This project determines the feasibility of using low grade power plant waste heat to dry lignite and sub-bituminous coals before they are burned in utility boilers. Fossil fuel steam plants reject large quantities of heat in the cooling water used to condense low pressure steam after it has exited the turbine. In this approach, the heat source for drying the coal is the hot circulating water leaving the condenser. Prior to the hot water entering the cooling tower to reject heat from the condensing steam, the water either flows directly to a coal dryer or an air stream is passed over the hot water to generate hot air to dry the coal, (see flow diagrams). This results in cooler water entering the cooling tower and therefore less evaporation of the water required to cool it to the required temperature for condensing the steam. Drying the coal prior to burning improves the heat rate and efficiency of the boiler since the associated water is not heated in the boiler. This also results in reduced air emissions from the boiler.

This investigation gathers data on low temperature drying kinetics for lignite and Powder River Basin (PRB) sub-bituminous coals and develops the drying models needed to design coal dryers. Both fluidized bed and fixed bed dryers are examined. It also determines the costs and performance impacts (reduction in cooling tower makeup water, heat rate, and emissions) of different drying system options.

The test site is the Great River Energy Corporation’s Coal Creek Generating Station in Underwood, North Dakota. There is an associated Clean Coal Power Initiative project, Lignite Fuel Enhancement [PDF-577KB]. This study assists with the design of a full-scale prototype dryer module for full power operation of one of the 546 MW units at the Coal Creek Station.