Biomass Cofiring Overview

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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

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Biomass Energy Economics

Typical biomass Cost (US$ per ton)

Cost of Electricity compared to feedstock prices, with various conditions,

incentives, or subsidies

Typical Cost of Energy from Conventional Co-firing Combustion

Acknowledgement: Graph provided by Antares Group Inc

PTC – proposed production tax credit Incentive, e.g., Green Pricing Premium

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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.

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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

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Fuel Properties

2.0 1.5 1.0 0.5 0.0 H :C M o la r R a tio 1.0 0.8 0.6 0.4 0.2 0.0

O:C Molar Ratio

Semianthracite Bituminous Coal

Subbituminous CoalLignite

Anthracite Cellulose Average Biomass Wood Grass Lignin anthracite bituminous coal subbituminous coal semianthracite lignite biomass average values

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NO

_x

Behavior Complex (No Surprises)

200 150 100 50 0 A xi al di st anc e ( cm ) -20 0 20 Radial distance (cm) 500 450 450 450 450 450 400 40 0 400 40 0 400 400 40 0 350 350 350 350 35 0 35 0 35 0 350 300 300 250 20 0 ₂₀0 150 150 100 100 50 50 200 150 100 50 0 A xi al di st a nc e ( c m ) -20 0 20 Radial distance (cm) 450 450 45 0 400 400 400 400 4 00 400 400 400 400 400 400 350 350 300 250 250 200 200 150 150 100 100 50 50 200 150 100 50 0 -30 -20 -10 0 10 20 30 600 60 0 600 600 550 550 550 550 500 500 45 0 450 400 40 0 400 350 350 350 300 300 250 250 200 150 100 100 100 50 50

Straw ( = 0.6) Coal ( = 0.9) 70:30 Straw:Coal ( = 0.9

NO

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Combustion History: Switchgrass

0 0.2 0.4 0.6 0.8 1 0 0.5 1 1.5 2 2.5 3 3.5 4

V

ol

u

m

e (

m

3

)

Time (s)

Char Oxidation Devolatilization Heat & Dry

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Particle Shape Impacts

0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 M a ss L o ss, d af Residence Time, s flake-like exp. flake-like model cylinder-like exp. cylinder-like model near-spherical exp. near-spherical model

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Reaction Time vs. Yield

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 5 10 15 20 0 5 10 15 20 C onv er si on T im e, s Equivalent Diameter, mm flake-like cylinder-like near-spherical aspect ratio: flake-like - 4.0 (width/thickness) cylinder-like - 6.0 near-spherical-1.65

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Deposition Rates Vary Widely

• Cofiring biomass can lead to either decrease or increase in deposition rates. • Cofiring decreases deposition relative to neat fuels. 0.01 0.1 1 10 100 D e p os it io n R a te (g m d e p o s it /k g f u e l) Wo o d Sw it c h g ra s s St ra w W h e at S tr aw Pi tt s b u rgh # 8 E a s te rn Ke n tuc k y

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Commercial Stoker

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

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Deposits Dissimilar to Fuel

SiO2 Al2O3 TiO2 Fe2O3 CaO MgO Na2O K2O P2O5 SO3

0 10 20 30 40 50 60 M as s P er cent [-] Fuel Ceiling/Corner Deposit

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Composition Maps Support Corrosion

Hypothesis

Cl S Fe

100% Imperial Wheat Straw

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Fuel Properties Predict Corrosion

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BL mechanisms

BL deposition flux [g/m2_/h]

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Vapor deposition

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Flyash Impacts on Setting Time

Penetration Resistance vs. Time

-1000 0 1000 2000 3000 4000 5000 6000 0 100 200 300 400 500 600 700 800 Time (min) P e n et rat io n R e si st a n c e (p s i) Pure Concrete Class F Wood Wood C Wood F Biomass 1 Biomass 2 Class C

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Freeze Thaw Cycles

Relative Dynamic Modulus of Elasticity (%) vs Freeze-Thaw Cycles 84 86 88 90 92 94 96 98 100 102 0 50 100 150 200 250 300 Number of Cycles R e lat iv e D y n a m ic M o d u lu s o f E la s ti c ity (% ) Class F1 Wood 1 Wood C1 Wood F1

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Required Aerating Agent

0 0.5 1 1.5 2 2.5 oz /1 00 l bs c em en t 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)

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Surface Conditions of Catalyst

0 0.2 0.4 0.6 0.8 1 1.2 1.4 No rmal iz ed C on cent rat ion Fr esh( 1) Fr esh( 2) Expo sed( 1) Expo sed( 2) Det ect ion Li mit CaO S SO3 Na2O V2O3

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Basic Compounds Poison Catalysts

Catalyst Activity vs. Na Poison Amount

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 0.5 1 1.5 2 2.5 3

Poison Ratio (Na:V)

A ct ivi ty ( k/ k0) BYU wet BYU dry Chen et al.

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Field Tests Indicate Little Poisoning

1.0 0.9 0.8 0.7 0.6 0.5 F ra ct io na l C on ver si o n, X 14000 12000 10000 8000 6000 4000 Space Velocity (hr-1) X NO fresh I X NH3 fresh I X NO fresh II X NH3 fresh II X NO exposed front X NH3 exposed front

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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.

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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

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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

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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.