Technology/IT ¦ IDM
Heat and cold from
one machine
Low-CO2 high-temperature heat pump for sterilising
dairy products
May/June 2022 ¦ international-dairy.com · 35
Author: Bernd Genath, trade journalist, Düsseldorf, berndgenath@t-online.de
In Trondheim, Norway, the Scandinavian research institute Sintef
realised the ideal energy cycle for both a heat pump and
operating costs in a dairy. The newly developed propane-butane
unit takes as its energy source for hot water production
the return flow of the ice water that the plant produces to cool
the raw milk with an ammonia chiller. The high-temperature heat
pump thus also supports the ice water production with its own
evaporator.
Considerable losses
The warm side of the high-temperature heat pump (HTHP) pushes
hot water temperatures of up to 115 °C into the food production
lines, including the pasteuriser. Despite the temperature swing of
more than 100 K, the cascaded structure operates with a COP of
up to more than 3.0. The cold required to cool the dairy products
to 3 to 4 °C, which already enters the megawatt range in
medium-sized dairies, is supplied in the form of ice water by the
chillers. The demand for heat for thermal sterilisation, for cleaning
the plants and halls and for heating purposes exists at about the
same amount as the demand for cooling. The energy consumption
is therefore enormous.
If you look around in dairies, however, many of them are not
particularly using the energy sources gas, oil and electricity economically.
This is often the normal case: An ammonia chiller pushes
the ice water to the storage tanks and blows the heat outdoors
via a dry cooler, an oil or gas boiler provides 70- or 80-gram washing
water for regular cleaning of the tanks and machines, and an
electric heater with a COP or efficiency of 0.9 is responsible for the
120 °C process hot water for sterilisation and other purposes. This
produces considerable losses. The simultaneous demand for high
and low temperature, on the other hand, makes such plants ideal
for a much more efficient system with HTHP, which is, however,
still in short supply.
Sintef know-how
However, since the Paris agreements were signed, the heat pump
industry on the one hand and potential customers, i.e. food manufacturers,
on the other hand, are now paying more attention to
CO2 savings in the production of food products. As said, HTHP is a
natural choice for dairies, as it can support the chiller with its cold
side and replace the boiler and electric heating with its hot side.
The first conversions are underway. Christian Schlemminger,
project engineer at the Norwegian Sintef Institute, reported on
such a retrofit at the German Refrigeration and Air Conditioning
Conference last November in Dresden. Sintef is an independent
research organisation and the largest of its kind in Scandinavia.
There is close cooperation with the Norwegian University of Technology
and Natural Sciences in Trondheim NTNU. One of Sintef's
focal points is energy research.
Sintef has already completed a number of projects with Tine
Norske Meierier BA. The cooperative is owned by its approximately
10,000 supplying farmers. It is considered one of the largest food
companies in the country, with cheese as one of its specialities.
Schlemminger presented two case studies with Tine. In the first,
his institute dealt with the retrofitting of a dairy in Trondheim,
which processes about 75 million litres of milk annually. The problem
of optimising efficiency here was to take into account the existing
equipment. The inventory requires process hot water of 115 °C.
Temperature swing of over 100 K
In the second example, a new Tine building in Bergen, the project
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