Gas turbine power applicationThe first gas turbine in production for electrical power generation was introduced by Brown Boveri of Switzerland in 1937. It was a standby unit with a thermal efficiency of 17%. Today the gas turbine is a major player in the huge power generation market, with orders of around 30GW per year. This success is due partly to large reserves of natural gas which provide a cheap fuel which is rich in hydrogen, and therefore produces less carbon dioxide than liquid fuels. The other major factor is thermal efficiency, which for combined cycle power plants approaches 60%. A final advantage is the viability of gas turbines in a very wide range of power levels, up to 300MW per engine for simple cycle and 500MW in combined cycle. The market is split evenly between 50 Hz areas such as much of western Europe and the former Soviet Union, and 60 Hz sectors such as North America
Some classes application:Plant type
generationPower per engine (MW)
Examples of applications
Examples of engineAlstom GT10 RR RB211 GE LM600
Peak lopping Supply to grid units, simple cycle gas turbine
Mid merit power station, simple cycle gas turbine
Supply to grid
GE LM6000 RR Trent
Base load power Supply to grid station, gas turbine in combined cycle
WEC 501F 50450 GEPG9331(FA)
Base load power Supply to grid station, coal fired steam plant Base load power Supply to grid station, nuclear powered steam plant
RR=Rolls-Royce WEC=Westinghouse Electric Company (now part of Siemens) GE=General Electric
COMBINED CYCLE POWER PLANTS:a. Definition. In general usage the term combined cycle power plant describes the combination of gas turbine generator(s) (Brayton cycle) with turbine exhaust waste heat boiler(s) and steam turbine generator(s) (Rankine cycle) for the production Of electric power. If the steam from the
waste heat boiler is used for process or space heating, the term "cogeneration is the more correct terminology (simultaneous production of electric and heat energy). b. General description. (1) Simple cycle gas turbine generators, when operated as independent electric power producers, are relatively inefficient with net heat rates at full load of over 15,000 Btu per kilowatt-hour. Consequently, simple cycle gas turbine generators will be used only for peaking or standby service when fuel economy is of small importance. (2) Condensing steam turbine generators have full load heat rates of over 13,000 Btu per kilowatthour and are relatively expensive to install and operate. The efficiency of such units is poor compared to the 8500 to 9000 Btu per kilowatt-hour heat rates typical of a large, fossil fuel fired utility generating station. (3) The gas turbine exhausts relatively large quantities of gases at temperatures over 900 F, In combined cycle operation, then, the exhaust gases from each gas turbine will be ducted to a waste heat boiler. The heat in these gases, ordinarily exhausted to the atmosphere, generates high pressure superheated steam. This steam will be piped to a steam turbine generator. The resulting combined cycle heat rate is in the 8500 to 10,500 Btu per net kilowatt- hour range, or roughly one-third less than a simple cycle gas turbine generator. (4) The disadvantage of the combined cycle is that natural gas and light distillate fuels required for low maintenance operation of a gas turbine areexpensive. Heavier distillates and residual oils are also expensive as compared to coal.
combined cycle plant
Unit 4-2 at Higashi Niigata Thermal Power Station ofTohoku Electric Power Co., Inc.
Small scale combined heat and power CHP:In this application the waste heat is typically utilized in an industrial process. The heat may be used directly in drying processes or more usually it is converted by an HRSG (heat recovery steam generator) into steam for other uses. Most CHP systems burn natural gas fuel. The electricity generated is often used locally, and any excess exported to the grid. The key power plant selection criteria in order of importance are: (1) Thermal efficiency, for both CHP and simple cycle operation. The latter becomes more significant if for parts of the year there is no use for the full exhaust heat. (2) Heat to power ratio is important as electricity is a more valuable commodity than heat. Hence a low ratio is an advantage as the unit may be sized for the heat requirement and any excess electricity sold to the grid. (3) The grade (temperature) of the heat is very important in that the process usually demands a high temperature. (4) Owing to the high utilisation, low unit cost, start and acceleration times are all of secondary importance, as are weight, volume and part speed torque. The attributes of the gas turbine engine best meet the above criteria, and hence it is the market leader. The diesel engine still retains a strong
presence however, particularly for applications where substantial low grade heat is acceptable, or where the importance of simple cycle thermal efficiency is paramount The microturbine market has emerged in recent years with a number of forecasts predicting dramatic growth. Small gas turbines of between 40kW and 250kW are installed in buildings, such as a store or restaurant, to generate electricity and provide space heating and hot water. A connection with the grid for import/export is usually maintained. The very small size of microturbine turbomachinery leads to low component efficiencies and pressure ratio, hence to achieve circa 30% thermal efficiency the gas turbine must be recuperated. Otherwise the configuration is extremely simple as low unit cost is critical. Usually it comprises a single centrifugal compressor, DLE pipe combustor, either a radial or two stage axial turbine and the recuperator. Another key feature is a directly driven high speed generator the size of a gearbox to step down from the turbomachinery speed of typically 90,000 rpm to 3000/3600 rpm is impractical. This also requires power electronics to rectify the wild high frequency generator output into DC, and then convert it back to 50 Hz or 60 Hz AC.
Large scale CHP:Here the waste heat is almost exclusively used to raise steam, which is then used in a large process application such as a paper mill, or for district heating. Again the electricity generated may be used locally or exported to the grid. The importance of
performance criteria to engine selection are as for small scale CHP, except that emissions legislation is more severe at the larger engine size. Here gas turbines are used almost exclusively. High grade heat is essential, and the weight and volume of diesel engines prohibitive at these power outputs. Furthermore the gas turbines used are often applicable to other markets, such as oil and gas, and marine, which reduces unit cost. Aero-derivative gas turbines are the most common, though some heavyweight engines are used. Aero-derivatives usually employ the core from a large civil turbofan as a gas generator, with a custom designed free power turbine for industrial use. Heavyweight engines are designed specifically for industrial applications and as implied are far heavier than aeroderivatives, their low cost construction employing solid rotors, thick casings, etc. The gas turbine configuration is usually a free power turbine. While this is not necessary for CHP applications, it is essential to also allow use in oil and gas and marine. Axial flow compressors are used exclusively with overall pressure ratios between 15 :1 and 25 :1. The aero-derivatives are at the top end of this range as this pressure ratio level results from a civil turbofan core. This pressure ratio is a compromise between that required for optimum CHP thermal efficiency of 20 :1, and the 35 :1 for optimum simple cycle efficiency. These values apply to the typical SOT of between 1450K and 1550 K. Advanced cooling systems are employed for at least both the HP turbine first stage nozzle guide vanes and blades.
Applications which supply solely to a grid system:Power plants supplying a grid fall into three categories: (1) Peak lopping engines have a low utilisation, typically less than 10%. They are employed to satisfy the peak demand for electrical power which may occur on mid-weekday evenings as people return home and switch on a multitude of appliances. (2) Base load power plant achieve as near to 100% utilisation as possible to supply the continuous need for electrical power. (3) Mid merit power plant typically have a 3050% utilisation. They serve the extra demand for electricity which is seasonal, such as the winter period in temperate climates where demand increases for domestic heating and lighting. The considerations in selecting the type of power plant for a base load power station are as follows. (1) Thermal efficiency and availability are paramount. (2) Unit cost is of high importance as the capital investment, and period of time before the power station comes on line to generate a return on the investment are large. (3) Cost of electricity is a key factor in selecting the type of power plant, and fuel price is a major contributor to this. Coal, nuclear and oil fired steam plants all compete with the gas turbine.
In all cases weight and volume are of secondary importance. Other specific comments are as follows: (1)For base load plant, start and acceleration times are unimportant. . (2) For peak lopping power stations unit cost is crucial, time onto full load is very important and thermal efficiency relatively unimportant. (3)Mid merit power stations are a compromise with some unit cost increase over and above peak loppers being acceptable in return for a moderate gain in thermal efficiency.
Application in nuclear field:Nuclear-assisted natural gastu