Examples of the Application of Computational Fluid Dynamics

1
Examples of the Application of Computational
Fluid Dynamics

• Eric G. Eddings
• Dept. of Chemical Engineering
• University of Utah

2
Air Injection into Hot Gas Stream
Problem Need to determine the most effective
design for mixing overfire air with fuel-rich
combustion gases. Approach Utilize CFD
simulation of different nozzle designs and
pressures to identify best mixing scenario.
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Conditions Used in Calculations

• CFD mixing simulation of two streams
• Air at 450 F with varying velocities
• Flue gas at 2000 F with a vertical velocity of
  1200 ft/min (20 ft/sec)
• Computational Domain
• 20 ft long grate
• 3 ft wide section w/nozzle centered
• Nozzle details
• Circular 3 Sc 40 pipe
• Oval 3 Sc 40 pipe with 3 long spacers
• Velocities used
• 5 H2O 195.9 ft/sec
• 10 H2O 273.6 ft/sec
• 15 H2O 332.8 ft/sec

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Proposed Nozzle Geometries
3 inch Sc 40 Pipe
3 inch Sc 40 Pipe cut in half w/3 inch spacer
in between two halves
Goal increased penetration and mixing of
oxygen Constraint only have 3 inch gap between
boiler tubes
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Nozzle Penetration at 5 Static Head
Injection across 20 ft. grate
3 Circular Nozzle
3 Oval Nozzle
O2 Concentration
21
0
Note Oval nozzle has greater cross-sectional
area and thus injects greater mass of air
6
Nozzle Penetration at 10 Static Head
Injection across 20 ft. grate
3 Circular Nozzle
3 Oval Nozzle
O2 Concentration
21
0
Note Oval nozzle has greater cross-sectional
area and thus injects greater mass of air
7
Nozzle Penetration at 15 Static Head
Injection across 20 ft. grate
3 Circular Nozzle
3 Oval Nozzle
O2 Concentration
21
0
Note Oval nozzle has greater cross-sectional
area and thus injects greater mass of air
8
Opposed-Wall-Fired Boiler
Problem Low NOx Firing System retrofit resulted
in an increase in carbon loss. Approach Examine
pre- and post-retrofit simulations to identify
changes and to test possible solutions.
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NOx Carbon-in-Ash Before and After Retrofit
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Burner Layout - Front Wall
Overfire Air Level
Burner Levels
Underfire Air
Symmetric about Furnace Mid-Plane
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Low NOx Burner - Detail
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Boundary of Complete CF/SF Coal Pipe
Computational Domain
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Coal Nozzle Modeling
Particle Mass Density shown in color, along with
typical trajectories for three particle sizes 20
m, 65 m, 200 m.
Most of coal mass found in elipses.
Non-uniformity in mass loading at outlet due to
tangential inlet to coal nozzle.
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Boiler Simulation
Furnace Mid-Plane

• Used furnace symmetry - modeled half of boiler
• Over 500,000 computational cells.

Close-up of Burner Belt
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Burner Specific Carbon-in-Ash Pre-Retrofit
Front Wall
Rear Wall
0.08
0.08
0.03
0.03
0.13
0.07
0.13
0.07
0.04
0.04
0.12
0.12
0.02
0.04
0.02
0.04
0.00
0.00
0.00
0.00
0.01
0.00
0.01
0.00
computational symmetry plane
computational symmetry plane
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Burner Specific Carbon-in-Ash Post-Retrofit
Front Wall
Rear Wall
0.27
0.03
0.27
0.03
0.03
0.03
0.32
0.32
0.28
0.02
0.28
0.02
0.02
0.02
0.20
0.20
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
computational symmetry plane
computational symmetry plane
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Char Burnout - Rear Bottom Burner
Rear Wall
1.0
Fraction of Carbon Remaining
Particles Exiting Inner Annulus
Particles Exiting Outer Elipses
0.0
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Char Burnout - Rear Top Burner
Rear Wall
1.0
Fraction of Carbon Remaining
Particles Exiting Inner Annulus
Particles Exiting Outer Elipses
0.0
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Char Burnout - Front Top Burner
Front Wall
1.0
Fraction of Carbon Remaining
Particles Exiting Inner Annulus
Particles Exiting Outer Elipses
0.0
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Location of Wing Walls