By Anna Magnus
Continuously increasing demands on production and quality force
tissue mills to push their machines to the maximum limits. Many
mills put a lot of effort looking for ways to improve the productivity
of the tissue machine and the quality of the end product.
In the service product Advantage capacity study, Metso Paper offers
its unique tissue machinery and process know-how to help mills
use the full potential of their production lines and to make profitable
investments.
The Advantage capacity study gives a thorough evaluation of the
tissue production line from a capacity, efficiency and quality
perspective. Bottleneck areas that limit the capacity are identified
and actions are recommended to fulfil future productionand quality
targets. The suggested recommendations cover a span from smaller
process changes and minor short term investments to strategic
long-term plans, which may require major rebuilds. The results
are presented in a detailed report, where also the expected economical
output of the proposed actions is included.
TAILOR-MADE STUDIES
Each study is tailor-made to fit the circumstances for the specific
tissue machine. The focus of the study can either be capacity,
efficiency, quality or as in most cases a combination of all three
areas. The scope includes the complete tissue making line from
stock preparation to reel, but it is possible for the customers
to choose separate parts of the production line according to their
specific needs.
In the capacity study
an extensive examination of the current machine capacity is performed.
Problem areas are identified and their effect on the overall machine
performance is determined. The study is based on calculations,
simulations, Metso’s
worldwide experience of new machines and rebuilds, together with
the mill’s own experience of the machine. The tissue machine
is thoroughly observed
during the three day mill visit by the team of tissue specialists.
A capacity study in the Middle East had the purpose to evaluate
what actions were
needed to increase
the machine speed by 25%. The results showed that the machine
was dryer-limited and management needed to modify the hood and
air system to be able to reach the speed target. Other bottlenecks
that restricted the machine performance were refiner capacity
and poor functionality of the bale pulper. Formation levels were
an issue and actions were recommended to improve the quality of
the paper. A vibration analysis showed high vibration levels for
some rolls in the felt section.
The dynamic behaviour of the machine is important to consider
when planning for a speed increase. In addition to being a safety
hazard, vibrations in machine equipment can cause severe problems
in the papermaking process and can limit both the machine speed
and the efficiency. A vibration analysis identifies different
types of mechanical problems such as roll unbalance, bearing failures,
section misalignment, gear damage, etc. The results of the capacity
study have served as the base for a well-planned rebuild proposal
in order to speed up the machine.
Another tissue mill planned to upgrade the drying section and
requested a capacity study to show how other parts of the tissue-making
line would fit the planned higher production. The results showed
that three pumps and some piping in the approach system needed
to be replaced and that larger lead rolls were needed in the felt
section. Other limitations found were shower flow- and drive capacity.
To ensure good runnability, actions were suggested for a more
stable sheet transfer and reel operation.
It is also important to consider the balance between higher production
and increased energy consumption when planning to improve the
capacity of the tissue machine. The continuous development of
the capacity study now makes it possible for the customer also
to choose energy focus.
TOGETHER AND IN CONFIDENCE
Many tissue mills
have already predefined
production targets,
but need assistance
to create the best possible roadmap to realise their plans. They
are quite aware of where their major bottlenecks are located in
the machine, but the tricky part is how to relieve them in the
best way. It is not hard to come up with investments that improve
the capacity. The hard part is to rank how different investments
affect the overall capacity and performance of the tissue machine.
This is systematically evaluated and explained in the capacity
study and serves as an excellent base for stepby- step actions
required for achieving future production and quality targets.
The customer and Metso work together and in confidence, which
makes the Advantage capacity study a good example of tomorrow’s
cooperation between
machinery suppliers
and tissue mills.
Anna Magnus is process engineer with Metso
Paper based in Karlstad,
Sweden.
Email: Anna.Magnus@metso.com
Capacity studies -
focus on tissue
