Much of what goes on in a refinery involves heating things to high temperatures and then cooling them, as in the distillation column. If heat is allowed to build up inside a refinery, it can damage the machinery, just as a car engine will be damaged if its radiator is not working.
Refineries have cooling systems that operate much like huge radiators.
Cooling water circulates through networks of pipes near refinery units that build up heat. The water then absorbs some of this heat and carries it away from the hot units. Most refinery cooling systems use additives to avoid certain problems, particularly corrosion and biological growth, and some of these additives may be toxic. For example, chlorine may be used to prevent biological growth. Any discharged wastewater thus would contain toxic chemicals.