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Conductive dryers

For conduction drying, the sludge is heated indirectly by bringing it into contact with a surface which is heated either by steam or a hot oil system. Examples of conductive processes include paddle dryers, disc dryers, and thin film dryers.

Sludge water fractions for flocs and particles: surface water, floc water, interstitial water and free water

Sludge drying

An overview of sludge drying − an introduction to sludge drying theory and technologies

Dried, "noodles" of sewage sludge

Introduction to sludge drying

Processes where moisture is removed from sludge as water vapour are known as 'sludge drying'

Sludge water fractions for flocs and particles: surface water, floc water, interstitial water and free water

Sludge treatment − properties of drying sludge

When sludge dries, it goes through three different phases as the water evaporates

Schematic showing integration of sludge drying with the downstream operations of anaerobic digestion and incineration, where the latent heat from the downstream processes is used to heat the dryer.

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

Hierarchy of sludge drying processes, showing convective and conductive dryers and including belt, fluidised bed, flash, rotating drum, paddle, disc and thin film dryers.

Sludge treatment − sludge dryer configurations

Sludge drying processes are generally configured as convective, conductive, or as solar dryers

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Sludge treatment − conductive sludge dryers

Conductive drying indirectly heats sludge by bringing the sludge particles into contact with an externally-heated surface

Conductive dryers related videos

Paddle dryer for sludge treatment Source: Klooth Alex / YouTube

Paddle dryer for sludge treatment

A video to demonstrate a paddle dryer for sludge in operation.

Conductive dryers features and blogs

HTC/AD integration flowsheet

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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Fig. 4. SP filtrate and acidified sludge samples

Phosphorus recovery by sludge acidification and dewatering

Figure 6. Pyrolysis process schematic

Sludge-to-energy recovery methods − a review

Feature combined hydrothermal carbonization header

Combined hydrothermal carbonization with anaerobic digestion:…

More Conductive dryers topics…

Convective dryers

Convective (or direct) dryers remove moisture from sludge by bringing the sludge particles into direct contact with hot gas

Belt dryers

Belt dryers comprise a conveyor belt which slowly transports the sludge solids through a stream of heated air

Flash dryers

Flash dryers use a rapid stream of rising hot air which both suspends and dries the solids.

Fluidised bed dryers

In fluidised-bed dryers the sludge particles are gently agitated and heated by a stream of upward-flowing pre-heated gas

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

Disc dryers

Disc dryers are based on vertical externally-heated discs or rings rotating in the sludge as it passes through the dryer.

Paddle dryers

Paddle dryers are based on externally-heated paddles rotating in the mass of sludge solids held in a stationary vessel

Solar dryers

Solar dryers comprise large greenhouses in which sludge is dried under the ambient conditions of the building.

Pelletizers

Pelletizers

Conditioning
Conditioning is the pretreatment of sludge upstream of thickening and dewatering to promote solid-liquid separation
- Heating
- Reagent dosing
Thickening
Thickening processes concentrate the sludge by removing part of the free water, such that the product can still be pumped
Dewatering
Dewatering processes mechanically remove a significant proportion of the sludge water to produce a 15-45% cake product
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…

Sludge stabilisation

Sludge stabilisation − alkaline stabilisation, lime and solids dosing, plus anaerobic and aerobic digestion

Thermochemical processes

Thermochemical methods are used to either significantly reduce the sludge solids content or pre-treat sludge upstream of AD

Sludge quality

Sludge is the main waste stream from the treatment of wastewater

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