A steam supply system and method coupling industrial waste heat recovery with molten salt energy storage

Abstract

This application relates to the field of industrial energy conservation and energy storage, and discloses a steam supply system and method coupling industrial waste heat recovery and molten salt energy storage, including a heat pump propellant subsystem, a molten salt energy storage subsystem, and a steam generation coupling unit. The heat pump propellant subsystem is configured to recover low-temperature industrial waste heat using a transcritical carbon dioxide heat pump to preheat the working fluid water to the intermediate temperature of the sensible heat section; the molten salt energy storage subsystem is configured to use electrical energy to heat the molten salt working fluid to a high-temperature state and store it; the steam generation coupling unit has a physically isolated channel internally, configured to use high-temperature molten salt to bear the latent heat of vaporization and superheat load of the working fluid water. This invention, through a temperature-gradient utilization architecture, significantly reduces the consumption of high-grade electrical energy by utilizing low-grade waste heat, enabling the system's overall energy efficiency to exceed the pure electrothermal limit. Simultaneously, the use of intermediate-temperature feedwater avoids the risk of freezing and blockage at the molten salt heat exchange interface, achieving safe and efficient production of high-quality steam.

Description

Technical Field

[0001] This invention relates to the field of industrial energy conservation and energy storage technology, specifically to a steam supply system and method that couples industrial waste heat recovery and molten salt energy storage. Background Technology

[0002] In the current industrial steam production sector, with the transformation of the energy structure and the advancement of decarbonization goals, using electricity to replace the combustion of traditional fossil fuels has become a mainstream trend. Among these technologies, molten salt energy storage heating technology is widely used due to its large-capacity heat storage capacity and flexible regulation characteristics. A typical molten salt energy storage steam system usually adopts a direct "electricity-heat" conversion mode, that is, during off-peak hours, electric heaters are used to heat molten salt to a high temperature for storage, and then during peak hours, the high-temperature molten salt is used to heat feedwater to generate steam. This method can utilize the peak-valley electricity price difference to reduce operating costs and promote the consumption of renewable energy.

[0003] However, existing molten salt energy storage steam supply systems have limitations in energy conversion efficiency. In the process of converting ambient temperature feedwater into high-temperature, high-pressure steam, whether it's the sensible heat enhancement stage of the water or the subsequent latent heat of vaporization and superheating stages, the entire heat load required depends entirely on high-grade electrical energy input. Because the electrothermal conversion process is constrained by the law of conservation of energy, its theoretical overall energy efficiency ratio cannot break through the physical limit of a single value. At the same time, low-grade waste heat resources widely existing in industrial sites cannot be directly utilized by existing molten salt heat exchange processes because their temperature grade is far below the working temperature range of molten salt. This results in a persistently high consumption of high-grade electrical energy per unit mass of steam produced, limiting further improvements in the overall energy utilization efficiency of this technology. Summary of the Invention

[0004] This invention primarily addresses the technical problems of ineffective utilization of low-grade waste heat in existing industrial steam supply technologies, the risk of freezing and blockage in direct coupling of molten salt thermal storage systems with low-temperature feedwater, and the limited overall energy efficiency of pure electric boilers. This invention proposes a system and method based on the principle of temperature-grade utilization, achieving safe and efficient production of high-quality steam through the physical and logical decoupling of the heat pump propellant subsystem and the molten salt energy storage subsystem.

[0005] The first aspect of the present invention provides a steam supply system that couples industrial waste heat recovery with molten salt energy storage.

[0006] The steam supply system that couples industrial waste heat recovery and molten salt energy storage adopts a temperature cascade utilization architecture. The main components of the steam supply system that couples industrial waste heat recovery and molten salt energy storage include a heat pump propellant subsystem, a molten salt energy storage subsystem, and a steam generation coupling unit.

[0007] The heat pump propellant boosting subsystem is located at the feedwater front end of the system and is configured to recover heat from low-temperature industrial waste heat sources. The subsystem uses electrical energy to raise the boiler feedwater or condensate from ambient temperature to an intermediate temperature within the sensible heat range. Preferably, the heat pump propellant boosting subsystem employs a transcritical carbon dioxide heat pump unit. This unit utilizes the temperature-changing heat release characteristics of carbon dioxide as the working fluid in its supercritical state, with countercurrent heat exchange between the carbon dioxide and water, thus achieving a temperature rise across the sensible heat range in a single-stage cycle. Furthermore, the subsystem includes a pressurized hot water buffer tank located at the output end of the heat pump unit. This buffer tank serves as an intermediate heat storage container, storing high-temperature feedwater at an intermediate temperature, thereby isolating the continuous operation of the heat pump unit from fluctuations in the downstream steam load over time.

[0008] The molten salt energy storage subsystem is independent of the system's water circulation loop. It is configured to use electrical energy to heat the molten salt working fluid to the high-temperature state required for phase change and superheating. The molten salt energy storage subsystem typically includes a cryogenic molten salt tank, a high-temperature molten salt tank, a molten salt circulation pump, and a molten salt electric heater, forming a closed-loop molten salt thermal storage circulation loop. This loop enables the molten salt energy storage subsystem to store thermal energy during off-peak grid periods or when renewable energy is curtailed, achieving temporal decoupling between energy supply and steam demand.

[0009] The steam generation coupling unit serves as the sole heat exchange interface between the water circulation loop and the molten salt circulation loop. Internally, the steam generation coupling unit contains physically isolated working fluid water channels and molten salt channels. The steam supply system, coupling industrial waste heat recovery and molten salt energy storage, is configured via pipeline connections. This allows the heat pump lifting subsystem to handle the sensible heat load of the working fluid water, while the molten salt energy storage subsystem, through the steam generation coupling unit, handles the latent heat of vaporization and superheat load of the working fluid water.

[0010] In the specific heat exchange structure, the steam generation coupling unit includes a feedwater preheater, a steam evaporator, and a steam superheater connected in series in spatial location. The flow direction of the working fluid water and the flow direction of the molten salt form a counter-current heat exchange layout in the overall steam generation coupling unit. The high-temperature molten salt flows sequentially through the steam superheater, steam evaporator, and feedwater preheater, with the temperature of the high-temperature molten salt decreasing step by step; the working fluid water flows sequentially through the feedwater preheater, steam evaporator, and steam superheater, with the temperature and enthalpy of the working fluid water increasing step by step.

[0011] This invention achieves freeze protection by controlling the temperature of the heat exchange interface. The intermediate temperature provided by the heat pump propellant system is set to be close to or higher than the freezing point of the molten salt working fluid. When high-temperature feedwater at the intermediate temperature enters the feedwater preheater, the high temperature of the feedwater ensures that the temperature of the heat exchange wall is always maintained above the safe threshold. The temperature matching mechanism physically avoids the risk of thermal shock caused by direct contact between the low-temperature fluid and the high-temperature molten salt pipeline, as well as the risk of the molten salt working fluid solidifying and blocking at the pipe wall.

[0012] This invention improves the overall energy efficiency of a system based on the first law of thermodynamics. The overall energy efficiency of the system depends on the ratio of the total enthalpy increase of the produced steam to the total electrical energy input. In traditional electric molten salt boilers, the sensible heat, latent heat, and superheat load of water are all provided by electrothermal conversion. Limited by the law of energy conversion, the overall energy efficiency ratio of electric molten salt boilers cannot exceed the theoretical limit. The steam supply system coupling industrial waste heat recovery and molten salt energy storage utilizes heat pump technology to recover the energy of external industrial waste heat fluids, converting low-grade heat energy into the sensible heat increment of the working fluid, water. To produce the same quality of steam, the steam supply system coupling industrial waste heat recovery and molten salt energy storage requires less external electrical energy input. The energy-saving logic of the system is as follows: the total heat absorption load of water is divided into sensible heat load and latent heat / superheat load. The sensible heat load is borne by a high-efficiency heat pump unit, and the latent heat / superheat load is borne by the molten salt electric heating system. Because the coefficient of performance (COP) of a heat pump unit is greater than one when producing hot water at intermediate temperatures, the overall output heat of the system is greater than the input electrical energy, thus enabling the system's overall energy efficiency ratio to break through the theoretical limit of one.

[0013] A second aspect of the present invention provides a method for producing steam using a steam supply system that couples industrial waste heat recovery with molten salt energy storage.

[0014] The method for producing steam using a steam supply system that couples industrial waste heat recovery with molten salt energy storage includes three main steps: low-temperature sensible heat enhancement, high-temperature thermal energy storage, and high-quality steam generation.

[0015] In the low-temperature sensible heat enhancement step, a heat pump proton system is used to recover industrial waste heat fluid with a temperature range of 30°C to 60°C. Through the operation of the heat pump unit, the ambient temperature working fluid water is raised to an intermediate temperature of 120°C to 150°C, and the high-temperature feedwater reaching this intermediate temperature is stored in a pressurized hot water buffer tank. This low-temperature sensible heat enhancement step completes the low-energy accumulation of the basic sensible heat of the working fluid water.

[0016] The high-temperature thermal energy storage step is mainly performed during off-peak electricity prices on the external power grid or during periods of renewable energy curtailment. The molten salt energy storage subsystem is activated in its thermal storage mode, using electricity to heat the low-temperature molten salt working fluid to a target high temperature of 400 to 550 degrees Celsius, and then stored in a high-temperature molten salt storage tank. This high-temperature thermal energy storage step completes the storage of high-grade thermal energy.

[0017] The high-quality steam generation step is executed when there is steam demand on the user side. High-temperature feedwater from the pressurized hot water buffer tank and high-temperature molten salt working fluid from the high-temperature molten salt storage tank are simultaneously introduced into the steam generation coupling unit. The high-temperature molten salt working fluid is used as a heat source, undergoing counter-current heat exchange with the high-temperature feedwater. The high-temperature feedwater sequentially undergoes sensible heat exchange, phase change heat transfer, and superheated heat transfer processes, ultimately producing industrial superheated steam at the target temperature and pressure. During the high-quality steam generation process, the flow rate regulation of the molten salt heat pump and the feedwater pump set is used to maintain the stability of the outlet steam parameters.

[0018] This invention provides a steam supply system and method that couples industrial waste heat recovery with molten salt energy storage. It has the following beneficial effects:

[0019] 1. This invention achieves a cascaded coupling of a transcritical carbon dioxide heat pump unit and a molten salt energy storage subsystem. The heat pump unit recovers low-grade industrial waste heat fluid to bear the heat load during the sensible heat enhancement stage of the working fluid water, while the molten salt energy storage subsystem bears the subsequent latent heat of vaporization and superheat load. This changes the traditional process that relies solely on electric heating, significantly reducing the amount of high-grade electrical energy input required to produce a unit mass of steam. It also breaks through the theoretical limit of pure electric heating in terms of the system's overall energy efficiency ratio and reduces the cost of steam production.

[0020] 2. This invention preheats ambient temperature feedwater to an intermediate temperature range of 120°C to 150°C by configuring a heat pump propellant system. This ensures that the initial temperature of the feedwater entering the steam generation coupling unit is maintained at or above the freezing point of the molten salt working medium. This eliminates the extreme temperature difference and cold shock inherent in direct heat exchange between ambient temperature water and high-temperature molten salt. It also avoids the hidden danger of the molten salt working medium undergoing phase change and solidifying at the low-temperature end of the heat exchanger due to excessively low wall temperature, thus blocking the pipeline. This provides an inherent safety guarantee for the unobstructed flow of the molten salt channel in the steam generation system under variable load operating conditions.

[0021] 3. This invention, by setting a pressurized hot water buffer tank at the output end of the heat pump propellant subsystem and cooperating with a molten salt energy storage subsystem in a dual-tank heat storage structure, supports the heat pump unit to continuously produce high-temperature feedwater according to the waste heat source status. At the same time, it supports the molten salt system to use off-peak electricity for intermittent heat energy storage. This achieves the decoupling of continuous industrial waste heat recovery, peak and valley fluctuations in grid electricity prices, and real-time changes in user-side steam load in the time dimension, realizing flexible scheduling of energy utilization in time and space and proactive response to grid peak shaving and valley filling strategies. Attached Figure Description

[0022] Figure 1 This is a system architecture diagram of the present invention; Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example: Please see the appendix Figure 1 - Appendix Figure 2 This invention provides a steam supply system that couples industrial waste heat recovery with molten salt energy storage. The steam supply system adopts a temperature cascade utilization architecture and mainly includes: a heat pump propellant boosting subsystem, a molten salt energy storage subsystem, and a steam generation coupling unit.

[0025] The heat pump protonation subsystem is located at the working fluid water input end of the steam supply system that couples industrial waste heat recovery and molten salt energy storage. The input end of the heat pump protonation subsystem is connected to an external low-temperature industrial waste heat source via a fluid pipeline, and the output end is connected to the water-side inlet of the steam generation coupling unit via a fluid pipeline. The heat pump protonation subsystem is configured to recover low-temperature industrial waste heat and preheat the working fluid water (such as boiler feedwater or condensate) from ambient temperature to the intermediate temperature T1 of the sensible heat section.

[0026] The molten salt energy storage subsystem is set up independently of the water circulation loop of the steam supply system that couples industrial waste heat recovery and molten salt energy storage. The molten salt energy storage subsystem is configured to use input electrical energy to heat the internally circulating molten salt working fluid to a high temperature and store it. The molten salt energy storage subsystem is connected to the salt-side interface of the steam generation coupling unit through high-temperature resistant pipelines, forming a closed molten salt heating loop.

[0027] The steam generation coupling unit serves as the sole heat exchange interface between the water circulation loop and the molten salt circulation loop. The steam generation coupling unit is connected to both the output of the heat pump propellant boosting subsystem and the output of the molten salt energy storage subsystem.

[0028] In the operation of the steam supply system that couples industrial waste heat recovery and molten salt energy storage, the heat pump boosting subsystem undertakes the sensible heat heating load of the working fluid water, raising its temperature to a preset intermediate temperature of 1T. The molten salt energy storage subsystem undertakes the latent heat of vaporization and superheat load of the working fluid water through the steam generation coupling unit.

[0029] The steam supply system coupling industrial waste heat recovery and molten salt energy storage is connected to the steam generation coupling unit via pipelines through a heat pump propellant subsystem, a molten salt energy storage subsystem, and a steam generation coupling unit, achieving physical decoupling between the water working fluid circulation and the molten salt working fluid circulation. The water working fluid and the molten salt working fluid exchange heat in a countercurrent manner only within the steam generation coupling unit, and the water working fluid and the molten salt working fluid do not come into contact with each other.

[0030] The intermediate temperature T1 provided by the heat pump propellant system is set to be close to or higher than the freezing point temperature of the molten salt working fluid. When the high-temperature working fluid water output by the heat pump propellant system enters the steam generation coupling unit, it eliminates the large temperature difference between the working fluid and the molten salt working fluid, thereby avoiding thermal shock and working fluid freezing caused by direct contact between the low-temperature fluid and the high-temperature molten salt pipeline.

[0031] The heat pump proton-raising system provided in this embodiment of the invention includes: a transcritical carbon dioxide heat pump unit, a feedwater pump unit, an industrial waste heat access pipeline, and a pressurized hot water buffer tank.

[0032] The transcritical carbon dioxide heat pump unit mainly consists of a compressor, a gas cooler, a throttling expansion valve, and an evaporator, all connected in a closed loop via refrigerant piping. The refrigerant piping is filled with carbon dioxide as the working fluid. The gas cooler has isolated refrigerant and water channels, while the evaporator has isolated refrigerant and waste heat fluid channels.

[0033] The industrial waste heat inlet pipeline is connected at both ends to the inlet and outlet of the waste heat fluid channel of the evaporator, respectively. The industrial waste heat inlet pipeline is configured to transport low-grade industrial waste heat fluid with a temperature range between [temperature range missing] degrees Celsius to the interior of the evaporator. As the low-grade industrial waste heat fluid flows through the evaporator, it releases heat. The carbon dioxide working fluid located in the evaporator's refrigerant channel absorbs this heat and transforms from a liquid to a gaseous state.

[0034] The output end of the feedwater pump set is connected to the water flow channel inlet of the gas cooler via a pipeline. The feedwater pump set is used to pressurize the boiler feedwater or condensate return water at normal temperature and pump the pressurized working fluid into the gas cooler.

[0035] Inside the gas cooler, high-temperature, high-pressure carbon dioxide working fluid, compressed to a supercritical state by the compressor, exchanges heat countercurrently with working fluid water pumped in by the feed water pump unit. After absorbing the heat released by the carbon dioxide working fluid, the working fluid water's temperature rises to an intermediate temperature T1. The numerical range of the intermediate temperature T1 is set to between [degrees Celsius] and [degrees Celsius].

[0036] A pressurized hot water buffer tank is located between the water flow channel outlet of the gas cooler and the steam generation coupling unit. The inlet of the pressurized hot water buffer tank is connected to the water flow channel outlet of the gas cooler via a pipe, and the outlet of the pressurized hot water buffer tank is connected to the water-side inlet of the steam generation coupling unit via a pipe.

[0037] The pressurized hot water buffer tank is configured as a pressure-resistant vessel externally covered with insulating material. It is used to receive and store high-temperature feedwater from the gas cooler. The tank has a preset buffer volume to balance the continuous heating operation flow rate of the transcritical CO2 heat pump unit with the real-time steam load flow rate required by the steam generation coupling unit.

[0038] The molten salt energy storage subsystem provided in this embodiment of the invention mainly includes: a low-temperature molten salt storage tank, a molten salt circulation pump, a molten salt electric heater, a high-temperature molten salt storage tank, and a molten salt heat pump.

[0039] Both cryogenic and high-temperature molten salt storage tanks are high-temperature resistant containers equipped with thermal insulation layers. Cryogenic molten salt storage tanks are used to store cryogenic molten salt working fluids in their liquid operating temperature range. The cryogenic molten salt working fluid is a binary nitrate or a low-melting-point mixed molten salt, and the temperature of the cryogenic molten salt working fluid inside the tank is maintained at a temperature close to but above the freezing point of the molten salt (e.g., 220°C to 290°C). High-temperature molten salt storage tanks are used to store high-temperature molten salt working fluids after absorbing heat, and the temperature range of the high-temperature molten salt working fluid inside the tank is set between 400°C and 550°C.

[0040] The molten salt energy storage subsystem includes a thermal storage circulation loop. In this loop, the outlet of the cryogenic molten salt tank is connected to the fluid inlet of the molten salt circulation pump via a high-temperature resistant pipeline. The fluid outlet of the molten salt circulation pump is connected to the fluid inlet of the molten salt electric heater. The fluid outlet of the molten salt electric heater is connected to the inlet of the high-temperature molten salt tank.

[0041] A molten salt circulation pump provides the fluid power to extract the cryogenic molten salt working medium from the cryogenic molten salt storage tank and deliver it to the molten salt electric heater. The molten salt electric heater is electrically connected to an external power grid or renewable energy generation equipment. It contains resistance heating elements or electromagnetic induction heating elements to heat the flowing cryogenic molten salt working medium to the target high temperature T2. The heated high-temperature molten salt working medium then enters the high-temperature molten salt storage tank for thermal energy storage.

[0042] The molten salt energy storage subsystem also includes an exothermic circulation loop. In this loop, the outlet of the high-temperature molten salt tank is connected to the fluid inlet of the molten salt heat pump. The fluid outlet of the molten salt heat pump is connected via piping to the salt-side inlet of the steam generation coupling unit. The salt-side outlet of the steam generation coupling unit is connected via a return piping to the return inlet of the low-temperature molten salt tank.

[0043] The molten salt heating pump uses a variable frequency speed-regulating high-temperature resistant pump. The molten salt heating pump is used to adjust the output flow rate of the high-temperature molten salt working fluid according to the real-time heat load required by the steam generation coupling unit. After releasing heat in the steam generation coupling unit, the high-temperature molten salt working fluid cools down and returns to the low-temperature molten salt storage tank through the return pipeline.

[0044] The external connecting pipes and valve assemblies of the molten salt energy storage subsystem are covered with electric heat tracing devices. The electric heat tracing devices are used to maintain the pipe wall temperature above the freezing point temperature of the molten salt working medium, thereby preventing the molten salt working medium from undergoing phase change and solidifying in the pipes during the system standby or startup phases, which could lead to pipe blockage.

[0045] The steam generation coupling unit provided in this embodiment of the invention mainly includes: a feedwater preheater, a steam evaporator, and a steam superheater. These three heat exchange components are connected in series in space. Each of the three heat exchange components has a working fluid water channel and a molten salt channel that are physically isolated from each other. The working fluid water channel and the molten salt channel transfer heat through the metal heat exchange wall.

[0046] In the connection structure of the working fluid flow channel, the outlet pipe of the pressurized hot water buffer tank is connected to the working fluid inlet of the feedwater preheater. The working fluid outlet of the feedwater preheater is connected to the working fluid inlet of the steam evaporator via a pipe. The steam outlet of the steam evaporator is connected to the steam inlet of the steam superheater via a pipe. The steam outlet of the steam superheater, as the output end of the entire system, is connected to the steam network on the user side.

[0047] In the connection structure of the molten salt flow channel, the outlet of the molten salt heat pump is connected to the molten salt inlet of the steam superheater. The molten salt outlet of the steam superheater is connected to the molten salt inlet of the steam evaporator via a high-temperature resistant pipe. The molten salt outlet of the steam evaporator is connected to the molten salt inlet of the feedwater preheater via a high-temperature resistant pipe. The molten salt outlet of the feedwater preheater is connected to the cryogenic molten salt storage tank via a return pipe.

[0048] Through the aforementioned connection structure, the flow direction of the working fluid water and the flow direction of the molten salt form a counter-current heat exchange layout in the overall steam generation coupling unit. The high-temperature molten salt working fluid flows sequentially through the steam superheater, steam evaporator, and feedwater preheater, with the temperature of the high-temperature molten salt working fluid decreasing step by step along the flow direction. The working fluid water flows sequentially through the feedwater preheater, steam evaporator, and steam superheater, with the temperature and enthalpy of the working fluid water increasing step by step along the flow direction.

[0049] The feedwater preheater is configured to perform a sensible heat exchange process. The working water temperature entering the feedwater preheater is the intermediate temperature T1 (120°C to 150°C) provided by the heat pump propellant subsystem. Since the inlet temperature setpoint of the working water is close to or higher than the physical freezing point of the molten salt working fluid, and the molten salt working fluid in the feedwater preheater is located in the low-temperature zone at the end of the heat exchange process, the higher working water inlet temperature ensures that the temperature of the metal heat exchange wall inside the feedwater preheater is always maintained above the freezing point of the molten salt during operation, thereby eliminating the risk of molten salt solidification and pipe blockage at the end of the low-temperature heat exchange zone.

[0050] The steam evaporator is configured to perform a phase change heat transfer process. The working fluid water, after being heated by sensible heat, absorbs the sensible heat released by the molten salt in the steam evaporator, and the working fluid water changes from liquid water to saturated water vapor. In this process, the working fluid water absorbs the latent heat of vaporization.

[0051] The steam superheater is configured to perform a superheated heat transfer process. Saturated steam output from the steam evaporator exchanges heat with molten salt working fluid at its highest temperature within the steam superheater. The saturated steam absorbs heat and transforms into superheated steam with a specific degree of superheat. The final output temperature of the superheated steam reaches the target setpoint (e.g., 250 degrees Celsius).

[0052] The present invention provides a method for steam generation using a steam supply system that couples industrial waste heat recovery with molten salt energy storage, performing a low-temperature sensible heat enhancement process. This low-temperature sensible heat enhancement process primarily relies on a heat pump proton system.

[0053] During the low-temperature sensible heat enhancement process, the industrial waste heat inlet pipeline continuously introduces industrial waste heat fluid with a temperature range of 30°C to 60°C into the waste heat channel of the evaporator included in the transcritical CO2 heat pump unit. Simultaneously, the feed water pump unit pumps ambient-temperature working fluid into the water flow channel of the gas cooler included in the transcritical CO2 heat pump unit. The feed water pump unit adjusts the flow rate of the working fluid according to the preset outlet temperature target value to match the heating power of the transcritical CO2 heat pump unit.

[0054] In the refrigerant-side circulation of a transcritical carbon dioxide heat pump unit, the liquid carbon dioxide working fluid, in a subcritical low-pressure state, absorbs heat released by industrial waste heat fluid in the evaporator. After absorbing heat, the liquid carbon dioxide working fluid evaporates into low-pressure gaseous carbon dioxide. The compressor draws in the low-pressure gaseous carbon dioxide and performs compression work, raising the pressure of the carbon dioxide working fluid to above the critical pressure, forming a supercritical state high-temperature and high-pressure carbon dioxide working fluid.

[0055] High-temperature, high-pressure carbon dioxide working fluid in a supercritical state enters the gas cooler. Inside the gas cooler, the high-temperature, high-pressure carbon dioxide working fluid undergoes countercurrent heat exchange with the working fluid water in the water flow channel. The working fluid water absorbs heat without undergoing a phase change, and its temperature gradually rises from room temperature to an intermediate temperature T1. Through the flow regulation of the feed water pump set, the intermediate temperature T1 is maintained between [insert temperature range here] degrees Celsius.

[0056] After releasing heat, the carbon dioxide working fluid is depressurized through a throttling expansion valve, returns to a subcritical low-temperature and low-pressure state, and then returns to the evaporator. In this way, the transcritical carbon dioxide heat pump unit forms a closed thermodynamic cycle.

[0057] The high-temperature feedwater, heated to an intermediate temperature T, is discharged from the water flow channel outlet of the gas cooler and transported through pipelines to the pressurized hot water buffer tank. The pressurized hot water buffer tank stores and insulates the high-temperature feedwater, maintaining the stored high-temperature feedwater at an intermediate temperature T1, thus reserving sensible heat energy for the subsequent steam generation process.

[0058] In this step, through the operation of the transcritical carbon dioxide heat pump unit, the working fluid water completes the sensible heat temperature rise from room temperature to the intermediate temperature T1, and the steam supply system coupled with industrial waste heat recovery and molten salt energy storage realizes the heat recovery and grade improvement of industrial waste heat fluid.

[0059] The method for steam generation provided by this invention utilizes a steam supply system that couples industrial waste heat recovery and molten salt energy storage, wherein a high-temperature thermal energy storage process is performed in step S2. The high-temperature thermal energy storage process mainly relies on the molten salt energy storage subsystem for operation.

[0060] When the external power grid experiences off-peak electricity prices or when renewable energy is being curtailed, the molten salt energy storage subsystem switches to thermal storage operation mode.

[0061] In the thermal regeneration operation mode, the molten salt circulation pump starts. The molten salt circulation pump extracts the cryogenic molten salt working medium stored in the cryogenic molten salt storage tank through high-temperature resistant pipelines. At this time, the temperature of the cryogenic molten salt working medium is maintained at a base temperature close to but higher than the freezing point of the molten salt working medium (e.g., 220 degrees Celsius to 290 degrees Celsius).

[0062] A molten salt circulation pump delivers cryogenic molten salt working fluid to the fluid inlet of the molten salt electric heater at a set flow rate. The molten salt electric heater is connected to an external power source, and uses an internal electrothermal conversion element to convert the input electrical energy into heat energy.

[0063] The low-temperature molten salt working fluid flows through the heating channels inside the molten salt electric heater. During the flow, the low-temperature molten salt working fluid exchanges heat with the electrothermal conversion element, absorbing heat and experiencing a sensible temperature rise. The molten salt electric heater adjusts its heating power based on the outlet temperature feedback, ensuring that the temperature of the high-temperature molten salt working fluid exiting the heater remains stable at the set target high temperature T2. The target high temperature T2 is set within a range of [degrees Celsius to [degrees Celsius]].

[0064] The heated high-temperature molten salt working medium is discharged from the fluid outlet of the molten salt electric heater and injected into the high-temperature molten salt storage tank through a high-temperature resistant pipeline. As the heat storage process continues, the molten salt level in the low-temperature molten salt storage tank decreases, while the molten salt level in the high-temperature molten salt storage tank rises. The high-temperature molten salt storage tank utilizes its thermal insulation structure to maintain the temperature of the stored high-temperature molten salt working medium at the target high temperature T2.

[0065] Step S2 continues until the cryogenic molten salt storage tank reaches the low liquid level limit or the external power supply period ends. The high-temperature molten salt working fluid stored in the high-temperature molten salt storage tank serves as the high-temperature heat source for the subsequent steam generation process.

[0066] The method for steam generation provided by the present invention utilizes a steam supply system that couples industrial waste heat recovery and molten salt energy storage, and performs a high-quality steam generation process in step S3.

[0067] When the steam supply system coupling industrial waste heat recovery and molten salt energy storage is in energy release steam supply mode, the molten salt heat pump starts. The molten salt heat pump extracts the high-temperature molten salt working medium stored in the high-temperature molten salt storage tank. The temperature of the high-temperature molten salt working medium is at the target high temperature T2 (400 degrees Celsius to 550 degrees Celsius). The molten salt heat pump delivers the high-temperature molten salt working medium to the salt-side inlet of the steam generation coupling unit.

[0068] The high-temperature molten salt working fluid flows sequentially through the steam superheater, steam evaporator, and feedwater preheater along the salt-side channel within the steam generation coupling unit. During its flow, the high-temperature molten salt continuously releases sensible heat, and its temperature decreases progressively. The molten salt exiting the feedwater preheater at the salt-side outlet reaches a cryogenic state (approximately 220 degrees Celsius), and returns to the cryogenic molten salt storage tank via a return pipeline.

[0069] Simultaneously with the establishment of the molten salt flow path, the feedwater pump unit pressurizes the high-temperature feedwater stored in the pressurized hot water buffer tank. The high-temperature feedwater enters the water-side inlet of the steam generation coupling unit at a preset operating pressure (e.g., above 1.6 MPa). The initial temperature of the high-temperature feedwater is an intermediate temperature T1 (120°C to 150°C). Within the steam generation coupling unit, the high-temperature feedwater flows sequentially through the feedwater preheater, steam evaporator, and steam superheater along the water-side channel.

[0070] Inside the feedwater preheater, high-temperature feedwater at an intermediate temperature T1 exchanges heat counter-currently with the molten salt working medium flowing through the salt-side channel of the feedwater preheater. The high-temperature feedwater absorbs the sensible heat released by the molten salt working medium, further increasing its temperature to the saturation temperature at the current pressure. Because the inlet temperature of the high-temperature feedwater is set close to or higher than the freezing point of the molten salt working medium, and because the high-temperature feedwater continuously flows and scours the heat exchange wall, the temperature of the heat exchange wall inside the feedwater preheater remains above the freezing point of the molten salt throughout the entire heat exchange process, physically preventing the freezing conditions of the molten salt working medium in the low-temperature region.

[0071] The working fluid, water that has reached saturation temperature, enters the steam evaporator. Inside the steam evaporator, the working fluid absorbs the sensible heat released by the molten salt working fluid flowing through the salt-side channel of the steam evaporator. During this stage, the working fluid undergoes a phase change, transforming from saturated liquid water into saturated water vapor.

[0072] Saturated steam enters the steam superheater. Inside the superheater, the saturated steam undergoes countercurrent heat exchange with the high-temperature molten salt working fluid, which has just been pumped in by the molten salt heat pump and is at its highest temperature. The saturated steam absorbs heat and further heats up, transforming into superheated steam.

[0073] Once the temperature and pressure of the superheated steam reach the preset industrial steam supply standard, the superheated steam is transported to the user-side pipeline network through the steam outlet pipeline.

[0074] During the operation of step S3, the control system of the steam supply system coupling industrial waste heat recovery and molten salt energy storage executes the following adjustment strategy: the control system adjusts the speed of the molten salt heating pump to change the molten salt circulation flow rate according to the real-time steam temperature data at the outlet of the steam superheater, thereby stabilizing the outlet steam temperature; the control system adjusts the feed water flow rate of the feed water pump group according to the steam pressure demand on the user side, thereby stabilizing the outlet steam pressure.

[0075] This invention also provides a method for constructing an energy efficiency calculation model and setting parameters for a steam supply system based on the aforementioned coupled industrial waste heat recovery and molten salt energy storage. The method establishes an energy balance equation using the first law of thermodynamics to calculate the theoretical energy-saving effect and energy efficiency improvement level of the present invention's technical solution compared to a traditional molten salt electric boiler solution.

[0076] In constructing the energy efficiency calculation model, a unified calculation benchmark and operating boundary conditions are first established. The model assumes the system is operating under adiabatic steady-state conditions and ignores heat loss along the pipeline. The production target is set as producing a specific quality. High-quality industrial steam, of which The value is set to 1000 kg. The initial feedwater temperature input to the feedwater pump unit is set. The initial feedwater temperature is set at 20 degrees Celsius, defined as ambient temperature softened water. The temperature of the industrial waste heat fluid introduced into the industrial waste heat access pipeline is set. The temperature is 40 degrees Celsius, and the heat source type for the industrial waste heat fluid is set to industrial cooling circulating water.

[0077] Set the target steam parameters for system output. The target superheated steam temperature ultimately produced by the steam generation coupling unit. The target superheated steam is set at 250 degrees Celsius, with an absolute pressure of [unspecified value]. It is set at 1.6 MPa.

[0078] The specific enthalpy parameters at each critical state point were determined based on the standard steam thermodynamic property table. The initial feedwater temperature was defined as... and specific enthalpy at normal pressure , The value is set at 84 kJ / kg. The high-temperature feedwater, preheated by the heat pump proton exchange system, is defined at an intermediate temperature. and the specific enthalpy under system operating pressure In this model, the intermediate temperature The specific enthalpy of pressurized liquid water is set to 120 degrees Celsius. The value is set at 504 kJ per kilogram. The target superheated steam is defined at a temperature... and pressure The specific enthalpy is , The value is set at 2919 kJ per kilogram.

[0079] Set the efficiency parameters for the energy conversion equipment. For the molten salt energy storage subsystem, set the overall efficiency of the molten salt energy storage subsystem, including electric heating and molten salt heat exchange. The coefficient of performance (COP) is 98%. For the heat pump proton-raising system, the comprehensive heating performance coefficient of the transcritical carbon dioxide heat pump unit is selected under the conditions of 40°C heat source inlet water and 120°C heating outlet water. , The value is set to 3.5.

[0080] Construct a reference model for existing technologies. The existing reference model uses an electric heater to directly heat molten salt, and then uses the molten salt to raise the temperature to [a certain value]. The water supply is directly heated to a temperature of The steam. In the existing technology reference model, the total heat load required for the production process is entirely provided by electrical energy through molten salt electrothermal conversion, without involving waste heat recovery.

[0081] The system model of this embodiment is constructed. This system model adopts the temperature gradient utilization architecture described in this invention. The system model of this embodiment divides the production process into two continuous thermodynamic stages: the first stage is driven by a heat pump proton system consuming electrical energy, utilizing industrial waste heat to transfer feedwater from... Upgraded to The second stage is driven by the molten salt energy storage subsystem, which consumes electrical energy to use high-temperature molten salt to transfer water from... Upgraded to .

[0082] Based on the constructed energy efficiency calculation model and the set operating parameters, this embodiment of the invention calculates the system energy balance process.

[0083] The first step is to calculate the total heat absorption required to produce one unit mass of steam. Total heat absorbed Defined as mass For 1000 kg of working fluid water, the initial feed water temperature is... The total amount of heat energy required to heat to the target superheated steam state. Based on the aforementioned specific enthalpy parameters, the total heat absorbed. The calculation formula and results are as follows:

[0084] The second step is to calculate the total power consumption of the existing technology reference model. In the existing technical reference model, the total heat load... This is handled by an electrically heated molten salt system. The overall efficiency of the molten salt is determined based on the set parameters. Total power consumption of existing technology reference models The calculation formula and results are as follows:

[0085] Converting electrical energy units from kilojoules (kJ) to kilowatt-hours (kWh), the power consumption of the existing technology reference model... for:

[0086] The third step is to calculate the power consumption of the system model in this embodiment. The calculation process is divided into a low-temperature sensible heat enhancement stage and a high-temperature latent heat superheating stage based on the temperature gradient utilization architecture.

[0087] During the low-temperature sensible heat enhancement phase, the heat pump proton system bears the sensible heat load. The heat pump proton system raises the working fluid water from the initial feedwater temperature. Raise to intermediate temperature Sensible heat load The calculation formula and results are as follows:

[0088] The comprehensive heating performance coefficient of a transcritical carbon dioxide heat pump unit under temperature rise conditions ranging from 20°C to 120°C is: The electrical energy consumed by the heat pump proton exchange system. The calculation formula and results are as follows:

[0089] Converted to electricity units, approximately .

[0090] During the high-temperature latent heat overheating stage, the molten salt energy storage subsystem bears the latent heat and overheating loads. The molten salt energy storage subsystem utilizes high-temperature molten salt to transfer the working fluid water from an intermediate temperature... Heat to the target superheated steam state. Latent heat and superheated load. The calculation formula and results are as follows:

[0091] Based on the set overall efficiency of molten salt The electrical energy consumed by the molten salt energy storage subsystem The calculation formula and results are as follows:

[0092] Converted to electricity units, approximately .

[0093] The fourth step is to calculate the total power consumption of the system model in this embodiment. The total power consumption of the system model in this embodiment. The sum of the power consumption of the heat pump proton subsystem and the power consumption of the molten salt energy storage subsystem:

[0094] Based on the obtained energy consumption calculation data, this embodiment of the invention compares and analyzes the calculation results of the existing technology reference model and the system model of this embodiment.

[0095] The first step is to calculate the energy saving per ton of steam of the system model in this embodiment compared to the existing technology reference model. The power consumption of the prior art reference model calculated above. Total power consumption of the system model in this embodiment Substituting into the difference formula, the calculation is as follows:

[0096] The second step is based on energy savings per ton of steam. Calculate the relative energy saving rate of the system model in this embodiment. The relative energy saving rate is calculated as follows:

[0097] The third step is to calculate and evaluate the system's overall energy efficiency ratio. Defined as the ratio of the total effective heat produced by the system to the total electrical energy input to the system. Total heat absorbed... The electrical energy consumed by the heat pump proton system And the electrical energy consumed by the molten salt energy storage subsystem Substitute into the energy efficiency ratio calculation formula:

[0098] The analysis of the energy efficiency improvement mechanism is as follows: Existing technology reference models use pure electric heating, and their theoretical energy efficiency ratio limit is less than or equal to 1.0 (typically, the overall efficiency is around 0.98). This embodiment introduces a heat pump proton-lifting system, which recovers industrial waste heat fluid at a temperature of 40 degrees Celsius. The heat pump proton-lifting system handles approximately 420,000 kJ of sensible heat load, which accounts for approximately [percentage missing] of the total heat load. The overall energy efficiency ratio of the steam supply system coupled with industrial waste heat recovery and molten salt energy storage is 15%. This is because the heat pump proton system transfers external waste heat energy into the system cycle. The value reached 1.097, exceeding the energy efficiency limit of pure electric heating.

[0099] The safety and benefit analysis is as follows: The heat pump protonation system preheats the working water entering the steam generation coupling unit to 120°C to 150°C. This preheating temperature of 120°C to 150°C reduces the temperature difference between the working water and the molten salt working fluid at the heat exchange interface, and ensures that the heat exchange wall temperature is higher than the freezing point of the molten salt working fluid. This temperature matching relationship, in its physical structure, avoids the risk of molten salt solidification and freezing blockage that may be caused by direct contact between the low-temperature fluid and the high-temperature molten salt pipeline, thus ensuring the operational stability of the steam generation coupling unit under varying operating conditions.

[0100] The economic benefits for large-scale application are estimated as follows: Based on the calculation result of saving 85.8 kWh of electricity per ton of steam, if the annual steam production of the steam supply system coupled with industrial waste heat recovery and molten salt energy storage is set at 100,000 tons, then the cumulative annual energy saving will be approximately 8.58 million kWh. The calculation results show that the embodiments of the present invention have quantifiable technical effects in reducing industrial steam production costs and carbon emissions.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A steam supply system coupling industrial waste heat recovery and molten salt energy storage, characterized in that, include: The heat pump propellant system, the molten salt energy storage system, and the steam generation coupling unit; The input end of the heat pump propellant subsystem is connected to an external low-temperature industrial waste heat source, and the output end is connected to the water-side inlet of the steam generation coupling unit through a pipeline. It is configured to preheat the working fluid water from room temperature to the intermediate temperature of the sensible heat section. The molten salt energy storage subsystem is set up independently of the system's water circulation loop. It is connected to the salt-side interface of the steam generation coupling unit through a high-temperature resistant pipeline to form a closed molten salt heating loop, which is configured to use electrical energy to heat the molten salt working medium to a high temperature. The steam generating coupling unit serves as the sole heat exchange interface between the water circulation loop and the molten salt circulation loop, and it is internally equipped with a working fluid water channel and a molten salt channel that are physically isolated from each other. The steam supply system is configured to handle the sensible heat heating load of the working fluid water through the heat pump propellant subsystem, and to handle the latent heat of vaporization load and superheat load of the working fluid water through the molten salt energy storage subsystem using the steam generation coupling unit.

2. The steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 1, characterized in that, The heat pump proton system includes: a transcritical carbon dioxide heat pump unit and a pressurized hot water buffer tank; The evaporator side of the transcritical carbon dioxide heat pump unit is connected to the industrial waste heat access pipeline, and the gas cooler side is connected to the raw water supply pipeline and the water supply pump set. The pressurized hot water buffer tank is located between the working fluid output end of the transcritical carbon dioxide heat pump unit and the steam generation coupling unit. It is configured as a pressure-resistant container with a heat insulation layer, used to receive and store the high-temperature feedwater at the intermediate temperature output by the gas cooler, and to balance the continuous heating operation flow rate of the transcritical carbon dioxide heat pump unit with the real-time steam load flow rate required by the steam generation coupling unit.

3. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 2, characterized in that, The transcritical carbon dioxide heat pump unit mainly consists of a compressor, a gas cooler, a throttling expansion valve, and an evaporator, which are connected in a closed loop through refrigerant pipelines. The gas cooler is provided with a refrigerant channel and a water channel that are isolated from each other, and the evaporator is provided with a refrigerant channel and a waste heat fluid channel that are isolated from each other. The water supply pump set is configured to pressurize the working fluid water at room temperature and pump the pressurized working fluid water into the water flow channel of the gas cooler to exchange heat with the supercritical carbon dioxide working fluid in a countercurrent state.

4. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 1, characterized in that, The molten salt energy storage subsystem includes: a cryogenic molten salt storage tank, a high-temperature molten salt storage tank, a molten salt electric heater, and a molten salt circulation pump; The molten salt energy storage subsystem includes a heat storage circulation loop. In the heat storage circulation loop, the outlet of the low-temperature molten salt storage tank is connected to the molten salt circulation pump through a pipeline, the outlet of the molten salt circulation pump is connected to the molten salt electric heater, and the fluid outlet of the molten salt electric heater is connected to the high-temperature molten salt storage tank. The low-temperature molten salt storage tank is used to store low-temperature molten salt working fluid in the liquid working temperature range, and the high-temperature molten salt storage tank is used to store high-temperature molten salt working fluid after heating to the target high temperature.

5. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 4, characterized in that, The molten salt energy storage subsystem also includes a molten salt heat pump, and the molten salt energy storage subsystem includes a heat release circulation loop; In the exothermic circulation loop, the outlet of the high-temperature molten salt storage tank is connected to the inlet of the molten salt heating pump, the outlet of the molten salt heating pump is connected to the salt-side inlet of the steam generating coupling unit, and the salt-side outlet of the steam generating coupling unit is connected to the low-temperature molten salt storage tank through a return pipeline. The molten salt heating pump is a variable frequency speed-regulating high-temperature resistant pump, configured to regulate the output flow rate of the high-temperature molten salt working fluid.

6. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 1, characterized in that, The steam generation coupling unit includes three heat exchange components connected in series in a spatial location: a feedwater preheater, a steam evaporator, and a steam superheater. In the connection structure of the working fluid flow channel, the output end of the heat pump propellant subsystem is connected to the working fluid inlet of the feedwater preheater, the working fluid outlet of the feedwater preheater is connected to the working fluid inlet of the steam evaporator, the steam outlet of the steam evaporator is connected to the steam inlet of the steam superheater, and the steam outlet of the steam superheater is connected to the user-side steam pipeline network.

7. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 6, characterized in that, In the connection structure of the molten salt flow channel, the output end of the molten salt energy storage subsystem is connected to the molten salt inlet of the steam superheater, the molten salt outlet of the steam superheater is connected to the molten salt inlet of the steam evaporator, and the molten salt outlet of the steam evaporator is connected to the molten salt inlet of the feedwater preheater. The working fluid water flow direction and the molten salt flow direction form a countercurrent heat exchange layout on the entire steam generation coupling unit. The working fluid water absorbs the sensible heat released by the molten salt working fluid in the feed water preheater, absorbs the sensible heat released by the molten salt working fluid in the steam evaporator and undergoes a phase change, and absorbs the sensible heat released by the molten salt working fluid in the steam superheater and transforms into superheated steam.

8. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to claim 4, characterized in that, The external connecting pipes and valve assemblies of the molten salt energy storage subsystem are covered with an electric heat tracing device. The electric heat tracing device is configured to maintain the pipe wall temperature above the freezing point temperature of the molten salt working medium in order to prevent the molten salt working medium from undergoing phase change and solidification in the pipes during the system standby or startup phases.

9. A steam supply system coupling industrial waste heat recovery and molten salt energy storage according to any one of claims 1 to 8, characterized in that, The intermediate temperature provided by the heat pump propellant subsystem is in the range of 120 degrees Celsius to 150 degrees Celsius; the target high temperature of the heated high-temperature molten salt working medium provided by the molten salt energy storage subsystem is in the range of 400 degrees Celsius to 550 degrees Celsius; the intermediate temperature is set to be close to or higher than the freezing point temperature of the molten salt working medium.

10. A steam supply method coupling industrial waste heat recovery and molten salt energy storage, based on a steam supply system coupling industrial waste heat recovery and molten salt energy storage as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Step S1: Low-temperature sensible heat enhancement. The heat pump proton system is used to recover industrial waste heat fluid with a temperature range of 30 degrees Celsius to 60 degrees Celsius, and the working fluid water at room temperature is enhanced to an intermediate temperature. The high-temperature feedwater that has reached the intermediate temperature is stored in a pressurized hot water buffer tank. Step S2: High-temperature thermal energy storage. During off-peak electricity price periods of the external power grid or periods of renewable energy curtailment, the thermal storage operation mode of the molten salt energy storage subsystem is activated. Electricity is used to heat the low-temperature molten salt working medium to the target high temperature and store it in the high-temperature molten salt storage tank. Step S3: High-quality steam generation. When there is a demand for steam on the user side, the high-temperature feedwater in the pressurized hot water buffer tank and the high-temperature molten salt working medium in the high-temperature molten salt storage tank are simultaneously introduced into the steam generation coupling unit. The high-temperature molten salt working medium is used as a heat source, so that the high-temperature feedwater undergoes sensible heat exchange, phase change heat transfer and superheat heat transfer processes in sequence to produce industrial superheated steam with target temperature and pressure.

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