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Auburn, WA, United States

Gorog J.P.,Houghton Cascade Holding LLC | Hemrick J.G.,Oak Ridge National Laboratory | Walter H.A.,Refratechnik North America Inc. | Leary W.R.,Houghton Cascade Holding LLC | Ellis M.,Australian Paper Maryvale Mill
Tappi Journal | Year: 2015

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.

Gorog J.P.,Houghton Cascade Holding LLC | Leary W.R.,Houghton Cascade Holding LLC | Wang D.,Reaction Engineering International | Davis K.,Houghton Cascade Holding LLC
Tappi Journal | Year: 2015

In response to the drop in the price of natural gas, the U.S. pulp and paper industry has switched from using fuel oil to natural gas to fire kilns used to regenerate lime in the kraft process. While being financially attractive, replacing fuel oil with natural gas can be challenging. This is particularity true when the capacity rating is constrained by the temperatures of the gas exiting the kiln. In the worst case scenario, the increase in flue gas temperatures associated with switching from fuel oil to natural gas can significantly de-rate the capacity of the kiln. This paper describes a range of computational modeling tools that can be used to estimate the impacts of kiln geometry, fuel type, operating conditions, and burner design on kiln performance. Data taken from operating kilns is presented, which validates the use of these models. A detailed case study is presented showing how small amounts of torrefied wood can be co-fired with natural gas as a replacement for fuel oil without de-rating the capacity of the kiln. The visualization of the flow fields, temperature distributions, and species concentrations provided by computer models are critical to optimizing kiln operations as new fuels are being considered as replacements for more expensive, carbon intensive fuel oil. Application: The computational modeling tools described in this paper can be used by mills to explore the impact of fuel type on kiln performance. These tools can also be used to improve burner designs, to optimize the layout of chain systems and refractory linings, and for other modifications to the kiln and/or to evaluate changes in operating practices.

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