DRYING OF SEWAGE SLUDGE USING AN APV SPIN FLASHˇ DRYER
IN A CLOSED LOOP ARRANGEMENT
Jakob Liedberg
Invensys APV Systems,
Ostmarken 7, DK-2860 Seborg - Copenhagen Denmark,
E-mail: jakob.liedberg@invensys.com
Keywords: Sludge, drying, spin flash, closed loop
ABSTRACT
Sewage sludge is an ever-growing global problem with increasing amounts
generated each year. As environmental issues are gaining more attention,
old methods of disposal of sludge are seen as harmful and are gradually
phased out either by legislation or by the demands of pressure groups.
This results in investigation into new ways of treating sludge prior to
disposal. Drying is one method that is considered appropriate. The APV
Spin Flashˇ Dryer (SFD) has been tested for this application in a series of
pilot trials carried out at the APV test center in Copenhagen. Municipal
sludge was successfully dried into a free flowing powder with a particle
size of less than 1500 microns.
There are several advantages to drying. Firstly, the weight and volume are
substantially reduced which gives a more easily handled product and reduces
the costs for deposition, since the dumping-fee is proportional to the
weight disposed off. Secondly dry sludge has a high heat value and can be
used as fuel for the dryer, creating a self-sustaining system and thereby
minimizing the usage of fossil fuels. This was proven in a theoretical
investigation made together with the University of Lund, which confirmed
that it is possible to use dry sludge as fuel and produce flue gases that
can be used in the process.
Using this solution excess fuel is only needed during start-up. If the
sludge is not used as fuel in the process the dry product might be sold as
fertilizer on condition that it meets minimum environmental and hygienic
requirements.
The practical test showed no operational problems with the SFD in this
application with the conclusion that the SFD is well suited to handle
municipal sludge.
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