JPH0564703A - Condenser - Google Patents

Abstract

PURPOSE:To provide a condenser which can condense steam at high heat exchanging efficiency even if the temperature difference is small and is especially useful for the installation for manufacture of pure water from warm discharged water of a thermal or a nuclear power plant by distillation. CONSTITUTION:Warm discharged water from a condenser 2 of a power plant is evaporated in a pressure decreased chamber 5 and the steam from which water drops are removed in a water drop removing chamber 6 wherein hydrophobic porous membrane is used, is condensed by a condenser 8 to obtain pure water. The condenser 8 contains a bundle of hollow yarns having no pore and made to be hydrophilic inside and made of an organic material (e.g. polysulfone) as a heat exchanger tube and the steam passing the insides of the hollow yarns is cooled by seawater flowing outside to be condensed. Consequently, since the surface area of the heat exchanger tube per unit volume is able to be made large and the heat exchanger tube is able to be made thin, a condenser having high heat exchanging efficiency and compact size and high efficiency is obtained. As a result, it is suitable as a condenser for a pure water manufacturing installation which can work with small temperature difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condenser for condensing steam into a liquid, for example, by using thermal energy contained in warm waste water generated in a nuclear power plant or a thermal power plant to generate warm waste water. The present invention relates to a condenser preferably used for steam condensation in a pure water production facility that produces pure water by distillation.

[0002]

2. Description of the Related Art At a nuclear power plant, one nuclear reactor has one
Pure water of about 000 ton / day is used. When a river exists near the power plant, the river is purified to produce pure water, but when a large amount of fresh water cannot be obtained nearby, seawater is desalinated. The methods mainly used for the desalination method include a distillation method, a multistage flash distillation method, an ion exchange membrane method, and a reverse osmosis membrane method.

In the distillation method, seawater is heated to change its phase into steam, and the steam is condensed in a condenser to be desalinated. Since the evaporation temperature of salts contained in seawater is higher than the evaporation temperature of water, the concentration of salts contained in water vapor can be reduced to about 1 / 10,000 of the concentration of seawater. Therefore, when this steam is condensed, the salt concentration is low. Fresh water is obtained.

The multi-stage flash distillation method, which is a kind of distillation method, focuses on the fact that the temperature of the cooling water used for the condensation of steam rises in the process of condensing the steam, and the seawater used as this cooling water is heated to the boiling pressure. A part of the cooling water is evaporated by lowering it below, and further, the cooling water used for condensing the generated steam is reduced in pressure and evaporated. In this way, evaporation is carried out in multiple stages, and the steam generated in each stage is collected and finally condensed in the condenser to become fresh water. This multi-stage flash distillation method can significantly reduce the thermal energy required to obtain the same amount of fresh water, as compared with a system in which the entire amount is evaporated in one stage.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The distillation method or the multi-stage flash distillation method has the following problems. That is, the area of the heat transfer tube required for the condenser for condensing the steam increases in inverse proportion to the temperature difference between the cooling water and the steam. Since the temperature difference between the seawater used as the coolant and the steam is low, the size of the condenser becomes enormous, which increases the manufacturing cost of pure water.

Therefore, a broad object of the present invention is to provide a condenser having far superior heat transfer efficiency as compared with a conventional condenser of the same size, and a more specific object is to provide a condenser. By using this condenser as a condenser of a pure water production facility by a distillation method, it is possible to reduce the pure water production cost.

[0007]

[Means for Solving the Problems] To achieve the above object,
The present invention provides a condenser as claimed in each of the claims.

[0008]

In general, in the condensation heat transfer in the condenser having the heat transfer tube, the heat transfer rate between the steam and the heat transfer tube is high, so that the heat transfer is rate-controlled by the heat transfer of the heat transfer tube. Conventionally, the heat transfer tube is made of metal, and when cooling with seawater, from the viewpoint of corrosion resistance,
In many cases, stainless steel, which has poor thermal conductivity, is used as the metal. In the case of a metal heat transfer tube, the wall thickness of the heat transfer tube is as thick as at least several mm from the viewpoint of workability, so that the shape of the heat exchanger of the entire condenser becomes large. On the other hand, when an organic non-porous hollow fiber is used for the heat transfer tube as in the present invention, the wall thickness of the heat transfer tube can be reduced to about 0.1 mm because the workability is good, and the heat transfer tube is Since the outer diameter can be 1 mm or less, the heat transfer surface area can be increased in the same volume. When the hollow fiber is used as the heat transfer tube of the condenser as described above, the heat transfer area per unit volume is increased, and the wall thickness of the heat transfer tube can be reduced, and the heat flux per heat transfer surface area is reduced. Due to its large size, the heat exchanger of the condenser can be significantly downsized.

[0009]

EXAMPLE An example in which the present invention is applied to an apparatus for producing pure water by utilizing thermal energy of hot waste water generated from a nuclear power plant or a thermal power plant will be described below with reference to FIG. The high-temperature steam generated in the reactor or the boiler rotates the turbine 1 to generate electricity, and then is condensed by the condenser 2 to return to water. As cooling water used for the condenser 2, seawater is used at a power station located on the coast. Pure water is produced by using the thermal energy of the seawater (heated wastewater) that has been used for cooling in this condenser and whose temperature has risen.

First, a part of the warm waste water is branched by the pump 3, dispersed into fine water droplets by the nozzle 4 and injected into the decompression chamber 5, and the atmospheric pressure is adjusted so that the boiling point becomes equal to or lower than the temperature of the warm waste water. Lower. Since the speed of heat conduction is inversely proportional to the square of the spherical diameter, by making fine water droplets, the water droplets fall to the center at a temperature corresponding to the saturation pressure of the atmosphere. Thermal energy corresponding to this temperature decrease amount is released, and a part of the water droplets evaporates to become water vapor. When water droplets collide with each other, their spheres become larger in size, but the smaller the sphere diameter of the water droplets, the better the heat transfer effect. Therefore, the nozzles 4 provided in the upper part of the decompression chamber 5 are arranged in a triangular lattice pattern so that the mutual distances are the same.

When the difference between the temperature of the hot waste water and the boiling temperature is 2 ° C., 0.37% of the water droplets flowing out from the nozzle 4 undergoes a phase change to steam. Now, when the required amount of pure water is 1000 tons / day and this is generated by the operation for 20 hours, the amount of water to be dropletized in the decompression chamber 5 is about 14000 tons per hour. When the inner diameter of the nozzle 4 is 2 mm and the discharge pressure is 2 MPa, the outflow rate is about 0.5 ton / h according to the experimental result, and the number of nozzles 4 required is 28,000.
When these are arranged in a triangular lattice pattern at 100 mm intervals, the decompression chamber 5 has a size of about 16 m square and a height of about 3 m. Since the decompression chamber 5 becomes a large negative pressure container in this manner, a beam is provided inside to withstand external pressure. Instead of using beams
It is also possible to partition into multiple decompression chambers.

The steam generated in the decompression chamber 5 is discharged to the water drop removing chamber 6, and the remaining water drops are accumulated in the lower portion of the decompression chamber 5 and discharged to the ocean via the U seal 7. By providing the check valve 7'in the middle of the U-seal 7, it is possible to prevent the pressure inside the decompression chamber 5 from fluctuating because the liquid level of the decompression chamber 5 changes periodically due to the fluctuation of the outflow amount. The steam generated in the decompression chamber 5 is discharged to the water droplet removal chamber 6 from the outlet at the upper part of the decompression chamber 5. The outlet is provided at the upper part in order to reduce the amount of water droplets contained in the steam as much as possible.

The water drop removing chamber 6 is a membrane having hydrophobic fine pores (hydrophobic porous membrane) such as polysulfone, polytetrafluoroethylene (PTFE), polyethylene, polyimide, polyacrylonitrile having the property of repelling water. Is used to remove water droplets from steam. That is, when the hydrophobic porous membrane is contacted with a vapor stream containing water droplets, the vapor permeates the membrane, but the water droplets having a spherical diameter larger than the pore diameter do not permeate the membrane. Generally, in a steam flow, small water droplets collide and coalesce into each other, and the sphere diameter gradually increases. Therefore, there are almost no water droplets having a sphere diameter of 1 μm or less. Therefore, the porosity is 1
By using a film having a thickness of less than μm, it is possible to remove water droplets, and the treatment liquid obtained by condensing the vapor that has permeated the film can be used as it is in the power plant as pure water.

Regarding the flow rate of vapor permeating through the hydrophobic porous membrane, the result of an experiment in which the pressure difference before and after the membrane was 10 kPa is shown in FIG.
Shown in. It has been found that the vapor flow rate is inversely proportional to the square of the membrane pore size (membrane pore size). Further, it was found that the steam flow rate was proportional to the pressure difference across the membrane when the experiment was conducted with the membrane having the same pore size. The qualitative relationship of these influencing factors to the steam flow rate is the same as that of the viscous flow through the circular pipe. The cause is
This is because the area of the pore wall is large because the pore diameter is small, and the viscous friction between the pore wall and the vapor flow is a controlling factor that influences the flow rate. Therefore, the influence of the membrane material on the vapor flow rate is not so large. Now, using a hydrophobic porous membrane having a pore size of 1 μm that can remove most of the water droplets, the pressure difference across the membrane is smaller by one digit than the experiment in FIG.
With kPa, the amount of vapor permeation is about 0.02 per hour.
It becomes ton. The required amount of pure water generated is 50to / hour
Since n (corresponding to 1000 ton / day), the required film area is 2500 m ² .

In order to obtain such a large film area, the structure of the film provided in the water drop removing chamber 6 is the laminated film element structure shown in FIGS. 3 and 4, whereby the water drop removing chamber 6 is downsized. In this laminated membrane element, a spacer 12 is inserted into a hollow disc 13 made of a PTFE membrane, and a large number of the discs 13 are stacked so as to communicate with a circular pipe 14 at the center.
It is connected to the body and one end is connected to the outlet hole 16 of the end plate 15. When the steam flows into the water droplet removal chamber 6, it flows from the outside of the laminated membrane element into the gap between the disks 13, and further permeates from the outside of the film of the disk 13 to the inside, passes through the spacer 12 portion, and the central circular tube 14 Flow out through the outlet hole 16 of the end plate 15. Since the disk 13 of the element is provided vertically, the water droplets removed on the film surface are repelled by the hydrophobic property of the film, and are collected in the lower part of the water droplet removal chamber 6 by gravity. In the water drop removing chamber 6, steam is injected from above,
By making the flow as downward as possible, the movement of the liquid film flowing down the film surface is accelerated. By adopting such a laminated film element, it is possible to absorb a film having an area of 50 m ² per 1 m ^{3 of} the water drop removing chamber, so that the water drop removing chamber 6 is 8 m long.
The size of the corner is enough.

The water drops separated in the water drop removing chamber 6 are returned to the original decompression chamber 5 through the U seal 6 '. Further, the vapor is transferred to the condenser 8. In the present embodiment, the laminated membrane element is used to reduce the size of the water droplet removal chamber 6, but a spiral type or a hollow fiber membrane may be used instead. After the laminated element is washed with chemicals at regular intervals,
Dry with dry air.

The condenser 8 is provided with a hollow fiber module 9 composed of a large number of nonporous hollow fibers made of an organic material. This non-porous hollow fiber is made of a material such as polysulfone, polytetrafluoroethylene (PTFE), polyethylene, polyimide, polyacrylonitrile, or the like. The inner surface of each hollow fiber is preferably hydrophilic. For example, among the above materials, hollow fibers excluding PTFE may be hydrophilized (PTFE is extremely hydrophobic and is not suitable for hydrophilization.) In this example, each hollow fiber is external. Diameter is 3m
m, the inner diameter is 2 mm, and it is made of hydrophilic polysulfone without pores. A module 9 in which a large number of the hollow fibers are bundled with a gap provided therebetween is fixed to the condenser 8 by flanges at the top and bottom. The seawater that cools the outside of the hollow fiber passes through the condenser 8 after removing solids with a stainless mesh filter. The steam flows into each hollow fiber from above, is cooled by seawater using the hollow fiber as a heat transfer tube, and the condensed water forms a liquid film on the inner surface of the hollow fiber. This condensed water flows down the hollow fiber membrane surface and accumulates in the lower part of the condenser due to gravity and the viscous force of the vapor flow descending inside the hollow fiber. Since the wall thickness of the hollow fiber that serves as the heat transfer tube is thin, the condensation heat transfer coefficient between the heat transfer tube and the steam on the inner surface side becomes large, and the laminar flow heat transfer between the outer surface of the hollow fiber and seawater is the rate-determining process of transfer. Seawater is injected into the condenser 8 from the lower part, and overflowed to flow out from the upper part.
This promotes heat transfer due to the natural convection effect on the seawater side, and improves the heat transfer efficiency by keeping the temperature difference in the flow direction of the hollow fiber constant by making the lower part of the hollow fiber the lowest temperature. Try. The lower part of the condenser 8 is the vacuum pump 1
Connect to 0. This vacuum pump reduces the pressure of the entire system including the decompression chamber 5, the water droplet removal chamber 6 and the condensation chamber 8. When the hot waste water is depressurized in the decompression chamber 5, the air dissolved in the seawater is mixed with the steam to raise the pressure of the entire system. However, by exhausting this air with the vacuum pump 10, the pressure in the system is increased. Keep constant. By connecting the vacuum pump 10 to the lower portion of the condenser 8, the lower portion of the condenser 8 can have a lower pressure. Therefore, even if the entire cross section of the hollow fiber inside the condenser 8 is filled with the condensed water, the condensed water can be discharged from the hollow fiber due to this pressure difference. Condensed water that has flowed down to the bottom of the condenser 8 is pure water and is transferred to the storage tank by the pump 11.

The life of the condenser 8 is governed by deterioration caused by the action of microorganisms contained in seawater. Therefore, the chlorine gas is blown in so that the seawater inlet is closed and the chlorine concentration of the seawater in the condenser 8 becomes 2 ppm while the operation is stopped during one day. By the bactericidal action of this chlorine,
The growth of microorganisms on the film surface can be suppressed. In this embodiment, the use of a small condenser makes it possible to produce pure water from warm waste water, and it is possible to effectively use the thermal energy released to the ocean.

[0019]

Since the condenser of the present invention uses the non-porous organic material hollow fiber as the heat transfer tube as the heat transfer tube, the heat transfer tube can be made thin and the heat transfer surface area per unit volume can be reduced. Since it can be made large, the heat transfer efficiency is very good. This condenser is
By using it as a steam condenser of a pure water production facility by a distillation method from hot wastewater of a power plant with a low temperature difference from seawater, the cost of the facility can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a facility for producing pure water from hot waste water using a condenser of the present invention.

FIG. 2 is a diagram showing experimental results of vapor flow rate of a hydrophobic porous membrane.

FIG. 3 is a perspective view of a laminated element.

FIG. 4 is a cross-sectional view of a laminated element.

[Explanation of symbols]

1 ... Turbine 2 ... Condenser 5 ... Decompression chamber 6 ... Water droplet removal chamber 8 ... Condenser 9 ... Hollow fiber module

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyomi Funabashi 1168 Moriyama-cho, Hitachi, Hitachi Ibaraki Energy Research Institute

Claims (3)

[Claims] 1. A multiplicity of organic nonporous hollow fibers, which are arranged with a gap between each other, are provided, and each hollow fiber serves as a heat transfer tube, and steam is passed to one side thereof through the heat transfer tube. A condenser characterized in that the cooling liquid is caused to flow to the other side. 2. The inner surface of each hollow fiber is hydrophilized,
The condenser according to claim 1, wherein steam is caused to flow inside each hollow fiber and a cooling liquid is caused to flow outside each hollow fiber. 3. The condenser according to claim 1, wherein the vapor is steam after removing water droplets in a pure water production facility by a distillation method or a multistage distillation method.