UUtilizing the unused energy flows inside the paper mills - Paper Technology International 2023 - Paper Technology International 2023 - Flipbook - Page 15

UUtilizing the unused energy flows inside the paper mills - Paper Technology International 2023

PAPERTECHNOLOGYINTERNATIONAL
Utilizing the unused energy flows inside the paper mills
Pyry Iltanen, Project Manager, BM Green Cooling
INTRODUCTION:
As the energy and material prices are going higher, it makes sense to take a look into the overlooked energy flows inside the
building. In the paper mills the heating is not usually the problem, but saving electricity never goes wasted.
One great way to save energy is to use more of the existing energy flows inside the building. This includes hot and cold water,
steam and exhaust gases that are not yet used in the process but are given out as waste. In hot side this is widely implemented already,
and less heat is wasted, but there are also possibilities in the lower temperatures that do not get so much attention.
In this article I am talking about the water flows
inside the paper mills, and how they can be utilized better
to lower the energy consumption of the mill. Included
are some example calculations and suggestions for the
utilization.
BM Green Cooling has over 30 years of
experience of cooling in paper mills. During recent years
heat recovery and heating has taken a bigger role, as the
technic is maturing and the focus in this field is turning
more and more to the total system efficiency instead of
optimizing separate parts of the process.
What are the overlooked flows?
Overlooked flows are usually found in the lower
end of the temperature range in the paper mills, meaning
100°C and under. These can include for example warm
process water, affluent water, and cold process water if
they are not needed in any particular task.
Cold process water means the fresh water before it is
warmed up to be used as process water. With special climate
cabinets this water can be used to cool down the e-rooms inside the
mill, saving in two places. When the cold water is used in cooling,
there is no need for a chiller, and the warmed water can be given
back to the process water, so it does not need to be warmed as
much, and therefore the heating energy needed is less than before.
This means 100% heat recovery and big savings in electrical energy.
Warm water that needs to be cooled down can be used
as a heat source for a high temperature heat pump. With a high
temperature heat pump up to 90°C temperatures can be reached,
allowing a more versatile use.
If there is too much warm process water that is not used
for anything and needs to be cooled down, an absorber cooler is a
great option. With as low as 70°C water the absorber can provide
you with energy efficient cooling.
Absorption chiller uses hot water to replace the electrical
energy of the compressor in the chiller. This means that by
implementing the warm water flow into the chiller, you are cooling
warm water, and you are getting chilled water in exchange, with
almost no electrical power. Only electrical power needed in this
process is in the automation and in the dry coolers that act as
condensation coolers for the absorber chiller.
Figure 1: Matrix of the temperatures and uses, “Diagram for the
temperatures and usability of the flows”.
Why use the energy flows?
Using the overlooked energy flows help to reduce the
emissions and decrease the costs and environmental impact of
running the mill. This can be achieved by using the existing energy
sources more effectively, reducing wasted energy and the energy
used.
Taking unused flows and turning them into used flows
increases the overall efficiency of the plant, as less energy is used
and less energy is given out. Using less of the energy coming from
outside and utilizing more energy that was inside the whole time, the
overall efficiency of the plant increases. The optimizing process is all
about using the least amount of energy while getting the work done.
As affluent water temperatures are getting warmer and the
regulations are getting tighter, cooling in the affluent water is needed
more often. This can be made for example with high temperature
heat pumps, producing warm enough water to be used in heating.
With high temperature heat pumps the water can be heated up to
90°C, allowing a more versatile use.
Using the energy flows
In the next part of the article, we are focusing on the flows,
dividing them by the temperature levels and suggesting some ways
to utilize them.
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