Process water for steel production from seawater

May 18, 2007
Siemens Industrial Solutions and Services (I&S) supplies seawater desalination technology for supplying process water for the steel industry. In a new project for a steelworks belonging to Shougang Jiantang Iron & Steel United Co. Ltd., CNC Water Technology Ltd., a Siemens Chinese subsidiary in Beijing, is installing a system which works according to the MED (Multi Effect Distillation) principle. The water treatment system will have a capacity of 25,000 metric tons per day...

LINZ, May 15, 2007 -- Siemens Industrial Solutions and Services (I&S) supplies seawater desalination technology for supplying process water for the steel industry. In a new project for a steelworks belonging to Shougang Jiantang Iron & Steel United Co. Ltd., CNC Water Technology Ltd., a Siemens Chinese subsidiary in Beijing, is installing a system which works according to the MED (Multi Effect Distillation) principle. The water treatment system will have a capacity of 25,000 metric tons per day.

In Bohai Bay on the north-east coast of China, 80 kilometers away from Tanshan, the capital of Hebei province, and around 220 kilometers from Beijing, Shougang Jiantang is building a steelworks for an annual steel production of 15 million metric tons. Steel production generates a large amount of heat due to the industrial processes involved. It is therefore necessary and makes economic sense to make use of the heat which is emitted. In the steel industry process heat can be used to treat seawater for use as process water. On average, 3 to 30 m3 of water are needed for each metric ton of crude steel where the water is provided in an internal circuit. This water is mainly used for cooling in the large number of processes where heat is involved. For a steelworks with an output of ten million metric tons of crude steel per year, the water requirement corresponds to the annual water consumption of a developed country with over 20 million inhabitants. Due to the high quantities needed for iron and steel production, the careful use of water is absolutely essential both from a business management and environmental point of view. Available in unlimited quantities, at least in principle, seawater is an interesting alternative to fresh water but before seawater can be used for the production process, it has to be desalinated. However, this requires a lot of energy. Siemens I&S therefore uses the multi-effect distillation method. Systems based on this technology operate at temperatures of 63 to 80 degrees Celsius. The raw water is sprayed over heat-exchange pipes 6 to 16 times, causing it to evaporate and allowing condensation heat to be recovered. The advantages of the MED method compared to the conventional multistage flash evaporation (MSF) method, which requires temperatures of 100 to 110 degrees Celsius, is the equipment's lower susceptibility to corrosion and deposits. Moreover, the pumping energy required is almost 50 per cent lower compared to an MSF installation of the same size. MED installations are employed in units with a daily output of 2,000 m3 to 25,000 m3. Their investment costs are 15 to 20 per cent less than comparable MSF systems and they produce almost salt-free sterile water. As the energy consumption does not increase as the salt content of the water rises, the method is especially suitable for seawater desalination. Although the method is energy-intensive -- the specific energy consumption in terms of electricity is between two and four kWh/m3 and the heat requirement is just under 200 MJ/m3 -- it makes economic sense as the process heat generated in the steelworks can be used in a form or recycling. If fossil fuels were used to desalinate the seawater, costs of 0.5 to 2.5 US$/m3 could be expected.

Further information on solutions for steelworks, rolling mills and processing lines at: http://www.siemens.com/metals.

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