docSelection of Refractory Bricks for Use in Lime Sludge Kilns
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Selection of Refractory Bricks for Use in Lime Sludge Kilns
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 Selec9on of Refractory Bricks 2 Key Factors to Optimize Performance of the Refractory Lining Operating Conditions Material Selection Burner Design Optimized Refractory Lining Selec9on of Refractory Bricks 3 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. Selec9on of Refractory Bricks 4 Kiln Refractory Linings Single Brick Lining Dual Brick Lining Metal Shell Refractory Brick Refractory Brick Insulating Brick 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. Selec9on of Refractory Bricks 5 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 Selec9on of Refractory Bricks 6 Refractory Zones in the Lime Kiln Burning Zone (~10 diameters) ©2014 Houghton Cascade Castable Selec9on of Refractory Bricks High Duty Fireclay (40-50% Al2O3) High Alumina (60-70% Al2O3) 7 Kiln Diameter, Dk Height Dam, hd Discharge Dam hd = kDk where k = 0.15 to 0.25 • 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. Selec9on of Refractory Bricks 8 Cup Tes9ng High Alumina Refractory Bricks Cut test bricks into 5 cm blocks Selec9on of Refractory Bricks Drill 25.4 mm diameter hole to a depth of 25.4 mm 9 Cup Testing High Alumina Refractory Bricks 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 10 Cup Testing High Alumina Refractory Bricks Cross-sectional area used measure the extent of chemical reaction Selec9on of Refractory Bricks 11 Typical Composition of Lime Mud Mill Location Al (ppm) Fe Mg (ppm) (ppm) Mill #1 807 506 Mill #2 726 753 Mill #3 92 120 Mill #4 742 691 Mill #5 1010 795 Mill #6 763 1310 Mill #7 1900 2150 Mill #8 376 1040 Average 802 921 †Below limit of detection Selec9on of Refractory Bricks 2870 3710 1760 2350 5470 2700 6600 5410 3859 Mn Na (ppm) (ppm) 43 117 158 81 98 260 210 305 159 7800 8500 7200 5800 6200 11000 7900 7800 7775 P (ppm) Si (ppm) Total S (%) 5000 3000 1070 827 2230 2460 6790 7440 3602 910 860 <200† 1300 990 1000 1100 1100 1037 0.09 0.18 0.06 0.12 0.17 0.31 0.33 0.18 0.18 12 Cross-Sections Showing Impact of Mud Compositions on Penetration 70% High Alumina Brick Mill #1 Mill #5 ©2014 Houghton Cascade Selec9on of Refractory Bricks Mill #2 Mill #3 Mill #4 Mill #6 Mill #7 Mill #8 25 mm 13 Mill$#8$ Mill$#7$ Mill$#6$ Mill$#5$ Mill$#4$ Mill$#3$ Mill$#2$ Mill$#1$ Impact of Mud Composition on Penetration • 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. Selec9on of Refractory Bricks 14 Cross-Sections for 70% High Alumina Bricks 70%High HighAlumina Alumina Brick 70% Bricks Brick #2 Brick #1 Brick #4 ©2014 Houghton Cascade Selec9on of Refractory Bricks Brick #3 Brick #5 25 mm 15 Cross-Sections for 60% High Alumina Bricks 60% High Alumina Bricks Brick #6 Brick #11 Brick #8 Brick #7 Brick #12 Brick #9 Brick #13 Brick #10 Brick #14 ©2014 Houghton Cascade Selec9on of Refractory Bricks 16 Penetration (cm 2) 4 2 0 3 4 5 Selec9on of Refractory Bricks Nike 60 AR Brick& Resisto 605 Brick& Refralusit Brick
&63 Tuff Zone Brick& 8 6 7 9 Sample& Sample Number Ufala Brick
& 8 Seneca Brick	&60 Mizzou Brick& 10 Arco 60 Brick& 12 GM 60 D Brick& CBBrick& 70 D 2 GMBrick& 70 DE 1 Arco 70 Brick& Alusa Brick& 6 Kruzite Brick& Penetration for 60% and 70% High Alumina Bricks 70% Alumina Brick Avg. 8.71 cm2 60% Alumina Brick Avg. 5.61 cm2 10 11 12 13 14 17 Photomicrograph Showing Unreacted Matrix for High Alumina Bricks 70% High Alumina Brick 60% High Alumina Brick Brick #1 Brick #12 ©2014 Houghton Cascade A ©2014 Houghton Cascade M M M M M A M M A M 100 mm A M M 100 mm M M Mullite (3Al2O3•2SiO2) A Corundum (Al2O3) • • 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). Selec9on of Refractory Bricks 18 Impact of Corundum Content on Penetration Brick Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Classification 70% Alumina 70% Alumina 60% Alumina 60% Alumina Selec9on of Refractory Bricks Penetration (cm2) Corundum Content (%) 7.55 8.38 10.38 9.03 8.19 7.61 7.61 5.68 5.74 5.29 4.58 4.19 5.16 4.84 18 18 23 21 18 22 12 8 4 0 0 Trace Trace Trace Corundum is used as starting material in the manufacture of these bricks. 19 Cross-Sections for 70% High Alumina Plastics 70% High Alumina Plastics Plastic #1 Plastic #2 Plastic #3 ©2014 Houghton Cascade In terms of chemical reaction with mud, plastics offer no advantage over bricks. Selec9on of Refractory Bricks 20 Impact of Temperature on Reaction of Mud with High Alumina Bricks Test Temperature Material 1400˚C 1450˚C 1500˚C 70% High Alumina Brick! ! ! ! 60% High Alumina Brick (<10% corundum) ©2014 Houghton Cascade 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. Selec9on of Refractory Bricks 21 Chemical Reactions of Soda with Alumina and Silica Na2O + 2 SiO2 + ≤0.2 Al2O3 Natrosilite (Na2Si2O5) + Liquid Na2O + 2 SiO2 + ≥0.2 Al2O3 Nepheline (Na2O⋅Al2O3⋅2SiO2) + Liquid Na2O + ≥0.4 Al2O3 + ≥3.5 SiO2 Albite (Na2O⋅Al2O3⋅6SiO2) + Liquid Na2O + ≤0.5 Al2O3 + ≤1.5 SiO2 Na2SiO3 + Liquid Na2O + ≥0.5 Al2O3 + ≥1.5 SiO2 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. Selec9on of Refractory Bricks 22 Lime Coating Protects Refractory Lining Metal Shell Refractory Lining Lime Coating • In some kilns a coating of material buildups on the inner refractory wall. • These coatings are typically between 2 and 10 cm thick. Selec9on of Refractory Bricks 23 Temperatures Profiles for the Refractory Lining 38mm 38mm 1600 Shell Backup Hot Face 180mm Coating 50.8mm Above 1450˚C the mud reacts with the alumina and silica in the brick to form liquids (rapid erosion) 1400 Temperature (˚C) 1200 1000 800 Maximum working Temperature Diatomite based insulating bricks are 950˚C 600 No Coating 400 50mm Coating 200 0 0 50 100 150 200 250 300 350 Refractory Lining Thickess (mm) The presence of a coating helps in keeping both the hot face and insulating bricks below their maximum working temperatures. Selec9on of Refractory Bricks 24 1600 Production = 290 t/day 5 1550 4 1500 3 1450 2 1400 1350 1300 66 1 Carbonate Temperature Residual Carbonate (%) Peak Refractory Temperature (˚C) Impact of Production Rate and Residual Carbonate on the Peak Refractory Temperatures 0 68 70 72 74 Firing Rate (GJ/tonne) 76 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. Selec9on of Refractory Bricks 25 Localized Overheating of the Refractory Lining Examples of concave heating pit formation (commonly referred to as "duck nesting") in refractory linings caused by flame impingement on the lining. Selec9on of Refractory Bricks 26 Cross-Sections for Magnesia Bricks Magnesia Bricks Romag X Basic Narco#1 ! Magnel BasicWalker #2 ! Harbison Radex A Basic Radex#3 ! Almag 85 Basic #4 ! Refractechnik ©2014 Houghton Cascade Magnesia bricks do not react with mud to form liquids at the operating temperatures in lime sludge kilns. Selec9on of Refractory Bricks 27 Comparison of Shell Temperatures for Refractory Linings Made Using Basic and High Alumina Bricks Shell Temperature (˚C) 600 Uninsulated Basic 500 Insulated High Alumina 400 300 200 100 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Distance Along Kiln (x/kiln length) 0.8 0.9 1 The shell temperatures of the kiln lined with the basic brick are nearly double those for the kiln lined with insulated high alumina brick. Selec9on of Refractory Bricks 28 Comparison of Shell Heat Loss for Refractory Linings Made Using Basic and High Alumina Bricks Uninsulated Basic 20.0 Insulated High Alumina 2 Heat Flux Flux (kW/m Heat (kW/m)2) 25.0 15.0 10.0 5.0 0.0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Distance Along Kiln (x/kiln length) 0.8 0.9 1 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. Selec9on of Refractory Bricks 29 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. Selec9on of Refractory Bricks 30 Examples of Refractory Bricks Used in Lime Kilns Density (gm/cm3) Thermal Conductivity (W/m˚K) 2.8 3.1 2.7 1.7 60% Al2O3 2.6 1.6 40% Al2O3 Super Duty 2.2 1.1 2.1 1.1 1.6 0.6 2.3 1.7 1.6 0.6 0.9 0.2 Classification Zone Hot Face Lining Basic 70% Al2O3 30% Al2O3 High Duty Burning Preheating <30% Al2O3 Low Al2O3 Fireclay Low Cement Castable Drying Backup Lining <30% Al2O3 Low Al2O3 Fireclay Diatomite Selec9on of Refractory Bricks Burning Preheating 31 Commonly Used Refractory Linings in Lime Sludge Kilns Conventional Dual Brick Lining Burning Dam Outlet Outlet Preheating 60% Alumina Brick Super Duty Drying High Duty Castable Bare Shell Insulating Brick 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Dam Outlet Dual Brick Lining with Single Layer of Low Alumina Fireclay in Preheating Zone 60% Alumina Brick Low Alumina Fireclay Castable Bare Shell Insulating Brick 0 0.1 0.2 Selec9on of Refractory Bricks 0.3 0.4 0.5 0.6 Distance Along Kiln (x/Lk) 0.7 0.8 0.9 1.0 32 Wear Rate (cm/yr) Brick Thickness Measurements for 60% High Alumina Bricks Mill #8 Brick #12 Mill #5 Brick #8 Distance Along Kiln (x/D) • 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). Selec9on of Refractory Bricks 33 Refractory Lining for Heavily Loaded Lime Sludge Kilns Dual Lining Using Magnesia and High Alumina Bricks in the Burning Zone Burning Dam Outlet Outlet Magesite Brick Preheating 60% Alumina Brick High Duty 0 0.1 0.2 Selec9on of Refractory Bricks Super Duty Drying High Duty Castable Bare Shell Insulating Brick 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 34 Shell Temperature Monitors Should be Used When Making Changes to the Refractory Lining Thermal Imaging System 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 Selec9on of Refractory Bricks 35 Sample Output from Shell Scanner Temperature Increase Due to Magnesia Brick upto150°C Access Door Access Door 1st Tire Magnesia Brick Selec9on of Refractory Bricks 2nd Tire 36 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. Selec9on of Refractory Bricks 37 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. Selec9on of Refractory Bricks 38
