Energy use per net ton of product
Reheat furnace: 1.6 X 106 Btu average; 1.4 X 106 Btu for modern furnaces Hot rolling: 0.8 X 106 Btu
Largest sources: machine scarfing, hydrochloric acid pickling (acid mists), reheat furnace (N0X)
Particulate: iron and other oxides
Typical acid mist generation: >10 tons/yr per facility
Acid pickling: 1.2 X 106 Btu
Largest sources: direct cooling and descaling
Typical wastewater volumes (gal/t)
Hot forming: 0 to >6000
Descaling: 300 to 1800
Pickling: 70 to 1000
Total generation: 3.7 X 106 t/yr
Reuse: most recycled
Total generation: about 1.0 X
106 t/yr Reuse: minimal K062, Spent pickle liquor Hazardous components: lead, nickel, chromium Total generation: about 6 million t/yr Reuse: some recycled
Cold rolling: 0.7 X 106 Btu
Cleaning/annealing: 1.0 X 106 Btu
Source: From Energetics, Inc., Energy and Environmental Profile of the U.S. Iron and Steel Industry, D0E/EE-0229, U.S. Department of Energy, Washington, DC, 2000.
from 300 to 1800gal/t, and are cotreated with wastewaters from other finishing operations.15 Acid pickling discharge water flows for the different pickling processes are as follows:
1. Between 280 and 1020 gal/t for hydrochloric acid processes
2. Between 90 and 500gal/t for sulfuric acid processes, and up to 1500gal/t for combination acid processes.1
Pickling done before coating may use a mildly acidic bath; such spent liquor is not considered hazardous. Waste pickle liquor flows typically range between 10 and 20 gal/t of pickled product. Rinsewater flows may range from less than 70 gal/t for bar products to more than 1000 gal/t for certain flat-rolled products. The principal pollutants in rinsewater include TSS, dissolved iron, and metals. For carbon steel operations, the principal metals are lead and zinc; for specialty and stainless steels the metals include chromium and nickel.15
Spent pickle liquor in the acid pickling wastewaters is listed as hazardous waste K062, regulated under RCRA, as it contains considerable residual acidity and high concentrations of dissolved iron salts.2 Exhausted pickling baths are mainly composed of nitrate (150 to 180 g/L), fluoride (60 to 80 g/L), iron (III) (30 to 45 g/L), chromium (III) (5 to 10 g/L), and nickel (II) (3 to 5 g/L).
Process wastewater from cold forming operations results from using synthetic or animal-fat based rolling solutions. The rolling solutions may be treated and recycled at the mill, used on a once-through basis, or a combination of the two. The principal pollutants are TSS, oil and grease (emulsified), and the metals lead and zinc for carbon steels and chromium and nickel for specialty and stainless steels. Chromium may also be a contaminant from cold rolling of carbon steels resulting from wear on chromium-plated work rolls. Toxic organic pollutants including naphthalene, other polynuclear aromatic compounds, and chlorinated solvents have been found in cold rolling wastewaters. Process wastewater discharge rates may range from less than 10 gal/t for mills with recirculated rolling solutions to more than 400 gal/t for mills with direct application of rolling solutions.15
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