Biomass Cofiring Overview

Biomass Cofiring Overview Larry Baxter Brigham Young University Provo, UT 84602 Second World Conference on Biomass for Energy, Industry, and World Climate Protection May 10-14, 2004 Rome, Italy

Biomass Energy Economics Typical Cost of Energy from Conventional Co-firing Combustion Cost of Electricity compared to feedstock prices, with various conditions, incentives, or subsidies Typical biomass Cost (US$ per ton) PTC proposed production tax credit Incentive, e.g., Green Pricing Premium Acknowledgement: Graph provided by Antares Group Inc

US Commercial Experience Over 40 commercial demonstrations Broad combination of fuel (residues, energy crops, herbaceous, woody), boiler (pc, stoker, cyclone), and amounts (1-20%). Good documentation on fuel handling, storage, preparation. Modest information on efficiency, emissions, economics. Almost no information on fireside behaviors, SCR impacts, etc.

Major Technical Cofiring Issues Fireside Issues Pollutant Formation Carbon Conversion Ash Management Corrosion SCR and other downstream impacts Balance of Process Issues Fuel Supply and Storage Fuel Preparation Ash Utilization Lab and field work indicate there are no irresolvable issues, but there are poor combinations of fuel, boiler, and operation.

Fuel Properties 2.0 1.5 Cellulose H:C Molar Ratio 1.0 0.5 Lignite Subbituminous Coal Bituminous Coal Semianthracite Lignin Wood Grass Average Biomass anthracite bituminous coal subbituminous coal semianthracite lignite biomass 0.0 Anthracite average values 0.0 0.2 0.4 0.6 0.8 1.0 O:C Molar Ratio

NO x Behavior Complex (No Surprises) NO Axial distance (cm) 0 50 100 150 300 450 450 350 350 50 100 200 450 450 150 250 100 350 50 200 350 450 500 Axial distance (cm) 0 50 100 150 50 50 100 150 100 200 200 250 300 250 350 450 350 0 50 100 300 550 500 100 100 50 50 250 200 100 300 350 250 350 150 600 500 550 550 350 450 450 550 600 600 600 150 350 150 150 200 300 350 350 350 200 450 450 200-20 0 20 Radial distance (cm) -20 0 20 Radial distance (cm) -30-20 -10 0 10 20 30 NH 3 Straw ( = 0.6) Coal ( = 0.9) 70:30 Straw:Coal ( = 0.9

Combustion History: Switchgrass 1 Volume (mm 3 ) 0.8 0.6 0.4 0.2 Heat & Dry Devolatilization Char Oxidation 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (s) Initial nominal diameter = 3 mm

Particle Shape Impacts 1.0 1.0 0.8 0.8 Mass Loss, daf 0.6 0.4 0.2 0.0 flake-like exp. flake-like model cylinder-like exp. cylinder-like model near-spherical exp. near-spherical model 0.6 0.4 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 Residence Time, s

Reaction Time vs. Yield Conversion Time, s 20 15 10 5 0 aspect ratio: flake-like - 4.0 (width/thickness) cylinder-like - 6.0 near-spherical-1.65 flake-like cylinder-like near-spherical 20 15 10 5 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Equivalent Diameter, mm

Cofiring Deposition

Deposition Rates Vary Widely Cofiring biomass can lead to either decrease or increase in deposition rates. Cofiring decreases deposition relative to neat fuels. 100 10 1 0.1 Wood Switchgrass Pittsburgh #8 Deposition Rate (gm deposit/kg fuel) Eastern Kentucky Straw Wheat Straw 0.01

Commercial Stoker Secondary Superheater Primary Superheater Boiler Generator Bank Slag Screen 1 5 Fuel Bin 2 3 Overfire Air Stoker Grate 4 Stokers

Deposits Dissimilar to Fuel 60 Mass Percent [-] 50 40 30 20 Fuel Ceiling/Corner Deposit 10 0 SiO2 Al2O3 TiO2 Fe2O3 CaO MgO Na2O K2O P2O5 SO3

Composition Maps Support Corrosion Hypothesis 100% Imperial Wheat Straw Cl S Fe 85% E. Kentucky 15% Wheat Straw

Fuel Properties Predict Corrosion Increasing Time

Oxygen Isosurfaces

BL mechanisms Inertial deposition flux [g/m 2 /h] BL deposition flux [g/m 2 /h]

Vapor deposition Vapor deposition flux [g/m 2 /h]

Flyash Impacts on Setting Time Penetration Resistance (psi) 6000 5000 0 3000 2000 1000 0-1000 Penetration Resistance vs. Time Pure Concrete Class F Wood Wood C Wood F Biomass 1 Biomass 2 Class C 0 100 200 300 500 600 700 800 Time (min)

Freeze Thaw Cycles Relative Dynamic Modulus of Elasticity (%) vs Freeze- Thaw Cycles Relative Dynamic Modulus of Elasticity (%) 102 100 98 96 94 92 90 88 86 84 Class F1 Wood 1 Wood C1 Wood F1 0 50 100 150 200 250 300 Number of Cycles

Required Aerating Agent oz/100 lbs cement 2.5 2 1.5 1 Pure Cement Class C Fly Ash (25%) Class F Fly Ash (25%) Co-fired Fly Ash (25%) (10% switchgrass) Co-fired Fly Ash (25%) (20% switchgrass) 0.5 0

Surface Conditions of Catalyst 1.4 1.2 1 0.8 0.6 0.4 0.2 Normalized Concentration 0 CaO S SO3 Na2O V2O3 Fresh(1) Fresh(2) Exposed(1) Exposed(2) Detection Limit

Basic Compounds Poison Catalysts Catalyst Activity vs. Na Poison Amount Activity (k/k0) 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0 0.5 1 1.5 2 2.5 3 Poison Ratio (Na:V) BYU wet BYU dry Chen et al.

Field Tests Indicate Little Poisoning Fractional Conversion, X 1.0 0.9 0.8 0.7 0.6 X NO fresh I X NH3 fresh I X NO fresh II X NH3 fresh II X NO exposed front X NH3 exposed front 0.5 0 6000 8000 10000 12000 10 Space Velocity (hr -1 )

Conclusions Major technical issues include fuel handling, storage, and preparation; NO x formation; deposition; corrosion; carbon conversion; striated flows; effects on ash; impacts on SCR and other downstream processes. Importance of these issues depends strongly on fuel, operating conditions, and boiler design. Proper choices of fuels (coal and biomass) and operating conditions can minimize or eliminate most impacts for most fuels. Ample short-term demonstrations illustrate fuel handling feasibility. Paucity of fireside and long-term data.

Summary Cofiring Statements Cofiring has been demonstrated succesfully in over 150 installations worldwide for most combinations of fuels and boiler types. Cofiring offers among the highest electrical conversion efficiencies of any biomass power option. Cofiring biomass residues in existing coal-fired boilers is among the lowest cost biomass power production options. Well-managed cofiring projects involve low technical risk. Cofiring biomass in existing coal-fired boilers provides an attractive approach to nearly every aspect of project development.

Outline Introduction Success stories Statements R&D&D for improvement Long term experience Fireside measurements in commercial scale facilities SCR deactivation Fly ash utilization Deposition and corrosion Striated flows Fuel specifications, preparations and limitations Public awareness/image Increasing cofiring percentages

Acknowledgements Financial support provided by the DOE/EE, EPRI, NREL, BYU, a dozen individual companies. Work performed by research group including four other faculty members, two post docs, ten graduate students, 30 undergraduate students.