B3 Unrefereed conference proceedings

Filtration and washing characteristics of green liquor dregs

Publication Details
Authors: Golmaei Mohammad, Kinnarinen Teemu, Jernström Eeva, Häkkinen Antti
Publication year: 2016
Language: English
Title of parent publication: The 16th Nordic Filtration Symposium
JUFO-Level of this publication: 0
Open Access: Not an Open Access publication

The formation of highly resistant compressible cake of dregs in filtration of green liquor makes the separation a challenging operation in kraft pulp mills. As a common method, lime mud is used as a filter aid to overcome the high resistance of formed dregs cake during the filtration. But the utilized filter aid is disposed to the landfilled together with green liquor dregs (GLD) and increase the amount of solid waste. The high alkalinity of GLD may cause environment impact in their over large disposal area. Furthermore, its high buffering capacity makes it suitable for using as an alkaline barrier. In chemical recovery cycle, green liquor is generated in smelt dissolving tank, where the obtained smelt from recovery boiler is dissolved in the weak white liquor. The green liquor sludge contains soluble sodium content (sodium carbonates, sulfides and sulfates) and suspended solids which are so called dregs. The cake filtration is one of the utilized techniques for separation of dregs from green liquor. The main goal of this separation process is to recover the highest possible amount of dissolved sodium content from dregs. Therefore the filtration is followed by dregs washing and drying to recover the remained sodium content in dregs before landfilling. Through the current study, the effect of filtration parameters such as permeability of filter cloth, sludge storage, filtration pressure and temperature on the filterability of green liquor sludge and characteristics of the filter cake was investigated. The filtration tests were done on the provided samples of green liquor sludge by two different pulp mills in Finland. The samples were collected from underflow of the GLD clarifier and filtered by laboratory scale pressure filters. Therefore the concentration of dregs in these samples (about 60 g/L to 90 g/L) were higher than in the row green liquor (0.6 g/L to 2 g/L). Through cake washing tests, effect of wash liquor on the recovery of sodium and other important elements has been studied as well. Through the filtration experiments, it was found that properties of filter cake such as average specific resistance and compressibility depends on the temperature of sludge.

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Last updated on 2018-19-03 at 15:30