Turbines are used to generate power; this power can be generated by gas turbine or steam turbine depending up on engineering requirement. In mechanical engineering, education of turbine is very interesting subject; at least I like it most. The basic working principle of gas turbine is nearly same as the working principle of internal combustion engine. The fuel used for combustion in gas turbine plant may be oil, coal, and procedure gas etc.
In steam turbine, the heat energy contained in the steam is first employed to set the steam itself in motion and this in turn is made to do work on blades mounted on a shaft or drum, which is free to rotate. However, gas turbine has certain advantages over steam turbine, which are as below.
Advantages of Gas Turbine
01) The gas turbine has been built to operate at the inlet temperature of 800 degree centigrade and even more, while the steam turbine and boiler have been built for temperatures up to about 580 degree centigrade. The efficiency of gas turbine is much higher than that of steam turbine due to high inlet temperature, when other things being equal in both turbines.
02) In steam turbine plant, water is used for cooling purpose; hence there are chances of freezing in winter nights. There is no likelihood of freezing in gas turbine plant.
03) The gas turbine does not require any boiler as like in steam turbine, hence the weight and space of gas turbines are less than those of steam turbine. For the same output, the gas turbine is more compact than a steam turbine. The capital cost of gas turbine is much lower than steam turbine.
04) The gas turbine plant is simple in design and construction. It has few reciprocating parts and is lighter in weight.
05) The gas turbine is quite useful in the regions where due to scarcity it is not possible to supply water in abundance for raising steam.
Steam turbines
The steam turbine on a page about engines? Maybe you wondered about it. It is hardly used in means of transport, but the steam turbine has many things in common with the combustion engine. The steam turbine changes chemically stored energy into mechanical energy, too. It's called a heat-force engine. The steam turbine works similarly to the water turbine, which is known probably by everyone. Not water, but steam is used as working medium.
Turbine types
When people began to use water power to win mechanical work, they looked first for the best forms of impellers. Three types were established thereby and variations of them are used today in various applications, among other in steam turbines in power stations, as marine propellers, as compressors in gas turbines etc. These three types are introduced here:
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Besides the types described above, there are still other types of water turbines, e.g. the Bànki turbine, which are not closer described here.
From the water- to the steam turbine
The won realizations with water power let the researchers expect similar results with steam, too. Numerous engineers took part in the development of the steam turbine in the second half of the 19. Century. To mention are the Englishman Charles Parsons, the Swede Carl Gustav Laval and the American Charles Curtis, who made crucial contributions for the development of the steam turbine.
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| Diagram: 2-step steam turbine after Parsons (1883). This turbine possesses two impellers and an idler in the center. enlarge (154 K, 510 * 570), Image (18 K, 255 * 285), Mini steam turbine (For your website) (11 K, 100 * 112) |
Mode of operation of the steam turbine
Since it is a steam jet and no more a water jet who meets the turbine now, the laws of thermodynamics are to be observed now. The modern steam turbine is an action turbine (no reaction turbine), i.e. the steam jet meets from a being certain nozzle the freely turning impeller. There's a high pressure in front of the turbine, while behind it a low pressure is maintained, so there's a pressure gradient: Steam shoots through the turbine to the rear end. It delivers kinetic energy to the impeller and cools down thereby: The pressure sinks.
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Multi-level steam turbines
In modern steam turbines not only one impeller is propelled, but several being in a series. Between them idlers are situated, which don't turn. The gas changes its direction passing an idler, in order to perform optimally work again in the next impeller. Turbines with several impellers are called multi-level. The principle was developed 1883 by Parsons. As you know, with the cooling gas expands. Therefore it is to be paid attention when building steam turbines to a further problem: With the number of passed impellers also the volume increases, which leads to a larger diameter of the impellers. Because of that, multi-level turbines are always conical.
Coupling of several turbines
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| Grafic: Coupled steam turbine. source: Helmut Hütten, "Motoren", Motorbuchverlag Stuttgart, S.379 |
In power stations today, different types of turbines are used in a series, e.g. one high pressure -, two medium- and four low pressure turbines. This coupling leads to an excellent efficiency (over 40%), which is even better than the efficiency of large diesel engines. This characteristic and the relatively favorable production make the steam turbine competitionless in power stations. Coupled with a generator and fired by an atomic reactor, they produce enormously much electric current. The strongest steam turbines achieve today performances of more than 1000 megawatts.
Gas & Steam Turbines
Gas and steam turbines are available in a wide range of sizes. They are commonly used for power generation and a variety of mechanical drive applications. Steam turbines operate in thermal and nuclear power plants; they also are being used more and more with gas turbines in combined-cycle power plants. Gas turbines are often favored for their flexibility and smaller footprint as well as their relative ease at bringing a new plant online or supplementing an existing plant.
A common goal for both machine types is high efficiency, which incorporates lower fuel usage and reduced carbon emissions. Advances in blading design and higher-temperature operation have contributed to improved steam turbine thermal efficiency. In the industrial gas turbine arena, advanced cooling strategies have contributed to increased efficiency, while improvements in combustor technology have yielded reduced pollutant emissions. These machines have much in common with aircraft engine gas turbines, and, indeed, aeroderivative engines are used in some industrial situations, particularly when flexibility and portability are important considerations.
Gas turbine combustor
Courtesy MTU Aero Engines Gmbh.
Even with such advanced technology, customers demand even greater performance. Gas and steam machines have a long service life. As customer requirements change, suppliers are asked to upgrade and modify existing machines — a challenging task due to the constraints imposed by the existing machine.
Engineering simulation tools from ANSYS provide high-fidelity advanced physics that turbine designers need, whether the application is new machine design or machine rerating. The suite’s flexibility means the tools can be applied for operation in interactive mode or in batch mode within the design system of the manufacturer or consultant. The technologies are integrated within a common and electronics software for which ANSYS is well known.
Blade Design: provides tools for the detailed geometric specification of compressor and turbine-bladed components, axial or radial. These tools can be used within the ANSYS Workbench environment or connected into an existing design system, enabling high-productivity design and analysis, including optimization.
