Paper Technology International 2020 - Journal - Page 24

PAPERTECHNOLOGYINTERNATIONAL
Natural Cooling in your paper mill – Closer than you think

Pyry Iltanen, Project Manager, BM Green Cooling GmbH
INTRODUCTION:
Cooling is a crucial part of the paper making process. However, control room cooling is an often overlooked part of the cooling
system, as it doesn’t take a great share of the total energy consumption. The energy saving potential in this part of the mill is however,
significant.
Natural cooling is simply cooling with natural sources, such as river water. By utilizing natural cooling, over 70% of the energy used
can be saved compared to mechanical cooling solutions. The extracted heat can also be easily recovered to be used elsewhere.
Previously natural cooling has not been thought of as a viable option in cooling control rooms. However, with modern technology
and special equipment, the natural cooling possibilities in all parts of your mill are closer than ever. Natural cooling is also a great solution
for energy-efficient production hall cooling to increase the comfort of the personnel.
What is natural cooling?
Natural cooling is simply cooling with natural sources. In effect it
is transferring heat energy directly into a different medium that is
available from the environment itself, compared to mechanically
removing heat energy with a compressor and transferring the heat
energy into the environment later. If we can remove the mechanical
cooling process from the middle, energy is saved and the system
runs more efficiently and with less moving parts.
Three ways to use natural cooling include natural water
cooling, free-cooling and direct free-cooling.
In natural water cooling the heat energy is transferred into
naturally available water, this can be for example water from a river
or a lake. Heat energy from air is transferred into the water using
air-water heat exchangers.
Free-cooling is transferring the heat energy into free air.
In this application the most common way to achieve this is with a
dry-cooler, where hot liquid is cooled down in a cooling coil with air,
by using a large heat transfer area and fans to move the air through
the coil.
In direct free-cooling the cool air is taken from outside and
used to directly cool the area down and remove the heated air
from the area. This is not usually utilized in the paper mill due to
aggressive air on the plant and varying weather conditions (like
changing humidity).
What are the benefits of natural cooling?
Energy efficiency is the cornerstone of natural cooling
benefits. When removing the mechanical element from the cooling
process the energy consumption significantly lowers.
When using natural water cooling the heat recovery is a
large part of the benefit. If the harvested heat energy can be used
elsewhere, it is possible that it can be transferred there with the
heated water. This way the savings can be achieved in two places;
in the cooling and also in the heating.
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Figure 1: 3MW of free-cooling power with dry-coolers.
Also investment costs can be lower as the technical
installation is less complicated. This however, is not always the
case, as a mechanical cooling system may have to be installed for
times of redundancy or for the times when natural cooling is not
available. Examples of this might be during the summer, if the air
temperature gets too high for free-cooling, or the level of the water
source becomes too low, or its temperature rises significantly.
Challenges of natural cooling
So why does everybody not use natural cooling? Even
though natural cooling is a great solution, it also comes with some
challenges.
The first big challenge is that the cooling source needs to
be readily available. In some locations there is not enough cool
water available, and ambient temperatures can be too high in the
summer. In Europe these adverse circumstances are mostly found
in southern countries, like Turkey.

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