Proceedings

ExelysTM Continuous Thermal Hydrolysis – from concept to reality to DFMA

Bigot, B., Gilbert, A. and Froom, M., Veolia Water Technologies, UK

(free)

Abstract:
Thermal hydrolysis is a well proven pre-treatment technology for sludge digestion which increases
digester throughput, pasteurises the sludge, enhances biogas production and reduces the final
biosolids volume for disposal. This paper will cover the evolution of the Exelys process from its conception in 2008, subsequent pilot trials and demonstration plants leading to its commercialisation. The paper will also reflect on the return on experience from the construction and operation of the first full scale plants and outline the development and completion of the DFMA project (Design for off site Manufacture and Assembly) to provide a standard range of ‘plug and play’ package ExelysTM plants for small to medium size plants. The paper will describe the technology, the design and product development process and the
advantages of the ExelysTM process compared to the traditional batch technologies on the market.

Introduction:
Veolia’s Thermal Hydrolysis processes include the traditional BioThelysTM batch process and the
ExelysTM process both of which fulfil the same process function to heat dewatered sludge to circa 165°C
and hold it at this temperature for 20 to 30 minutes.

ExelysTM differentiates from the existing TH process on the market by the fact that it is a continuous
process instead of a batch process. Therefore the retention volume is used for 100% of the time
whereas the batch reaction vessel needs to be filled and discharged, so is only effectively handling
sludge for between ~40% – 20% of the time. Thus the retained volume can treat twice to 5 times as
much sludge volume. In addition because the feed sludge is ~25% greater concentration than a batch
system can successfully process the overall solids treatment capacity is between ~3.1 – 6.25 greater
per unit reactor volume. Consequently the continuous ExelysTM system is much more than an
equivalent batch system and is much more compact. The advantages are a simpler processing
technology, with both continuous sludge feed and steady steam demand by the process, together with
the possibility to treat sludge with a high Dry Solids (DS) content significantly reducing the steam
demand per tonne of DS.

The Package ExelysTM range has four standard plants with dry solids capacities up to 30 t/day. The
plants have all the features of the Exelys process but are assembled at works off site on skids and
include feed sludge heating and steam injection equipment. Package ExelysTM is designed as a “Plugand-Play” system, fully tested before leaving the factory, minimising site installation and commissioning
time.

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