JPS6352955B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for neutralizing an acidic liquid and an alkaline liquid, in which an acidic liquid piping and an alkaline liquid piping are connected to a mixer such as an ejector, and the respective acidic liquid and alkaline liquid are connected to both pipings. The conventional instant mixing neutralization method involves passing liquid through the mixer and adjusting the flow rate of the acidic or alkaline liquid with a flow control valve so that the pH on the outflow side of the mixer is around neutral. It is about improvement.

Conventionally, when neutralizing acidic waste liquid and alkaline waste liquid discharged from a pure water production equipment, for example, a mixer such as an ejector is used to instantly mix both waste liquids as a neutralization method that does not generate suspended substances in the neutralized liquid. A method of mixing the two has been proposed. One aspect of this conventional instant mixing neutralization method will be explained with reference to Fig. 1. First, the acidic waste liquid 1 discharged from processes such as chemical passing, extrusion, and washing during the regeneration of cation exchange resin and the anionic The alkaline liquid waste liquid 2 discharged from processes such as chemical passage, extrusion, and washing during the regeneration of ion exchange resin is separately received in an acidic waste liquid receiving tank 3 and an alkaline waste liquid receiving tank 4, and both waste liquids are sufficiently collected in each tank. After mixing, a certain amount of acidic waste liquid 1 is passed through acidic liquid piping 6 using acidic waste liquid pump 5, and alkaline waste liquid pump 7
The alkaline waste liquid 2 is made to flow through the alkaline liquid piping 8 using an alkali liquid pipe 8, and both waste liquids are instantaneously mixed in a mixer 9 such as an ejector. When mixing, the PH on the outflow side of the mixer 9 is measured with a PH detector 10, and the PH on the outflow side of the mixer 9 is around neutral, for example 6.
The alkaline waste liquid is mixed while adjusting the flow rate of the alkaline waste liquid using the flow rate control valve 12 linked to the pH indicator controller 11 so that the alkaline waste liquid falls within the range of 9 to 9. PH indicator controller 1
1 and the flow control valve 12 are such that when the PH at the measurement point becomes lower than the arbitrarily set PH value, which is the neutralization point input in advance to the PH indicator controller 11, the opening of the flow control valve 12 is adjusted. When the PH is increased, and vice versa, the opening of the flow rate control valve 12 is decreased, and the normal setting PH is around 7.0. Additionally, due to instrumentation delays, the flow control valve 12 is generally closed immediately after the start of neutralization.
The opening degree of the opening is not appropriate, and therefore, the pH of the neutralized liquid often does not fall within the pH range that can be discharged for about 2 minutes immediately after the start of neutralization. Therefore
A circulation pipe 14 is branched into a neutralization liquid pipe 13 after the PH detector 10, and an automatic valve 1 is linked with a PH indicator controller 11 until the pH of the neutralization liquid reaches a value that can be discharged.
5 is opened to circulate the neutralized liquid to the acidic waste liquid receiving tank 3, and when the pH of the neutralized liquid reaches a value that can be discharged, the automatic valve 15 is closed and the automatic valve 16 is opened to circulate the neutralized liquid to the acidic waste liquid receiving tank 3. I'm trying to release it.

When both waste liquids are neutralized by instantaneously mixing them in this way, suspended solids caused by calcium carbonate or polymerized silica are not generated. The so-called instant mixing neutralization method, which follows the flow shown in , is often adopted. By the way, the neutralization flow shown in FIG.
Since neutralization is performed while adjusting the flow rate of one liquid using only the flow rate control valve on the stand, the operating accuracy of the flow rate control valve can be improved.
The important point is the neutralization titration curve between the liquids to be neutralized. Figure 2 shows a typical neutralization titration curve of acidic waste liquid and alkaline waste liquid discharged from a two-bed, three-column water purification system, i.e., a mixture obtained when alkaline waste liquid is gradually added to a fixed amount of acidic waste liquid. However, the alkaline waste liquid generally contains a certain amount of carbonate ions and hydrogen carbonate ions, and these ions act as PH buffering substances, so the appropriate pH changes as shown in Figure 2. The slope of the fixed curve becomes relatively gentle. For example, the pH of the neutralized solution is 6 to 9.
When performing neutralization treatment within the range _of
Addition amount of alkaline waste liquid required to reach pH 9 T ₂
The difference is relatively large. In general, the operation of the flow rate control valve has an operating error of about 1% over the entire lift range, but if the adaptation curves for both waste liquids are relatively gentle as shown in Figure 2, this operating error will occur. is well within the range of _T2 - _T1 , so even if there is only one flow control valve, the neutralization process can be carried out stably without any hindrance.

However, in the case of waste liquid with extremely low content of PH buffering substances such as carbonate ions or bicarbonate ions, the slope of the neutralization titration curve becomes steep as shown in Figure 3. In the case of the waste liquid shown in FIG. 1, so-called one-stage neutralization using only one flow control valve 12 as shown in FIG. 1 cannot be carried out successfully. In other words, when neutralizing the neutralized liquid with a pH in the range of 6 to 9, as shown in Figure 3, the amount of alkaline waste liquid added T1' required to reach pH ₆ and the amount of alkaline waste liquid added required to reach pH 9. The difference in T ₂ ' is minute, so the operational error of the flow rate control valve 12 mentioned above is
It becomes larger than T ₂ ′−T ₁ ′ and cannot be controlled with one flow control valve. Therefore, a two-stage neutralization method has conventionally been adopted in the neutralization treatment of so-called strong acids and strong alkalis in which the content of PH buffering substances is extremely small. In other words, two sets of PH detectors, PH indicating controllers, and flow control valves linked to them are used, and the first stage performs some rough neutralization (for example, PH 2 to 3, or 11 to 12), and then the second stage performs precise neutralization. It performs sum (around PH7).

However, with this method, if the pH of the neutralization solution in the first stage becomes hunting, it becomes impossible to adjust the pH in the second stage due to the hunting effect, so a buffer tank is installed between the first stage neutralization and the second stage neutralization. Requires extra operations and baths such as erasing the PH hunting of the eye neutralization treatment solution,
Moreover, it requires two sets of expensive PH detectors, PH indicating controllers, and flow control valves linked to them, as well as two mixers such as ejectors, which makes the piping complicated, which imposes a heavy economic burden and is not a desirable process. It's hard to call it a method.

The present invention eliminates the shortcomings of conventional processing methods and performs stable neutralization processing using a simple device when instantaneously mixing and neutralizing acidic and alkaline solutions containing extremely low PH buffering substances as described above. The purpose of this system is to connect acidic liquid piping and alkaline liquid piping to a mixer, allow each liquid to flow through each piping, and mix both liquids while adjusting the flow rate of one liquid with a flow control valve. In the method of instantly mixing and neutralizing using the mixer, one pipe is divided into a main pipe and a secondary pipe, and a flow path is provided in which the main pipe is equipped with a main flow control valve and the secondary pipe is equipped with a subflow control valve. The other liquid is made to flow through the other pipe at a constant flow rate, and one liquid is first made to flow through the main pipe, and the PH on the outflow side of the mixer is adjusted using the main flow control valve.
When forming a neutralization titration curve using both solutions, the PH
Adjust the pH to an arbitrary value before it changes rapidly,
Next, the opening degree of the main flow control valve is fixed at the desired PH setting, and one of the liquids is continued to flow through the secondary pipe so that the PH on the outflow side of the mixer becomes near neutral. The present invention relates to a method for neutralizing an acidic liquid and an alkaline liquid, which comprises mixing and neutralizing the liquid while adjusting the flow rate of one of the liquids flowing through the secondary pipe using a secondary flow rate control valve.

The present invention will be explained in detail below with reference to the drawings.

FIG. 4 is an explanatory diagram showing a flow of an example of an embodiment of the present invention, in which an acidic waste liquid receiving tank 3 and an alkaline waste liquid receiving tank 4 are installed respectively, one end of an acidic liquid pipe 6 is connected to the acidic waste liquid receiving tank 3, and an acidic waste liquid receiving tank 3 and an alkaline waste liquid receiving tank 4 are installed. Liquid piping 6
The other end is connected to a mixer 9 via an acid waste pump 5. On the other hand, one end of the alkaline liquid piping 8 is connected to the alkaline waste liquid receiving tank 4, and a bypass path is provided in the alkaline liquid piping 8 to configure it into a main pipe 17 and a secondary pipe 18, and the main pipe 17 and the secondary pipe 18 are joined together again. One alkaline liquid pipe 8 is formed, and the other end of this alkaline liquid pipe 8 is connected to a mixer 9.
An alkaline waste liquid pump 7 is installed between the connection point of the alkaline liquid pipe 8 and the alkaline waste liquid receiving tank 4 and the branch point of the bypass path, and a main flow control valve 19 is attached to the main pipe 17, and the secondary pipe 18
A sub-flow control valve 20 is attached to the auxiliary flow control valve 20. Furthermore, mixer 9
Connect one end of the neutralized liquid pipe 13 to the outflow side of the
Connect the other end to a discharge point (not shown). In addition, a PH detector 10 is installed in the neutralized liquid pipe 13 immediately after the mixer 9.
One end of the circulation pipe 14 is branched and communicated with the neutralized liquid pipe 13 after the PH detector 10 is attached, and the other end of the circulation pipe 14 is connected to the acidic waste liquid receiving tank 3. Note that 15 and 16 are automatic valves. Further PH
An indicating controller 11 is installed separately, and a PH detector 10, automatic valves 15 and 16, and a sub-flow control valve 20 are connected to the PH indicating controller 11 in an instrumented manner, and the main flow rate is controlled via an opening setting device 21. It is connected to the control valve 19 in an instrumentation manner.

Next, to explain the neutralization process in this device, first, 1 acidic waste liquid is placed in the receiving tanks 3 and 4 for both waste liquids.
After receiving the alkaline waste liquid 2, the liquid in each tank is thoroughly mixed using a stirrer or the like (not shown). After completing this mixing, the automatic valve 15 is opened and the acidic waste liquid pump 5 and the alkaline waste liquid pump 7 are driven to flow the respective waste liquids through the acidic liquid piping 6 and the alkaline liquid piping 8, and both waste liquids are mixed into the mixer. 9, and the mixed liquid is circulated through the circulation pipe 14 to the acidic waste liquid receiving tank 3. Note that when the alkaline waste liquid 2 is allowed to flow through, the sub-flow control valve 20 is fully closed, and the main flow control valve 19 is gradually opened by the opening setting device 21 while the alkaline waste liquid 2 is passed through the main pipe. When the PH on the outflow side of the mixer 9 reaches the arbitrary setting PHS before the PH suddenly changes when both liquids are used to form a neutralization titration curve. The opening degree of the flow rate control valve 19 is fixed to the opening degree of the set PHS. This setting
The PHS and the opening setting device 21 will be explained in more detail below.

In carrying out the present invention, a neutralization titration curve is prepared in advance using acidic waste liquid and alkaline waste liquid to be neutralized. This neutralization titration curve is created by a known method. For example, a certain amount of acidic waste liquid is placed in a beaker, etc., and alkaline waste liquid is gradually added to the liquid in the beaker while stirring.The change in the pH of the mixed liquid is measured, and the PH value relative to the amount of alkaline waste liquid added is calculated. Plot on the graph.

When neutralization titration is performed in this way and a neutralization titration curve as shown in Figure 3 is obtained, the set pH
Determine S as follows. In FIG. 3, the point where the pH changes rapidly is about 3 or more on the acidic side, and about 10 or less on the alkaline side. In other words, changes in PH are relatively slow below PH3 or above PH10.

Therefore, for example, in the flow shown in Figure 4, when acidic waste liquid is passed through at a constant flow rate and alkaline waste liquid is neutralized while adjusting its flow rate,
Set any PH below PH3 as the set PHS. However, if the setting PHS is set to a pH that is too low, the operating range of the auxiliary flow control valve 20, which will be explained later, becomes too large, which is undesirable, and if the set PHS is set to a PH close to PH3.0, the operation error of the main flow control valve 19 may occur. This is not preferable because it may exceed the neutralization point and become alkaline all at once. Therefore, when a neutralization titration curve as shown in FIG. 3 is obtained, it is desirable to set the PHS to around PH2.0 as shown in FIG.

In addition, when neutralizing in the present invention, when the alkaline waste liquid is passed through at a constant flow rate and the acidic waste liquid is neutralized while adjusting the flow rate, the setting PHS' is changed as shown in Fig. 3 for the same reason. It is best to set it to around 11.5. In this way, a neutralization titration curve is created in advance using the acidic waste liquid and the alkaline waste liquid to be neutralized, and once the set PHS is determined, the set PHS is input into the opening setting device 21.

Next, the opening degree setting device 21 will be explained.The opening degree setting device 21 has a function of gradually opening the opening degree of the main flow control valve 19 according to a preset program, and also has the function of gradually opening the opening degree of the main flow control valve 19. The opening degree of the main flow control valve 19 is fixed at the point where the PH on the outflow side reaches the above-mentioned set PHS value. When the PH on the outflow side of the mixer 9 is set in advance to the above-mentioned setting PHS using the opening setting device 21 and the main flow control valve 19, the next step is to
The auxiliary flow rate control valve 20 linked to the PH indicator controller 11 is operated, the alkaline waste liquid 2 is also passed through the secondary pipe 18, and the auxiliary flow rate control valve 20 is operated so that the pH on the outflow side of the mixer 9 is near neutralization. Perform the operation to adjust the opening degree.

The present invention mixes acidic waste liquid and alkaline waste liquid using the main flow control valve 19 in this way, and adjusts the pH after mixing.
Since the sub-flow control valve 20 is operated after increasing the PHS to the above-mentioned setting PHS, even if the sub-flow control valve 20 has the above-mentioned operational error, the sub-flow control valve can be operated without any problem. This is because when the sub-flow control valve 20 is used to neutralize the pH of the neutralized liquid in the range of 6 to 9, the operating range of the sub-flow control valve 20 is t ₁ as shown in FIG. or t ₂ , and even if the values of t ₂ − _{t 1} and T ₂ ′−T ₁ ′ are the same, t ₂ − t ₁ will be extremely large compared to the entire operating range, that is, t ₂ , and thus the analogy Even if there is an operational error in the sub-flow control valve 20, this error will be sufficiently within the range of _t2 - _t1 , and the problem will soon disappear. Furthermore, since the opening degree of the main flow control valve 19 is fixed at the point at which the setting PHS is reached, after the main flow control valve 19 is fixed, a constant flow rate of the alkaline waste liquid 2 can be passed through the main pipe 17.
Therefore, even if two flow rate control valves are used, the hunting phenomenon of the first stage flow rate control valve, which occurs in conventional two-stage neutralization, will not occur at all, and therefore the secondary flow rate control will not occur. It becomes possible to operate the valve 20 effectively.

It goes without saying that when the pH on the outflow side of the mixer 9 falls within the dischargeable pH range through the above operations, the automatic valve 15 is closed and the automatic valve 16 is opened to discharge the neutralized liquid. stomach.

In addition to the embodiments of the present invention described below, other embodiments of the present invention will be described below. FIG. The main pipe 17 of the alkaline liquid piping 8 is connected to the mixer 9 at the front stage, and the main pipe 17 of the alkaline liquid piping 8 is connected to the mixer 9 at the former stage, and the main pipe 17 of the alkaline liquid piping 8 is connected to the mixer 9 at the rear stage, and the alkali liquid piping 8 is connected to the mixer 9 at the rear stage, and the main pipe 17 of the alkaline liquid piping 8 is connected to the mixer 9 at the former stage. The secondary pipes 18 are connected to each other. In addition, the fifth
In the figure, the same parts as in FIG. 4 are given the same reference numerals, and the explanation thereof will be omitted. The present invention achieves similar functions and effects even with such a flow, however, since the flow shown in Fig. 5 requires two mixers 9, the equipment cost is lower compared to the flow shown in Fig. 4. slightly disadvantageous in terms of

In addition, in Figures 4 and 5, a fixed amount of acidic waste liquid is passed through and the alkaline waste liquid is neutralized while adjusting the flow rate. It is okay to neutralize while adjusting the flow rate. In this case, the setting PH of the main flow control valve 19 becomes S', which is on the alkaline side, as shown in FIG.

Furthermore, the present invention can be applied not only to mixing and neutralizing alkaline waste liquid and acidic waste liquid, but also to neutralizing alkaline waste liquid with acid aqueous solution and acidic waste liquid with alkaline aqueous solution. It can also be applied to the case where both waste liquids are neutralized by adding an acid aqueous solution or an alkaline aqueous solution to either one beforehand.

The mixer 9 used in the present invention may be of any structure as long as it can instantaneously mix both liquids, but it is preferable to use an ejector, static mixer (trade name), or the like. In addition, the PH detector 10, flow rate control valves 19, 20, PH indicating controller 11, and opening setting device 21 used in the present invention can all be of the known type, and the opening setting device 21 is used to adjust the main flow rate. It is desirable that the valve 19 has a mechanism in which the opening time of the valve 19 can be arbitrarily adjusted little by little. As explained above, according to the present invention, it is possible to effectively neutralize a liquid to be neutralized that has an extremely small content of a PH buffering substance by a simple means, and it is possible to effectively neutralize the liquid to be neutralized by using a relatively expensive PH detector and PH indicator. The various devices conventionally required for the two-stage neutralization system, such as controllers, buffer tanks, and extra piping, can be significantly eliminated, resulting in great economic benefits.

Examples of the present invention will be described below.

Example: Acidic waste liquid discharged during the regeneration of the cation exchange resin and anion exchange resin discharged during the regeneration of the cation exchange resin of a pure water production equipment that uses raw water with almost no bicarbonate ion content as the water to be treated In neutralizing the alkaline waste liquid, first, neutralization titration was performed on both waste liquids as shown below, and a neutralization titration curve was created.

That is, 50 ml of the acidic waste liquid was placed in a beaker, and the alkaline waste liquid was gradually added thereto while stirring well, and the change in PH with respect to the amount of the alkaline waste liquid added was measured. Then, with the vertical axis representing the pH and the horizontal axis representing the amount of alkaline waste liquid added, the relationship between the pH and the amount of alkaline waste liquid added was plotted to create a neutralization titration curve as shown in Figure 6. Next, both waste liquids were subjected to neutralization treatment according to the method of the present invention using the apparatus shown in FIG. In addition, the setting PHS of the opening degree setting device 21 is set to 2.5, which is the value before the PH rapidly changes from FIG. Then, it gradually opens, and the pH on the outflow side of the mixer 9 increases in about 5 minutes.
was set to 2.5, and the PH setting of the PH indicator controller 11 was set to 7.3.

The acidic waste liquid is passed through the acidic liquid pipe 6 at a constant flow rate of 20 m ³ /H, and at the same time the alkaline waste liquid is passed through the alkaline liquid pipe 8. The flow rate of the alkaline waste liquid flowing through the main pipe 17 which is gradually opened increases gradually, and when the flow rate of the alkaline waste liquid flowing through the main pipe 17 is 26 m ³ /H, the pH on the outflow side of the mixer 9 is 2.5.
From then on, the opening degree of the main flow control valve 19 is fixed, and the flow rate of the alkaline waste liquid flowing into the main pipe 17 is controlled.
26 m ² /H, then the sub-flow control valve 20 opens and the opening degree of the sub-flow control valve 20 is adjusted by the signal emitted from the PH indicator controller 11, so that the neutralized liquid has a pH of
I was able to stably process around 7.5. Note that approximately 4 m ³ /h of alkaline waste liquid flowed through the secondary pipe 18 .

On the other hand, for comparison, when neutralization was carried out using the conventional flow shown in Fig. 1, the flow rate control valve 12 caused hunting, and the neutralized liquid did not fall within the range of 6 to 9 and the neutralization process was completed. That was impossible.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the flow of conventional one-stage neutralization, and Figures 2 and 3 are graphs showing neutralization titration curves when acidic waste liquid is neutralized with alkaline waste liquid. PH is shown on the horizontal axis, and the amount of alkaline waste liquid added is shown on the horizontal axis. FIG. 4 is an explanatory diagram of a flow showing an example of an embodiment of the present invention, and FIG. It is an explanatory diagram showing the flow, and FIG. 6 is a graph showing a neutralization titration curve when acidic waste liquid is neutralized with alkaline waste liquid in an example of the present invention, where the vertical axis is PH and the horizontal axis is alkaline waste liquid. This shows the amount of addition. 1... Acidic waste liquid, 2... Alkaline waste liquid, 3...
...Acidic waste liquid receiving tank, 4...Alkaline waste liquid receiving tank, 5
...Acidic waste liquid pump, 6...Acidic liquid piping, 7...
Alkaline waste liquid pump, 8... alkaline liquid piping,
9... Mixer, 10... PH detector, 11... PH indicator controller, 12... Flow rate control valve, 13... Neutralized liquid piping, 14... Circulation piping, 15... Automatic valve,
16... Automatic valve, 17... Main pipe, 18... Slave pipe,
19... Main flow control valve, 20... Sub-flow control valve,
21... Opening setting device, S... Setting PH.

Claims (1)

[Scope of Claims] 1. Connecting acidic liquid piping and alkaline liquid piping to a mixer, allowing each liquid to flow through each piping, and mixing both liquids while adjusting the flow rate of one liquid with a flow rate control valve. In the method of instantaneously mixing and neutralizing in a container,
One pipe is divided into a main pipe and a secondary pipe, a main flow control valve is attached to the main pipe, and a sub flow control valve is attached to the secondary pipe to form a flow path, and the other liquid is passed through the other pipe at a constant flow rate. At the same time, first, one of the liquids is made to flow through the main pipe, and the PH on the outflow side of the mixer is adjusted using the main flow control valve.When a neutralization titration curve is formed using both liquids, the PH Adjust and set the opening to an arbitrary PH before the PH suddenly changes, then fix the opening of the main flow control valve to the set opening of the arbitrary PH, and continue to allow one of the liquids to flow through the secondary pipe. , an acidic liquid that is mixed and neutralized while adjusting the flow rate of one liquid flowing through the secondary pipe using a secondary flow rate control valve so that the pH on the outflow side of the mixer is near neutral. and methods of neutralizing alkaline liquids. 2. Connect acidic liquid piping and alkaline piping to one mixer, use one of the pipes leading to the mixer as the main pipe, install a secondary pipe in a bypass manner in the main pipe, and install a main flow control valve on the main pipe, and A method for neutralizing an acidic liquid and an alkaline liquid according to claim 1, characterized in that neutralization is carried out by constructing a flow path in which a sub-flow control valve is attached to the secondary pipe.