Paper Technology International 2024 - Journal - Page 144
PAPERTECHNOLOGYINTERNATIONAL
MCE pumping application examples
High production rate single-line pulp transfer
The new MC pumping performance (up to 10’000 admt/d)
makes it possible to create high production rate bleaching
sequences without parallel pumping and chemical mixing
arrangements. Another very interesting possibility is to retro昀椀t
the existing MC pumps of earlier generations to improve process
economy and increase production rate. Thanks to the high-ef昀椀ciency
MCE retro昀椀t and MCA/MCV hydro昀椀t products, this is possible with
minor constructional changes. Often neither piping nor drive unit
changes are needed.
High-temperature high-consistency pumping from a low- level
pumping vessel
The most common application of MC pumping is to pump
stock from washers and thickeners. The stock falls into the MDL
dropleg and is then transferred to the subsequent process stage by
the MCE pump. MC pumping is controlled so that all the pulp falling
into the MDL dropleg can be pumped further at the highest possible
consistency and temperature.
High temperatures, e.g. +95-98°C, can now be pumped at
a consistency of 12-16% from a low-level pumping vessel with the
new MCE pump innovation. This is a signi昀椀cant process cost saving
(as chemical and steam costs) and layout advantage for example in
the oxygen deligni昀椀cation, EOP (alkali, oxygen, and peroxide) and
PO (peroxide and oxygen) stages.
Figure 7: MCE pumps with innovative Fluider™ technology.
The stock level in the MDL dropleg is measured by means
of radiometric, capacitive or pressure transmitter measurement. The
昀氀ow rate through the MC pump can be adjusted – depending on
the circumstances – by a control valve, by changing the speed of
the pump, or by applying a combination of these two methods. The
level controller keeps the stock level in the MDL dropleg constant,
neither allowing it to drop nor to enter the previous equipment such
as the washer and maintains stable operation in the process. The
separate or built-in degassing system adapts itself to the respective
volume of air contained in the stock and to the 昀氀ow rate used. If
great consistency variations occur in the incoming stock, caused
by a disturbance at the thickener or washer, the control system with
automatic dilution will stabilize the MC pumping.
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Booster pumping to feed pressurized bleaching reactors
In the modern pressurized bleaching stages (oxygen
deligni昀椀cation and PO stages), it is necessary to create very high
pulp line pressures with the MC pump feeding the stage so that
the required process pressures can be achieved in the reactors. In
these process applications, steam is fed and mixed into the pulp
suspension to reach the process temperature. Chemicals such as
oxygen are also fed and mixed into the stock in the pressurized
pipeline.
It is possible that the head requirement of the MC pump
results in such a high stock line pressure that the available steam
or oxygen pressures are not high enough to enable steam/oxygen
feed and control. In these cases, it is necessary to 昀椀nd a way to
reduce the stock line pressure where steam and chemicals are fed.
The solution is to install another MC pump, a booster pump, in the
stock line and this way divide the head generation between two MC
pumps. The advisable location of the booster MC pump depends on
the detailed process data and on the mill arrangements.
Figure 8: Typical MC pumping arrangements. The stock level
in the MDL dropleg is measured and controlled, thus providing
constant operating conditions for the pump.
Figure 9: MC booster pumps for feeding pressurized bleaching
reactors.
