Pilot Fluidized-Bed Testing of Black Liquor Gasification and its Direct Causticization with TiO2, 1996 Minimum Effluent Mills Symposium Proceedings

Le Zeng and A.R.P. van Heiningen -

Dr. Jack McKenzie Limerick Pulp and Paper Research and Education Centre

Kraft black liquor (KBL) gasification combined with direct causticization by TiO2 has been investigated in a 1 kg dry KBL/hr pilot fluidized bed set-up with atmospheric air as the gasifying agent at temperatures between 700 and 900°C. In this process the sodium salts of KBL react with TiO2 to form sodium titanates, while almost all organics and part of the sulfur are gasified. Subsequently, NaOH is directly generated by hydrolysis of the formed sodium titanates in a separate leaching operation. This alternative process of KBL recovery has unique characteristics such as a smelt-free, compact reactor, and the elimination of the conventional lime cycle. Additional advantages are that the high melting point of the sodium titanates allows high temperature fluid bed operation with high carbon gasification and direct causticization rates, while the affinity of sodium to titanium leads to low sodium emission rates. The present paper reports on the effects of temperature, Na2 O/TiO2 molar ratio and air ratio on the gasification and direct causticization reactions. The experimental results show that increasing bed temperature and lower air ratios significantly increase the CO concentration in the gas phase. Complete carbon gasification, acceptable sulfur reduction and very high causticizing efficiencies are obtained at most conditions. Mass balances show that almost no sodium emission occurs and that the titanium loss during gasification and hydrolysis is minimal. Comparisons with conventional KBL recovery confirm that this alternative process has potential

KEYWORDS: Kraft black liquor, Gasification, Direct causticization, Titanium dioxide, Fluidized bed.