Could biomass boilers be

operated at higher steam

efficiencies (higher temps.)?

Sandy Sharp (SharpConsultant, Columbia, MD)

Jim Keiser (Oak Ridge National Laboratory, Oak Ridge, TN)

Doug Singbeil (FPInnovations, Vancouver, BC, Canada)

Jim Frederick (Table Mountain Consulting, Golden, CO)

Curtis Clemmons, (MeadWestvaco, Covington, VA)

Laurie Frederick, (FPInnovations, Vancouver, BC, Canada)

Project tasks

Could existing alloys serve in biomass boiler SHs

at temperatures 100 Celsius degrees above

current operating temperatures?

1. Strategies for managing superheater corrosion

2. Lab and field tests of candidate alloys

3. Would value of the increased power generated

justify the costs of the increased steam

temperature? 2

Project funding and support

22

U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Industrial

Technologies Program, contract DE-AC05-00OR22725 with Oak Ridge National Laboratory

Budget: Research: €1,150,000 ($1,568,000); In-kind:

€588,000; Total: €1,730,000 ($2,360,000)

Project partners (in-kind contributions): Åbo Akademi

University, Andritz Oy, Babcock & Wilcox, Catalyst Paper,

Chalmers University of Technology, Domtar Corporation,

E.ON UK, FM Global, FPInnovations, Foster Wheeler,

Georgia Institute of Technology, Haynes International, Howe

Sound Pulp & Paper, International Paper, MeadWestvaco,

Metso Power, Outokumpu Stainless, Rolled Alloys, Sandvik

Materials Technology, SharpConsultant, Southern Company,

Special Metals, Table Mountain Consulting, ThyssenKrupp

VDM, University of Toronto Pulp and Paper Centre, Vattenfall

Power and the Weyerhaeuser Company.

Advanced biomass boilers

achieve higher steam

temperatures using

Modified boiler designs

Fuel modifications or chemical additions

Corrosion-resistant superheater alloys

4

Design modification 1a:

Remove deposits before SH

• Add an empty pass between furnace and SH

Iglesta CHP boiler

Södertälje, Sweden

(wood and waste)

5

Design modification 1b:

Remove deposits before SH

Add a “Chlorine trap” upstream of the SH Molten outer layer of ash may restrict penetration of

corrosives

WTE boiler, Schweinfurt, Germany Straw-fired boilers (Maribø, Avedøre 2, Denmark; Grenå, Norway) also

operate with molten outer layer of SH ash 6

Design modification 2: Move

CFB SH from flue gases into

recirculated fluidizing medium

Foster Wheeler INTREX

7

Metso

(Valmet)

CYMIC

Lurgi FBHE

Design modification 3: Move

SH outside boiler and heat it

with a less-corrosive fuel

8

Ensted (Åbenrå, Denmark) straw/wood fired boiler raised SH temperature

from 470°C to 542°C by installing an external wood-fired SH

Design modification 4::Design

SH for very rapid replacement

WTE boiler, City of Amsterdam, The Netherlands, with KEMA

9

Design modification 5: Operate

SH above ash dew point temp.

Raise tube surface temperature to convert NaCl

deposits to less-corrosive HCl(g)

10 Skog, et al., 2008

Palonen et al., 2009:

Norrköping, Langerbrugge, etc.

Process modification 1:

Dilute corrosive biofuels

Simplest approach: dilute corrosive biofuels

with less corrosive fuel e.g. diluting straw with ≥80% coal does not

significantly increase SH corrosion

11

Process modification 2:

Wash corrosives out of

biofuels

Water-soluble alkali chlorides are among the

most corrosive species faced by biomass boiler

SHs

Water leaching removes >80% of K, Na; >90% of Cl

from biomass crop fuels

But drying wet fuels can be expensive

12

Process modification 3:

Convert chlorides to sulfates

K2SO4 deposits are much less corrosive than

KCl because they have a higher melting temp. -

1,069°C rather than 770°C

Sulfation reduces conversion of Cr2O3 to alkali

chromate: can halve the corrosion rate

can be achieved by SO2 or SO3 2KCl(s) + SO2(g) + ½ O2(g) + H2O → K2SO4(s) + 2HCl(g)

e.g. WTE boiler, Norrköping, Sweden

(NH4)2SO4 → SO3 + 2NH3 + H2O

(ChlorOut®) 13

Process modification 4:

Convert chlorides to silicates

Silica or kaolinite additives react with alkali

chlorides to form alkali silicates or alkali

aluminum silicates

silicates have much higher melting

temperatures, reduce SH fouling and

corrosion

e.g. KCl concentrations in FBHE of Grenå CFB

boiler (co-firing straw/coal) were reduced by two

OOMs by silica or kaolinite additions 14

Alloy modifications: use more

corrosion-resistant SH alloys

15

Alloy rankings depend on biomass fuel,

operational parameters, tube temps.

Corrosion rates

increase rapidly at

ash melting temp.

Conclusions of tasks 1, 2

SH corrosion control strategies and alloy

rankings had been developed for boilers burning

wood, straw, black liquor and municipal wastes

3 empirical models had been developed to

predict fouling and corrosion in biomass boilers Fuel composition is used to predict ash composition;

(T° - FMT°) to predict fouling tendency;

field data to predict corrosion rate

In each of 4 challenging biomass boiler

environments, some alloys could have useful

lives at 100 Celcius degrees above current limits 16

Is the juice worth the

squeeze?

Use Rankine cycle software to calculate value

of additional power that could be generated by

operating typical biomass boilers at higher

steam conditions without changing fuel or firing

conditions

Compare the value of this additional power with

the costs of installing more corrosion-resistant

superheater alloys, using fuel additives or

changing the boiler design 2

Underlying principle

1200

1400

1600

1800

400 500 600 700

Sp

ec

ific

Ava

ila

ble

E

ne

rgy,

kJ

/kg

Temperature, °C

100 bars

50 bars

Increasing our steam temperature by 100 Celsius degrees

will increase the energy available from a biomass fuel by

11.4% at 100 bars and 11.0% at 50 bars 4

Availability of energy in steam (ability to do work) increases

with increasing steam temperature

Project collaborators

supplied steam data for

five biomass boilers

Two Black Liquor Recovery Boilers (52,54 MW)

Typical data from a boiler manufacturer

Process simulation model of 1,500 ODT pulp mill

Three wood-fired Biomass Boilers (27,28,43 MW)

West Coast pulp mill unit firing sea-floated logs

West Coast pulp mill unit firing 2/3 beetle-killed

pine, 1/3 sea-floated logs, some construction waste

Recently constructed BFB firing wood waste 6

Value of increased power in

5 biomass-fueled boilers

Conditions Recovery Boilers Biomass Boilers

B M C H M

+50°C steam

@$40/MWh +$1.54m +$2.52m/y +$2.94m/y +$1.33m/y +$1.26m/y

@$80/MWh +$3.08m +$5.05m/y +$5.89m/y +$2.66m/y +$2.52m/y

+100°C steam

@$40/MWh +$2.45m/y +$4.45m/y +$5.61m/y +$2.60m/y +$2.42m/y

@$80/MWh +$4.91m/y +$8.90m/y +$11.21m/y +$5.19m/y +$4.84m/y

Potential costs of maintaining process steam flows in biomass

boilers (likely not large) are not included in these calculations 16

Could value of increased

power generation justify cost

of increasing steam temps by

100 Celsius degrees?

Value of additional power generated from hotter

steam at constant firing conditions could pay: $5,378/m - $24,911/m for 2,250 m for more

corrosion-resistant SH tubes replaced every 5

years (45p x 10t x 5m)

$2,420,000 - $11,210,000 per year to remove

corrosives from biomass fuel or to apply additives

$12m - $56m over 5 years to redesign boiler,

upgrade steam turbine 17

Project results are available

in 7 publications

Energy From Biomass – Lessons From European Boilers

Sharp, Singbeil & Keiser, TAPPI PEERS conference, 2011

Superheater Corrosion Produced By Biomass Fuels

Sharp, Singbeil & Keiser, Paper 1308 at NACE Intl. Corrosion/2012 conference

Superheater Corrosion In Biomass Boilers: Today’s Science and Technology

Sharp, Oak Ridge National Laboratory TM-2011/399, 2012

Performance of Alternate Superheater Materials in a Potassium-Rich Recovery

Boiler Environment

Keiser, Sharp, Singbeil, Frederick & Clemmons, TAPPI J, 12 (7), 45-56, 2013

Could Biomass-Fueled boilers be Operated at Higher Steam Temperatures?

1. Laboratory Evaluation of Candidate Superheater Alloys

Singbeil, Frederick, Keiser & Sharp, TAPPI Journal, to be published June 2014

Could Biomass-Fueled boilers be Operated at Higher Steam Temperatures?

2. Field Tests of Candidate Superheater Alloys

Keiser, Sharp, & Singbeil, TAPPI Journal, to be published June 2014

Could biomass-fueled boilers be operated at higher steam temperatures?

3. Initial analysis of costs and benefits

Sharp, Frederick, Keiser & Singbeil, TAPPI Journal, to be published June 2014

Measuring corrosion rates is

difficult

25

Sample temps.

are not constant

Corrosion is

irregular How many cross-sections?

Max. or avg. metal loss beneath “original surface”? Image analysis of cross-sections of lab test specimens

produced 28,800 measurements

Corrosion tests

Example of field corrosion data

300

350

400

450

500

550

600

650

-0,1 0,1 0,3 0,5 0,7 0,9 1,1 1,3 1,5

Ave

rag

e E

xp

os

ure

Te

mp

era

ture

(°C

)

Total Material Affected (mm)

Covington Recovery Boiler

S31009

N07214

N08028

N06025

N08120

S21500

S34709

N12160

N06690

Current

max T

Goal

Nine alloys were selected

for exposure in the RB

corrosion probe

Alloy UNS number

Fe Ni Cr Mo Co Mn Al Si C Other

310H SS S31009 Bal 19.10 24.30 0.25 0.55 0.045

Haynes 214 N07214 3.56 Bal 16.08 0.03 4.22 0.12 0.04 Y=.004, Zr=.011

Sanicro 28* N08028 35 31 27 3.5 1.8 0.2 0.01

602CA N06025 9.60 62.20 25.30 2.30 0.03 0.170 Y=0.07, Zr=0.09

HR160 N12160 0.63 Bal 28.00 0.27 30.20 2.75 0.056

Inconel 690* N06690 9 62 29 0.02

HR120 N08120 36.26 36.68 24.74 0.07 0.11 0.16 0.73 0.057 N=0.21

Esshete 1250* S21500 72 10 15 1 6.3 0.5 0.1 Nb=1, V=2.5,

B=0.006

347H SS S34709 Bal 9.02 17.21 0.57 0.048

*Nominal values

Conclusion from field and

lab tests

In SH environments simulating boilers burning sea-floated logs w and w/o demolition waste

coal-wood blends

kraft black liquor

existing alloys could serve useful lives in

superheaters operating 100 Celcius degrees

above current operating temperatures 29

300

350

400

450

500

550

600

650

0 0,5 1 1,5

Ave

rag

e E

xp

os

ure

Te

mp

era

ture

(°C

)

Total Material Affected (mm)

Covington Recovery Boiler

S31009N07214N08028N06025N08120S21500