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Chemical recovery and inorganic chemistry


Sodium and sulphur balances must be managed in order to maintain a reasonable process economy in the kraft pulp mill. At Innventia, we have extensive experience of establishing sodium and sulphur balances at kraft pulp mills with customers from Europe and from North and South America. Our approach involves detailed sampling and implementation of process data into process simulation tools, which facilitates the study of future cases.

For instance, the composition and amount of recovery boiler dust removal is essential when discussing Na/S balances at kraft pulp mills.

Behaviour of non-process elements (NPEs) in the kraft pulp mill

The wood raw material brings elements that do not take part in the desired chemical reactions into the kraft pulp mill. Calcium, magnesium, manganese, potassium, chlorine, phosphorus and silicon are examples of such elements. They cause different kinds of problems depending on the process chemistry of each individual element.

At Innventia we deal with the process chemistry of these non-process elements, with the aim of minimising their negative effects. This might be performed in several ways; one example is the formulation of solubility models for problematic salts, providing tools to estimate the effect of process changes. This method is closely associated with process simulation and mass balances of kraft pulp mills.

Process-foreign elements
Non-process elements (NPE) can form troublesome deposits on process equipment in the pulp mill.

Some NPE-related mill problems where Innventia can help:


Negative effect

Al, Si, Ca, Ba

Scaling, deposits in cooking, evaporation and bleach plant


Hampered bleaching, scaling in digester, evaporation and washing equipment

K, Cl

Plugging and corrosion of recovery boiler

Si,P, Al, Mg

Inert in lime cycle


Scaling in evaporation

N, P, Cd, Pb etc.

Environmental issues



New challenges regarding nonprocess elements in the liquor and lime cycle
Bialik M, Jensen A, Ahlroth M
Tappi J. 14(7), 421-42 (2015)

Scaling of manganese in kraft pulping process
Bialik M, Jensen A, Kulander I
2014 Tappi/Paptac International Chemical Recovery Conference, 9-12 June 2014, Tampere, Finland (2014) 

Increasing the Availability of the Kraft Pulp Mill by the Use of Process Simulation
Bialik M, Hoffstedt C, Björklund Jansson M, Samuelsson Å, Wadsborn R.
The 45th ABTCP International Pulp and Paper Congress and VII IberoAmerican Congress on Pulp and Paper Research, October, 9-11. 2012, Sao Paulo Brazil (2012)

Assessment of scaling risk in a pressurized black liquor gasification pilot plant
Bialik M, Wadsborn R, Karlholm I, Berglin N
2010 TAPPI/PAPTAC International Chemical Recovery Conference, March 29 - April 1, 2010, Williamsburg, Virginia, USA (2010)

Modeling of the solubility of different inorganic sodium salts in black liquor under varying conditions
Wadsborn R, Rådeström R
Tappi J, 8(3) pp. 9-13 (2009)

Konvertering av mesaugnar från olje- till biobränsleeldning – drifterfarenheter och modellering (in Swedish)
Wadsborn R, Berglin N, Richards T
Värmeforskrapport 1040,, 2007

Metal profiles in the bleach plant: modelling and mill validation
Wadsborn R, Samuelsson Å, Rådeström R, Edebo A, Lendrup H, Hedlund-Björnwall T
2005 Int. Pulp Bleaching Conference Stockholm, Sweden, June 14-16 (2005)