Method for avoiding temperature internal pinch point problem in s-co2 cryogenic recuperation system

Abstract

The present application relates to a kind of methods for avoiding temperature internal pinch point problem in S-CO2 low temperature recuperation system, S-CO2 low temperature recuperation system includes low temperature recuperator, low temperature recuperator has high pressure tube bundle and low pressure tube bundle, first fluid flows into high pressure tube bundle, second fluid flows into low pressure tube bundle, the temperature of the inlet end of high pressure tube bundle is lower than the temperature of the inlet end of low pressure tube bundle;The method comprises: the intermediate flow of first fluid in low temperature recuperator is divided, and the heat capacity flow rate of first fluid in low temperature recuperator is kept less than the heat capacity flow rate of second fluid.The present application solves the internal pinch point problem that can appear in low temperature recuperator by the way of intermediate flow of low temperature recuperator, and cold fluid that is divided off is absorbed flue gas waste heat in boiler by low temperature economizer, on the one hand, the temperature of fluid after being divided off and the fluid that flows out from the outlet of low temperature recuperator is matched when being converged, on the other hand, energy-saving effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of S-CO2 coal-fired power generation technology, and specifically to a method for avoiding internal temperature pinch-point problems in S-CO2 low-temperature regenerative systems. Background Technology

[0002] Traditional coal-fired power generation systems employ the Rankine cycle with steam as the working fluid; however, due to cycle characteristics and material limitations, it is difficult to further improve plant efficiency. Supercritical carbon dioxide (S-CO2) power cycles offer advantages in efficiency and compactness, and are expected to replace traditional steam power cycles. The flue gas temperature of existing S-CO2 coal-fired power generation systems is generally around 120°C, with a trend towards further reduction.

[0003] Previous research on S-CO2 coal-fired power generation systems has largely focused on thermodynamic optimization, aiming to improve boiler and power plant efficiency, but lacking optimization for techno-economic efficiency. To address this lack of techno-economic optimization in existing research, some experts and scholars have focused on low-temperature waste heat recovery in S-CO2 coal-fired power generation systems, optimizing the system configuration and then optimizing system parameters to achieve optimal techno-economic efficiency (lowest cost per kilowatt-hour), analyzing the feasibility of various improved configurations. Existing improved configurations include adding a low-temperature economizer to the basic configuration, then diverting a portion of the main compressor outlet working fluid to the low-temperature economizer for heating, thereby cooling the boiler tail gas; adding an auxiliary air preheater to the system; and dividing the boiler tail flue into two parts: one part of the flue gas is used to heat air, and the other part is used to heat the S-CO2 working fluid in the low-temperature economizer. The aforementioned improvements only target increasing boiler efficiency and utilizing waste heat from the boiler tail flue. However, the supercritical carbon dioxide entering and exiting the low-temperature regenerator is located in the quasi-critical region. Because the specific heat at constant pressure of supercritical carbon dioxide varies drastically in the quasi-critical region, it may lead to an internal pinch-point problem in the low-temperature regenerator of the S-CO2 coal-fired power generation system. If the pinch-point occurs in the middle of the heat exchanger, it may result in increased heat exchanger size, deterioration of heat exchange efficiency, and other adverse effects, increasing the complexity of heat exchanger design. This heat exchange deterioration problem caused by the minimum temperature difference between the hot and cold fluids occurring in the middle of the heat exchanger is called the pinch-point problem.

[0004] In addition, although the existing S-CO2 coal-fired power generation system has solved some of the internal pinch problem that may occur in the low-temperature regenerator through the diversion and recompression measures, the internal pinch problem may still occur in the low-temperature regenerator after diversion. Therefore, measures are still needed to solve the internal pinch problem in the low-temperature regenerator after diversion and recompression. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a method for avoiding internal temperature pinch-point problems in an S-CO2 low-temperature regenerative system.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A method for avoiding internal temperature pinch-up problems in an S-CO2 low-temperature regenerative system, wherein the S-CO2 low-temperature regenerative system includes a low-temperature regenerator, the low-temperature regenerator having a high-pressure tube bundle and a low-pressure tube bundle, a first fluid flowing into the high-pressure tube bundle, and a second fluid flowing into the low-pressure tube bundle, the temperature at the inlet end of the high-pressure tube bundle being lower than the temperature at the inlet end of the low-pressure tube bundle; the method includes:

[0008] The first fluid in the low-temperature regenerator is split in the middle so that the heat capacity flow rate of the first fluid in the low-temperature regenerator is kept lower than that of the second fluid.

[0009] Furthermore, the S-CO2 low-temperature regenerative system also includes a control valve. The outlet end of the high-pressure tube bundle is provided with multiple branch tube bundles. One end of each branch tube bundle is connected to a corresponding section of the high-pressure tube bundle near its outlet end, and the other end of each branch tube bundle is connected to the control valve.

[0010] Furthermore, each of the aforementioned shunt tube bundles has a different cross-sectional dimension.

[0011] Furthermore, each control valve is equipped with multiple control units, each control unit is connected to one end of its corresponding shunt tube bundle, and each control unit can be used to control the opening degree of its corresponding shunt tube bundle.

[0012] Furthermore, the cross-sectional dimensions of one or more of the shunt tube bundles are selected, and the opening degree of the corresponding shunt tube bundle is controlled by a corresponding control unit to verify that the heat capacity flow rate of the first fluid after shunting in the low-temperature regenerator remains less than that of the second fluid.

[0013] Furthermore, both the first fluid and the second fluid are supercritical carbon dioxide.

[0014] Furthermore, the S-CO2 low-temperature regenerative system also includes a re-compressor, a main compressor, a low-temperature economizer, a boiler, and a high-temperature regenerator;

[0015] The low-temperature economizer is installed in the tail flue of the boiler; the low-temperature regenerator is connected to the outlet end of the main compressor through pipeline I; the low-temperature regenerator is connected to the outlet end of the high-temperature regenerator through pipeline II; and the low-temperature regenerator is connected to the inlet end of the high-temperature regenerator through pipeline III.

[0016] The control valve is connected to the inlet of the cryogenic economizer via pipeline IV. The outlet of the cryogenic economizer is connected to pipeline V. The outlet of the recompressor is connected to pipeline VI. Both pipeline V and pipeline VI are connected to pipeline III.

[0017] Furthermore, the method specifically includes:

[0018] The first fluid in the main compressor flows into the high-pressure tube bundle of the low-temperature regenerator through pipeline I. At the inlet end of the low-temperature regenerator, the corresponding first fluid is diverted and flows into the corresponding diversion tube bundle. The opening of the corresponding diversion tube bundle is controlled by the control valve to keep the heat capacity flow rate of the first fluid in the low-temperature regenerator less than that of the second fluid.

[0019] The first fluid diverted flows into the cryogenic economizer via pipeline IV, and then into pipeline V;

[0020] The first fluid inflow line VI within the recompressor;

[0021] The remaining first fluid in the low-temperature regenerator flows into pipeline III, and merges with the first fluid in pipeline V and the first fluid in pipeline VI in pipeline III, and then flows into the high-temperature regenerator.

[0022] The first fluid after heat exchange in the high-temperature regenerator flows into the low-temperature regenerator via pipeline II, and finally flows into the re-compressor via the precooler.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention solves the potential internal pinch-point problem in low-temperature regenerators by using a mid-stream diversion method. The diverted cold fluid is then used in a low-temperature economizer to absorb waste heat from the flue gas in the boiler. This ensures temperature matching when the diverted fluid merges with the fluid exiting the low-temperature regenerator, thus achieving energy savings. This invention has a simple structure and solves the potential internal pinch-point problem in low-temperature regenerators without affecting the process.

[0025] 2. This invention uses an intermediate flow splitting measure for the first fluid in the low-temperature regenerator to match the thermal capacity flow rates of the first fluid and the second fluid, thereby avoiding the internal pinch problem inside the low-temperature regenerator.

[0026] 3. This invention can adapt to the working conditions where the thermal capacity flow rates of the first fluid and the second fluid with different flow rates through the low-temperature regenerator are mismatched by selecting different cross-section shunt tube bundles and controlling the valve opening.

[0027] 4. In this invention, the first fluid diverted flows through the low-temperature economizer, which is beneficial for the recovery of waste heat from the boiler flue gas. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the S-CO2 low-temperature regenerative system in Embodiment 1 of the present invention.

[0029] Figure 2 This is a schematic diagram of the intermediate flow splitting of the low-temperature regenerator in Embodiment 1 of the present invention.

[0030] Figure 3 These are curves showing the temperature changes of the fluid in the high-pressure tube bundle and the low-pressure tube bundle in the low-temperature regenerator before the flow split in Embodiment 1 of the present invention, as a function of heat exchange.

[0031] Figure 4 These are curves showing the temperature changes of the fluid in the high-pressure tube bundle and the low-pressure tube bundle in the low-temperature regenerator after diversion in Embodiment 1 of the present invention as a function of heat exchange.

[0032] In the diagram, 1. Low-temperature regenerator; 11. High-pressure tube bundle; 12. Low-pressure tube bundle; 13. Diversion tube bundle; 2. Control valve; 21. Control unit; 3. Recompressor; 4. Main compressor; 5. Low-temperature economizer; 6. Boiler; 7. High-temperature regenerator; 8. Precooler. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In this embodiment of the invention, the fluid flow rate of the corresponding branch tube bundle is controlled by controlling the valve opening.

[0036] In this embodiment of the invention, the first fluid is supercritical carbon dioxide, i.e., a cold fluid; the second fluid is supercritical carbon dioxide, i.e., a hot fluid. S-CO2 is supercritical carbon dioxide.

[0037] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0038] Example 1

[0039] Please see Figures 1 to 2The S-CO2 low-temperature regenerative system provided in this embodiment of the invention includes a low-temperature regenerator 1, a control valve 2, a recompressor 3, a main compressor 4, a low-temperature economizer 5, a boiler 6, a high-temperature regenerator 7, and a precooler 8.

[0040] The cryogenic regenerator 1 contains a high-pressure tube bundle 11 and a low-pressure tube bundle 12. A first fluid flows into the high-pressure tube bundle 11, and a second fluid flows into the low-pressure tube bundle 12. The temperature at the inlet of the high-pressure tube bundle 11 is lower than the temperature at the inlet of the low-pressure tube bundle 12. Specifically, both the first and second fluids are supercritical carbon dioxide. In this embodiment of the invention, the flow is split in the middle of the cryogenic regenerator, and tube bundles are led out at different cross-sections at different locations in the outlet section of the cryogenic regenerator and controlled by valves. This solution not only further solves the internal pinch problem existing in the cryogenic regenerator, but also flexibly addresses the problem of heat capacity flow rate mismatch when different flow rates of cold fluid flow through the cryogenic regenerator are selected by choosing the tube bundle control valve opening.

[0041] The outlet end of the high-pressure tube bundle 11 is provided with multiple shunt tube bundles 13, each with a different cross-sectional size. One end of each shunt tube bundle 13 is connected to a corresponding section of the high-pressure tube bundle 11 near its inlet end, and the other end of each shunt tube bundle 13 is connected to a control valve 2. Specifically, the control valve 2 is provided with multiple control units 21, each control unit 21 being connected to one end of its corresponding shunt tube bundle 13, and each control unit 21 can be used to control the opening degree of its corresponding shunt tube bundle 13.

[0042] The low-temperature economizer 5 is installed in the tail flue of the boiler 6; the low-temperature regenerator 1 is connected to the outlet end of the main compressor 4 through pipeline I, the low-temperature regenerator 1 is connected to the outlet end of the high-temperature regenerator 7 through pipeline II, and the low-temperature regenerator 1 is connected to the inlet end of the high-temperature regenerator 7 through pipeline III.

[0043] Control valve 2 is connected to the inlet end of cryogenic economizer 5 via pipeline IV. The outlet end of cryogenic economizer 5 is connected to pipeline V, and the outlet end of compressor 3 is connected to pipeline VI. Both pipeline V and pipeline VI are connected to pipeline III.

[0044] Example 2

[0045] The method for avoiding internal temperature pinch-point problems in the S-CO2 low-temperature regenerative system based on Example 1 includes: performing intermediate diversion of the first fluid in the low-temperature regenerator 1 so that the heat capacity flow rate of the first fluid in the low-temperature regenerator 1 is kept lower than the heat capacity flow rate of the second fluid.

[0046] In this embodiment of the invention, in order to match the thermal capacity flow rates of the hot and cold fluids passing through the low-temperature regenerator and thus avoid the internal pinch problem, we adopt a cold fluid intermediate diversion measure in the low-temperature regenerator. Several sets of tube bundles are led out from different positions of the hot section of the low-temperature regenerator and converge at the valve. By controlling different valve openings, the internal pinch problem that occurs when different flow rates pass through the low-temperature regenerator is solved.

[0047] Specifically, the cross-sectional dimensions of one or more branch tube bundles 13 are selected, and the opening degree of the corresponding branch tube bundle 13 is controlled by the corresponding control unit 21 to verify that the heat capacity flow rate of the first fluid after branching in the low-temperature regenerator 1 is less than that of the second fluid.

[0048] The method specifically includes:

[0049] The first fluid in the main compressor 4 flows into the high-pressure tube bundle 11 of the low-temperature regenerator 1 through pipeline I. At the inlet end of the low-temperature regenerator 1, the corresponding first fluid is diverted and flows into the corresponding diversion tube bundle 13. The opening degree of the corresponding diversion tube bundle 13 is controlled by the control valve 2 so that the heat capacity flow rate of the first fluid in the low-temperature regenerator 1 is kept less than the heat capacity flow rate of the second fluid.

[0050] The first fluid diverted flows into the cryogenic economizer 5 via pipeline IV, and then into pipeline V;

[0051] The first fluid inflow line VI is located within the compressor 3;

[0052] The remaining first fluid in the low-temperature regenerator 1 flows into pipeline III and merges with the first fluid in pipeline V and the first fluid in pipeline VI in pipeline III, and then flows into the high-temperature regenerator 7.

[0053] The first fluid after heat exchange in the high-temperature regenerator 7 flows into the low-temperature regenerator 1 through pipeline II, and finally flows into the re-compressor 3 through the precooler 8.

[0054] Figure 3 and Figure 4 The curves show the temperature changes with heat exchange before and after the flow split.

[0055] like Figure 3As shown, the inlet and outlet fluids of the low-temperature regenerator have the same temperature difference. Due to the changes in the properties of carbon dioxide in the quasi-critical region, the temperature difference inside the low-temperature regenerator first decreases and then increases along the flow path. This is because the heat capacity flow rate at the high-pressure side inlet is initially lower than the heat capacity flow rate of carbon dioxide at the low-pressure side outlet. As the temperature approaches the quasi-critical point, the heat capacity flow rate of carbon dioxide on the high-pressure side gradually increases and becomes greater than that of carbon dioxide at the low-pressure side outlet. When the heat capacity flow rates of the cold and hot fluids are equal, the temperature difference between the cold and hot fluids is minimized, i.e., the pinch temperature difference is reached. This heat transfer deterioration problem caused by the minimum temperature difference between the cold and hot fluids occurring in the middle of the heat exchanger is called the pinch problem.

[0056] Therefore, to avoid internal pinch-point problems within the low-temperature regenerator, an intermediate flow diversion measure is used to reduce the thermal capacity flow rate of the cold fluid before the temperature difference between the hot and cold fluids decreases to the minimum allowable temperature difference in engineering. This allows the thermal capacity flow rates of the hot and cold fluids to be matched, thereby avoiding internal pinch-point problems. The effect is as follows: Figure 4 As shown.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Method for avoiding temperature internal pinch point problem in S-CO2 cryogenic recuperation system, said S-CO2 cryogenic recuperation system comprising a cryogenic recuperator (1) having a high pressure tube bundle (11) and a low pressure tube bundle (12) inside, a first fluid flowing inside said high pressure tube bundle (11) and a second fluid flowing inside said low pressure tube bundle (12), the temperature at the inlet end of said high pressure tube bundle (11) being lower than the temperature at the inlet end of said low pressure tube bundle (12); characterized in that, The S-CO2 low-temperature regenerative system further comprises a control valve (2), the outlet end of the high-pressure tube bundle (11) is provided with a plurality of shunt tube bundles (13), one end of each of the shunt tube bundles (13) is connected to a corresponding section of the high-pressure tube bundle (11) close to the inlet end thereof, and the other end of each of the shunt tube bundles (13) is connected to the control valve (2); a plurality of control units (21) are arranged on the control valve (2), one end of each of the control units (21) is connected to a corresponding shunt tube bundle (13), and each of the control units (21) can be used to control the opening degree of the corresponding shunt tube bundle (13); and the method comprises the following steps: The first fluid in the low-temperature regenerator (1) is subjected to intermediate shunting, the opening degree of the corresponding shunt tube bundle (13) is controlled by the control valve (2), and the heat capacity flow rate of the first fluid in the low-temperature regenerator (1) is kept less than the heat capacity flow rate of the second fluid.

2. The method of claim 1, wherein the S-CO2 cryogenic recuperated system is free of internal temperature pinch problem, characterized in that, The cross-sectional dimensions of the shunt tube bundles (13) are different.

3. The method of claim 1, wherein the S-CO2 cryogenic recuperated system is free of internal temperature pinch problem, characterized in that, The cross-sectional dimensions of one or more of the shunt tube bundles (13) are selected, and the opening degree of the corresponding shunt tube bundle (13) is controlled by the corresponding control unit (21), so as to verify that the heat capacity flow rate of the first fluid in the low-temperature regenerator (1) after shunting is kept less than the heat capacity flow rate of the second fluid.

4. The method of claim 1, wherein the S-CO2 cryogenic recuperated system avoids the temperature internal pinch problem, characterized in that, The first fluid is supercritical carbon dioxide, and the second fluid is supercritical carbon dioxide.

5. The method of claim 1, wherein the S-CO2 cryogenic recuperated system avoids the temperature internal pinch problem, and wherein the method further comprises: The S-CO2 low-temperature regenerative system further comprises a re-compressor (3), a main compressor (4), a low-temperature economizer (5), a boiler (6) and a high-temperature regenerator (7); The low-temperature economizer (5) is arranged in the tail flue of the boiler (6); the low-temperature regenerator (1) is connected to the outlet end of the main compressor (4) through a pipeline I, connected to the outlet end of the high-temperature regenerator (7) through a pipeline II, and connected to the inlet end of the high-temperature regenerator (7) through a pipeline III; The control valve (2) is connected to the inlet end of the low-temperature economizer (5) through a pipeline IV, the outlet end of the low-temperature economizer (5) is connected to a pipeline V, the outlet end of the re-compressor (3) is connected to a pipeline VI, and the pipeline V and the pipeline VI are both connected to the pipeline III.

6. The method of claim 5, wherein the S-CO2 cryogenic recuperated system is configured to avoid the temperature internal pinch point problem by: The method specifically comprises the following steps: The first fluid in the main compressor (4) flows into the high-pressure tube bundle (11) of the low-temperature regenerator (1) through the pipeline I, a corresponding first fluid is shunted out at the inlet end of the high-pressure tube bundle (11) of the low-temperature regenerator (1) and flows into a corresponding shunt tube bundle (13), the opening degree of the corresponding shunt tube bundle (13) is controlled by the control valve (2), the heat capacity flow rate of the first fluid in the low-temperature regenerator (1) is kept less than the heat capacity flow rate of the second fluid, the first fluid is supercritical carbon dioxide and serves as a cold fluid, and the second fluid is supercritical carbon dioxide and serves as a hot fluid; The first fluid branched out flows into the low-temperature economizer (5) through pipeline IV to absorb the waste heat of the flue gas, and then flows into pipeline V; The first fluid in the re-compressor (3) flows into pipeline VI; The remaining first fluid in the high-pressure tube bundle (11) of the low-temperature regenerator (1) flows into pipeline III, and is combined with the first fluid in pipeline V and the first fluid in pipeline VI in pipeline III, and then flows into the high-temperature regenerator (7); The first fluid in the high-temperature regenerator (7) after heat exchange flows into the low-pressure tube bundle (12) of the low-temperature regenerator (1) through pipeline II, and finally flows into the re-compressor (3) through the pre-cooler (8).

Images