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Iron and Steel Manufacturing

Industry Description and Practices

Steel is manufactured by the chemical reductionof iron ore, using an integrated steel manufac-turing process or a direct reduction process. Inthe conventional integrated steel manufacturingprocess, the iron from the blast furnace is con-verted 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, fromdirect reduced iron. BOF is typically used forhigh-tonnage production of carbon steels, whilethe EAF is used to produce carbon steels and low-tonnage specialty steels. An emerging technol-ogy, direct steel manufacturing, produces steeldirectly from iron ore. This document deals onlywith integrated iron and steel manufacturing;that on Mini Steel Mills addresses the electric arcsteel process and steel finishing processes. Steelmanufacturing and finishing processes discussedin that document are also employed in integratedsteel plants. See also Coke Manufacturing.

In the BOF process, coke making and ironmaking precede steel making; these steps are notnecessary with an EAF. Pig iron is manufacturedfrom sintered, pelletized, or lump iron ores us-ing coke and limestone in a blast furnace. It isthen fed to a BOF in molten form along with scrapmetal, fluxes, alloys, and high-purity oxygen tomanufacture steel. In some integrated steel mills,sintering (heating without melting) is used toagglomerate fines and so recycle iron-rich mate-rial such as mill scale.

Waste Characteristics

Sintering operations can emit significant dust lev-els of about 20 kilograms per metric ton (kg/t)of steel. Pelletizing operations can emit dust lev-

els of about 15 kg/t of steel. Air emissions frompig iron manufacturing in a blast furnace includeparticulate matter (PM), ranging from less than10 kg/t of steel manufactured to 40 kg/t; sulfuroxides (SOx), mostly from sintering or pelletiz-ing operations (1.5 kg/t of steel); nitrogen oxides(NOx), mainly from sintering and heating (1.2kg/t of steel); hydrocarbons; carbon monoxide;in some cases dioxins (mostly from sintering op-erations); and hydrogen fluoride.

Air emissions from steel manufacturing usingthe BOF may include PM (ranging from less than15 kg/t to 30 kg/t of steel). For closed systems,emissions come from the desulfurization step be-tween the blast furnace and the BOF; the particu-late matter emissions are about 10 kg/t of steel.

In the conventional process without recircula-tion, wastewaters, including those from coolingoperations, are generated at an average rate of80 cubic meters per metric ton (m3/t) of steelmanufactured. Major pollutants present in un-treated wastewaters generated from pig ironmanufacture include total organic carbon (typi-cally 100–200 milligrams per liter, mg/l); totalsuspended solids (7,000 mg/l, 137 kg/t); dis-solved solids; cyanide (15 mg/l); fluoride (1,000mg/l); chemical oxygen demand, or COD (500mg/l); and zinc (35 mg/l).

Major pollutants in wastewaters generatedfrom steel manufacturing using the BOF includetotal suspended solids (up to 4,000 mg/l, 1030kg/t), lead (8 mg/l), chromium (5 mg/l), cadmium(0.4 mg/l), zinc (14 mg/l), fluoride (20 mg/l), andoil and grease. Mill scale may amount to 33 kg/t.The process generates effluents with high tem-peratures.

Process solid waste from the conventional pro-cess, including furnace slag and collected dust,is generated at an average rate ranging from 300

Pollution Prevention and Abatement HandbookWORLD BANK GROUP

Effective July 1998

328 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES

kg/t of steel manufactured to 500 kg/t, of which30 kg may be considered hazardous dependingon the concentration of heavy metals present.Approximately, 65% of BOF slag from steel manu-facturing can be recycled in various industriessuch as building materials and, in some cases,mineral wool.

Pollution Prevention and Control

Where technically and economically feasible, di-rect reduction of iron ore for the manufactureof iron and steel is preferred because it doesnot require coke manufacturing and has fewerenvironmental impacts. Wherever feasible, pel-letizing should be given preferences over sinter-ing for the agglomeration of iron ore. Thefollowing pollution prevention measures shouldbe considered.

Pig Iron Manufacturing

• Improve blast furnace efficiency by using coaland other fuels (such as oil or gas) for heatinginstead of coke, thereby minimizing air emis-sions.

• Recover the thermal energy in the gas from theblast furnace before using it as a fuel. Increasefuel efficiency and reduce emissions by im-proving blast furnace charge distribution.

• Improve productivity by screening the chargeand using better taphole practices.

• Reduce dust emissions at furnaces by cover-ing iron runners when tapping the blast fur-nace and by using nitrogen blankets duringtapping.

• Use pneumatic transport, enclosed conveyorbelts, or self-closing conveyor belts, as well aswind barriers and other dust suppression mea-sures, to reduce the formation of fugitive dust.

• Use low- NOx burners to reduce NOx emissionsfrom burning fuel in ancillary operations.

• Recycle iron-rich materials such as iron orefines, pollution control dust, and scale in a sin-ter plant.

• Recover energy from sinter coolers and ex-haust gases.

• Use dry SOx removal systems such as caronabsorption for sinter plants or lime sprayingin flue gases.

Steel Manufacturing

• Use dry dust collection and removal systemsto avoid the generation of wastewater. Recyclecollected dust.

• Use BOF gas as fuel.• Use enclosures for BOF.• Use a continuous process for casting steel to

reduce energy consumption.

Other

Use blast furnace slag in construction materials.Slag containing free lime can be used in ironmaking.

Target Pollution Loads

The recommended pollution prevention and con-trol measures can achieve the following targetlevels.

Liquid Effluents

Over 90% of the wastewater generated can bereused. Discharged wastewaters should in allcases be less than 5 m3/t of steel manufacturedand preferably less than 1 m3/t.

Solid Wastes

Blast furnace slag should normally be generatedat a rate of less than 320 kg/t of iron, with a tar-get of 180 kg/t. The generation rate, however,depends on the impurities in the feed materials.Slag generation rates from the BOF should bebetween 50 and 120 kg/t of steel manufactured,but this will depend on the impurity content offeed materials. Zinc recovery may be feasible forcollected dust.

Treatment Technologies

Air Emissions

Air emission control technologies for the removalof particulate matter include scrubbers (orsemidry systems), baghouses, and electrostaticprecipitators (ESPs). The latter two technologiescan achieve 99.9% removal efficiencies for par-

329Iron and Steel Manufacturing

ticulate matter and the associated toxic metals:chromium (0.8 milligrams per normal cubicmeter, mg/Nm3), cadmium (0.08 mg/Nm3), lead(0.02 mg/Nm3), and nickel (0.3 mg/Nm3).

Sulfur oxides are removed in desulfurizationplants, with a 90% or better removal efficiency.However, the use of low-sulfur fuels and oresmay be more cost-effective.

The acceptable levels of nitrogen oxides canbe achieved by using low-NOx burners and othercombustion modifications.

For iron and steel manufacturing, the emis-sions levels presented in Table 1 should beachieved.

Wastewater Treatment

Wastewater treatment systems typically includesedimentation to remove suspended solids, physi-cal or chemical treatment such as pH adjustmentto precipitate heavy metals, and filtration.

The target levels presented in Table 2 can beachieved for steel-making processes.

Solid Waste Treatment

Solid wastes containing heavy metals may haveto be stabilized, using chemical agents, beforedisposal.

Emissions Guidelines

Emissions levels for the design and operation ofeach project must be established through the en-

vironmental assessment (EA) process on the ba-sis of country legislation and the Pollution Pre-vention and Abatement Handbook, as applied tolocal conditions. The emissions levels selectedmust be justified in the EA and acceptable to theWorld Bank Group.

The guidelines given below present emis-sions levels normally acceptable to the WorldBank Group in making decisions regardingprovision of World Bank Group assistance. Anydeviations from these levels must be describedin the World Bank Group project documenta-tion. The emissions levels given here can beconsistently achieved by well-designed, well-operated, and well-maintained pollution con-trol systems.

The guidelines are expressed as concentrationsto facilitate monitoring. Dilution of air emissionsor effluents to achieve these guidelines is unac-ceptable.

All of the maximum levels should be achievedfor at least 95% of the time that the plant or unitis operating, to be calculated as a proportion ofannual operating hours.

Air Emissions

For integrated iron and steel manufacturingplants, the emissions levels presented in Table 3should be achieved.

Liquid Effluents

The effluent levels presented in Table 4 shouldbe achieved.

Table 1. Load Targets per Unit of Production,Iron and Steel Manufacturing

Parameter Maximum value

PM10 100 g/t of product (blast furnace,basic oxygen furnace); 300 g/t fromsintering process

Sulfur oxides For sintering: 1,200 g/t; 500 mg/m3

Nitrogen oxides For pelletizing plants: 500 g/t; 250–750 mg/Nm3; for sintering plants:750 mg/Nm3

Fluoride 1.5 g/t; 5 mg/Nm3

Table 2. Target Load per Unit of Production,Steel Manufacturing(emissions per metric ton of product)

Blast Basic oxygenParameter furnace furnace

Wastewater 0.1 m3 0.5 m3

Zinc 0.6 g 3 gLead 0.15 g 0.75 gCadmium 0.08 g n.a.

n.a. Not applicable.

330 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES

Sludges

Sludges should be disposed of in a secure land-fill after stabilization of heavy metals to ensurethat heavy metal concentration in the leachatesdo not exceed the levels presented for liquideffluents.

Ambient Noise

Noise abatement measures should achieve eitherthe levels given below or a maximum increase inbackground levels of 3 decibels (measured on theA scale) [dB(A)]. Measurements are to be taken

at noise receptors located outside the projectproperty boundary.

Maximum allowable logequivalent (hourly

measurements), in dB(A)Day Night

Receptor (07:00–22:00) (22:00–07:00)

Residential,institutional,educational 55 45

Industrial,commercial 70 70

Monitoring and Reporting

Air emissions should be monitored continuouslyafter the air pollution control device for particu-late matter (or alternatively an opacity level ofless than 10%) and annually for sulfur oxides, ni-trogen oxides (with regular monitoring of sulfurin the ores), and fluoride. Wastewater dischargesshould be monitored daily for the listed param-eters, except for metals, which should be moni-tored at least on a quarterly basis. Frequentsampling may be required during start-up andupset conditions.

Monitoring data should be analyzed and re-viewed at regular intervals and compared withthe operating standards so that any necessarycorrective actions can be taken. Baseline data onfugitive PM emissions should be collected andused for comparison with future emissions esti-mates, which should be performed every threeyears based on samples collected. Records ofmonitoring results should be kept in an accept-able format. The results should be reported to theresponsible authorities and relevant parties, asrequired.

Key Issues

The key production and control practices that willlead to compliance with emissions guidelines aresummarized here.

• Prefer the direct steel manufacturing processwhere technically and economically feasible.

• Use pelletized feed instead of sintered feedwhere appropriate.

Table 3. Air Emissions from Iron and SteelManufacturing(milligrams per normal cubic meter)

Parameter Maximum value

PM 50Sulfur oxides 500 (sintering)Nitrogen oxides 750Fluorides 5

Table 4. Effluents from Iron and SteelManufacturing(milligrams per liter, except pH and temperature)

Parameter Maximum value

pH 6–9TSS 50Oil and grease 10COD 250Phenol 0.5Cadmium 0.1Chromium (total) 0.5Lead 0.2Mercury 0.01Zinc 2Cyanide

Free 0.1Total 1

Temperature increase £ 3oCa

Note: Effluent requirements are for direct discharge to surfacewaters. a. The effluent should result in a temperature increase of nomore than 3° C at the edge of the zone where initial mixing anddilution take place. Where the zone is not defined, use 100meters from the point of discharge.

331Iron and Steel Manufacturing

• Replace a portion of the coke used in the blastfurnace by injecting pulverized coal or by us-ing natural gas or oil.

• Achieve high-energy efficiency by using blastfurnace and basic oxygen furnace off-gas asfuels.

• Implement measures (such as encapsulation)to reduce the formation of dust, including ironoxide dust; where possible, recycle collecteddust to a sintering plant.

• Recirculate wastewaters. Use dry air pollutioncontrol systems where feasible. Otherwise,treat wastewaters.

• Use slag in construction materials to the ex-tent feasible.

Sources

British Steel Consultants. 1993. “Research Study, In-ternational Steel Industry.” Prepared for the Inter-national Finance Corporation, Washington, D.C.

The Netherlands. 1991. “Progress Report on the Studyof the Primary Iron and Steel Industry.” Third Meet-ing of the Working Group on Industrial Sectors,Stockholm, January 22–24.

Paris Commission. 1991. Secondary Iron and Steel Pro-duction: An Overview of Technologies and EmissionStandards Used in the PARCOM Countries.

World Bank. 1996. “Pollution Prevention and Abatement:Iron and Steel Manufacturing”. Draft Technical Back-ground Document. Environment Department, Wash-ington, D.C.