Technical documents for compressors and turbines

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Technical Documents on Compressors and Turbines I. Definition and Classification of Compressors On the broad stage of industrial production, there is often a need for gases at specific pressures to meet various application requirements, and compressors are the key devices that fulfill this need, being responsible for transporting gases and increasing their pressure. The pressure of a gas is essentially a reflection of the frequency and intensity of collisions between gas molecules and a unit area per unit of time. By raising the temperature within the gas volume, the movement of gas molecules is accelerated, thereby increasing the force of collisions; this seems to enable an increase in gas pressure ； However, once the temperature drops, the gas pressure also decreases. Normally, the compressed gas is expected to be maintained at a relatively low temperature range. Therefore, increasing the number of gas molecules per unit area, that is, reducing the distance between molecules, has become the main strategy for raising gas pressure; the realization of this process relies on the efficient operation of compressors. Currently, the two most widely used categories in the compressor industry are positive-displacement compressors and turbine compressors. Positive displacement compressors increase pressure by reducing the volume occupied by the gas; they include various types such as piston, vane, Roots, and screw compressors ； Turbo compressors, on the other hand, generate pressure by having rotating blades do work on the airflow; through the inertial compression that occurs as the airflow accelerates and decelerates continuously, the distance between molecules is reduced. Turbocompressors are further divided into centrifugal and axial flow types: 1. Centrifugal compressors: In this type of compressor, the gas moves in a direction perpendicular to the compressor axis. The increase in gas pressure arises as the airflow accelerates due to centrifugal force as it passes through the rotating impeller, and then slows down in channels with gradually increasing cross-sectional area such as diffusers, converting kinetic energy into pressure energy. 2. Axial flow compressors: In axial flow compressors, the direction of gas flow is parallel to the compressor axis. The acceleration of the gas is also due to the rotation of the rotor; as the gas flow passes through the stator vanes arranged alternately with the rotor blades, its speed gradually decreases, and this loss of speed is converted into pressure energy. In terms of application selection, positive-displacement compressors are more suitable for high-pressure and medium-to-low flow rate applications ； Turbo compressors, on the other hand, are well-suited for applications involving low to medium pressures and high flow rates; among them, axial flow types excel in terms of flow rate, while the pressure levels are relatively low. II. Definition and Classification of Turbines A turbine, also known as a steam turbine, is a rotary power machine that uses steam energy to generate work. Steam originating from boilers or other steam sources enters the turbine through a throttle valve, and then passes at high speed through a series of nozzles (or stationary vanes) and rotating vanes arranged in a circular pattern. During this expansion process, work is done, which drives the turbine rotor to rotate, converting the kinetic energy of the steam into mechanical energy. This mechanical energy is then used to drive load devices such as motors, compressors, and pumps. Turbines can be classified as follows based on their thermodynamic processes: 1. Condensing turbines: After doing work in the turbine, the steam is completely discharged into the condenser where it condenses; the pressure inside the condenser is maintained at a level lower than atmospheric pressure. 2. Extraction-condensing steam turbine: At a certain stage of expansion within the turbine, part of the steam is extracted for use by other steam consumers, while the remaining steam continues to do work before being discharged into the condenser. This type is used for the air compressors/boosters and generator-driven turbines in Weihua Phase II. 3. Back-pressure steam turbine: After doing work, the steam is discharged from the cylinder at a pressure higher than atmospheric pressure and supplied to other low-pressure users. 4. Multi-pressure (injection) steam turbines: When there is some pressure steam that is not fully utilized in the process, this excess steam is injected through pipes into an intermediate stage of the steam turbine, where it expands together with the existing steam to generate power, thereby enabling energy recovery. In addition, turbines can also be classified according to steam pressure into low-pressure (below 2.0 Mpa), medium-pressure (2.0–5.0 Mpa), high-pressure (5.0–10.0 Mpa), ultra-high-pressure (12.0–14.0 Mpa), and supercritical (above 22.5 Mpa) categories ； Or, based on their working principle, they can be classified as impulse turbines, reaction turbines, and combined turbines that combine both impulse and reaction mechanisms.