For the second year in a row, Professors Honghi Tran (PhD 8T2) and Vlad Papengelakis were recognized with the TAPPI PEERS Conference Best Paper Award for their paper titled Formation of pirsonnite in green liquor handling systems.
The formation of pirssonite is commonly believed to be the cause of hard-scale buildup in green liquor handling systems in kraft pulp mills. The precipitation occurs when the concentration of sodium carbonate in the liquor exceeds the solubility of pirssonite.
A laboratory study was conducted to systematically determine the causticizing conditions under which pirssonite precipitates. The results confirmed literature data showing that the solubility of pirssonite increases with temperature but decreases with increased concentrations of sodium carbonate and other sodium salts present in the green liquor. The solubility data obtained were used to create a database for pirssonite formation in OLI, a thermodynamic program for predicting phase stabilities of alkali salts in aqueous solutions. The OLI program, with the newly created database, was subsequently used to generate a series of pirssonite solubility curves in terms of saturated total titratable alkali that can be used as operational guidelines to prevent pirssonite precipitation and hard-scale formation in green liquor handling systems. A case study was performed using these solubility curves to explain the occurrence of the pirssonite deposition problem at a kraft pulp mill.
The significance – mill engineers can determine the maximum total titratable alkali that the mill can operate without having problems with pirssonite precipitation and hard-scale formation in green liquor handling systems.
This year’s award will be presented to Professors Tran and Papengelakis at the 2013 TAPPI PEERS Conference to be held from September 15-18, 2013 in Green Bay, Wisconsin.To read the full paper, click here.