Biomass and Coal Characteristics: Implications for Cofiring

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Biomass and Coal Characteristics Implications
for Cofiring

• David A. Tillman
• Foster Wheeler Power Group, Inc.
• Clinton, NJ 
•  

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Abstract
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Basis of the Analysis

• Fuel Characterization Research at The Energy
  Institute of Pennsylvania State University
• Proximate and Ultimate Analysis
• Drop Tube Reactor Testing (400 1700oC)
• Determine maximum volatile release
• Determine fuel reactivity
• Determine nitrogen and carbon volatile release
• 13C NMR Testing
• Develop Relationships to Full Scale Cofiring
  Testing

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Focus of the PSU Research

• Nitrogen Evolution from Solid Fuels Governs NOx
  Formation from Fuel Nitrogen
• NOx Control is Favored by Volatile Nitrogen
• NOx Control is Favored by Nitrogen Rapidly
  Evolving from the Fuel Mass
• Understanding Nitrogen Evolution Patterns can
  Assist in Explaining NOx Reduction with Biomass
  and Low Rank Coals
• Understanding Nitrogen Evolution Patterns for a
  Given Suite of Fuels can Influence Fuel Selection

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Support for this Research

• USDOE NETL and USDOE EERE in Sponsoring
  Biomass Cofiring Technology Assessment
• USDOE NETL, USDOE EERE, and EPRI in
  Sponsoring Cofiring Research and Demonstration
  Projects with a Variety of Coals in Cyclone and
  PC Boilers
• Albright Station, Willow Island Station
• Bailly Station, Michigan City Station
• Seward Station, Shawville Station
• Allen Fossil Plant, Colbert Fossil Plant

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Background Previous Studies

• Baxter et. al., 1995. Seminal Paper on Nitrogen
  Evolution from Coals as a Function of Residence
  Time
• Research for USDOE and EPRI, Sponsored by USDOE
  and Performed by The Energy Institute of
  Pennsylvania State University and by Foster
  Wheeler Power Group, Inc.

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Methodology - 1

• Select Representative Biomass Fuels
• Sawdust
• Urban Wood Waste
• Fresh Switchgrass
• Weathered Switchgrass
• Basis of Selection
• Commonly used in cofiring applications
• Represent woody and herbaceous biomass
• Select Reference Coals
• Black Thunder PRB
• Pittsburgh 8

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Methodology - 2

• Sawdust source West Virginia Willow Island
  Cofiring Project
• Urban Wood Waste source produced from a blend
  of plywood, particleboard, and paneling to be
  highly similar to the urban wood waste at Bailly
  Generating Station, with particular attention to
  nitrogen content
• Weathered Switchgrass source Gadsden, Alabama
  Southern Co. and Southern Research Institute
  Cofiring Project
• Fresh Switchgrass source Southern Co. and
  Auburn University

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Methodology - 3

• Characterize the Incoming Fuel
• Proximate and Ultimate Analysis
• Heating Value
• Air Dry and Grind Fuel
• Pyrolyze Fuel in Drop Tube Reactor (DTR)
• 400oC 1700oC
• Argon Environment
• Determine Distribution of Nitrogen in Incoming
  Fuel (volatile N vs char N)
• Determine Nitrogen, Carbon, and Total Volatile
  Evolution as a Function of Temperature

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Methodology - 4

• Basic Premise
• If nitrogen is in volatile form, and if nitrogen
  volatiles evolve more rapidly than carbon
  volatiles or total volatile matter, then NOx
  formation is more easily controlled by combustion
  mechanisms
• If nitrogen is in char form, or if nitrogen
  volatile evolution lags behind carbon volatile
  evolution or total volatile evolution, then NOx
  formation control by combustion mechanisms is
  more difficult and less effective

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Analysis of Biomass Fuels
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Distribution of Fuel Nitrogen
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Maximum Volatile Nitrogen Yield
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Sawdust Nitrogen and Carbon Volatile Yields
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Sawdust Nitrogen and Carbon Evolution Normalized
to Total Volatile Matter Evolution
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Nitrogen and Carbon Volatile Evolution from Urban
Wood Waste
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Nitrogen and Carbon Volatile Evolution from Fresh
Switchgrass
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Nitrogen and Carbon Volatile Evolution from
Weathered Switchgrass
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Nitrogen and Carbon Volatile Evolution from
Weathered Switchgrass Normalized to Total
Volatile Evolution
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Nitrogen and Carbon Evolution from Black Thunder
PRB Coal
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Nitrogen and Carbon Volatile Evolution from
Pittsburgh 8 Coal
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Nitrogen and Carbon Volatile Evolution from
Pittsburgh 8 Coal Normalized to Total Volatile
Yield
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Nitrogen/Carbon Atomic Ratios in Char Normalized
to N/C Ratio in Initial Fuel
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NOx Reductions at Albright
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NOx Reductions at Albright (2)

• NOx 0.361 0.0043(Cm) 0.022(EO2)
  0.00055(SOFA)
• Definitions
• Cm is cofiring percentage, mass basis 0 10
• EO2 is excess O2 at furnace exit (wet basis) 1
  4
• SOFA is separated overfire air damper positions
  for all 3 levels 0 240
• r2 0.87, 68 observations
• Probabilities of random occurrence equation,
  4.2x10-28 intercept, 2.3x10-24 Cm, 1.2x10-5
  EO2, 5.9x10-4 SOFA, 5.0x10-22

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NOx Reduction at Seward Station
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NOx Reduction at all EPRI Demos
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Conclusions

• Fuel reactivity is a key to NOx control using
  staged combustion
• Biomass fuels, in general, are highly reactive
  although weathering reduces nitrogen reactivity
  in switchgrass
• The relative reactivity of biomass, and various
  coals, can be used as a technique to evaluate
  potential in NOx management
• The DTR technique for analyzing fuels has
  significant benefits in evaluating initial
  combustion processes applied to NOx management