Convective dryers

Convective (or direct) dryers are the most commonly used type of dryer for removing moisture from sewage sludge using heat. The sludge particles are in direct contact with hot gas – air or steam – which provides the heat needed to evaporate the water. They can be configured as conveyer belts (belt dyers), fluidised beds, rotating drums, or flash (pneumatic) dryers. Belt, fluidised bed, rotating drum dryers are the most often used configurations in sewage sludge drying. Since these dryers demand a significant air volume, the air is often recirculated prior to venting to conserve energy.

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

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Sludge drying

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

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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

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.

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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

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

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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

Convective dryers related videos

Example of a flash dryer for drying slurries Source: Hosokawa Micron B.V. / YouTube

Example of a flash dryer for drying slurries

Animation demonstrating the workings of the flash dryer for drying slurries, from Hosokawa Micron B.V.

Convective 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