The Behaviour of Monolithic Refractory and its Importance for the Design of Refractory Structures
by Greg Palmer and Renee Ellis, Palmer Technologies Pty Ltd

Abstract
Understanding the behaviour of monolithic refractory concrete is critically important for engineers when designing refractory linings for high temperature environments. As cement plants, power plants and other industries push for longer runtimes to reduce maintenance costs, the performance of refractory linings is critical in maintaining plant reliability.

A successful refractory lining requires consistent quality materials, the highest quality installation techniques to ensure the installed material properties meet specification and a thorough understanding of the material behaviour.

Numerical analysis of refractory lined structures using non-linear fracture mechanics model, ATENA, has shown that refractory linings, in particular, the dense hotface can fail to some extent in the early stage of heating. However, it was known that refractory lined vessels like secondary reformers and gassifiers which are lined without any expansion joints with a high alumina dense castable do not catastrophically fail. Even when the permanent linear change (PLC) of the hotface is subtracted from the thermal expansion our analysis has shown that there is still sufficient thermal expansion to crack the refractory in a fully constrained condition.

Serendipitously, it was found that dense refractory concrete behaves very differently between the green and fired state. By green it is meant that the material has stiffened but has not been fired. A green refractory when tested at temperature has a very plastic behaviour while the same material when pre-fired behaves in a quasi-brittle nature. Analysis of refractories by the Refractoriness Under Load (RUL) test is one method for testing a material in a constrained state as opposed to an unconstrained state. We believe the constrained state better represents what happens in real life. By observing refractory linings with minimal thermal expansion it has been found that green castable refractory will behave in a plastic manner when loaded during the firing.

Detailed understanding of the mechanical behaviour of refractory concrete with temperature and loading is the key for engineers to successfully study, model and design refractory linings. If these materials can be described in engineering terms then computer modelling can more closely replicate what is seen in practice. This will lead to improved refractory lining design for many industrial applications.