Containment Materials Issues in High-Temperature Black Liquor Gasification

James Keiser, James Hemrick, Roberta Meisner, Gorti Sarma and Kimberly Choudhury

Oak Ridge National Laboratory

Peter Gorog and Ray LearyWeyerhaeuser Company

7th International Colloquium onBlack Liquor Combustion and Gasification

July 31-August 2, 2006Jyväskylä, Finland

2

Our Study Of Containment Materials For High-Temperature Gasification Has Concentrated On The New Bern Gasifier

Construction of the New Bern high-temperature gasifier began in November, 1995

This gasifier had its first production run in December, 1996

Several refractory repairs or replacements were made in 1997 and 1998

In early 1999, the lining was replaced with a fusion cast alumina refractory

In December, 1999, cracking was discovered in the stainless steel gasifier vessel, and the gasifier was taken out of service

The rebuilt gasifier resumed operation in late June, 2003, with a different fusion cast alumina refractory

In October, 2004, a fusion cast magnesia-alumina spinel refractory lining was installed

3

The High-Temperature Gasifier Subjects The Structural Materials To Very Hostile Environments

The hot-face refractory is exposed to molten smelt at temperatures of 950-1000°C

The back-up refractory is exposed to somewhat lower temperatures (800-900°C) and to smelt components that are transported through cracks and joints in the hot-face refractory

The temperature gradients and the volume increase resulting from reaction with smelt components produce highly compressive stresses on the surface of the hot-face refractory

Expansion of the refractory lining can create large tensile stresses in the metallic shell

4

Containment Materials Used In The New Bern HT Gasifier

Time period Reactor shell Back-up refractory lining

Hot-face refractory lining

Dec 1996 –Early 1999

316L stainless steel

Super duty refractory brick

60% Al2O3, SiO2brick

Early 1999 –Dec 1999

316L stainless steel

Fusion cast βAl2O3

Fusion cast α/βAl2O3 –manufacturer A

Jan 2000 –June 2003

Gasifier out of service

June 2003 –Sept 2004

Carbon steel High-alumina bonded brick

Fusion cast α/βAl2O3 –manufacturer B

Oct 2004 –present

Carbon steel Bonded mullite –based refractory

Fusion cast MgO-Al2O3 spinel

5

ORNL Examined Two Mullite Bricks Removed From The Original Lining Of The New Bern Gasifier

After about ten months of operation, less that half the brick remained at time of removal. Samples taken from the bulk, reaction zone and surface regions of both

bricks were analyzed using XRD and microscopic techniques, and compounds were identified that were a result of reaction of the smelt with the refractory.

7.3 cm7.3 cm

2.5 cm2.5 cm

“Bulk”“Bulk”

Intermediate ZoneIntermediate Zone

4.7 cm4.7 cm

“Bulk”“Bulk”

Reaction ZoneReaction Zone

SurfaceSurface

0.5 cm0.5 cm

6

ORNL’s Smelt Immersion Test Facility Simulates Exposure Of Materials To Molten Smelt In The New Bern Gasifier

Exposures are typically conducted at 900 or 1000°C for 50 or 100 hours

7

Immersion Tests Are Able To Reproduce The Degradation Seen In Refractories Exposed In High-Temperature Gasifiers

Alumina-silica (mullite) based samples exposed in the New Bern gasifier and in the immersion test system have reaction products such as nosean (Na8Al6Si6O24SO4) and nepheline (Na2O·Al2O3·2SiO2) on their surfaces

Fusion cast alumina refractories exposed in the gasifier and the test system show an increase in the sodium content near the surface with a surface layer enriched in Na2O-Al2O3, sodium aluminate (NaAlO2)

8

The Sodium Oxide – Aluminum Oxide Phase Diagram Shows The Series Of Compounds That Can Form

Increasing the amount of Na2O in Al2O3 results in phase changes and volume increases, so it is not unreasonable to expect significant stresses to develop and some degradation to occur

9

Samples Of New Bern’s Fusion Cast α/β Al2O3 Replacement Lining Contained The NaAlO2 Reaction Product

10

NaAlO2 Was Found On The Surface And In The Reaction Zones Of Fusion Cast Alumina Samples From The Skoghall

High-Pressure Black Liquor Gasifier

11

Core-Drilled Samples Of The Fusion Cast Alumina Linings Provided Information About Extent Of Reaction With Smelt

NaAlO2 found on hot face Increased Na content found at back of the working lining and front of backup lining No NaAlO2 detected in backup lining

Working Lining: α/β alumina Backup Lining: β alumina

1 inch

0%10%20%30%40%50%60%70%80%90%

100%

1.5 24.5 41.5 61.0

Distance from Hot Face (mm)

Cum

mul

ativ

e Ph

ase

(%)

Distance From Hot Face (mm)

Cum

ulat

ive

Phas

e (

%)

α-Al2O3

β-Al2O3

NaAlO2

1 inch

12

Material Volume Expansion

(%) Al2O3 - β-Al2O3 31 β’-Al2O3 32 NaAlO2 133

Reaction Of Alumina Refractory With Sodium Compounds Caused Dimensional And Microstructural Changes

~50% Conversion to NaAlO2

~25% Conversion to NaAlO2

<5% Conversion to NaAlO2

Original Structure

Hot

Fac

e

13

The New Bern Gasifier Was Out Of Service For More Than Two Years. When A Decision Was Made To Rebuild The Gasifier, A Number Of

Design And Material Changes Were Made

New Refractory/Shell System Design

Hemispherical Dome

Carbon steel refractory containment which is not susceptible to Cl- SCC

Crushable metal foam used between refractory and carbon steel shell

Fusion-cast alumina working lining (from different supplier) over high alumina backup lining

Expansion allowance for growth of refractory based on data collected after one year of operation

Test bricks of alternate materials were also installed

14

Laboratory Testing And Evaluation Of Previously Exposed Materials Guided Selection Of Alternate Refractories

Molten salt immersion test facility allowed immersion of refractory samples in molten salt at 1000°C

Light microscopy, scanning electron microscopy and electron microprobe were used to characterize the extent of reaction between refractories and salt

Studies of refractories exposed previously in operating gasifiers and exposed in the immersion test facility provided guidance on selection of the refractory lining material

Refractory studies also identified alternate materials to be exposed as test bricks in the lining of the rebuilt gasifier

15

In February 2004, The Gasifier Was Shut Down For Quench System Repairs And Refractory Examination

Pieces of refractory brick were being recovered on a regular basis from the trap on the quench tank

Visual inspection of the lining showed considerable damage of the refractory lining in some areas, while other areas appeared to be relatively unaffected

Core-drilling was used to collect samples from eight different bricks in the lining including samples from test bricks of threealternate refractories

Examination also showed severe thinning in some sections of the cooled support ring

16

Cross-Sections Of The Core-Drilled Samples Removed In January 2004 Showed Cracking And Discoloration

Fusion-cast magnesia-alumina refractory

Bonded magnesia-alumina refractory(outlined at left)

Fusion-cast alumina refractory

Alternate fusion-cast alumina refractory

Microprobe examinations showed extensive sodium penetration in the alumina samples

17

In September 2004, A Fusion-Cast Spinel Lining Was Installed And 40 Strain Gauges Were Mounted On The Vessel Shell

Strain gauges are installed on five levels of the gasifier vessel

Strain gauges replace some previously installed by Weyerhaeuser at different locations

Two strain gauges and a thermocouple are located in four positions around the circumference on each of the five levels

L1

L2

L3

L4

L5

18

During The First 7+ Months Of Operation, Strain On The Shell Increased At A Fairly Low Rate

Hoop and Axial 5-Day Averages for Levels 3-4 New Bern Gasifier Oct 2004 - May 25, 2005

-200

0

200

400

600

800

100015

-Oct

20-O

ct25

-Oct

30-O

ct4-

Nov

9-N

ov14

-Nov

19-N

ov24

-Nov

29-N

ov4-

Dec

9-D

ec14

-Dec

19-D

ec24

-Dec

29-D

ec3-

Jan

8-Ja

n13

-Jan

18-J

an23

-Jan

28-J

an2-

Feb

7-Fe

b12

-Feb

17-F

eb22

-Feb

27-F

eb4-

Mar

9-M

ar14

-Mar

19-M

ar24

-Mar

29-M

ar3-

Apr

8-A

pr13

-Apr

18-A

pr23

-Apr

28-A

pr3-

May

8-M

ay13

-May

18-M

ay23

-May

stra

in

Ave Hoop Ave Axial w revision Linear (Ave Hoop) Linear (Ave Axial w revision)

19

Strain Showed A Perturbation After The Lining Was Partially Quenched In Water; Hoop Resumed Linear Increase

Hoop and Axial 5-Day Averages for Levels 3-4 New Bern Gasifier Oct 2004 - June 30, 2006

-200

0

200

400

600

800

1000

15-O

ct25

-Oct

4-N

ov14

-Nov

24-N

ov4-

Dec

14-D

ec24

-Dec

3-Ja

n13

-Jan

23-J

an2-

Feb

12-F

eb22

-Feb

4-M

ar14

-Mar

24-M

ar3-

Apr

13-A

pr23

-Apr

3-M

ay13

-May

23-M

ay2-

Jun

12-J

un22

-Jun

2-Ju

l12

-Jul

22-J

ul1-

Aug

11-A

ug21

-Aug

31-A

ug10

-Sep

20-S

ep30

-Sep

10-O

ct20

-Oct

30-O

ct9-

Nov

19-N

ov29

-Nov

9-D

ec19

-Dec

29-D

ec8-

Jan

18-J

an28

-Jan

7-Fe

b17

-Feb

27-F

eb9-

Mar

19-M

ar29

-Mar

8-Ap

r18

-Apr

28-A

pr8-

May

18-M

ay28

-May

7-Ju

n17

-Jun

27-J

un

stra

in

Axial 0ct '04 - Jul '05 Hoop 0ct '04 - Jul '05 Axial Aug '05 - June '06

Hoop Aug '05 - June '06 Linear (Axial 0ct '04 - Jul '05) Linear (Hoop 0ct '04 - Jul '05)

Linear (Axial Aug '05 - June '06) Linear (Hoop Aug '05 - June '06)

20

An Explanation Was Needed ForThe Increasing Strain Of The Shell

The fusion cast spinel refractory did not appear to be undergoing extensive reaction or volume change

Inspections of the foam lining showed it was being crushed by the refractory

These observations led to a question about the integrity of the back-up lining

In order to assess the condition of the back-up lining, a core-drilled sample was taken by drilling through the hot-face lining into the back-up lining

21

Only A Portion Of The Back-Up Lining Was Collected, But This Sample Showed Extensive Degradation On The Hotter Side

The sample was visibly degraded, and X-ray diffraction studies showed extensive reaction with components of the smelt suggesting the back-up lining likely made a

significant contribution to the strain on the gasifier shell

She

ll si

de

Hot

sid

e

22

The Observed Degradation Of The Back-up Lining Led To A Concentrated Effort To Find Alternate Refractories

At the urging of project participants, a number of high mullite content materials were tested

Results of tests conducted previously were reviewed, and vendors were sought for some of the promising materials

A company specializing in calcia-alumina refractories for the aluminum industry was found, and special compositions more suitable for smelt resistance were formulated and tested

Samples of magnesia-rich refractories from several manufacturers were obtained and tested

23

The Suggested Mullite Refractories Reacted Extensively, And In Some Cases, Completely, With Molten Smelt

Beforeexposure

Afterexposure

24

Formulations Of The Calcia-Alumina Refractories Showed Very Good Resistance To Molten Smelt at 900°C

A sample of an alkaline aluminate is shown in the badly reacted metal holder. This refractory will be installed during the next lining replacement.

25

Two Magnesia-Rich Refractories Have Demonstrated Good Resistance To Molten Smelt At 900°C

Magnesia-rich refractories after 100 h in molten smelt at 900°C

Further studies are planned

26

Summary

Degradation of the refractory linings has been attributed to reaction of the refractories with sodium compounds in the smelt and particularly with Na2O

Experience and laboratory studies have shown that a fusion-cast magnesia-alumina spinel refractory has very good resistance to molten smelt at 1000°C

Degradation of the back-up refractory lining appears to be a significant contributor to the stresses on the gasifier shell, but studies have found two refractory types with better resistance to molten smelt at 900°C

The refractory lining to be installed in October will employ therecommended materials – fusion cast magnesia-alumina spinelfor the “hot-face” lining and calcia-alumina refractory for the “back-up” lining