How to save energy up to 30-70% in paper machine vacuum system? - Paper Technology International 2023 - Paper Technology International 2023 - Flipbook - Page 42

How to save energy up to 30-70% in paper machine vacuum system? - Paper Technology International 2023

PAPERTECHNOLOGYINTERNATIONAL How to save energy up to 30-70% in paper machine vacuum system? - Paper Technology International 2023
Figure 2a & 2b: Combining all vacuum consumers with different vacuum levels to one unit can destroy system efficiency due to
expansion/throttling losses.
Figure 3a & 3b: In these rebuild cases, existing liquid ring pump or pumps are compared to a hybrid system to find an optimal
balance between investment and operating costs. A containerboard machine achieved even higher energy savings than expected.
The start-up was very smooth and provided instant savings with a flexible vacuum system that provided good vacuum control
to the mill. In addition, water savings were significant. On a fine paper machine, eight liquid ring pumps were replaced with three
EP Turbo Blowers, and an LRP remained to provide vacuum for high vacuum consumers. The rebuild provided energy savings of
1,000 kW, dropping the specific energy consumption to 24 kWh/t, with Turbo Blower exhaust air also saving one ton of steam per
hour. In addition, a cooling water tower was stopped, bringing the mill substantial water savings.
The airflow from a lower vacuum level (higher abs. p)
expands over the valve to a higher vacuum level (lower abs.
p) at the blower/header and thus the actual airflow seen by the
equipment can be doubled or even tripled. An often seen vacuum
level difference of e.g. 20 kPa (-60 kPa vs. -40 kPa) between two
consumers at the machine can lead to a 100% increase in the
air volume through expansion and thus naturally lead to a large
increase in the blower’s energy consumption.
To improve efficiency, vacuum connections, vacuum levels
and system operation need to be surveyed thoroughly for each
case. Based on customer needs and targets, as well investment
payback, in some cases, given the results of this audit, the decision
to go forward with a hybrid vacuum system gives the biggest bang
for the buck.
However, to save energy maximally up to 30-70% takes
more than just switching over from LRP’s to turbo blowers. You need
other optimization measures, too. Read on to find out what they are.
Measure water flow to optimize vacuum levels
To save energy, it is essential to use the optimal vacuum
level in the forming and press sections. Often paper mills use too
high vacuum levels because they do not know the accurate water
flow.
The primary function of a wire- and press section in a
paper machine is to remove water from the paper sheet. In order
to understand the effectiveness of individual elements (such as
save-all pans and suction boxes) of a wire- and press section, the
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dewatering rate must be measured. Without this, critical air flow
(i.e. vacuum level) review and consequent optimization cannot
be successfully carried out. Water removed from the paper sheet
contains air, and is often subject to foaming. Traditional magnetic
liquid flow meters demand a homogenous flow and will not be able
to provide accurate data. Runtech’s Ecoflow dewatering meters are
designed to measure water flow across a mechanical restriction and
are not sensitive to entrained air or foaming. These devices are used
both under vacuum (in a separator drop leg) and in atmospheric
conditions.
EcoFlow dewatering measurement system optimizes
dewatering and vacuum levels in the forming and press sections.
EcoFlow provides maximized sheet dryness after the press section,
improved machine runnability and maximum energy efficiency, while
providing papermakers with accurate real-time feedback about the
dewatering performance along the paper machine.
Go for nip dewatering
EcoFlows are designed to work with doctoring to gain
maximum energy efficiency. Dewatering and doctoring are not only
related to energy consumption, but they also have big effect on
whole machine runnability, efficiency and profitability, as well as
the paper profiles. A well-designed and operated dewatering and
doctoring system is one of the key issues to a well-performing and
energy-efficient machine. A lot a paper machines have them but they
are not effective and do not have the adjustability that is needed
to optimize them effectively. In order to get the full benefits from

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