Effects of potassium and carbonate on the deposition of synthetic recovery boiler carryover particles

Massive carryover deposit formation on superheater and boiler bank tubes in many kraft recovery units can cause a critical and production-limiting problem, which leads to an unscheduled boiler shutdown. It is therefore crucial to understand the tendency of molten carryover particles to accumulate on heat transfer surfaces in the upper furnace of recovery boilers. Plugging of flue gas passages is strongly related to deposit composition. Deposits accumulate as deposition exceeds the deposit removal capability of the sootblowers.;Understanding the conditions that affect carryover deposition is important for better control of deposits and for optimizing boiler operation. Of the many components in deposits, potassium and carbonate are of great important since they lower the first melting temperature of carryover deposits.;This project studies the effects of potassium and carbonate in carryover deposits using the Entrained Flow Reactor at the University of Toronto. The experimental results show that potassium has an effect on the deposition rate of carryover particles only when the chloride content is between 1 and 5 mole% Cl/(Na + K).;The effect of carbonate in deposits containing various chloride and potassium contents on deposition was also examined. The results show that carbonate has an insignificant effect on the carryover deposition even when carbonate content is as high as 60 mole% CO3(Na2 + K2).;The deposition rate of particles is affected mainly by liquid content, and a minimum liquid content of 15--20 wt% is essential for particles to deposit.