Boiler peak shaving system and method based on metal oxide heat storage

Abstract

The invention relates to the field of boiler peak regulation, and particularly provides a boiler peak regulation system and method based on metal oxide heat storage, which can consider the service life of a heat storage module and the use efficiency of energy in the system. The boiler peak shaving system comprises a primary air outlet, a secondary air outlet, a boiler, a heat storage device, a heat regenerator and a heat exchange pipeline, the heat exchange pipeline is arranged in the boiler, and a metal oxide heat storage module is arranged in the heat storage device; the heat storage device is provided with a first heat storage device air inlet communicating with the external environment, a second heat storage device air inlet connected with an air outlet of the heat exchange pipeline, a second heat storage device air outlet connected with a hot fluid inlet of the heat regenerator and a first heat storage device air outlet connected with the boiler. A cold fluid inlet of the heat regenerator communicates with the primary air outlet, a cold fluid outlet of the heat regenerator is connected with an air inlet of the heat exchange pipeline, and airflow flowing out of the hot fluid outlet and the secondary air outlet is converged and then communicates with the boiler.

Description

Technical Field

[0001] The present invention relates to the technical field of boiler peak regulation, and in particular to a boiler peak regulation system and a boiler peak regulation method based on metal oxide heat storage. Background Art

[0002] In recent years, with the rapid growth of installed capacity of clean energy such as wind power and solar energy, my country's power generation structure and power consumption structure have been constantly changing, and the peak-shaving problem of the power grid has become increasingly prominent, mainly manifested in insufficient peak-shaving capacity. There is a huge contradiction between supply and demand between peak-shaving capacity and electricity demand.

[0003] In order to improve the peak-shaving capability, some peak-shaving systems in the prior art use sensible heat storage materials for heat storage. However, the heat storage density of sensible heat storage is generally low, the peak-shaving system occupies a large area, and the storage / release temperature of sensible heat storage varies greatly, resulting in the inability to provide stable heat energy during heat release, making it difficult to reuse.

[0004] At present, there are some boiler peak-shaving systems based on thermochemical heat storage, but there is still much room for improvement. For example, in patent CN114623431A, the thermochemical heat storage device is heated by electric heating, so that the excess power generated by the boiler is stored and then released when needed. However, this method has the disadvantages of multiple energy conversions, low efficiency, and reduced energy quality. There are also some boiler peak-shaving systems that directly use flue gas and thermochemical heat storage modules for heat exchange. This method is more efficient than the former, but it has the disadvantages of flue gas interfering with thermochemical reactions, affecting the storage / release effect, and damaging the life of the thermochemical heat storage module. Summary of the invention

[0005] In view of the above problems, the present invention provides a boiler peak-shaving system based on metal oxide heat storage, which can take into account both the service life of the heat storage module and the energy utilization efficiency in the system.

[0006] A first aspect of the present invention provides a boiler peak-shaving system, which includes a primary air outlet, a secondary air outlet, a boiler, a heat storage device, a regenerator and a heat exchange pipe, the heat exchange pipe is arranged inside the boiler, the heat storage device has a metal oxide heat storage module built in, the heat storage device has a first heat storage device air inlet connected to the external environment, a second heat storage device air inlet connected to the air outlet of the heat exchange pipe, a second heat storage device air outlet connected to the hot fluid inlet of the regenerator, and a first heat storage device air outlet connected to the boiler; the regenerator has a hot fluid inlet, a hot fluid outlet, a cold fluid inlet and a cold fluid outlet, the cold fluid inlet is connected to the primary air outlet, the cold fluid outlet is connected to the air inlet of the heat exchange pipe, and the airflow flowing out from the hot fluid outlet and the secondary air outlet is connected to the boiler after merging.

[0007] Optionally, a first valve is provided between the cold fluid inlet and the primary air outlet.

[0008] Optionally, a bypass is connected between the first valve and the primary air outlet and is connected to the boiler through the coal mill.

[0009] Optionally, a second valve is further provided between the confluence of the hot fluid outlet and the secondary air outlet and the hot fluid outlet.

[0010] Optionally, the air inlet of the first heat storage device is connected to the external environment or the primary air outlet by a three-way valve.

[0011] Optionally, a third valve is further provided between the primary air outlet and the three-way valve.

[0012] Optionally, the airflows flowing out of the hot fluid outlet and the secondary air outlet merge and are connected to the combustion chamber of the boiler.

[0013] The second aspect of the present invention provides a boiler peak-shaving method based on metal oxide heat storage, which is applicable to the aforementioned boiler peak-shaving system based on metal oxide heat storage. The boiler peak-shaving method includes the following heat storage step and heat release step, wherein the heat storage step is, when the load demand of the external power grid decreases below a first specified value, opening the first valve and the second valve, and closing the third valve; the heat release step is, when the load demand of the external power grid increases to above a second specified value, opening the third valve, and closing the first valve and the second valve.

[0014] Optionally, in the heat release step, the three-way valve is connected to the primary air outlet.

[0015] Beneficial Effects

[0016] 1. When the power grid dispatch requires the thermal power plant to reduce the load, that is, when the electric energy generated by the power generation cycle is greater than the electric energy required by the power grid, the heat storage device can be used to store the excess heat energy burned by the boiler to reduce the online power, thereby ensuring the low-load stable combustion of the boiler and avoiding the impact of load reduction on the service life of the boiler; when the power grid dispatch is restored or increased, the thermal power plant can also reduce or close the flow rate of the heat storage air flow through the heat storage device to increase the power load output to the power grid by the power generation cycle, thereby achieving deep peak regulation of the thermal power plant.

[0017] 2. The oxygen and hot air generated in the heat storage / release reaction of metal oxides are used in a targeted manner. The oxygen released in the heat storage process of metal oxides is mixed with air to form oxygen-enriched air. The oxygen-enriched air can heat the primary air that passes through the regenerator in the opposite direction, and then mixed with the secondary air and sent to the boiler, so that the fuel in the boiler can be stably burned in an oxygen-enriched state. The hot air generated in the heat release process of metal oxides is passed into the boiler, mixed with high-temperature flue gas and participates in the subsequent work and power generation conversion process, so that the heat energy released by the metal oxides can be reused. In this process, the heat released by the metal oxides directly enters the boiler after heat transfer through the air, without other energy losses, and the utilization rate of the stored energy is close to 100%.

[0018] 3. Because air rather than flue gas is used to participate in the reaction of the metal oxide heat storage module, it can avoid the presence of more complex components in the flue gas, such as dust, sulfur oxides, nitrogen oxides and other acidic or toxic pollutants that affect the life of the heat storage material and the heat storage effect, ensuring that the metal oxide can still maintain excellent heat storage performance after multiple cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the composition of a boiler deep peak regulation system based on metal oxide heat storage in an embodiment of the present invention;

[0020] Figure 2 This is a flow chart of a boiler peak-shaving method based on metal oxide heat storage in an embodiment of the present invention.

[0021] Figure markings: 1-boiler; 2-heat storage device; 3-regenerator; 4-pulverizer; 5-heat exchange pipe; 6-primary air outlet; 7-secondary air outlet; 8-air outlet; 9, 10, 11-air inlet; 12-first valve; 13-second valve; 14-third valve; 201-first heat storage device air inlet; 202-second heat storage device air inlet; 203-second heat storage device air outlet; 204-first heat storage device air outlet; 301-hot fluid inlet; 302-hot fluid outlet; 303-cold fluid inlet; 304-cold fluid outlet. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] This embodiment provides a boiler deep peak regulation system based on metal oxide heat storage. Figure 1Schematic diagram of the composition of the boiler deep peak regulation system based on metal oxide heat storage in this embodiment. Figure 1 As shown, the peak-shaving system includes: a boiler 1, a heat storage device 2, a heat regenerator 3, a coal mill 4, a heat exchange pipe 5, a primary air outlet 6, a secondary air outlet 7 and an air outlet 8 (ie, the external environment).

[0024] The boiler 1 has air inlets 9, 10 and 11, the air inlet 9 is connected to the air flow outlet of the coal mill 4, the air inlet 10 is connected to the secondary air outlet 7, and the air inlet 11 is connected to the first heat storage device outlet 204 of the heat storage device 2. In the initial stage of combustion of the boiler 1, the air inlet 9 can be used to introduce primary air carrying coal powder into the combustion chamber of the boiler 1; in the stage of combustion of the boiler 1, the air inlet 10 can be used to introduce secondary air rich in oxygen into the boiler 1 to help combustion; in the stage of low combustion energy supply (for example, combustion is close to the end), the air inlet 11 can be used to introduce high-temperature air into the boiler 1 to ensure subsequent stable work. Therefore, the gas introduced into the boiler 1 can be adjusted by opening and closing different air inlets at different stages of the combustion of the boiler 1, so that the combustion in the boiler 1 can be promoted by continuously introducing fuel (coal powder) and increasing the contact between coal powder and air in the initial stage of combustion of the boiler 1; when the combustion of the boiler 1 is in progress, oxygen-rich gas is introduced to make the combustion reaction in the boiler 1 more stable; when the combustion energy supply of the boiler 1 is low, high-temperature air is introduced to increase the thermal energy of the boiler, thereby quickly increasing the output power of the boiler 1.

[0025] The heat storage device 2 has a first heat storage device air inlet 201, a second heat storage device air inlet 202, a second heat storage device air outlet 203 and a first heat storage device air outlet 204. The first heat storage device air inlet 201 is connected to the air outlet 8 via the third valve 14 and the three-way valve 15, and the other port of the three-way valve 15 is also connected to the primary air outlet 6, so that air or primary air can be selectively introduced into the heat storage device 2. The first heat storage device air outlet 204 is connected to the air inlet 11, and when the heat storage device 2 releases heat, the heated air or primary air can be sent to the boiler 1. The air inlet 202 of the second heat storage device is connected to the air outlet of the heat exchange pipe 5. The hot air heated by the regenerator 3 and the heat exchange pipe 5 in turn enters the heat storage device 2, transfers the heat to the metal oxide heat storage module in the heat storage device 2, and carries the oxygen generated by the reduction reaction and transports it to the regenerator 3 through the air outlet 203 of the second heat storage device.

[0026] The regenerator 3 has a hot fluid inlet 301, a hot fluid outlet 302, a cold fluid inlet 303 and a cold fluid outlet 304. The cold fluid inlet 303 is connected to the primary air outlet 6 via the first valve 12. The cold fluid outlet 304 is connected to the air inlet of the heat exchange pipe 5. The hot fluid inlet 301 is connected to the second heat storage device outlet 203 of the heat storage device 2. The hot fluid outlet 302 is connected to the air inlet 11 of the boiler 1 after converging with the secondary air outlet 7. A second valve 13 is also provided between the hot fluid outlet 302 and the secondary air outlet 7, on the side biased toward the hot fluid outlet 302.

[0027] In addition, a bypass is connected between the primary air outlet 6 and the first valve 12. Specifically, the primary air outlet 6 is connected to the air inlet 9 of the boiler 1 via the coal mill 4 by using the bypass.

[0028] The air flow of a thermal power plant is as follows: primary air 6 passes through a coal mill 4, carries pulverized coal, and enters the boiler 1 through the primary air inlet 9 of the boiler 1 for combustion. Secondary air supplied by the secondary air outlet 7 enters the boiler 1 through the secondary air inlet 10 of the boiler 1, provides oxygen for combustion, and makes the pulverized coal and oxygen mix more fully, so that combustion is more complete.

[0029] Among them, the primary air parameters of the thermal power plant can be set according to the actual situation of the system, the temperature can be 300℃, the pressure can be 10kPa, and the secondary air parameters are similar, the temperature can be 300-400℃, the pressure can be 1.5kPa.

[0030] The heat storage device 2 has a metal oxide heat storage module inside. The metal oxide can be a binary oxide or a multi-element oxide, which is not limited here. The metal oxide can store heat energy through redox reactions, and various metal oxide materials such as manganese-based and copper-based can be used. Taking copper oxide as an example, the reaction formula for heat storage / release is as follows:

[0031]

[0032] When the metal oxide stores heat, the metal oxide with a higher valence undergoes a reduction reaction to generate metal oxide with a lower valence and oxygen. The nutrient-enriched air enters the regenerator 3 through the air outlet 203 of the second heat storage device, heats the primary air that passes through the regenerator in the opposite direction, and then is mixed with the secondary air through the hot fluid outlet 302 of the regenerator 3 and sent to the boiler 1. When the metal oxide releases heat, the air or primary air enters the first heat storage device air inlet 201 of the heat storage device 2 through the three-way valve 15, and the metal oxide with a lower valence combines with the oxygen in the air to undergo an oxidation reaction to obtain a metal oxide with a higher valence. The released heat is absorbed by the air, and the heated air enters the boiler 1 through the air outlet 204 of the first heat storage device.

[0033] For example, when the power grid dispatch requires the thermal power plant to reduce the power load output to the power grid, in order to ensure stable combustion at low load, the electric energy generated in the power generation cycle of the thermal power plant is greater than the electric energy required by the power grid, and the surplus electric energy is converted into thermal energy and stored through the heat storage device 2. Specifically, the metal oxide in the metal oxide heat storage module receives thermal energy and first heats up. The metal oxide stores the thermal energy in the form of sensible heat. When the temperature of the metal oxide itself reaches the reduction reaction temperature, the metal oxide stores the thermal energy in the form of chemical energy, that is, the metal oxide undergoes a reduction reaction to release oxygen. The released oxygen mixes with air to form oxygen-enriched air. The oxygen-enriched air enters the regenerator 3 through the air outlet 203 of the second heat storage module, heats the primary air passing through the regenerator 3 in the opposite direction, and then is mixed with the secondary air through the hot fluid outlet 302 of the regenerator 3 and sent to the combustion chamber of the boiler 1 to participate in combustion, thereby enabling the fuel in the boiler 1 to stably burn in an oxygen-enriched state.

[0034] When the power grid dispatch requires the thermal power plant to restore or increase the power load output to the power grid, the thermal power plant can reduce or shut down the flow of the heat storage air flow through the heat storage device 2 to increase the power load output to the power grid by the power generation cycle. The heat stored in the heat storage device 2 can also be reused. Specifically, the air or primary air is transported into the heat storage device 2 through the first heat storage device air inlet 201 of the heat storage device 2, the metal oxide undergoes an exothermic reaction, the oxygen in the air or primary air participates in the reaction, and the remaining gas absorbs heat and is discharged from the first heat storage device air outlet 204 of the heat storage device 2. This high-temperature air directly enters the boiler 1 and mixes with the high-temperature flue gas to participate in the subsequent power generation process.

[0035] In this embodiment, when the grid dispatch requires the thermal power plant to reduce the load, that is, when the electric energy generated by the power generation cycle is greater than the electric energy required by the grid, the heat storage device 2 can be used to store the excess heat energy burned by the boiler to reduce the online power, thereby ensuring the low-load stable combustion of the boiler 1 and avoiding the load reduction affecting the service life of the boiler 1; when the grid dispatch is restored or increased, the thermal power plant can also reduce or shut down the heat storage air flow through the heat storage device 2 to increase the power load output to the grid by the power generation cycle, thereby achieving deep peak regulation of the thermal power plant.

[0036] In addition, in the embodiment of the present invention, the oxygen and hot air generated in the heat storage / release reaction of the metal oxide are used in a targeted manner. The oxygen released in the heat storage process of the metal oxide is mixed with air to form oxygen-enriched air. The oxygen-enriched air can heat the primary air passing through the regenerator 3 in the opposite direction, and then mixed with the secondary air and sent to the boiler 1, so that the fuel in the boiler 1 can be stably burned in an oxygen-enriched state. The hot air generated in the heat release process of the metal oxide is passed into the boiler 1, mixed with the high-temperature flue gas and then participates in the subsequent work power generation conversion process, so that the heat energy released by the metal oxide can be reused.

[0037] This embodiment also provides a boiler peak-shaving method applicable to the above boiler peak-shaving system. Figure 2 Flow chart of the boiler peak load regulation method based on metal oxide heat storage in the embodiment of the present invention. Figure 2 As shown, the boiler deep peak regulation method based on metal oxide heat storage includes:

[0038] Heat storage step S1, when the power load output by the thermal power plant to the external power grid drops below a first specified value, the heat storage air process is started, the first valve 12 and the second valve 13 are opened, and the third valve 14 is closed, so that part of the primary air is mixed with the secondary air after undergoing the heat storage air process.

[0039] Heat release step S2, when the power load output by the thermal power plant to the external power grid rises above the second specified value, the heat release air process is started, the first valve 12 and the second valve 13 are closed, and the third valve 14 is opened, so that the air enters the boiler 1 after undergoing the heat release air process.

[0040] The "first specified value" and the "second specified value" can be freely selected according to the actual application situation and are not limited here. Among them, the "second specified value" is greater than or equal to the "first specified value". For example, the "first specified value" can be the minimum load for the stable operation of the thermal power plant under normal circumstances. When the total power load of the thermal power plant is lower than the minimum load, the total power load of the thermal power plant is no longer reduced, but the heat storage air process is started, the first valve 12 and the second valve 13 are opened, and the third valve 14 is closed. The heat storage of the metal oxide reduction reaction in the heat storage device 2 is used to continue to reduce the power load output from the thermal power plant to the external power grid. The "second specified value" can be a load value higher than the minimum load. When the power load of the thermal power plant is equal to or higher than the minimum load, the heat storage air process is closed, the heat release air process is started, the first valve 12 and the second valve 13 are closed, and the third valve 14 is opened. The metal oxide releases heat, and the high-temperature hot air generated enters the boiler 1.

[0041] In this embodiment, when the power load required to be output by the generator to the external power grid is reduced to below the first specified value, the boiler deep peak regulation system executes the heat storage step S1, at which time the heat storage air process is started, the first valve 12 and the second valve 13 are opened, the third valve 14 is closed, and part of the primary air is transported into the heat storage air process. The heat storage air process includes: part of the primary air is heated to the first temperature for the first time through the regenerator 3, and then heated to the second temperature through the heat exchange pipe 5 in the boiler 1, and then passes through the heat storage device 2, the metal oxide in the heat storage device 2 undergoes a reduction reaction, absorbing heat while releasing oxygen, and the air flowing in is cooled to the third temperature and enriched with oxygen when it flows out. At this time, the oxygen-enriched air heats part of the primary air through the regenerator 3, and itself is reduced to the fourth temperature, and then mixed with the secondary air to enter the boiler 1 to support the combustion of the boiler 1 under oxygen-enriched conditions. When the power grid dispatch requires the thermal power plant to resume or increase the load, the total power load of the thermal power plant continues to rise. When it rises to the second specified value, the heat release step S2 is executed, the first valve 12 and the second valve 13 are closed, the third valve 14 is opened, and the conveyed air or primary air enters the heat release air process. The heat release air process includes: air or primary air enters the heat storage device 2 through the conveying equipment, the metal oxide in the heat storage device 2 undergoes an oxidation reaction, and releases a large amount of heat, and the input air is heated to the fifth temperature and then enters the boiler 1 to mix with the high-temperature flue gas to generate electricity. Among them, according to the actual situation, the introduction of air or primary air can be controlled by the three-way valve 15.

[0042] Among them, the first temperature to the fifth temperature are determined by the actual operating parameters of the boiler deep peak regulation system. For example, the first temperature is generally around 750°C, the second temperature is generally around 1100°C, the third temperature is generally around 850°C, the fourth temperature is generally around 400°C, and the fifth temperature is around 850°C.

[0043] In the above manner, because the heat exchange pipe 5 is used to indirectly heat the air in the embodiment of the present invention, air is used instead of flue gas to contact and react with the metal oxide, which can ensure the service life of the metal oxide heat storage module and avoid the presence of more complex components in the flue gas, such as dust, sulfur oxides, nitrogen oxides and other acidic or toxic pollutants affecting the life of the heat storage material and the heat storage effect. In addition, the regenerator 3 can recover part of the heat that is not stored, so that the thermal efficiency of the oxygen recovery process is improved, and the secondary air with a higher oxygen concentration is obtained to help the stable combustion of the boiler 1. Some other existing boiler peak-shaving systems based on thermochemical heat storage usually use an electric heating system to heat the thermochemical heat storage device, so as to store the excess power generation of the boiler, and then release it when needed, but this method converts energy multiple times and has low efficiency. The final energy utilization rate is only about 40%. In the embodiment of the present invention, when storing energy, the excess heat energy of the boiler combustion is converted into chemical energy storage of the metal oxide after heat transfer through the air; when releasing energy, the hot air generated in the heat release process of the metal oxide is introduced into the boiler, mixed with the high-temperature flue gas and participates in the subsequent work power generation conversion process, and the heat energy stored in the metal oxide is directly transferred to the boiler after heat transfer through the air. During the entire process, there is no other energy loss except the heat loss generated during the heat exchange in the regenerator and the heat transfer between the air and the metal oxide. The energy utilization rate is much higher than that of the boiler peak-shaving system using electric heating.

[0044] The above are only preferred embodiments of the present invention and are 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 in the protection scope of the present invention.

Claims

1. A boiler peak-shaving system based on metal oxide heat storage, the boiler peak-shaving system comprising a primary air outlet, a secondary air outlet, a boiler, a heat storage device, a regenerator and a heat exchange pipe, The heat exchange pipeline is arranged inside the boiler, the heat storage device has a metal oxide heat storage module built in, and the heat storage device has a first heat storage device air inlet communicated with the external environment, a second heat storage device air inlet connected to the air outlet of the heat exchange pipeline, a second heat storage device air outlet connected to the hot fluid inlet of the regenerator, and a first heat storage device air outlet connected to the boiler; The regenerator has a hot fluid inlet, a hot fluid outlet, a cold fluid inlet and a cold fluid outlet. The cold fluid inlet is connected to the primary air outlet, and the cold fluid outlet is connected to the air inlet of the heat exchange pipe. The airflows flowing out of the hot fluid outlet and the secondary air outlet merge and are connected to the boiler.

2. The boiler peak load regulation system based on metal oxide heat storage according to claim 1 is characterized in that: A first valve is provided between the cold fluid inlet and the primary air outlet.

3. The boiler peak load regulation system based on metal oxide heat storage according to claim 2 is characterized in that: A bypass is also connected between the first valve and the primary air outlet and is connected to the boiler through the coal mill.

4. The boiler peak load regulation system based on metal oxide heat storage according to claim 3 is characterized in that: A second valve is further provided between the confluence of the hot fluid outlet and the secondary air outlet and the hot fluid outlet.

5. The boiler peak load regulation system based on metal oxide heat storage according to claim 4 is characterized in that: The air inlet of the first heat storage device is connected to the external environment or the primary air outlet via a three-way valve.

6. The boiler peak load regulation system based on metal oxide heat storage according to claim 5 is characterized in that: A third valve is also provided between the primary air outlet and the three-way valve.

7. The boiler peak load regulation system based on metal oxide heat storage according to claim 1 is characterized in that: The airflows flowing out from the hot fluid outlet and the secondary air outlet merge and are connected to the combustion chamber of the boiler.

8. A boiler peak load regulation method based on metal oxide heat storage, applicable to the boiler peak load regulation system based on metal oxide heat storage according to claim 6, characterized in that: The following steps are involved: Heat storage step: when the load demand of the external power grid decreases below a first specified value, opening the first valve and the second valve, and closing the third valve; Heat release step: when the load demand of the external power grid rises above a second specified value, the third valve is opened, and the first valve and the second valve are closed.

9. The boiler peak load regulation method based on metal oxide heat storage according to claim 8, characterized in that: In the heat release step, the three-way valve is connected to the primary air outlet.

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