【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20191120

Within a turbine stage, the main losses include nozzle loss, blade kinetic energy loss, residual velocity loss, blade height loss, fan loss, partial steam inlet loss, frictional blowing loss, steam leakage loss, and wet steam loss. 1) Nozzle loss and rotor blade loss are caused by the mutual friction between the steam flow as it passes through the nozzle and rotor blades, as well as the friction between the steam flow and the surface of the blades. 2) The residual velocity loss refers to the fact that steam still possesses a certain velocity when it leaves the moving blades; this kinetic energy is not utilized in this stage, and thus it represents a loss for that stage. However, when the vapor flow enters the next stage, its kinetic energy can be partially utilized by that stage. 3) Leaf height loss refers to the loss caused by vortices formed by the steam flow at the base and top of the nozzle and moving blade cascade. 4) Fan-shaped loss refers to the fact that, due to the radial arrangement of the blades around the rim, the flow passage cross-section takes on a fan shape. As a result, the pitch, circumferential speed, and inlet angle vary along the blade height, which causes the steam flow to strike the blades and result in energy loss. Additionally, the steam flow generates radial movements that further consume its energy. 5) Some of the steam inlet losses are due to \"blowing\" losses that occur when the moving blades pass through the arc sections without nozzles, as well as gas expulsion losses that occur when the moving blades move from the non-operating arc sections into the operating arc sections with nozzles. 6) Frictional blowing loss refers to the fact that the high-speed rotating impeller comes into friction with the steam surrounding it, causing this steam to rotate; as a result, part of the impeller’s useful work is consumed. Additionally, the vapor flow between the partition and the nozzle forms vortices due to centrifugal force, which also consumes the impeller’s useful work. 7) Steam leakage loss refers to the loss that occurs in a steam turbine due to pressure differences; as a result, part of the steam escapes through various static and dynamic gaps, rather than passing through the nozzles and rotor blades, and thus does not contribute to power generation, leading to losses. 8) Wet steam loss refers to the situation in the low-pressure section of the turbine where the steam is in a wet steam state. The water contained in this wet steam not only expands to generate work more rapidly, but it also consumes the kinetic energy of the steam flow; it further exerts a braking effect on the movement of the blades, thereby wasting useful work, and it also causes erosion of the blades.

Blowing loss occurs only in the stages with partial steam admission. When the impeller moves to the area without nozzles, it is unable to do work; instead, it has to rotate together with the steam, pushing the steam out like a blower, resulting in some energy loss, which is known as blowing loss. Frictional blowing loss refers to the fact that the high-speed rotating impeller comes into friction with the steam surrounding it, causing this steam to rotate; as a result, part of the impeller’s useful work is consumed. Additionally, the vapor flow between the partition and the nozzle forms vortices due to centrifugal force, which also consumes the impeller’s useful work. A turbine is a rotating device that spins at high speeds driven by high-temperature, high-pressure steam. When the main engine reaches its operating speed, or when the generator load is low and thus less steam flows into the turbine, the blades on the rotor spin rapidly, stirring the surrounding air. A large amount of mechanical energy is quickly converted into thermal energy, which heats the air and metals inside the cylinder, causing the temperature of both the rotor and the metals within the cylinder to rise sharply. The blowing friction loss is proportional to the length of the moving blades and to the cube of the circumferential velocity; therefore, the blowing friction loss in low-pressure rotors is much greater than that in high- and medium-pressure rotors. The heat generated by this blowing friction loss heats the flow-through parts, thereby increasing the thermal expansion difference, and its impact is significant at low flow rates. As the flow rate increases, its impact gradually decreases. When the flow rate reaches a certain value, the heat generated by blower friction losses can be completely removed, at which point the effect on the expansion difference disappears.

The principle of turbine blowing loss: Blowing loss occurs only in those stages where there is a partial supply of steam. When the impeller moves to a position without nozzles, it is unable to do work; instead, it has to rotate together with the steam, acting like a blower to push the steam out. As a result, some energy is lost, which is referred to as blowing loss. Frictional blowing loss refers to the fact that the high-speed rotating impeller experiences friction with the steam surrounding it, and this friction requires a portion of the impeller’s useful work to rotate that steam; moreover, the steam flow between the partition and the nozzle forms vortices due to centrifugal force, which also consumes the impeller’s useful work. A turbine is a rotating device that spins at high speeds driven by high-temperature, high-pressure steam. When the main engine reaches its operating speed, or when the generator load is low and thus less steam flows into the turbine, the blades on the rotor spin rapidly, stirring the surrounding air. A large amount of mechanical energy is quickly converted into thermal energy, which heats the air and metals inside the cylinder, causing the temperature of both the rotor and the metals within the cylinder to rise sharply. The blowdown friction loss is proportional to the length of the moving blades and to the cube of the circumferential velocity; therefore, the blowdown friction loss in low-pressure rotors is much greater than that in high- and medium-pressure rotors. The heat generated by the blowdown friction loss heats the flow-through parts, thereby increasing the expansion difference, and this effect is more significant at low flow rates. As the flow rate increases, its impact gradually decreases. When the flow rate reaches a certain value, the heat generated by blower friction losses can be completely removed, at which point the effect on the expansion difference disappears.

Blowing loss, as the name implies, refers to the impeller pushing the steam forward like a blower. In other words, originally steam was used as the power source to rotate the impeller; now, due to poor expansion of the steam (caused by issues with the design of the nozzles as well as insufficient steam parameters), there is not enough kinetic energy in the steam, and as a result it absorbs the kinetic energy of the impeller instead. On the first floor, it is discussed about friction losses (disk losses). There are many types of losses within a turbine stage, such as blowing loss, friction loss, moisture loss, air leakage loss, and so on

It is related to factors such as the number of nozzle stages and whether a shield device is used. Reducing the number of nozzle stages and using shielding devices can minimize blowing losses

Blowing loss occurs when the impeller moves to the segment of the partition without nozzle vanes; in this case, the moving vanes do not convert the kinetic energy of the steam into mechanical energy, but rather function like blowers, pushing the steam that is not in use from one side to another, thereby consuming energy and resulting in losses. Principle: Blowing loss occurs only in the stages with partial steam inlet. When the impeller reaches the area without nozzles, it is unable to do work; instead, it has to rotate together with the steam, acting like a blower to expel the steam, resulting in some energy loss. Furthermore, the frictional blowing loss refers to the fact that the high-speed rotating impeller comes into friction with the steam surrounding it, causing this steam to rotate; as a result, part of the impeller’s useful work is consumed. Additionally, the steam flow between the partition and the nozzles forms vortices due to centrifugal force, and this also results in a consumption of the impeller’s useful work. Related to: It is related to factors such as the number of nozzle stages and whether a shield device is used.

Blowing loss occurs only in the stages with partial steam admission. When the impeller moves to the area without nozzles, it is unable to do work; instead, it has to rotate together with the steam, pushing the steam out like a blower, resulting in some energy loss, which is known as blowing loss. Frictional blowing loss refers to the fact that the high-speed rotating impeller comes into friction with the steam surrounding it, causing this steam to rotate; as a result, part of the impeller’s useful work is consumed. Additionally, the vapor flow between the partition and the nozzle forms vortices due to centrifugal force, which also consumes the impeller’s useful work. A turbine is a rotating device that spins at high speeds driven by high-temperature, high-pressure steam. When the main engine reaches its operating speed, or when the generator load is low and thus less steam flows into the turbine, the blades on the rotor spin rapidly, stirring the surrounding air. A large amount of mechanical energy is quickly converted into thermal energy, which heats the air and metals inside the cylinder, causing the temperature of both the rotor and the metals within the cylinder to rise sharply. The blowing friction loss is proportional to the length of the moving blades and to the cube of the circumferential velocity; therefore, the blowing friction loss in low-pressure rotors is much greater than that in high- and medium-pressure rotors. The heat generated by this blowing friction loss heats the flow-through parts, thereby increasing the thermal expansion difference, and its impact is significant at low flow rates. As the flow rate increases, its impact gradually decreases. When the flow rate reaches a certain value, the heat generated by blower friction losses can be completely removed, at which point the effect on the expansion difference disappears.

It is proportional to the length of the moving blades and to the cube of the circumferential velocity; therefore, the blowdown friction loss in low-pressure rotors is much greater than that in high- and medium-pressure rotors. The heat generated by this blowdown friction loss heats the flow-through sections, thereby increasing the expansion difference, and this effect is more significant at low flow rates.

Blowing loss refers to the fact that the high-speed rotating impeller comes into friction with the steam surrounding it, causing this steam to rotate; as a result, part of the impeller’s useful work is consumed. Additionally, the steam flow between the partition and the nozzles forms vortices due to centrifugal force, which also consumes the impeller’s useful work.