POWER March 2013 - 31

FUELS
Honolulu Refuse Division Chief Manny
Lanuevo, the plant is now capable of processing
85% of Oahu's post-recycled municipal
solid waste and supplying up to10%
of the island's electricity needs (Figure 2).
The renewable power produced by the
plant is sold to Hawaiian Electric Co.
(HECO), offsetting its need to import about
one million barrels of oil each year. HECO
purchases electricity based upon a time-ofday
rate linked to a price index plus a 5
cents per kWh capacity payment. Uniquely,
the contract purchase price is lower than
HECO's current avoided cost, and HECO
passes the purchased electricity through to
its customers.
The original plant consists of two waterwall
furnace boilers (Boilers 1 and 2) with
reverse-traveling stoker grates that can
process up to approximately 2,100 tons per
day of refuse-derived fuel (RDF). The two
boilers produce steam for a single 57-MW
steam turbine (Turbine 1). Boilers 1 and 2
are fitted with a semi-dry flue gas scrubber
with lime injection and a fabric filter
baghouse.
The RDF is prepared by first preprocessing
municipal solid waste through a series
of conveyers and shredders for removal
of any nonprocessible and nonburnable
materials. The preprocessing system uses
magnets to pull ferrous metals (tin cans)
and uses eddy current separators to extract
nonferrous metals (aluminum cans) from
the waste stream for recycling. The volume
of ash produced by the boilers is one-tenth
of the volume of municipal waste volume
combusted (Figure 3).
A continuous emissions monitoring
system (CEMS) measures the stack gas
for emissions, such as carbon monoxide,
sulfur dioxide, nitrogen oxides, oxygen,
and opacity. The CEMS also sends signals
to the control room so that operators can
continuously monitor flue gas quality and
the performance of each boiler. The CEMS
data is electronically saved, reviewed, and
summarized into routine reports submitted
to the Hawaii Department of Health.
For the entire plant, exceedances are rare,
and the plant is routinely recognized by
the State of Hawaii for reliably meeting its
emissions limits.
Burn What Comes
Covanta Energy received a contract from
the City and County of Honolulu to design,
build, and operate the expanded facility in
mid-2009. Covanta hired Parsons Corp. as its
general contractor in December 2009 for the
fast-track project. Parsons was responsible
for plant design and engineering, installation,
and commissioning-all without interfering
with operation of the existing facility. Burns
& Roe provided process design services and
technical support to Covanta for direct purchase
of the plant's major equipment.
The expansion project added a Chinabased
Anhui Jinding Boiler Co. Ltd. massburn
boiler (Boiler 3) and a Siemens 33-MW
steam turbine (Turbine 2) that increased the
plant's solid waste processing capacity to
2. Outdoor plant. The structural steel in the center of the photo houses the new Boiler 3.
Moving from the boiler to the right is the spray dryer absorber (SDA) scrubber, the fabric filter
baghouse, and the stack. A continuous emissions monitoring house is located on top of the
stack inlet ductwork. The enclosed Boilers 1 and 2 are located behind Boiler 3, and the steam
turbine building is located in between. Courtesy: Covanta Energy
about 3,000 tons per day and electricity capacity
to 90 MW.
Additional equipment installed during
the expansion project included a Martin
GmbH reverse reciprocating grate system
that is integrated with the boiler, a tipping/
receiving building, and an AMEREX spray
dryer absorber (SDA) and a fabric filter
baghouse. The SDA uses a lime/water slurry
mixture to neutralize and cool acid gases,
such as sulfur dioxide and hydrogen chloride.
The fabric filter baghouse removes
particulate matter (fly ash) and provides a
secondary acid gas neutralization surface
on the filter cake. The stack of Boiler 3 is
monitored with a CEMS like that used on
Boilers 1 and 2. A Jervis B. Webb materialhandling
system collects the ash produced,
ready for transportation to the landfill.
The addition of a mass-burn boiler adjacent
to the two existing RDF-fueled boilers
provides increased operating flexibility
to the plant and is unique among the 40
municipal waste-fired plants that Covanta
owns and/or operates. Instead of preprocessing
solid wastes prior to burning, the
mass-burn boiler burns anything and everything
that is placed on the traveling grate.
For example, a mattress or tire placed on
the grate will burn to completion, and the
steel that remains is recycled, not sent to
the landfill. Covanta operators are now
able to direct large waste items to the new
Boiler 3 instead using landfill disposal, as
in the past (Figure 4).
Unique Operations Scheme
Increased operating flexibility is achieved
by using a combined steam header system;
that is, the steam from all three boilers is
piped to a common header from which
3. Remote fuel handling. Waste entering
the new section of the building is managed
by a remote-controlled overhead bridge
crane with an electro-hydraulic orange-peel
grapple directed by manipulation of joysticks
located in the new main control room. The
fuel for Boilers 1 and 2 is pushed on the floor
to the in-feed conveyors by loaders and bulldozers.
Courtesy: Covanta Energy
March 2013 | POWER
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POWER March 2013

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