1 GENERAL INFORMATION
1.5 Main environmental issues in the production of iron and steel steel
1.5 Main environmental issues in the production of iron and
• Sinter plants
Sinter, as a product of an agglomeration process of materials which contain iron, represents a major part of the burden of blast furnaces. The main stack emissions of sinter plants account for up to 50 % of the total dust emissions from an integrated steelworks. Other relevant pollutants in the off-gas emissions from the sinter strand and the cooler are heavy metals, SO2, HCl, HF, PAH and persistent organic pollutants (such as PCB and PCDD/F). Furthermore, the recovery of sensible heat and the utilisation of solid wastes are severe issues. Environmental benefits are linked to this process with the recycling of iron-rich solid by-products of downstream processes and the potential for heat recovery.
• Pelletisation plants
Pelletisation is another process used to agglomerate materials which contain iron where emissions to air dominate the environmental issues. Other main issues in pellet plants are the use of sensible heat, the treatment of waste water and the internal utilisation of process residues.
• Coke oven plants
A coke plant consists of one or more coke oven batteries with a coke oven firing system (under firing) and the process gas treatment unit where emissions to air are the most significant. The main point source for emissions to air is the waste gas from under firing. Additionally, many of the emissions are diffuse emissions from various sources such as the unloading, storage, handling, crushing and blending (preparation) of coal, the leakages from lids and adherences onto frames, oven and leveller doors, the ascension pipes and charging holes of coal into and the pushing of coke out of the chambers, and finally, coke quenching and coke grading (crushing and screening), transport, handling and storage. Diffuse/fugitive VOC emissions to air can occur from coke oven batteries and diffuse/fugitive ammonia and BTX emissions from by-products plants which all have the potential to create odour nuisances. Dust and SO2 emissions at coke oven plants and other plants where coke oven gas is used as a fuel is a concern. Thus the desulphurisation of coke oven gas is a measure of high priority for minimising these emissions.
Waste water disposal is another major issue for coke oven plants. Optimised management of coke oven gas and its use in other processes of integrated plants allow energy savings and minimise air emissions.
• Blast furnace plants
Significant emissions to all media occur where the blast furnace process for producing hot metals from materials which contain iron are used. Because of the high input of reducing agents (mainly coke and coal), this process consumes most of the overall energy input of an integrated steelworks. Relevant emissions to all media occur and these are described in detail. The main environmental issues are dust, waste water from blast furnace gas scrubbing, emissions from slag treatment such as SO2 and H2S which can lead to odour nuisances, dusts and sludge, and finally, the minimisation of energy consumption.
• Basic oxygen furnace plants
Emissions to air from various sources such as primary and secondary dedusting, hot metal pre- treatment and secondary steelmaking and various solid process residues are the main environmental issues in oxygen steelmaking. In addition, waste water arises from wet dedusting (when applied) and from continuous casting. Particular attention should be paid to diffuse dust emissions which occur when secondary emission collecting systems are insufficient.
• Electric arc furnace plants
The direct smelting of materials which contain iron (mainly scrap) is usually performed in electric arc furnaces which need considerable amounts of electrical energy and causes substantial emissions to air and solid process residues such as wastes and by-products (mainly filter dust and slag). The emissions to air from the furnace consist of a wide range of inorganic compounds (iron oxide dust and heavy metals) and organic compounds such as persistent organic pollutants (e.g. PCB and PCDD/F).
Energy consumption
Energy consumption in iron and steel making is considerable. CO2 as a greenhouse gas is generated when energy is consumed. There are many emissions points of CO2 in the iron and steel processes and they are related to three main factors: a) providing the sufficient temperature in order to carry out the chemical reactions and physical treatment needed, b) providing a reductant (mainly CO) to the system in order to reduce the iron oxide, and c) providing the power and steam necessary to run the steelworks.
The specific energy consumption for steel production in electric arc furnaces in Europe is on average about 1.8 GJ/t liquid steel. Considering the efficiency of energy supply, primary energy consumption will be considerably higher. Additionally there is a fossil fuel input of about 0.5 GJ/t liquid steel on average (according to Table 8.1).
Specifically, because the CO2which is generated when energy is consumed is a greenhouse gas (GHG), energy savings have undergone a major change in purpose, and are now considered part of the solution to the problem of global warming which is a global-scale environmental issue.
As mentioned in the IPCC Climate Change Synthesis Report 2007, there is no unique option for climate change mitigating policies. The solution is rather a sequence of mitigating options for the stabilisation of atmospheric greenhouse gas concentrations [ 40, IPCC 2007 ].
Regarding iron and steel making, the CO2 emissions depend very much on the types and amounts of reducing agents (e.g. coke, coal, and oil) used in the blast furnace (see Sections 6.1.3.1 and 6.2.2.4). For this reason, the steel industry has actively implemented a variety of measures to reduce the energy consumption in general and emissions of GHG such as CO2 in particular. Extensive efforts have been made to reduce the reducing agent demand close to the stoichiometric minimum demand (see Section 6.3). Since 1980 the specific energy demand has been reduced from 23 GJ/t of liquid steel to approximately 18 GJ/t liquid steel in 2004 for modern integrated steelworks [ 35, Dr. Luengen, H.B. 2005 ].
The energy consumption has been constantly reduced by introducing energy-saving equipment in steel manufacturing processes and improving the efficiency of energy conversion facilities such as power plants. Energy-saving equipment includes waste energy recovery equipment.
Another measure is the optimisation of energy consumption and costs by the implementation of a total energy management system. All of these measures are covered in this document.
To a certain extent, direct reduction (DR) can be an option to reduce CO2emissions (see Section 10.1).
Additionally, beyond energy savings and efficiency improvements, carbon dioxide mitigation projects are being developed to capture and store CO2which are also covered in this document (see Sections 11.1.1 and 11.1.2)
Other issues
Other relevant issues covered in this document are nuisance by odour and noise emissions which can be quite considerable for certain processes.
Matters of concern for the iron and steel industry not covered by this document are local soil pollution and groundwater pollution.
Table 1.8 to Table 1.10 provide a detailed overview of the releases in the different parts of the iron and steel making processes.
Table 1.8: First table showing potential release routes for prescribed substances and other substances that may cause environmental harm
C
SOURCES
RELEASES
D
Rawmaterial handling Sinterplant: flue-gascleaning Sinterplant: secondaryemissions Pelletplants Coalpulverisation Hotblaststoves Stockhouse Blastfurnace primarygascleaning Cast-house Desulphurisation BOF:blowing (primaryemissions) BOF: charging/tapping (secondaryemissions) EAF:charging EAF:melting andrefining EAF:steeland slagtapping
Oxides of sulphur A A A A A A A A
Oxides of nitrogen A A A A A
Carbon dioxide A A A A A A A A A
Carbon monoxide A A A A A A A A
Hydrogen chloride A A A A
Hydrogen fluoride A A A
Hydrogen sulphide A
Ammonia w
Oxides of iron Aw A A A A A A A A A A A A
Alkali metals A A A A A AL A A
Alkaline earth
metals A A A A A A AL A A
Metal oxide
particulates Aw A A A A A A A A A
Non-metallic
particulates Aw A A A A A A A A A A
Metallic iron A
Inorganic fluorides A A A A A
Hydrogen cyanide w
Cadmium and
cadmium oxide W A A A A A A A
Zinc, lead and
their oxides w A A A A A A A
Other metals and
their oxides Aw A A A A A
Phosphorus
compounds wl Awl
Sulphur l A
Carbon A A
Other inorganic chemicals
A
W A A
Oils and greases w
Slag Ll Ll Ll Ll
Sludges wLl Ll wLl
Refractory waste Aw
PCDD/F A a A A A
PAH A A
PCB A A
Volatile organic
compounds A a A A A
NB: — Main polluting substances: A = Release to air W = Release to water L = Release to land
— Other substances: a = Release to air w = Release to water l = Release to land
— Substances include their compounds except where a separate reference to the compound is made. Releases to air may also be released to land or water, depending upon the abatement technique employed, e.g. via collected dusts, sludges or liquors.
Table 1.9: Second table showing potential release routes for prescribed substances and other substances that may cause environmental harm
C
SOURCES
RELEASES
D
EAF:furnaceand ladleliningrepairs Alloying Ladletreatment Reladlingand recarburisation Degassing Decarburisation Electroslagremelting Vacuuminduction melting Inductionmelting Ferrousalloypowders Continuouscasting Ingotcasting Scarfing Slagprocessing Skullburning
Oxides of sulphur A A A A
Oxides of
nitrogen A A
Carbon dioxide A A A A A
Carbon
monoxide A A A A
Hydrogen chloride Hydrogen
fluoride A A
Hydrogen
sulphide A
Ammonia
Oxides of iron Al A A A A l A Awl Al Awl wl Al
Alkali metals wL AL
Alkaline earth
metals wL AL
Metal oxide
particulates Awl Al Awl wl Al
Non-metallic
particulates wl
Metallic iron Al A wl
Inorganic
fluorides Al A
Hydrogen
cyanide ALl A
Cadmium and
Cadmium oxide Wl A l
Zinc, lead and
their oxides wl A l Awl Al Awl Al
Other metals and
their oxides A A wLl A Ll A Awl Awl ALl
Phosphorus
compounds A
Sulphur wl
Carbon
Other inorganic
chemicals Al ALl A
Oils and greases w
Slag waste Al Ll ALl l Ll Ll Ll Ll Ll Ll Ll
Sludges wl
Refractory waste ALl l Ll Ll Ll Ll Ll Ll Ll
PCDD/F
Volatile organic compounds
NB: — Main polluting substances: A = Release to air W = Release to water L = Release to land
— Other substances: a = Release to air w = Release to water l = Release to land
— Substances include their compounds except where a separate reference to the compound is made. Releases to air may also be released to land or water, depending upon the abatement technique employed, e.g. via collected dusts, sludges or liquors.
Table 1.10: Third table showing potential emission releases from prescribed substances and other substances that may cause environmental harm
C
SOURCES
RELEASES
D
Chargingemissions Topsleakage Doorleakage Pushingemissions Cokeovenflue-gas (batterystack) Emergencyventing Emergencyflaring Ammoniaincinerator tailgas Effluenttreatment discharge Effluenttreatment sludge Sulphurandscrubber liquorremovaland desulphurisation Decantersandstorage tankvents
Particulates A A A A A A A A
Sulphur dioxide A A A A
Hydrogen sulphide A A A A A
Oxides of nitrogen A A A A
BTX A A A A A A
PAH a a A A A a
VOC A A A A a A A
Phenols A A A A A A
Methane A A A A A A
Carbon monoxide A A A A A A
Tar fume A A A A A A
Hydrogen cyanide A A A A A
Suspended solids w
Ammonia A A A A A w
Cyanide w
SCN w
Metals W l l
Sulphur l
NB: — Main polluting substances: A = Release to air W = Release to water L = Release to land
— Other substances: a = Release to air w = Release to water l = Release to land
— Substances include their compounds except where a separate reference to the compound is made. Releases to air may also be released to land or water, depending upon the abatement technique employed, e.g. via collected dusts, sludges or liquors.
Source: [ 240, UKEA 2004 ]Additions: [ 110, Brouhon 2008 ] [ 318, Eurofer 2007 ].
Table 13.4 in Section 13.5 Annex V is an example of a template for compiling relevant environmental data in the iron and steel sector.