Fate of biosludge nitrogen in black liquor evaporation and combustion

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Vaha-Savo N, Demartini N, Hupa M
Publisher: TECH ASSOC PULP PAPER IND INC
Publication year: 2012
Journal: Tappi Journal
Journal acronym: TAPPI J
Volume number: 11
Issue number: 9
Start page: 53
End page: 59
Number of pages: 7
ISSN: 0734-1415


Abstract

At many mills, biosludge, which has a high nitrogen content, is added to black liquor and burned in kraft recovery boilers. The aim of this work was to determine the fate of biosludge nitrogen in the high solids black liquor concentrators and in the recovery boiler. Specifically, does biosludge addition result in higher nitric oxide (NO) and cyanate formation during black liquor combustion? To obtain this information, samples were collected from the chemical recovery cycle of a Finnish kraft pulp mill along with relevant process data. Laboratory combustion experiments clearly showed an increase in NO formation for the mill black liquor with biosludge, but no clear increase in nitrogen oxide emissions was detected in the recovery boiler after biosludge addition. Analysis of the green liquor samples from the dissolving tank showed a significant increase in nitrogen exiting the recovery boiler as cyanate. This finding was supported by laboratory tests studying cyanate formation. The increased cyanate results in increased ammonia formation in the recausticizing cycle, which can lead to higher NO emissions, as seen in the non-condensible gas incinerator at the mill.

Last updated on 2019-23-10 at 03:31