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Sludge drying
An overview of sludge drying − an introduction to sludge drying theory and technologies
Flash dryers
Flash dryers are employed for industrial process slurries which have a relatively easily-removed moisture content, and are not currently applied to sewage sludge.The sludge is dried using a rising hot air stream, flowing at 20–30 m/s, to both suspend and dry the particles, and the dried product is separated using cyclones and/or bag filters. They operate at very short residence times, and so have a relatively small footprint.
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Introduction to sludge drying
Processes where moisture is removed from sludge as water vapour are known as 'sludge drying'
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Sludge treatment − properties of drying sludge
When sludge dries, it goes through three different phases as the water evaporates
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Sludge treatment − sludge drying operation
Sludge drying processes operate at solids temperatures of 60-93 °C to encourage water to evaporate and leave a solid residue
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Sludge treatment − sludge dryer configurations
Sludge drying processes are generally configured as convective, conductive, or as solar dryers
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Sludge treatment − convective sludge dryers
Convective sludge dryers are the most commonly used type of dryer for sewage sludge
Flash dryers related videos
Example of a flash dryer for drying slurries
Animation demonstrating the workings of the flash dryer for drying slurries, from Hosokawa Micron B.V.
Flash dryers features and blogs
Feature
Co-processing of sewage digestate by hydrothermal carbonisation
Hydrothermal carbonisation (HTC) can be used to co-process anaerobic digestion (AD) digestate and lignocellulosic (or plant-based) feedstocks to improve the the hydrochar product quality. This AD waste co-processing route has been studied at bench scale. Read article
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Convective dryers
Convective (or direct) dryers remove moisture from sludge by bringing the sludge particles into direct contact with hot gas
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Belt dryers
Belt dryers comprise a conveyor belt which slowly transports the sludge solids through a stream of heated air
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Fluidised bed dryers
In fluidised-bed dryers the sludge particles are gently agitated and heated by a stream of upward-flowing pre-heated gas
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Rotary drum dryers
Rotating drum dryers have a drum rotating at 4-8 RPM through which the sludge passes along with a stream of warm air
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Conductive dryers
For conduction drying, the sludge is heated indirectly by bringing it into contact with a heated surface
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Disc dryers
Disc dryers are based on vertical externally-heated discs or rings rotating in the sludge as it passes through the dryer.
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Paddle dryers
Paddle dryers are based on externally-heated paddles rotating in the mass of sludge solids held in a stationary vessel
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Solar dryers
Solar dryers comprise large greenhouses in which sludge is dried under the ambient conditions of the building.
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Pelletizers
Pelletizers
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Conditioning
Conditioning is the pretreatment of sludge upstream of thickening and dewatering to promote solid-liquid separation
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Thickening
Thickening processes concentrate the sludge by removing part of the free water, such that the product can still be pumped
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Dewatering
Dewatering processes mechanically remove a significant proportion of the sludge water to produce a 15-45% cake product
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Drying
In sludge drying the sludge moisture is removed as water vapour by heating, generating a pelleted or powdered product
More process and operation topics…
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Sludge stabilisation
Sludge stabilisation − alkaline stabilisation, lime and solids dosing, plus anaerobic and aerobic digestion
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Thermochemical processes
Thermochemical methods are used to either significantly reduce the sludge solids content or pre-treat sludge upstream of AD
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Sludge quality
Sludge is the main waste stream from the treatment of wastewater