Success story

1. Modelling reveals pulp bleaching secrets
with far-reaching benefits
A phenomena-based simulation of pulp bleaching will help to develop and optimise
the bleaching process. It can even be used to study bleaching in conditions where
it is not currently possible.
“The bleaching model we are developing simu- ing process experimentally. It can only be
lates basic chemical reactions, so it is universal done by modelling. Although there is a long
and unique. Bleaching has often been modelled experimental and industrial history of pulp
before, but the models have been experimental bleaching, it is only now – with the help of the
and have simulated only certain stages of the model – that we understand what chemical
process. Our model covers the whole bleach- reactions are impor tant. When we know
ing process,” says Professor Tapani Vuorinen how and why something happens, we can
of Aalto University. He is responsible for the develop ways to produce better quality pulp
modelling project commissioned by Forestclus- more economically and with less environmen-
ter Ltd to a multidisciplinary research group. tal impact.”
Participating in the project alongside Aalto Uni-
versity are VTT Technical Research Centre and For example, pH is known to influence the
Lappeenranta University of Technology. bleaching result, but the overall picture of
effects and causality has remained unclear.
“The chemistry of bleaching is very complex The model has provided an answer to this
and it is impossible to study the whole bleach- question.

2. It has also produced surprises, even for ex- For the next stage, the multidisciplinary re-
perts in the field. search group is planning to expand the model
to pulp cooking.
“It shows that certain reactions produce plenty
of aldehydes. This finding will allow us to con- “We aim to model wood chips and the reac-
trol conditions so that the bleaching chemicals tions taking place in kraft and sulphite diges-
are used in exactly the right place to promote tion, and also under a wide range of other pos-
the desired reaction most effectively.” sible cooking processes that are hard or even
impossible to study experimentally. One of our
Benefits here and now... aims is to find a solution for cooking at room
“A bleaching plant is a large investment so temperature instead of the temperatures of at
there have to be substantive reasons for least 140°C used at present.”
changing the process. Using the model, a pulp
mill can seek optimal ways of bleaching with Testing radical concepts
existing equipment, aiming to reduce consump- “Revolutionary new ideas for bleaching can be
tion of chemicals and thereby produce lower studied virtually, without the costs or delays
environmental emissions,” Vuorinen notes. of creating laboratory or plant conditions. The
results can be combined with the energy and
Depending on the size of the pulp mill and the material balances of the pulp mill, to produce
initial state of the bleaching process, the econ- a comprehensive assessment of the conse-
omies obtainable from optimised bleaching can quences of new process concepts and chang-
amount to millions. es,” says Kari Kovasin, Head of Research at
Metsä-Botnia, a leading pulp producer.
“Alternatively, the production of some mill
might be limited by a factor related to bleach- “The results that the model has given us have
ing. The model could help solve a bottleneck so been credible. We’ve used it to calculate condi-
that its capacity could be increased.” tions that we have also measured in laboratory
experiments. The results have been consist-
For companies delivering equipment to the ent. The expertise of the research group that
pulp industry, the model will serve as a tool has built the model also gives us confidence
for developing technology. in it.”
“A simulation tool is of the greatest benefit to Kovasin hopes that the model will be used as
suppliers of new equipment.” widely as possible to develop pulp mill pro-
cesses or test new ideas.
... and in the future
“Building the model has developed our skills “Continuous revision, development and en-
and we are well placed both for basic research largement will ensure that the model stays
and for collaborative studies. The model is the up to date. A phenomena-based simulation of
result of long development work that began cooking will complement the bleaching model
back in the 1990’s.” and improve everyone’s understanding of the
processes involved.”
“Because the basic phenomena are always
the same, the model has a very wide area
of application. It can be used for all possible
feedstocks and new chemicals, and even for For additional information
bleaching processes that are not being used at
present. It can also study things that cannot Lars Gädda
be measured experimentally.” Research Director
Forestcluster Ltd.
A unique tool Tel. +358 50 322 2471
The model will be a valuable tool for Finnish
lars.gadda@forestcluster.fi
pulp producers and equipment suppliers.
“We are giving a simply, user-friendly inter- Tapani Vuorinen
face for people who do not know how the pro- Professor
gramme works. The new interface will allow Aalto University, Forest Products Technology
commercial use of the model.” Tel. +358 9 470 24236
tapani.vuorinen@aalto.fi
www.forestcluster.fi