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A simple gas turbine has a compressor, combustion chamber, and turbine. The turbine and the compressor are on the same shaft. The compressor raises the pressure of atmospheric air and sends this air to the combustion chamber. Here, a fuel (oil, gas, or pulverized coal) burns, raising the temperature and increasing the heat energy. The hot gas in the turbine expands to develop mechanical energy, as expanding steam does in a steam turbine. This simple unit has a thermal efficiency of about 20 percent.
An open-cycle gas turbine also takes air from the atmosphere and discharges exhaust to the atmosphere. Open-cycle hookups differ in many ways, but the compressor inlet is atmospheric and there is a relatively narrow range of best pressure ratios. This puts a limit on the top-cycle pressure. These units can have a regenerator, intercooler, and other refinements and can still be open-cycle gas turbines.
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Adding steam in the combustion zone of the turbine lowers both the flame and gas temperature, preventing up to 80% percent of uncontrolled NOx for mation.
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To know how gas turbines behave, we must understand the basic steps in the simple cycle. Heat energy of tile fuel is converted into mechanical energy. The compressor and the combustion chamber produce a high-energy working fluid that can be expanded in the turbine. This develops mechanical energy similar to expanding steam in a steam turbine.
The volume of the working fluid is smallest at the compressor outlet, though its temperature is higher than at the compressor inlet. High excess air ratio in the combustor keeps air and gas temperatures below a maximum limit. At the turbine outlet, gas volume is at maximum. The main elements of the gas-turbine plant must be proportional to handle the flow of working fluid with minimum pressure loss through the system.
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Converting more heat energy to mechanical energy increases gas-turbine efficiency. One way to do this is to raise the turbine inlet gas temperature, which, in turn, raises thermal efficiency. At higher temperatures, the best efficiency occurs at the higher-pressure ratios. Increasing the temperature of the gas also betters both the air rate and the work ratio.
The next step is to add a regenerator to transfer heat from the exhaust to compressed air. The hotter air temperature recovered from waste heat cuts the fuel needed to bring the air up to the turbine inlet temperature. Next, add an intercooler. Divide the compression.
The next step is to split the turbine in two and to place a combustor before each turbine. The first combustor discharges high-temperature gas into the high-pressure turbine. As the gas does work on the turbine rotor, both its pressure and temperature drop partly expanded.
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Hot gases of 687°C and 2400 kPa go into the high-pressure turbine from the combustor, and exhaust goes from the low-pressure turbine at 443°C and 670 kPa. Air enters the low-pressure compressor at 16°F and 645 kPa and leaves at 58°C and 2430 kPa.
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Most gas turbines for industrial use is hooked up to pipeline -quality natural gas with liquid fuel, usually no.2, as backup. The natural gas should go through water knockout vessels before entering the gas turbine room. These vessels normally contain coalescing and filtering elements. To avoid condensation, the natural gas temperature should be maintained at least 10°C above its dew point. Pockets must be avoided in pipe runs so that condensate will not collect in low spots. Piping is usually stainless steel.
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The manufacturers express this as used-up service life based on their methods of calculating remaining life.
Factors to consider include:
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The basic components for a simple gas-turbine system include a compressor, combustor, and the turbine. A rotating compressor draws in air from the atmosphere, pressurizes it, and forces it into the combustor (the furnace) in a steady flow. Fuel forced into the air burns, raising the temperature of the mixture of air and combustion products. This high-energy mixture then flows through the turbine, dropping in pressure and temperature as it does work on the moving blades. The spent gases then leave at atmospheric pressure but at high temperature. The turbine drives the compressor rotor through a shaft and also an external load through the load coupling.
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Air-diluted ammonia vapor is injected into the flue gas stream before it enters the catalyst units consisting of honeycomb-shaped ceramic material. These cells, with the ammonia vapor, convert nitrogen oxides to nitrogen and water vapor for discharge into the atmosphere.
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A booster machine compresses air or gas from a pressure above atmospheric to a still higher pressure. Booster machines have many uses, especially in oil and gas fields and related industries. Compression may be either single or multistage, depending upon the ratio of compressions, horsepower, and gas analysis
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A combined cycle using a gas turbine or diesel, usually driving a generator in which the exhaust gases are directed to a waste heat-recovery boiler or heat-recovery steam generator (HRSG). The steam from the HRSG is then directed to a steam turbo-generator for additional electric power production. The use of the exhaust heat from a gas turbine improves the overall thermal efficiency. In cogeneration, electric power is produced, but part of the steam from the HRSG or from extraction from the steam turbine is used for process heat, hence the term cogeneration-the simultaneous production of electric power and process heat steam.
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Compression efficiency is the ratio of the work needed for ideal adiabatic compression through a given pressure range to the work actually needed by the compressor.
Engine efficiency is the ratio of tile work actually developed by expanding hot gas in the turbine through a given pressure range to the work that would be yielded for ideal adiabatic expansion.
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For gas turbines, machine efficiency is the combined efficiencies of the compressor and the turbine.
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It is the ratio of the highest pressure in a cycle to the lowest pressure. It is usually the ratio of the highest pressure in the compressor discharge to the lowest pressure in the compressor inlet.
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This is the basic gas turbine cycle of adiabatic compression of air in a compressor, constant pressure burning in a combustor, followed by adiabatic expansion of the working fluid in a turbine to produce mechanical power.
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Most designs are based on an air temperature of 16°C entering the air compressor. In general, unless preheating is used, the thermal efficiency will decrease about one percentage point for each 7°C rise in air inlet temperature.
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The high-alloy materials may show a loss of ductility at high temperature over a period and thus becomes brittle and prone to cracking. The higher the temperature, the more rapidly the material loses its strength and ductility.
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Thermal efficiency is the percentage of the total fuel energy input that appears as the net work output of the cycle.
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It is the ratio of the uct work output of the cycle to the total work developed in the turbine or turbines.
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It is important to consider the use of a bypass stack that will permit operating the gas turbo-generator in case of a forced outage on the HRSG or steam turbo-generator. However, in certain states, such as California, also to be considered are NO limits that require steam injection and loading to limit the exhaust temperature coming out of the simple-cycle gas turbine so that they do not exceed jurisdictional limits.
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Thermal stress cracks appear in those components, which are subjected to high temperatures, such as combustors, entrance nozzle segments, and first stage blades, and which have abrupt changes in stiffness or configuration that produce stress concentration.
Answer:The products of combustion come in direct contact with turbine blading. This dictates using fuels those produce combustion products that do not cause high-temperature corrosion or oxidation, erosion, and deposition of ash on blades. Preferred are natural gas, properly prepared syngas, and distillate oils. Most other liquid fuels require external treatment to remove harmful vanadium and sodium. Vanadium pentoxide and sodium sulfate are the principal ash components formed at higher temperatures. This ash adheres to blades and causes corrosion on the blades
1. A combined gas-vapor power cycle includes only the combination of a gas turbine with a steam turbine.