GAS TURBINE PLANTS

INTRODUCTION

At the first stages of gas turbine development, two types of combustion chambers were used to burn fuel. Fuel and oxidizer (air) were supplied continuously into the combustion chamber of the first type, their combustion was also maintained continuously, and the pressure did not change. Fuel and oxidizer (air) were supplied in portions to the combustion chamber of the second type. The mixture was ignited and burned in a closed volume, and then the combustion products entered the turbine. In such a combustion chamber, the temperature and pressure are not constant: they increase sharply at the moment of fuel combustion.

Over time, the undoubted advantages of combustion chambers of the first type emerged. Therefore, in modern gas turbine plants, fuel is burned in most cases at constant pressure in the combustion chamber.

The first gas turbines had low efficiency, since gas turbines and compressors were imperfect. As these units were improved, the efficiency of gas turbine units increased, and they became competitive with other types of heat engines.

Currently, gas turbine units are the main type of engines used in aviation, due to the simplicity of their design, the ability to quickly gain load, high power with low weight, the ability to fully automate control. An airplane powered by a gas turbine engine first flew in 1941.

In the energy sector, gas turbine plants operate mainly at times when electricity consumption increases sharply, that is, during load peaks. Although the efficiency of gas turbine plants is lower than the efficiency of steam turbine units (with a power of 20-100 MW, the efficiency of gas turbine plants reaches 20-30%), using them in peak mode turns out to be beneficial, since start-up takes much less time.

In some peak gas turbine engines, aviation turbojet engines that have served their service life in aviation are used as gas sources for the turbine that rotates the electric generator. Along with internal combustion engines, gas turbines are used as the main engines in mobile power plants.

In technological processes of oil refining and chemical production combustible waste is used as fuel for gas turbines.

Gas turbine units are also found wide application on railway, sea, river and road transport. Thus, on high-speed hydrofoil and hovercraft, gas turbine engines are the engines. On heavy duty vehicles they can be used as either a main motor or an auxiliary motor designed to supply air to the main engine internal combustion and running on its exhaust gases.

In addition, gas turbine units serve as a drive for superchargers natural gas on main gas pipelines, backup electric generators for fire pumps.

! The main direction in which gas turbine engineering is developing is increasing the efficiency of gas turbines by increasing the temperature and pressure of the gas in front of the gas turbine. For this purpose, complex cooling systems are being developed for the most stressed parts of turbines or new, high-strength materials are being used - heat-resistant nickel-based materials, ceramics, etc.

Gas turbine plants are generally reliable and easy to operate, provided they are strictly followed established rules and operating modes, deviation from which can cause destruction of turbines, breakdown of compressors, explosions in combustion chambers, etc.

MAIN ELEMENTS OF GAS TURBINE PLANTS

GENERAL INFORMATION ABOUT GAS TURBINE PLANTS

Gas turbine engine(GTD) - one of the types heat engine, in which the gas is compressed and heated, and then the energy of the compressed and heated gas is converted into mechanical work on the shaft of a gas turbine. A gas turbine plant consists of three main elements: a gas turbine, combustion chambers and air compressor.

The conversion of heat into work is carried out in several gas turbine engines units (Fig. 1)

Rice. 1. Scheme gas turbine engine:

TN – fuel pump; KS – combustion chamber; K – compressor; T – turbine; EG – electric generator.

Into the combustion chamber fuel pump Fuel and compressed air are supplied after the compressor. The fuel is mixed with air, which serves as an oxidizer, ignited and burned. Clean combustion products are also mixed with air so that the temperature of the gas resulting from mixing does not exceed a predetermined value. From the combustion chambers, the gas enters a gas turbine, which is designed to convert its potential energy into mechanical work. While doing work, the gas cools and its pressure decreases to atmospheric pressure. Gas is released from a gas turbine into environment.

From the atmosphere enters the compressor clean air. In the compressor, its pressure increases and the temperature rises. The compressor drive takes a significant part of the turbine power.

Gas turbine plants operating according to this scheme are called open cycle installations. Most modern gas turbines operate according to this scheme.

Rice. 2. Gas turbine engine cycle.

Replacing the combustion of fuel with an isobaric heat supply (line 2-3 in Fig. 2), and the cooling of combustion products emitted into the atmosphere with an isobaric heat removal (line 1-4), we obtain the gas turbine engine cycle:

1-2 – compression of the working fluid from atmospheric pressure to engine pressure;

2-3 – combustion in the chamber;

3-4 – process of adiabatic expansion of the working fluid;

4-1 – exhaust gases are released into the atmosphere

In addition, they apply closed gas turbines(Fig. 3). Closed gas turbines also have a compressor 3 and a turbine 2 . Instead of a combustion chamber, heat source 1 is used , in which heat is transferred to the working fluid without mixing with fuel. The working fluid can be air, carbon dioxide, mercury vapor or other gases.

The working fluid, the pressure of which is increased in the compressor, is heated in the heat source 1 and enters the turbine 2 , in which he gives his energy. After the turbine, the gas enters the intermediate heat exchanger 5 (regenerator), in which it heats the air and is then cooled in the cooler 4 , enters compressor 3, and the cycle repeats. Special boilers for heating the working fluid with the energy of burned fuel or nuclear reactors can be used as a heat source.

Rice. 3. Diagram of a gas turbine engine operating in a closed cycle: 1 - surface heater; 2 - turbine; 3 - compressor; 4 - cooler; 5 - regenerator; 6 - air accumulator; 7 - auxiliary compressor.

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Gas turbine is an engine that combines the advantages of a steam turbine and an internal combustion engine. Unlike a steam turbine, the working fluid here is not steam from boilers, but gases formed during the combustion of fuel in special chambers. Unlike an internal combustion engine, the energy of the working fluid is converted into mechanical energy of rotation of the shaft not as a result of the reciprocating movement of the piston in the cylinder, but by rotating the turbine wheel under the action of a high-speed stream of gases flowing from the nozzle.

A gas turbine, like a steam turbine, is a non-reversible mechanism; therefore, for reverse in gas turbine installations it is necessary to provide a reverse turbine or some other device, for example, a controlled pitch propeller (CPG).

Gas turbine plant(GTU) consists of the following main parts: gas turbine, in which thermal energy hot gases are converted into mechanical; air compressor, sucking in and compressing the air necessary for fuel combustion; combustion chambers(gas generator), in which atomized liquid fuel is mixed with air and burned, forming a working fluid - hot gas; pipelines for supplying air to the gas generator, supplying gases from the generator to the gas turbine and discharging exhaust gases into the atmosphere; recycling devices, ensuring the use of heat from exhaust gases.

Rice. 124. General view(a) and diagram of a gas turbine unit with a combustion chamber (b) (power 4040 kW).

1 - low pressure compressor; 2 - air heater; 3 - theater; 4 - compressor high pressure; 5 - starting turbine; 6 - combustion chamber; 7 - nozzle; 8 - TND;

9 - air cooler; 10 - gearbox

In addition, the GTU includes fuel and oil systems, supplying fuel to the combustion chamber and oil to the turbine bearings and gear transmission, as well as a small-power starting steam turbine that uses steam from the auxiliary boiler.

The gas turbine design is similar steam turbine. But a gas turbine experiences higher temperature loads: its working blades operate at a temperature of hot gases (650-850°), while the temperature of the working steam is 400-500°. This significantly reduces the service life of the gas turbine. Depending on the adopted method of air compression and the formation of hot gases, a distinction is made between gas turbines with a combustion chamber and gas turbines with free-piston gas generators (SPGG).

In a gas turbine unit with a combustion chamber (Fig. 124) outside air is sucked in by a low-pressure centrifugal compressor and supplied through an air cooler to a high-load compressor: pressure, and from there through an air heater into the combustion chamber.

At the same time, fuel is injected into the combustion chamber through the nozzle. Combustion occurs and hot gases are formed, which sequentially enter the high and low pressure gas turbines and are released into the atmosphere through the exhaust pipeline. An air heater and a recovery boiler are installed along the path of the exhaust gases, the steam from which can be used for a turbogenerator or for an auxiliary turbine operating on the propeller shaft. Low and high pressure centrifugal compressors are driven by low and high pressure turbines respectively. Only the low pressure turbine drives the propeller through a gearbox.

Rice. 125. General view (a) and diagram of the SPGG (b).

1 - compressor inlet valves; 2 - compressor exhaust valves;

3 - compressor piston; 4 - compressor cylinder;

5 - inlet windows; 6 - exhaust windows; 7 - nozzle; 8 - working cylinder; 9 - buffer cylinder; 10 - buffer piston; 11 - purge air receiver; 12 - working piston; 13 - piston synchronization mechanism

A gas turbine unit with free-piston gas generators (LPGG) (Fig. 125) differs from a gas turbine unit with a combustion chamber in that hot gases are generated in a special gas generator operating on the principle of an internal combustion engine with freely diverging pistons. The SGNG is a symmetrical unit consisting of a two-stroke single-cylinder engine with opposing pistons, a single-stage single-acting compressor and two buffer cylinders. The cylinder contains two working pistons connected to compressors and buffer pistons.

Rice. 126. Layout of a gas turbine power plant with LNG.

1 - SPGG; 3 - gas turbine; 3 - gearbox; 4 - diesel generator

The working (divergent) stroke of the piston groups is carried out under the influence of gas expanding in the working cylinder. In this case, the air in the compressor cylinders is first compressed and then flows through the exhaust valves into the purge air receiver. Simultaneously with the compression of air in the compressor cylinders, the air in the buffer cylinders is compressed, after which its energy is spent on reversing the working pistons and compressing the air in the working cylinder.

At the end of the piston stroke, first the exhaust windows open, and then the intake windows. Through the exhaust ports, the exhaust gases enter the gas turbine, and through the intake ports, compressed purge air from the receiver fills the working cylinder.

Excess scavenging air is mixed with the hot exhaust gases and is also supplied to the gas turbine.

During the reverse stroke of the working pistons, under the influence of air compressed in the buffer cylinders, the inlet windows close, then the outlet windows, and at the same time air is sucked into the compressor cylinders through the valves. At the moment the pistons approach each other, fuel is injected into the working cylinder through the nozzle, and the process is repeated.

Gas turbines and LPGGs are compact, have a relatively low weight of 16-24 kg/kW and low fuel consumption of 260 g/(kWh). The advantage is the ability to compose power plant from several SPGGs, which allows for more rational use of the volume of MCO (Fig. 126). In addition to the above-mentioned types of gas turbines, lightweight aviation-type gas turbines (1.5-4.0 kg/kW) are widely used on small high-speed vessels, especially on hydrofoils. But they have a short service life and increased fuel consumption (340-380 g/kWh).

The disadvantage of all types of gas turbines, in addition to increased fuel consumption and short service life, is the high noise level in the MKO, to reduce which it is necessary to resort to special measures.

A modern gas turbine unit (GTU) is a combination of an air compressor, a combustion chamber and a gas turbine, as well as auxiliary systems that ensure its operation. The combination of a gas turbine unit and an electric generator is called a gas turbine unit. A turbine in which gas expands to atmospheric pressure converts the potential energy of the compressed and heated gas into kinetic energy of rotation of the turbine rotor. The turbine drives an electric generator, which converts the kinetic energy of rotation of the generator rotor into electric current. An electric generator consists of a stator, in the electrical windings of which current is generated, and a rotor, which is an electromagnet powered by an exciter.

Unlike steam turbine units (STU), where the working fluid is steam, gas turbine units operate on fuel combustion products. In addition, unlike a gas turbine unit, the steam turbine unit does not include a boiler; more precisely, the boiler is considered as a separate heat source. A steam turbine plant cannot operate without a boiler as a physical object. In a gas turbine unit, on the contrary, the combustion chamber is its integral part. In this sense, the GTU is self-sufficient. According to the method of supplying heat at constant pressure p= const and at constant volume v= const. All modern gas turbine plants operate with heat input at p= const. There are open (open) and closed (closed) circuits of gas turbine plants

The simplest diagram of an open gas turbine unit in symbols, as well as its thermodynamic cycle, are presented in Figure 1. Air from the atmosphere enters the inlet of the air compressor (point 1 ), which is a rotary turbomachine with a flow part consisting of rotating and stationary grids. The ratio of the pressure behind the compressor to the pressure in front of it is called the compression ratio of the air compressor and is usually denoted as. The compressor rotor is driven by a gas turbine. A stream of compressed air is supplied to one, two or more combustion chambers (point 2 ). In most cases, the air flow coming from the compressor is divided into two streams. The first flow is directed to the burner devices, where fuel (gas or liquid fuel) is also supplied, due to the combustion of which at constant pressure p= const high temperature combustion products are formed. Relatively cold air from the second flow is mixed with them in order to obtain gases (they are called working gases) with a temperature acceptable for the gas turbine parts.

Figure 1 – The simplest diagram of an open gas turbine unit and its thermodynamic cycle

Working gases with pressure due to the hydraulic resistance of the combustion chamber) are supplied to the flow part of the gas turbine (point 3 ), where they expand almost to atmospheric pressure (point 4 ). Next they enter the output diffuser , from where - or immediately to chimney, which will cause significant heat losses, or first to some heat exchanger that uses the heat of the gas turbine exhaust gases.

In a closed circuit (Fig. 2), instead of a combustion chamber, surface heaters of the working fluid are used, and the gas exhausted in the turbine (for example, helium) is cooled in special coolers to the lowest temperature, after which it enters the compressor. The thermodynamic cycle of this scheme is similar to the cycle of an open gas turbine unit.

Due to the expansion of gases in a gas turbine, the latter produces power. A significant part of it is spent on driving the compressor, and the remaining part is spent on driving the electric generator. This part is called the useful power of the gas turbine unit and is indicated when marking it.

In real gas turbines, all ongoing processes are accompanied by work losses in the compressor and turbine, as well as pressure losses along the gas turbine path. Taking into account these losses, the real cycle differs from the ideal one. A real gas turbine plant includes a combustion chamber (working fluid heater in a closed circuit), a gas turbine, a compressor, a starting engine, heat exchangers for various purposes (regenerative heaters, intermediate heaters in turbines) and various auxiliary equipment, as well as an electric generator if the purpose of the gas turbine plant is production electrical energy. The turbine, compressor and generator are located on the same shaft. The starting motor is connected by a release clutch. In the simplest gas turbines, approximately 70% of the power developed by the turbine is spent on driving the compressor, and 30% on driving the generator. Pressure increase ratio in the compressor = 6…7, installation efficiency 24…27%, temperature in front of the turbine 750…800 °C. The range of initial temperatures in front of the gas turbine in a gas turbine unit is 750...1150 °C, therefore, based on strength conditions, plant elements operating at high temperatures are made of high-alloy steels, and for increased reliability provide for air cooling.

Figure 2 – The simplest diagram of a closed gas turbine

Turbine exhaust gases have a high temperature, so their removal into the environment is open circuit Gas turbines lead to significant energy losses. In order to increase the efficiency of the installation, regenerative heating of compressed air using turbine exhaust gases is used. This increases the degree of utilization of the heat of the fuel burned in the combustion chamber and the energy efficiency of the installation.

In an ideal gas turbine unit with regeneration, the diagram and cycle of which are shown in Figure 3, the turbine exhaust gases can be cooled to a temperature equal to the air temperature behind the compressor, i.e. to , and the air compressed by the compressor can be heated to a temperature corresponding to the temperature at the turbine exhaust, i.e. to. In a real installation, the air in the regenerative heat exchanger will be heated to a temperature that is lower, and the exhaust gases will be cooled in the same heat exchanger to a temperature that is higher, usually equal to 60 ... 80 ° C in open circuits. Real gas turbine plants operating in an open circuit at an initial temperature of 750...850 °C have a degree of regeneration, and an effective efficiency of 26.5...30%.

Figure 3 – Scheme and cycle of a gas turbine unit with regeneration

GTUs that provide combined production of electrical and thermal energy are called heating plants. Thermal energy is generated by using the heat of gases leaving the turbine at a high temperature to heat water and produce steam. Heating water used for heating and domestic needs with turbine exhaust gases is the simplest way to increase the thermal efficiency of a gas turbine plant.

Gas turbines use gaseous and light liquid fuels. When using heavy grade liquid fuel containing harmful impurities, a special fuel preparation system is needed to prevent corrosion of turbine parts under the influence of sulfur and vanadium compounds contained in heavy fuel. The problem of using solid fuel in gas turbine plants is at the stage of intensive pilot development.

The technology for starting a turbine largely depends on the temperature state of the equipment in front of it. There are starts from cold, uncooled and hot states. If the turbine temperature does not exceed 150 °C, then it is considered that the start was made from a cold state. For powerful power units, it takes up to 90 hours to cool to this temperature. Starts from a hot state correspond to a turbine temperature of 420-450 °C and higher (reached in 6-10 hours). The uncooled state is intermediate. Any lengthening of the start leads to additional fuel consumption. Therefore, startup must be done quickly, but not at the expense of reliability. Starting the turbine is prohibited:

in the event of a malfunction of the main instruments showing the progress of the thermal process in the turbine and its mechanical condition (tachometers, thermometers, pressure gauges, etc.);

if the lubrication system that provides lubrication of the bearings is faulty;

in case of malfunction of protection and regulation systems;

with a faulty turning device.

To put a gas turbine into operation, it is necessary to use a starting device (PU) to rotate the turbocharger rotor; air from the compressor must be supplied simultaneously with fuel into the combustion chamber to ignite it and to perform further operations to start the gas turbine. Various means can be used as a starting device: an electric motor, a steam or gas (air) turbine, an internal combustion engine. For large power turbines, as a rule, the gas turbine's own electric generator is used as a control unit, which turns the gas turbine rotor to a rotation speed equal to 0.2 - 0.3 nominal. During the start-up period, the compressor control guide vanes must be covered to reduce air consumption. At the beginning of the start, the anti-surge valves are open. Fuel is supplied to the combustion chamber, and the air-fuel mixture formed in the mixing device of the combustion chamber is ignited using an ignition device (plasma igniter). Fuel consumption is increased by opening the fuel valve. This causes an increase in the temperature of the gases in front of the turbine, the turbine power and the rotor speed. At a certain gas temperature in front of the turbine and a certain rotation speed, the power of the gas turbine is equal to the power consumed by the air compressor. In this state, after a slight additional increase in fuel consumption, the starting device is turned off and the gas turbine unit switches to self-propelled mode. With a further increase in fuel consumption, the turbine unit is turned by the gas turbine until the rated rotation speed is reached, then the electric generator is synchronized with the network and connected to the network. This puts the unit into idle mode. During the startup process, the anti-surge valves are closed and the adjustable guide vanes are set to the positions prescribed by the startup program.

In the process of loading the gas turbine unit to the rated power, the fuel consumption increases by opening the control valve, the installation angles of the adjustable guide vanes of the compressor change according to the corresponding program, and the air consumption increases to the nominal value. Operation of a gas turbine unit generally consists of start-up, operation with electrical and thermal loads, and shutdown. The simplest is to work at a constant load. The main task of the personnel servicing the turbine installation during normal operation is to provide the specified electrical and thermal power with full guarantee reliable operation and maximum possible savings.

GTU operating modes can be divided into stationary and variable.

The stationary mode corresponds to the operation of the turbine at a certain fixed load. It can occur both at rated and at partial load. Until recently, this mode was the main one for gas turbines. The turbine stopped several times a year due to problems or scheduled repairs.

Variable modes of gas turbines are determined by the following reasons in relation to gas turbines. The first reason is the need to change the power generated by the gas turbine unit if the power consumed, for example, by an electric generator has changed due to a change in the electrical load of consumers connected to the generator. If the gas turbine unit is driven by an electric generator connected in parallel with other power producers, i.e. operating on a common network (power system), then it is necessary to change the power of this gas turbine in the event of a change in the total power consumption in the system. The second reason is a change in atmospheric conditions: pressure and especially temperature of the atmospheric air taken in by the compressor. The most complex non-stationary mode is the start-up of a gas turbine unit, which includes numerous operations before the rotor is pushed. Non-stationary modes include sudden changes in load (dumping or charging), as well as stopping the turbine (unloading, disconnecting from the network, running out the rotor to cool).

Thus, for gas turbine plants, the main management task is to ensure required power, and for power gas turbines – the constancy of the rotation frequency of the driven electric generator. Variable operating modes of gas turbine plants should be carried out in such a way that the efficiency in each mode is as high as possible. The gas turbine mode is regulated by influencing the control fuel valves that supply fuel directly to the combustion chamber, which determines the low inertia of the process of supplying heat to the working fluid in the combustion chamber. GTUs are sensitive to changes in atmospheric conditions. They are at risk of compressor surge. To start a gas turbine unit, it is necessary that surge be eliminated in all possible operating modes. To start a gas turbine unit, it is necessary to first spin up the rotor using a starting device.

Modern large gas turbine plants use automated control systems that perform the following functions:

– automatic remote control of starting, loading and stopping the gas turbine unit;

– regulation of such parameters as the rotation speed of a turbine unit with a given degree of unevenness, gas temperature in front of and behind the turbine, the active load of the electric generator, the operating mode of the compressor at the required distance from the surge boundary;

– protection of gas turbines, namely shutdown and shutdown in emergency situations, the most serious of which are such as an unacceptable increase in gas temperatures in front of and behind the gas turbine, an unacceptable increase in gas temperatures in front of and behind the gas turbine, an unacceptable increase in gas temperatures in front of the gas turbine and behind it, an unacceptable increase in the rotor frequency, an unacceptable drop in oil pressure for lubricating the bearings, an unacceptable axial shift of the rotor, extinction of the flame in the combustion chamber, approaching the compressor surge limit, an unacceptable increase in the vibration velocity of the rotor necks and bearing housings.

An event that involves a disruption in the performance of a gas turbine unit is called a failure. To maintain high reliability and reliability, equipment undergoes maintenance, current, medium or major repairs. During current and medium repairs, damaged parts and assemblies are replaced or restored, and during major repairs, full functionality is restored. During normal operation of a gas turbine, careful maintenance and regular checks of the protection and control systems are required by the watch personnel and the engineer responsible for the operation of this system. The reliability of its operation depends on a thorough inspection of the available components of the control and protection systems, comparison of the current indicators of the devices with the previous ones, the implementation of all checks and operations provided for by the instructions drawn up taking into account the requirements of turbine manufacturers, operating rules (PTE) and guidelines for checking and tests. Special attention The inspection should pay attention to potential sources of oil leaks. It is necessary to monitor the position of nuts, locking parts and other fasteners on rods and spools, since these parts operate under vibration conditions, causing them to unscrew and malfunction. It is necessary to monitor the mechanical condition of all accessible components: cam mechanisms, their shafts, bearings, springs, etc. Particular attention should be paid to vibration of the control elements, which can cause the actuator rods to break due to fatigue. It is necessary to monitor pressure changes and pulsations in the main oil lines of the control and protection systems: oil supply lines for lubrication, in impulse lines, protection lines and servomotor cavities. A change in these pressures indicates abnormalities in the control and oil supply systems: leakage of valves, piston seals and servomotor rods, clogging of adjusting washers. Spool pulsations are caused by abnormal operation of the impeller, contamination of the oil lines, solid particles between the spools and axle boxes, increased air content in the oil and other reasons.

The primary attention of maintenance personnel should be given to eliminating the possibility of turbine acceleration when the electric generator is disconnected from the network, which is ensured by sufficient density of stop and control valves and check valves on the pipelines. The check is carried out when the turbine is stopped at least once a year, and also without fail during startup after installation. For normal operation of the turbine, the oil tank must function properly, ensuring long-term preservation of the oil and separation of air, sludge and solid particles from it. The oil level in the tank should be checked once per shift. At the same time, it is necessary to monitor the serviceability of the minimum permissible level alarm and the difference in levels in the dirty and clean compartments of the oil tank. Backup and emergency oil pumps and their automatic switching devices must be regularly inspected twice a month. The quality of operation of oil coolers is checked by the difference in pressure at the inlet and outlet of oil and cooling water and by heating the cooling water and cooling the oil. The chemical laboratory of the power plant must regularly analyze the operating oil in order to carry out its regeneration and replacement in a timely manner.

When observing an operating turbine, it is necessary to pay attention primarily to the relative elongation of the rotor and its axial displacement. When installing and repairing a turbine, the rotor in the housing is installed so that under operating conditions, when these parts warm up, there are sufficiently small gaps between them that prevent interference, otherwise a serious accident may occur.

The turbine is unloaded by gradually closing the control valves (using a control mechanism). Particular attention must be paid to the relative contraction of the rotor, and if, despite all the measures taken, the contraction approaches a dangerous limit, it is necessary to stop unloading, and perhaps even increase the load. The load is usually reduced to 15-20% of the nominal load, after which the gas supply to the turbine is stopped. From this moment on, it is rotated by a generator at the frequency of the electrical network. In the short time specified in the instructions (usually a few minutes), you need to make sure that the stop and control valves on the extraction lines are closed, and the wattmeter shows negative power (power consumption from the network). After this, you can disconnect the generator from the network. After stopping the turbine rotor, it is necessary to immediately turn on the turning device to avoid its thermal deflection. It is not allowed to turn off the oil supply. During the first 8 hours, the rotor rotates continuously, and then it is periodically rotated 180°. An emergency shutdown of the turbine unit is carried out by immediately stopping the supply of the working fluid.

A stopped turbine requires careful maintenance. The greatest danger during downtime for the turbine and some other elements of the turbine installation is static corrosion, the main cause of which is the simultaneous presence of moisture and air. To prevent this from happening, it is necessary to open the valves that allow the parts to communicate with the atmosphere. When the turbine stops, it is taken into long-term reserve additional measures. It is disconnected from all pipelines by plugs. The turbine shaft is additionally sealed with a cord, oil is pumped through the bearings at least once a week to create a protective layer of oil on the bearing journals, and the rotor is turned by a turning device several revolutions. The most effective way to combat standstill corrosion is to preserve the turbine.

The gas turbine unit is assembled at a turbine plant after individual parts and assemblies have been manufactured in its workshops. Unlike a steam turbine, after assembly at the factory, the gas turbine does not undergo testing. As a result, several separately transported units leave the turbine plant for the TPP installation site: a turbine group (compressor and turbine), two combustion chambers, an oil tank with equipment installed on it, a compressor inlet pipe, and an outlet diffuser. All parts are closed with plugs. Unlike a steam turbine, a gas turbine unit is placed at a thermal power plant not on a frame foundation, but directly on concrete base, installed at the zero level of the turbine hall. The compressor inlet shaft is connected via an air box to the KVOU, where thorough air filtration occurs, eliminating wear of the compressor flow path, clogging of the cooling channels in the working blades and other troubles. KVOU is placed on the roof of the building, saving building space. The rotor of the electric generator is connected to the output end of the compressor shaft, and a transition diffuser is connected to the output diffuser of the gas turbine unit, directing gases to the waste heat boiler.

The gas turbine engine is a universal engine that has various purposes. They are most widespread in aviation and long-distance gas supply. In stationary power engineering, thermal power plants use gas turbine units for various purposes. GTUs for peak purposes operate during periods of maximum electrical energy consumption. Reserve gas turbine units provide the own needs of thermal power plants during the period when the main equipment is not in operation. Industries where the use of gas turbines creates great advantages include blast furnace production, where the gas turbine, being the drive of the blower that supplies air to the blast furnace, uses blast furnace gas, which is a by-product, as a working fluid blast furnace. In railway transport, gas turbine locomotives (gas turbine locomotives) have received some use on long lines. A number of gas turbine units are used in the merchant and navy fleets, mainly on light and high-speed patrol vessels, where special meaning It has a compact and light engine weight. A gas turbine car is currently in the research stage of experimental samples. The best experimental engines have reached the level of efficiency of modern gasoline car engines with less weight.

A gas turbine unit (GTU) consists of two main parts - a power turbine and a generator, which are housed in one housing. Gas flow high temperature acts on the blades of the power turbine (creates torque). Heat recovery through a heat exchanger or waste heat boiler increases the overall efficiency of the installation.

The gas turbine unit can operate on both liquid and gaseous fuels. In normal operating mode it runs on gas, and in reserve (emergency) mode it automatically switches to diesel fuel. The optimal operating mode of a gas turbine unit is the combined generation of thermal and electrical energy. The gas turbine unit can operate both in basic mode and to cover peak loads.

A simple gas turbine installation for continuous combustion and the design of its main elements

A schematic diagram of a simple gas turbine plant is shown in Figure 1.

Figure 1. Schematic diagram of a gas turbine unit: 1 - compressor; 2 - combustion chamber; 3 - gas turbine; 4 – electric generator

Compressor 1 sucks air from the atmosphere, compresses it to a certain pressure and supplies it to combustion chamber 2. Liquid or gaseous fuel. Fuel combustion in this scheme occurs continuously, at a constant pressure, therefore such gas turbine plants are called gas turbine units of continuous combustion or gas turbine plants with combustion at constant pressure.

Hot gases formed in the combustion chamber as a result of fuel combustion enter turbine 3. In the turbine, the gas expands and its internal energy is converted into mechanical work. Exhaust gases exit the turbine into the environment (atmosphere).

Part of the power developed by a gas turbine is spent on rotating the compressor, and the remaining part (net power) is given to the consumer. The power consumed by the compressor is relatively high and simple circuits at moderate temperature working environment can be 2-3 times the useful power of a gas turbine unit. This means that the total power of the gas turbine itself will long be significantly greater than the useful power of the gas turbine unit.

Since a gas turbine can only operate in the presence of compressed air, obtained only from a compressor driven by the turbine, it is obvious that the gas turbine must be started from an external energy source (starting motor), with the help of which the compressor rotates until it leaves the chamber. combustion will not begin to supply gas of certain parameters and in quantities sufficient to start the operation of the gas turbine.

From the above description it is clear that a gas turbine installation consists of three main elements: a gas turbine, a compressor and a combustion chamber. Let's consider the principle of operation and structure of these elements.

Turbine. Figure 2 shows a diagram of a simple single-stage turbine. Its main parts are; housing (cylinder) of the turbine 1, in which guide vanes 2 and working blades 3 are mounted, mounted along the entire circumference on the rim of a disk 4 mounted on a shaft 5. The turbine shaft rotates in bearings 6. End seals 7 are installed where the shaft exits the housing , limiting the leakage of hot gases from the turbine housing. All rotating parts, turbines (blades, disk, shaft) make up its rotor. The housing with fixed guide vanes and seals forms the turbine stator. The disk with blades forms the impeller.

Figure 2. Diagram of a single-stage turbine

The combination of a number of guide and rotor blades is called a turbine stage. Figure 3 above shows a diagram of such a turbine stage and below shows a cross-section of the guide and working blades of a cylindrical surfaces a-a, then expanded onto the drawing plane.

Figure 3. Turbine stage diagram

The guide vanes 1 form tapering channels in cross-section, called nozzles. The channels formed by the working blades 2 also usually have a tapering shape.

Hot gas at high blood pressure enters the turbine nozzles, where it expands and a corresponding increase in speed occurs. At the same time, the pressure and temperature of the gas drop. Thus, the potential energy of the gas is converted into kinetic energy in the turbine nozzles. After leaving the nozzles, the gas enters the interblade channels of the working blades, where it changes its direction. When gas flows around the rotor blades, the pressure on their concave surface turns out to be greater than on the convex surface, and under the influence of this pressure difference the impeller rotates (the direction of rotation in Figure 3 is shown by arrow u). Thus, part of the kinetic energy of the gas is converted into mechanical energy on the working blades, which is unacceptable for reasons of strength of the working blades or turbine disk. In such cases, the turbines are multistage. The diagram of a multistage turbine is shown in Figure 4.

Figure 4. Diagram of a multi-stage turbine: 1-bearings; 2-end seals; 3-inlet pipe; 4-body; 5-guide vanes; 6-working blades; 7-rotor; 8-outlet turbine pipe

The turbine consists of a number of individual stages arranged in series, in which the gas gradually expands. The pressure drop per each stage, and, consequently, the speed c1 in each stage of such a turbine, is less than in a single-stage turbine. The number of stages can be chosen such that at a given peripheral speed the desired ratio is obtained

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Compressor. The diagram of a multi-stage axial compressor is shown in Figure 5.

Figure 5. Diagram of a multi-stage axial compressor: 1-inlet pipe; 2-end seals; 3-bearings; 4-input guide vane; 5-working blades; 6-guide vanes; 7-body 8-straightening apparatus; 9-diffuser; 10-outlet pipe; 11-rotor.

Its main components are: rotor 2 with working blades 5 attached to it, housing 7 (cylinder), to which guide vanes 6 and end seals 2, and bearings 3 are attached. The combination of one row of rotating working blades and one row of fixed guide blades located behind them is called compressor stage. The air sucked in by the compressor sequentially passes through the following elements of the compressor, shown in Figure 5: inlet pipe 1, inlet guide vane 4, group of stages 5, 6, straightener 8, diffuser 9 and outlet pipe 10.

Let's consider the purpose of these elements. The inlet pipe is designed to uniformly supply air from the atmosphere to the inlet guide vane, which must give the required direction to the flow before entering the first stage. In the steps, the air is compressed due to transmission mechanical energy air flow from the rotating blades. From the last stage, the air enters the straightening apparatus, which is designed to give the flow an axial direction before entering the diffuser. The compression of the gas continues in the diffuser due to a decrease in its kinetic energy. The outlet pipe is designed to supply air from the diffuser to the bypass pipeline. The blades of compressor 1 (Figure 6) form a series of expanding channels (diffusers). When the rotor rotates, air enters the interblade channels at a high relative speed (the speed of air movement observed from the moving blades). As air moves through these channels, its pressure increases as a result of a decrease in relative speed. In the expanding channels formed by fixed guide vanes 2, further increase air pressure, accompanied by a corresponding decrease in its kinetic energy. Thus, energy conversion in the compressor stage occurs in the opposite direction compared to the turbine stage.

Figure 6. Axial compressor stage diagram

Combustion chamber

The purpose of the combustion chamber is to increase the temperature of the working fluid due to the combustion of fuel in a compressed air environment. The combustion chamber diagram is shown in Figure 7.

Figure 7. Combustion chamber

The combustion of fuel injected through nozzle 1 occurs in the combustion zone of the chamber, limited by flame tube 2. Only the amount of air that is necessary for complete and intensive combustion of the fuel enters this zone (this air is called primary air).

The air entering the combustion zone passes through the swirler 3, which promotes good mixing of fuel with air. In the combustion zone, the gas temperature reaches 1300... 2000°C. According to the strength conditions of gas turbine blades, such a temperature is unacceptable. Therefore, the hot gases produced in the combustion zone of the chamber are diluted with cold air, which is called secondary. Secondary air flows through the annular space between the flame tube 2 and the housing 4. Part of this air enters the combustion products through the windows 5, and the rest is mixed with the hot eyes after the flame tube. Thus, the compressor must supply several times more air to the combustion chamber than is necessary to burn the fuel, and the combustion products entering the turbine are highly diluted with air and cooled.