Print from ”HEAT PROCESSING” Issue 1, May 2004 pages 29-31Modern heating system with flat flame burners on rolling mill furnaceDipl.-Ing. Gerrit Wohlschlger, Dipl.-Ing. Christoph Dossow, G. Kromschrder AG, Osnabrck (Germany)V U L K A N - V E R L A G H U Y S S E N A L L E E 5 2 - 5 6 4 5 1 2 8 E S S E N G E R M A N YInitial situationThe stringent and constantly increasing technical and economic requirements and an expansion of production capacity necessitate modernising existing, old rolling mill furnaces or replacing them by a state-of-the-art furnace system. The requirements frequently demanded in this case are as follows: Flexible furnace relining with various steels Optimum thermal treatment of the steels Exact compliance with temperature profiles Precise dosing of the oxygen content in the furnace Minimising material loss as the result of rework Output of products with a constantly high quality Enhanced competitiveness overallComplying with or achieving values better than the prescribed untreated gas emission values are self-evident require- ments even if not simple ones. From an economic point of view, time-optimised passage of the material through the furnace is just as essential as efficient utilisation of the gas fuel.Maerz-Gautschi (Dsseldorf), Germany, specialising in furnace installations for the steel and metallurgical industries, in very close cooperation with G. Krom- schrder AG (Osnabrck), Germany, a competent contact in gas engineering, used state-of-the-art technologies to implement a new lifting hearth furnace (Fig. 1) so as to meet the applicable requirements. We shall explain a few technical details below by way of example of a modern rolling mill furnace.Requirements on the heating system of the lifting hearth furnaceThe requirements applicable to the heating system of a modern preheating furnace are many and varied. On the one hand it is necessary to cover a wide control range and on the other hand the atmosphere in the furnace must meet the stringent quality demands of the operation over this broad radius of action. The firing system must adapt to the differing requirements flexibly.Essential requirements are as followed: Uniform temperature profile over the entire furnace width or furnace zone:Uniform heating of the product over the entire cross-section is an important criterion for the anticipated quality of the rolled product (Fig. 2). Material-specific temperature curves must be complied with accurately, even in the case of differing geometrical dimensions and varying material qualities. Thermal material overstressing is avoided by material- adapted temperature curves. In addition, the variable drive speed of the lifting hearth is used to influence material heating. Economical operation with preheated combustion air: The lifting hearth furnace for stainless steel sheets explained in this article by way of example is operated in continuous mode in the temperature range between 1,050 and 1,250 C. Use of a recuperator proves to be economically practical with the above-specified temperature range. The firing system and the entire control concept must thus be adapted to the anticipated air preheat temperatures of approx. 450 C. Temperature resistance is an important factor in selection of the valves and fittings. Even adequate insulation of the air piping must be included in considerations. High-quality combustion with low free oxygen share: Free oxygen “O2” forms oxide layers on the material surface with the known, negative properties, such asModern heating system with flat flame burners on rolling mill furnaceUse of an optimum firing system was aimed primarily at flexible adaptability to requirements such as uniform furnace temperature, economical operation, high- quality combustion and high availability. Both the flat flame burners of Type BIO/ZIO.K and the new actuators IC 40 are convincing components. These products meet the optimum preconditions for enhancing quality, flexibility and performance of a lifting hearth furnace. In addition, use of the burner control unit BCU 480 with Profibus ensures maximum safety, reliability and system availability for the furnace constructor together with a higher level of convenience.Dipl.-Ing. Christoph Dossow G. Kromschrder AG, Osnabrck (Germany) Phone: +49 (0) 541 / 1214486 Email: c.dossow kromschroeder.comDipl.-Ing. Gerrit Wohlschlger G. Kromschrder AG, Osnabrck (Germany) Phone: +49 (0) 541 / 1214462 Email: g.wohlschlaeger kromschroeder.comFig. 1: Interior view of a lifting hearth furnace with flat flame burner quarts in the roofimpaired surface quality and material loss. The formation of scale thus has a negative influence on the economic efficiency of the overall furnace installation. Scale formation is directly (proportionally) related to the set gas- air mixture ( value) on the burner. Precise burner mixture setting over the entire control range and even at the variable air preheat tempe