Recent Developments in Wet Carbonization of Peat

摘要

Wet carbonization is a generic term for a thermal beneficiation process in which wet peat is heated to temperatures of 150 to 325 deg C at elevated pressures so that water present remains in liquid form. Wet carbonization produces a solid product with a higher heating value than raw peat. Wet-carbonized peat can be mechanically dewatered to a significantly lower moisture content than raw peat. A continuous-flow Process Research Unit (PRU), capable of processing 375 kg/h of peat slurry at temperatures and pressures up to 290 deg C and 7.60 MPa, respectively, was used to study the effect of wet-carbonization operating conditions on the peat. Thirteen tests were made with peats from Minnesota and Maine. For the Minnesota peat tests, the feed slurry solids concentration ranged from 6.1 to 13.7%. The average reactor operating temperatures and residence times ranged from 175 to 260 deg C and 1 to 60 minutes, respectively. The heating value enhancement of the wet-carbonized peats was as high as 21%, and the moisture content of mechanically-dewatered wet-carbonized peat was as low as 39% (compared with >65% for raw peat). A bench-scale, continuous two-phase anaerobic digestion system to recover energy and to treat wet-carbonization effluent water was designed, fabricated, and tested with effluent water from the PRU tests. At a short hydraulic retention time of 2.9 days, the system provided COD and BOD sub 5 removal efficiencies of 56 and 75%, respectively. The methane yield was approximately 86% of the average ultimate biodegradable yield. 6 refs., 10 figs., 2 tabs. (ERA citation 12:015274)