RU2787622C1 - Thermal power plant with a regeneration system and method of its operation - Google Patents

Abstract

FIELD: thermal power engineering.

SUBSTANCE: invention relates to thermal power engineering and can be used in circuits of thermal power plants, including small distributed energy. The thermal power plant with a regeneration system comprises a boiler unit, a superheated steam pipeline, a steam turbine, an exhaust steam pipeline, an absorber, a pipeline, a feed pump and a regenerative heat exchanger connected in series. At the same time, the steam of the working fluid exhausted after the steam turbine enters the absorber and is absorbed in the solvent, while the absorption temperature is controlled by supplying the coolant to the absorber cooling circuit, and the resulting strong solution, with a high concentration of the working fluid, enters the pump, where its pressure rises and it enters the regenerative heat exchanger, heated by a weak solution with a low concentration of the working fluid coming from the boiler. In turn, after the heat exchanger, a strong solution enters the boiler unit, with its heating and evaporation of the working fluid from it, and the solvent, which has a high boiling point, remains in a liquid state and from the boiler unit under high pressure enters the regenerative heat exchanger, with heat transfer strong solution and then through the pressure reduction unit returns to the absorber to absorb the exhaust steam. A method for operating a thermal power plant with a regeneration system is also presented.

EFFECT: increasing the energy efficiency of thermal power plants by replacing steam condensation with its absorption using a solution heat recovery system in a cycle.

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Description

The invention relates to thermal power engineering and can be used in circuits of thermal power plants, including small distributed power generation.

Thermal power plants are known in which thermal energy (obtained most often as a result of burning fossil fuels) is transferred to the working fluid and converted into work in order to generate electrical energy (condensing power plants) or thermal and electrical energy (thermal power plants). Thermal power plants using a similar principle operate according to the Rankine thermodynamic cycle [Ryzhkin V.Ya. Thermal power stations: Textbook for thermal power. specialist. universities. - M.-L.: Energy, 1967. - 26 p.]. A schematic diagram of a thermal power plant operating on the Rankine cycle includes a steam turbine connected to an electric generator and a condenser, the condenser is connected in series with a feed pump and a boiler unit.

These power plants are widely used in the energy sector to generate electrical and thermal energy, but they have a number of disadvantages:

- large heat losses (about 40-60% of the total heat received in the boiler as a result of fuel combustion), most of which are observed in the steam turbine condenser, where the steam exhausted after the turbine is cooled by cold water;

– significant emissions of harmful substances into the atmosphere caused by excessive fuel consumption due to significant heat losses;

- significant consumption of water from natural sources for cooling the condenser, thermal pollution of the hydrosphere;

- a significant decrease in energy efficiency with a decrease in the initial and increase in the final steam parameters, which limits the use in small-scale power generation.

The prototype of the thermal power plant device is the device of a thermal power plant described in the patent "Thermal power plant and its method of operation" patent
RU 2759583 C1, F01K 25/08 (2006.01), F25B 15/00 (2006.01). Publication: 11/15/2021.

The main elements of this power plant, operating on the Rankine cycle using the absorption principle, are a boiler unit, a steam turbine, a feed pump that form a vapor-liquid path, as well as an electric generator connected to the steam turbine, an absorber with an absorbent return circuit. A steam generator is built into the boiler, the absorber is connected to the steam generator through a feed pump, the steam generator is connected to the absorber through an absorbent cooler and a pressure reducing device, the expansion valve is connected to the absorber.

The disadvantages of the prototype described in this patent are:

- the use of a separate apparatus for cooling the absorbent (absorbent cooler), which increases the metal intensity of the power plant and reduces its reliability;

– decrease in the accuracy of temperature and absorption pressure control due to the presence of an expansion valve and a pipeline section between the absorber and the absorbent cooler;

– high probability of the solution boiling up after the throttling process in the expansion valve, which impairs the absorption process.

Known technology of operation of a thermal power plant operating on the thermodynamic Rankine cycle [Ryzhkin V.Ya. Thermal power stations: Textbook for thermal power. specialist. universities. - M.-L.: Energy, 1967. - 26 p.], in which thermal energy is converted into work in order to generate electrical (in some cases also thermal) energy.

In the boiler unit, as a result of burning fossil fuels, thermal energy is transferred to the heating surfaces, through which the working fluid (most often water) circulates. As a result of flowing through the pipes of the boiler unit, the working fluid perceives the received heat, heats up and evaporates. The steam of the working fluid is sent to the steam turbine, where the energy of steam expansion is converted into mechanical work of rotation of the turbine rotor. The mechanical work of the turbine rotor is transferred to the rotor of the electric generator, in the stator windings of which electrical energy is generated. After expansion in the steam turbine, the steam is sent to the condenser where it must be condensed. Steam condensation is achieved by cooling the steam with cold water. The resulting condensate is then sent by a feed pump to the boiler for reuse. The cycle closes.

To increase the energy efficiency, reheating of steam (due to increasing the steam parameters before the turbine) or regenerative steam extractions (due to increasing the average heat supply temperature in the cycle) can be used.

The disadvantages of operating technologies for power plants operating on the Rankine cycle are:

- large heat losses (about 40-60% of the total heat received in the boiler as a result of fuel combustion), most of which are observed in the steam turbine condenser, where the steam exhausted after the turbine is cooled by cold water;

– significant emissions of harmful substances into the atmosphere caused by excessive fuel consumption due to significant heat losses;

- significant consumption of water from natural sources for cooling the condenser, thermal pollution of the hydrosphere;

- reduction in the generation of electrical energy when using regenerative extractions;

- a significant decrease in energy efficiency with a decrease in the initial and increase in the final steam parameters, which limits the use in small-scale power generation.

The technology prototype is the method of operation of the energy system described in the patent "Thermal power plant and the method of its operation" patent RU 2759583 C1, F01K 25/08 (2006.01), F25B 15/00 (2006.01). Publication: 11/15/2021.

The steam exhausted after the steam turbine, which still has a sufficiently high potential, enters the absorber, in which the absorbent is located. When two media interact - the absorbent in the absorber and the exhaust steam coming from the steam turbine, the steam is absorbed by the absorber and the resulting solution - a weak solution is pumped by the feed pump to the boiler unit. Fuel is supplied to the boiler unit with a built-in steam generator as a result of its combustion, heat is generated, which is transferred to the steam generator. As a result of the heat supply to the steam generator, the solution is separated into a working fluid and an absorbent. The working fluid is sent for further superheating of the steam in the boiler unit and to the steam turbine to perform useful work and generate electrical energy by an electric generator. The absorbent, which has a higher evaporation temperature than the working fluid, is sent through the absorbent return circuit (“strong solution”) through the absorbent cooler and expansion valve to the absorber. In the absorbent cooler, the temperature of the absorbent is reduced, and in the expansion valve, the pressure of the absorbent is reduced. After the “strong solution” enters the absorber, the cycle closes.

The disadvantages of the prototype described in this patent are:

- the use of a separate apparatus for cooling the absorbent (absorbent cooler), which increases the metal consumption and reduces the reliability of operation;

– decrease in the accuracy of temperature and absorption pressure control due to the presence of an expansion valve and a pipeline section between the absorber and the absorbent cooler;

– high probability of the solution boiling up after throttling in the expansion valve, which impairs the absorption process.

A significant part of large thermal power plants operate on the Rankine cycle on water vapor. Despite a number of advantages that are characteristic of thermal power plants, which have become the reason for their widespread use in the world, they are characterized by a number of significant drawbacks that still remain unresolved today. The most characteristic negative aspects of the use of the Rankine cycle are a large need for technical water supply for cooling condensers, metal consumption of units, a significant negative impact on the atmosphere and hydrosphere, and high fuel consumption. At the same time, the root cause of most of the shortcomings can be considered low energy efficiency - even large modern thermal power plants have an efficiency of 35-40%. Thus, about half of all thermal energy received in the boiler unit as a result of fossil fuel combustion. is simply lost. It is low efficiency that causes high fuel consumption and, as a result, a significant burden on the environment due to a large amount of harmful emissions into the atmosphere, as well as a significant impact on the hydrosphere. With a decrease in steam parameters, the efficiency of the installation also decreases. For this reason, low-power steam turbine plants have not gained wide distribution.

The solution presented in the prototype described in the patent RU No. 2759583 C1 allows to reduce heat losses at thermal power plants, reduce fuel consumption and emissions into the environment. However, the prototype has a number of disadvantages that may affect the energy efficiency and performance of the station.

The developers were faced with the task of increasing energy efficiency by modernizing the heat and power cycle.

The technical result consists in increasing the energy efficiency of thermal power plants by replacing steam condensation with its absorption using a solution heat recovery system in a cycle.

The technical result of the invention in terms of the device is achieved by the fact that a thermal power plant with a regeneration system contains: a boiler unit connected in series with a steam turbine, an absorber, a feed pump, as well as an electric generator connected to the steam turbine, a steam generator is built into the boiler unit, the absorber is connected to the boiler unit through a feed pump , the steam generator is connected to the absorber through the absorbent return circuit and the pressure reducing device, and the boiler unit is connected to the steam turbine by a superheated steam line, the absorber is connected to the steam turbine by means of an exhaust steam line, the feed pump is connected to the boiler unit through a pipeline and a regenerative heat exchanger, the boiler unit is connected to the absorber through the absorbent return circuit, the regenerative heat exchanger and the pressure reducing device in the form of a reduction unit, the absorber cooling circuit is located in the absorber.

The technical result of the invention in terms of the method of operation is achieved by the fact that the method of operation of a thermal power plant with a regeneration system, which consists in supplying and evaporating the working fluid in the boiler and supplying steam from the working fluid to the steam turbine, with its rotation and with the conversion of the expansion energy of the steam of the working fluid into mechanical, with the transfer of mechanical energy to an electrical generator and the generation of electrical energy, the exhaust steam from the steam turbine enters the absorber containing the solvent of the working fluid, which absorbs the vapor of the working fluid and forms a solution with a high concentration of the working fluid, the resulting solution is pumped by a feed pump to the steam generator, heated solution with separation into the solvent of the working fluid - a weak solution and steam of the working fluid, from the boiler steam of the working fluid enters the steam turbine, and the solvent of the working fluid enters the absorbent return circuit through the pressure reducing device into the absorber, and the working fluid steam body from the boiler unit enters the steam turbine through the superheated steam pipeline, the working fluid steam exhausted after the steam turbine through the exhaust steam pipeline enters the absorber containing the solvent with an admixture of the working fluid, and the working fluid and the solvent are mixed with an admixture of the working fluid, with the formation of a strong solution with a high concentration of the working fluid, which enters the regenerative heat exchanger through the pipeline through the feed pump, and is heated by the heat of a weak solution with a low concentration of the working fluid, which comes from the steam generator through the absorbent return circuit to the pressure reducing unit, where it is throttled to the pressure in the absorber and enters it to absorb the vapor of the working fluid, the absorption temperature is controlled by supplying the coolant.

In FIG. 1 is a diagram of a thermal power plant illustrating the operation of a power plant with a solution recovery system.

A thermal power plant with a regeneration system comprises: a boiler unit 1 connected in series, a superheated steam pipeline 2, a steam turbine 3, an exhaust steam pipeline 13, an absorber 4, a pipeline 5, a feed pump 6 and a regenerative heat exchanger 7, as well as an electric generator 8 connected to the steam turbine 3, the absorber has a built-in cooling circuit of the absorber 9, the steam generator 10 is built into the boiler, the absorber 4 is connected to the boiler unit 1 through the pipeline 5, the feed pump 6 and the regenerative heat exchanger 7, the steam generator 8 through the return circuit of the absorbent 11, the regenerative heat exchanger 7 and the pressure reducing device reduction unit 12 is connected to the absorber 4.

An example of a specific implementation of the method, consider the example of the operation of a thermal power plant. The principle of operation of a thermal power plant with a regeneration system is as follows.

The working fluid steam exhausted after the steam turbine 3, which may contain a small concentration of the working fluid solvent and still has a sufficiently high potential, enters the absorber 4 through the exhaust steam line 13, which contains the working fluid solvent (which may contain a small concentration of the working fluid) ( not indicated in Fig.). When two media interact - the solvent of the working fluid located in the absorber and the steam of the working fluid coming from the steam turbine, the latter is absorbed by the solvent of the working fluid and the resulting solution, which has a high concentration of the working fluid - a strong solution, is pumped through the pipeline 5 by the feed pump 6 to the regenerative heat exchanger 7 The absorption temperature is controlled by supplying the coolant flow required for the effective absorption process (not shown in the figure) to the absorbent cooling circuit 9 built into the absorber 4. In the regenerative heat exchanger 7, a solution having a high concentration of the working fluid is a strong solution, when the regenerative heat exchanger is heated by the heat of the solution having a low concentration of the working fluid - a weak solution coming from the steam generator 10 through the return circuit of the absorbent 11 to the reducing unit 12. After the regenerative heat exchanger 7 the solution having a high concentration p of the working body - a strong solution is sent through the pipeline 5 to the boiler unit 1 and the steam generator 10. Waste heat is supplied to the boiler unit 1 or fuel is burned, as a result of which the solution that enters the steam generator 10, which has a high concentration of the working fluid - a strong solution, is heated from it the working fluid is evaporated. The steam of the working fluid (which may contain a small concentration of the solvent of the working fluid) is sent to the heating surfaces of the boiler unit 1, where it overheats and reaches the parameters required for the operation of the steam turbine 3, provided for by the power and purpose of the power plant. Further, through the superheated steam pipeline 2, the steam of the working fluid is sent to the steam turbine 3 to rotate the latter by converting the expansion energy of the steam of the working fluid into mechanical energy of rotation of the rotor of the electric generator and generating electrical energy. The solution remaining in the steam generator 10, which has a low concentration of the working fluid - a weak solution (not indicated in the figure), under the action of high pressure, is sent through the return circuit of the absorbent 11 to the regenerative heat exchanger 7, where it gives off heat to the strong solution. After the regenerative heat exchanger 7, the solution, which has a low concentration of the working fluid - a weak solution, is sent to the reduction unit 12, where it is throttled to the pressure in the absorber 4 and enters it. The cycle closes.

The advantage of the proposed invention over the prototype is the presence of a regeneration system that reduces fuel consumption and harmful emissions into the environment (when fuel is burned). This is achieved by regenerating the heat of the weak solution coming after the steam generator and transferring this heat to the strong solution coming from the absorber. Regeneration takes place in a regenerative heat exchanger in absorption heat pumps, this heat exchanger is called a solution heat exchanger - RTO-R.

In addition to fuel reduction, the use of a regenerative heat exchanger makes it possible to increase the efficiency of the absorption process. If there is no regenerative heat exchanger, then a weak solution with high temperature and pressure leaves the generator, which is then throttled in the reducing plant to low pressure. As a result of a sharp decrease in pressure at an almost constant temperature, a weak solution boils up and partially separates the saturated liquid and wet vapor. The steam released during throttling is called flash gas in technology. In this case, only a part of the weak solution, which is in the liquid state, can participate in the absorption process. Thus, in order for the wet steam released during throttling to start absorbing the steam of the working fluid after the turbine, it must first be condensed. In this case, the flow rate of the cooling heat carrier will be the sum of the flow rate required to remove the heat of absorption and the flow rate that ensures the condensation of wet steam. This increases the flow of coolant and reduces the efficiency of the cycle. Therefore, in absorption cycles, care is taken to avoid boiling the weak solution upstream of the expansion device, and this is most commonly done by placing a regenerative heat exchanger upstream of the expansion device.

Also, instead of the absorbent cooler, a cooling circuit is used, built directly into the absorber. This eliminates the section of pipeline with an expansion valve between the cooler and the absorber, which has a certain inertia. By moving the refrigeration circuit directly to the absorber, the absorption temperature and pressure can be more precisely controlled (for example, under variable heat load conditions).

Due to the use of low-boiling working substances, it is possible to generate electrical and thermal energy not only from fuel combustion, but also through the utilization of waste heat from enterprises or power plants (GTP or CCGT).

A wide range of selection of a pair of "working body-absorbent" is possible, including both two- and three-component mixtures can be used. To date, a significant number of working substances are known that are used in the energy sector, including for generation (for example, as part of the organic Rankine cycle). Substances that can be used in the proposed technical solution can be water, carbon dioxide, hydrocarbons (alkanes, arenes), ammonia and its derivatives, solutions of salts or alcohols, organosilicon compounds, fluorine- and chlorine-containing substances (freons). By changing the working substances used in the cycle, it is possible to vary not only the efficiency and operating conditions of the cycle, but also the scope of its application.

The presented method of operation allows various parameters of the working fluid, that is, it can be used both in the cycles of large generation facilities and in small power facilities.

Claims (2)

1. Thermal power plant with a regeneration system, containing a boiler unit connected in series with a steam turbine, an absorber, a feed pump, as well as an electric generator connected to the steam turbine, a steam generator is built into the boiler unit, the absorber is connected to the boiler unit through a feed pump, the steam generator through the absorbent return circuit and the pressure reducing device is connected to the absorber, characterized in that the boiler unit is connected to the steam turbine by a superheated steam line, the absorber is connected to the steam turbine by means of an exhaust steam line, the feed pump is connected to the boiler unit through a pipeline and a regenerative heat exchanger, the boiler unit is connected to the absorber through an absorbent return circuit, a regenerative heat exchanger and a pressure reducing device in the form of a reduction unit, the absorber cooling circuit is located in the absorber. 2. The method of operation of a thermal power plant with a regeneration system, which consists in supplying and evaporating the working fluid in the boiler unit and supplying the steam of the working fluid to the steam turbine, with its rotation and converting the expansion energy of the steam of the working fluid into mechanical energy, with the transfer of mechanical energy to an electric generator and the generation of electric energy, the exhaust steam from the steam turbine enters the absorber containing the solvent of the working fluid, which absorbs the vapor of the working fluid and forms a solution with a high concentration of the working fluid, the resulting solution is pumped by a feed pump to the steam generator, the solution is heated with separation into the solvent of the working fluid - a weak solution and steam of the working fluid, from the boiler steam of the working fluid enters the steam turbine, and the solvent of the working fluid enters through the return circuit of the absorbent through the pressure reducing device into the absorber, characterized in that the steam of the working fluid from the boiler into the steam turbine enters through the steam pipeline superheated steam exhausted after the steam turbine, the steam of the working fluid through the steam line of the exhaust steam enters the absorber containing the solvent with an admixture of the working fluid, and the working fluid and the solvent are mixed with the admixture of the working fluid, with the formation of a strong solution with a high concentration of the working fluid, which pipeline through the feed pump enters the regenerative heat exchanger and is heated by the heat of a weak solution with a low concentration of the working fluid, which comes from the steam generator through the absorbent return circuit to the reduction unit, where it is throttled to the pressure in the absorber and enters it to absorb the vapor of the working fluid , regulation of the absorption temperature is carried out by supplying a coolant.

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