Potential use of biosolids-fuelled boilers to meet thermal demands of THP & sludge drying: PAPER & PRESENTATION

Merry, J., Stantec, UK



Restrictions to the UK practice of applying treated biosolids to agricultural land could require storage of biosolids for periods of several months, so drying and pelletising of digested sludge is being widely considered to reduce the associated storage requirements. If carbon considerations preclude fossil fuel use, biogas could be burnt to provide the heat for THP and sludge drying, but less than a third of the biogas would be available for upgrading to biomethane.

One alternative approach could be to burn the dried sludge pellets in a “biomass-fuelled boiler” (BFB), with energy balances demonstrating that sufficient steam would be generated to meet the thermal demands of both the THP and the dryer. For design resilience and operational flexibility, use of a biogasfuelled “assist” steam boiler in parallel is proposed, sized to meet the THP steam demand when the BFB is offline.

One potential drawback is that whilst there are existing full-scale BFBs fuelled with a mix of biosolids and biomass, there are no examples where biosolids only are burnt. Chemical analysis of the biosolids would be required to confirm concentrations of contaminants (e.g. heavy metals), and the fouling potential (soot and clinker formation).

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