What does it mean to approve the efficiency of a gas turbine 40. The operating principle of gas turbine units (GTU)

A traditional 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.

It is necessary to emphasize one important difference between GTU and PTU. The PTU does not include a boiler; more precisely, the boiler is considered as a separate heat source; with this consideration, the boiler is a “black box”: feed water enters it with a temperature of $t_(p.v)$, and steam exits with the parameters $р_0$, $t_0$. A steam turbine plant cannot operate without a boiler as a physical object. In a gas turbine unit, the combustion chamber is its integral element. In this sense, the GTU is self-sufficient.

Gas turbine plants are extremely diverse, perhaps even more diverse than steam turbine plants. Below we will consider the most promising and most used simple cycle gas turbine plants in the energy sector.

Schematic diagram such a gas turbine unit is shown in the figure. Air from the atmosphere enters the inlet of an air compressor, which is a rotary turbomachine with a flow path consisting of rotating and stationary gratings. Pressure ratio downstream of compressor p b to the pressure in front of him p a is called the compression ratio of an air compressor and is usually denoted as pk (pk = p b/p a). The compressor rotor is driven by a gas turbine. A stream of compressed air is supplied to one, two or more combustion chambers. 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. When fuel is burned, high-temperature fuel combustion products are formed. Relatively cold air from the second stream is mixed with them in order to obtain gases (usually called working gases) with a temperature acceptable for the gas turbine parts.

Working gases with pressure r s (r s < p b due to the hydraulic resistance of the combustion chamber) are fed into the flow part of a gas turbine, the principle of operation of which is no different from the principle of operation of a steam turbine (the only difference is that the gas turbine operates on fuel combustion products, and not on steam). In a gas turbine, the working gases expand to almost atmospheric pressure p d, enter the output diffuser 14, and from it - either directly into chimney, or previously into some heat exchanger that uses the heat of the exhaust gases of the gas turbine plant.

Due to the expansion of gases in a gas turbine, the latter produces power. A very significant part of it (about half) is spent on driving the compressor, and the remaining part on driving the electric generator. This is the useful power of the gas turbine unit, which is indicated when it is labeled.

To depict gas turbine circuits, use symbols, similar to those used for vocational schools.

A gas turbine cannot be simpler, since it contains a minimum of necessary components that ensure sequential processes of compression, heating and expansion of the working fluid: one compressor, one or more combustion chambers operating under the same conditions, and one gas turbine. Along with simple cycle gas turbine plants, there are complex cycle gas turbine plants, which can contain several compressors, turbines and combustion chambers. In particular, gas turbines of this type include the GT-100-750, built in the USSR in the 70s.

It is made of two shafts. The high pressure compressor is located on one shaft KVD and the high-pressure turbine driving it theater of operations; this shaft has a variable rotation speed. The low pressure turbine is located on the second shaft TND, driving the low pressure compressor KND and electric generator EG; therefore this shaft has a constant rotation speed of 50 s -1. Air in an amount of 447 kg/s comes from the atmosphere into KND and is compressed in it to a pressure of approximately 430 kPa (4.3 at) and then fed into the air cooler IN, where it is cooled with water from 176 to 35 °C. This reduces the work required to compress air in a high-pressure compressor KVD(compression ratio p k = 6.3). From it, air enters the high-pressure combustion chamber KSWD and combustion products with a temperature of 750 °C are sent to theater of operations. From theater of operations gases containing significant amounts of oxygen enter the low-pressure combustion chamber KSND, in which additional fuel is burned, and from it into TND. Exhaust gases at a temperature of 390 °C exit either into the chimney or into a heat exchanger to use the heat of the flue gases.

Gas turbines are not very economical due to the high temperature of the exhaust gases. Increasing the complexity of the scheme makes it possible to increase its efficiency, but at the same time requires increased capital investment and complicates operation.

The figure shows the device of the Siemens V94.3 gas turbine unit. Atmospheric air from an integrated air purification device (ACP) enters the mine 4 , and from it - to the flow part 16 air compressor. The compressor compresses air. The compression ratio in typical compressors is pc = 13-17, and thus the pressure in the gas turbine unit does not exceed 1.3-1.7 MPa (13-17 at). This is another serious difference between a gas turbine and a steam turbine, in which the steam pressure is 10-15 times greater than the gas pressure in the gas turbine. Low pressure working environment determines the small thickness of the walls of the housings and the ease of heating them. This is what makes the gas turbine very maneuverable, i.e. capable of rapid starts and stops. If it takes from 1 hour to several hours to start a steam turbine, depending on its initial temperature state, then a gas turbine unit can be put into operation in 10-15 minutes.

When compressed in a compressor, the air heats up. This heating can be estimated using a simple approximate relationship:

$$T_a/T_b = \pi_к^(0.25)$$

in which T b And T a- absolute air temperatures behind and in front of the compressor. If, for example, T a= 300 K, i.e. ambient air temperature is 27 °C, and p k = 16, then T b= 600 K and, therefore, the air is heated by

$$\Delta t = (600-273)-(300-273) = 300°C.$$

Thus, behind the compressor the air temperature is 300-350 °C. The air between the walls of the flame pipe and the combustion chamber body moves to the burner device, to which fuel gas is supplied. Since the fuel must enter the combustion chamber, where the pressure is 1.3-1.7 MPa, the gas pressure must be high. To be able to regulate its flow into the combustion chamber, gas pressure is required approximately twice as high as the pressure in the chamber. If there is such pressure in the supply gas pipeline, then gas is supplied to the combustion chamber directly from the gas distribution point (GDP). If the gas pressure is insufficient, then a booster gas compressor is installed between the hydraulic fracturing unit and the chamber.

Fuel gas consumption is only approximately 1-1.5% of the air consumption coming from the compressor, so creating a highly economical gas booster compressor presents certain technical difficulties.

Inside the flame pipe 10 high temperature combustion products are formed. After mixing secondary air at the exit from the combustion chamber, it decreases somewhat, but nevertheless reaches 1350-1400 °C in typical modern gas turbines.

From the combustion chamber, hot gases enter the flow part 7 gas turbine. In it, gases expand to almost atmospheric pressure, since the space behind the gas turbine communicates either with a chimney or with a heat exchanger, the hydraulic resistance of which is low.

When gases expand in a gas turbine, power is created on its shaft. This power is partially consumed to drive the air compressor, and its excess is used to drive the rotor 1 electric generator. One of characteristic features The gas turbine system consists of the fact that the compressor requires approximately half the power developed by the gas turbine. For example, in a gas turbine unit with a capacity of 180 MW being created in Russia (this is the useful power), the compressor power is 196 MW. This is one of fundamental differences GTU from PTU: in the latter, the power used to compress the feed water even to a pressure of 23.5 MPa (240 atm) is only a few percent of the power of the steam turbine. This is due to the fact that water is a poorly compressible liquid, and air requires a lot of energy to compress.

In a first, rather rough approximation, the temperature of the gases behind the turbine can be estimated using a simple relationship similar to:

$$T_c/T_d = \pi_к^(0.25).$$

Therefore, if $\pi_к = 16$, and the temperature in front of the turbine T s= 1400 °C = 1673 K, then the temperature behind it is approximately K:

$$T_d=T_c/\pi_к^(0.25) = 1673/16^(0.25) = 836.$$

Thus, the temperature of the gases behind the gas turbine plant is quite high, and a significant amount of heat obtained from fuel combustion literally goes into the chimney. Therefore, when a gas turbine operates autonomously, its efficiency is low: for typical gas turbines it is 35-36%, i.e. significantly less than the efficiency of the PTU. The matter, however, changes radically when a heat exchanger (network heater or waste heat boiler for a combined cycle) is installed on the “tail” of the gas turbine unit.

A diffuser is installed behind the gas turbine - a smoothly expanding channel, during which the high-speed pressure of gases is partially converted into pressure. This makes it possible to have a pressure behind the gas turbine that is less than atmospheric, which increases the efficiency of 1 kg of gases in the turbine and, therefore, increases its power.

Air compressor device. As already indicated, an air compressor is a turbomachine to the shaft of which power is supplied from a gas turbine; this power is transferred to the air flowing through the compressor flow path, as a result of which the air pressure increases up to the pressure in the combustion chamber.

The figure shows a gas turbine rotor placed in support bearings; The compressor rotor and stator elements are clearly visible in the foreground.

From the mine 4 air enters the channels formed by the rotating blades 2 non-rotating input guide vane (VNA). The main task of the VNA is to impart rotational motion to the flow moving in the axial (or radial-axial) direction. The VNA channels are not fundamentally different from the nozzle channels of a steam turbine: they are confuser (tapered), and the flow in them accelerates, simultaneously acquiring a circumferential velocity component.

In modern gas turbines, the input guide vane is rotary. The need for a rotary VNA is caused by the desire to prevent a decrease in efficiency when the load on the gas turbine plant decreases. The point is that the shafts of the compressor and electric generator have the same rotation frequency, equal to the network frequency. Therefore, if you do not use VNA, then the amount of air supplied by the compressor to the combustion chamber is constant and does not depend on the turbine load. And the power of a gas turbine can only be changed by changing the fuel flow into the combustion chamber. Therefore, with a decrease in fuel consumption and a constant amount of air supplied by the compressor, the temperature of the working gases decreases both in front of the gas turbine and behind it. This leads to a very significant decrease in the efficiency of the gas turbine unit. Rotation of the blades when the load around the axis is reduced 1 by 25 - 30° allows you to narrow the flow sections of the VNA channels and reduce the air flow into the combustion chamber, maintaining a constant ratio between air and fuel flow. Installing an inlet guide vane makes it possible to maintain the temperature of the gases in front of and behind the gas turbine constant in the power range of approximately 100-80%.

The figure shows the drive of the VNA blades. A rotating lever is attached to the axes of each blade 2 which through the lever 4 connected to the turning ring 1 . If it is necessary to change the air flow, the ring 1 rotates using rods and an electric motor with a gearbox; in this case all levers turn simultaneously 2 and accordingly the VNA blades 5 .

The air swirled with the help of a VHA enters the 1st stage of the air compressor, which consists of two gratings: rotating and stationary. Both grilles, unlike turbine grilles, have expanding (diffuser) channels, i.e. area for air passage at the inlet F 1 less than F 2 on output.

When air moves in such a channel, its speed decreases ( w 2 < w 1), and the pressure increases ( R 2 > R 1). Unfortunately, making a diffuser grille economical, i.e. so that the flow rate w 1 would be converted to the maximum extent into pressure, and not into heat, only possible with a small degree of compression R 2 /R 1 (usually 1.2 - 1.3), which leads to a large number of compressor stages (14 - 16 with a compressor compression ratio p k = 13 - 16).

The figure shows the air flow in the compressor stage. Air comes out of the inlet (fixed) rotary nozzle apparatus at a speed c 1 (see the upper triangle of speeds), having the necessary circumferential twist (a 1< 90°). Если расположенная за ВНА вращающаяся (рабочая) решетка имеет скорость u 1, then the relative speed of entry into it w 1 will be equal to the vector difference c 1 and u 1, and this difference will be greater than c 1 i.e. w 1 > c 1 . When moving in the channel, the air speed decreases to the value w 2, and it comes out at an angle b2, determined by the inclination of the profiles. However, due to rotation and the supply of energy to the air from the rotor blades, its speed With 2 in absolute motion will be greater than c 1 . The blades of the fixed grille are installed so that the air entry into the channel is shock-free. Since the channels of this lattice are expanding, the speed in it decreases to the value c"1, and the pressure increases from R 1 to R 2. The grid is designed so that c" 1 = c 1, a a " 1 = a 1. Therefore, in the second stage and subsequent stages, the compression process will proceed in a similar way. At the same time, the height of their gratings will decrease in accordance with the increased air density due to compression.

Sometimes the guide vanes of the first few stages of the compressor are rotatable in the same way as the VNA blades. This makes it possible to expand the power range of the gas turbine unit, at which the temperature of the gases in front of and behind the gas turbine remains unchanged. Accordingly, efficiency increases. The use of several rotary guide vanes allows you to work economically in the range of 100 - 50% power.

The last stage of the compressor is designed in the same way as the previous ones, with the only difference being that the task of the last guide vane is 1 is not only to increase the pressure, but also to ensure an axial outlet of the air flow. Air enters the annular outlet diffuser 23 , where the pressure rises to its maximum value. With this pressure, air enters the combustion zone 9 .

Air is taken from the air compressor housing to cool the gas turbine elements. For this purpose, annular chambers are made in its body, communicating with the space behind the corresponding step. Air is removed from the chambers using pipelines.

In addition, the compressor has so-called anti-surge valves and bypass pipes 6 , bypassing air from the intermediate stages of the compressor into the outlet diffuser of the gas turbine when it starts and stops. This eliminates unstable operation of the compressor at low air flow rates (this phenomenon is called surging), which is expressed in intense vibration of the entire machine.

The creation of highly efficient air compressors is an extremely complex task, which, unlike turbines, cannot be solved only by calculation and design. Since the compressor power is approximately equal to the power of the gas turbine unit, a deterioration in the efficiency of the compressor by 1% leads to a decrease in the efficiency of the entire gas turbine unit by 2-2.5%. Therefore, creating a good compressor is one of the key issues creation of GTU. Typically, compressors are created by simulation (scaling), using a model compressor created through lengthy experimental development.

The combustion chambers of gas turbine plants are very diverse. Shown above is a gas turbine unit with two remote chambers. The figure shows a 140 MW type 13E gas turbine unit from ABB with one remote combustion chamber, the design of which is similar to that of the chamber shown in the figure. The air from the compressor from the ring diffuser enters the space between the chamber body and the flame tube and is then used for gas combustion and for cooling the flame tube.

The main disadvantage of remote combustion chambers is their large dimensions, which are clearly visible from the figure. A gas turbine is located to the right of the chamber, and a compressor is located to the left. At the top of the housing you can see three holes for placing anti-surge valves and then the VNA drive. Modern gas turbine plants mainly use built-in combustion chambers: annular and tubular-ring.

The figure shows an integrated annular combustion chamber. The annular combustion space is formed by the inner 17 and outdoor 11 flame pipes. The inside of the pipes is lined with special inserts 13 And 16 having a thermal barrier coating on the side facing the flame; on the opposite side, the inserts have fins that improve their cooling by air entering through the annular gaps between the inserts inside the flame tube. Thus, a flame tube temperature of 750-800 °C is achieved in the combustion zone. The front micro-flare burner device of the chamber consists of several hundred burners 10 , to which gas is supplied from four collectors 5 -8 . By turning off the collectors one by one, you can change the power of the gas turbine unit.

The burner structure is shown in the figure. Gas enters from the manifold through drilling in the rod 3 to the inner cavity of the blades 6 swirler. The latter is a hollow radial straight blades that force the air coming from the combustion chamber to twist and rotate around the axis of the rod. This rotating air vortex receives natural gas from the internal cavity of the swirler blades 6 through small holes 7 . In this case, a homogeneous fuel-air mixture is formed, emerging in the form of a swirling jet from the zone 5 . An annular rotating vortex ensures stable gas combustion.

The figure shows the tubular-ring combustion chamber of GTE-180. Into the annular space 24 between the outlet of the air compressor and the inlet of the gas turbine using perforated cones 3 place 12 flame tubes 10 . The flame tube contains numerous holes with a diameter of 1 mm, located in annular rows with a distance of 6 mm between them; the distance between rows of holes is 23 mm. “Cold” air enters from the outside through these holes, providing convective film cooling and a flame tube temperature of no higher than 850 °C. On inner surface The flame pipe is coated with a thermal barrier coating 0.4 mm thick.

On the front plate 8 flame tube, a burner device is installed, consisting of a central pilot burner 6 igniting fuel at start-up using a spark plug 5 , and five main modules, one of which is shown in the figure. The module allows you to burn gas and diesel fuel. Gas through the fitting 1 after the filter 6 enters the annular fuel gas manifold 5 , and from it into cavities containing small holes (diameter 0.7 mm, pitch 8 mm). Through these holes, gas enters the annular space. Six tangential grooves are made in the walls of the module 9 , through which the main amount of air supplied for combustion from the air compressor enters. In the tangential grooves, the air swirls and, thus, inside the cavity 8 a rotating vortex is formed, moving towards the exit of the burner device. To the periphery of the vortex through the holes 3 gas enters, mixes with air, and the resulting homogeneous mixture leaves the burner, where it ignites and burns. Combustion products enter the nozzle apparatus of the 1st stage of the gas turbine.

The gas turbine is the most complex element of a gas turbine unit, which is primarily due to the very high temperature working gases flowing through its flow part: the gas temperature in front of the turbine of 1350 °C is currently considered “standard”, and leading companies, primarily General Electric, are working to master the initial temperature of 1500 °C. Let us recall that the “standard” initial temperature for steam turbines is 540 °C, and in the future - a temperature of 600-620 °C.

The desire to increase the initial temperature is associated, first of all, with the gain in efficiency that it gives. This is clearly seen from the figure summarizing the achieved level of gas turbine construction: increasing the initial temperature from 1100 to 1450 °C results in an increase in absolute efficiency from 32 to 40%, i.e. leads to fuel savings of 25%. Of course, part of this saving is associated not only with an increase in temperature, but also with the improvement of other elements of the gas turbine plant, and the determining factor is still the initial temperature.

To ensure long-term operation of a gas turbine, a combination of two means is used. The first remedy is the use of heat-resistant materials for the most loaded parts that can resist high mechanical loads and temperatures (primarily for nozzles and working blades). If steels (i.e., iron-based alloys) with a chromium content of 12-13% are used for steam turbine blades and some other elements, then nickel-based alloys (nimonics) are used for gas turbine blades, which are capable of bearing actual mechanical loads. and the required service life to withstand temperatures of 800-850 °C. Therefore, together with the first, a second means is used - cooling the hottest parts.

To cool most modern gas turbines, air is taken from various stages of the air compressor. Gas turbines are already operating in which water vapor is used for cooling, which is a better cooling agent than air. The cooling air, after heating in the cooled part, is discharged into the flow path of the gas turbine. This cooling system is called open. There are closed cooling systems in which the coolant heated in the part is sent to a refrigerator and then returned again to cool the part. Such a system is not only very complex, but also requires the recovery of heat collected in the refrigerator.

The cooling system of a gas turbine is the most complex system in a gas turbine plant, which determines its service life. It provides not only the maintenance permissible level working and nozzle blades, but also housing elements, disks carrying working blades, locking bearing seals where oil circulates, etc. This system is extremely branched and is organized so that each cooled element receives cooling air of the parameters and in the quantity necessary to maintain its optimal temperature. Excessive cooling of parts is just as harmful as insufficient cooling, since it leads to increased costs of cooling air, the compression of which in the compressor requires turbine power. In addition, increased air flow rates for cooling lead to a decrease in the temperature of gases behind the turbine, which very significantly affects the operation of equipment installed behind the gas turbine unit (for example, a steam turbine unit operating as part of a steam turbine unit). Finally, the cooling system must provide not only required level temperatures of parts, but also the uniformity of their heating, eliminating the occurrence of dangerous temperature stresses, the cyclic action of which leads to the appearance of cracks.

The figure shows an example of the cooling circuit of a typical gas turbine. The values ​​of gas temperatures are shown in rectangular frames. In front of the 1st stage nozzle apparatus 1 it reaches 1350 °C. Behind him, i.e. in front of the 1st stage working grid it is 1130 °C. Even before the working blade of the last stage it is at the level of 600 °C. Gases of this temperature wash the nozzle and working blades, and if they were not cooled, their temperature would be equal to the temperature of the gases and their service life would be limited to several hours.

To cool the elements of a gas turbine, air is used, taken from the compressor at that stage where its pressure is slightly higher than the pressure of the working gases in the zone of the gas turbine into which air is supplied. For example, to cool the nozzle blades of the 1st stage, cooling air in the amount of 4.5% of the air flow at the compressor inlet is taken from the compressor outlet diffuser, and to cool the nozzle blades of the last stage and the adjacent section of the housing - from the 5th stage of the compressor. Sometimes, to cool the hottest elements of a gas turbine, air taken from the compressor outlet diffuser is first sent to an air cooler, where it is cooled (usually with water) to 180-200 ° C and then sent for cooling. In this case, less air is required for cooling, but at the same time costs arise for the air cooler, the gas turbine becomes more complicated, and part of the heat removed by the cooling water is lost.

A gas turbine usually has 3-4 stages, i.e. There are 6-8 rows of gratings, and most often the blades of all rows are cooled, except for the working blades of the last stage. Air for cooling the nozzle blades is brought in through their ends and discharged through numerous (600-700 holes with a diameter of 0.5-0.6 mm) openings located in the corresponding zones of the profile. Cooling air is supplied to the rotor blades through holes made in the ends of the shanks.

In order to understand how cooled blades are designed, it is necessary to at least in general consider the technology of their manufacture. Due to the exceptional difficulty machining For the production of nickel alloys, precision investment casting is mainly used to produce blades. To implement it, first, casting rods are made from ceramic-based materials using a special molding and heat treatment technology. The casting core is an exact copy of the cavity inside the future blade, into which cooling air will flow and flow in the required direction. The casting core is placed in a mold, the internal cavity of which completely corresponds to the blade that needs to be obtained. The resulting free space between the rod and the wall of the mold is filled with a heated low-melting mass (for example, plastic), which hardens. The rod together with the solidifying mass enveloping it, repeating external form blades, is a lost wax model. It is placed in a casting mold, to which the nimonic melt is fed. The latter melts the plastic, takes its place and as a result a cast blade appears with an internal cavity filled with a rod. The rod is removed by etching with special chemical solutions. The resulting nozzle blades require virtually no additional mechanical processing (except for the manufacture of numerous holes for the exit of cooling air). Cast working blades require processing of the shank using a special abrasive tool.

The technology briefly described is borrowed from aviation technology, where the temperatures achieved are much higher than in stationary steam turbines. The difficulty in mastering these technologies is associated with the much larger sizes of blades for stationary gas turbine plants, which grow in proportion to the gas flow rate, i.e. GTU power.

The use of so-called monocrystalline blades, which are made from a single crystal, seems very promising. This is due to the fact that the presence of grain boundaries during prolonged exposure to high temperatures leads to a deterioration in the properties of the metal.

The gas turbine rotor is a unique prefabricated structure. Before assembly, individual discs 5 compressor and disk 7 gas turbine are bladed and balanced, end parts are manufactured 1 And 8 , spacer part 11 and central tie bolt 6 . Each of the disks has two annular collars on which hirths are made (named after the inventor - Hirth), - strictly radial teeth of a triangular profile. Adjacent pieces have exactly the same collars with exactly the same hilts. At good quality The manufacture of the Hirth connection ensures absolute alignment of adjacent disks (this ensures the radius of the Hirths) and repeatable assembly after disassembling the rotor.

The rotor is assembled on a special stand, which is an elevator with a ring platform for installation personnel, inside which the assembly is carried out. First, the end part of the rotor is assembled on the thread 1 and tie rod 6 . The rod is placed vertically inside the ring platform and the disk of the 1st stage of the compressor is lowered onto it using a crane. Centering of the disk and the end part is carried out by hirths. Moving upward on a special elevator, the installation staff disc by disc [first the compressor, then the spacer part, and then the turbine and the right end part 8 ] assembles the entire rotor. A nut is screwed onto the right end 9 , and a hydraulic device is installed on the remaining part of the threaded part of the tie rod, squeezing the disks and pulling out the tie rod. After drawing out the rod, the nut 9 screwed in until it stops and the hydraulic device is removed. The stretched rod reliably pulls the disks together and turns the rotor into a single rigid structure. The assembled rotor is removed from the assembly stand, and it is ready for installation in the gas turbine unit.

The main advantage of the gas turbine is its compactness. Indeed, first of all, the gas turbine plant does not have a steam boiler, a structure that reaches a great height and requires a separate room for installation. This circumstance is connected primarily with high pressure in the combustion chamber (1.2-2 MPa); in the boiler, combustion occurs at atmospheric pressure and, accordingly, the volume of hot gases formed is 12-20 times greater. Further, in a gas turbine unit, the process of gas expansion occurs in a gas turbine consisting of only 3-5 stages, while a steam turbine having the same power consists of 3-4 cylinders containing 25-30 stages. Even taking into account both the combustion chamber and the air compressor, a gas turbine unit with a power of 150 MW has a length of 8-12 m, and the length of a steam turbine of the same power with a three-cylinder design is 1.5 times longer. At the same time, for a steam turbine, in addition to the boiler, it is necessary to provide for the installation of a condenser with circulation and condensate pumps, a regeneration system of 7-9 heaters, feed turbopumps (from one to three), and a deaerator. As a result, the gas turbine unit can be installed on a concrete base at the zero level of the turbine room, and the steam turbine unit requires a frame foundation with a height of 9-16 m with the placement of the steam turbine on the upper foundation slab and auxiliary equipment in the condensing room.

The compactness of the gas turbine allows it to be assembled at a turbine plant and delivered to the turbine room by rail or road for installation on a simple foundation. Thus, in particular, gas turbine units with built-in combustion chambers are transported. When transporting gas turbine units with remote chambers, the latter are transported separately, but are easily and quickly connected to the compressor - gas turbine module using flanges. A steam turbine is supplied with numerous units and parts; installation of both itself and numerous auxiliary equipment and connections between them takes several times longer than a gas turbine unit.

The gas turbine unit does not require cooling water. As a result, the gas turbine unit does not have a condenser and a technical water supply system with pumping unit and cooling tower (with recycling water supply). As a result, all this leads to the fact that the cost of 1 kW of installed capacity of a gas turbine power plant is significantly less. At the same time, the cost of the gas turbine unit itself (compressor + combustion chamber + gas turbine), due to its complexity, turns out to be 3-4 times more than the cost of a steam turbine of the same power.

An important advantage of a gas turbine is its high maneuverability, determined by a low pressure level (compared to the pressure in a steam turbine) and, therefore, easy heating and cooling without the occurrence of dangerous temperature stresses and deformations.

However, gas turbine plants also have significant disadvantages, of which, first of all, it is necessary to note their lower efficiency than that of a steam power plant. The average efficiency of fairly good gas turbine units is 37-38%, and that of steam turbine power units is 42-43%. The ceiling for powerful power gas turbines, as it is currently seen, is an efficiency of 41-42% (and maybe higher, taking into account the large reserves for increasing the initial temperature). The lower efficiency of gas turbines is associated with the high temperature of the exhaust gases.

Another disadvantage of gas turbine plants is the impossibility of using low-grade fuels in them, at least at the present time. It can only work well on gas or good liquid fuel, such as diesel. Steam power units can operate on any fuel, including the lowest quality.

The low initial cost of thermal power plants with gas turbines and at the same time the relatively low efficiency and high cost of the fuel used and maneuverability determine the main area of ​​​​individual use of gas turbines: in power systems they should be used as peak or reserve power sources operating several hours a day.

At the same time, the situation changes radically when the heat from the exhaust gases of gas turbine plants is used in heating plants or in a combined (steam-gas) cycle.

A turbine is an engine in which the potential energy of a compressible fluid is converted into kinetic energy in the blade apparatus, and the latter in the impellers is converted into mechanical work transmitted to a continuously rotating shaft.

By design, steam turbines are a heat engine that is constantly in operation. During operation, superheated or saturated water steam, which enters the flow part, and, due to its expansion, forces the rotor to rotate. Rotation occurs as a result of the action of steam flow on the blade apparatus.

The steam turbine is part of a steam turbine structure, which is designed to generate energy. There are also installations that, in addition to electricity, are capable of generating thermal energy - steam that passes through the steam blades is supplied to network water heaters. This type of turbine is called the industrial heating or district heating type of turbine. In the first case, steam extraction in the turbine is provided for industrial purposes. Complete with a generator, the steam turbine is a turbine unit.

Types of steam turbines

Turbines are divided, depending on the direction in which the steam moves, into radial and axial turbines. The steam flow in radial turbines is directed perpendicular to the axis. Steam turbines can be single-, double- and triple-casing. The steam turbine is equipped with a variety of technical devices that prevent ambient air from entering the housing. These are various seals to which small amounts of water vapor are supplied.

A safety regulator is located on the front section of the shaft, designed to shut off the steam supply when the turbine rotation speed increases.

Characteristics of the main parameters of nominal values

· Turbine rated power- the maximum power that the turbine must develop for a long time at the terminals of the electric generator, at normal values ​​of the main parameters or when they change within the limits specified by industry and state standards. A turbine with controlled steam extraction can develop power above its rated value if this meets the strength conditions of its parts.

· Economic turbine power- power at which the turbine operates most efficiently. Depending on the parameters of the fresh steam and the purpose of the turbine, the rated power can be equal to or more than the economic power by 10-25%.

· Nominal temperature of regenerative feedwater heating- temperature of the feed water behind the last heater along the water flow.

· Nominal cooling water temperature- temperature of cooling water at the entrance to the condenser.

Gas turbine(French turbine from Latin turbo vortex, rotation) is a continuous heat engine, in the blade apparatus of which the energy of compressed and heated gas is converted into mechanical work on the shaft. It consists of a rotor (working blades mounted on disks) and a stator (guide vanes fixed in the housing).

Gas, which has a high temperature and pressure, enters through the turbine nozzle into the low-pressure area behind the nozzle, simultaneously expanding and accelerating. Next, the gas flow hits the turbine blades, giving them part of its kinetic energy and imparting torque to the blades. The rotor blades transmit torque through the turbine disks to the shaft. Beneficial features gas turbine: a gas turbine, for example, rotates a generator located on the same shaft, which is the useful work of the gas turbine.

Gas turbines are used as part of gas turbine engines (used for transport) and gas turbine units (used at thermal power plants as part of stationary gas turbine units, combined cycle gas turbine units). Gas turbines are described by the Brayton thermodynamic cycle, which involves adiabatic compression of air, combustion at constant pressure, and then adiabatic expansion back to the starting pressure.

Types of gas turbines

- Aviation and jet engines

- Auxiliary power unit

- Industrial gas turbines for electricity production

- Turboshaft engines

- Radial gas turbines

- Microturbines

Mechanically, gas turbines can be significantly simpler than piston internal combustion engines. Simple turbines may have one moving part: the shaft/compressor/turbine/alternate rotor assembly (see image above), not including the fuel system.

More complex turbines (those used in modern jet engines) may have multiple shafts (coils), hundreds of turbine blades, moving stator blades, and an extensive system of complex piping, combustion chambers, and heat exchangers.

In general, the smaller the engine, the higher the shaft(s) speed required to maintain maximum linear speed of the blades. Maximum speed turbine blades determines maximum pressure which can be achieved, resulting in maximum power, regardless of engine size. The jet engine rotates at about 10,000 rpm and the micro-turbine at about 100,000 rpm.

A gas turbine is usually called a continuously operating engine. Next we will talk about how a gas turbine is designed and what the operating principle of the unit is. The peculiarity of such an engine is that inside it, energy is produced by compressed or heated gas, the result of the transformation of which is mechanical work on the shaft.

History of the gas turbine

It is interesting that turbine mechanisms began to be developed by engineers a very long time ago. The first primitive steam turbine was created back in the 1st century BC. e.! Of course, its essential
This mechanism has only now reached its peak. Turbines began to be actively developed in late XIX century simultaneously with the development and improvement of thermodynamics, mechanical engineering and metallurgy.

The principles of mechanisms, materials, alloys changed, everything was improved and now, today, humanity knows the most perfect of all previously existing forms gas turbine, which is divided into Various types. There is an aviation gas turbine, and there is an industrial one.

A gas turbine is usually called a kind of heat engine; its working parts are predetermined with only one task - to rotate due to the influence of a gas jet.

It is designed in such a way that the main part of the turbine is represented by a wheel to which sets of blades are attached. , acting on the blades of a gas turbine, causes them to move and rotate the wheel. The wheel, in turn, is rigidly connected to the shaft. This tandem has a special name – turbine rotor. As a result of this movement occurring inside the gas turbine engine, mechanical energy is obtained, which is transmitted to an electric generator, to a ship propeller, to an aircraft propeller and other working mechanisms of a similar operating principle.

Active and reaction turbines

The effect of a gas jet on turbine blades can be twofold. Therefore, turbines are divided into classes: the class of active and reactive turbines. Reactive and active gas turbines differ in their design principles.

Impulse turbine

An active turbine is characterized by the fact that there is a high rate of gas flow to the rotor blades. With the help of a curved blade, the gas stream deviates from its trajectory. As a result of the deviation, a large centrifugal force develops. With the help of this force, the blades are set in motion. During the entire described path of the gas, part of its energy is lost. This energy is directed towards the movement of the impeller and shaft.

Jet turbine

In a jet turbine everything is somewhat different. Here, gas flows to the rotor blades at a low speed and under the influence of a high level of pressure. The shape of the blades is also different, due to which the gas speed increases significantly. Thus, the gas stream creates a kind of reactive force.

From the mechanism described above it follows that the design of a gas turbine is quite complicated. In order for such a unit to operate smoothly and bring profit and benefit to its owner, its maintenance should be entrusted to professionals. Service profile companies provide service maintenance installations using gas turbines, supplies of components, all kinds of parts and components. DMEnergy is one of such companies (), which provide their clients with peace of mind and confidence that they will not be left alone with the problems that arise during the operation of a gas turbine.

A continuous thermal turbine 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 the compressed gas usually 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 design they were close to a steam turbine. A gas turbine is structurally a series of orderedly arranged stationary blade rims of the nozzle apparatus and rotating rims of the impeller, which as a result form the 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, bandage rings), and a rotor, which is a set of rotating parts (such as rotating blades, disks, shaft).

Gas turbine classification 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. Based on the direction of the gas flow, gas turbines can be distinguished between 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, gas flows at a certain angle to the axis of rotation of the turbine. The impeller of a tangential turbine does not have blades; such turbines are used for very low gas flow rates, usually in measuring instruments. Gas turbines come in single, double and multi-stage types.

The number of stages is determined by many factors: the purpose of the turbine, its design, the total power developed by one stage, as well as the pressure drop being triggered. According to the method of using the available heat difference, a distinction is made between turbines with speed stages, in which only the flow turns in the impeller, without changing the pressure (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 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 sequential processes in individual stages. Compressed and heated gas is supplied to the interblade channels of the nozzle apparatus at an initial speed, where, during the expansion process, part of the available heat difference is converted into the kinetic energy of the outflow jet. Further expansion of the gas and conversion of heat transfer into useful work occurs in the inter-blade channels of the impeller. The gas flow, acting on the rotor blades, creates torque on the main shaft of the turbine. In this case, the absolute gas velocity decreases. The lower this speed, the most of gas energy was 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 multi-stage turbines is quite high and reaches 92-94%.

The operating principle of a gas turbine is as follows: gas is pumped 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 lead to rotation of the turbine. The resulting mechanical energy of the shaft is transmitted through a gearbox to a generator that generates electricity.

Thermal energy The 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 gaseous fuels. But at the same time, gas turbines are very capricious and place increased demands on the quality of its preparation (certain mechanical inclusions and humidity are required).

The temperature of the gases emanating from the turbine is 450-550 °C. The quantitative ratio of thermal energy to electrical energy for 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 hot exhaust 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) high pressure steam production.

Soviet scientists B. S. Stechkin, G. S. Zhiritsky, N. R. Briling, V. V. Uvarov, K. V. Kholshchevikov, I. I. Kirillov and others made a great contribution to the development of gas turbines. the creation of gas turbines for stationary and mobile gas turbine units has achieved foreign companies(Swiss Brown-Boveri, where the famous Slovak scientist A. Stodola worked, and Sulzer, American General Electric, etc.).

IN further development 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 working blades with significant improvements in the flow part, etc.

Thanks to the widespread transition in the 1990s. Gas turbines have occupied a significant market segment for the use of natural gas as the main fuel for electric power generation. Although maximum efficiency equipment is achieved at powers of 5 MW and higher (up to 300 MW), some manufacturers produce models in the range of 1-5 MW.

Gas turbines are used in aviation and power plants.

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“Turbocharging”, “turbojet”, “turboprop” - these terms have firmly entered the vocabulary of 20th century engineers involved in design and maintenance Vehicle and stationary electrical installations. They are even used in related fields and advertising, when they want to give the product name some hint of special power and efficiency. The gas turbine is most often used in aviation, rockets, ships and power plants. How is it structured? Does it run on natural gas (as you might think from the name), and what types of gas are they? How does a turbine differ from other types of internal combustion engine? What are its advantages and disadvantages? An attempt to answer these questions as fully as possible is made in this article.

Russian engineering leader UEC

Russia, unlike many other independent states formed after the collapse of the USSR, managed to largely preserve the machine-building industry. In particular, the Saturn company is engaged in the production of special-purpose power plants. The company's gas turbines are used in shipbuilding, the raw materials industry and the energy sector. The products are high-tech; they require a special approach during installation, debugging and operation, as well as special knowledge and expensive equipment for routine maintenance. All these services are available to customers of the company "UEC - Gas Turbines", as it is called today. There are not so many such enterprises in the world, although the principle of the device main products at first glance it is simple. The accumulated experience is of great importance, allowing us to take into account many technological subtleties, without which it is impossible to achieve durable and reliable operation of the unit. Here is just part of the UEC product range: gas turbines, power plants, gas pumping units. Among the customers are Rosatom, Gazprom and other “whales” chemical industry and energy.

Manufacturing of such complex machines requires an individual approach in each case. The calculation of a gas turbine is currently fully automated, but the materials and features of the installation diagrams matter in each individual case.

And it all started so simply...

Searches and pairs

Humanity carried out the first experiments in converting the translational energy of a flow into rotational force in ancient times, using an ordinary water wheel. Everything is extremely simple, liquid flows from top to bottom, and blades are placed in its flow. The wheel, equipped with them around the perimeter, spins. A windmill works the same way. Then came the age of steam, and the rotation of the wheel accelerated. By the way, the so-called “aeolipil”, invented by the ancient Greek Heron about 130 years before the birth of Christ, was a steam engine operating on precisely this principle. In essence, it was the first gas turbine known to historical science (after all, steam is a gaseous state of aggregation water). Today it is still customary to separate these two concepts. At that time in Alexandria they reacted to Heron’s invention without much enthusiasm, although with curiosity. Turbine-type industrial equipment appeared only at the end of the 19th century, after the creation by the Swede Gustaf Laval of the world's first active power unit equipped with a nozzle. Engineer Parsons worked in approximately the same direction, equipping his machine with several functionally related stages.

Birth of gas turbines

A century earlier, a certain John Barber came up with a brilliant idea. Why do you need to heat the steam first? Isn’t it easier to directly use the exhaust gas generated during the combustion of fuel, and thereby eliminate unnecessary mediation in the energy conversion process? This is how the first real gas turbine turned out. The 1791 patent outlines the basic idea for use in a horseless carriage, but its elements are today used in modern rocket, aircraft tank and automobile engines. The process of jet engine construction was started in 1930 by Frank Whittle. He came up with the idea of ​​using a turbine to propel an airplane. Subsequently, it was developed in numerous turboprop and turbojet projects.

Nikola Tesla gas turbine

The famous scientist-inventor always approached the issues he studied in a non-standard way. It seemed obvious to everyone that wheels with paddles or paddles “catch” the movement of the medium better than flat objects. Tesla, in his characteristic manner, proved that if you assemble a rotor system from disks arranged sequentially on the axis, then due to the gas flow picking up the boundary layers, it will rotate no worse, and in some cases even better, than a multi-bladed propeller. True, the direction of the moving medium must be tangential, which is not always possible or desirable in modern units, but the design is significantly simplified - it does not require blades at all. A gas turbine according to Tesla’s scheme is not yet being built, but perhaps the idea is just waiting for its time.

Schematic diagram

Now about the basic structure of the machine. It is a combination of a rotating system mounted on an axis (rotor) and a stationary part (stator). A disk with working blades is placed on the shaft, forming a concentric lattice; they are exposed to gas supplied under pressure through special nozzles. The expanded gas then enters the impeller, which is also equipped with blades called workers. Special pipes are used for the intake of the air-fuel mixture and the outlet (exhaust). also in general scheme a compressor is involved. It can be made according to different principles, depending on the required operating pressure. To operate it, part of the energy is taken from the axis and used to compress the air. A gas turbine operates through the combustion process of an air-fuel mixture, accompanied by a significant increase in volume. The shaft rotates, its energy can be used usefully. Such a circuit is called single-circuit, but if it is repeated, then it is considered multi-stage.

Advantages of aircraft turbines

Around the mid-fifties, a new generation of aircraft appeared, including passenger aircraft (in the USSR these were Il-18, An-24, An-10, Tu-104, Tu-114, Tu-124, etc.), in designs in which aircraft piston engines were finally and irrevocably replaced by turbine engines. This indicates the greater efficiency of this type of power plant. The characteristics of a gas turbine are superior to those of carburetor engines in many respects, in particular in the power/weight ratio, which is of paramount importance for aviation, as well as in equally important reliability indicators. Lower fuel consumption, fewer moving parts, better environmental parameters, reduced noise and vibration. Turbines are less critical to fuel quality (which cannot be said about fuel systems), they are easier to maintain, and they do not require as much lubricating oil. In general, at first glance it seems that they are not made of metal, but of solid advantages. Alas, this is not true.

Gas turbine engines also have disadvantages.

The gas turbine heats up during operation and transfers heat to the surrounding structural elements. This is especially critical, again, in aviation, when using a modified layout scheme that involves washing the lower part of the tail unit with a jet stream. And the engine housing itself requires special thermal insulation and the use of special refractory materials that can withstand high temperatures.

Cooling gas turbines is a complex technical challenge. It's no joke, they operate in a mode of virtually permanent explosion occurring in the body. The efficiency in some modes is lower than that of carburetor engines; however, when using a dual-circuit circuit, this drawback is eliminated, although the design becomes more complicated, as is the case when “boosting” compressors are included in the circuit. Accelerating the turbines and reaching operating mode takes some time. The more often the unit starts and stops, the faster it wears out.

Correct Application

Well, no system can do without its shortcomings. It is important to find a use for each of them in which its advantages will be more clearly demonstrated. For example, tanks such as the American Abrams, whose power plant is based on a gas turbine. It can be filled with anything that burns, from high-octane gasoline to whiskey, and produces great power. The example may not be very successful, since experience in Iraq and Afghanistan has shown the vulnerability of compressor blades to sand. Gas turbines have to be repaired in the USA, at the manufacturing plant. To take the tank there, then back, and the cost of the maintenance itself plus components...

Helicopters, Russian, American and other countries, as well as powerful speedboats, suffer less from blockages. Liquid rockets cannot do without them.

Modern warships and civilian vessels also have gas turbine engines. And also energy.

Trigenerator power plants

The problems that aircraft manufacturers faced are not as worrying to those who produce industrial equipment for the production of electricity. In this case, weight is no longer so important, and you can focus on parameters such as efficiency and overall efficiency. Gas turbine generator units have a massive frame, a reliable frame and thicker blades. It is quite possible to utilize the generated heat, using it for a variety of needs - from secondary recycling in the system itself, to heating domestic premises and thermal supply of absorption-type refrigeration units. This approach is called trigenerator, and the efficiency in this mode approaches 90%.

Nuclear power plants

For a gas turbine, it makes no fundamental difference what the source of the heated medium is that gives its energy to its blades. This could be a burnt air-fuel mixture, or simply superheated steam (not necessarily water), the main thing is that it ensures uninterrupted power supply. At its core power plants all nuclear power plants, submarines, aircraft carriers, icebreakers and some military surface ships ( missile cruiser"Peter the Great", for example) are based on a gas turbine (GTU) rotated by steam. Safety and environmental issues dictate a closed primary circuit. This means that the primary thermal agent (in the first samples this role was played by lead, now it has been replaced by paraffin) does not leave the reactor zone, flowing around the fuel elements in a circle. The working substance is heated in subsequent circuits, and the evaporated carbon dioxide, helium or nitrogen rotates the turbine wheel.

Wide Application

Complex and large installations are almost always unique; they are produced in small batches or even single copies are made. Most often, units produced in large quantities are used in peaceful sectors of the economy, for example, for pumping hydrocarbon raw materials through pipelines. These are exactly the ones produced by the ODK company under the Saturn brand. Gas turbines of pumping stations fully correspond to their name. They actually pump natural gas, using its energy for their work.