JPH11156374A - Method and apparatus for controlling injection of hydrogen sulfide removing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly control the injection amt. of nitrate added to sewage as a hydrogen sulfide removing agent in order to prevent the generation of hydrogen sulfide in a sewage pressure feed pipe. SOLUTION: The addition amt. of nitrate is controlled on the basis of a value C calculated by C= A×(0.1+0.9×100/D)×1.07<(t-15)> ×T}<2> /4 [wherein A is a consumption speed constant (mg-N/hr) of nitrate at a water temp. of 15 deg.C; (t) is water temp. ( deg.C); T is the stagnagtion time (hr) of sewage in a pressure feed pipe; D is the inner diameter (mm) of the pressure feed pipe; and C is a nitrate addition ratio (mg-N/L-sewage)]. By this constitution, by measuring sewage flow velocity or flow rate for calculating the water temp. (t) and the stagnation time T and calculating C from the other constants A, D, chemical injection control can be easily and properly performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical injection control method for properly controlling the amount of nitrate to be added to sewage as a hydrogen sulfide removing agent in order to prevent the generation of hydrogen sulfide in a sewage pressure pipe. The present invention relates to a medicine injection control device.

[0002]

2. Description of the Related Art The sewage pumping method has the advantages of reducing construction costs and shortening the construction period.
On the other hand, while having such advantages, there is a problem in that corrosion of peripheral facilities and generation of odor near the outlet of the pressure feed pipe due to generation of hydrogen sulfide.

Conventionally, in order to prevent such corrosion and odor due to hydrogen sulfide, a method of adding nitrate to sewage has been adopted at an inlet of a sewage pressure pipe, for example, at a pump well of a pumping station. Nitrate can oxidize hydrogen sulfide to sulfate ions at a high rate, can also prevent the generation of hydrogen sulfide, and can effectively solve the problems of corrosion and odor due to hydrogen sulfide.

However, in this case, the generation of hydrogen sulfide cannot be prevented if the amount of addition of the nitrate is insufficient, and the cost of chemicals increases if the amount is excessively high. It is desired to add it in an amount.

On the other hand, the required amount of nitrate varies depending on various conditions such as sewage water quality and water temperature. In particular, seasonal fluctuations are large.

[0006]

However, conventionally,
No method for estimating the required amount of nitrate has been proposed, and the amount of nitrate added is set by estimating an appropriate amount from the results of trial and error based on actual machine tests. . For this reason, a test using an actual machine is performed every season every year to change the discharge amount of the chemical injection pump.

Conventionally, no automatic control system for nitrate injection has been provided, and a great deal of labor is required for setting the injection amount and changing the injection amount based on this.

The present invention has been made to solve the above-mentioned conventional problems and to provide a chemical injection control method and a chemical injection control device for a hydrogen sulfide remover which can easily and properly automatically control the amount of nitrate injected. Aim.

[0009]

The method for controlling chemical injection of a hydrogen sulfide removing agent according to the present invention comprises adding nitrate to sewage as a hydrogen sulfide removing agent based on a value C calculated by the following formula (I). Features.

[0010] C = {A × (0.1 +0.9 × 100 / D) × 1.07 (t-15) × T} 2/4 ... (I) ( where in the formula (I), A is a water temperature 15 ℃ , T is the water temperature (° C.), T is the residence time in the sewage pumping pipe (hr), D is the inner diameter of the pumping pipe (mm), and C is the nitrate addition rate (mg-N / hr). N / L-
Sewage)) The hydrogen sulfide remover chemical injection control device of the present invention further comprises a chemical injection means for adding nitrate as a hydrogen sulfide remover to sewage, and a chemical injection control method based on the value C calculated by the above formula (I). Control means for controlling the amount of nitrate added to the chemical dosing means.

By controlling the chemical injection based on the value C calculated by the above formula (I), the nitrate can be added without excess and deficiency, and the generation of hydrogen sulfide can be reliably prevented.

Among the items for calculating C using the above equation (I), the nitrate consumption rate constant A at a water temperature of 15 ° C.
(Mg-N / hr) is a value that differs depending on the sewage system to be treated and the pumping pipe, and may be obtained by performing an actual machine test in advance for each sewage pumping pipe. This actual machine test can be performed in any season, and by substituting the nitrate consumption, water temperature and residence time into the equation (I), A at a water temperature of 15 ° C. can be calculated. Subsequent actual machine tests are not required.

The inner diameter D (mm) of the pumping tube may be checked in advance for each pumping tube.

The temperature t (° C.) of the sewage can be easily measured by a temperature sensor or the like.

The sewage residence time T (hr) in the sewage pipe is the time during which the sewage remains in the sewage pipe, and the total amount of sewage (m ³ ) in the sewage pipe is determined by the sewage flow rate (hereinafter referred to as “F (m ³ / h)
r) ". ) Or the total length of the pumping pipe (hereinafter referred to as “L (m)”) divided by the flow rate (hereinafter referred to as “S (m / hr)”). Value. Here, the total length L (m) of the pumping pipe is the distance from the water pump (the inlet of the pumping pipe) to the end point of the pumping pipe (the outlet of the pumping pipe). The total amount of sewage in the pumping pipe can be calculated from the total length L of the pumping pipe and the inner diameter of the pumping pipe. Therefore, the residence time T (hr) is a measurement of the total length L (m) of the pumping tube or the inner diameter D (mm) of the pumping tube and the flow rate S (m / hr) or the flow rate F (m ³ / hr) which have been checked in advance. It can be easily calculated from the values.

Accordingly, the nitrate addition rate C (mg-N / L-
The sewage is measured by measuring the temperature t (° C.) of the sewage with a temperature sensor or the like, and the flow rate F (m ³ / hr) or the flow rate S (m /
hr) by measuring with a flow meter or the like, and these values are compared with the nitrate consumption rate constant A and the pumping pipe inner diameter D which have been determined in advance.
(Mm) and the total length L (m) of the pumping pipe can be easily calculated.

[0017]

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 sewage in the sewage storage tank 1 is pumped by the water supply pump 3 by the pressure feed pipe 2, nitrate is added from the chemical storage tank 4 by the chemical injection pump 5 to prevent generation of hydrogen sulfide. I do. The sewage storage tank 1 is provided with a temperature sensor 6, and the pressure feed pipe 2 is provided with a flow meter 7.
Is provided, and the sewage water temperature t ° C. and the flow rate Fm ³ / hr are measured. This measured value is inputted to the control means 8, and the nitrate addition rate C is calculated from the previously inputted constant according to the above formula (I).
Is calculated, and a control signal of the chemical injection pump 5 is output from the control means 8 based on the calculation result.

The control means 8 includes an input part for the water temperature t and a flow rate F, a consumption rate A (mg-N / hr) of the nitrate, an inner diameter D (mm) of the pressure feed pipe, and a total length L (position 2A of the water feed pump 3).
(M) from the exit to the end (end point) 2B)
The residence time T (hr) was calculated from these values, and
A calculation unit for calculating the nitrate addition rate C according to (I) and an output unit for outputting the calculation result are provided. First, the residence time T is calculated as follows.

That is, since the total amount of sewage (m ³ ) in the pressure feed pipe is calculated by the following equation, it is calculated as follows by dividing this by the flow rate. Note that d is the radius (m) of the pumping pipe,
d = D / (2 × 10 ³ ).

The total amount of sewage in the pressure feed 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 measuring r), the residence time is the total extension L of the pumping pipe.
(M) is divided by the flow velocity S (m / hr), and is obtained as follows.

Residence time T (hr) = L ÷ S Residence time T (hr) calculated in this manner, measured value of water temperature t (° C.), consumption rate of nitrate A (mg-N / h)
r) and the inner diameter D (mm) of the pumping pipe, the nitrate addition rate C (mg-N / L-sewage) is calculated from the above formula (I), and the chemical injection pump is adjusted so that the nitrate addition rate C becomes such. 5 is output.

The nitrate consumption rate A (mg-N / hr) at a water temperature of 15 ° C. can be determined by the actual machine test as follows, for example, as described above.

That is, nitrate is evenly injected to a concentration of 2 to 30 mg-N / L-sewage in a state in which sewage is supplied to the pressure-feeding pipe to be treated, and the concentration of residual nitrate at the outlet of the pressure-feeding pipe at that time is measured with time. The change is examined for about 1 to 24 hours to determine the average nitrate reduction concentration.

The reduced concentration (mg-N / L) is substituted into the formula (I) as a required addition amount C, and A at a water temperature of 15 ° C. is obtained. Although the consumption rate A of the nitrate is affected by the water temperature and the like, the effect of the water temperature is taken into account in the formula (I), and if the sewage and the pressure feed pipe are determined, they can be regarded as substantially equal values. Therefore, once a test is performed on the chemical injection treatment target system regardless of the season, chemical injection control can be performed using the value for a long period of time as long as there is no large change in the sewage water quality.

The chemical injection control in the present invention is performed so that the nitrate addition rate C calculated by the above formula (I) or the addition rate in the range of ± 10% of this value C may be attained. You.

In the present invention, the nitrate is usually
The nitrate is added to the sewage storage tank 1 or the inlet of the pumping pipe 2, but a nitrate may be added to an intermediate portion of the pumping pipe 2.

As the nitrate, calcium nitrate,
An aqueous solution having a concentration of 10 to 80% by weight such as sodium nitrate can be used.

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

[0031]

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

Example 1 As shown in FIG. 1, sewage having the following water quality (sewage after passing through a sedimentation basin in a sewage treatment plant) in a sewage storage tank 1 is pressure-pumped by a water supply pump 3 (inner diameter D = 100 mm, d). = 0.05
m), a system in which continuous feeding is performed at a flow rate of 0.6 m / sec (2160 m / hr) at a flow rate of 0.6 m / sec (2160 m / hr) in a ductile cast iron pipe with a total length of 900 m).
(° C.) and the flow meter 7 measures the flow rate F (m ³ / h).
r), the measured values t and F, the inner diameter D (mm) of the pumping tube, and the total length L of the pumping tube input to the control means 8 in advance.
(M), nitrate consumption rate constant A at a water temperature of 15 ° C.
(Mg-N / hr) and the nitrate addition rate C (mg-N / hr).
/ L-sewage) was calculated, and based on this value, the chemical injection pump 5 was controlled to add nitrate (50% by weight calcium nitrate aqueous solution) to the sewage storage tank 1.

Sewage water solubility COD: 80 to 166 mg / L pH: 7.1 to 7.3 SS: 142 to 232 mg / l The tests were conducted in winter (January: sewage temperature t = 16 ° C.) and summer (7
Month: sewage water temperature t = 25 ° C.) and fall (November: sewage water temperature t = 21 ° C.) for 15 days.

The nitrate consumption rate constant A (mg-N / hr) at a water temperature of 15 ° C. was determined as follows.
First, the sewage was fed into the pressure feed pipe, a 50% by weight aqueous solution of calcium nitrate was added to the sewage to a concentration of 15 mg-N / L, and the N concentration was measured with a colorimeter to examine the change with time. Then, the nitrate consumption rate constant A (mg-N / h) at a water temperature of 15 ° C. was determined from the decrease in the N concentration at the inlet and outlet.
When r) was determined, the nitrate consumption rate constant A at a water temperature of 15 ° C. was A = 9 mg-N / hr. The water temperature during this test was 26 ° C.

The flow rate F (m ³ / hr) is set at a flow rate of 0.
6 m / sec (S = 2160 m / hr), the flow rate (21) determined from the inner diameter d (m) of the pumping pipe and the total length L (m)
60 × 0.05 × 0.05 × 3.14 = 17 m ³ / h
r), so that the residence time T (hr) is 0.42 (= the total length of the pumping pipe L ÷ flow rate S = 900 ÷ 21).
60) hr.

Accordingly, for example, the nitrate addition rate C _{16 at} t = 16 ° C. can be obtained as follows by substituting the following value into the above equation (I).

A = 9 mg-N / hr t = 16 ° C. L = 900 m D = 100 mm T = 0.42 hr C ₁₆ = ｛9 × (0.1 + 0.9 × 100/100) × 1.07 ^(16-15) × 0.42 ^{} 2/4 = (9 ×} 1.07 × 0.42) 2/4 = 4.09 (mg-N / L- sewage) Further, t = 25 ° C. or 21 ° C. nitrate addition rate C ₂₅ when the, C ₂₁ is similarly obtained as follows.

[0038] _{C 25 = {9 × (0.1} +0.9 × 100/100) × 1.07 (25-15) × 0.42} 2/4 = (9 × 1.07 10 × 0.42) 2/4 = 13 .82 (mg-N / L- _{sewage) C 21 = {9 × (} 0.1 +0.9 × 100/100) × 1.07 (21-15) × 0.42} 2/4 = (9 × 1.07 6 × 0 ^{.42) 2/4 = 8.05 (} mg-N / L- sewage) performs dosing control of nitrate based on the nitrate added amounts calculated in this way, measures the concentration of hydrogen sulfide in the pumping tube exit As a result, during the test, the hydrogen sulfide concentration in water could be maintained at 0.01 mg / L or less in any season.

Further, under the same sewage pumping conditions, a test was carried out by changing the amount of nitrate added, and the minimum addition rate of nitrate to make the concentration of hydrogen sulfide in water at the outlet of the pumping pipe 0.02 mg / L or less was determined. However, the results shown in Table 1 were obtained.

As shown in Table 1, the measured values are in good agreement with the calculated values, and it is clear that according to the present invention, it is possible to control the injection of nitrate with a substantially required minimum addition rate.

[0041]

[Table 1]

[0042]

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 chemical amount is automatically controlled so that the amount of nitrate is properly and appropriately added. In addition, it is possible to reliably prevent the generation of hydrogen sulfide while suppressing the chemical cost.

[Brief description of the drawings]

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

[Explanation of symbols]

 Reference Signs List 1 sewage storage tank 2 pressure feed pipe 3 water supply pump 4 chemical storage tank 5 chemical injection pump 6 temperature sensor 7 flow meter 8 control means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuo Kitagawa 2-1905 Wada, Fukui-shi, Fukui Japan Sewerage Corporation Fukui Construction Office (72) Inventor Nobumi Maejima 3- 4-7 Nishishinjuku, Shinjuku-ku, Tokyo No. Kurita Kogyo Co., Ltd. (72) Inventor Mitsuhiro Mashiko 3-4-7 Nishi Shinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A method for controlling injection of hydrogen sulfide remover, comprising adding nitrate as a hydrogen sulfide remover to sewage based on a value C calculated by the following formula (I). C = {A × (0.1 +0.9 × 100 / D) × 1.07 (t-15) × T} 2/4 ... (I) ( where in the formula (I), A is a nitrate in water temperature 15 ℃ Consumption rate constant (mg-N / hr), t is water temperature (° C), T is residence time in sewage pumping pipe (hr), D is pumping pipe inner diameter (mm), C is nitrate addition rate (mg-N / L) −
sewage)) 2. A chemical injection means for adding nitrate as a hydrogen sulfide removing agent to sewage, and a value C calculated by the following formula (I):
A control means for controlling the amount of nitrate added to said chemical dosing means based on the control of the hydrogen sulfide removing agent. C = {A × (0.1 +0.9 × 100 / D) × 1.07 (t-15) × T} 2/4 ... (I) ( where in the formula (I), A is a nitrate in water temperature 15 ℃ Consumption rate constant (mg-N / hr), t is water temperature (° C), T is residence time in sewage pumping pipe (hr), D is pumping pipe inner diameter (mm), C is nitrate addition rate (mg-N / L) −
sewage))