CN118009781A - A flue gas waste heat recovery and utilization system based on thermochemical heat storage - Google Patents

Abstract

The present invention discloses a flue gas waste heat recovery and utilization system based on thermochemical heat storage, which relates to the technical field of thermal energy storage. When waste heat is recovered and stored, in the first heat exchanger, normal temperature air absorbs heat in the high temperature flue gas discharged by the boiler flue gas discharge device, and the flue gas after cooling is discharged from the first heat exchanger; in the second heat exchanger, the hydrated salt provided by the first sealed storage tank absorbs heat in the high temperature air to obtain dehydrated hydrated salt and water vapor, and the dehydrated hydrated salt enters the second sealed storage tank for storage, 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 the wet and cold air to obtain hydrated salt and hot air, and the hydrated salt enters the first sealed storage tank for storage. The present invention improves the waste heat recovery and utilization efficiency.

Description

A flue gas waste heat recovery and utilization system based on thermochemical heat storage

Technical Field

The present invention relates to the technical field of thermal energy storage, and in particular to a flue gas waste heat recovery and utilization system based on thermochemical heat storage.

Background technique

Coal-fired power generation is the main form of electricity production in China. In recent years, with the development of technology, the thermal efficiency of power plants with advanced units can exceed 45%. Under the current conditions, it will be difficult to further improve the thermal efficiency of power plants, but the utilization of flue gas waste heat is one of the effective ways to improve the thermal efficiency of thermal power plants. This is because the exhaust temperature of China's coal-fired units before dust removal is mostly between 90℃ and 150℃. The exhaust temperature is high, and the flue gas will carry a lot of heat, resulting in more losses. The exhaust loss can reach 3% to 8% of the heat loss of the entire boiler body, which is the most important factor affecting the thermal efficiency of the boiler. In addition to thermal power plants, industrial equipment such as boilers, internal combustion engines, smelting furnaces, etc. used in metallurgy, chemical industry, building materials, machinery and other industries also emit a large amount of flue gas. The exhaust temperature is mostly between 120℃ and 300℃, and the flue gas waste heat of some industrial equipment is even as high as 40% to 60% of its own fuel consumption. The flue gas waste heat accounts for more than half of the total industrial waste heat resources. Therefore, the energy-saving potential of flue gas waste heat recovery is relatively large.

At present, it is common to use flue gas waste heat to heat water or condensate and preheat air. However, the utilization of these low-grade waste heat has time (across day and night or even across seasons) and space (within the plant area or even wider) mismatch problems, so it is necessary to recycle and store waste heat to achieve cross-season and cross-distance utilization of energy. In the field of thermal energy storage, sensible heat storage technology is the most mature and the earliest application, but due to the low heat storage density, the device is bulky, inconvenient to install, and has a large heat loss. The temperature variation range is large when outputting heat, and a control device is required, which is not conducive to large-scale application. Latent heat storage is currently a popular research direction with a high heat storage density, but the phase separation and stability of the material have never been effectively solved. In addition, compared with sensible heat storage, the actual heat storage density and performance of latent heat storage have not been significantly improved. Compared with sensible heat storage and latent heat storage, thermochemical heat storage has the advantages of high heat storage density and long-term heat storage with almost no heat loss. Among them, hydrated salt thermochemical adsorption heat storage, as a type of thermochemical heat storage, inherits the advantages of thermochemical heat storage. Its adsorption/desorption temperature matches the flue gas temperature and the waste heat utilization temperature well, and is very suitable for waste heat recovery, storage and utilization. However, hydrated salt thermochemical adsorption heat storage also has some problems. Taking the conversion between CaCl ₂ ·6H ₂ O and CaCl ₂ ·2H ₂ O as an example, when CaCl ₂ ·6H ₂ O absorbs heat and decomposes into water and CaCl ₂ ·2H ₂ O, the energy-storing CaCl ₂ ·2H ₂ O is easily liquefied due to excessive humidity, resulting in poor waste heat recovery. In addition, whether in the process of waste heat recovery or utilization, there is a problem of insufficient contact between the hydrated salt solid and the gas, resulting in low waste heat recovery and utilization efficiency.

Summary of the invention

The purpose of the present invention is to provide a flue gas waste heat recovery and utilization system based on thermochemical heat storage, thereby improving the waste heat recovery and utilization efficiency.

To achieve the above object, the present invention provides the following solutions:

A flue gas waste heat recovery and utilization system based on thermochemical heat storage, comprising: a waste heat recovery storage system and a waste heat storage and utilization system;

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: the second heat exchanger, the first sealed storage tank and the second sealed storage tank;

The first heat exchanger is connected to the boiler smoke exhaust 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;

When waste heat recovery and storage is performed, in the first heat exchanger, normal temperature air absorbs heat from the high temperature flue gas discharged by the boiler flue gas discharge device to obtain high temperature air and flue gas after cooling, the flue gas after cooling is discharged from the first heat exchanger, and the high temperature air enters the second heat exchanger; in the second heat exchanger, the hydrated salt provided by the first sealed storage tank absorbs heat from the high temperature air to obtain dehydrated hydrated salt and water vapor, the dehydrated hydrated salt enters the second sealed storage tank for storage, and under the action of the fan, the water vapor is discharged from the second heat exchanger;

When waste heat storage is performed, wet and cold air enters the second heat exchanger, in which the dehydrated hydrated salt provided by the second sealed storage tank reacts with water in the wet and cold air to obtain hydrated salt and hot air, and the hydrated salt enters the first sealed storage tank for storage, and the hot air is discharged from the second heat exchanger.

Optionally, the first sealed storage tank and the second sealed storage tank are both connected to the second heat exchanger in a detachable manner;

When waste heat recovery and storage is performed, the first sealed storage tank is arranged on the upper side of the second heat exchanger, and the second sealed storage tank is arranged on the lower side of the second heat exchanger;

When waste heat storage is performed, the first sealed storage tank is arranged at the lower side of the second heat exchanger, and the second sealed storage tank is arranged at the upper side of the second heat exchanger.

Optionally, the first heat exchanger is a plate heat exchanger.

Optionally, the second heat exchanger is a spiral feed heat exchanger, and spiral fins with circular openings are provided inside the second heat exchanger.

Optionally, the circular openings are arranged on opposite sides of the spiral fins.

Optionally, a smoke inlet, a smoke exhaust port, a first air inlet and a first exhaust port are provided on the side wall of the first heat exchanger;

The first heat exchanger is connected to the boiler smoke exhaust device through the smoke inlet, and the first heat exchanger is connected to the second heat exchanger through the first exhaust hole;

The high-temperature flue gas enters the first heat exchanger through the smoke inlet, the normal-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 smoke exhaust port, and the high-temperature air is discharged from the first heat exchanger through the first exhaust port.

Optionally, a second air inlet, a second air outlet, a feed inlet and a feed outlet are provided on the side wall of the second heat exchanger;

The first heat exchanger is connected to the second heat exchanger through the first exhaust hole and the second air inlet hole; 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;

The high-temperature air and the wet 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 port, the water vapor and the hot air are discharged from the second heat exchanger through the second exhaust port, the hydrated salt enters the second sealed storage tank through the discharge port, and the dehydrated hydrated salt enters the first sealed storage tank through the discharge port.

Optionally, the hydrated salt is CaCl ₂ ·6H ₂ O, and the dehydrated hydrated salt is CaCl ₂ ·2H ₂ O.

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

The invention discloses a flue gas waste heat recovery and utilization system based on thermochemical heat storage, comprising: when waste heat recovery and storage is performed, in a first heat exchanger, normal temperature air absorbs heat from high temperature flue gas discharged by a boiler flue gas discharge device to obtain high temperature air and flue gas after cooling, the flue gas after cooling 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 high temperature air to obtain dehydrated hydrated salt and water vapor, the dehydrated hydrated salt enters a second sealed storage tank for storage, and under the action of a fan When the waste heat is stored and utilized, the wet and cold air enters the second heat exchanger, in which the dehydrated hydrated salt provided by the second sealed storage tank reacts with the water in the wet and cold air to obtain hydrated salt and hot air, and the hydrated salt enters the first sealed storage tank for storage, and the hot air is discharged from the second heat exchanger, thereby improving the waste heat recovery efficiency and realizing the cross-distance and cross-season utilization of waste heat, thereby meeting the needs of the power, metallurgy, chemical industry, building materials and other industries for flue gas waste heat recovery, reducing energy loss and improving economic benefits.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the working process of waste heat recovery and storage by a flue gas waste heat recovery and utilization system based on thermochemical heat storage provided by an embodiment of the present invention;

FIG2 is a schematic diagram of the working process of waste heat storage and utilization of the flue gas waste heat recovery and utilization system based on thermochemical heat storage provided by an embodiment of the present invention.

Symbol Description:

The first heat exchanger 10, the smoke inlet 11, the smoke exhaust port 12, the first air inlet 13, the first exhaust port 14, the second heat exchanger 20, the feed inlet 21, the feed outlet 22, the second air inlet 23, the second exhaust port 24, the spiral fin 25, the first sealed storage tank 31, the second sealed storage tank 32, and the fan 40.

Detailed ways

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.

The purpose of the present invention is to provide a flue gas waste heat recovery and utilization system based on thermochemical heat storage, aiming to improve the waste heat recovery and utilization efficiency.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 and FIG. 2 , the flue gas waste heat recovery and utilization system based on thermochemical heat storage in this embodiment includes: a waste heat recovery storage system and a waste heat storage and utilization system.

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 .

The first heat exchanger 10 is connected to the boiler flue gas discharge 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 .

When waste heat recovery and storage is performed, in the first heat exchanger 10, normal temperature air absorbs heat from the high temperature flue gas discharged from the boiler flue gas discharge device to obtain 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 to obtain dehydrated hydrated salt and water vapor. The dehydrated hydrated salt enters the second sealed storage tank 32 for storage, and under the action of the fan 40, the water vapor is discharged from the second heat exchanger 20.

When waste heat is stored and utilized, the 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 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.

As an optional embodiment, the first sealed storage tank 31 and the second sealed storage tank 32 are both detachably connected to the second heat exchanger 20 .

When waste heat is recovered and stored, the first sealed storage tank 31 is disposed on the upper side of the second heat exchanger 20 , and the second sealed storage tank 32 is disposed on the lower side of the second heat exchanger 20 .

When the waste heat is stored and utilized, the first sealed storage tank 31 is disposed at the lower side of the second heat exchanger 20 , and the second sealed storage tank 32 is disposed at the upper side of the second heat exchanger 20 .

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

As an optional implementation, the second heat exchanger 20 is a spiral feed type heat exchanger, and a spiral fin 25 with a circular opening is provided inside the second heat exchanger 20 .

As an optional embodiment, the circular openings are provided on opposite sides of the spiral fin 25 .

Specifically, the circular openings are arranged on the opposite sides of the spiral fins to facilitate the flow of fluid in the spiral feeding heat exchanger, and can achieve relative movement of solid materials, which is beneficial to full contact between the fluid and the solid materials, and better realize waste heat recovery and utilization.

As an optional implementation, a smoke inlet 11 , a smoke exhaust port 12 , a first air inlet 13 and a first exhaust port 14 are provided on the side wall of the first heat exchanger 10 .

The first heat exchanger 10 is connected to the boiler flue gas discharge device through the smoke inlet 11, and the first heat exchanger 10 is connected to the second heat exchanger 20 through the first exhaust hole.

High-temperature flue gas enters the first heat exchanger 10 through the smoke inlet 11, and normal-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 smoke exhaust port 12, and the high-temperature air is discharged from the first heat exchanger 10 through the first exhaust port 14.

Specifically, the smoke inlet 11 and the smoke exhaust port 12 are arranged on the upper side of the side wall of the first heat exchanger 10 , and the first air inlet 13 and the first exhaust port 14 are arranged on the lower side of the side wall of the first heat exchanger 10 .

As an optional implementation, a second air inlet 23 , a second air outlet 24 , a feed inlet 21 and a discharge outlet 22 are provided on the side wall of the second heat exchanger 20 .

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

High-temperature air and wet 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 port 21, water vapor and hot air are discharged from the second heat exchanger 20 through the second exhaust port 24, hydrated salt enters the second sealed storage tank 32 through the discharge port 22, and dehydrated hydrated salt enters the first sealed storage tank 31 through the discharge port 22.

Specifically, the feed port 21 and the second exhaust port 24 are disposed on the upper side of the side wall of the second heat exchanger 20 , and the discharge port 22 and the second air inlet 23 are disposed on the lower side of the side wall of the second heat exchanger 20 .

As an optional embodiment, the hydrated salt is CaCl ₂ ·6H ₂ O, and the dehydrated hydrated salt is CaCl ₂ ·2H ₂ O.

Specifically, when the waste heat is recovered and stored, the hydrated salt descends and is fully in contact with the ascending high-temperature air, which is conducive to the hydrated salt absorbing heat and decomposing into water and dehydrated hydrated salt; when the waste heat is stored and utilized, the descending dehydrated hydrated salt is in full contact with the ascending wet and cold air, which is conducive to the dehydrated hydrated salt combining with water to form hydrated salt and releasing heat, and at the same time is conducive to the heated air being automatically discharged from the second exhaust port 24 to realize the utilization of waste heat.

In the waste heat recovery and storage system, a fan 40 is provided at the lower side of the second exhaust port 24 to accelerate the gas flow in the spiral feed heat exchanger, accelerate the discharge of water vapor decomposed by the hydrated salt absorbing heat, and prevent the dehydrated hydrated salt from being liquefied due to excessive relative humidity in the spiral feed heat exchanger; the second sealed storage tank 32 is provided at the lower side of the discharge port 22 and can be tightly matched and split with the discharge port 22. The tight fit prevents the dehydrated hydrated salt from being liquefied when encountering wet air, and the splitting can realize the long-term storage/transportation of the second sealed storage tank 32 storing the dehydrated hydrated salt separately, thereby realizing the storage and utilization of waste heat across seasons and distances; the first air outlet is connected to the second air inlet 23 by a pipeline to realize the transportation of high-temperature air output by the plate heat exchanger to the spiral feed heat exchanger.

Taking the hydrated salt as CaCl ₂ ·6H ₂ O and the dehydrated hydrated salt as CaCl ₂ ·2H ₂ O as an example, the waste heat recovery storage process and the waste heat storage and utilization process are described.

(1) Waste heat recovery and storage process:

The plate heat exchanger is composed of a series of plates arranged in parallel. There are gaps between these plates to form a fluid channel. The flue gas at the tail of the boiler (i.e., high-temperature flue gas) enters the channel through the smoke inlet 11, and the air at normal temperature enters the channel through the first air inlet 13. The two fluids flow through the gaps between the plates and transfer the heat of the high-temperature flue gas to the air during the flow. The high-temperature air obtained is discharged from the first exhaust port 14. The high-temperature air enters the interior of the spiral feed heat exchanger from the second air inlet 23 and ascends along the pipeline to contact _CaCl2 · _6H2O . CaCl2· _6H2O absorbs the heat of the hot air and decomposes into water vapor and _CaCl2 · _2H2O . Under the influence of the fan 40, the water vapor continues to ascend and is discharged along the second exhaust port 24 under the action of the pressure difference. _{The CaCl2} · _2H2O descends and enters the second sealed storage tank 32 for storage, thereby realizing the recovery and storage of waste heat.

(2) Waste heat storage and utilization process:

The humid cold air enters from the second air inlet 23 of the spiral feed heat exchanger, goes up along the pipeline, and contacts with the descending CaCl2· _2H2O provided by the second sealed storage tank 32. The _CaCl2 · _2H2O combines with the water in the humid cold air to form _CaCl2 · _6H2O and releases heat. The air absorbs heat and heats up. The hot air is discharged from the second exhaust port ₂₄ of the spiral feed heat exchanger for utilization. For example, the _CaCl2 · _6H2O is discharged through the discharge port 22 and enters the first sealed storage tank 31 for storage, so as to be used for the next waste heat recovery and storage.

The technical features of the above embodiments may be arbitrarily combined. To make the description concise, 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.

This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the system and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (8)

1. Flue gas waste heat recovery utilizes system based on thermochemical heat accumulation, its characterized in that includes: the waste heat recovery storage system and the waste heat storage utilization system;

The waste heat recovery storage system includes: the system comprises 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 comprises: the second heat exchanger, the first sealed storage tank, and the second sealed storage tank;

The first heat exchanger is connected with a 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 with the second heat exchanger;

When waste heat is recovered and stored, in the first heat exchanger, the normal-temperature air absorbs heat in high-temperature flue gas discharged by the boiler flue gas discharge device to obtain 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, the hydrated salt provided by the first sealed storage tank absorbs heat in the high-temperature air to obtain dehydrated hydrated salt and water vapor, the dehydrated hydrated salt enters the second sealed storage tank for storage, and the water vapor is discharged from the second heat exchanger under the action of the fan;

When waste heat storage is utilized, wet and cold air enters the second heat exchanger, dehydrated hydrated salt provided by the second sealed storage tank reacts with water in the wet and cold air in the second heat exchanger to obtain hydrated salt and hot air, the hydrated salt enters the first sealed storage tank for storage, and the hot air is discharged from the second heat exchanger.

2. The thermochemical heat storage-based flue gas waste heat recovery and utilization system according to claim 1, wherein the connection between the first sealed storage tank and the second heat exchanger is detachable connection;

When waste heat recovery and storage are performed, the first sealed storage tank is arranged on the upper side of the second heat exchanger, and the second sealed storage tank is arranged on the lower side of the second heat exchanger;

when waste heat storage utilization is carried out, the first sealed storage tank is arranged at the lower side of the second heat exchanger, and the second sealed storage tank is arranged at the upper side of the second heat exchanger.

3. The thermochemical heat storage-based flue gas waste heat recovery and utilization system according to claim 1, wherein the first heat exchanger is a plate heat exchanger.

4. The thermochemical heat storage-based flue gas waste heat recycling system according to claim 1, wherein the second heat exchanger is a spiral feeding type heat exchanger, and spiral fins with circular openings are arranged inside the second heat exchanger.

5. The thermochemical heat storage-based flue gas waste heat recovery and utilization system according to claim 4, wherein the circular openings are arranged on opposite sides of the spiral fins.

6. The thermochemical heat storage-based flue gas waste heat recycling system according to claim 1, wherein a flue gas inlet, a flue gas outlet, a first air inlet and a first air outlet are formed in the side wall of the first heat exchanger;

The first heat exchanger is connected with the boiler flue gas emission device through the flue gas inlet, and the first heat exchanger is connected with the second heat exchanger through the first exhaust hole;

The high-temperature flue gas enters the first heat exchanger through the flue gas inlet, the normal-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 smoke outlet, and the high-temperature air is discharged from the first heat exchanger through the first air outlet.

7. The thermochemical heat storage-based flue gas waste heat recycling system according to claim 6, wherein a second air inlet, a second air outlet, a feed inlet and a discharge outlet are formed in the side wall of the second heat exchanger;

The first heat exchanger is connected with the second heat exchanger through the first exhaust hole and the second air inlet hole; the first sealed storage tank is connected with the second heat exchanger through the feed inlet or the discharge outlet, and the second sealed storage tank is connected with the second heat exchanger through the feed inlet or the discharge outlet;

The high-temperature air and the wet and 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 feeding hole, the water vapor and the hot air are discharged from the second heat exchanger through the second air outlet, the hydrated salt enters the second sealed storage tank through the discharging hole, and the dehydrated hydrated salt enters the first sealed storage tank through the discharging hole.

8. The thermochemical heat storage-based flue gas waste heat recovery and utilization system according to claim 1, wherein the hydrated salt is CaCl ₂·6H₂ O and the dehydrated hydrated salt is CaCl ₂·2H₂ O.