Steel Manufacturing

Summary

At steel mills, a complex set of processes are employed to convert iron ore, carbon, and trace amounts of other metals into the various grades of steel products.  Water is used in almost all of the processes and in most cases a wastewater stream is generated.  The wastewater that is generated during these processes can generally be categorized into three sub groups: 

• Wet Air Pollution Control (WAPC) Wastewater
• Direct Contact Wastewater
• Machinery cooling and cooling water

In many cases the wastewater streams are recycled multiple times prior to being discharged to the final wastewater treatment systems.  In order to recycle these streams some form of water treatment is needed to remove excess solids, contaminants or FOG. Often these wastewater streams are then co-mingled prior to reaching the final wastewater treatment systems.   In order to provide economical and efficient treatment it is critical to get the correct treatment processes in place, Salt Creek Technologies can help you with the selection, sizing and design of that equipment.   

Water Uses and Wastewater Sources 

Below is a table based off the EPA's Iron and Steel Effluent Guidelines Development Document that provides a brief overview of the water uses and wastewater sources at each stage of the steel manufacturing process.  

Process	Water Uses	​Wastewater Sources
​​Cokemaking	Coke Quenching ​Wet Air Pollution Control (WAPC)	Ammonia Liquor Coke Oven Gas Desulfurization Crude light oil recovery Process Condensates
Sintering	Sinter Moisture Control Sinter Cooling Belt Sprayes	WAPC system blowdown
Ironmaking	Wet gas cleaning Furnace off-gas cooling Slag quenching	​​Scrubbers and gas coolers
​​Steelmaking (BOF)	WAPC system make up	WAPC system blowdown Semi-wet (no recirc) Wet-suppressed combustion (recirc, CO2) wet-open combustion (recirc, CO2) Slag quench water Cooling tower blowdown
Steelmaking (EAF)	WAPC system make up	None, Semi-wet systems achieve ZLD
Vacuum Degassing​	Steam ejector	Degassing Condensates
Continuous Casting	Direct contact spray cooling make up Flume flushing	O&G and scale contaminated spray water ​
Hot Forming	Scale removal Roll and Machinery Cooling Product Cooling Flume flushing	Scale pit purge
Acid Pickling	WAPC Rinse water Pickle Liquor	Spent Rinse Water Spent Pickling Liquor WAPC blowdown
Alkaline Cleaning	Rinse water Alkaline cleaning solution	Blowdown
Hot Coating / Electropating	Rinse water Plating solution	Blowdown Spent plating solution

Process Steps

Cokemaking - Turns carbon in raw coal into metallurgical coke which is used in the ironmaking process.  
Sintering - Recovers iron from a mixture of mill waste streams and upgrades them to suitable size and weight for the blast furnace.
Ironmaking - Blast furnaces are used to produce molten iron from a mixture of coke, limestone, refined iron ores and sinter. 
Steelmaking

• Basic Oxygen Furnace - Oxygen and lime are added to the molten iron from the blast furnace to remove phosphorus and sulfur impurities in the form of slag.  
• Electric Arc Furnace - Scrap steel, pig iron and alloying elements are melted by passing an electric current through the furnace.   Limestone slag removes steel impurities like sulfur and phosphorus. 

Vacuum Degassing - A refining process where gases like oxygen and oxygen are removed from the molten steel prior to casting to produce high quality products.
Continuous Casting - Molten steel is poured, cooled and formed into a desired shape.

Hot Forming - Preheated solidified steel is reshaped through a series of forming steps in which mechanical pressure is applied through work rolls. 
Descaling - Molten salt baths or abrasive compounds are used to loosen and remove heavy scale from stainless and high alloy steels.   
Acid Pickling - Chemically removes oxides and scale from the surface of steel using inorganic acid solutions.  
Cold Forming - Steel is rolled at ambient temperature to impart desired mechanical and surface properties like hardness, surface finishes and thickness. 
Alkaline Cleaning - Steel is passed through alkaline solutions to remove mineral and animal fats and oils.  
Hot Coating - Precleaned steel is immersed into molten baths of metals to improve the resistance to corrosion or appearance. 

Example Treatment Processes

Wastewater from the coke making process is some of the more difficult wastewater to treat at integrated steel mills. 

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Salt Creek Technologies, Inc. 188 Industrial Drive, Suite 14C, Elmhurst, IL  60126  630-530-2808, FAX: 630-626-0684, [email protected]