Paper Technology International 2024 - Journal - Page 136
PAPERTECHNOLOGYINTERNATIONAL
other’s efforts to implement cutting edge technologies.
The format of the EESF is frequently hailed as a model for other
industries’ collaborative decarbonisation efforts.
“When Cepi launched the EESF in 2020, heat pumps
were investigated but were not yet reaching high enough
temperatures. Through the candid collaboration between both
sectorial associations, the technology now matches our needs. It
will be an important building block in reducing the energy needs
in the paper industry,” says Jori Ringman, Director General of
Brussels-based Cepi, the trade association of European paper
industry.
Why heat pumps?
The most common type of heat pump is the compression
heat pump. It transfers and upgrades thermal energy from waste
heat sources, to ‘heat sinks’ using a small amount of additional
‘driving’ energy - usually electricity.
The thermal energy from the heat source is transferred
via a refrigerant liquid. Inside what’s called a ‘heat exchanger’ the
refrigerant turns into a gas. The gas reaches a ‘compressor’ which,
with the help of a small amount of extra energy, ‘squeezes’ the gas
to a high pressure, causing a rise in temperature. This hot and highly
pressurised refrigerant gas then releases its heat into the ‘heat sink’,
the refrigerant turning back into a liquid as it cools. Its pressure is
lowered, and the cycle begins again.
The ef昀椀ciency of a heat pump is expressed as the
Coef昀椀cient of Performance or COP. It is the relationship between the
power input and the useful heat output of the heat pump. The higher
the number, the more ef昀椀cient a heat pump is and the less energy it
consumes. This COP highly depends on the temperature difference
between the heat source (TC) and the heat sink (TH), where the
‘Carnot curve’ indicates the theoretically maximum ef昀椀ciency (COP),
depending on the source and sink temperature. For example, a heat
pump system with a COP of 2,5 means 60% energy savings can be
achieved.
How would it work in a paper mill?
The ideal heat source would be exhaust air of drying hood.
Currently 60 °C is the maximum dewpoint in paper production. This
is an ideal source of waste heat that heat pumps could use.
Developments are ongoing to reach higher dewpoints to
improve the system COP. This requires further closing the drying
hood. Airless or superheated steam drying would result in the
optimum energy ef昀椀ciency.
Figure 2: Range of typical steam pressures in a paper machine.
70% of steam use in the European paper industry is below 5
bar.
The heat sink in paper machine would be steam heated
cylinders. The amount of steam sections depends on the product
manufactured, but paper machines normally have four to six drying
sections. The drying is done by steam-heated cylinders.
On average, the total electricity needed for the steam used
by one paper mill is 30 MW. The cylinders normally require between
four tonnes to more than 70 tonnes per hour of steam each.
Typical steam pressures range from 0 to 8 barg. In most
paper mills, steam pressures are different in each drying section,
with low pressures in the 昀椀rst sections and higher pressures in the
last drying sections. Pressure levels also 昀氀uctuate by a maximum of
20% depending on paper grades and grammages.
Using lower steam pressures in paper drying, by decreasing
the heat sink temperature, also increases the heat pump system’s
ef昀椀ciency.
Business case requires correct policy
“The progressive phase-out of the fossil fuel alternative
in industrial applications will be essential to building a business
case. It will also be driven by high energy costs and the increasing
CO2 price where clean energy clearly offers a bene昀椀cial solution,”
said Thomas Nowak Secretary General of European Heat Pump
Association at the launch of the collaboration results.
Whether or not heat pumps can be rapidly deployed in paper
mills across Europe now depends on the regulatory incentives that
national government and EU Institutions can provide for electrifying
the sector, which will require large amounts of affordable clean
energy to meet the challenges set in the recently announced EU
Green Deal Industry Plan.
“The industry will continue doing its part in reducing energy
consumption and heat pumps can play
an important role in that. Combined with
access to affordable fossil-free energy
heat pumps will allow for a full transition
towards a decarbonised and circular
economy based on bio-products,” says
Ringman.
Figure 1: How a heat pump can be
integrated into the paper production
process
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