JPS6327041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for promoting evaporation in a multi-stage flash evaporator.

Multi-stage flash evaporators are often used as a means of seawater desalination. In addition to seawater desalination, it is also used to obtain clean steam from heated wastewater or wastewater that contains impurities, and to extract clean steam from hot water that contains toxic components such as geothermal water. In particular, when used for seawater desalination, there are restrictions on the flash evaporation temperature due to the problem of scale precipitation in the seawater and the temperature of the seawater used as cooling water, and the flash evaporation temperature is generally relatively low at 110°C to 30°C. .

Incidentally, multi-stage flash evaporators used as seawater desalination devices tend to become larger year by year, and the amount of seawater to be handled, that is, the flow rate of brine, is also increasing accordingly. As the brine flow rate increases, the brine level in the multi-stage flash evaporation chamber also tends to increase, resulting in a difference in evaporation rate between the upper brine layer and the lower brine layer. However, according to the conventional multistage flash evaporator, the difference in evaporation rate is not large when the evaporation temperature is 80°C or higher, but the difference increases as the temperature decreases, and the difference becomes quite large below 50°C. This can cause problems such as inhibiting evaporation. The reason for this is that at low temperatures, the vapor pressure is small, so the evaporation of the lower brine that receives the liquid head of the upper brine is significantly suppressed. This is because the brine with a .

The purpose of the present invention is to solve this problem, and the present invention aims to provide a multi-stage flash evaporation chamber in which the length of the brine in the flow direction is in the range of 1/3 to 1/5 of the length of the evaporation chamber on the downstream side of the interstage orifice of the multi-stage flash evaporation chamber. This object is achieved by providing a method for promoting evaporation in a multi-stage flash evaporator, which is characterized by promoting evaporation using a raised bottom section or weir section provided with a raised bottom section or weir section. Of course, even when the evaporation temperature is low, the evaporation of brine can be promoted very well.

The method of the present invention will be explained in detail below based on the drawings showing one embodiment thereof. FIG. 1 shows the main parts of a multi-stage flash evaporation device used for seawater desalination according to the method of the present invention, in which the internal space of the device is partitioned at appropriate intervals in the longitudinal direction by partition plates 1 with openings at the bottom.
A plurality of evaporation chambers 2, 3, 4 are formed. Reference numeral 5 denotes an interstage orifice provided at the lower end of the partition plate 1. Reference numeral 6 denotes a rectangular raised bottom part provided at the bottom of each evaporation chamber 2, 3, 4, located downstream of the interstage orifice 5, and having a predetermined length in the flow direction of the brine 7. . In the drawing, the raised bottom portions 6 provided in the upstream evaporation chamber 2 and the downstream evaporation chamber 4 are omitted.

Strictly speaking, the position and size of the rectangular raised bottom part 6 in the evaporation chamber 3 are related to the process conditions such as the flow rate of the brine 7 and the evaporation temperature, so it is difficult to specify them clearly. In the example, it is within the following range. In other words, the brine flow rate is 600 to 1000 t/mh, the evaporation temperature is 80 to 35°C, the position is upstream from the center of the evaporation chamber 3, and the length is 1/3 to 1 of the length of the evaporation chamber 3. /5, and the height was in the range of 40 to 70% of the outlet brine 7 level of the evaporation chamber 3. In standard terms, the position of the raised bottom 6 is approximately 1/3 of the length of the evaporation chamber 3, the length is approximately 1/4 of the length of the evaporation chamber 3, and the height is at the level of the outlet brine 7 of the evaporation chamber 3. It can be said that around 55% is optimal for each.

With such a configuration, as shown by the arrow in the figure, the brine 7
When flowing, the brine 7 passes through the lower opening of the upstream partition plate 1, and at this time, it is regulated by the interstage orifice 5 and flows into the evaporation chamber 3 so as to be released into the evaporation chamber 3. 6 and some of it evaporates. The steam is cooled and condensed by appropriate means and then used. After the remaining brine 7 climbs over the raised bottom part 6, it passes through the lower opening of the downstream partition plate 1 and advances to the downstream evaporation chamber 4, where it is further evaporated.

Next, an experiment was conducted to determine the degree of completion of evaporation when the raised bottom part 6 was provided and when the raised bottom part 6 was not provided, and the results will be explained based on FIG. 2. Figure 2 shows the brine flow rate (displayed as flow rate per unit width of the evaporation chamber) constant at 800t/mh.
The effect was examined by varying the evaporation temperature. In the figure, NETD is an index indicating the degree of completion of evaporation, and is defined as the difference between the temperature of the brine 7 exiting the evaporation chamber 3 and the evaporation temperature. The smaller the NETD, the more complete the steam is. Second
As is clear from the figure, the device provided with the raised bottom portion 6 according to the present invention can significantly reduce NETD compared to the device not provided with the raised bottom portion 6. Although the difference can be seen even around 80℃, it is especially noticeable at evaporation temperatures of 50℃ or lower. From this, the present invention relates to
Even if the evaporation temperature of the brine 7 becomes low and a difference in evaporation rate occurs between the upper layer and the lower layer, it is possible to prevent the brine 7 with evaporation ability from penetrating into the lower layer where evaporation is suppressed. One thing is clear.

3 to 5 show other embodiments in which the shape of the raised bottom portion 6 is changed. The arrows shown in the figure each represent the flow direction of the brine 7. The one in FIG. 3 has a slope 9 on the downstream end of the raised bottom part 8, and the one in FIG. 4 has a slope 11 on the upstream end of the raised bottom part 10.
The one shown has slopes 13 on both the upstream and downstream ends of the raised bottom portion 12, and these configurations allow the brine 7 to flow smoothly and reduce flow resistance. This makes it possible to more effectively prevent the brine 7 having evaporation ability from penetrating into the lower layer where evaporation is to be suppressed.

In FIGS. 6 to 9, instead of the raised bottom part 6,
A rectangular weir is provided. In the one shown in FIG. 6, a through hole 15 is provided at the lower end of the downstream end face of the weir section 14 for, for example, water drainage, measurement, and reinforcement purposes. 7 is not allowed to pass. Even if some through holes 15 are provided in this way, a large amount of brine 7 will not flow into the through holes 15, so
While the same effects as the above-mentioned raised bottom part 6 can be obtained, the required purpose can be achieved by using the through hole 15. Weir section 16 in Fig. 7
is constructed by removing a part of the member 17 on the downstream end face at appropriate intervals in the width direction as shown in FIG. 8, and the weir part 18 in FIG. It is constructed by completely removing the . By reducing or eliminating some of the members of the weir parts 16 and 18 in this way, it is possible to obtain the same effects as the above-mentioned raised bottom part 6, while reducing costs.

Although each of the above embodiments has been described with a focus on desalination of seawater, it is clear that the invention can be similarly applied to geothermal water, other hot wastewater, or hot wastewater.

As described above, according to the method of the present invention, even when the evaporation temperature of the brine is high as well as when the evaporation temperature of the brine is low, the brine with evaporation ability can sneak into the lower layer where evaporation is suppressed by the liquid head of the upper layer brine. Since the evaporation of brine can be prevented, the evaporation of brine can be promoted extremely well.
In addition, since the length of the raised bottom or weir in the brine direction is set to range from 1/3 to 1/5 of the length of the evaporation chamber, the brine on the raised bottom or weir becomes shallow, resulting in excellent evaporation. performance can be obtained.

[Brief explanation of drawings]

The drawings show an embodiment of the method of the present invention; FIG. 1 is an enlarged vertical sectional side view of the main parts of the multi-stage flash evaporator according to the present invention, FIG. 2 is a diagram showing the relationship between NETD and evaporation temperature, and FIGS. FIG. 5 is a vertical sectional side view showing other embodiments of the raised bottom portion, and FIGS.
The figure shows an example of the weir part, FIGS. 6 and 7 are longitudinal sectional side views of the rectangular weir part, and FIG. 8 is the A of FIG.
-A sectional view and FIG. 9 are longitudinal sectional side views of a rectangular dam. 5... Interstage orifice, 6, 8, 10, 12...
...Raised bottom, 7...Brine, 14, 16, 18
...Weir.

Claims (1)

[Claims] 1. A raised bottom or weir provided on the downstream side of the interstage orifice of the multi-stage flash evaporation chamber so that the length in the brine flow direction ranges from 1/3 to 1/5 of the length of the evaporation chamber. A method for promoting evaporation in a multi-stage flash evaporator, characterized in that evaporation is promoted by a portion of the flash evaporator.