CN110759405B

CN110759405B - Waste heat utilization process and system for seawater direct-flow cooling water of power plant

Info

Publication number: CN110759405B
Application number: CN201911075592.2A
Authority: CN
Inventors: 董勇; 陈桂芳; 崔琳
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2019-11-06
Filing date: 2019-11-06
Publication date: 2021-02-05
Anticipated expiration: 2039-11-06
Also published as: CN110759405A

Abstract

The invention relates to a waste heat utilization process and a waste heat utilization system for seawater direct-flow cooling water of a power plant. The seawater absorbing the heat of the dead steam is atomized into small droplets by a spraying system and then enters air-seawater heat and mass transfer equipment to directly contact with air naturally rising under the density difference for heat and mass transfer, the air absorbing water vapor recovers fresh water by a water vapor recovery device, and the fresh water is collected and then enters a fresh water tank for storage and standby; the seawater cooled by the air-seawater heat and mass transfer equipment is discharged into the sea. The method reasonably utilizes the waste heat of the seawater direct-current cooling water of the power plant, obtains low-cost fresh water resources, and provides a new idea for the waste heat utilization of the direct-current cooling water of the power plant.

Description

Waste heat utilization process and system for seawater direct-flow cooling water of power plant

Technical Field

The invention belongs to the field of energy and environment, and particularly relates to a waste heat utilization process and system for direct-current cooling water of a power plant.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

At present, most of steam turbine units of thermal power plants and nuclear power plants are of a condensing type, steam is subjected to work by all impellers of a steam turbine to become exhaust steam (steam) with the temperature of 25-45 ℃, and the exhaust steam is subjected to heat exchange (cooling) with circulating water (cooling water) so as to be condensed into water to realize recycling of water in the exhaust steam. The cooling water supply mode of the power plant is mainly determined according to the natural environment of the plant area, particularly the conditions of water source, water consumption and the like, and can be generally divided into an open system and a closed system. An open system is also called direct-current water supply, the water supply mode is very simple, a bank pump station is generally built in rivers and seas to take water, the water enters a condenser through a circulating water system to exchange heat and raise the temperature is discharged to the downstream of the rivers or the seas, the circulating water in the mode is discharged after being used once and is not reused, and the water supply mode is shown in figure 1. The results of the technical-economic comparison show that 50-80kg of cooling water is consumed for every 1kg of steam condensed (i.e. the cooling rate is in the range of 50-80). The cooling water of the power plant near the sea is usually taken from the sea by the above-mentioned direct-current water supply methodAnd the cooling water absorbing the waste heat of the exhaust steam is directly discharged back to the sea. A large amount of waste heat is discharged to the sea area, which causes energy waste and environmental heat pollution. Taking a 1000MW thermal power generating unit as an example, the flow rate of direct-current cooling water is about 80000t/h, the temperature rise of the cooling water is calculated according to 10 ℃, and the heat released per hour is about 3.36 x 10⁹kJ, 7000h of operation per year, discharges approximately 80 million tons of heat equivalent standard coal into the environment per year. The cooling water quantity of the nuclear power plant is about 1.2-1.5 times of that of the thermal power plant, and the heat loss is more.

The main utilization mode of the low-grade waste heat is to use the low-grade waste heat after upgrading by adopting a heat pump technology. Heat pumps are mainly classified into steam-driven absorption heat pumps, which use high-grade steam as a driving force, and motor-driven heat pumps, which use electricity as a driving force, and both extract heat from a low-temperature heat source for heat supply and other purposes. The heat pump technology needs a high-grade heat source as a driving force, and meanwhile, the system is complex and the operation cost is high. The seawater cooling water waste heat has low utilization value and higher heat pump operation cost due to lower temperature; on the other hand, seawater cooling water causes problems such as corrosion and scaling, and is difficult to continuously operate for a long time.

Disclosure of Invention

In order to overcome the problems, the invention provides a process and a method for utilizing the waste heat of seawater direct-flow cooling water of a power plant. Cooling seawater after absorbing the heat of dead steam from the condenser enters air-seawater heat and mass transfer equipment, the heat of the cooling seawater is transferred to air, water vapor on the surface of the cooling water is subjected to mass transfer under the action of pressure difference to enter the air, then the water vapor in the air is recovered in a water vapor recovery device, and high-quality fresh water is obtained while low-grade waste heat of the cooling water is utilized. The invention combines the waste heat utilization of the seawater cooling water discarded by the power plant with the fresh water preparation, and can provide low-cost desalted water for the power plant or users.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

a waste heat utilization system of power plant seawater direct current cooling water comprises: the heat and mass transfer device is characterized in that a water vapor recovery device is arranged at the top of the heat and mass transfer device, a spraying device is arranged below the water vapor recovery device, and the water vapor recovery device is also connected with a liquid collecting device.

The invention aims to utilize the principle of air humidification and dehumidification heat and mass transfer, does not need to be driven by a high-grade heat source, realizes the low-grade waste heat utilization of the seawater and simultaneously recovers fresh water resources. The technology is characterized in that an air-seawater heat and mass transfer device is additionally arranged in a direct-current cooling water supply system, seawater absorbing the heat of exhaust steam is subjected to heat and mass transfer with air in the device, the heat in the seawater and water vapor partially vaporized on the surface are transferred to the air under the action of water vapor pressure difference and temperature difference, and then the water transferred to the air is recovered in a water vapor recovery device to recover fresh water. In the process, the water temperature can be cooled to be lower than the air temperature, and the limit cooling temperature is the air wet bulb temperature. Therefore, the evaporation mode based on the air humidification heat and mass transfer principle can effectively utilize low-grade heat, can recover fresh water, and has simple and reliable system and low operation cost. In practical application, the temperature of the final cooling water is generally 2-3 ℃ higher than the wet bulb temperature of air. Taking a 1000MW unit as an example, the amount of cooling seawater is about 80000t/h, air-seawater heat and mass transfer equipment is set, and about 800-1200 t/h of cooling water is evaporated into air. The heat required by water evaporation in the process is actually from the heated cooling water, and the steam pressure difference between the surface of the cooling seawater and the steam in the air is fully utilized to transfer the steam to the air, so that the low-grade waste heat of the cooling seawater which is extremely difficult to utilize is utilized, the environmental heat pollution is avoided, and the steam in the air is recycled to obtain the fresh water with higher quality.

In some embodiments, the spray device is connected to the condenser cooling water outlet. The seawater absorbing the heat of the dead steam is subjected to humidifying heat mass transfer with the air below through spraying; meanwhile, the cold air below moves upwards after being heated, and the external air is naturally supplemented, so that the natural circulation of the humidifying heat mass transfer is realized, and the energy consumption and the operation cost are low.

In some embodiments, a booster pump is arranged between the spraying device and the cooling water outlet of the condenser, the booster pump is used for lifting the seawater absorbing the heat of the exhaust steam to a certain height, and then the spraying device is used for enabling the seawater and the air to carry out humidification heat mass transfer.

The collection method of the water vapor is not particularly limited in the application, and in some embodiments, the recovery method of the water vapor collection device is condensation cooling, a moisture absorption solution, an adsorption material or a membrane method, wherein the condensation cooling method can recycle the fresh water or the salt-free circulating water collected before the condensation cooling method, and compared with the seawater desalination method adopting the membrane method, the cost is greatly reduced.

In some embodiments, the ventilation mode of the heat and mass transfer equipment is natural ventilation, and the characteristics of temperature difference and humidity difference between seawater absorbing heat of exhaust steam and air and flowing of air from cold to hot are fully utilized, so that the low-grade waste heat of seawater can be effectively utilized without forced ventilation, the construction and operation cost is low, the requirement of industrial popularization is met, the problem of waste heat recovery of the existing power plant seawater direct-current cooling water is solved, and energy waste and environmental heat pollution caused by direct discharge of the power plant seawater direct-current cooling water are avoided.

The heat and mass transfer equipment in the application can adopt the existing industrial heat and mass transfer equipment, and the specific device can be determined according to field conditions.

The method is not limited to processing the seawater direct-current cooling water of the power plant, and in some embodiments, the cooling water is concentrated brine or industrial wastewater so as to solve the problem of low-grade waste heat recovery of the existing industrial water in a wider range.

In some embodiments, the liquid collection device is a fresh water tank that collects fresh water for later use.

In some embodiments, a cooling water outlet at the bottom of the heat and mass transfer equipment is connected with the sea, the temperature of the seawater transferred by the humidifying heat and mass transfer equipment is only 2-3 ℃ different from that of natural seawater, and the heat pollution to the marine environment is basically avoided.

The invention also provides a waste heat utilization process of the seawater direct-current cooling water of the power plant, which comprises the following steps:

cooling water from the condenser is atomized into small liquid drops by a spraying device and enters heat and mass transfer equipment, the small liquid drops directly contact with air in the heat and mass transfer equipment to transfer heat and mass, the air absorbing water vapor passes through a water vapor recovery device, and fresh water is collected and then enters a fresh water tank to be stored for later use; the seawater cooled by the heat and mass transfer equipment is discharged into the sea.

The invention also provides a cooling water system of a power plant, which comprises: any one of the above power plant seawater direct current cooling water waste heat utilization systems.

The invention has the beneficial effects that:

(1) the waste heat of the seawater direct-flow cooling water of the power plant is utilized, so that the local ecological deterioration caused by directly discharging a large amount of heat to a sea area is avoided;

(2) the water quality is good after the water vapor evaporated from the seawater by utilizing the waste heat is condensed, and a simple, reliable and low-cost seawater desalination technology is provided;

(3) the method can utilize the low-grade waste heat, and provides a new idea for utilizing the low-grade waste heat.

(4) The device of the application has the advantages of simple structure, low operation cost and strong practicability.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.

FIG. 1 is a prior art direct (open) water supply system;

fig. 2 shows a process and a method for utilizing the residual heat of the seawater dc cooling water of the power plant in embodiment 1.

In the figure: 1-a booster pump, 2-a spraying system, 3-air-seawater heat and mass transfer equipment, 4-a water vapor recovery device and 5-a fresh water tank.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As introduced in the background art, the method aims at the problems that the seawater direct-current cooling water of the existing power plant is directly discharged back to the sea, and a large amount of waste heat causes energy waste and environmental heat pollution. Therefore, the invention provides a waste heat utilization process and a waste heat utilization method for seawater direct-current cooling water of a power plant, which comprise a booster pump, a spraying system, air-seawater heat and mass transfer equipment, a water vapor collecting device, a fresh water tank and the like. The inlet of the booster pump is connected with the cooling water outlet of the condenser, the outlet of the booster pump is connected with the spraying system, seawater absorbing heat of exhaust steam is atomized into small droplets by the spraying system and enters air-seawater heat and mass transfer equipment, air in the equipment naturally rises under the driving of density difference and directly contacts with the atomized seawater to transfer heat and mass, the air absorbing water vapor passes through the water vapor recovery device, and fresh water enters the fresh water tank for storage and standby after being collected; the seawater cooled by the air-seawater heat and mass transfer equipment is discharged into the sea.

The process and the method for utilizing the waste heat of the seawater direct-flow cooling water of the power plant comprise the following specific steps:

(1) absorbing seawater of exhaust steam of a steam turbine, raising the temperature to about 8-12 ℃, spraying the seawater into air-seawater heat and mass transfer equipment through a spraying system, and carrying out heat and mass transfer on the seawater and naturally rising air under the driving of temperature difference and steam pressure difference, wherein the final temperature of the seawater is reduced to be 2-4 ℃ higher than the temperature of a local air wet bulb;

(2) after the air absorbed with the water vapor passes through the water vapor recovery device, the fresh water is collected into a fresh water tank, and the water vapor recovery mode can be condensation (water spraying) cooling, moisture absorption solution, adsorption material, membrane method and the like;

(3) the seawater cooled by the air-seawater heat and mass transfer equipment is discharged into the sea again.

Further, the seawater in the step (1) and the step (3) can be replaced by strong brine, industrial wastewater and the like;

further, the heat and mass transfer equipment in the step (1) is natural ventilation, and the structural form can be determined according to field conditions;

furthermore, the water vapor recovery device in the step (2) has various forms, and is not limited to condensation (water spraying) cooling, moisture absorption solution, adsorption material and membrane method, but also comprises other feasible schemes.

The present invention is described in further detail below with reference to specific examples, which are intended to be illustrative of the invention and not limiting.

Example 1:

as shown in fig. 1, the present invention is further explained by taking an example of the operation of a 1000MW thermal power generating unit.

The temperature of fresh seawater at about 80000t/h is raised by about 8-12 ℃ after entering a condenser to absorb the heat of exhaust steam, the fresh seawater enters a spraying system 2 through a booster pump 1, the fresh seawater is atomized into liquid drops and enters an air-seawater heat and mass transfer device 3, the temperature of the seawater in an evaporation tower 3 is reduced by about 5-10 ℃, meanwhile, the seawater at about 800-1200 t/h is evaporated and mass transferred into air, the seawater is recovered and stored in a fresh water tank 5 through a recovery device 4, and the rest of the seawater is returned to the sea (the final temperature of the seawater is reduced to be 2-4 ℃ higher than the.

Example 2:

a waste heat utilization system of power plant seawater direct current cooling water comprises: the heat and mass transfer device comprises a heat and mass transfer device 3, wherein a water vapor recovery device 4 is arranged at the top of the heat and mass transfer device 3, a spraying device 2 is arranged below the water vapor recovery device 4, and the water vapor recovery device 4 is also connected with a liquid collecting device 5.

Example 3:

And the spraying device 2 is connected with a cooling water outlet of the condenser. The seawater absorbing the heat of the dead steam is subjected to humidifying heat mass transfer with the air below through spraying; meanwhile, the cold air below moves upwards after being heated, and the external air is naturally supplemented, so that the natural circulation of the humidifying heat mass transfer is realized, and the energy consumption and the operation cost are low.

Example 4:

A booster pump 1 is arranged between the spraying device 2 and a cooling water outlet of the condenser, seawater absorbing heat of exhaust steam is lifted to a certain height by the booster pump 1, and then the seawater and air are subjected to heat and humidity transfer through the spraying device 2.

Example 5:

The recovery mode of the water vapor collecting device 4 is condensation cooling, moisture absorption solution, adsorption material or membrane method, wherein the condensation cooling method can circularly adopt the previously collected fresh water or salt-free circulating water, and compared with the seawater desalination method adopting the membrane method, the cost is greatly reduced.

Example 6:

The ventilation mode of the heat and mass transfer equipment 3 is natural ventilation, and the characteristics of temperature difference and humidity difference between seawater absorbing exhaust steam heat and air and flowing of air from cold to hot are fully utilized, so that the effective utilization of low-grade seawater waste heat can be effectively carried out without forced ventilation, the construction and operation cost is low, the requirement of industrial popularization is met, the problem of waste heat recovery of the existing power plant seawater direct-flow cooling water is solved, and energy waste and environmental heat pollution caused by direct discharge of the power plant seawater direct-flow cooling water are avoided.

The heat and mass transfer device 3 is an evaporation tower in the application.

Example 7:

The cooling water is strong brine or industrial wastewater, so that the problem of low-grade waste heat recovery of the existing industrial water is solved in a wider range.

Example 8:

The liquid collecting device 5 is a fresh water tank and collects fresh water for later use.

Example 9:

The cooling water outlet at the bottom of the heat and mass transfer equipment 3 is connected with the sea, the temperature of the seawater subjected to humidifying heat and mass transfer is only 2-3 ℃ different from that of natural seawater, and the heat pollution to the marine environment is basically avoided.

Example 10:

a waste heat utilization process of seawater direct-flow cooling water of a power plant comprises the following steps:

Example 11:

a power plant cooling water system comprising: the system for utilizing waste heat of the power plant seawater dc cooling water according to any one of embodiments 1 to 9.

It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications and equivalents can be made in the technical solutions described in the foregoing embodiments, or equivalents thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims

1. The utility model provides a waste heat utilization system of power plant's sea water direct current cooling water which characterized in that includes: the top of the heat and mass transfer equipment is provided with a water vapor recovery device, a spraying device is arranged below the water vapor recovery device, and the water vapor recovery device is also connected with a liquid collecting device; the heat and mass transfer equipment is an evaporation tower;

the ventilation mode of the heat and mass transfer equipment is natural ventilation;

the spraying device is connected with a cooling water outlet of the condenser;

a cooling water outlet at the bottom of the heat and mass transfer equipment is connected with the sea;

cooling water from the condenser is atomized into small liquid drops by the spraying device and enters the heat and mass transfer equipment to directly contact with air in the heat and mass transfer equipment for heat and mass transfer, and the air absorbing water vapor passes through the water vapor recovery device.

2. The system for utilizing the residual heat of the seawater once-through cooling water in the power plant according to claim 1, wherein a booster pump is arranged between the spraying device and the cooling water outlet of the condenser.

3. The system for utilizing the residual heat of the seawater direct-flow cooling water in the power plant according to claim 1, wherein the recovery mode of the water vapor collecting device is condensation cooling, a moisture absorption solution, an adsorption material or a membrane method.

4. The system for utilizing the residual heat of the seawater dc cooling water in the power plant according to claim 1, wherein the cooling water is concentrated brine or industrial wastewater.

5. The system for utilizing the residual heat of the seawater dc cooling water in the power plant as claimed in claim 1, wherein the liquid collecting device is a fresh water tank.

6. A process for utilizing the residual heat of seawater once-through cooling water of a power plant, which is carried out in the system of any one of claims 1 to 5, is characterized by comprising the following steps:

7. A power plant cooling water system, comprising: the system for utilizing the residual heat of the seawater once-through cooling water of the power plant as claimed in any one of claims 1 to 5.