How it began
Paul Wurth traces its origin to 1870, when Eugene Muller built a boilermaking works in Hollerich, in Luxembourg City, and it grew into an engineering supplier to the iron and steel industry. In 1969 engineers of S.A. Paul Wurth invented the Bell Less Top charging system for blast furnaces. Its first successful industrial application followed in 1972.
Before it existed
Early furnaces were filled through an open mouth, so gas escaped and material landed unevenly. From 1832 lids and then cup and cone devices captured gas. Bells, inverted cones that opened downward, improved distribution, and the two-bell system put a second bell and hopper above the first to form a gas-tight lock. The bells took heavy impact and abrasion and needed replacing two or three times per furnace campaign. It was very hard to hold a seal above 100 kilopascals of top pressure because the sealing surfaces sat in the flow of material, and the bells limited how the burden could be spread.
How it works
A skip or conveyor fills one or two lock hoppers above the furnace. Each hopper has an upper and a lower seal valve and a material flow gate, and is sealed and pressurized to furnace top pressure before it discharges. The seal valves sit out of the path of the falling material, so they do not wear. Material drops through a central spout onto a chute that rotates and can be tilted to any angle, laying the charge in rings, spirals, sectors or at a point. With two hoppers used in turn, charging is nearly continuous.
What changed first
The system solved the gas sealing problem of high-pressure operation and gave operators control over where each layer of ore and coke was placed. The technical literature credits it with steadier furnace operation, higher productivity, a lower coke rate, higher rates of pulverized coal injection and longer campaign life through lower heat loads on the walls. The chute can be replaced quickly, and the top is lighter and more compact than a bell top.
What lasted
After its first industrial application in 1972 the bell-less top rapidly gained popularity and quickly took over from the two-bell system. Press releases from steel plants show the pattern: a bell-less top installed at Salzgitter in Germany in 1977 was replaced decades later by a newer parallel hopper version of the same system. Paul Wurth is now part of the SMS group and still supplies the equipment.
