Maximizing Recovery Boiler Performance with Combustion Air System Upgrades, 2004 International Chemical Recovery Conference

As pulp mills continue to demand more operating capacity from existing equipment, the recovery boiler continues to be a bottleneck in the production of pulp. The focus is to push the limits of this equipment and maximize the black liquor throughput capacity while maintaining environmental compliance.

Improvements in the way combustion air is introduced into the recovery boiler has contributed directly to continuous operation at increased load conditions.

Many areas of the boiler including auxiliary boiler equipment and the boiler heat transfer surface contribute to the limitations of the current boiler operation. However, the primary reason for current boiler performance limits is the combustion process and the associated air system configuration with regard to the delivery of air into the furnace. Depending on the demand for increased black liquor combustion, the level or degree of changes to the combustion air system can be determined. This is sometimes dictated by the current boiler load conditions as well as other factors affecting the current boiler operating limits. In many cases the upper operating limits have been achieved with changes involving the addition of only one combustion air level. When and where additional levels of air are introduced in the furnace to improve black liquor combustion, depends largely on the combustion air system arrangement and the current method of operation. The ability to improve black liquor combustion with enhanced air system designs offers a substantial cost benefit to the mill.

This paper will review various enhancements implemented recently on combustion air systems in recovery boilers and the level of improved performance of these boilers.