The ELFUEL coal drying facility is designed to utilize the high heat
transfer characteristics of a moving packed bed counter-current heat
exchanger to efficiently "hot-water dry" lignite coal. Past research into hot
water drying of lignite indicates the process is energy inefficient, requiring
greater energy input than what can be extracted from the treated lignite.
The novel approach of the ELFUEL coal drying facility utilizes the high
heat transfer characteristics of a counter-current solid/liquid packed bed to
efficiently add and later remove heat to and from descending coal in a
pressurized cylindrical vessel. This approach uses raw coal continuously
descending in a vertical cylindrical refractory. Coal, upon entering the
refractory at the top, gradually heats to process temperatures near the
location of hot water injection through contact with hot water flowing
upward. Below the point of hot water injection, cool water is forced
upward past the descending coal to trap or conserve heat or energy in the
system. Sufficient energy is conserved by this design to economically
hot-water dry lignite coal.
Design of a counter-current energy efficient system which adds and
then removes heat has not been reported in the literature. Wonchala and
Wynnyckyj (1986) reports counter-current packed bed processes are common
in the metallurgical industries. Some important example include the iron
blast furnace and iron-ore pelletizing shaft furnace which are very useful
since they exhibit a very high potential heat transfer efficiency. However,
the metallurgical counter-current gas-solid heat exchangers have not been
found to be energy efficient due to channeling of hot gases (Wonchala and
It was the purpose of this study to determine whether the ELFUEL
coal drying facility outlined in Minnesota Power's proposal "ELFUEL
Demonstration of Low-Rank Coals" to the U. S. Department of Energy,
Clean Coal Technology, Round #3 will perform as described and meet the
objectives of the process, the economical hot-water drying of lignite coal.
Rindels, Alan J.; Gulliver, John S.; Wetzel, Joseph M.; Voller, Vaughan.
Analysis of the Elfuel Coal Drying Facility.
St. Anthony Falls Hydraulic Laboratory.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.