heat demand of the hospital. The O&M annual
expenditures
are
evaluated
at
approximately
0.01$CAN/kW
th
, which corresponds to approximately
CAN$400,000, given a heat utilization factor of 75% and
a cogeneration unit availability of 96% [25].
G. Waste-to-Energy Plant
In addition to generating large quantities of heat,
biomass can also be used to economically and viably
generate electricity, which is generally cost competitive
with other sources of electricity generation. In this
section, a case study is presented for a 14 MW
e
waste-to-
energy (WTE) plant operated by an organization called
“ecomaine” based in Portland, Maine, on the north-east
coast of the United States (USA) [26].
Based in the State of Maine (USA), ecomaine is a non-
profit waste disposal and recycling organization owned
and operated by 21 municipalities in Southern Maine,
USA.
In the State of Maine, residential garbage is separated
at the source (i.e. at the household level) into recyclable
materials and waste (items and materials which are not
recyclable). ecomaine’s WTE plant provides its owner-
municipalities with a practical and ecologically sensitive
disposal system for their waste.
For its part, waste energy is considered as a renewable
energy source in Maine. In addition, by converting waste
into electricity, the ecomaine’s WTE plant is able to
reduce the waste bulk by 90%. Revenue from the sales of
electricity (at an average of 0.035$US/kWh, sold on
short-term one-year bids), along with the collection of
tipping fees, contributes to underwriting the costs of the
operations of the WTE plant.
ecomaine’s WTE plant has an installed electrical
generating capacity of 14 MW
e
, whereas 2 MW
e
are used
in-house and for the organization’s recycling and waste
management facilities. Approximately 110,000 MWh of
electricity is generated annually, which is enough to
power 15,000 homes.
The WTE plant has two stocker grate boilers that are
operated independently in which, approximately 550 tons
of waste is burned on a daily basis. The plant operates in
a mass burn process and has a post burn recovery process
for the ash produced and items that have not been fully
incinerated. A single steam turbine is used to generate
electricity from the steam produced by both boilers.
Emission control systems, including an electrostatic
precipitator along with carbon, urea and lime slurry
injections, are used to minimize the plant’s emissions
which generally, are lower than the United States
Environmental Protection Agency (EPA) regulatory
standards. In contrast to other WTE plants that use front-
end processing of waste, which can cause the release of
pollutants before they reach their boilers, all pollutants
from ecomaine’s WTE plant are accounted for via the
stack monitoring devices due to the mass burn process
used by the plant. Finally, the resulting ash from the
waste-to-energy process is buried at the organization’s
nearby landfill site. Fig 2 shows a schematic of the WTE
plant process.
Fig. 2. Waste-to-energy plant process [19].
Between 30 to 40 employees are employed at the WTE
plant, which operates 365 days/year. Typically, 3 weeks
of general maintenance is required per year. The plant’s
boiler availability is generally above 91%.
For its part, the WTE plant is not operated as a
cogeneration facility: waste heat is evaporated at the
plant’s cooling tower because there is no economical
local end user for it. This is due to low natural gas prices
in the region.
Finally, ecomaine’s WTE plant is ISO14001 certified
for environmental management and has been named by
the American Society of Mechanical Engineers (ASME)
as Small Combustion Facility of the Year in 2009
because of its innovative and technical contributions to
solid waste processing environmental performance, and
health and safety records.
C
ONCLUSION
In this work, a methodology was presented for the
large scale assessment of biomass available over a
territory to determine the technical power potential of this
biomass for the commercial cogeneration of heat and
power in industrial-sized combined heat and power
plants. An application of the methodology, in regards to
forest biomass, was made for the province of New
Brunswick, Canada.
Results showed that the total annual potential harvest
of forest biomass in the study area is approximately 15.5
Mt green weight at harvest. In terms of electric and
thermal power potential, the findings indicated that if all
the forest biomass harvested annually in the study area
was to be used as fuel input in dedicated CHP plants, a
total of 1.2 GW
e
of electricity and 3.0 GW
th
of thermal
heat could be produced.
Finally, two case studies were presented of
commercial and industrial applications of biomass for
energy generation (heat and/or power). The first case
study consisted of a 5.25 MW forestry biomass-fired
cogeneration unit installed in a hospital, while the second
case study consisted of a 14 MW
e
municipal waste
biomass-fired waste-to-energy plant. These case studies
showed that biomass can be an economical alternative for
energy (heat and/or power) generation.
2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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