A flue gas waste heat recycling system based on thermochemical heat storage

Abstract

The application discloses a flue gas waste heat recycling system based on thermochemical heat storage, and relates to the technical field of heat storage, wherein when waste heat is recycled and stored, in the first heat exchanger, normal temperature air absorbs heat in high temperature flue gas discharged by a boiler flue gas discharge device, and the cooled flue gas is discharged from the first heat exchanger; in the second heat exchanger, hydrated salt provided by the first sealed storage tank absorbs heat in high temperature air, and dehydrated hydrated salt and water vapor are obtained, the dehydrated hydrated salt is stored in the second sealed storage tank, and under the action of the fan, the water vapor is discharged from the second heat exchanger; when waste heat is stored and utilized, in the second heat exchanger, the dehydrated hydrated salt provided by the second sealed storage tank reacts with water in wet cold air, and hydrated salt and hot air are obtained, and the hydrated salt is stored in the first sealed storage tank. The application improves the waste heat recycling efficiency.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage technology, and in particular to a flue gas waste heat recovery and utilization system based on thermochemical thermal storage. Background Technology

[0002] Coal-fired power generation is the main form of electricity production in China. In recent years, with technological advancements, the thermal efficiency of advanced power plants can exceed 45%. Further improving the thermal efficiency of power plants under current conditions presents certain difficulties, but flue gas waste heat utilization is one of the effective ways to improve the thermal efficiency of thermal power plants. This is because the flue gas temperature before dust removal in current Chinese coal-fired units is mostly between 90℃ and 150℃. The high flue gas temperature means the flue gas carries a significant amount of heat, resulting in substantial losses. Flue gas losses can reach 3% to 8% of the total heat loss of the boiler itself, making it the most significant factor affecting boiler thermal efficiency. Besides thermal power plants, industrial equipment such as boilers, internal combustion engines, and smelting furnaces used in industries such as metallurgy, chemicals, building materials, and machinery also emit large amounts of flue gas, with flue gas temperatures often ranging from 120℃ to 300℃. In some industrial equipment, the waste heat from the flue gas can even reach 40% to 60% of its own fuel consumption, accounting for more than half of the total industrial waste heat resources. Therefore, flue gas waste heat recovery has significant energy-saving potential.

[0003] Currently, the use of waste heat from flue gas for heating water or condensate and preheating air is quite common. However, the utilization of these low-grade waste heats suffers from mismatches in time (spanning day and night, even seasons) and space (within the plant area or even further). Therefore, it is essential to recover and store waste heat to achieve cross-seasonal and cross-distance energy utilization. In the field of thermal energy storage, sensible heat storage technology is the most mature and earliest applied, but its low heat storage density results in large device size, inconvenient installation, significant heat loss, and a large temperature variation range when outputting heat, requiring control devices, thus hindering large-scale applications. Latent heat storage is currently a popular research direction, offering higher heat storage density, but issues such as material phase separation and stability have not been effectively resolved. Furthermore, compared to sensible heat storage, the actual heat storage density and performance of latent heat storage are not significantly improved. Compared to sensible and latent heat storage, thermochemical heat storage has advantages such as high heat storage density and near-zero heat loss during long-term storage. Among them, hydrated salt thermochemical adsorption thermal storage, as a type of thermochemical thermal storage, inherits the advantages of thermochemical thermal storage. Its adsorption / desorption temperature matches well with the flue gas temperature and waste heat utilization temperature, making it very suitable for waste heat recovery, storage, and utilization. However, hydrated salt thermochemical adsorption thermal storage also has some problems. Taking the conversion between CaCl2·6H2O and CaCl2·2H2O as an example, when CaCl2·6H2O absorbs heat and decomposes into water and CaCl2·2H2O, the stored energy CaCl2·2H2O is prone to liquefaction due to excessive humidity, resulting in poor waste heat recovery. Furthermore, in both waste heat recovery and utilization processes, there is insufficient contact between the hydrated salt solid and the gas, leading to low waste heat recovery and utilization efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a flue gas waste heat recovery and utilization system based on thermochemical thermal storage, which improves the efficiency of waste heat recovery and utilization.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A flue gas waste heat recovery and utilization system based on thermochemical thermal storage includes: a waste heat recovery and storage system and a waste heat storage and utilization system;

[0007] The waste heat recovery and storage system includes: a first heat exchanger, a second heat exchanger, a first sealed storage tank, a second sealed storage tank, and a fan; the waste heat storage and utilization system includes: a second heat exchanger, a first sealed storage tank, and a second sealed storage tank;

[0008] The first heat exchanger is connected to the boiler flue gas emission device, and the first heat exchanger, the first sealed storage tank, the second sealed storage tank and the fan are connected to the second heat exchanger;

[0009] When waste heat recovery and storage are performed, in the first heat exchanger, ambient temperature air absorbs heat from the high-temperature flue gas emitted by the boiler flue gas emission device, resulting in high-temperature air and cooled flue gas. The cooled flue gas is discharged from the first heat exchanger, and the high-temperature air enters the second heat exchanger. In the second heat exchanger, hydrated salt provided by the first sealed storage tank absorbs heat from the high-temperature air, resulting in dehydrated hydrated salt and water vapor. The dehydrated hydrated salt is stored in the second sealed storage tank, and the water vapor is discharged from the second heat exchanger under the action of the fan.

[0010] When waste heat is stored and utilized, humid cold air enters the second heat exchanger. In the second heat exchanger, the dehydrated hydrated salt provided by the second sealed storage tank reacts with the water in the humid cold air to obtain hydrated salt and hot air. The hydrated salt is stored in the first sealed storage tank, and the hot air is discharged from the second heat exchanger.

[0011] Optionally, the connection between the first sealed storage tank and the second sealed storage tank and the second heat exchanger is detachable;

[0012] When waste heat is recovered and stored, the first sealed storage tank is located on the upper side of the second heat exchanger, and the second sealed storage tank is located on the lower side of the second heat exchanger.

[0013] When waste heat is stored and utilized, the first sealed storage tank is located below the second heat exchanger, and the second sealed storage tank is located above the second heat exchanger.

[0014] Optionally, the first heat exchanger is a plate heat exchanger.

[0015] Optionally, the second heat exchanger is a spiral feeder heat exchanger, and the second heat exchanger is provided with spiral fins with circular openings inside.

[0016] Optionally, the circular openings are provided on opposite sides of the spiral fins.

[0017] Optionally, the side wall of the first heat exchanger is provided with a flue gas inlet, a flue gas outlet, a first air inlet, and a first exhaust outlet;

[0018] The first heat exchanger is connected to the boiler flue gas emission device through the flue gas inlet, and the first heat exchanger is connected to the second heat exchanger through the first exhaust port;

[0019] The high-temperature flue gas enters the first heat exchanger through the flue gas inlet, the ambient temperature air enters the first heat exchanger through the first air inlet, the cooled flue gas is discharged from the first heat exchanger through the flue gas outlet, and the high-temperature air is discharged from the first heat exchanger through the first exhaust outlet.

[0020] Optionally, the second heat exchanger has a second air inlet, a second exhaust outlet, a feed inlet, and a discharge outlet on its side wall;

[0021] The first heat exchanger is connected to the second heat exchanger through the first exhaust port and the second air inlet; the first sealed storage tank is connected to the second heat exchanger through the feed port or the discharge port, and the second sealed storage tank is connected to the second heat exchanger through the feed port or the discharge port.

[0022] The high-temperature air and the humid cold air enter the second heat exchanger through the second air inlet. The hydrated salt and the dehydrated hydrated salt enter the second heat exchanger through the feed inlet. The water vapor and the hot air are discharged from the second heat exchanger through the second exhaust outlet. The dehydrated hydrated salt enters the second sealed storage tank through the discharge outlet, and the hydrated salt enters the first sealed storage tank through the discharge outlet.

[0023] Optionally, the hydrated salt is CaCl2·6H2O, and the dehydrated hydrated salt is CaCl2·2H2O.

[0024] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0025] This invention discloses a flue gas waste heat recovery and utilization system based on thermochemical thermal storage, comprising: when waste heat recovery and storage is performed, in a first heat exchanger, ambient temperature air absorbs heat from the high-temperature flue gas emitted by the boiler flue gas emission device, resulting in high-temperature air and cooled flue gas; the cooled flue gas is discharged from the first heat exchanger, and the high-temperature air enters a second heat exchanger; in the second heat exchanger, hydrated salt provided by a first sealed storage tank absorbs heat from the high-temperature air, resulting in dehydrated hydrated salt and water vapor; the dehydrated hydrated salt enters the second sealed storage tank for storage, and under the action of a fan... In the first heat exchanger, water vapor is discharged from the second heat exchanger. When waste heat is stored and utilized, humid and cold air enters the second heat exchanger. In the second heat exchanger, the dehydrated hydrated salt provided by the second sealed storage tank reacts with the water in the humid and cold air to obtain hydrated salt and hot air. The hydrated salt is stored in the first sealed storage tank, and the hot air is discharged from the second heat exchanger, thereby improving the efficiency of waste heat recovery and utilization, realizing the utilization of waste heat across distances and seasons, and thus meeting the needs of industries such as power, metallurgy, chemical, and building materials for waste heat recovery and utilization from flue gas, reducing energy consumption, and improving economic efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram illustrating the working process of the flue gas waste heat recovery and utilization system based on thermochemical thermal storage provided in an embodiment of the present invention for waste heat recovery and storage;

[0028] Figure 2 This is a schematic diagram illustrating the working process of the flue gas waste heat recovery and utilization system based on thermochemical thermal storage provided in an embodiment of the present invention.

[0029] Symbol explanation:

[0030] First heat exchanger—10, flue gas inlet—11, flue gas outlet—12, first air inlet—13, first exhaust outlet—14, second heat exchanger—20, feed inlet—21, discharge outlet—22, second air inlet—23, second exhaust outlet—24, spiral fins—25, first sealed storage tank—31, second sealed storage tank—32, fan—40. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The purpose of this invention is to provide a flue gas waste heat recovery and utilization system based on thermochemical thermal storage, which aims to improve the efficiency of waste heat recovery and utilization.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 and Figure 2 As shown, the flue gas waste heat recovery and utilization system based on thermochemical thermal storage in this embodiment includes: a waste heat recovery and storage system and a waste heat storage and utilization system.

[0035] The waste heat recovery and storage system includes: a first heat exchanger 10, a second heat exchanger 20, a first sealed storage tank 31, a second sealed storage tank 32, and a fan 40; the waste heat storage and utilization system includes: a second heat exchanger 20, a first sealed storage tank 31, and a second sealed storage tank 32.

[0036] The first heat exchanger 10 is connected to the boiler flue gas emission device, and the first heat exchanger 10, the first sealed storage tank 31, the second sealed storage tank 32 and the fan 40 are connected to the second heat exchanger 20.

[0037] When waste heat recovery and storage are carried out, in the first heat exchanger 10, ambient temperature air absorbs heat from the high-temperature flue gas emitted by the boiler flue gas emission device, resulting in high-temperature air and cooled flue gas. The cooled flue gas is discharged from the first heat exchanger 10, and the high-temperature air enters the second heat exchanger 20. In the second heat exchanger 20, the hydrated salt provided by the first sealed storage tank 31 absorbs heat from the high-temperature air, resulting in dehydrated hydrated salt and water vapor. The dehydrated hydrated salt is stored in the second sealed storage tank 32, and the water vapor is discharged from the second heat exchanger 20 under the action of the fan 40.

[0038] When waste heat is stored and utilized, humid cold air enters the second heat exchanger 20. In the second heat exchanger 20, the dehydrated hydrated salt provided by the second sealed storage tank 32 reacts with the water in the humid cold air to obtain hydrated salt and hot air. The hydrated salt enters the first sealed storage tank 31 for storage, and the hot air is discharged from the second heat exchanger 20.

[0039] As an optional implementation, the connection between the first sealed storage tank 31 and the second sealed storage tank 32 and the second heat exchanger 20 is detachable.

[0040] When waste heat recovery and storage are carried out, the first sealed storage tank 31 is located on the upper side of the second heat exchanger 20, and the second sealed storage tank 32 is located on the lower side of the second heat exchanger 20.

[0041] When waste heat is stored and utilized, the first sealed storage tank 31 is located on the lower side of the second heat exchanger 20, and the second sealed storage tank 32 is located on the upper side of the second heat exchanger 20.

[0042] As an optional implementation, the first heat exchanger 10 is a plate heat exchanger.

[0043] As an optional implementation, the second heat exchanger 20 is a spiral feed heat exchanger, and the second heat exchanger 20 is provided with spiral fins 25 with circular openings inside.

[0044] As an alternative implementation, circular openings are provided on opposite sides of the helical fins 25.

[0045] Specifically, the circular openings on opposite sides of the spiral fins facilitate fluid flow within the spiral feed heat exchanger and enable relative movement of the solid material, allowing for full contact between the fluid and the solid material and better realizing waste heat recovery and utilization.

[0046] As an optional implementation, the side wall of the first heat exchanger 10 is provided with a flue gas inlet 11, a flue gas outlet 12, a first air inlet 13, and a first exhaust outlet 14.

[0047] The first heat exchanger 10 is connected to the boiler flue gas emission device through the flue gas inlet 11, and the first heat exchanger 10 is connected to the second heat exchanger 20 through the first exhaust port.

[0048] High-temperature flue gas enters the first heat exchanger 10 through the flue gas inlet 11, while room-temperature air enters the first heat exchanger 10 through the first air inlet 13. The cooled flue gas is discharged from the first heat exchanger 10 through the flue gas outlet 12, and the high-temperature air is discharged from the first heat exchanger 10 through the first exhaust outlet 14.

[0049] Specifically, the flue gas inlet 11 and the flue gas outlet 12 are located on the upper side of the side wall of the first heat exchanger 10, and the first air inlet 13 and the first exhaust outlet 14 are located on the lower side of the side wall of the first heat exchanger 10.

[0050] As an optional implementation, the second heat exchanger 20 has a second air inlet 23, a second exhaust outlet 24, a feed inlet 21, and a discharge outlet 22 on its side wall.

[0051] The first heat exchanger 10 is connected to the second heat exchanger 20 through the first exhaust port and the second air inlet; the first sealed storage tank 31 is connected to the second heat exchanger 20 through the inlet 21 or the outlet 22, and the second sealed storage tank 32 is connected to the second heat exchanger 20 through the inlet 21 or the outlet 22.

[0052] High-temperature air and humid cold air enter the second heat exchanger 20 through the second air inlet 23. Hydrated salt and dehydrated hydrated salt enter the second heat exchanger 20 through the feed inlet 21. Water vapor and hot air are discharged from the second heat exchanger 20 through the second exhaust outlet 24. Dehydrated hydrated salt enters the second sealed storage tank 32 through the discharge outlet 22. Hydrated salt enters the first sealed storage tank 31 through the discharge outlet 22.

[0053] Specifically, the feed inlet 21 and the second exhaust outlet 24 are located on the upper side of the side wall of the second heat exchanger 20, and the discharge outlet 22 and the second air inlet 23 are located on the lower side of the side wall of the second heat exchanger 20.

[0054] As an optional implementation method, the hydrated salt is CaCl2·6H2O, and the dehydrated hydrated salt is CaCl2·2H2O.

[0055] Specifically, during waste heat recovery and storage, the hydrated salt descends and comes into full contact with the rising high-temperature air, which facilitates the hydrated salt absorbing heat and decomposing into water and dehydrated hydrated salt. During waste heat storage and utilization, the descending dehydrated hydrated salt and the rising humid and cold air come into full contact, which facilitates the dehydrated hydrated salt combining with water to form hydrated salt and release heat. At the same time, it facilitates the heated air to be discharged from the second exhaust port 24 to realize waste heat utilization.

[0056] In the waste heat recovery and storage system, a fan 40 is installed below the second exhaust port 24 to accelerate the gas flow in the spiral feeder heat exchanger and accelerate the discharge of water vapor generated by the decomposition of hydrated salts by absorbing heat, preventing the dehydration of hydrated salts due to excessive relative humidity in the spiral feeder heat exchanger; the second sealed storage tank 32 is located below the discharge port 22 and can be both tightly fitted and disassembled with the discharge port 22. The tight fit prevents the dehydration of hydrated salts from decomposing when exposed to humid air, while the disassembly allows the second sealed storage tank 32 containing dehydrated hydrated salts to be stored / transported separately for a long time, realizing the storage and utilization of waste heat across seasons and distances; the first air outlet and the second air inlet 23 are connected by a pipeline to transport the high-temperature air output from the plate heat exchanger to the spiral feeder heat exchanger.

[0057] Taking CaCl2·6H2O as the hydrated salt and CaCl2·2H2O as the dehydrated hydrated salt as an example, the waste heat recovery and storage process and the waste heat storage and utilization process are explained.

[0058] (1) Waste heat recovery and storage process:

[0059] The plate heat exchanger consists of a series of parallel plates with gaps between them to form fluid channels. Boiler tail flue gas (i.e., high-temperature flue gas) enters the channel through the flue gas inlet 11, and ambient air enters the channel through the first air inlet 13. The two fluids flow through the gaps between the plates, and in the process of flow, the heat of the high-temperature flue gas is transferred to the air. The resulting high-temperature air is discharged through the first exhaust port 14. The high-temperature air is introduced into the spiral feed heat exchanger through the second air inlet 23 and rises along the pipe, contacting CaCl2·6H2O. CaCl2·6H2O absorbs the heat of the hot air and decomposes into water vapor and CaCl2·2H2O. Affected by the fan 40, the water vapor continues to rise under the pressure difference and is discharged through the second exhaust port 24. CaCl2·2H2O descends and enters the second sealed storage tank 32 for storage, realizing the recovery and storage of waste heat.

[0060] (2) Waste heat storage and utilization process:

[0061] Moist, cold air enters from the second inlet 23 of the spiral feeder heat exchanger and travels upward along the pipeline. It comes into contact with the downward CaCl2·2H2O supplied by the second sealed storage tank 32. The CaCl2·2H2O combines with the water in the moist, cold air to form CaCl2·6H2O and releases heat. As a result, the air absorbs heat and its temperature rises. The hot air is discharged from the second exhaust port 24 of the spiral feeder heat exchanger for use. Alternatively, the CaCl2·6H2O is discharged through the outlet 22 and enters the first sealed storage tank 31 for storage, to be used for the next waste heat recovery.

[0062] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the system and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A flue gas waste heat recovery and utilization system based on thermochemical thermal storage, characterized in that, include: Waste heat recovery and storage systems and waste heat storage and utilization systems; The waste heat recovery and storage system includes: a first heat exchanger, a second heat exchanger, a first sealed storage tank, a second sealed storage tank, and a fan; the waste heat storage and utilization system includes: a second heat exchanger, a first sealed storage tank, and a second sealed storage tank; The first heat exchanger is connected to the boiler flue gas emission device, and the first heat exchanger, the first sealed storage tank, the second sealed storage tank and the fan are all connected to the second heat exchanger; When waste heat recovery and storage are performed, in the first heat exchanger, ambient temperature air absorbs heat from the high-temperature flue gas emitted by the boiler flue gas emission device, resulting in high-temperature air and cooled flue gas. The cooled flue gas is discharged from the first heat exchanger, and the high-temperature air enters the second heat exchanger. In the second heat exchanger, hydrated salt provided by the first sealed storage tank absorbs heat from the high-temperature air, resulting in dehydrated hydrated salt and water vapor. The dehydrated hydrated salt is stored in the second sealed storage tank, and the water vapor is discharged from the second heat exchanger under the action of the fan. When waste heat is stored and utilized, humid cold air enters the second heat exchanger. In the second heat exchanger, the dehydrated hydrated salt provided by the second sealed storage tank reacts with the water in the humid cold air to obtain hydrated salt and hot air. The hydrated salt is stored in the first sealed storage tank, and the hot air is discharged from the second heat exchanger.

2. The flue gas waste heat recovery and utilization system based on thermochemical thermal storage according to claim 1, characterized in that, The connections between the first sealed storage tank and the second sealed storage tank and the second heat exchanger are both detachable connections; When waste heat is recovered and stored, the first sealed storage tank is located on the upper side of the second heat exchanger, and the second sealed storage tank is located on the lower side of the second heat exchanger. When waste heat is stored and utilized, the first sealed storage tank is located below the second heat exchanger, and the second sealed storage tank is located above the second heat exchanger.

3. The flue gas waste heat recovery and utilization system based on thermochemical thermal storage according to claim 1, characterized in that, The first heat exchanger is a plate heat exchanger.

4. The flue gas waste heat recovery and utilization system based on thermochemical thermal storage according to claim 1, characterized in that, The second heat exchanger is a spiral feeder heat exchanger, and the interior of the second heat exchanger is provided with spiral fins with circular openings.

5. The flue gas waste heat recovery and utilization system based on thermochemical thermal storage according to claim 1, characterized in that, The first heat exchanger has a flue gas inlet, a flue gas outlet, a first air inlet, and a first exhaust outlet on its side wall; The first heat exchanger is connected to the boiler flue gas emission device through the flue gas inlet, and the first heat exchanger is connected to the second heat exchanger through the first exhaust port; The high-temperature flue gas enters the first heat exchanger through the flue gas inlet, the ambient temperature air enters the first heat exchanger through the first air inlet, the cooled flue gas is discharged from the first heat exchanger through the flue gas outlet, and the high-temperature air is discharged from the first heat exchanger through the first exhaust outlet.

6. The flue gas waste heat recovery and utilization system based on thermochemical thermal storage according to claim 5, characterized in that, The second heat exchanger has a second air inlet, a second exhaust outlet, a feed inlet, and a discharge outlet on its side wall; The first heat exchanger is connected to the second heat exchanger through the first exhaust port and the second air inlet port; When waste heat recovery and storage are performed, the first sealed storage tank is connected to the second heat exchanger through the feed port, and the second sealed storage tank is connected to the second heat exchanger through the discharge port; the high-temperature air enters the second heat exchanger through the second air inlet, the hydrated salt enters the second heat exchanger through the feed port, the water vapor is discharged from the second heat exchanger through the second exhaust port, and the dehydrated hydrated salt enters the second sealed storage tank through the discharge port; When waste heat is stored and utilized, the first sealed storage tank is connected to the second heat exchanger through the discharge port, and the second sealed storage tank is connected to the second heat exchanger through the inlet port; the humid and cold air enters the second heat exchanger through the second air inlet, the dehydrated hydrated salt enters the second heat exchanger through the inlet port, the hot air is discharged from the second heat exchanger through the second exhaust port, and the hydrated salt enters the first sealed storage tank through the discharge port.

7. The flue gas waste heat recovery and utilization system based on thermochemical thermal storage according to claim 1, characterized in that, The hydrated salt is CaCl2·6H2O, and the dehydrated hydrated salt is CaCl2·2H2O.

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