Abstract
AbstractCoke oven liquor is one of the most contaminated liquid streams generated by the coal processing industry, thus its proper treatment and utilization is crucial for sustainable and environmentally neutral plant operation. The conventional wastewater treatment process comprises of chemical and biological processes. Within the current research the detailed role of chemical treatment is described. Commercially available iron-based coagulants (PIX100, PIX100COP, PIX113, PIX116) were tested to understand their removal efficiency and impact on the stream parameters. The influence of iron dose in the range of 300-500 mgFe/L on the process performance was also examined.It was found that the main role of chemical treatment was to bind toxicants harmful to activated sludge microorganisms, i.e. free and complex cyanides and sulphides. Among the tested iron-based conventional coagulants ferrous salts were more efficient than ferric salts. It was also observed that efficiency of the process strongly depended on wastewater properties (especially in regard to pH, which should be in the range of 9-10) and the coagulant selection needed to be done individually for a given wastewater type. The removal rates of particular contaminants were diversified and for free cyanides, complex cyanides and sulphides they were in the range of 23-91%, -156-77% and -357-98%, respectively. The expected, simultaneous removal of chemical oxygen demand (COD) during the treatment was not observed and even the parameter value increased after the process due to probable formation of compounds less vulnerable to oxidation.
Highlights
Coke is produced during pyrolysis of coal carried out in coke oven batteries comprised of special chambers called coke ovens operated at temperatures reaching up to 1,200°C
The processing of coke oven gas starts with cooling, during which condensation of organic compounds and water vapor, which washes out some inorganic gas components like ammonia, hydrogen cyanide and hydrogen sulphide from the gas, occurs [3,4]
It was found that coagulation efficiency strongly depended on all considered process parameters, i.e. coagulant type, dose and coke oven wastewater properties and any relevant relationship between these parameters could not be found
Summary
Coke is produced during pyrolysis of coal carried out in coke oven batteries comprised of special chambers called coke ovens operated at temperatures reaching up to 1,200°C. The second product of coal pyrolysis, i.e. coke oven gas, after the treatment and recovery of so called coal derivatives, i.e. tars and benzol, is used for heating of coke ovens and for other energy generation purposes, usually inside the plant. The remaining aqueous phase, from this stage called ammoniacal liquor, is used for flushing cooling of coke oven gas and, in case of plants operated with ammoniacal method of gas desulphurization, is involved in further washing of hydrogen sulphide from the gas [5,6,7]. The amount of ammoniacal liquor is always higher than the amount required for technological purposes This excess liquor is directed to ammonia stripping carried out at alkaline conditions, and the stripping column downstream is the influent of coke oven wastewater
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