JPS6118490A - Method and device for distillation of salt water basing on coolant vapor compression system - Google Patents

Abstract

PURPOSE:To improve heat efficiency of salt water evaporating process by using salt water distillation process basing on a coolant vapor compression system including thin film evaporation stage for the evaporation of salt water, and providing also a coolant evaporator, coolant compressore, and a coolant condenser. CONSTITUTION:Dusts and suspended matters, etc. are removed by passing sea water through a strainer 24, and the sea water is passed through a preheater 22, and then sprayed from a spraying device 11 on the uppermost stage tube bundle 10 of a coolant condenser 4 in a vessel 9 under reduced pressure. The sea water is then evaporated by exchanging heat with coolant gas at high temp. in the tubes, and generated steam enters a coolant evaporator 7 after passing through a passage 25, where it is condensed by exchanging heat with cold coolant in the pipes. The condensed water accumulates in a tray 20 and discharged to the outside with a pump 26 through a pipe 27. Concentrated sea water passes through a brine pump 28 and a preheater 22, exchanges heat with feed sea water, then discharged from a pipe 29. The coolant is circulated through a heat pump circuit.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a method for desalinating salt water, in which water vapor evaporated from salt water is manually compressed to raise its temperature, and this is used as heat of evaporation of salt water. The present invention relates to a vapor compression salt water distillation method and apparatus using a heat pump using a refrigerant in the evaporative compression method for condensing heated steam.

(Prior Art) In the desalination of salt water, it is preferable to evaporate it at as low a temperature as possible in order to prevent scale from adhering to heat transfer tubes. Therefore, even in the case of pneumatic compression, atmospheric pressure type high temperature type and vacuum type low temperature type are used.However, the specific volume of water vapor is 1.67rrf at 100℃.
/kg, compared to 19.5n at 40℃? /kg
As the temperature decreases, the specific volume of water vapor increases, so the compressor used becomes larger, which is impractical.

On the other hand, if we exchange heat between water vapor and refrigerant vapor and compress the refrigerant, a small compressor will be sufficient, but the latent heat of vaporization of water is approximately 550 Kcal/kg, and the latent heat of refrigerant is R-113.
In this case, the amount of refrigerant is about 35 KCal/kg, which is more than 10 times as much refrigerant as in the case of steam, but the volume is only 1.3 rri, and the 19.5 n? This will be reduced to 1/15 compared to .

The prior art of a salt water desalination evaporator that compresses refrigerant vapor using a heat pump circuit is shown in Japanese Patent Publication No. 56-6348 and Japanese Utility Model Publication No. 57-8955. Since the saline coil is configured to maintain the brine level at a desired height, this liquid depth manifests itself as an increase in the boiling point and the brine is less likely to evaporate. Therefore, the refrigerant temperature must be increased, that is, the compression ratio of the refrigerant compressor must be increased, and therefore, for example, a piston-type high-pressure compressor must be used. This compressor has the problem that it is difficult to increase the amount of compression, and it is also inefficient.

In the latter prior art disclosed in Utility Model Publication No. 57-8955, as a means to prevent scale precipitation, seawater is not directly heated with a high-pressure, high-temperature liquefied refrigerant, but water, etc. is first heated, and then this heated water and seawater are combined. Since heat exchange is performed, that is, a two-stage heat exchange is performed, the temperature difference between the evaporation and condensation of the refrigerant is naturally large, and a compressor with a high compression ratio is required. If the temperature difference between evaporation and condensation is large, the coefficient of performance of the compressor will deteriorate, leading to a problem of lowering the thermal efficiency of the distillation apparatus.

(Problems to be Solved by the Invention) Therefore, the present invention circulates a refrigerant such as R-113, which has a low vapor pressure and a high specific gravity, through the heat pump circuit.
In addition to preventing scale build-up, the compressor has been made smaller, and if the pressure is low, the deeper the liquid is, the more difficult it is to evaporate, so the refrigerant is kept at a shallow depth for evaporation, and the temperature difference is further reduced. In addition, the evaporation of salt water is done by thin film evaporation, which is difficult to evaporate due to the depth of salt water (at low temperatures, water vapor pressure is small, so this effect is large), and by increasing the coefficient of performance of the compressor and improving thermal efficiency. , aims to eliminate the above-mentioned conventional problems.

(Means for Solving the Problems) Therefore, the present invention utilizes the heat of refrigerant condensation and the heat of refrigerant evaporation of a heat pump circuit in which refrigerant circulates to evaporate salt water and condense generated steam, respectively, and evaporate the refrigerant into liquid. A refrigerant vapor compression brine distillation method characterized by keeping the depth shallow and evaporating brine using thin film evaporation, and a refrigerant evaporator having a horizontal heat transfer tube bundle, a refrigerant compressor, a refrigerant condenser, and an expansion valve. A heat pump circuit is formed in which the refrigerant circulates by connecting through a pipe, and the refrigerant evaporator has means for keeping the liquid depth of the refrigerant shallow;
The refrigerant condenser is equipped with a salt water thin film evaporation means, and the condensation side of the refrigerant evaporator and the evaporation side of the refrigerant condenser are connected through a steam passage to form a refrigerant vapor compression type salt water distillation device, and the liquid depth of the refrigerant is kept shallow. The means is to divide the horizontal heat transfer tube bundle of the refrigerant evaporator and place it above and below, provide weirs on the inlet and outlet sides of the divided tube bundle to maintain the refrigerant liquid level at the required level, and thin film evaporation of salt water. The means is arranged such that refrigerant vapor flows in series through a plurality of horizontal heat transfer tube bundles of a refrigerant condenser, and a salt water dispersion device is placed above the horizontal heat transfer tube bundles to evaporate non-condensable gas from the final tube bundle of the refrigerant condenser. This invention provides a refrigerant vapor compression type salt water distillation apparatus characterized in that an air vent pipe leading to a vessel tube bundle is provided, R-113 low-pressure refrigerant is used as the refrigerant, and a centrifugal blower type compressor is used as the refrigerant compressor. .

(Function) That is, the present invention is configured as described above, and thus,
Refrigerant circulates in the heat pump circuit, and the refrigerant, whose temperature has risen after being compressed by a centrifugal blower compressor, is led to the condensation side inside the pipe of the refrigerant condenser, where it condenses by exchanging heat with the salt water sprayed on the evaporation side of the outside of the pipe, and then The pressure is reduced through an expansion valve, the temperature is reduced, and the temperature is reduced to a low temperature, which is then led to the refrigerant evaporator's pipe Naito output side, where it evaporates into a thin film in the refrigerant condenser, and heat exchanges with the water vapor introduced into the condensation side of the refrigerant evaporator's pipe outer surface, resulting in water vapor. while the refrigerant evaporates,
The generated refrigerant vapor is sucked back into the centrifugal blower compressor.

In this heat pump circuit, in the refrigerant condenser, salt water is sprayed on the outer surface of the horizontal heat transfer tube from an upper spraying device, causing thin film evaporation, and the generated water vapor condenses on the condensation side of the tube outer surface of the refrigerant evaporator, collects in a saucer, and is taken out. be done.

The tube bundle of the refrigerant condenser is configured so that the refrigerant vapor flows in series in multiple directions, and in this embodiment, the refrigerant liquid condensed in the tubes of the first bent flow is acted upon without being blown away by the refrigerant gas flow rate, thereby thinning the liquid film. The aim is to improve heat transfer performance. Note that if only thin film evaporation is considered, a vertical heat exchanger tube bundle can also be used.

Furthermore, if a low-pressure refrigerant is used in the heat pump circuit, it will operate at below atmospheric pressure, so there is a risk of air leaking from pipe joints and other places. The partial pressure is large and has a significant effect on deteriorating heat transfer performance. Therefore, the refrigerant condenser has a structure that increases the flow velocity in the pipe to reduce air stagnation on the condensing surface and reduce its influence.

At the final turn of the refrigerant condensing tube bundle, non-condensable gas such as air accumulates, so an air vent tube is provided to release air etc. into the tubes of the refrigerant evaporator. Promote further.

When the air content in the heat pump circuit increases in this way, it is sucked in with a separate vacuum pump and the refrigerant is replaced.

The refrigerant evaporator is provided with means for reducing the depth of the refrigerant to activate the evaporation of the refrigerant. That is, in a conventional heat exchanger structure in which a horizontal heat exchanger tube bundle is provided between headers on the inlet side and the outlet side, the liquid depth becomes large and evaporation becomes difficult to occur. In the present invention, the tube bundle is divided into upper and lower sections to form multiple stages, and in order to evaporate the refrigerant on the inner surface of the heat transfer tube, it must be filled with liquid, so a weir is provided at the entrance and exit of each tube bundle, and a weir is provided at the entrance and exit of each tube bundle. Although the tube is filled with refrigerant liquid, there is no risk of the liquid becoming too deep since it is divided into a large number of tube bundles.

For example, if the low-pressure refrigerant R7,113 has a large liquid depth, evaporation will not occur if the liquid evaporates.If the liquid depth is 270°C in a container with a saturated pressure of 30°C, the liquid will evaporate unless there is a temperature difference of 35°C or more. depth 27
The influence of 0+n is about 40%.

(Example) An example of the present invention will be described below with reference to the accompanying drawings.

The heat pump circuit 1 circulates a low-pressure refrigerant such as R-113, and is composed of a compressor 2, a pipe 3, a refrigerant condenser 4, a pipe 5, an expansion valve 6, a refrigerant evaporator 7, and a pipe 8. The refrigerant condenser 4 and refrigerant evaporator 7 are housed in the same container 9.

The refrigerant condenser 4 uses a horizontal heat transfer tube bundle as a thin film evaporation means for raw salt water, for example, to form a two-fold flow. A seawater spraying device 11 is arranged above the uppermost tube bundle 10, and a header 13 on the outlet side of the lowermost tube bundle 12 is provided with a seawater spraying device 11. In addition to the pipe line 5, an air vent pipe 14 is open.

The refrigerant evaporator 7 uses, for example, 16 mφ pipes as a means to keep the liquid depth of the refrigerant shallow, and a horizontal pipe bundle divided into a plurality of pipe bundles is arranged between the inlet/outlet side header 15 and the folded side header 16, and the low-pressure refrigerant in the pipes is In order to maintain a shallow liquid depth and prevent evaporation, weirs 17 and 18 are provided on the inlet and outlet sides of each tube bundle to fill the tubes with refrigerant liquid, so that the liquid depth is approximately the same as the height of each tube bundle. , thus the liquid depth is shallow and evaporation is easy. The weirs on the inlet side described above, except for the weir at the top stage, have means for receiving refrigerant overflow from the weir above. Means for receiving this overflow is provided, for example, in the weir 17' of the lower tube bundle, which extends to both sides, and receives the refrigerant overflowing from above, so that all the outer tubes are filled with refrigerant liquid. Note that the means for accepting this overflow may be of other forms.

The uppermost tube bundle 19 is a part of the super heater, and if mist gets mixed into the refrigerant gas, the compressor 2 may be damaged. Therefore, only the refrigerant vapor that has completely gasified the mist is sent to the compressor 2. Make it absorb.

20 is a condensed water receiver, 21 is a pressure reducing valve provided in the air vent pipe 14 communicating with the refrigerant evaporator inlet side bottom, 22 is a preheater for supplied seawater using concentrated brine, and 23 is a vacuum device.

In the refrigerant vapor compression type salt water distillation apparatus configured as described above, the seawater passes through the strainer 24 to remove dust, suspended matter, etc. After passing through the preheater 22, the seawater is placed in the container 9 under reduced pressure, where the refrigerant is mixed with the spraying device 11. Top tube bundle 1o of condenser 4
The refrigerant gas exchanges heat with the high-temperature refrigerant gas inside the pipe and evaporates.
The generated water vapor enters the refrigerant evaporator 7 through the passage 25, condenses by exchanging heat with the cold refrigerant in the pipe, and the condensed water collects in the saucer 2o, and is taken out to the outside through the pipe 27 by the pump 26. The concentrated seawater passes through a brine pump 28 and a preheater 22, exchanges heat with raw seawater, and is then discharged from a pipe 29. Refrigerant circulates through the heat pump circuit.

(Effects of the invention) In the present invention, the refrigerant condenser and refrigerant evaporator of the heat pump circuit in which refrigerant circulates are used for evaporating salt water and condensing generated water vapor, and the refrigerant is evaporated by keeping the liquid depth shallow. Since the evaporation of is done by thin film evaporation, the temperature difference between evaporation and condensation is small, and the coefficient of performance of the compressor is improved. Furthermore, when a low pressure high density refrigerant such as R-113 is used, a centrifugal compressor can be used and high efficiency can be obtained.

In addition, heat transfer tube bundles for refrigerant condensation connect multiple tube bundles in series,
In addition, since the flow is multi-fold, the refrigerant in the tube becomes a high-speed flow, and the condensed refrigerant is blown away, reducing the thickness of the liquid film, which is an obstacle to heat transfer, and maintaining good heat transfer.

Furthermore, the air vent pipe that connects the final tube bundle of the refrigerant condenser and the refrigerant side of the refrigerant evaporator is designed so that the refrigerant repeatedly evaporates and condenses below atmospheric pressure. Even if air leaks from a flange joint, etc., this air will not evaporate. Since this air is sucked into the condenser side, this air does not remain in the condensing tube, and factors that inhibit heat transfer are eliminated, and in cooperation with the multi-fold flow configuration of the condensing tube bundle, heat transfer becomes even better.
Seawater can evaporate sufficiently even at low temperatures.

In addition, the refrigerant evaporator has a plurality of tube bundles arranged above and below, and a weir is provided at the inlet and outlet of the tube bundle, so the refrigerant liquid introduced fills the outer tube and the liquid depth is kept low to the height of the weir. The increase in boiling point due to liquid depth is virtually negligible, and even a slight temperature difference between evaporation and condensation can maintain vigorous evaporation of the refrigerant.

As described above, in the present invention, which utilizes a heat pump circuit that circulates a refrigerant for desalination of salt water by distillation, it becomes possible to use a compact and highly efficient compressor by taking advantage of the characteristics of the refrigerant, and also to reduce the temperature of evaporation and condensation. This has the effect of providing a brine distillation method and apparatus with overall high thermal efficiency, such as reducing the difference and making it possible to obtain a high coefficient of performance for the compressor.

[Brief explanation of drawings]

The figure is an explanatory cross-sectional view of one embodiment of the present invention. 1... Heat pump circuit, 2... Compressor, 4...
Refrigerant condenser, 6... Expansion valve, 7... Refrigerant evaporator, 9... Container, 10... Top stage tube bundle,
11...Seawater spraying device, 12...Lowermost pipe bundle,
14...Air vent pipe, 17.17', 18...
・Weir, 20... Condensed water receiver, 21... Pressure reducing valve,
22... Preheater, 23... Vacuum device,
24... Strainer.

Claims (11)

[Claims] (1) The heat of refrigerant condensation and the heat of refrigerant evaporation in the heat pump circuit in which the refrigerant circulates are used for the evaporation of salt water and the condensation of generated steam, respectively.The evaporation of the refrigerant is performed by keeping the liquid depth shallow, and the evaporation of salt water is performed using thin film evaporation. A refrigerant vapor compression brine distillation method characterized by: (2) a refrigerant evaporator and a refrigerant compressor having a horizontal heat transfer tube bundle;
A refrigerant condenser and an expansion valve are connected by a pipe line to form a heat pump circuit in which refrigerant circulates, the refrigerant evaporator has means for keeping the refrigerant liquid depth shallow, and the refrigerant condenser has means for thin film evaporation of salt water. A refrigerant vapor compression salt water distillation apparatus, characterized in that the condensing side of the refrigerant evaporator and the evaporating side of the refrigerant condenser are connected through a steam passage. (3) The means for keeping the liquid depth of the refrigerant shallow is a means in which horizontal heat transfer tube bundles are divided into upper and lower parts of the refrigerant evaporator, and weirs are provided at the inlet and outlet sides of the divided tube bundles. Range 2nd
Refrigerant vapor compression type brine distillation apparatus as described in 2. (4) The weir installed at the inlet of the horizontal heat transfer tube bundle of the refrigerant condenser is
4. A refrigerant vapor compression brine distillation apparatus according to claim 3, further comprising means for receiving overflow from upper weirs except for the uppermost weir. (5) The refrigerant vapor compression type salt water distillation method according to claim 1, wherein the thin film evaporation of the salt water is carried out by dispersing the salt water into the refrigerant condenser tube bundle. (6) The refrigerant vapor compression type salt water distillation apparatus according to claim 2, wherein the thin film evaporation means for salt water uses a horizontal heat transfer tube bundle in the refrigerant condenser, and a salt water spraying device faces above the horizontal heat transfer tube bundle. . (7) The refrigerant vapor compression salt water distillation apparatus according to claim 2, wherein the thin film evaporation means for salt water is a refrigerant condenser that uses a vertical heat exchanger tube bundle to perform thin film evaporation. (8) The refrigerant vapor compression salt water distillation apparatus according to claim 2, wherein the refrigerant condenser has a plurality of horizontal heat transfer tube bundles arranged in series with multi-fold flow. (9) A refrigerant vapor compression brine distillation apparatus according to claim 2, wherein the air vent pipe leading to the final tube bundle of the refrigerant condenser is connected to the refrigerant evaporator tube bundle. (10) The refrigerant vapor compression type salt water distillation apparatus according to claim 2, wherein the refrigerant compressor is a centrifugal blower type compressor. (11) A refrigerant vapor compression salt water distillation method and apparatus according to claims 1 and 2, wherein the refrigerant is an R-113 low-pressure refrigerant.