Zero-carbon steam generator and working method

Abstract

The invention relates to the technical field of new energy and energy system engineering, in particular to a zero-carbon steam generator which comprises an SOFC power generation system, a cascade heat pump circulation system and a hot water circulation flash evaporation system. The SOFC power generation system supplies power to the cascade heat pump circulation system and the hot water circulation flash evaporation system; a condenser of the high-temperature-stage heat pump subsystem is coupled with a water circulation pipeline of the hot water circulation flash evaporation system for heat exchange so as to provide heat required by flash evaporation; the cascade type heat pump circulation system adopts a natural working medium as a circulation medium, and complete recycling of waste heat and water vapor is achieved. High-temperature waste heat generated by the SOFC power generation system and hydrothermal resources in tail gas are recycled through the cascade heat pump and the steam generation device, and the system is novel and reliable in operation. The device can effectively solve the problems of high energy consumption and high pollution of traditional steam production, widens the hydrogen energy utilization field, and realizes clean energy and efficient utilization.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy and energy system engineering, and particularly to a zero-carbon steam generator and a working method thereof. Background Art

[0002] Industrial steam production has long relied on fossil fuel boilers, accounting for more than 15% of global terminal energy consumption. Moreover, the carbon emission problem of traditional gas / coal-fired boilers is prominent, resulting in high greenhouse gas emissions. There is an urgent need for a zero-carbon and efficient steam generation technology.

[0003] As a new generation of high-efficiency energy conversion device, a solid oxide fuel cell (SOFC) can directly convert fuel chemical energy into electrical energy under high-temperature conditions, and has significant advantages such as high power generation efficiency, strong fuel adaptability, environmental friendliness, and high waste heat quality. In recent years, it has received extensive attention and rapid development. A large amount of high-temperature waste heat is generated during the power generation process of SOFC. Its temperature is usually above 500°C. If directly discharged into the environment, it will cause a large amount of energy loss; the overall heat recovery efficiency of existing SOFC waste heat recovery technologies for heat energy is low, resulting in a large amount of energy being wasted. At the same time, the water vapor content in the tail gas generated by SOFC power generation is high, but the traditional scheme does not design a water vapor recovery link, and the system water consumption is high. Due to the limitation of the Carnot cycle, the efficiency of traditional heat pumps decreases significantly in the scenario of high-temperature steam generation, and a single-stage heat pump cannot cover the requirements of a wide temperature range. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a zero-carbon steam generator and a working method thereof.

[0005] To achieve the above object, the present invention is realized through the following technical solutions: A zero-carbon steam generator, characterized by comprising: an SOFC power generation system, a cascaded heat pump cycle system, and a hot water circulation flash evaporation system;

[0006] The SOFC power generation system supplies power to the cascaded heat pump cycle system and the hot water circulation flash evaporation system; the condenser of the high-temperature stage heat pump subsystem is coupled and heat-exchanged with the water circulation pipeline of the hot water circulation flash evaporation system to provide the heat required for flash evaporation; the cascaded heat pump cycle system uses natural working medium as the circulation medium to realize the complete recovery and utilization of waste heat and water vapor.

[0007] The SOFC power generation system includes an air flow path, a fuel flow path, a solid oxide fuel cell stack, and a tail gas waste heat flow path. The SOFC power generation system is used for generating electricity through an electrochemical reaction and providing high-temperature tail gas;

[0008] The cascade heat pump cycle system includes a low-temperature stage heat pump subsystem and a high-temperature stage heat pump subsystem. The low-temperature stage heat pump subsystem is an air source heat pump, and the cold source is room temperature water, and the water volume is controlled by a water flow regulating valve. The high-temperature stage heat pump subsystem is provided with a primary evaporator and a secondary evaporator. The heat medium end of the primary evaporator is connected to the waste heat flow path of the tail gas of the SOFC power generation system for recovering high-temperature tail gas waste heat. The outlet end of the condenser of the low-temperature stage heat pump subsystem is connected to the outlet end of the primary evaporator of the high-temperature stage heat pump subsystem through a pipeline and extends to the heat medium end of the secondary evaporator.

[0009] The hot water circulation flash evaporation system includes a circulation water pump, a flash evaporation water storage tank, a flash evaporation tank and a steam pressurizing pump. The feed water is heated by the third evaporator and then connected to the circulation water pump through a pipeline. The circulation water pump is used to drive the water circulation of the flash evaporation loop. A steam outlet is provided at the top of the flash evaporation tank, and a condensate outlet is provided at the bottom. The steam pressurizing pump is used to pressurize the high-temperature steam.

[0010] Preferably, the low-temperature stage heat pump subsystem uses CO2 as the circulating refrigerant, and the high-temperature stage heat pump subsystem uses R600 as the circulating refrigerant.

[0011] Preferably, the primary evaporator of the high-temperature stage heat pump subsystem is directly coupled with the high-temperature tail gas waste heat flow path of the SOFC power generation system, and the waste heat of the tail gas is transferred to the heat pump refrigerant through heat exchange.

[0012] Preferably, the water flow regulating valve is arranged at the cold source inlet end of the low-temperature stage heat pump subsystem, and the heat of the heat pump cycle and the steam generation flow are controlled by adjusting the input water volume.

[0013] Preferably, a pressure balancing device is arranged in the flash evaporation tank of the hot water circulation flash evaporation system to ensure that there is no pressure interference when the waste heat of the normal pressure tail gas enters the flash evaporation process after heat exchange.

[0014] Preferably, the high-temperature tail gas waste heat generated by the SOFC power generation system is heated in stages through the cascade heat pump cycle system, and finally the high-temperature heat required for flash evaporation is provided by the condenser of the high-temperature stage heat pump subsystem.

[0015] Preferably, the system only needs to externally input hydrogen fuel and supplementary water source, and the rest of the electricity, heat and water vapor are recycled within the system to achieve zero carbon emissions.

[0016] Preferably, temperature and pressure sensors are provided at the outlet of the steam compressor to adjust the steam parameters in real time to meet the requirements of different working conditions.

[0017] Preferably, the low-temperature stage and the high-temperature stage heat pump subsystems of the cascade heat pump cycle system are serially coupled through an evaporative condenser to form a cascade waste heat utilization structure.

[0018] Preferably, a dust removal and condensate recovery device is provided in the high-temperature exhaust gas waste heat flow path of the SOFC power generation system to ensure that the water vapor in the exhaust gas is completely recovered and used for steam generation.

[0019] The present invention also discloses a working method of a zero-carbon steam generator, which is characterized by including the following steps:

[0020] Step 1: Perform an electrochemical reaction through the SOFC power generation system to react the input hydrogen fuel with the oxygen in the air to generate electric energy and high-temperature exhaust gas;

[0021] Step 2: Introduce the high-temperature exhaust gas into the high-temperature stage heat pump subsystem of the cascade heat pump cycle system, and exchange heat with the heat pump working medium through the primary evaporator to recover the waste heat in the exhaust gas;

[0022] Step 3: Through the low-temperature stage heat pump subsystem of the cascade heat pump cycle system, using room temperature water as the cold source, use CO2 working medium to preliminarily heat the water, and transfer the heat to the high-temperature stage heat pump subsystem through the evaporation condenser;

[0023] Step 4: The high-temperature stage heat pump subsystem further raises the temperature of the preliminarily heated water through the secondary evaporator and transports the high-temperature water to the high-temperature liquid storage tank of the hot water circulation flash evaporation system;

[0024] Step 5: Introduce the water in the high-temperature liquid storage tank into the flash tank for flashing to generate saturated steam, and pressurize the steam through a steam compressor to output high-temperature and high-pressure steam at the required temperature and pressure;

[0025] Step 6: Dynamically control the generation flow rate, temperature, and pressure of the steam by adjusting the water flow regulating valve of the low-temperature stage heat pump subsystem and the operating parameters of the high-temperature stage heat pump subsystem.

[0026] The beneficial effects of the present invention are: (1) The present invention recovers the high-temperature waste heat and the water heat resources in the exhaust gas generated by the SOFC power generation system through the cascade heat pump and the steam generating device, and the system operation is novel and reliable. This device can effectively improve the problems of high energy consumption and high pollution in traditional steam production, broaden the field of hydrogen energy utilization, and achieve clean energy and efficient utilization.

[0027] (2) The present invention combines the cascade heat pump with the flash evaporation system, realizes the coupling of the low-temperature stage and the high-temperature stage heat pumps by setting an evaporation condenser, and converts the reuse of low-grade waste heat into high-temperature steam resources. Compared with the traditional boiler steam generator, this system can effectively reduce heat loss, can achieve no pollutant emissions with the SOFC solid oxide fuel cell as the power system, and the additional heat pump cycles all use harmless working media, ensuring that the system is green, environmentally friendly and efficient, and meets the policy requirements of energy conservation and emission reduction. Description of the Drawings

[0028] Figure 1 Overall structural schematic diagram of the "zero-carbon" steam generation system of the present invention

[0029] In the figure: 1. SOFC battery stack; 2. First evaporator; 3. First compressor; 4. First condenser; 5. First throttle valve; 6. Water flow regulating valve; 7. Second evaporator; 8. Third evaporator; 9. Second compressor; 10. Second condenser; 11. Second throttle valve; 12. Circulating water pump; 13. Flash storage tank; 14. Flash tank; 15. Steam pressurizing pump. Specific embodiments

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0031] The following will be combined with Figure 1 Describe the algorithm process and principle.

[0032] As Figure 1 shown, a "zero-carbon" steam generator coupling SOFC waste heat utilization and cascade heat pump includes an SOFC power generation system, a cascade heat pump cycle system, and a hot water circulation flash system. When the fuel utilization rate and power generation efficiency of the SOFC power generation system are certain, saturated steam with corresponding temperature and flow can be generated according to different requirements, realizing dynamic adjustment of steam output. At the same time, when the external environmental temperature changes, stable production of saturated steam is maintained by adjustment.

[0033] The SOFC battery stack 1 can generate electricity and has a general battery structure such as battery cathode, anode, and electrolyte layer. The fuel gas of the SOFC cathode and the fuel gas of the anode respectively undergo electrochemical reactions inside the battery, converting the chemical energy of the fuel into electrical energy; the SOFC system can supply power to the system and generate high-temperature tail gas. The high-temperature tail gas enters the second evaporator through a pipeline for heat exchange.

[0034] The cascade heat pump cycle system includes a low-temperature stage heat pump subsystem and a high-temperature stage heat pump subsystem. The low-temperature stage heat pump system is provided with a first evaporator 2, a first compressor 3, a first condenser 4, a first throttle valve 5 and a water flow regulating valve 6. The outlet end of the water flow regulating valve is connected to the first condenser and is used to regulate the water volume of the coupled hot water between the high- and low-temperature stage heat pump subsystems. The low-temperature stage heat pump subsystem is an air source heat pump using CO2 as the working medium and is used to initially heat the input room temperature water at the first condenser. The first compressor is powered by the SOFC power generation system. The high-temperature stage heat pump subsystem is provided with a second evaporator 7, a third evaporator 8, a second compressor 9, a second condenser 10 and a second throttle valve 11; the second evaporator is used to cool and exchange heat with the high-temperature tail gas generated by the SOFC power generation system. The third evaporator is used to cool the feed water to meet the normal operation of the high-temperature stage heat pump sub-cycle. The second condenser is used to heat the circulating water in the flash evaporation system to the high temperature required for flash evaporation. The cascade heat pump realizes the heat recovery and water recovery of the high-temperature tail gas generated by the SOFC power generation system through two-stage temperature rise and provides the high-temperature normal pressure water required for subsequent flash evaporation operations.

[0035] The hot water circulation flash evaporation system is provided with a circulation water pump 12, a flash evaporation water storage tank 13, a flash evaporation tank 14 and a steam pressurizing pump 15. The feed water is heated by the third evaporator and then connected to the circulation water pump through a pipeline. The circulation water pump is used to drive the water circulation in the flash evaporation loop. A steam outlet is arranged at the top of the flash evaporation tank, and a condensed water outlet is arranged at the bottom. The steam pressurizing pump is used to pressurize the high-temperature steam.

[0036] Working principle:

[0037] As shown in the Figure 1 annotation in the appendix, taking the ambient temperature as 15°C and the generation of 110°C saturated steam at the outlet valve of the flash evaporation tank as an example. Hydrogen enters the SOFC solid oxide fuel cell as fuel for reaction, generating electricity W and high-temperature tail gas (water vapor and excess air) during the reaction. The energy utilization rate in the power generation system is 75%, and the power generation efficiency is 45%. At this time, this part of the high-temperature waste heat is denoted as Q, and the temperature is about 350°C. The high-temperature waste heat Q enters the second evaporator for heat exchange. Since the high-temperature tail gas generated by the SOFC power generation system has a high temperature but a low heat capacity and is at normal pressure, it can be directly mixed with the feed water heated by the first condenser and then enter the third evaporator for appropriate cooling. The cooled feed water enters the flash evaporation loop and is then pressed into the flash evaporation water storage tank by the circulation water pump for flash evaporation circulation.

[0038] Power flow: All the power W generated by the SOFC power generation system is supplied to the compressor in the heat pump (HP) and the flash tank of the flash system. The heat pump is designed as a cascade type and is divided into two parts: The low-temperature stage heat pump cycle uses CO2 as the working medium. The high-temperature stage heat pump cycle uses R600 as the working medium, and two-stage evaporators are arranged in this cycle. The low-temperature stage cycle heats the feed water at the condenser, and the feed water flow rate can be controlled by a water flow regulating valve. At the same time, the high-temperature exhaust gas generated by the SOFC power generation system is introduced into the first-stage evaporator of the high-temperature stage heat pump for heat exchange. The two gas and liquid streams are mixed and stabilized in the pipeline and then heated by the second-stage evaporator and enter the flash cycle for flashing. The heating link of the flash cycle is carried out at the condenser of the high-temperature stage heat pump, and then it enters the flash tank for flashing. The water vapor obtained by flashing the high-temperature and high-pressure water is discharged from the upper part of the flash tank and introduced into the subsequent compressor for pressurization to obtain the required high-temperature steam. The liquid water obtained by flashing flows back from the bottom of the flash tank to the flash liquid storage tank. In this example, the steam generation rate is 0.205 kg / s, and the comprehensive system efficiency can reach 110%. Another example takes the generation of 120°C saturated steam at the outlet valve of the flash tank as an example. At this time, the steam generation rate is 0.185 kg / s, and the comprehensive system efficiency can reach 100%.

[0039] As mentioned above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent replacements or changes should be covered within the protection scope of the present invention.

Claims

1. A zero-carbon steam generator, characterized in that: include: SOFC power generation system, cascade heat pump circulation system and hot water circulation flash evaporation system; The SOFC power generation system supplies power to the cascade heat pump circulation system and the hot water circulation flash evaporation system; the condenser of the high-temperature heat pump subsystem is coupled with the water circulation pipeline of the hot water circulation flash evaporation system for heat exchange to provide the heat required for flash evaporation; the cascade heat pump circulation system uses natural working fluid as the circulation medium to achieve complete recovery and utilization of waste heat and water vapor. The SOFC power generation system comprises an air flow path, a fuel flow path, a solid oxide fuel cell stack and an exhaust gas waste heat flow path, and the SOFC power generation system is used to generate electricity through electrochemical reaction and provide high-temperature exhaust gas; The cascade heat pump circulation system comprises a low-temperature heat pump subsystem and a high-temperature heat pump subsystem, wherein the low-temperature heat pump subsystem is an air source heat pump, the cold source is room temperature water and the water volume is controlled by a water flow regulating valve; the high-temperature heat pump subsystem is provided with a primary evaporator and a secondary evaporator, wherein the heat medium end of the primary evaporator is connected to the exhaust gas waste heat flow path of the SOFC power generation system for recovering the high-temperature exhaust gas waste heat; the condenser outlet end of the low-temperature heat pump subsystem is connected to the primary evaporator outlet end of the high-temperature heat pump subsystem through a pipeline, and extends to the heat medium end of the secondary evaporator; The hot water circulation flash evaporation system comprises a circulation water pump, a flash water storage tank, a flash tank and a steam booster pump. The feed water is heated by the third evaporator and connected to the circulation water pump through a pipeline. The circulation water pump is used to drive the flash evaporation loop water circulation. The top of the flash tank is provided with a steam outlet, the bottom is provided with a condensed water outlet, and the steam booster pump is used to pressurize the high-temperature steam.

2. The zero-carbon steam generator according to claim 1, characterized in that: The low-temperature heat pump subsystem uses CO2 as a circulating working fluid, and the high-temperature heat pump subsystem uses R600 as a circulating working fluid.

3. The zero-carbon steam generator according to claim 1, characterized in that: The primary evaporator of the high-temperature heat pump subsystem is directly coupled to the high-temperature tail gas waste heat flow path of the SOFC power generation system, and transfers the tail gas waste heat to the heat pump working medium through heat exchange.

4. The zero-carbon steam generator according to claim 1, characterized in that: The water flow regulating valve is arranged at the cold source inlet end of the low temperature heat pump subsystem, and controls the heat of the heat pump circulation and the steam generation flow by adjusting the input water volume.

5. The zero-carbon steam generator according to claim 1, characterized in that: A pressure balancing device is provided in the flash tank of the hot water circulation flash evaporation system to ensure that there is no pressure interference when the atmospheric pressure tail gas enters the flash evaporation process after heat exchange with waste heat.

6. The zero-carbon steam generator according to claim 1, characterized in that: The high-temperature exhaust waste heat generated by the SOFC power generation system is heated in stages through a cascade heat pump circulation system, and finally the high-temperature heat required for flash evaporation is provided by the condenser of the high-temperature heat pump subsystem.

7. The zero-carbon steam generator according to claim 1, characterized in that: The system only requires external input of hydrogen fuel and water supply, and the remaining electricity, heat and water vapor are recycled within the system to achieve zero carbon emissions.

8. The zero-carbon steam generator according to claim 1, characterized in that: The steam compressor outlet is provided with a temperature and pressure sensor for adjusting steam parameters in real time to meet the requirements of different working conditions.

9. The zero-carbon steam generator according to claim 1, characterized in that: The low-temperature stage and high-temperature stage heat pump subsystems of the cascade heat pump circulation system are coupled in series through an evaporative condenser to form a cascade waste heat utilization structure.

10. A method for operating a zero-carbon steam generator, characterized in that: The following steps are involved: Step 1: The SOFC power generation system conducts an electrochemical reaction to react the input hydrogen fuel with oxygen in the air to generate electricity and high-temperature exhaust gas; Step 2: introducing the high-temperature tail gas into the high-temperature heat pump subsystem of the cascade heat pump circulation system, exchanging heat with the heat pump working fluid through the primary evaporator, and recovering the waste heat in the tail gas; Step 3: Using the low-temperature heat pump subsystem of the cascade heat pump circulation system, room temperature water is used as a cold source, CO2 working fluid is used to preliminarily heat the water, and the heat is transferred to the high-temperature heat pump subsystem through the evaporative condenser; Step 4: The high-temperature heat pump subsystem further heats the initially heated water through the secondary evaporator, and transports the high-temperature water to the high-temperature liquid storage tank of the hot water circulation flash evaporation system; Step 5: passing the water in the high-temperature liquid storage tank into a flash tank for flash evaporation to generate saturated steam, and pressurizing the steam through a steam compressor to output high-temperature and high-pressure steam of the required temperature and pressure; Step 6: Dynamically control the steam generation flow, temperature and pressure by adjusting the water flow control valve of the low-temperature heat pump subsystem and the operating parameters of the high-temperature heat pump subsystem.

Images