A dual-fluid combined cycle power generation system and method

Abstract

The present invention discloses a dual-working fluid combined cycle power generation system and method, the system includes a heat source, a turbine, a high-temperature regenerator, a medium-temperature regenerator, a medium-temperature gas-liquid separator, a recompressor, a low-temperature regenerator, a low-temperature gas-liquid separator, a precooler, a main compressor and a liquid pump. In the system, a mixture of H2O and C2O is used as a working fluid, the working fluid is in a supercritical mixed state at the high-temperature part, and part of H2O is separated from CO2 at the low-temperature part. CO2 is compressed and pressurized by a recompressor and a main compressor, and H2O is pressurized by a liquid pump. Since CO2 and H2O are separated at the low-temperature end, the system avoids the limitation of supercritical mixture parameters, and the temperature and pressure application range is greatly increased. At the same time, the phenomenon of liquid carrying during gas compression and vaporization during liquid compression is avoided. The safety and stability of the equipment are improved.

Description

Technical Field

[0001] The invention relates to a power generation system, and in particular to a dual-fluid combined cycle power generation system and method. Background Art

[0002] Under the background of energy shortage and environmental crisis, people pay more and more attention to improving energy utilization. Among many thermodynamic cycles, supercritical Brayton cycle is the most advantageous cycle. New supercritical working fluids (carbon dioxide, helium and nitrous oxide, etc.) have inherent advantages such as high energy density, high heat transfer efficiency and simple system. They can greatly improve the heat-to-work conversion efficiency, reduce the size of equipment and have high economy.

[0003] However, this type of cycle also has an obvious technical difficulty, namely the cooling problem. The supercritical cycle, especially the supercritical cycle like carbon dioxide, has a critical temperature close to the ambient temperature (31°C). When the cold end temperature is low, the compression power consumption is small and the thermal efficiency is very high. However, it is very sensitive to the cold end temperature. After slightly exceeding the designed cold end temperature, its thermal efficiency will drop significantly. Therefore, its cold end temperature, that is, the compressor inlet temperature, must be controlled very accurately. However, when summer comes, it is difficult to cool to the required cold end temperature in a large area of ​​China, which will greatly affect its efficiency and thus affect the promotion of this technology.

[0004] This problem can be solved by mixing working fluids. When other working fluids, such as H2O, are added to CO2, the critical point of the mixture will change. The addition of some working fluids, such as H2O, will increase the critical point of the mixture, which means that at a high pressure of 31°C, the mixture can be cooled to a liquid state. In this way, even in the summer when the ambient temperature is high, the mixture can be cooled to a liquid state, and the compression power consumption can be controlled to a smaller level.

[0005] However, CO2 mixtures also encounter some problems. For example, adding H2O to CO2 can adjust the physical properties of the mixture very well. However, due to the large difference in the physical properties of the two substances, the mixture is more likely to separate, especially in the parts of the system where throttling or mutation occurs, such as filters, valves, tank inlets and outlets, etc. In addition, to maintain a supercritical mixed state, the ratio of the two substances must be relatively precise, and there are great restrictions on the setting of system parameters, otherwise it will affect the mixing state and physical properties. This greatly limits the practical application of the mixture cycle.

[0006] If there is a system that can realize a mixture state in some parts and two single-phase working fluid states in other parts, and ensure the normal operation of important equipment such as compressors and pumps without cavitation, liquid hammer and other phenomena, the application range of the system can be greatly improved. The present invention is proposed to solve this problem. Summary of the invention

[0007] The purpose of the present invention is to solve the problem of cold end heat dissipation of a supercritical Brayton cycle power generation system in summer, and proposes a dual-fluid combined cycle power generation system and method, which adopts a method with relatively low technical difficulty and high feasibility to improve the thermal efficiency of the system.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme:

[0009] A dual-working medium combined cycle power generation system, comprising a heat source 1, wherein the outlet of the heat source 1 is connected to the inlet of a turbine 2, the outlet of the turbine 2 is connected to the hot side inlet of a high-temperature regenerator 3, the hot side outlet of the high-temperature regenerator 3 is connected to the hot side inlet of a medium-temperature regenerator 4, the hot side outlet of the medium-temperature regenerator 4 is connected to the middle inlet of a medium-temperature gas-liquid separator 5, the top outlet of the medium-temperature gas-liquid separator 5 is connected to the inlet of a recompressor 6, the bottom outlet of the medium-temperature gas-liquid separator 5 is connected to the hot side inlet of a low-temperature regenerator 7, and the low-temperature regenerator 7 The hot side outlet of the low-temperature gas-liquid separator 8 is connected with the middle inlet of the low-temperature gas-liquid separator 8, the top outlet of the low-temperature gas-liquid separator 8 is connected with the hot side inlet of the precooler 9, the hot side outlet of the precooler 9 is connected with the inlet of the main compressor 10, the outlet of the main compressor 10 is connected with the cold side inlet of the low-temperature regenerator 7, the bottom outlet of the low-temperature gas-liquid separator 8 is connected with the inlet of the liquid pump 11, the outlet of the liquid pump 11 is connected with the cold side outlet of the low-temperature regenerator 7 and then connected with the cold side inlet of the medium-temperature regenerator 4, the cold side outlet of the medium-temperature regenerator 4 is connected with the outlet of the re-compressor 6 and then connected with the cold side inlet of the high-temperature regenerator 3, and the cold side outlet of the high-temperature regenerator 3 is connected with the inlet of the heat source 1.

[0010] The pressure in the medium-temperature gas-liquid separator 5 and the low-temperature gas-liquid separator 8 is 7.2MPa-7.6MPa, the temperature of the medium-temperature gas-liquid separator 5 is 130°C-170°C, and the temperature of the low-temperature gas-liquid separator 8 is 65°C-85°C.

[0011] The ratio of the tank diameter to the inlet pipe diameter of the medium-temperature gas-liquid separator 5 and the low-temperature gas-liquid separator 8 is greater than 10, and the ratio of the effective volume height of the tank to the tank diameter is greater than 1.

[0012] The working method of the dual-medium combined cycle power generation system is as follows: the supercritical mixed working medium of CO2 and H2O in a mixed state is heated in a heat source 1, and then enters a turbine 2 to perform work. After the pressure is reduced, it is still in a supercritical state, and then enters the hot side of a high-temperature regenerator 3 and the hot side of a medium-temperature regenerator 4 in turn to release heat. As the working medium temperature decreases, part of the H2O in the mixture can be separated, and the mixed working medium is separated in a medium-temperature gas-liquid separator 5. The CO2 flows out from the top outlet and enters the re-compressor 6 to be pressurized. The gas-liquid mixture flows out from the bottom of the medium-temperature gas-liquid separator 5 and enters the hot side of the low-temperature regenerator 7 to continue to release heat. In the low-temperature regenerator 7, most of the H2O is cooled to liquid and enters the low-temperature gas-liquid separator 8 to be separated again. CO2 flows out from the top of the low-temperature gas-liquid separator 8, enters the pre-cooler 9 to be further cooled, and then is pressurized in the main compressor 10, and then enters the cold side of the low-temperature regenerator 7 to absorb heat. The H2O flowing out from the bottom of the low-temperature gas-liquid separator 8 enters the liquid pump 11, and after being pressurized by the liquid pump 11, it is mixed with the CO2 at the cold side outlet of the low-temperature regenerator 7 and enters the cold side of the medium-temperature regenerator 4 to continue to absorb heat. The two working fluids absorb heat in the medium-temperature regenerator 4 and are mixed into a supercritical mixed working fluid, and then merge with the outlet working fluid of the re-compressor 6 and enter the high-temperature regenerator 3 and the heat source 1 in turn to continue to absorb heat, completing the whole cycle.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The dual-working fluid combined cycle power generation system adopts a mixture of H2O and CO2 as the working fluid. The working fluid is in a supercritical mixed state at the high temperature part, and part of H2O is separated from CO2 at the low temperature part. CO2 is compressed and pressurized by a compressor, and H2O is pressurized by a water pump. Since CO2 and H2O are separated at the low temperature end, the system avoids the limitation of supercritical mixture parameters, and the temperature and pressure application range is greatly increased. At the same time, the phenomenon of liquid carrying during gas compression and vaporization during liquid compression is avoided. The safety and stability of the equipment are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of the system of the present invention.

[0016] Among them, there are heat source 1, turbine 2, high-temperature regenerator 3, medium-temperature regenerator 4, medium-temperature gas-liquid separator 5, re-compressor 6, low-temperature regenerator 7, low-temperature gas-liquid separator 8, precooler 9, main compressor 10, and liquid pump 11. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0018] like Figure 1As shown, the dual-fluid combined cycle power generation system described in the present invention includes a heat source 1, a turbine 2, a high-temperature regenerator 3, a medium-temperature regenerator 4, a medium-temperature gas-liquid separator 5, a re-compressor 6, a low-temperature regenerator 7, a low-temperature gas-liquid separator 8, a precooler 9, a main compressor 10 and a liquid pump 11.

[0019] The outlet of the heat source 1 is connected to the inlet of the turbine 2, the outlet of the turbine 2 is connected to the hot side inlet of the high-temperature regenerator 3, the hot side outlet of the high-temperature regenerator 3 is connected to the hot side inlet of the medium-temperature regenerator 4, the hot side outlet of the medium-temperature regenerator 4 is connected to the middle inlet of the medium-temperature gas-liquid separator 5, the top outlet of the medium-temperature gas-liquid separator 5 is connected to the inlet of the recompressor 6, the bottom outlet of the medium-temperature gas-liquid separator 5 is connected to the hot side inlet of the low-temperature regenerator 7, the hot side outlet of the low-temperature regenerator 7 is connected to the middle inlet of the low-temperature gas-liquid separator 8, the top outlet of the low-temperature gas-liquid separator 8 is connected to the hot side inlet of the precooler 9, and the precooler 9 The hot side outlet is connected with the inlet of the main compressor 10, the outlet of the main compressor 10 is connected with the cold side inlet of the low-temperature regenerator 7, the bottom outlet of the low-temperature gas-liquid separator 8 is connected with the inlet of the liquid pump 11, the outlet of the liquid pump 11 is connected with the cold side outlet of the low-temperature regenerator 7 and then connected with the cold side inlet of the medium-temperature regenerator 4, the cold side outlet of the medium-temperature regenerator 4 is connected with the outlet of the re-compressor 6 and then connected with the cold side inlet of the high-temperature regenerator 3, and the cold side outlet of the high-temperature regenerator 3 is connected with the inlet of the heat source 1.

[0020] As a preferred embodiment of the present invention, the pressure in the medium-temperature gas-liquid separator 5 and the low-temperature gas-liquid separator 8 is 7.2MPa-7.6MPa. Within this pressure range, the low-temperature liquid can be kept liquid, the low-temperature CO2 is close to the critical point, and the compression work is minimum; the temperature of the medium-temperature gas-liquid separator 5 is 130°C-170°C, and the temperature of the low-temperature gas-liquid separator 8 is 65°C-85°C. Within this temperature range, the outlet temperature of the liquid pump (11) can be guaranteed to match the outlet temperature of the low-temperature regenerator (7), and the system efficiency is optimal.

[0021] As a preferred embodiment of the present invention, the ratio of the tank diameter of the medium-temperature gas-liquid separator 5 and the low-temperature gas-liquid separator 8 to the inlet pipe diameter is greater than 10, and the ratio of the effective volume height of the tank to the tank diameter is greater than 1. Under this size ratio, the mixture can produce an obvious sudden expansion effect at the tank inlet, which is beneficial to gas-liquid separation.

[0022] The specific working process of the system of the present invention is:

[0023] The supercritical mixed working medium of CO2 and H2O in a mixed state is heated in the heat source 1, and then enters the turbine 2 to do work. After the pressure is reduced, the temperature of the mixed working medium is still relatively high and is still in a supercritical state. Then, it enters the hot side of the high-temperature regenerator 3 and the hot side of the medium-temperature regenerator 4 in turn to release heat. As the working medium temperature decreases, part of the H2O in the mixture can be separated. The mixed working medium is separated in the medium-temperature gas-liquid separator 5, and CO2 flows out from the top outlet and enters the recompressor 6 to be pressurized. The gas-liquid mixture flows out from the bottom of the medium-temperature gas-liquid separator 5 and enters the hot side of the low-temperature regenerator 7 to continue to release heat. In the low-temperature regenerator 7, most of the H2O is cooled to Liquid, enters the low-temperature gas-liquid separator 8 and is separated again. CO2 flows out from the top of the low-temperature gas-liquid separator 8, enters the precooler 9 to be further cooled, and then is pressurized in the main compressor 10, and then enters the cold side of the low-temperature regenerator 7 to absorb heat. The H2O flowing out from the bottom of the low-temperature gas-liquid separator 8 enters the liquid pump 11, is pressurized by the liquid pump 11, and is mixed with the CO2 at the cold side outlet of the low-temperature regenerator 7 and enters the cold side of the medium-temperature regenerator 4 to continue absorbing heat. The two working fluids absorb heat in the medium-temperature regenerator 4 and are mixed into a supercritical mixed working fluid, and then merge with the outlet working fluid of the recompressor 6 and enter the high-temperature regenerator 3 and the heat source 1 in turn to continue absorbing heat, completing the whole cycle.

[0024] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A working method of a dual-medium combined cycle power generation system, characterized in that: The dual-medium combined cycle power generation system comprises a heat source (1), wherein the outlet of the heat source (1) is connected to the inlet of a turbine (2), the outlet of the turbine (2) is connected to the hot side inlet of a high-temperature regenerator (3), the hot side outlet of the high-temperature regenerator (3) is connected to the hot side inlet of a medium-temperature regenerator (4), the hot side outlet of the medium-temperature regenerator (4) is connected to the middle inlet of a medium-temperature gas-liquid separator (5), the top outlet of the medium-temperature gas-liquid separator (5) is connected to the inlet of a recompressor (6), the bottom outlet of the medium-temperature gas-liquid separator (5) is connected to the hot side inlet of a low-temperature regenerator (7), the hot side outlet of the low-temperature regenerator (7) is connected to the middle inlet of a low-temperature gas-liquid separator (8), and the low-temperature regenerator (8) is connected to the hot side inlet of a low-temperature regenerator (9). The top outlet of the warm gas-liquid separator (8) is connected to the hot side inlet of the precooler (9), the hot side outlet of the precooler (9) is connected to the inlet of the main compressor (10), the outlet of the main compressor (10) is connected to the cold side inlet of the low-temperature regenerator (7), the bottom outlet of the low-temperature gas-liquid separator (8) is connected to the inlet of the liquid pump (11), the outlet of the liquid pump (11) merges with the cold side outlet of the low-temperature regenerator (7) and then connects to the cold side inlet of the medium-temperature regenerator (4), the cold side outlet of the medium-temperature regenerator (4) merges with the outlet of the recompressor (6) and then connects to the cold side inlet of the high-temperature regenerator (3), and the cold side outlet of the high-temperature regenerator (3) is connected to the inlet of the heat source (1); The working method is as follows: a supercritical mixed working medium of CO2 and H2O in a mixed state is heated in a heat source (1), then enters a turbine (2) to perform work, remains in a supercritical state after the pressure is reduced, then enters the hot side of a high-temperature regenerator (3) and the hot side of a medium-temperature regenerator (4) in sequence to release heat, as the working medium temperature is reduced, part of the H2O in the mixture can be separated, the mixed working medium is separated in a medium-temperature gas-liquid separator (5), CO2 flows out from the top outlet, enters a recompressor (6) to be pressurized, the gas-liquid mixture flows out from the bottom of the medium-temperature gas-liquid separator (5), enters the hot side of a low-temperature regenerator (7) to continue to release heat, most of the H2O is cooled to a liquid state in the low-temperature regenerator (7), and enters a low-temperature regenerator (8). The CO2 is separated again in the gas-liquid separator (8), and flows out from the top of the low-temperature gas-liquid separator (8), enters the precooler (9) to be further cooled, and then is pressurized in the main compressor (10), and then enters the cold side of the low-temperature regenerator (7) to absorb heat. The H2O flowing out from the bottom of the low-temperature gas-liquid separator (8) enters the liquid pump (11), is pressurized by the liquid pump (11), and is mixed with the CO2 at the cold side outlet of the low-temperature regenerator (7) and enters the cold side of the medium-temperature regenerator (4) to continue absorbing heat. The two working fluids absorb heat in the medium-temperature regenerator (4) and are mixed into a supercritical mixed working fluid, and then merge with the outlet working fluid of the recompressor (6) and enter the high-temperature regenerator (3) and the heat source (1) in turn to continue absorbing heat, completing the entire cycle.

2. The working method of a dual-medium combined cycle power generation system according to claim 1, characterized in that: The pressure in the medium-temperature gas-liquid separator (5) and the low-temperature gas-liquid separator (8) is 7.2 MPa to 7.6 MPa, the temperature of the medium-temperature gas-liquid separator (5) is 130° C. to 170° C., and the temperature of the low-temperature gas-liquid separator (8) is 65° C. to 85° C.

3. The working method of a dual-medium combined cycle power generation system according to claim 1, characterized in that: The ratio of the tank diameter of the medium-temperature gas-liquid separator (5) and the low-temperature gas-liquid separator (8) to the diameter of the inlet pipe is greater than 10, and the ratio of the effective volume height of the tank to the tank diameter is greater than 1.

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