FiberSpectrum - ANDRITZ Vertical volute pumps

watering and Bleaching with Andritz’s
Paper Engineered Services group.
“The Hylte Mill wanted to increase
sludge production to about 82 t/d on
each gravity table and maintain the current
level of dryness (65%) after each
screw press,” Salawa says. “They
needed that level of dryness since
they incinerate their sludge to recover
energy and reduce the amount going to
landfill.”
Salawa noted that the existing gravity
tables were equipped with beds two
meters wide and six meters long, without
floating rolls. “We recommended
that the Hylte Mill extend the length of
the inlet end of each gravity table by
two meters and add a floating roll to
the outlet end. This would get them the
production and dryness they wanted.”
“After meeting and discussing with
Artur, I knew that he was the right
person with the right expertise we
needed,” Kurkimäki says. “There was
no question in my mind about which
supplier would do the best job on the
rebuild. He was the key driver of this
project from the outside and Andritz
was the right choice.”
The rebuild project
Salawa gives a brief description of the
gravity dewatering process: “A flocculent
(polymer) is added to the sludge
and the suspension stays in the headbox
of the gravity table until flocs form.
Then it flows onto a fast-moving wire,
where the free water drains through the
wire and the thickened sludge continues
on the wire. The dewatering is
assisted by chicanes mounted in rows
so that the sludge cake is gently turned
over.
“For additional dryness, we installed
a new floating roll at the end of the
table to gently remove remaining water
from the thickened sludge cake. The
thickened sludge cake is removed by a
spring-loaded take-off doctor and then
fed to the sludge screw press. In the
press, the volutions of the slowly rotating
shaft press the sludge against the
outlet casing. The retention time in the
press is about 15 minutes.”
Andritz was required to rebuild the
Hylte Mill’s equipment during scheduled
shutdowns, so precision planning was
crucial. “Working with professionals
certainly made the project achievable in
a relaxed yet fast-paced atmosphere,”
says Johansson.
Each gravity table was extended by two
meters on the inlet side. The new floating
roll was installed on the outlet side
and the original wire was replaced with
a new longer spiral wire.
The rebuild work was staged so that
the DIP-line 1 was completed first.
After the usual checks, the rebuilt gravity
table was started up on February 2,
2007. The upgraded units for sludge
handling lines 2 and 3 were started up
April 16, 2007.
Very dry results
During the performance test for Line 1
in February, technicians from the Hylte
Mill took samples to check the outlet
Stora Enso Hylte
◄ Artur Salawa from Andritz (left) talks with Tommy
Johansson (center) and Mauri Kurkimäki, DIP
Operating Technician, about the performance of
the rebuilt sludge dewatering system.
dryness of the gravity tables and the
screw press. The samples were evaluated
in the mill’s laboratory. Similar
tests were done in April when the other
two lines started up.
“Our objective was fully met by
Andritz,” says Kurkimäki. “The equipment
was able to handle an increased
flow of sludge with the same dryness
as before.”
“All gravity tables easily fulfill the
guaranteed values of 82 admt/d sludge
production at 20.0 -23.6% dryness,”
Salawa says. “The highest production
we measured during the performance
test was 90 admt/d. This with an inlet
consistency of 3.5% and an ash content
of 64%. After the screw presses,
the dryness increases to 65%.”
The dewatering process is also using
less polymer than before while achieving
higher production.
“Currently with the rebuild we are
reaching 790 tonnes of deinked pulp
per day,” Johansson says. “By Christmas,
we will reach our goal of 800
tonnes per day.”
“Improving production and using energy
in the most effective manner possible
is a priority issue for us,” says Sundkvist.
“It is our responsibility to utilize
investment funds where they do the
most good. Well-planned projects like
this rebuild lead to reduced costs and
provide a high return.”
►► find out more at
www.fiberspectrum.andritz.com
▲ (From left) Artur Salawa, Mauri Kurkimäki, Sven-Åke Bertilsson, and Tommy Johansson check the
performance of the gravity table. The rebuilt units are designed to handle 82 t/d of sludge at a dryness of up to
23.6%.
Sludge is not a dirty word.
Removing the ink, clay, coatings, and
contaminants from wastepaper in order
to salvage reusable fibers creates
deinking sludge, and deinking sludge
creates disposal concerns.
Wastepaper with high amounts of filler,
such as clay-coated magazine paper,
produces much lower yields of usable
fiber than does wastepaper that is
mostly cellulose fiber, such as computer
printout or old newspaper. Paper
that is only lightly printed will produce
less sludge than paper that is heavily
printed. Post-consumer papers generally
produce more sludge because they
tend to be more heavily contaminated.
In the past, the greatest percentage of
hazardous material in deinking sludge
came from the inks and pigments. In
recent years, however, ink manufacturers
have made enormous strides in
eliminating heavy metals from commercial
printing inks.
Along with the inks, deinking removes
other non-cellulose materials from the
fiber, including coatings, adhesives,
dyes and fillers like calcium carbonate
and clay, as well as trash like metals
and plastics. All wind up in the sludge.
What can be done with all that
sludge?
Traditionally, deinking sludge has been
handled in three different ways: landfilling,
incinerating, and landspreading.
Landfilling is the most widely used
method for disposal of deinking sludge.
Before the sludge is landfilled, water is
removed from it to make it about 40%
solids. Some mills are permitted to use
municipal landfills, but most use their
own private disposal facilities.
A few mills burn deinking sludge in their
boilers as “hog” fuel. The high moisture
of the sludge affects its ability to
burn efficiently. To enhance its heating
value, the sludge is sometimes mixed
with dry waste material (such as wood
chips). Fluidized bed combustion is
one emerging technology that works
particularly well with the wet sludges
produced by deinking mills.
Several mills landspread sludge. The
sludge is spread on farmland and
adds some organic matter to the soil
and provides trace nutrients, including
nitrogen, phosphorous, and potassium.
The calcium carbonate acts as a lime
substitute, which helps balance overly
acidic conditions. The clay increases
the soil’s capacity to hold nutrients and
is particularly effective for sandy soils.
Recognizing that sludge disposal is a
growing concern, the paper industry is
engaged in intensive research (much
of it proprietary) to develop alternative
uses for the material. Other applications
include composting, agricultural
use, cement production, brick manufacturing,
furnish for fiberboard production,
wet oxidation, fermentation, pyrolysis,
hydrolysis, and absorbent material like
cat litter.
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