Steel Manufacturing and Environment

Steel plant environment is combining heat, water and corrosive elements that are tough on parts and machinery. The business environment facing steel producers is equally tough, requiring them to work leaner and smarter, modernizing equipment while streamlining manufacturing processes. From integrated mills to new electric-arc-furnace based mini-mills, companies strive to reduce costs and implement efficiencies, no matter how small, to improve their competitive global position. Steel is manufactured by the chemical reduction of iron ore, using an integrated steel manufacturing process or a direct reduction process. In the conventional integrated steel manufacturing process, the iron from the blast furnace is converted to steel in a basic oxygen furnace (BOF). Steel can also be made in an electric arc furnace (EAF) from scrap steel and, in some cases, from direct reduced iron. BOF is typically used for high-tonnage production of carbon steels, while the EAF is used to produce carbon steels and low tonnage specialty steels. An emerging technology, direct steel manufacturing, produces steel directly from iron ore. Steel manufacturing and finishing processes are also employed in integrated steel plants.

Sintering operations can emit significant dust levels of about 20 kilograms per metric ton (kg/t) of steel. Pelletizing operations can emit dust levels of about 15 kg/t of steel. Air emissions from pig iron manufacturing in a blast furnace include particulate matter (PM), ranging from less than 10 kg/t of steel manufactured to 40 kg/t; sulfur oxides (SOx), mostly from sintering or pelletizing operations (1.5 kg/t of steel); nitrogen oxides (NOx), mainly from sintering and heating (1.2 kg/t of steel); hydrocarbons; carbon monoxide; in some cases dioxins (mostly from sintering operations); and hydrogen fluoride.
Air emissions from steel manufacturing using the BOF may include PM (ranging from less than 15 kg/t to 30 kg/t of steel). For closed systems, emissions come from the desulfurization step between the blast furnace and the BOF; the particulate matter emissions are about 10 kg/t of steel.
In the conventional process without recirculation, wastewaters, including those from cooling operations, are generated at an average rate of 80 cubic meters per metric ton (m3/t) of steel manufactured. Major pollutants present in untreated wastewaters generated from pig iron manufacture include total organic carbon (typically 100–200 milligrams per liter, mg/l); total suspended solids (7,000 mg/l, 137 kg/t); dissolved
solids; cyanide (15 mg/l); fluoride (1,000 mg/l); chemical oxygen demand, or COD (500mg/l); and zinc (35 mg/l).
Major pollutants in wastewaters generated from steel manufacturing using the BOF include total suspended solids (up to 4,000 mg/l, 1030 kg/t), lead (8 mg/l), chromium (5 mg/l), cadmium (0.4 mg/l), zinc (14 mg/l), fluoride (20 mg/l), and oil and grease. Mill scale may amount to 33 kg/t.
To reduce global CO2 emissions, as is being called for in the post-Kyoto Protocol world, the development of innovative steel making process technology is required.

Recom Systems Limited provides consulting services to improve your processes to become environmentally friendly.