Technical Bulletin No. 0083: A Survey and Analysis of Design Criteria and Performance of New Generation Black Liquor Oxidation Systems (AQTB)

This technical bulletin is based on a 1975 survey and analysis of design criteria and performance of new generation black liquor oxidation (BLO) systems. It encompasses new and recently modified heavy BLO installations that have incorporated design features aimed at improving both the level and continuity of performance. To summarize briefly, the survey identified several design and operational features of new generation BLO systems that have led to improved performance. These include (a) continuous air and liquor flow measurement, (b)availability of standby blowers, pumps and oxidizers, (c) anticipated routine identification and correction of malfunctions such as nozzle plugging, (d) maintenance of uniform operating conditions, (e) adequate oxidation time and air to sulfide ratio and, (f) a well-identified trend toward two-stage oxidation. Observations made during the survey suggest that sulfidity increases associated with more effective BLO and other TRS emission control activities which return sulfur to the system continue to be underestimated. BLO may of itself be considered as a very low grade source of TRS emission under certain conditions, as a consequence of air stripping of organic sulfides during aeration in the BLO liquor. Council studies are currently being directed toward finding ways of dealing with these emissions as well. Taken as a whole, the results show that with efficient black liquor oxidation coupled with optimal operation of the recovery furnace itself, the direct contact evaporator recovery furnace system remains a worthwhile means of processing spent black liquor consistent with effective control of TRS emissions from the recovery furnace system.