JPH06162B2 - Multiple effect evaporator - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of a multiple-effect evaporation device for producing fresh water from seawater or the like by evaporation.

[Conventional technology]

Examples of a multi-stage evaporator for producing fresh water from seawater by evaporation include a multi-stage flash evaporator as described in JP-A-54-18469 and JP-B-49-29070. 50-5098
There is a multiple-effect evaporator as described in Japanese Patent Publication No. 1 or the like, but generally, the latter multiple-effect evaporator has lower equipment cost and lower power consumption than the former multi-stage flash evaporator, and Since it has advantages such as easy automatic control, it is often used in small and medium-sized desalination facilities.

This multiple-effect evaporator is disclosed in the above-mentioned Japanese Patent Laid-Open No. 49-2.
As described in Japanese Patent No. 9070 and Japanese Patent Application Laid-Open No. 50-20981, a plurality of effect cans are formed adjacent to each other, and a large number of heat transfer tubes extending in the horizontal direction are provided in each effect can. Each of them is provided with a spraying means for spraying seawater (brine) on the outer surface of the heat transfer tube, and is provided outside the heat transfer tube in the highest temperature first stage effect can among the effect cans. The seawater sprayed by the spraying means in the first-stage effect can is sprayed by the spraying means to the outside of the heat transfer tube in the next stage, while heated steam is placed in the heat-transfer tube in the first-stage effect can. Introduced as a heating source, the steam generated outside the heat transfer tube of the effect can in the previous stage is introduced into the heat transfer tube of the effect can excluding the first-stage effect can as a heating source, and the effect of each stage The condensed water in the heat transfer tube of the can is taken as fresh water. It is configured in Suyo.

Further, in the multiple effect evaporators described in both the above-mentioned publications, the outer surface of the heat transfer tube is sprayed by spraying seawater (brine) onto the outer surface of the heat transfer tube in each effect can by a spraying means. A thin liquid film of seawater is formed on the seawater, and seawater is boiled and evaporated in the state of this thin liquid film.

[Problems to be solved by the invention]

This thin-film multi-effect evaporator evaporates seawater in a thin liquid film state on the outer surface of the heat transfer tube by boiling, so that it has better heat transfer than the so-called immersion type in which the heat transfer tube is immersed in seawater. Although it has the advantage that a high heat transfer coefficient can be obtained, scale is likely to occur on the outer surface of the heat transfer tube. In particular, this scale generation increases remarkably in proportion to temperature. There is a problem in that the temperature of the can cannot be increased and therefore the temperature difference between the first effect can and the last effect can cannot be increased.

That is, when a thin liquid film of seawater is formed on the outer surface of the heat transfer tube by the sprinkling means, the thickness of the liquid film is not uniform due to clogging by foreign matter or pressure fluctuations in the sprinkling means, and there is a portion that becomes extremely thin. Or the liquid film is missing on the outer surface of the heat transfer tube, and local overconcentration of seawater occurs in this area, which creates a severe environment for scale formation on the outer surface of the heat transfer tube. In addition, since the scale formation on the outer surface of the heat transfer tube tends to increase in proportion to the temperature, the scale produced on the outer surface of the heat transfer tube in each effect can has a higher temperature than that of the first stage effect can. Most noticeable in heat transfer tubes.

Therefore, in the conventional thin-film multiple-effect evaporator,
Since the temperature of the first-stage effect can, which is the highest temperature among the effect cans, must be set to about 70 ° C. in consideration of the safety of scale formation on the outer surface of the heat transfer tube,
If the temperature of the final-stage effect can determined by the temperature of seawater is 40 ° C., for example, a conventional general-purpose multiple-effect evaporator is used in an operating temperature range of 70 ° C.-40 ° C. = 30 ° C. It's a reality.

However, when the operating temperature range is about 30 ° C. as described above, the temperature difference between the effect cans becomes small. Therefore, the heat transfer area of the heat transfer tube in each effect can must be increased by this amount. This is because the size of the apparatus is increased and the manufacturing cost is increased, and moreover, the number of effect cans cannot be increased in order to increase the ratio of fresh water (the ratio of the fresh water produced to the heated steam).

[Means for solving problems]

The present invention provides the above-mentioned prior art multi-effect evaporator,
The above problem is solved by applying the liquid immersion type in which the heat transfer tube is immersed in seawater to some of the effect cans having a high temperature among the effect cans.

That is, the present invention forms a plurality of effect cans adjacent to each other,
A large number of heat transfer tubes are arranged in each effect can, and heating steam is supplied into the heat transfer tubes of the first-stage effect can having the highest temperature to transfer heat to effect cans other than the first-stage effect can. In a multiple-effect evaporator in which steam generated in the effect can of the previous stage is introduced into the pipe, a liquid for immersing the heat transfer pipe in the effect can of high temperature including the first-stage effect can into seawater. It is characterized in that the heat transfer tubes in the remaining other effect cans are formed in a thin film method in which seawater is sprayed onto the outer surface thereof by a spraying means.

[Operation and effect of invention]

In this way, the heat transfer tubes in the high temperature effect cans including the first-stage effect cans are configured by the immersion type soaked in seawater. The boiling evaporation of seawater does not occur, and the boiling evaporation of seawater occurs at the liquid surface, while the outer surface of the heat transfer tube immersed in seawater has a dry portion on the outer surface of the heat transfer tube as in the case of the thin film type. In this case, the amount of scale generated on the outer surface of the heat transfer tube due to the heating and evaporation of seawater is significantly smaller than that of the thin film type because the local condensation does not occur. Therefore, the temperature of the first-stage effect can can be made higher than that of the conventional set temperature by this amount. On the other hand, the remaining heat transfer tubes in other effect cans
By using a thin-film system in which seawater is sprayed to the outer surface by means of a spraying device, in the effect can with a low temperature, good heat transfer can be obtained with a high heat transfer coefficient, and the final stage effect can. The temperature can be kept low.

Therefore, according to the present invention, the temperature of the first-stage effect can of the multiple-effect evaporator can be set to a high temperature while suppressing the generation of scale for the heat transfer can in the first-stage effect can and the high-temperature effect can. As a result, the temperature difference between the first-effect can and the last-effect can, that is, the operating temperature range of the multiple-effect evaporator can be expanded. Since the heat transfer area of the heat transfer tube in the effect can is reduced and the evaporator can be downsized, the manufacturing cost of the evaporator can be reduced, and moreover, since the operating temperature range of the multiple effect evaporator can be expanded, The effect is that the number of stages of each effect can is increased to improve the water production ratio.

〔Example〕

An embodiment in which the present invention is applied to a rigid multiple-effect evaporator will now be described with reference to the drawings. In the figure, reference numeral 1 denotes a rigid multiple-effect evaporator main body, in which a plurality of horizontal partition plates are provided. 2, 3, 4, are divided into a first-stage effect can 5, a second-stage effect can 6, a third-stage effect can 7, and a condensing chamber 8 from the top, and these effect cans 5, 6, 7 and The condensing chamber 8 is maintained by a bleeder 9 such as a vapor ejector or a vacuum pump connected to the condensing chamber 8 so that the temperature and the pressure are sequentially lowered from the upper side to the lower side.

A large number of heat transfer tubes 5a, 6a, 7a extending in the horizontal direction are provided in each of the effect cans 5, 6, 7 and a multi-tube condensing chamber 8a is provided in the condensing chamber 8. The heating steam supply pipe 10 is connected to the steam chamber 5b for the heat transfer pipe 5a of the first-stage effect can 5, and the first-stage effect can 5 is connected to the steam passage 6b for the heat-transfer pipe 6a of the second-stage effect can 6. Three-stage effect can 7
The second-stage effect can 6 is connected to the inlet header 7b for the heat transfer tube 7a, and the third-stage effect can 7 is connected to the condensing chamber 8.

Further, the seawater pumped from the sea by the seawater pump 11 is supplied to the condensing chamber 8a in the condensing chamber 8 and most of the seawater discharged from the condensing pipe 8a is discarded through the pipe 12, while a part of the seawater is discharged. The seawater is supplied to the steam passage 7b of the heat transfer pipe 7a of the third effect can 7 and the heat transfer pipe 6 of the second effect can by the water supply pump 13.
After passing through the water supply preheaters 14 and 15 provided in the steam passage 6b to the a, the water is supplied from the seawater supply pipe 16 into the first effect can 5. In this case, a pipe 17 from the water supply pump 13 to the water supply preheater 14 is provided with a scale injection device 18 for a scale inhibitor.

On the partition plate 2 that defines the first-stage effect can 5 and the second-stage effect can 6, the un-evaporated seawater brine accumulated in the bottom of the first-stage effect can 5 is added to the second-stage effect can 6. In the partition plate 3 that divides the second-stage effect can 6 and the third-stage effect can 7 into a plurality of distribution holes 2a for distributing to the outer surface of the heat transfer tube 6a in the second-stage effect can 6 in the same manner. Brine that collects at the bottom inside is a third-stage effect can 7.
While a large number of spray holes 3a for spraying are provided on the outer surface of the heat transfer can 7a, the flow regulating plate 19 having a plurality of throttle holes 19a at the bottom of the first effect pipe 5 is provided.
So that the seawater in the first-stage effect can 5 accumulates up to the upper part of the heat transfer tube 5a. In other words, the liquid level 20 of seawater in the first-stage effect can 5 is immersed in the seawater by the heat transfer tube 5a. It is configured to be held at the desired height. In this case, the first
The effect can 5 is provided with an overflow pipe 21 for controlling the maximum water level in the can.

In this way, the seawater accumulated in the first-stage effect can 5 to the height at which the heat transfer pipe 5a is immersed is heated by the steam supplied from the supply pipe 10 into the heat transfer pipe 5a, and at the liquid level 20 thereof. The brine that evaporates by boiling and then the non-evaporated seawater is sprayed from the spray holes 2a in the partition plate 2 to the outer surface of the heat transfer pipe 6a in the second effect can 6 while passing through the flow regulating plate 19 while the first effect is applied. The steam generated in the can 5 passes through the steam separator 22, preheats the feed water in the preheater 15 via the steam passage 6b, and then the heat transfer pipe 6 in the second effect can 6
Entering inside a, the thin-film brine formed on the outer surface of the heat transfer tube 6a is heated and evaporated.

The brine flowing down by the outer surface of the heat transfer tube 6a of the second effect can 6 is sprayed from the spray holes 3a of the partition plate 3 to the outer surface of the heat transfer tube 7a of the third effect can 7, while the second step The steam generated in the effect can 6 is steam-water separator 23.
Through the steam passage 7b to preheat the feed water in the preheater 14 and then enter the heat transfer pipe 7a in the third-stage effect can 7.
The thin-film brine formed on the outer surface of the heat transfer tube 7a is heated and evaporated.

The brine flowing down from the outer surface of the heat transfer tube 7a of the third-stage effect can 7 accumulates on the upper surface of the partition plate 4, and then the brine pump 2
4, the steam generated in the third-stage effect can 7 is discharged to the outside of the system, passes through the steam separator 25, and then is condensed in the condensing chamber 8
After entering the inside and condensing on the outer side surface of the condensing pipe 8a, it accumulates at the bottom of the condensing chamber 8.

Further, the heat transfer tubes 5a, 6a, 7 of the respective effect cans 5, 6, 7
Condensed water collects in each of the condensed water chambers 5c, 6c, 7c for a, and is introduced into the condensed chamber 8 through the pipes 26, 27, 28, and then together with the condensed water in the condensed chamber 8. First, it is taken out as fresh water from the manufacturing water pump 29.

As described above, the heat transfer tube 5a in the first-stage effect can 5 is configured to be a liquid immersion type that is immersed in seawater, so that the outer surface of the heat transfer tube 5a has a scale of scale generated by heating and evaporation of seawater. Since the amount is remarkably reduced, the temperature of the first-stage effect can 5 can be made higher than that of the conventional set temperature by this amount. On the other hand, the second effect can 6 and the third effect can 7
The second-stage effect can 6 and the third-stage effect can 7 are configured by the heat transfer tubes 6a and 7a in the above-mentioned structure being of a thin film type in which seawater is sprayed to the outer surfaces thereof at the spray holes 2a and 3a.
The heat transfer of the heat transfer tubes 6a and 7a is good, a high heat transfer coefficient is obtained, and the temperature of the third-stage effect can 7 can be kept low.

In the above-described embodiment, in the three-stage multiple-effect evaporator, only the heat transfer tube 5a in the first-stage effect can 5 having the highest temperature was immersed, but when the number of stages was large,
It suffices if the heat transfer tubes in a plurality of high-temperature effect cans, including the highest-temperature first-effect effect can, are of the immersion type, and the present invention is not limited to the rigid multiple-effect evaporator of the above embodiment. , A horizontal type in which a plurality of effect cans are arranged side by side, for example, Japanese Patent Publication No. 51-
It goes without saying that the invention can also be applied to a case where a plurality of effect cans are arranged side by side in a rigid manner of two series as described in Japanese Patent No. 19425. Furthermore, in the above-mentioned embodiment, the flow regulating plate 1
Although the liquid level 20 of the first-stage effect can 5 is held at a high position by means of 9, instead of this, the liquid-level level connecting the plurality of overflow pipes 21 to the middle part of the first-stage effect can 5. The predetermined liquid level 20 may be retained by providing a bypass line provided with a regulating valve.

[Brief description of drawings]

The drawing is a vertical sectional front view showing an embodiment of the present invention. 1 ... Multi-effect evaporator main body, 2, 3, 4 ... Partition plate, 5 ... First stage effect can, 6 ... Second stage effect can, 7
... Third-stage effect cans, 5a, 6a, 7a ... Heat transfer tubes,
16 ... Seawater supply pipe, 2a, 3a ... Spraying hole, 19
... Flow rate control plate, 20 ... Liquid level.

Claims (1)

[Claims] 1. A plurality of effect cans are formed adjacent to each other, and a large number of heat transfer tubes are arranged in each effect can, and the maximum temperature
Heating steam is supplied into the heat transfer tubes of the stage effect cans, and steam generated in the effect cans of the preceding stage is introduced into the heat transfer tubes of the effect cans other than the first stage effect can. In the evaporator, the heat transfer tube in the high temperature effect tube including the first-stage effect can is immersed in seawater,
A multi-effect evaporation device, characterized in that the heat transfer tubes in the remaining other effect cans are each of a thin film type in which sea water is sprayed to the outer surface thereof by a spraying means.