The working principle of steam turbines

A steam turbine is a rotary prime mover that uses steam to generate power; it converts the thermal energy of steam into mechanical energy that drives the rotation of the turbine rotor. This conversion process involves two stages of energy transformation: first, as the steam passes through the turbine nozzles (stator blades), its thermal energy is converted into kinetic energy due to the high-speed flow of the steam; then, as this high-speed gas flows past the rotor blades, its kinetic energy is converted into mechanical energy that causes the turbine rotor to rotate. Based on their working principle, steam turbines are divided into two categories: impulse turbines and reaction turbines. In impulse turbines, the conversion of steam’s thermal energy into kinetic energy occurs solely within the nozzle; the working blades merely convert the steam’s kinetic energy into mechanical energy. As the steam expands in the nozzle, its velocity increases while its temperature and pressure decrease. In the blades, only part of the steam’s kinetic energy is converted into mechanical energy (the velocity of the gas decreases). Since the cross-sectional area of the channels along the flow direction in the blades remains constant, the steam does not expand any further, and its pressure also does not decrease ； In a reaction turbine, steam expands within the stationary blades, resulting in a decrease in pressure and temperature as well as an increase in flow velocity. The steam then enters the rotating blades (working blades). Since the cross-sectional shape of the channels in these rotating blades along the flow direction is similar to that of the channels in the stationary blades, the steam continues to expand within the rotating blades, causing further drops in pressure. As the steam flows along the inner curve of the rotating blades, its direction changes; as a result, the blades are subjected to both impact forces and reactive forces generated by the high-speed expulsion of steam from the blades. The combined effect of these forces is what acts on the rotating blades. In other words, in a reaction turbine, the conversion of steam’s thermal energy into kinetic energy occurs not only in the stationary blades but also in the rotating blades. Classified by thermodynamic process, turbines can be divided into three types: back-pressure type, condensing type, and extraction-condensing type. In the back-pressure turbine, the steam that has been used in the turbine is discharged at a higher pressure (greater than 0.1 MPa) for other purposes ； KT2501, KT1503, etc. belong to condensing turbines – the steam does work in the turbine before being completely discharged into the condenser for condensation ； KT1501B belongs to the extraction-condensing type turbine – a portion of the steam that has done work in the high-pressure turbine stage is extracted for other uses, while the remaining steam continues to do work in the low-pressure turbine stage before being entirely discharged into the condenser to be condensed. A steam turbine with only one impeller is called a single-stage turbine. Such turbines have low power, high rotational speed, and low efficiency; they are generally used to drive small oil pumps or water pumps ； To improve the efficiency of energy conversion, turbines often do not have just one impeller; instead, steam passes through several impellers in sequence (with each impeller representing one stage), thereby reducing its pressure and temperature step by step. Each time steam undergoes the conversion from thermal energy to kinetic energy to mechanical energy, it is considered one working stage. The stages are separated from one another by partitions. The steam exiting the first stage enters the second stage, and the nozzles in the first stage are located on the partition of the cylinder. As the steam passes through the nozzles in the second stage, its pressure and temperature are reduced further while its velocity increases, and this drives the second impeller. This process repeats itself, and such turbines are known as multi-stage turbines. In multi-stage turbines, the nozzles and moving blades are arranged alternately. High-power turbines incorporate several impellers within a single cylinder, and depending on the operating pressure of the steam, these cylinders can be classified as high-pressure, medium-pressure, or low-pressure cylinders. Sometimes, a single cylinder can also be divided into several sections, with each section containing several impellers. The turbine structure mainly consists of rotating parts, stationary parts, and control parts. The rotating parts (rotor: the assembly of all rotating components) mainly include the main shaft, impeller (or drum), moving blades, thrust disk, emergency safety device, coupling, etc. The function of the rotor is to convert the kinetic energy of steam into mechanical energy, and to transmit the torque generated by the circumferential force of the steam acting on the blades, thereby delivering mechanical work outward. Main shaft: A component that supports rotation and transmits torque. Impeller: Used to mount and support the blades, and consists of a rim, a wheel body, and a hub. Blades: In the moving blades, the steam flow is deflected in direction and speed due to the resistance exerted by these blades. Driven by this steam flow, the impeller and the main shaft rotate, and the torque generated by the force exerted by the steam flow on the moving blades is transmitted to the main shaft to perform work. At this time, the steam flow necessarily exerts a reaction force on the moving blades; the component of this reaction force along the circumference of the rotor drives the rotor to rotate, performing work and converting the kinetic energy of the steam into mechanical energy. Thrust disc: Balances the axial thrust, protects the turbine, and prevents friction between the rotating and stationary parts of the turbine. The stationary parts include cylinders, diaphragms, nozzles, static blades, steam seal bearings, etc. Cylinder: It separates the flow-through components of the turbine (nozzles, diaphragms, rotor, etc.) from the atmosphere, ensuring that steam can perform work within the turbine. Separator: It separates different pressure levels, allowing the work done by steam to be carried out in several stages ； Change the direction of the steam flow and install nozzles. nozzle ； The thermal energy of the steam is converted into kinetic energy; in other words, the steam is expanded and its pressure is reduced, which increases its flow velocity and allows the gas to be ejected in a certain direction to drive the moving blades and perform work. Stator blade: It changes the direction of the steam exiting the first set of rotor blades, directing it into the subsequent rotor blades so that the remaining kinetic energy can be utilized to generate power. Steam seals: The steam seals installed at both ends of the turbine shaft that extend outside the cylinder are known as end steam seals. The high-pressure end steam seal serves to reduce steam leakage from the high-pressure cylinder, and it directs this leaked steam to be utilized properly ； The low-pressure end steam seal serves a sealing function to prevent air from leaking into the cylinder and disrupting the vacuum. The steam seal installed on the partition is known as a partition steam seal; its function is to maintain the pressure difference before and after the partition and reduce steam leakage between stages. The steam seal structure is generally of the labyrinth type. Bearings: Radial bearings support the turbine’s main shaft, while thrust bearings bear the axial forces. The control section includes adjustment devices and protection devices. Function of the control device: To maintain a constant rotational speed at stable operating conditions, at a specified value ； When the load changes, the control system ensures that the deviation in rotational speed remains within the specified range. Protection device: In the event of abnormal operating conditions in the turbine, it can automatically ensure the safety of the equipment and prevent serious accidents.

The comprehensive explanation gave me a basic understanding of steam turbines; thanks to the second floor! ! ! ! ! ! ! ! !