In an integrated steelworks, water is used, e.g. for direct and indirect cooling, gas cleaning, scale breaking and washing operations including waste gas cleaning with scrubbers.
There can be various water systems in operation: completely closed, semi-closed or open circuits. There are only a few completely closed loops. Closed circuits can be used, e.g., for cooling circuits operated with demineralised or softened water at specific installations, i.e. for continuous casting moulds or at boilers in power plants, which are generally cooled through an exchanger water/water. Here the second circuit of water is used as a semi-closed circuit with a cooling tower.
Below are three examples where semi-closed systems are used:
• in cooling towers for decreasing the water temperature. There is a need to bleed off a small discharge flow to limit the salt concentration in the water preventing the deposition of these salts and consequently corrosion and further possible leakages
• for the recycling of waste water after treatment for further uses not requiring such high quality water as for the first use. Since some undesirable substances can build up, a small amount of water has to be bleed off and lead to a waste water treatment plant before final discharge. This amount needs to be replenished with fresh water
• for process water which can be led in a close cycle. Since some undesirable substances can build up, a small amount of water is led to a waste water treatment plant before discharging. This amount needs to be replenished with fresh water.
The water management in an integrated steelworks primarily depends on local conditions, above all on the availability and quality of fresh water and on legal requirements.
Figure 2.12 gives an example of water management with an indication of the water treatment of an integrated steelworks with almost unlimited fresh water availability, thus explaining the presence of once-through cooling systems, resulting in a specific water intake of more than 100 – 200 m3/t of steel. This is valid for plants close to large bodies of water, e.g. big rivers.
Source: [ 140, Eurofer 2009 ]
Figure 2.12: Example of water management of an integrated steelworks at a location with a high surplus of fresh water availability
A driving factor for steadily improving the intake and outlet of water are the costs. The costs for waste water treatment and releasing costs based on legal tax on discharging water into the municipal system can be considerable. Another cost-related factor is that the water taken from the aforementioned bodies depending on the water quality for many applications should undergo a conditioning step before it can be used. Furthermore, the pumping of such heavy water flows requires much electric energy.
For these reasons, water consumption has been constantly reduced since 1980.
In particular, at sites with very low fresh water availability, where the water demand should be covered by groundwater or spring water, there may be a need to reduce water consumption intensely. In such cases, the specific water consumption can be lower than 5 m3/t of steel and the interdependencies can be much more intensive.
Table 2.8 illustrates a comparison between the intake water requirements of a once-through system and a system involving extensive recirculation in a typical integrated steelworks. The extensive recirculation in indirect and direct cooling systems reduces the total water intake to 2.4 % of the requirement of the once-through system.
Table 2.8: Comparison in water intake required for integrated steelworks with once-through systems versus extensive recirculation
Water intake
Once-through system Extensive recirculation
Water Use Quality
(m3/min) (% of total) (m3/min) (% of total)
Indirect cooling General 675 70.7 7.4 32
Direct cooling General 265 27.8 6.2 26.8
Process water Low grade 7.7 0.8 5.1 22.1
Potable water High grade 1.5 0.2 1.5 6.5
Evaporation losses 4.8 0.5 2.9 12.6
Total 954 100 23.1 100
NB: It is not known if this data also includes the water used in downstream operations (not included in this document, e.g. rolling).
Source: [ 279, IISI 2002 ].
The following two figures present other examples of two different global systems from two integrated steelworks with separate circuits due to the local design of the plant (see Figure 2.13) and with a counterflow cascade system with steel production steps (from a cold rolling mill to the blast furnace) (see Figure 2.14).
Source: [ 316, Eurofer 2009 ]
Source: [ 316, Eurofer 2009 ]
In the example plant depicted in Figure 2.13, the overall quantity of water in 2005 was nearly 1.2 billion m3/yr. The recirculation rate in this case was 97.2 % and only 2.8 % needed to be replenished with fresh water. The discharge as waste water was only 1.2 % and the rest were losses of about 1.6 %.
As a result, the water intake was about 3.16 m3/t crude steel.
Techniques which led to a reduced water intake and a minimised amount of discharged waste water in the aforementioned case include:
• avoiding the use of potable water for production lines
• increasing the number and/or capacity of water circulating systems when building new plants or modernising/revamping existing plants
• centralising the distribution of incoming fresh water
• using the water in cascades until single parameters reach their legal or technical limits
• using the water in other plants if only single parameters of the water are affected and further usage is possible
• keeping treated and untreated waste water separated. By this measure it is possible to dispose of waste water in different ways at a reasonable cost