JP7790215B2 - Neutralization method - Google Patents

Description

The present invention relates to a neutralization method for adjusting wastewater to a near-neutral pH, and in particular to a neutralization method for adjusting the pH to a near-neutral pH by adding an acid or alkali aqueous solution to the wastewater.

When neutralizing chemical wastewater, the neutralization titration curve for the wastewater in question is unknown, so even if the pH value is known, it is difficult to determine the amount of neutralizing agent (acid or alkali) needed. Therefore, in the actual chemical wastewater neutralization process, a trial-and-error method is used in which the pH is monitored while gradually adding neutralizing agent to bring the pH closer to neutral.

As a result, the process of stirring, measuring the pH value, and adding neutralizing agent must be repeated multiple times before neutralization is complete, which takes a long time. Furthermore, if an excessive amount of neutralizing agent is added during the neutralization process, there is the issue that unnecessary chemicals are used to neutralize the excess chemicals.

JP 05-253579 A discloses a method in which a set amount of neutralizing agent is added based on the pH value using a theoretical curve from a group of neutralization titration curves stored in advance in a memory unit, the pH value is measured again after stirring, the pH change and pH change rate relative to the amount of neutralizing agent added are then determined, the initial pH value and pH change rate are compared with the group of neutralization titration curves stored in the memory, and the closest neutralization titration curve (a curve representing the amount of chemical added versus the reaction characteristics) is selected. With this method, the initial addition of neutralizing agent provides information on the waste liquid properties (such as the buffering effect of the waste liquid), allowing the amount of neutralizing agent added the second time to be appropriate.

JP 2011-240298 A describes the use of a model information storage unit that stores physicochemical model information for the control tank, an evaluation function storage unit that stores an evaluation function that evaluates at least one of the state of the liquid to be adjusted or the amount of pH adjuster to be injected, and a calculation unit that determines the optimal amount of pH adjuster to be injected based on the pH value of the liquid to be adjusted, the physicochemical model information, and the evaluation function.

Japanese Patent Application Publication No. 05-253579 JP 2011-240298 A

The methods described in Patent Documents 1 and 2 require preparation of curves and modeling of the chemical injection-reaction characteristics in advance.

Furthermore, while Patent Documents 1 and 2 simply calculate the chemical injection amount, they do not take into account the actual behavioral trends of the chemical injection device. In other words, in a typical chemical injection device, the valve or pump operates for a predetermined period of time based on an electrical signal sent to the valve or pump, injecting the neutralizing chemical. However, the operating time of the chemical injection device is based on this electrical signal and does not completely match the actual chemical injection time; there is a discrepancy. Furthermore, the initial chemical injection amount when the valve begins to open or the pump begins to operate is not strictly the same as the subsequent chemical injection amount, which stabilizes and stabilizes. Furthermore, in chemical injection devices that use gravity to drain the chemical solution from a tank into a neutralization treatment tank, the amount of chemical solution flowing per unit time varies depending on the liquid level in the tank. Furthermore, because the viscosity of the chemical and the valve's open/close status change very slightly from day to day, the chemical injection amount can vary slightly even for the same chemical injection time. As a result, the pH after chemical injection may not reach the target value. Patent Documents 1 and 2 could also address this issue by using equipment to measure and control the chemical injection amount, but this would be extremely costly.

The objective of the present invention is to provide a neutralization method that can accurately neutralize wastewater when applied to actual equipment.

The present invention solves the above problems by:

[1] A neutralization method in which waste liquid is introduced into a neutralization tank and a neutralizing agent consisting of an acid or alkali is added to the waste liquid in the neutralization tank by a neutralizing agent adding device to neutralize the waste liquid to a target pH,
a first step of introducing the waste liquid into the neutralization treatment tank, measuring the pH (primary pH), adding a predetermined amount of neutralizing agent, stirring the waste liquid, and measuring the pH (secondary pH);
a second step of determining an amount of neutralizing agent to be added based on the amount of neutralizing agent added and the pH change value in the first step, the primary pH, the secondary pH, and the target pH, and adding the determined amount of neutralizing agent,
The amount of neutralizing agent to be added in the first step is determined based on the target pH, the primary pH, a coefficient, and the addition time by the neutralizing agent addition device;
A neutralization method characterized in that the amount of neutralizing agent to be added in the second step is determined based on the target pH, the primary pH, the secondary pH, the coefficient, and the addition time.

[2] The waste liquid is acidic,
When the primary pH is a, the secondary pH is b, and the target pH is m, the amount of neutralizing agent added in the first step is (10 ^−a −10 ^−m ) × (conversion coefficient) × (dosing coefficient) × (addition time).
It was decided by
The amount of neutralizing agent added in the second process is (10 ^−b −10 ^−m ) × (10 ^−a −10 ^−m ) / (10 ^−a −10 ^−b ) / [(conversion factor) × (dosing factor) × (addition time)]
The neutralization treatment method [1] is determined by the following.

Here, the conversion coefficient is a unit conversion coefficient that converts the chemical dosage amount into the valve opening and closing time, and the chemical dosage coefficient is a value set according to the pH change conditions during wastewater neutralization. For example, the chemical dosage coefficient is adjusted so that the pH changes by approximately 1.5 to 3 when the wastewater pH is less than 10, by approximately 0.5 to 1.5 when the wastewater pH is 10 to less than 12, and by approximately 0.3 to 0.5 when the wastewater pH is 12 or higher. The chemical dosage coefficient is adjusted so that the pH changes within the above ranges over a specified chemical dosage time (e.g., 10 to 15 seconds).

[3] The waste liquid is alkaline, having a pH of 10 or more;
When the primary pH is a, the secondary pH is b, and the target pH is m, the amount of neutralizing agent added in the first step is (10 ^−(14−a) −10 ^−(14−m) )/[(conversion coefficient) × (dosing coefficient) × (dosing time)]
It was decided by
The amount of neutralizing agent added in the second process is (10 ^{− (14-b)} − 10 ^{− (14-m)} ) × (10 ^{− (14-a)} − 10 ^{− (14-m)} ) / (10 ^{− (14-a)} − 10 ^{− (14-b)} ) / [(conversion factor) × (dosing factor) × (addition time)]
The neutralization treatment method [1] is determined by the following.

[4] The waste liquid is alkaline with a pH of less than 10,
If the primary pH is a, the secondary pH is b, the target pH in the first step is m1, and the target pH in the second step is m2, the amount of neutralizer added in the first step is (10 ^{- (14 - a)} - 10 ^{- (14 - 7)} + 10 ^{- m1} ) x (conversion coefficient) x (dosing coefficient) x (addition time).
It was decided by
The amount of neutralizing agent added in the second process is (10 ^{− (14-b)} − 10 ^{− (14-7)} + 10 ^{− m2} ) × (10 ^{− (14-a)} − 10 ^{− (14-7)} + 10 ^{− m1} ) / [(10 ^{− (14-a)} − 10 ^{− (14-b)} ) × (conversion factor) × (dosing factor) × (addition time)]
The neutralization method of claim 1, wherein the neutralization is determined by the following formula.

however,
m1=log(-(10- ^(14-a) -c)
m2=log(-(10- ^(14-b) -c)
and c is the value obtained by subtracting the amount of ions at pH 7 from the amount of ions at pH 10 in order to calculate values below pH 10, which is 0.0000999 (10 ⁻⁴ −10 ⁻⁷ ).

[5] A neutralization method according to any one of [1] to [4], in which the waste liquid is introduced into the neutralization tank, stirred, and then the primary pH is measured, and the first step is performed if the pH of the waste liquid is not neutral.

This invention provides a neutralization control method adapted to actual equipment by determining a dosing coefficient in the theoretical pH calculation formula that will result in an effective pH change in the first dosing. In this invention, it is sufficient to set a coefficient or dosing time that will allow the pH to be adjusted in the first dosing to calculate the second dosing amount; a strict pH change range is not required. Therefore, dosing can be completed in a shorter time than the methods of Patent Documents 1 and 2, which determine reaction characteristic curves and modeling.

In addition, even if the chemical dosing-pH change situation in the actual machine fluctuates, it is only necessary to set a coefficient or chemical dosing time that allows the second chemical dosing amount to be calculated using the first chemical dosing, and there is no need to re-create the reaction characteristic curve or modeling. Furthermore, because the second chemical dosing amount is calculated from the pH change due to the first chemical dosing, it is possible to continuously respond to pH changes, improving the accuracy of pH adjustment compared to the methods in Patent Documents 1 and 2 that use reaction characteristic curves and modeling.

FIG. 2 is a schematic vertical cross-sectional view of a neutralization treatment tank. 1 is a flow chart illustrating the method of the present invention.

Figure 1 is a schematic vertical cross-sectional view of a neutralization treatment tank to which a neutralization treatment method according to an embodiment of the present invention is applied. Waste liquid is introduced into this neutralization treatment tank 1 through pipe 2. An acid (in this embodiment, hydrochloric acid) or alkali (in this embodiment, caustic soda) is added as a neutralizing agent into neutralization treatment tank 1.

Hydrogen chloride solution is stored in the hydrochloric acid tank 3, and by opening the valve 3a, the solution is added by gravity from the hydrochloric acid tank 3 to the neutralization tank 1.

The caustic soda solution is stored in caustic soda tank 4, and by opening valve 4a, the solution is added by gravity from caustic soda tank 4 to neutralization treatment tank 1.

Air from the blower 5 is supplied to the air diffuser 6 to agitate the liquid in the neutralization treatment tank 1.

A pH meter 7 is installed to detect the pH of the liquid in the neutralization treatment tank 1.

A transfer pipe 9 with a pump 8 is provided to transfer the liquid after neutralization from the neutralization tank 1.

In this embodiment, the waste liquid is ion exchange resin regeneration waste liquid, which is an acidic or alkaline waste liquid containing hydrochloric acid or caustic soda and salts, and other substances stripped from the ion exchange resin, but is not limited to this.

To neutralize this waste liquid, as shown in Figure 2, it is introduced into neutralization treatment tank 1, stirred, and the pH (primary pH) is measured using pH meter 7.

If the pH is neutral (e.g., 5-8), the solution is transferred using pump 8 without neutralization. If the pH is acidic or alkaline, the first process is carried out. That is, a predetermined amount of neutralizing agent is added, followed by stirring and measurement of the pH (secondary pH). The first chemical dosage is determined to be the amount of chemical that produces a pH change that allows for the second chemical dosage calculation (an amount that produces a change in pH of approximately 1.5-3 when the waste liquid pH is less than 10, approximately 0.5-1.5 when the waste liquid pH is 10-12, and approximately 0.3-0.5 when the waste liquid pH is 12 or higher. This is determined through preliminary testing or empirical values).

If the measured secondary pH is neutral (e.g., 5 to 8), transfer it using pump 8. If the secondary pH is not neutral, perform the second process.

That is, the amount of neutralizer to be added for the second time is determined taking into account the results of the pH adjustment in the first process, and this amount of neutralizer is added and stirred, and the pH (tertiary pH) is measured. If the result shows that the pH is neutral (e.g., 5 to 8), the mixture is transferred using pump 8. If the tertiary pH is not neutral, the process returns to the first process.

Next, we will explain how to determine the amount of neutralizing agent to be added in each of the first and second steps.

In one embodiment of the present invention, the waste liquid is acidic. In this embodiment, when the primary pH is a, the secondary pH is b, and the target pH is m, the amount of neutralizing agent added in the first step is calculated by (10 ^−a −10 ^−m ) × (conversion coefficient) × (chemical dosing coefficient) × (addition time).
It was decided by
The amount of neutralizing agent added in the second process is (10 ^−b −10 ^−m ) × (10 ^−a −10 ^−m ) / (10 ^−a −10 ^−b ) / [(conversion factor) × (dosing factor) × (addition time)]
The decision will be made at the following.

The conversion coefficient is a unit conversion coefficient that converts the chemical dosage amount into the valve opening and closing time, and is set according to the pH change during wastewater neutralization. For example, the chemical dosage coefficient is adjusted so that the pH changes by approximately 1.5 to 3 when the wastewater pH is less than 10, by approximately 0.5 to 1.5 when the wastewater pH is 10 to less than 12, and by approximately 0.3 to 0.5 when the wastewater pH is 12 or higher. The chemical dosage coefficient is adjusted so that the pH changes within the above ranges over a specified chemical dosage time (e.g., 10 to 15 seconds).

In another aspect of the present invention, the waste liquid is alkaline with a pH of 10 or more. In this aspect, when the primary pH is a, the secondary pH is b, and the target pH is m, the amount of neutralizing agent added in the first step is (10 ^−(14−a) −10 ^−(14−m) )/[(conversion coefficient) × (chemical dosing coefficient) × (dosing time)]
It was decided by
The amount of neutralizing agent added in the second process is (10 ^{− (14-b)} − 10 ^{− (14-m)} ) × (10 ^{− (14-a)} − 10 ^{− (14-m)} ) / (10 ^{− (14-a)} − 10 ^{− (14-b)} ) / [(conversion factor) × (dosing factor) × (addition time)]
The conversion coefficient and chemical dosing coefficient are as above.

In yet another aspect of the present invention, the waste liquid is alkaline with a pH of less than 10. In this aspect, when the primary pH is a, the secondary pH is b, the target pH in the first step is m1, and the target pH in the second step is m2, the amount of neutralizing agent added in the first step is (10 ^{- (14 - a)} - 10 ^{- (14 - 7)} + 10 ^{- m1} ) x (conversion coefficient) x (chemical dosing coefficient) x (addition time).
It was decided by
The amount of neutralizing agent added in the second addition step is (10 ^{− (14-b)} − 10 ^{− (14-7)} + 10 ^{− m2} ) × (10 ^{− (14-a)} − 10 ^{− (14-7)} + 10 ^{− m1} ) / [(10 ^{− (14-a)} − 10 ^{− (14-b)} ) × (conversion factor) × (dosing factor) × (addition time)]
However,
m1=log(-(10- ^(14-a) -c)
m2=log(-(10- ^(14-b) -c)
and c is the value obtained by subtracting the amount of ions at pH 7 from the amount of ions at pH 10 in order to calculate values below pH 10, which is 0.0000999 (10 ⁻⁴ −10 ⁻⁷ ).

In this embodiment, even if the properties of the regenerated wastewater change, the pH can be adjusted satisfactorily by performing a second chemical injection based on the primary and secondary pH.

In addition, even if the level in the pH adjuster storage tank fluctuates, pH adjustment can be carried out satisfactorily by performing a second chemical injection based on the primary and secondary pH values.

In addition, even if the viscosity of the pH adjuster changes due to temperature changes, the pH can be adjusted satisfactorily by performing a second injection based on the primary and secondary pH values.

Even if the amount of regeneration waste fluid fluctuates, pH adjustment can be performed effectively by performing a second chemical injection based on the primary and secondary pH.

For these reasons, the pH after chemical administration efficiently reaches the target neutral value.

1 Neutralization tank 3 Hydrochloric acid tank 4 Caustic soda tank 5 Blower 6 Aeration pipe

Claims (4)

A neutralization method for introducing regenerated wastewater from an ion exchange resin into a neutralization tank, and adding a neutralizing agent consisting of an acid or alkali stored in a tank to the wastewater in the neutralization tank by a neutralizing agent adding device to neutralize the wastewater to a target pH, wherein the neutralizing agent adding device adds the neutralizing agent from the tank into the neutralization tank by gravity when a valve is opened,
a first step of introducing the waste liquid into the neutralization treatment tank, measuring the pH (primary pH), adding a predetermined amount of neutralizing agent, stirring the waste liquid, and measuring the pH (secondary pH);
a second step of determining the amount of neutralizing agent to be added based on the amount of neutralizing agent added and the pH change value in the first step, the primary pH, the secondary pH, and the target pH, and adding the determined amount of neutralizing agent;
A neutralization treatment method comprising:
The amount of neutralizing agent to be added in the first step is determined based on the target pH, the primary pH, a coefficient, and the addition time by the neutralizing agent addition device ;
A neutralization method in which the amount of neutralizing agent to be added in the second step is determined based on a target pH, a first pH, a second pH, the coefficient, and the addition time,
the waste liquid is acidic,
When the primary pH is a, the secondary pH is b, and the target pH is m, the amount of neutralizing agent added in the first step is (10 ^−a −10 ^−m ) × (conversion coefficient) × (dosing coefficient) × (addition time).
It was decided by
The amount of neutralizing agent added in the second process is (10 ^−b −10 ^−m ) × (10 ^−a −10 ^−m ) / (10 ^−a −10 ^−b ) / [(conversion factor) × (dosing factor) × (addition time)]
The neutralization treatment method is determined by the above.
The conversion factor is a unit conversion factor for converting the dosage amount into the valve open time. The dosage factor is a value determined by preliminary tests or empirical values so that the pH changes by 1.5 to 3 over a specified dosage time (10 to 15 seconds). A neutralization method for introducing regenerated wastewater from an ion exchange resin into a neutralization tank, and adding a neutralizing agent consisting of an acid or alkali stored in a tank to the wastewater in the neutralization tank by a neutralizing agent adding device to neutralize the wastewater to a target pH, wherein the neutralizing agent adding device adds the neutralizing agent from the tank into the neutralization tank by gravity when a valve is opened,
a first step of introducing the waste liquid into the neutralization treatment tank, measuring the pH (primary pH), adding a predetermined amount of neutralizing agent, stirring the waste liquid, and measuring the pH (secondary pH);
a second step of determining the amount of neutralizing agent to be added based on the amount of neutralizing agent added and the pH change value in the first step, the primary pH, the secondary pH, and the target pH, and adding the determined amount of neutralizing agent;
A neutralization treatment method comprising:
The amount of neutralizing agent to be added in the first step is determined based on the target pH, the primary pH, a coefficient, and the addition time by the neutralizing agent addition device ;
A neutralization method in which the amount of neutralizing agent to be added in the second step is determined based on a target pH, a first pH, a second pH, the coefficient, and the addition time,
The waste liquid has an alkaline pH of 10 or more,
When the primary pH is a, the secondary pH is b, and the target pH is m, the amount of neutralizing agent added in the first step is (10 ^{− (14 − a)} − 10 ^{− (14 − m)} ) / [((conversion coefficient) × (dosing coefficient) × (dosing time)]
It was decided by
The amount of neutralizing agent added in the second process is (10 ^{− (14-b)} − 10 ^{− (14-m)} ) × (10 ^{− (14-a)} − 10 ^{− (14-m)} ) / (10 ^{− (14-a)} − 10 ^{− (14-b)} ) / [(conversion factor) × (dosing factor) × (addition time)]
The neutralization treatment method is determined by the above.
The conversion factor is a unit conversion factor for converting the dosage amount into the valve open time. The dosage factor is a value determined by preliminary tests or empirical values so that the pH changes by 0.5 to 1.5 in a predetermined dosage time (10 to 15 seconds) when the pH of the waste liquid is less than 10 to 12, and the pH changes by 0.3 to 0.5 in a predetermined dosage time (10 to 15 seconds) when the pH of the waste liquid is 12 or higher. A neutralization method for introducing regenerated wastewater from an ion exchange resin into a neutralization tank, and adding a neutralizing agent consisting of an acid or alkali stored in a tank to the wastewater in the neutralization tank by a neutralizing agent adding device to neutralize the wastewater to a target pH, wherein the neutralizing agent adding device adds the neutralizing agent from the tank into the neutralization tank by gravity when a valve is opened,
a first step of introducing the waste liquid into the neutralization treatment tank, measuring the pH (primary pH), adding a predetermined amount of neutralizing agent, stirring the waste liquid, and measuring the pH (secondary pH);
a second step of determining the amount of neutralizing agent to be added based on the amount of neutralizing agent added and the pH change value in the first step, the primary pH, the secondary pH, and the target pH, and adding the determined amount of neutralizing agent;
A neutralization treatment method comprising:
The amount of neutralizing agent to be added in the first step is determined based on the target pH, the primary pH, a coefficient, and the addition time by the neutralizing agent addition device ;
A neutralization method in which the amount of neutralizing agent to be added in the second step is determined based on a target pH, a first pH, a second pH, the coefficient, and the addition time,
The waste liquid is alkaline with a pH of less than 10,
If the primary pH is a, the secondary pH is b, the target pH in the first step is m1, and the target pH in the second step is m2, the amount of neutralizer added in the first step is (10 ^{- (14 - a)} - 10 ^{- (14 - 7)} + 10 ^{- m1} ) x (conversion coefficient) x (dosing coefficient) x (addition time).
It was decided by
( Note that the conversion factor is a unit conversion factor for converting the dosage amount into the valve open time. The dosage factor is a value determined by preliminary tests or empirical values so that the pH changes by 1.5 to 3 over a specified dosage time (10 to 15 seconds).)
The amount of neutralizing agent added in the second process is (10 ^{− (14-b)} − 10 ^{− (14-7)} + 10 ^{− m2} ) × (10 ^{− (14-a)} − 10 ^{− (14-7)} + 10 ^{− m1} ) / [(10 ^{− (14-a)} − 10 ^{− (14-b)} ) × (conversion factor) × (dosing factor) × (addition time)]
The neutralization treatment method is determined by the above.
however,
m1=log(-(10- ^(14-a) -c)
m2=log(-(10- ^(14-b) -c)
and c is 0.0000999. 4. The neutralization method according to claim 1 , wherein the primary pH is measured after the waste liquid is introduced into the neutralization tank and stirred, and the first step is carried out if the pH of the waste liquid is not neutral.