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Sludge drying
An overview of sludge drying − an introduction to sludge drying theory and technologies
Fluidised bed dryers
The fluidised-bed dryer employs a fixed vertical vessel with a perforated base through which hot gases (air or steam) pass. Sludge particles entering the vessel are gently agitated in a stream of pre-heated gas, so that the gas stream is used for both heating and mixing. Fluidised bed dryers require operation with backmixing of part of the dried sludge product stream with the feed to prevent the sludge going through the sticky phase.
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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
Fluidised bed dryers related videos
Fluidised bed dryer, Andritz
Video to demonstrate sludge drying in a fluidized bed dryer.
Fluidised bed 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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Flash dryers
Flash dryers use a rapid stream of rising hot air which both suspends and dries the solids.
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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