JPS6025586A - Post-treatment of distilled water - Google Patents

Abstract

PURPOSE:To contrive to reduce the size and the operating cost of a device for converting saline water into fresh water by an evaporation method, by a method wherein gaseous carbon dioxide finally discharged from the terminal end of a vacuum generator provided in the converting device is dissolved in distilled water obtained by the converting device. CONSTITUTION:The gas finally discharged from the terminal end of the vacuum generator 16 contains noncondensable gases such as air and contains gaseous carbon dioxide generated from saline water in each evaporating chamber. The gas is fed through a pipe 17 into a water seal type compressor 18, where it is compressed, and is fed into a separator 19 to be used for water seal of the compressor, whereby it is separated into seal water containing gaseous carbon dioxide and a gas containing gaseous carbon dioxide, which are supplied into a feeding-out pipe 9 for distilled water respectively through pipes 20, 21.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a post-treatment method for converting distilled water obtained in a desalination apparatus using an evaporation method to a water quality suitable for tap water.

Distilled water obtained from salt water by evaporation contains almost no minerals, corrodes piping materials in the water supply system, and has a poor taste as drinking water. For this reason, a method is adopted in which calcium carbonate, slaked lime, and carbon dioxide gas are added to distilled water produced from salt water by evaporation. In this case, carbon dioxide gas produced by burning petroleum or fuel gas has been used, but it has the disadvantage that a large amount of equipment and operating costs are required to produce carbon dioxide gas.

Therefore, Japanese Patent Application Laid-Open No. 55-35971 as a prior art discloses that when producing distilled water from salt water using an evaporation method desalination device, the purpose is to prevent corrosion and scale formation in the evaporation method desalination device. By using the fact that carbon dioxide gas is generated when an acid such as hydrochloric acid or sulfuric acid is added to the salt water before it is supplied to the desalination equipment, decarboxylation is performed before the acid-added salt water is supplied to the desalination equipment. Carbon dioxide gas is generated under reduced pressure in the tower, which is extracted by an extraction ejector operated by high-pressure steam from the boiler, and after condensing and removing moisture from the high-pressure steam in a condenser, the water is removed from the desalination equipment. It is suggested that it be mixed with distilled water from

In this way, since carbon dioxide gas is not produced in a separate process, operating costs can be reduced accordingly, and the equipment can be made smaller compared to the conventional method, but in this method, a sufficient amount of carbon dioxide gas cannot be As stated in the specification, the inside of the decarboxylation tower must be brought to a high vacuum of 0.2 atm, that is, about -600 mmHg, using the ejector, so the drive of the decarbonation ejector requires In addition to the increased consumption of high-pressure steam, a large amount of cooling water is required to condense the steam used for this extraction, which increases operating costs.Moreover, as the extraction engine becomes larger,
The piping for this has to be quite thick, so
The equipment cannot be sufficiently miniaturized, and the decarboxylation tower must be of a closed type, which increases equipment costs.

According to the present invention, scale formation in salt water desalination equipment using the evaporation method can be prevented by using a scale inhibitor such as a polymerized phosphate, while the carbonic acid component in the salt water is bicarbonate sulfur (
Contains about 140 ppm as IICO3),
By heating during salt water desalination by evaporation method, 2 HCO3-g CO;-±H,00 Co↑CO
, -tH0 → 20H-10Co, Carbon dioxide (COa) is generated by thermal decomposition as shown in the figure, and this carbon dioxide, along with other non-condensable gases such as air, is converted into salt water and fresh water by the evaporation method. Considering that the vacuum generator in the desalination equipment releases extracted gas into the atmosphere, by dissolving this carbon dioxide released into the atmosphere into the distilled water produced in the desalination equipment, it is possible to improve the efficiency of the equipment. This is aimed at downsizing and reducing operating costs.

To explain the present invention with reference to the drawings below, the evaporation method brine desalination apparatus of the present invention includes all types of desalination apparatus such as a multi-stage flail type brine desalination apparatus, a multi-effect brine desalination apparatus, a vapor compression type brine desalination apparatus, etc. FIG. 1 is a flow sheet showing an example of the implementation when the present invention is applied to a brine circulation multi-stage flash type desalination apparatus which is better known than the conventional one.

This apparatus has a brine heater 1, a multistage evaporation chamber 2, and a scale inhibitor injection device 3, and each steaming and waste chamber 2 is equipped with an evaporation stage 4 and a condenser 5, respectively.

Salt water, which is raw water, is supplied to the system through a pipe 6, and after passing through a heat release condenser 5', a portion is discharged, and the remaining salt water is added with an anti-scaling agent by an anti-scaling agent injection device 3. After that, it is introduced into the evaporation chamber. After the concentrated salt water (brine) that has reached the final stage evaporation chamber is mixed with the above-mentioned salt water, it sequentially flows through the tubes of the condenser 5 of each evaporation chamber 2 from the low temperature stage to the high temperature stage, and is caused by the steam generated from the evaporation stage. It is successively heated to a high temperature, and then further heated in a brine heater 1 by high temperature steam sent, for example, from a boiler through a tube 7,
Then, the salt water is supplied to the high temperature evaporation stage of the evaporation chamber 2, and then flash evaporation is repeated, and from the final low temperature evaporation stage, a part is recirculated by the pump 45 and a part is discharged to the outside of the system via the pipe 8. The steam generated in each evaporation stage is condensed outside the pipe of the condenser 5, becomes distilled water, and is sent out of the system from the delivery pipe 9 by the pump 10 via the calcium carbonate dissolving device 11. 2, a vacuum generator 16 consisting of bleed ejectors 12 and 13 and condensers 14 and 15 connected to the low-temperature evaporation chamber bleeds non-condensable gas, thereby removing the low-temperature evaporation chamber. It is constructed to provide a high degree of vacuum. Note that the multi-stage flash type saltwater freshwater apparatus may be a once-through type or other type.

The gas finally released from the end of the vacuum generator 16 contains non-condensable gas such as air, and
Since each evaporation chamber contains carbon dioxide gas generated from salt water, it is sent through a pipe 17 to a water-ring compressor 18 and compressed, and then sent to a separator 19, and within the separator 19,
By using the compressor 18 as a water seal, the water seal in which carbon dioxide gas is dissolved is separated into the water seal water in which carbon dioxide gas is dissolved and the gas containing carbon dioxide gas, and the water seal water in which carbon dioxide gas is dissolved and the gas containing carbon dioxide gas are transferred to the pipe 20.2.
1, it is supplied to the distilled water delivery pipe 9.

In addition, as the water seal of the water ring compressor 18, the pipe 20.
A portion of the distilled water from 21 before dissolving the carbon dioxide gas is transferred to pipe 2.
2 and the pump 23 for use, the amount of fresh water used can be reduced. Of course, the fresh water may also be switched and supplied from the pipe 24 as water seal water.

In order to supply the sealed water and gas containing carbon dioxide from the separator 19 to the distilled water delivery pipe 9, the separator 19 is
It is preferable to place the seal water from the pipe 20 downstream from the point where the gas containing carbon dioxide is supplied from the pipe 21, because if the dirt is the opposite, in other words, the carbon dioxide gas is dissolved. This is because when carbon dioxide is dissolved in distilled water mixed with water seal water, the amount of dissolved carbon dioxide gas decreases due to the carbon dioxide gas dissolved in the water seal water. (Of course, there may be cases where the injection order is unavoidably reversed due to arrangement etc.a) Also, if slaked lime is used to dissolve salts whose main component is calcium, the slaked lime should be poured into the distilled water delivery pipe. However, when the calcium carbonate dissolving device 11 is used, the calcium carbonate dissolving device ff1l is installed downstream of the water seal and carbon dioxide gas supply point from the separator 19. It has the advantage of increasing the amount of calcium dissolved.

In the above embodiment, the vacuum generator 16 is composed of the bleed ejectors 12, 13 and condensers 14, 15, but the vacuum generator of the present invention is not limited to the above embodiment. As shown in Figure 3, the bleed air ejector 12
, a condenser 14 and a vacuum pump 25, or as shown in FIG. Needless to say, this includes cases in which the vacuum pump 25 is configured in combination with a vacuum pump and a case in which the vacuum pump 25 is configured only in the vacuum pump 25.

FIG. 2 shows an example of implementation when applied to a conventionally well known multi-effect brine desalination system, in which brine is supplied to the system through pipe 28 and passes through a final condenser.
A predetermined amount of water is first added with an anti-scaling agent by the anti-scaling agent injection device 3, and then is added to the preheater 30 of the evaporation chamber 29.
It flows sequentially through the pipe from the low temperature section to the high temperature section and is heated.
This heated salt water is the first effect evaporator) 31 heat exchanger tube 32
The unevaporated salt water is sprayed on the outer surface of the heat transfer tube 35 of the second effect evaporation chamber 34, and is evaporated by the heated steam supplied from the tube 33 into the heat transfer tube 32. is supplied to the effect evaporation chamber, and the final effect evaporation chamber 3
The steam generated in the first effect evaporation chamber 31 is discharged from the heat exchanger tube 3 of the second effect evaporation chamber 34 to the outside of the system through the pipe 37.
At the same time as the salt water supplied to the final effect evaporation chamber 36 is condensed, the salt water sprayed on the outer surface of the chamber is evaporated. It is cooled and condensed by the salt water flowing through the heat exchanger tubes 39 in the heat exchanger tubes 38, and is combined with the condensed water from the heat exchanger tubes in each of the effect evaporation chambers, and is sent from the delivery tube 40 through the calcium carbonate dissolving device 11 as the target distilled water. It is sent out of the system.

Each evaporation chamber is configured so that a low-temperature evaporation chamber can attain a high degree of vacuum by extracting non-condensable gas using a vacuum generator 16. The gas finally released from the end of the vacuum generator is sent to the water ring compressor 18 and compressed, and then separated by the separator 19 into water ring water and gas containing carbon dioxide. Water and gas are supplied to the distilled water delivery pipe 40 via the pipe 20.2.

The vacuum generating device used here is not limited to the one shown in FIG. 2, but also the bleed ejector 1 shown in FIGS. It goes without saying that the present invention also includes various configurations in which a condenser and a vacuum pump are combined.

Now, in both the multi-stage flash type and multi-effect type brine desalination devices mentioned above, non-condensable gases including carbon dioxide are separated and extracted from the brine in each evaporation chamber from high temperature to low temperature. However, as shown by the two-dot chain line in Figures 1 and 2, when the gas is taken out from the high-temperature part, depending on the pressure, it may not pass through some or all of the bleed ejectors in the vacuum generator and may be removed from the pipe 42. condenser 14 and/or 15 directly in the vacuum generator by
In some cases, it may be introduced into the air or taken out through another condenser 27 as shown in FIG. 4 for use.

The same applies to the case where non-condensable gas separated and extracted in the steam-water separator 43 from the salt water before being introduced into the highest temperature evaporation chamber is used as shown by the broken line. This is determined by the designer.

When a steam-driven extraction ejector is used in this vacuum generator, the steam from the boiler that is the driving source contains hydrazine (N≧114) as a deoxidizing agent, and this removes the carbon dioxide from the distilled water. If there is a risk that it will be mixed with the supply and have no adverse effect on the human body, install an oxidizing agent injection device 44 in the distilled water line and inject an oxidizing agent such as chlorine or ozone. A reaction takes place and detoxification can be achieved.

In summary, the present invention provides a method for post-treatment of distilled water in which a salt containing calcium as a main component and carbon dioxide gas are dissolved in distilled water obtained by a salt water desalination apparatus using an evaporation method. A method for post-treatment of distilled water, which is characterized in that the carbon dioxide gas finally released from the end of the vacuum generator in the desalination equipment using the evaporation method is used as the carbon dioxide gas, which has not been used in the past. It uses carbon dioxide gas, which was previously released into the atmosphere, to flavor distilled water and prevent corrosion of pipes, making it extremely economically advantageous. By using the carbon dioxide gas extracted together with non-condensable gas by the vacuum generator in the desalination equipment using the evaporation method, as mentioned above, a closed decarboxylation tower for generating carbon dioxide gas and a carbonation tower inside the carbonation tower have been developed. Since there is no need for a bleed ejector to create a high vacuum, the equipment can be made cheaper and smaller, and since a large amount of high pressure steam is not required to bleed the carbon dioxide gas, operating costs can be reduced. It is. In addition, since the carbon dioxide gas that is finally released from the end of the vacuum generator is used, it is sufficient to simply connect the pipe to the end of the final gas release pipe when taking out the carbon dioxide gas, and it is sufficient to extract the carbon dioxide gas from salt water and fresh water. There is no need to make any major changes to the design of the desalination device, and it can be easily installed alongside an existing desalination device, so it is efficient and economically advantageous.

In addition to the above invention, another invention is to compress carbon dioxide gas extracted from a desalination apparatus using a water ring type compressor and supply it to distilled water together with the water ring type water ring type compressor. During compression in the compressor, carbon dioxide gas can be sufficiently dissolved in the water seal in the compressor.

Still another invention is that since oxidizing agents such as chlorine or ozone are injected into distilled water, even if hydrazine is used in boiler feed water and is mixed into distilled water through a vacuum generator, it will not be oxidized by ozone, etc. It has the effect of effectively preventing corrosion of the boiler and prolonging its lifespan without requiring any restrictions on the use of lactic acid agents in the boiler.

[Brief explanation of drawings]

This is a flow sheet showing an example, and FIGS. 3 and 4 are flow sheets of essential parts showing a case where another type of vacuum generator is used. 1...Brine heater, 2...Multi-stage evaporation chamber,
3...Scale inhibitor injection device, 4...Evaporation stage, 5...Condenser, 6...Pipe, 7...Pipe, 8
... pipe, 9 ... delivery pipe, 10 ... pump,
11... Calcium carbonate dissolving device, 12.13...
...Bleed air ejector-114, 15...Condenser, 16
...Vacuum generator, 17...Tube, 18...
Water ring compressor, 19...Separator, 20.21.
...Pipe, 22 ...Pipe, 23 ...Pump, 24
... pipe, 25 ... vacuum pump, 26 ... bleed ejector-127 ... condenser, 28 ... pipe,
29... Evaporation chamber, 30... Preheater, 31...
・First effect evaporation chamber, 32... Heat exchanger tube, 33...
Pipe, 34...Second effect chamber, 35...Heat transfer tube, 3
6...final utility chamber, 37...tube, 38...
Condenser, 39... Heat transfer tube, 40... Sending pipe, 4
2...Pipe, 43...Steam water separator, 44...
Oxidizing agent injection device, 45...pump.

Claims (4)

[Claims] (1) In a method for post-treatment of distilled water, in which salt containing calcium as a main component and carbon dioxide gas are dissolved in distilled water obtained by a salt water desalination apparatus using an evaporation method, the carbon dioxide gas dissolved in the distilled water A method for post-treatment of distilled water, characterized in that the carbon dioxide gas finally released from the end of the vacuum generator of the desalination apparatus using the evaporation method is used. (2) In a distilled water post-treatment method of dissolving a salt containing calcium as a main component and carbon dioxide gas in the distilled water obtained by the evaporation method, the evaporation method is used in the evaporation method. The carbon dioxide gas extracted by the vacuum generator is compressed by a water ring compressor, and is supplied together with the water ring of the compressor to the distilled water from the desalination equipment using the multistage evaporation method. Distinctive post-treatment method for distilled water. (3) The method for post-treatment of distilled water according to claim 2, characterized in that distilled water from the desalination apparatus is used as water sealing water for a water ring compressor. (4) A method for post-treatment of distilled water in which a salt containing calcium as a main component and carbon dioxide gas are dissolved in distilled water obtained by a salt water desalination apparatus using an evaporation method, in which carbon dioxide gas is dissolved in the distilled water. Distilled water, characterized in that the carbon dioxide gas finally released from the end of the vacuum generator of the desalination equipment using the evaporation method is used, and an oxidizing agent such as chlorine or ozone is injected into the distilled water. Post-processing method.