RU2335641C2 - Method of enhancing efficiency and output of two-loop nuclear power station - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: turbine is made up of a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder. Steam, that passed through the aforesaid stages, is fed into the condenser and the condensate produced in pumped over in to the reactor steam generator. In compliance with the invention, the steam temperature in the super heater boiler is increased to 800-850°C whereat the final low-pressure cylinder stage produces saturated steam with aridity not less that 99% or slightly superheated steam with the superheat temperature not over 5°C. This invention can be used in updating the existing nuclear power stations to increase their output.

EFFECT: higher efficiency.

5 dwg

Description

The invention relates to the field of heat engineering and can be used to modernize existing nuclear power plants (NPPs) in order to increase power and efficiency.

Known thermal circuit of nuclear power plants [1] (p. 10), containing a reactor, a separator, a main circulation pump, a steam turbine, a condenser, a feed pump. The real efficiency of such a device is 0.29 at a pressure in the condenser P _k = kPa. In this block, a significant part of the losses is accounted for by the steam turbine, where the humidity continuously increasing along the steam very greatly reduces the internal relative efficiency of the turbine. In this case, the final humidity of the steam behind the turbine reaches 24%.

An effective way to reduce the final moisture is an intermediate superheat of steam. The known thermal circuit of a dual-circuit nuclear power plant [1] (p. 11), containing in the first circuit a series-connected reactor, a circulation pump, in the second circuit a steam generator, the output of which is connected to a steam turbine consisting of a high pressure cylinder (CVP) and a low pressure cylinder ( LPC) connected by a shaft to the generator, the LPC output is connected to a capacitor and then connected to the steam generator through the feed pump. In this case, the steam generator has a coil of intermediate steam overheating, connected by the input to the output of the high-pressure cylinder, and the output to the input of the low-pressure cylinder. In this case, through the use of intermediate superheating of the steam, it is possible to reduce the humidity of the steam behind the turbine at an intermediate superheating temperature of 260 ° C to 11%. The real thermal efficiency of the cycle under consideration differs little from the efficiency of the simplest single-loop cycle and, according to [1] (p. 26), is 0.3–0.32.

Other proposals are known for using the thermal energy of an external heat source for superheating steam at nuclear power plants [2, 3, 4, 5].

So, in [2], steam overheating after the reactor is carried out using an additional (tertiary) steam circuit connected by a heater to the main steam circuit.

In [3, 5], for the superheating of steam, the exhaust gases of a special gas turbine are used, which pass through three heat exchangers of the main circuit.

In [4], intermediate superheating of the steam after the high-pressure turbine is carried out in a heat exchanger included in a special heating circuit.

A common drawback of all the proposed solutions is the relatively low temperature level of superheated steam. In [3, 4], the maximum temperatures of superheated steam do not exceed 400 ° C. When using the thermal energy of the exhaust gases of a gas turbine [3, 5], even at an initial gas temperature of 1350 ° C, the maximum temperature of superheated steam does not exceed 500-510 ° C. At the indicated temperature levels of superheated steam, the low pressure cylinders of the turbines used continue to operate in the wet steam region. The value of steam humidity before the last stages of the low pressure cylinder remains at the level of 4-7%, and the increase in the absolute efficiency of the cycle does not exceed 5-6%.

Closest to the proposed method is a method of superheating steam at a nuclear power plant using a gas turbine unit [3] (Fig. 1), in which the exhaust gases after the gas turbine 23 are sent to superheaters of high 3b and medium pressure 3c, as well as to the feed water heater 3a, entering the reactor 11a. In the high-pressure superheater 3b, saturated steam is heated to 500-510 ° C, expanding in the CVP 12 the steam becomes wet again, then goes to the medium-pressure superheater 3c, where its temperature rises again to 500 ° C, and then passes sequentially through the medium-pressure cylinder (DAC) 17 and the low-pressure cylinder 13. At the last stages of the low-pressure cylinder, the steam humidity is about 4-7%. In this state, the steam enters the condenser 15, the condensate formed in the condenser is pumped to the feed water heater 3a, the heated water enters the steam generator 32.

The disadvantages of the known solutions adopted for the prototype is the relatively low cycle efficiency due to the limited temperature of the superheat of the steam and the presence of wet steam in the low-pressure cylinder. The presence of two superheaters with long piping increases the cost of the device. In addition, when using the exhaust gases of a high-temperature gas turbine for superheating the steam after the reactor, the efficiency of the entire station is dependent on the operation of the gas-turbine unit, which has a relatively low service life. When it stops, the steam-turbine part of the station, connected to the reactor, is forced to work with very high humidity at all stages (up to 24% in the last stages) in deeply off-design modes, which inevitably leads to the rapid failure of the entire turbine blade apparatus. This danger is especially great for the scheme considered in [5], where it is proposed to lower the temperature of the steam behind the reactor and to supply wet steam to the high-pressure superheater 3b.

To eliminate the noted drawbacks, it is proposed to increase the initial temperature of the steam in the boiler superheater external to the reactor to a level at which the steam humidity will not exceed 0.5-1.0% beyond the last stage of the steam turbine. This condition for the initial vapor pressures used at nuclear power plants corresponds to an initial vapor temperature of 800-850 ° C.

The technical problem solved by the invention is to increase the power and efficiency of nuclear power plants by increasing the available enthalpy drop across the entire steam turbine while maintaining the existing reactor power by introducing high-temperature superheating of the steam from an external source of thermal energy, and the upper level of the superheating temperature of the steam should not exceed the above values (850 ° C).

The stated technical problem is solved in that in the known method of increasing the efficiency of a dual-circuit nuclear power plant by superheating the steam after the reactor steam generator, this superheating is carried out in a superheater with an independent source of thermal energy, followed by supplying superheated steam to the turbine, consisting of a high-pressure cylinder, an average cylinder pressure and low pressure cylinder, then sent to the condenser, with condensate pumping to the reactor steam generator, according to the invention in a steam boiler revatele steam temperature was increased to 800-850 ° C, at which from the last stage of the low pressure cylinder is obtained saturated steam having a degree of dryness of at least 99% or slightly superheated steam superheat temperature not exceeding 5 ° C.

Figure 1 presents a known method of increasing the efficiency and power of a dual-circuit nuclear power plant in which superheating of steam at a nuclear power plant is carried out using a gas turbine plant.

Figure 2 presents the first variant of the thermal diagram of the device of a dual-circuit nuclear power plant with high-temperature superheating of steam in a boiler superheater for implementing the proposed method, figure 3 is a second variant of the thermal diagram of the proposed device of a dual-circuit nuclear power plant with high-temperature superheating of steam in a hydrogen combustion chamber for implementation of the proposed method, figure 4 is a thermal diagram of the proposed device of a dual-circuit nuclear power plant with high-temperature superheating of steam in a boiler superheater with a turbo-expander for implementing the proposed method, Fig. 5 is an hs diagram illustrating steam expansion processes in a turbine of a conventional nuclear power plant and an NPP device with an external superheater for implementing the proposed method.

The unit of the nuclear power plant for implementing the proposed method (Fig. 2) contains a series-connected reactor 1, a reactor steam generator 2, a circulation pump 3, and a turbine consisting of a high-temperature high-pressure cylinder 4, a medium-pressure cylinder 5 and a low-pressure cylinder 6, connected by a shaft with a generator 7, a condenser 8, a feed pump 9, a boiler superheater 10, an independent heat source 11, an air heater 12, a fan 13 connected to it. In this case, the first input of the boiler is a superheater I have 10 in a couple connected to the output of the steam generator 2, and the steam superheater output in a couple with the entrance to the high-temperature high-pressure cylinder 4. The second output of the boiler-superheater 10 is connected to the other input of the air heater 12 by the combustion products, the second input of the boiler-superheater 10 is connected to an independent a source of thermal energy 11, its third air inlet - with the outlet of the air heater 12.

A device for implementing the proposed method works as follows. In the first circuit, the water heated in the reactor 1 under the action of the pressure created by the circulation pump 3 enters the steam generator 2, where it gives its heat to the coolant of the second circuit. Dry saturated or slightly superheated steam after the steam generator 2 enters the boiler superheater 10, where due to the combustion of any organic or other fuel supplied from an independent heat source 11, the necessary superheating of the steam is carried out. After the superheater, 10 steam at a temperature of t ₀ = 800-850 ° C and a pressure of P ₀ = 6.6 MPa is sent to a high-temperature high-pressure cylinder (CVP) 4. Then it is transferred to a medium-pressure cylinder (TsSD) 5, after which the pressure that is characteristic of the pressure behind the CVP of a conventional wet-steam turbine is maintained. Low pressure cylinder (LPC) 6 remains unchanged. After the low-pressure cylinder, steam enters the condenser 8. From the condenser by the feed pump 9, water is supplied to the steam generator 2. The combustion products after the boiler-superheater 10 are fed to the inlet of the air heater 12 at the second outlet, where they are used to heat the air, where it is supplied by the fan 13.

Thus, when using the considered scheme, all existing reactor equipment is saved. In addition to it, a boiler superheater 10 with an air heater 12 and a fan 13 is installed. In the turbine workshop, the existing high-pressure cylinder is changed to two new cylinders - a high-temperature CVP and TsSD. The most metal-intensive low pressure cylinder 6 is stored from the original turbine.

At the same time, due to a sharp increase in the temperature of superheated steam in the superheater to 800-850 ° С, the internal relative efficiency of the turbine increases significantly, since in this case all its stages work in the area of superheated steam and moisture losses typical of all turbines of nuclear power plants, practically absent. It should be especially noted that for the steam pressures now accepted in the second circuit of the NPP (6.6 MPa), steam overheating above 850 ° C does not lead to an increase in efficiency, since in this case superheated steam comes out of the turbine, which must be cooled before condensation starts, thereby removing a significant amount of thermal energy from the cycle.

An increase in the initial temperature of the vapor to the above values leads to an increase in the thermal efficiency of the nuclear power plant and increases the available enthalpy drop by 60%. The turbine power also increases by about the same 60%, without increasing the steam flow through the second circuit of the nuclear power plant.

A greater effect can be achieved when using hydrogen fuel for superheating steam at nuclear power plants. In this case, at the same time as the temperature rises, the steam increases by about 20% and its consumption, because the product of hydrogen combustion is superheated steam. When using hydrogen as a fuel, the superheater 10 (Fig. 2) is replaced by a special hydrogen combustion chamber, the principle of operation of which coincides with the principle of operation of the combustion chamber of a gas turbine.

According to the second option, the thermal circuit of the proposed technical solution will look like that shown in Fig.3.

A device for implementing the proposed method for increasing the efficiency of a dual-circuit nuclear power plant with high-temperature superheating of steam contains a series-connected reactor 1, a steam generator 2, a circulation pump 3 connected through a hydrogen nozzle 14 to the output of the steam generator 2, a hydrogen combustion chamber 15, a turbine consisting of a high-temperature high-pressure cylinder 4, a medium-pressure cylinder 5 and a low-pressure cylinder 6, connected to a generator 7 by a shaft, a capacitor 8 mounted at the outlet of the cylinder pressure 6, connected through the feed pump 9 to the input of the steam generator 2. The output of the steam generator 2 is simultaneously connected to the input to the hydrogen nozzle 14 of the hydrogen combustion chamber 15 through the valve 16 and, using the steam pipe 17 with the inside of the hydrogen combustion chamber 15, the output of the hydrogen chamber combustion 15 in a couple connected to the entrance to the high pressure cylinder 4.

The work is as follows. Dry saturated steam after the steam generator 2 through the valve 16 is supplied to the hydrogen nozzle 14 of the hydrogen combustion chamber 15 at a temperature of about 280 ° C. Hydrogen and oxygen are also supplied here. When hydrogen is burned in a vapor atmosphere, superheated steam is formed with a temperature of about 1600 ° C. Then, as in a conventional combustion chamber, the high-temperature steam is mixed with the main dry saturated steam, which is supplied to the mixing chamber 18 of the hydrogen combustion chamber through the steam line 17. At the same time, the optimal from the point of view of the operation of the turbine and the cycle as a whole is established at the outlet from the hydrogen combustion chamber steam temperature equal to 800-850 ° C.

When using the natural gas as an independent source of thermal energy for superheating steam, the proposed device can be supplemented with a turboexpander unit (Fig. 4) containing a turboexpander 14 connected by a shaft to an electric power generator 15, a natural gas heater 16, the first input of which is connected through a first valve 17 to the main pipeline 18, the first outlet of the natural gas heater 16 is connected via gas to the inlet to the turboexpander 14, its second entrance to the combustion products - with the outlet of the air heater Atelier 12 by means of a gas pipeline 19, the gas inlet to the boiler-superheater 10 through a second valve 20 is connected to the outlet of the turboexpander 14 and, simultaneously, through a third valve 21 installed on the gas pipeline 22, with a main pipeline 18.

In this case, natural gas after the first valve 17 is sent to the natural gas heater 16, where its temperature rises to 80-90 ° C. The natural gas heated in the heater 16 enters the turboexpander 14 connected to the generator 15 and, expanding in the stages of the turboexpander 14 to the pressure necessary for the operation of the nozzles of the boiler, superheater 10, produces additional electricity. With such a combination of the turboexpander cycle with the main thermal cycle of a nuclear power plant, a further increase of 1.0-1.5% in the absolute efficiency of the station in question is possible.

After the superheater, 10 steam at a temperature of t ₀ = 825 ° C and a pressure of P ₀ = 6.6 MPa is sent to the first high-temperature high-pressure cylinder (CVP) 4. Then it is transferred to a medium-pressure cylinder (TsSD) 5, which is then supported pressure characteristic of the pressure behind the CVP of a conventional wet-steam turbine. Low pressure cylinder (LPC) 6 remains unchanged. After the low-pressure cylinder, steam enters the condenser 8. From the condenser by the feed pump 9, water is supplied to the steam generator 2.

The process of steam overheating in the superheater to the optimum temperature is illustrated by the corresponding lines in the hs diagram (Fig. 5), where h ₀₁ is the enthalpy of dry saturated steam after the steam generator 2 (Fig. 2), h _1t is the enthalpy of steam behind the turbine in the absence of energy loss, h ₁ - enthalpy of steam behind the turbine with real expansion of the steam in the turbine, h ₀₂ - enthalpy of steam after the boiler superheater 10 (Fig. 2), h _2t - enthalpy of steam behind the turbine of the proposed NPP device in the absence of losses, h ₂ - enthalpy of steam behind real expansion turbine for pre proposed device NPP. Figure 5 shows the expansion processes of steam in the turbine of a conventional nuclear power plant (line O ₁ -1) and the proposed device NPP with a boiler superheater (line O ₂ -2). Line AA is a boundary curve separating the wet steam region (the region below curve AA) from the dry steam region. Point O ₁ corresponds to the state of steam after the reactor steam generator 2 (Fig. 2) in front of the turbine of a conventional NPP unit operating at a steam pressure of P ₀ = 6.6 MPa and almost zero humidity y = 0. Enthalpy h ₀₁ = 2777.6 kJ / kg corresponds to this point. Steam with the indicated parameters enters the superheater 10 (Fig. 2), where at a constant pressure P ₀ = 6.6 MPa heat is supplied to it, and its temperature continuously rises to a certain value t ₀₂ (i.e., O ₂ in FIG. 5). This superheat temperature, as already noted above, is determined from the condition of obtaining saturated steam behind the last stage of the low-pressure cylinder at a given pressure P _k in the condenser (in this case P _k = 4 kPa).

The temperature of the steam after the superheater was determined from the condition that the internal efficiency of the turbine would be η _oi = 0.9. The accepted value of the efficiency of a steam turbine is due to the fact that in the proposed NPP device all its stages operate in the area of superheated steam and, therefore, there are no losses from humidity.

, где y_ср=0.5·(y₀+y₂) - средняя влажность пара в проточной части турбины, а

- КПД турбины без учета потерь от влажности.At the same time for wet steam turbines

where y _cf = 0.5 · (y ₀ + y ₂ ) is the average humidity of the steam in the flow part of the turbine, and

- Turbine efficiency excluding moisture losses.

относительный внутренний КПД турбины будет равен η_oi=0.9·(1-0.8·0.132)=0.805.For the compared options y _cf = 0.132 (point 1, figure 5) [1] and for

the relative internal efficiency of the turbine will be η _oi = 0.9 · (1-0.8 · 0.132) = 0.805.

For the indicated efficiency values and the steam parameters existing at the NPP, the temperature after the steam generator should be increased to a temperature of t ₀ = 825 ° C in a steam boiler with an independent source of thermal energy.

According to preliminary estimates, the efficiency of the attached heat cycle, fully implemented in the area of superheated steam, reaches 60%, which allows to increase the efficiency of the new NPP unit by 8-10% compared to the existing unit.

At the same time, due to the increase in the available enthalpy difference, an increase in the power of the new unit by about 60% is achieved in comparison with the existing NPP unit.

When using hydrogen fuel for superheating steam simultaneously with an increase in the available enthalpy drop by 20%, the steam flow through the turbine also increases. Accordingly, the total increase in power of the unit can reach 80%.

Information sources

1. Troyanovsky B.M., Filippov G.A., Bulkin A.E. Steam and gas turbines of nuclear power plants. M .: Energoatomizdat, 1985.

2. Deutsches Patentamt DE 3021965 A1 G21D 5/16 Offenlegungstag 12/17/81.

3. Europalsche Patentschreft 0424 660 B1 G21D 5/16 Veroffentlichungstag der Patentschreft 12/20/95 Patentblatt 95/51.

4. European Patent Specification 0128252 B1 G21D 5/16, F22G 1/16. Date of publication of patent specification 10.06.87.

5. International Publication Number: WO 95/32509 G21D 5/16, F01K 3/18. International Publication Date: 11/30/95.

Claims (1)

A method of increasing the efficiency and power of a dual-circuit nuclear power plant by superheating steam after a reactor steam generator in a superheater with an independent heat source, supplying superheated steam to a turbine consisting of a high pressure cylinder, a medium pressure cylinder and a low pressure cylinder, then sent to a condenser followed by pumping condensate into a reactor steam generator, characterized in that in the boiler-superheater, the steam temperature is increased to 800-850 ° C, at which from the last stage Low pressure pulses receive saturated steam with a dryness of not less than 99% or slightly superheated steam with an overheating temperature of not more than 5 ° C.

Images