Goal of the chapter 2
Acquire knowledge about the steelmaking / steel manufacturing process in English.
Step 1 : Read the text carefully and highlight the main information
There are many pollution problems faced by the steel industry and are not confined to any one processing stage. As the size of the industry is large, pollution control is a costly (= expensive) proposition. Major pollution sources and types in iron and steel industry are presented.
There are emissions to the atmosphere in the form of dust, fume (= toxic smoke) and steam (= vapor), acid emissions, fugitive emissions and toxic gases.
Large quantities of fumes may be created due to high temperatures in high intensity oxygen steel refining processes or in electric arc furnaces. The size of dusts and fumes vary depending on the source of emission.
Oxides of nitrogen and sulphur and to a much lesser extent fluorides and chlorides (=oxydes à base de fluor ou chlore) may be released as they are present in the materials being burnt.
About 99% of the total fumes and dust generated in steel-making process escape as fugitive emissions whereas slags also lead to release of fumes in the form of iron oxide, kish (= graphite), soot (=suie) and silica.
Coke ovens are another major source of emissions. About 50 harmful (= dangerous) substances are emitted in the atmosphere (some are concentrated and harmful), e.g. benzopyrene and unsaturated hydrocarbons (= hydrocarbure insaturé).
Two types of polluting substances exist in the air – hard substances and gaseous substances. The most acute problem in the whole of steel industry is from secondary emissions. Steel industry has been able to a large extent reduce the emission of dust. However, less effort has been made against controlling the gaseous pollutants.
Many operations within steel-making complex require large quantities of water and is in direct contact with process materials, e.g., cooling and purification of coke oven gas can lead to pollutants such as tar oils, ammonia, phenols, cyanides, etc…. This polluted water required extensive purification before it can be recycled or discharged to the environment or to a local sewage treatment plant (=a factory in charge of purifying wastewater).
Cyanides, fluorides, lead, zinc and dust particles compounds emanating from blast furnaces can find their way into cooling and cleaning waters because of direct contact with gases. Casting, scale (= scories/ calamine), lubricating oils and hydraulic fluids can also contaminate the water. Similar pollution can also arise from rolling mills coating operations ( = opérations de laminage) and scarfing (= suppression des défauts par oxycoupage) .
The risk of water pollution from steel industry depends to a large extent on water management plan adopted.
The pollution can be of the following kinds – thermal (increase in the temperature of water used), suspended matter including oil and tar, toxic substances like cyanide, heavy metals and waste acids, solutions and rinse waters from finishing processes.
A single operation of pig iron (=fonte brute) production requires about 150 tons of water and 3.5 tons of air to produce one ton of iron. Likewise, every tonne of steel produced gives about 20 tonnes of liquid wastes, 5 tonnes of waste gases and 1 ton of solid wastes. Primary pollutants in waste gases are iron oxide, dust and oxides of sulphur, carbon etc. of these, dust is by far the most important air pollutant in the industry.
Solid waste mainly comprises of slags from blast furnace and steel melting shops and dust separated in gas cleaning plants and ventilation systems.
Step 2 : Prepare an oral synthesis of this document by taking notes.
Put the stress on the following information:
At the end of your synthesis, imagine at least three possible consequences of this pollution onto the environment (for example: global warming ….)