Coal/Natural Gas CoFiring
Solutions
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Coal/Natural Gas CoFiring Solutions
INTRODUCTION:
Faced with continued pressure from
the EPA, many small to medium
sized coal-fired generating stations
are facing economic uncertainty. Do
they invest in the high-capital-cost
systems needed to comply with NOx
and SO2 limits, do they operate on a
limited basis when demand allows or
do they close altogether.
Enhanced gas cofiring removes many of the
economic and environmental problems that face
coalfired generating assets
In the middle of this environmental
compliance dilemma sits natural gas.
Lauded by environmental interest
groups as the low cost, low emissions
alternative to coal, gas certainly
has its appeal. However, as recent
activity has shown, gas pricing can be
volatile, easily reaching two, or even
three, times the price of coal on a per
unit basis. Complete conversion from
coal to gas could be disastrous if gas
prices continue to rise.
Dual Orifice Cofiring, the key
component in Breen’s Enhanced Gas
Cofiring process, provides a reliable
NFPA Class 1 Igniter coupled with
a high volume, annular, secondary
gas supply. With the ability to control
natural gas heat input up to 35% of
Maximum Unit Continuous Rating,
significant improvements in Minimum
Unit Load, load control and emissions
per mmBTU can be realized.
It isn’t just the addition of variable
gas volume that makes Dual Orifice
Cofiring effective. Managing the
combination of coal, igniter and
cofire-gas fuel streams to create
the optimum environmental and
commercial result is a non-trivial
task. But the creation and control of a
viable, Enhanced Gas Cofiring system
will move your coal-fired asset into a
truly Fuel-Flexible plant.
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Environmental and Commercial Impact
A coal plant needs to burn coal to operate correctly. The emissivity of the
coal particles as they burn is assumed in the heat transfer surface design.
However, some portion of the coal can be replaced with cleaner burning
natural gas to capture the cost/enironmental benefits of both fuels.
The goal of EGC is to replace 35% of
the coal with gas as shown in this
diagram.
1. Placing 5% - 7% of the Unit heat
input as gas in the upper furnace
provides NOx reduction and SCR
benefits,
2. Placing 25% - 30% of the Unit MCR
heat input as gas at the burner level
provides dramatic flexibility in unit
turn-down,
3. Any amount of coal replaced with
natural gas provides a reduction in
SO2 /SO3, Hg, HCl, particulate and CO2
emissions
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Minimum Load Reduction
Environmental Impact
The ability of the unit to operate at its absolute minimum is critical in today’s operating environment. Coal-fired assets must be able to rapidly
adjust to changes in customer demand and to changing availability of wind and solar power.
Minimum load is generally driven by two major variables:
2. An NFPA driven need to maintain
two pulverizers in service.
Cofiring substantial quantities of gas at low load can relieve both of these
drivers. Replacing up to half of the total heat input with gas reduces the
amount of SO3 by a base of 50%, essentially eliminating the SO3 factor in the
MOT calculation.
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From an NFPA standpoint, replacing half of the heat input with gas essentially
replicates the presence of the heat input of one mill, eliminating the need for two.
Stack C02 (%)
Temperature
1 - 20% reduction in CO2
2 - 35% reduction in SO2/SO3
3 - 45% reduction in NOx
4 - 35% reduction in Particulate
5 - 35% reduction in Mercury
Stack C02 (%)
1. The SCR’s Minimum Operating
Replacing 35% of the coal input with
natural gas yields:
320
340
360
380
400
420
Load (MW)
440
460
480
0.45
Breen provides a variety of solutions for Acid Gas
Management and Fuel Flexibility.
NOx (lb/MMBTU)
0.4
0.35
0.3
0.25
NOx - Expected Achievable Control Level
0.2
0
1
2
3
4
5
6
7
8
GHI from Gas (%)
Our Enhanced Gas CoFiring solution may be your key
to low-cost compliance with today’s environmental and
economic demands.
Environmental Operating Co-Benefits
According to a 2010 study, the annual cost of operating wet FGD and SCR
equipment amounted to $135/Ton and $410/Ton respectively. A similar cost for
Hg is estimated at $5,000/Lb and SO3 requires almost $2,500/Ton to control.
Commercial Impact
Besides the positive environmental
effects, Enhanced Gas Cofiring has
two major commercial benefits:
1. Reduction in Unit Minimum Load
2. Reduction in Environmental Operating Costs
For fuel cost conditions where natural gas is less than $1.00/mmBTU more
expensive than coal, these environmental operating co-benefits actually offset
the added fuel cost.
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Co-benefit Areas Include: FGD Limestone Use, SCR Ammonia Use, Dry Sorbent
Use for SO3, Activated Carbon Use for Mercury control and reduced Byproduct
disposal costs for Scrubber sludge and flyash. Maintenance cost improvements
due to lower equipment loading and extended catalyst operating times can also
be considered.
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450
400
350
300
200
150
100
50
0
0%
10%
20% 30%
40%
50%
60%
70% 80%
90% 100%
% of Operating Observations (1 per hour)
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The Science Behind Dual Orifice Cofiring:
The concept of adding natural gas to a coal fired boiler is nothing new. Gas
igniters have been used for many years as both ignition and coal-flame
stabilization devices. But, with the rebirth of plentiful, and relatively inexpensive
natural gas, many plant operators want to add more gas to the mix.
The problem has historically been how and where to put this variable gas input.
Placing it at the igniter location has value since gas needs to be present there,
anyway. But placing 35% of the unit MCR heat input through a device designed
for 10% creates significant competition between the gas flame and the coal
flame for available oxygen.
Additionally, doubling, or tripling the gas throughput also places the resulting
flame near the center of the boiler, minimizing waterwall steam creation and
increasing superheat/reheat steam temperatures.
Dual Fuel Outlets
An NFPA Class 1
Core Igniter
An annular
gas outlet
surrounding the
core igniter
The core igniter is a fixed flow device
sized for the burner it supports.
The second, annular, gas outlet is
controlled separately and can be
fixed or variable depending on the
application.
The ratio between the two fuel outlets
is site specific to provide optimum
flame stabilization from the core and
variable, annular, flow to keep cofire
heat input near the walls for better
steam production and minimal coal
flame disruption
Breen Energy Solutions
104 Broadway Street
Carnegie, PA 15106
Direct: 412-431-4499
Fax: 412-431-4104
www.breenes.com
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