The Carver‐Greenfield Process: Dehydration/solvent extraction technology for waste treatment

Abstract

AbstractA combination dehydration/solvent extraction treatment technology, the proprietary Carver‐Greenfield (C‐G) Process, can be used to separate solid/liquid waste materials into three separate product streams convenient for reuse or disposal: clean, dry solids suitable for fixation of non‐hazardous landfilling; water virtually free of solids and oils which can be processed in an industrial or public wastewater treatment facility; and, oil indigenous to the feed, a mixture of extracted hydrocarbon‐soluble compounds which typically includes any hazardous contaminants which are present. As normally practiced, this dehydration/solvent extraction technology involves slurrying water‐wet waste in a hydrocarbon solvent which extracts indigenous oil from contaminated solid particles and concentrates it in the solvent phase. Dehydration also takes place during the treatment; water is evaporated and condensed as a separate product. Dry solids are reslurried in fresh solvent one or more additional times depending on the degree of extraction required. Extracted solids are centrifuged away from the solvent and residual solvent in the centrifuge cake vaporized off the final product solids stream in a desolventizer. Indigenous oil from the waste is separated from the solvent by distillation with recovered solvent being recycled to the process.For commercial applications, this process is very flexible in its ability to be efficiently adapted to waste processability and treatment objectives. For example, if the contaminants are very heavy organics like PCB's, they may be further concentrated in a portion of the indigenous oil such that only a very small highly concentrated contminant stream need be disposed of and uncontaminated oil may be recovered for a process credit. In some cases where the feed has a high water concentration, the dry solids need not be separated from the indigenous oil but they can be recovered/disposed of together.This dehydration/solvent extraction technology has been licensed to over 80 facilities over the past 30 years to solve waste disposal problems in a wide variety of fields. More than half of the plants were designed to dry and deoil slaghterhouse wastes (in rendering plants). The other units are used to evaporate water and extract indigenous oil from a broad spectrum of other materials, including municipal and industrial sewage sludges, wool scouring wastes, petrochemical sludges, wood‐pulp waste, pharmaceutical wastes, dairy and food products, textile wastes and animal manure.This paper discusses the C‐G Process flexibility and economics as applied to various hazardous waste examples including PCB contaminated sediments, soils and sludges, spent drilling fluids (U.S. EPA SITE Program), refinery wastes, manufactured gas plant (MGP) sites, etc.