In-Plant
Coal Handling System Modification Study
for
Tri-State G&T's 110 MWe Nucla
Station
Client
Tri-State Generation & Transmission Association
Nucla Plant
P.O. Box 698
Nucla, Colorado
Completion Date
May, 1995
Project Description
The Nucla Station originally consisted of three 1959
vintage, 36 (3 x 12) MWe, stoker-fired boilers. In
1988, the stokers were replaced by a new, dual combustor, 110 MWe AFBC boiler. A new 74 MWe
topping steam turbine/generator, with extraction to the existing turbines, was
installed at that time.
The in-plant coal handling system of the Nucla Station was altered in 1985. Pyropower
Corporation of San Diego, California designed an extension to accommodate the
AFBC combustors. Later
modifications, the addition of a sampling system and revamping of the conveyor
drives and platforms were also completed.
Tri-State
engaged Energy Associates to investigate improvements for the in-plant coal
handling system, which was part of the 1985 AFBC addition. This portion of the
conveying system consisted of Stephens-Adamson Redler
conveyors and tertiary crushers. The Redler conveyors
featured an en-mass conveying design that allows these conveyors to elevate
coal at a 66 degree incline. The plant was, however, experiencing wear and
other problems with these conveyors. The conveyors were operating 20 hours per
day. The plant considered conventional
belt conveyors to be more reliable.
Belt conveyors are used on the unloading, stacking, and reclaim portions
of the coal handling system.
Several alternative configurations for new
conveyors were investigated. The
steep incline of the existing Redler conveyors
dictated a configuration favoring high angle conveying technology. Accordingly,
the substitution of high angle belt conveyors for the Redler
conveyors was evaluated as a primary candidate improvement. Since belt conveyors require more space
than the Redler conveyors, structural modifications
to the building structures would be necessary. To minimize these modifications,
improved en-mass conveyors were also considered. Since the tertiary crushers represented
a bottleneck in the in-plant system, the ability to increase the capacity of
the existing crushers and substitution of new higher capacity crushers were
investigated. One alternative was
selected by Tri-State as best meeting their operating objectives. These modifications were approved by
Tri-State for a 1996 construction program.
The modification utilizes high-angle conveyor technology. One of the steeply inclined en-mass
conveyors is being removed and a "C" high-angle conveyor
configuration is being added. Other
changes include the elimination of a surge bin, addition of a splitter gate,
and replacement of horizontal drag conveyors with belt conveyors.