Rapid Mix Burner™ Case Study 103
U.S. Borax
TODD Ultra Low Emissions
Burner Installation
The Situation
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Fig. 1
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In November 1994, a TODD® Combustion
Rapid Mix Burner (RMB), utilizing induced
Flue Gas Recirculation (FGR), was retrofitted
into a 21,500 lb/hr Nebraska boiler located at
the U.S. Borax facility in Wilmington, CA. The
RMB burner replaced an induced FGR
burner permitted for 30 ppm NOx and 400
ppm CO. The TODD retrofit consisted of
replacing the existing burner and fan, and
reusing the gas train and most of the control
system components. The objective was to
demonstrate the RMB's ability to operate at
less than 9 ppm NOx and CO across the load
range (5:1 turndown).
The Boiler
A natural gas only, 26 MMBtu/hr RMB
was installed on a Nebraska model NS-B-35
watertube boiler rated for 21,500 lb/hr
steam flow and equipped with an economizer.
The burner installation included the RMB, an
induced FGR system and windbox baffles to
provide uniform air distribution to the burner.
The characterizable fuel valve and air dampers
were physically linked to provide single-point
positioning control over the air / fuel ratio across
the load range, while the FGR damper had a
separate actuator and controller.
The TODD Result
The test results in fig. 2 illustrate the
burner performance with the boiler in
automatic operation. The FGR rate varied from
about 18% at low load to 25% at full load. The
NOx levels varied between 6 and 7 ppm over
the load range, while the CO varied from less
than 1 ppm at full load to approximately 3 ppm
at low load. The excess O2 varied from about
4.5% at low load to 3.2% at full load.
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| Fig. 2: Borax Data |
The flame length was approximately 6-ft
long, and the flame was extremely stable across
the entire load range. There was no measurable
impact on the boiler's efficiency. The burner
operates with a 6.5-in. draft loss and 5 psig
gas pressure at full load. The RMB burner on
this boiler has been in operation since
November 1994.
Third Party Test
On November 7, 1994, the boiler was
source-tested per SCAQMD protocol by the
Almega Corporation. The test results are
shown below. The CO and NOx numbers
are corrected to 3% O2.
Source Test Data
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| Load % |
O2% |
CO ppm |
NOx ppm |
|
| 25 |
3.4 |
3.0 |
8.2 |
|
| 53 |
2.6 |
0.9 |
7.1 |
|
| 98 |
2.7 |
0.1 |
6.8 |
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