JPH0673601B2 - Evaporative concentrator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporative concentrator, and more particularly to an evaporative concentrator for evaporating and concentrating water from an aqueous solution having a large boiling point such as an aqueous solution of sodium hydroxide (NaOH).

[0002]

2. Description of the Related Art For example, when evaporating and concentrating an aqueous solution having a large boiling point, such as an aqueous NaOH solution, a high concentration (for example, in the case of an aqueous NaOH solution, the NaOH concentration is 40% by weight or more) is used. Then, the degree of boiling point increase becomes large. Therefore, although not shown in particular, for example, by using a liquid film drop type evaporative concentrator using an evaporator equipped with a liquid film drop type heat exchanger and a liquid chamber, NaO
In the case of evaporating and concentrating the H aqueous solution, when the liquid to be concentrated is circulated in the heat exchanger, the concentration of the liquid to be concentrated in the heat exchanger is higher than that in the case where it is not circulated, especially near the inlet of the heat exchanger, Since the degree of boiling point rise is large, the effect on the entire heat exchanger is reduced, and the temperature difference with the steam that is the heating source is reduced, and the heat transfer area of the heat exchanger is increased in order to secure a predetermined amount of heat transfer. However, there is a problem that equipment costs increase.

Therefore, in the high concentration region, it is necessary to carry out the evaporative concentration while suppressing the influence of the boiling point increase over the entire heat exchanger as described above. For that purpose, it is possible to extract the liquid to be concentrated (concentrated liquid) that has been heated and concentrated in the heat exchanger from the liquid chamber without circulating it to the heat exchanger and collect it, or use it as the supply liquid for the subsequent concentration process. . However, in this method, when the supply amount of the concentrated liquid to the heat exchanger fluctuates, for example, the supply amount to the liquid film drop type heat exchanger is insufficient, and liquid runs out in the heat transfer tube, which is good. There is a problem that it is not possible to perform efficient heat exchange.

The present invention solves the above problems and provides an evaporative concentrator capable of efficiently evaporating and concentrating an aqueous solution of NaOH or the like having a small equipment cost and running cost and a large boiling point increase. With the goal.

[0005]

In order to achieve the above object, the evaporative concentration apparatus of the present invention heats a liquid to be concentrated supplied in an evaporative concentration apparatus for concentrating an aqueous solution of a substance having a large boiling point. An evaporator comprising a heat exchanger for evaporating water, a liquid chamber for separating concentrated liquid heated and concentrated in the heat exchanger from evaporated steam, and a supply amount of the concentrated liquid to the heat exchanger If the supply amount of the concentrated liquid to the heat exchanger, which is detected by the detection unit and the detection unit, satisfies the amount required to perform the predetermined heat exchange in the heat exchanger, the liquid chamber is covered. If the concentrated liquid is not circulated to the heat exchanger and the amount of the concentrated liquid to be supplied to the heat exchanger does not meet the amount required to perform the specified heat exchange in the heat exchanger, the heat exchanger The amount of liquid to be concentrated to be supplied to the To be concentrate liquid chamber so as to characterized by comprising a circulating means for circulating the heat exchanger.

Further, the heat exchanger is a liquid film lowering type heat exchanger.

[0007]

When the amount of the liquid to be concentrated supplied to the heat exchanger (heater) of the evaporator is sufficient to cause a predetermined heat exchange in the heat exchanger, the liquid chamber The liquid to be concentrated (concentrated liquid) is not circulated in the heat exchanger, and the influence of the boiling point increase is suppressed. Further, when the amount of the concentrated liquid to be supplied to the heat exchanger does not satisfy the amount required to perform a predetermined heat exchange in the heat exchanger, the supply of the concentrated liquid to the heat exchanger is performed. The amount (the total amount of the liquid to be concentrated supplied from the supply line and the liquid to be concentrated (concentrated liquid) circulated from the liquid chamber) is set to the amount necessary for performing predetermined heat exchange in the heat exchanger. The concentrated liquid (concentrated liquid) in the liquid chamber is circulated to the heat exchanger, but the circulation amount of the concentrated liquid (concentrated liquid) circulated from the liquid chamber varies in the supply amount of the concentrated liquid. In order to maintain a normal heat exchange state (operating state), the amount is unavoidable (minimum necessary amount), so even if there is a variation in the supply amount of the concentrated liquid, the effect of the boiling point increase is significantly large. (That is, as in the case where the liquid to be concentrated is constantly circulated from the liquid chamber to the heat exchanger) , The concentration of the concentrated liquid near the inlet of the heat exchanger becomes high and the boiling point rises, affecting the entire heat exchanger), while the concentrated liquid in the heat transfer tube of the heat exchanger runs out. It is possible to prevent a decrease in efficiency due to.

Therefore, it is not necessary to increase the heat transfer area of the heat exchanger in order to cope with the excessive influence of the boiling point increase, and the liquid to be concentrated (concentrated liquid) is steadily transferred from the liquid chamber to the heat exchanger. There is no need to install a circulation pump for circulation, reducing equipment costs and running costs,
It is possible to efficiently evaporate and concentrate an aqueous solution of a substance having a large boiling point increase.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an evaporative concentration apparatus according to an embodiment of the present invention. The evaporative concentrator of this embodiment is a triple-effect evaporative concentrator for concentrating a NaOH aqueous solution (concentrated liquid) having a large boiling point, and a first evaporator ( A liquid film falling evaporator 1), a second evaporator (liquid film falling evaporator) 2, and a third evaporator (forced circulation evaporator) 3 for evaporating and concentrating in a low concentration region are provided.

A heat exchanger (heater) 4 for heating the liquid to be concentrated is connected to the third evaporator 3, and a NaOH aqueous solution (concentrated liquid) of about 30% by weight supplied from a pipe 5 is supplied.
Is heated in the heat exchanger 4, and water is evaporated in the third evaporator 3.

The second evaporator 2 is a liquid film drop type heat exchanger 2.
a and a liquid chamber 2b, and the liquid chamber 2b is a separator 2
It communicates with c. The separator 2c has a second
The third evaporation can 3 using the evaporation vapor in the evaporation can 2 as a heating source.
17 is connected to the heat exchanger 4 of FIG. Further, a supply pipe 6 for supplying the concentrated liquid of the third evaporator 3 (concentrated liquid of the second evaporator 2) is connected to the second evaporator 2, and the supply pipe 6 is further connected to the supply pipe 6. , The liquid feed pump 19,
A detection means 8 for detecting the amount of the liquid to be concentrated (concentrated liquid of the third evaporator 3) supplied to the heat exchanger 2a of the second evaporator 2 is provided. Further, in the second evaporator 2, the concentrated liquid of the second evaporator 2 (concentrated liquid of the first evaporator 1) is added to the first evaporator 1
A liquid feed pump 9 for supplying the liquid to the supply pipe 7 is connected to the supply pipe 7. When the liquid to be concentrated is supplied from the second evaporator to the first evaporator 1 to the supply pipe 7, and the supply amount of the liquid to be concentrated to the heat exchanger 2a detected by the detection means 8 becomes equal to or less than a predetermined amount. A circulation line 10 for circulating the liquid to be concentrated (concentrated liquid) extracted from the liquid chamber 2b to the heat exchanger 2a via the supply pipe 6.
Is provided. Further, the circulation line 10 is provided with a flow rate control valve 11 having a closing function, and the flow rate control valve 11 is configured so that the supply amount of the concentrated liquid supplied from the third evaporator 3 is the heat exchanger 2a. When the liquid is cut off in the heat transfer tube 2d and the heat transfer tube 2d has decreased to the extent that good heat transfer (heat exchange) cannot be performed, it opens to supply the concentrated liquid (concentrated liquid) in the liquid chamber 2b to the supply pipe 6. It is circulated to the heat exchanger 2a via the heat exchanger 2a, and the total amount of the circulation amount of the concentrated liquid (concentrated liquid) and the concentrated liquid supplied from the third evaporator 3 enables efficient heat exchange in the heat exchanger 2a. To the amount that can be done,
The circulation amount of the concentrated liquid (concentrated liquid) from the liquid chamber 2b is controlled.

The first evaporator 1 has a liquid film lowering heat exchanger 1a and a liquid chamber 1b, like the second evaporator 2, and the liquid chamber 1b communicates with a separator 1c. . A pipe 18 is connected to the separator 1c to supply the vaporized vapor in the first evaporator 1 to the heat exchanger 2a of the second evaporator 2 as a heat source. In addition, the first evaporator 1
A supply pipe 7 for supplying a liquid to be concentrated (concentrated liquid of the second evaporator 2), a withdrawal pump 15 for withdrawing the liquid to be concentrated (concentrated liquid), and an extraction pipe 12 are connected. And
The supply pipe 7 is provided with detection means 13 for detecting the supply amount of the liquid to be concentrated (concentrated liquid of the second evaporator 2) to the heat exchanger 1a of the first evaporator 1 and is withdrawn. The liquid to be concentrated (concentrated liquid) is taken out of the system to the pipe 12, and when the amount of the liquid to be concentrated to be supplied to the heat exchanger 1a detected by the detection means 13 becomes a predetermined amount or less, the liquid in the liquid chamber 1b is covered. A circulation line 14 that circulates the concentrated liquid (concentrated liquid) through the supply pipe 7 to the heat exchanger 1a is provided. In addition, in the circulation line 14,
A flow rate adjusting valve 16 having a closing function similar to that of the flow rate adjusting valve 11 provided in the circulation line 10 is provided.

Using the evaporative concentration apparatus of this embodiment, NaO
When the H aqueous solution is concentrated, the NaOH concentration is about 30% by weight.
At this point, the liquid to be concentrated whose boiling point is not so large is supplied to the third evaporator and concentrated to a predetermined concentration. Concentrated liquid (concentrated liquid) concentrated to a predetermined concentration in the third evaporator 3
Is supplied to the second evaporator 2 via the liquid feed pump 19 and the supply pipe 6. The to-be-concentrated liquid (concentrated liquid in the third evaporator 3) supplied to the second evaporator 2 is heated by the liquid film descending heat exchanger 2a, and is evaporated and concentrated in the heat exchanger 2a, so that the liquid chamber Two
b, gas-liquid separation is performed in the separator 2c.

Then, in the above-mentioned evaporative concentration step, the supply amount of the liquid to be concentrated to the heat exchanger 2a detected by the detection means 8 is such that heat exchange cannot be performed efficiently in the heat exchanger 2a. When it decreases, the flow rate adjusting valve 11 opens, and the total amount of the liquid to be concentrated supplied from the third evaporator 3 becomes the amount that enables efficient heat exchange in the heat exchanger 2a. Liquid to be concentrated (concentrated liquid) is supplied from 2b to the supply pipe 6
And is circulated to the heat exchanger 2a. Further, the supply amount of the liquid to be concentrated to the heat exchanger 2a detected by the detecting means 8 is such that the heat transfer pipe 2d of the heat exchanger 2a does not run out of liquid and heat can be efficiently exchanged. When the flow rate is recovered, the flow rate adjusting valve 11 is closed and the circulation of the concentrated liquid (concentrated liquid) from the liquid chamber 2b is stopped.

In the first evaporator 1 as well, evaporative concentration is performed in the same manner as in the second evaporator 2 described above, and the concentrated liquid concentrated to a NaOH concentration of about 50% by weight is taken out from the discharge pipe 12.
Will be collected as a product from

As described above, in the evaporative concentration apparatus of this embodiment, in the second evaporator 1 and the first evaporator 1 which evaporate and condense in the concentration range where the boiling point increases largely, the liquid film falling heat exchange is performed. When the amount of the concentrated liquid to be supplied to the vessels 2a, 1a is in a range that allows efficient heat exchange without running out of liquid in the heat exchangers 2a, 1a,
The liquid to be concentrated (concentrated liquid) in the liquid chambers 2b, 1b is transferred to the heat exchanger 2a,
The liquid to be concentrated (concentrated liquid) from the liquid chambers 2b and 1b is not exchanged in the heat exchangers 2a and 1a only when it does not circulate in the heat exchangers 2a and 1a and does not satisfy the amount required to perform a predetermined heat exchange. Since it is circulated in 2a and 1a, even if the supply amount of the concentrated liquid is varied, the boiling point of the concentrated liquid is excessively affected (that is, the concentrated liquid is removed from the liquid chamber). As in the case of constant circulation to the heat exchanger, the concentration of the concentrated liquid near the inlet of the heat exchanger becomes high and the boiling point rises, affecting the entire heat exchanger) It is possible to prevent a decrease in heat exchange efficiency due to a liquid out of the heat transfer tube in the exchanger.

Further, although the triple effect evaporative concentrator is described in the above embodiment, the present invention is not limited to the triple effect evaporative concentrator, but the double effect or the four effect is used.
The present invention can be applied to each effect evaporator of a multi-effect evaporative concentrator having more than a heavy effect, and can also be applied to a single effect evaporative concentrator.

In the above embodiment, the case where the heat exchanger is a liquid film lowering type heat exchanger has been described. However, the present invention is not limited to the liquid film lowering type heat exchanger, and a liquid film rising type It is particularly significant in the heat exchanger and other evaporative concentrators that use a heat exchanger (heater) that causes a rapid decrease in heat transfer efficiency due to liquid shortage to the heat transfer tube due to a decrease in the supply liquid amount.

[0019]

As described above, the evaporative concentration apparatus of the present invention detects the supply amount of the concentrated liquid to the heat exchanger, and the supply amount of the concentrated liquid causes the predetermined heat exchange in the heat exchanger. The liquid to be concentrated from the liquid chamber is adjusted so that the supply amount of the liquid to be concentrated passing through the heat exchanger is the amount necessary to perform the predetermined heat exchange only when the amount necessary to perform the heat exchange is not satisfied. Since the (concentrated liquid) is circulated to the heat exchanger, even if the supply amount of the concentrated liquid varies, the heat transfer temperature difference can be significantly reduced due to the excessive boiling point of the concentrated liquid. It is possible to prevent a decrease in heat transfer efficiency in the heat exchanger while preventing the above. Therefore, it is possible to suppress an increase in the heat transfer area of the heat exchanger to cope with a large decrease in the heat transfer temperature difference, and to circulate the concentrated liquid (concentrated liquid) from the liquid chamber to the heat exchanger steadily. It becomes possible to eliminate the need for the circulation pump, and it becomes possible to reduce the equipment cost and the running cost and to evaporate and concentrate the aqueous solution of the substance having a large boiling point efficiently.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an evaporative concentration apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st evaporator 1a 1st evaporator heat exchanger 1b 1st evaporator liquid chamber 2 2nd evaporator 2a 2nd evaporator heat exchanger 2b 2nd evaporator liquid chamber 8, 13 Detection means 9 , 19 Liquid feed pump 15 Extraction pump

Claims (2)

[Claims] 1. An evaporative concentrator for concentrating an aqueous solution of a substance having a large increase in boiling point, a heat exchanger for heating a liquid to be concentrated to evaporate water, and a liquid to be concentrated concentrated in the heat exchanger. And a vaporization chamber comprising a liquid chamber for separating vaporized water vapor, detection means for detecting the amount of the liquid to be concentrated supplied to the heat exchanger, and liquid to be concentrated to the heat exchanger detected by the detection means. If the amount supplied is sufficient to perform the specified heat exchange in the heat exchanger, the liquid to be concentrated in the liquid chamber is not circulated to the heat exchanger, and the liquid to be concentrated in the heat exchanger is not circulated. If the supply amount does not meet the amount required to perform the specified heat exchange in the heat exchanger, the supply amount of the concentrated liquid to the heat exchanger is required to perform the specified heat exchange. And a circulation means for circulating the liquid to be concentrated in the liquid chamber through the heat exchanger so that the amount of the liquid to be concentrated becomes large. An evaporative concentrator, which is characterized in that 2. The evaporative concentrator according to claim 1, wherein the heat exchanger is a liquid film drop type heat exchanger.