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Compounding of steam turbines
In steam turbine design, compounding is a method of extracting steam energy in multiple stages rather than a single one. Each stage of a compounded steam turbine has its own set of nozzles and rotors. These are arranged in series, either keyed to the common shaft or fixed to the casing. The arrangement allows either the steam pressure or the jet velocity to be absorbed incrementally.
Compounded steam turbines are used to reduce rotor speeds to achieve optimal operating revolutions per minute. The steam produced in the boiler has sufficiently high enthalpy when superheated. In all turbines the blade velocity is directly proportional to the velocity of the steam passing over the blade. Now, if the entire energy of the steam is extracted in one stage, i.e. if the steam is expanded from the boiler pressure to the condenser pressure in a single stage, then its velocity will be very high. Hence the velocity of the rotor (to which the blades are keyed) can reach to about 30,000 rpm, which is too high for practical uses due to very high vibration. Moreover, at such high speeds the centrifugal forces are immense, and can damage the structure. Hence, compounding is needed. The high velocity steam just strikes on a single ring of rotor that causes wastage of steam ranging 10% to 12%. To overcome the wastage of steam, compounding of steam turbines are used.
In an impulse steam turbine, compounding can be achieved in the following three ways:
In a reaction turbine, compounding can be achieved only by pressure compounding.
In general, the types of steam turbine include:
The velocity compounded Impulse turbine was first proposed by C.G. Curtis to solve the problem of single stage Impulse turbine for use of high pressure and temperature steam.
The rings of moving blades are separated by rings of fixed blades. The moving blades are keyed to the turbine shaft and the fixed blades are fixed to the casing. The high pressure steam coming from the boiler is expanded in the nozzle first. The Nozzle converts the pressure energy of the steam into kinetic energy. The total enthalpy drop and hence the pressure drop occurs in the nozzle. Hence, the pressure thereafter remains constant.
This high velocity steam is directed on to the first set (ring) of moving blades. As the steam flows over the blades, due to the shape of the blades, it imparts some of its momentum to the blades and loses some velocity. Only a part of the high kinetic energy is absorbed by these blades. The remainder is exhausted on to the next ring of fixed blade. The function of the fixed blades is to redirect the steam leaving from the first ring of moving blades to the second ring of moving blades. There is no change in the velocity of the steam as it passes through the fixed blades. The steam then enters the next ring of moving blades; this process is repeated until practically all the energy of the steam has been absorbed.
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Compounding of steam turbines
In steam turbine design, compounding is a method of extracting steam energy in multiple stages rather than a single one. Each stage of a compounded steam turbine has its own set of nozzles and rotors. These are arranged in series, either keyed to the common shaft or fixed to the casing. The arrangement allows either the steam pressure or the jet velocity to be absorbed incrementally.
Compounded steam turbines are used to reduce rotor speeds to achieve optimal operating revolutions per minute. The steam produced in the boiler has sufficiently high enthalpy when superheated. In all turbines the blade velocity is directly proportional to the velocity of the steam passing over the blade. Now, if the entire energy of the steam is extracted in one stage, i.e. if the steam is expanded from the boiler pressure to the condenser pressure in a single stage, then its velocity will be very high. Hence the velocity of the rotor (to which the blades are keyed) can reach to about 30,000 rpm, which is too high for practical uses due to very high vibration. Moreover, at such high speeds the centrifugal forces are immense, and can damage the structure. Hence, compounding is needed. The high velocity steam just strikes on a single ring of rotor that causes wastage of steam ranging 10% to 12%. To overcome the wastage of steam, compounding of steam turbines are used.
In an impulse steam turbine, compounding can be achieved in the following three ways:
In a reaction turbine, compounding can be achieved only by pressure compounding.
In general, the types of steam turbine include:
The velocity compounded Impulse turbine was first proposed by C.G. Curtis to solve the problem of single stage Impulse turbine for use of high pressure and temperature steam.
The rings of moving blades are separated by rings of fixed blades. The moving blades are keyed to the turbine shaft and the fixed blades are fixed to the casing. The high pressure steam coming from the boiler is expanded in the nozzle first. The Nozzle converts the pressure energy of the steam into kinetic energy. The total enthalpy drop and hence the pressure drop occurs in the nozzle. Hence, the pressure thereafter remains constant.
This high velocity steam is directed on to the first set (ring) of moving blades. As the steam flows over the blades, due to the shape of the blades, it imparts some of its momentum to the blades and loses some velocity. Only a part of the high kinetic energy is absorbed by these blades. The remainder is exhausted on to the next ring of fixed blade. The function of the fixed blades is to redirect the steam leaving from the first ring of moving blades to the second ring of moving blades. There is no change in the velocity of the steam as it passes through the fixed blades. The steam then enters the next ring of moving blades; this process is repeated until practically all the energy of the steam has been absorbed.