Specialty chemical technologies for high-quality, sustainable and cost-effective chemical pulp production - Paper Technology International 2023 - Paper Technology International 2023 - Flipbook - Page 32

Specialty chemical technologies for high-quality, sustainable and cost-effective chemical pulp production - Paper Technology International 2023

PAPERTECHNOLOGYINTERNATIONAL Specialty chemical technologies for high-quality, sustainable and cost-effective chemical pulp production - Paper Technology International 2023
You just need to know what to look for and how to do it – the
pulp specialists at BIM can provide that expertise. Through their
profound knowledge combined with our chemical solutions and
analysis tools, they can add real value to the pulp process and help
produce pulp according to required needs.
Improving drainage for an efficient pulp washing
The pulp mill’s performance is only as good as its washing
performance. Inefficient pulp washing can lead to production
bottlenecks, reduced quality and increase chemical and production
costs. Poor drainage and washing occur when there is much
entrained air in the stock. Foaming and high entrained air content
are big problems for many pulp and paper manufacturers due to
the negative effects they have on the process and the quality of
pulp and paper. Air or foam caught in the mat interferes with liquid
passing through thus slowing drainage and giving a poorer washing
efficiency. The maintenance of vat consistency and vat levels is
directly attributed to both the air attached to the fibre and the air in
the liquor.
The most successful mills realise that to be viable in this
challenging market, you need to break the foam/air cycle. That
means finding out what’s really impacting washing performance,
with the expertise to solve problems at their source and introduce
long-term improvements across the entire process.
But what is actually air/foam?
Air is a component which is always present during pulp
production and appears as bubbles or foam in the process. Bubble
is a small gas particle entrained and dispersed in the fluid. The
amount of dissolved air in water increases with pressure and
decreases with temperature increase.
Figure 2: Foaming and high entrained air content have negative
effects on the process and the quality of pulp and paper.
Foam is formed by many gas pockets surrounded by a
thin film of liquid. Foam is created when fluid is mixed with free
surface air or when bubbles gets bigger and rise to the fluid surface.
Surface-active materials can create foam when they get stabilised.
Foam control and drainage improvement are integral parts
of ensuring downstream productivity and cost efficiency. When the
process is closed, the level of undesirable substances increases,
which leads in turn to foaming and deposit problems.
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There is much to be gained by using effective chemical
products that deaerate the system and reduce foam formation,
such as:
•
Reduced air content
•
Improved drainage, which gives cleaner pulp, which
gives lower COD and chemical savings
•
Reduced surface foam
•
Elimination of process bottlenecks
•
Improved process stability and in some cases
increased soap separation
•
Increases washing yield, pulp quality and chemical
recovery
•
decreases bleaching chemical usage, water usage, and
energy need.
Advantages of a talc free pulp production
Talc has been widely used for many years in chemical
pulp mills with sulphate and sulphite process in order to change
physically the surface of aggregated wood pitch particles. This
surface change makes the wood pitch particles less likely to attach
themselves to metals surfaces in the process which, in turn, lessens
the tendency for build-up in the form of deposits. However, one
major disadvantage for using talc is its relatively poor retention to the
wood pitch particles and fibres as well as its hydrophobicity. To cover
for the poor retention talc is dosed at high rates. This overdosage
causes in many cases deposit problems, a counter act towards its
purpose. In addition, talc is often found with a lot of impurities, such
as iron - calcium - and aluminium containing minerals. All of them,
not desirable in the pulp process. In recent years, there has also
been growing concerns regarding the health risks posed by talc
which has led to some paper producers not buying pulp which has
been produced using talc.
Talc free pitch control – organic and inorganic
One of the most common challenges pulp producers face is
pitch control. As long as people have been making paper from trees,
pulp manufacturers have struggled to eliminate pitch. Pitch deposits
in open and closed systems often lead to quality problems in both
pulp and paper mills. Many times we talk of pitch, but several times
it is a blend of organic and inorganic materials.
Pitch is a complex organic colloidal contamination released
during the pulp production process and can contain resin acids,
fatty acids, triglyceride fats, stearyl esters, sitosterols and other
unsaponifiable materials. Pitch can vary in amount, tackiness, and
composition, and poses a major challenge for pulp manufacturers,
as it can agglomerate and its sticky nature causes production and
quality issues. One of the requirements for high product quality is
properly functioning pitch control.
Wood types used in pulp and paper production have
species-specific compositions of wood extractives, which often
cause a variety of process technical and quality related problems.
Although the pitch is a minor component of the wood, its effects on
the pulp and papermaking process can be quite intense.
In paper making, pitch can cause:
•
lowered tensile strength,
•
spots and holes in the paper,
•
deposits on paper machine parts, wires and felts,
•
unwanted foaming and problems with odour and taste.

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