Partial sludge drying
Partial sludge drying

Partial sludge drying

Many wastewater treatment plants handle a waste stream of digested sludge. the sludge is normally dewatered on a centrifuge or belt filter press. After dewatering, the sludge has a typical dry solids content of approx. 20-25%, which is very suitable for thermal treatment i an ANDRITZ Gouda paddle dryer. More and more sludges are being incinirated, requiring a partial drying process to 35-40% dry solids to make the sludge auto-thermic.

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Flyer partial drying

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Features

  • Compact
  • High evaporation rates
  • Flexible on different sludges

 The heart of the installation consists of a trough containing two counter rotating shafts, arrayed with paddles. Thermal oil or saturated steam of 180 - 250 OC flows continously through the jacket, hollow shafts and paddles. As the sludge feeds in, the wedge-shaped paddles ensure perfect local mixing and mechanical fluidisation. The shafts are precisely aligned, and thus enable the paddles to interweave as they turn. This ensures the ideal surface to product contact and sludge flow, leading to high evaporation rates per squared meter inside the machine.

Indirect dryer

The paddle dryer is based on a system of indirect sludge heating. The indirect heat transfer avoids air flows while the fully enclosed operation enables the safe treatment of any sludge type. Due to the low operating speed of the shafts, wear of the installation is reduced to a minimum. Another advantage of the indirect drying system is its low energy consumption as all heat is used to evaporate the water.

Flexible on different sludges

The ANDRITZ Gouda paddle dryer also has many references for full drying (90% dry solids) based on a once-through drying process without back-mixing. The plastic phase in sludge around 45-60% DS never causes problems in this dual shaft machine. The self cleaning effect of the two shafts with intermeshing paddles easily works its way through the plastic phase without problems.

Due to the dual shafted process any type of sludge variation is accepted by this machine making it extremely suitable for centralized drying plants, accepting different sludges from different regions.

Vapor treatment


All evaporated water is fed to a wet scrubber without adding sweep gas. This means that the volume is limited to the amount of water vapor created in the dome of the dryer. The small amount of non-condensibles in the exhaust vapours can be thermally oxidized to minimize the emissions to an absolute minimum.

The whole unit is installed at a slight incline, and the sludge flows by gravity alone to the opposite end of the installation for discharge by a mechanical overflow weir . The predried sludge -with a dry solids content of 35 - 40 % - is conveyed by means of a shaftless screw to the incinerator.

The ANDRITZ Gouda paddle dryer comes in a variety of sizes, ranging from 1.5 m2 of heat transfer area to a megaprocessor with an interior of 300 m2 and a water evaporation capacity of 10 tonnes/hr for partial drying. More than 220 ANDRITZ Gouda paddle dryers are operational around the world, of which 30 units are used for municipal sludge drying.

Apart from the paddle dryer ANDRITZ Gouda also realizes total process solutions - from dump station for digested sludge to loading station for the dried sludge, including sludge conveyors, wet sludge tanks, vapour handling system, sludge distributor, sludge cooler, pelletizer and truck silo.

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Paddle dryer
Paddle dryer
Sludge incineration
Sludge incineration
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