaged, the repair cost is high because it requires high manufacturing accuracy and balance of the components.
Screw compressor: compact structure and small volume. Its moving parts are mainly screw rotors, and due to the gap between rotors, gas leakage problems are prone to occur. The maintenance work includes rotor inspection, seal replacement, etc., and the maintenance cost is between reciprocating and centrifugal.
5. Requirements for intake quality
Reciprocating compressor: It has certain requirements for intake quality, but relatively has a certain tolerance. A small amount of impurities entering may affect the sealing between the piston and cylinder or damage the air valve, but the problem can be solved to some extent by installing simple filters and other equipment at the intake port.
Centrifugal compressor: requires high gas quality. Because high-speed rotating impellers are easily damaged by impurities, efficient pre-treatment equipment such as filters and separators are usually installed at the inlet to ensure that the associated gas entering the compressor is relatively pure.
Screw compressor: has a certain tolerance to intake quality and can handle associated gas containing small amounts of impurities. However, if there are too many impurities, it can also affect the meshing and sealing of the screw rotor, thereby affecting the performance and service life of the compressor.
