How is a gas turbine different from a steam turbine? Steam and gas turbines: purpose, principle of operation, design, technical characteristics, operation features. How much does a gas turbine power plant cost? What is its full price? What's Included

Every now and then in the news they say that, for example, at such and such a state district power station full swing the construction of a CCGT -400 MW is underway, and at another CHPP-2, a GTP installation is put into operation - so many MW. Such events are written about, they are covered, since the inclusion of such powerful and efficient units is not only a “tick” in the implementation state program, but also a real increase in the efficiency of power plants, the regional energy system and even the unified energy system.

But I would like to bring to your attention not about the implementation of state programs or forecast indicators, but about CCGT and GTU. In these two terms, not only the layman, but also the novice power engineer can get confused.

Let's start with the easier one.

GTU - gas turbine plant - is a gas turbine and an electric generator combined in one building. It is advantageous to install it at a thermal power plant. This is effective, and many CHP reconstructions are aimed at installing just such turbines.

Here is a simplified cycle of operation of a thermal plant:

Gas (fuel) enters the boiler, where it burns and transfers heat to water, which leaves the boiler in the form of steam and turns the steam turbine. The steam turbine turns the generator. We get electricity from the generator, and we take steam for industrial needs (heating, heating) from the turbine if necessary.

And in a gas turbine plant, the gas burns out and turns the gas turbine, which generates electricity, and the outgoing gases turn water into steam in the waste heat boiler, i.e. gas works with a double benefit: first it burns and turns the turbine, then it heats the water in the boiler.

And if the gas turbine plant itself is shown in even more detail, it will look like this:

This video clearly shows what processes take place in a gas turbine plant.

But it will be even more useful if the resulting steam is made to work - put it into a steam turbine so that another generator works! Then our GTU will become a STEAM-GAS UNIT (CCGT).

As a result, PSU is a broader concept. This plant is an independent power unit where fuel is used once and electricity is generated twice: in a gas turbine plant and in a steam turbine. This cycle is very efficient, and has an efficiency of about 57%! This is a very good result, which allows you to significantly reduce fuel consumption for obtaining a kilowatt-hour of electricity!

In Belarus, to improve the efficiency of power plants, gas turbines are used as a “superstructure” to the existing CHP scheme, and CCGTs are being built at state district power plants as independent power units. Working at power plants, these gas turbines not only increase the "forecast technical and economic indicators", but also improve the management of generation, as they have high maneuverability: speed of start-up and power gain.

That's how useful these gas turbines are!

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 (GTUs) for use in large-scale power generation has made it possible to increase their efficiency to 36% or more, and the use of a combined steam-gas cycle (CCGT) has increased the electrical efficiency of TPPs 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 the construction of large power plants on obsolete projects, which can already be attributed to the domestic project of a 325 MW CCGT, 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 both power plants.
Promising Russian manufacturer diesel power units up to 22 MW is 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) is building a distribution network of 240 distributors in North America providing 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 a calculated resource, confirmed by tests, but not by statistics of work 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 CHPPs reach 0.02 kroons per 1 kWh produced at 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 high performance gas engines more than makes up for their higher operating costs.
Danish specialists believe that most CHP plants below 10 MW will be equipped with gas engines in the coming years."

findings
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). This technical solution has been tested in full-scale field tests in previous years. power plant"Vodoley" in Nikolaev (Ukraine) NPP "Mashproekt" and PA "Zarya", which allowed to increase the capacity 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 compared with that of diesel engines, and the specific power increases so much that capital expenditures can be as much as 50% lower than in gas-powered CHP plants, 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 who can offer design organizations, but a wide range of issues, taking into account the capabilities and interests of domestic and regional equipment manufacturers.

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

A turbine is any rotating device that uses the energy of a moving working fluid (fluid) to produce work. Typical turbine fluids are: wind, water, steam and helium. Windmills and hydroelectric power stations have used turbines for decades to turn electric generators and produce energy for industry and housing. Simple turbines have been known for much longer, the first of them appeared in ancient Greece.

In the history of power generation, however, gas turbines themselves appeared not so long ago. The first practical gas turbine started generating electricity in Neuchatel, Switzerland in 1939. It was developed by the Brown Boveri Company. The first gas turbine to power an aircraft also ran in 1939 in Germany, using a gas turbine designed by Hans P. von Ohain. In England in the 1930s, the invention and design of the gas turbine by Frank Whittle led to the first turbine-powered flight in 1941.

Figure 1. Scheme of an aircraft turbine (a) and a gas turbine for ground use (b)

The term "gas turbine" is easily misleading because for many it means a turbine engine that uses gas as fuel. In fact, a gas turbine (shown schematically in Figure 1) has a compressor that supplies and compresses gas (usually air); the combustion chamber, where the combustion of fuel heats the compressed gas and the turbine itself, which extracts energy from the flow of hot, compressed gases. This energy is enough to power the compressor and remains for useful applications. A gas turbine is an internal combustion engine (ICE) that uses the continuous combustion of fuel to produce useful work. In this, the turbine differs from carburetor or diesel internal combustion engines, where the combustion process is intermittent.

Since the use of gas turbines began in 1939 at the same time in the power industry and in aviation, different names are used for aviation and land-based gas turbines. Aviation gas turbines are called turbojet or jet engines, and other gas turbines are called gas turbine engines. AT English language there are even more names for these generally similar engines.

Use of gas turbines

In an aircraft turbojet, the energy from the turbine drives a compressor that draws air into the engine. The hot gas leaving the turbine is expelled into the atmosphere through the exhaust nozzle, which creates thrust. On fig. 1a shows a diagram of a turbojet engine.

Figure 2. Schematic representation of an aircraft turbojet engine.

A typical turbojet engine is shown in fig. 2. Such engines create thrust from 45 kgf to 45,000 kgf with a dead weight of 13 kg to 9,000 kg. The smallest engines drive cruise missiles, the largest are huge planes. The gas turbine in fig. 2 is a turbofan engine with a large diameter compressor. Thrust is created both by the air that is sucked in by the compressor and the air that passes through the turbine itself. The engine is large and capable of generating high thrust at low takeoff speeds, making it the most suitable for commercial aircraft. The turbojet engine does not have a fan and creates thrust with air that passes completely through the gas path. Turbojet engines have small frontal dimensions and produce the most thrust at high speeds, making them the most suitable for use on fighter aircraft.

In non-aeronautical gas turbines, part of the energy from the turbine is used to drive the compressor. The remaining energy - "useful energy" is removed from the turbine shaft at an energy utilization device such as an electric generator or a ship's propeller.

A typical land based gas turbine is shown in fig. 3. Such installations can generate energy from 0.05 MW to 240 MW. The setup shown in fig. 3 is a gas turbine derived from the aircraft, but lighter. Heavier units are designed specifically for ground use and are called industrial turbines. Although aircraft-derived turbines are increasingly being used as primary power generators, they are still most commonly used as compressors for pumping natural gas, power ships and are used as additional power generators for periods of peak loads. Gas turbine generators can turn on quickly, supplying power when it is most needed.

Figure 3. The simplest, single-stage, land-based gas turbine. For example, in energy. 1 - compressor, 2 - combustion chamber, 3 - turbine.

Most important benefits gas turbine are:

1. It is able to generate a lot of power with a relatively small size and weight.
2. The gas turbine operates in a constant rotation mode, unlike reciprocating engines operating with constantly changing loads. Therefore, turbines last a long time and require relatively little maintenance.
3. Although the gas turbine is started using auxiliary equipment such as electric motors or another gas turbine, starting takes minutes. For comparison, the start-up time of a steam turbine is measured in hours.
4. A gas turbine can use a variety of fuels. Large land-based turbines typically use natural gas, while aviation turbines tend to use light distillates (kerosene). Diesel fuel or specially treated fuel oil can also be used. It is also possible to use combustible gases from the process of pyrolysis, gasification and oil refining, as well as biogas.
5. Typically, gas turbines use atmospheric air as the working fluid. When generating electricity, a gas turbine does not need a coolant (such as water).

In the past, one of the main disadvantages of gas turbines was their low efficiency compared to other internal combustion engines or steam turbines in power plants. However, over the past 50 years, improvements in their design have increased thermal efficiency from 18% in 1939 on a Neuchatel gas turbine to the current efficiency of 40% in simple cycle operation and about 55% in combined cycle (more on that below). In the future, the efficiency of gas turbines will increase even more, with efficiency expected to rise to 45-47% in the simple cycle and up to 60% in the combined cycle. These expected efficiencies are substantially higher than other common engines such as steam turbines.

Gas turbine cycles

The sequence diagram shows what happens when air enters, passes through the gas path and exits the gas turbine. Typically, a cyclogram shows the relationship between air volume and system pressure. On fig. 4a shows the Brayton cycle, which shows the change in the properties of a fixed volume of air passing through a gas turbine during its operation. The key areas of this cyclogram are also shown in the schematic representation of the gas turbine in fig. 4b.

Figure 4a. Brayton cycle diagram in P-V coordinates for the working fluid, showing work (W) and heat (Q) flows.

Figure 4b. Schematic illustration of a gas turbine showing points from the Brayton cycle diagram.

The air is compressed from point 1 to point 2. The pressure of the gas increases while the volume of the gas decreases. The air is then heated at constant pressure from point 2 to point 3. This heat is produced by the fuel being introduced into the combustion chamber and burning continuously.

Hot compressed air from point 3 begins to expand between points 3 and 4. The pressure and temperature in this interval fall, and the volume of gas increases. In the engine in Fig. 4b, this is represented by the flow of gas from point 3 through the turbine to point 4. This produces energy that can then be used. In fig. 1a, the flow is directed from point 3" to point 4 through the outlet nozzle and produces thrust. "Useful work" in Fig. 4a is shown by curve 3'-4. This is the energy capable of driving the drive shaft of a ground turbine or creating thrust for an aircraft engine. Cycle Brighton ends in Fig. 4 with a process in which the volume and temperature of the air decrease as heat is released into the atmosphere.

Figure 5. Closed loop system.

Most gas turbines operate in an open cycle mode. In an open circuit, air is taken from the atmosphere (point 1 in Figs. 4a and 4b) and expelled back into the atmosphere at point 4, so the hot gas is cooled in the atmosphere after it is expelled from the engine. In a gas turbine operating in a closed cycle, the working fluid (liquid or gas) is constantly used to cool the exhaust gases (at point 4) in the heat exchanger (shown schematically in Fig. 5) and is sent to the compressor inlet. Since a closed volume with a limited amount of gas is used, a closed cycle turbine is not an internal combustion engine. In a closed cycle system, combustion cannot be sustained and the conventional combustion chamber is replaced by a secondary heat exchanger that heats the compressed air before it enters the turbine. Heat provided external source, for example, a nuclear reactor, coal fluidized bed furnace or other heat source. It was proposed to use closed-cycle gas turbines in flights to Mars and other long-term space flights.

A gas turbine that is designed and operated according to the Bryson cycle (Figure 4) is called a simple cycle gas turbine. Most gas turbines on aircraft operate on a simple cycle, as it is necessary to keep the weight and frontal dimension of the engine as small as possible. However, for land or sea use, it becomes possible to add additional equipment to the simple cycle turbine in order to increase the efficiency and/or power of the engine. Three types of modifications are used: regeneration, intermediate cooling and double heating.

Regeneration provides for the installation of a heat exchanger (recuperator) on the way of exhaust gases (point 4 in Fig. 4b). Compressed air from point 2 in fig. 4b is preheated on the heat exchanger by exhaust gases before entering the combustion chamber (Fig. 6a).

If the regeneration is well implemented, that is, the efficiency of the heat exchanger is high, and the pressure drop in it is small, the efficiency will be greater than with a simple turbine cycle. However, the cost of the regenerator should also be taken into account. Regenerators were used in gas turbine engines in Abrams M1 tanks - the main battle tank operation "Desert Storm" and in experimental gas turbine engines of cars. Gas turbines with regeneration increase efficiency by 5-6% and their efficiency is even higher when operating under partial load.

Intercooling also involves the use of heat exchangers. An intercooler (intercooler) cools the gas during its compression. For example, if the compressor consists of two modules, high and low pressure, an intercooler should be installed between them to cool the gas flow and reduce the amount of work required to compress in the high pressure compressor (Fig. 6b). The cooling agent can be atmospheric air (so-called air coolers) or water (eg sea water in a ship's turbine). It is easy to show that the power of a gas turbine with a well designed intercooler is increased.

double heating is used in turbines and is a way to increase the power output of a turbine without changing the operation of the compressor or increasing the operating temperature of the turbine. If the gas turbine has two modules, high and low pressure, then a superheater (usually another combustor) is used to reheat the gas flow between the high and low pressure turbines (Fig. 6c). It can increase the output power by 1-3%. Dual heating in aircraft turbines is realized by adding an afterburner at the turbine nozzle. This increases traction, but significantly increases fuel consumption.

Combined cycle gas turbine power plant is often abbreviated as CCGT. Combined cycle means a power plant in which a gas turbine and a steam turbine are used together to achieve greater efficiency than when used separately. The gas turbine drives an electric generator. Turbine exhaust gases are used to produce steam in a heat exchanger, this steam drives a steam turbine which also produces electricity. If steam is used for heating, the plant is called a cogeneration power plant. In other words, in Russia the abbreviation CHP (Heat and Power Plant) is commonly used. But at CHP plants, as a rule, not gas turbines work, but ordinary steam turbines. And the used steam is used for heating, so CHP and CHP are not synonymous. On fig. 7 simplified diagram cogeneration power plant, it shows two heat engines installed in series. The top engine is a gas turbine. It transfers energy to the lower engine - the steam turbine. The steam turbine then transfers the heat to the condenser.

Figure 7. Diagram of a combined cycle power plant.

The efficiency of the combined cycle \(\nu_(cc) \) can be represented by a rather simple expression: \(\nu_(cc) = \nu_B + \nu_R - \nu_B \times \nu_R \) In other words, it is the sum of the efficiency of each of the stages minus their work. This equation shows why cogeneration is so efficient. Assume \(\nu_B = 40%\) is a reasonable upper bound for the efficiency of a Brayton cycle gas turbine. A reasonable estimate of the efficiency of a steam turbine operating on the Rankine cycle at the second stage of cogeneration is \(\nu_R = 30% \). Substituting these values ​​into the equation, we get: \(\nu_(cc) = 0.40 + 0.30 - 0.40 \times 0.3 = 0.70 - 0.12 = 0.58 \). That is, the efficiency of such a system will be 58%.

This is the upper bound for the efficiency of a cogeneration power plant. The practical efficiency will be lower due to the inevitable loss of energy between stages. Practically in the cogeneration systems put into operation in recent years, an efficiency of 52-58% has been achieved.

Gas turbine components

The operation of a gas turbine is best broken down into three subsystems: compressor, combustion chamber, and turbine, as shown in Fig. 1. Next, we will briefly review each of these subsystems.

Compressors and turbines

The compressor is connected to the turbine by a common shaft so that the turbine can turn the compressor. A single shaft gas turbine has a single shaft connecting the turbine and compressor. A two-shaft gas turbine (Fig. 6b and 6c) has two conical shafts. The longer one is connected to a low pressure compressor and a low pressure turbine. It rotates inside a shorter hollow shaft that connects the high pressure compressor to the high pressure turbine. The shaft connecting the turbine and high pressure compressor rotates faster than the shaft of the turbine and low pressure compressor. A three-shaft gas turbine has a third shaft connecting the turbine and the medium pressure compressor.

Gas turbines can be centrifugal or axial, or a combination. The centrifugal compressor, in which compressed air exits around the outer perimeter of the machine, is reliable, usually costs less, but is limited to a compression ratio of 6-7 to 1. They were widely used in the past and are still used today in small gas turbines.

In more efficient and productive axial compressors, compressed air exits along the axis of the mechanism. This is the most common type of gas compressor (see figures 2 and 3). Centrifugal compressors consist of a large number of identical sections. Each section contains a rotating wheel with turbine blades and a wheel with fixed blades (stators). The sections are arranged in such a way that the compressed air sequentially passes through each section, giving some of its energy to each of them.

Turbines have a simpler design than a compressor, since it is more difficult to compress the gas flow than to cause it to expand back. Axial turbines like those shown in fig. 2 and 3 have fewer sections than a centrifugal compressor. There are small gas turbines that use centrifugal turbines (with radial gas injection), but axial turbines are the most common.

The design and manufacture of a turbine is difficult because it is required to increase the lifetime of the components in the hot gas stream. The design reliability issue is most critical in the turbine's first stage, where temperatures are highest. Special materials and a sophisticated cooling system are used to make turbine blades that melt at a temperature of 980-1040 degrees Celsius in a gas stream whose temperature reaches 1650 degrees Celsius.

The combustion chamber

A successful combustion chamber design must meet many requirements, and its proper design has been a challenge since the days of the Whittle and von Ohin turbines. The relative importance of each of the requirements for the combustion chamber depends on the application of the turbine and, of course, some requirements conflict with each other. When designing a combustion chamber, compromises are inevitable. Most of the design requirements are related to the price, efficiency and environmental friendliness of the engine. Here is a list of basic requirements for a combustion chamber:

1. High fuel combustion efficiency under all operating conditions.
2. Low fuel underburning and carbon monoxide (carbon monoxide) emissions, low nitrogen oxide emissions under heavy load and no visible smoke emissions (minimization of environmental pollution).
3. Small pressure drop when gas passes through the combustion chamber. 3-4% pressure loss is a typical pressure drop.
4. Combustion must be stable in all modes of operation.
5. Combustion must be stable at very low temperatures and low pressure at high altitude (for aircraft engines).
6. Burning should be even, without pulsations or disruptions.
7. The temperature must be stable.
8. Long service life (thousands of hours), especially for industrial turbines.
9. Usability different types fuel. Land turbines typically use natural gas or diesel fuel. For aviation kerosene turbines.
10. The length and diameter of the combustion chamber must match the size of the engine assembly.
11. The total cost of owning a combustion chamber should be kept to a minimum (this includes initial cost, operating and maintenance costs).
12. The combustion chamber for aircraft engines must have a minimum weight.

The combustion chamber consists of at least three main parts: shell, flame tube and fuel injection system. The shell must withstand the operating pressure and may be part of the gas turbine design. The shell closes a relatively thin-walled flame tube in which combustion and the fuel injection system take place.

Compared to other types of engines, such as diesel and reciprocating automobile engines, gas turbines produce the least amount of air pollutants per unit of power. Among gas turbine emissions, unburned fuel, carbon monoxide (carbon monoxide), oxides of nitrogen (NOx) and smoke are of greatest concern. Although the contribution of aircraft turbines to total pollutant emissions is less than 1%, emissions directly into the troposphere doubled between 40 and 60 degrees north latitude, causing a 20% increase in ozone concentrations. In the stratosphere, where supersonic aircraft fly, NOx emissions cause ozone depletion. Both effects are detrimental. environment, so reducing nitrogen oxides (NOx) in aircraft engine emissions is what needs to happen in the 21st century.

This is a fairly short article that tries to cover all aspects of turbine applications, from aviation to energy, without relying on formulas. To get better acquainted with the topic, I can recommend the book "Gas Turbine in Railway Transport" http://tapemark.narod.ru/turbo/index.html. If we omit the chapters related to the specifics of using turbines on railway– the book is still very clear, but much more detailed.

A gas turbine, as a heat engine, combines the characteristic features of a steam turbine and an internal combustion engine, in which the energy of the fuel during its combustion is converted directly into mechanical work. The working fluid of gas turbines operating on an open cycle is the products of fuel combustion, and the working fluid of gas turbines operating on a closed cycle is clean air or gas continuously circulating in the system. On ships, gas turbine units (GTUs) operating in an open cycle, with fuel combustion at constant pressure (p = const) and GTUs operating in a closed cycle, are used.

Currently, marine gas turbines are of two types: 1) turbocompressor and 2) with free-piston gas generators (SPGG).

A diagram of the simplest turbocompressor gas turbine plant operating at a constant fuel combustion pressure is shown in fig. 101. Compressor 9 sucks in clean atmospheric air, compresses it to high pressure and delivers it through the air duct3 into the combustion chamber 2, where simultaneously through the nozzle1 fuel is supplied. Fuel, mixed with air, forms a working mixture, which burns whenR = const. The resulting combustion products are cooled by air and sent to the flow path of the turbine. In the fixed blades 4, the combustion products expand and enter the rotor blades 5 at high speed, where the kinetic energy of the gas flow is converted into the mechanical work of the shaft rotation. Through pipe 6, the exhaust gases leave the turbine. The gas turbine drives the compressor 9 and through the gearbox7 propeller 8. To start the unit, a starting motor 10 is used, which spins the compressor to the minimum speed.

The same figure shows the theoretical cycle of the considered GTP in the coordinates p - ? andS - T: AB - the process of air compression in the compressor; VS-combustion of fuel at constant pressure in the combustion chamber; SD - gas expansion in the turbine, YES - heat removal from the exhaust gases.

To increase the efficiency of the gas turbine operation, regenerative heating of the air entering the combustion chamber is used, or staged combustion of fuel in several sequential combustion chambers that serve individual turbines. Due to the design complexity, staged combustion is rarely used. In order to increase the effective efficiency of the installation, along with regeneration, two-stage air compression is used, while an intercooler of air is included between the compressors, which reduces the required power of the high-pressure compressor.

On fig. 102 is a diagram of the simplest gas turbine plant with fuel combustion atR = const and heat recovery. Air compressed in the compressor1 , passes through the regenerator 2 into the combustion chamber3 , where it is heated by the heat of the exhaust gases leaving the turbine 4 with a relatively high temperature. The actual cycle of this installation is shown in the S-T diagram (Fig. 103): the process of compressing air in the compressor1 - 2 ; air heating in the regenerator, accompanied by a pressure drop fromR 2 beforeR 4 2 - 3; heat supply in the process of fuel combustion 3 - 4; actual gas expansion process in turbines4-5 ; gas cooling in the regenerator, accompanied by pressure loss p 5 -R 1 5-6; gas exhaust - heat removal6-1 . The amount of heat received by the air in the regenerator is represented by an area of ​​2"-2-3-3", and the amount of heat given off by the exhaust gases in the regenerator by an area of ​​6"-6-5-5". These areas are equal.

In a closed-cycle gas turbine, the spent working fluid does not enter the atmosphere, and after pre-cooling it is again sent to the compressor. Consequently, the working fluid circulates in the cycle, not contaminated with combustion products. This improves the working conditions of the flow parts of the turbines, resulting in increased reliability of the installation and increases its motor resource. Combustion products do not mix with the working fluid and therefore any type of fuel is suitable for combustion.

On fig. 104 shows a schematic diagram of an all-mode ship gas turbine of a closed cycle. Air after pre-cooling in the air cooler 4 enters the compressor5 , which is driven by a high pressure turbine7 . Air is sent from the compressor to the regenerator.3 , and then into the air heater 6, which performs the same role as the combustion chamber in open-type installations. From the air heater, working air at a temperature of 700 ° C enters the high-pressure turbine7 , which rotates the compressor and then into the low pressure turbine2 , which through the reducer1 actuates the adjustable pitch propeller. The starting motor 8 is designed to start the installation. The disadvantages of closed-cycle gas turbines include the bulkiness of heat exchangers.

Of particular interest are gas turbines of a closed cycle with a nuclear reactor. In these installations, helium, nitrogen, carbon dioxide are used as the working fluid of gas turbines (coolant). These gases are not activated in nuclear reactor. The gas heated in the reactor to a high temperature is directly sent to work in the gas turbine.

The main advantages of gas turbines compared to steam turbines are: low weight and dimensions, since there is no boiler and condensing unit with auxiliary mechanisms and devices; quick start-up and development of full power within 10-15 minutes; very low consumption of cooling water; ease of maintenance.

The main advantages of gas turbines compared to internal combustion engines are: the absence of a crank mechanism and associated inertial forces; low weight and dimensions at high power (GTUs are 2-2.5 times lighter in weight and 1.5-2 times shorter in length than diesel engines); the ability to work on low-grade fuel; lower operating costs. The disadvantages of gas turbines are as follows: a short service life at high gas temperatures (for example, at a gas temperature of 1173 ° K, the service life is 500-1000 hours); less than diesel engines, efficiency; significant noise during operation.

Currently, gas turbines are used as the main engines of marine transport ships. In some cases, low-power gas turbines are used to drive pumps, emergency power generators, auxiliary boost compressors, etc. Gas turbines are of particular interest as the main engines for hydrofoils and hovercraft.

Thermal turbine of constant action, in which thermal energy compressed and heated gas (usually fuel combustion products) is converted into mechanical rotational work on the 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. Gas turbines first appeared at the end of the 19th century. 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: according to 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 supplied to the interblade channels of the nozzle apparatus at an 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 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 gas energy 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 generating 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 of gaseous fuels. 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. the creation of gas turbines for stationary and mobile gas turbine plants was achieved by foreign companies (the 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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