Ocean thermal energy conversion system

Abstract

The application discloses a marine temperature difference energy power generation system, wherein a temperature difference energy power generation module comprises two-stage circulation loops in parallel overheat; the inlet of a warm seawater pipeline is installed at the surface layer seawater, the inlet of a cold seawater pipeline is installed at deep seawater, the cold seawater pipeline is connected with a cold seawater pump, the warm seawater pipeline is connected with a warm seawater pump, the warm seawater pump draws the warm seawater to the hot end of the temperature difference energy power generation module as a heat source, the cold seawater pump draws the deep cold seawater to the cold end of the temperature difference energy power generation module as a cold source, and the temperature difference energy power generation module converts the marine temperature difference energy between the warm seawater and the cold seawater into electric energy and outputs the electric energy. The application widens the energy release temperature zone of the warm seawater and the cold seawater by adopting the two-stage circulation loops in parallel overheat, improves the utilization rate of the warm seawater and the cold seawater and the marine temperature difference energy heat-electricity conversion efficiency, and provides a new method for economically developing the marine temperature difference energy.

Description

Technical Field

[0001] This invention relates to the field of renewable energy utilization technology, and in particular to an ocean thermal energy conversion power generation system. Background Technology

[0002] With the depletion of traditional fossil fuels and the increasing awareness of environmental protection, the development and utilization of renewable energy is urgently needed. Ocean thermal energy, as a renewable energy source with vast reserves and relatively stable heat sources, is less affected by environmental factors and has strong sustainability. Fully utilizing ocean thermal energy for power generation has promising development prospects and is of great significance for reducing or even replacing the use of fossil fuels.

[0003] When the temperature difference between warm and cold seawater is constant, i.e., when the temperatures of the cold and heat sources in the system are constant, the performance of the power generation system is mainly affected by the cycle power configuration and the working fluid used. Constructing a more efficient cycle power configuration and selecting a working fluid that more efficiently matches the temperature changes of warm and cold seawater are the best ways to reduce energy loss and enhance thermal performance in ocean thermal energy power generation systems. Commonly used cycle power generation configurations still have relatively low power generation efficiency, resulting in high research and operating costs. A multi-stage parallel Rankine cycle configuration can utilize ocean thermal energy in a cascade manner. Furthermore, introducing a superheater into the power configuration can bring the working fluid to a superheated state, further ensuring safe operation of the turbine. Non-azeotropic working fluids have non-isothermal phase change characteristics; using a binary non-azeotropic mixture as a working fluid in ocean thermal energy-driven thermodynamic cycles helps reduce irreversible losses in the cycle.

[0004] Therefore, exploring efficient thermoelectric energy cycle configurations and mixed working fluids still has a significant driving effect on improving the efficiency and power generation capacity of power generation systems.

[0005] Therefore, there is an urgent need for an ocean thermal energy conversion system with high efficiency in utilizing temperature differences. Summary of the Invention

[0006] This invention provides an ocean thermal energy conversion system to solve problems such as low efficiency and large irreversible losses in conventional pure working fluid power cycles; low efficiency of conventional evaporators and condensers for low-temperature heat source heat exchange, requiring optimization of heat exchange structure to improve heat exchange efficiency.

[0007] This invention provides an ocean thermal energy conversion system, comprising a warm seawater pump, a cold seawater pump, a cold seawater pipeline, a warm seawater pipeline, and an ocean thermal energy conversion module; The thermoelectric power generation module includes an evaporator mechanism, a superheater mechanism, a turbine mechanism, a condenser mechanism, a working fluid pump mechanism, a throttle valve mechanism, and a generator mechanism. The evaporator mechanism, the superheater mechanism, the turbine mechanism, the condenser mechanism, the working fluid pump mechanism, the throttle valve mechanism, and the generator mechanism form a parallel superheated two-stage circulation loop. The inlet of the warm seawater pipeline is installed at the surface seawater, and the inlet of the cold seawater pipeline is installed at the deep cold seawater. The cold seawater pipeline is connected to the cold seawater pump, and the warm seawater pipeline is connected to the warm seawater pump. The warm seawater pump draws warm seawater to the hot end of the thermoelectric power generation module as a heat source, and the cold seawater pump draws deep cold seawater to the cold end of the thermoelectric power generation module as a cold source. The thermoelectric power generation module converts the thermoelectric energy contained between the warm seawater and the cold seawater into electrical energy and outputs it. The outlet of the warm seawater pipe is installed at the hot end of the thermoelectric power generation module and is connected to the evaporator mechanism and the superheater mechanism in the circulation loop. The outlet of the cold seawater pipe is installed at the cold end of the thermoelectric power generation module and is connected to the condenser mechanism in the circulation loop.

[0008] The ocean thermal energy conversion power generation system, preferably, includes an evaporator mechanism comprising a primary evaporator and a secondary evaporator, a superheater mechanism comprising a primary superheater and a secondary superheater, a condenser mechanism comprising a primary condenser and a secondary condenser, a turbine mechanism comprising a primary turbine and a secondary turbine, a generator mechanism comprising a primary generator and a secondary generator, a working fluid pump mechanism comprising a primary working fluid pump and a secondary working fluid pump, and a throttling valve mechanism comprising a primary valve and a secondary valve; The first-stage evaporator, the first-stage superheater, the first-stage turbine, the first-stage condenser, the first-stage working fluid pump, and the first-stage valve constitute the first-stage loop. This allows the working fluid to absorb heat and undergo an evaporative phase change in the first-stage evaporator. The generated steam enters the first-stage superheater, is reheated to the superheat temperature, and then enters the first-stage turbine to perform work, driving the first-stage generator to generate electricity. The exhaust steam flowing out of the first-stage turbine enters the first-stage condenser and is cooled by cold seawater pumped by the cold seawater pump. Subsequently, it is pressurized by the first-stage working fluid pump and transported to the first-stage evaporator, completing one first-stage cycle. The secondary evaporator, secondary superheater, secondary turbine, secondary condenser, secondary working fluid pump, and secondary valve constitute a second-stage loop. Warm seawater flows from the outlet of the primary evaporator into the secondary superheater and secondary evaporator. The working fluid, pressurized by the secondary working fluid pump, enters the secondary evaporator to exchange heat with the warm seawater, evaporating into gas. It then enters the secondary superheater to absorb heat from the warm seawater, reaching a superheated state before entering the secondary turbine. There, it expands and performs work, driving the secondary generator to generate electricity. The expanded exhaust gas flows into the secondary condenser, where it exchanges heat with the cold seawater pumped by the cold seawater pump, condensing into liquid. This liquid is then pressurized and transported by the secondary working fluid pump, completing one cycle of the second-stage loop.

[0009] Preferably, in the aforementioned ocean thermal energy conversion power generation system, the primary evaporator and the secondary evaporator each include a guide rod, a support rod, multiple evaporator heat exchange plates, and two end plates. Multiple evaporator heat exchange plates are arranged between the end plates. The support rod is located at the upper and lower ends of the evaporator heat exchange plates, and both ends of the support rod are connected to the end plates. The guide rod is provided on both sides of the evaporator heat exchange plates. The evaporator heat exchange plate includes a plate body, an evaporator medium inlet, an evaporator medium outlet, a groove structure for the initial boiling zone, a low aspect ratio corrugated zone and a high aspect ratio corrugated zone. The upper end of the plate body is provided with the evaporator medium outlet, and the lower end of the plate body is provided with the evaporator medium inlet. The plate body is provided with the low aspect ratio corrugated zone, the high aspect ratio corrugated zone and the groove structure for the initial boiling zone from top to bottom. The working fluid flows in from the evaporator medium inlet, is guided through the groove structure of the initial boiling zone, and then passes through the high aspect ratio corrugated zone and the low aspect ratio corrugated zone of the evaporator in sequence, which enhances the disturbance and boiling. Finally, the working fluid flows out from the evaporator medium outlet.

[0010] Preferably, in the aforementioned ocean thermal energy conversion system, the groove structure of the initial boiling zone is a V-shaped groove structure.

[0011] Preferably, in the ocean thermal energy conversion power generation system, both the primary condenser and the secondary condenser include guide rods, support rods, condenser heat exchange plates, and end plates. Multiple condenser heat exchange plates are arranged between the end plates. The support rods are located at the upper and lower ends of the condenser heat exchange plates, and both ends of the support rods are connected to the end plates. The guide rods are located on both sides of the condenser heat exchange plates. The condenser heat exchange plate includes a plate body, a condenser medium inlet, a high aspect ratio corrugated region, a hydrophobic structure region, a low aspect ratio corrugated region, and a condenser medium outlet. The upper end of the plate body is provided with the condenser medium inlet, and the lower end of the plate body is provided with the condenser medium outlet. The plate body is provided with the high aspect ratio corrugated region, the low aspect ratio corrugated region, and the hydrophobic structure region from top to bottom. This allows the working fluid exhaust gas to flow in from the condenser medium inlet, undergo enhanced fluid disturbance and heat exchange in the high aspect ratio corrugated region, and then condense into liquid in the low aspect ratio corrugated region and the hydrophobic structure region before flowing out from the condenser medium outlet.

[0012] Preferably, in the aforementioned ocean thermal energy conversion system, the hydrophobic structure region of the condenser is a U-shaped groove structure.

[0013] In the aforementioned ocean thermal energy conversion system, preferably, the working fluid is any one of a binary mixture of R717 and R134a, a binary mixture of R717 and R125, and a binary mixture of R134a and R32.

[0014] In the aforementioned ocean thermal energy conversion system, preferably, the mass of R717 in the R717 and R134a mixed working fluid accounts for 8-12% of the total mass of the mixture, with the remainder being R134a.

[0015] In the aforementioned ocean thermal energy conversion system, preferably, the mass of R717 in the R717 and R125 mixed working fluid accounts for 40%-60% of the total mass of the mixture, with the remainder being R125.

[0016] In the aforementioned ocean thermal energy conversion system, preferably, the mass of R32 in the R134a and R32 mixed working fluid accounts for 3-5% of the total mass of the mixture, with the remainder being R134a.

[0017] The beneficial effects are: The parallel superheated two-stage Rankine cycle power configuration used in this invention, compared with the traditional single-stage Rankine cycle power configuration, achieves the cascade utilization of warm and cold seawater. The two-stage parallel superheater raises the working fluid temperature to a superheated state, improving the working capacity of the circulating working fluid and mitigating the turbine's operational risks.

[0018] This invention utilizes a non-azeotropic working fluid to enhance the thermodynamic performance of a thermoelectric power generation system and reduce the inherent irreversible losses of pure fluid working fluids in the Rankine cycle heat exchange process. A specific ratio of non-azeotropic working fluid is employed to better match the used cycle power configuration. The use of a non-azeotropic working fluid increases the matching degree between the temperature changes in the evaporator / condenser / cold seawater and the working fluid temperature changes. Completely evaporable non-azeotropic mixtures are preferable in terms of operational simplicity and system complexity, minimizing irreversible cycle losses and achieving deep utilization of ocean thermal energy.

[0019] This invention utilizes a micro-surface design in the evaporator and condenser. Micro-grooves are incorporated into the boiling zone of the evaporator plates to enhance fluid turbulence and increase the heat exchange area, thereby improving heat exchange efficiency. High aspect ratio corrugations are employed in the condenser plates to further enhance fluid turbulence. The fluid then passes through low aspect ratio corrugated zones and hydrophilic / hydrophobic structures, reducing the accumulation of condensate along the heat exchange plates and the thickness of the liquid film, thus improving condensation efficiency. Simultaneously, the use of low aspect ratio corrugations minimizes pressure loss during fluid flow. The optimized evaporator and condenser are more suitable for fluid heat exchange processes at low temperatures, enabling greater heat exchange between warm seawater and the circulating working fluid, which is beneficial for enhancing the efficiency of the circulating system and its power generation capacity.

[0020] This invention improves the tiered utilization of warm and cold seawater energy by employing a parallel superheated two-stage Rankine cycle power configuration. It is particularly effective in utilizing cold seawater, which is difficult to extract. The introduction of the superheater increases the temperature of the working fluid entering the turbine, improving the overall system thermal efficiency and power generation capacity. Simultaneously, the power generation system uses a non-azeotropic mixture as the circulating working fluid. Utilizing the non-isothermal phase change characteristics of the working fluid improves the matching degree of the warm and cold working fluid temperature curves within the evaporator / condenser, reducing irreversible losses in the cycle and achieving efficient thermoelectric conversion and power output. This invention provides an efficient and stable power supply solution for nearshore power plants and power consumption sites, realizing the effective utilization of clean energy. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the parallel superheated two-stage Rankine cycle power configuration of the present invention; Figure 3 This is a schematic diagram of the overall structure of the evaporator / condenser of the present invention; Figure 4 This is a schematic diagram of the heat exchange plate structure of the evaporator of the present invention; Figure 5 This is a schematic diagram of the heat exchange plate structure of the condenser of the present invention; Figure 6 The impact of component allocation on the levelized cost of energy for a 30kW thermoelectric power generation system.

[0022] In the picture: 1. Warm seawater pump; 2. Cold seawater pump; 3. Cold seawater pipeline; 4. Warm seawater pipeline; 11. First-stage superheater; 12. First-stage turbine; 13. First-stage generator; 14. First-stage evaporator; 15. First-stage condenser; 16. First-stage working fluid pump; 17. Primary valve; 18. Secondary superheater; 19. Secondary turbine; 20. Secondary evaporator; 21. Second-stage generator; 22. Second-stage condenser; 23. Second-stage working fluid pump; 24. Second-stage valve; 25. Guide rod; 26. Support rod; 27. Evaporator heat exchange plates; 28. End plate; 29. ​​Evaporator medium inlet; 30. Groove structure of the initial boiling zone; 31. Evaporator medium outlet; 32. Low depth-to-width ratio corrugated area of ​​the evaporator; 33. High depth-to-width ratio corrugated area of ​​the evaporator; 34. Condenser medium inlet; 35. Condenser high aspect ratio corrugated area; 36. Condenser hydrophobic structure area; 37. Low depth-to-width ratio corrugated area of ​​the condenser; 38. Medium outlet of the condenser. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the system or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the use of terms such as "first," "second," etc., to define components is merely for the convenience of distinguishing the aforementioned components; unless otherwise stated, these terms have no special meaning and should not be construed as indicating or implying relative importance.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] The present invention provides an ocean thermal energy conversion system, comprising a warm seawater pump, a cold seawater pump, a cold seawater pipeline, a warm seawater pipeline, and an ocean thermal energy conversion module; The thermoelectric power generation module includes an evaporator mechanism, a superheater mechanism, a turbine mechanism, a condenser mechanism, a working fluid pump mechanism, a throttle valve mechanism, and a generator mechanism. The evaporator mechanism, the superheater mechanism, the turbine mechanism, the condenser mechanism, the working fluid pump mechanism, the throttle valve mechanism, and the generator mechanism form a parallel superheated two-stage circulation loop. The inlet of the warm seawater pipeline is installed at the surface seawater, and the inlet of the cold seawater pipeline is installed at the deep cold seawater. The cold seawater pipeline is connected to the cold seawater pump, and the warm seawater pipeline is connected to the warm seawater pump. The warm seawater pump draws warm seawater to the hot end of the thermoelectric power generation module as a heat source, and the cold seawater pump draws deep cold seawater to the cold end of the thermoelectric power generation module as a cold source. The thermoelectric power generation module converts the thermoelectric energy contained between the warm seawater and the cold seawater into electrical energy and outputs it. The outlet of the warm seawater pipe is installed at the hot end of the thermoelectric power generation module and is connected to the evaporator mechanism and the superheater mechanism in the circulation loop. The outlet of the cold seawater pipe is installed at the cold end of the thermoelectric power generation module and is connected to the condenser mechanism in the circulation loop.

[0027] This invention proposes a parallel superheated two-stage Rankine cycle power configuration. A parallel two-stage Rankine cycle is constructed based on a multi-stage organic Rankine cycle, with superheaters added to the cycle system and arranged at the turbine inlets of the first and second stage loops, respectively. This enables multi-stage utilization of warm and cold seawater. Simultaneously, the working fluid exchanges heat with the warm seawater through the superheaters, achieving a superheated state and improving the work-capacity of the circulating working fluid. This power configuration improves upon the low work efficiency and large irreversible losses inherent in single-stage organic Rankine cycles, increasing the overall power output and energy utilization efficiency of the power generation system, significantly reducing energy losses, and thus achieving a more efficient power supply.

[0028] To enhance the thermodynamic performance of the ocean thermal energy conversion system and reduce the inherently large energy losses of pure fluid working fluid in the Rankine cycle heat transfer structure, the system also employs a non-azeotropic mixture of working fluids in a specific ratio to better match the cycle power configuration. The use of a non-azeotropic mixture increases the matching degree between the temperature changes in the evaporator / condenser / cold seawater and the working fluid temperature changes. A completely evaporable non-azeotropic mixture is preferable in terms of operational simplicity and system complexity, minimizing irreversible cycle losses and achieving deep utilization of ocean thermal energy.

[0029] To improve heat exchange efficiency and achieve miniaturization and weight reduction of heat exchangers, optimized evaporator and condenser configurations are proposed. These optimized heat exchangers are based on plate heat exchangers, utilizing micro-surface design to partition the heat exchanger plates. This enhances fluid turbulence in the boiling zone of the evaporator, reducing bubble and gas flow resistance. It also enhances fluid turbulence in the condenser heat exchange plates, using hydrophilic and hydrophobic structures to condense gas while reducing liquid accumulation on the plates and the thickness of the liquid film along the flow direction. The optimized heat exchanger structures are better suited for low-temperature fluid heat exchange, such as ocean thermal energy transfer, and can achieve greater heat exchange between warm seawater and the circulating working fluid, thus improving the efficiency of the circulating system and enhancing power generation capacity.

[0030] The following section uses an ocean thermal energy conversion system as an example to illustrate the entire technical process in detail.

[0031] Example 1 like Figure 1As shown, an ocean thermal energy conversion system includes a warm seawater pump 1, a cold seawater pump 2, and an ocean thermal energy conversion module. The inlet of the warm seawater pipe 4 is installed at the surface seawater, and the inlet of the cold seawater pipe 3 is installed at the deep cold seawater. The cold seawater pipe 3 is connected to the cold seawater pump 2, and the warm seawater pipe 4 is connected to the warm seawater pump 1. The warm seawater pump 1 draws warm seawater to the hot end of the ocean thermal energy conversion module as a heat source, and the cold seawater pump 2 draws deep cold seawater to the cold end of the ocean thermal energy conversion module as a cold source. The ocean thermal energy conversion module converts the thermal energy difference between the warm seawater and the cold seawater into electrical energy and outputs it. The first-stage evaporator 14, the first-stage superheater 11, the first-stage turbine 12, the first-stage condenser 15, the first-stage working fluid pump 16, and the first-stage valve 17 constitute the first-stage loop. The working fluid absorbs heat in the first-stage evaporator 14 and undergoes an evaporation phase change. The generated steam enters the first-stage superheater 11 and is heated to the superheat temperature again before entering the first-stage turbine 12 to do work and drive the first-stage generator 13 to generate electricity. The exhaust steam flowing out of the first-stage turbine 12 enters the first-stage condenser 15 and is cooled by cold seawater pumped by the cold seawater pump 2. Then, it is pressurized and transported to the first-stage evaporator 14 by the first-stage working fluid pump 16 to complete one first-stage cycle. The secondary evaporator 20, secondary superheater 18, secondary turbine 19, secondary condenser 22, secondary working fluid pump 23, and secondary valve 24 constitute the second-stage loop. Warm seawater flows into the secondary superheater 18 and secondary evaporator 20 through the outlet of the primary evaporator 14. The working fluid is pressurized by the secondary working fluid pump 23 and enters the secondary evaporator 20 to exchange heat with the warm seawater, evaporating into gas. It then enters the secondary superheater 18 to absorb heat from the warm seawater, reaching a superheated state and entering the secondary turbine 19. It expands and does work, driving the secondary generator 21 to generate electricity. The expanded exhaust gas flows into the secondary condenser 22, exchanges heat with the cold seawater pumped by the cold seawater pump 2, and condenses into liquid. It is then pressurized and transported by the secondary working fluid pump 23 and controlled by the secondary valve 24 to complete one cycle of the second-stage loop.

[0032] like Figure 3 and Figure 4 As shown, the first-stage evaporator 14 and the second-stage evaporator 20 respectively include a guide rod 25, a support rod 26, multiple evaporator heat exchange plates 27 and two end plates 28. Multiple evaporator heat exchange plates are arranged between the end plates. The support rod is set at the upper and lower ends of the evaporator heat exchange plates, and the two ends of the support rod are connected to the end plates. Guide rods are provided on both sides of the evaporator heat exchange plates. The evaporator heat exchange plate includes a plate body, an evaporator medium inlet 29, an evaporator medium outlet 31, an initial boiling zone groove structure 30, an evaporator low depth-to-width ratio corrugated zone 32, and an evaporator high depth-to-width ratio corrugated zone 33. The upper end of the plate body is provided with the evaporator medium outlet 31, and the lower end of the plate body is provided with the evaporator medium inlet 29. The plate body is provided with the evaporator low depth-to-width ratio corrugated zone 32, the evaporator high depth-to-width ratio corrugated zone 33, and the initial boiling zone groove structure 30 from top to bottom. The working fluid flows in from the evaporator medium inlet 29, and after being guided, it flows through the groove structure 30 of the initial boiling zone. Then, the working fluid passes through the high aspect ratio corrugated zone 33 and the low aspect ratio corrugated zone 32 of the evaporator in sequence, which enhances the disturbance and boiling. Finally, the working fluid flows out from the evaporator medium outlet 31.

[0033] The groove structure 30 in the initial boiling zone is a V-shaped groove structure.

[0034] The flow region on the surface of the heat exchange plates in the segmented boiling enhancement evaporator is divided into an initial boiling zone and a stable boiling zone. The evaporator plates are optimized using micro-surface treatment techniques. In the initial boiling zone, a surface with micro-grooves is added to increase the vaporization nucleus and heat exchange area, enhancing the boiling process during fluid heat exchange. The aspect ratio of the plate corrugation curve is controlled, maintaining a constant corrugation depth. Sections with smaller corrugation widths are high aspect ratio corrugation zones with steep corrugation changes, while sections with larger corrugation widths are low aspect ratio corrugation zones with gentler corrugation changes. The steep characteristics of the high aspect ratio corrugations enhance the disturbance of small bubbles and the working fluid in the initial boiling zone, improving the local heat transfer coefficient. The gentle characteristics of the low aspect ratio corrugations reduce the flow resistance of large bubbles and gas in the stable boiling zone, minimizing pressure loss.

[0035] Both the primary condenser 15 and the secondary condenser 22 include guide rods, support rods, condenser heat exchange plates and end plates. Multiple condenser heat exchange plates are arranged between the end plates. Support rods are set at the upper and lower ends of the condenser heat exchange plates, and both ends of the support rods are connected to the end plates. Guide rods are provided on both sides of the condenser heat exchange plates. like Figure 5 As shown, the condenser heat exchange plate includes a plate body, a condenser medium inlet 34, a high aspect ratio corrugated region 35, a condenser hydrophobic structure region 36, a low aspect ratio corrugated region 37, and a condenser medium outlet 38. The upper end of the plate body is provided with the condenser medium inlet, and the lower end of the plate body is provided with the condenser medium outlet. The plate body is provided with the high aspect ratio corrugated region, the low aspect ratio corrugated region, and the hydrophobic structure region from top to bottom. This allows the working fluid exhaust steam to flow in from the condenser medium inlet 34, undergo enhanced fluid disturbance and heat exchange in the high aspect ratio corrugated region 35, and then be condensed into liquid in the low aspect ratio corrugated region 37 and the hydrophobic structure region 36 before flowing out from the condenser medium outlet 38.

[0036] The hydrophobic structure area of ​​the condenser has a U-shaped groove structure.

[0037] The heat exchange plates in the segmented condenser are divided into flow zones: a main condensation zone and a liquid accumulation zone. The main condensation zone uses high aspect ratio corrugations to enhance fluid turbulence and heat transfer through its steep structural characteristics. The liquid accumulation zone uses low aspect ratio corrugations and a biomimetic hydrophobic structure. The condensed liquid does not easily accumulate in the grooves of the flat plates, and the hydrophobic structure quickly discharges the condensed working fluid droplets, reducing liquid accumulation on the plates and the thickness of the liquid film along the flow direction.

[0038] The working fluid is any one of the following: a binary mixture of R717 and R134a, a binary mixture of R717 and R125, and a binary mixture of R134a and R32.

[0039] In the R717 and R134a mixed working medium, the mass of R717 accounts for 8-12% of the total mass of the mixture, and the remainder is R134a.

[0040] In the R717 and R125 mixed working fluid, R717 accounts for 40%-60% of the total mass of the mixture, with the remainder being R125. Preferably, R717 accounts for 50% of the total mass of the mixture.

[0041] In the R134a and R32 mixed working fluid, R32 accounts for 3-5% of the total mass of the mixture, and the remainder is R134a. Preferably, R32 accounts for 4% of the total mass of the mixture.

[0042] Among them, R717, R134a, R125 and R32 are common refrigerant types in the prior art.

[0043] Example 2 The following embodiments are provided using the quantitatively proportioned non-azeotropic working fluids proposed in this invention: Three mixtures of R717 and R134a, R717 and R125, and R134a and R32 were used as research objects. The given warm seawater temperature was 30℃, the cold seawater temperature was 4℃, the evaporator outlet temperature was 28℃, the pinch temperature was 1℃, and the allowable pressure loss per meter of straight-line pipe was 50 Pa / m. Based on the Rankine cycle energy analysis equation, the energy, net efficiency, and levelized cost of electricity of the thermoelectric power generation system were obtained through numerical calculations.

[0044] (1) Net power of ocean thermal energy conversion system w net To analyze the performance of non-azeotropic mixtures in a thermoelectric power generation system, a thermodynamic model of the system needs to be established for parameter discussion and analysis. The basic equations for Rankine cycle energy analysis are shown in Table 1.

[0045] Table 1 Energy equations for the working fluid in the cycle

[0046] In equation (1), Q in , Q e These represent heat input and evaporator heat load, respectively. m sws , m wf These represent the mass flow rates of warm seawater and the circulating working fluid, respectively. c p,sws The specific heat capacity of warm seawater; T sws,in , T sws,out These are the seawater temperatures at the evaporator inlet and outlet, respectively. h 2. h 3 represents the specific enthalpy of the circulating working fluid at the evaporator inlet and outlet, respectively.

[0047] In equation (2), W tur This refers to the turbine shaft power. h 3. h 4 represents the specific enthalpy of the circulating working fluid at the turbine inlet and outlet, respectively.

[0048] In equation (3), W ele Power generation capacity; η mec This indicates the motor efficiency.

[0049] In equation (4), Q out , Q c These represent heat output and condenser heat load, respectively. m dcs This refers to the mass flow rate of cold seawater. c p,dcs The specific heat capacity of cold seawater; T dcs,in , T dcs,out These are the seawater temperatures at the condenser inlet and outlet, respectively. h 1 represents the specific enthalpy of the circulating working fluid at the condenser outlet.

[0050] In equation (5), W pump,wf This refers to the power consumption of the working fluid pump.

[0051] For ocean thermal energy conversion systems, the power consumption of the seawater pumps is significant due to the long seawater transport distance. The formula is: (6) In the formula, Power consumption of the warm seawater (cold seawater) pump; Mass flow rate of warm seawater (cold seawater); Density of warm seawater (cold seawater); Efficiency of the warm seawater (cold seawater) pump; Pressure drop during the flow of warm (cold) seawater; Pressure drop during the transport of warm seawater from the ocean surface ΔP sws Mainly due to the flow resistance inside the surface temperature seawater pipe Δ P sws,p Flow resistance within the evaporator ΔP sws,e and the height difference between the outlet of the warm seawater pipe and sea level ΔP sws,g The resulting gravitational pressure head consists of three parts. Therefore, it can be calculated as: (7) In addition, the total pressure drop during the transport of cryogenic seawater can be given by the following formula: (8) In the formula: ΔP dcs,p The flow resistance inside the cryogenic seawater pipe; ΔP dcs,c This refers to the flow resistance within the condenser. ΔP sws,g The gravity head caused by the height difference between the cryogenic pipeline outlet and sea level; ΔP dcs,vd This refers to the hydrostatic head loss caused by the change in seawater density along the vertical depth.

[0052] After determining the power consumption of the seawater pump, the net power of the ocean thermal energy conversion system is obtained as follows: (9) In the formula, W net Net power output for ocean thermal energy conversion systems; W pump,sws Power consumption of the warm seawater pump; W pump,dcs Power consumption of the cold seawater pump; To objectively evaluate the utilization level of heat sources and heat sinks in ocean thermal energy conversion (OTEC) power generation systems under different fluid conditions, a specific net power output index is introduced, defined as the ratio of the net power of the OTEC power generation system to the mass flow rate of warm or cold seawater: (10) in, net The net power output of the ocean thermal energy conversion system; m sws(dcs) This represents the mass flow rate of warm or cold seawater.

[0053] (2) Levelized Cost of Electricity (LCOE) for Ocean Thermal Energy Generation Systems To estimate the economic cost of an ocean thermal energy conversion (OTEC) power generation system, an economic model was established using a suitable Chemical Engineering Product Cost Index (CEPCI) for 2021, based on typical cost estimation methods. Since the raw materials for OTEC are free, only component costs are considered in the cost estimation. Furthermore, the costs of the working fluid and piping connections are ignored because they constitute a small proportion of the total cost.

[0054] The cost of plate evaporators and condensers is: (11) In the formula, The basic cost of carbon steel plate heat exchangers operating under near-environmental pressure; F M,PHE and F P,PHE These are material factors and pressure factors, respectively; Z 1,PHE and Z 2,PHE Constant factors for plate heat exchangers; F s To account for the additional material, labor, transportation, and superheating costs in the manufacturing process of system heat exchangers that utilize ocean thermal energy conversion; CEPCI Used to update equipment procurement costs for different years.

[0055] The basic cost of a plate heat exchanger is: (12) In the formula: K 1,PHE , K 2,PHE ,K 3,PHE For plate heat exchangers, the constant factor is ; A PHE This refers to the heat exchange area per square meter.

[0056] Titanium was introduced to prevent seawater corrosion, thus determining the material correction factor. The pressure factor depends on the operating pressure. (13) In the formula: This is the pressure correction factor; B 1,PHE , B 2,PHE , B 3,PHE It is a constant factor; P PHE This represents the working pressure value, expressed in bars.

[0057] The pumps in an ocean thermal energy conversion system include working fluid pumps and seawater pumps, both of which are centrifugal pumps. Their cost can be expressed as: (14) In the formula, The investment cost of the pump; The basic cost of the pump; F M,pump and F P,pump The material factor and pressure factor of the pump; Z 1,pump and Z 2,pump This is a constant value for centrifugal pumps.

[0058] The basic cost of a pump, determined by its power consumption, is: (15) In the formula, K 1,pump , K 2,pump , and K 3,pump This is a constant factor for centrifugal pumps; W pump This represents the pump's power, measured in kW.

[0059] Material factors are selected based on the type of stainless steel, resulting in the pressure factors: (16) In the formula: The pump's operating pressure; B 1,pump , B 2,pump and B 3,pump All are constant factors, and the pump outlet pressure is in bar.

[0060] The formula for calculating the cost of a turbine is: (17) In the formula: The investment cost of the turbine; The basic cost of a turbine; F tur The mixing coefficient for turbine material (stainless steel) and pressure correction.

[0061] The basic cost of a turbine can be calculated using the following formula: (18) In the formula: K 1,tur , K 2,tur , and K 3,tur For turbine constant factors, W tur The turbine shaft power is expressed in kW, and all the constant factors required in the formula are listed in Table 3.

[0062] Table 3. Constant Factors in the Economic Model

[0063] The cost of the generator is: (19) In the formula, The investment cost of the generator; W ele The system power generation is measured in kW, taking into account mechanical losses and rectifier heat exchanger losses.

[0064] Basically, the cost of all the aforementioned equipment accounts for only half of the system cost; the remaining cost mainly comes from the seawater pipelines, especially the deep cold seawater pipelines, which are much longer than the warm seawater pipelines. The cost of seawater pipelines is generally related to the diameter and length of the pipelines. The standard data used in this article for calculations comes from the seawater pipeline cost report of the Okinawa Ocean Thermal Energy Conversion Project: (20) In the formula, C p C represents the investment cost of seawater pipelines. p,b For the basic attribute equipment cost, the deep cold seawater pipe (diameter 1.2m, length 3700m) and the surface warm seawater pipe (diameter 1.4m, length 250m) located in Okinawa, Japan were selected as the basic attribute equipment, with costs of US$52.461 million and US$11.427 million respectively. D p , D p,b These are the actual pipe diameter and the basic attribute equipment pipe diameter, respectively. L p , L p,b These are the actual pipe length and the base attribute pipe length, respectively.

[0065] In summary, the initial cost of an ocean thermal energy conversion (OTEC) power generation system can be given by the following formula: (twenty one) In the formula, C OTEC The total cost of the ocean thermal energy conversion system; C PHX This represents the total investment cost of the heat exchanger. C pump,wf , C pump,sws , C pump,dcs The investment costs are for working fluid pumps, warm seawater pumps, and cold seawater pumps, respectively. C tur , C gen These are the investment costs for the turbine and generator, respectively. C p,sws , C p,dcs The investment costs are for warm seawater pipelines and cold seawater pipelines, respectively.

[0066] Therefore, the levelized cost of electricity (LCOE) of an ocean thermal energy conversion system can be calculated as follows: (twenty two) In the formula, CRE For capital cost recovery,C M For operating and maintenance costs, set as C OTEC 1.5%, t op The annual operating time is set to 8000 hours per year.

[0067] (twenty three) In the formula, i The interest rate is set at 5%. k The lifespan of the ocean thermal energy conversion system is selected as 20 years.

[0068] like Figure 6 As shown: In a 30 kW OTEC system, the levelized cost of electricity (LCOE) for the binary mixture of R717 and R134a is lowest at $2.1 / kWh when the R717 mass fraction is 0.15, which is 67% lower than that for pure R717. When the R717 mass fraction is 0.5, the LCOE for the binary mixture of R717 and R125 is lowest at $2.76 / kWh, which is 57.8% lower than that for pure R717. When the R32 mass fraction is 0.04, the LCOE for the binary mixture of R134a and R32 is lowest at $4.4 / kWh, which is 30.8% lower than that for pure R717. This demonstrates that the proposed OTEC system, using the aforementioned fixed-ratio non-azeotropic working fluid, significantly increases the system's net power output and reduces operating costs compared to traditional single-component working fluids.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A marine thermal energy conversion power generation system, characterized in that, It includes a warm seawater pump (1), a cold seawater pump (2), a cold seawater pipeline (3), a warm seawater pipeline (4), and a thermoelectric power generation module; The thermoelectric power generation module includes an evaporator mechanism, a superheater mechanism, a turbine mechanism, a condenser mechanism, a working fluid pump mechanism, a throttle valve mechanism, and a generator mechanism. The evaporator mechanism, the superheater mechanism, the turbine mechanism, the condenser mechanism, the working fluid pump mechanism, the throttle valve mechanism, and the generator mechanism form a parallel superheated two-stage circulation loop. The inlet of the warm seawater pipe (4) is installed at the surface seawater, and the inlet of the cold seawater pipe (3) is installed at the deep cold seawater. The cold seawater pipe (3) is connected to the cold seawater pump (2), and the warm seawater pipe (4) is connected to the warm seawater pump (1). The warm seawater pump (1) draws warm seawater to the hot end of the temperature difference power generation module as a heat source, and the cold seawater pump (2) draws deep cold seawater to the cold end of the temperature difference power generation module as a cold source. The temperature difference power generation module converts the temperature difference energy contained between the warm seawater and the cold seawater into electrical energy and outputs it. The outlet of the warm seawater pipe (4) is installed at the hot end of the thermoelectric power generation module and is connected to the evaporator mechanism and the superheater mechanism in the circulation loop. The outlet of the cold seawater pipe (3) is installed at the cold end of the thermoelectric power generation module and is connected to the condenser mechanism in the circulation loop.

2. The ocean thermal energy conversion power generation system according to claim 1, characterized in that, The evaporator mechanism includes a primary evaporator (14) and a secondary evaporator (20); the superheater mechanism includes a primary superheater (11) and a secondary superheater (18); the condenser mechanism includes a primary condenser (15) and a secondary condenser (22); the turbine mechanism includes a primary turbine (12) and a secondary turbine (19); the generator mechanism includes a primary generator (13) and a secondary generator (21); the working fluid pump mechanism includes a primary working fluid pump (16) and a secondary working fluid pump (23); and the throttle valve mechanism includes a primary valve (17) and a secondary valve (24). The first-stage evaporator (14), the first-stage superheater (11), the first-stage turbine (12), the first-stage condenser (15), the first-stage working fluid pump (16), and the first-stage valve (17) constitute the first-stage loop, so that the working fluid absorbs heat in the first-stage evaporator (14) and undergoes an evaporation phase change. The generated steam enters the first-stage superheater (11), is heated again to the superheat temperature, and then enters the first-stage turbine (12) to do work, driving the first-stage generator (13) to generate electricity. The exhaust steam flowing out of the first-stage turbine (12) enters the first-stage condenser (15) and is cooled by the cold seawater pump (2). Then, it is pressurized and transported to the first-stage evaporator (14) by the first-stage working fluid pump (16), completing one first-stage circulation loop. The secondary evaporator (20), the secondary superheater (18), the secondary turbine (19), the secondary condenser (22), the secondary working fluid pump (23), and the secondary valve (24) constitute a second-stage loop. Warm seawater flows into the secondary superheater (18) and the secondary evaporator (20) through the outlet of the primary evaporator (14). The working fluid is pressurized by the secondary working fluid pump (23) and enters the secondary evaporator (20) to exchange heat with the warm seawater, evaporates into gas, and then enters the secondary superheater (18) to absorb heat from the warm seawater, reaches a superheated state, and enters the secondary turbine (19) to expand and do work, driving the secondary generator (21) to generate electricity. The expanded exhaust gas flows into the secondary condenser (22) to exchange heat with the cold seawater pumped by the cold seawater pump (2), condenses into liquid, and is pressurized and transported by the secondary working fluid pump (23) to complete one second-stage circulation loop.

3. The ocean thermal energy conversion power generation system according to claim 2, characterized in that, The primary evaporator (14) and the secondary evaporator (20) respectively include a guide rod (25), a support rod (26), multiple evaporator heat exchange plates (27) and two end plates (28). Multiple evaporator heat exchange plates are arranged between the end plates. The support rod is set at the upper and lower ends of the evaporator heat exchange plates, and both ends of the support rod are connected to the end plates. The guide rod is provided on both sides of the evaporator heat exchange plates. The evaporator heat exchange plate (27) includes a plate body, an evaporator medium inlet (29), an evaporator medium outlet (31), a groove structure (30) for the initial boiling zone, a low aspect ratio corrugated zone (32) for the evaporator, and a high aspect ratio corrugated zone (33) for the evaporator. The upper end of the plate body is provided with the evaporator medium outlet (31), and the lower end of the plate body is provided with the evaporator medium inlet (29). The plate body is provided with the low aspect ratio corrugated zone (32), the high aspect ratio corrugated zone (33), and the groove structure (30) for the initial boiling zone from top to bottom. The working fluid flows in from the evaporator medium inlet (29), and after being guided, it flows through the groove structure (30) of the initial boiling zone. Then, the working fluid passes through the high aspect ratio corrugated zone (33) and the low aspect ratio corrugated zone (32) of the evaporator in sequence, which strengthens the disturbance and boiling. Finally, the working fluid flows out from the evaporator medium outlet (31).

4. The ocean thermal energy conversion power generation system according to claim 3, characterized in that, The groove structure (30) of the initial boiling zone is a V-shaped groove structure.

5. The ocean thermal energy conversion power generation system according to claim 4, characterized in that, Both the primary and secondary condensers include guide rods, support rods, condenser heat exchange plates, and end plates. Multiple condenser heat exchange plates are arranged between the end plates. The support rods are located at the upper and lower ends of the condenser heat exchange plates, and both ends of the support rods are connected to the end plates. The guide rods are located on both sides of the condenser heat exchange plates. The condenser heat exchange plate includes a plate body, a condenser medium inlet (34), a condenser high aspect ratio corrugated area (35), a condenser hydrophobic structure area (36), a condenser low aspect ratio corrugated area (37), and a condenser medium outlet (38). The upper end of the plate body is provided with the condenser medium inlet, and the lower end of the plate body is provided with the condenser medium outlet. The plate body is provided with the condenser high aspect ratio corrugated area, the condenser low aspect ratio corrugated area, and the condenser hydrophobic structure area from top to bottom. This is to enable the working fluid exhaust gas to flow in from the condenser medium inlet (34), enhance fluid disturbance and heat exchange through the condenser high aspect ratio corrugated area (35), and then condense into liquid through the condenser low aspect ratio corrugated area (37) and the condenser hydrophobic structure area (36), and flow out from the condenser medium outlet (38).

6. The ocean thermal energy conversion power generation system according to claim 5, characterized in that, The hydrophobic structure area of ​​the condenser is a U-shaped groove structure.

7. The ocean thermal energy conversion power generation system according to any one of claims 2 to 6, characterized in that, The working fluid is any one of the following: a binary mixture of R717 and R134a, a binary mixture of R717 and R125, and a binary mixture of R134a and R32.

8. The ocean thermal energy conversion power generation system according to claim 7, characterized in that, In the R717 and R134a mixed working fluid, R717 accounts for 8-12% of the total mass of the mixture, and the remainder is R134a.

9. The ocean thermal energy conversion power generation system according to claim 7, characterized in that, In the R717 and R125 mixed working fluid, R717 accounts for 40%-60% of the total mass of the mixture, and the remainder is R125.

10. The ocean thermal energy conversion power generation system according to claim 7, characterized in that, In the R134a and R32 mixed working fluid, R32 accounts for 3-5% of the total mass of the mixture, and the remainder is R134a.

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