Alternatives for Future Coal Waste Disposal - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 125

during the drying processes. Other dewatering methods being developed
include ceramic capillary filters, electro-acoustic dewatering, microwave
dewatering, vacuum pressure hybrid filters, and pulsating vacuum filters (B.
K.Parekh, University of Kentucky, personal communication, 2001).
Dewatering technologies represent one alternative to reduce the volume of
waste deposited in coal slurry impoundments, but they do not eliminate the
need for an impoundment. Many dewatering technologies are currently
available for specific applications, though none is likely to be universally
applicable. The committee believes that equipment vendors' current research
and development will lead to improvements in these technologies and that
operators of coal waste impoundments should monitor them carefully.
DIRECT UTILIZATION OF SLURRY
Slurry refuse can be utilized directly for power generation, either in
conventional boilers or with advanced combustion and gasification
technologies. These technologies have the advantage of turning a waste into a
resource. Some of them can reduce cleaning requirements for coal in the
preparation plant, but the use of low quality coal feed will increase the amount
of waste generated at the power plant.
Conventional Pulverized Coal-Fired Boilers
Direct utilization of fine coal waste in conventional pulverized coalfired
boilers is an important alternative to its disposal in an impoundment. This does
not require a significant change to the system of mining, cleaning, and burning
coal. However, use of this material presents significant challenges to existing
boilers, because the moisture content is high and the heating value and trace
element quantities are inconsistent (Harrison and Akers, 1997). If the fine waste
material alone does not meet the required specifications for end-users, it can
either be combined with a variety of other feeds, such as cleaned coal or
biomass, to achieve the desired fuel consistency or be agglomerated to improve
handling.
Fine coal is difficult to handle, even when dewatered, because it clogs
equipment and is dusty and explosive. Agglomeration technologies can
reconstitute the fine coal by briquetting, pelletizing, or extrusion and can solve
the handling and transportation problems. The advantages and disadvantages of
the various forms of agglomeration are summarized in Table 7.1 . Which
agglomeration technology is appropriate depends on the