Are degraded by alkali-catalyzed reactions. Thus, the organic material of the black

Liquor consists primarily of lignin fragments (mainly high molecular-mass fragments)

And low molecular-weight aliphatic carboxylic acids originating from wood

Carbohydrates. The approximate composition of a black liquor from birch and

Pine kraft cooks is shown in Tab. 9.1.

Organic material also contains minor amounts of polysaccharides mainly derived

from xylan (part of “Other organics” in Tab. 9.1). Quite recently, it was

Shown that black liquor from Eucalyptus globulus kraft cooking contains substantial

amounts of dissolved polysaccharides (BLPS = black liquor dissolved polysaccharides)

[4]. BLPS represent about 20% of the total dissolved and/or degraded

Wood polysaccharides. The major component of BLPS is xylan, with a molecular

Handbook of Pulp. Edited by Herbert Sixta

Copyright © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ISBN: 3-527-30999-3

©2006 WILEY-VCHVerlag GmbH&Co.

Handbook of Pulp

Edited by Herbert Sixta

Tab. 9.1 Composition of the dry matter of pine (Pinus sylvestris)

and birch (Betula pendula) kraft black liquors. Values are % of

total dry matter [2,3].

Component Pine Birch

Lignin

Aliphatic carboxylic acids

Formic acid

Acetic acid

Glycolic acid

Lactic acid

Hydroxybutanoic acid

Dideoxypentonic acid

Deoxypentonic acid

Xyloisosaccharinic acid

Glucoisosacharinic acid

Others

Other Oganics 8 12

Inorganicsa

Sodium bound to organics

Inorganic compounds

Total 100 100

A. Including sodium bound to organic material.

weight in the range 17–19 kDa. During pulping, the black liquor xylans are progressively

Enriched in hexenuronic acid.

Black liquor is concentrated by evaporation and then combusted in the recovery

Furnace for the recovery of cooking chemicals and the generation of energy. The

Heating value of black liquor has a major impact on the steam generation rate,

Knowledge of which is essential in the design and operation of a recovery boiler.

The higher heating (gross calorific) value (HHV) is determined by oxidizing the

Black liquor quantitatively, condensing the water vapor produced, and cooling the

products to 25 °C (TAPPI method T 684 om-90). The net heating (net calorific)

Value (NHV), which better reflects the actual energy release, accounts for the fact

That the generated water is not condensed during combustion and steam generation.

NHV is obtained by subtracting the heat of vaporization of the water from

The HHV value. In addition, any sulfur is completely oxidized in the oxygen bomb

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