Sofi Filtration’s mechanically self-cleaning filter

In response to growing environmental concerns and increasing water scarcity Sofi Filtration and Ferriere Nord have collaborated in WHAM (Water and related energy Hub Advanced Management system in steelwork) EU project.

Pittini Ferrire and Nord Steel Plant
Pittini Ferrire and Nord Steel Plant

In response to growing environmental concerns and increasing water scarcity Sofi Filtration and Ferriere Nord have collaborated in WHAM (Water and related energy Hub Advanced Management system in steelwork) EU project. The aim of this project is to study the water usage in steel production processes to deploy a comprehensive solution that combines on-line monitoring and optimisation with innovative water treatment technologies developed by Sofi Filtration, Finland.

In this collaborative project with Sofi Filtration, Finland, the Ferriere Nord, Italy was specifically seeking for a filtration solution for hot rolling mill to remove the fine suspended solid particles that remain in the water following the decantation process. Sofi Filtration has developed a filter system with highly efficient mechanical self-cleaning features that was regarded as promising technology for hot rolling mill cooling water application because the innovative technology is efficient in treating very fine solid particles even down to 0.3 micron with minimal operating expenses (OPEX). 

Ferriere Nord, based in Rivoli di Osoppo, Italy, is one of the world's largest steel producers. The company headquarter is based in Osso, Italy and has offices around the country. The product produced in the facility includes concrete billets, wire rods, rebars, meshes, lattice girders, granella and coils.

As the part of zero waste programme and the mounting water scarcity the steel maker has an ambitious target to minimize the freshwater consumption in the hot rolling mill operation. The hot rolling mill of the steel plant uses 1 million m3 / year from wells for the cooling operation and they plan to significantly reduce it to contribute to United Nation Development goals. Aside from rising water scarcity, Sofi’s project partner faced two main challenges while using the sand filter technology. First, the water from a hot rolling mill contains oil and compounds that is comprised of various elements such as iron, copper, boron, and manganese, resulting in corrosion and microbial development. The second is high total suspended solids (TSS) in the effluent from sand filters.

To protect the operational environment from corrosion, microbial growth, and to provide consistent flow rate, the plant expected the TSS should be reduced to 5 mg/l from current average of approximately 50 mg/l. It has been highlighted by the plant technical manager that no added chemicals were used for pre-treatment. Furthermore, the plant's sand filters’ media must be replaced on a regular basis since it becomes cemented with time. Besides, sand filter requires several large modules to obtain the required flow rate which take up lot of space.

Several experiments were conducted to test the capabilities and performance of Sofi Filter against sand filter technology. For this study Sofi Filter model SF1000 is used with a 10 μm (nominal) multilayer sintered metal wire mesh screen made up of stainless steel 316L. Because the filter is made of metal wire mesh, it does not need to be changed frequently, resulting in very low maintenance requirements. The compact size filter holds 1m2 of active filtration area. In this experiment both sand filter and Sofi Filter technology were fed with the same water in conjunction and sampling program took place for the total suspended solids. To prevent the filter element from clogging and fouling, Sofi’s self-cleaning feature with ultrasound and air backpulse triggers automatically with pressure differential and timed cleaning intervals.

Filtration parameters were measured continuously while samples for TSS were taken between wash cycles at 1-, 2- and 3-minute marks.  The effluent TSS was gradually reduced by 58%, 93% and 99% after 1 minutes, 2 minutes and 3 minutes respectively, compared to the inlet TSS. The average feed concentration was 58 mg/l with a minimum of 20 mg/l and a maximum inlet feed of 153 mg/l, while effluent solids concentration of 0.4 mg/l was achieved at the 3-minute sampling point. During the sampling program the flow rate of the cycle varied between 13.3 m3/h to 8.5 m3/h with an average flowrate of 10.2 m3/h over the wash cycle of 4 minutes. It was found that average reject TSS was 434 mg/l.

The pilot operation demonstrated the viability of using Sofi Filter in hot rolling mill operation. The Sofi Filter was remarkably efficient in attaining high effluent quality. Furthermore, the effective backwash technology feature prevents the filter element from clogging and fouling, resulting in a steady flowrate over time. Additionally, the ability to modify recirculation rates and cleaning cycles to handle varying feedwater, elegant compact design and low OPEX is seen advantageous over sand filter technology.

Disclaimer: The work described in this paper was developed within the project entitled “WHAM-Water and related energy Hub Advanced Management system in steelwork” (Grant Agreement number: 800654 – WHAM), which has received funding from the Research Fund for Coal and Steel of the European Union. The sole responsibility of the issues treated in this paper lies with the authors; the Commission is not responsible for any use that may be made of the information contained therein.