POWER October 2013 - 46

COAL-TO-GAS CONVERSIONS
2. Just add gas. Modifications to the
tangent-fired burners to burn natural gas are
common and usually require minimal modification
to the existing corner buckets. The existing
coal buckets are often retained with no changes.
Courtesy: Combustion Components Associates
Table 1. Comparison of NOx reduction technologies in descending order
of NOx removal cost. Typical uncontrolled NOx emissions from a natural gas boiler
range from 0.12 to 0.3 lb/million Btu depending on boiler type and furnace design. The control
methods described in this article can be layered to further reduce NOx emissions to approximately
0.04 lb/million Btu. Source: Combustion Components Associates
NOx reduction method
Reduced excess air
Low-NOx burners
Overfire air/burners out of service
Flue gas recirculation
Separated overfire air and flue gas recirculation
Selective catalytic reduction
Selective noncatalytic reduction
to coal or oil. The cycling of burners in and out
as load swings can also be reduced.
Tangent-fired burners perform differently
than wall-fired burners. In wall-fired boilers,
each flame is independently controlled, but
tangential-fired burners are designed so that
each level of four burners function as a single
burner. Each corner has nozzles ( " buckets " )
providing combustion air and fuel into the
furnace. Tangent-fired burner designs also
permit firing of coal, oil, or gas using an integrated
burner design (Figure 2).
Low-NOx
gas and coal modifications are
possible by incorporating current generation
swirlers to stabilize a core flame and enhance
fuel staging
Emissions Control Methods
Refueling with natural gas will most likely
necessitate meeting emissions limits for NOx
Approximate percentage decrease in NOx,
compared to conventional gas burners
0-20%
25%
25%
25-75%
50-80%
90%
30%
in natural gas fired boilers. Low-NOx
nologies include: low-NOx
techburners,
overfire
(OFA), separated overfire air (SOFA), burners
out of service (BOOS), flue gas recirculation
(FGR), selective catalytic (SCR), and
non-catalytic reduction (SNCR). Table 1
summarizes the NOx
reduction capability and
cost of each option.
Low-NOx Burners. Fuel staging, air stag.
There
are several technologies available on
the market today to control NOx
formation
ing, balancing, and air/fuel ratio control are all
techniques that low-NOx
burners use. Proper air
and fuel flow distribution between burners is
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POWER October 2013

Table of Contents for the Digital Edition of POWER October 2013

Contents
POWER October 2013 - Cover1
POWER October 2013 - Cover2
POWER October 2013 - Contents
POWER October 2013 - 2
POWER October 2013 - 3
POWER October 2013 - 4
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POWER October 2013 - Cover3
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