200 psig. Combustion temperature of
the flame inside the firebox is around
2,200 F, and flue gas leaving the boilers
is 450-550 F.
While the mezzanine floor was under
construction, Super Radiator Coils began
manufacturing two sets of four condensing heat exchanger coils, one set each for
boilers No. 5 and 6, which were the first
to be upgraded. The condensing heat
exchangers were part of BAE’s exclusive
CondiMax® system as well as the firm’s
CataMizers®, both of which were custom-designed for the boilers at Pearl.
A CataMizer combines a selective
catalytic reduction system with a high-efficiency economizer coil that uses
small-diameter tubes and small tightly
spaced fins, weighs about 4,000 lb and
stands only 14 inches high. It also operates at a much lower approach temperature than a typical standard economizer,
which weighs 25,000-30,000 lb and
stands 6 ft tall.
Prior to the 1960s, standard economizers were designed for use with boilers that burned high sulfur and thick No.
6 diesel oil. Economizer coils were manufactured with large-diameter tubes to
minimize condensation that would create sulfuric acid when mixed with SO2.
They also used large fin spacing for easy
cleaning to prevent clogging from ash. If
standard economizers had been used to
upgrade Pearl, the roof would have needed to be raised to make room.
Courtesy Super Radiator Coils.
No Entryway? No Problem
Champion International, based in
Modesto, Calif., fabricated the stainless
steel housing for the heat recovery systems, emissions controls and chambers
for the coils to generate condensate.
About the same time, a Toronto contractor opened a large hole in the wall at
Pearl for new equipment to be hoisted by
a crane through the wall and set directly
on the new mezzanine floor. Steel doors
soon covered the new entryway.
By March 2011, system upgrades for
boilers No. 5 and 6 were completed and
commissioned. Early results showed an
increase in combustion efficiency from
79 percent to 96 percent and a reduction
in stack temperature from 550 F to 95 F
with no precooling.
Large stainless steel coils like these are used by each boiler to produce condensate.
The efficiency increase will boost
the output of the boilers to more than
120,000 lb/hr and would save 11. 5 billion Btu per boiler, if operated for a full
170-day heating season. At CAN$7 per
MMBtu per hour, each boiler would save
approximately CAN$3,840 per day and
CAN$652,000 per heating season with a
combined savings for all eight boilers of
more than CAN$5.2 million. In addition,
Enwave will receive incentives of
CAN$100,000 per boiler from Enbridge
Gas Toronto.
Since March, NOx emissions from
boilers No. 5 and 6 plummeted from
130 ppm to less than 3 ppm, and carbon
dioxide was reduced by an estimated
2,000 metric tons per year. In addition,
the plume was virtually eliminated from
the stack by extracting up to 95 percent
of the water that is formed as a byprod-uct of combustion in the boilers.
NOx emissions plummeted,
carbon dioxide was reduced,
and the plume was virtually
eliminated from the stack.
The next major phase of the upgrading project at Pearl was dismantling and
