Energy has always been – and will always remain – one of the most important production factors within the iron and steel industry.
In former times, iron and steel works were located next to rivers which provided hydro power, and in forest districts with access to fuels for charcoal production. The majority of steel plants in Sweden are still to be found in the mining and metallurgic district of Bergslagen.
The Swedish steel industry has a leading position when it comes to using today’s best process technology. The development of new processes requires very large resources and the Swedish steel industry is consequently dependent on developments taking place abroad. Most of the major energy-saving inputs are made in connection with new investments or exstensive renovation of process equipement.
From an energy consumption viewpoint, the ore-based steel plants are wholly dominant. This is due to coke, which is required as a reducing agent and for alloying processes, being included in the energy balance.
One characteristic of the steel industry is that most of the energy-intensive processes take place at extremely high temperatures. The energy is used mainly in processes where the working temperature exceeds 1 000 °C. These circumstances mean that steel plants – in order to maintain production – need to have access to energy resources of high calorific value such as coal and oil products, gas and electric power.
The combustion of fuel occurs in the same "compartment" as the material to be heated; this places special requirements on the atmosphere and the fuel’s ash content in order to ensure that the material quality does not undergo deterioration or show too much variation.
In line with the expanded possibility for transporting liquified natural gas, natural gas is increasingly being used as a replacement for oil. To a certain extent the use of fuel is also being replaced by electric power. On the other hand, coal cannot be replaced to any extent since it is primarily used as a reducing agent.
Coke is produced from pit coal and is used mainly in the reduction processes, i.e. in blast furnaces.
A certain portion of the coke can be replaced by pulverised coal, oil and tar/pitch etc. The coke oven gas from the coking process is used as fuel in coking plants and blast furnaces but also in the reheating and heat treatment furnaces of rolling mills.
Electricity is used for the operation of rolling mill motor systems, the melting of scrap in electric arc furnaces and for reheating and heat treatment in rolling mills. Certain plants have electric ladle arc furnaces.
Despite increased use of electric power for automated operations and investments in environmental improvements, among other things, the steel industry’s use of electricity remains relatively stable.
Oil is used especially in oil-fired furnaces for reheating and heat treatment operations in rolling mills. The use of oil has been sharply reduced since the 1970’s for several reasons:
- Changeover to continuous casting has led to reduced demand for heat in rolling mills
- Pulverised coal injection instead of oil in the blast furnaces
- Phasing out of all Siemens-Martin furnaces
- Changeover to LPG and natural gas
- Energy efficiency measures
LPG and natural gas
In reheating and heat treatment furnaces, increasing use is made of LPG and natural gas. The use of natural gas has risen in line with the enhanced possibilities for transporting liquid natural gas (LNG). When the combustion system for oil is adapted for natural gas, this brings with it opportunities for future use of biogas where this is available.
Increased use of residual energy recovery
Since the steel industry’s processes require high temperatures, there are good opportunities for using the energy further for other purposes that calls for e.g. lower temperatures.
Residual heat recovery
In a number of plants the residual heat is used internally by the companies for e.g. the drying or heating of premises. The waste heat is also conveyed out in to the district heating network.
The ore-based plants also generate energy-rich process gases such as blast furnace gas, coke oven gas and LD gas. These process gases are utilised for such purposes as the heating of blast air in blast furnaces and as fuel in coking plants. The greater share, however, is used in the production of electricity and heat in combined heat and power (CHP) plants. The companies forming "Industrigruppen Återvunnen Energi" are working hard to achieve increased recovery and utilisation of industrial waste heat.