Comprehensive Creep and Thermophysical Performance of Refractory Materials

Abstract

Furnace designers and refractory engineers recognize that optimized furnace superstructure design and refractory selection are needed as glass production furnaces are continually striving toward greater output and efficiencies. Harsher operating conditions test refractories to the limit, while changing production technology (such as the conversion to oxy-fuel from traditional air-fuel firing) can alter the way the materials perform [1-3]. Refractories for both oxy- and air-fuel fired furnace superstructures (see Fig. 1) are subjected to high temperatures that may cause them to creep excessively or subside during service if the refractory material is not creep resistant, or if it is subjected to high stress, or both. Furnace designers can ensure that superstructure structural integrity is maintained if the creep behavior of the refractory material is well understood and well represented by appropriate engineering creep models. Several issues limit the abilities of furnace designers to (1) choose the optimum refractory for their applications, (2) optimize the engineering design, or (3) predict the service mechanical integrity of their furnace superstructures. Published engineering creep data are essentially nonexistent for almost all commercially available refractories used for glass furnace superstructures. The limited data that do exist are supplied by the various refractory suppliers. Unfortunately, the suppliers generally have different ways of conducting their mechanical testing, and they interpret and report their data differently. This inconsistency makes it hard for furnace designers to draw fair comparisons between competing grades of candidate refractories. Furthermore, the refractory suppliers' data are often not available in a form that can be readily used for furnace design or for the prediction and design of long-term structural integrity of furnace superstructures. As a consequence, the U.S. Department of Energy (DOE) Industrial Technology Program (ITP) Glass Industry of the Future sponsored research and development at industry, university, and national laboratory sites with the intent to help domestic glass manufacturers improve their energy and operating efficiencies. The optimization of furnace superstructure design using valid engineering creep data is a means to achieving these ITP goals. The present project at Oak Ridge National Laboratory (ORNL) aided in this endeavor by conducting creep testing and analysis on refractories of interest to glass manufacturers at representative service temperatures, enabling the availability of new and improved refractories by refractories suppliers and by generating creep data on equivalent refractories that furnace designers could use for optimizing the design of their superstructures or for predicting their long-term structural integrity. Similar refractory creep-testing projects have been conducted at ORNL [4-6], so many of the unique experimental nuances and difficulties associated with the high-temperature creep testing of refractories have been encountered and overcome.