Overview

The generation of coke oven effluent is linked to the manufacturing of coke at a number of coke oven plants across the world. The wastewater is a highly laden stream that is contaminated with a variety of organic and inorganic chemicals, necessitating extensive treatment processes before it can be used again.

Coke oven plant operation

Coke oven plants are technologically complicated plants that consist of various technological sites where coal preparation, coking, and coal by-product gathering and upgrading take place.

Processes carried out at coking facilities include a number of technological procedures, the most notable of which are:

• Coal blend preparation from coals laid on the coal site;

• Coal supply for the coal blend tower;

• Extracting coal from the coal tower and loading coal into the coke ovens;

• Coke ovens are heated by coke oven gas and coal blend coking;

• Drug trafficking;

• Quenching coke (wet or dry);

• The collecting of unprocessed coke oven gas;

• Cleansing the coke oven's gas;

• Processing of coal by-products

Coke oven wastewater formation

The separation of tars and ammonia from coke oven effluent results from the processing of coke oven gas and the retrieval of coal derivatives, resulting in a highly polluted liquor. The liquor is created during the cooling stage of the coke oven gas, when tars, water vapour, and other compounds in the gas condense or are partially washed out.

The liquid is first routed to the tars separation unit, where it is separated into two principal streams: organic (tars) and aqueous. The later phase is used to produce water for the gooseneck spray machinery, while the remainder can be used for further gas treatment, such as absorption, to extract hydrogen sulphide. The excess liquid is directed to ammonia stripping, and the still effluent from the stripping column is delivered to the coke oven wastewater treatment plant.

How is coke oven effluent treated in ETPs?

Coke oven effluents are one of many complicated effluents that, in addition to BOD and COD, contain harsh pollutants such as cyanides, thiocyanates, phenols, sulphides, and ammonia. Before being discharged into the environment, these effluents require a highly efficient and reliable treatment system. The Effluent Treatment Plant's main purpose is to make the harsh coke oven effluents suitable for discharge to the environment while also meeting regulatory standards.

Effluents generated from coke oven

Coke is made by carbonising bituminous coal in an oven in the absence of air at temperatures ranging from 900 to 1000 degrees Celsius, which burns off all of the coal's volatile components. The gas, which contains volatile materials, is collected through standpipes and cooled in stages by spraying cool liquor from over gas, resulting in a condensate that is mostly tar. Condensate with more tar and ammonia liquid is produced by further cooling procedures. These condensate liquors are recycled after being separated from the tar in tar-decanters. The surplus liquor, known as "ammonia liquor," is transported to be treated because it contains mostly ammonia and tar. The Ammonia scrubber, Tar separator, NO-Oxidizer plant, and Quenching Tower are the most common effluent streams created by a Coke Oven Plant.

Physico-chemical and biological Treatment in effluent treatment plant

The effluent treatment plant treats different trains of effluents totalling 1000 cu.m/day, including contaminated streams from scrubbers, coal tar decanters, and other sources.

A combination of physico-chemical treatment (clarification, stream stripping, and alkaline chlorination) followed by a two-stage biological treatment (Extended mode activated sludge process) is a rigorous and cost-effective option for the treatment of effluents from coke.

With stage-wise treatments, highly complex nitrogen molecules like cyanide and thiocyanates, as well as high levels of ammonia, can be decreased. Ammonia scrubber and tar separator effluents are equalised and clarified in tar clarifier for elimination of floating tar, oils, and grease, and steam stripping of ammonia is performed in Ammonia stripper.

NOx gas plant effluents are introduced and treated in a two-stage alkaline chlorination process to eliminate cyanide and thiocynates, followed by hydrogen peroxide dosing to oxidise sulphides. pH is adjusted by adding quenching water and the appropriate acid/alkali. Then, for biological degradation of contaminants like BOD/COD and soluble phenols, as well as nitrification/denitrification of balancing ammonia, a two-stage activated sludge biological treatment is used.

Conclusion

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