De-scaling equipment offers improved efficiency with customised high pressure pumps

Paul Boughton

Steel rolling mills, like most modern industries across the world, are looking to improve efficiency and product quality by investing in technology which has a short return on investment. One plant in Italy has decided to invest in new de-scaling equipment with a view to improving product quality while reducing overall energy and water costs.

De-scaling equipment basically consists of a high pressure pump, powered by an AC motor which is by RMI design controlled by a variable speed drive; all of which supplies water through specifically designed nozzles, which are directed at the hot steel.

The combined action of the water pressure and the rapid cooling of the steel results in the scale removal. This is an important part of the steel production process as scale which is not properly removed can be combined with the steel billet as it passes through the rollers, resulting in lower quality steel and imperfections.

The design of de-scaling equipment is an exact science with nozzle design and water pressures carefully calculated for the best results. Some steel variants can require a water pressure of up to 400 bar but this application used 200bar. The volume of water can also vary, however, with high alloyed steel grades, the water flow can typically be reduced by 50 per cent based on system design. This is done by design to find the correct impact force and the erosion rates required. Steels with high silicon content are very problematical because of the intense adherence of scale, requiring high impact pressures as well as increased quantities of water for this kind of scale. It's important to use the correct pressures to achieve the proper impact force and to have the ultimate cleaning capability, as too low can result in scale being left while too high will be inefficient and lead to unnecessary costs.

With modern steel rolling mills producing an array of different steels, it is important that the facility has the ability to adjust any settings as easily as possible when the next product is about to be produced to make sure that the process is reliable and efficient for all steel types. These differing requirements pose potential problems for the production facility and, unless they are optimised, could lead to increased production costs and reduced margins. This places added pressure on the de-scaling equipment as, not only must it perform reliably at all times, it is also required to allow for the adjustment of pressures and water flow rates as the steel type changes. This is how RMI differentiates itself from the traditional methods.

One of the leading manufacturers of de-scaling equipment, Siemens VAI, was asked to design a new system for an Italian billet and bloom mill which would offer absolute reliability and efficiency to keep operating and maintenance costs to a minimum. In order to meet the design brief it was decided that the pumping system should be sourced from RMI Pressure Systems, the leading high pressure pump specialist.

In the first instance, Siemens presented the initial scope and design to RMI, who used its expertise in high pressure pumping systems to produce a more economical design while still achieving the desired impact and coverage using pumps from the RMI product range. These pumps are purpose built for each individual customer to suit their application which allows RMI's design engineers to supply the most cost effective solution.

The Trimax range of reciprocating plunger pumps are capable of producing flow rates of 50-670 litres/min at system pressures up to 1,000 bar making it an ideal choice for de-scaling plants.  Every component of the pump is selected for robust and reliable performance with every pump assembly undergoing a comprehensive test procedure prior to delivery to the customer.

By working with the client, RMI was also able to modify the control system to ensure that it would integrate with the existing arrangement with the minimum of additional cost. The designers were also able to minimise the total number of pumps and associated control gear, while still meeting the required design scope, which ensured that the final costs of the installation were optimised and the ROI period was kept to a minimum.

Mike Sherman, Marketing Manager for RMI comments: "This de-scaling solution has been characterised by the use of variable speed pumps with high flow rates powered by inverter-driven AC motors and the application of an optimised nozzle pattern. The benefits of this de-scaling package are reduced investment costs and lower maintenance costs as well as substantial energy savings due to flexible operation according to process requirements."

The completed design for Siemens included the pump skids, control systems, interlocks and the de-scale headers, all of which had been optimised for this particular application. Working in partnership with other system component suppliers, RMI accepted the responsibility for the verification of the performance of the completed system and was able to provide engineers on site to assist with the installation and commissioning.

Previous experience with similar projects has helped RMI develop an excellent understanding of the exact requirements of de-scaling plants and how to deliver them.  Based on this experience, RMI has been able to deliver individual high pressure pumping solutions to the steel industry with a calculated payback period of less than 2 years; an important factor when deciding on the most suitable package.

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