The following are the working principles of different types of natural gas booster compressors:
Piston compressor
Working cycle: The electric motor drives the crankshaft to rotate, and the piston reciprocates in the cylinder through the connecting rod. The crankshaft rotates once, the piston reciprocates once, and the cylinder sequentially completes the process of suction, compression, and exhaust, thus completing a working cycle
Inhalation process: As the piston moves to the left, the working volume inside the cylinder gradually increases while the pressure gradually decreases. When the pressure drops slightly below the pressure in the intake pipe, the gas in the intake pipe opens the suction valve and enters the cylinder until the piston reaches the leftmost position (also known as the inner dead center), at which point the working volume reaches its maximum and the suction valve begins to close
Compression process: When the piston moves to the right, the working volume inside the cylinder decreases, while the gas pressure gradually increases. Due to the check function of the intake valve, the gas in the cylinder cannot flow back into the intake pipe. At the same time, due to the gas pressure in the exhaust pipe being higher than the pressure inside the cylinder, the gas in the cylinder cannot flow out of the exhaust valve, and the gas in the exhaust pipe cannot enter the cylinder due to the check effect of the exhaust valve. At this point, the amount of gas inside the cylinder remains constant, and as the piston moves to the right, the gas pressure continues to increase
Exhaust process: When the piston moves to the right to a certain position, the gas pressure in the cylinder rises slightly higher than the gas pressure in the exhaust pipe, and the gas opens the exhaust valve and enters the exhaust pipe until the piston moves to the rightmost position (also known as the outer dead center). The exhaust valve is closed, the piston moves left again, and the above process is repeated
Screw compressor
Basic principle: Two rotating screws compress gas from low pressure to high pressure within their common gap. Two screws mesh with each other, one of which is a male screw and the other is a female screw. Their helical teeth cooperate with each other to form a series of sealed chambers. When the screw rotates, gas is drawn into these chambers and continuously moves forward as the screw rotates, gradually reducing the volume of the chambers and achieving gas compression
Inhalation process: Gas enters the suction chamber of the screw compressor from the inlet. As the screw rotates, the meshing area between the suction chamber and the screw gradually increases, and the gas is sucked into the spiral groove of the screw, forming a continuous inhalation process.
Compression process: As the screw rotates further, the inhaled gas is enclosed in the sealed chamber between the spiral groove and the casing, and moves forward along the axial direction of the screw. During this process, as the spiral groove of the screw gradually becomes shallower, the volume of the chamber gradually decreases, and the gas is compressed by compression, resulting in a gradual increase in pressure.
Exhaust process: When the compressed gas reaches the predetermined pressure, the sealed chamber is connected to the exhaust port, and the high-pressure gas is discharged from the compressor.
Diaphragm compressor
Collaboration between gas compression system and hydraulic oil system: The gas compression system includes a metal diaphragm and gas inlet and outlet valves; The hydraulic oil system includes a crankshaft, connecting rods, and pistons driven by an electric motor. By reciprocating the piston, hydraulic oil pressure is generated, which drives the diaphragm to move towards the gas side, compressing the gas and discharging it
Inhalation process: When the piston is at the bottom, the hydraulic system is automatically refilled with hydraulic oil by the oil pump. Gas enters the diaphragm chamber through the intake valve under inlet pressure, pushing the diaphragm to the bottom of the chamber and filling it with gas
Compression and exhaust process: The crankshaft rotates, the piston moves from bottom to top, and the hydraulic oil system pressure increases. When the hydraulic oil pressure reaches the compressed gas pressure, the diaphragm moves to the top of the chamber, compressing the gas. When the gas pressure inside the membrane chamber reaches the opening pressure of the exhaust valve, the exhaust valve opens and the gas is discharged. The hydraulic system pressure continues to increase, and the membrane continues to move towards the top, ensuring maximum gas displacement and efficiency. When the diaphragm has fully entered the top of the chamber, the piston continues to move to the top. At this point, the hydraulic oil pressure regulating valve is opened by the hydraulic oil pressure, and the hydraulic oil returns to the crankcase
Cycle completion: When the piston moves towards the bottom, the clearance gas and suction gas push the diaphragm assembly towards the bottom of the cavity, completing the entire cycle
Centrifugal compressor
Impeller rotation accelerates gas: Centrifugal compressors are mainly composed of impellers, diffusers, bends, refluxers, and other components. When the impeller rotates, the gas is driven by the impeller to rotate and obtain centrifugal force, thereby forming a low-pressure zone at the center of the impeller, and the gas is sucked into the center of the impeller from the inlet. As the impeller rotates at high speed, the gas is accelerated by centrifugal force and thrown outward along the radial direction of the impeller.
Dilator deceleration and pressure increase: The gas ejected at high speed enters the expander, and the channel area of the expander gradually increases, causing the flow rate of the gas to gradually decrease. According to the law of conservation of energy, the kinetic energy of the gas is converted into pressure energy, thereby increasing the pressure of the gas.
Bend and reflux guide gas: After passing through the diffuser, the gas changes its flow direction through the bend and reflux, allowing it to smoothly enter the next stage impeller for further compression or ultimately be discharged from the compressor.
The following is a comparison of the advantages and disadvantages of different types of natural gas booster compressors:
Piston compressor
advantage:
Wide pressure range: Suitable for a wide pressure range, regardless of the flow rate, the required pressure can be achieved. The single-stage pressure ratio is high, the output pressure is stable, and it can adapt to a wider pressure range
High thermal efficiency: low unit power consumption, relatively high energy utilization efficiency
Strong adaptability: With a wide exhaust range, it is not affected by high or low pressure and can adapt to diverse pressure and cooling requirements
Strong maintainability: mature technology, rich production and usage experience, relatively simple structure, low maintenance difficulty, and low maintenance cost
Low material requirements: ordinary steel materials are commonly used, which are easy to process and cost-effective
Disadvantages:
Low speed: The machine has a large volume, heavy weight, and occupies a large area, making it unsuitable for places with strict requirements for space and weight
Complex structure: There are many vulnerable parts, such as air valves, piston rings, packing, etc., which require a large amount of maintenance work, and frequent maintenance may affect the continuity of production
Discontinuous exhaust: causing airflow pulsation, which may lead to pipeline vibration, have adverse effects on the stability of the pipeline system, and also affect the smooth operation of subsequent equipment
High vibration: During operation, there is a large amount of vibration, which requires a stable foundation and may generate significant noise, causing some interference to the surrounding environment
Screw compressor
advantage:
High reliability: with few components, no vulnerable parts, reliable operation, long service life, and a maintenance interval of up to 480000 hours, it can operate stably for a long time, reducing downtime caused by equipment failures
Easy operation and maintenance: Operators can operate without long professional training, achieving unmanned operation and reducing labor costs and intensity
Good power balance: There is no unbalanced inertia force, and the machine can work smoothly and at high speed, achieving no foundation operation. It is particularly suitable for use as a mobile compressor, and has small size, light weight, small footprint, and flexible installation
Strong adaptability: It has the characteristic of forced gas transmission, and the exhaust volume is almost not affected by exhaust pressure. It can maintain high efficiency in a wide pressure range and can adapt to various working conditions
Multiphase mixed transmission: There is a gap between the rotor tooth surfaces, which can withstand liquid impact, and can compress gases containing liquid, dust, and easily polymerized gases. The requirements for the intake medium are relatively low
Disadvantages:
High cost: The rotor tooth surface is a spatial curved surface that requires special cutting tools to be machined on expensive specialized equipment, and the machining accuracy requirements for the cylinder are also high, resulting in high cost and large initial investment.
Pressure limitation: Due to limitations in rotor stiffness and bearing life, it is generally only suitable for medium and low pressure ranges, and the exhaust pressure usually does not exceed 4.5 MPa, which cannot meet the requirements of high-pressure applications.
Cannot be made into micro: relying on gap sealing gas, generally only when the volumetric flow rate is greater than 0.2m ³/min, it has superior performance and is not suitable for low flow application scenarios.
Diaphragm compressor
advantage:
Good sealing: With a high compression ratio and excellent cylinder sealing, the gas will not come into contact with lubricating oil and other solid impurities, ensuring the purity of the compressed gas. It is suitable for compressing high-purity, rare and valuable, flammable and explosive, toxic and harmful, corrosive, and high-pressure gases.
No leakage and no pollution: Avoiding the risk of gas leakage and oil pollution, providing good protection for the environment and the quality of compressed gases, especially suitable for occasions with extremely high gas purity requirements, such as electronics, medicine, food and other industries.
Stable operation: The structure is simple, the operating sound is minimal, the vibration is small, the reliability is high, the pressure output is stable, and it can operate stably in harsh working environments with minimal impact on surrounding equipment and personnel.
Disadvantages:
Small displacement: Compared to other types of compressors, the displacement is usually small and cannot meet the needs of large-scale gas transportation and processing. It is generally suitable for situations with small displacement.
The lifespan of the diaphragm is limited: The diaphragm is a critical and vulnerable component, and its service life is affected by factors such as material, pressure, and temperature. It needs to be replaced regularly, which increases maintenance costs and downtime.
Technical difficulties: There are technical challenges such as sealing and material hydrogen corrosion, which require high manufacturing processes and material properties for core components such as membranes and membrane heads. The research and production costs are also relatively high.
Centrifugal compressor
advantage:
Large displacement: The exhaust is uniform, continuous, without periodic pulsation, and the airflow is stable, which can meet the large-scale and continuous gas delivery and boosting needs, suitable for high flow natural gas boosting occasions
Compact structure: small size, light weight, small footprint, can effectively save installation space, especially suitable for use in places with limited space
Stable operation: low vibration, low noise, high reliability, can operate stably for a long time, reduces equipment maintenance and repair frequency, and lowers operating costs
Less vulnerable parts: There are no reciprocating parts inside, fewer friction parts, less spare parts required, low maintenance costs and personnel requirements, which can reduce equipment maintenance costs and management difficulties
Can be used in conjunction with steam turbines: suitable for direct drag of industrial or gas turbines, facilitating comprehensive utilization of thermal energy, improving energy utilization efficiency, reducing energy consumption and operating costs
Disadvantages:
Limited applicability: Not suitable for situations where the gas volume is too small and the pressure ratio is too high. Under low flow and high compression ratio conditions, the efficiency is low, the performance is unstable, and the ideal boosting effect cannot be achieved
Narrow stable operating range: Although gas volume regulation is convenient, the economy is poor, and the stable operating range is relatively narrow. When the load changes greatly, unstable phenomena such as surge may occur, posing a threat to the safety and stability of the equipment
Relatively low efficiency: In general, its efficiency is lower than that of piston compressors, especially during partial load operation, where energy consumption is relatively high and more energy is required to achieve the same boosting effect
