JPH0141108B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a multi-stage flash type fresh water generator.

First, an outline of this type of multi-stage flash type freshwater generating apparatus will be explained based on FIG. 1. In Figure 1, 1
2 indicates a heat recovery section including multiple evaporation chambers, 3 indicates a brine heater, and the brine heated here is transferred to the first evaporation chamber _F1. The gas is introduced into the evaporation chamber, and is caused to flow through the evaporation chambers of each stage in sequence toward the final stage evaporation chamber FL.

The indoor pressure of each evaporation chamber is maintained so as to decrease sequentially from the first stage evaporation chamber _F1 to the final stage evaporation chamber FL, so that when the brine flows through the evaporation chambers of each stage, it flashes at each chamber pressure. This flash vapor is evaporated and preheats the brine supplied to the brine heater 3 in the condenser K of each stage, and is also condensed and liquefied, and the condensed liquid is received in the tray 8 of each stage, and Finally, the fresh water extraction line 1 passes through the tray 8' of
It is extracted as fresh water from 3.

A part of the concentrated brine is sent to the final stage evaporation chamber FL
It is extracted from the seawater and blown down through the seawater discharge line 16, and the remainder is sent to the lowermost condenser K of the heat recovery section 2 together with make-up seawater, which will be described later, and then sequentially flows through the upper condenser K to be recirculated.
Fresh seawater is introduced from the cooling seawater line 7 into the final stage condenser K of the heat dissipation section 1, and after flowing through several condensers K in the upper stage, the fresh seawater is introduced into the heat dissipation section 1.
most of the line 18 from the top capacitor K
A portion of the water is discharged through the deoxidizing tower 5 and sucked into the pump 6 as make-up seawater. After the brine is preheated in the process of successively passing through the condenser K of the heat recovery section 2, it enters the heat exchanger tube of the brine heater 3, and is heated inside the heater 3 by heating steam supplied from the heating steam line 10. The temperature is increased by heating. The heated steam is cooled by brine, becomes condensate, and is discharged from condensate line 14.

Next, the seawater heated and heated in the brine heater 3 is introduced into the first stage evaporation chamber _F1 , flows through the evaporation chambers of each stage as described above, and enters the final stage evaporation chamber FL.
leading to. Note that 15 indicates an ejector.

As shown in FIGS. 2 and 3, the evaporation chambers at each stage of the above-mentioned multi-stage flash water generator are partitioned by partition walls 22, and the upper evaporation chamber 21a
The lower evaporation chamber 21b is in communication with the lower evaporation chamber 21b through a throttling mechanism 23 at the bottom of the partition wall 22, from which brine flows into the lower evaporation chamber 21b, and further into the evaporation chamber 21.
It flows over the weir 24 erected on the bottom plate 26 of b and flows to the next stage.

In such a structure, the brine that has flowed into the lower evaporation chamber 21b flash-evaporates at the entrance of the evaporation chamber because its pressure is lower than that in the front evaporation chamber 21a, and the brine containing water vapor passes over the weir 24 and flows into the evaporation chamber 21b. while flowing horizontally along the bottom plate 26 of the
A portion of the liquid evaporates as a flash from the liquid surface and flows out to the next stage.

On the other hand, the steam generated by flash evaporation is
Demister 27 installed at the top of the evaporation chamber 21b
After the brine mist entrained in the vapor is collected and removed by the demister 27, circulating brine having a temperature lower than that of the brine flowing above the evaporation chamber bottom plate 26 flows inside the evaporation chamber. The heat exchanger tubes 28 are guided to a condenser chamber 29 in which the heat exchanger tubes 28 are placed, and are cooled by the cooling water (circulating brine) flowing inside the heat exchanger tubes 28 and condensed to become manufactured fresh water.

In the above flash evaporation, the interstage pressure difference (the pressure difference between each evaporation chamber) changes depending on the operating conditions, etc., but this adjustment is absorbed by the change in the brine level difference between the two evaporation chambers. However, when this difference becomes large, it is necessary to adjust the brine flow rate, and this is accomplished by manually adjusting the interstage throttle orifice plate 30 disposed within the throttle mechanism 23 to change the opening area.

Generally, in conventional apparatuses, a flat interstage drawing orifice plate 30 is used, as shown in FIG. The loss head h in this orifice portion is expressed by the following equation.

h=ζ ² /2g Here, h: Loss head (m): Average flow velocity at orifice (m/sec) ζ: Pressure loss coefficient (-) This pressure loss coefficient ζ is determined by the roundness of the corner of the orifice inlet. If the edges are sharp as shown in Figure 3, the edges are once contracted at the entrance and then expanded again, causing most of the entrance loss here.

This pressure loss can be reduced to 1/10 or less by rounding the inlet.

Generally, in a multi-stage flash water generator, the temperature difference between each stage is maintained at about 2 to 4°C, and this difference in saturated vapor pressure, that is, the pressure difference between the stages, flash-evaporates the circulating brine. As shown in FIG. 4, this saturated vapor pressure increases in increments as the temperature rises. Therefore, even if the temperature difference is the same, the higher the temperature (upstream stage), the larger the interstage pressure difference. Therefore,
In order to maintain this interstage pressure difference, different differential pressure adjustments are required at each stage.

Therefore, in conventional equipment, the brine level is maintained by moving the inter-stage throttle orifice plate 30 shown in FIG. At the same time, the pressure difference between stages was adjusted.
However, in this method, the adjustment range of the interstage pressure difference is narrow in response to large evaporation load fluctuations.

The present invention proposes an apparatus that can handle a wide range of interstage pressure differences in order to deal with large evaporation load fluctuations.

As shown in FIG. 2, the brine that has passed through the interstage throttling mechanism 23 collides with the weir 24, overcomes it, and flows further rearward. When it collides with this weir 24, flow resistance occurs. This resistance differs in magnitude depending on the height of the weir 24, but in the past, the height of each weir 24 was the same (l ₁₀ =l ₂₀ ).

Therefore, the present invention proposes to maintain the pressure difference between stages by changing the height of this weir 24 according to the pressure difference between stages.

The present invention will be explained below based on examples.

FIG. 5 shows an embodiment in which a rounded orifice plate 31 (hereinafter referred to as a round orifice) is used in place of a conventional flat plate orifice plate (hereinafter referred to as a thin-blade orifice).

FIG. 6 shows the results of an operation using a conventional thin-blade type and round orifice in an apparatus having the evaporation chamber structure shown in FIG. 5 and at the same flow rate.

According to this embodiment, in the case of the conventional thin-blade orifice, when the height l ₂ of the weir 24 is 0.25 m or more, the interstage pressure difference ΔPu (P ₁ − P ₂ ) increases as l ₂ increases. ,
When l ₂ is less than 0.2 m, the interstage pressure difference is almost constant.

On the other hand, in the case of the round orifice 31, l ₂
△Pu increases as . That is, by changing l ₂ ΔPu can be adjusted over a wide range.

Here, the interstage pressure difference △Pu is h ₁ shown in Fig. 5.
Interstage steam pressure difference (P ₁ − P ₂ ) when = h ₂ = 0.5 m
means.

That is, as shown in FIG. 5, a round orifice 31 is adopted, and the weir 24 of each flash
If the height of the weir 24 is lowered stepwise toward the low-temperature stage, such as l ₂ > l ₃ , the pressure difference between the stages will increase or decrease, especially when the height of the weir 24 is less than 0.2 m, as shown in Figure 6. Furthermore, by gradually lowering the height of the weir 24 toward the low temperature stage, the desired interstage pressure difference △Pu can be lowered from a low range of 0.05 m (converted to liquid level height) or less.
It can be increased or decreased over a wide range up to a high range of 0.2 m (converted to liquid level height) or higher.

Therefore, a tall weir 24 is installed on the high temperature stage (upstream stage) side where the interstage pressure difference △Pu is large, and a short weir 24 is installed on the low temperature stage (downstream stage) side where the interstage pressure difference △Pu is smaller than the high temperature stage. A weir 24 may be provided.

As shown in Figure 6, even if a conventional thin-blade orifice is used, if the weir height l ₂ is 0.2 m or more, the height of the weir 24 should be gradually lowered toward the low-temperature stage. The interstage pressure difference ΔPu can be adjusted by .

As described above, in the present invention, the height of the weir installed on the bottom plate of the evaporation chamber of each stage is gradually lowered toward the low-temperature stage, making it possible to maintain and adjust the pressure difference between stages over a wide range. There is an effect that can be done.

[Brief explanation of drawings]

Figure 1 is a system diagram of a general multistage flash evaporator, Figure 2 is a sectional view of the evaporation chamber, Figure 3 is a sectional view of a conventional flat plate throttle orifice between stages, and Figure 4 shows the saturated vapor pressure. A graph showing the correlation with temperature, Fig. 5 is a cross-sectional view showing one embodiment of the present invention, and Fig. 6 shows the relationship between weir height and pressure difference between stages when using round and thin-blade orifices. FIG. 21a, 21b: Evaporation chamber, 22: Partition wall, 24:
Weir, 26: Bottom plate, 31: Round orifice.

Claims (1)

[Claims] 1. A multi-stage flash-type fresh water generator characterized in that the height of a weir installed on the bottom plate of the evaporation chamber of each stage is gradually lowered to lower temperature stages.