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Magazine8 Min

Cost-efficient water recovery from blowdown water

Modular desalination with up to four stages until Zero Liquid Discharge for metallurgical plants

Within the scope of the WEISS joint project, SMS group - in collaboration with other project partners - has developed a new process for water recovery. Now, customers can test the efficiency of the method at their site by themselves and rent the remote-controlled pilot plant.

It is not often that water is on the agenda as an essential resource in steelmaking, as, until now, it has been available nearly everywhere and at any time wanted. However, water will become increasingly scarce and more expensive all around the globe. The resulting water shortage will hence have a growing impact on the production capacities in steelmaking plants in many parts of the world.

In order to offer a solution to plant operators who are facing or will face temporary or even permanent water shortages, SMS group has developed, within the scope of the WEISS joint project, a cost-efficient process to recover water from blowdown water.

Multi-stage desalination system in a container

For this purpose, SMS group has set up a containerized pilot plant and installed an automated, three-stage desalination system in cooperation with its partners. From the multitude of processes tested with real water made available by project partner Deutsche Edelstahlwerke in Hagen, Germany, a modularized plant concept for desalination of blowdown water in one to four stages turned out to be best suited for SMS group to flexibly meet a wide range of customer requirements.

Overview over the desalination steps (DSS = Desalination step).

Cost comparison to other water recovery processes

The specific costs involved in this water recovery process are lower than all other conceivable alternatives for water procurement, if there is no water source like groundwater or surface water available free of charge. Seawater desalination is distinctly more expensive, even for production sites located on the coast, on the one hand, because it is necessary to construct and maintain a separate pipeline for water transport and, on the other, because there is an increased demand for energy due to the higher salt content by more than a power of ten.

Conventional cooling water circuits need huge amounts of fresh water, which often is becoming scarce.

Also, the operating costs of closed cooling towers are considerably higher than with the new desalination process due to the enormous energy consumption of the ventilators, which, even though they may be considered minor in the context of a steelworks’ energy requirements, are a crucial factor in total costs. In addition, there is the large space required which has not been considered in the cost analysis as land prices may vary strongly depending on the customer’s location. To treat municipal wastewater is definitely more expensive, just because of the inevitable need to remove the persistent organic residues. In Germany in particular, but also in other industrial nations, the procurement of water from the public supply is definitely more expensive, at the latest when it comes to paying wastewater charges.

Zero Liquid Discharge for wastewater-free production

To protect the bodies of water, highly industrialized countries and others with a small number of surface waters have provided incentives or passed laws favoring or even stipulating wastewater-free production processes. Such a process, known among experts as strict ZLD (Zero Liquid Discharge), includes additional evaporation and subsequent drying of the separated salt particles. The evaporation system integrated in the WEISS concept is characterized by an extremely high resistance to corrosion, a clearly reduced tendency to scaling and a minimum energy demand thanks to heat exchangers made of plastics.

Test the new system

Interested customers can test for themselves the efficiency of the method at their own site and rent the remote-controlled pilot plant to pilot the desalination of their own blowdown or circuit water. This way of proceeding permits the best possible and economical plant design to be prepared.

For small to medium-size plants, SMS group has developed a variable, modularized concept housed in insulated, air-conditioned and electrified containers. This means minimum engineering effort for the customers and a high degree of cost certainty. The only required construction activities are to build a foundation. So, the plant can be expanded with minimum effort whenever necessary either to integrate another desalination stage or to enhance the installed desalination capacity.

Pilot plant with 3-stage desalination of blowdown water at Deutsche Edelstahlwerke in Hagen (Germany).

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