A CRITICAL REVIEW OF THE USE OF FIRESIDE ADDITIVES FOR DEPOSIT CONTROL IN KRAFT RECOVERY BOILERS

摘要

Various additives have been used to control fireside deposit accumulation in recovery boilers. The results have not been conclusive, due primarily to the high "ash" content of the black liquor, the high alkali content of the deposits, and the small amount of additives used. Most additives are claimed to work through one of three main mechanisms: dilution, combustion catalysis, or cleavage plane formation. None of these mechanisms can satisfactorily explain how a small amount of additive can alter deposit properties. Additives should have no direct impact on fume deposition in the generating bank and economizer due to the low temperature in these region. Laboratory and field studies suggest that MgO and Mg(OH)_2 may be effective in controlling carryover deposition in the superheater region, but they have to be applied in a large quantity and be effectively delivered to the tube surface. Among the common additives, these Mg-compounds are also expected to cause the least side-effect in the recovery cycle, owing to their extremely low solubility in alkaline solutions.