This paper describes the design of an experimental radio frequency (RF) heating system for efficiently heating waste activated sludge (WAS), a byproduct of wastewater treatment plants. Thermal pretreatment is used to increase the bio-gas yield from subsequent anaerobic processes which use WAS. The RF heating system operates at a frequency of 13.56 MHz and the frequency was selected based on a study of the electrical properties of WAS. RF heating has advantages over microwave heating including access to very efficient RF generators, and RF applicators can be designed to provide uniform heating through large load volumes, overcoming limitations of microwave heating which has a shallow penetration depth in the load. Experimental results for the RF heating system show a dc to RF power conversion efficiency of 85% and a power transfer efficiency from the amplifier to load of more than 86% over a temperature range from 20˚C to 120˚C.
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