PAPERTECHNOLOGYINTERNATIONALMCE pumping application examplesHigh production rate single-line pulp transferThe new MC pumping performance (up to 10’000 admt/d)makes it possible to create high production rate bleachingsequences without parallel pumping and chemical mixingarrangements. Another very interesting possibility is to retro昀椀tthe existing MC pumps of earlier generations to improve processeconomy and increase production rate. Thanks to the high-ef昀椀ciencyMCE retro昀椀t and MCA/MCV hydro昀椀t products, this is possible withminor constructional changes. Often neither piping nor drive unitchanges are needed.High-temperature high-consistency pumping from a low- levelpumping vesselThe most common application of MC pumping is to pumpstock from washers and thickeners. The stock falls into the MDLdropleg and is then transferred to the subsequent process stage bythe MCE pump. MC pumping is controlled so that all the pulp fallinginto the MDL dropleg can be pumped further at the highest possibleconsistency and temperature.High temperatures, e.g. +95-98°C, can now be pumped ata consistency of 12-16% from a low-level pumping vessel with thenew MCE pump innovation. This is a signi昀椀cant process cost saving(as chemical and steam costs) and layout advantage for example inthe oxygen deligni昀椀cation, EOP (alkali, oxygen, and peroxide) andPO (peroxide and oxygen) stages.Figure 7: MCE pumps with innovative Fluider™ technology.The stock level in the MDL dropleg is measured by meansof radiometric, capacitive or pressure transmitter measurement. The昀氀ow rate through the MC pump can be adjusted – depending onthe circumstances – by a control valve, by changing the speed ofthe pump, or by applying a combination of these two methods. Thelevel controller keeps the stock level in the MDL dropleg constant,neither allowing it to drop nor to enter the previous equipment suchas the washer and maintains stable operation in the process. Theseparate or built-in degassing system adapts itself to the respectivevolume of air contained in the stock and to the 昀氀ow rate used. Ifgreat consistency variations occur in the incoming stock, causedby a disturbance at the thickener or washer, the control system withautomatic dilution will stabilize the MC pumping.144Booster pumping to feed pressurized bleaching reactorsIn the modern pressurized bleaching stages (oxygendeligni昀椀cation and PO stages), it is necessary to create very highpulp line pressures with the MC pump feeding the stage so thatthe required process pressures can be achieved in the reactors. Inthese process applications, steam is fed and mixed into the pulpsuspension to reach the process temperature. Chemicals such asoxygen are also fed and mixed into the stock in the pressurizedpipeline.It is possible that the head requirement of the MC pumpresults in such a high stock line pressure that the available steamor oxygen pressures are not high enough to enable steam/oxygenfeed and control. In these cases, it is necessary to 昀椀nd a way toreduce the stock line pressure where steam and chemicals are fed.The solution is to install another MC pump, a booster pump, in thestock line and this way divide the head generation between two MCpumps. The advisable location of the booster MC pump depends onthe detailed process data and on the mill arrangements.Figure 8: Typical MC pumping arrangements. The stock levelin the MDL dropleg is measured and controlled, thus providingconstant operating conditions for the pump.Figure 9: MC booster pumps for feeding pressurized bleachingreactors.
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