Steel is ‘iron with most of the carbon removed’. Iron constitutes about five per cent of the Earth’s crust and is the fourth most abundant element in the crust.98% of the iron ore mined is used to make steel. 6.5% of CO2 emissions derive from iron and steel production. Steel production has a number of impacts on the environment, including air emissions (CO, SOx, NOx, PM2), wastewater contaminants, hazardous wastes, and solid wastes. The reputed Integrated Steel Plants are always aware of the impacts on environmentthat occurs due to coking and iron-making. Here we would discuss about those impacts with a little detail.
Virtually all of the greenhouse gas emissions associated with steel productions are from the carbon dioxide emissions related to energy consumption.
Emissions to air
Coke production is one of the major pollution sources from steel production. Air emissions such as coke oven gas, naphthalene, ammonium compounds, crude light oil, and sulfur and coke dust are released from coke ovens.
Emissions to water
Water emissions come from the water used to cool coke after it has finished baking. Quenching water becomes contaminated with coke breezes and other compounds. While the volume of contaminated water can be great, quenching water is fairly easy to reuse. Most pollutants can be removed by filtration.
Slag, the limestone and iron ore impurities collected at the top of the molten iron make up the largest portion of iron-making by-products. Sulfur dioxide and hydrogen sulfide are volatized and captured in air emissions control equipment and the residual slag is sold to the construction industry. While this is not a pollution prevention technique, the solid waste does not reach landfills.
Recycling and reuse can be a partially eligible measure that can be used to lower the adverse effect of steel production. Iron and steel are the world’s most recycled materials, and among the easiest materials to reprocess, as they can be separated magnetically from the waste stream. Recycling is via a steelworks: scrap is either re-melted in an electric arc furnace (90-100% scrap), or used as part of the charge in a Basic Oxygen Furnace (around 25% scrap). Any grade of steel can be recycled to top quality new metal, with no ‘downgrading’ from prime to lower quality materials as steel is recycled repeatedly.
Re-use of structural steel
Steel reuse is any process where end-of-life steel is not re-melted but rather enters a new product use phase.
Steel buildings and products are intrinsically demountable. Easily re-usable components include:
- Piles (sheet and bearing piles)
- Structural members including hollow sections
- Light gauge products such as purlins and rails.
Design for reuse
To facilitate greater reuse it is important that designers not only use steel but also do what they can to optimize future reuse. Steps that the designer can take to maximize the opportunity for reusing structural steel that includes:
- Use of bolted connections in preference to welded joints to allow the structure to be dismantled during deconstruction
- Use of standard connection details including bolt sizes and the spacing of holes
- Ensuring easy and permanent access to connections
- Where feasible, try to ensure that the steel is free from coatings or coverings that will prevent the visual assessment of the condition of the steel.
- Minimizing the use of fixings to structural steel elements that require welding, drilling holes, or fixing with Hilt nails; using clamped fittings where possible
- Using long-span beams as they are more likely to allow flexibility of use and to be reusable by cutting the beam to a new length. (source: SteelConstruction.info)
These steps of reusing and recycling can lead to a better outlook on the environmental impact of the Steel industry on a global basis. Major Integrated Steel Plants is already having started their responsible ventures to set up a more sustainable and eco-friendly procedures and to minimize the impact on the environment. Advance technologies and Innovations are showing us a path that can lead to a better future where the environment and Industry can co-exist peacefully.