Design of refractory linings for balanced energy efficiency, uptime, and capacity in lime kilns

In this work a computer model is used to examine how refractory linings with both high alumina and basic refractory bricks affect kiln operations. Recommendations are made based on the results to aid mill personnel in designing optimized refractory linings for specific situations. Kilns used to regenerate lime in the kraft process are highly energy intensive. Throughout the 1990s, in response to increasing fuel prices, the pulp and paper industry primarily used backup insulation in conjunction with high alumina brick to line calcining zones of their kilns. The dramatic decline in price of natural gas over the past decade, in combination with mounting pressures to increase production of existing assets, has led many mills to focus more on increasing uptime and capacity rather than on energy savings. To this end, a growing number of mills are using basic (magnesia based) brick instead of high alumina brick to line calcining zones. While the use of basic brick can increase the uptime and reduce the cost to maintain the refractory lining, it can dramatically increase the shell temperatures and heat losses. Tradeoffs, therefore, are created among energy efficiency, capacity, and uptime. Application: Mills can use this information when selecting refractory bricks to optimize life of the refractory lining and increase kiln utilization factors.