What is Gas Turbine Power Plant?

GAS TURBINE POWER PLANT:

Gas Turbine, also combustion turbine, engine that employ gas flow as the working medium which heat transforms energy into mechanical energy. Gas is produce in the engine by the combustion of certain fuels. Stationary nozzle discharge jets of this gas against the blades of a turbine wheel. The impulse force of the jets causes the shaft to turn. A simple-cycle gas turbine includes a compressor that pumps compressed the air into a combustion chamber. Fuel in gaseous or liquid-spray from is also injected into this chamber, and combustion take place there. The combustion products pass from the chamber through the nozzle to the turbine wheel.

In a compressor or turbine, a row of fixed blades and a corresponding row of fixed blades attached to a rotor is called a stage. Large machines employ multi-stage axial-flow compressor and turbines.

In shaft arrangements, in initial turbine stage (or stages) powers the compressor on one shaft while the later turbine stage (or stages) powers the external load on a separate shaft.

The efficiency of the gas-turbine cycle is limited by the need for continuous operation at high temperatures in the combustion chamber and early turbine stages. A small, simple-cycle gas turbine may have a relatively low thermodynamic efficiency, comparable to a conventional gasoline engine. Advances in heat-resistant materials, protecting coatings, cooling arrangements have made possible large units with simple-cycle efficiencies of 34 percent or higher.

The efficiency of gas-turbine cycle can be enhanced by the use of auxiliary equipment such as intercoolers, regenerators, and reheaters. These devices are expensive, however, and economic considerations usually preclude their use.

In a combined-cycle power plant, the considerable heat remaining in the gas turbine exhaust is directed t the boiler called a heat-recovery steam generator. The heat so recovered is used to raise steam for an associated steam turbine. The combined output is approximately 50 percent greater than that of the gas turbine alone. Combined cycle with thermal efficiency of 52 percent and higher are being put into service. Gas turbines have been applied to the propulsion of ships and railroad locomotives. A modified form of gas turbine, the turbojet, is used for airplane propulsion. Heavy-duty gas turbines in both simple and combined cycles have become important for large scale generation of electricity. Unit rating is exceeds of 200 megawatts (MW) are available. The combined cycle output can exceed 300 MW.

The usual fuels used in gas turbine are natural gas and liquids such as kerosene and diesel oil. Coal can be used after conversion to gas in a separate Gasifier.

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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

Classification of Power Plants

There are several different types of power plants used across the world today. Each of these plants has their own set of advantages and drawbacks from various perspectives and various factors govern which type of power plant is best suited for a particular region or situation.

                                                                                            

• Thermal Power Plants – as the name suggests, these power plants convert heat energy into electrical energy. The working fluid of these plants is steam or a gas. Depending upon the working fluid, they are mainly of two types, Steam Turbine and Gas Turbine power plant.

• Hydro Power Plants – these plants use the kinetic energy of flowing water to rotate the turbine blades, hence converting kinetic energy into electrical energy. These types of power plants are very good for peak loads. Their main disadvantage lies in the fact that their location depends on a number of factors which are beyond the control of human beings such as the hydrological cycle of the region and so forth. If there is shortage of water it could lead to shut down of these plants. For this reason alternative arrangements such as thermal power plants need to be made to ensure uninterrupted generation of power.

Apart from these main two types there are plants which use nuclear energy, solar energy and even wind energy to generate power.

Introduction to Thermal Power plants

A Power Plant is used to convert one form of energy to mechanical energy through different reactions & processes. The energy may be Coal, Oil, Gas, Wind, Water, Solar, Nuclear, Ocean thermal, Wave, Geothermal energy. The mechanical energy is further converted into Electrical energy with the help of generators.

A Power Plant is of great importance in residential as well as in industrial sector, as electricity is one of the basic needs of today’s life. May large industries produce electricity by their own power plants, whereas in residential sector & small industries usually buy electricity either from government or from independent power producers.