Coal-fired power plant coupled with molten salt thermal storage and carbon capture system and method

Abstract

The application provides a coal-fired power generating unit coupled with a molten salt heat storage and carbon capture system, comprising a coal-fired unit, a molten salt heat storage system, a carbon capture system and a steam heat storage tank, the molten salt heat storage system comprising a hot molten salt tank, a cold molten salt tank and a heat exchanger, the heat exchanger being arranged between the hot molten salt tank and the cold molten salt tank; the steam heat storage tank is arranged between the molten salt heat storage system and the carbon capture system; in the heat storage process of the molten salt heat storage system, the reheated steam of the coal-fired unit exchanges heat with the molten salt in the cold molten salt tank, the steam after heat release enters the reboiler of the carbon capture system through the steam heat storage tank, and energy is provided for the regeneration of carbon dioxide; when the steam quantity exceeds the set value, the steam heat storage tank plays a role in buffering and controlling the steam flow, so that the steam quantity entering the reboiler is always within a reasonable range.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal-fired generating units, and relates to a coal-fired generating unit coupled with a molten salt heat storage and carbon capture system and a method. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] At present, renewable energy is developing rapidly, and the grid-connected power generation of large-scale renewable energy affects the stability of the power grid, and the power grid has further improved the flexibility requirements of coal-fired power plants. Molten salt heat storage is one of the effective methods for improving the flexibility of coal-fired power plants, and its working principle is as follows: when the power generation of the power plant is higher than the demand of the power grid, a part of high-temperature steam is extracted to heat the molten salt, the energy in the high-temperature steam is transferred to the molten salt, and then the power generation load of the power plant is reduced; when the power generation of the power plant is lower than the demand of the power grid, the heat stored in the molten salt is used for power generation of the coal-fired power plant.

[0004] In addition, while renewable energy is developing rapidly, clean utilization of fossil energy is still important, so it is of great significance to install a carbon dioxide capture system on a coal-fired unit. The principle of a conventional carbon capture system is as follows: the flue gas after desulfurization and denitrification is cooled and pressurized, then enters the absorption tower, the absorption liquid that has absorbed carbon dioxide is preheated and then enters the desorption tower, under certain temperature conditions, the absorption liquid and carbon dioxide are separated, and high-concentration carbon dioxide flows out from the top of the desorption tower and is compressed. The separated absorption liquid enters the absorption tower to complete the cycle.

[0005] The main energy consumption in the carbon capture system is the regeneration energy consumption in the desorption tower, and in the heat storage process of the molten salt heat storage system, because the melting point of the molten salt is high, the temperature of the cold molten salt after heat release by the high-temperature steam is still high, and if it is directly introduced into the condenser, energy will be wasted. SUMMARY

[0006] In order to solve the above problems, the present application proposes a coal-fired generating unit coupled with a molten salt heat storage and carbon capture system and a method, which couples the molten salt heat storage system and the carbon dioxide capture system, and more fully utilizes the energy in the heat storage system.

[0007] According to some embodiments, the present application adopts the following technical solutions:

[0008] A coal-fired generating unit coupled with a molten salt heat storage and carbon capture system, comprising a coal-fired unit, a molten salt heat storage system, a carbon capture system and a steam heat storage tank, wherein:

[0009] The molten salt heat storage system comprises a hot molten salt tank, a cold molten salt tank and a heat exchanger, the heat exchanger is arranged between the hot molten salt tank and the cold molten salt tank;

[0010] The molten salt heat storage system and the carbon capture system are provided with a steam heat storage tank;

[0011] In the heat storage process of the molten salt heat storage system, the reheated steam of the coal-fired unit exchanges heat with the molten salt in the cold molten salt tank, the steam after heat release passes through the steam heat storage tank and then enters the reboiler of the carbon capture system to provide energy for the regeneration of carbon dioxide;

[0012] When the steam quantity exceeds the set value, the steam heat storage tank plays a role in buffering and controlling the steam flow, so that the steam quantity entering the reboiler is always within a reasonable range.

[0013] As an alternative embodiment, a molten salt-feedwater heat exchanger is arranged on the pipeline through which the hot molten salt tank leads to the cold molten salt tank, and a molten salt-steam heat exchanger is arranged on the pipeline through which the cold molten salt tank leads to the hot molten salt tank.

[0014] As an alternative embodiment, the molten salt-steam heat exchanger and the reboiler of the carbon capture system are provided with the steam heat storage tank.

[0015] As an alternative embodiment, the condensed water at the outlet of the reboiler enters the deaerator.

[0016] As an alternative embodiment, the boiler of the coal-fired unit is connected to the molten salt-steam heat exchanger.

[0017] As an alternative embodiment, the boiler is connected to a high-pressure cylinder and a medium-pressure cylinder.

[0018] Further, the medium-pressure cylinder is connected to the reboiler.

[0019] Based on the working method of the coal-fired power generation unit, the following steps are included:

[0020] When load reduction operation is required, if the steam quantity flowing out of the molten salt-steam heat exchanger is insufficient to meet the energy consumption requirement of the reboiler of the carbon capture system, the steam extraction of the reheated steam flows out of the boiler and enters the molten salt-steam heat exchanger to exchange heat with the molten salt flowing out of the cold molten salt tank, the molten salt after heat absorption flows into the hot molten salt tank, the reheated steam after heat release passes through the steam heat storage tank and then enters the reboiler;

[0021] If the steam quantity flowing out of the molten salt-steam heat exchanger is greater than the energy consumption requirement of the reboiler of the carbon capture system, the steam heat storage tank stores the excess steam, the steam extraction from the medium-pressure cylinder for the reboiler is stopped, the reboiler is only powered by the steam flowing out of the molten salt-steam heat exchanger, and when the heat storage process is completed, the steam heat storage tank releases the steam for the reboiler.

[0022] As an alternative embodiment, when the load needs to be raised or the load is not changed, the heat of the molten salt flowing out of the hot molten salt tank is exchanged with the feed water flowing out of the feed water pump, the molten salt after heat release enters the cold molten salt tank, and the feed water after heat absorption enters the boiler.

[0023] Further, the regeneration energy consumption in the carbon capture system is only provided by the exhaust steam of the intermediate pressure cylinder.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] The application uses the steam energy after heat release in the molten salt-steam heat exchanger in the heat storage process to provide energy for the reboiler in the carbon capture system, so that the reheat steam energy for heat storage is fully utilized.

[0026] The application adds a steam heat storage tank between the molten salt heat storage system and the carbon capture system: when the steam flow from the molten salt-steam heat exchanger is too large, the steam heat storage tank can buffer and control the steam flow, so that the steam flow into the reboiler is always within a reasonable range.

[0027] In order to make the above-mentioned purposes, characteristics and advantages of the application more obvious and easy to understand, the following preferred embodiments are described in detail below, together with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings accompanying the specification of the application form part of the application and serve to provide a further understanding of the application. The exemplary embodiments of the application and their description serve to explain the application without constituting an inappropriate limitation thereof.

[0029] Figure 1 It is a system structure diagram of the application;

[0030] Wherein: 1 is a boiler, 2 is a high pressure cylinder, 3 is a medium pressure cylinder, 4, 5 is a low pressure cylinder, 6 is a condenser, 7, 8, 9, 10 is a low pressure heater, 11 is a deaerator, 12, 13, 14 is a high pressure heater, 15 is a small steam turbine, 16 is a hot molten salt tank, 17 is a cold molten salt tank, 18 is a molten salt-steam heat exchanger, 19 is a molten salt-feed water heat exchanger, 20, 21, 22 is a heat exchanger, 23 is an absorption tower, 24 is a rich liquid pump, 26 is a lean liquid pump, 27 is a stripping tower, 25, 28, 29, 30, 31, 32 is a heat exchanger, 33 is a fan, 34 is a generator, 35 is a condensate pump, 36 is a feed water pump, 37 is a reboiler, 38 is a steam heat storage tank. DETAILED DESCRIPTION

[0031] The application will be further described below in combination with the drawings and embodiments.

[0032] It should be noted that the following detailed description is illustrative only, and is intended to provide further description in order to provide a thorough understanding of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the application pertains.

[0033] It is also important to note that the terms used herein are not intended to limit the particular embodiments of the present application which can be practiced with the examples disclosed. As used herein, unless expressly stated to the contrary, all technical and scientific terms are intended to remainarly understood by one of ordinary skill in the art to which the application pertains. Furthermore, it is to be understood that the use of certain specific terms will not function to limit the scope of the application.

[0034] A coal-fired unit coupled with a molten salt thermal storage system and a carbon capture system, including a coal-fired unit, a hot molten salt tank, a cold molten salt tank, a heat exchanger, a steam thermal storage tank and a carbon capture system. In the thermal storage process of the molten salt thermal storage system, the reheated steam of the coal-fired unit exchanges heat with the molten salt in the cold molten salt tank, and the heat-released steam enters the reboiler of the carbon capture system to provide energy for the regeneration of carbon dioxide. The condensed water at the outlet of the reboiler enters the deaerator.

[0035] The heat-released steam is led to the reboiler in the carbon capture system, and a steam thermal storage tank is added between the molten salt-steam heat exchanger and the reboiler. The thermal storage tank can act as a buffer when the flow of heat-released steam is too large, so that the energy of the steam in the molten salt thermal storage process can be fully utilized.

[0036] Specifically, as shown in Figure 1 When the coal-fired power plant needs to operate at a reduced load:

[0037] i. The thermal storage time is long, and the amount of steam flowing out of the molten salt-steam heat exchanger 18 is insufficient to meet the energy consumption requirements of the reboiler of the carbon capture system. The extraction steam of the reheated steam flows out of the boiler 1 into the molten salt-steam heat exchanger 18, exchanges heat with the molten salt flowing out of the cold molten salt tank 17, and the heat-absorbed molten salt flows into the hot molten salt tank 16. The heat-released reheated steam still has a relatively high temperature, and if it is directly led into the condenser 6 to release heat, it will cause a large amount of steam loss. Therefore, it is led into the steam thermal storage tank 38, and then into the reboiler 37 to provide energy for the regeneration of carbon dioxide in the stripping column 27. After releasing heat, it becomes liquid water and finally enters the deaerator 11. Since the steam flowing into the reboiler in this case cannot meet the energy consumption requirements of the regeneration, steam is extracted from the exhaust steam of the intermediate pressure cylinder 3 and led into the reboiler 37 to provide energy for the reboiler 37 together with the steam flowing out of the steam thermal storage tank 38.

[0038] i. The heat storage time is short, and the steam quantity from the molten salt-steam heat exchanger is greater than the regeneration energy requirement of the carbon capture system reboiler. Unlike the working condition i, the steam quantity from the molten salt-steam heat exchanger 18 is greater than the steam requirement of the reboiler 37. In this case, the steam heat storage tank 38 will store the excess steam. At the same time, the steam extraction from the intermediate pressure cylinder 3 is stopped to supply energy to the reboiler, and the reboiler is only supplied with energy by the steam from the molten salt-steam heat exchanger 18. When the heat storage process is completed, the steam heat storage tank 38 releases the steam to supply energy to the reboiler 37. During the entire heat storage process, the steam heat storage tank 38 plays a buffering role, so that the energy of the steam from the molten salt-steam heat exchanger 18 is fully utilized.

[0039] When the coal-fired power plant needs to be operated at a higher load or is not operated at a variable load:

[0040] The hot molten salt from the hot molten salt tank 16 and the feed water from the feed water pump 36 are heat-exchanged in the molten salt-feed water heat exchanger 19, the heat-released molten salt enters the cold molten salt tank 17, and the heat-absorbed feed water enters the boiler 1. In this case, the regeneration energy of the carbon capture system is only provided by the exhaust steam of the intermediate pressure cylinder 3.

[0041] Other connection relationships can be obtained by using the prior art, and will not be described here.

[0042] In summary, the embodiment uses the steam energy released in the molten salt-steam heat exchanger during the heat storage process to supply energy to the reboiler in the carbon capture system, so that the reheated steam energy used for heat storage is fully utilized.

[0043] A steam heat storage tank is added between the molten salt heat storage system and the carbon capture system: when the steam quantity from the molten salt-steam heat exchanger is too large, the steam heat storage tank can play a role in buffering and controlling the steam flow, so that the steam quantity entering the reboiler is always within a reasonable range.

[0044] The above describes the specific embodiments of the application in conjunction with the accompanying drawings, but is not a limitation on the protection scope of the application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the application without creative labor are still within the protection scope of the application.

Claims

1. A coal-fired power plant coupled with a molten salt thermal storage and carbon capture system, characterized in that, The system comprises a coal-fired unit, a molten salt heat storage system, a carbon capture system and a steam storage tank, wherein: The molten salt heat storage system comprises a hot molten salt tank, a cold molten salt tank and a heat exchanger, and the heat exchanger is arranged between the hot molten salt tank and the cold molten salt tank; The steam storage tank is arranged between the molten salt heat storage system and the carbon capture system; the boiler of the coal-fired unit is connected to the molten salt-steam heat exchanger; the boiler is connected to a high-pressure cylinder and a medium-pressure cylinder; During the heat storage process of the molten salt heat storage system, the reheat steam of the coal-fired unit exchanges heat with the molten salt in the cold molten salt tank, the steam after heat release passes through the steam storage tank and then enters the reboiler of the carbon capture system to provide energy for the regeneration of carbon dioxide; When the steam quantity exceeds the set value, the steam storage tank functions as a buffer and controls the steam flow, so that the steam quantity entering the reboiler is always within a reasonable range, specifically: When the steam quantity flowing out of the molten salt-steam heat exchanger is greater than the steam quantity required by the reboiler, the steam storage tank stores the excess steam, stops the steam extraction from the medium-pressure cylinder for the energy supply of the reboiler, and the reboiler is only supplied with steam flowing out of the molten salt-steam heat exchanger; when the heat storage process ends, the steam storage tank releases the steam for the energy supply of the reboiler.

2. A coal-fired power plant coupled to a molten salt thermal storage and carbon capture system as claimed in claim 1, characterized in that, The molten salt-feedwater heat exchanger is arranged on the pipeline through which the hot molten salt tank is connected to the cold molten salt tank, and the molten salt-steam heat exchanger is arranged on the pipeline through which the cold molten salt tank is connected to the hot molten salt tank.

3. A coal-fired power plant coupled to a molten salt thermal storage and carbon capture system as claimed in claim 2, characterized in that, The steam storage tank is arranged between the molten salt-steam heat exchanger and the reboiler of the carbon capture system.

4. A coal-fired power plant coupled to a molten salt thermal energy storage and carbon capture system as claimed in claim 1, characterized by, The condensed water at the outlet of the reboiler enters the deaerator.

5. A coal-fired power plant coupled to a molten salt thermal energy storage and carbon capture system as claimed in claim 1, characterized in that, The medium-pressure cylinder is connected to the reboiler.

6. The method of operating a coal-fired power plant according to any one of claims 1-5, characterized in that, The system comprises the following steps: When load reduction is required, if the steam quantity flowing out of the molten salt-steam heat exchanger is insufficient to meet the energy consumption requirement of the reboiler of the carbon capture system, the steam extraction of the reheat steam flows out of the boiler and enters the molten salt-steam heat exchanger to exchange heat with the molten salt flowing out of the cold molten salt tank; the molten salt after heat absorption flows into the hot molten salt tank, and the reheat steam after heat release enters the steam storage tank and then enters the reboiler; If the steam quantity flowing out of the molten salt-steam heat exchanger is greater than the energy consumption requirement of the reboiler of the carbon capture system, the steam storage tank stores the excess steam, stops the steam extraction from the medium-pressure cylinder for the energy supply of the reboiler, and the reboiler is only supplied with steam flowing out of the molten salt-steam heat exchanger; when the heat storage process ends, the steam storage tank releases the steam for the energy supply of the reboiler.

7. The method of claim 6, wherein the step of operating comprises the step of: When load increase is required or no load variation is performed, the hot molten salt flowing out of the hot molten salt tank exchanges heat with the feedwater flowing out of the feedwater pump; the molten salt after heat release enters the cold molten salt tank, and the feedwater after heat absorption enters the boiler.

8. The method of claim 7, wherein the step of operating comprises the step of: The energy consumption of the regeneration of the carbon capture system is only provided by the exhaust steam of the medium-pressure cylinder.

Images