What is Steam Power

STEAM POWER PLANT:

In steam turbine power plants Steam is used as working fluid. This steam is generated in boiler. The steam produced is then passed through steam turbine where it expands isentropically.  After moving through the turbine steam is fed to the condenser where it is again converted to water. The action of the steam turbine is based on the thermodynamic principle that when a vapor is allowed to expand, its temperature drops, and it’s internal energy is thereby decreased. This reduction in internal energy is transferred into mechanical energy in the form of an acceleration of the particles of the vapor (see thermodynamics). This transformation makes the large amount of energy directly available. In the case of expanding steam, a reduction of 100 Btu in internal energy through expansion can result in increasing the speed of the steam particles to rate of almost 2900 km/h (almost 1800mph) at such speed the energy available is great, even though the particles are extremely light.

In order to use the energy available in steam efficiently in a turbine of either type, it is necessary to employ a no of stages, in each of which a small amount of thermal energy is converted to kinetic energy. If the entire conversion of energy took place instead in a single expansion stage, the rotating speed of the turbine wheel would be excessive. In general, reaction turbines require more stages than impulse turbine. It can be shown that for the same diameter energy range, a reaction turbine require twice the number of stages for peak stage efficiency. Large turbines that are nominally of the impulse variety employ some reaction at the root of the steam path to assure efficient flow through the buckets. Many turbines that are nominally reactive have an impulse control stage first, which allows for saving in the total number of stages.

Because of increase in volume as the steam expands through the various stages of the turbine, the size of the opening through which the steam passes must increase from stage to stage. In the practical engineering design of turbines, this increase is accomplish by lengthening the blades from stage to stage and by increasing the diameter of the drum or wheel upon which the blades are mounted and by adding two or more turbine sections in parallel. As a result, a small industrial turbine may be more or less conical in shape. With its smallest diameter at high-pressure, or inlet, end, and its largest at low-pressure, or exhaust, end. A large unit for a nuclear power station may have four rotors consisting of one double-flow high pressure section followed by three double-flow low-pressure section. Sponsored by; www.funtostudy.com Revolutionizing Education