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 of 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 the 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 (ATES), Atom stations heat supply (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. Reactor loading nuclear fuel usually much higher than the critical value. 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. During nuclear fission, a large number of heat that 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 plant CCGT is a combined plant consisting of a gas turbine unit, a waste heat boiler (HRB) and a steam turbine (ST). The implementation of the steam and gas cycles is carried out in separate circuits, i.e., in the absence of contact between the combustion products and the vapor-liquid working fluid. The interaction of working bodies is carried out only in the form of heat exchange in heat exchangers of the surface type.
The use of combined cycle plants is one of the possible and promising ways to reduce fuel and energy costs.
CCGTs thermodynamically successfully combine the parameters of gas turbines and steam power plants:
GTUs operate in the zone of elevated temperatures of the working fluid;
Steam-powered - are driven by the products of combustion that have already been exhausted, leaving the turbine, i.e. play the role of utilizers and use waste energy.
The efficiency of the installation is increased as a result of the thermodynamic superstructure of the high-temperature gas cycle by the steam cycle, which reduces heat losses with exhaust gases in the gas turbine.
Thus, CCGT can be considered as the third stage in the improvement of turbine units. CCGTs are promising engines, as they are highly economical, with low capital investments. The excellent qualities of combined cycle plants have determined their areas of application. CCGTs are widely used in the power industry and other areas of the fuel and energy complex.
The widespread use of such installations is hindered by the lack of a unified point of view on the most rational directions for the utilization of heat from gas turbines.
At present, a promising CCGT scheme for use at main gas pipelines is also a purely utilization CCGT scheme with a full cycle superstructure, in which the steam generator is heated only by the exhaust gases of the gas turbine (Fig. 6.1).
According to this scheme, the combustion products of the gas turbine after the low-pressure turbine (LPT) enter the waste heat boiler (HRB) to generate high-pressure steam. The resulting steam from the KU enters the steam turbine (ST), where, expanding, it performs useful work that goes to the drive of the electric generator or blower. The exhaust steam after the PT enters the condenser K, where it is condensed and then fed back to the waste heat boiler by the feed pump (PN). The thermodynamic cycle of a steam-gas plant is shown in fig. 6.2. The high-temperature gas cycle of a gas turbine begins with the process of compressing air into axial compressor: 1 → 2. In the combustion chamber (as well as in the regenerator, if any), heat is supplied 2 → 3; the generated combustion products enter the gas turbine, where, expanding, they do work, process 3 → 4; and finally, the exhaust gases give up their heat in the waste heat boiler, heating water and steam, 4 → 5. The rest of the low-temperature heat remains unused and is transferred to environment, 5 → 1.
Figure 6.1 - Schematic diagram of a CCGT unit with a waste heat boiler
Figure 6.2 - Scheme of the cycle of a combined cycle plant in T-S coordinates
The steam-gas cycle is formed by a sequence of processes: 1 "- 2" - 3 "- 4" - 5 "- 1" (Fig. 6.2). Conventionally, the cycle begins with the process 1" - 2" - heat supply in the economizer. The water coming from the condenser has a low temperature equal to 39 °C (at a pressure in the condenser Р np = 0.007 MPa). It is heated to the boiling point, about 170 ... 210 ° C, at a constant pressure corresponding to the operating pressure of the boiler 0.8 ... 2.0 MPa. 2" - 3" - the process of evaporating water in the evaporator and turning it into saturated steam. 3" - 4" - superheating of steam in the superheater; 4" - 5" - the process of steam expansion in a steam turbine with the completion of work and loss of temperature; 5" - 1" - steam is condensed in the condenser K, and the resulting water is again fed into the waste heat boiler KU. The cycle closes.
The power of the steam turbine itself (ST) depends on the actual heat drop, or enthalpy, through the steam turbine and the steam flow rate. Steam consumption and steam parameters are determined by the operation of the waste heat boiler. Schematic diagram of the waste heat boiler is shown in fig. 6.3.
A waste heat boiler is a forced circulation steam boiler that does not have its own furnace and is heated by flue gases from any power plant.
Therefore, the waste heat of the gas turbine exhaust gases, with a temperature of about 400 ° C, is quite enough for effective work recycling facilities.
In the course of the boiler, heat exchangers are installed in series: water economizer "E", evaporator "I" and superheater "P".
A water economizer is a heat exchanger in which water is heated by low-temperature hot gases (combustion products) before it is fed into the boiler drum (separator).
Steam is generated in the running gear of the boiler as follows. Feed water, preheated in the economizer to the boiling point by flue gases, enters the boiler drum. The temperature of hot gases in the tail section of the boiler must not fall below 120 °C*.
In steam generation mode, water circulates through the evaporator. In the evaporator there is an intense absorption of heat, due to which vaporization occurs. The process of vaporization in the evaporator occurs at the boiling temperature of the feed water, corresponding to a certain saturation pressure.
LOW-PRESSURE AND HIGH-PRESSURE STEAM PRODUCTION INSTALLATIONSFor the production of electricity, combined steam and gas plants (CCGT), combined in a single thermal circuit, are used. At the same time, a reduction in specific fuel consumption and capital costs is achieved. CCGT units with a high-pressure steam generating unit (VNPPU) and with a low-pressure steam generating unit (NNPPU) are most widely used. Sometimes VNPPU are called high-pressure boilers.
Unlike boilers operating under vacuum from the gas side, in the combustion chamber and gas ducts of high-pressure and pressurized boilers, relatively low pressure is created at NNPPU (0.005-0.01 MPa) and increased at VNPPU (0.5-0.7 MPa) .
The work of the boiler under pressure is characterized by a number of positive features. Thus, air suction into the furnace and gas ducts is completely excluded, which leads to a decrease in heat loss with outgoing gases, as well as to a decrease in
reducing the consumption of electricity for their pumping. An increase in pressure in the combustion chamber opens up the possibility of overcoming all air and gas resistances due to the blower fan (smoke draft may be absent), which also leads to a decrease in electricity consumption due to the operation of the blower device in cold air.
The creation of excess pressure in the combustion chamber leads to a corresponding intensification of the fuel combustion process and allows you to significantly increase the speed of gases in the convective elements of the boiler up to 200-300 m/s. At the same time, the coefficient of heat transfer from gases to the heating surface increases, which leads to a decrease in the dimensions of the boiler. At the same time, its operation under pressure requires dense lining and various devices to prevent combustion products from being knocked out into the room.
Rice. 15.1. Schematic diagram of a combined cycle plant with VNPPU:
/ - air intake; 2 - compressor; 3 - fuel; 4 - combustion chamber; 5 - gas turbine; 6 - exhaust gases; 7 - electric generator; 8 - boiler; 9 - steam turbine; 10 - capacitor; // - pump; 12 - high pressure heater; 13 - regenerative exhaust gas heater (economizer)
On fig. 15.1 shows a diagram of a combined cycle plant (CCGT) with a high-pressure boiler. Combustion of fuel in the furnace of such a boiler occurs under pressure up to 0.6-0.7 MPa, which leads to a significant reduction in the cost of metal on heat-receiving surfaces. After the boiler, the combustion products enter the gas turbine, on the shaft of which there are an air compressor and an electric generator.
torus The steam from the boiler enters the turbine with another electric generator.
The thermodynamic efficiency of a combined steam-gas cycle with a high-pressure boiler, gas and steam-water turbines is shown in fig. 15.2. On the T, n-diagram: areas 1-2-3-4-1 - the work of the gas stage bt, the area sye\abc - the work of the steam stage bn; 1-5-6-7-1 - heat loss with outgoing gases; cbdc - loss of heat in the condenser. The gas stage is partially built over the steam stage, which leads to a significant increase in the thermal efficiency of the installation.
The high-pressure boiler in operation, developed by NPO TsKTI, has a capacity of 62.5 kg/s. The boiler is water-tube, with forced circulation. Steam pressure 14 MPa, superheated steam temperature 545 °C. Fuel---gas (fuel oil), is burned with a heat release volumetric density of about 4 MW/m3. Combustion products leaving the boiler at temperatures up to 775 ° C and pressures up to 0.7 MPa expand in the gas turbine to a pressure close to atmospheric. The exhaust gases at a temperature of 460 °C enter the economizer, after which the exhaust gases have a temperature of about 120 °C.
The principal thermal diagram of a CCGT with a VNPPU with a power of 200 MW is shown in fig. 15.3. The installation includes a K-160-130 steam turbine and a GT-35/44-770 gas turbine. From the compressor, air enters the VNPPU furnace, where fuel is also supplied. High-pressure gases after the superheater at a temperature of 770 ° C enter the gas turbine, and then into the economizer. The scheme provides for an additional combustion chamber, which provides the nominal temperature of the gases in front of the GTU when the load changes. In combined CCGTs, the specific fuel consumption is 4-6% less than in conventional steam turbines, and capital investments are also reduced. 
Rice. 15.2. Т, ї-diagram for combined steam-gas cycle
The modernization work on the territory of the Kirovskaya CHPP-3 with the use of a CCGT (combined-cycle plant) is coming to an end. The station provides thermal energy (heating and hot water) to the city of Kirovo-Chepetsk and electricity to consumers in the Kirov region. The power plant began its work in 1942 and before the commissioning of new power equipment, the installed electric power of the plant was 160 MW, and the thermal power was 813 Gcal/h. The station's power boilers burn natural gas, fuel oil, Kuznetsk coal. The use of a CCGT unit will make it possible to more than double the electric and thermal power of the station, up to 390 MW.
The construction of a 230 MW CCGT at Kirovskaya CHPP-3 began on February 29, 2012. Power engineers of IES-Holding have done a lot of work in a short time, and already in the summer of 2014, a ceremonial launch is scheduled.
The electric power of the combined cycle plant is 230 MW, the thermal power is 136 Gcal/h. The combined cycle plant being commissioned is the most economical and environmentally friendly generating equipment in the Kirov region. Distinctive feature stations - the use of the first fan-type cooling tower in the region. The cost of the project amounted to 10.3 billion rubles.
To date, the use of combined cycle technology is the optimal solution for traditional thermal energy. Blocks of this type have optimal parameters for the cost of a unit of installed capacity and economic efficiency. Due to the reuse of gas combustion energy, their efficiency is significantly higher than traditional steam power units. Thus, the total capacity of the constructed block is 230 megawatts. The entire old part of Kirovskaya CHPP-3 has a maximum capacity of 149 megawatts. At the same time, the CCGT efficiency is 52% versus 30% for the old unit. Another feature of CCGT is the low level of emissions of harmful substances into the atmosphere. Finally, the combined cycle unit has a significantly smaller building cycle compared to traditional steam power units.
The road to CCGT passes by an open switchgear. That's where all the Chepetsky asphalt!
Oil painting "2.5 pipes at CHPP-3".
The pipe has been decommissioned and is in the process of being dismantled.
New switchgear.
Brand new transformers are separated from each other by fireproof partitions.
Outdoor switchgear equipment (switches, current and voltage transformers, disconnectors).
Photo from the roof of the RCHU building (Relay Control Board).
Overpass of conductors in the area open installation transformers.
New and old.
The building of CHPP-3 is made of brick, all subsequent CHPPs are built using concrete and reinforced concrete.
Now let's go through the stages of obtaining energy.
Fuel for CCGT (gas) is first supplied to the gas treatment station, and then it enters the turbine through the overpass.
Cleaned air from a complex cleaning device is supplied to the gas turbine from above. At the same time, the requirements for air purity are such that personnel can enter the air duct only in dressing gowns and without shoes. This air, after special treatment, is much purer than that which we breathe.
The structure inside the building is comparable in size to two freight railcars.
Work is underway on the installation of communications.
The principle of operation of this turbine is similar to the operation of an airliner engine. The air is purified, compressed in a compressor, then natural gas is supplied to it. The gases generated during its combustion rotate the turbine, and it, in turn, the generator.
To reduce vibration, the turbine was installed on special springs.
The resulting electricity is fed through the conductors to the transformers.
Further, the combustion products enter the waste heat boiler. It is also manufactured by the domestic company OAO EMAlliance. This unique boiler unit is designed specifically for this facility and has no analogues. Its height is 30 meters, it has two circuits in which low and high pressure steam is produced.
communications at the top.
Smoke exhaust pipe.
Steam from the waste heat boiler rotates the T-63 steam turbine with an 80 megawatt generator. It was manufactured in the Urals specifically for this project and is designed to operate only as part of a combined cycle unit. This turbine incorporates the latest advanced developments of domestic turbine building.
The installation of the turbogenerator stator (the heaviest element of the steam turbine weighing 105 tons) on the foundation was carried out by the Dutch specialists of ALE Heavylift LLC. They mounted a special rigging system and, with the help of special jacks and heavy-duty cables, the stator was raised to a height of 20 meters for several hours and installed on the foundation.
An overhead crane was assembled to service all the equipment.
Condensate storage tanks.
Main control panel.
In the valve assembly room, the installation of equipment and the laying of cables for the process control system of the boiler room also began. Works on the installation of structures for cables have been completed, cable ducts are being installed, power cables are being laid, and equipment is being connected.
Combined-cycle power plants are those 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. It differs from steam-powered and gas turbine plants by increased efficiency.
Schematic diagram of a combined cycle plant (from a lecture by Fomina).
GT EG steam
compressor Waste heat boiler K
air EG
feed water
CS - combustion chamber
GT - gas turbine
K - condensing steam turbine
EG - electric generator
Combined-cycle plant consists of two separate units: steam power and gas turbine.
In a gas turbine plant, the turbine is rotated by the gaseous products of fuel combustion. Both natural gas and products of the oil industry (fuel oil, diesel fuel) can serve as fuel. On the same shaft with the turbine is the first generator, which, due to the rotation of the rotor, generates an electric current. Passing through the gas turbine, the combustion products give it only a part of their energy and still have a high temperature at the outlet of the gas turbine. From the outlet of the gas turbine, the combustion products enter the steam power plant, into the waste heat boiler, where they heat water and the resulting steam. The temperature of the combustion products is sufficient to bring the steam to the state required for use in a steam turbine (a flue gas temperature of about 500 degrees Celsius makes it possible to obtain superheated steam at a pressure of about 100 atmospheres). The steam turbine drives a second electric generator.
Prospects for the development of CCGT (from Ametistov's textbook).
1. Combined-cycle plant is the most economical engine used to generate electricity. A single-circuit CCGT with a GTP having an initial temperature of about 1000 °C can have an absolute efficiency of about 42%, which will be 63% of the theoretical efficiency of the CCGT. The efficiency of a three-circuit CCGT with reheating of steam, in which the temperature of the gases before gas turbine is at the level of 1450 °C, already today it reaches 60%, which is 82% of the theoretically possible level. There is no doubt that the efficiency can be increased even more.
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 will be exactly to the extent that less consumption fuel for electricity generation.
3. Combined-cycle plant is a very maneuverable engine, which can only be compared in maneuverability by an autonomous gas turbine.
4. With the same capacity of steam-powered and combined-cycle TPPs, the consumption of CCGT cooling water is approximately three times less.
5. The CCGT has a moderate cost per installed unit of capacity, which is associated with a smaller volume of the construction part, with 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.
6. CCGT units have a significantly shorter construction cycle. CCGTs, especially single-shaft ones, can be introduced in stages. This simplifies the investment problem.
Combined-cycle plants have practically no drawbacks; rather, we should talk about certain limitations and requirements for equipment and fuel. Installations about which in question, require the use natural gas. For Russia, where the share of relatively inexpensive gas used for energy exceeds 60% and half of it is used for environmental reasons at thermal power plants, there are all possibilities for the construction of a CCGT.
All this suggests that the construction of CCGT units is the prevailing trend in modern thermal power engineering.
Efficiency of utilization type CCGT:
ηPGU = ηGTU + (1- ηGTU)*ηKU*ηPTU
PTU - steam turbine plant
KU - waste heat boiler
In the general case, the CCGT efficiency:
Here - Qgtu is the amount of heat supplied to the working fluid of the gas turbine;
Qpsu - the amount of heat supplied to the steam medium in the boiler.
1. Principal thermal schemes for the supply of steam and heat from a CHP. Heat supply coefficient α CHP. Ways to cover the peak heat load at CHP,
CHP (combined heat and power plants)- designed for centralized supply of consumers with heat and electricity. Their difference from IES is that they use the heat of the steam exhausted in the turbines for the needs of production, heating, ventilation and hot water supply. Due to this combination of electricity and heat generation, significant fuel savings are achieved in comparison with separate energy supply (electricity generation at IES and heat at local boiler houses). Thanks to this method of combined production, a sufficiently high efficiency is achieved at the CHPP, reaching up to 70%. Therefore, CHP plants have become widespread in areas and cities with high heat consumption. Max power CHPP is smaller than IES.
CHP plants are tied to consumers, because the radius of heat transfer (steam, hot water) is approximately 15 km. Country CHPPs transmit hot water at a higher initial temperature over a distance of up to 30 km. Steam for production needs with a pressure of 0.8-1.6 MPa can be transferred to a distance of no more than 2-3 km. With an average heat load density, the CHP capacity usually does not exceed 300-500 MW. Only in major cities, such as Moscow or St. Petersburg with a high heat load density, it makes sense to build plants with a capacity of up to 1000-1500 MW.
The power of the CHP and the type of turbogenerator are selected in accordance with the heat demand and the parameters of the steam used in production processes and for heating. Turbines with one and two controlled steam extractions and condensers have received the greatest application (see fig.). Adjustable extractions allow you to regulate the production of heat and electricity.
CHP mode - daily and seasonal - is determined mainly by heat consumption. The station operates most economically if its electric power corresponds to the heat output. At the same time, a minimum amount of steam enters the condensers. In winter, when the demand for heat is maximum, at the estimated air temperature during the hours of operation of industrial enterprises, the load of CHP generators is close to the nominal one. During periods when heat consumption is low, for example, in summer, as well as in winter when the air temperature is higher than the calculated one and at night, the electric power of the CHPP, corresponding to heat consumption, decreases. If the power system needs electrical power, the CHP plant must switch to mixed mode, which increases the flow of steam to the low pressure part of the turbines and to the condensers. At the same time, the efficiency of the power plant is reduced.
The maximum generation of electricity by cogeneration stations "on heat consumption" is possible only when working together with powerful CPPs and HPPs, which take on a significant part of the load during hours of reduced heat consumption.
comparative analysis ways to control the heat load.
quality regulation.
Advantage: stable hydraulic mode of heating networks.
Flaws:
■ low reliability of sources of peak thermal power;
■ the need to use expensive methods of treatment of make-up water of the heating network when high temperatures coolant;
■ an increased temperature schedule to compensate for the withdrawal of water for hot water supply and the associated reduction in electricity generation for heat consumption;
■ large transport delay (thermal inertia) of regulating the heat load of the heat supply system;
■ high intensity of corrosion of pipelines due to the operation of the heat supply system for most of the heating period with coolant temperatures of 60-85 °C;
■ fluctuations in indoor air temperature due to the influence of the DHW load on the operation of heating systems and the different ratio of DHW and heating loads for subscribers;
■ decrease in the quality of heat supply when the heat carrier temperature is regulated according to the average outdoor air temperature over several hours, which leads to fluctuations in the indoor air temperature;
■ at a variable temperature of network water, the operation of compensators is significantly complicated.
