Processing preparation plant effluent using a packed column

Abstract

This paper presents the results of testing conducted to demonstrate the feasibility of using a packed column to recover clean coal from coal preparation plant waste (effluent) streams. The research program was funded by the Illinois Clean Coal Institute. In Phase I, effluent samples from four Illinois preparation plants containing between 50 and 60% ash were tested using a laboratory-scale column. Typically, clean coal containing 7-11% ash was recovered at Btu recoveries of 91-98% and pyritic sulfur rejection levels of 61-74%. In Phase II, a new sample collected from one of the plants was characterized prior to running bench-scale confirmatory tests at Michigan Technological University using a 4-in. I.D. × 10-ft tall column. The effluent sample, which contained 50-54% ash, was processed to recover clean coal containing 5-10% ash. A 4-in. I.D. × 20-ft tall column and other equipment were installed at the Illinois State Geological Survey's Applied Laboratory for pilot-scale testing. Extensive tests were conducted to study the effects of primary variables (feed rate, percent solids, and reagent dosage) and operating variables (air rate, wash water, and pulp level) with the objective of optimizing the packed column performance using feed rates ranging from 20 to 108 lb/hour. Typically, clean coal products containing 7-10% ash were obtained at 40% yield for column feed rates of 32.6-40.8 lb/hour. The best results were obtained at a feed rate of 35.5 lb/hour (407 lb/h/ft 2 ), with a clean coal product containing 5.3% ash and 2.52% total sulfur at 32.8% yield. The pyritic sulfur rejection level for this test was 87% at 87% Btu recovery.