Paper Technology International 2024 - Journal - Page 86
PAPERTECHNOLOGYINTERNATIONAL
The water re-use approach requires an advanced water
treatment plant with speci昀椀c puri昀椀cation technologies such as
昀氀otation, biological reactors, and membrane 昀椀ltration, as described
by M. Karthink et al [4].
Toscotec has taken up this technological challenge and is
actively contributing to the reduction of water consumption in tissue
making through the development of new technologies and strategies
which require less water consumption.
Toscotec has achieved a remarkable reduction of water use
by focusing on four main areas already mentioned.
In this paper, we present the best practices adopted by
Toscotec, which ensure an overall plant freshwater consumption of
less than 4 m3/ton paper. All values reported below refer to a typical
Toscotec tissue plant 2.2 with a max production capacity of 125 tpd.
All water consumption 昀椀gures calculated do not include freshwater
use for chemicals preparation.
Machine showers
Tissue machine showers are the most demanding utilities
in a tissue plant that uses virgin 昀椀bres. All sections of the paper
machine need showers for different functions including cleaning,
moisturizing, lubricating, edge trimming, etc.
Depending on their function and position on the tissue
machine, showers can be managed with different types of water
(clari昀椀ed water (CW), 昀椀ltered clari昀椀ed water (FCW), fresh water
(FW)), with speci昀椀c 昀氀ows and pressures as described in the
Technical Information Paper TIP 0404-61 recommendations.
Toscotec has optimized the design of machine showers by
reducing their water pressure, expecially on lubrication showers
and by preferring the use of CW or FCW over fresh water whenever
possible.
Morover, the upgrade of their mechanical design (nozzle
spacing and pitch, and ori昀椀ce size) was aimed at reducing water
consumption.
In the chart below, optimized shower’s 昀氀ows for Toscotec
AHEAD 2.2 tissue machine plant are summarized:
Tab. 1 Tissue machine shower requirement for 2.2 plant
The above values have been obtained by using 昀椀ltered
clari昀椀ed water (which typically has a suspended solid content of
about 20 ppm) and enhancing its quality through cascade 昀椀ltration
steps to reach an average suspended solid content of about 10 ppm.
Among all tissue machine showers, some positions are more
critical than others. Firstly, high pressure showers are fundamental
to keep the machine cloths clean from contaminants, avoid open
area reduction and guaranteeing proper water drainage during sheet
formation. Secondly, chemical cleaning showers play a crucial role
in preserving the good functioning of the wire and the felt during the
paper making process.
Traditionally, both high pressure showers and chemical
showers used fresh water. Thanks to the higher quality of 昀椀ltered
water, it is possible to feed high pressure showers with 昀椀ltered
clari昀椀ed water, thereby reducing freshwater consumption.
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In summary, the use of continuous fresh water is required by
the following showers:
•
Chemicals showers
•
Suction roll seal lubrication shower
•
Trim showers
•
Tail cutter shower
In this con昀椀guration, Toscotec ensures a tissue machine
water consumption lower than 2 m3/ton paper while guaranteeing
optimal machine performances.
Suction roll sealing technologies
A traditional suction roll seal lubrication shower for a
Toscotec AHEAD 2.2 tissue machine requires a freshwater 昀氀ow of
about 66 lpm to guarantee proper seal lubrication. Thanks to Voith’s
new HydroSeal technology, this freshwater requirement has been
reduced by approximately 87%. The required 昀氀ow with HydroSeal is
around 8 lpm.
HydroSeal is a seal strip with a lubrication system designed
to drastically lower water consumption in suction rolls installed in
the forming and press section. Along with its water savings, it also
increases drive operation ef昀椀ciency, thereby reducing energy costs
[5].
Upon installation of the HydroSeal seal strips, the mill
realizes the following bene昀椀ts [5]:
• 78% reduction in water lubrication for seals, producing
$17,500 and 11 million gallons of water in annual
savings
•
Improved seal strip lubrication performance for the
mill’s tissue production
Additional bene昀椀ts and advantages of Voith’s HydroSeal:
•
Improvement of moisture pro昀椀le due to uniform
lubrication
•
No unwanted remoistening
•
Constant and even lubricant feed at each seal strip
•
Higher operational safety of roll, fewer downtimes,
lower maintenance costs
Homogeneous lubrication over the complete width
Cooling utilities management
The management of process water cooling can make the
difference in water saving strategies.
In paper making plants, lubrication units, gearboxes and other
utilities are usually cooled down by water. The management of
this water stream plays an important role in the overall freshwater
consumption. Generally, cooling water can be managed through an
open or a closed loop:
In open loop con昀椀guration, cold water is fed to the utilities
and the resulting warm water can be used in the process for other
purposes. In closed loop con昀椀guration, the warm water is cooled
down through a dedicated cooling system and re-used to cool down
the utilities again. Compared with the open loop, the close loop
con昀椀guration reduces the amount of incoming fresh water through
recirculation.
With the adoption of a closed loop management approach, it
is possible to lower total water consumption to less than 4 m3/tons.
This approach is usually more energy demanding than an open loop
one, due to the cooling unit energy consumption.
There are several cooling units available on the market which have
different operation concepts leading to different energy and water
consumption 昀椀gures.
