JPH05103906A - Ammonia removal control method in gas liquid - Google Patents

Abstract

(57) [Summary] [Purpose] Regarding the removal of ammonia in gas liquid, control is performed so that changes in the ammonia load can be accurately and promptly dealt with. [Structure] Ammonia in the gas liquid in the stripper 5 is removed by blowing steam into the stripper 5. A relational expression between the amount of steam blown and the ammonia removal rate in the gas liquid is obtained in advance. This relational expression is p of gas liquid
Depends on H value. The ammonia concentration of the gas liquid on the outlet side of the stripper 5 and the pH on the inlet side of the stripper 5 are measured. From these measured values and the relational expression,
The amount of alkali added on the inlet side of the stripper 5 and the amount of steam blown into the stripper 5 are adjusted, and the ammonia concentration of the gas liquid on the outlet side of the stripper 5 is automatically controlled to a target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a gas liquid on the stripper outlet side when removing ammonia in a gas liquid generated when carbon is dry-distilled to produce coke by a stripper (ammonia stripping device). The present invention relates to a method for automatically controlling the ammonia concentration of.

In the iron and steel industry, coal is carbonized to produce coke. At that time, an ammonia waste liquid called a gas liquid is by-produced together with coke oven gas (C gas) and coal tar. This gas liquid is one in which water adhering to coal and water produced by a thermal reaction in the carbonization process are entrained in C gas and condensed and separated in the gas cooling and refining process. The gas liquid contains phenol, ammonia, thiocyan, etc., and it is necessary to perform wastewater treatment.

At present, as a method of treating a gas liquid, the gas liquid is passed through a stripper, and steam is blown into the stripper to strip (remove) ammonia.
At the same time as the treatment, components such as phenol and thiocyan are removed in the microbial treatment step using activated sludge in the subsequent step. Ammonia emissions may lead to eutrophication, so optimal treatment is required.

[0004]

2. Description of the Related Art A gas liquid is temporarily stored in a gas liquid tank after being separated from an oil component in a decanter collecting / separating tank. The gas liquid discharged from the gas liquid tank is sent into the stripper, and by blowing steam into the stripper,
Stripping processing, that is, ammonia removal processing is performed. The gas liquid discharged from the stripper is usually 50
There is a temperature of about 60 to 60 ° C. A part of the gas liquid is recovered by a vaporizer, combined with the injected vapor by using the negative pressure generated by the ejector for injecting the vapor, and then injected into the stripper.

The removed ammonia is recovered in the C gas and then recovered as liquid ammonia in the lower step.
On the other hand, in the gas liquid from which ammonia has been removed, phenol, thiocyan, etc. are removed in the lower step.

In the stripping method as described above for removing ammonia in a gas liquid, generally,
It is said that the lower the pressure, the higher the temperature, and the higher the alkali, the higher the ammonia removal rate.

Therefore, in the conventional ammonia removal method, the amount of steam blown in and the amount of alkali added are manually adjusted while confirming the temperature at the top of the stripper and the concentration of ammonia at the stripper outlet side. The ammonia concentration was set close to the target value.

[0008]

However, in the prior art,
The influence of the pH value of the gas liquid on the relationship between the amount of injected steam and the ammonia concentration is unknown, and since the control operation was performed manually, the appropriate amount of steam and alkali can be promptly added to the fluctuation of the ammonia load. I couldn't throw it in. As a result, it has not been possible to perform the ammonia removal work that is efficient in terms of time and cost.

Therefore, an object of the present invention is to provide a control method relating to the removal of ammonia in a gas liquid, which can respond accurately and promptly to changes in the ammonia load amount.

[0010]

In order to solve the above-mentioned problems, according to the present invention, in a method of removing ammonia in a gas liquid in a stripper by blowing steam into the stripper, depending on pH, vapor A relational expression between the blowing amount and the ammonia removal rate in the gas liquid is obtained in advance, and the ammonia concentration of the gas liquid at the stripper outlet side and the pH at the stripper inlet side are measured,
From these measured values and the above relational expression, adjust the amount of alkali added on the stripper inlet side and the amount of steam blown into the stripper to automatically control the ammonia concentration of the gas liquid on the stripper outlet side to a target value. A method for controlling removal of ammonia in a gas liquid is provided.

In the automatic control, the target value of the ammonia concentration can be achieved under the condition of the cost minimum in consideration of the unit prices of the blown steam and the added alkali.

[0012]

The above relational expression can be stored in the CPU in advance. Then, the ammonia concentration of the treated gas liquid on the stripper outlet side and the pH value on the stripper inlet side are input to the CPU as signals, and the alkali addition amount and vapor injection amount such that the ammonia concentration of the treated gas liquid reaches the target value are set. Calculated by CPU and output as output signal. In response to this output signal, the alkali addition adjusting valve and the steam injection adjusting valve are operated, and an appropriate amount of alkali and steam is injected. This series of operations is performed by continuous automatic control so that the ammonia concentration of the treated gas liquid reaches the target value.

If the unit prices of alkali and steam are input to the CPU in advance, the CPU calculates an appropriate amount of alkali and steam so that the target value of the ammonia concentration can be achieved under the condition of the cost minimum, and outputs the output signal. Is possible.

[0014]

EXAMPLE FIG. 1 is a schematic view showing equipment for removing ammonia in a gas liquid by using the control method of the present invention together with peripheral equipment.

The gas liquid in the gas liquid tank 1 is introduced into the stripper 5 from the alkali tank 2 through the alkali adjusting valve 13 while being introduced into the stripper 5 (for example, 20% NaOH).
A solution) is charged, and the blocking agent is charged from the blocking agent tank 3 through the blocking agent adjusting valve 15. Alkaline flow meter 14
And, it is measured by the blocking agent flow meter 16 and is input to the CPU (control device) 12 as a signal.

Furthermore, the amount of the gas liquid introduced into the stripper 5 after being mixed with the alkali and the blocking agent by a line mixer (not shown) is measured by the gas liquid flow meter 20, and the pH of the introduced gas liquid is measured. The value is measured by the pH meter 11, and each value is used as a signal by the CPU 12
Is input to.

The steam from the steam pipe 19 is used as a steam adjusting valve 17.
And is blown into the stripper 5 through the ejector 7. The amount of steam sent is measured by the steam flow meter 18, and the value is input to the CPU 12 as a signal.

The gas liquid from which ammonia has been removed in the stripper 5 is sent to the vaporizer 6 via the liquid sending pipe 4. A part of the gas liquid is recovered by the vaporizer 6 and is combined with the steam from the steam sending pipe 19 by utilizing the negative pressure generated by the ejector 7 and blown into the stripper.

Ammonia removed in the stripper 5 is taken out from the top of the stripper, recovered in C gas (coke oven gas), and then recovered by a deaeration device (not shown) in the lower step. It becomes liquid ammonia.

On the other hand, the gas liquid from which ammonia has been removed is
It is taken out from the bottom of the stripper, and in the next step, phenol, thiocyan, etc. are removed by the water treatment facility 8 using activated sludge.

The ammonia concentration and pH of the gas liquid passed through the vaporizer 6 are respectively measured by an ammonia concentration meter 9
The pH is measured by the pH meter 10, and the value is input to the CPU 12 as a signal.

Based on various input data to the CPU 12,
A target value of the ammonia concentration of the gas liquid on the outlet side of the stripper 5 is set.

Further, the CPU 12 has the following p
The relational expression of the amount of steam blown in and the ammonia removal rate in the gas liquid, which depends on H, is built in.

When 7 ≦ pH <8 y = (− 10) + (19.4) × ln (x) Equation (1) When 8 ≦ pH <9 y = (− 170) + (57 .2) × ln (x) ... Equation (2) when 9 ≦ pH <10 y = (− 134) + (50.3) × ln (x) ... Equation (3) where y Is the ammonia removal rate (%) in the gas liquid on the stripper exit side, x is the amount of steam blown into the stripper (kg / ton gas), and x is 80 to 1
It takes a value within the range of 00.

Further, the CPU 12 also incorporates the following relational expression between the amount of alkali added and the pH.

Y = 61 + 0.86x + (− 0.046) x ² (4) where y is the pH value of the gas liquid, and x is the amount of alkali (20% NaOH solution) input to the gas liquid. And x is a unit of 1 / gas liquid ton.

The relational expressions shown in the equations (1) to (4) are
It is obtained from the graphs of experimental values as shown in FIGS. 2 and 3, but it is not absolute. That is,
Since these relational expressions may fluctuate depending on the operating conditions, the online data for a certain period will be aggregated and analyzed to be reviewed as needed.

In the CPU 12, the signal from the pH meter 11 indicating the pH value on the inlet side of the stripper 5, the signal from the ammonia concentration meter 9 indicating the ammonia concentration of the gas liquid on the outlet side of the stripper 5, and the above relational expression ( From 1) to (4), the amount of alkali addition and the amount of steam injection required to achieve the set target value of ammonia concentration are obtained, and based on the results, the alkali control valve 1
3 and signals for operating the steam regulating valve 17 are output.
To operate the alkali adjusting valve 13 and the steam adjusting valve 17,
Feedback signals from the pH meter 11 and the steam flow meter 18 to the CPU 12 are used.

In this way, continuous automatic control is performed so that the ammonia concentration on the outlet side of the stripper 5 reaches the target value. In the usual case, the slight difference between the actual and the target value of the ammonia concentration can be eliminated by a fine adjustment of the steam injection rate.

If the unit price of alkali and the unit price of steam are input to the CPU 12 in advance, the sum of the required amount of alkali addition and the amount of steam obtained from the above relational expressions (1) to (4) multiplied by each unit price is calculated. It is possible to perform automatic control so that the ammonia concentration target value is achieved under the condition that the minimum value is obtained.

[0031]

According to the control method of the present invention, based on the finding that the relationship between the amount of steam blown into the stripper and the ammonia removal rate in the gas liquid depends on the pH value, it is possible to prevent fluctuations in the ammonia load amount. It is possible to perform an automatic control such that a proper amount of steam and alkali are rapidly added to achieve the ammonia concentration target value.

As a result, it is possible to perform the ammonia removal work which is efficient in terms of time and cost.

Further, if the automatic control is performed in consideration of the unit prices of the injected steam and the added alkali, it is possible to achieve the target value of the ammonia concentration under the condition of the cost minimum.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing equipment for removing ammonia in a gas liquid using a control method of the present invention together with peripheral equipment.

FIG. 2 is a graph showing the relationship between the amount of steam blown into the stripper and the ammonia removal rate of the gas liquid.

[Fig. 3] Amount of alkali added to gas liquid and pH of gas liquid
The graph which shows the relationship with a value.

[Explanation of symbols]

1 gas liquid tank, 2 alkali tank, 4 liquid transfer pipe, 5
Stripper, 6 vaporizer, 7 ejector, 9 ammonia concentration meter, 11 pH meter, 12CP
U, 13 alkali adjustment valve, 14 alkali flow meter, 1
7 steam regulating valve, 18 steam flow meter, 19 steam pipe,
20 Gas liquid flow meter.

Claims (2)

[Claims] 1. In a method of removing ammonia in a gas liquid in a stripper by blowing steam into the stripper, a relational expression between the amount of steam blown and the ammonia removal rate in the gas liquid, which depends on pH, is obtained in advance. Every, measure the ammonia concentration of the gas liquid on the stripper outlet side and the pH on the stripper inlet side, and from these measured values and the above relational expression, adjust the amount of alkali added on the stripper inlet side and the amount of steam blown into the stripper. A method for controlling ammonia removal in a gas liquid, characterized by automatically controlling the ammonia concentration of the gas liquid on the outlet side of the stripper to a target value. 2. The control method according to claim 1, wherein, in the automatic control, the target value of the ammonia concentration is achieved under the condition of the cost minimum in consideration of the unit prices of the injected steam and the added alkali.