Engineering Development of Advanced Physical Fine Coal Cleaning for Premium Fuel Applications: Task 9 - Selective agglomeration Module Testing and Evaluation.

The primary goal of this project was the engineering development of two advanced physical fine coal cleaning processes, column flotation and selective agglomeration, for premium fuel applications. The project scope included laboratory research and bench-scale testing of both processes on six coals to optimize the processes, followed by the design, construction, and operation of a 2 t/hr process development unit (PDU). The project began in October, 1992, and is scheduled for completion by September 1997. This report summarizes the findings of all the selective agglomeration (SA) test work performed with emphasis on the results of the PDU SA Module testing. Two light hydrocarbons, heptane and pentane, were tested as agglomerants in the laboratory research program which investigated two reactor design concepts: a conventional two-stage agglomeration circuit and a unitized reactor that combined the high- and low-shear operations in one vessel. The results were used to design and build a 25 lb/hr bench-scale unit with two-stage agglomeration. The unit also included a steam stripping and condensation circuit for recovery and recycle of heptane. It was tested on six coals to determine the optimum grind and other process conditions that resulted in the recovery of about 99% of the energy while producing low ash (1-2 lb/MBtu) products. The fineness of the grind was the most important variable with the D80 (80% passing size) varying in the 12 to 68 micron range. All the clean coals could be formulated into coal-water-slurry-fuels with acceptable properties. The bench-scale results were used for the conceptual and detailed design of the PDU SA Module which was integrated with the existing grinding and dewatering circuits. The PDU was operated for about 9 months. During the first three months, the shakedown testing was performed to fine tune the operation and control of various equipment. This was followed by parametric testing, optimization/confirmatory testing, and finally a 72-hour round the clock production run for each of the three project coals (Hiawatha, Taggart, and Indiana VII). The parametric testing results confirmed that the Taggart coal ground to a D80 of 30 microns could be cleaned to 1 lb ash/MBtu, whereas the Hiawatha and Indiana Vil coals had to be ground to D80s of 40 and 20 microns, respectively, to be cleaned to 2 lb ash/MBtu. The percent solids, residence time, shear intensity (impeller tip speed and energy input per unit volume), and heptane dosage were the main variables that affected successful operation (phase inversion or microagglomerate formation in the high-shear reactor and their growth to 2-3 mm in size during low shear). Downward inclination of the vibrating screen and adequate spray water helped produce the low ash products. Btu recoveries were consistently greater than 98%. Two-stage steam stripping achieved about 99% heptane recovery for recycle to the process. Residual hydrocarbon concentrations were in the 3000 to 5000 ppm range on a dry solids basis