This is a paper about recycling of ships, but it shows how much energy could be saved by recycling steel rather than making it from scratch with iron ore in blast furnaces (mainly powered by coal).
Ship Recycling markets and the impact of. April 2013. International Conference on Ship Recycling.
Conclusion: The annual average of 3.6 million tonnes of melting steel scrap from the global ship recycling industry is about 1.5% of the needs of the global steel making industry for old steel scrap, so the impact of ship recycling to the steel making industry is low and therefore can’t dictate pricing.
There are two main processes in modern steel making:
- production from pig iron ore in a blast furnace, refined into steel in a Basic Oxygen Furnace (BOF). Some steel scrap is also added in the refining process. Around 70% of the world’s steel is produced this way
- production from steel scrap in an Electric Arc Furnace (EAF), around 30% of the world’s steel production. The usage of steel scrap in steel making makes absolute sense, both from the economic and the environmental points of view. The energy requirements for making 1 tonne of steel from iron ore is 23 GJ as opposed to 7 GJ when using steel scrap. Also, recycling of steel saves natural resources. Every tonne of recycled steel saves around 1.1 tonnes of iron ore, 0.6 tonnes of coal, and reduces pollution: 86% less air pollution, 76% less water pollution, a 40% reduction in water usage, and avoidance of generation of about 1.3 tonnes of solid waste. Nevertheless, reliance on iron ore is unavoidable as steel scrap is available in relatively limited quantities.
Usage of steel scrap in steel production. Contrasted to the world’s 70/30 mix (70% v 30%) of BOF and EAF in 2011, China’s mix was 90/10, India’s 40/60, and Turkey’s 25/75.
There are three sources of steel scrap for steel making :
- 35% “own arisings” (a.k.a. “circulating scrap”, or “home scrap”) which arise internally in steel mills as rejects from melting, casting, rolling, etc;
- (ii) 21% “new steel scrap” (or “process scrap”) which is generated when steel is fabricated into finished products; and
- (iii) 44% “old steel scrap” (or “capital scarp”) which is steel scrap from obsolete products and which is collected, traded and sold to steel plants for remelting. Ship steel scrap obviously falls in the third category of sources of steel scrap. In recent times the market of old steel scrap is around 225 million tonnes annually
Ships are recycled primarily to recover their steel, which forms approximately 75% to 85% of a ship’s lightweight, or light ship weight (the mass of the ship’s structure, propulsion machinery, other machinery, outfit and constants).
In addition to steel, the recycling process recovers non-ferrous metals (i.e. copper), machinery, equipment, and fittings. Non-ferrous metals are particularly valuable and although just 1% of a ship’s LDT, they can recover for the recycler up to 10% to 15% of the price paid for the ship. Machinery from recycled ships is often reconditioned and sold for further use in maritime or land industries, or when it is beyond repair , it is cut and sold as steel scrap. Because the chemical composition of the steel used in shipbuilding is controlled by classification society rules and surveys, ship steel has good yield strength, ductility and impact strength. Ship steel scrap is therefore attractive for steel making.