Immersion frying for the thermal drying of sewage sludge: An economic assessment

Abstract

This paper presents an economic study of a novel thermal fry-drying technology which transforms sewage sludge and recycled cooking oil (RCO) into a solid fuel. The process is shown to have significant potential advantage in terms of capital costs (by factors of several times) and comparable operating costs. Three potential variants of the process have been simulated and costed in terms of both capital and operating requirements for a commercial scale of operation. The differences are in the energy recovery systems, which include a simple condensation of the evaporated water and two different heat pump configurations. Simple condensation provides the simplest process, but the energy efficiency gain of an open heat pump offset this, making it economically somewhat more attractive. In terms of operating costs, current sludge dryers are dominated by maintenance and energy requirements, while for fry-drying these are comparatively small. Fry-drying running costs are dominated by provision of makeup waste oil. Cost reduction could focus on cheaper waste oil, e.g. from grease trap waste.

Simulation study of improved biomass drying efficiency for biomass gasification plants by integration of the water gas shift section in the drying process

“…Most technology solutions to improve the energy balance of the drying process are based on complex heat integration with heat pumps [5,6] or more often with steam recompression [7e10]. These solutions invariably lead to an additional electrical load, suffer from fouling and are expensive.…”

Analysis the fry-drying process of oily sludge sample

“…Consequently, the emigrating water evaporates inside the oily sludge and an evaporation interface is created. This drying process is known as the moving boundary problem or the Stefan problem (Peregrina et al, 2008). In fact, when water presented on the sample surface completely evaporates, two distinct regions are formed.…”

Technological options for the management of biosolids

“…Generally, all types of stabilized biosolids may be applied to land in the form of a liquid, slurry, dewatered cake, or as dried pellets. To minimize transport, handling, and spreading cost, a thermally dried biosolid product has an advantage over other forms (Peregrina et al 2008). To ensure sustainable land application of biosolids, regulators in most countries have set limits for biosolids and soil to eliminate pathogen activity and avoid accumulation of heavy metals and persistent organic compounds in soil (USEPA 1994;CEC 2000;NZWWA 2003;Laturnus et al 2007).…”