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A S Jessup-Bould:

Pyrolysis Experience














Whilst I worked at OSC, the company built a plant for the pyrolysis of dried sewage sludge.

On the basis of my experience in gasification and gas cleaning I was often consulted during the design and commissioning phases of the project.

Once in operation, I was also consulted on how process performance could be improved.

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At CPL Biomass, now Novera Energy (Europe) Limited, I was the Process Engineer for a proposed pyrolysis plant for Suffolk Biomass Power Limited. The plant was designed to process short rotational coppice and forestry residues. The design was based on rotating kiln using performance data from a similar pilot unit being operated by CPL.

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 Illustrations by courtesy of Novera Energy (Europe) Limited








Process Description

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The proposed process involves handling and drying wood chips delivered to the site. Dried material is fed to three rotating kiln pyrolysis units fired by pyrolisis gas in normal operation, but capable of using natural gas for start-up. Waste heat is recovered from the flue gases and is used for combustion air preheating and steam generation.

Pyrolysis gas from the kilns is contaminated with various materials. Char also spills out from the gas producing end of the unit. The char is separated by gravity and leaves the system via cooling screws into skips for subsequent disposal.

The fouling nature of the hot pyrolysis gas, which contains a significant amount of tar, prohibits recovery of sensible heat. As a result, the produced gas is quenched with circulating water, tars recovered for re-sale and excess liquors treated prior to disposal.

Exhausters draw the gas from the quench towers for processing through electrostatic precipitators to remove the remaining tar droplets. Further conditioning of the gas takes place before it is fed to the gas engines.

Waste heat from the gas engine exhaust is used for combustion air preheating and wood chip drying.














Documents Produced

PFDs & mass balances.


Process & instrument data sheets.


Unit Operations

Wood drier.

Rotating pyrolysis chamber.


Gas quench tower.

Tar and liquor circulation and decantation.

Effluent treatment.


Fuels (producer gas; explosive / toxic).

Hot surfaces and materials (eg Char).





Fans / Blowers.

Electrostatic precipitators.

Power generation (Gas engines).

Steam raising system.

Solids cooling & mechanical conveying.