Southern Company Biomass Co-firing Research

Southern Company Biomass Co-firing

Research

Doug Boylan & Steve Wilson Southern Company

Bill Zemo Alabama Power

Kathy Russell Georgia Power

Southern Company Participants

Switchgrass Co-firingSponsors and Participants

•Southern Company•Auburn University•EPRI•Southern Research

Institute•Wilson Farms•Sunbelt Expo•U.S. DOE•McBurney

Plant StaffGadsden and Mitchell

Co-milling - mix biomass with coal and introduce into the furnace through the coal handling system

• Simple procedure• Reduced capital cost• Reduced transport cost • Considerable system experience

Direct injection - introduce ground biomass pneumatically into the furnace through dedicated burners

• Higher co-firing percentages• Direct biomass control

Biomass Co-firing Technologies

Co-Milling Switchgrass and Coal

Coal does not flow when mixed with low percentages of grass

Pellet Co-firing –Potential Advantages

• Improved efficiency• Reduced plant capital• Reduced transportation• Reduced labor• Reduced dust

Cubing Setup - Switchgrass farm in Lincoln,

AL

Cubes sensitive to • Moisture• Binder type and

percentage• Grass type and rate

Mitchell – Cube Combustion

•One week of testing completed•Cubes handle and burn fairly well•Serious bunker issues– Rat-holing

Tub grinder

Metering Bin

Transport Fan

3 Levels of coal at each corner

Boiler

Pneumatic Transport Lines

Upper Grass Burner

Lower Grass Burner (not connected)

Switchgrass Bales

Upper Grass Burner

Switchgrass Co-firing Schematic

Gadsden – Co-Firing Facilities

Gadsden – Co-Firing Facilities

82.883

83.283.483.683.8

8484.284.484.684.8

85

2 2.5 3 3.5 4

Furnace Exit O2

Bo

iler

Eff

icie

ncy

zero

u65

l65

82.883

83.283.483.683.8

8484.284.484.684.8

85

2 2.5 3 3.5 4

Furnace Exit O2

Bo

iler

Eff

icie

ncy

zero

u65

l65

(Full Load - 7% by heat input)

Switchgrass Co-firing and Boiler Efficiency

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

0 28 56 84 112 140 168 196 224 252 280 308 336 364

Time (days)Co

mpre

ssive

Stre

ngth

(psi)

Go 0 - 0% wood

Go 1 - 10% wood 500-100

Go 2 - 20% wood

Go 3 - 30% wood

Go 0 - 0% wood

Go 1 - 10% wood 500-200

Go 2 - 20% wood

Go 3 - 30% wood

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

0 28 56 84 112 140 168 196 224 252 280 308 336 364

Time (days)Co

mpre

ssive

Stre

ngth

(psi)

Go 0 - 0% wood

Go 1 - 10% wood 500-100

Go 2 - 20% wood

Go 3 - 30% wood

Go 0 - 0% wood

Go 1 - 10% wood 500-200

Go 2 - 20% wood

Go 3 - 30% wood

Cement and Ash Tests• ASTM specifications

exclude biomass ash with coal ash for cement

• Conducted tests with University of Alabama in Birmingham to evaluate effect of wood ash on cement properties

• Coordinating efforts with ASTM

SCR Catalyst Effects

•SCR (Selective Catalytic Reduction) is NOx emission control device

•Catalyst is affected by biomass ash

•Pilot study at Plant Gadsden with EPRI

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

costs now benefits now total now

Co

st D

iffe

ren

tial

($/

kwh

)

total

Sulfur benefit

NOx benefit

milling energy cost

Labor cost

Capital cost

fuel diff cost

Grass Co-Firing Energy CostPresent

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

costs now benefitsnow

total now futurecosts

futurebenefits

future total

Co

st

Dif

fere

nti

al

($/k

wh

)

total

Sulfur benefit

NOx benefit

milling energy cost

Labor cost

Capital cost

fuel diff cost

Grass Co-Firing Energy CostFuture

Conclusions1. Direct injection with grass was technical

success2. Co-firing reduced emissions,

but was a little less efficient3. Cubes have problems4. Grass co-firing cost predictions were about

2.6¢/kWh to 3.0¢/kWh higher than coal power5. Results suggest a subsidy will be required to make

grass co-firing viable for an RPS6. Biomass cannot be co-fired at some units for

technical and cost reasons at this time7. Research is on-going at Southern Company to

address these issues

Questions?