Global Climate & Energy Project

Advanced Coal WorkshopMarch 15 & 16, 2005

Gary A. WallingAlliant Energy

CoCo--Firing Switch GrassFiring Switch GrassAtAt

Ottumwa Generating StationOttumwa Generating Station

Alliant EnergyAlliant Energy’’s Perspectives Perspective

Biomass Co-Firing

Presentation Contents

• Summary Issues• Material Handling• Pulverization of Biomass• Combustion Science Questions• Ash Impacts• Market Economics• Summary & Conclusions

Over-arching Issues

• Public policy is focused on broad, universal solutions.• Biomass is “local.”• Low bulk-density of material constrains economics of transport.• Biomass source is often dispersed - - Small-scale by nature & not

amenable to large-scale solutions.• Biomass is not homogeneously distributed.• Until recently, agriculture industry has focused research on genetics

to achieve “nutrition” value not energy value.• Production of electricity is low-value commodity - - biomass

resources may require a high-value product to make economic sense.

• Because of the “local” nature, collaboration on research may be limited to small groups (larger groups do not have common resource interest).

Material Handling of Biomass

• Equipment has been derived from agriculture industry as result of “blacksmith” evolution.

• Seasonal harvest, combined with low bulk density causes economic issues with collection, transport, and storage.

Forage harvest of prairie grass

Loading for transport

Arrival at process facility

Unloading truck at process facility

Research Needs for Material Handling

• Each project needs a “queuing” study to optimize delivery infrastructure.– Forest Products industry may already have delivery

infrastructure.

• Handling is very dusty and has fire hazards.

• Need more economic, automated systems for handling.

• Dense, baled product (for efficient transport) requires a number of pre-process steps prior to combustion.

Loading 1000 lb. bale to process conveyor during test; commercial process requires automation.

Example of Automated Bale Handling

Moisture sensors

Twine remover was problematic deviceD-Stringer – A cutter and a set of hooks remove twine from bales before they enter the de-baler.

400 Hp de-baler provides first-stage of particle size reduction.

Flail-type hammer-mill grinder employed for final size reduction.

Research issues for Pulverization

• Better grinding process is required – Need better grinding model. Cellulose materials are “stringy” , as

compared to conventional coal pulverizing of “crystalline” material.– Agriculture product pulverizers, e.g., flour milling, are low through-put,

high-horsepower devices, compared to coal pulverizers.– Coal pulverization provides 70% through 200 mesh, straw grinders

typically achieve only 35 % through 200 mesh.– Co-mingling straw with coal may be limited by existing pulverizers

• Concerned that lignin will liquefy & adhere to rolling-contact surfaces.– Need to solve the problem of material distribution in flail-type hammer-

mills. Straw materials will “float” above hammer-mills due to windage. Stones and other tramp materials must be removed prior to this process step.

Secondary Grinder Internals

600 Hp grinder

24 TPH 2in screen

Hammers 30,000 t/set Screens 20,000 t/set

De-baled and ground switchgrass – results at 13 tons per hour output

De-baled Switch grass

Ground Switch grass

Research Issues for Combustion

• Combustion characteristics have caused few problems. Low sulfurand low mercury content are desirable features.

• Higher moisture content and low heat content may limit co-firing in boilers designed for bituminous coals.

• Need to design combustion to take advantage of better volatility of biomass– Could use biomass for reburn fuel, but need to achieve complete

particle burnout.

• High chlorine content may limit biomass co-firing concentration to limit high-temperature corrosion of super-heater materials.

Hoop Building(Straw Storage)

Straw Storage

OGS MainPlant Building (Straw Storage &

Processing)

Ground switch grassand pressurized transportair to OGS boiler

Ground switch grassand pressurized transportair into OGS boiler

Switch grass Blow Lines Transporting Ground Switchgrass into Boiler House (left)and Boiler (right).

Chariton Valley Biomass Project--Interim Test BurnNOx & SO2 vs. Load, Ottumwa Generating Station

0.2

0.3

0.4

0.5

0.6

0.7

0.8

600 620 640 660 680 700 720 740 760Load (MW)

lb /

MM

Btu

SO2, Coal Only SO2, Cofiring NOx, Coal Only NOx, Cofiring

Continuous Emissions Monitoring System Data for: December 1 to 12, 24 hours per day

Average SO2 :Coal only = 0.65SWG Cofire = 0.62(4.3% lower SO2)

Average NOx :Coal only = 0.35SWG Cofire = 0.35

Opacity Emissions; Dec 2, 2003Opacity vs. Load, 12/02/03

(with and without Switchgrass Cofiring)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

650 660 670 680 690 700 710 720 730 740 750

Load (MW)

Opa

city

, %

Opacity (Coal Only) Opacity (Cofiring)

Average Emissions:Opacity Coal = 16.0%Opacity Cofire = 17.1%

Research Issues for Ash

• Ash mineral content of biomass may limit co-firing.– P & K associated with fertilization is detrimental to ash slagging and

boiler fouling.

• Ash from Powder River Basin (PRB) coals is high in calcium and is sold to concrete industry to displace cement.– ASTM standard C618 does not allow for ash from biomass co-firing.– Surfactant issues for cement with biomass-ash is research focus.

• Can an economic water-wash process be designed to remove the minerals (found as water-soluble chloride-salts) and the product dried with power-plant waste heat? Such a process could resolves much of the combustion issues.

Research Issues for Market Economics

• Biomass economic elements: $/dry ton– Producer ownership costs (closed loop) 13– Production costs to edge of field 30– Collection & transport 10– Handling & grinding 16– Process facility ownership costs 10

Sub-total: 79 $/dry ton

However, biomass must compete with other fuels and must account for other impacts.

Economics of competition is dependent upon public policies.

Summary & Final Issues• There are development opportunities to improve the science.

– However, some major cost elements may be less amenable to science solutions.

• Some parts of the country have viable sources but the “science”associated with each resource may be different.

• Absent competitive costs, external policy drivers are required (e.g., Production tax credits, Renewable Portfolio Standard requirements, or CO2 control) to shift the cost drivers in favor of renewables.

Questions?

Acknowledgement to switchgrass co-sponsors:

Chariton Valley Biomass Project DOE Project DE-FC36-96GO10148