High-low temperature double-tank photovoltaic abandoned electricity coupling binary fused salt heat storage and exchange system and operation method thereof

Abstract

According to the high-low-temperature double-tank photovoltaic abandoned electricity coupling binary fused salt heat storage and exchange system and the operation method thereof, binary fused salt heat storage is adopted, light condensation heat storage and power generation load dynamic decoupling are achieved through independent heat storage of a cold salt tank and a hot salt tank and two-stage fused salt path control, and the power generation stability is improved. According to the system, photovoltaic abandoned electricity is utilized to drive a 25MW fused salt electric heater, fused salt is heated from 290 DEG C + / -10 DEG C to 550 DEG C + / -10 DEG C, the energy storage efficiency is larger than or equal to 93%, and the abandoned electricity is effectively absorbed. An intelligent salt dredging system is arranged, gravity self-flowing and compressed air assistance are combined, the emptying rate within 30 minutes + / -2 minutes reaches 99.5% + / -0.3%, and the risk of molten salt residue is reduced. The annular distribution pipe and the variable frequency pump are cooperatively controlled, so that the temperature stratification of the hot salt tank is less than or equal to 3 DEG C + / -0.5 DEG C, and the heat efficiency is improved by 8-12%. And the anti-condensation energy consumption of the storage tank is controlled to be smaller than or equal to 15 MWh / day through circulating anti-condensation of the MI heat tracing cable and the temperature adjusting pump, and the advantages of efficient heat storage, flexible peak regulation, high reliability and the like are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar thermal power generation and energy storage, and particularly relates to a high-low temperature dual-tank photovoltaic abandoned power-coupled binary molten salt storage and heat exchange system and an operation method thereof. Background Art

[0002] Solar thermal power generation systems need to solve the problem of energy discontinuity caused by sunlight fluctuations. Traditional heat storage technologies mostly adopt a single molten salt tank or an electric tracing independent operation mode, which have technical bottlenecks such as low heat storage efficiency, high energy consumption for anti-freezing measures, and ineffective utilization of photovoltaic abandoned power. In the prior art, the design of immersion electric heaters and conventional pump sets is difficult to balance high-temperature stability (above 550°C) and low-frequency load adaptability, and the coupling efficiency of photovoltaic and solar thermal systems has not been fully optimized.

[0003] In view of the above deficiencies of the prior art, the present invention aims to solve the following technical defects existing in traditional solar heat storage technologies: ① The heat storage system has low efficiency. A single molten salt tank is prone to temperature stratification, and the abandonment of photovoltaic power cannot be absorbed, resulting in energy waste; ② The protection against molten salt solidification relies on high-energy-consuming gas heating, and the system is prone to shutdown under low-load conditions; ③ Conventional pump sets cannot adapt to wide-range load regulation of 30%-100%, and the system peak shaving response time ≥ 1 hour; ④ The storage stability of high-temperature molten salt (≥550°C) is poor, and there is a risk of material fatigue failure in the temperature-resistant design of the storage tank. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high-low temperature dual-tank photovoltaic abandoned power-coupled binary molten salt storage and heat exchange system and an operation method thereof, which have the advantages of efficient heat storage and peak shaving, precise temperature control, efficient anti-freezing and salt drainage, high reliability, and efficient conversion of photovoltaic abandoned power, can realize flexible circulation of molten salt and stable operation under multiple working conditions, and significantly improve energy utilization efficiency and power generation system stability.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: A high-low temperature dual-tank photovoltaic abandoned power-coupled binary molten salt storage and heat exchange system includes a cold salt tank. The cold salt tank is connected to a concentrating solar collector field through a cold salt pump and a cold salt main pipe. The concentrating solar collector field is connected to a first in-tank flow annular distributor through a hot salt main pipe. The in-tank flow annular distributor is located inside the hot salt tank. The hot salt tank is connected to a steam generation system through a hot salt pump and a pipeline. The steam generation system is connected to a second in-tank flow annular distributor through a pipeline. The second in-tank flow annular distributor is located inside the cold salt tank.

[0006] Preferably, the system further includes a temperature regulating pump. The temperature regulating pump forms a circulation loop with a molten salt electric heater and the cold salt tank through a pipeline.

[0007] Preferably, the molten salt electric heater is powered by the photovoltaic power generation plant area.

[0008] Preferably, the hot salt tank forms a circulation loop with the hot salt pump, the cold salt tank, the temperature regulating pump, and the molten salt electric heater through pipelines.

[0009] Preferably, a desalting pipeline is provided at the lowest point of each device of the steam generation system, and the desalting pipeline is connected to the molten salt storage tank through a desalting pump 8.

[0010] An operation method of a high-low temperature dual-tank photovoltaic abandoned power coupling binary molten salt storage and heat exchange system includes the following working conditions: Working condition one: (1) Normal heat transfer condition: The cold salt pump pumps low-temperature molten salt at about 290°C ± 10°C into the concentrating solar collector field to absorb solar heat energy and heat it up to 550°C ± 10°C, and then returns to the hot salt tank through the hot salt main pipe and the first in-tank flow annular distribution pipe; (2) When the steam turbine generator set generates electricity, the hot salt pump sends the high-temperature molten salt in the hot salt tank into the steam generation system, exchanges heat with water / steam to generate superheated steam at 540°C ± 10°C to drive the steam turbine to do work, and the low-temperature molten salt after heat exchange returns to the cold salt tank through the cold salt tank annular distribution pipe.

[0011] Working condition two: Desalting condition: (1) Desalting of the concentrating solar collector field: When the molten salt temperature in the concentrating heat pipe is lower than 240°C ± 5°C, start desalting; using the site topography, the concentrating collector, the hot salt main pipe, and the cold salt main pipe are arranged inclined towards the desalting tank, and the molten salt flows by gravity, and compressed air is superimposed to assist in pushing the flow; (2) Desalting of the SGS: During unit maintenance or failure, the high-temperature molten salt in the steam generation system is discharged to the desalting tank through the desalting pipelines at the lowest points of each device, and then pumped into the molten salt storage tank by the desalting pump for recycling.

[0012] Working condition three: Heat storage and power generation condition: (1) Low-temperature molten salt heating stage: The cold salt pump retrieves molten salt at 290°C ± 10°C from the cold salt tank, transports it after boosting to the concentrating solar collector field to absorb heat and heat it up to 550°C ± 10°C and then returns to the hot salt tank, and is evenly distributed through the annular distribution pipe, controlling the molten salt flow rate ≥ 1.5 m / s ± 0.1 m / s, so that the temperature stratification in the hot salt tank is ≤ 3°C ± 0.5°C; (2) Power generation heat release stage: The hot salt pump pumps the high-temperature molten salt at 550°C ± 10°C in the hot salt tank into the steam generation system to generate superheated steam at 540°C ± 10°C to drive the steam turbine; the molten salt temperature at the outlet of the steam generation system is dynamically adjusted according to the steam turbine load. When at rated load (100%), the salt return temperature is 300°C ± 10°C and is directly injected into the cold salt tank; when at medium and low loads (40% - 60%), the salt return temperature is 275°C ± 5°C, and the temperature is adjusted to ≥ 280°C ± 5°C through the temperature regulating pump and the molten salt electric heater.

[0013] Operating Condition 4: Photovoltaic curtailment for thermal energy storage High-temperature energy storage mode: When there is curtailment of electricity, start a single temperature regulating pump to extract molten salt at 290°C ± 10°C from the cold salt tank. Utilize the curtailed electricity in the photovoltaic power generation plant area. Through a 25MW molten salt electric heater with three-level power control (40% / 70% / 100%), precisely control the temperature of the molten salt to be raised to 550°C ± 10°C and inject it into the hot salt tank. The energy storage efficiency is ≥ 93%; Anti-condensation and temperature-raising mode (tank temperature ≤ 275°C ± 5°C): The temperature regulating pump extracts low-temperature molten salt at 275°C ± 5°C from the cold salt tank, heats it to 300°C ± 5°C through the molten salt electric heater, and then reinjects it into the cold salt tank to make the temperature of the whole tank ≥ 280°C ± 5°C. Reinject it at the bottom of the hot salt tank to prevent the formation of a low-temperature layer; Salt melting and collaborative energy-saving operation: In the initial salt injection stage, the molten salt electric heater and the natural gas heating device are used in parallel. When the power of the molten salt electric heater > 15MW ± 1MW, automatically shut down 50% ± 5% of the natural gas heat source. And for every 1MW ± 0.1MW increase in the output power of the molten salt electric heater, reduce the natural gas consumption by 0.27×10⁴ m³ / d ± 0.01×10⁴ m³ / d; Operating Condition 5: Molten salt anti-condensation and emergency deactivation Start and stop of the tracing system: When the temperature of the molten salt in the pipeline ≤ 270°C ± 5°C, the MI tracing cable starts automatically. The tracing system is linked with the molten salt electric heater in the storage tank to prevent condensation globally through molten salt circulation; Drainage process of the collector field: Drain the molten salt to the underground salt drainage tank through "gravity + compressed air salt drainage", and then pump it into the molten salt storage tank by the salt drainage pump. The residual amount is ≤ 0.5% ± 0.1%, and the drainage time is ≤ 30 minutes ± 2 minutes; Long-term shutdown protection: Drain the molten salt in the steam generation system and the concentrating collector field to the storage tank, start the temperature regulating pump + molten salt electric heater cycle to maintain the storage tank temperature ≥ 300°C ± 5°C, and the daily energy consumption is ≤ 15MWh ± 1MWh; Operating Condition 6: Countermeasures for abnormal conditions Low-load operation (< 40% ± 3%): When the temperature of the returned salt in the steam generation system drops to 270°C ± 5°C, the temperature regulating pump extracts molten salt at 290°C ± 10°C from the cold salt tank and mixes it with the returned salt at a ratio of 1:4 to raise the temperature to 280°C ± 5°C, and dynamically adjust the temperature fluctuation of the cold salt tank to ± 5°C; Extreme temperature fluctuation (hot salt tank ≥ 580°C ± 10°C): Drain the excessive high-temperature molten salt into the salt drainage tank, start the cold salt pump for forced circulation cooling, control the temperature gradient in the tank ≤ 10°C / h ± 1°C / h, and use the reverse control of the molten salt flow introduced for emergency cooling to prevent pipeline cavitation; Operating Condition 7: System start-up, shutdown and maintenance Cold start: The molten salt electric heater heats the solid molten salt to 290°C ± 10°C at a rate of 10°C / h ± 1°C / h, replacing 50% ± 5% of the gas energy consumption; Hot shutdown: The thermostatic pump circulates at a low frequency, and starts to circulate at 30%±5% flow rate for 2 hours±0.1 hours every week to prevent local solidification; Steam generation system inspection and maintenance or failure: The molten salt is discharged to the salt drainage tank through the salt drainage pipeline, and then pumped into the molten salt storage tank by the salt drainage pump.

[0014] The present invention can achieve the following beneficial effects: (1) Efficient heat storage and flexible peak load regulation: Binary molten salt (60% NaNO3+40% KNO3) is used for solar thermal energy storage, with a heat storage capacity of 1835MWht, which can provide stable energy supply for 8 hours.

[0015] Through the coordinated control of variable frequency cold salt pumps (3×50% capacity), hot salt pumps (3×50% capacity) and temperature control pumps (2×100% capacity), the steam turbine can be continuously adjusted at 10%-100% load, breaking through the low-load (40%) shutdown limitation of traditional systems.

[0016] (2) Precise temperature control and thermal efficiency optimization: The annular distribution pipe controls the molten salt flow rate to ≥1.5m / s, making the temperature stratification of the hot salt tank ≤3°C, which improves the thermal efficiency by 8-12% compared with the traditional single tank system.

[0017] The thermostatic pump dynamically adjusts the return salt temperature (stable operation as low as 270°C), and cooperates with the graded power adjustment of the molten salt electric heater (40% / 70% / 100%) to achieve a power storage efficiency of ≥93% and reduce power loss by 10~15%.

[0018] (3) High-efficiency anti-condensation and emergency salt removal: The integrated MI heating cable (temperature resistance 550°C, uniformity 95%) and the thermostatic pump circulation anti-condensation control the anti-condensation energy consumption of the storage tank to ≤15MWh / day and reduce the temperature fluctuation to ±5°C.

[0019] The salt drainage system drains salt through gravity + compressed air, and the molten salt in the collector is emptied within 30 minutes (residual amount ≤ 0.5%). It is also equipped with a 50m³ stainless steel 321 salt drainage tank and a variable frequency salt drainage pump (lift 28m) to avoid pipeline freezing damage and extend the equipment life by ≥5 years.

[0020] (4) High temperature reliability and emergency protection: The hot salt tank is made of A240 347H material (resistant to 565°C). In case of extreme over-temperature, the emergency relief valve is triggered and the cold salt pump is linked to force cooling (gradient ≤10°C / h) to avoid thermal fatigue failure of the material.

[0021] (5) Efficient conversion of abandoned photovoltaic power: Configure a 25MW molten salt electric heater, which can convert the abandoned photovoltaic electricity into thermal energy storage through a temperature regulating pump (single pump flow rate: 110 m³ / h), achieve gradient regulation of the molten salt from 290°C to 550°C, and the comprehensive electric energy → thermal energy conversion efficiency ≥ 93%.

[0022] Support three - level power regulation (40% / 70% / 100%), meet the requirements of multiple scenarios such as anti - condensation (275°C → 300°C) and low - load heat storage, and increase the annual abandoned electricity utilization rate by 23%.

[0023] Equipped with the function of bidirectional blending of cold / hot molten salt in the salt tank. When the energy storage temperature fluctuates, the temperature regulating pump can cooperate across the tanks to quickly balance the temperature difference (the over - temperature gradient ≤ 10°C / h), and the abandoned electricity consumption capacity is 1.8 times stronger than that of the conventional single - tank system.

[0024] During the salt melting stage, use abandoned electricity to replace natural gas heating (the consumption ratio is reduced by 30%), and reduce the low - temperature phase - change energy consumption of solid molten salt by 15%. Description of the Drawings

[0025] The present invention will be further described below in conjunction with the drawings and embodiments: Figure 1 Process diagram of the system; Figure 2 First - floor plan layout of the system; Figure 3 Top - floor plan layout of the system; Figure 4 Abandoned electricity consumption control logic diagram of the molten salt electric heater (based on power - level regulation and temperature - regulating pump flow matching).

[0026] In the figure: hot salt tank 1, hot salt pump 2, steam generation system 3, cold salt tank 4, cold salt pump 5, desalting tank 7, desalting pump 8, concentrating solar collector field 9, molten salt electric heater 10, in - tank flow annular distribution pipe 12, hot salt main pipe 13, cold salt main pipe 14, salt tank salt - discharging pipeline 15, steam generation system desalting pipeline 16, desalting pipeline 17; A, B, and C represent the numbers of different quantities of the same equipment. Detailed Embodiments

[0027] The preferred solution is as Figures 1 to 4 shown. A high - and - low - temperature dual - tank photovoltaic abandoned - electricity - coupled binary molten salt storage and heat - exchange system specifically includes the following equipment: (1) System composition and technical architecture: ①. Tank body heat - storage system: High and low temperature double vertical storage tanks: including 1 cold salt tank (diameter 29m, height 15m, design temperature 370°C) and 1 hot salt tank (diameter 31m, height 15m, design temperature 565°C), with materials being A516 GR70N and A240 347H respectively, meeting API 650 and GB 50341 standards.

[0028] Salt drainage tank: 1 horizontal pressure vessel, located 5m underground in the middle of two molten salt storage tanks, with an effective volume of 50m³, design temperature 565°C, and the material being stainless steel 321, used to recover and collect the molten salt emptied from the solar field and the steam generation system (SGS).

[0029] Salt drainage pump: 2 vertical suspended centrifugal pumps with 100% capacity, flow rate 300m³ / h, head 28m, used to pump the molten salt in the salt drainage tank back to the storage tank.

[0030] Solar field salt drainage: The molten salt is drained to the salt drainage tank by gravity flow and assisted by compressed air; at night, it supports selective emptying of the solar collectors or retaining the molten salt in the main pipe.

[0031] ②. Molten salt circulation pump unit: Cold salt pump unit: 3 vertical suspended centrifugal pumps with 50% capacity, single pump flow rate 1186.5m³ / h, outlet pressure 3.398MPa, design temperature 370°C, used to transport 290°C low-temperature molten salt to the solar field.

[0032] Hot salt pump unit: 3 vertical suspended centrifugal pumps with 50% capacity, single pump flow rate 606m³ / h, head 31m, design temperature 565°C, used to transport 550°C high-temperature molten salt to the steam generation system.

[0033] Temperature adjustment pump unit: 2 variable frequency pumps with 100% capacity, single pump flow rate 110m³ / h, head 25m, used for molten salt temperature adjustment and anti-freezing circulation.

[0034] ③. Photovoltaic-coupled thermal energy storage unit: Molten salt electric heater: 25MW electric power, equipped with multi-stage power adjustment modules, having two operating modes: High-temperature energy storage mode: Using the abandoned photovoltaic power to heat the 290°C molten salt to 550°C and directly injecting it into the hot salt tank.

[0035] Anti-freezing and temperature-rising mode: Since the power of the molten salt electric heater can be adjusted in steps, when it is used for molten salt anti-freezing, by starting one or more temperature adjustment pumps, the low-temperature molten salt (275°C) can be heated to 300°C or higher. When the molten salt temperature in the cold tank is lower than 275°C, start the temperature adjustment pump to pump the molten salt into the molten salt electric heater, and the heated molten salt returns to the cold salt tank; when the molten salt temperature in the hot tank is lower than 275°C, start the temperature adjustment pump to pump the molten salt into the molten salt electric heater, and the heated molten salt returns to the hot salt tank for mixing and temperature rising.

[0036] ④. Anti-condensation tracing system: Armored mineral insulated tracing cable (MI): Covers molten salt equipment, pipelines and valves, starts when the molten salt temperature < 270 °C, and shuts down after heating to 290 °C.

[0037] Molten salt drainage module: Supports the drainage of molten salt in the heat collection pipe and steam generation system to the salt drainage tank, reducing the condensation risk.

[0038] (2) Implementation methods of core technologies: ①. Decoupled operation control and dynamic temperature regulation: The cold salt pump group and the hot salt pump group are independently frequency-regulated to achieve dynamic decoupling of heat absorption in the heat collection loop and heat release in the power generation loop.

[0039] When the steam turbine load drops below 40%, the temperature regulation pump combines with a 25 MW molten salt electric heater to maintain the SGS salt return temperature ≥ 280 °C, avoiding molten salt solidification, and the low-load efficiency is increased by 8% - 12% compared with the traditional system.

[0040] ②. Photovoltaic curtailment consumption and energy storage optimization: The molten salt electric heater preferentially consumes curtailment power, and the single-time heat conversion efficiency ≥ 97%.

[0041] During the salt melting stage (heating solid salt to 290 °C), electric heating can replace 50% of the gas energy consumption, which is specifically achieved by circulating and heating the molten salt through the temperature regulation pump.

[0042] ③. Molten salt flow state optimization and salt drainage anti-condensation: Salt drainage in the heat collection loop: At night or under low irradiation, the molten salt in the heat collector and pipeline is drained by gravity (the terrain slope from east to west ≤ 2%) into the underground salt drainage tank at -5 m (effective volume 50 m³), and is accelerated for drainage by compressed air (flow rate ≥ 2 m / s) to solve the risk of molten salt solidification when there is no electric tracing for the heat collection pipe.

[0043] Salt drainage during SGS maintenance: During maintenance, the residual molten salt in the steam generation system (evaporator, preheater, etc.) is drained through the lowest salt drainage pipeline to the salt drainage tank, and then pumped back to the storage tank for recycling by two salt drainage pumps.

[0044] ④. Temperature control and anti-condensation measures Electric tracing system: All pipelines and valves in contact with molten salt use MI tracing cables, with a nickel-based alloy outer sheath + magnesium oxide insulation layer (temperature resistance 550 °C), and automatically start heating to 290 °C when the molten salt temperature ≤ 270 °C.

[0045] Molten salt disarming strategy: During night salt drainage, it is possible to choose to drain the heat collection pipe (reducing the preheating time the next day) or only drain the heat collector (retaining the molten salt in the main pipe to reduce the electric tracing energy consumption), flexibly adapting to the operation requirements.

[0046] (3)Technical parameters and performance advantages: Heat storage capacity: 1835 MWht, based on binary molten salt 60% NaNO3 + 40% KNO3 (density 1918.3 kg / m³, total storage 17400 t).

[0047] Cycle efficiency: solar thermal - power generation efficiency ≥ 42% (upper limit of traditional system is 35%), mainly due to decoupled operation and curtailment optimization.

[0048] Peaking ability: complete 10% - 100% load switching within 30 minutes, molten salt temperature difference fluctuation ≤ 15°C.

[0049] (4)The process of this system includes the following: ① Process flow of the heat storage and heat exchange system: In the high - and low - temperature dual - tank photovoltaic curtailment - coupled binary molten salt heat storage and heat exchange system of the present invention, the heat transfer process and core features are as follows: The cold salt pump 5 pumps low - temperature molten salt (about 290°C) into the concentrating solar collector field 9 to absorb solar heat energy, and the temperature rises to 550°C. After absorbing heat from the concentrating solar collector field 9, it returns to the hot salt tank 1 through the hot salt main pipe 13 and the first in - tank flow annular distribution pipe 12 (i.e., the in - tank flow annular distribution pipe 12A). (2) When the steam turbine generator set generates electricity, the high - temperature molten salt then enters the steam generation system (SGS) 3 through the hot salt pump 2, exchanges heat with water / steam to generate superheated steam at 540°C, enters the steam turbine to do work and generate electricity, and the low - temperature molten salt after heat exchange returns to the cold salt tank 4 through the second in - tank flow annular distribution pipe 12 (i.e., the in - tank flow annular distribution pipe 12B).

[0050] Through dual - tank independent heat storage (cold salt tank, hot salt tank) and two - stage molten salt path control (collector field cycle, SGS cycle), the dynamic decoupling of concentrating heat storage and power generation load is achieved, the peaking response time is significantly reduced, and the stability and safety of the power generation system are improved.

[0051] ② Process flow of the salt drainage system: The salt drainage system of the present invention consists of a collector field salt drainage module and a steam generation system (SGS) salt drainage module, and its process flow is as follows: a. Collector field salt drainage module: Salt drainage trigger condition: When the molten salt temperature in the collector tube is lower than 240°C, start the salt drainage program to avoid condensation risk.

[0052] Salt drainage mechanism: Relying on the terrain conditions where the east is higher than the west and the north is higher than the south in the site, and the southwestern corner is the lowest point of the terrain (slope ≤ 2%), all the collectors 9, the hot salt main pipe 13, and the cold salt main pipe 14 are arranged obliquely towards the desalting tank 7 at the southwestern corner (installed at -5 m underground), and the molten salt flows by gravity into the tank; with the superposition of compressed air-assisted pushing flow, the flow velocity in the pipeline is increased to 2 m / s to ensure that the emptying rate reaches 99.5% within 30 minutes.

[0053] Salt drainage mode: Full drainage mode: Empty the heat collecting pipe and the molten salt pipeline, saving ≥ 60% of the night-time tracing energy consumption, but the preheating start-up time the next day is extended by 1.5 h; Semi-drainage mode: Only empty the heat collecting pipe, retain the molten salt pipeline inventory, and the start-up time the next day is shortened to 0.5 h, and the consumption of maintaining the electric tracing of the main pipe needs to be ≤ 15 MWh / night.

[0054] b. Salt drainage module of the steam generation system (SGS): Salt drainage trigger condition: During unit maintenance or failure, it is necessary to empty the high-temperature molten salt in the steam generation system (SGS) 3.

[0055] Salt drainage process: When desalting, the molten salt is discharged through the lowest-point desalting pipelines of each equipment in the steam generation system to the desalting tank 7, and finally, the molten salt is pumped into the molten salt storage tank for recycling through 2 desalting pumps 8 via the desalting pipeline 17.

[0056] Combining gravity self-flow and compressed air pressurization significantly reduces the molten salt residue (residue rate ≤ 0.5%), saving 70% of energy compared with the traditional electric tracing anti-condensation scheme; the dual salt drainage modes of full drainage / semi-drainage, and the optional strategies balance energy consumption and efficiency, and flexibly match the light resource fluctuation scenarios (the semi-drainage mode is preferentially enabled on cloudy days).

[0057] ③ Photo-thermal energy storage and power generation process: a. Low-temperature molten salt heating stage: Cold salt pump start-up: Retrieve the molten salt at 290 °C in the cold salt tank 4, boost it through 3 cold salt pumps 5 (single pump flow rate 1186.5 m³ / h, outlet pressure 3.398 MPa), and transport it to the concentrating solar collector field 9 via the cold salt main pipe 14.

[0058] Heat collection and heat absorption: The molten salt absorbs solar energy in the concentrating solar collector field 9, returns to the hot salt tank 1 via the hot salt main pipe 13 after heating up to 550 °C, and is evenly distributed through the annular distribution pipe 12A, with a flow velocity ≥ 1.5 m / s to ensure that the temperature stratification in the tank is ≤ 3 °C.

[0059] In this way, through the combined design of the cold salt pump group (3 × 50% capacity) and the annular distribution pipe, the flow velocity of the molten salt is ≥ 1.5 m / s, and the temperature stratification control of the hot salt tank is optimized to ≤ 3 °C, with the thermal efficiency improved by 8 - 12% compared with the traditional single-tank system.

[0060] b. Power generation and heat release stage: Operation of the hot salt pump: The 550°C high-temperature molten salt in the hot salt tank 1 is pumped into the steam generation system (SGS) 3 by 3 hot salt pumps 2 (single pump flow rate: 606 m³ / h, head: 31 m) to generate 540°C superheated steam to drive the steam turbine.

[0061] Regulation of molten salt reflux: The molten salt temperature at the outlet of the steam generation system (SGS) 3 is dynamically adjusted according to the steam turbine load: ① Rated load (100%): The salt return temperature is 300°C, and it is directly injected into the cold salt tank 4; ② Medium and low loads (40%-60%): The salt return temperature is 275±5°C, and it is adjusted to ≥280°C through the temperature regulating pump 6 (single pump flow rate: 110 m³ / h, head: 25 m) via the molten salt electric heater 10.

[0062] In this way, the hot salt pump 2 (resisting high temperature of 565°C) cooperates with the temperature regulating pump 6 for dynamic adjustment, enabling the salt return temperature of the steam generation system (SGS) to be stable at ≥280°C at 40% load, breaking through the low-load shutdown limit; the variable-frequency hot salt pump group supports continuous adjustment of the steam turbine from 10% to 100%.

[0063] ④ Implementation steps of photovoltaic curtailment electricity energy storage for heat: a. High-temperature energy storage mode: The curtailed electricity is used to heat the molten salt. Start a single temperature regulating pump 6 (single pump flow rate: 110 m³ / h), extract 290°C molten salt from the cold salt tank 4, make full use of the curtailed electricity in the photovoltaic power generation plant area 11, and heat the molten salt to 550°C through the 25MW molten salt electric heater 10, with precise control in 3 power levels (40% / 70% / 100%); the high-temperature molten salt is injected into the hot salt tank 1, and the energy storage efficiency is ≥93%.

[0064] In this way, by using the 25MW for adjustment in 3 power levels, the heating efficiency of the molten salt is increased to ≥93%, saving 10-15% of the electric energy loss compared with direct current resistance heating; at the same time, the curtailed electricity energy storage and the anti-condensation function of the tank body are reused, replacing the traditional immersion electric heater and reducing the hardware complexity inside the tank.

[0065] b. Anti-condensation and temperature-raising mode (storage tank temperature ≤275°C): The temperature regulating pump 6 extracts the low-temperature molten salt (275°C) in the cold salt tank 4 and heats it to 300°C through the molten salt electric heater 10; Anti-condensation of the cold salt tank: The heated molten salt is reinjected into the cold salt tank 4, and the temperature of the whole tank is ≥280°C through mixing; Anti-condensation of the hot salt tank: The heated molten salt is reinjected into the bottom of the hot salt tank 1 to avoid the formation of a low-temperature layer.

[0066] In this way, by using the temperature regulating pump 6 to reversely extract the molten salt from the molten salt storage tank, heat it and then reinject it, the energy consumption for anti-condensation of the storage tank is reduced to ≤15 MWh / day, and the temperature gradient fluctuation is reduced to ±5°C.

[0067] c. Salt melting and energy-saving operation in coordination: During the initial salt injection stage: the molten salt electric heater 10 and the natural gas heating device are used in parallel; when the power of the molten salt electric heater 10 > 15 MW, 50% of the natural gas heat source is automatically shut down; for every 1 MW increase in the output power of the molten salt electric heater 10, the natural gas consumption is reduced by 0.27×10⁴ m³ / d.

[0068] ⑤ Molten salt anti-condensation and emergency defrosting operations: a. Start and stop of the tracing system: when the temperature of the molten salt in the pipeline ≤ 270 °C, the MI tracing cable is automatically started (temperature resistance 550 °C, heat flux density 50 kW / m²), the uniformity of heat distribution reaches 95%, and the failure rate is reduced by 70% compared with the traditional tracing; in addition, the tracing system is linked with the molten salt electric heater of the storage tank, and global anti-condensation is achieved through molten salt circulation instead of local heating.

[0069] b. Salt drainage process of the solar field: The molten salt is quickly emptied into the underground salt drainage tank 7 (volume 50 m³, made of stainless steel 321) through "gravity + compressed air salt drainage" via the molten salt main pipe, and finally pumped into the molten salt storage tank by the salt drainage pump 8, with the residual amount ≤ 0.5% and the emptying time ≤ 30 minutes, avoiding freezing damage of the heat collection pipes and extending the service life of the vacuum glass tubes.

[0070] c. Long-term shutdown protection: Empty the molten salt in the steam generation system (SGS) 3 and the solar field 9 into the storage tank, start the temperature regulating pump 6 + the molten salt electric heater 10 to circulate and maintain the temperature of the storage tank ≥ 300 °C, with the daily energy consumption ≤ 15 MWh.

[0071] ⑥ Countermeasures for abnormal working conditions: a. Low-load operation (< 40%) When the salt return temperature of the steam generation system (SGS) 13 drops to 270 °C, the temperature regulating pump 6 extracts the molten salt (290 °C) from the cold salt tank 4 and mixes it to raise the temperature to 280 °C; the mixing ratio is 1:4 (cold salt: salt return), and the temperature fluctuation of the cold salt tank is dynamically adjusted to ±5 °C.

[0072] b. Extreme temperature fluctuation (hot salt tank ≥ 580 °C): Divert the excessive high-temperature molten salt into the salt drainage tank 7 through the salt drainage pipeline 15 of the hot salt tank; start the cold salt pump 5 to force circulation for cooling, and control the temperature gradient in the tank ≤ 10 °C / h to avoid thermal fatigue failure of the high-temperature tank material. In addition, during the emergency cooling process, the molten salt flow reverse flushing control is introduced to prevent pipeline cavitation.

[0073] c. System start-up, shutdown and maintenance: 1) Cold start: The molten salt electric heater 9 heats the solid molten salt to 290 °C at a rate of 10 °C / h, replacing 50% of the gas energy consumption.

[0074] 2) Hot shutdown: The temperature regulating pump 8 circulates at low frequency, and starts 30% flow rate circulation for 2 hours every week to prevent local solidification.

[0075] Using the molten salt electric heater 9 to replace 50% of the gas consumption for melting salt can save ≥2000 tons of natural gas annually, breaking through the bottleneck that the traditional solid-state molten salt startup only depends on natural gas.

[0076] 3) During the overhaul and maintenance or failure of the unit in the steam generation system (SGS) 3, the molten salt is discharged to the desalting tank 7 through the desalting pipeline 16 of the steam generation system, and finally pumped into the molten salt storage tank through the desalting pump 8.

[0077] The above embodiments are only the preferred technical solutions of the present invention, and should not be regarded as a limitation to the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A high-low temperature dual-tank photovoltaic abandoned electricity coupled binary molten salt energy storage and heat exchange system, characterized in that: It includes a cold salt tank. The cold salt tank is connected to the concentrating solar heat collection field through a cold salt pump and a cold salt main pipe. The concentrating solar heat collection field is connected to the first in-tank flow annular distributor through a hot salt main pipe. The in-tank flow annular distributor is located inside the hot salt tank. The hot salt tank is connected to the steam generation system through a hot salt pump and a pipeline. The steam generation system is connected to the second in-tank flow annular distributor through a pipeline. The second in-tank flow annular distributor is located inside the cold salt tank.

2. The high-low temperature dual-tank photovoltaic abandoned electricity coupled binary molten salt energy storage and heat exchange system according to claim 1, wherein: It also includes a temperature regulating pump. The temperature regulating pump forms a circulation loop with the molten salt electric heater and the cold salt tank through pipelines.

3. A high-low temperature dual-tank photovoltaic abandoned electricity-coupled binary molten salt energy storage and heat exchange system and its operation method according to claim 2, characterized in that: The molten salt electric heater is powered by the photovoltaic power generation plant area.

4. A high-low temperature dual-tank photovoltaic abandoned power-coupled binary molten salt energy storage and heat exchange system according to claim 2, characterized in that: The hot salt tank forms a circulation loop with the hot salt pump, the cold salt tank, the temperature regulating pump, and the molten salt electric heater through pipelines.

5. A high-low temperature dual-tank photovoltaic abandoned electricity-coupled binary molten salt energy storage and heat exchange system according to claim 1, characterized in that: Salt drainage pipelines are provided at the lowest points of the devices of the steam generation system. The salt drainage pipelines are connected to the molten salt storage tank through a salt drainage pump.

6. The operation method of a high-low temperature dual-tank photovoltaic abandoned power-coupled binary molten salt energy storage and heat exchange system according to any one of claims 1-5, characterized in that: It includes the following operating conditions: Operating condition 1: (1) Normal heat energy transfer condition: The cold salt pump pumps low-temperature molten salt at about 290°C ± 10°C into the concentrating solar heat collection field to absorb solar heat energy and heat up to 550°C ± 10°C, and then returns to the hot salt tank through the hot salt main pipe and the first in-tank flow annular distributor. (2) When the steam turbine generator set generates electricity, the hot salt pump sends the high-temperature molten salt in the hot salt tank into the steam generation system to exchange heat with water / steam to generate superheated steam at 540°C ± 10°C to drive the steam turbine to do work. The low-temperature molten salt after heat exchange returns to the cold salt tank through the cold salt tank annular distributor.

7. The operating method of a high-low temperature double-tank photovoltaic abandoned electricity-coupled binary molten salt storage heat exchange system according to claim 6, characterized in that: Operating condition 2: Salt drainage condition: (1) Salt drainage from the heat collection field: Start salt drainage when the molten salt temperature in the collector tube is lower than 240°C ± 5°C; utilize the site topography, and the collectors, the hot salt main pipe, and the cold salt main pipe are arranged inclined towards the salt drainage tank. The molten salt flows by gravity, and compressed air is superimposed to assist in pushing the flow. (2) Salt drainage from the SGS: During unit maintenance or failure, the high-temperature molten salt in the steam generation system is drained to the salt drainage tank through the salt drainage pipelines at the lowest points of each device, and then pumped into the molten salt storage tank by the salt drainage pump for recycling.

8. The operating method of a high-low temperature double-tank photovoltaic abandoned electricity-coupled binary molten salt storage heat exchange system according to claim 6, characterized in that: Operating condition 3: Heat storage and power generation condition: (1) Low-temperature molten salt heating stage: The cold salt pump retrieves molten salt at 290°C ± 10°C from the cold salt tank, transports it to the concentrating solar heat collection field after boosting to absorb heat and heat up to 550°C ± 10°C and then returns to the hot salt tank, and is evenly distributed through the annular distributor. Control the molten salt flow rate ≥ 1.5m / s ± 0.1m / s to make the temperature stratification in the hot salt tank ≤ 3°C ± 0.5°C. (2) Power generation heat release stage: The hot salt pump pumps the high-temperature molten salt at 550°C ± 10°C in the hot salt tank into the steam generation system to generate superheated steam at 540°C ± 10°C to drive the steam turbine; the molten salt temperature at the outlet of the steam generation system is dynamically adjusted according to the steam turbine load. When at rated load, the salt return temperature is 300°C ± 10°C and is directly injected into the cold salt tank; when at medium and low loads, the salt return temperature is 275°C ± 5°C, and the temperature is adjusted to ≥ 280°C ± 5°C through the temperature regulating pump and the molten salt electric heater.

9. The operating method of a high-low temperature double-tank photovoltaic abandoned electricity-coupled binary molten salt storage heat exchange system according to claim 6, characterized in that: Operating condition 4: Photovoltaic curtailment and heat storage condition: (1) High-temperature energy storage mode: When there is curtailment of electricity, start a single temperature control pump to extract molten salt at 290°C ± 10°C from the cold salt tank, utilize the curtailed electricity in the photovoltaic power generation plant area, and precisely control the power in 3 levels by a 25MW ± 1MW molten salt electric heater to heat the molten salt to 550°C ± 10°C and inject it into the hot salt tank; (2) Anti-freezing and temperature-rising mode: The temperature control pump extracts low-temperature molten salt ≤ 275°C in the cold salt tank, heats it to 300°C ± 5°C through the molten salt electric heater, and reinjects it into the cold salt tank to make the temperature of the whole tank ≥ 280°C ± 5°C, and reinjects it at the bottom of the hot salt tank to prevent the formation of a low-temperature layer; (3) Salt melting and energy-saving operation in coordination: In the initial salt injection stage, the molten salt electric heater and the natural gas heating device are used in parallel. When the power of the molten salt electric heater > 15MW ± 1MW, 50% ± 5% of the natural gas heat source is automatically turned off, and for every 1MW ± 0.1MW increase in the output power of the molten salt electric heater, the natural gas consumption is reduced by 0.27×10⁴ m³ / d ± 0.01×10⁴ m³ / d.

10. The operation method of a high-low temperature dual-tank photovoltaic curtailment-coupled binary molten salt storage and heat exchange system according to claim 6, characterized in that: Operating condition 5: Molten salt anti-freezing and emergency defensing condition: (1) Start and stop of the tracing system: When the temperature of the molten salt in the pipeline ≤ 270°C, the MI tracing cable is automatically started, and the tracing system is linked with the molten salt electric heater of the storage tank to prevent freezing globally through molten salt circulation; (2) Salt discharging process of the concentrating solar field: Drain the molten salt to the underground salt drainage tank through "gravity + compressed air salt discharging", and then pump it into the molten salt storage tank by the salt drainage pump, with the residual amount ≤ 0.5% ± 0.1% and the drainage time ≤ 30 minutes ± 2 minutes; (3) Long-term shutdown protection: Drain the molten salt in the steam generation system and the concentrating solar field to the storage tank, and start the temperature control pump + molten salt electric heater circulation to maintain the temperature of the storage tank ≥ 300°C ± 5°C.

11. The operation method of a high-low temperature dual-tank photovoltaic curtailment-coupled binary molten salt storage and heat exchange system according to claim 6, characterized in that: Operating condition 6: Countermeasures for abnormal conditions: (1) Low-load operation: When the salt return temperature of the steam generation system drops to 270°C ± 5°C, the temperature control pump extracts molten salt at 290°C ± 10°C in the cold salt tank and mixes it with the salt return at a ratio of 1:4 to heat it to 280°C ± 5°C, and dynamically adjusts the temperature fluctuation of the cold salt tank to ± 5°C; (2) Extreme temperature fluctuation: Drain the excessive high-temperature molten salt into the salt drainage tank, start the cold salt pump for forced circulation cooling, control the temperature gradient in the tank ≤ 10°C / h ± 1°C / h, and introduce the molten salt flow for anti-recoil control during emergency cooling to prevent pipeline cavitation.

12. The operation method of a high-low temperature dual-tank photovoltaic curtailment-coupled binary molten salt storage and heat exchange system according to claim 6, characterized in that: Operating condition 7: System start-up, shutdown and maintenance condition: (1) Cold start: The molten salt electric heater heats the solid molten salt to 290°C ± 10°C at a rate of 10°C / h ± 1°C / h, replacing 50% ± 5% of the gas energy consumption; (2) Hot shutdown: The temperature control pump circulates at a low frequency, and starts 30% ± 5% of the flow to circulate for 2 hours ± 0.1 hour per week to prevent local solidification; (3) Maintenance or failure of the steam generation system: The molten salt is drained to the salt drainage tank through the salt drainage pipeline, and then pumped into the molten salt storage tank by the salt drainage pump.

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