Paper Technology International 2020 - Journal - Page 42

PAPERTECHNOLOGYINTERNATIONAL
CASE: Increased speed and improved working conditions
In an example case, the Runtech Survey Team carried out a
ventilation survey on two machines – PMA and PMB – located at the
same site. The survey consisted of a machine hall ventilation, hood
ventilation and heat recovery survey. One main target was to check
the machine hall ventilation functioning and the air climate inside
the machine hall. The drying section operation and influence on the
machine hall were measured.
The outside temperature varied a lot during the survey.
Some days were rainy and windy, which affected the air conditioning
in the hall.
The mill’s future target is to increase the maximum speed
of PMA to 1,100 m/min and get 10% more production with all
grades. Higher production causes a disadvantage for the machine
hall air climate, which is already relatively poor. For this reason,
the machine room ventilation was checked and measured as well
as the ventilation of both drying hoods on PMA and PMB. When
increasing production rates, the machine hall climate gets worse
without improving the machine hall ventilation. Increasing production
requires an investigation on how to get a complete balance on
the PMA and a good working climate and proper conditions for
the machine and the operators all year round. The big issues are
insufficient ventilation, moisture and working climate. Runtech
studied the machine hall ventilation and balance of the process
air flows into and out from the hood as well as other processing
equipment.
The main reason for the survey was to clarify the machine
hall operation and drying section ventilation system and to check the
sufficiency. The climate in the machine hall was not at an optimal
level. The temperature and humidity of the hall were high, causing
condensation to the structures in the winter season. The situation
will worsen with a higher production rate.
The adequacy of drying capacity and runnability for targeted
speed and production increase were checked.
After the study, Runtech recommended several
improvements for the drying. On the PMA’s hood, exhaust capacity
could increase by replacing the existing exhaust fans. This would
result in a higher zero level, lower hood exhaust humidity and less
leaking from the hood to the machine room. New pocket ventilators
would increase the drying capacity. A humidity sensor could monitor
and control the hood ventilation system and leakages. In addition,
the air system’s runnability components should be serviced to
ensure that sheet runnability and hood removable roof sealings are
repaired.
To improve PMA’s and PMB’s machine hall ventilation, the
existing room ventilation system would need maintenance and
repair. Secondly, the machine room air balance could be equalized
by increasing the machine room supply air amount. As a third step,
evacuation hatches should be closed.
By implementing the proposed changes, the mill would be
able to increase machine speed and thus gain greater production.
The grades with limited drying capacity would benefit the most.
Another main benefit is better air quality in the machine hall, thanks
to eliminating the moisture load coming in from the drying section.
Machine operators would benefit from improved working conditions.
Increasing the hood’s exhaust air enables a larger amount of
replacement air for the drying section, which means that all pocket
ventilation boxes would have sized air volume, thus maximizing
drying capacity.
Figure 7: Hood exhaust fan assembly on site. Modifications to existing machine hall ventilation systems can be
done by installing additional ventilation units, both supply and exhaust air units, locating them in positions where
they give the best benefit.
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