Fluidized bed combustion systems use a heated bed of sand-like material suspended
(fluidized) within a rising column of air to burn many types and classes of fuel. This
technique results in a vast improvement in combustion efficiency of high moisture content
fuels, and is adaptable to a variety of "waste" type fuels. The scrubbing action
of the bed material on the fuel particle enhances the combustion process by stripping away
the carbon dioxide and char layers that normally form around the fuel particle. This
allows oxygen to reach the combustible material much more readily and increases the rate
and efficiency of the combustion process.
Bed Recycle System
The key to EPI's dominance of the difficult waste fuel combustion market is our patented
bed recycle system. EPI is the only company that offers uniform bed drawdown, integrated
air cooling and automatic cleaning and reinjection of the bed material. This innovative
feature enables EPI systems to operate on fuels with significant quantities of 4-inch
minus noncombustible tramp material (contaminants such as rocks, metal etc.). In
grate-style systems, tramp material and ash slag can cause significant problems, requiring
a shutdown to correct. In other fluidized bed systems, tramp material can build to the
point that fluidization is no longer possible, allowing clinkers to form. In these
systems, a shutdown is usually also required to clean out the accumulation.
Complete and Efficient Combustion
The turbulence in the combustor vapor space, combined with the tumultuous scouring effect
and thermal inertia of the bed material, provide for complete, controlled and uniform
combustion. These factors are key to maximizing thermal efficiency, minimizing char, and
controlling emissions. The high efficiency of a fluid bed combustor makes it particularly
well suited to problem fuels with low Btu value and high moisture characteristics. EPI's
systems have consistently achieved high combustion efficiencies. In typical units, the
carbon burnout percentages within the combustor are well in excess of 99 percent.
Waste Fuel Diversity
EPI systems have operated on fuels as diverse as agricultural waste, municipal solid
waste, wood wastes, industrial and municipal sludges, plastic, tires and coal. Fluidized
bed systems are also capable of efficiently combusting fuels of varying consistency. EPI
units have demonstrated the ability to handle a variety of wastes within a single
combustor. EPI's San Joaquin Valley Energy Project units have logged operating time on
over 68 varieties of agricultural and urban wood waste. EPI's patented bed cleaning
system, which removes large non-combustible material from the bottom of the bed, allows
EPI units to burn otherwise problematic fuels with a minimal amount of processing.
Low Emissions
Emissions from a fluidized bed unit are inherently lower than conventional technologies
for the following reasons:
These features, combined with EPI's vast experience with a variety of fuels, have
allowed EPI units to comply with some of the most stringent air quality regulations in the
country, including six operating plants in California. EPI units have consistently been
accepted as the Best Available Control Technology "BACT" by environmental
regulatory agencies.
Favorable Ash Properties
The high combustion efficiency of a fluid bed results in a reduced amount of inorganic
material as fine ash. The remaining larger material consists mainly of non-combustibles,
such as rocks and wire brought in with the fuel, and coarse sand-like neutral particles.
Low combustion temperatures in the fluidized bed minimize the formation of toxic materials
that might go into the ash. Ash samples from EPI systems have consistently tested
nontoxic, and in many instances the ash is being sold as input for other products such as
cement.
Operating Flexibility
EPI's fluidized bed systems have demonstrated the ability to operate under a wide range of
load conditions. The thermal "fly-wheel" effect of the bed material allows
swings in moisture and heating content of the fuel to be absorbed by the system without
negative impact. Conversely, the low fuel inventory present in the unit makes it very
responsive to varying loads. The fluidized bed also maintains efficiency during system
turn-down. The operating flexibility demonstrated by existing EPI units has proven quite
valuable for some of EPI's customers allowing them to take advantage of utility incentive
programs for generation that follows electric demand.
Low Operating Costs
The lack of moving parts in a fluid bed reduces maintenance costs and down time. EPI units
have achieved operating availabilities above 98% and have kept operating costs relatively
low given the difficult fuels they are burning.
Environmentally Sound Energy Production from Waste
Fluidized bed combustion is an environmentally favorable, proven technology for disposal
of solid wastes and generation of energy. The combination of EPI's vast experience in
developing solutions for a wide variety of applications, with the favorable
characteristics of fluidized bed combustion make EPI the leader in providing
environmentally sound waste disposal solutions.
