Power generation system with optimized inlet conditions for supercritical carbon dioxide compressor and its operating method

Abstract

This invention discloses a power generation system and its operating method with optimized inlet conditions for a supercritical carbon dioxide compressor, belonging to the technical field of power generation systems. It includes a supercritical carbon dioxide compressor, a carbon dioxide heat exchanger, a heat source, a supercritical carbon dioxide turbine, a cooling device, a pressure balancing chamber, a constant-temperature heat exchanger, a throttling valve, a motor, and a supercritical carbon dioxide tank. This invention can stabilize the inlet conditions of the supercritical carbon dioxide compressor and, by rationally designing these conditions, reduces the possibility of condensation at the compressor inlet, thereby improving the overall performance of the compressor and ultimately enhancing the power generation efficiency of the entire power generation system.

Description

Technical Field

[0001] This invention belongs to the field of power generation system technology, specifically relating to a power generation system with optimized inlet conditions for a supercritical carbon dioxide compressor and its operating method. Background Technology

[0002] Driven by market demand and continuous advancements in energy utilization and materials technology, the Rankine cycle (using steam as the working fluid) and the Brayton cycle (using natural gas as the working fluid) have been developing towards larger sizes, higher power outputs, and higher temperatures over the past few decades. However, this results in large generator sets, requiring significant land area, making component manufacturing more difficult, and exposing the blades to the effects of high imported temperatures, making them highly susceptible to thermal erosion. Therefore, the development of large generator sets faces significant technological bottlenecks.

[0003] Near the critical point, carbon dioxide has a high density, resulting in a smaller size for supercritical carbon dioxide power units. Simultaneously, carbon dioxide has a low compressibility factor in this state, leading to lower power consumption in supercritical carbon dioxide compressors. Therefore, in recent years, academia and industry have widely focused on and proposed a closed-loop Brayton cycle power generation technology using supercritical carbon dioxide as the working fluid. The supercritical carbon dioxide compressor, as the core component of the entire Brayton cycle, has received widespread attention.

[0004] Although it has been theoretically and practically proven that the supercritical carbon dioxide Brayton cycle is more compact and more efficient than the traditional steam Rankine cycle, it still has the following disadvantages: 1) Near the critical point, the working fluid may liquefy at the compressor inlet, affecting the stable operation of the compressor and causing water erosion on the blades; 2) Near the critical point, the physical properties of carbon dioxide exhibit strong nonlinearity, and small changes in pressure and temperature can have a huge impact on properties such as density and compressibility factor. Changes in inlet conditions can have a significant impact on the overall performance of the compressor; 3) Current research on the performance of supercritical carbon dioxide compressors mainly suggests that the performance of supercritical carbon dioxide compressors decreases and the possibility of condensation decreases when the compressor is far from the critical point, but there is no reasonable method for selecting inlet conditions when operating a supercritical carbon dioxide compressor. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a power generation system and its operating method that optimizes the inlet conditions of a supercritical carbon dioxide compressor. This system can stabilize the inlet conditions of the supercritical carbon dioxide compressor and rationally design the inlet conditions to reduce the possibility of condensation at the inlet of the supercritical carbon dioxide compressor, thereby improving the overall performance of the compressor and ultimately enhancing the power generation efficiency of the entire power generation system.

[0006] This invention is achieved through the following technical solution:

[0007] The present invention discloses a power generation system with optimized inlet conditions for a supercritical carbon dioxide compressor, comprising a supercritical carbon dioxide compressor, a carbon dioxide heat exchanger, a heat source, a supercritical carbon dioxide turbine, a cooling device, a pressure balance chamber, a constant temperature heat exchanger, a throttle valve, a motor, and a supercritical carbon dioxide gas tank.

[0008] The working fluid outlet of the supercritical carbon dioxide compressor is connected to the low-temperature inlet of the carbon dioxide heat exchanger. The low-temperature outlet of the carbon dioxide heat exchanger is connected to the inlet of the heat source. The outlet of the heat source is connected to the inlet of the supercritical carbon dioxide turbine. The outlet of the supercritical carbon dioxide turbine is connected to the high-temperature inlet of the carbon dioxide heat exchanger. The high-temperature outlet of the carbon dioxide heat exchanger is connected to the inlet of the cooling device. The outlet of the cooling device is connected to the inlet of the pressure balance chamber. The outlet of the pressure balance chamber is connected to the inlet of the isothermal heat exchanger. The outlet of the isothermal heat exchanger is connected to the inlet of the supercritical carbon dioxide compressor. A throttling valve is installed between the outlet of the isothermal heat exchanger and the inlet of the supercritical carbon dioxide compressor. The outlet of the supercritical carbon dioxide tank is connected to the inlet of the pressure balance chamber. The supercritical carbon dioxide turbine is connected to the supercritical carbon dioxide compressor and the motor via a drive shaft.

[0009] Preferably, a supercritical carbon dioxide pump is provided between the outlet of the supercritical carbon dioxide gas cylinder and the inlet of the pressure balance chamber.

[0010] Preferably, the carbon dioxide heat exchanger is a printed circuit board heat exchanger.

[0011] Preferably, the constant temperature heat exchanger is a plate-fin heat exchanger.

[0012] The operating method of the power generation system with optimized inlet conditions for the supercritical carbon dioxide compressor disclosed in this invention includes:

[0013] The exhaust gas from the supercritical carbon dioxide compressor absorbs energy from the exhaust gas from the supercritical carbon dioxide turbine in the carbon dioxide heat exchanger, and then absorbs energy in the heat source to rise to the maximum operating temperature; the working fluid enters the supercritical carbon dioxide turbine, expands and does work, and the shaft work drives the supercritical carbon dioxide compressor and drives the motor to generate electricity; the exhaust gas from the supercritical carbon dioxide turbine transfers energy to the exhaust gas from the supercritical carbon dioxide compressor in the carbon dioxide heat exchanger, and then enters the cooler to transfer heat to the atmosphere; the exhaust gas from the cooler outlet replenishes the working fluid leaked in the cycle and controls the pressure to the specified pressure in the pressure balance chamber; the exhaust gas from the pressure balance chamber outlet is controlled to the preset temperature in the constant temperature heat exchanger, and then the exhaust gas enters the inlet of the supercritical carbon dioxide compressor through the throttle valve; the supercritical carbon dioxide in the supercritical carbon dioxide tank enters the pressure balance chamber to control the pressure in the pressure balance chamber and to compensate for the working fluid leaked in the cycle.

[0014] Preferably, the pressure in the pressure balancing chamber is 7.37–9.00 MPa.

[0015] Preferably, the preset temperature controlled in the constant temperature heat exchanger is 31 to 35°C.

[0016] Preferably, the inlet pressure and temperature of the supercritical carbon dioxide turbine are higher than the critical point of carbon dioxide.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] This invention discloses a power generation system for optimizing the inlet conditions of a supercritical carbon dioxide compressor. It employs a simple regenerative Brayton cycle power generation method, utilizing the waste heat from the supercritical carbon dioxide turbine's exhaust to heat the exhaust gas from the supercritical carbon dioxide compressor. This fully utilizes the exhaust heat from the supercritical carbon dioxide cycle, further improving the overall cycle efficiency. Simultaneously, a pressure balancing chamber, a constant-temperature heat exchanger, and a throttling valve are added at the inlet of the supercritical carbon dioxide compressor to ensure stable inlet conditions and prevent fluctuations in inlet conditions from affecting the compressor's stability.

[0019] The prevailing view in the industry is that compression performance improves as the compressor approaches its critical point; however, near the critical point, compressor performance becomes unstable and difficult to control, potentially entering the two-phase region, which negatively impacts compressor efficiency and overall aerodynamic performance. Compared to traditional supercritical carbon dioxide compressor inlet condition selection, this invention does not improve compressor performance by bringing the inlet temperature and pressure closer to the critical point. Instead, it utilizes physical definitions to derive suitable inlet pressure and temperature by selecting appropriate compressibility factors and densities. By reducing the compressor's compressibility factor, the compression work of the supercritical carbon dioxide compressor can be reduced. Adjusting the density can mitigate the increase in condensation region caused by lowering the compressibility factor and bringing inlet conditions closer to the critical point, thereby effectively improving compressor performance and overall cycle efficiency.

[0020] Furthermore, the carbon dioxide heat exchanger uses a printed circuit board heat exchanger, which has good high temperature and high pressure resistance, compact structure, corrosion resistance, long service life, and high heat exchange efficiency.

[0021] Furthermore, the constant temperature heat exchanger adopts a plate-fin heat exchanger, which has a compact structure and high heat transfer efficiency.

[0022] The power generation system operating method for optimizing the inlet conditions of the supercritical carbon dioxide compressor disclosed in this invention effectively utilizes the waste heat of the supercritical carbon dioxide turbine exhaust through a simple regenerative cycle. A pressure balancing chamber and a constant-temperature heat exchanger ensure the stability of the supercritical carbon dioxide compressor inlet conditions, preventing performance degradation due to fluctuations in inlet conditions. Simultaneously, by adjusting the compressibility factor and density at the compressor inlet, the inlet conditions are controlled, effectively improving performance and increasing the efficiency of the supercritical carbon dioxide compressor, thereby significantly improving the overall cycle efficiency. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall system structure of the present invention;

[0024] Figure 2 A schematic diagram illustrating the performance of a supercritical carbon dioxide compressor after optimization of inlet conditions.

[0025] Figure 3 This is a schematic diagram of the potential condensation zone at the inlet of a supercritical carbon dioxide compressor.

[0026] In the diagram: 1 is a supercritical carbon dioxide compressor, 2 is a carbon dioxide heat exchanger, 3 is a heat source, 4 is a supercritical carbon dioxide turbine, 5 is a cooling device, 6 is a pressure balance chamber, 7 is a constant temperature heat exchanger, 8 is a throttle valve, 9 is a motor, 10 is a supercritical carbon dioxide tank, and 11 is a supercritical carbon dioxide pump. Detailed Implementation

[0027] Theoretical basis of this invention:

[0028] When carbon dioxide approaches its critical point, its properties deviate significantly from those of an ideal gas. Even minor changes in pressure and temperature can cause drastic changes in properties such as compressibility factor and density, severely impacting the stable operation of the compressor. Furthermore, near the critical point, carbon dioxide may liquefy, leading to water erosion of the compressor blades and affecting compressor performance. This invention presents a high-efficiency power generation system based on optimized inlet conditions for a supercritical carbon dioxide compressor. This system determines the inlet conditions of the supercritical carbon dioxide compressor and ensures their stability by combining compressibility factor and density.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This description is intended to explain the invention and not to limit it.

[0030] like Figure 1The present invention provides a power generation system with optimized inlet conditions for a supercritical carbon dioxide compressor, comprising a supercritical carbon dioxide compressor 1, a carbon dioxide heat exchanger 2, a heat source 3, a supercritical carbon dioxide turbine 4, a cooling device 5, a pressure balance chamber 6, a constant temperature heat exchanger 7, a throttle valve 8, a motor 9, and a supercritical carbon dioxide tank 10.

[0031] The working fluid outlet of the supercritical carbon dioxide compressor 1 is connected to the low-temperature side inlet of the carbon dioxide heat exchanger 2. The low-temperature side outlet of the carbon dioxide heat exchanger 2 is connected to the inlet of the heat source 3. The outlet of the heat source 3 is connected to the inlet of the supercritical carbon dioxide turbine 4. The outlet of the supercritical carbon dioxide turbine 4 is connected to the high-temperature side inlet of the carbon dioxide heat exchanger 2. The high-temperature side outlet of the carbon dioxide heat exchanger 2 is connected to the inlet of the cooling device 5. The outlet of the cooling device 5 is connected to the inlet of the pressure balance chamber 6. The outlet of the pressure balance chamber 6 is connected to the inlet of the constant-temperature heat exchanger 7. The outlet of the constant-temperature heat exchanger 7 is connected to the inlet of the supercritical carbon dioxide compressor 1. A throttling valve 8 is provided between the outlet of the constant-temperature heat exchanger 7 and the inlet of the supercritical carbon dioxide compressor 1. The outlet of the supercritical carbon dioxide tank 10 is connected to the inlet of the pressure balance chamber 6. The supercritical carbon dioxide turbine 4 is connected to the supercritical carbon dioxide compressor 1 and the motor 9 respectively through a drive shaft.

[0032] In a preferred embodiment of the present invention, a supercritical carbon dioxide pump 11 is provided between the outlet of the supercritical carbon dioxide tank 10 and the inlet of the pressure balance chamber 6.

[0033] In a preferred embodiment of the present invention, the carbon dioxide heat exchanger 2 is a printed circuit board heat exchanger.

[0034] In a preferred embodiment of the present invention, the constant temperature heat exchanger 7 is a plate-fin heat exchanger.

[0035] After being pressurized by the supercritical carbon dioxide compressor 1, the carbon dioxide working fluid absorbs the waste heat from the exhaust gas of the supercritical carbon dioxide turbine 4 in the carbon dioxide heat exchanger 2. The exhaust gas on the high-temperature side of the carbon dioxide heat exchanger 2 is cooled by air in the cooler. The carbon dioxide heat exchanger 2 contains both supercritical carbon dioxide exhaust gas and supercritical carbon dioxide turbine exhaust gas. The inlet pressure of the supercritical carbon dioxide compressor is controlled in the pressure balance chamber 6. The inlet temperature of the supercritical carbon dioxide compressor is controlled in the isothermal heat exchanger 7. Any gas leakage during the cycle is replenished through the supercritical carbon dioxide gas tank 10.

[0036] The operating method of the power generation system with optimized inlet conditions for the supercritical carbon dioxide compressor mentioned above includes:

[0037] The exhaust gas from the supercritical carbon dioxide compressor 1 absorbs energy from the exhaust gas from the supercritical carbon dioxide turbine 4 in the carbon dioxide heat exchanger 2, and then absorbs energy in the heat source 3, raising its temperature to the maximum operating temperature; the working fluid enters the supercritical carbon dioxide turbine 4, expands and does work, and the shaft work drives the supercritical carbon dioxide compressor 1 and drives the motor 9 to generate electricity; the exhaust gas from the supercritical carbon dioxide turbine 4 transfers energy to the exhaust gas from the supercritical carbon dioxide compressor 1 in the carbon dioxide heat exchanger 2, and then enters the cooler 5 to transfer heat to the atmosphere; the exhaust gas from the outlet of the cooler 5 replenishes the working fluid leaked in the cycle and controls the pressure to the specified pressure in the pressure balance chamber 6; the exhaust gas from the outlet of the pressure balance chamber 6 is controlled to the preset temperature in the constant temperature heat exchanger 7, and then the exhaust gas enters the inlet of the supercritical carbon dioxide compressor 1 through the throttle valve 8; the supercritical carbon dioxide in the supercritical carbon dioxide tank 10 enters the pressure balance chamber 6 through the supercritical carbon dioxide pump 11 to control the pressure in the pressure balance chamber 6 and to compensate for the working fluid leaked in the cycle.

[0038] The pressure in pressure balancing chamber 6 is 7.37–9.00 MPa; the preset temperature controlled in constant-temperature heat exchanger 7 is 31–35 °C. The pressure in pressure balancing chamber 6 and the temperature in constant-temperature heat exchanger 7 are not improved by approaching the critical point as closely as possible, as is traditionally understood, to enhance compressor performance. Instead, the performance of the supercritical carbon dioxide compressor is improved by reducing the compressibility factor to a suitable value and controlling the inlet density. The compressibility factor is controlled within the range of 0.21–0.25.

[0039] The inlet pressure and temperature of the supercritical carbon dioxide turbine 4 are higher than the critical point of carbon dioxide.

[0040] The following verification example illustrates the effectiveness of the present invention:

[0041] The power generation system employing the optimized inlet conditions of the supercritical carbon dioxide compressor according to the present invention has an initial design inlet temperature of 7.69 MPa and 32°C for the supercritical carbon dioxide compressor 1 (compressibility factor of 0.223, density of 599 kg / m³). 3 By adjusting the compressibility factor at the inlet of supercritical carbon dioxide compressor 1 to 0.215, the density becomes 677 kg / m³. 3 At this point, the inlet pressure was 8.40 MPa and the inlet temperature was 32.4℃. Although both the temperature and pressure were far from the critical point compared to the initial design, from... Figure 2 It can be observed that the compressor's compression performance (pressure ratio) did not decrease and remained essentially unchanged, while the maximum efficiency increased from 73.2% to 75.4%. This demonstrates that the present invention can effectively improve the performance of a supercritical carbon dioxide compressor.

[0042] Figure 3This is a schematic diagram of the potential condensation zone at the inlet of a supercritical carbon dioxide compressor, where a dryness fraction of 1 indicates that no condensation has occurred. Figure 3 It can be observed that, under the same flow coefficient, although the inlet conditions are far from the critical point, the condensation region optimized by this invention is significantly reduced, the stability of compressor operation is improved, the efficiency of the compressor is increased, while the pressure ratio remains basically unchanged.

[0043] The above description is merely an embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, or equivalent structural or procedural transformations made using the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, should all be covered within the scope of protection of the present invention.

Claims

1. A method for operating a power generation system with optimized inlet conditions of a supercritical carbon dioxide compressor, characterized in that, The supercritical carbon dioxide compressor inlet condition optimized power generation system includes a supercritical carbon dioxide compressor (1), a carbon dioxide heat exchanger (2), a heat source (3), a supercritical carbon dioxide turbine (4), a cooling device (5), a pressure balance chamber (6), a constant temperature heat exchanger (7), a throttle valve (8), a motor (9), and a supercritical carbon dioxide tank (10). The working fluid outlet of the supercritical carbon dioxide compressor (1) is connected to the low-temperature side inlet of the carbon dioxide heat exchanger (2). The low-temperature side outlet of the carbon dioxide heat exchanger (2) is connected to the inlet of the heat source (3). The outlet of the heat source (3) is connected to the inlet of the supercritical carbon dioxide turbine (4). The outlet of the supercritical carbon dioxide turbine (4) is connected to the high-temperature side inlet of the carbon dioxide heat exchanger (2). The high-temperature side outlet of the carbon dioxide heat exchanger (2) is connected to the inlet of the cooling device (5). The outlet of the cooling device (5) is connected to the pressure balance chamber (6). The outlet of the pressure balance chamber (6) is connected to the inlet of the constant temperature heat exchanger (7), and the outlet of the constant temperature heat exchanger (7) is connected to the inlet of the supercritical carbon dioxide compressor (1). A throttle valve (8) is provided between the outlet of the constant temperature heat exchanger (7) and the inlet of the supercritical carbon dioxide compressor (1). The outlet of the supercritical carbon dioxide tank (10) is connected to the inlet of the pressure balance chamber (6). The supercritical carbon dioxide turbine (4) is connected to the supercritical carbon dioxide compressor (1) and the motor (9) respectively through the drive shaft. The working method includes: The exhaust gas from the supercritical carbon dioxide compressor (1) absorbs energy from the exhaust gas from the supercritical carbon dioxide turbine (4) in the carbon dioxide heat exchanger (2), and then absorbs energy in the heat source (3) to raise the temperature to the maximum operating temperature; the working fluid enters the supercritical carbon dioxide turbine (4) to expand and do work, and the shaft work drives the supercritical carbon dioxide compressor (1) and drives the motor (9) to generate electricity; the exhaust gas from the supercritical carbon dioxide turbine (4) transfers energy to the exhaust gas from the supercritical carbon dioxide compressor (1) in the carbon dioxide heat exchanger (2), and then enters the cooling device (5) to transfer heat to the atmosphere; the exhaust gas from the outlet of the cooling device (5) replenishes the working fluid leaked in the cycle and controls the pressure to the specified pressure in the pressure balance chamber (6); the exhaust gas from the outlet of the pressure balance chamber (6) is controlled to the preset temperature in the constant temperature heat exchanger (7), and then the exhaust gas enters the inlet of the supercritical carbon dioxide compressor (1) through the throttle valve (8); the supercritical carbon dioxide in the supercritical carbon dioxide tank (10) enters the pressure balance chamber (6) to control the pressure in the pressure balance chamber (6) and to compensate for the working fluid leaked in the cycle; The pressure inside the pressure balance chamber (6) is 7.37~9.00 MPa; The preset temperature controlled in the constant temperature heat exchanger (7) is 31~35℃; The performance of supercritical carbon dioxide compressors can be improved by reducing the compressibility factor and controlling the inlet density.

2. The operating method of the power generation system with optimized inlet conditions for a supercritical carbon dioxide compressor according to claim 1, characterized in that, A supercritical carbon dioxide pump (11) is provided between the outlet of the supercritical carbon dioxide tank (10) and the inlet of the pressure balance chamber (6).

3. The operating method of the power generation system with optimized inlet conditions of the supercritical carbon dioxide compressor according to claim 1, characterized in that, The carbon dioxide heat exchanger (2) is a printed circuit board heat exchanger.

4. The operating method of the power generation system with optimized inlet conditions for a supercritical carbon dioxide compressor according to claim 1, characterized in that, The constant temperature heat exchanger (7) is a plate-fin heat exchanger.

5. The operating method of the power generation system with optimized inlet conditions of the supercritical carbon dioxide compressor according to claim 1, characterized in that, The inlet pressure and temperature of the supercritical carbon dioxide turbine (4) are higher than the critical point of carbon dioxide.

Images