PILOT-SCALE STUDY AND DESIGN OF A GRANULAR ACTIVATED CARBON REGENERATION PROCESS USING SUPERCRITICAL FLUIDS

A technology which has great potential for environmental control and w aste remediation is contaminant removal and separation with supercriti cal fluids (SCF's) or supercritical fluid extraction (SFE). Pressure t uning of solvent power allows SCF processes to adapt to a wide variety of small batch oriented separations typified by environmental cleanup operations. The ability of supercritical CO2 to extract model contami nant compounds from GAC and subsequently drop out most of the contamin ant in a liquid phase has been investigated in a pilot scale apparatus . Typical desorption profiles indicate an 85% removal of the compound from the carbon which allows for reuse. The desorption results have be en interpreted with a generalized desorption-mass transfer model. The results of the pilot plant studies have been applied to the design of a fixed-site GAC regeneration unit consisting of a three-element desor ber with two-stage flash separation. Optimization of the process cente rs around minimizing the cost of recycling the SCF through an efficien t recompression scheme and cycle configuration in the desorber unit. A n economic evaluation shows a processing cost of 10.6cent/lb (23cent/k g) GAC which compares favorably with thermal regeneration and incinera tion. This non-destructive process allows re-use of the GAC while main taining a high adsorbate capacity, which reduces carbon replacement co sts and significantly decreases the need for carbon disposal by landfi ll or incineration.