Paper Technology International 2024 - Journal - Page 88
PAPERTECHNOLOGYINTERNATIONAL
Stock preparation
The following water-demanding utilities can be found in the
stock preparation system:
•
Agitator and pump seal lubrication
•
Hoses
•
Chemical preparation units
Selecting the right sealing type can make the difference in the water
consumption of the overall plant.
Each seal type has speci昀椀c seal water 昀氀ow and pressure
requirements. Gland packing seal is the most common seal type
used for pumps and agitators. Gland packing offers a lower upfront
cost and easier installation compared to mechanical seals, as it
does not require decoupling of drive shaft, resulting in a shorter
turnaround time but lead to higher water consumption.
In general, glad packing seals require 5 to10 lpm which can
increase if the sealing unit is not well regulated. In a typical Toscotec
AHEAD 2.2 tissue machine plant with a max production capacity
of 125 tpd where pumps and agitators are equipped with gland
packing, the required water seal is about 100 lpm which accounts for
30% of the entire incoming freshwater 昀氀ow.
By installing mechanical seals on all pumps and agitators,
it is possible to drastically reduce the total water seal 昀氀ow (even
though for certain equipment it is not possible to change seal type)
reaching an overall stock preparation freshwater consumption of
lower than 2 m3/ton of paper.
Another aspect worth mentioning is the amount of fresh
water required for chemicals preparation and dosage. Chemical
dosages and therefore fresh water required for chemicals strongly
depend on water quality (conductivity, impurities content, cationic
charge demand, suspended solid content, pH, temperature).
All the above-mentioned parameters are strictly connected
with the plant’s water degree of closure.
Therefore, it is crucial to 昀椀nd the right balance between
plant water closure (which mean freshwater reduction) and plant
runnability.
The water requirement for the use of chemicals is not
investigated in detail in this study, because there are several aspects
that may come into play, including the sort of chemicals used, the
type of production, raw materials, freshwater characteristics, etc.
CONCLUSION
Water reduction approaches are very complex and lead to a progressive closure of the process water loop which gives rise
to contaminant accumulation, and may cause paper defects, deterioration of product quality and machine run-ability issues.
The water consumption of today’s papermaking processes varies between 5 and 20 m3/ton paper. 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.
In this paper we summarized all the best practise and technological developments which allow to reach an overall plant
freshwater consumption lower than 4 m3/ton paper. The above 昀椀gure can be reached acting on the different aspects of the tissue
plant.
Thanks to machine showers optimization and Voith’s new HydroSeal technology, it is possible to obtain a total tissue
machine water consumption lower than 2 m3/ton paper. To this result, we have to add the stock preparation water consumption
that can be lowered down to 2 m3/ton paper through cooling utilities strategies and seal selection.
REFERENCES
[1] K. Olejnik, “Water consumption in paper industry – Reduction capabilities and consequences”, (2011) 113-129
[2] J. Boguniewicz-Zabłocka, I. Kłosok-Bazan “Sustainable Processing of Paper Industry Water and Wastewater: A Case Study on
the Condition of Limited Freshwater Resources” 29 (2020) 2063-2070
[3] J. A. Neun “Paper machine water ef昀椀ciency” (2021)
[4] M. Karthink, R. Dhodapkar, P. Manekar, P. Aswale, T. Nandy “Closing water loop in a paper mill section for water conservation and
reuse” 281 (2011) 172-178
[5] https://voith.com/corp-en/VP_HydroSeal-Case-Study_19_1067_en.pdf
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