Tata saves £250k on fume-extraction energy costs

Rotheram, UK – Tata Steel has cut annual energy costs by £250,000 following the installation of variable-speed drives on the fume-extraction system at its Rotherham steel casting plant.

The extraction plant is used to remove fumes produced by the two casting machines and two ladle arc furnaces within Tata’s Aldwarke Bloom Caster complex at the south Yorkshire site. The fumes are then passed through a filter system where the particles are removed and discarded.

The original installation used four 3.3 kV motors: two 650 kW and two 410 kW. The two large motors were used as the primary extraction motors, with the smaller motors used to provide additional extraction as required.

For the upgrade, ABB system integrator Drives and Automation Ltd replaced existing fixed speed direct-on-line motors in the plant with low voltage motors, controlled by four ABB low harmonic variable-speed drives, two at 400 kW and two at 570 kW.

The turnkey project included the supply of transformers, a form 4 distribution panel, inverter cubicles, electrical and mechanical installation, plant room ventilation and integration of a PLC /SCADA with the existing plant control system.

Previously, motor limitations meant the fans were restricted to four starts per hour, as additional starts would risk damaging the windings, according to Ben Holroyde, planning project engineer for the Aldwarke Bloom Caster.

Due to the starting restrictions, the motors would be forced to run-on for 15 minutes even if demand for extraction was reduced. In addition to these issues, several of the motors suffered multiple failures, Holroyde added.

“We estimate we were spending around £3,000 a year in motor repairs,” the engineer said. “And although not excessive for these types of motors, the downtime was becoming a major problem.

“Each failure took up to six weeks to rectify, during which we had to cut back our production to ensure that we were within environmental limits of fume and dust levels.

“We could incur fines for not meeting the required environmental standards and there was a risk that production workers in the area could suffer from dust inhalation. Fume extraction is a vital part of the process and without it we simply cannot work to full capacity.”

Another issue was that as the motors were 3.3 kV, any maintenance on them required special permits to work.

Tata aimed to save in the region of £240,000 a year on energy costs for the extraction plant by more closely matching the speed of the motors to the dust extraction demand.

The new drives have also helped to cut maintenance requirements at the Yorkshire plant by reducing wear and tear on the motors and the duct work. The units also help engineers to ‘fine tune’ the extraction capacity to match demand.

“We are continually looking at the plant’s request for extraction and reducing the fan motor speeds still further, whilst still achieving good fume extraction,” said Holroyde. “We are well on target to achieve the projected savings of £250,000 with a payback time of three years.”