Integrated heat storage SOFC-GT combined cycle power generation system and method

Abstract

The invention discloses an integrated heat storage SOFC-GT combined cycle power generation system which comprises a gas compressor, an SOFC electric pile, a combustion chamber, a gas turbine, a reformer, a first heat exchanger, a second heat exchanger, a third heat exchanger, a booster pump, a heat storage unit and a waste heat utilization device. And an outlet of the heat storage unit is connected with the waste heat utilization device. The heat storage unit is introduced to serve as energy buffering, and the waste heat utilization efficiency and operation flexibility of the system are improved. By means of the heat storage and heat release functions of the heat storage unit, efficient utilization of energy can be achieved under different working conditions. When the waste heat is sufficient, the redundant heat is stored; and when the waste heat is insufficient, the stored heat is released to meet requirements. By means of the energy buffering mechanism, the waste heat utilization efficiency is improved, and the system can operate efficiently within a wider working condition range.

Description

Technical Field

[0001] This invention belongs to the field of coupled power generation technology, and more specifically, relates to an SOFC-GT combined cycle power generation system and method with integrated thermal storage. Background Technology

[0002] A solid oxide fuel cell (SOFC) is a highly efficient energy conversion device that directly converts the chemical energy of fuel into electrical energy. Its working principle is based on the oxygen ion conduction characteristics of solid oxide electrolytes, achieving efficient energy conversion through electrochemical reactions. SOFCs have high power generation efficiency and can operate at high temperatures, generating high-quality waste heat. This waste heat can be used to drive a gas turbine (GT) for further power generation, thus achieving cascaded energy utilization and improving the overall power generation efficiency of the system.

[0003] A gas turbine (GT) is a highly efficient heat engine with advantages such as high power density, rapid start-up, and strong fuel adaptability. A gas turbine generates high-temperature, high-pressure gas by burning fuel, which drives the turbine to perform work, converting thermal energy into mechanical energy, and then into electrical energy through a generator. The exhaust temperature of a gas turbine is typically high; directly releasing this high-temperature waste heat would result in significant energy waste.

[0004] Integrating SOFC and GT into a combined cycle system allows for the full utilization of the high-temperature waste heat generated by the SOFC to drive the gas turbine for power generation, thus achieving cascaded energy utilization. This combined cycle system can significantly improve the overall power generation efficiency of the system, typically reaching 60%-70%. In the SOFC-GT combined cycle system, the SOFC converts the chemical energy of the fuel into electrical energy at a high temperature of 800℃-850℃. Its high-temperature exhaust gas (still containing combustible components and a large amount of sensible heat) enters the combustion chamber for supplementary combustion, driving the gas turbine to perform work and further generate electricity. This combined cycle system not only improves power generation efficiency but also reduces fuel consumption and pollutant emissions.

[0005] However, existing SOFC-GT combined cycle systems have some technical problems that limit their further application and development.

[0006] First, waste heat utilization is inflexible. SOFC-GT systems generate a large amount of waste heat, but user heat demand is time-varying. When the heat load is low, the waste heat cannot be fully utilized, resulting in energy waste; when the heat load suddenly increases, the system's waste heat cannot meet the demand in time, requiring the activation of auxiliary heating equipment, which reduces the system's overall energy efficiency. This inflexibility in waste heat utilization makes it difficult for the system to achieve efficient energy management when facing dynamic heat loads.

[0007] Secondly, power generation and heat consumption are tightly coupled. Existing SOFC-GT systems lack energy buffering mechanisms, requiring the system's operating conditions to constantly adapt to changes in electrical and thermal loads. This tightly coupled operating mode limits the system's flexibility, making it difficult for the SOFC stack and gas turbine to operate stably under high-efficiency conditions. For example, when heat load demand suddenly increases, the system needs to quickly adjust its operating conditions to meet the demand, which may cause the SOFC stack to deviate from its optimal operating temperature range, affecting its power generation efficiency and lifespan.

[0008] Existing SOFC-GT systems also have some problems with fuel handling. Methanol, as an ideal liquid fuel, has advantages such as high energy density, convenient storage and transportation, and low reforming temperature. However, the reforming reaction of methanol requires a large amount of water vapor, and the water vapor generated by the SOFC anode reaction is usually directly discharged, failing to achieve effective water recycling. This not only increases the system's external water demand but also reduces the overall efficiency of the system.

[0009] Furthermore, existing SOFC-GT combined cycle systems typically employ complex gas compression equipment to pressurize methanol. This approach not only increases system complexity and cost but also leads to higher auxiliary power consumption. In contrast, using liquid methanol for pressurization can significantly reduce system power consumption and improve the system's net power generation efficiency. Summary of the Invention

[0010] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides an SOFC-GT combined cycle power generation system and method with integrated thermal storage, which improves the waste heat utilization efficiency and operational flexibility of the system by introducing thermal storage units as energy buffers.

[0011] To achieve the above objectives, according to one aspect of the present invention, an integrated thermal storage SOFC-GT combined cycle power generation system is provided, comprising a compressor, an SOFC stack, a combustion chamber, a gas turbine, a reformer, a first heat exchanger, a second heat exchanger, a third heat exchanger, a booster pump, a thermal storage unit, and a waste heat recovery device, wherein: The compressor outlet is connected to the cold-side inlet of the first heat exchanger, the cold-side outlet of the first heat exchanger is connected to the cathode of the SOFC stack, the cathode of the SOFC stack is connected to the first inlet of the combustion chamber, the outlet of the combustion chamber is connected to the gas turbine, the exhaust port of the gas turbine is connected to the hot-side inlet of the first heat exchanger and the hot-side inlet of the second heat exchanger, the hot-side inlet of the third heat exchanger is connected to the hot-side outlet of the first heat exchanger and the hot-side outlet of the second heat exchanger, the hot-side outlet of the third heat exchanger is connected to the inlet of the thermal storage unit, and the thermal storage unit is connected to the waste heat utilization device. The inlet of the booster pump is connected to the methanol storage tank to pressurize the liquid methanol coming out of the methanol storage tank. The outlet of the booster pump is connected to the cold side inlet of the third heat exchanger. The cold side outlet of the third heat exchanger is connected to the first inlet of the reformer. The outlet of the reformer is connected to the cold side inlet of the second heat exchanger. The cold side outlet of the second heat exchanger is connected to the anode inlet of the SOFC stack. The anode outlet of the SOFC stack is connected to the inlet of the steam separator. The dry gas outlet of the steam separator is connected to the combustion chamber. The steam outlet of the steam separator is connected to the reformer.

[0012] Preferably, the waste heat utilization device includes at least one of an organic Rankine cycle power generation device, an absorption refrigeration device, a hot water supply system, a steam supply system, or a seawater desalination device.

[0013] Preferably, the gas discharged from the third heat exchanger at a temperature of 200°C to 250°C enters the heat storage unit.

[0014] Preferably, the heat storage medium of the heat storage unit is water, thermal oil, or phase change heat storage material.

[0015] Preferably, the air temperature entering the cathode of the SOFC stack after being heated by the first heat exchanger is the same as the temperature of the reforming gas entering the anode of the SOFC stack after being heated by the second heat exchanger.

[0016] Preferably, the output shaft of the gas turbine is connected to a generator.

[0017] Preferably, the SOFC stack outputs DC power, which is then converted into AC power by a DC / DC converter and an inverter.

[0018] Preferably, the compressor pressurizes ambient air to 3-5 bar, and the booster pump pressurizes liquid methanol to 3-5 bar.

[0019] According to another aspect of the present invention, a power generation method for the aforementioned integrated thermal storage SOFC-GT combined cycle power generation system is also provided, comprising the following steps: 1) The compressor compresses the air, and the compressed air is preheated by the first heat exchanger before being sent to the cathode of the SOFC stack. 2) The booster pump pressurizes the liquid methanol in the methanol storage tank. After the pressurized methanol is preheated and vaporized by the third heat exchanger, it enters the reformer together with the water vapor from the water vapor separator to react and generate reformed gas. The reformed gas is preheated by the second heat exchanger and then sent to the anode of the SOFC stack. 3) Electrochemical reactions occur at the cathode and anode of the SOFC stack to generate direct current; 4) The cathode exhaust gas of the SOFC stack, together with the dry gas separated by the steam separator, enters the combustion chamber for supplementary combustion; the gas discharged from the combustion chamber enters the gas turbine for expansion and does work, driving the generator to generate electricity; 5) The exhaust gas from the gas turbine enters the first heat exchanger and the second heat exchanger respectively. The two exhaust gas streams merge and then enter the third heat exchanger. The gas discharged from the third heat exchanger enters the heat storage unit to realize the utilization and storage of waste heat.

[0020] Preferably, in step 5), the control of the thermal storage unit is as follows: Thermal storage control: When the available waste heat of the SOFC-GT combined cycle power generation system is greater than the heat load demand of the SOFC-GT combined cycle power generation system, it is determined that the SOFC-GT combined cycle power generation system is in a heat surplus state. The exhaust gas of the gas turbine still has residual heat after passing through the third heat exchanger. The exhaust gas at the hot side outlet of the third heat exchanger is controlled to enter the thermal storage unit to heat the thermal storage medium using the surplus heat. The exhaust gas at the hot side outlet of the third heat exchanger is cooled down and discharged, thereby storing heat. Heat release control: When the available waste heat of the SOFC-GT combined cycle power generation system is less than the heat load demand of the SOFC-GT combined cycle power generation system, it is determined that the SOFC-GT combined cycle power generation system is in a state of insufficient heat. The working fluid of the waste heat utilization device is controlled to flow through the heat storage unit. The heat stored in the heat storage medium of the heat storage unit is used to supplement the heating of the working fluid. After compensating for the heat gap, it returns to the waste heat utilization device, thereby releasing heat.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1) The SOFC-GT combined cycle power generation system with integrated thermal storage of the present invention can achieve efficient energy utilization under different operating conditions through the heat storage and heat release functions of the thermal storage unit. When there is sufficient waste heat, excess heat is stored; when there is insufficient waste heat, the stored heat is released to meet demand. This energy buffering mechanism not only improves the efficiency of waste heat utilization, but also enables the system to maintain efficient operation over a wider range of operating conditions.

[0022] 2) The SOFC-GT combined cycle power generation system with integrated thermal storage of the present invention introduces a thermal storage unit, which buffers the fluctuation of heat load. The SOFC-GT combined cycle power generation system no longer needs to frequently change its operating conditions to match the heat load. The SOFC stack and gas turbine can operate stably at their designed high-efficiency operating points for a long time, thereby significantly improving the overall power generation efficiency and economy of the system.

[0023] 3) The SOFC-GT combined cycle power generation system with integrated thermal storage of the present invention places the thermal storage unit at the end of the waste heat recovery chain to recover the waste heat remaining after three-stage heat exchange. It ensures that almost all waste heat from high temperature to low temperature is fully utilized by the system, resulting in extremely high comprehensive energy efficiency.

[0024] 4) The SOFC-GT combined cycle power generation system with integrated thermal storage of the present invention uses a booster pump to pressurize liquid methanol. Compared with the scheme of first vaporizing and then compressing gaseous methanol with a compressor, the power consumption of liquid boosting is extremely low (far lower than the power consumption of gas compression) due to the incompressibility of liquid. This liquid boosting design of methanol fuel significantly reduces the auxiliary power consumption of the system and greatly improves the net power generation efficiency of the system.

[0025] 5) In the SOFC-GT combined cycle power generation system with integrated thermal storage of the present invention, the methanol steam reforming reaction requires the consumption of steam. Simultaneously, the anode reaction of the SOFC stack generates steam. The present invention separates the steam from the SOFC anode exhaust by incorporating a steam separator and returns it to the inlet of the reformer. This constitutes an internal water circulation self-balancing system. Its advantages are that the system requires little or no external water replenishment during operation, greatly simplifying the system structure and operation and maintenance, reducing dependence on external water sources, and making it particularly suitable for applications with limited water resources, such as ships, islands, or remote areas.

[0026] 6) The SOFC-GT combined cycle power generation system with integrated thermal storage of the present invention uses the SOFC stack as the core component, which is extremely sensitive to operating conditions (especially temperature). The gas turbine exhaust is divided into two paths, entering in parallel into the first heat exchanger (for preheating air) and the second heat exchanger (for preheating reformed gas). This parallel heat exchange structure ensures that the intake air (air and reformed gas) for both the SOFC cathode and anode is heated by the same high-temperature heat source (gas turbine exhaust), thus easily controlling both at a substantially consistent preheating temperature (e.g., 600℃-700℃). This consistency in intake air temperature is crucial for the safe and stable operation of the SOFC stack. It effectively avoids the large temperature gradient and thermal stress caused by excessive temperature differences between the anode and cathode inside the stack, reducing the risk of thermal cracking of SOFC ceramic components, thereby significantly improving the operational stability and service life of the SOFC stack. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the SOFC-GT combined cycle power generation system with integrated thermal storage according to the present invention; In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. Compressor; 2. First heat exchanger; 3. Second heat exchanger; 4. SOFC stack; 5. Steam separator; 6. Combustion chamber; 7. Gas turbine; 8. Generator; 9. Reformer; 10. Third heat exchanger; 11. Booster pump; 12. Thermal storage unit; 13. Waste heat recovery device. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Reference Figure 1 The SOFC-GT combined cycle power generation system with integrated thermal storage includes a compressor 1, an SOFC stack 4, a combustion chamber 6, a gas turbine 7, a reformer 9, a first heat exchanger 2, a second heat exchanger 3, a third heat exchanger 10, a booster pump 11, a steam separator 5, a thermal storage unit 12, and a waste heat utilization device 13.

[0030] The outlet of the compressor 1 is connected to the cold-side inlet of the first heat exchanger 2, the cold-side outlet of the first heat exchanger 2 is connected to the cathode of the SOFC stack 4, the cathode of the SOFC stack 4 is connected to the first inlet of the combustion chamber 6, the outlet of the combustion chamber 6 is connected to the gas turbine 7, the exhaust port of the gas turbine 7 is connected to the hot-side inlet of the first heat exchanger 2 and the hot-side inlet of the second heat exchanger 3, the hot-side inlet of the third heat exchanger 10 is connected to the hot-side outlet of the first heat exchanger 2 and the hot-side outlet of the second heat exchanger 3, the hot-side outlet of the third heat exchanger 10 is connected to the inlet of the thermal storage unit 12, and the thermal storage unit 12 is connected to the waste heat utilization device 13.

[0031] The inlet of the booster pump 11 is connected to the methanol storage tank to pressurize the liquid methanol coming out of the methanol storage tank. The outlet of the booster pump 11 is connected to the cold side inlet of the third heat exchanger 10. The cold side outlet of the third heat exchanger 10 is connected to the first inlet of the reformer 9. The outlet of the reformer 9 is connected to the cold side inlet of the second heat exchanger 3. The cold side outlet of the second heat exchanger 3 is connected to the anode inlet of the SOFC stack 4. The anode outlet of the SOFC stack 4 is connected to the inlet of the water vapor separator 5. The dry gas outlet of the water vapor separator 5 is connected to the combustion chamber 6. The water vapor outlet of the water vapor separator 5 is connected to the reformer 9.

[0032] In a heat exchanger, the hot side and cold side refer to the high-temperature fluid side and the low-temperature fluid side, respectively. The hot side is the region within the heat exchanger where the high-temperature fluid resides. It has a hot-side inlet and a hot-side outlet, and heat is transferred from the hot side to the cold side. For example, in a plate heat exchanger, the high-temperature fluid flows in the hot-side channels, transferring heat to the cold-side medium through the tube walls. The cold side is the region within the heat exchanger where the low-temperature fluid resides, absorbing the heat transferred from the hot side. It has a cold-side inlet and a cold-side outlet. For example, in a shell-and-tube heat exchanger, cooling water or chilled brine flows in the cold-side channels, absorbing heat through thermal convection.

[0033] This invention achieves spatiotemporal decoupling of power generation and waste heat utilization through the integration of the thermal storage unit 12. It balances efficiency and cost through energy cascade utilization and end-point thermal storage. It reduces power consumption and simplifies the system through methanol liquid pressurization and water self-balancing. It ensures the stability of SOFC stack 4 through parallel preheating of the first heat exchanger 2 and the second heat exchanger 3. This is a highly integrated, flexible, efficient, economical and reliable SOFC-GT combined cycle power generation system.

[0034] The following is a detailed description of each component.

[0035] Compressor 1: Pressurizes ambient air to provide high-pressure air for the cathode of SOFC stack 4 and gas turbine 7. Compressor 1 can be centrifugal or axial flow type, coaxially driven by gas turbine 7, or independently driven by electric motor.

[0036] First heat exchanger 2: Utilizes the waste heat from the exhaust of gas turbine 7 to preheat the compressed air at the outlet of compressor 1. It employs a plate-fin or shell-and-tube heat exchanger structure, with the hot-side medium being a portion of the exhaust from gas turbine 7 and the cold-side medium being compressed air. The preheated high-temperature air enters the cathode of SOFC stack 4.

[0037] Second heat exchanger 3: Used to preheat the reformed gas using the waste heat from the exhaust of gas turbine 7. It adopts a plate-fin or shell-and-tube heat exchanger structure. The hot-side medium is another portion of the exhaust from gas turbine 7, and the cold-side medium is the reformed gas from the outlet of reformer 9. The preheated high-temperature reformed gas enters the anode of SOFC stack 4.

[0038] SOFC Stack 4: SOFC Stack 4 is the core power generation unit of the system, operating at a temperature of 800℃-850℃ and a pressure of 3bar-5bar. SOFC Stack 4 consists of a three-layer structure: anode, electrolyte, and cathode. Preheated reformed gas (mainly containing H2, CO2, and H2O) enters from the anode side, where hydrogen undergoes an oxidation reaction (H2 + O2) at the anode. 2- →H₂O + 2e - Preheated air enters from the cathode side, where oxygen undergoes a reduction reaction (O2 / 2 + 2e). - →O 2-The oxygen ions generated migrate to the anode through the solid electrolyte.

[0039] Water vapor separator 5: Separates water vapor from the anode exhaust of SOFC stack 4. Water vapor separator 5 adopts the principle of condensation separation or membrane separation to condense or separate water vapor and lead it out. A portion of the water vapor is returned to reformer 9 as the water vapor source for the reforming reaction (achieving water circulation), and the remaining dry gas (containing unreacted H2 and CO2) enters combustion chamber 6.

[0040] Combustion Chamber 6: Combustion Chamber 6 is the site for exhaust gas refueling of SOFC stack 4, providing high-temperature and high-pressure gas for gas turbine 7. The anode exhaust gas (containing residual H2 and CO2 after treatment by steam separator 5) and cathode exhaust gas (containing residual O2 and N2) of SOFC stack 4 enter combustion chamber 6 for combustion. The combustion reaction is as follows: H₂ + O₂ / ₂ → H₂O (exothermic) Gas turbine 7: Gas turbine 7 converts the thermal and pressure energy of high-temperature, high-pressure gas into mechanical energy. The gas (temperature approximately 900℃-1000℃) from the outlet of combustion chamber 6 enters gas turbine 7 and undergoes adiabatic expansion, reducing the pressure to near atmospheric pressure and the temperature to 600℃-700℃. A portion of the mechanical work output by gas turbine 7 can be used to drive compressor 1, and the remaining power drives generator 8 to generate electricity.

[0041] Generator 8: An AC generator 8, coaxially connected to the gas turbine 7, converts the mechanical energy output by the gas turbine 7 into electrical energy. The generator 8 can be a permanent magnet synchronous generator or an asynchronous generator, and the output voltage is regulated by a frequency converter before being connected to the grid or supplied to the power supply.

[0042] Reformer 9: Reformer 9 is the core equipment for fuel processing, converting liquid methanol into hydrogen-rich reformed gas. Reformer 9 is filled with a catalyst (such as Cu / ZnO / Al2O3), where methanol and water vapor undergo an endothermic reforming reaction at 200℃-300℃ under the action of the catalyst. CH3OH + H2O → 3H2 + CO2 The heat required by reformer 9 mainly comes from the preheating of methanol feedstock by the third heat exchanger 10. The main components of the reformed gas at the outlet of reformer 9 are H2 (about 65%-75%), CO2 (about 20%-25%), and H2O steam (about 5%-10%).

[0043] The third heat exchanger 10 utilizes the waste heat from the exhaust gas of the gas turbine 7 to preheat and vaporize liquid methanol. It employs a plate or tubular heat exchanger structure. The hot-side medium is the exhaust gas from the gas turbine 7, which converges after passing through the first heat exchanger 2 and the second heat exchanger 3. The cold-side medium is liquid methanol (entering from the outlet of the booster pump 11). The methanol is heated and vaporized in the third heat exchanger 10, providing gaseous feedstock for the reforming reaction.

[0044] Booster pump 11: Used to pressurize liquid methanol from the methanol storage tank (at atmospheric pressure) to the system operating pressure (3 bar-5 bar). Booster pump 11 is a plunger pump or gear pump. After pressurization, the liquid methanol enters the third heat exchanger 10. Utilizing the incompressibility of liquids, the power consumption for pressurization is much lower than that for compressing gaseous methanol, significantly improving system energy efficiency.

[0045] Thermal storage unit 12: Stores residual heat during system operation and releases heat when needed. Thermal storage unit 12 is located at the end of the waste heat recovery chain and exchanges heat with the exhaust gas of the gas turbine 7 after passing through the third heat exchanger 10 (at which time the exhaust temperature is about 200℃-250℃).

[0046] Waste heat utilization device 13 is used to convert the waste heat of the system into useful work or to meet the heat load requirements.

[0047] Furthermore, the waste heat utilization device 13 includes at least one of the following: an organic Rankine cycle (ORC) power generation device that uses waste heat to drive an organic working fluid cycle for power generation; an absorption refrigeration device that uses waste heat to drive a lithium bromide or ammonia absorption refrigeration cycle; a hot water / steam supply system that uses waste heat to heat water or generate steam; and a seawater desalination device that uses waste heat for multi-effect distillation or membrane distillation (for marine applications). The heat source for the waste heat utilization device 13 can be either the exhaust gas from the gas turbine 7 or the heat released from the heat storage unit 12.

[0048] Furthermore, the gas discharged from the third heat exchanger 10 at a temperature of 200℃~250℃ enters the thermal storage unit 12. 200℃ to 250℃ is a temperature window precisely matched to the thermal storage medium. This temperature range of 200℃~250℃ is suitable for industrially mature and low-cost heat transfer oils (whose common operating temperature is 150℃-300℃) and medium-temperature phase change thermal storage materials (such as paraffin wax, hydrated salts, etc.). If the temperature is too high, the thermal storage unit 12 will have to use expensive high-temperature and high-pressure resistant materials and special thermal storage media, significantly increasing the initial investment in the system. If the temperature is too low (e.g., below 150℃), the energy (work capacity) will be greatly reduced, meaning the heat released by the thermal storage unit 12 can only be used for low-temperature hot water supply and cannot drive the Organic Rankine Cycle (ORC) for power generation or steam production, greatly reducing the value of waste heat utilization.

[0049] A core objective of this invention is to achieve efficient, tiered energy utilization within a specific temperature range, with 200°C to 250°C serving as the dividing point for this tiered utilization. The system utilizes the high-grade heat energy (600°C-700°C) discharged from the gas turbine 7 for high-temperature intake preheating of the SOFC stack 4 (via the first heat exchanger 2 and the second heat exchanger 3), and then uses the medium-high temperature heat energy (450°C-500°C) for methanol vaporization (via the third heat exchanger 10). This ensures maximum utilization and recovery of heat within the SOFC-GT combined cycle system. When the gas temperature discharged from the third heat exchanger 10 drops to 200°C-250°C, it means that the heat utilization value within the SOFC-GT main cycle has been essentially exhausted. At this point, this waste heat is sent into the heat storage unit 12, which not only avoids wasting the thermal efficiency inside the SOFC-GT main cycle, but also ensures that the heat entering the heat storage unit 12 still has sufficient quality for the waste heat utilization device 13 to use when needed. This achieves the best balance between maximizing the internal thermal efficiency of the system and flexibly storing and utilizing external waste heat, and significantly improves the overall energy efficiency and operational flexibility of the system.

[0050] Furthermore, the structure of the thermal storage unit 12 includes a thermal storage tank, a heat exchange device, and pipelines and valves, and temperature stratification design can be implemented for sensible heat storage. The thermal storage medium can be water (operating temperature 90℃-180℃, low cost, safe and environmentally friendly), heat transfer oil (operating temperature 150℃-300℃, suitable for higher temperatures), or phase change thermal storage materials (such as paraffin wax, hydrated salts, which utilize the latent heat of phase change to increase the thermal storage density), etc.

[0051] When used as a heat storage medium, water has significant advantages such as high specific heat capacity, extremely low cost, safety, environmental friendliness, and easy availability. Although the boiling point of water is only 100°C at normal pressure, it remains a very low-cost solution when used with heat sources at 200°C-250°C, either by pressurization (e.g., forming saturated steam or high-temperature hot water) or by utilizing its sensible heat for storage at lower temperatures (such as 90°C-180°C as mentioned in the specification). This makes the present invention highly competitive in applications requiring only domestic hot water or low-temperature steam (such as hot water supply systems and shipboard living quarters).

[0052] Thermal oil is a mature choice for medium-temperature thermal storage in industry, and its operating temperature (150℃-300℃) perfectly covers the operating range of 200℃-250℃ of this invention. The most critical benefit is that the thermal oil can maintain a liquid phase without high pressure at this temperature, which greatly reduces the manufacturing, installation and maintenance costs of the thermal storage tank of the thermal storage unit 12, and also significantly improves the operational safety of the system.

[0053] Phase change thermal energy storage (PCM) materials utilize the latent heat generated during phase changes (such as solid-liquid transitions) to store energy. Compared to the sensible heat storage of water or thermal oil, their heat storage density per unit volume or per unit mass is increased by orders of magnitude. Another major advantage of PCM is its ability to achieve isothermal heat storage and release near the phase change temperature. When waste heat recovery devices (such as organic Rankine cycle power generation devices) require a stable heat source, the isothermal heat released by PCM can significantly improve the thermoelectric conversion efficiency and operational stability of downstream equipment (such as ORC).

[0054] Furthermore, the air temperature entering the cathode of the SOFC stack 4 after being heated by the first heat exchanger 2 is the same as the temperature of the reformed gas entering the anode of the SOFC stack 4 after being heated by the second heat exchanger 3.

[0055] The core components of SOFC stack 4, especially the electrolyte and electrodes, are made of brittle ceramic materials. These materials are extremely sensitive to temperature changes and temperature gradients (temperature differences). If there is a significant temperature difference between the inlet gases on the cathode side (air) and the anode side (reformed gas), it will generate severe thermal shock and uneven thermal expansion at the inlet end of SOFC stack 4 (i.e., the gas distribution flow field and the front end of the stack). This thermal mismatch will generate huge internal thermal stress. This stress is enough to cause microcracks in brittle ceramic components, or even catastrophic structural damage, such as electrolyte cracking and electrode layer peeling off from the electrolyte. Once cracking or peeling occurs, it will lead to direct contact between the anode fuel and cathode air (i.e., gas crosstalk), causing localized combustion, burning out SOFC stack 4, leading to system shutdown or even a safety accident. By forcing the two inlet gas temperatures to be consistent, the temperature difference at the inlet end of SOFC stack 4 is fundamentally eliminated, minimizing thermal stress. This greatly improves the structural robustness and operational reliability of SOFC stack 4, which is a prerequisite for achieving long-life operation of SOFC stack 4, and significantly reduces system maintenance costs and failure risks.

[0056] Furthermore, the reaction rates of both the hydrogen oxidation reaction at the anode and the oxygen reduction reaction at the cathode are strongly correlated with temperature. Simultaneously, the oxygen ion conductivity of the solid electrolyte increases exponentially with temperature. If the inlet temperatures of the cathode and anode are inconsistent, it will inevitably lead to an uneven temperature distribution within the stack, resulting in a severely uneven current density distribution: in lower-temperature regions, both the electrochemical reaction rate and ion conductivity are lower, contributing less to power generation and lowering the overall average efficiency of the stack. In higher-temperature regions, although the reaction is faster, they will be subjected to excessively high current densities and heat loads, which will accelerate the aging and degradation of materials (such as electrodes and connectors) in these regions, thus shortening the stack's lifespan. Ensuring consistent inlet temperatures for both the cathode and anode is the initial condition for achieving a uniform temperature field distribution within the stack. A uniform temperature field ensures that the entire active region of the stack operates within its optimal temperature range, thereby maximizing the effective power generation area, resulting in more stable system output power and maximizing the overall power generation efficiency (SOFC efficiency + GT efficiency).

[0057] Furthermore, the output shaft of the gas turbine 7 is connected to a generator 8. The gas turbine 7 expands and performs work, converting its thermal and pressure energy into mechanical energy. The core function of the generator 8 is to further convert this high-quality mechanical energy, derived from the waste heat of the SOFC, into high-quality electrical energy. Therefore, the generator 8 can fully utilize the SOFC-GT energy gradient, successfully converting the waste heat potential energy that the SOFC stack 4 cannot utilize into a second source of electrical energy output, thus maximizing the depth of energy utilization.

[0058] The SOFC stack 4 itself can achieve a power generation efficiency of 50%-60%. However, if the waste heat of the SOFC (accounting for approximately 40%-50% of the total energy) is only used for heat exchange or directly emitted, the overall efficiency of the system will be limited. This invention utilizes the combustion chamber 6 for afterburner combustion and the gas turbine 7 for power generation, thus reusing this waste heat. It is precisely because of the generator 8 that this system can combine the chemical energy power generation of the SOFC stack 4 with the thermodynamic cycle power generation of the gas turbine, achieving an overall power generation efficiency of 60%-70%. Therefore, by adding generator 8, the total power output of the system is significantly increased. This additional electricity generated from waste heat is obtained without increasing (or even reducing) fuel consumption, greatly improving the system's economy and fuel utilization.

[0059] Furthermore, the SOFC stack 4 outputs DC power, which is then converted into AC power by a DC / DC converter and an inverter. The DC / DC converter transforms the fluctuating low-voltage DC output from the SOFC stack 4 into a stable high-voltage DC bus voltage. Regardless of changes in the operating conditions of the upstream SOFC, the inverter always draws energy from a stable DC bus, thus continuously outputting high-quality, highly stable AC power to meet stringent grid connection requirements. The DC / DC converter performs maximum power point tracking (MPPT) or highest efficiency point tracking. It can actively maintain the SOFC's operating point within its highest efficiency range through high-speed adjustment, while the downstream inverter is responsible for matching the grid's power demand. This two-stage topology of DC / DC converter and inverter ensures that the SOFC stack 4, as the core unit of the system, always operates under optimal conditions, while the inverter also operates in its high-efficiency region due to the stable bus voltage. This maximizes the system's overall net power generation efficiency (from fuel to AC).

[0060] Furthermore, the compressor 1 pressurizes the ambient air to 3-5 bar, and the booster pump 11 pressurizes the liquid methanol to 3-5 bar.

[0061] Compressor 1 is used to pressurize ambient air to 3-5 bar to provide high-pressure air for SOFC cathode and gas turbine 7.

[0062] Thermodynamic principles dictate that the pumping work required to raise liquid methanol from atmospheric pressure (e.g., in a methanol storage tank) to a target pressure (3-5 bar) is far less than the compression work required to compress the same mass of gas to the same pressure. Liquids are essentially incompressible, resulting in extremely low power consumption for pressurization, while gas compression requires enormous mechanical work. The SOFC-GT system of this invention is a pressurization cycle. If the traditional approach of vaporization followed by pressurization is adopted, a complex gas compressor must be used after methanol vaporization to compress the high-temperature reformed gas (H2, CO2, etc.) to 3-5 bar. This would result in significant parasitic energy losses. However, the ingenious process of first pressurizing the liquid and then vaporizing it in the third heat exchanger 10 replaces the high-power gas compressor with a low-power booster pump 11, minimizing the system's auxiliary power consumption.

[0063] By precisely setting the methanol pressure between 3 and 5 bar, it is ensured that the reformed gas, after vaporization in the third heat exchanger 10 and reaction in the reformer 9, can perfectly match the pressure on the air side (cathode). This precise pressure balance is the foundation for the safe and stable operation of SOFC stack 4, avoiding damage to the stack structure due to excessive pressure differential or fuel shortage due to insufficient pressure, thus ensuring the reliability of the entire combined cycle system.

[0064] According to another aspect of the present invention, a power generation method for the aforementioned integrated thermal storage SOFC-GT combined cycle power generation system is also provided, comprising the following steps: 1) The compressor 1 compresses the air, and the compressed air is preheated by the first heat exchanger 2 and then sent to the cathode of the SOFC stack 4. 2) The booster pump 11 pressurizes the liquid methanol in the methanol storage tank. After the pressurized methanol is preheated and vaporized by the third heat exchanger 10, it enters the reformer 9 together with the water vapor from the water vapor separator 5 to generate reformed gas. The reformed gas is preheated by the second heat exchanger 3 and then sent to the anode of the SOFC stack 4. 3) An electrochemical reaction occurs at the cathode and anode of the SOFC stack 4 to generate direct current; 4) The cathode exhaust gas of the SOFC stack 4, together with the dry gas separated by the water vapor separator 5, enters the combustion chamber 6 for supplementary combustion; the gas discharged from the combustion chamber 6 enters the gas turbine 7 to expand and do work, driving the generator 8 to generate electricity. 5) The exhaust gas from the gas turbine 7 enters the first heat exchanger 2 and the second heat exchanger 3 respectively. The two exhaust gas paths merge and then enter the third heat exchanger 10. The gas discharged from the third heat exchanger 10 enters the heat storage unit 12 to realize the storage and release of waste heat.

[0065] In step 5), the control of the thermal storage unit is as follows: Thermal storage control: When the available waste heat of the SOFC-GT combined cycle power generation system exceeds its heat load demand, the system is considered to be in a heat surplus state. Even after the exhaust gas from the gas turbine 7 passes through the third heat exchanger 10, there is still residual heat. The exhaust gas from the hot side outlet of the third heat exchanger 10 is controlled to enter the thermal storage unit 12, utilizing the surplus heat to heat the thermal storage medium. The exhaust gas from the hot side outlet of the third heat exchanger 10 is then cooled before being discharged, thus storing heat. Thermal storage control means that the SOFC-GT combined cycle power generation system no longer wastes excess heat but actively stores it in the thermal storage medium. This directly avoids energy waste and significantly improves the system's waste heat utilization efficiency and overall energy efficiency.

[0066] Heat release control: When the available waste heat of the SOFC-GT combined cycle power generation system is less than the heat load demand of the SOFC-GT combined cycle power generation system, it is determined that the SOFC-GT combined cycle power generation system is in a heat shortage state. The working fluid of the waste heat utilization device 13 is controlled to flow through the heat storage unit 12, using the heat stored in the heat storage medium of the heat storage unit 12 to supplement the heating of the working fluid. After compensating for the heat gap, it returns to the waste heat utilization device 13, thereby releasing heat. This heat release control precisely compensates for the deficiency of traditional SOFC-GT combined cycle systems where waste heat cannot meet demand in a timely manner, ensuring a stable heat supply during peak periods and avoiding the energy consumption and costs associated with starting additional auxiliary heating equipment.

[0067] The aforementioned heat storage and heat release controls enable the thermal storage unit 12 to truly function as an energy buffer, thereby decoupling power generation from heat consumption. This eliminates the need for the SOFC-GT combined power generation system to frequently adjust power output to accommodate fluctuating user-side heat loads. The power generation system can operate stably at its most efficient operating point to achieve maximum power generation efficiency; while fluctuations in user-side heat load are entirely handled by the heat storage and heat release of the thermal storage unit 12, which performs peak shaving, valley filling, and dynamic balancing.

[0068] The more detailed workflow of this system is as follows: (1) Fuel-side process (anode side): Liquid methanol is pressurized to 3-5 bar from the methanol storage tank via booster pump 11, then enters the third heat exchanger 10 where it is heated to 200-300°C and vaporized. It then enters the reformer 9 along with water vapor separated by the water vapor separator 5 to undergo a reforming reaction, producing hydrogen-rich reformed gas (mainly composed of H2, CO2, and H2O) at approximately 200-300°C. This reformed gas enters the second heat exchanger 3 where it is heated to 600-700°C, then enters the anode side of the SOFC stack 4, where hydrogen undergoes an electrochemical oxidation reaction (H2 + O2). 2- →H₂O + 2e - The electrochemical reaction releases heat to maintain the operating temperature of SOFC stack 4 at 800℃-850℃. The anode exhaust (containing unreacted H2, a large amount of water vapor and CO2) enters the water vapor separator 5. After the water vapor is separated, part of it flows back to the reformer 9, and the separated dry gas (containing the remaining H2 and CO2) enters the combustion chamber 6.

[0069] (2) Air-side process (cathode side): Ambient air is compressed to 3-5 bar by compressor 1, then preheated to 600-700℃ in the first heat exchanger 2, and then enters the cathode side of the SOFC stack 4, where oxygen undergoes an electrochemical reduction reaction (O2 / 2 + 2e-). - →O 2-→ The cathode exhaust (containing residual O2 and N2) directly enters the combustion chamber 6.

[0070] (3) Combustion and Gas Turbine Process 7: In combustion chamber 6, the SOFC anode exhaust gas (containing residual H2) is thoroughly mixed with the cathode exhaust gas (containing residual O2) and completely combusted. The outlet gas temperature of combustion chamber 6 can reach 900℃-1000℃. The high-temperature and high-pressure gas enters gas turbine 7 and undergoes adiabatic expansion to do work. The exhaust temperature of gas turbine 7 drops to 600℃-700℃. Part of the mechanical work output by gas turbine 7 can be used to drive compressor 1, and the remaining power drives generator 8 to generate electricity.

[0071] (4) Waste heat recovery process (parallel structure): The exhaust gas from gas turbine 7 (temperature 600℃-700℃) is split into two paths after exiting gas turbine 7: First path: Enters the first heat exchanger 2, preheats the compressed air, and reduces the exhaust temperature to 450℃-500℃; Second route: Enters the second heat exchanger 3, preheats the reformed gas, and reduces the exhaust temperature to 450℃-500℃; After the two exhaust streams merge, they enter the third heat exchanger 10, where methanol is preheated and vaporized. The exhaust temperature drops to 200℃-250℃. Then, the exhaust enters the heat storage unit 12 (which stores residual heat during heat storage operation). The exhaust temperature decreases, and the exhaust enters the waste heat utilization device 13 for further utilization or discharge into the atmosphere.

[0072] (5) Coordination between heat storage and waste heat utilization: When the heat demand of the waste heat recovery device 13 is high and the waste heat of the SOFC-GT system is insufficient, the heat storage unit 12 releases the stored heat to supplement the supply; when the SOFC-GT system has more waste heat and the heat demand is lower, the heat storage unit 12 stores the remaining heat to avoid waste. Through the buffering and adjustment of the heat storage unit 12, the decoupling between system operation and heat demand is achieved.

[0073] This invention introduces a heat storage unit 12 into the SOFC-GT combined cycle system and places it at the end of the waste heat recovery chain (the exhaust temperature of the third heat exchanger 10 at the end is approximately 200℃-250℃), making full use of all the waste heat of the system. The heat storage temperature is moderate, and a low-cost heat storage medium (such as water or heat transfer oil) can be selected to reduce system costs.

[0074] The first heat exchanger 2 (air preheating) and the second heat exchanger 3 (fuel preheating) of this invention adopt a parallel structure. The exhaust gas of the gas turbine 7 is divided into two paths to preheat the air and the reformed gas simultaneously, ensuring that the inlet air temperature of the SOFC cathode and anode is consistent, meeting the SOFC's requirement for consistent inlet air temperature, and improving the stack's operational stability and efficiency.

[0075] This invention achieves temporal and spatial decoupling of "power generation and heat consumption" through the thermal storage unit 12. The SOFC-GT combined cycle power generation system can operate stably under high-efficiency conditions without having to follow heat load fluctuations in real time; the heat demand fluctuations of the waste heat utilization device 13 are buffered and regulated by the thermal storage unit 12, improving the system's operational flexibility.

[0076] This invention uses a booster pump 11 to pressurize liquid methanol (instead of compressing gaseous methanol), taking advantage of the incompressibility of liquids to significantly reduce auxiliary power consumption and improve the net efficiency of the system.

[0077] In this invention, the water vapor in the anode exhaust of the SOFC stack 4 is separated by the water vapor separator 5 and then returned to the reformer 9, thereby achieving system water self-balancing, reducing the demand for external water sources, and simplifying the system structure.

[0078] This method introduces a thermal storage unit 12 as an energy buffer, allowing the power generation process to operate stably at its most efficient condition without constantly following heat load fluctuations. Simultaneously, heat load fluctuations are balanced by the thermal storage unit 12, achieving temporal decoupling between power generation and heat consumption, greatly improving the system's operational flexibility and adaptability to heat load fluctuations. This method provides a complete, operable, efficient, and flexible power generation solution. It not only achieves multi-stage energy utilization and ultra-high net efficiency but also innovatively solves the decoupling problem between power generation and heat consumption through thermal storage and reduces system complexity through a water self-balancing design.

[0079] This invention is applicable to various distributed energy application scenarios, including but not limited to: (1) Marine power system: used for auxiliary power and combined cooling, heating and power supply for ocean-going cargo ships, passenger ships, research vessels, etc. Methanol as a marine fuel conforms to the International Maritime Organization (IMO)'s development direction of low-carbon and zero-carbon fuels. The heat storage unit 12 can store waste heat during navigation and release heat to supply the ship's air conditioning and domestic hot water when berthed in port, achieving zero-emission berthing in port and meeting the increasingly stringent ship emission regulations.

[0080] (2) Distributed power station: Distributed combined cooling, heating and power system for industrial parks, commercial complexes, data centers and other places. The thermal storage unit 12 realizes the spatiotemporal decoupling of power production and heat demand. It generates power at full power and stores heat during peak power consumption periods, and releases the stored heat to meet the heat load during peak heat consumption periods, thereby improving the system's economic efficiency.

[0081] (3) Independent power supply for islands: Independent power supply systems for islands, border outposts, offshore platforms and other scenarios far from the mainland. Methanol is easy to store and transport, and the thermal storage unit 12 provides energy buffering, improving the system's adaptability to load fluctuations and power supply reliability.

[0082] (4) Backup power and emergency power: Used in places with high requirements for power supply reliability, such as hospitals, communication base stations, and emergency command centers. SOFC-GT generates electricity efficiently, and the thermal storage unit 12 can release heat for a short time to maintain the operation of critical equipment when the main power supply fails.

[0083] (5) Industrial waste heat recovery and cogeneration: Integrate with existing industrial facilities to use industrial waste heat to assist in heating the SOFC-GT system, or supply the waste heat of the SOFC-GT to industrial heat (such as steam, hot water, heat transfer oil, etc.). The heat storage unit 12 balances the fluctuations of industrial heat load and improves the overall energy utilization efficiency.

[0084] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An SOFC-GT combined cycle power generation system with integrated thermal storage, characterized in that, It includes a compressor, SOFC stack, combustion chamber, gas turbine, reformer, first heat exchanger, second heat exchanger, third heat exchanger, booster pump, steam separator, thermal storage unit, and waste heat recovery device, wherein: The compressor outlet is connected to the cold-side inlet of the first heat exchanger, the cold-side outlet of the first heat exchanger is connected to the cathode of the SOFC stack, the cathode of the SOFC stack is connected to the first inlet of the combustion chamber, the outlet of the combustion chamber is connected to the gas turbine, the exhaust port of the gas turbine is connected to the hot-side inlet of the first heat exchanger and the hot-side inlet of the second heat exchanger, the hot-side inlet of the third heat exchanger is connected to the hot-side outlet of the first heat exchanger and the hot-side outlet of the second heat exchanger, the hot-side outlet of the third heat exchanger is connected to the inlet of the thermal storage unit, and the thermal storage unit is connected to the waste heat utilization device. The inlet of the booster pump is connected to the methanol storage tank to pressurize the liquid methanol coming out of the methanol storage tank. The outlet of the booster pump is connected to the cold side inlet of the third heat exchanger. The cold side outlet of the third heat exchanger is connected to the first inlet of the reformer. The outlet of the reformer is connected to the cold side inlet of the second heat exchanger. The cold side outlet of the second heat exchanger is connected to the anode inlet of the SOFC stack. The anode outlet of the SOFC stack is connected to the inlet of the steam separator. The dry gas outlet of the steam separator is connected to the combustion chamber. The steam outlet of the steam separator is connected to the reformer.

2. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The waste heat utilization device includes at least one of an organic Rankine cycle power generation device, an absorption refrigeration device, a hot water supply system, a steam supply system, or a seawater desalination device.

3. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The gas discharged from the third heat exchanger at a temperature of 200°C to 250°C enters the heat storage unit.

4. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The heat storage medium of the heat storage unit is water, heat transfer oil, or phase change heat storage material.

5. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The air temperature entering the cathode of the SOFC stack after being heated by the first heat exchanger is the same as the temperature of the reforming gas entering the anode of the SOFC stack after being heated by the second heat exchanger.

6. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The output shaft of the gas turbine is connected to a generator.

7. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The SOFC stack outputs DC power, which is then converted into AC power by a DC / DC converter and an inverter.

8. The SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 1, characterized in that, The compressor pressurizes ambient air to 3-5 bar, and the booster pump pressurizes liquid methanol to 3-5 bar.

9. A power generation method for an SOFC-GT combined cycle power generation system with integrated thermal storage as described in any one of claims 1 to 8, characterized in that, Includes the following steps: 1) The compressor compresses the air, and the compressed air is preheated by the first heat exchanger before being sent to the cathode of the SOFC stack. 2) The booster pump pressurizes the liquid methanol in the methanol storage tank. After the pressurized methanol is preheated and vaporized by the third heat exchanger, it enters the reformer together with the water vapor from the water vapor separator to react and generate reformed gas. The reformed gas is preheated by the second heat exchanger and then sent to the anode of the SOFC stack. 3) Electrochemical reactions occur at the cathode and anode of the SOFC stack to generate direct current; 4) The cathode exhaust gas of the SOFC stack, together with the dry gas separated by the steam separator, enters the combustion chamber for afterburning; The gas discharged from the combustion chamber enters the gas turbine, expands, and does work, driving the generator to generate electricity; 5) The exhaust gas from the gas turbine enters the first heat exchanger and the second heat exchanger respectively. The two exhaust gas streams merge and then enter the third heat exchanger. The gas discharged from the third heat exchanger enters the heat storage unit, where the heat storage unit stores and releases waste heat.

10. The power generation method of the SOFC-GT combined cycle power generation system with integrated thermal storage according to claim 9, characterized in that, In step 5), the control of the thermal storage unit is as follows: Thermal storage control: When the available waste heat of the SOFC-GT combined cycle power generation system is greater than the heat load demand of the SOFC-GT combined cycle power generation system, it is determined that the SOFC-GT combined cycle power generation system is in a heat surplus state. The exhaust gas of the gas turbine still has residual heat after passing through the third heat exchanger. The exhaust gas at the hot side outlet of the third heat exchanger is controlled to enter the thermal storage unit to heat the thermal storage medium using the surplus heat. The exhaust gas at the hot side outlet of the third heat exchanger is cooled down and discharged, thereby storing heat. Heat release control: When the available waste heat of the SOFC-GT combined cycle power generation system is less than the heat load demand of the SOFC-GT combined cycle power generation system, it is determined that the SOFC-GT combined cycle power generation system is in a state of insufficient heat. The working fluid of the waste heat utilization device is controlled to flow through the heat storage unit. The heat stored in the heat storage medium of the heat storage unit is used to supplement the heating of the working fluid. After compensating for the heat gap, it returns to the waste heat utilization device, thereby releasing heat.

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