Xylem Water Solutions - Pumping a highly corrosive cocktail of abrasive iron and sinter particles

Pumping a highly corrosive cocktail of abrasive iron and sinter particles

Averaging temperatures in excess of 100 degrees Celsius, the gases from a blast furnace contain sufficient energy to provide heat for other processes in and around a steel plant. But first they have to be cleaned of flue dust and other solids. And that takes large quantities of water. Water that having picked up a high concentration of abrasive and corrosive solids, must itself be cleaned.

Steel city by the sea
With considerable iron ore resources, the metal industry has always played an important part in the Swedish economy. Oxelösund, 120 km south of Stockholm, boasts one of Sweden's largest iron and steel works. With a population of 14,000, some 2,750 people are employed at the plant. The first iron works were built in Oxelösund in 1917. Today production exceeds 1,200,000 tons annually and the works are acknowledged as the leading manufacturer of heavy plate in northern Europe. With an extensive system for quality assurance, Oxelosund has been certified by both Lloyds and Det Norske Veritas.

Feeding 4,800 M3/H of water to a thirsty monster
The manufacture of steel requires huge quantities of water. At Oxelösund over 4,800 m3 are circulated around the plant every hour. Kent Eriksson, supervisor, is responsible for the 150 odd pumps that feed the plant. Apart from the summer break, production is continuous, around the dock, throughout the year. So it is vital the pumps are reliable. The main station pumps, for example, below the Water Central have been out of operation for just 2 minutes in over 30 years.

Transporting 60 tons of solids per day, all day, every day
The gases from the blast furnace contain a large quantity of impurities that have to be removed before the heat from the gases can be used. This is achieved by passing them through electrofilters and scrubbers, a process which requires over 900 m3/h of water; which itself has to be used again. But before it can be reused, the acidic content must be reduced and the solids extracted.

The first step in recycling the water is to increase the pH level to just over 6 in an aeration tank. The addition of sodium hydrate then adjusts pH to a suitable level and a polymer is added, to cause flocculation.

The water is then lead into a sedimentation basin. Here the solids sink to the floor of the basin and a scraper pushes them down to the center. A mammoth pump lifts the resulting slurry into a tank to the side of the basin.

Pumping 40% sinter and 30% iron, 100% of the time
The water, containing a solids concentration of 3 - 4%, has to be pumped 400 meters to a sedimentation lagoon. 40% of the solids are accounted for by iron, 30% by sinter: a particularly abrasive cocktail, with the iron working as a corrosive, and the sinter as an abrasive, stripping away the corrosion-softened surface.

A new range of wear-resitant pumps
To handle such high wear applications, ITT Flygt have launched a new range of abrasion resistant submersibles. The new pumps, the 5500 series, feature a wet end that is entirely lined and what is possibly the most efficient slurry seal system available. The lining comes in up to four different hard wearing materials, protecting all hydraulic parts that come into contact with the pumped medium.

Two 13.5 kW 5540 pumps deliver 101/s of the slurry to the sedimentation lagoon over 400 meters away. Replacing dry-installed units, one of the Flygt pumps is installed beneath the side tank, attached to the existing inlet and outlet connections, and the second 5540 is submerged in the media itself.

The new pumps, the 5500 and 5600 series, feature a wet end that is entirely lined and what is possibly the most efficient slurry seal system available.

12,000 hours and still going strong
The pumps are in continuous operation, 24 hours a day, 7 days a week. After 12,000 hours of duty, the volute shows few signs of wear, and the seals are still performing efficiently. The impellers should be checked once a year, and a general service run every 6 months, to check wear on the other wear parts.

"They're close at hand and they'll work overtime"
There are over 100 Flygt submersibles in use around the works, with everything from small, portable emergency units, to larger pumps, circulating 250 liters per second.

With little manpower to spare for maintenance work, Kent finds himself relying on the local Flygt service team. "When I tell them it's urgent, they come fast, put in extra hours and really try to get the pump back into action as soon as possible." He appreciates their proximity and dedication: "they're close at hand, and they'll work overtime", he adds.

Quiet and flood-proof
A Flygt Pump, whether submerged or dry-installed is a very quiet worker. When submerged, the media acts as a sound (and heat) buffer, and when dry-installed, the encapsulated motor and shaft, together with the balanced action of the impeller, ensure a surprisingly low noise-level. And a Flygt pump is of course completely floodproof in applications that demand dry installation.