CN112944726A

CN112944726A - Open type heat absorption heating system with high heat storage density

Info

Publication number: CN112944726A
Application number: CN202110233295.7A
Authority: CN
Inventors: 叶碧翠; 王征; 崔海蛟
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2021-03-03
Filing date: 2021-03-03
Publication date: 2021-06-11
Anticipated expiration: 2041-03-03
Also published as: CN112944726B

Abstract

The invention discloses a high-heat-storage-density open type absorption heat warming system which comprises an open type absorber, a cooler, an evaporator/condenser and a closed type absorber, wherein the open type absorber is arranged in the cooler; the open absorber is communicated with the high-humidity flue gas, a solution and a cooling water pipe are arranged in the cooler, a solution outlet of the open absorber is respectively connected to solution inlets of the cooler and the closed absorber, and a solution outlet of the cooler is connected to a solution spraying end of the open absorber; the evaporation/condenser is internally provided with condensed water and a cooling coil, and the top of the evaporation/condenser is connected to the closed absorber through a steam pipe; a water pipe to be heated and a solution spraying device are arranged in the closed absorber, the solution spraying device is arranged above the water pipe to be heated, and an outlet of the water pipe to be heated is connected to the heat supply tail end. The invention has the functions of heat storage and heat temperature rise, and meanwhile, because the closed absorber plays a role in improving the heat output temperature, the open absorber obviously reduces the solution temperature through multi-stage cooling, and can obtain higher latent heat recovery rate.

Description

Open type heat absorption heating system with high heat storage density

Technical Field

The invention relates to the field of absorption heat pumps and flue gas waste heat recovery, in particular to a high-heat-storage-density open type absorption heat temperature rising system.

Background

In recent years, industrial energy consumption of China exceeds 29 hundred million tons of standard coal, and more than 14% of the coal is discharged by industrial production equipment or systems in a low-grade heat energy mode. A large amount of industrial waste heat, especially waste heat resources with low temperature grade (generally below 150 ℃), can not be effectively recycled under the existing energy utilization technology, so that the primary energy utilization efficiency of China is lower than the international advanced level. The low-temperature flue gas is one of the important sources of low-grade waste heat resources, and has higher moisture content due to hydrogen radicals of fuel, moisture brought in the production process and the like. The steam in the flue gas of the oil-fired boiler accounts for 10-12%, the steam in the flue gas of the gas-fired boiler accounts for 15-19%, the steam in the dried exhaust smoke is as high as 80%, and the energy density of the latent heat of phase change of the steam is far higher than that of sensible heat, so that the low-temperature flue gas not only contains sensible heat, but also has considerable latent heat utilization value. The utilization of the waste heat of the low-temperature high-humidity flue gas has important significance and value from the aspects of energy efficiency and environmental protection.

The condensation type waste heat recovery based on heat transfer is the most widely used technology in the prior high-humidity flue gas waste heat recovery, the heat exchange of media on two sides of a dividing wall is realized by means of dividing wall type condensation heat exchange equipment, and the recovery of condensation heat in flue gas can be realized only when the temperature of a cooling medium side is lower than the condensation temperature. However, the low-temperature cooling medium side temperature in the single condensation regenerative equipment greatly limits the potential and application range of recycling the recovered waste heat.

The heat pump and the dividing wall type condensation heat exchanger coupling system produces low-temperature water through the evaporator of the heat pump, so that the condensation effect of flue gas is improved, the heat recovered by the flue gas is carried back to the absorption heat pump by the low-temperature water, and the heat with higher grade is output outwards through the absorber and the condenser. Obviously, the lower the evaporation temperature, the more sufficient the flue gas total heat recovery, and the higher the condensation temperature, the more favorable the supply heat demand, however, the low evaporation temperature and the high condensation temperature lead to the difficulty in increasing the performance coefficient of the conventional absorption heat pump.

The open type absorption heat pump circulation based on the gas-liquid direct contact process realizes the coupling type centralized heat recovery of the sensible heat and the latent heat of the low-temperature high-humidity flue gas through the heat mass transfer between gas and liquid. However, in the existing single-effect open type absorption heat pump cycle, for example, CN101922821A can realize latent heat recovery of wet flue gas, but due to the influence of temperature rise of solution, partial pressure of water vapor rises, so that sensible heat of wet flue gas is difficult to recover and the moisture absorption capacity is reduced. Patent CN 110513905 a improves sensible heat recovery of wet flue gas by adding a subcooler on the basis of single-effect open-type absorption heat pump cycle, but is still affected by temperature rise of solution and partial pressure rise of water vapor, resulting in reduced moisture absorption capacity. Therefore, the single-effect open type absorption heat pump is limited by the system circulation form and the refrigeration working medium, and the external heat supply temperature is concentrated in the application of a heat supply pipe network at 50-60 ℃. However, most of the industrial heat ranges from 80 ℃ to 150 ℃, wherein the temperature of the high-temperature water vapor is 100 ℃ to 150 ℃, and the high-temperature water vapor is a relatively common heat carrier due to the advantages of high latent heat, high heat transfer and the like, and is widely applied to industrial processes such as chemical industry, textile industry, printing and dyeing industry, food industry, medicine industry, cement industry and the like.

Disclosure of Invention

Aiming at the bottleneck and the requirement of waste heat grade improvement in the prior art, the invention aims to provide the open type heat absorption heating system with high heat storage density, which has the advantages of high heat storage density, high-temperature steam output and high-efficiency total heat recovery.

To achieve the above technical objects, some embodiments of the present invention include:

an open type absorption heat temperature rising system with high heat storage density comprises an open type absorber, a cooler, an evaporator/condenser and a closed type absorber; the open absorber is communicated with the high-humidity flue gas, a solution and a cooling water pipe are arranged in the cooler, a solution outlet of the open absorber is respectively connected to solution inlets of the cooler and the closed absorber, and a solution outlet of the cooler is connected to a solution spraying end of the open absorber; the evaporation/condenser is internally provided with condensed water and a cooling coil, the cooling water pipe is communicated with the cooling coil, and the top of the evaporation/condenser is connected to the closed absorber through a steam pipe; a water pipe to be heated and a solution spraying device are arranged in the closed absorber, the solution spraying device is arranged above the water pipe to be heated, and an outlet of the water pipe to be heated is connected to the heat supply tail end.

The reactor is connected with a low-grade heat source, and the top of the reactor is connected to the heat storage evaporator/condenser through a steam pipe; the bottom of the reactor stores a concentrated solution, and the concentrated solution is respectively conveyed to the open absorber and the closed absorber; the bottom of the heat-storage evaporator/condenser stores condensed water, and the condensed water is conveyed to the evaporator/condenser.

As one of the preferable schemes of the invention, the solution outlet of the open absorber is also connected to the solution inlet of the closed absorber, and the solution outlet of the closed absorber is connected to the bottom of the reactor.

The cooling water system further comprises a controller, wherein an electromagnetic valve is arranged between the cooling water pipe and the cooling coil, and the controller controls the evaporation temperature of the cooling water by adjusting the electromagnetic valve and the solution pump.

As one of the preferable schemes of the invention, the device also comprises a direct evaporation cooler which is arranged at one side of the cooler; the heat storage evaporator/condenser is internally provided with a heat exchange tube which is connected to the direct evaporative cooler.

As one preferable scheme of the invention, the high-humidity flue gas is directly contacted with the solution for heat exchange to form dry flue gas, and the dry flue gas is discharged after passing through the direct evaporative cooler.

As one preferable scheme of the invention, a spray header and a water storage tank are arranged in the direct evaporative cooler, the outlet of a heat exchange tube in the heat storage evaporation/condenser is connected to the spray header, and the inlet of the heat exchange tube is connected to the water storage tank.

As one of the preferable schemes of the invention, the closed absorber is also connected with low-grade waste heat, and the low-grade waste heat is used for solution regeneration in the closed absorber.

Compared with the prior art, the invention has the following advantages:

1. a thermal heating function: latent heat obtained by the open absorber from high-humidity flue gas is transferred to the evaporator through heat transfer between the solution and cooling water, and the evaporation temperature can be controlled by adjusting the flow of the solution and the cooling water. If the temperature of the cooling water is 60 ℃ and is obviously higher than the ambient temperature, the concentrated solution in the closed absorber can output high-temperature steam of 120-150 ℃ to the outside after absorbing the high-pressure steam, and the grade of the industrial waste heat is obviously improved.

2. High-efficiency total heat recovery: because the closed absorber plays a role in improving the heat output temperature, the normal-pressure open absorber can obviously reduce the temperature of the solution through multi-stage cooling, thereby reducing the partial pressure of water vapor on the surface of the absorbent, improving the mass transfer rate and obtaining higher latent heat recovery rate.

3. Heat storage function: when the driven low-grade waste heat is not matched with the supply of the high-humidity flue gas to be recovered, the heat is stored in the form of solution chemical potential by circulating through the reactor, and the stored heat and the high-humidity flue gas are released by heat mass transfer of the high-humidity flue gas and the absorbent at the same time. The multistage cooling absorption and the low-pressure absorption processes in series in the open absorber form a large concentration difference on the heat supply side, and high-density heat storage is facilitated.

4. The high-humidity flue gas with the reduced temperature of the heat source passes through the open absorber and is dehumidified by the moisture absorbent solution with lower surface vapor partial pressure to obtain dry flue gas, the dry flue gas passes through the direct evaporative cooler to generate 15-20 ℃ chilled water by utilizing the evaporation of water, and the chilled water is used as a low-temperature cold source with lower temperature than the environment temperature to reduce the condensation pressure, so that the generation temperature required by the generator is reduced.

Drawings

For purposes of explanation, several embodiments of the present technology are set forth in the following figures. The following drawings are incorporated herein and constitute a part of the detailed description. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology.

Fig. 1 is a schematic diagram of the high heat storage density open type absorption heat temperature increasing system according to embodiment 1.

Fig. 2 is a schematic diagram of the high heat storage density open type absorption heat temperature increasing system according to embodiment 2.

Description of the drawings: 1-open absorber, 2-cooler, 3-evaporation/condenser, 4-closed absorber, 5-generator, 6-heat storage evaporation/condenser; 10-a solution pump, 20-a cooling water pipe, 21-an electromagnetic valve, 30-a cooling coil, 40-a water pipe to be heated, 31/50-a steam pipe and 60-a heat exchange pipe.

Detailed Description

The specific embodiments illustrated below are intended as descriptions of various configurations of the subject technology and are not intended to represent the only configurations in which the subject technology may be practiced. Specific embodiments include specific details for the purpose of providing a thorough understanding of the subject technology. It will be apparent, however, to one skilled in the art that the subject technology is not limited to the specific details shown herein and may be practiced without these specific details.

Example 1

As shown in fig. 1, the present embodiment provides an open type absorption heat warming system with high heat storage density, which includes a heat warming unit, the heat warming unit includes an open absorber 1, a cooler 2, an evaporator/condenser 3 and a closed absorber 4; wherein, the open absorber 1 is communicated with the high-humidity flue gas, the cooler 2 is internally provided with a solution and a cooling water pipe 20, a solution outlet of the open absorber 1 is connected to a solution inlet of the cooler through one side of a three-way pipe, and the other side is connected to a solution inlet of the closed absorber; the solution outlet of the cooler 2 is connected to the solution spraying end of the open absorber 1; the evaporation/condenser 3 is internally provided with condensed water and a cooling coil 30, the cooling water pipe 20 is communicated with the cooling coil 30, and the top of the evaporation/condenser 3 is connected to the closed absorber 4 through a steam pipe 31; the closed absorber 4 is internally provided with a water pipe 40 to be heated and a solution spraying device, the solution spraying device is arranged above the water pipe to be heated, and an outlet of the water pipe 40 to be heated is connected to the heat supply tail end.

The thermal heating system of the embodiment further comprises a heat storage unit, the heat storage unit comprises a reactor 5 and a heat storage evaporator/condenser 6, the reactor 5 is connected with a low-grade heat source, and the top of the reactor 5 is connected to the heat storage evaporator/condenser 6 through a steam pipe 50; the bottom of the reactor 5 stores concentrated solution which is respectively conveyed to the open absorber 1 and the closed absorber 4; the condensed water is delivered to the evaporator/condenser 3.

The embodiment further comprises a controller, wherein an electromagnetic valve 21 is arranged between the cooling water pipe 20 and the cooling coil 30, and the controller controls the evaporation temperature of the cooling water by adjusting the electromagnetic valve 21 and the solution pump 10.

This embodiment open absorption heat of high heat-storage density intensification system includes following heat-storage process and exothermal process:

the heat storage process:

the low-grade industrial waste heat drives the reactor 5, the temperature of the solution in the reactor 5 is raised, water vapor is evaporated and separated from the dilute solution and enters the heat storage evaporator/condenser 6 through a steam pipeline, the concentration of the solution is increased, and the obtained concentrated solution is stored at the bottom of the reactor. The condenser is cooled by an environmental cold source or other cold sources, and obtained condensed water is stored at the bottom of the condenser. The process is a heat charging process, and when the heat storage process is finished, a valve between the reactor 5 and the heat storage evaporation/condenser 6 is closed. The low-grade industrial waste heat is stored in the moisture absorbent in the form of chemical potential energy.

When the driven low-grade waste heat is not matched with the supply of the high-humidity flue gas to be recovered, the system stores heat in the form of solution chemical potential through the reactor, and releases the stored heat and the high-humidity flue gas through heat and mass transfer of the high-humidity flue gas and the absorbent at the same time. The multistage cooling absorption and the low-pressure absorption processes in series in the open absorber form a large concentration difference on the heat supply side, and high-density heat storage is facilitated.

An exothermic process:

when high-humidity flue gas is discharged and a heating and heating cycle needs to be started, concentrated solution stored at the bottom of the reactor 5 is respectively connected to the solution spraying device of the open absorber 1 and the solution spraying device of the closed absorber 4 through a three-way pipe under the action of a pump. The spraying solution is directly contacted with the high-humidity flue gas in the open absorber 1 to generate heat and mass exchange, the solution absorbs water vapor in the high-humidity flue gas, the temperature of the solution is increased, and the moisture content in the high-humidity flue gas is reduced. The heated solution pump is respectively connected to the cooler 2 and the solution spraying device of the closed absorber 4 through a three-way pipe. The solution in the cooler 2 transfers heat to cooling water through heat transfer, the temperature of the solution is reduced, the partial pressure of water vapor is reduced, the moisture absorption capacity is regained, and the solution is mixed with the concentrated solution from the reactor 5 and then enters the open absorber 1 to absorb the water vapor in the wet flue gas. The cooling water gains heat and the temperature rises. The temperature of the cooling water is controlled by adjusting the flow of the solution and the cooling water.

The heated cooling water flows to the cooling coil 30 of the evaporator/condenser 3, the condensed water at the bottom of the evaporator/condenser is heated and evaporated, and the generated steam flows to the closed absorber 4. The mixed solution from the solution outlet of the reactor 5 and the solution outlet of the open absorber 1 is connected to the top spraying device of the closed absorber 4 through a throttle valve, the solution absorbs the steam from the evaporator/condenser 3 to obtain high-temperature heat, the water in the water pipe 40 to be heated is heated to form high-temperature steam, the high-temperature steam is output outwards, and meanwhile, the concentration of the solution is reduced after the solution absorbs the steam. And the dilute solution with the reduced concentration in the closed absorber 4 enters the reactor 5 through a throttle valve, is driven by low-grade industrial waste heat again, is regenerated to a concentrated solution to obtain the moisture absorption capacity again, and the cycle is repeated.

The high-humidity flue gas in the open absorber 1 directly contacts with the solution to exchange heat to form dry flue gas, the waste heat of the flue gas is fully utilized, and energy conservation and emission reduction are realized.

Optionally, in the thermal heating unit, the closed absorber 4 and the evaporator/condenser 3 have a structure similar to that of the heat storage unit, and can realize the same heat storage function of the heat storage unit. Therefore, the low-grade waste heat can drive the closed absorber to realize solution regeneration. At this time, the thermal temperature increasing means intermittently increases the temperature.

According to practical situations and experience, taking the drying smoke of paper making as an example, the temperature T of the high humidity smoke is 80 ℃, the relative humidity RH is 45%, the moisture content d is 166g/kg, and the pressure P is 1 bar. Lithium bromide-water is used as an absorption working medium pair, the temperature T of flue gas at the outlet of the open absorber is 70 ℃, the moisture content d is 14g/kg, and the recovery efficiency of latent heat of high-humidity flue gas reaches 88.4%. The temperature T of the solution at the outlet of the open absorber is 70 ℃, the concentration X is 62% (i.e. the solution state at the inlet of the cooler), the temperature T of the solution at the outlet of the cooler is 62 ℃, and the concentration X is 60% (i.e. the solution state at the inlet of the heat exchanger). The heat exchanger outlet solution T is 30 ℃ and the concentration X is 62% (i.e. open absorber inlet solution state). The outlet solution T of the open absorber was 70 ℃ and the concentration X was 60% (i.e. the cooler inlet solution state). The temperature T of cold water at the inlet of the cooler is 60 ℃, and the temperature T of cold water at the outlet of the cooler is 65 ℃ (namely the state of cold water at the inlet of the evaporator). The state T of the cooling water at the outlet of the evaporator is 60 ℃. The evaporator outlet steam T is 60 deg.c and the saturation pressure P is 19.93kPa (i.e. closed absorber inlet steam state). The temperature T of cooling water at the inlet of the closed absorber is 60 ℃, the pressure P is 1bar, the temperature T of cooling water at the outlet of the closed absorber is 110 ℃, and the pressure P is 143.2 kPa. The inlet solution temperature T of the closed absorber was 75 ℃, the concentration X was 62%, the outlet solution temperature T of the closed absorber was 110 ℃, the pressure P was 19.92kPa, and the concentration X was 60% (i.e., the reactor inlet solution state). The temperature T of the solution at the outlet of the reactor was 80 ℃ and the concentration X was 65% (i.e. the solution at the inlet of the open absorber). The steam temperature T at the outlet of the reactor was 80 ℃ and the saturation pressure P was 3.4 kPa. The above calculation shows that the system can be used for obtaining the water vapor with the high temperature of 110 ℃, and the latent heat recovery efficiency of the high-humidity flue gas is 88.4%. However, with the traditional single-stage open absorption heat pump cycle, high temperature water vapor at 110 ℃ is obtained, and the latent heat recovery rate is only 28.7%. The greater the humidity of the high humidity flue gas inlet, the more significant the advantages over traditional single stage open absorption heat pump cycles. The method can effectively realize the recovery of the latent heat of the high-humidity flue gas and simultaneously improve the grade of the waste heat.

Example 2

As shown in fig. 2, the present embodiment is different from embodiment 1 only in that the high heat storage density open type absorption heat temperature increasing system further includes an evaporative cooler 7, and optionally, the evaporative cooler 7 may be a direct evaporative cooler or an indirect evaporative cooler. The high-humidity flue gas in the open absorber 1 is dehumidified and discharged through a solution, and is connected to the evaporative cooler 7 through a flue gas pipeline. In the evaporative cooler 7, the sensible heat of the drying flue gas and the sensible heat of the chilled water are taken away by the evaporation of water, the temperature of the flue gas and the chilled water is reduced, and low-temperature chilled water is obtained. The limit outlet temperature of the low-temperature chilled water in the direct evaporative cooler is the wet bulb temperature corresponding to the dry flue gas, and the limit outlet temperature of the low-temperature chilled water in the indirect evaporative cooler is the dew point temperature corresponding to the dry flue gas. The low-temperature chilled water outlet at the bottom of the evaporative cooler 7 is connected to a heat exchange pipe 60 arranged in the heat storage evaporation/condenser 6, and the heat exchange pipe obtains low-temperature chilled water and then cools steam in the evaporation/condenser 6. The humidity of the dry flue gas obtained from the open absorber 1 is low, and the dew point temperature of the dry flue gas is lower than the ambient temperature, so that the pressure in the heat storage subsystem is reduced, and the concentration of the concentrated solution obtained from the reactor 5 is increased under the condition that the temperature of the low-grade heat source in the reactor 5 is the same, thereby realizing the improvement of the heat storage density at the heat storage side; if the concentration of the concentrated solution in the reactor 5 is kept constant, the temperature of the heat source required for the reactor 5 can be reduced.

Still taking the paper making drying smoke in the embodiment 1 as an example, the temperature T of the high humidity smoke is 80 ℃, the relative humidity RH is 45%, the moisture content d is 166g/kg, and the pressure P is 1 bar. In this embodiment, as the pressure of the heat storage subsystem decreases, the concentration of the concentrated solution increases to 68%, the outlet temperature T of the dry flue gas in the open absorber 1 is 70 ℃, the moisture content d is 12g/kg, and the corresponding dew point temperature T is 16 ℃, and assuming that the temperature difference between the low-temperature chilled water and the steam in the condenser is 4 ℃, the condensation temperature T is 20 ℃, and the corresponding condensation pressure is 2.3 kPa. At this time, the latent heat recovery rate of the high humidity flue gas is improved to 92.7%.

While the subject matter of the present invention has been described with reference to the accompanying drawings and detailed description thereof, it is to be understood that the foregoing is merely illustrative of some embodiments of the subject matter of the present invention and that certain details may be omitted.

In addition, in some of the embodiments disclosed above, there is a possibility that a plurality of embodiments may be combined and implemented, and various combinations are not listed at length. The implementation embodiments can be freely combined according to the requirements when the technical personnel in the field carry out the implementation so as to obtain better application experience.

While practicing the subject matter of the present invention, it will be apparent to those skilled in the art that other arrangements of details or figures can be made in accordance with the subject matter of the present invention and the accompanying drawings, and that such details are within the scope of what is encompassed by the subject matter of the present invention without departing from the subject matter of the present invention.

Claims

1. An open type absorption heat temperature rising system with high heat storage density is characterized by comprising an open type absorber, a cooler, an evaporator/condenser and a closed type absorber; the open absorber is communicated with the high-humidity flue gas, a solution and a cooling water pipe are arranged in the cooler, a solution outlet of the open absorber is respectively connected to solution inlets of the cooler and the closed absorber, and a solution outlet of the cooler is connected to a solution spraying end of the open absorber; the evaporation/condenser is internally provided with condensed water and a cooling coil, the cooling water pipe is communicated with the cooling coil, and the top of the evaporation/condenser is connected to the closed absorber through a steam pipe; a water pipe to be heated and a solution spraying device are arranged in the closed absorber, the solution spraying device is arranged above the water pipe to be heated, and an outlet of the water pipe to be heated is connected to the heat supply tail end.

2. The high heat storage density open absorption heat warming system according to claim 1 further comprising a heat storage unit comprising a reactor and a heat storage evaporator/condenser, the reactor being connected to a low grade heat source, the top of the reactor being connected to the heat storage evaporator/condenser through a steam pipe; the bottom of the reactor stores a concentrated solution, and the concentrated solution is respectively conveyed to the open absorber and the closed absorber; the bottom of the heat-storage evaporator/condenser stores condensed water, and the condensed water is conveyed to the evaporator/condenser.

3. The high heat storage density open absorption heat temperature rise system of claim 2 wherein the solution outlet of the open absorber is further connected to the solution inlet of the closed absorber and the solution outlet of the closed absorber is connected to the bottom of the reactor.

4. The high heat storage density open absorption heat warming system according to claim 2, further comprising a controller, wherein an electromagnetic valve is provided between the cooling water pipe and the cooling coil, and the controller controls the evaporation temperature of the cooling water by adjusting the electromagnetic valve and the solution pump.

5. The high thermal storage density open absorption heat temperature elevation system of claim 4 further comprising a direct evaporative cooler disposed on one side of the cooler; the heat storage evaporator/condenser is internally provided with a heat exchange tube which is connected to the direct evaporative cooler.

6. The high heat storage density open absorption heat temperature rising system of claim 5, wherein the high humidity flue gas directly contacts with the solution to exchange heat to form dry flue gas, and the dry flue gas is discharged through the direct evaporative cooler.

7. The high heat storage density open absorption heat temperature rise system as claimed in claim 6, wherein a shower head and a water storage tank are provided in the direct evaporative cooler, the outlet of the heat exchange tube in the heat storage evaporation/condenser is connected to the shower head, and the inlet of the heat exchange tube is connected to the water storage tank.

8. The high heat storage density open absorption heat temperature rising system according to any one of claims 1 to 7, wherein the closed absorber is further connected with low grade waste heat for solution regeneration.