Comparing Thermal Hydrolysis Processes (CAMBI™ and EXELYS™) For Solids Pretreatmet Prior To Anaerobic Digestion

Abstract

Thermal hydrolysis is a sludge conditioning process applied to dewatered cake upstream of anaerobic digestion. The advantages of thermal hydrolysis are producing a Class A biosolids product, making residuals more digestible, and improving the dewatering characteristics of the resulting biosolids. Applying thermal hydrolysis to dewatered cake significantly reduces the viscosity allowing digesters to operate at much higher solids contents than conventional digesters significantly reducing volume requirements. There are currently two commercially available thermal hydrolysis processes, Cambi and Exelys (which is the second generation of Biothelys). They both apply pressure (120-130 psi) and temperature (330°F) for a set retention time of about 30 minutes to hydrolyze the solids prior to digestion. The major difference between the two processes is that Cambi consists of a series of batch tanks while Exelys utilizes a continuous plug flow reactor. The Cambi process is a more established technology with more than 25 installations worldwide while the Exelys process is still new with only one demonstration plant. The thermal hydrolysis process is normally applied as a pretreatment to anaerobic digesters in the Lysis -Digestion (LD) mode, however, the Exelys process can also be placed between two digestion steps which is known as the Digestion -Lysis -Digestion (DLD) mode of operation. Results from a desktop study for a "green field" 40 dtpd plant indicate that both thermal hydrolysis processes in the LD mode are economically favorable when compared to conventional mesophilic digestion; however, Exelys LD provides a thermal hydrolysis solution at a lower cost yielding a more favorable life cycle cost then the more traditional Cambi process. The Exelys system in the DLD mode was not found to be economically favorable for a "green field" system.

Economics

“…It should be noted that cost analyses are geographically dependent and subsequently difficult to apply. Other studies have also shown costing data for thermal hydrolysis facilities (Abu-Orf & Goss, 2012;Childress et al, 2019;Goss, 2015;Jolly & Gillard, 2009;Loomis et al, 2016;Smith & Rus, 2019;Van Horn 2015;Williams, 2014) but some of these vary significantly even for projects of similar size and scope. The project in Medina, Ohio (Childress et al, 2019) cost $35 million USD for a facility with a design capacity of approximately 20 t DS/d.…”

Anaerobic Digestion for Producing Renewable Energy—The Evolution of This Technology in a New Uncertain Scenario

“…Batch processes are well developed and several years of experience have been gained in the operation of these units. The future development of thermal hydrolysis of lignocellulosic biomass under continuous operation should be closely related to those designs that are currently being tested under industrial large scale for continuous thermal pre-treatment of sludge [ 12 , 178 ] operating at high solid content as the Cambi Solidstream ® (Cambi, Asker, Norway) process [ 179 ].…”

“…The first full-scale plant for sludge disintegration through the Cambi process was started in Hamar, Norway, in 1995 [ 11 ]. Since then, this company has installed several other plants worldwide [ 12 ]. Other commercial technologies include BioThelys™, which is a batch technology just as it is the Cambi TM Process (Cambi, Asker, Norway) [ 13 ].…”

A Review of Pretreatment Methods to Enhance Solids Reduction during Anaerobic Digestion of Municipal Wastewater Sludges and the Resulting Digester Performance: Implications to Future Urban Biorefineries

“…The former process uses a series of batch units and the latter uses a continuous plug flow reactor. Cambi process has more application history because it has been commercially available for a longer period; however, the Exelys process shows potential as it is reported to have a lower capital investment compared to the Cambi process [36].…”