Ben Kumfer Scott Skeen Richard Axelbaum Laboratory for Advanced Combustion & Energy Research

1. Cofiring of Coal and Biomass Under Oxycombustion Conditions: NOx Formation and PM Characterization Ben Kumfer Scott Skeen Richard Axelbaum Laboratory for Advanced Combustion & Energy Research Dept. of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, MO

2. Oxy-Fuel with Carbon Capture CO2 • High CO2 concentration in flue gas • Parasitic load for air-separation • Large reduction in NOx can result through RFG • Potential for improved boiler efficiency [CO2] > 95% (dry) FGR N2 air purification air separation unit compression O2 • Cofiring Biomass: • Potentially Carbon negative means of power generation • Utilizes renewable fuels coal geo - sequestration biomass

3. Conventional vs. Oxy-Combustion Conventional Coal/Air Combustion Oxy-Coal Combustion air Secondary O2+RFG Secondary Primary coal+air Primary fuel+RFG+O2 air Secondary O2+RFG Secondary Questions: • Is there an optimum set of PO and SO compositions for NOx? • What is the influence of oxy-combustion on ash properties? • What are the consequences of cofiring biomass under air-fired and oxy-combustion conditions?

4. diffusion dryer ELPI 30 kW, Horizontally-Fired Test System • Instruments (Thermo Inc): • 100:1 Dilution probe system for gas sampling • CEM w/ chemiluminescence NOx analyzer • Dekati ELPI particle analyzer • Fuels: • Coal: Powder River Basin, HV = 30 MJ/kg • Waste Sawdust, HV = 22 MJ/kg

5. Fuel Properties coal 10 µm sawdust 10 µm

6. SO coal+PO SO Air-Fired Results: Variable Primary Stoichiometry Constant Thermal Input Constant PO Flow Rate SO flow: axial tangential (full swirl)

7. SO coal+PO SO Effects of Variable Secondary Swirl Air-fired vs. Oxy-combustion = 5.2 m3/hr Run conditions: synthetic oxidizer: 30%(v) O2, 70% CO2, in PO and SO 3%(v) O2 in exhaust 30 kW SO_tangential / SO_total

8. SO coal+PO SO Variable [O2] in PO and SO axial SO tangential SO tangential SO 30 kW 3%(v) O2 in exhaust constant total O2:CO2

9. Sawdust Cofiring sawdust sieved 20 mesh sawdust sieved 50 mesh

10. Summary: NOx Nitric oxide emissions are strongly dependent on flame attachment Flow rate reductions required under oxy-fuel conditions can dramatically influence flame hydrodynamics and thus NOx An optimum PO & SO composition was observed Fuel particle size is an important consideration for NOx when cofiring with biomass.

11. PM Size Distribution & Morphology 100% coal dpaero = 5.18 µm cofired, (50% wt. sawdust) dpaero = 5.18 µm cofired, (50% wt. sawdust) dpaero = 330 nm 5.0 µm 5.0 µm 1.0 µm

12. Elemental Analysis: Oxycoal

13. Elemental Analysis: Cofired

14. Effect of Temperature • Oxidizer is a mixture of O2 and CO2 • Formation of submicron PM increases with O2 concentration. • This effect is due to increased combustion temperature.

15. Acknowledgments Consortium for Clean Coal Utilization at Washington University http://www.c3u.wustl.edu/ DOE UCR Program Ameren UE

16. Extras Base/Acid ratio, an indication of slagging propensity, is higher in submicron PM. B/A = (Fe2O3+CaO+MgO+Na2O+K2O)/(Al2O3+SiO2+TiO2)

17. Effect of Temperature

18. SO coal+PO SO Critical PO Stoichiometry • No SO Swirl • 40 vol.% O2 in PO • 28 vol.% O2 in SO • Vary thermal input (i.e. vary λPO)