31 July 2007
Mintek process control commissioned on SA’s largest ferrochrome furnace
Mintek has commissioned its FurnStar MinstralTM control system for submerged-arc furnaces to optimise the smelting process on the new No. 4 furnace at Hernic Ferrochrome, near Brits in the Northwestern Province.
The furnace, a closed unit that employs Outokumpu technology, is the largest ferrochromium furnace in the southern hemisphere, with a power rating of 78 Megavolt-Amperes (MVA).
“All four of the furnaces at Hernic are now under Minstral control,” said Paul Brereton Stiles, head of Furnace Control in the Measurement and Control Division at Mintek. “The first controller was installed on the 37 MVA No. 1 furnace in 1996, and subsequent installations followed on the second (37 MVA) and third (54 MVA) furnaces, and now the fourth.”
Hernic, whose major shareholders are Mitsubishi Corporation and the Industrial Development Corporation (IDC), is the world’s fourth-largest ferrochromium producer, with an annual capacity of 420 000 tons.
“Hernic has, after ten years’ experience with Minstral, only the highest appreciation for the capabilities and benefits of the control system, confidence in the technology applied, and the after sales service. We had no doubt in trusting Minstral for controlling our newest and biggest furnace”, said Hannes Visser, production manager at Hernic.
“With large transformers such as those on the Hernic furnace, and the restrictions on excessive electrode movement, the ability to carry out effective differential tapping is a major advantage of the Minstral system. For a furnace of this size under balanced load conditions, differentially tapping the transformers can increase the power input by up to 1.5 MW, and under unbalanced conditions by more than 5 MW (10 per cent), compared with conventional balanced tap-position control,” explained Stiles.
The Minstral control system optimises operation of submerged-arc furnaces by means of a patented resistance algorithm, enabling stable operation at optimal power. Typical benefits of Minstral control include:
- Improved power input (MWh);
- Lower specific energy consumption (MWh/t);
- Improved load factor;
- Reduced electrode consumption;
- Reduced electrode breakages; and,
- Improved recovery.
“Minstral integrates with the existing plant automation infrastructure via a central PLC. The system uses measurements from the primary side of the transformers, which are inherently more accurate than other measurements and explicitly avoids the need for an electrode-to-hearth voltage measurement, which is both problematic and inaccurate,” concluded Stiles.
There are more than ninety installations of the Minstral controller worldwide, with the latest including DSCL in India, Pechiney in France, and two at Assmang’s Cato Ridge plant in South Africa. Forthcoming installations will include units on the first two 63 MVA furnaces at the Xstrata-Merafe Project Lion ferrochromium joint venture, which are due to be commissioned in the third quarter of 2006.
The FurnStar Minstral advanced process control (APC) system is one of a family of APC systems developed by Mintek to enhance the operation of a number of different metallurgical operations.
“Mintek is currently supporting more than hundred APC installations worldwide, the largest concentration of which is on the African continent,” said Dr Dave Hulbert, manager of Mintek’s Measurement and Control Division. “Our Star Control System (StarCS) is a widely applicable software platform with modules aimed specifically at metallurgical processes. Mintek has developed specific solutions on the StarCS platform to address typical mineral-processing control challenges in the areas of milling (MillStar™), flotation (FloatStar™), furnaces (FurnStar™) and leaching (LeachStar™).”
Mintek has installed its APC systems in about fifteen countries and has an overseas office in Australia.
Tel: +27 11 709 4265
Mobile: +27 82 551 6857
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