Molten salt heat storage system coupled with ocean temperature difference power generation and supercritical seawater desalination device

Abstract

The present invention belongs to the technical field of new energy industries, and particularly relates to a molten salt thermal energy storage system coupled with an ocean thermal energy conversion power generation and supercritical seawater desalination device and method, including a trough solar molten salt collector, a hot molten salt storage tank, a cold molten salt storage tank, a low-temperature molten salt heater, a high-temperature molten salt heater, a liquid nitrogen storage tank, pumps, coolers, a first recuperator, heaters, turbines, gate valves, compressors, a second recuperator, a gravity separator, etc.; The molten salt (NaNO3 (60%) and KNO3 (40%)) stored in the cold molten salt tank is transported to the trough solar collector for heating, and the heated molten salt flows into the hot molten salt tank. Under the action of a pump, the high-temperature molten salt in the hot molten salt tank is transported to the high-temperature molten salt heater, and then to the low-temperature molten salt heater for step-by-step utilization of energy. The molten salt finally reaches the low-temperature molten salt storage tank from the low-temperature molten salt heater, completing a closed loop. The flow direction of the molten salt is opposite to the flow direction of the high-temperature seawater, enabling the high-temperature seawater to absorb more heat.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy industry, and in particular relates to a molten salt heat storage system coupled with ocean temperature difference power generation and a supercritical seawater desalination device. Background Art

[0002] The principle of ocean temperature difference power generation (OTEC) is to heat the low boiling point working fluid with the surface seawater (24-28℃) to vaporize it, or to vaporize the seawater by pressure drop to drive the turbine to do work, but the ocean temperature difference is small and the power output is low. The operation mode of solar thermal power generation system is flexible, but the solar thermal power generation system is affected by unstable factors such as weather and day and night alternation. This will cause the operation of the solar thermal power generation system to be unstable, and the molten salt heat storage system can overcome this defect and become the preferred medium for heat storage in solar power stations. The current working temperature of binary molten salt is generally (290-565℃). The molten salt heated by solar energy complements the ocean temperature difference power generation technology, which can increase the temperature difference of seawater and enable the device to output more energy to the outside. When seawater is under supercritical conditions (P>22.1MPa; T>374℃), the solubility of salt in water drops sharply, so under high temperature and high pressure conditions, seawater is desalinated. The use of solar molten salt to provide heat for supercritical seawater desalination makes the device more energy-saving and environmentally friendly, and the energy output is more stable.

[0003] Through the above analysis, the problems and defects of the existing technology are as follows: the ocean temperature difference power generation technology requires a lot of energy to extract seawater from the deep sea and the high-temperature seawater from the shallow sea area. The seawater in the existing ocean temperature difference power generation technology is directly discharged into the sea after use, resulting in energy waste; in the existing ocean temperature difference power generation technology, the temperature difference between high-temperature seawater and low-temperature seawater is small, so that the external energy output of the device is low; the existing supercritical seawater desalination technology requires heating the seawater to make it reach a supercritical state. In the initial stage, it is necessary to mix nitrogen with the seawater in a certain proportion so that the seawater can quickly reach the pressure required for the supercritical state, which makes the device complicated and consumes more energy. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a molten salt heat storage system coupling ocean temperature difference power generation and a supercritical seawater desalination device.

[0005] The present invention is implemented as follows: a molten salt heat storage system couples ocean temperature difference power generation and supercritical seawater desalination device, including a trough type solar molten salt collector, a hot molten salt storage tank, a cold molten salt storage tank, a low temperature molten salt heater, a high temperature molten salt heater, a liquid nitrogen storage tank, a pump, a cooler, a first regenerator, a heater, a turbine, a gate valve, a compressor, a second regenerator, a gravity separator, a brine pool, and a desalination pool;

[0006] The molten salt (NaNO3 (60%) and KNO3 (40%)) stored in the cold molten salt tank is transported to the trough solar collector for heating. The heated molten salt flows to the hot molten salt tank. Under the action of the pump, the high-temperature molten salt in the hot molten salt tank is transported to the high-temperature molten salt heater, and then to the low-temperature molten salt heater for step-by-step energy utilization. The molten salt from the low-temperature molten salt heater finally reaches the low-temperature molten salt storage tank, completing a closed loop. The flow direction of the molten salt is opposite to that of the high-temperature seawater, so that the high-temperature seawater absorbs more heat.

[0007] Furthermore, ammonia, a low-boiling-point substance, is used as the working fluid of the closed cycle. The ammonia in the liquid ammonia storage tank is pressurized by a pump and transported to the regenerator to absorb part of the waste heat before reaching the heater. The low-temperature molten salt heater reuses the molten salt with low-grade heat from the high-temperature molten salt heater, and the high-temperature seawater is heated in the low-temperature molten salt heater. The seawater absorbs the heat and then goes to the heater of the heat recovery cycle to heat the ammonia in the closed cycle, so that the ammonia becomes a high-temperature and high-pressure gas. The ammonia then reaches the turbine to drive the turbine to do work and output power to the outside world. The ammonia coming out of the turbine is cooled by the low-temperature seawater in the cooler to become liquid, and finally reaches the liquid ammonia storage tank to complete a cycle. In the heat recovery cycle of ocean temperature difference power generation, in order to prevent the seawater from reaching a supercritical state, thereby causing the salt to separate and damage the low-temperature molten salt heater, the molten salt temperature and the seawater pressure must be controlled to prevent the seawater from reaching a supercritical state.

[0008] Furthermore, the high-temperature seawater coming out of the heat recovery circulation heater is in a coexistence of gas and liquid phases. The gate valve can control the closing of the process line, and the pressure of the seawater is increased by the compressor to reach the pressure in the supercritical state. Then, it passes through the regenerator in the supercritical seawater desalination device to absorb the waste heat from the desalinated water, and the temperature of the high-temperature seawater is further increased. Then, it reaches the high-temperature molten salt heater to absorb the high-grade energy from the molten salt. The temperature of the molten salt in the high-temperature molten salt heater is much higher than the temperature of the supercritical state point of the seawater, which can ensure that the seawater reaches the supercritical state. The seawater that reaches the supercritical state passes through the gravity separator. Because the solubility of the salt in the supercritical seawater drops sharply, NaCl and other components in the gravity separator reach the brine pool; and the desalinated water flows to the regenerator to transfer the heat to the high-temperature seawater pressurized by the compressor. By controlling the switch of the gate valve, the desalinated water can reach the condenser, and the low-temperature seawater in the condenser is cooled to become liquid, and finally flows to the desalination pool.

[0009] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0010] First, in the existing molten salt heat storage and ocean temperature difference power generation technology, there are problems such as low energy utilization efficiency and high system complexity. When molten salt stores and transfers heat, it can often only achieve a single energy utilization method, while ocean temperature difference power generation is limited by the selection of working fluids and circulation efficiency. The present invention achieves multi-level utilization and efficient conversion of energy by coupling the molten salt heat storage system with the ocean temperature difference power generation technology, effectively solving the problem of low energy utilization efficiency in traditional technologies.

[0011] The high-temperature seawater discharged from ocean temperature difference power generation is used for supercritical seawater desalination. At this time, the temperature and pressure of the high-temperature seawater are relatively high, which reduces the heat required for the seawater to reach a supercritical state. The high-grade heat of molten salt is used to heat the seawater, which can avoid the pollution to the environment caused by using fossil fuels to provide heat.

[0012] In addition, the traditional technology is not precise enough in the processing and control of molten salt and seawater, which can easily lead to equipment damage and environmental pollution. The present invention avoids the problem of salt separation caused by seawater reaching a supercritical state by precisely controlling the temperature of molten salt and the pressure of seawater, thereby protecting the equipment from damage and reducing the risk of environmental pollution. This refined control method significantly improves the safety and stability of the system.

[0013] In terms of supercritical seawater desalination, traditional technologies often have difficulty in achieving an efficient and continuous desalination process. The present invention achieves efficient desalination of seawater in a supercritical state and heat recovery by introducing equipment such as a gravity separator and a regenerator, greatly improving desalination efficiency and water resource utilization. This innovative technical route has brought new development opportunities to the field of seawater desalination.

[0014] In summary, the present invention not only solves the problems of low energy utilization efficiency and high system complexity in traditional technologies by coupling the molten salt heat storage system with the ocean temperature difference power generation technology, but also realizes efficient energy conversion and effective utilization of water resources through precise control and efficient desalination technology. This significant technological progress not only improves energy utilization efficiency and environmental protection performance, but also provides new ideas and directions for the development of technologies in related fields.

[0015] Second, the technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0016] It fills the gap between solar molten salt heating ocean temperature difference power generation technology and supercritical seawater desalination technology, and uses finite-time thermodynamics theory to analyze and calculate the ocean temperature difference power generation model of the device.

[0017] The technical solution of the present invention solves the technical problems that people have been eager to solve but have never been successful: the problem of small temperature difference and low external output energy in ocean temperature difference power generation technology is solved. The technology refers to the parameters of the national sea cycle. After increasing the temperature difference, the net power of the technology is improved; the problem of direct discharge of seawater after providing energy to the cycle in ocean temperature difference power generation technology is solved, and the high-temperature seawater is transported to the supercritical seawater desalination part for desalination; the initial conditions of high temperature and high pressure required for supercritical seawater desalination are solved, and solar energy is used to provide energy to the supercritical seawater desalination system.

[0018] The technical solution of the present invention overcomes technical prejudice: it overcomes the problems of supercritical seawater desalination technology under high temperature and high pressure conditions, such as large energy consumption, poor economic benefits, and large capital investment. It uses a solar molten salt heat storage system to heat seawater, which is more energy-saving and environmentally friendly.

[0019] Third, the present invention solves the problems of low solar energy utilization efficiency, unstable heat storage system, and high energy consumption of seawater desalination in the prior art by coupling the ocean temperature difference power generation with the supercritical seawater desalination device through the molten salt heat storage system. Traditional solar energy utilization methods usually have the defects of low heat collection efficiency and insufficient energy utilization. The present invention greatly improves the efficiency of solar energy collection and storage by using a trough-type solar molten salt collector. At the same time, molten salt, as a heat storage medium, has the characteristics of high specific heat capacity and high temperature stability, which can effectively ensure the heat storage stability and durability of the system.

[0020] In the prior art, ocean temperature difference power generation is often limited by the problems of small temperature difference and low efficiency. The present invention introduces ammonia, a low-boiling-point substance, as a working fluid, and combines heat recovery cycle and turbine power generation technology to achieve efficient temperature difference energy conversion and utilization, significantly improving power generation efficiency. In addition, the step-by-step energy utilization design using high-temperature molten salt and low-temperature molten salt heaters makes the thermal energy gradient more fully utilized, reduces energy loss, and improves the energy efficiency of the overall system.

[0021] In the prior art, supercritical seawater desalination technology is difficult to achieve large-scale application due to high energy consumption and complex equipment. The present invention couples supercritical seawater desalination with a molten salt heat storage system and an ocean temperature difference power generation system, and utilizes the high-quality thermal energy provided by high-temperature molten salt to heat seawater to a supercritical state, effectively separating salt and producing fresh water. This process not only improves desalination efficiency, but also reduces energy consumption, achieving energy conservation and environmental protection in the seawater desalination process.

[0022] The present invention achieves multi-energy complementarity and efficient utilization by integrating trough solar thermal collection, molten salt heat storage, ocean temperature difference power generation and supercritical seawater desalination technology. Compared with the existing technology, the present invention has made significant technological progress in energy utilization efficiency, system stability, power generation efficiency and seawater desalination energy consumption, and provides an innovative solution for the efficient utilization of renewable energy and seawater desalination. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 It is a schematic diagram of a molten salt heat storage system coupled with ocean temperature difference power generation and a supercritical seawater desalination device provided in an embodiment of the present invention;

[0025] Figure 2 is a Ts diagram of a regenerative cycle provided in an embodiment of the present invention;

[0026] Figure 3 The embodiment of the present invention provides m wf To W net Schematic diagram of the impact of -π relationship;

[0027] Figure 4 The embodiment of the present invention provides m wf Schematic diagram of the impact on the η-π relationship;

[0028] Figure 5 The embodiment of the present invention provides m wf For η ex Schematic diagram of the impact of -π relationship;

[0029] Figure 6 is n provided in the embodiment of the present invention t , η c To W net Schematic diagram of the impact of -π relationship;

[0030] Figure 7 is n provided in the embodiment of the present invention t , η c Schematic diagram of the impact on the η-π relationship;

[0031] Figure 8 is n provided in the embodiment of the present invention t , η c For η ex Schematic diagram of the impact of -π relationship;

[0032] Fig. 9 The embodiment of the present invention provides m H To W net Schematic diagram of the impact of -π relationship;

[0033] Fig.10 The embodiment of the present invention provides m H Schematic diagram of the impact on the η-π relationship;

[0034] Fig.11 The embodiment of the present invention provides m H For η ex Schematic diagram of the impact of -π relationship;

[0035] Fig.12 is T provided by the embodiment of the present invention H,in To W net Schematic diagram of the impact of -π relationship;

[0036] Fig.13 is T provided by the embodiment of the present invention H,in Schematic diagram of the impact on the η-π relationship;

[0037] Fig.14 is T provided by the embodiment of the present invention H,in For η ex Schematic diagram of the impact of -π relationship. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] In view of the problems existing in the prior art, the present invention provides a molten salt heat storage system coupled with ocean temperature difference power generation and a supercritical seawater desalination device. The present invention is described in detail below in conjunction with the accompanying drawings.

[0040] like Figure 1 As shown, the molten salt heat storage system provided by the embodiment of the present invention couples ocean temperature difference power generation and supercritical seawater desalination device, including a trough solar molten salt collector, a hot molten salt storage tank, a cold molten salt storage tank, a low-temperature molten salt heater, a high-temperature molten salt heater, a liquid nitrogen storage tank, a pump, a cooler, a first regenerator, a heater, a turbine, a gate valve, a compressor, a second regenerator, a gravity separator, a brine pool, and a desalinated water pool;

[0041] The molten salt (NaNO3 (60%) and KNO3 (40%)) stored in the cold molten salt tank is transported to the trough solar collector for heating. The heated molten salt flows to the hot molten salt tank. Under the action of the pump, the high-temperature molten salt in the hot molten salt tank is transported to the high-temperature molten salt heater, and then to the low-temperature molten salt heater for step-by-step energy utilization. The molten salt from the low-temperature molten salt heater finally reaches the low-temperature molten salt storage tank, completing a closed loop. The flow direction of the molten salt is opposite to that of the high-temperature seawater, so that the high-temperature seawater absorbs more heat.

[0042] Ammonia, a low-boiling-point substance, is used as the working fluid of the closed cycle. The ammonia in the liquid ammonia storage tank is pressurized by a pump and transported to the regenerator to absorb part of the waste heat before reaching the heater. The low-temperature molten salt heater reuses the low-grade heat from the molten salt passing through the high-temperature molten salt heater. The high-temperature seawater is heated in the low-temperature molten salt heater. The seawater absorbs the heat and then goes to the heater of the heat recovery cycle to heat the ammonia in the closed cycle, turning the ammonia into a high-temperature and high-pressure gas. The ammonia then reaches the turbine to drive the turbine to do work and output power to the outside world. The ammonia coming out of the turbine is cooled by the low-temperature seawater in the cooler to become liquid, and finally reaches the liquid ammonia storage tank to complete a cycle. In the heat recovery cycle of ocean temperature difference power generation, in order to prevent the seawater from reaching a supercritical state, thereby causing the salt to separate and damage the low-temperature molten salt heater, the molten salt temperature and seawater pressure must be controlled to prevent the seawater from reaching a supercritical state.

[0043] The high-temperature seawater coming out of the heat recovery circulation heater is in the coexistence of gas and liquid phases. The gate valve can control the closing of the process line. The pressure of the seawater is increased by the compressor to reach the pressure in the supercritical state. Then, it passes through the regenerator in the supercritical seawater desalination device to absorb the waste heat from the desalinated water and further increase the temperature of the high-temperature seawater. Then, it reaches the high-temperature molten salt heater to absorb the high-grade energy from the molten salt. The temperature of the molten salt in the high-temperature molten salt heater is much higher than the temperature of the supercritical state point of the seawater, which can ensure that the seawater reaches the supercritical state. The seawater that reaches the supercritical state passes through the gravity separator. Because the solubility of salt in the supercritical seawater drops sharply, NaCl and other components in the gravity separator reach the brine pool; and the desalinated water flows to the regenerator to transfer heat to the high-temperature seawater pressurized by the compressor. By controlling the switch of the gate valve, the desalinated water can reach the condenser, and the low-temperature seawater in the condenser is cooled to become liquid, and finally flows to the desalination pool.

[0044] The Ts diagrams of the heat recovery cycle device are as follows Figure 2 As shown. The device is mainly composed of pumps, regenerators, heaters, turbines, coolers and other equipment. Figure 2 Middle, process line 1-2 Srepresents the ideal reversible adiabatic compression process in the pump, 1-2 represents the actual irreversible adiabatic compression process in the pump, 2-3 represents the constant pressure heat absorption process in the regenerator, 3-4 represents the constant pressure heat absorption process in the heater, 4-5 represents the actual irreversible adiabatic expansion process in the turbine, 4-5 S It represents the ideal reversible adiabatic expansion process in the turbine, 5-6 represents the constant pressure heat release process in the regenerator, and 6-1 represents the process of the working fluid releasing heat to the low-temperature heat source.

[0045] The molten salt heat storage system provided by the present invention couples ocean temperature difference power generation with a supercritical seawater desalination device, combines trough-type solar thermal collection, molten salt heat storage, ocean temperature difference power generation and supercritical seawater desalination technology, and realizes efficient utilization of solar energy and ocean energy resources.

[0046] 1) Trough type solar molten salt collector:

[0047] The collector absorbs solar energy, heats the cold molten salt, and transports it to the hot molten salt storage tank.

[0048] 2) Hot molten salt storage tank and cold molten salt storage tank:

[0049] The cold molten salt storage tank stores unheated molten salt, which is then stored in the hot molten salt storage tank after being heated.

[0050] 3) Low temperature molten salt heater and high temperature molten salt heater:

[0051] The high-temperature molten salt heater uses hot molten salt to heat high-temperature seawater, and the heat is transferred from the high-temperature molten salt to the seawater.

[0052] Low-temperature molten salt heaters perform secondary heating, using the remaining heat to further heat the seawater.

[0053] 4) Liquid nitrogen storage tank, pump, cooler, first regenerator, heater, turbine, gate valve, compressor, second regenerator, gravity separator, brine pool, desalination pool:

[0054] Ammonia is stored in the liquid ammonia tank and pumped to the regenerator and heater after being pressurized, where it drives the turbine after evaporation.

[0055] The cooler cools the ammonia gas discharged from the turbine into liquid form and then returns it to the liquid ammonia storage tank.

[0056] The heated seawater is separated from the salt by a gravity separator, and the desalinated water flows into the desalination pool.

[0057] Working principle:

[0058] 1) Molten salt heating and storage:

[0059] The cold molten salt is transported from the cold molten salt storage tank to the trough solar molten salt collector. After absorbing solar energy, the heated molten salt flows into the hot molten salt storage tank.

[0060] The high-temperature molten salt in the hot molten salt storage tank is transported to the high-temperature molten salt heater through a pump to heat the seawater for the first time, and then enters the low-temperature molten salt heater for secondary heating, completing a closed-loop cycle.

[0061] 2) Ocean temperature difference power generation:

[0062] Ammonia, a low-boiling-point substance, is used as the working fluid. It is pressurized by a pump and enters the regenerator, absorbs part of the waste heat, and then enters the heater.

[0063] In the heater, ammonia absorbs heat from the low-temperature molten salt heater and evaporates into high-temperature and high-pressure gas, driving the turbine to generate electricity.

[0064] The ammonia gas discharged from the turbine is cooled into liquid through a cooler and returned to the liquid ammonia storage tank, completing a closed cycle.

[0065] 3) Supercritical seawater desalination:

[0066] After the high-temperature seawater comes out of the heater, it is pressurized to a supercritical state through a compressor and enters the supercritical seawater desalination device.

[0067] Under supercritical conditions, the solubility of salt in seawater decreases, and the salt is separated by a gravity separator and enters the brine pool.

[0068] The desalinated water is further cooled through the regenerator and condenser and finally enters the desalination water tank.

[0069] Ts chart analysis:

[0070] -Process line description:

[0071] 1-2s (ideal reversible adiabatic compression) and 1-2 (actual irreversible adiabatic compression): The ammonia in the pump is pressurized from liquid to high pressure.

[0072] 2-3 (Constant-pressure heat absorption process in the regenerator): The pressurized ammonia absorbs waste heat in the regenerator.

[0073] 3-4 (Constant-pressure endothermic process in the heater): Ammonia further absorbs heat in the heater and becomes a high-temperature and high-pressure gas.

[0074] 4-5 (actual irreversible adiabatic expansion) and 4-5s (ideal reversible adiabatic expansion): High temperature and high pressure ammonia expands in the turbine to do work.

[0075] 5-6 (Constant-pressure heat release process in the regenerator): The ammonia gas discharged from the turbine releases heat in the regenerator.

[0076] 6-1 (Process of working fluid releasing heat to low-temperature heat source): Ammonia gas is cooled in the cooler, becomes liquid, and returns to the liquid ammonia storage tank.

[0077] Through the above detailed description of the connection relationship and working principle, it can be seen that the system provided by the present invention can efficiently utilize solar energy and ocean temperature difference to achieve multifunctional integration of heat storage, power generation and seawater desalination, and has significant energy-saving and environmental protection benefits.

[0078] The efficiency of the pump and turbine are expressed as η c and η t To express:

[0079] η c =(h 2s -h1) / (h2-h1) (1)

[0080] η t =(h4-h5) / (h4-h 5s ) (2)

[0081] Where h1 is the specific enthalpy of ammonia before entering the pump, h 2s is the specific enthalpy of ammonia after an ideal reversible adiabatic compression process, h2 is the specific enthalpy of ammonia after an actual irreversible compression process; h3 is the specific enthalpy of ammonia after constant pressure preheating in a regenerator, h4 is the specific enthalpy of ammonia before entering the turbine, h 5s is the specific enthalpy of the working fluid ammonia after an ideal reversible adiabatic expansion process, h5 is the specific enthalpy of the working fluid ammonia after an actual irreversible expansion process, and h6 is the specific enthalpy of the working fluid ammonia after constant pressure precooling in the regenerator.

[0082] By consulting the literature, we know that the two-phase boundary of 3.2% NaCl solution is completely consistent with the two-phase boundary of seawater. Therefore, in the program calculation, the specific constant pressure heat capacity formula of 3.2% NaCl solution is used instead of the specific constant pressure heat capacity formula of high temperature seawater. p,H , because the specific constant-pressure heat capacity of NaCl solution at high temperature and high pressure is difficult to calculate, so it is simplified. The standard constant-pressure heat capacity of each component i is as follows:

[0083]

[0084] Table 1 Initial design parameters

[0085]

[0086] C p，H =0.034*C p，Nacl +0.966*C p，H2O (4)

[0087] Assume the pressure ratio is π; T H,in and T H,out are the inlet and outlet temperatures of high-temperature seawater, respectively; T L,in and T L,outare the inlet and outlet temperatures of low-temperature seawater, respectively; T0 and P0 are the ambient temperature and pressure, respectively; m H 、m L and m wf are the mass flow rates of high-temperature seawater, low-temperature seawater and working fluid ammonia, kg·s -1 ;c p,L are the specific heat capacity of low-temperature seawater at constant pressure, kJ·(kg·K) -1 Thermal conductivity is defined as the product of the heat transfer area and the heat transfer coefficient of the heat exchanger, which represents the heat transfer capacity of the heat exchanger. The thermal conductivity of the heater, cooler and regenerator are represented by U H , U L and U R According to the heat transfer between the working fluid and the heat source, the properties of the heat source and the heat exchanger theory, the cycle heat absorption rate Q H , heat release rate Q L , heat recovery rate Q R They are:

[0088]

[0089]

[0090] From the thermodynamic properties of the working fluid, we can get Q H , Q L and Q R They are:

[0091] Q H =m wf ·(h4-h3) (8)

[0092] Q L =m wf ·(h6-h1) (9)

[0093] Q R =m wf (h3-h2) = m wf ·(h5-h6) (10)

[0094] Total thermal conductivity U T is the sum of the thermal conductivity of each heat exchanger:

[0095] U T =U H +U R +U L (11)

[0096] This paper assumes that the total thermal conductivity is a constant. The thermal conductivity distribution ratio ψ is defined as the ratio of the thermal conductivity of each heat exchanger to the total thermal conductivity. The thermal conductivity distribution ratio of the regenerator is ψ R =U R / UT , the heater thermal conductivity distribution ratio is ψ H =U H / U T , the cooler thermal conductivity distribution ratio is ψ L =U L / U T , and the following relationship exists:

[0097] ψ H +ψ R +ψ L =1 (12)

[0098] The definition of the net power of the heat recovery cycle is W net is the difference between turbine power and pump power:

[0099] W net =m wf ·(h4-h5)-m wf ·(h2-h1) (13)

[0100] The definition of thermal efficiency η is net power W net The cycle heat absorption Q H Ratio:

[0101] η=W net / Q H =1-Q L / Q H (14)

[0102] Input for this loop e H The heat released by high temperature flue gas to the circulation Heat absorbed by cooling water The difference is calculated as:

[0103]

[0104] The efficiency definition is:

[0105] η ex =W net / e H (16)

[0106] In this chapter, a finite time thermodynamic analysis and optimization program of the regenerative cycle is written by MATLAB software. H,in ,T L,in ,U H ,U L ,U R ,η c and η t) The fsolve function can be used to solve the temperature and specific enthalpy of each state point.

[0107] The specific initial design point parameters are shown in Table 2.

[0108] Table 2 Initial design parameters

[0109]

[0110] Performance Analysis

[0111] Figure 3 Given m wf At 100 kg·s -1 -120kg·s -1 In the range of π, when π changes from 1 to 2, the cycle W net As π changes. Figure 3 It can be seen that the cycle W net As π increases, it presents a parabolic shape, first increasing and then decreasing. wf For a certain value, there exists a unique π such that W net reaches the optimal value. As m wf The increase of W net The pressure ratio corresponding to the optimal value decreases accordingly. This is because as the mass flow rate of the working fluid increases, the heat absorbed by the device increases and the output work to the outside world increases.

[0112] Figure 4 Given m wf At 100 kg·s -1 -120kg·s -1 In the range of π, when π changes from 1 to 2, the relationship between cycle η and π changes. As can be seen from the figure, with the increase of π, η first increases and then decreases. When the pressure ratio is a constant, with the increase of mass flow rate, η decreases, because the work capacity of unit working fluid ammonia decreases.

[0113] Figure 5 Given m wf At 100 kg·s -1 -120kg·s -1 In the range of π, when π changes from 1 to 2, the cogeneration cycle η ex As π changes, the cycle η ex As π increases first and then decreases, η is cycled when π is in the range of 1.2-1.5. ex It reaches the extreme value. As can be seen from the figure, exceeding η ex After the optimal value of m wf The increase of η ex Showing a decreasing trend.

[0114] Figure 6 Given η t , η c In the range of 0.7-0.8, cycle W net With the change of π. Under the same conditions of π, with η t , η c The increase of W net This is because η t , η c Reflects the internal irreversibility of the turbine and pump in the cycle, η t , η c The larger the W, the lower the irreversibility of the turbine and pump, the less energy loss, and net The larger it is; and for every given η t , η c , there exists an optimal π such that W net reaches the maximum. As can be seen from the figure, η t , η c The corresponding W net The numerical values ​​are quite different, and the performance of the circulation device can be improved subsequently by increasing the efficiency of the pump and turbine.

[0115] Figure 7 Given η t , η c The relationship between cycle η and π in the range of 0.7-0.8. Under the condition that π is a fixed value, as η t , η c With the increase of m, η shows a trend of increasing first and then decreasing. wf- η under the change of π, η t , η c After parameter adjustment, the η of the loop is improved.

[0116] Figure 8 Given different η t , η c Next ex The maximum value of and the corresponding optimal π. Under the same π, as η t , η c The increase of η ex This is because η t , η c Reflects the irreversibility of the turbine and pump in the cycle, η t , η c The larger the W, the lower the irreversibility of the turbine and pump, and the less energy loss, which is consistent with W net The changing trend is similar.

[0117] Fig. 9The relationship between the mass flow rate of high-temperature seawater and the circulation W is given when π is in the range of 1-2. net The influence relationship of m H The value is 800kg·s -1 -1000kg·s -1 Under the condition of m H The increase of cycle W net The larger the result value is, the greater the H The increase in the energy provided to the cycle increases, making the cycle W net Showing an upward trend.

[0118] Fig.10 Given in m H The value is 800kg·s -1 -1000kg·s -1 , under the condition that π is 1-2, the relationship between the device η and the pressure ratio. Fig.10 It can be seen that under the same conditions of π, as m H The increase of m H Provides more energy to the system.

[0119] Fig.11 Given in m H The value is 800kg·s -1 -1000kg·s -1 Under the condition of different π, the cycle η ex Influence relationship. As can be seen from the figure, with the increase of π, the cycle η shows a trend of first increasing and then decreasing. When π is in the range of 1.3-1.5, the cycle η is the extreme point.

[0120] Fig.12 The effect of high-temperature seawater inlet temperature on circulating W under the condition of π being 1.2-1.5 is given. net The influence relationship of H,in Under the condition of 633K-639K, as T H,in The increase of cycle W net The larger the result value, the higher the value. H,in The larger the value, the more heat the working fluid ammonia absorbs, and the more heat it can provide to the outside. As π increases, the cycle W net It shows a trend of increasing first and then decreasing. There is a unique determination of π such that the cycle W net Reached maximum value.

[0121] Fig.13 Given T H,inThe influence of different π on the cycle η under the condition of 633K-639K. As can be seen from the figure, with the increase of π, the cycle η shows a trend of first increasing and then decreasing. net The corresponding optimal pressure ratio and the optimal pressure ratio corresponding to η are not the same. As two different evaluation indicators that affect the cycle performance, they need to be analyzed separately.

[0122] Fig.14 The T of the heater is given in the range of π 1.2-1.5. H,in For cycle η ex As can be seen from the figure, as π increases, the cycle η ex It shows a trend of increasing first and then decreasing, which also shows that T H,in Changes to the cycle Efficiency has a corresponding impact.

[0123] This technology uses the finite time thermodynamics theory to establish a thermodynamic model of the heat recovery cycle, and uses matalb software to calculate the net power, thermal efficiency and The efficiency is analyzed. Through the change of pressure ratio, the pressure ratio range with the largest net power output of the device is found, which is more comprehensive and accurate than the existing calculation method. In the field of ocean temperature difference power generation, domestic scholars are studying systems such as the Rankine cycle, Shangyuan cycle and Guohai cycle with ammonia as the working fluid. The existing technology research shows that the Guohai cycle has the largest net power output, with a maximum value of 8.33KW. This cycle improves the net power output of the device by increasing the temperature difference of the device and finding a suitable pressure ratio.

[0124] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0125] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A molten salt heat storage system coupled with ocean temperature difference power generation and supercritical seawater desalination device, comprising: Trough solar molten salt collectors for heating molten salt; The hot molten salt storage tank and the cold molten salt storage tank are used to store the heated molten salt and the molten salt to be heated respectively; Low-temperature molten salt heaters and high-temperature molten salt heaters are used for the utilization of low-grade and high-grade heat, respectively; A molten salt pump, used to drive the circulation of molten salt in the system; An ocean temperature difference power generation system, comprising a liquid nitrogen storage tank, a pump, a cooler, a first heat recovery device, a heater, a turbine and a compressor, for generating power through ocean temperature difference; A supercritical seawater desalination system, including a gravity separator, a brine tank, a desalination tank and a second regenerator, for desalinating seawater to a supercritical state and separating salt; The flow direction of molten salt is opposite to that of high-temperature seawater to improve energy utilization efficiency. The molten salt heat storage system further includes at least one closed cycle, which uses ammonia, a low-boiling-point substance, as a working fluid, and includes a liquid ammonia storage tank, a pump, a cooler, a first regenerator, and a heater, wherein the heater is connected to the low-temperature molten salt heater, and is used to receive low-grade heat from the low-temperature molten salt heater and heat the ammonia in the closed cycle to drive the turbine to do work; The ocean temperature difference power generation system also includes at least one heat recovery cycle, which includes a first heat regenerator and a second heat regenerator, wherein the first heat regenerator is used to receive low-grade heat from the low-temperature molten salt heater and heat the ammonia in the closed cycle, and the second heat regenerator is used to receive waste heat from desalinated water from the supercritical seawater desalination system and to preheat high-temperature seawater that is about to enter the supercritical state.

2. The device according to claim 1, characterized in that The supercritical seawater desalination system also includes a high-temperature molten salt heater, which is connected to the supercritical seawater desalination device and is used to receive high-temperature molten salt from the hot molten salt storage tank and heat the seawater to a supercritical state through the high-grade heat in the high-temperature molten salt heater; the gravity separator is arranged after the supercritical seawater desalination device, and is used to separate salt from seawater through the characteristic that the solubility of salt drops sharply in the supercritical state, and collect it into the brine pool and the desalination water pool respectively.

3. A method for coupling ocean temperature difference power generation and supercritical seawater desalination using a molten salt heat storage system coupled with ocean temperature difference power generation and a supercritical seawater desalination device according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: The molten salt is heated by a trough-type solar molten salt collector and the heated molten salt is stored in a hot molten salt storage tank; Molten salt is extracted from the cold molten salt storage tank and driven by a pump into the trough solar molten salt collector for heating. The heated molten salt returns to the hot molten salt storage tank; High-temperature molten salt is extracted from the hot molten salt storage tank, and passes through the high-temperature molten salt heater and the low-temperature molten salt heater in sequence for step-by-step energy utilization, and finally the low-temperature molten salt is returned to the cold molten salt storage tank to complete the thermal cycle of the molten salt; During the flow of molten salt, high-temperature seawater in the opposite direction of the molten salt flow is used to absorb the heat of the molten salt to improve energy utilization efficiency.

4. The method according to claim 3, characterized in that: The method further comprises the following steps: In the ocean temperature difference power generation system, ammonia, a low-boiling-point substance, is used as the working fluid of the closed cycle. The liquid ammonia is pressurized by a pump and transported to the regenerator to absorb waste heat. It then enters the heater and is heated by high-temperature seawater, turning the ammonia into high-temperature and high-pressure gas. High-temperature and high-pressure ammonia drives the turbine to work and output power; The ammonia gas discharged from the turbine is cooled in the cooler, liquefied, and returned to the liquid ammonia storage tank to complete the closed cycle.

5. The method according to claim 3, characterized in that: The method further comprises the following steps: In a supercritical seawater desalination system, high-temperature seawater is pressurized to a supercritical state and passed through a high-temperature molten salt heater to absorb high-grade heat to maintain the supercritical state; In the gravity separator, the salt is separated from the seawater by utilizing the characteristic that the solubility of salt drops sharply under the supercritical state to obtain desalinated water and brine; The desalinated water recovers waste heat through the second heat exchanger and flows to the desalinated water pool, while the brine is collected in the brine pool.

6. The method according to claim 3, characterized in that The method further comprises the following steps: In the supercritical seawater desalination system, the molten salt temperature and seawater pressure are controlled to prevent the seawater from reaching a supercritical state and causing the salt to separate, thus protecting the equipment from damage; By controlling the opening and closing of the gate valve, the flow direction of desalinated water is adjusted to achieve effective utilization and storage of desalinated water.

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