CN116282375A

CN116282375A - Waste heat recovery system based on supercritical carbon dioxide Brayton cycle

Info

Publication number: CN116282375A
Application number: CN202310179716.1A
Authority: CN
Inventors: 张怿; 沙浩; 包继雄; 冯晓华; 席勤琴; 张建东; 郑永峰; 韦巍
Original assignee: Huaneng Suzhou Thermal Power Co ltd
Current assignee: Huaneng Suzhou Thermal Power Co ltd
Priority date: 2023-02-28
Filing date: 2023-02-28
Publication date: 2023-06-23

Abstract

The invention discloses a waste heat recovery system based on supercritical carbon dioxide Brayton cycle, which comprises: the waste heat recovery unit is used for carrying out supercritical carbon dioxide Brayton cycle on the high-temperature high-pressure carbon dioxide, using electric energy generated by the supercritical carbon dioxide Brayton cycle for reverse osmosis separation of the seawater, and using low-temperature waste heat in the waste heat recovery unit for preheating the seawater; the reverse osmosis unit is used for performing reverse osmosis separation of seawater, so that electric energy generated by supercritical carbon dioxide circulation in the waste heat recovery unit is used for driving a reverse osmosis system, and meanwhile, low-temperature waste heat is used for preheating intake seawater of the reverse osmosis system, so that efficient utilization of the waste heat is realized, and the efficiency of the waste heat recovery system is improved.

Description

Waste heat recovery system based on supercritical carbon dioxide Brayton cycle

Technical Field

The application relates to the technical field of waste heat recovery, and more particularly relates to a waste heat recovery system based on supercritical carbon dioxide Brayton cycle.

Background

A gas turbine using natural gas as fuel is a high-efficiency and clean power generation system, but most of heat energy is discharged into the environment in the form of waste heat, so that the thermal efficiency of a single gas turbine is still limited, and the waste heat recovery of the gas turbine becomes an important means for improving the efficiency of the gas turbine.

The supercritical carbon dioxide is a carbon dioxide fluid with the temperature and the pressure above the critical value, and the supercritical carbon dioxide fluid is used as a heat energy cycle working medium and has the following advantages: (1) The critical density is 0.448g/m < 3 > close to liquid and is 2 orders of magnitude larger than gas, the heat transfer efficiency is high, and the functional capability is strong; (2) The viscosity is close to that of gas, and the viscosity is smaller than 2 orders of magnitude than that of liquid; the fluidity is strong, the diffusion is easy, and the system circulation loss is small; (3) The critical temperature and pressure are lower, so that the supercritical state is easy to be achieved, and engineering application is facilitated; (4) Compared with the common inert gas supercritical fluid, the supercritical fluid has the advantages of high density, good compressibility, compact system equipment structure and small volume; (5) less corrosive than water vapor; (6) Is nontoxic, incombustible, stable, free of damage to ozone layer, and low cost.

Carbon dioxide is used as a working medium for power circulation, and can transfer a large amount of energy in a small volume. The supercritical carbon dioxide cycle is used as a working medium for power generation, and has the characteristics of environmental friendliness, high thermal efficiency, good economical efficiency and the like. The brayton cycle is a typical thermodynamic cycle, which uses gas as a working medium, and realizes efficient energy conversion through four processes of adiabatic compression, isobaric heat absorption, adiabatic expansion and isobaric cooling. Compared with the traditional steam Rankine cycle, the Brayton cycle has higher cycle efficiency, and when the working medium is in a supercritical state, the cycle efficiency can be greatly improved due to the fact that the change of the phase state of the working medium is avoided, the consumption of compression work is reduced.

The reverse osmosis technology is the most widely applied technology because of simple layout and high efficiency, and the reverse osmosis desalination process is a high-energy consumption process and needs to consume a large amount of electricity.

Therefore, how to provide a waste heat recovery system based on supercritical carbon dioxide brayton cycle, to realize the combination of waste heat recovery and reverse osmosis, reduce energy loss, and realize the efficient utilization of energy is a technical problem to be solved at present.

Disclosure of Invention

The invention provides a waste heat recovery system based on supercritical carbon dioxide Brayton cycle, which is used for solving the technical problems of low waste heat recovery efficiency and high energy consumption in a reverse osmosis process in the prior art, and comprises the following components:

the waste heat recovery unit is used for carrying out supercritical carbon dioxide Brayton cycle on the high-temperature high-pressure carbon dioxide, using electric energy generated by the supercritical carbon dioxide Brayton cycle for reverse osmosis separation of the seawater, and using low-temperature waste heat in the waste heat recovery unit for preheating the seawater;

and the reverse osmosis unit is used for performing reverse osmosis separation of seawater.

In some embodiments of the present application, the waste heat recovery unit includes a turbine, a heat exchanger, a cooler, a compressor, a low temperature heater, and a high temperature heater.

In some embodiments of the present application, the reverse osmosis unit comprises a preheater, a high pressure pump, a reverse osmosis membrane, a water tank, and an energy recovery turbine.

In some embodiments of the present application, the turbine is connected to the high temperature heater and the heat exchanger, the heat exchanger is connected to the cooler and the high temperature heater, the cooler is connected to the compressor and the high pressure pump, the compressor is connected to the heat exchanger and the low temperature heater, and the low temperature heater is connected to the preheater and the high temperature heater.

In some embodiments of the present application, the high pressure pump is connected to the cooler, the reverse osmosis membrane, and the preheater, respectively, and the reverse osmosis membrane is connected to the water tank and the energy recovery turbine, respectively.

In some embodiments of the present application, the waste heat recovery unit is specifically configured to:

the high-temperature high-pressure carbon dioxide is expanded in the turbine to generate electricity and then is discharged into working fluid;

the working fluid flows into the heat exchanger and the cooler in sequence to release heat, and the working fluid after releasing heat flows into the compressor;

the compressor carries out high-pressure compression on the working fluid after heat release and generates high-pressure compression working media, wherein the high-pressure compression working media comprise a first path of compression working media and a second path of compression working media;

the first path of compressed working medium flows into the low-temperature heater and absorbs heat from the flue gas, and the second path of compressed working medium flows into the heat exchanger and absorbs heat of low-pressure carbon dioxide;

the first path of compressed working medium flowing out through the low-temperature heater and the second path of compressed working medium flowing out through the heat exchanger are mixed and then flow into the high-temperature heater together to absorb heat, and the supercritical carbon dioxide Brayton cycle is completed.

In some embodiments of the present application, the reverse osmosis unit is specifically configured to:

preheating seawater through a preheater and a cooler, and inputting the preheated seawater into a high-pressure pump;

the high-pressure pump is used for carrying out high-pressure treatment on the seawater, and the reverse osmosis separation is carried out on the seawater through a reverse osmosis membrane;

the water produced by reverse osmosis separation is conveyed to a water tank for storage, and the brine produced by reverse osmosis separation is discharged after passing through an energy recovery turbine.

In some embodiments of the present application, the cooler is a dual stage cooler, the cooler being specifically configured to;

the cooler receives seawater, cools carbon dioxide through the seawater and preheats the seawater through the carbon dioxide;

and discharging a predetermined volume of seawater through the cooler, and continuously preheating the rest of the seawater.

Through the application of the technical scheme, the waste heat recovery system comprises: the waste heat recovery unit is used for carrying out supercritical carbon dioxide Brayton cycle on the high-temperature high-pressure carbon dioxide, using electric energy generated by the supercritical carbon dioxide Brayton cycle for reverse osmosis separation of the seawater, and using low-temperature waste heat in the waste heat recovery unit for preheating the seawater; the reverse osmosis unit is used for performing reverse osmosis separation of seawater, so that electric energy generated by supercritical carbon dioxide circulation in the waste heat recovery unit is used for driving a reverse osmosis system, and meanwhile, low-temperature waste heat is used for preheating intake seawater of the reverse osmosis system, so that efficient utilization of the waste heat is realized, and the efficiency of the waste heat recovery system is improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 shows a schematic structural diagram of a waste heat recovery system based on supercritical carbon dioxide brayton cycle according to an embodiment of the present invention;

description of the reference numerals:

11. a turbine; 12. a heat exchanger; 13. a cooler; 14. a compressor; 15. a low temperature heater; 16. a high temperature heater; 17. a preheater; 18. a high pressure pump; 19. a reverse osmosis membrane; 20. a water tank; 21. an energy recovery turbine.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

In the description of the present application, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate description of the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present application.

The terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, unless otherwise indicated, the meaning of "a plurality" is two or more.

In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art in a specific context.

The embodiment of the application provides a waste heat recovery system based on supercritical carbon dioxide brayton cycle, as shown in fig. 1, the system includes:

As shown in fig. 1, in the scheme, waste heat recovery and reverse osmosis are combined with each other, and the waste heat recovery system of the scheme adopts two modes of electricity and heat to drive the reverse osmosis to produce fresh water. Typically, the high pressure pump of the reverse osmosis unit is electrically driven. And the performance of the reverse osmosis system increases with increasing operating temperature. The electric energy generated by the supercritical carbon dioxide Brayton cycle in the system is used for driving the reverse osmosis system, meanwhile, the low-temperature waste heat is used for preheating the inlet seawater of the reverse osmosis system, and the seawater enters the reverse osmosis system in two ways and is preheated by the waste heat of the supercritical carbon dioxide cycle and the low-temperature flue gas.

In addition, compared with water vapor, when the temperature is higher than 400 ℃, the supercritical carbon dioxide is used as a working medium with higher efficiency, and when the temperature reaches 550 ℃, the efficiency of converting the heat energy of the supercritical carbon dioxide power generation system into the output electric energy can reach 45 percent generally. Supercritical carbon dioxide does not require very high circulation temperatures to achieve the desired conversion efficiency. Meanwhile, supercritical carbon dioxide has stable chemical property, and compared with high-temperature and high-pressure steam, the supercritical carbon dioxide has slower erosion rate to metal pipeline equipment, so that the requirement on the material of pressure-bearing equipment is relatively lower. Meanwhile, the power generation system of the cogeneration system does not need a matched water treatment system, thereby saving a great deal of water resources, water treatment medicament consumption and the like. In addition, because the supercritical carbon dioxide has the physical characteristics of small viscosity and large density, the supercritical carbon dioxide has the typical advantages of good fluidity, high heat transfer efficiency, small compressibility and the like, so that the critical components such as a compressor, a turbine and the like of the system have small volume, compact structure and small occupied space.

To further illustrate the waste heat recovery unit, in some embodiments of the present application, the waste heat recovery unit includes a turbine, a heat exchanger, a cooler, a compressor, a low temperature heater, and a high temperature heater.

To further illustrate the reverse osmosis unit, in some embodiments of the present application, the reverse osmosis unit includes a preheater, a high pressure pump, a reverse osmosis membrane, a water tank, and an energy recovery turbine.

In order to ensure the normal operation of the waste heat recovery unit, in some embodiments of the present application, the turbine is connected to the high temperature heater and the heat exchanger, the heat exchanger is connected to the cooler and the high temperature heater, the cooler is connected to the compressor and the high pressure pump, the compressor is connected to the heat exchanger and the low temperature heater, and the low temperature heater is connected to the preheater and the high temperature heater.

The relation of all components in the waste heat recovery unit is shown in figure 1, the circulation sequence of the flue gas circulates according to the flow of g1-g2-g3-g4, and the process of the supercritical carbon dioxide Brayton cycle in the scheme is started by a turbine and circulates according to the arrow direction of the reference numerals 1-6 in figure 1.

To further illustrate the reverse osmosis unit, in some embodiments of the present application, the high pressure pump is connected to a chiller, a reverse osmosis membrane, and the preheater, respectively, and the reverse osmosis membrane is connected to the water tank and the energy recovery turbine, respectively.

In order to ensure the normal operation of the supercritical carbon dioxide brayton cycle, in some embodiments of the present application, the waste heat recovery unit is specifically configured to:

In this embodiment, high-temperature and high-pressure carbon dioxide expands in a turbine to generate electricity. The discharged working fluid then flows into the heat exchanger and the cooler in order to release heat. And then, the working fluid with heat released flows into a compressor, and the compressor compresses the working fluid with heat released at high pressure. The high-pressure compressed working medium is divided into two parts (a first path of compressed working medium and a second path of compressed working medium): the first path of compressed working medium flows into the low-temperature heater to absorb heat from the flue gas; the second path of compressed working medium enters the heat exchanger to absorb the heat of the low-pressure carbon dioxide. The first path of compressed working medium and the second path of compressed working medium are mixed at the 6 th point, and then heat is absorbed in a high-temperature heater to complete the supercritical carbon dioxide Brayton cycle.

In order to ensure proper operation of reverse osmosis of seawater, in some embodiments of the present application, the reverse osmosis unit is specifically configured to:

In this embodiment, as shown in fig. 1, reference numerals 01-07 denote operation flows of reverse osmosis work of seawater, the seawater is preheated by flue gas and carbon dioxide waste heat in the circulation, respectively, that is, sources of seawater include input from a preheater and input from a cooler, the seawater input from the preheater is preheated by the flue gas in the circulation, and the seawater input from the cooler is preheated by the carbon dioxide waste heat in the circulation. The preheated seawater is pumped to high pressure by a high-pressure pump and is subjected to reverse osmosis separation by a reverse osmosis membrane. The produced water is collected in a water tank and brine is discharged after passing through an energy recovery turbine.

In the embodiment, the reverse osmosis is driven to produce fresh water in two modes of electricity and heat. Typically, the high pressure pump of the reverse osmosis unit is electrically driven, and the performance of the reverse osmosis unit increases with increasing operating temperature. The electric energy generated by the supercritical carbon dioxide circulation in the system is used for driving the reverse osmosis unit, meanwhile, the low-temperature waste heat is used for preheating the inlet seawater of the reverse osmosis unit, the seawater enters the reverse osmosis system in two ways, and meanwhile, the seawater is preheated by the waste heat of the supercritical carbon dioxide circulation and the low-temperature flue gas, so that the carbon dioxide waste heat is fully utilized, and the energy loss is reduced.

In order to provide sufficient waste heat to the seawater, in some embodiments of the present application, the cooler is a dual stage cooler, particularly for use with;

In this embodiment, the cooler is a two-stage cooler in which feed seawater first flows into the cooler to cool the carbon dioxide. Then, a part of the seawater is directly discharged, and another part of the seawater is further preheated to a higher temperature. When the state point is far from the critical point, the heat capacity of the carbon dioxide is almost unchanged. However, as the state point gets closer to the critical point, the heat capacity increases rapidly. In contrast, the heat capacity of the cooling water is almost constant. If a conventional heat exchanger is used as the cooler, the heat exchange temperature difference may be small when the flow rate of the cooling water is small. On the other hand, when the flow rate of the cooling water is large, the outlet temperature of the seawater may not be able to be preheated to a given temperature, and in order to overcome this problem, a two-stage cooler is employed. By discharging a large portion of the feed seawater in the middle of the cooler, the average temperature difference of the cooler can be controlled within an acceptable range and the remaining portion of the seawater can be sufficiently preheated.

Therefore, a two-stage cooler is used to raise the carbon dioxide preheating temperature as much as possible. Due to the unique thermodynamic properties of carbon dioxide, the specific heat capacity of high pressure carbon dioxide is much higher than that of low pressure carbon dioxide as the operating temperature approaches the critical point. Thus, a portion of the carbon dioxide is fed to the low temperature heater to match the heat capacity of the recuperator. Obviously there is an optimum split ratio at which the heat capacities on both sides of the heat exchanger are exactly matched. If the split ratio is greater than the optimum, the carbon dioxide on the cold side of the heat exchanger cannot be sufficiently preheated. If the split ratio is less than the optimum value, the residual heat of carbon dioxide on the hot side of the heat exchanger cannot be completely recovered.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting thereof; although the present application has been described in detail with reference to the foregoing embodiments, one of ordinary skill in the art will appreciate that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not drive the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A waste heat recovery system based on a supercritical carbon dioxide brayton cycle, the system comprising:

2. The waste heat recovery system of claim 1, wherein the waste heat recovery unit comprises a turbine, a heat exchanger, a cooler, a compressor, a low temperature heater, and a high temperature heater.

3. The waste heat recovery system of claim 1, wherein the reverse osmosis unit comprises a preheater, a high pressure pump, a reverse osmosis membrane, a water tank, and an energy recovery turbine.

4. The waste heat recovery system as claimed in claim 2, wherein,

the turbine is respectively connected with the high-temperature heater and the heat exchanger, the heat exchanger is respectively connected with the cooler and the high-temperature heater, the cooler is respectively connected with the compressor and the high-pressure pump, the compressor is respectively connected with the heat exchanger and the low-temperature heater, and the low-temperature heater is respectively connected with the preheater and the high-temperature heater.

5. The waste heat recovery system as claimed in claim 3, wherein,

the high-pressure pump is respectively connected with the cooler, the reverse osmosis membrane and the preheater, and the reverse osmosis membrane is respectively connected with the water tank and the energy recovery turbine.

6. The waste heat recovery system of claim 1, wherein the waste heat recovery unit is specifically configured to:

7. The waste heat recovery system of claim 1, wherein the reverse osmosis unit is specifically configured to:

8. The waste heat recovery system of claim 7, wherein the cooler is a dual stage cooler, the cooler being specifically configured to;