Reduction of furnace wall corrosion by the use of fuel additives Tests in fluidised bed test rig with waste and demolition wood

• World BioEnergy, 4 June 2014

• Anders Hjörnhede

• SP – Energy Technology

• Sweden

Background

• Increasing waterwall corrosion due to more frequent use of cheaper and more corrosive fuel ”waste and demolition wood”

• Focus has been on super heater corrosion

• Underestimation of furnace wall corrosion ”several mm/year” for mild steel

• High steam data: 500 – 560°C, 90 -140bar

Countermeasures:

• Cladding: Inconel 625 – commonly used in waste fired grate boilers or use higher alloyed steels

• Installation/expand the area of refractory materials in the furnace

• Reduction of steam data (temperature) – if possible

• Or make use of additives

Additives

• Elemental sulphur (S)

•Digested sewage sludge from municipal waste water (SWS)

• Kaolin kaolinite (Al2Si2O5(OH)4) clay minerals (Kao)

• Burnt lime CaO (Lime)

• Foundry sand (bentonite, kaolin) (FS)

• + Reference case (Ref)

Test conditions

• Furnace Wall (BW) probe metal temperature: 400C

• Super heater (SH) probe metal temperature: 550C

• Bed temperature: 800C

• Exposure time: >8h

• Fuel: waste and demolotion wood : Some wood, plastics, metals, stones Cl: 0,3 wt%, Pb, Zn and alkalimetals

Tested Steels

• 16Mo3 Fe0.7Mn0.3Mo0.9SiCuCr

• 253 MA Fe21Cr11Ni1.7Si

• Kanthal A1 Fe22Cr5.8Al

Laboratory FB-reactor

• Max load about 20 kW

• Continuous fuel feeding

• Mass flow controlled air supply

• Bottom ash removal

• Deposit sampling for 8 h

• O2 at BW-probe < Detection Limit

lpm – normal liters per minute

d.g. – dry gas

Results

• Deposition rate Furnace Wall (BW) and Super Heater (SH)

• Chemical composition of deposits BW and SH

• Chemical composition of bottom ash (+sand)

• Chemical composition of fly ash

• Corrosion attacks on test materials

Furnace Wall – Deposit Growth Rate

0

10

20

30

40

50

60

70

80

90

100

Ref 1 FS Kao Lime SWS1 S Ref 2 SWS2 PbO PbO+SWS

De

po

siti

on

Rat

e [

g/m

2/h

]

BW Loose

BW Hard

Ref: Reference

FS: Foundry Sand

Kao: Kaolin

Lime

SWS: Sewage Sludge

S: Sulphur

Chemical analysis of Bottom ash + sand

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Elem

enta

l Co

mp

osi

tio

n [

% b

y m

ass]

Ni

Cr

Mn

Ti

Fe

Ca

Al

Si

Zn

Pb

K

P

S

Cl

Ref: Reference

FS: Foundry Sand

Kao: Kaolin

Lime

SWS: Sewage Sludge

S: Sulphur

SuperHeater – Deposit Growth Rate

0

5

10

15

20

25

30

De

po

siti

on

Rat

e [

g/m

2/h

]

SH Loose

SH Hard

Ref: Reference

FS: Foundry Sand

Kao: Kaolin

Lime

SWS: Sewage Sludge

S: Sulphur

SuperHeater – Average composition of hard deposits

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Elem

enta

l dis

trib

uti

on

in d

epo

sits

[%

, by

mas

s]

Cu

Mn

Ti

Ca

Al

Si

Zn

Pb

K

P

S

Cl

Ref: Reference

FS: Foundry Sand

Kao: Kaolin

Lime

SWS: Sewage Sludge

S: Sulphur

Composition of Fly Ash on Filter

00

00

00

01

01

01

01

Fly

Ash

in F

ilter

[g

/Nm

3]

BalNiCuNaMnTiFeCaMgAlSiZnPbKPSCl

Ref: Reference

FS: Foundry Sand

Kao: Kaolin

Lime

SWS: Sewage Sludge

S: Sulphur

0

2

4

6

8

10

12

0 50 100 150 200

Ele

me

nt

con

cen

trat

ion

[%

, by

mas

s]

Angle relative flow [°]

Cl

S

P

K

Pb

Zn

Furnace Wall Chemical analysis of surface before cleaning (XRF)

Reference case (Waste and demolition wood) and Sewage Sludge

Reduction of: Cl, S, K

Increase of: P

No change: Pb

Reference

0

2

4

6

8

10

12

0 50 100 150 200

Ele

me

nt

co

nc

en

tra

tio

n [

%,

by m

as

s]

Angle relative flow [°]

Cl

S

P

K

Pb

Zn

Sewage Sludge

Chemically analysis of Deposit on Furnace Wall rings

A B C

D E F

A) Reference

B) Foundry Sand

C) Kaolin

D) Lime

E) Sewage Sludge

F) Sulphur

SEM-EDX mapping, Furnace wall 16Mo3 probe, reference (wind)

KME

512 -

Fuel

additiv

es to

reduce

corrosi

on |

Annika

Stålen

heim |

2014.0

3.18

14

Spectrum 1: Pb 17 at% (62 Wt%)

• Cl in corrosion front

• S somewhat further out

• Pb, K, Na, Zn furthest out

Corrosion attacks, furnace probe, macro images of 16Mo3 ring surfaces

A B C

D E F

A) Reference, B) Foundry Sand, C) Kaolin, D) Lime, E) SWS F) Sulphur.

Lime Furnace (above) / Superheater (below) - corrosion Lime

15Mo3 253 MA A1

Corroded

slightly corroded, discoloured very slightly corroded spots,

can be removed with some effort

Lime

15Mo3 253 MA A1

Corroded -20 - +20 Slight corrosion in front Dispersed stains in front

16Mo3 253 MA Kanthal A1

16Mo3 253 MA Kanthal A1

Reference

Reference

Sulphur Furnace (above) / Superheater (below) - corrosion Sulphur

15Mo3 253 MA A1

Corrosion -40 - + 40, discoloured (-)90 sporadic corrosion

Sulphur

15Mo3 253MA A1

Slightly corroded -90 - +90 Slightly discoloured by heat -90 - +90 Almost clean

16Mo3 253 MA Kanthal A1

16Mo3 253 MA Kanthal A1

Reference

Reference

Summary of results

• Digested sewage sludge and kaolin reduce waterwall and superheater (not shown) corrosion

• These two additives also reduce the risk for bed sintering

• All additives except Lime reduce the chlorine concentrations in superheater deposits

• Corrosion resistance: Kanthal A1 performs better than 253 MA, which is far better than 16Mo3.

• The best element to monitor as an indicator of corrosivity in the deposits is chlorine (Cl)

Financiers

• KME: Constortium: Materials Technology for demonstration and development of thermal energy processes

• STEM: Swedish Energy Agency

• SP: Swedish Technical Research Institute