JP7093443B1 - Freeze concentration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a freeze-concentration method in which ice is completely melted at the end of an ice-melting step. SOLUTION: In a freeze-concentration method in which a liquid to be treated is concentrated by a freeze-concentration treatment to obtain an ice content and a treated liquid, the obtained ice content is melted by sprinkling warm water to obtain thawed water. It has a deicing step in which the step of heating the defrosted water and using it as hot water for melting ice again is repeated, and in the deicing step, the temperature (t3) of the defrosted water becomes 7 ° C. or higher. It is solved by a freeze-concentration method, characterized in that it is sometimes terminated. [Selection diagram] Fig. 1

Description

The present invention relates to a freeze-concentration method.

Recently, the technology related to freeze concentration has become more important, such as being used for mask cleaning wastewater at the Fukushima Daiichi Nuclear Power Station, and various proposals have been made. Freezing concentration is a technique for achieving concentration by freezing only the water content of the aqueous solution and separating the generated ice crystals from the unfrozen treated liquid. Basically, a predetermined amount of the liquid to be treated is specified. In addition to freeze-concentrating to the concentration limit of, the treated liquid concentrated to the concentration limit and the ice content are separated.

From the viewpoint of separation of the treated liquid and ice, freeze concentration is a batch type in which the separation operation is performed after one concentration treatment up to the concentration limit, and a continuous type in which the ice is continuously separated in the concentration process. It is roughly divided into. From the viewpoint of ice formation / growth form, it is roughly classified into a forward freezing method in which ice is attached / grown on a cooling heat transfer surface and a suspended crystal method in which granular ice is formed / grown in a solution.

In particular, as an example of the forward freezing method, there is a freeze-concentration (freeze separation) apparatus proposed in Patent Document 1. In this freeze-concentrator, a cooling coil is provided in the freeze-concentration tank, a spraying section is provided above the cooling coil, a water storage section is provided below the cooling coil, and the liquid to be treated is sprayed from the spraying section to the cooling coil. The liquid to be treated is configured so that the liquid to be treated is sequentially dropped to the lower stage side while in contact with each cooling coil, and the liquid to be treated is cooled and frozen in the process of flowing down while being in contact with the cooling coil in a liquid film state. Further, the liquid to be treated that reaches the water storage portion without freezing is circulated and supplied to the spraying portion and cooled again. By continuing this circulation supply, a predetermined amount of the liquid to be treated can be concentrated to the concentration limit (about 10 times). The treated liquid that has reached the concentration limit is discharged to the outside of the system. In the following, this technique will be referred to as a flow-down liquid film type freeze concentration.

Further, those described in Patent Document 2 also fall into the category of the forward freezing method. This prior art is to solve the uptake of solutes into ice crystals due to the excessive degree of supercooling when ice is formed on the surface of the cooling body, and for this purpose, distilled water is used on the surface of the cooling body. By generating pure ice in advance, excessive supercooling of the treatment liquid in the vicinity of the cooling body is suppressed.

Japanese Unexamined Patent Publication No. 2001-47034 Japanese Unexamined Patent Publication No. 10-54629

However, the conventional freeze-concentration technique has the following problems. During normal operation, the freeze-concentrator concentrates the liquid to be treated by repeating the process of making ice and the process of thawing, but the amount of ice formed in the cooling coil is transferred to the freeze-concentrating tank. The amount of deicing is measured by the change in the liquid level of the liquid to be treated tank that supplies the liquid to be treated, and the amount of deicing is the liquid in the deicing water tank, which is a container for deiced water (hereinafter, also referred to as "deicing water"). It is measured by the change of position. However, when a power outage or the like occurs, the operation history up to that point becomes unknown, and it may be difficult to grasp how much ice is formed in the cooling coil. When automatic operation is restarted with ice on the cooling coil, an amount of liquid to be treated that exceeds the maximum amount of ice that should be formed on the cooling coil is supplied to the liquid tank to be treated, resulting in ice making. Minutes are excessively formed in the cooling coil. This can cause ice bridging and damage to the cooling coil.

Therefore, a main object of the present invention is to make the ice content completely melted at the end of the deicing process.

The aspects of the invention for solving the above problems are as follows.
(First aspect)
In the freeze-concentration method in which the liquid to be treated is concentrated by freeze-concentration treatment to obtain ice content and the treated liquid.
It has a deicing step of repeating the steps of sprinkling hot water on the obtained ice to melt it to obtain defrosted water, heating the defrosted water, and using it as hot water to melt the ice again.
The deicing step ends when the temperature (t3) of the deicing water reaches 7 ° C. or higher.
A freeze-concentration method characterized by this.

The present inventor has repeated diligent research, and when melting ice with warm water in the deicing process, the deicing water stays at a low temperature while the ice remains, but above the above temperature, the ice is completely depleted. I was able to confirm that it was melted. If the ice is completely melted, the ice will not be overproduced even if the ice making process is performed, and there is no risk of bridging the ice or damaging the cooling coil. be able to.

(Second aspect)
The liquid to be treated is cooled, a part of the liquid to be treated is frozen to separate the ice content generated, and the remaining liquid to be treated is used again for the cooling treatment, and the process is repeated to concentrate the liquid to a predetermined level. It has an ice making process to obtain the processed liquid.
The ice making process and the ice defrosting process are alternately repeated,
When the temperature (t1) of the liquid to be treated is higher than the temperature (t4) of the remaining liquid to be treated, the ice making step is terminated and the ice defrosting step is started.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above.

If, for example, a power failure occurs and the power is restored during the ice making process, the operation history up to that point is reset depending on the control program of the freeze concentration process, and the replenishment process is restarted. Then, when the supply tank is replenished with the liquid to be treated and the process shifts to the ice making process to make ice, the ice is made in excess of the original ice that should be made, which is the bridging of the ice and the cooling coil. It can cause damage. In this embodiment, when the temperature (t1) of the liquid to be treated is higher than the temperature (t4) of the remaining liquid to be treated, the ice making step is terminated and the ice defrosting step is started. Even if the ice making process is started with the ice content remaining, the ice making process is completed by the determination of t1> t4, and as a result, the ice is not produced in excess of the ice content.

(Third aspect)
The liquid to be treated is cooled, a part of the liquid to be treated is frozen to separate the ice content generated, and the remaining liquid to be treated is used again for the cooling treatment, and the process is repeated to concentrate the liquid to a predetermined level. It has an ice making process to obtain the processed liquid.
The ice making process and the ice defrosting process are alternately repeated,
When the difference between the temperature of the liquid to be treated (t1) and the temperature of the remaining liquid to be treated (t4) is 1 ° C. or more, the ice making step is terminated and the ice defrosting step is started.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above.

Similar to the second aspect, as a result of the ice making process being completed by the determination of | t1-t4 | ≧ 1 ° C., the ice content is not exceeded and the ice is not made.

(Fourth aspect)
The liquid to be treated is cooled, a part of the liquid to be treated is frozen to separate the ice content generated, and the remaining liquid to be treated is used again for the cooling treatment, and the process is repeated to concentrate the liquid to a predetermined level. It has an ice making process to obtain the processed liquid.
The ice making process and the ice defrosting process are alternately repeated,
When the temperature (t4) of the remaining liquid to be treated is 7 ° C. or lower, the ice making step is terminated and the ice defrosting step is started.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above.

Similar to the second aspect, as a result of the ice making step being completed by the determination of t4 ≦ 7 ° C., the ice content is not exceeded and the ice is not made.

(Fifth aspect)
The deicing step is terminated when the difference between the temperature of the hot water (t2) and the temperature of the deicing water (t3) becomes 0.5 ° C. or less.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above.

The fact that the temperature of the deicing water (t3) approaches the temperature of the hot water (t2) means that the deicing water warms up, and the ice content is completely melted by the judgment of | t2-t3 | ≤0.5 ° C. It can be said that we are ready to move to the ice making process.

(Sixth aspect)
It has a replenishment step of replenishing the liquid to be treated used in the ice making step from outside the system.
The replenishment step is performed after the ice making step is completed.
The freeze-concentration method according to claim 2.

If the replenishment process is performed during the ice making process, it causes excessive production of ice content. Therefore, by performing the replenishment process after the ice making process is completed, it is possible to avoid excessive production of ice content. ..

According to the present invention, it is a freeze-concentration method in which the ice content is completely melted at the end of the deicing step.

It is a figure which shows one Embodiment of this invention. It is a schematic diagram which shows the operation example using an embodiment. It is a schematic diagram which shows the operation example using an embodiment. It is a schematic diagram which shows the operation example using an embodiment. It is a schematic diagram which shows the operation example using an embodiment. It is a schematic diagram which shows the operation example using an embodiment. It is a schematic diagram which shows the operation example using an embodiment. It is a schematic diagram which shows the operation example using an embodiment. It is a graph which shows the time-dependent change of the temperature and the liquid amount in each process. It is a graph which shows the time-dependent change of temperature and liquid volume. It is a graph which shows the time-dependent change of temperature and liquid volume. It is a graph which shows the time-dependent change of temperature and liquid volume. It is a flow chart of a freeze-concentration process.

Next, a mode for carrying out the invention will be described. The embodiment of the present invention is an example of the present invention. The scope of the present invention is not limited to the scope of the present embodiment.

The freeze-concentrator 1 according to the present invention shown in FIG. 1 has a freeze-concentration tank 4 that freezes a liquid to be treated and separates it into ice and a treated liquid, and a supply tank 2 that supplies the liquid to be treated to the freeze-concentrate tank 4. The liquid to be treated J1 replenished from outside the system is temporarily stored, and the liquid to be treated storage tank 6 to be supplied to the supply tank 2 and the defrosted water obtained by deicing the ice content are received. It is mainly composed of a tank 3 and a deicing water storage tank 7 that temporarily stores the deicing water supplied from the deicing water tank 3 and flows out of the system.

The freeze-concentration treatment performed in the present invention refers to a treatment in which a liquid to be treated containing impurities is cooled, a part of the liquid to be treated is frozen as ice and separated to obtain a residue, that is, a treated liquid. The obtained treated liquid has a higher concentration of impurities than the initially treated liquid. Here, as a method for cooling the liquid to be treated, for example, a method such as passing the liquid to be treated through an object having a temperature lower than that of the liquid to be treated can be mentioned. Hereinafter, a series of steps of the freeze concentration treatment will be described in detail.

(Liquid storage tank to be treated)
The liquid J1 to be treated is supplied from outside the system, flows from the outside of the system through the flow path 6B connected to the liquid storage tank 6, is guided to the liquid storage tank 6 to be treated, and is temporarily stored. The liquid to be treated storage tank 6 and the supply tank 2 provided downstream thereof are connected by a flow path 6A, and the liquid to be treated J1 flows and is supplied through the flow path 6A by a pump P5 provided in the liquid to be treated storage tank 6. It is supplied to the tank 2.

(Supply tank)
The supply tank 2 is provided with a pump P3 and a flow path 2B for discharging the treated liquid J2 concentrated to a predetermined level by the freeze-concentration treatment to the outside of the system. Further, the supply tank 2 is provided with a flow path 2A connecting the pump P1, the supply tank 2 and the freeze-concentration tank 4, and the liquid to be treated in the supply tank 2 flows through the flow path 2A due to the pressure of the pump P1. It is supplied to the freeze concentration tank 4. The flow path 2A is provided with a temperature sensor T1 that measures the temperature (t1) of the liquid to be treated flowing through the flow path 2A.

(Freezing concentration tank)
In the freeze-concentration tank 4, the cooling coil 4C, the spraying section 4G provided above the cooling coil 4C, the liquid storage section 4W provided below the cooling coil 4C, and the liquid collected in the liquid storage section 4W are contained. It mainly has an outflow portion that flows out from the freeze concentration tank 4. The liquid storage unit 4W is preferably configured so that the liquid level of the accumulated liquid is maintained below the cooling coil 4C. The outflow portion is provided with a flow path 4A through which the liquid flows out, the downstream end of the flow path 4A is branched into two, one is connected to the supply tank 2 and the other is the deicing water tank 3. It is connected to the flow path 4D connected to. The flow path 4A is provided with a temperature sensor T3 for measuring the temperature of the liquid flowing through the flow path 4A, the flow path 4B is provided with a valve V1, and the flow path 4D is provided with a valve V2. The cooling coil 4C is composed of a cooling pipe, and the refrigerant flowing in the cooling pipe is circulated by the pressure of the pump P7 provided in the cooling coil 4C and cooled by the refrigerator 4F. The spraying unit 4G sprays the liquid on the cooling coil 4C, and examples of the liquid sprayed from the spraying unit 4G include a liquid to be treated, deicing water, hot water, and purified water G2. The purified water G2 flows through the flow path 4E connected to the spraying portion 4G and is sprayed from the spraying portion 4G. A valve V3 can be provided in the flow path 4E. The freeze-concentration tank 4 itself is basically the same as that described in Japanese Patent Application Laid-Open No. 2001-47034, and is a flow-down liquid film type. The refrigerator 4F is not particularly limited and a general one can be used, and the evaporation temperature is preferably −5 to −10 ° C.

(Thawed water tank)
The liquid flowing through the flow path 4D flows into the deicing water tank 3. The thawing water tank 3 is provided with a flow path 3A connecting the pump P2, the thawing water tank 3 and the freeze concentration tank 4, and the thawing water in the thawing water tank 3 flows through the flow path 3A due to the pressure of the pump P2. Is supplied to the freeze concentration tank 4. The flow path 3A is provided with a heat exchanger 5 and a temperature sensor T2 for measuring the temperature of the liquid that passes through the heat exchanger 5 and is supplied to the spraying portion 4G from the upstream side to the downstream side.

Further, the defrosting water tank 3 is provided with a pump P4 and a flow path 3B connecting the defrosting water tank 3 and the defrosting water storage tank 7, and the defrosting water in the defrosting water tank 3 flows by the pressure of the pump P4. It flows through 3B and is supplied to the defrosted water storage tank 7.

(Thawed water storage tank)
The defrost water storage tank 7 temporarily stores the defrost water supplied from the defrost water tank 3 and causes it to flow out of the system. The defrosted water storage tank 7 is supplied from the discharge part where the defrosted water is discharged, the flow path 7A through which the defrosted water flows from the outflow part to the outside of the system, the pump P6 provided in the flow path 7A, and the outside of the system. It has a flow path 7B into which purified water G1 flows and an inflow portion. A valve V4 can be provided in the flow path 7B.

(Operation example)
The present embodiment is a freeze-concentration method in which a liquid to be treated is concentrated by a freeze-concentration treatment to obtain an ice content and a treated liquid, and the obtained ice content is melted by sprinkling warm water to obtain thawed water. It has a deicing step in which a step of heating the deicing water and using it as hot water for melting ice again is repeated, and the deicing step is when the temperature (t3) of the defrosting water becomes 7 ° C. or higher. It is characterized by the fact that it ends in. According to this embodiment, ice making is not performed in the presence of icing, and excessive ice making can be prevented. Further, the liquid to be treated can be finally separated into the treated liquid and the thawed water. A series of steps for separating the liquid to be treated into the thawed water and the treated liquid by using the freeze-concentrator 1 will be described below.

The series of steps of separating the liquid to be treated into ice-melting water and the treated liquid by the freeze-concentration treatment is roughly divided into an ice-making step and an ice-melting step, and the ice-making step and the ice-melting step are alternately repeated. The ice making step is further divided into an ice making concentration step and a washing step, and a deicing water transfer step can be further provided after the deicing step. The ice making step and the ice defrosting step may not be performed at the same time. An example of the flow of the freeze-concentration treatment is shown in FIG. 13, but the flow is not limited to this figure. It should be noted that the determination of the end of a certain process and the instruction to start the next process can be performed by a central processing unit (not shown).

In addition, a replenishment step for replenishing the liquid to be treated from outside the system can be provided. The replenishment step may be performed after the ice making step is completed. Assuming that the replenishment process is performed during the ice making process, if the freeze-concentrator 1 is stopped due to a power failure or some other factor during the ice making process, the liquid to be replenished by the replenishment process is used when the freeze-concentrator 1 is restarted. When ice making is resumed, ice is further formed on the surface layer of ice that has already landed on the cooling coil 4C at the time of stop, and excessive growth occurs, and the ice bridges between the cooling pipes. There is a problem that the cooling coil 4C is damaged. Further, by performing the deicing step after restarting, the excessively formed ice may be melted to become deicing water and overflow from the deicing water tank 3. In order to prevent such a situation from occurring, the timing of performing the replenishment process may be after the ice making process is completed. In the ice making step or the deicing step, the defrosting water accumulated in the deicing water storage tank 7 may be discharged as discharged water to the outside of the system by starting the pump P6 from the flow path 7A at an arbitrary timing.

(On standby)
Before explaining the ice making process, the standby time will be described. FIG. 2 is a schematic view showing standby time. During standby, no ice has landed on the cooling coil 4C. During standby, the liquid to be treated J1 flows from outside the system through the flow path 6B and is supplied to the liquid to be treated storage tank 6. Before performing the deicing step, the deicing water tank 3 may store an amount of water necessary for circulating the deicing water tank 3 and the freezing and concentrating tank 4. It should be noted that the equipment, flow paths, etc. used in each process are shown in thick or black in the drawings.

(Replenishment process)
In the replenishment step shown in FIG. 3, the pump P5 is started, the liquid to be treated flows from the liquid storage tank 6 to be replenished through the flow path 6A, and the amount of liquid to be iced on the cooling coil 4C is prepared in the supply tank 2. It is a process to do. The amount of liquid to be iced on the cooling coil 4C can be controlled by the liquid level of the supply tank 2, for example, when the liquid level is the H level which is a predetermined liquid level, the ice is landed on the cooling coil 4C. It can be determined that the amount of liquid has been prepared. The amount of liquid in the supply tank 2 at this H level is particularly called the initial amount of liquid. The temperature of the liquid to be treated prepared in the supply tank 2 is not particularly limited and depends on the surrounding atmosphere, but for example, 10 to 30 ° C. is preferable because it does not hinder the subsequent steps.

(Ice making concentration process)
In the ice making step, the process of cooling the liquid to be treated, separating the ice content generated by freezing a part of the liquid to be treated, and using the remaining liquid to be treated again for the cooling treatment is repeated. This is a step of obtaining a treated liquid concentrated to a predetermined level. The ice making concentration step in the ice making step should be performed after the replenishment step is completed. In the ice making concentration step shown in FIG. 4, the liquid to be treated starts from the supply tank 2, flows through the flow path 2A, reaches the freeze concentration tank 4, flows through the flow path 4A and the flow path 4B, and returns to the supply tank 2. This is a step of performing a cooling process in which ice is landed on the cooling coil 4C and grown. The refrigerator 4F and the pump P7 are started, and the cooling coil 4C is cooled to about −5 to −10 ° C. by the circulation of the refrigerant flowing through the cooling pipe. The valve V1 provided in the flow path 4B may be left open during the ice making concentration step.

The liquid to be treated, which has reached the freeze-concentration tank 4 by starting the pump P1 and flowing through the flow path 2A, is sprayed on the cooling coil 4C provided at a lower distance from the spraying portion 4G provided in the freeze-concentration tank 4. The sprayed liquid to be treated flows down on the surface of the cooling coil 4C or the surface of ice adhering to the cooling coil 4C in the form of a liquid film, and the liquid to be treated (flowing liquid) is cooled in the flow-down process. Will be done. Only a part of the pure water content of the flowing liquid lands on the surface of the cooling coil 4C or the surface of the ice content attached to the cooling coil, and the rest becomes the concentrated liquid to be treated (concentrated content). As a result, the ice and the concentrate are separated by freezing and concentration. Then, this residual concentrate is sequentially taken into the liquid to be treated flowing down through the icing site by continuous circulation of the liquid to be treated, and is washed away. The liquid to be treated, which flows down while taking in the concentrated portion and reaches the liquid storage unit 4W, is returned to the supply tank 2 via the flow paths 4A and 4B, mixed with the liquid to be treated in the tank, and then sprayed again. It is continuously circulated to 4G. In the continuous circulation of the liquid to be treated between the supply tank 2 and the freeze concentration tank 4, substantially only water in the liquid to be treated becomes ice and is stored in the cooling coil 4C, and impurities are not taken into the ice storage. Since the circulation continues, the impurity concentration of the circulating liquid to be treated increases with time, and pure water is separated from the liquid to be treated as ice.

Characteristically, as described above, the surface of the ice attached to the cooling coil is constantly flowed down so that the flowing liquid is licked, and the concentrated component is taken in and washed. Impurities are less likely to be incorporated into the produced ice, and ice production efficiency is also improved. As a result, 90% or more of the liquid to be treated can be stored as ice containing substantially only pure water. The ice making concentration step is determined to be completed based on, for example, the liquid level (L level) of the supply tank 2 when 90% of the liquid to be treated (initial liquid amount) prepared in the supply tank 2 becomes ice content. be able to.

In the ice making step, the liquid to be treated is concentrated by the freeze concentration treatment to separate the ice content, and the remaining liquid to be treated is used again for the freeze concentration treatment, but the temperature (t1) of the liquid to be treated remains. When the temperature is higher than the temperature (t4) of the liquid to be treated, the ice making step may be terminated and the ice melting step may be started. If the temperature (t1) of the liquid to be treated is higher than the temperature (t4) of the remaining liquid to be treated, ice content may remain in the cooling coil 4C, and if the ice making process is continued, the ice content may remain. May be excessively formed.

Further, when the ice making process is started and the difference between the temperature of the liquid to be treated (t1) and the temperature of the remaining liquid to be treated (t4) is 1 ° C. or more, or the temperature of the remaining liquid to be treated (t4). When the temperature is 7 ° C. or lower, the ice making step may be terminated and the ice melting step may be started.

The treated liquid is not particularly limited, but can be, for example, a liquid in which the concentration of impurities contained in the liquid to be treated before the ice making concentration step is increased 10 times (concentrated).

(Washing process)
The washing step shown in FIG. 6 may be performed after the completion of the ice making and concentration step. The washing step is a step of washing off the liquid to be treated remaining on the surface of the spraying portion 4G and the ice component adhering to the cooling coil in the ice making concentration step. The valve V3 provided in the flow path 4E is opened, the purified water G2 is supplied to the spraying portion 4G via the flow path 4E, and the purified water G2 is sprayed from the spraying portion 4G to the cooling coil 4C. The purified water drips while mixing with the liquid to be treated remaining in the cooling coil 4C, flows from the liquid storage unit 4W through the flow paths 4A and 4B, flows into the supply tank 2, and mixes with the mixed liquid contained in the supply tank 2. It is advisable to use purified water in a predetermined amount per cleaning process. Here, as the purified water, for example, clean water, distilled water, or the like can be used. After finishing the cleaning process, the valve V3 and the valve V1 are closed. The cleaning step may be completed when the purified water supplied to the freeze-concentration tank 4 is collected in the supply tank 2.

As shown in FIG. 5, the concentrated treated liquid accumulated in the supply tank 2 can be discharged from the flow path 2B to the outside of the system by starting the pump P3 after the cleaning step is completed. However, if the treated liquid J2 is discharged after the cleaning step is completed, the treated liquid is mixed with purified water, and the concentration of impurities contained in the treated liquid is reduced. Therefore, it is preferable to set the timing of discharging the treated liquid J2 between the ice making concentration step and the washing step because the treated liquid can be discharged while being concentrated. The discharge amount of the treated liquid J2 is, for example, 10 of the liquid amount (replenishment amount) of the liquid to be treated that has been replenished from the liquid storage tank 6 to the supply tank 2 in the replenishment step in consideration of the balance of the liquid amount. %. The liquid level of the supply tank 2 after the treated liquid J2 is discharged is particularly called the LL level.

(Ice defrosting process)
The deicing process is a process of repeating the process of sprinkling hot water on the ice obtained in the ice making process to melt it to obtain defrosted water, heating the defrosted water, and using it as hot water to melt the ice again. be. In the deicing step shown in FIG. 7, the deicing water collected in the deicing water tank 3 starts from the deicing water tank 3 and is heated by the heat exchanger 5 while flowing through the flow path 3A to reach the freeze concentration tank 4, the flow path 4A and the flow path 4A. The ice that has landed on the cooling coil 4C is melted by continuously performing a circulation of flowing through the flow path 4D and returning to the deicing water tank 3. During the ice-melting process, the heat exchanger 5 is started and the valve V2 provided in the flow path 4D is opened.

The ice that has landed on the cooling coil 4C in the ice making process is sprayed with hot water supplied from the spraying section 4G and melts to become deicing water, which falls into the liquid storage section 4W and is thawed via the flow paths 4A and 4D. It is collected in the ice water tank 3. While a large amount of ice remains in the cooling coil 4C, the hot water is cooled by the ice, and the temperature (t3) of the defrosted water flowing through the flow path 4A becomes lower than the temperature (t2) of the hot water to be sprayed. As the ice content of the cooling coil 4C decreases, the temperature of the thawed water (t3) approaches the temperature of the hot water to which it is sprayed (t2). If the temperature of the deicing water contained in the deicing water tank 3 is heated to about 60 ° C. before the deicing process is started, the deicing process can be completed without spending a lot of time, which is preferable. .. As a device for heating the temperature of the defrosted water, for example, the amount of heat discharged from cooling or waste heat, an electric heater, or the like can be used.

The deicing step may be completed when the temperature (t3) of the deicing water reaches 7 ° C. or higher. At that temperature, all the ice that has landed on the cooling coil 4C is in a melted state. Here, when all the ice content that has landed on the cooling coil 4C has melted, it can be determined as follows. For example, when the temperature (t3) of the deicing water reaches 7 ° C. or higher, more preferably 10 ° C. or higher, it can be determined that all the ice content that has landed on the cooling coil 4C has melted. The temperature (t3) of the thawed water can be measured by the temperature sensor T3 provided in the flow path 4A. It can also be determined as follows. For example, when the difference between the temperature of hot water (t2) and the temperature of deicing water (t3) is 0.5 ° C or less, more preferably 0.2 ° C or less, all the ice content that has landed on the cooling coil 4C is all. It can be judged that it has melted. In the past, the deicing process was continued for a sufficient time for the ice landed on the cooling coil 4C to completely melt, but as described above, the end of the deicing process should be determined based on the temperature. Therefore, the time required for the deicing process can be managed, and the processing time can be shortened.

It seems that the deicing process may be appropriately terminated when the ice content on the cooling coil 4C is not completely melted but is melted to some extent. However, if the ice content remains, when the ice making process is started, new ice content adheres to the surface of the remaining ice content and grows, resulting in more ice content than expected. There is a risk that ice will land on the cooling coil 4C, forming bridging between the cooling pipes of the cooling coil 4C, or damaging the cooling coil 4C. Further, if an excessive amount of ice is landed on the cooling coil 4C, the deicing water may overflow from the deicing water tank 3 when the subsequent deicing step is performed. Considering these points, it is desirable that the deicing process is completed when all the ice that has landed on the cooling coil 4C has melted.

After the deicing step is completed, the heat exchanger 5 may be stopped and the valve V2 may be closed.

(Movement process of thawed water)
After the deicing step is completed, the deicing water of the deicing water tank 3 may be directly discharged to the outside of the system, but a deicing water moving step may be provided. As shown in FIG. 8, the thawing water moving step is a step of providing a thawing water storage tank 7 and temporarily storing the thawing water of the thawing water tank 3 in the thawing water storage tank 7 and discharging the thawing water to the outside of the system. In the thawing water moving step, the pump P4 provided in the thawing water tank 3 is started to move the thawing water from the thawing water tank 3 to the thawing water storage tank 7 via the flow path 3B and store the thawing water. The defrosted water stored in the defrosted water storage tank 7 is discharged as discharged water K1 from the flow path 7A by starting the pump P6 in response to the demand for the discharged water outside the system. Further, purified water G1 may be mixed with defrosted water according to the demand for water outside the system. The purified water G1 can open the valve V4 and flow into the deicing water storage tank 7 via the flow path 7B.

The defrosting water transfer step can be terminated, for example, when the amount of defrosting water equal to the amount of ice landed on the cooling coil 4C is transferred from the defrosting water tank 3 to the defrosting water storage tank 7. The liquid level of the deicing water tank 3 at the end of this is particularly called the L level.

After the deicing step or the deicing water transfer step is completed, it is advisable to shift to the standby time or the ice making step.

Time-series changes in the temperature, liquid volume, etc. of each tank in the ice making process and the ice defrosting process (may include the deicing water transfer step) will be described with reference to FIG. FIG. 9 is an example. The horizontal axis is the passage of time (unit: time), the vertical axis on the left scale is the temperature (unit: ° C.), and the vertical axis on the right scale is the liquid volume (unit: m ³ ). The liquid amount L2 of the supply tank 2 is at the H level at the start of the ice making concentration step, and ends when it decreases to the L level as the liquid to be treated is circulated. The amount of liquid in the supply tank 2 increases in the subsequent cleaning step, is discharged as a treated liquid, decreases to the LL level, and then increases to the H level in the replenishment step. In the cleaning step, for example, about 50 L of purified water may be sprayed from the spraying portion 4G, and the time required for the cleaning step may be about 1 minute. In FIG. 9, reference numeral F1 is a replenishment step, reference numeral F2 is an ice making concentration step, reference numeral F3 is a washing step, reference numeral F4 is a deicing step, reference numeral F5 is a deicing water moving step, and reference numeral J2 is a treated liquid discharged to the outside of the system. Are shown respectively. Each temperature sensor T1, T2, T3 can measure the temperature of the liquid flowing through the sensor during each of the above steps F1 to F5. Further, the calculation of the measured temperature, for example, the calculation of the difference between t1 and t4, the calculation of the difference difference between t2 and t3, and the like can be performed by a central processing unit (not shown). In addition, the central processing unit can receive input of temperature measurement information over time measured by each temperature sensor T1, T2, T3, and can store and store the measurement information.

The temperature (t1) of the liquid to be treated in the supply tank 2 drops when the ice making concentration step is started, and is maintained at about 0 ° C. during the ice making concentration step. The temperature (t1) of the liquid to be treated gradually rises toward the temperature of the atmosphere because there is no factor for cooling in the subsequent steps.

The evaporation temperature V of the refrigerator 4F decreases toward −10 ° C. at which the ice making concentration step is started, and rises after the ice making concentration step is completed.

The liquid amount L3 of the deicing water tank 3 is constant during the ice making concentration step and the washing step, and when the deicing step is started, the ice content landed on the cooling coil 4C is thawed and the solution is taken. Ice content increases.

The temperature (t6) of the deicing water tank 3 may be set to a desired temperature (60 ° C. in FIG. 9) before the deicing step is started. The temperature of the deicing water tank 3 drops toward 0 ° C. when the deicing process is started, then gradually rises until the deicing process is completed, and becomes constant after the deicing process is completed.

The freeze-concentration treatment was performed using the freeze-concentrator 1. After performing the replenishment step and confirming that no ice had landed on the cooling coil 4C, the ice making concentration step was started. The flow rate of the liquid to be treated in the ice making concentration step was 30 m ³ / h. The temperature (t1) of the liquid to be treated supplied to the spraying unit 4G was measured by the temperature sensor T1, and the temperature (t4) of the concentrated liquid to be treated discharged from the liquid storage unit 4W was measured by the temperature sensor T3. Further, the liquid amount L2 of the liquid to be treated in the supply tank 2 was measured. FIG. 10 shows these measurement results in chronological order.

After completing the ice making concentration step and the washing step, the ice defrosting step was started. The flow rate of the deicing water in the deicing step was set to 30 m ³ / h. The temperature (t2) of the hot water supplied to the spraying unit 4G was measured by the temperature sensor T2, and the temperature (t3) of the defrosted water discharged from the liquid storage unit 4W was measured by the temperature sensor T3. Moreover, the liquid amount L3 of the deicing water in the deicing water tank 3 was measured. FIG. 12 shows these measurement results in chronological order.

When the deicing process was started, the temperature of the deicing water (t3) gradually increased and the temperature of the hot water (t2) gradually decreased. The liquid volume L3 of the deicing water tank 3 increased when the deicing process was started, and leveled off after 1 hour. Further, one hour after the start of the deicing process, the difference between the temperature of the hot water (t2) and the temperature of the deicing water (t3) becomes 0.2 ° C., and the ice content is not icing on the cooling coil 4C. Was confirmed.

In the embodiment, the deicing step is set to end when the temperature (t3) of the deicing water reaches 15 ° C. or higher. From the right end of FIG. 12, it can be read that the liquid level L3 of the deicing water tank 3 is increasing, but this is because the temperature (t3) of the deicing water reaches 15 ° C. and it is judged that the deicing process is completed. This is because the operation of the pump P2 was stopped, and the liquid flowing through the circulation path (specifically, the flow path 3A, the freeze concentration tank 4, the flow path 4A, 4D) flowed down to the deicing water tank 3.

As a comparative example, FIG. 11 shows that the ice making concentration step was started in a state where ice was landed on the cooling coil 4C. The flow rate of the liquid to be treated in the ice making concentration step was 30 m ³ / h. The temperature (t1) of the liquid to be treated supplied to the spraying unit 4G was measured by the temperature sensor T1, and the temperature (t4) of the concentrated liquid to be treated discharged from the liquid storage unit 4W was measured by the temperature sensor T3. Further, the liquid amount L2 of the liquid to be treated in the supply tank 2 was measured. In FIGS. 10 to 12, the horizontal axis is the passage of time (unit: time), the vertical axis left scale is the temperature (unit: ° C.), and the vertical axis right scale is the liquid volume (unit: m ³ ).

The present invention can be used for a flow-down liquid film type freeze concentration treatment, and in addition to reducing the volume of wastewater and desalinating seawater, industrial fields such as food, fermentation, chemical industry, concentration treatment in pharmaceuticals, wastewater / sewage treatment, etc. It is available for.

1 Freezing and concentrating device 2 Supply tank 3 Freezing water tank 4 Refrigerator 4C Cooling coil 4G Spraying part 4W Liquid storage part 5 Heat exchanger 6 Processed liquid storage tank 7 Freezing water storage tank

Claims (6)

In the freeze-concentration method in which the liquid to be treated is concentrated by freeze-concentration treatment to obtain ice content and the treated liquid.
It has a deicing step of repeating the steps of sprinkling hot water on the obtained ice to melt it to obtain defrosted water, heating the defrosted water, and using it as hot water to melt the ice again.
The deicing step ends when the temperature (t3) of the deicing water reaches 7 ° C. or higher.
A freeze-concentration method characterized by this. The liquid to be treated is cooled, a part of the liquid to be treated is frozen to separate the ice content generated, and the remaining liquid to be treated is used again for the cooling treatment, and the process is repeated to concentrate the liquid to a predetermined level. It has an ice making process to obtain the processed liquid.
The ice making process and the ice defrosting process are alternately repeated,
When the temperature (t1) of the liquid to be treated is higher than the temperature (t4) of the remaining liquid to be treated, the ice making step is terminated and the ice defrosting step is started.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above. The liquid to be treated is cooled, a part of the liquid to be treated is frozen to separate the ice content generated, and the remaining liquid to be treated is used again for the cooling treatment, and the process is repeated to concentrate the liquid to a predetermined level. It has an ice making process to obtain the processed liquid.
The ice making process and the ice defrosting process are alternately repeated,
When the difference between the temperature of the liquid to be treated (t1) and the temperature of the remaining liquid to be treated (t4) is 1 ° C. or more, the ice making step is terminated and the ice defrosting step is started.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above. The liquid to be treated is cooled, a part of the liquid to be treated is frozen to separate the ice content generated, and the remaining liquid to be treated is used again for the cooling treatment, and the process is repeated to concentrate the liquid to a predetermined level. It has an ice making process to obtain the processed liquid.
The ice making process and the ice defrosting process are alternately repeated,
When the temperature (t4) of the remaining liquid to be treated is 7 ° C. or lower, the ice making step is terminated and the ice defrosting step is started.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above. The deicing step is terminated when the difference between the temperature of the hot water (t2) and the temperature of the deicing water (t3) becomes 0.5 ° C. or less.
The freeze-concentration method according to claim 1, wherein the method is characterized by the above. It has a replenishment step of replenishing the liquid to be treated used in the ice making step from outside the system.
The replenishment step is performed after the ice making step is completed.
The freeze-concentration method according to claim 2.

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