Paper Technology International 2024 - Journal - Page 145
PAPERTECHNOLOGYINTERNATIONAL
Booster pumping in long-distance pulp transfer applications
In an integrated pulp and paper mill, the distance between
the pulp mill and the paper mill is often in the range of 300 to 400
meters. Pulp is generally pumped in a diluted form, but the MC
pump enables pumping at a consistency of 10 to 12%. Mediumconsistency stock enters the MDL drop leg of the MCE pump from
the 昀椀lter. The MCE pump, which is provided with degassing and
rotates at a 昀椀xed or
variable speed, pumps the stock to a booster MC pump of
the same size, which requires no degassing. The booster MC pump,
which is provided with variable speed control, pumps the pulp to a
storage tower.
Figure 11: MC tower discharge pumping system.
Figure 10: MC pumping system in long transfer line into MC
storage tower.
Tower discharge pumping
The discharge of large high-consistency storage or
bleaching towers is often dif昀椀cult, especially when a well- controlled
pulp 昀氀ow to a bleaching stage or to the washer is required. The
MC tower discharge pumping system consists of the following
key components: MC discharge scraper, MTB feed chute, tower
isolation valve, MCE pump and MDS degassing system. The MC
discharge scraper manufactured by Sulzer operates in connection
with a medium-consistency tower discharge MCE pump. The MC
discharge scraper scrapes the pulp over the complete bottom area
of the tower and leads it into the MTB feed chute of the MCE pump,
thus enabling an even discharge and simultaneously preventing
channeling of the stock in the tower.
The MC discharge scraper also stabilizes the pumping
procedure. It is available as a diluting or non-diluting model. The
diluting MC discharge scraper simultaneously dilutes the pulp
uniformly and discharges the tower without interference. When using
diluting MC discharge scrapers, the consistency of the pulp in the
tower can be high (e.g. 20 to 35%), and the pumping consistency is
then within the MC range. Pulp can also be diluted to the process
consistency with the tower bottom water connections, with a diluting
MC discharge scraper or in the MTB feed chute.
MC discharge scrapers are manufactured in different sizes
up to a diameter of 6’500 mm. Each size is available with or without
the possibility for dilution. The smallest MC discharge scraper sizes
with a planetary gear are suspended from the tower bottom, while
the bigger sizes are provided with a spur gear 昀椀xed to the 昀氀oor
under the tower. These constructions do not require any separate
bearing units. The MC discharge scraper material alternatives are
EN 1.4404 stainless steel or 254SMO.
MC pumping and controlled 昀氀ow splitting to storage towers or
to intermediate mixing chests with an MCE pump and an MC
discharger
It is often necessary to transfer bleached pulp from the pulp
mill to several storage towers, which are all located relatively far (50
to 400 meters) from the bleached pulp washer and, therefore, also
far from the corresponding MCE pump. This application is carried
out so that there is only one discharge pipeline from the MCE pump
to the area of the storage towers. At the end of the pipeline, the 昀氀ow
is divided into several 昀氀ows that are directed to the different towers.
The same type of application is also useful near the
paper machines, when the stock must be distributed into several
intermediate mixing chests. MC pump feeds the chests through the
MC discharger. The MC discharger is used to split the 昀氀ow in equal
or in wished proportions to the intermediate mixing chests. A plug
昀氀ow is generated in the pipe when pumping medium-consistency (8
to 16%) pulp, and the 昀椀ber network holds the plug together. Dividing
this kind of a 昀氀ow to precisely controlled partial 昀氀ows at the end of
a pipeline is not possible with a valve only, but an MC discharger is
used in this application to 昀氀uidize the stock and to divide and control
the partial 昀氀ows to the towers or mixing chests.
The MC discharger operates so that the pulp entering the
chamber is 昀氀uidized by a rotor, and the outlet 昀氀anges are directly
connected to the same chamber. Depending on the application, up
to four outlet connections are available in one MC discharger, all of
them with control or on/off valves. The MC discharger itself does
not generate pressure, so an MC pump is required to pump the
pulp through it. The MC discharger can be installed either vertically
or horizontally or in any other desired position, depending on the
application. The MC discharger can also be used in the bleaching
reactor feed and discharge applications.
Figure 12: Stock 昀氀ow splitting with MCE pump and 昀氀ow divider
into three storage towers.
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