JPH10328676A - Method and apparatus for controlling injection of hydrogen sulfide removing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely remove hydrogen sulfuide and to surely prevent the formation thereof without excessively adding a hydrogen sulfide removing agent by measuring the sending flow rate and water temp. of waste water and the concn. of hydrogen sulfide in the waste water or gas in a storage tank and controlling the addition amt. of the hydrogen sulfuide removing agent on the basis of the measured results. SOLUTION: When the waste water in a waste water storage tank 1 is sent through a water sending pipe 2 by a water sending pump 3, a hydrogen sulfide removing agent such as nitrate is added from a chemicals storage tank 4 by a chemicals injection pump 5. A temp. sensor 6 and a hydrogen sulfide sensor 7 are provided in the storage tank 1 and a flowmeter 8 is provided to the water sending pipe 2 and the temp. of the waste water and the concn. of hydrogen sulfide in the gas within the tank 1 are measured. These measured values are inputted to a control part 9 and the target addition amt. of the hydrogen sulfide removing agent is set from these values and, on the basis of this set value, the output signal of the chemicals injection pump 5 is outputted from the control part 9. As mentioned above, the addition amt. of the hydrogen sulfide removing agent is properly controlled corresponding to a change in the sending amt. and quality of waste water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the addition of a hydrogen sulfide remover to wastewater to remove hydrogen sulfide in the wastewater and prevent the generation of hydrogen sulfide, and to cope with a change in the amount of water sent and the quality of the wastewater. And properly control the amount of hydrogen sulfide remover added,
The present invention relates to a chemical injection control method and a chemical injection control device for reliably removing hydrogen sulfide and preventing generation of hydrogen sulfide without excessively adding a hydrogen sulfide removing agent.

[0002]

2. Description of the Related Art Conventionally, there is a method of injecting air or oxygen into waste water or a method of adding a chemical for removing hydrogen sulfide for the purpose of preventing generation of hydrogen sulfide in waste water and removing hydrogen sulfide.

[0003] In this case, if the amount of air, oxygen or chemical added is insufficient, hydrogen sulfide will remain, and if it is added excessively, the processing cost will be high. It is desired to be added to

Conventionally, a constant amount of air or oxygen has been injected or an injection system linked with a water pump has been adopted.

[0005] On the other hand, as a method of adding a chemical, the addition of a hydrogen sulfide removing agent such as ferric chloride to sewage requires a water temperature,
A chemical injection method has been proposed in which the water level in a storage tank and the concentration of dissolved oxygen in wastewater are measured, and a chemical injection pump and a water supply pump are synchronously controlled based on these measured values (Japanese Patent Application Laid-Open No. Hei 7-14848).
No. 2).

[0006] A method has also been proposed in which the amount of nitrate added to wastewater is determined by the residence time of the wastewater, COD, TOC, and oxidation-reduction potential (US Pat. No. 5,114,587).

[0007] In such a chemical injection control, the required amount of chemical injection changes depending on the residence time of the wastewater in the water supply pipe and the water temperature is described in Japanese Patent Application Laid-Open No. 7-148482 and US Pat. 587, which is a well-known matter.

[0008]

The conventional method of injecting air or oxygen into waste water does not employ an injection method corresponding to a change in water temperature and water quality of the waste water and a change in the flow rate of water supply. The effect cannot be obtained reliably. In addition, when air or oxygen is injected, the pressure loss of the water pump becomes large due to the gas injection, and water cannot be smoothly fed;
There is also a drawback that sufficient effect cannot be obtained when the wastewater stays in the water pipe for a long time.

[0009] Japanese Patent Application Laid-Open No. 7-148482 and USP
In the chemical injection control method described in US Pat. No. 5,114,587, control taking into account the change in the flow rate of drainage is not sufficiently performed,
In particular, there is a problem that it is not possible to perform chemical injection control that sufficiently responds to fluctuations in the quality of wastewater. That is, in the case of wastewater containing a large amount of impurities such as fibers, the measurement of the dissolved oxygen concentration, the oxidation-reduction potential, and the like is obstructed by these impurities and the like, and a reliable measurement value cannot be obtained. For this reason, it is not possible to stably perform appropriate chemical injection control corresponding to fluctuations in the quality of drainage water for a long period of time.

The present invention solves the above-mentioned conventional problems and excessively adds the hydrogen sulfide removing agent by appropriately controlling the addition amount of the hydrogen sulfide removing agent in response to a change in the amount of wastewater and the change in water quality. An object of the present invention is to provide a chemical injection control method and a chemical injection control device for a hydrogen sulfide remover that can reliably remove hydrogen sulfide and prevent the generation of hydrogen sulfide without causing the problem.

[0011]

According to the present invention, there is provided a method for controlling chemical injection of a hydrogen sulfide removing agent, which comprises adding a hydrogen sulfide removing agent to a means for supplying wastewater from a storage tank or a pump well.
The flow rate of the wastewater, the water temperature of the wastewater in the storage tank or pump well, and the sulfide concentration in the wastewater in the storage tank or pump well or the concentration of hydrogen sulfide in the air in the storage tank or pump well, The addition amount of the hydrogen sulfide removing agent is controlled based on these measurement results.

[0012] The chemical injection control device for a hydrogen sulfide removing agent of the present invention comprises a chemical injection means for adding a hydrogen sulfide removing agent to a means for supplying wastewater from a storage tank or a pump well, and a water supply flow rate of the wastewater. Measuring means, measuring means for measuring the temperature of waste water in the storage tank or pump well, measuring means for measuring the concentration of sulfide in the waste water in the storage tank or pump well or the concentration of hydrogen sulfide in the air in the storage tank or pump well, And control means for controlling the addition amount of the hydrogen sulfide removing agent of the chemical dosing means based on the measurement result of (1).

In the present invention, the chemical injection control is performed based on the flow rate of the wastewater, the temperature of the wastewater, and the concentration of sulfide in the wastewater in the storage tank or pump well or the concentration of hydrogen sulfide in the air in the storage tank or pump well. Do. That is, in the present invention, the water quality fluctuation of the wastewater is
Obtain a highly reliable value without being affected by impurities in the wastewater because it monitors the concentration of sulfide in the wastewater in the storage tank or pump well or the concentration of hydrogen sulfide in the air in the storage tank or pump well. Can be. Therefore, appropriate chemical injection control corresponding to fluctuations in the flow rate, water temperature, and water quality of drainage can be performed.

In the present invention, it is particularly preferable to use a nitrate as a hydrogen sulfide removing agent.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the present invention.

In this embodiment, when the wastewater in the wastewater storage tank 1 is supplied by the water supply pump 3 with the water supply pipe 2, a hydrogen sulfide removing agent such as nitrate is added from the chemical storage tank 4 by the chemical injection pump 5. And removes hydrogen sulfide and prevents the generation of hydrogen sulfide. The wastewater storage tank 1 is provided with a temperature sensor 6 and a hydrogen sulfide sensor 7, and the water pipe 2 is provided with a flow meter 8. The water temperature t (° C.) of the wastewater and the concentration of airborne hydrogen sulfide in the tank 1 are measured. S ₁ (ppm) and flow rate F
(M ³ / hr) is measured. These measured values are input to the control unit 9, and the target addition amount of the hydrogen sulfide removing agent is set from these values, and the control unit 9 outputs a control signal of the chemical injection pump 5 based on the set values.

Hereinafter, a method for setting the target amount of the hydrogen sulfide removing agent in the present invention will be described.

The control section 9 is preliminarily input with the pipe shape, the pipe length, and the pipe inner diameter of the water supply pipe 2. Is calculated.

For example, when the water pipe 2 is a straight pipe, the residence time T is calculated as follows.

The residence time T (hr) is the time during which the waste water stays inside the water pipe 2, and is the total amount of water discharged in the water pipe (m).
³ ) divided by the drainage flow rate F (m ³ / hr),
Alternatively, it is a value obtained by dividing a pipe length of the water supply pipe 2 (hereinafter, referred to as “L (m)”) by a flow velocity (hereinafter, referred to as “S (m / hr)”). Here, the pipe length L of the water pipe 2
(M) is the distance from the water pump (water pipe inlet 2A) 3 to the water pipe outlet 2B. Further, the total drainage amount in the water pipe can be calculated from the pipe length L of the water pipe 2 and the water pipe inner diameter (hereinafter, the water pipe radius is referred to as d (m)). Accordingly, the residence time T (hr) is determined in advance by the length L (m) of the water pipe 2 or the radius d (m) of the water pipe 2 and the flow velocity S (m / hr) or the flow rate F (m ^3). / Hr) can be easily calculated from the measured value.

That is, since the total drainage (m ³ ) in the water pipe is calculated by the following equation, the residence time T is calculated by dividing the residence time T by the flow rate.

The total drainage amount in the water pipe (m ³ ) = d ² × 3.14 × L Residence time T (hr) = d ² × 3.14 × L ÷ F Note that not the flow rate F (m ³ / hr) Flow rate S (m / h
When r) is measured, the residence time T is obtained as follows by dividing the length L (m) of the water pipe by the flow velocity S (m / hr).

Residence time T (hr) = L ÷ S Instead of using the time during which the wastewater stays in the water pipe, the time during which the wastewater stays in the water pipe and the time during which the wastewater stays in the tank 1 are used instead of using the time during which the wastewater stays in the water pipe. It is also possible to use a time that is obtained by adding the time that has elapsed. In this case, the calculation is performed using the drainage amount obtained by adding the total drainage amount in the water pipe and the drainage amount in the tank, instead of the total drainage amount in the water pipe.

In the present invention, for example, when nitrate is used as the hydrogen sulfide removing agent, the amount of 0.1 g / g BOD of the wastewater is used.
With the addition of 001 to 1.5 g of nitrate ions as a guide, the retention time T (hr) calculated as described above is used.
And the measured value t (° C.) of the water temperature of the waste water and the measured value S ₁ (ppm) of the concentration of hydrogen sulfide in the air in the tank, the target amount C (g-nitrate ion / hr) of nitrate is set. . T,
The value of t or S ₁ is, the larger than the respective reference value, increasing the C, is smaller than the reference value in the reverse, reduce C.

Note that a sulfide measuring device is used instead of the hydrogen sulfide sensor, and the sulfide concentration S ₂ (pp
Also when measuring m), since S ₁ and S ₂ have a correlation, they can be used as control factors.

The chemical dosing control in the present invention is performed so that the target addition amount C of the hydrogen sulfide removing agent set as described above or the addition rate within a range of ± 10% of this value C. Will be implemented.

Examples of the hydrogen sulfide removing agent used in the present invention include metal salts such as nitrate and ferric chloride, and oxidizing agents such as potassium permanganate and hydrogen peroxide. Of these, nitrates are particularly excellent in the effect of removing hydrogen sulfide, can oxidize hydrogen sulfide to sulfate ions at a relatively high rate, can prevent the generation of hydrogen sulfide, and are dangerous in handling. This is extremely advantageous because there is no property. As the nitrate, an aqueous solution having a concentration of 10 to 60% by weight such as sodium nitrate or calcium nitrate can be used.

Further, the flow rate of the waste water can be obtained from an on / off signal of a constant flow rate pump in addition to the measurement by the flow meter.

The present invention is particularly effective in controlling the chemical injection of a hydrogen sulfide removing agent into sewage, but is also effective in advanced treatment of general wastewater with activated carbon or the like.

[0031]

The present invention will be described more specifically with reference to the following examples.

Example 1 and Comparative Example 1 As shown in FIG. 1, sewage in a drainage (sewage) storage tank 1 is supplied to a water supply pipe (radius d = 0.3 m, pipe length L = 4700 m) 2 by a water supply pump 3. In a system that supplies water to a treatment plant (not shown), chemical injection control of the hydrogen sulfide removing agent was performed according to the present invention. Note that a 50% by weight aqueous solution of calcium nitrate was used as the hydrogen sulfide removing agent, and was added to the storage tank 1.

Water flow rate is 400 m ³ / hr or 800 m
The flow rate changed at a flow rate of ³ / hr, and there were several times during which water was not supplied halfway.

In Comparative Example 1, the hydrogen sulfide removing agent was injected at a rate of 40 mg-nitrate ion / l in proportion to the flow rate.
A high concentration peak of hydrogen sulfide of about ppm was detected.

On the other hand, in Example 1, the temperature t (° C.), the concentration of hydrogen sulfide in the air S ₁ (ppm), and the flow rate F (m ³ / hr)
Was measured, and the chemical dosing control was performed by increasing or decreasing the target addition amount C according to this value. As a result, a high concentration peak of hydrogen sulfide in the treatment plant was not detected, and the hydrogen sulfide concentration could be suppressed to an average of 1 ppm or less. .

Examples 2 and 3 and Comparative Example 2 In a system in which sewage in a sewage storage tank 1 is sent to a treatment plant by a water supply pump through a water supply pipe (radius d = 0.05 m, pipe length L = 900 m). , 50 as hydrogen sulfide remover
Water solution of 20% by weight of calcium nitrate
Added downstream.

The flow rate of the water was constant at 0.6 m ³ / hr, and the water was constantly supplied. In addition, the quality of the sewage varies depending on time and weather, and it was therefore expected that the required amount of the added hydrogen sulfide removing agent would vary greatly.

In Comparative Example 2, when the hydrogen sulfide removing agent was injected at a constant rate of 55 mg-nitrate / l in proportion to the flow rate, residual nitrate was detected at the outlet of the water pipe, and its concentration was 0 to 20 mg-NO ₃ / NO. 1 and fluctuated greatly.

On the other hand, in Example 2, the temperature t (° C.), the concentration of hydrogen sulfide in air S ₁ (ppm), and the flow rate F (m ³ / hr)
Was measured and the target addition amount C was increased or decreased according to this value to perform chemical injection control. As a result, the concentration of residual nitrate at the outlet of the water pipe was constant at a low concentration of 4 to 5 mg-NO ₃ / l, and The concentration of hydrogen sulfide could be kept below the lower detection limit (0.01 mg-S / l).

The third embodiment is different from the second embodiment in that
In the same manner as in Example 2 except that the sulfide concentration S ₂ (ppm) in the sewage in the tank was measured instead of the air hydrogen sulfide concentration S ₁ , and the target addition amount C was increased or decreased based on this value. In the same manner, the residual nitrate concentration was similarly increased to 4 to 5 mg-NO ₃ / l.
, And the concentration of hydrogen sulfide in water could be kept below the lower detection limit.

[0041]

As described above in detail, according to the chemical injection control method and the chemical injection control device for a hydrogen sulfide removing agent of the present invention, the change in the amount of wastewater and the quality of the water are obtained under the following effects. By properly controlling the addition amount of the hydrogen sulfide removing agent in response to the above, it is possible to reliably remove the hydrogen sulfide and prevent the generation of the hydrogen sulfide without excessively adding the hydrogen sulfide removing agent.

Since the water supply flow rate is used for chemical injection control, even when the water supply flow rate fluctuates due to an increase or decrease in the number of operating pumps or the use of a variable capacity pump, it is possible to automatically cope with the operation without any manual operation. Since the concentration of hydrogen sulfide and sulfide in the head space, which is hardly obstructed by contaminants in wastewater, is used as a factor of water quality fluctuation, chemical injection control corresponding to water quality fluctuation can be performed without requiring frequent maintenance. The residence time of the drainage in the pipe can always be estimated from the flow rate signal and used for control, and the residence time in the pipe can be automatically updated without any manual operation. For this reason, almost appropriate control can be performed even at the time of abnormality due to irregular weather.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drainage storage tank 2 Water supply pipe 3 Water supply pump 4 Chemical storage tank 5 Chemical injection pump 6 Temperature sensor 7 Hydrogen sulfide sensor 8 Flow meter 9 Control part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobumi Maejima 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Kurita Industries Co., Ltd. (72) Inventor Mitsuhiro Mashiko 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo No. Kurita Industrial Co., Ltd.

Claims (4)

[Claims] 1. A method for adding a hydrogen sulfide removing agent to a means for feeding wastewater from a storage tank or a pump well, comprising: a flow rate of the wastewater, a water temperature of the wastewater in the storage tank or the pump well, and the storage tank. Or a sulfide concentration in wastewater in a pump well or an air hydrogen sulfide concentration in the storage tank or the pump well, and a hydrogen sulfide remover that controls the amount of the hydrogen sulfide remover based on the measurement results. Dosing control method. 2. The method according to claim 1, wherein the hydrogen sulfide removing agent is a nitrate. 3. A chemical injection means for adding a hydrogen sulfide removing agent to a means for feeding wastewater from a storage tank or a pump well, a means for measuring a flow rate of the wastewater, and a method for measuring the temperature of the wastewater in the storage tank or the pump well. Measuring means, measuring means for measuring the sulfide concentration in the drainage water in the storage tank or pump well or measuring the concentration of hydrogen sulfide in the air in the storage tank or pump well, and removing hydrogen sulfide by the chemical dosing means based on the measurement results. And a control means for controlling the amount of the agent added. 4. The apparatus according to claim 3, wherein the hydrogen sulfide removing agent is a nitrate.