Paper Technology International 2020 - Journal - Page 25

PAPERTECHNOLOGYINTERNATIONAL
Also with natural cooling the medium
temperatures need to be higher than with traditional
cooling solutions. This results in a smaller
temperature difference between the cooling medium
and the cooled medium, this requires bigger
capacity of the cooling units, raising the investment
costs. When the temperature difference gets
smaller, the heat transfer area needs to be bigger to
achieve the same cooling power.
The water quality can be challenging in
some locations when it is needed in the cooling
process. Particles, acids, and too high pH values
can often be found in the water in the paper mill,
making the engineering of the cooling system
crucial. For longevity of the system, all of this should
be taken into a consideration.
Figure 2: Chillers for redundancy and for warmer times of the year.
Overcoming the challenges
How do we overcome the challenges in natural cooling?
Fortunately, most paper mills are located near a water
source as water is also used in the paper making process. In most
cases the process water can also be used as a source for cooling.
In this approach the process water is “loaned” for cooling and given
back to circulation after it has absorbed the heat energy from the
cooled place. This way the water also gets pre-heated, and we
achieve 100% heat recovery.
Small temperature differences between air and water can be
solved with specially designed heat transferring units. By designing
the units for natural cooling usage, we can achieve the required
results when cooling.
For the water quality we can approach the problem in two
different ways. We can build an independent circulation, where we
insulate the process water from the cooling equipment. Here we
can use plate heat exchangers that are specially designed for the
process water, and on the other side to have normal Water-Glycol
mixture or technical water.
The other way is to build the cooling equipment to endure
the aggressive water. This can be achieved with stainless steel
pipes inside the coil to prevent corrosion of copper.
Figure 3: Specially engineered climate cabinet, A-shape coil and Siemens S7.
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