Selection of Refractory Bricks for Use in Lime Sludge Kilns · Selection of Refractory Bricks for...
Transcript of Selection of Refractory Bricks for Use in Lime Sludge Kilns · Selection of Refractory Bricks for...
Selection of Refractory Bricks for Use in Lime Sludge Kilns
Corrosion in Pulp and Paper Mills and Biorefieries November 13-14, 2015
Georgia Tech
By: J. Peter Gorog
www.HoughtonCascade.com 253.670.2867
11104 SE 283rd St, Auburn, WA, 98092-‐4026
Outline
• Function of the refractory lining • Selection of refractory bricks • Recommended refractory linings
2 Selec9on of Refractory Bricks
Key Factors to Optimize Performance of the Refractory Lining
3
Optimized Refractory
Lining
Material Selection
Operating Conditions
Burner Design
Selec9on of Refractory Bricks
Function of the Refractory Lining
• A kiln cannot be operated without the use of a refractory lining to insulate the metal shell. This is because the temperatures required for calcination are so high that a bare metal shell would be destroyed.
• The most important physical characteristics of the refractory lining are its ability to withstand high temperatures and direct chemical attack by the sodium compounds that are introduced into the kiln with the mud.
• The secondary role of the refractory lining is to reduce heat losses through the shell so that the kiln can be operated with the highest energy efficiency possible.
4 Selec9on of Refractory Bricks
Kiln Refractory Linings
5
Modern kilns typically use a dual lining consisting of a high temperature brick at the inner hot surface backed by an insulating brick next to the steel shell. The intent of the dual lining is to minimize shell heat losses.
Single Brick Lining
Refractory Brick
Dual Brick Lining
Refractory Brick
Insulating Brick
Selec9on of Refractory Bricks
Metal Shell
Factors to Consider in Selecting Refractory Materials
• Resistance to chemical attack (solids and gases) • Abrasion resistance • Thermal conductivity • Resistance to spalling • Fusion and softening temperatures • Strength • Cost
6 Selec9on of Refractory Bricks
Refractory Zones in the Lime Kiln
7
High Alumina (60-70% Al2O3)
High Duty Fireclay
(40-50% Al2O3)
Castable
Burning Zone (~10 diameters)
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Discharge Dam
• Dams are installed at the discharge of the kiln to increase the depth and heat transfer to the bed, increase the residence time of the solids, and help to protect the refractory lining from being overheated in the hottest region of the kiln.
• The heights of dams vary between 15 to 25 percent of the inner diameter of the kiln. More recently, the trend has been to install shorter dams.
8
Kiln
Dia
met
er, D
k
Hei
ght D
am, h
d hd = kDk where k = 0.15 to 0.25
Selec9on of Refractory Bricks
Cup Tes9ng High Alumina Refractory Bricks
9
Cut test bricks into 5 cm blocks
Drill 25.4 mm diameter hole to a depth of 25.4 mm
Selec9on of Refractory Bricks
Cup Testing High Alumina Refractory Bricks
10
Fill with 50 grams of dried mud
Heat samples to 1500°C and hold for 4 hours cool for 12 hours
Section for examination
Selec9on of Refractory Bricks
Cup Testing High Alumina Refractory Bricks
11
Cross-sectional area used measure the extent of chemical reaction
Selec9on of Refractory Bricks
Typical Composition of Lime Mud
12
Mill Location
Al (ppm)
Fe (ppm)
Mg (ppm)
Mn (ppm)
Na (ppm)
P (ppm)
Si (ppm)
Total S (%)
Mill #1 807 506 2870 43 7800 5000 910 0.09 Mill #2 726 753 3710 117 8500 3000 860 0.18 Mill #3 92 120 1760 158 7200 1070 <200† 0.06 Mill #4 742 691 2350 81 5800 827 1300 0.12 Mill #5 1010 795 5470 98 6200 2230 990 0.17 Mill #6 763 1310 2700 260 11000 2460 1000 0.31 Mill #7 1900 2150 6600 210 7900 6790 1100 0.33 Mill #8 376 1040 5410 305 7800 7440 1100 0.18 Average 802 921 3859 159 7775 3602 1037 0.18 †Below limit of detection
Selec9on of Refractory Bricks
Cross-Sections Showing Impact of Mud Compositions on Penetration
13
Mill #2 Mill #3 Mill #4 Mill #1
Mill #7 Mill #8 Mill #6
Mill #5
25 mm
70% High Alumina Brick
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Impact of Mud Composition on Penetration
14
• No relationship between penetration depth of reaction and mud composition and the area of penetration.
• Mud from Mill #1 was used for the cup tests reported here.
Mill$#1$
Mill$#2$
Mill$#5$
Mill$#6$
Mill$#7$
Mill$#8$
Mill$#4$
Mill$#3$
Selec9on of Refractory Bricks
Cross-Sections for 70% High Alumina Bricks
15
70% High Alumina Brick
Brick #1 Brick #2 Brick #3
Brick #5
25 mm
Brick #4
70% High Alumina Bricks
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Cross-Sections for 60% High Alumina Bricks
16
Brick #6 Brick #7 Brick #8 Brick #9 Brick #10
Brick #11 Brick #12 Brick #13 Brick #14
60% High Alumina Bricks
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Penetration for 60% and 70% High Alumina Bricks
17
1 2 3 4 5 6 7 8 9 10 11 12 13 140
2
4
6
8
10
12
Pene
trat
ion
(cm
2 )
70% Alumina Brick
60% Alumina Brick
Kruz
ite
Alu
sa Arc
o 70
GM 7
0 D
E
CB 7
0 D
GM 6
0 D
Arc
o 60
Miz
zou
Sene
ca 6
0
Ufa
la
Nik
e 60
AR
Resi
sto
605
Refr
alus
it 6
3
Tuff
Zon
e
Avg. 5.61 cm2
Avg. 8.71 cm2
Sample Number
Brick&
Brick&
Brick&
Brick&
Brick&
Brick&
Brick&
Brick&
Brick	&
Brick
&
Brick&
Brick&
Brick
&
Brick&
Sample&
Selec9on of Refractory Bricks
Photomicrograph Showing Unreacted Matrix for High Alumina Bricks
18
A
M
M
M
M
A
MM
M100 mm
A
A
100 mm
70% High Alumina Brick Brick #1
60% High Alumina Brick Brick #12
• Brick #1 (70% alumina) is made using bauxite and corundum (to meet alumina content). • Brick #12 (60% alumina) is made using Andalusite (naturally occurring mineral that
transforms to mullite when heated above 1000˚C during manufacturing).
M Mullite (3Al2O3•2SiO2) A Corundum (Al2O3)
©2014 Houghton Cascade ©2014 Houghton Cascade
Selec9on of Refractory Bricks
M
M
M
M
Impact of Corundum Content on Penetration
19
Brick Number
Classification Penetration (cm2)
Corundum Content
(%)
1 70% Alumina 7.55 18 2 8.38 18 3 10.38 23 4 9.03 21 5 70% Alumina 8.19 18 6 60% Alumina 7.61 22 7 7.61 12 8 5.68 8 9 5.74 4
10 5.29 0 11 4.58 0 12 4.19 Trace 13 5.16 Trace 14 60% Alumina 4.84 Trace
Corundum is used as starting material in the manufacture of these bricks.
Selec9on of Refractory Bricks
Cross-Sections for 70% High Alumina Plastics
20
In terms of chemical reaction with mud, plastics offer no advantage over bricks.
70% High Alumina Plastics
Plastic #1 Plastic #2 Plastic #3
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Impact of Temperature on Reaction of Mud with High Alumina Bricks
For high alumina bricks, the mud reacts with the brick to form liquid calcium alumino-silicates above 1450°C. Once formed, these liquids can readily penetrate deep into the matrix of the brick leading to rapid erosion and failure of the lining.
21
Material Test Temperature
1400˚C 1450˚C 1500˚C
70% High Alumina Brick!
! ! !
60% High Alumina Brick
(<10% corundum)
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Chemical Reactions of Soda with Alumina and Silica
Na2O + 2 SiO2 + ≤0.2 Al2O3
Na2O + 2 SiO2 + ≥0.2 Al2O3
Na2O + ≥0.4 Al2O3 + ≥3.5 SiO2
Na2O + ≤0.5 Al2O3 + ≤1.5 SiO2
Na2O + ≥0.5 Al2O3 + ≥1.5 SiO2
Natrosilite (Na2Si2O5) + Liquid
Nepheline (Na2O⋅Al2O3⋅2SiO2) + Liquid
Albite (Na2O⋅Al2O3⋅6SiO2) + Liquid
Na2SiO3 + Liquid
Nephelite (Na2O⋅Al2O3⋅2SiO2) + Liquid
The hot-face temperatures of the bricks are thought to approach 1500oC which enables the formation of new sodium silicate phases accompanied by liquid.
22 Selec9on of Refractory Bricks
Lime Coating Protects Refractory Lining
23
• In some kilns a coating of material buildups on the inner refractory wall.
• These coatings are typically between 2 and 10 cm thick.
Refractory Lining
Lime Coating
Metal Shell
Selec9on of Refractory Bricks
Temperatures Profiles for the Refractory Lining
24
Shell
38mm 180mm Hot Face Backup Coating
50.8mm 38mm
0
200
400
600
800
1000
1200
1400
1600
0 50 100 150 200 250 300 350
Tem
pera
ture
(˚C
)
Refractory Lining Thickess (mm)
No Coating
50mm Coating
Maximum working Temperature Diatomite based insulating bricks are 950˚C
Above 1450˚C the mud reacts with the alumina and silica in the brick to form liquids (rapid erosion)
The presence of a coating helps in keeping both the hot face and insulating bricks below their maximum working temperatures.
Selec9on of Refractory Bricks
Impact of Production Rate and Residual Carbonate on the Peak Refractory Temperatures
Increasing the firing rate increases peak temperatures of the refractory lining. The increase in temperature is more pronounced once all carbonate has been completely calcined.
1300
1350
1400
1450
1500
1550
1600
0
1
2
3
4
5
66 68 70 72 74 76
Pea
k R
efra
ctor
y Te
mpe
ratu
re (˚
C)
Res
idua
l Car
bona
te (%
)
Firing Rate (GJ/tonne)
Carbonate Temperature
Production = 290 t/day
25 Selec9on of Refractory Bricks
Examples of concave heating pit formation (commonly referred to as "duck nesting") in refractory linings caused by flame impingement on the lining.
Localized Overheating of the Refractory Lining
26 Selec9on of Refractory Bricks
Cross-Sections for Magnesia Bricks
27
Magnesia bricks do not react with mud to form liquids at the operating temperatures in lime sludge kilns.
Magnesia Bricks
Romag X Narco!
Magnel Harbison Walker! Radex A
Radex! Almag 85 Refractechnik!Basic #1 Basic #2 Basic #3 Basic #4
©2014 Houghton Cascade
Selec9on of Refractory Bricks
Comparison of Shell Temperatures for Refractory Linings Made Using Basic and High Alumina Bricks
0
100
200
300
400
500
600
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
She
ll Te
mpe
ratu
re (˚
C)
Distance Along Kiln (x/kiln length)
Uninsulated Basic
Insulated High Alumina
The shell temperatures of the kiln lined with the basic brick are nearly double those for the kiln lined with insulated high alumina brick.
28 Selec9on of Refractory Bricks
Comparison of Shell Heat Loss for Refractory Linings Made Using Basic and High Alumina Bricks
Since the heat transfer due to radiation is proportional to the fourth power of temperature, the corresponding shell heat losses for kilns lined with uninsulated basic brick can be as much as four times higher than those lined with insulated high alumina brick.
2
0.0
5.0
10.0
15.0
20.0
25.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Hea
t Flu
x (k
W/m
)
Distance Along Kiln (x/kiln length)
Uninsulated Basic
Insulated High Alumina
Hea
t Flu
x (k
W/m
2 )
29 Selec9on of Refractory Bricks
Infiltration of Basic Refractory Bricks by Volatile Components
Basic refractories do not react with lime mud to form liquids at the operating temperatures in lime sludge kilns. Physical infiltration of sodium and potassium salts and condensation is possible. The salt condensation leads to densified horizons in the basic bricks which become brittle. If the lining is exposed to thermo or mechanical loads, the salt infiltrated horizons can spall off.
30 Selec9on of Refractory Bricks
Examples of Refractory Bricks Used in Lime Kilns
Classification Zone Density (gm/cm3)
Thermal Conductivity
(W/m˚K)
Hot Face Lining
Basic
Burning
2.8 3.1
70% Al2O3 2.7 1.7
60% Al2O3 2.6 1.6
40% Al2O3 Super Duty
Preheating
2.2 1.1
30% Al2O3 High Duty 2.1 1.1
<30% Al2O3 Low Al2O3 Fireclay 1.6 0.6
Low Cement Castable Drying 2.3 1.7
Backup Lining <30% Al2O3
Low Al2O3 Fireclay Burning Preheating
1.6 0.6
Diatomite 0.9 0.2
31 Selec9on of Refractory Bricks
Commonly Used Refractory Linings in Lime Sludge Kilns
32
Distance Along Kiln (x/Lk) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
60% Alumina Brick Castable Bare Shell Low Alumina Fireclay Dam
Outlet
Insulating Brick
Burning Preheating Drying
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
60% Alumina Brick High Duty Castable Bare Shell Super Duty Dam
Outlet
Outlet
Insulating Brick
Conventional Dual Brick Lining
Dual Brick Lining with Single Layer of Low Alumina Fireclay in Preheating Zone
Selec9on of Refractory Bricks
Brick Thickness Measurements for 60% High Alumina Bricks
33
Mill #8 Brick #12
Distance Along Kiln (x/D)
Wea
r Rat
e (c
m/y
r)
• The burning zone refractory lining should go 2 to 3 years between major repairs.
• Paying more for bricks does not always improve performance (Brick #12 is three time more expensive than Brick #8).
Mill #5 Brick #8
Selec9on of Refractory Bricks
Refractory Lining for Heavily Loaded Lime Sludge Kilns
34
Burning Preheating Drying
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Magesite Brick High Duty Castable Bare Shell Super Duty Dam
Outlet
Outlet
High Duty
60% Alumina Brick
Insulating Brick
Dual Lining Using Magnesia and High Alumina Bricks in the Burning Zone
Selec9on of Refractory Bricks
Shell Temperature Monitors Should be Used When Making Changes to the Refractory Lining
35
Benefits of Monitoring Shell Temperatures • Detect hotspots on the kiln shell due to refractory lining loss, damage or wear • Detect ring formation • Extend service life of kiln shell and refractory lining
Thermal Imaging System
Selec9on of Refractory Bricks
Sample Output from Shell Scanner
36
Magnesia Brick
Temperature Increase Due to Magnesia Brick upto150°C
1st Tire
Access Door Access Door
2nd Tire
Selec9on of Refractory Bricks
Conclusions
• Kilns could not be run without refractory linings because the temperatures required to calcine the mud are so high they would destroy the metal shell.
• Most kilns use a dual brick lining to reduce shell heat losses in burning and preheat zones.
• Insulating the refractory lining can reduce heat consumption by 1.5 GJ/t CaO.
• High Alumina (60% or 70% Al2O3) refractory bricks are the most commonly used materials in hot face of the burning zone.
• The use of single component low alumina fireclay refractory bricks in the preheat zone is gaining more acceptance within the industry.
• Magnesia bricks can be use as a means to extend the working life of the refractory lining in the burning zone for heavily loaded kilns.
37 Selec9on of Refractory Bricks
Final Comments
• Optimizing the performance of the refractory lining is an ongoing process.
• Care must the take to keep good records – Installation (type of refractory and location). – Inspection (wear patterns and thickness measurements).
• Careful planning of schedule maintenance (avoid patchwork of odds and ends).
• Work with the brick suppliers and contractors to insure the refractory lining is properly installed.
38 Selec9on of Refractory Bricks