To manufacture steel requires very high temperatures for both smelting and processing. These combustion processes imply some emissions of nitrogen oxides and dust, for example. The steel industry, over a long period, has worked to reduce emissions through different measures:
- More efficient use of energy.
- Modified production processes.
- Cleaning equipment.
Emissions to the environment from the processes persist but have declined considerably within several important areas. The diagrams below illustrate, on the one hand, the total emissions per year (left axis and the bars) and, on the other hand, the specific emissions i.e. the emissions per tonne of crude steel production (right axis and the curve).
High temperatures mean that the formation of nitrogen oxides is hard to avoid in connection with the combustion of fuel since the nitrogen is in the air. Emissions of nitrogen oxides have fallen, however, with the aid of new burner technology, the cleaning of exhaust gases and acid recovery methods in the pickling process.
Dust is formed in many of the steel industry’s processes. Cleaning technology, filtration and ventilation systems have meant that dust emissions have been substantially reduced. The dust is reprocessed for the sake of the metal content that is then reused in the blast furnace process.
Emissions of sulphur dioxide are directly related to the combustion of oil in reheating furnaces and for coke production. Oils with lower sulphur content, a greater use of gas and improved cleaning processes have all served to minimise steel plant emissions.