Design of refractory linings for balanced energy efficiency, uptime, and Capacity in Lime Kilns

Kilns used to regenerate lime in the Kraft process are very energy intensive. Throughout the 90's, in response to increasing fuel prices, the pulp and paper industry used back up insulation in conjunction with the high alumina brick to line the calcining zones of their kilns. Due to the dramatic decline in the price of natural gas in combination with mounting pressures to increase production of existing assets, in some areas, over the last decade, many mills are currently focusing more on increasing uptime and capacity as opposed to energy savings. To this end, a growing number of mills are using basic (magnesia based) brick instead of high alumina brick to line the calcining zone of the kiln. 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. There are tradeoffs between energy efficiency, capacity and uptime. In this work a computer model is used to examine how refractory linings using both high alumina and basic refractory bricks impact kiln operations. Recommendations are made based on the results of this work to help mill personnel to design a refractory lining that is optimized for their specific situation.