Jun 2 2005
Heating specialists Kanthal, a product area within Sandvik Materials Technology, has supplied Superthal heating modules, fitted with Kanthal Super CS elements, as part of a forehearth redesign project in a major glass plant.
Part of a two year project to improve production efficiency, increase capacity, reduce energy consumption and maintain or improve glass quality by building and installing a larger furnace, Kanthal has been responsible for the design and production of special forehearth heating elements.
Kanthal used a Computational Fluid Dynamics (CFD) or 3D Fluid Dynamic computer programme to determine the optimum design of the system. Given the insulating refractories and the power to be utilised, a thermal map and profile of the forehearth in 3D colour could be presented. It was possible to recommend the height and the spacing of the Superthal units above the glass channel for example. The CFD computer model is a useful tool in the design and planning for such systems and can be used in any industrial furnace application if the relevant data is available.
UK engineering consultants Industrial Analysis and in-house engineers were responsible for the overall project management which involved both the melter and forehearth.
The furnaces are electrically heated via immersed tin oxide electrodes and historically the main heat source for the forehearth also came from tin oxide electrodes. These electrodes are water cooled and fitted through holes in the refractory sub structure. The top heating in the forehearth was provided by silicon carbide elements operating at around 1250°C.
Redesigning the forehearth top heating system to accommodate the specially designed Kanthal Super multi-shank elements has yielded several advantages, including uniform forehearth heating which optimises glass quality.
The new muffle elements and improved muffle design have enabled the removal of some of the immersed water cooled electrodes and the result has been a reduction in forehearth energy consumption of 48%.
The forehearth has 11 outlets and each has Kanthal’s specially developed Superthal heating elements in the gob-feeder and orifice heaters to maintain and control glass temperatures.
The improved forehearth design has seen the percentage of forehearth power supplied by muffle increase by 20% to around 60%. Also contributing to energy and operating efficiency is the reduction in forehearth cross sectional area, which was undertaken having been identified from glass flow modelling.
The Kanthal heating system and superstructure are supplied in preformed shapes, enabling much shorter construction time. The design of the muffle provides for quick replacement of an element without the need to adjust the muffle construction.
Each Superthal panel assembly contains one Kanthal Super CS multi-shank element comprising 20 shanks at a distance of 50mm, located on a ceramic fibre panel hot face measuring 650mm x 460mm. Total power is 20.5 kW, 40 volts per element delivered from a step down transformer. A total of 51 panels have been supplied. The element shape has been critical to the installation to make sure that power is concentrated where it is needed and that a large element surface is contained in a small space. The multi-shank design also means that the element can be cooled down and reheated. This enables reuse after furnace rebuilds and results in longer life.
http://www.kanthal.se/