Impact of cofiring biofuels and fossil fuels on lime kiln operation

Abstract

Lime kilns are used to calcine lime mud to produce lime for reuse in the causticizing plant of pulp mills. With significant increase in fossil fuel costs and the sustained drive to minimize carbon footprint, there has been a great deal of research and development of the biorefinery concept and production of biofuels for use within pulp mills. Several new biofuels will become available, together with traditional mill derived fuels such as tall oil. In considering use of biofuels for replacement of fossil fuels in the lime kiln, each fuel has a different impact on kiln performance. An assessment on kiln performance can be achieved and compared to either heavy fuel oil or natural gas. In most cases, the lime kiln fuels with high oxygen content and moderately low calorific values burn in a similar manner as natural gas; hence, in assessing impact on kiln performance, production and induced draft fan limits together with kiln exit gas temperatures need to be considered.