Cluster Rule Impact on Recovery Boiler Operations: Chloride and Potassium Concentrations in the Kraft Liquor Cycle, 1995 Pulping Conference Proceedings

J. Miles Jordan & Patrick S. Bryant

Institute of Paper Science and Technology

The proposed EPA cluster rules require the implementation of Best Management Practices (BMPs) to contain pulp and liquor spills. The proposed rules also impose strict final effluent COD limits which imply closed screen rooms and improved washing to minimize carryover to the bleach plant. In essence, the cluster rules require that the liquor cycle be closed to a higher degree than has typically been practiced. The melting point of ash generated in recovery boilers is influenced by the chloride and potassium concentrations in the tired liquor. An increase in either chloride or potassium concentrations can result in a lower ash melting point, leading to accelerated plugging in the upper furnace sections and subsequent downtime required for water washing the boiler. Computer simulation was used to predict the effect of increased liquor cycle closure on the concentrations of chloride and potassium in the kraft liquor cycle. A sensitivity analysis has been performed to relate the concentrations of chloride and potassium in the liquor cycle to inputs with the wood and water, fume enrichment in the recovery boiler, and purging of recovery boiler electrostatic precipitator dust. The analysis revealed that wood species, recovery boiler enrichment ratio, and liquor spills have the greatest influence on the concentrations of chloride and potassium in the liquor cycle. Chloride and potassium concentrations were found to build up substantially with very tight spill collection. However, purging a small fraction of the precipitator dust results in substantially lower concentrations of chloride and potassium.