JPH11128972A - For waste-water treatment in coke production equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe regulation value while keeping the cost of waste-water treatment low, by steam stripping a surplus gas liquor to reduce the content of ammonia in total waste water which flows into a waste-water treatment system within a prescribed range. SOLUTION: A surplus gas liquor is supplied through a pipe 1, and a part of the liquor flows into a waste water storage tank 3 through a stripping column 2. Steam is supplied to the stripping column 2, ammonia in surplus gas liquor together with steam flows out from a column top, and waste water flows into a waste water treatment system including an activated sludge method. The concentration of ammonia in the waste water is measured with an azotometer and the ammonia content in the surplus gas liquor is measured with an azotometer and a flow meter. The amount of ammonia which should be removed from the stripping column 2 is calculated from these measured values. Thereby, steam stripping of a required minimum is carried out according to the amount of ammonia which should be removed from the waste water so that the amount of steam can be greatly reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater in a coke making facility, and more particularly to a method for removing ammonia from wastewater.

[0002]

2. Description of the Related Art Various kinds of wastewater are generated in coke making equipment. The first is excess gas liquid. In coke production, water is injected into a high-temperature coke oven gas flowing out of the coke oven to cool the gas and condense the contained tar. The coke oven gas is then further cooled by indirect cooling and sent to a gas purification unit. In these gas cooling processes, water is recovered, and the tar content contained in the gas is removed by a decanter or the like, and then recycled for injection into coke oven gas. This water is called a gas liquid, and absorbs ammonia in coke oven gas and contains several thousand ppm of ammonia. A part of this ammonia exists as fixed ammonia which forms a salt with an acid, and the other exists as free ammonia. In addition, the coke oven gas flowing out of the coke oven contains water adhering to coal and water generated from coal during the carbonization process as steam. Therefore, the amount of gas liquid gradually increases by the amount of water generated from the water vapor when left undisturbed. ing. The extracted gas liquid is a surplus gas liquid, contains several thousand ppm of ammonia as described above, and is highly contaminated with organic substances. It cannot be discharged into water bodies. In a coke production facility, various wastewaters are discharged from a coke oven gas purification process and a tar treatment process in addition to the surplus gas liquid. Wastewater from these various sources also often contains significant amounts of ammonia and organics,
They, like surplus gas liquids, can only be discharged into public waters after activated sludge treatment.

[0003]

SUMMARY OF THE INVENTION The concentration of ammonia in wastewater discharged into public waters is strictly regulated. Therefore, in the treatment of wastewater containing a high concentration of ammonia, such as wastewater from coke production equipment, how to reduce the concentration of ammonia when discharged to public waters to or below the regulation value has a significant effect on wastewater treatment costs. I do. That is, since the amount of wastewater generated and its ammonia content constantly fluctuate, if the ammonia content is always removed with a sufficient margin so that the regulation value can be complied with even if such a fluctuation occurs,
Naturally, processing costs increase. Conversely, a method that treats wastewater based on the average amount of wastewater generated and its ammonia content can reduce the cost of treatment, but it is necessary to install large-capacity storage tanks to average fluctuations at the source Unless measures are taken to absorb fluctuations, such as by doing so, it will not be possible to comply with the regulation values. The present invention seeks to provide a method that allows compliance with regulatory values while keeping wastewater treatment costs low.

[0004]

SUMMARY OF THE INVENTION According to the present invention, excess gas liquid discharged from a gas liquid circulation system is combined with contaminated wastewater from another discharge source to treat wastewater containing activated sludge. In a method of treating wastewater in a coke manufacturing facility for treating in a system, at least an excess gas liquid is subjected to steam stripping so that the ammonia content of all wastewater flowing into the wastewater treatment system falls within a predetermined range. The wastewater treatment cost can be reduced by flowing the wastewater into the wastewater treatment system after the reduction, and adjusting the amount of ammonia removed in the steam stripping in accordance with the amount of ammonia carried into the wastewater.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the ammonia content of wastewater flowing into a wastewater treatment system falls within a predetermined range by removing ammonia content from wastewater in advance by steam stripping. As described above, in the coke making facility, various wastewaters having different discharge sources flow into the wastewater treatment system. A considerable portion of the total ammonia of the wastewater, usually 50% or more, is the ammonia content of the surplus gas liquid. .
The surplus gas liquid is obtained by extracting a part of the gas liquid circulating in a large amount, and the amount and the fluctuation of the ammonia content are relatively slow. In the present invention, this surplus gas liquid is subjected to steam stripping. Normally, only the excess gas liquid is subjected to steam stripping, but if desired, wastewater from other discharge sources may be subjected to steam stripping in addition to the excess gas liquid. The amount of ammonia removed from wastewater in steam stripping is determined so that the amount of ammonia in wastewater flowing into the wastewater treatment system falls within a predetermined range. In steam stripping, the amount of ammonia removed can be arbitrarily controlled with little time delay by adjusting the amount of wastewater and the amount of steam supplied. Therefore, it is possible to immediately cope with a change in the amount of ammonia brought into the wastewater.

[0006] Control of the amount of ammonia removed by steam stripping can be accomplished in several ways.
For example, the entire amount of excess gas liquid is always supplied to steam stripping, and the amount of ammonia removed can be controlled by controlling the amount of steam. However, usually, it is preferable to control the amount of the ammonia gas removed by controlling the amount of excess gas liquid supplied to the steam stripping. FIG. 1 shows an example of a liquid flow when such a method is carried out. The surplus gas liquid is supplied through a conduit 1, and a part of the liquid gas is supplied through a stripping column 2.
The remainder directly flows into the wastewater storage tank 3. Steam is supplied to the stripping column 2 via a conduit 4, and the ammonia in the surplus gas liquid flows out of the column via the conduit 5 together with the steam. This ammonia is treated by an appropriate method such as introduction into a deammonification system of coke oven gas.
Wastewater from another discharge source also flows into the wastewater storage tank 3 via the conduit 6. From the wastewater storage tank 3, wastewater flows out at a constant speed via a conduit 7, and flows into a wastewater treatment system including the activated sludge method. In FIG. 1, the concentration of ammonia in the wastewater flowing through the conduit 7 is measured with a nitrogen meter, and the ammonia in the surplus gas liquid is measured with a nitrogen meter and a flow meter. The amount of ammonia to be removed in the stripping tower 2 is calculated based on the measured values, and the amount of excess gas liquid to be supplied to the stripping tower is calculated based on the removal rate of ammonia in the stripping tower. Further, the ammonia content in the surplus gas liquid flowing out of the stripping tower is measured, and the amount of steam supplied is adjusted so that the removal rate becomes a predetermined value.

The wastewater treatment system for receiving the wastewater flowing out of the wastewater storage tank 3 is mainly composed of an activated sludge method, and may be further combined with another treatment as required. Most simply, after the BOD is reduced by the activated sludge method, the suspended solids (S
S) is removed by filtration or sedimentation and discharged to public waters. If desired, the activated sludge method can be combined with nitrification and denitrification by nitrifying bacteria and denitrifying bacteria to further reduce the ammonia content in the wastewater.

According to the present invention, there is no need to provide a large wastewater storage tank for averaging the ammonia content of the wastewater flowing into the wastewater treatment system. Although the surplus gas liquid contains cyan, which is harmful to the growth of microorganisms, it is possible to prevent the subsequent wastewater treatment system from being adversely affected by the cyan.
For example, nitrifying bacteria and denitrifying bacteria are susceptible to cyanide, and it is said that the growth is significantly inhibited when the cyanide concentration is about 30 ppm or more in a denitrification tank. Activated sludge is also affected by cyanide, and its growth is inhibited if the cyanide concentration is about 50 ppm or more in an aeration tank. However, according to the present invention, when ammonia is removed by steam stripping, cyan in the surplus gas liquid is also easily distilled off, so that the subsequent wastewater treatment system is prevented from being hindered by cyan in the surplus gas liquid. can do. Furthermore, in the present invention, the necessary minimum steam stripping may be performed in accordance with the amount of ammonia to be removed from the wastewater so that the ammonia flowing into the wastewater treatment system has a predetermined value. Can be greatly reduced. For example, on average, the surplus gas liquid converts free ammonia to 195 kg / hr,
Fixed ammonia is brought into the wastewater treatment system at 105 kg / hr, and wastewater from other sources brings 100 kg / hr of ammonia into the wastewater treatment system, but ammonia in the wastewater discharged to public waters. It is assumed that only 300 kg / hr of ammonia can be flowed into the subsequent wastewater treatment system due to the regulation of minute. If the amount of wastewater and its ammonia concentration are always constant, 100 kg / free ammonia of excess gas liquid is removed by steam stripping.
hr may be removed. Assuming that the removal rate of free ammonia by steam stripping is 90%, about 57% of the surplus gas liquid may be subjected to steam stripping.
However, if the amount of ammonia brought in by the wastewater from another discharge source reaches a maximum of 150 kg / hr, even in this case, excess 300 mm / hr of ammonia is required to flow into the subsequent wastewater treatment system. 150 kg / hr of the free ammonia in the gas liquid must be removed. For that purpose, about 86% of the surplus gas liquid must be subjected to steam stripping, and the surplus gas liquid to be subjected to steam stripping increases by about 50%. Since the amount of liquid to be subjected to steam stripping is substantially proportional to the amount of steam consumed, the amount of steam consumed also increases by about 50%. As is clear from this assumption,
If steam stripping is always performed with a margin so that it is OK even if the amount of ammonia brought into the wastewater fluctuates, compared to adjusting the amount of ammonia removed by steam stripping according to the amount of ammonia brought into the wastewater, Steam consumption increases significantly. In addition, the activated sludge of the succeeding wastewater treatment system is also troublesome to manage because the concentration of ammonia fluctuates.

[Brief description of the drawings]

FIG. 1 shows an example of the flow of a liquid in the case of performing steam stripping of a surplus gas liquid by the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Supply pipe of surplus gas liquid 2 Stripping tower 3 Wastewater storage tank 4 Steam supply pipe 5 Ammonia gas outlet pipe 6 Supply pipe of wastewater from other sources 7 Wastewater outlet pipe

Claims (2)

[Claims] 1. A wastewater treatment system for a coke making facility, comprising: processing excess gas liquid discharged from a gas liquid circulation system together with contaminated wastewater from another discharge source in a wastewater treatment system including an activated sludge method. In the treatment method, at least an excess gas liquid is subjected to steam stripping to reduce the ammonia content before flowing into the wastewater treatment system so that the ammonia content brought into the wastewater treatment system is within a predetermined range, and A method for adjusting the amount of ammonia removed in steam stripping according to the amount of ammonia carried into wastewater. 2. A part of the surplus gas liquid is supplied to a wastewater treatment system after being subjected to steam stripping, and the remainder is supplied to a wastewater treatment system without being subjected to steam stripping, and the ratio between the two is adjusted. 2. The method according to claim 1, wherein the amount of ammonia introduced into the wastewater treatment system is adjusted by the method.