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Dust and flue gas chemistry during rapid changes in the operation of black liquor recovery boilers part II--dust composition.

Application: This work adds insights on the topic of dust composition in kraft recovery boilers.

This paper is the second of three papers on the dust and flue gas chemistry of two kraft recovery boilers. It reports results of changes in fume composition, especially the behavior of potassium (K) and chloride (Cl) during rapid changes in boiler load. For the first time, dust concentrations and composition (K, Cl) and the size distributions of fume were measured online during changes in boiler dynamics. We also analyzed size-fractionated dust samples.

In these dynamic tests the dust composition [Na, K, and Cl] behaved about the same in the two boilers. Both boilers burned softwood liquor, but the dry solids contents of the black liquor were different. Between 6% and 9% of the input sodium was released in fume. Some 11%-15% of input potassium and 25%-35% of input chloride were found in fume.

The release of sodium from the char bed surface during the total interruption of black liquor flow was about 300 mg Na/s per floor square meter in both boilers. In boiler B, the increase in potassium content of dust during the liquor stop test indicated differences in the volatilization rates or mechanisms of potassium as compared to sodium. The in-flight release of sodium and potassium from liquor droplets was the main source for fume formation. In-flight release may also be the main source for sulfur release.

During the complete interruption of black liquor flow, particle size distribution moved towards smaller size fractions. The composition of size fractionated dust samples (Na, K, Cl, S[O.sub.4] C[O.sub.3]) analyzed either with IC and ICP-MS or SEM/EDXA showed equal trends as the operating conditions of the boilers were changed.

Tamminen, Lauren, and Hupa are with Abo Akademi University, Process Chemistry Group, c/o Combustion and Materials Chemistry, Turku, Finland; Janka is with Kvaerner Pulping Oy, Tampere, Finland; email Tamminen at or
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Title Annotation:Recovery boilers: summary of peer-reviewed material
Author:Hupa, Mikko
Publication:Solutions - for People, Processes and Paper
Date:Aug 1, 2002
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