Unfortunately, the transition to the construction of combined cycle CHPPs (CCGT CHPPs) instead of steam turbines has led to an even sharper decrease in heat generation in the overall energy production. This, in turn, leads to an increase in the energy intensity of GDP and a decrease in the competitiveness of domestic products, as well as an increase in the cost of housing and communal services.

¦ high efficiency of electricity generation at the CCGT CHPP according to the condensation cycle up to 60%;

¦ Difficulties in locating CCGT CHPPs in conditions of dense urban development, as well as an increase in fuel supplies to cities;

¦ According to the established tradition, CCGT CHPPs are equipped, as well as steam turbine stations, with T-type cogeneration turbines.

Construction of a CHP plant with P-type turbines since the 1990s. the last century, was practically discontinued. In pre-perestroika times, industrial enterprises accounted for about 60% of the heat load in cities. Their need for heat for the implementation of technological processes during the year was quite stable. During the hours of the morning and evening peaks in urban power consumption, power supply peaks were smoothed out by introducing appropriate regimes for limiting the supply of electrical energy to industrial enterprises. The installation of P-type turbines at the CHPP was economically justified due to their lower cost and more efficient use of energy resources compared to T-type turbines.

Over the past 20 years, due to a sharp decline in industrial production, the energy supply regime of cities has changed significantly. Currently, city CHPPs operate according to the heating schedule, in which the summer heat load is only 15-20% of the calculated value. The daily schedule of electricity consumption has become more uneven due to the inclusion of electrical load by the population in the evening hours, which is associated with a massive increase in the supply of electrical household appliances to the population. In addition, leveling the energy consumption schedule by introducing appropriate restrictions on industrial consumers due to their small share in total energy consumption turned out to be impossible. The only not very effective way to solve the problem was to reduce the evening maximum by introducing reduced tariffs at night.

Therefore, in steam turbine CHP plants with P-type turbines, where the generation of thermal and electrical energy is strictly interconnected, the use of such turbines turned out to be unprofitable. Backpressure turbines are now produced only at low power to improve the efficiency of urban steam boilers by switching them to cogeneration mode.

Such an established approach was also preserved at the construction of the CCGT CHPP. At the same time, there is no rigid relationship between the supply of heat and electricity in the combined cycle. At these stations with turbines of the P type, the coverage of the evening maximum electrical load can be carried out by temporarily increasing the supply of electricity in the gas turbine cycle. A short-term decrease in heat supply to the heat supply system does not affect the quality of heating due to the heat storage capacity of buildings and the heating network.

The schematic diagram of the CCGT CHPP with counterpressure turbines includes two gas turbines, a waste heat boiler, a P-type turbine, and a peak boiler (Fig. 2). The peak boiler, which can be installed outside the CCGT site, is not shown in the diagram.

From fig. 2, it can be seen that the CCGT CHPP consists of a gas turbine plant consisting of a compressor 1, a combustion chamber 2 and a gas turbine 3. heat exchangers in which water is heated, steam is separated in low pressure drums 7 and high pressure 8, is sent to a steam turbine unit (STP) 11. Moreover, low pressure saturated steam enters the intermediate section of the STP, and high pressure steam is preheated in the waste heat boiler and sent to the head of the STP The steam leaving the STP is condensed in the network water heat exchanger 12 and is sent by condensate pumps 13 to the gas condensate heater 14, and then sent to the deaerator 9 and from it to the CU.

With a thermal load not exceeding the base one, the station operates completely according to the heating schedule (ATES=1). If the heat load exceeds the base load, the peak boiler is switched on. The required amount of electricity comes from external sources of generation through the city's power grids.

However, situations are possible when the demand for electricity exceeds the volume of its supply from external sources: on frosty days with an increase in electricity consumption by household heating appliances; in case of accidents at generating facilities and in electrical networks. In such situations, the capacity of gas turbines in the traditional approach is closely related to the performance of the waste heat boiler, which in turn is dictated by the need for thermal energy in accordance with the heating schedule and may not be sufficient to meet the increased demand for electricity.

In order to cover the shortage of electricity that has arisen, the gas turbine switches partially to the discharge of waste combustion products, in addition to the waste heat boiler, directly into the atmosphere. Thus, the CCGT CHPP is temporarily transferred to a mixed mode - with combined cycle and gas turbine cycles.

It is known that gas turbine plants have high maneuverability (the rate of gain and loss of electrical power). Therefore, even in Soviet times, they were supposed to be used, along with pumped-storage stations, to smooth the power supply regime.

In addition, it should be noted that the power developed by them increases with a decrease in the outdoor temperature, and it is at low temperatures in the coldest season that the maximum power consumption is observed. This is shown in the table.

When the power reaches more than 60% of the calculated value, emissions of harmful gases NOx and CO are minimal (Fig. 3).

In the non-heating period, in order to prevent a decrease in the power of gas turbines by more than 40%, one of them is turned off.

Increasing the energy efficiency of CHPPs can be achieved through centralized refrigeration supply to urban microdistricts. In emergency situations at the CCGT CHPP, it is advisable to build gas turbine units of low power in separate buildings.

In areas of dense urban development of large cities, when reconstructing existing CHPPs with exhausted steam turbines, it is advisable to create on their basis a CCGT CHPP with R-type turbines. As a result, significant areas occupied by the cooling system (cooling towers, etc.) are released, which can be used for other purposes.

Comparison of CCGT CHP with backpressure turbines (P type) and CCGT CHP with condensate extraction turbines (T type) allows us to make the following conclusions.

  • 1. In both cases, the fuel efficiency depends on the share of electricity generation based on heat consumption in the total generation volume.
  • 2. In CCGT CHPPs with turbines of type T, heat losses in the condensate cooling circuit occur throughout the year; the greatest losses are in the summer period, when the amount of heat consumption is limited only to hot water supply.
  • 3. In CCGT CHPPs with turbines of the R type, the efficiency of the plant decreases only for a limited period of time, when it is necessary to cover the shortage in electricity supply.
  • 4. Maneuvering characteristics (speeds of loading and unloading) of gas turbines are many times higher than those of steam turbines.

Thus, for the conditions of construction of stations in the centers of large cities, CCGT CHPPs with counterpressure turbines (P type) are superior to combined-cycle CHP plants with condensate extraction turbines (T type) in all respects. They require a much smaller area to accommodate, they are more economical in terms of fuel consumption and their environmental impact is also less.

However, for this it is necessary to make appropriate changes to the regulatory framework for the design of combined cycle plants.

The practice of recent years shows that investors constructing suburban CCGT CHPPs and in fairly free territories give priority to electricity generation, and heat supply is considered by them as a side activity. This is explained by the fact that the efficiency of stations, even in the condensing mode, can reach 60%, and the construction of heating mains requires additional costs and numerous agreements with different structures. As a result, the heat supply coefficient of the CHPP can be less than 0.3.

Therefore, when designing a CCGT CHPP, it is not advisable for each individual plant to include in the technical solution the optimal value of ATES. The task is to find the optimal share of district heating in the heat supply system of the entire city.

Now the concept of building powerful thermal power plants in places where fuel is extracted, far from big cities, developed in Soviet times, has again become relevant. This is dictated both by an increase in the share of using local fuels in the fuel and energy complex of the regions, and by the creation of new designs of heat pipelines (air laying) with an almost negligible drop in the temperature potential during the transportation of the coolant.

Such thermal power plants can be created both on the basis of a steam turbine cycle with direct combustion of local fuel, and a combined cycle with the use of gas produced at gas generators.


The combination of steam turbine and gas turbine plants, combined by a common technological cycle, is called a combined-cycle plant (CCGT) of a power plant. The combination of these units into a single whole makes it possible to reduce the loss of heat with the exhaust gases of the gas turbine or steam boiler, use the gases behind gas turbines as a heated oxidizer during fuel combustion, obtain additional power by partially displacing the regeneration of steam turbine plants and, ultimately, increase the efficiency of the combined cycle power plant by compared with steam turbine and gas turbine power plants.

The use of CCGT for today's power industry is the most effective means of significantly increasing the thermal and overall efficiency of fossil fuel power plants. The best operating CCGTs have an efficiency of up to 46%, and those under design - up to 48-49%, i.e., higher than at the designed MHD plants.

Among the various CCGT options, the following schemes are most widely used: CCGT with a high-pressure steam generator (HPG), CCGT with discharge of gases from a gas turbine into the steam boiler furnace, CCGT with a waste steam boiler (HRB), semi-dependent CCGT, CCGT with intra-cycle gasification of solid fuel.

Developed by NPO CKTI CCGT with high-pressure steam generator operate on natural gas or on liquid gas turbine fuel (Fig. 9.8). The air compressor supplies compressed air to the housing annulus HSV and in the additional combustion chamber DCS, where its temperature rises. Hot gases after fuel combustion in the combustion chamber have a pressure of 0.6-1.2 MPa, depending on the air pressure behind the compressor, and are used to generate steam and superheat it. After the reheater - the last heating surface HSV- gases with a temperature of about 700 °C enter the additional combustion chamber, where they are heated to 900 °C and enter the gas turbine. The gases exhausted in the gas turbine are sent to a three-stage gas-water economizer, where they are cooled by feed water and the main condensate of the steam turbine. Such connection of economizers provides a constant temperature of flue gases of 120-140 °C before they exit into the chimney. At the same time, in such a CCGT there is a partial displacement of regeneration and an increase in the power of the steam turbine plant.


Rice. 9.8. Principal thermal diagram of the steam-gas plant PGU-250 with a high-pressure steam generator VPG-600-140:

BS - separator drum; PE- superheater; PP - intermediate superheater; AND- evaporative heating surfaces; TsN- circulation pump; EC1 - EKSh- gas-water economizers for utilizing the heat of gas turbine exhaust gases; WPV - feed water deaerator; DCS- additional combustion chamber

A high-pressure steam generator is a common fuel combustion chamber for a steam turbine and a gas turbine plant. A feature of such a CCGT is that the excess gas pressure in the circuit makes it possible not to install smoke exhausters, and the air compressor replaces the blower fan; no need for an air heater. The steam from the HSV is sent to a steam turbine plant, which has a conventional thermal scheme.

A significant advantage of this installation is the reduction in dimensions and mass parameters of the VPG operating at a pressure of 0.6-1.2 MPa in the gas path. The high-pressure steam generator is completely manufactured in the factory. In accordance with the requirements of transportation, the steam capacity of one VPG body does not exceed 350-10 3 kg/h. Steam generator VPG-650-140-545/545 PO TKZ, for example, consists of two buildings. Its gas ducts are shielded by welded gas-tight panels of finned tubes.

It is expedient to use CCGT with HSV at moderate gas temperatures upstream of GTP. With an increase in this temperature, the proportion of heat transferred by the gases of the heating surface of the high-pressure steam generator decreases.

Autonomous operation of the steam stage of the CCGT with HSV is impossible, which is a disadvantage of this scheme, which requires equal reliability of the gas turbine plant, steam turbine, and steam generator. The use of gas turbines with built-in combustion chambers (for example, GTE-150) is also unacceptable.

The use of CCGT with HSV is promising in schemes with intracycle gasification of coal.

On fig. 9.9 shows the layout of CCGT-200-250 with turbines K-160-130 and GT-35-770 or K-210-130 and GT-45-3. A similar unit has been successfully operating for a number of years at Nevinnomysskaya GRES. The use of such CCGTs can provide fuel savings at thermal power plants by 15%, a reduction in specific capital investments by 12-20%, a reduction in equipment metal consumption by 30% compared to a steam turbine power plant.

CCGT with gas discharge gas turbine into the furnace of a steam boiler are characterized by the fact that the exhaust gases of the gas turbine are highly heated (450-550°C) ballasted oxidizer with an oxygen content of 14-16%. For this reason, it is advisable to use them for burning the bulk of the fuel in a steam boiler (Fig. 9.10). A CCGT according to this scheme has been implemented and is successfully operating at the Moldavskaya GRES (station power units No. 11 and 12). Serial equipment was used for the CCGT: steam turbine K-210-130 POT LMZ for steam parameters of 13 MPa, 540/540 °C, gas turbine GT-35-770 POAT KhTZ, electric generators of steam and gas stages TGV-200 and TVF-63- 243, single-casing steam boiler with natural circulation type TME-213, capacity 670*10 3 kg/h. The boiler is supplied without an air heater and can operate both under forced draft and with balanced draft. For this, smoke exhausters are provided in the scheme. DS. This CCGT scheme allows operation in three different modes: CCGT mode and autonomous operation modes of gas and steam stages.

Rice. 9.9. The layout of the main building of CCGT-250 with a high-pressure steam generator:

a- cross section; b - plan; see designations in fig. 9.8

The main mode of operation of the plant is the steam-gas cycle. The exhaust gases of the gas turbine (liquid gas turbine fuel is burned in its combustion chamber) are fed into the main burners of the boiler. The burner also receives the air heated in the heater, which is missing for the combustion process, and is pumped by an additional air fan. Airborne. The flue gases of the steam boiler are cooled in high and low pressure economizers and then sent to the chimney. Via high pressure economizer EKVD both in the CCGT mode and during autonomous operation of the steam stage, approximately 50% of the feed water is supplied after the feed pumps. Then all the feed water enters the main economizer of the boiler at a temperature of 250°C. To the low pressure economizer ECND the main condensate of the turbine enters after PND5(at loads over 50%) or after HDPE4(at loads below 50%). In this regard, the regenerative selections of the steam turbine are partially unloaded, and the steam pressure in its flow part increases slightly; increased steam flow to the turbine condenser.

Rice. 9.9. Continuation

During autonomous operation of the steam stage, the air required for fuel combustion in the boiler is supplied by a blower fan. DV into heaters, where it is heated to 180 °C and then sent to the burners. The steam boiler operates under vacuum created by smoke exhausters DS. During autonomous operation of the gas stage, the exhaust gases are directed to the chimney.

The possibility of CCGT operation in various modes is ensured by the installation of an automatically controlled system of quick-closing gas-air dampers (flaps) of large diameter, mounted on gas ducts to shut off one or another element of the installation. This increases the cost of the circuit and reduces its reliability.

With an increase in the gas temperature in front of the CCGT gas turbine and at a lower degree of air compression in the compressor, the oxygen content in the exhaust gases of the gas turbine decreases, which requires the supply of additional air. This leads to an increase in the volume of gases passing through the convective heating surfaces of the steam boiler, as well as heat losses with the exhaust gases. . The power consumption for the blower fan drive also increases. When solid fuel is burned in the boiler, the heated air is used in the pulverizing system.

The operating experience of CCGT-250 at the Moldavskaya GRES has shown that its efficiency largely depends on the load of the steam and gas stages. The specific consumption of reference fuel at a nominal load of 240-250 MW reaches 315 g/(kWh).

Combined-cycle power plants of this type are widely used abroad (USA, England, Germany, etc.). The advantage of this type of CCGT lies in the fact that a steam boiler of a conventional design is used, in which any type of fuel, including solid fuel, can be used. In the combustion chamber of a gas turbine, no more than 15-20% of the fuel required for the entire CCGT is burned, which reduces the consumption of its scarce grades. The start-up of such a CCGT usually begins with the start-up of the GTU, the use of the heat of the exhaust gases of which makes it possible to increase the steam parameters in the steam boiler and reduce the amount of fuel consumed to start the steam turbine equipment.

Rice. 9.10. Principal thermal diagram of CCGT-250 with discharge of GTU gases into the steam boiler furnace:

PE- fresh steam superheater; PP-intermediate superheater; EC, EKVD, EKND- economizers: main, high and low pressure; P1–P7 - heaters of the steam stage regeneration system; DPA- feed water deaerator; PEN, KN, DN- nutritious, condensate, drainage pumps; HP- main condensate recirculation pump in EKND; DV, VDV- blower and additional air fans ; CL1,CL11- heaters of the first and second stages ; V- injection of feed water from the intermediate stage of the PEN; DC- smoke exhauster

CCGT with recycling steam boilers allow the use of exhaust gases from gas turbines to generate steam. On such installations, it is possible to implement a purely binary cycle without additional combustion of fuel with the production of steam of low parameters. On fig. 9.11 shows the scheme proposed by MPEI for such a CCGT, which uses a GTE-150-1100 gas turbine and a K-70-29 saturated steam turbine used at nuclear power plants. Steam parameters in front of the turbine 3 MPa, 230 °С. According to the condition of permissible temperature differences between gases and steam and the most complete use of the heat of the exhaust gases, the intermediate superheater is made of gas-steam and is located behind the economizer along the gases. Part of the flue gases behind the gas turbine is introduced into the cut between the evaporative and economizer heating surfaces of the utilizing steam boiler Code of Criminal Procedure, which provides the desired temperature difference. Such plants are characterized by high values ​​of the CCGT energy factor and the use of only high-quality fossil fuels, mainly natural gas. At an outside air temperature of +15°C and a flue gas temperature of 160°C, the total electric power of the CCGT is approximately 220 MW, the efficiency is 44.7%, and the specific fuel consumption is 281 g/(kWh).

Rice. 9.11. Schematic diagram of CCGT-220 with waste heat boiler and saturated steam turbine without fuel afterburning:

Code of Criminal Procedure- utilization boiler (steam generator); C - moisture separator; DN- drainage pump; see other designations in fig. 20.8, 20.10

The All-Union Thermal Engineering Institute and ATEP have developed a variant of a maneuverable CCGT without afterburning fuel in front of a waste steam boiler. The CCGT includes one gas turbine GTE-150-1100, a single-cylinder steam turbine with a capacity of 75 MW for steam parameters of 3.5 MPa, 465 ° C at a steam flow rate of 280-10 3 kg / h, a waste steam boiler with a heating surface of 40-10 3 m 2 from finned tubes. The module of the main building of the power plant of such a CCGT-250 is designed as a single-span with a span width of 24 m. The gas turbine plant, the steam turbine and the electric generator between them are mounted in the form of a single-shaft unit. At an outside air temperature of +5 °C, CCGT-250 has a specific reference fuel consumption of 279 g/(kWh).

The use of more powerful serial steam turbine plants in the CCGT scheme with waste heat boilers will require a higher flow rate of steam of high parameters. This is possible when the gas temperature at the boiler inlet rises to 800-850 °C due to additional combustion of up to 25% of the total fuel consumption (natural gas) in the boiler burners. On fig. 20.12 shows a schematic thermal diagram of CCGT-800 of this type according to the project of VTI and ATEP. It includes two gas turbine units GTE-150-1100 POT LMZ, a double-casing utilization steam boiler ZiO with a total steam output of 1150-10 3 kg / h and steam parameters of 13.5 MPa, 545/545 ° C, a steam turbine K-500- 166 POT LMZ. This scheme has a number of features. Turbine regenerative bleeds (except for the last one) are plugged; in the regeneration system there is only mixing HDPE. A non-deaerator circuit was used with turbine condensate deaeration in the condenser and in the mixing heater. Condensate with a temperature of 60 °C is supplied by two feed pumps PE-720-220 to the economizer of the boiler. The absence of regenerative steam extraction increases its passage to the turbine condenser, the electric power of which is therefore limited to 450 MW.

Utilization steam boiler U-shaped layout direct-flow type consists entirely of convective heating surfaces. Outgoing gases in the amount of 680 kg / s with a temperature of 430-520 ° C and an oxygen content of 14-15.5% enter each of the buildings of the UPC after the gas turbine unit. Natural gas is burned in the main burners of the UPC. and the gas temperature in front of the heating surfaces of the boiler rises to 840-850 °C. The combustion products are sequentially cooled in the superheaters (intermediate and main), in the evaporative and economizer heating surfaces and at a temperature of ~125°C are sent to the chimney. A specific feature of the boiler is its operation with a significant mass flow of gases. The ratio of its steam output to the consumption of combustion products is 5-6 times lower than that of conventional steam boilers of power units. As a result, the minimum temperature difference moves from the area of ​​the reheater (for a once-through gas-oil boiler) to the hot end of the economizer. The small value of this temperature difference (20-40 °C) forced the designers of the UPC to make an economizer from finned tubes with a diameter of 42X4 mm, which reduced its weight, but increased the aerodynamic resistance of the boiler. As a result, the electric power of the gas turbine plant and the entire CCGT has somewhat decreased.

The main mode of CCGT-800 is its operation on a combined cycle, while the utilization steam boiler operates under pressurization. The advantage of such CCGT units is the possibility of autonomous operation of the gas and steam stages. Independent operation of the CCGT takes place at a slightly reduced power due to the increased resistance of the exhaust carried out by the transit of gases through the waste heat boiler. To ensure the autonomous operation of the steam turbine unit, some complication of the circuit is necessary, in which dampers and smoke exhausters must additionally be included. In this mode of operation, the gates are closed 1 and 2 (Fig. 9.12) and open the gates 3 -5. The main amount of flue gases of the boiler (about 70%) is enriched with air and with the help of a recirculation smoke exhauster DR with a temperature of 80 ° C is sent to additional burners in front of the boiler. At the same time, the amount of fuel burned in the CPC increases threefold. Unused amount of flue gases from the boiler (about 30%) by the smoke exhauster DC thrown down the chimney.

To operate the CCGT on standby liquid gas turbine fuel, it is necessary to provide additional heating of water up to 130-140°C in the thermal circuit in order to avoid corrosion of the tail heating surfaces. This mode of operation will therefore be less economical.

Combined-cycle plants with utilizing steam boilers are highly manoeuvrable. They are designed for approximately 160 launches per year; start-up time after a downtime of 6-8 hours is 60 minutes, and after a stop for 40-48 hours - 120 minutes. When unloading CCGT, first of all, the load of gas turbine units is reduced from 100 to 80% by covering the inlet guide vanes (VNA) of the compressors. Further lowering of the load is carried out by reducing the consumption of fuel burned in the burners of the UPC, reducing the steam capacity of the latter while maintaining the temperature of the gases in front of the gas turbines. Upon reaching 50% of the rated load of the CCGT, one of the GTP and the corresponding casing of the CPC are switched off. With a decrease in the load of the steam stage and the steam capacity of the CPC, the temperatures are redistributed along the path, and the temperature of the flue gases increases to 170-190°C (at 50% of the boiler load). This increase in temperature is unacceptable due to the operating conditions of the smoke exhausters and the chimney. To maintain the permissible temperature of the flue gases, the utilization steam boiler at reduced loads is transferred from direct-flow to separator mode of operation with the discharge of excess heat into the steam turbine condenser. The scheme of the steam turbine plant includes a built-in separator and a kindling expander. The transition to the separator mode increases fuel consumption at the CCGT compared to the direct-flow mode of operation by 5-10%.

It is expedient to install a CCGT with utilization steam boilers in the gas-bearing regions of Western Siberia, Central Asia, etc. According to the All-Russian Technical Institute, CCGT-800 has high energy performance. At an outside air temperature of +5°С, a gas temperature in front of gas turbines of 1100°С, the capacity of the CCGT unit will be approximately 766 MW, and the specific reference fuel consumption (net) will be 266 g/(kWh). With a change in air temperature in the range from +40 to -40 °C, the CCGT power changes in the range of 550-850 MW due to a significant change in the power of two GTPs. Savings from the introduction of CCGT-800 instead of a conventional power unit of 800 MW will amount to 5.7-10 6 rubles per year. (204-10 6 kg of reference fuel).

Rice. 9.12. Principal thermal diagram of CCGT-800 with a waste heat boiler and afterburning fuel:

1-5 - switchable gas-tight gates; DC- smoke exhauster; DR- smoke exhauster for gas recirculation; WITH- moisture separator; RR- kindling expander; AIDS- low pressure mixing heater

A variant of the layout of the main building of CCGT-800 according to the design of VTI and ATEP is shown in fig. 9.13. Estimated investment in the main building of the CCGT is 89 rubles/kW. Its construction will make it possible to save up to 9-10 6 kg of steel and up to 8-10 6 kg of reinforced concrete at the CPP with six CCGT-800 units compared to the installation of six gas-oil power units of 800 MW.

The combination of gas turbine and steam turbine plants using standard serial equipment is carried out in semi-dependent combined cycle plant(Fig. 9.14). It is intended for use during the peaks of the electrical load curve and involves the complete or partial shutdown of high pressure steam heaters. As a result, its passage through the flow path of the steam turbine increases and the steam stage power increases by approximately 10-11%. The decrease in the temperature of the feed water is compensated by its additional heating in the gas-water economizer by the exhaust gases of the gas turbine. The temperature of the exhaust gases of the GTU decreases in this case to approximately 190 °C. The total increase in peak power, taking into account the operation of the gas turbine, is 35-45% of the base power of the steam turbine unit. The specific consumption of reference fuel is close to the consumption during autonomous operation of this unit .



Rice. 9.13. Layout option for the main building of the CCGT-800 combined cycle plant:

1 gas turbine GTE-150-1100; 2 - GTU electric generator; 3-air intake to the GTU compressor; 4 – utilization steam boiler; 5 - steam turbine K-500-166; 6- smoke exhauster; 7 - blower fan; 8 - flue

Rice. 9.14. Schematic diagram of a semi-dependent combined cycle gas plant:

GVE- gas-water economizer; PC- steam boiler; see other designations in fig. 9.8.

It is advisable to install semi-dependent CCGTs in the European part of the USSR. According to the LMZ, the following combinations of steam and gas turbines are recommended: 1 X K-300-240+1 X GTE-150-1100; 1 X K-500-130+ 1 X GTE-150-1100; 1 x K-1200-240 + 2 x GTE-150-1100, etc. The increase in the estimated capital investments in the gas turbine plant will be about 20%, and the equivalent fuel saving in the power system during the operation of the CCGT in peak mode will be (0.5-1, 0) X X10 6 kg/year. To obtain peak power, it is also promising to use heating plants in the scheme of semi-dependent CCGTs.

The considered CCGT schemes imply partial or full use of high-quality organic fuel (natural gas or liquid gas turbine fuel), which hinders their widespread introduction. Of considerable interest are the various schemes of steam-gas plants developed by CKTI with high-pressure steam generators and intracycle gasification of solid fuel (Fig. 20.15), which make it possible to convert combined-cycle plants entirely to coal.

Rice. 9.15. Principal thermal scheme of CCGT with HSV and intracycle gasification of coal:

/- fuel drying ; 2 - gas generator; 3 - high-pressure steam generator (HSG); 4 - separator drum; 5 - additional HSV combustion chamber; 6- circulation pump VPG; 7-economizer for utilization of the heat of the exhaust gases of the gas turbine; 8-chimney; 9- scrubber; 10- generator gas heater; DC- booster compressor; Fri- steam drive turbine; RGT- expansion gas turbine; / - fresh steam; // - reheat steam ; /// - compressed air after the compressor; IV- purified producer gas; V- ash; VI-IX- turbine feed water and condensate

Pre-crushed coal (crushed coal 3-10 mm) is fed into the dryer for drying and through the oxidizer (to prevent slagging) into the gas generator. One of the options for the scheme is the gasification of coal in a fluidized bed gasifier on steam-air blast. Fuel gasification is ensured by supplying air to the gas generator after the booster compressor and steam from the "cold" reheat line. Air for gasification in the amount of approximately 3.2 kg per 1 kg of Kuznetsk coal is sequentially compressed in the main and booster compressors (the pressure increases by 10%) and, after mixing with steam, enters the gas generator. Coal gasification occurs at a temperature close to 1000 °C.

The generator gas is cooled, giving off its heat to the working fluid of the steam turbine part, then it is cleaned of mechanical impurities and sulfur-containing compounds, and after expansion in the expansion gas turbine (to reduce steam consumption by the drive turbine of the booster compressor), it enters the high-pressure steam generator and its additional combustion chamber for combustion . The rest of the thermal circuit coincides with the circuit of a conventional CCGT with HSV.

VNIPIenergoprom, together with NPO TsKTI, has developed a project for a 225 MW cogeneration combined-cycle power unit with intracycle gasification of coal. For this purpose, standard power equipment was used: a double-hull high-pressure steam generator VPG-650-140 TKZ, a gas turbine unit GTE-45-2 KhTZ, a heat-and-power steam turbine T-180-130 LMZ, as well as two gas generators with steam-air blast GGPV-100-2 with a capacity of 100 t/h of Kuznetsk coal. Feasibility studies have shown that, compared with a conventional steam turbine heat and power unit of 180 MW, the use of a combined cycle power unit makes it possible to increase the specific generation of electricity for heat consumption by 1.5 times, ensure fuel savings of up to 8%, significantly reduce harmful emissions into the atmosphere, obtain a total annual economic effect of 2.6-10 6 rubles. The combined cycle power unit considered will be used to create more powerful CCGT-1000 on the coals of the Kuznetsk, Ekibastuz and Kansk-Achinsk basins.

Combined-cycle plants have been widely used in the USA, Germany, Japan, France, etc. CCGTs mainly burn natural gas and liquid fuels of various types. The introduction of CCGT was facilitated by the appearance of powerful gas turbines (70-100 MW) with an initial gas temperature of 900-1100°C. This made it possible to use a CCGT with utilization steam boilers (Fig. 9.16) of a drum type with forced circulation of the medium and a steam pressure of 4-9 MPa, depending on whether they additionally burn fuel or not. On fig. 9.17 shows a diagram of a utilizing steam boiler for a CCGT with a gas turbine МW701. The boiler is designed for two steam pressures. It has heating surfaces of low and high pressure finned tubes with its drums in a block with a feed water deaerator.

To thermal power plants(CHP) includes power plants that produce and supply consumers not only electrical, but also thermal energy. In this case, steam from intermediate turbine extractions, partially already used in the first stages of turbine expansion for generating electricity, as well as hot water with a temperature of 100-150 ° C, heated by steam taken from the turbine, serve as heat carriers. Steam from a steam boiler enters the turbine through a steam pipeline, where it expands to the pressure in the condenser and its potential energy is converted into mechanical work of rotation of the turbine rotor and the generator rotor connected to it. Part of the steam after several stages of expansion is taken from the turbine and sent through the steam pipeline to the steam consumer. The place of steam extraction, and hence its parameters, are set taking into account the requirements of the consumer. Since the heat at the CHP is spent on the production of electrical and thermal energy, the efficiency of the CHP for the production and supply of electricity and the production and supply of heat differ.

Gas turbine plants(GTP) consist of three main elements: an air compressor, a combustion chamber and a gas turbine. Air from the atmosphere enters the compressor, driven by the starting motor, and is compressed. Then, under pressure, it is fed into the combustion chamber, where liquid or gaseous fuel is simultaneously supplied by a fuel pump. In order to reduce the gas temperature to an acceptable level (750-770°C), 3.5-4.5 times more air is fed into the combustion chamber than is necessary for fuel combustion. In the combustion chamber, it is divided into two streams: one stream enters the flame tube and ensures complete combustion of the fuel, and the second flows around the flame tube from the outside and, mixing with the combustion products, reduces their temperature. After the combustion chamber, the gases enter the gas turbine, which is located on the same shaft as the compressor and generator. There, they expand (to about atmospheric pressure), do work by rotating the turbine shaft, and then are ejected through the chimney. The power of a gas turbine is much less than the power of a steam turbine and at present the efficiency is about 30%.

Combined-cycle plants(CCP) are a combination of steam turbine (STU) and gas turbine (GTU) installations. Such a combination makes it possible to reduce the waste heat losses of gas turbines or the heat of exhaust gases from steam boilers, which ensures an increase in efficiency compared to separately taken STPs and GTPs. In addition, with such a combination, a number of design advantages are achieved, leading to a reduction in the cost of the installation. Two types of CCGT are widely used: those with high-pressure boilers and those with discharge of turbine exhaust gases into the combustion chamber of a conventional boiler. The high-pressure boiler runs on gas or purified liquid fuel. Flue gases leaving the boiler with high temperature and overpressure are directed to the gas turbine, on the same shaft with which there are a compressor and a generator. The compressor pumps air into the combustion chamber of the boiler. The steam from the high-pressure boiler is directed to the condensing turbine, which has a generator on the same shaft. The steam exhausted in the turbine passes into the condenser and, after condensation, is pumped back into the boiler by a pump. Turbine exhaust gases are fed to the economizer to heat the boiler feed water. In such a scheme, a smoke exhauster is not required to remove the flue gases of a high-pressure boiler, the compressor performs the function of a blast pump. The efficiency of the installation as a whole reaches 42-43%. In another scheme of the combined cycle plant, the heat of the exhaust gases of the turbine in the boiler is used. The possibility of discharge of exhaust gases from the turbine into the combustion chamber of the boiler is based on the fact that in the combustion chamber of the gas turbine fuel (gas) is burned with a large excess of air and the oxygen content in the exhaust gases (16-18%) is sufficient to burn the bulk of the fuel.



29. NPP: device, types of reactors, parameters, operating characteristics.

Nuclear power plants are thermal power plants, because in their device there are heat emitters, a coolant and an electric generator. current - turbine.

Nuclear power plants can be condensing, heating plants (ATES), nuclear heat supply stations (AST).

Nuclear reactors are classified according to various criteria:

1. according to the neutron energy level:

On thermal neutrons

On fast neutrons

2. according to the type of neutron moderator: water, heavy water, graphite.

3. by type of coolant: water, heavy water, gas, liquid metal

4. by the number of circuits: one-, two-, three-circuit

In modern reactors for the fission of nuclei of the original fuel, mainly thermal neutrons are used. All of them have, first of all, the so-called core, into which nuclear fuel containing uranium 235 is loaded moderator(usually graphite or water). To reduce the leakage of neutrons from the core, the latter is surrounded reflector , usually made of the same material as the moderator.

Behind the reflector outside the reactor is placed concrete protection from radioactive radiation. Loading of the reactor with nuclear fuel usually considerably exceeds the critical one. In order to continuously maintain the reactor in a critical state as the fuel burns out, a strong neutron absorber in the form of boron carbamide rods is introduced into the core. Such rods called governing or compensatory. In the process of nuclear fission, a large amount of heat is released, which is removed coolant into the heat exchanger steam generator, where it turns into a working fluid - steam. The steam enters turbine and rotates its rotor, the shaft of which is connected to the shaft generator. The exhaust steam in the turbine enters capacitor, after which the condensed water again goes to the heat exchanger, and the cycle repeats.

combined-cycle are called power plants (PSU), in which the heat of the exhaust gases of the gas turbine is directly or indirectly used to generate electricity in the steam turbine cycle.

On fig. 4.10 shows a schematic diagram of the simplest combined-cycle plant, the so-called utilization type. Outgoing gases from the gas turbine are fed into waste heat boiler- a counterflow type heat exchanger, in which, due to the heat of hot gases, steam of high parameters is obtained, which is directed to a steam turbine.

Figure 4.10. Schematic diagram of the simplest combined cycle plant

The waste heat boiler is a rectangular shaft, in which heating surfaces are located, formed by ribbed pipes, inside which the working fluid of the steam turbine plant (water or steam) is supplied. In the simplest case, the heating surfaces of the waste heat boiler consist of three elements: economizer 3, evaporator 2, and superheater 1. The central element is the evaporator, consisting of a drum 4 (a long cylinder half-filled with water), several downcomers 7 and rather densely installed vertical pipes of the evaporator 8 itself. The evaporator works on the principle of natural convection. The evaporator pipes are located in the zone of higher temperatures than the downcomers. Therefore, in them, the water heats up, partially evaporates and therefore becomes lighter and rises up into the drum. The vacated space is filled with colder water through downpipes from the drum. Saturated steam is collected in the upper part of the drum and sent to the pipes of the superheater 1. The steam flow from the drum 4 is compensated by the supply of water from the economizer 3. In this case, the incoming water, before completely evaporating, will repeatedly pass through the evaporation pipes. Therefore, the described waste heat boiler is called boiler with natural circulation.

In the economizer, the incoming feed water is heated almost to the boiling point. From the drum, dry saturated steam enters the superheater, where it is superheated above the saturation temperature. The temperature of the resulting superheated steam t 0 is always, of course, less than the temperature of the gases q Г coming from the gas turbine (usually 25 - 30 °C).

Under the scheme of the waste heat boiler in fig. 4.10 shows the change in the temperatures of the gases and the working fluid as they move towards each other. The temperature of the gases gradually decreases from the value q Г at the inlet to the value q ux of the temperature of the exhaust gases. moving towards Feed water raises its temperature in the economizer to the boiling point(dot a). With this temperature (on the verge of boiling), water enters the evaporator. It evaporates water. At the same time, its temperature does not change (process a - b). At the point b the working fluid is in the form of dry saturated steam. Further, in the superheater, it overheats to a value t 0 .

The steam formed at the outlet of the superheater is sent to the steam turbine, where, expanding, it does work. From the turbine, the exhaust steam enters the condenser, condenses and with the help of a feed pump 6 , which increases the pressure of the feed water, is sent back to the waste heat boiler.

Thus, the fundamental difference between a steam power plant (SPU) of a CCGT and a conventional CCP of a thermal power plant is only that the fuel is not burned in the waste heat boiler, and the heat necessary for the operation of the CCGT CCGT is taken from the exhaust gases of the gas turbine. The general view of the waste heat boiler is shown in Figure 4.11.

Figure 4.11. General view of the waste heat boiler

The power plant with CCGT is shown in fig. 4.12, which shows a TPP with three power units. Each power unit consists of two adjacent gas turbines 4 type V94.2 Siemens, each of which sends its high-temperature flue gases to its waste heat boiler 8 . The steam generated by these boilers is sent to one steam turbine 10 with electric generator 9 and a condenser located in the condensation room under the turbine. Each such power unit has a total capacity of 450 MW (each gas turbine and steam turbine has a capacity of approximately 150 MW). Between outlet diffuser 5 and waste heat boiler 8 installed bypass (bypass) chimney 12 and gas-tight gate 6 .

Figure 4.12. Power plant with CCGT

The main advantages of PGU.

1. Combined-cycle plant is currently the most economical engine used to generate electricity.

2. Combined-cycle plant is the most environmentally friendly engine. First of all, this is due to the high efficiency - after all, all the heat contained in the fuel, which could not be converted into electricity, is released into the environment and its thermal pollution occurs. Therefore, the reduction in thermal emissions from a CCGT compared to a steam power plant approximately corresponds to a decrease in fuel consumption for electricity generation.

3. Combined-cycle plant is a very maneuverable engine, which can only be compared in maneuverability by an autonomous gas turbine. Potentially high maneuverability of the PTU is ensured by the presence of a GTP in its scheme, the load change of which occurs within a few minutes.

4. With the same capacity of steam-powered and combined-cycle TPPs, the consumption of CCGT cooling water is approximately three times less. This is determined by the fact that the power of the steam-power part of the CCGT is 1/3 of the total power, and the GTU practically does not require cooling water.

5. The CCGT has a lower cost per installed unit of capacity, which is associated with a smaller volume of the construction part, the absence of a complex power boiler, an expensive chimney, a regenerative feed water heating system, the use of a simpler steam turbine and a service water supply system.

CONCLUSION

The main disadvantage of all thermal power plants is that all types of fuel used are irreplaceable natural resources that are gradually running out. In addition, thermal power plants consume a significant amount of fuel (every day, one state district power plant with a capacity of 2000 MW burns two railway trains of coal per day) and are the most environmentally “dirty” sources of electricity, especially if they operate on high-ash sulphurous fuels. That is why at present, along with the use of nuclear and hydraulic power plants, the development of power plants using renewable or other alternative energy sources is underway. However, in spite of everything, thermal power plants are the main producers of electricity in most countries of the world and will remain so for at least the next 50 years.

CONTROL QUESTIONS FOR LECTURE 4

1. Thermal scheme of CHPP - 3 points.

2. Technological process of electricity generation at thermal power plants - 3 points.

3. The layout of modern thermal power plants - 3 points.

4. Features of GTU. Structural diagram of the GTU. GTU efficiency - 3 points.

5. Thermal diagram of the gas turbine - 3 points.

6. Features of CCGT. Structural scheme of PGUU. CCGT efficiency - 3 points.

7. Thermal diagram of CCGT - 3 points.


LECTURE 5

NUCLEAR POWER PLANTS. FUEL FOR NPP. OPERATING PRINCIPLE OF A NUCLEAR REACTOR. POWER GENERATION AT NPP WITH THERMAL REACTORS. FAST NEUTRON REACTORS. ADVANTAGES AND DISADVANTAGES OF MODERN NPPs

Basic concepts

Nuclear power plant(NPP) is a power plant, generating electrical energy by converting the thermal energy released in a nuclear reactor (reactors) as a result of a controlled chain reaction of fission (splitting) of the nuclei of uranium atoms. The fundamental difference between a nuclear power plant and a thermal power plant is that instead of a steam generator, a nuclear reactor is used - a device in which a controlled nuclear chain reaction is carried out, accompanied by the release of energy.

The radioactive properties of uranium were first discovered by a French physicist Antoine Becquerel in 1896. English physicist Ernest Rutherford first carried out an artificial nuclear reaction under the action of particles in 1919. German physicists Otto Hahn and Fritz Strassman opened in 1938 , that the fission of heavy uranium nuclei when bombarded by neutrons accompanied by the release of energy. The actual use of this energy has become a matter of time.

The first nuclear reactor was built in December 1942 in the USA a group of physicists at the University of Chicago led by an Italian physicist Enrico Fermi. The undamped uranium nuclear fission reaction was realized for the first time. The nuclear reactor, called SR-1, consisted of graphite blocks, between which were located balls of natural uranium and its dioxide. Fast neutrons that appear after nuclear fission 235 U, were slowed down by graphite to thermal energies, and then caused new nuclear fission. Reactors in which the main share of fissions occurs under the action of thermal neutrons are called thermal (slow) neutron reactors; in such reactors there is much more moderator than uranium.

In Europe, the first F-1 nuclear reactor was manufactured and launched in December 1946 in Moscow. a group of physicists and engineers headed by Academician Igor Vasilyevich Kurchatov. The F-1 reactor was assembled from graphite blocks and had the shape of a ball with a diameter of about 7.5 m. In the central part of the ball with a diameter of 6 m, uranium rods were placed in the holes of the graphite blocks. The F-1 reactor, like the SR-1, did not have a cooling system, so it operated at low power levels: from fractions to units of a watt.

The results of research at the F-1 reactor served as the basis for projects for industrial reactors. In 1948, under the leadership of I. V. Kurchatov, work began on the practical application of atomic energy to generate electricity.

The world's first industrial nuclear power plant with a capacity of 5 MW was launched on June 27, 1954 in the city of Obninsk, Kaluga Region. In 1958, the 1st stage of the Siberian NPP was put into operation with a capacity of 100 MW (full design capacity of 600 MW). In the same year, the construction of the Beloyarsk industrial nuclear power plant began, and in April 1964, the generator of the 1st stage provided electricity to consumers. In September 1964, the 1st block of the Novovoronezh NPP with a capacity of 210 MW was launched. The second unit with a capacity of 350 MW was launched in December 1969. In 1973, the Leningrad NPP was launched.

In the UK, the first industrial nuclear power plant with a capacity of 46 MW was commissioned in 1956 at Calder Hall. A year later, a 60 MW nuclear power plant was put into operation in Shippingport (USA).

The world leaders in the production of nuclear electricity are: USA (788.6 billion kWh/year), France (426.8 billion kWh/year), Japan (273.8 billion kWh/year), Germany (158.4 billion kWh/year) ) and Russia (154.7 billion kWh/year). At the beginning of 2004, there were 441 nuclear power reactors operating in the world, the Russian TVEL OJSC supplies fuel for 75 of them.

The largest nuclear power plant in Europe is the Zaporozhye NPP in Energodar (Ukraine) - 6 nuclear reactors with a total capacity of 6 GW. The world's largest nuclear power plant - Kashiwazaki-Kariva (Japan) - five boiling nuclear reactors ( BWR) and two advanced boiling water reactors ( ABWR), the total capacity of which is 8.2 GW.

Currently, the following nuclear power plants operate in Russia: Balakovo, Beloyarskaya, Bilibinskaya, Rostovskaya, Kalininskaya, Kola, Kurskaya, Leningradskaya, Novovoronezhskaya, Smolenskaya.

The developments of the draft Energy Strategy of Russia for the period up to 2030 provide for an increase in electricity production at nuclear power plants by 4 times.

Nuclear power plants are classified according to the reactors installed on them:

l thermal neutron reactors , using special moderators to increase the probability of absorption of a neutron by the nuclei of fuel atoms;

l fast neutron reactors .

According to the type of energy supplied, nuclear power plants are divided into:

l nuclear power plants (NPPs) designed to generate electricity only;

l nuclear combined heat and power plants (ATPPs) that produce both electricity and heat.

Currently, only in Russia are options for the construction of nuclear heat supply stations.

NPP does not use air to oxidize fuel, does not emit ash, sulfur oxides, carbon, etc. into the atmosphere, has a lower radioactive background than at a thermal power plant, but, like a thermal power plant, consumes a huge amount of water to cool the condensers.

Fuel for nuclear power plants

The main difference between a nuclear power plant and a thermal power plant is use of nuclear fuel instead of fossil fuels. Nuclear fuel is obtained from natural uranium, which is mined either in mines (Niger, France, South Africa), or in open pits (Australia, Namibia), or by underground leaching (Canada, Russia, USA). Uranium is widely distributed in nature, but there are no rich deposits of uranium ores. Uranium is found in various rocks and water in a dispersed state. Natural uranium is a mixture of the predominantly non-fissile isotope of uranium 238 U(more than 99%) and fissile isotope 235 U (about 0.71%), which is a nuclear fuel (1 kg 235 U releases energy equal to the calorific value of about 3000 tons of coal).

For the operation of nuclear power plant reactors, uranium enrichment. To do this, natural uranium is sent to an enrichment plant, after processing, where 90% of natural depleted uranium is sent for storage, and 10% is enriched to 3.3 - 4.4%.

From enriched uranium (more precisely, uranium dioxide UO 2 or uranium oxides U 2 O 2) are made fuel elements - fuel rods- cylindrical tablets with a diameter of 9 mm and a height of 15-30 mm. These tablets are placed in airtight zirconium(neutron absorption by zirconium is 32.5 times less than by steel) thin wall tubes about 4 m long. Fuel rods are assembled into fuel assemblies (FA) in several hundred pieces.

All further nuclear fission processes 235 U with the formation of fission fragments, radioactive gases, etc. are happening inside sealed tubes of fuel rods.

After gradual splitting 235 U and reducing its concentration to 1.26%, when the reactor power is significantly reduced, fuel assemblies are removed from the reactor, are stored in the spent fuel pool for some time, and then sent to the radiochemical plant for processing.

Thus, unlike thermal power plants, where they tend to burn fuel completely, it is impossible to split nuclear fuel by 100% at nuclear power plants. Therefore, it is impossible to calculate the efficiency at NPPs based on the specific consumption of standard fuel. To assess the efficiency of the NPP power unit, the net efficiency factor is used

,

where is the generated energy, is the heat released in the reactor at the same time and the same time.

The NPP efficiency calculated in this way is 30–32%, but it is not entirely legitimate to compare it with the TPP efficiency of 37–40%.

In addition to the uranium 235 isotope, the following are also used as nuclear fuel:

  • uranium isotope 233 ( 233 U) ;
  • plutonium isotope 239 ( 239 Pu);
  • thorium isotope 232 ( 232Th) (by converting to 233 U).

Depending on what is chosen steam-gas cycles, what choice will be optimal, and what will the CCGT process flow diagram look like?

Once the capital parity and the roll configuration are known, the cycle pre-selection can begin.

The range extends from very simple “single pressure cycles” to extremely complex “reheat triple pressure cycles”. The efficiency of the cycle increases with increasing complexity, but capital costs also increase. The key to choosing the right cycle is to determine the pressure cycle that is best suited for a given efficiency and given costs.

Combined-cycle plant with single pressure cycle

This cycle is often used for more favorable degraded quality fuels such as crude oil and high sulfur heavy fuel oil.

Compared to complex cycles, investments in CCGT of simple cycles are insignificant.

The diagram shows a CCGT with an additional evaporator coil at the cold end of the waste heat boiler. This evaporator removes additional heat from the exhaust gases and gives steam to the deaerator in order to use it to heat the feed water.

This eliminates the need for steam extraction for the deaerator from the steam turbine. The result, compared to the simplest single pressure scheme, is an improvement in efficiency, but the capital investment increases accordingly.

PGU with a cycle of two pressures

Most combined plants in operation have dual pressure cycles. Water is supplied by two separate feed pumps to the dual pressure economizer.

Read also: Plans for the introduction of combined cycle power plants in Russia

The low pressure water then enters the first evaporator coil and the high pressure water is heated in the economizer before it evaporates and superheats in the hot end of the HRSG. Extraction from the low pressure drum supplies steam to the deaerator and steam turbine.

The efficiency of the dual pressure cycle, as shown in the T-S diagram in the figure, is higher than the efficiency of the single pressure cycle, due to the more complete use of the energy of the gas turbine exhaust gases (additional area SS"D"D).

However, this increases the capital investment for additional equipment, such as feed pumps, dual pressure economizers, evaporators, low pressure pipelines and two LP steam lines to the steam turbine. Therefore, the considered cycle is applied only at high capital parity.

CCGT with triple pressure cycle

This is one of the most complex schemes that are currently being used. It is used in cases of very high capital parity, where high efficiency can only be obtained at high cost.

A third stage is added to the waste heat boiler, which additionally uses the heat of the exhaust gases. The high pressure pump supplies feed water to the three-stage high pressure economizer and then to the high pressure drum separator. The medium pressure feed pump supplies water to the medium pressure separator drum.

Part of the feed water from the medium pressure pump through the throttle device enters the drum - low pressure separator. The steam from the high pressure drum enters the superheater and then to the high pressure part of the steam turbine. The steam exhausted in the high pressure part (HPP) mixes with the steam coming from the medium pressure drum, overheats and enters the inlet of the low pressure part (LPP) of the steam turbine.

Read also: How to choose a gas turbine plant for a CCGT plant

The efficiency can be further increased by heating the fuel with high pressure water before it enters the gas turbine.

Cycle Selection Diagram

Cycle types from single pressure cycle to triple pressure cycle with reheat are presented as functions of supply parity.

The cycle is selected by determining which of the cycles are appropriate for a given capital parity for a particular application. If, for example, the capital parity is $1,800. US/kW, the dual or triple pressure cycle is selected.

As a first approximation, the decision is made in favor of the triple pressure cycle, since at a constant capital parity, the efficiency and capacity are higher. However, on closer examination of the parameters, it may be more appropriate to choose a dual pressure cycle to meet other requirements.

There are cases for which the cycle selection diagram is not applicable. The most common example of this is when the customer wants to have electrical power available as soon as possible and optimization is less important to him than short delivery times.

Depending on the circumstances, it may be advantageous to prefer a single pressure cycle to a multi-pressure cycle, as the time required is less. For this purpose, a series of standardized cycles with given parameters can be developed, which are successfully used in such cases.

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