JPH0141109B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the brine level of a multi-stage flash 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 The fresh water extraction line 1 is connected sequentially through the trays 8' of
3, it is extracted as fresh water.

A part of the concentrated brine is transferred to the lowest 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 most compressed stage condenser K of the heat release section 1, and after flowing through several capacitors K in the upper stage, the fresh seawater is introduced into the heat release 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 set 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=ζυ ² /2g Where, h: Loss head (m) υ: 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 FIG. 3, most of the loss at the entrance occurs because it contracts once at the entrance and then expands again.

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, in order to match the interstage pressure difference determined by the upper air operating conditions, the interstage throttle orifice plate 30 shown in FIG. I was adjusting the difference. However, with this method, every time the operating conditions change, that is, every time the evaporation load fluctuates, the operation must be stopped and the orifice opening area must be adjusted.

The present invention proposes an apparatus that can easily accommodate a wide range of interstage pressure differences in order to cope 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 ).

Hereinafter, the present invention will be explained based on examples.

FIG. 5 shows an embodiment using a rounded orifice plate 31 (hereinafter referred to as a round orifice).

FIG. 6 shows the operation results of a conventional flat plate interstage orifice plate (hereinafter referred to as thin-blade type) and a round type at the same flow rate. Here, the interstage pressure difference △Pυ is
Refers to the interstage steam pressure difference (P ₁ − P ₂ ) when h ₁ = h ₂ . In the case of a constant flow rate, as the brine level _h2 decreases, the interstage pressure difference △Pυ increases as shown in Figure 6.
increases. Further, as the brine level _h2 increases, the interstage pressure difference ΔPυ decreases as shown in FIG. The present invention has been made focusing on this phenomenon. The rate of this increase in △Pυ increases as the height l ₂ of the weir increases. Also, when comparing the conventional thin-blade type and round-shaped orifice, the round type has a wider range of △
It can be seen that Pυ can be adjusted.

In the conventional operation method, in order to adjust the interstage pressure difference △Pυ in response to evaporation load fluctuations, operation was temporarily stopped and the orifice opening area was adjusted by moving the thin-blade orifice plate up and down. . However, this method requires very complicated adjustment work.

The present invention improves this method and proposes to adjust △Pυ according to load fluctuations by adjusting the brine level without changing the orifice opening area, that is, without moving the orifice plate up or down. It is something to do.

As shown in Figure 4, in the case of the same temperature difference between stages,
The interstage pressure difference △Pυ is larger in the high temperature stage than in the low temperature stage. Therefore, the height of the weir 24 is adjusted according to the interstage pressure difference required for each evaporation stage, as shown in _FIG .
We have previously filed an application for a technology to gradually lower the height of the weir 24 toward the low-temperature stage, as in l ₃ .

The present invention is particularly effective when applied to the above-mentioned multi-stage flash water generator in which the weir height of each stage is lowered stepwise toward lower temperatures; however, in contrast to the conventional type where the weir height of each stage is the same. It is applicable and valid even if the

The load fluctuation in the present invention means a fluctuation in the amount of produced water, and the amount of produced water Wp is determined by the following relational expression.

Wp=λ×WR×(TBT−BBT) λ: Proportionality constant WR: Circulating brine flow rate (circulating brine pump discharge amount) TBT: First stage inlet brine temperature BBT: Final stage brine temperature Generally, the produced water volume is set at rated operation. If the amount is to be increased (during overload), the brine temperature at the first input port is increased without changing the circulating brine flow rate WR. As a result, the temperature difference between each stage (TBT - BBT/number of stages) increases, and the differential pressure between stages also increases. In addition, when reducing the amount of produced water compared to the rated operation (at low load), lower the circulating brine flow rate WR within the range of the pipe flow velocity limit, and also lower the first input port brine temperature TBT.
Then, the temperature difference between each stage decreases, and the differential pressure between stages also decreases.

FIG. 7 shows the relationship between the brine level _h2 of each stage of the evaporation chamber and the evaporation load.

In conventional operation, the orifice opening is set so that the brine level is, for example, 0.5 m based on the rated evaporation load. If overload occurs with this opening degree, the brine level h ₂ will decrease as the temperature increases, so the orifice plate is lowered to adjust the h ₂ of each stage to 0.5 m and the opening area is adjusted. . In addition, when the evaporation load becomes low, if the orifice opening is kept as described above, the higher the temperature, the higher the h ₂ becomes. Therefore, in order to adjust the h ₂ of each stage to 0.5 m, the orifice plate is raised to increase the opening area. There is.
The above operations are very complicated and require the installation of a remote control device or manual adjustment after stopping the operation.

On the other hand, in the operating method according to the present invention, the final stage brine level h ₂
This can be dealt with by increasing or decreasing the amount. That is, the brine level _h2 at rated evaporation load (100% operation) is 0.4
For example, if the overload (120%
By adjusting h ₂ = 0.3 m during operation) and h ₂ = 0.6 m during low evaporation load (65% operation),
It is possible to make h ₂ of all stages almost the same.

That is, at the time of rated evaporation load, a liquid level controller 32 is provided in the final stage evaporation chamber FL shown in FIG. When the brining level of 0.4 m is set, the brining level of each stage becomes almost the same as shown in Fig. 7a.

Furthermore, when overloaded, the brine level of the final stage is set to 0.3 m using the same method as above, and the brine level of each stage becomes almost the same as shown in FIG. 7b.

Furthermore, at low loads, by the same method as above,
When the brine level of the final stage evaporation chamber FL is set to 0.6 m, the brine level of each stage becomes almost the same as shown in FIG. 7c.

To explain the above-mentioned phenomenon during overload in more detail, first, when overload occurs, the brine level of the final stage
Lowering h ₂ from 0.4 m to 0.3 m increases the resistance provided by the weir to brine flow, reducing the weir height l ₂ in Figure 6.
= 0.35m, as shown in the graph curve when using a round orifice, the differential pressure between stages △Pυ is approximately 0.27 (unit: m,
The result is the same as constricting the orifice as in the past, and a stable and almost uniform brine level can be obtained. Furthermore, when the load is low, a similar effect can be obtained due to the opposite phenomenon.

In addition, as shown by a in FIG. 8, the height h ₀ of the weir 24
is greater than the brine level _h3 , the resistance is approximately constant. In addition, as shown by h in Fig. 8, when the height _h0 of the weir 24 is smaller than the brine level _h3 , the larger the head difference h between the brine level on the upstream side and the brine level on the downstream side of the weir 24, The resistance of the weir to the brine flow increases, and as the head h becomes smaller, as shown by c in FIG. 8, the resistance becomes smaller and finally reaches zero. Note that the brine level in the intermediate stage may be adjusted without adjusting the brine level in the final stage, but in that case, unevaporated high-temperature brine will be extracted from the intermediate stage, so heat loss will be large and such I usually don't drive.

As described above, the present invention aims to make the brine level of each stage almost uniform in a multi-stage flash water generation system equipped with a weir installed vertically on the bottom plate of a multi-stage evaporation chamber. The gist of this is to lower the brine level than the brine level at rated load, and to make the brine level at the final stage higher than the brine level at rated load at low loads. By adjusting only the level, the differential pressure between stages can be changed, and the brine level at each stage can be maintained stably and uniformly as during rated operation, resulting in always efficient operation despite load fluctuations. becomes possible. In addition, the brine level adjustment method according to the present invention does not require adjusting the orifice opening area.
Only by adjusting the brine level at the final stage, the differential pressure between stages can be kept at an appropriate level and a wide range of load fluctuations can be coped with. Therefore, operation is easy, and the load can be changed continuously without stopping operation in response to load fluctuations as in conventional methods.

[Brief explanation of drawings]

Figure 1 is a system diagram of a general multistage flash type evaporator, Figure 2 is a cross-sectional view of the evaporation chamber, Figure 3 is a cross-sectional view of a conventional flat plate throttle orifice between stages, and Figure 4 is a diagram showing the saturated vapor pressure. Brine temperature correlation graph, 5th
Figure 6 is a cross-sectional view illustrating the present invention, Figure 6 is a graph showing the correlation between stage differential pressure and brine level, and Figure 7 shows the relationship between brine level and evaporation load when operated according to the method of the present invention. The graph diagram and FIG. 8 are cross-sectional views illustrating flow resistance due to the weir. 21a, 21b: Evaporation chamber, 24: Weir, 26: Bottom plate.

Claims (1)

[Claims] 1. In a multi-stage flash water generator equipped with a weir installed on the bottom plate of a multi-stage evaporation chamber, in order to keep the brine level of each stage almost uniform, in the event of overload, the brine level of the final stage is changed to the brine level at the rated load. A brine level adjustment method for a multi-stage flash water generator, characterized in that the brine level in the final stage is made higher than the brine level at the rated load when the load is low.