JP4711070B2 - Multi-effect evaporator - Google Patents

Description

  The present invention relates to an evaporator for a multi-effect type fresh water generator used for producing fresh water from seawater, for example.

  Multi-effect fresh water generators are attracting attention as compact and efficient devices. Conventionally, the multi-effect fresh water generator is limited to a relatively small fresh water generator. However, in recent years, the size of the multi-effect freshwater generator has been increased, and the medium-scale class freshwater generator, which has been mainly employed in the flash type so far, is replacing the multi-effect freshwater generator.

  In the multi-effect freshwater generator, seawater is sprayed on the outside of the evaporator heat transfer tube, and steam is generated by liquid film evaporation / boiling on the surface of the heat transfer tube using the latent heat of condensation of the steam supplied into the tube. . On the other hand, the steam inside the pipe (steam generated by the effect of the previous stage) is condensed by the latent heat of vaporization of the seawater outside the pipe to obtain product water.

  The feature of the multi-effect type fresh water generator (particularly the horizontal heat transfer pipe type multi-effect type fresh water generator) is that the outside of the tube is liquid film evaporation / boiling heat transfer, and a very high overall heat transfer coefficient is obtained. Since the heat exchange between the inside and outside of the pipe is performed at a constant temperature (saturation temperature), the temperature difference can be used more efficiently than in the multistage flash type fresh water generator.

  However, when the seawater sprayed on the heat transfer tube is non-uniform, the thermal resistance increases and the heat transfer rate decreases at the thick liquid film. On the other hand, the thermal resistance decreases and the heat transfer rate increases in the part where the amount of seawater spray is small and the liquid film is thin, but the liquid film is further thinned by evaporation / boiling, and the liquid film is broken and the dry part (dry spot) is formed. If it occurs, there is a possibility that the heat transfer rate is drastically decreased and sufficient performance cannot be obtained.

  Conventionally, this type of evaporator includes a heat transfer tube group composed of heat transfer tube rows arranged in multiple stages, and a supply device that supplies seawater to the heat transfer tube group from above at a constant time. However, what is comprised by the spray nozzle is known (for example, refer patent document 1).

  In this spray nozzle supply system, distribution occurs in the seawater supplied to all the heat transfer tubes in the uppermost heat transfer tube row, and there may be a case where the dried portion or the extremely thick portion of the liquid film is generated as described above. Furthermore, a space for spreading the sprayed seawater is required, and the height of the entire apparatus is increased by that space.

  As another evaporator, a perforated plate tray is arranged in place of the spray nozzle and seawater is sprayed through the holes of the tray, for example, see Patent Document 1. ).

  In the method using the tray, although seawater can be supplied relatively uniformly, it is necessary to install the tray on the entire upper surface of the uppermost heat transfer tube row, which is expensive compared to the spray method.

Further, among the heat transfer tube arrays arranged in multiple stages through the evaporators according to the above two methods, a dry spot is likely to occur in the heat transfer tube array at the lowest stage or a stage close thereto. Therefore, there is a limit to increasing the height of the evaporator in order to improve the performance of the evaporator.
JP 2003-190701 A Japanese Utility Model Publication No. 63-160996

  An object of the present invention is to provide a multi-effect fresh water generator evaporator that can supply seawater uniformly to all evaporator heat transfer tubes without causing dryout, and that can be configured compactly. There is to provide to.

The evaporator for a multi-effect fresh water generator according to the present invention includes a heat transfer tube group including heat transfer tube rows arranged in multiple stages, and each heat transfer tube row is constituted by a plurality of parallel horizontal heat transfer tubes. In the evaporator for a multi-effect water generator, the heat transfer tube in the uppermost heat transfer tube row is replaced with a seawater spray tube with a seawater spray opening, and the inside of the heat transfer tube excluding the seawater spray tube The steam generated in the previous stage is supplied to the seawater and the seawater spray pipe

In the evaporator for a multi-effect water freshener according to the present invention, seawater can be uniformly supplied from the uppermost heat transfer tube array to the heat transfer tubes below it. Further, since a device corresponding to the tray described at the beginning is not required, the apparatus can be configured at low cost. In addition, since a spray nozzle or the like is unnecessary, it is possible to keep the height of the entire evaporator low.

The seawater spray opening is preferably a plurality of upward slits or holes positioned at intervals on a straight line extending in the length direction of the seawater spray pipe .

Further, the seawater sparge tube outer surface, the plurality of parallel shaped grooves seawater diffusion extending in the longitudinal direction of which is formed, be expanded seawater is caused to flow out from the slit or hole in the sea water spraying pipe outer surface axis it can.

  According to this invention, seawater can be uniformly supplied to all the evaporator heat transfer tubes without causing dryout, and the evaporator for a multi-effect fresh water generator that can be configured compactly is inexpensive. Can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of an evaporator for a multi-effect type water freshener, and mainly shows a cross-sectional portion of a heat transfer tube.

  The evaporator includes a heat transfer tube group 11. The heat transfer tube group 11 includes heat transfer tube arrays 21 arranged in multiple stages. Each stage of the heat transfer tube row 21 is composed of a plurality of parallel horizontal heat transfer tubes 31. The tube pitch P0 of the heat transfer tubes 31 in the heat transfer tube row 21 of each stage is constant. Further, the outer diameter D of the heat transfer tubes 31 is constant.

All the heat transfer tubes 31 constituting the heat transfer tube group 11 are arranged in a staggered pattern, but may be a grid pattern . In other words, in two adjacent upper and lower stages, one heat transfer tube 31 of the lower heat transfer tube array 21 is positioned below the adjacent two heat transfer tubes 31 of the upper heat transfer tube array 21. In the heat transfer tube rows 21 in all stages, the pitch P1 of the two heat transfer tube rows 21 adjacent to each other in the upper and lower sides is the same.

Of the heat transfer tube rows 21 in all stages, a heat transfer tube 31 of the heat transfer tube row 21 described below is replaced with a seawater spray tube 41 that does not perform the heat transfer function. The inside of the seawater spray pipe 41 is indicated by hatching.

  Heat transfer tubes 31 of the first and second heat transfer tube rows 21 from the top, the heat transfer tubes 31 of the two upper and lower heat transfer tube rows 21 in the middle, and the two heat transfer tube rows adjacent to the upper and lower sides near the lowermost step. 21 heat transfer tubes 31 are seawater spray tubes 41.

  As shown in FIG. 2, a plurality of upward slits 51 are formed at the top of the seawater spray pipe 41 so as to extend intermittently on a straight line extending in the length direction of the seawater spray pipe 41.

  In FIG. 3, a round hole 61 is formed as an opening in place of the slit 51. The plurality of round holes 61 are located on a straight line extending upward in the length direction of the top of the seawater spray pipe 41. Further, a plurality of parallel grooves 62 are formed on the outer surface of the seawater spray pipe 41. The groove 62 extends in the length direction at intervals in the circumferential direction of the outer surface of the seawater spray tube 41 except for the straight portion where the round hole 61 is provided.

  A constant amount of seawater per unit time is supplied to the seawater spray pipe 41 by the supply means. Steam generated by the effect of the previous stage is supplied to the inside of the heat transfer pipe 31 that is not replaced by the seawater spray pipe 41. The seawater supplied to the seawater spray pipe 41 flows out from the slit 51 or the round hole 61, and sequentially flows down the heat transfer pipe 31 below it. Steam is generated on the surface of the heat transfer tube 31 by liquid film evaporation. The generated steam is sent to the subsequent utility.

  Seawater that flows out from the slit 51 or the round hole 61 flows along the groove 62 and is diffused in the axial direction of the outer surface of the seawater spray pipe 41. As a result, the seawater is sprayed from a portion extending over the entire length of the outer surface of the seawater spray pipe 41.

1 is a vertical cross-sectional view of an evaporator according to the present invention. It is a perspective view of the seawater spray pipe of the evaporator. It is a perspective view which shows the modification of the seawater spray pipe. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3.

Explanation of symbols

11 Heat transfer tube group
21 Heat transfer tube array
31 Heat transfer tube
41 Seawater spray pipe

Claims (3)

In the evaporator for a multi-effect type fresh water generator comprising a heat transfer tube group consisting of heat transfer tube rows arranged in multiple stages, each heat transfer tube row being constituted by a plurality of parallel horizontal heat transfer tubes, The heat transfer tubes of the first and second heat transfer tube rows from the top, the heat transfer tubes of the two upper and lower adjacent heat transfer tube rows, and the heat transfer tubes of the two upper and lower heat transfer tube rows near the lowermost step , it has been made with seawater sparge tube spaced seawater spraying openings, together with steam generated in the previous stage of the utility within the heat transfer tube, except for the sea water spray pipe is supplied, seawater is supplied to the inside of sea water spraying pipe An evaporator for a multi-effect fresh water generator, characterized in that The evaporator for a multi-effect fresh water generator according to claim 1 , wherein the seawater spray opening is a plurality of upward slits or holes positioned at intervals on a straight line extending in the length direction of the seawater spray pipe . The evaporator for a multi-effect fresh water generator according to claim 2 , wherein a plurality of parallel strips for seawater diffusion extending in the length direction are formed on the outer surface of the seawater spray pipe .

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