Gritsyna V.P.
In connection with the multiple growth of electricity tariffs in Russia, many enterprises are considering the construction of their own low-capacity power plants. In a number of regions, programs are being developed for the construction of small or mini thermal power plants, in particular, as a replacement for obsolete boiler houses. At a new small CHP plant with a fuel utilization rate of up to 90% with full use of the body in production and for heating, the cost of electricity received can be significantly lower than the cost of electricity received from the power grid.
When considering projects for the construction of small thermal power plants, power engineers and specialists of enterprises are guided by the indicators achieved in the large power industry. Continuous improvement of gas turbines (GTU) for use in large-scale power generation has made it possible to increase their efficiency up to 36% or more, and the use of a combined steam-gas cycle (CCGT) has increased the electrical efficiency of thermal power plants up to 54% -57%.
However, in the small-scale power industry it is inappropriate to consider the possibility of using complex schemes of combined cycles of CCGT for the production of electricity. In addition, gas turbines, in comparison with gas engines, as drives for electric generators, lose significantly in terms of efficiency and performance, especially at low powers (less than 10 MW). Since in our country neither gas turbines nor gas piston engines have yet been widely used in small-scale stationary power generation, the choice of a specific technical solution is a significant problem.
This problem is also relevant for large-scale energy, i.e. for power systems. In modern economic conditions, in the absence of funds for construction large power plants according to obsolete projects, which can already include the domestic project of a CCGT 325 MW, designed 5 years ago. Energy systems and RAO UES of Russia should pay special attention to the development of small-scale power generation, at whose facilities new technologies can be tested, which will make it possible to begin the revival of domestic turbine-building and machine-building plants and subsequently switch to large capacities.
In the last decade, large diesel or gas engine thermal power plants with a capacity of 100-200 MW have been built abroad. The electrical efficiency of diesel or gas engine power plants (DTPP) reaches 47%, which exceeds the performance of gas turbines (36%-37%), but is inferior to the performance of CCGTs (51%-57%). CCGT power plants include a large range of equipment: a gas turbine, a waste heat steam boiler, a steam turbine, a condenser, a water treatment system (plus a booster compressor if natural gas of low or medium pressure is burned. Diesel generators can run on heavy fuel, which is 2 times cheaper than gas turbine fuel and can operate on low-pressure gas without the use of booster compressors.According to S.E.M.T. PIELSTICK, the total cost over 15 years for the operation of a diesel power unit with a capacity of 20 MW is 2 times less than for a gas turbine thermal power plant of the same capacity when using liquid fuel by both power plants.
Promising Russian manufacturer diesel power units up to 22 MW is the Bryansk Machine-Building Plant, which offers customers power units with increased efficiency up to 50% for operation both on heavy fuel with a viscosity of up to 700 cSt at 50 C and a sulfur content of up to 5%, and for operation on gaseous fuel.
The option of a large diesel thermal power plant may be preferable to a gas turbine power plant.
In small-scale power generation, with unit capacities of less than 10 MW, the advantages of modern diesel generators are even more pronounced.
Let us consider three variants of thermal power plants with gas turbine plants and gas piston engines.
The fuel utilization factor for the first two options of power plants (with different electrical efficiency) due to heat supply can reach 80% -94%, both in the case of gas turbines and for motor drives.
The profitability of all variants of power plants depends on the reliability and efficiency, first of all, of the "first stage" - the drive of the electric generator.
Enthusiasts for the use of small gas turbines are campaigning for their widespread use, noting the higher power density. For example, in [1] it is reported that Elliot Energy Systems (in 1998-1999) creates a distribution network of 240 distributors in North America with the provision of engineering and service support for the sale of "micro"-gas turbines. The power grid ordered a 45 kW turbine to be ready for delivery in August 1998. It also stated that the electrical efficiency of the turbine was as high as 17%, and noted that gas turbines were more reliable than diesel generators.
This statement is exactly the opposite!
If you look at Table. 1. then we will see that in such a wide range from hundreds of kW to tens of MW, the efficiency of the motor drive is 13% -17% higher. The indicated resource of the motor drive of the company "Vyartsilya" means a guaranteed resource until a complete overhaul. The resource of new gas turbines is the calculated resource, confirmed by tests, but not by operation statistics in real operation. According to numerous sources, the resource of gas turbines is 30-60 thousand hours with a decrease with a decrease in power. The resource of diesel engines of foreign production is 40-100 thousand hours or more.
Table 1
Main technical parameters of electric generator drives
G-gas-turbine power plant, D-gas-piston generating plant of Vyartsilya.
D - diesel from the Gazprom catalog
* The minimum value of the required pressure of the fuel gas = 48 ATA!!
Performance characteristics
Electrical efficiency (and power) According to Värtsilä data, when the load is reduced from 100% to 50%, the efficiency of an electric generator driven by a gas engine changes little.
The efficiency of a gas engine practically does not change up to 25 °C.
The power of the gas turbine drops evenly from -30°C to +30°C.
At temperatures above 40 °C, the reduction in gas turbine power (from nominal) is 20%.
Start time gas engine from 0 to 100% load is less than a minute and emergency in 20 seconds. It takes about 9 minutes to start a gas turbine.
Gas supply pressure for a gas turbine it should be 16-20 bar.
The gas pressure in the network for a gas engine can be 4 bar (abs) and even 1.15 bar for a 175 SG engine.
Capital expenditures at a thermal power plant with a capacity of about 1 MW, according to Vartsila specialists, they amount to $1,400/kW for a gas turbine plant and $900/kW for a gas piston power plant.
Combined cycle application at small CHPPs, by installing an additional steam turbine is impractical, since it doubles the number of thermal and mechanical equipment, the area of the turbine hall and the number of maintenance personnel with an increase in power only 1.5 times.
With a decrease in the capacity of the CCGT from 325 MW to 22 MW, according to the data of the NPP "Mashproekt" plant (Ukraine, Nikolaev), the front efficiency of the power plant decreases from 51.5% to 43.6%.
The efficiency of a diesel power unit (using gas fuel) with a capacity of 20-10 MW is 43.3%. It should be noted that in the summer, at a CHPP with a diesel unit, hot water supply can be provided from the engine cooling system.
Calculations on the competitiveness of power plants based on gas engines showed that the cost of electricity at small (1-1.5 MW) power plants is approximately 4.5 cents / kWh), and at large 32-40 MW gas-powered plants 3, 8 US cents/kWh
According to a similar calculation method, electricity from a condensing nuclear power plant costs approximately 5.5 US cents/kWh. , and coal IES about 5.9 cents. US/kWh Compared to a coal-fired CPP, a plant with gas engines generates electricity 30% cheaper.
The cost of electricity produced by microturbines, according to other sources, is estimated at between $0.06 and $0.10/kWh
The expected price for a complete 75 kW gas turbine generator (US) is $40,000, which corresponds to the unit cost for larger (more than 1000 kW) power plants. The big advantage of power units with gas turbines is their smaller dimensions, 3 or more times less weight.
Note that the unit cost of power generating sets Russian production on the basis of automobile engines with a power of 50-150 kW, it can be several times less than the mentioned turboblocks (USA), given the serial production of engines and the lower cost of materials.
Here is the opinion of Danish experts who evaluate their experience in the implementation of small power plants.
"Investment in a completed turnkey natural gas CHP plant with a capacity of 0.5-40 MW is 6.5-4.5 million Danish krone per MW (1 krone was approximately equal to 1 ruble in the summer of 1998) Combined cycle CHP plants below 50 MW will achieve an electrical efficiency of 40-44%.
Operating costs for lubricating oils, Maintenance and the maintenance of personnel at CHPs reach 0.02 kroons per 1 kWh produced by gas turbines. At CHP plants with gas engines, operating costs are about 0.06 dat. kroons per 1 kWh. At current electricity prices in Denmark, the high performance of gas engines more than offsets their higher operating costs.
Danish specialists believe that most CHP plants below 10 MW will be equipped with gas engines in the coming years."
conclusions
The above estimates, it would seem, unambiguously show the advantages of a motor drive at low power of power plants.
However, at present, the power of the proposed Russian-made motor drive on natural gas does not exceed the power of 800 kW-1500 kW (RUMO plant, N-Novgorod and Kolomna Machine Plant), and several plants can offer turbo drives of higher power.
Two factories in Russia: plant im. Klimov (St. Petersburg) and Perm Motors are ready to supply complete power units of mini-CHP with waste heat boilers.
In the case of organizing a regional service center, issues of maintenance and repair of small turbines of turbines can be resolved by replacing the turbine with a backup one in 2-4 hours and its further repair in the factory conditions of the technical center.
The efficiency of gas turbines can currently be increased by 20-30% by applying power injection of steam into a gas turbine (STIG cycle or steam-gas cycle in one turbine). In previous years, this technical solution was tested in full-scale full-scale field tests of the Vodoley power plant in Nikolaev (Ukraine) by Mashproekt Research and Production Enterprise and Zarya Production Association, which made it possible to increase the power of the turbine unit from 16 to 25 MW and the efficiency was increased from 32 .8% to 41.8%.
Nothing prevents us from transferring this experience to smaller capacities and thus implementing a CCGT in serial delivery. In this case, the electrical efficiency is comparable to that of diesels, and the specific power increases so much that capital costs can be 50% lower than in a gas engine driven CHP plant, which is very attractive.
This review was carried out in order to show: that when considering options for the construction of power plants in Russia, and even more so the directions for creating a program for the construction of power plants, it is necessary to consider not individual options that design organizations can offer, but a wide range of issues taking into account the capabilities and interests of domestic and regional manufacturers equipment.
Literature
1. Power Value, Vol.2, No.4, July/August 1998, USA, Ventura, CA.
The Small Turbine Marketplace
Stan Price, Northwest Energy Efficiency Council, Seattle, Washington and Portland, Oregon
2. New directions of energy production in Finland
ASKO VUORINEN, Assoc. tech. Sciences, Vartsila NSD Corporation JSC, "ENERGETIK" -11.1997. page 22
3. District heating. Research and development of technology in Denmark. Ministry of Energy. Energy Administration, 1993
4. DIESEL POWER PLANTS. S.E.M.T. PIELSTICK. POWERTEK 2000 Exhibition Prospectus, March 14-17, 2000
5. Power plants and electrical units recommended for use at the facilities of OAO GAZPROM. CATALOG. Moscow 1999
6. Diesel electrical station. Prospect of OAO "Bryansk Machine-Building Plant". 1999 Exhibition brochure POWERTEK 2000/
7. NK-900E Block-modular thermal power plant. OJSC Samara Scientific and Technical Complex named after V.I. N.D. Kuznetsova. Exhibition brochure POWERTEK 2000
Like a diesel or gasoline engine, a gas turbine is an internal combustion engine with an intake-compression-combustion (expansion)-exhaust duty cycle. But, the basic movement is significantly different. The working body of the gas turbine rotates, and in the piston engine it moves reciprocating.
The working principle of a gas turbine is shown in the figure below. First, the air is compressed by the compressor, then the compressed air is fed into the combustion chamber. Here, the fuel, continuously burning, produces gases with high temperature and pressure. From the combustion chamber, the gas, expanding in the turbine, presses on the blades and rotates the turbine rotor (a shaft with impellers in the form of discs carrying rotor blades), which in turn again rotates the compressor shaft. The remaining energy is removed through the working shaft.
Features of gas turbines
Types of gas turbines by design and purpose
The most basic type of gas turbine is the jet thruster, which is also the simplest in design.
This engine is suitable for aircraft flying on high speed, and is used in supersonic aircraft and jet fighters.
This type has a separate turbine behind the turbojet that spins a large fan in front. This fan increases airflow and draft.
This type is quiet and economical at subsonic speeds, which is why gas turbines of this type are used for passenger aircraft engines.
This gas turbine delivers power as torque, with the turbine and compressor sharing a common shaft. Part of the useful power of the turbine goes to the rotation of the compressor shaft, and the rest of the energy is transferred to the working shaft.
This type is used when a constant rotation speed is needed, for example, as a generator drive.
In this type, the second turbine is placed after the gas generator turbine and the rotational force is transferred to it by the jet. This rear turbine is called the power turbine. Since the shafts of the power turbine and compressor are not mechanically connected, the speed of rotation of the working shaft is freely adjustable. Suitable as a mechanical drive with a wide range of rotational speeds.
This type is widely used in propeller-driven aircraft and helicopters, as well as in applications such as pump/compressor drives, marine main engines, generator drives, etc.
What is GREEN series gas turbine?
The principle that Kawasaki has followed in the gas turbine business since the development of our first gas turbine in 1972 has allowed us to offer customers ever more advanced equipment, i.e. more energy efficient and environmentally friendly. The ideas embodied in our products have been highly appreciated by the world market and have allowed us to accumulate references for more than 10,000 turbines (at the end of March 2014) as part of standby generators and cogeneration systems.
Kawasaki gas turbines have always been a great success, and we have given them the new name "GREEN Gas Turbines" to show our even greater commitment to this principle.
Thermal turbine of constant action, in which the thermal energy of compressed and heated gas (usually fuel combustion products) is converted into mechanical rotational work on a shaft; is a structural element of a gas turbine engine.
Heating of compressed gas, as a rule, occurs in the combustion chamber. It is also possible to carry out heating in a nuclear reactor, etc. For the first time, gas turbines appeared in late XIX in. as a gas turbine engine and in terms of design, they approached a steam turbine. Structurally, a gas turbine is a series of orderly arranged stationary blade rims of the nozzle apparatus and rotating rims of the impeller, which as a result form a flow part. The turbine stage is a nozzle apparatus combined with an impeller. The stage consists of a stator, which includes stationary parts (housing, nozzle blades, shroud rings), and a rotor, which is a set of rotating parts (such as rotor blades, disks, shaft).
The classification of a gas turbine is carried out according to many design features: in the direction of the gas flow, the number of stages, the method of using the heat difference and the method of supplying gas to the impeller. In the direction of the gas flow, gas turbines can be distinguished axial (the most common) and radial, as well as diagonal and tangential. In axial gas turbines, the flow in the meridional section is transported mainly along the entire axis of the turbine; in radial turbines, on the contrary, it is perpendicular to the axis. Radial turbines are divided into centripetal and centrifugal. In a diagonal turbine, the gas flows at some angle to the axis of rotation of the turbine. The impeller of a tangential turbine has no blades; such turbines are used at very low gas flow rates, usually in measuring instruments. Gas turbines are single, double and multi-stage.
The number of stages is determined by many factors: the purpose of the turbine, its design scheme, the total power and developed by one stage, as well as the actuated pressure drop. According to the method of using the available heat difference, turbines with speed stages are distinguished, in which only the flow turns in the impeller, without pressure change (active turbines), and turbines with pressure stages, in which the pressure decreases both in the nozzle apparatus and on the rotor blades (jet turbines). In partial gas turbines, gas is supplied to the impeller along a part of the circumference of the nozzle apparatus or along its full circumference.
In a multistage turbine, the energy conversion process consists of a number of successive processes in individual stages. Compressed and heated gas is fed into the interblade channels of the nozzle apparatus with initial speed, where in the process of expansion, a part of the available heat drop is converted into the kinetic energy of the outflow jet. Further expansion of the gas and the conversion of the heat drop into useful work occur in the interblade channels of the impeller. The gas flow, acting on the rotor blades, creates a torque on the main shaft of the turbine. In this case, the absolute velocity of the gas decreases. The lower this speed, the greater part of the energy of the gas is converted into mechanical work on the turbine shaft.
Efficiency characterizes the efficiency of gas turbines, which is the ratio of the work removed from the shaft to the available gas energy in front of the turbine. The effective efficiency of modern multistage turbines is quite high and reaches 92-94%.
The principle of operation of a gas turbine is as follows: gas is injected into the combustion chamber by a compressor, mixed with air, forms a fuel mixture and is ignited. The resulting combustion products with a high temperature (900-1200 °C) pass through several rows of blades mounted on the turbine shaft and cause the turbine to rotate. The resulting mechanical energy of the shaft is transmitted through a gearbox to a generator that generates electricity.
Thermal energy gases leaving the turbine enter the heat exchanger. Also, instead of producing electricity, the mechanical energy of the turbine can be used to operate various pumps, compressors, etc. The most commonly used fuel for gas turbines is natural gas, although this cannot exclude the possibility of using other types gaseous fuel. But at the same time, gas turbines are very capricious and place high demands on the quality of its preparation (certain mechanical inclusions, humidity are necessary).
The temperature of gases leaving the turbine is 450-550 °С. The quantitative ratio of thermal energy to electrical energy in gas turbines ranges from 1.5: 1 to 2.5: 1, which makes it possible to build cogeneration systems that differ in the type of coolant:
1) direct (direct) use of exhaust hot gases;
2) production of low or medium pressure steam (8-18 kg/cm2) in an external boiler;
3) production of hot water (better when the required temperature exceeds 140 °C);
4) production of high pressure steam.
A great contribution to the development of gas turbines was made by Soviet scientists B. S. Stechkin, G. S. Zhiritsky, N. R. Briling, V. V. Uvarov, K. V. Kholshchevikov, I. I. Kirillov, and others. creation of gas turbines for stationary and mobile gas turbine plants reached foreign firms (Swiss "Brown-Boveri", in which the famous Slovak scientist A. Stodola worked, and "Sulzer", the American "General Electric", etc.).
In the future, the development of gas turbines depends on the possibility of increasing the gas temperature in front of the turbine. This is due to the creation of new heat-resistant materials and reliable cooling systems for rotor blades with a significant improvement in the flow path, etc.
Thanks to the widespread transition in the 1990s. natural gas as the main fuel for power generation, gas turbines have occupied a significant segment of the market. Despite the fact that the maximum efficiency of the equipment is achieved at capacities from 5 MW and higher (up to 300 MW), some manufacturers produce models in the 1-5 MW range.
Gas turbines are used in aviation and power plants.
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In autonomous generation - small power generation in recent times considerable attention is given gas turbines different power. Power plants at the base gas turbines are used as the main or backup source of electricity and heat for industrial or domestic facilities. gas turbines as part of power plants are designed for operation in any climatic conditions of Russia. Areas of use gas turbines practically unlimited: oil and gas industry, industrial enterprises, structures housing and communal services.
Positive use factor gas turbines in the field of housing and communal services is that the content of harmful emissions in the exhaust gases of NO x and CO is at the level of 25 and 150 ppm, respectively (for piston plants, these values are much higher), which allows you to install a power plant near residential areas. Usage gas turbines as power units of power plants avoids the construction of high chimneys.
Depending on the needs gas turbines equipped with steam or hot water waste heat boilers, which allows you to receive from the power plant either steam (low, medium, high pressure) for process needs, or hot water (DHW) with standard temperature values. You can get steam and hot water at the same time. The power of thermal energy produced by a power plant based on gas turbines, as a rule, is twice that of electricity.
At the power plant gas turbines in this configuration, the fuel efficiency increases to 90%. High usage efficiency gas turbines as power units is provided during long-term operation with maximum electrical load. With enough power gas turbines there is the possibility of combined use of steam turbines. This measure allows to significantly increase the efficiency of using the power plant, increasing the electrical efficiency up to 53%.
How much does a gas turbine power plant cost? What is its full price? What is included in the turnkey price?
Autonomous thermal power plant based on gas turbines has a lot of additional expensive, but often, just necessary equipment(a real-life example is a completed project). With the use of first-class equipment, the cost of a power plant of this level, on a turnkey basis, does not exceed 45,000 - 55,000 rubles per 1 kW of installed electric capacity. The final price of a power plant based on gas turbines depends on the specific tasks and needs of the consumer. The cost includes design, construction and commissioning. Gas turbines themselves, as power units, without additional equipment, depending on the manufacturer and power, cost from 400 to 800 dollars per 1 kW.
To obtain information on the cost of building a power plant or thermal power plant in your particular case, you must send a completed questionnaire to our company. After that, after 2-3 days, the customer-client receives a preliminary technical and commercial proposal - TCH (short example). Based on the TCH, the customer makes the final decision on the construction of a power plant based on gas turbines. As a rule, before making a decision, the client visits an existing facility in order to see a modern power plant with his own eyes and “touch everything with his hands”. Directly at the facility, the customer receives answers to existing questions.
The concept of block-modular construction is often taken as the basis for the construction of power plants based on gas turbines. Block-modular design provides a high level of factory readiness of gas turbine power plants and reduces the construction time for energy facilities.
Gas turbines - some arithmetic on the cost of energy produced
To produce 1 kW of electricity, gas turbines consume only 0.29–0.37 m³/h of gas fuel. When burning one cubic meter of gas, gas turbines generate 3 kW of electricity and 4-6 kW of thermal energy. With the price (averaged) for natural gas in 2011, 3 rubles. per 1 m³, the cost of 1 kW of electricity received from a gas turbine is approximately 1 ruble. In addition to this, the consumer receives 1.5–2 kW of free thermal energy!
With autonomous power supply from a power plant based on gas turbines, the cost of electricity and heat produced is 3–4 times lower than the tariffs in force in the country, and this does not take into account the high cost of connecting to state power grids (60,000 rubles per 1 kW in the Moscow region, 2011).
Construction of autonomous power plants based on gas turbines allows for significant savings Money By eliminating the costs of construction and operation of expensive power lines (TL), power plants based on gas turbines can significantly increase the reliability of electrical and thermal supply of both individual enterprises or organizations, and regions as a whole.
The degree of automation of the power plant based on gas turbines makes it possible to abandon a large number of maintenance personnel. During the operation of a gas power plant, only three people ensure its operation: an operator, an electrician on duty, and a mechanic on duty. When emergencies Reliable protection systems are provided to ensure the safety of personnel, the safety of systems and units of the gas turbine.
Atmospheric air is fed through an air intake equipped with a filter system (not shown in the diagram) to the inlet of a multistage axial compressor. The compressor compresses atmospheric air and delivers it at high pressure to the combustion chamber. At the same time, a certain amount of gas fuel is supplied to the combustion chamber of the turbine through the nozzles. Fuel and air mix and ignite. The air-fuel mixture burns, releasing a large amount of energy. The energy of the gaseous products of combustion is converted into mechanical work due to the rotation of the turbine blades by jets of hot gas. Part of the energy received is used to compress the air in the turbine compressor. The rest of the work is transferred to the electric generator through the drive axle. This work is the useful work of the gas turbine. The combustion products, which have a temperature of about 500-550 °C, are removed through the exhaust tract and the turbine diffuser, and can be further used, for example, in a heat exchanger, to obtain thermal energy.
Gas turbines, as engines, have the highest specific power among internal combustion engines, up to 6 kW/kg.
As a gas turbine fuel, kerosene, diesel fuel, gas can be used.
One of the advantages of modern gas turbines is the long life cycle- engine life (full up to 200,000 hours, before overhaul 25,000–60,000 hours).
Modern gas turbines are highly reliable. There is evidence of continuous operation of some units for several years.
Many gas turbine suppliers produce overhaul equipment on site, replacing individual components without transporting them to the manufacturing plant, which significantly reduces time costs.
The possibility of long-term operation in any power range from 0 to 100%, the absence of water cooling, operation on two types of fuel - all this makes gas turbines popular power units for modern autonomous power plants.
The use of gas turbines is most effective at medium power plants, and at capacities above 30 MW, the choice is obvious.
Steam turbine. Attempts to design a steam turbine that could compete with a steam engine until the middle of the 19th century. were unsuccessful because mechanical energy rotation of the turbine, it was possible to convert only a small fraction of the kinetic energy of the steam jet. The point is that inventors
we did not take into account the dependence of the turbine efficiency on the ratio of the steam velocity and the linear velocity of the turbine blades.
Let us find out at what ratio of the gas jet velocity and the linear velocity of the turbine blade the most complete transfer of the kinetic energy of the gas jet to the turbine blade will occur (Fig. 36). When the kinetic energy of the steam is completely transferred to the turbine blade, the jet velocity relative to the Earth should be equal to zero, i.e.
In the frame of reference moving with velocity, the velocity of the jet is: .
Since in this reference frame the blade is stationary at the moment of interaction with the jet, the jet velocity after elastic reflection remains unchanged in absolute value, but changes direction to the opposite:
Passing again to the reference frame associated with the Earth, we obtain the velocity of the jet after reflection:
Since then
We have obtained that the complete transfer of the kinetic energy of the jet to the turbine will occur under the condition that the linear speed of the turbine blades is half the speed of the jet. The first steam turbine, which found practical use, was made by the Swedish engineer Gustav Laval in 1889. Its power was less at rpm.
Rice. 36. Transfer of kinetic energy of a steam jet to a turbine blade
A high gas outflow velocity, even at medium pressure drops, of approximately 1200 m/s, requires effective work turbine giving its blades a linear velocity of about 600 m/s. Therefore, to achieve high efficiency values, the turbine must be high-speed. It is easy to calculate the inertial force acting on a turbine blade with a mass of 1 kg, located on the rotor rim with a radius of 1 m, at a blade speed of 600 m/s:
A fundamental contradiction arises: for the economical operation of the turbine, supersonic rotor speeds are required, but at such speeds the turbine will be destroyed by inertia forces. To resolve this contradiction, it is necessary to design turbines rotating at a speed less than optimal, but to make full use of the kinetic energy of the steam jet, make them multistage by mounting several rotors of increasing diameter on a common shaft. Due to the insufficiently high speed of rotation of the turbine, the steam gives only part of its kinetic energy to the rotor of a smaller diameter. Then the steam exhausted in the first stage is sent to the second rotor of a larger diameter, giving its blades a part of the remaining kinetic energy, etc. The exhaust steam is condensed in the cooler-condenser, and warm water is sent to the boiler.
The cycle of a steam turbine plant in coordinates is shown in Figure 37. In the boiler, the working fluid receives an amount of heat, heats up and expands at a constant pressure (AB isobar). In the turbine, the steam expands adiabatically (BC adiabat), doing work to rotate the rotor. In the condenser-cooler, washed, for example, by river water, the steam gives off the amount of heat to the water and condenses at a constant pressure. This process corresponds to an isobar. Warm water from the condenser is pumped to the boiler. This process corresponds to an isochore. As can be seen, the cycle of a steam turbine plant is closed. The work done by steam in one cycle is numerically equal to the area of figure ABCD.
Modern steam turbines have a high conversion efficiency of kinetic
Rice. 37. Diagram of the working cycle of a steam turbine plant
steam jet energy into mechanical energy, slightly exceeding 90%. Therefore, electric generators of almost all thermal and nuclear power plants of the world, providing more than 80% of all electricity generated, are driven by steam turbines.
Since the temperature of the steam used in modern steam turbine plants does not exceed 580 C (heater temperature), and the steam temperature at the outlet of the turbine is usually not lower than 30 °C (cooler temperature), the maximum value of the efficiency of a steam turbine plant as a heat engine is:
and the real values of the efficiency of steam turbine condensing power plants reach only about 40%.
The power of modern power units boiler - turbine - generator reaches kW. Next in line in the 10th five-year plan is the construction of power units with a capacity of up to kW.
Steam turbine engines are widely used in water transport. However, their use in land transport, and even more so in aviation, is hampered by the need to have a furnace and a boiler for generating steam, as well as a large amount of water for use as a working fluid.
gas turbines. The idea of eliminating the furnace and boiler in a heat engine with a turbine by transferring the fuel combustion site to the working fluid itself has long occupied designers. But the development of such internal combustion turbines, in which the working fluid is not steam, but air expanding from heating, was constrained by the lack of materials capable of operating for a long time at high temperatures and high mechanical loads.
The gas turbine plant consists of an air compressor 1, combustion chambers 2 and a gas turbine 3 (Fig. 38). The compressor consists of a rotor mounted on the same axis as the turbine, and a fixed guide vane.
When the turbine is running, the compressor rotor rotates. The rotor blades are shaped so that when they rotate, the pressure in front of the compressor decreases, and after it increases. Air is sucked into the compressor, and its pressure behind the first row of rotor blades increases. Behind the first row of rotor blades there is a row of blades of a stationary compressor guide vane, with the help of which the direction of air movement is changed and it is possible to further compress it using the blades of the second stage of the rotor, etc. Several stages of the compressor blades provide 5-7 times higher air pressure .
The compression process proceeds adiabatically, so the air temperature rises significantly, reaching 200 ° C or more.
Rice. 38. The device of a gas turbine plant
Compressed air enters the combustion chamber (Fig. 39). At the same time, liquid fuel - kerosene, fuel oil - is injected into it under high pressure through the nozzle.
When fuel is burned, the air serving as a working fluid receives a certain amount of heat and heats up to a temperature of 1500-2200 ° C. Heating the air occurs at a constant pressure, so the air expands and its speed increases.
moving with high speed air and combustion products are sent to the turbine. Passing from stage to stage, they give their kinetic energy to the turbine blades. Part of the energy received by the turbine is used to rotate the compressor, while the rest is used, for example, to rotate the propeller of an aircraft or the rotor of an electric generator.
To protect the turbine blades from the destructive action of a hot and high-velocity gas jet into the combustion chamber
Rice. 39. Combustion chamber
significantly more air is pumped by the compressor than is necessary for complete combustion of the fuel. The air entering the combustion chamber behind the fuel combustion zone (Fig. 38) reduces the temperature of the gas jet directed to the turbine blades. Lowering the gas temperature in the turbine leads to a decrease in efficiency, so scientists and designers are looking for ways to increase the upper limit of the operating temperature in a gas turbine. In some modern aircraft gas turbine engines, the gas temperature in front of the turbine reaches 1330 °C.
Exhaust air, together with combustion products at a pressure close to atmospheric and a temperature of more than 500 ° C at a speed of more than 500 m / s, is usually released into the atmosphere or, to increase efficiency, is sent to a heat exchanger, where it gives off part of the heat to heat the air entering the combustion chamber .
The cycle of operation of a gas turbine plant in the diagram is shown in Figure 40. The process of air compression in the compressor corresponds to the adiabat AB, the process of heating and expansion in the combustion chamber corresponds to the isobar BC. The adiabatic process of expansion of hot gas in the turbine is represented by the section CD, the process of cooling and reducing the volume of the working fluid is represented by the isobar DA.
The efficiency of gas turbine plants reaches 25-30%. Gas turbine engines do not have bulky steam boilers, like steam engines and steam turbines, there are no pistons and mechanisms that convert reciprocating motion into rotational motion, like steam engines and internal combustion engines. Therefore, a gas turbine engine takes up three times less space than a diesel engine of the same power, and its specific gravity (mass-to-power ratio) is 6–9 times less than that of an aircraft piston internal combustion engine. Compactness and speed, combined with high power per unit mass, determined the first practically important field of application of gas turbine engines - aviation.
Aircraft with a propeller mounted on the shaft of a gas turbine engine appeared in 1944. Such well-known aircraft as AN-24, TU-114, IL-18, AN-22 - "Antey" have turboprop engines.
The maximum mass of the Antey at takeoff is 250 tons, the carrying capacity is 80 tons, or 720 passengers,
Rice. 40. Diagram of the working cycle of a gas turbine plant
speed 740 km/h, power of each of the four engines kW.
Gas turbine engines are beginning to replace steam turbine engines in water transport, especially on ships. navy. The transition from diesel engines to gas turbines made it possible to increase the carrying capacity of hydrofoils four times, from 50 to 200 tons.
Gas turbine engines with a capacity of 220-440 kW are installed on heavy vehicles. A 120-ton BelAZ-549V with a gas turbine engine is being tested in the mining industry.
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