FAST TRACK TRAINING PROGRAM
Table of Content
Refractory Handouts (Reference)
1. Refractory Description... 1 2. Refractory Classification... 6 3. Refractory Properties ... 17 4. Brick Selection ... 21 5. Monolithics... 26 6. Refractory Installations ... 40 7. Refractory Management... 68
SECTION 1
REFRACTORIES DESCRIPTION
1.1 Manufacturing Processes 1.2 Manufacturing Variations
1.1 Manufacturing Processes
Crushing
Grinding
Screening
Batching
Mixing
Forming step(s)
Packaging
Heating step(s)
Palletizing
Semi-finishing step(s)
Shipping
Finishing step(s)
Palletizing
1.2 Manufacturing Variations
Crushing and grinding: Coarse crushers:
jam;
gyratory and cone;
dry pan; roll crusher; hammer mill. Intermediate pulverizers: cage disintegrator; hammer mill; disk mill; autogenous mill.
Fine grinding mills: ball;
rod;
roller;
hammer mill.
Screening (single or multi-decked): Stationary screens: grizzly Dynamic screens: inclined vibrating; horizontal vibrating; oscillating; reciprocating; sifter; centrifugal.
1.2 Manufacturing Variations (cont’d.)
Batching:
Manual and automatic weighing equipment
Mixing: Ribbon Muller Rotating screw Drum-type blender Double-cone blender Twin-shell blender Sigma blade Planetary Plow High-intensity Forming: Hand-molding Air-ramming
Pressing (toggle, friction, hydraulic, wet and dry bag isostatic) Casting Palletizing Heating: Drying Curing Tempering Baking
1.2 Manufacturing Variations (cont’d.)
Semi-finishing or finishing: Impregnating Grinding Drilling Plating Banding Coating Glazing Sizing Insulating Packing: Bag (paper, plastic) Carton
Supersack
Can (plastic, metal)
Drum
Many thousands of products… and formats
Many variations between products of the same types
SECTION 2
REFRACTORIES CLASSIFICATION
2.1 Basis of ISO Classification
2.2 ISO Coding Systems
2.3 Shaped Basic Refractory Products 2.4 ISO Classification for Unshaped
2.5 Unshaped Refractory Products Installation 2.6 Bonding Mechanisms of Refractory Materials
2.1
Basis of ISO classification
1- Product type
2- Chemical composition
3- Classification temperature 4- Principal raw material
5- State of raw material
6- Nature of bond
7- Post treatment of product
8- Bulk density
9- Shot content
10- Strength
2.2
ISO - CODING SYSTEMS
Shaped refractory products Ceramic fiber
products Unshaped refractory products Category 1 Insulating products 3 Alumina, silica and alumino-silicate products 6 Basic products containing less than 7% carbon 7 Basic products containing more than 7% carbon 9 Blankets, mats, felts and paper
10 Alumina, silica and alumino-silicate products 11 Basic products
Code SIN S SM SM C UAS UM
Clause 5.1 Product type combined with chemical composition SIN Table 2 SHA98, SHA87, SHA68, SHA56, SHA45, SFC40, SFC35, SFC30, SLA10, SSS85, SSL93 Table 3 SMM98C07 to SMS40C07 Table 4 SMM98C10 to SMS30C30 Table 5 CBV, CBC, CMV, CMC, CFV, CFC, CPV, CPC Table 6 UAS95F05 Clause 5.2 Chemical composition Included in the
above Included in the above Included in the above X01 to X06 Table 6
Included in the
above Included in the above Clause 5.3 Classification temperature /075/ to /180/ Clause 5.3 /075/ to /180 Clause 5.3 /075/ to /180 plus E when needed Clause 5.3 /075/ to /180 Clause 5.3 Clause 5.4 Principal raw material M0 to M7 Table 11 Clause 5.5 State of raw material R4 to R7 Table 12 R3 to R7 Table 12 R4 to R4, R6, R7 Table 12 Clause 5.6 Nature of bond B1 to B3 Table 13 B1 to B4 Table 13 B3, B4 Table 13 Clause 5.7 Post treatment of product T1 to T4 Table 14 T1 to T4 Table 14 Clause 5.8
Bulk density 550 to 1600plus L when needed Table 15 048, 064, 96, 128, 160, 192 Clause 5.8 090, 125, 160 Table 16 Clause 5.9
Shot content S0 to S4Table 17 Clause 5.10
Strength C, H, CH, STables 18 and 19 C Table 20 Clause 5.11 Installation DVP,DPX, DPY, DPZ, LVP, LPX, LPY, LPZ, MVP, MPX, MPY, MPZ, RVP, RPX, RPY, RPZ, Table 21 DVP,DDV, DPX, DPY, DPZ, LPX, LPV, LPZ, MPX, MPY, MPZ, RVP,RDV, RPX, RPY, RPZ, GPX, GPY, GPZ Table 21
Product Types and Codes
Which includes broad chemical classes and physical appearance
Shaped refractory products
Ceramic fiber
products Unshapedrefractory products Category 1 Insulating products 3 Alumina, silica and alumino-silicate products 6 Basic products containing less than 7% carbon 7 Basic products containing more than 7% carbon 9 Blankets, mats, felts and paper 10 Alumina, silica and alumino-silicate products 11 Basic products
Product type Code
No subdivision SIN
High alumina SHA
Fireclay SFC Low alumina fireclay SLA Siliceous SSS Silica SSL Magnesia SMM SMM UMM
Magnesia-alumina SMA UMA
Magnesia-chrome SMK UMK Chrome-magnesia SMK UMK Magnesia-doloma SMD SMD UMD Doloma SMD SMD UMD Forsterite SMS UMS Blanket vitreous CBV Blanket crystalline CBC Mat vitreous CMV Mat crystalline CMC Felt vitreous CFV Felt crystalline CFC Paper vitreous CPV Paper crystalline CPC
Alumina, silicate and
2.3
Shaped Basic Refractory Products
Description Range of MgO content (%) Code
Magnesia 98 SMM98C07 95, <98 SMM95C07 90, <95 SMM90C07 85, <90 SMM85C07 Magnesia-alumina 80, <85 SMA80C07 70, <80 SMA70C07 60, <70 SMA60C07 50, <60 SMA50C07 40, <50 SMA40C07 30, <40 SMA30C07 Magnesia-chrome 80, <85 SMK80C07 70, <80 SMK70C07 60, <70 SMK60C07 Chrome-magnesia 50, <60 SMK50C07 40, <50 SMK40C07 30, <40 SMK30C07 Magnesia-doloma 80, <85 SMD80C07 70, <80 SMD70C07 60, <70 SMD60C07 Doloma 50, <60 SMD50C07 40, <50 SMD40C07 30, <40 SMD30C07 Forsterite 50, <60 SMS50C07 40, <50 SMS40C07
Description Range of MgO
content in the oxide
Code, the last two digits showing the upper % limit of residual carbon content raw material (%) 7, <10 10, <15 15, <20 20, <25 25, <30 Magnesia- 98 SMM98C10 SMM98C15 SMM98C20 SMM98C25 SMM98C30 carbon 95, <98 SMM95C10 SMM95C15 SMM95C20 SMM95C25 SMM95C30 90, <95 SMM90C10 SMM90C15 SMM90C20 SMM90C25 SMM90C30 85, <90 SMM85C10 SMM85C15 SMM85C20 SMM85C25 SMM85C30 Magnesia- 80, <85 SMD80C10 SMD80C15 SMD80C20 SMD80C25 SMD80C30 doloma- 70, <80 SMD70C10 SMD70C15 SMD70C20 SMD70C25 SMD70C30
2.4 Part B - ISO Classification For Unshaped
Description Range of Al2O3
content Code, the last two digits show the lower % limit of iron oxide x10
1.5 > 1.5, 3.0 > 3.0
Alumina, silica and 95 UAS95F05 UAS95F15 UAS95F30
alumino-silicate 85, < 95 UAS85F05 UAS85F15 UAS85F30
75, < 85 UAS75F05 UAS75F15 UAS75F30
65, < 75 UAS65F05 UAS65F15 UAS65F30
55, < 65 UAS55F05 UAS55F15 UAS55F30
45, < 55 UAS45F05 UAS45F15 UAS45F30
35, < 45 UAS35F05 UAS35F15 UAS35F30
25, < 35 UAS25F05 UAS25F15 UAS25F30
15, < 25 UAS15F05 UAS15F15 UAS15F30
5, < 15 UAS05F05 UAS05F15 UAS05F30
< 5 UAS00F05 UAS00F15 UAS00F30
Description Range of MgO content (%) Code
Magnesia 98 UMM98 95, <98 UMM95 90, <95 UMM90 85, <90 UMM85 Magnesia-alumina 80, <85 UMA80 70, <80 UMA70 60, <70 UMA60 50, <60 UMA50 40, <50 UMA40 30, <40 UMA30 Magnesia-chrome 80, <85 UMK80 70, <80 UMK70 60, <70 UMK60 Chrome-magnesia 50, <60 UMK50 40, <50 UMK40 30, <40 UMK30 Magnesia-doloma 80, <85 UMD80 70, <80 UMD70 60, <70 UMD60 Doloma 50, <60 UMD50 40, <50 UMD40 30, <40 UMD30 Forsterite 50, <60 UMS50 40, <50 UMS40
2.5 Unshaped Refractory Products Installation
Product type Installation technique Gunning installation
temperature Code
Dense castable Vibration poker - DVP
Dry vibration - DDV
Pneumatic projection None stated DP
Ambient DPX
Elevated DPY
Ambient and elevated DPZ
Insulating castable Pneumatic projection None stated LP
Ambient LPX
Elevated LPY
Ambient and elevated LPZ
Mouldable Pneumatic projection None stated MP
Ambient MPX
Elevated MPY
Ambient and elevated MPZ
Ramming mix Vibration poker - RVP
Dry vibration - RDV
Pneumatic projection None stated RP
Ambient RPX
Elevated RPY
Ambient and elevated RPZ
Gunning material Pneumatic projection None stated GP
Ambient GPX
Elevated GPY
2.6 Bonding Mechanism of Refractory Materials
Introduction
For refractory materials, the cement industry applies the term “bond” to the cohesion occurring in the natural state because it is of primary interest in subsequent processes. Depending on the firing temperature, the natural bond will be replaced by a ceramic bond.
If the transition to a ceramic bond occurs without significant loss of strength, the bond is considered to be “permanent” (example: phosphate bond). In contrast, a pronounced loss of strength prior to ceramic bonding is called “discontinuous bonding” (example: sulphate bonded magnesia bricks). The minimum strength remaining in the “intermediate” temperature zone may drop to 10-20% of the initial strength.
Classification of Bonds According to Bonding Agents
Class of Bond Bonding Agent
Ceramic Bond Eutectic melts,
Sintering
Hydraulic bond High-alumina cement,
Calcium aluminates
Chemical bond Phosphates, Sulphates
Chlorides, Chromates
Organic bond Tar, pitch, resins, dextrin, linseed
Refractory Bonding Systems in Brick (B), Mortar (M), Plastics (P), Castables (C)
Class Type Temp. of Set Usage
Air-set Silicate Cement Phosphates (basic) Alum R.T. R.T. / 600C R.T. (R.T.) 500C M, (P), (B) C, (B) C M, P. (B) Air / Heat Phosphoric (acid)
Sulphates
> 400 C > 800 C
M, P B, M Heat / Ceramic All of above + Clay > 1000 C B, M, P Combination of above
Classification of Bonding According to Hardening Process
Manufacture and delivery to end users
Manufacturing characteristics and
physical-chemical state
Refractory products
Unfired refractories Unfired, preliminary drying, presence of capillary and chemically suspended water, high temperate phases only partially present (pre-fired lean clay)
Phosphate bonded bricks and mixtures, sulfate bonded magnesite bricks, mixtures, mortars, water-glass bonded mixtures, mortars
Hydraulically bonded bricks, mixtures, mortars
Tar bonded magnesite and dolomite bricks plastic mixtures with and without chemical pre-binders
Stabilized refractories Stabilized at temperatures between 400 - 1000° C chemically suspended water expelled, partial initial reactions while still in solid state or intermediate melt development
Phosphate bonded stabilized bricks, tar bonded stabilized bricks
Fired refractories Fired, at least up to planned
application temperature,
fritting or sintering, high temperature phase required, state of equilibrium not completely reached
Ceramically bonded bricks, all refractories bonded in melting phase or through sintering (primary bond, formation of spinel, periclase)
Classification of Bonding According to Manufacturing Process
Bonding method Bonding agent Bonding process Refractories Air setting
- Natural
Bonding clays Drying (clay-water
systems) Plastic building materials ramming, mixes, mortars Pitch, tar Viscosity increase Dolomites
Sorel cement Formation of hydrate and
gel Unfired magnesite bricksMortars, ramming mixes Silicate of sodium Formation of gel and
hydrate carbonation Mortars
- Artificial Air hardening lime Carbonation Refractory building boards, mortars Magnesium oxides Linseed oil Polyester resins Carbonation Oxidation Polymerization Mortars Hydraulic setting High-alumina cement
(Alumina bonding)
Formation of hydrate hydrate gel
Unfired bricks and finished pieces ramming casting and spraying mixtures
Heat setting Acidic phosphates (reactive bond) (phosphate bond) (stabilized bond)
Condensation
(Chained and interlaced phosphates)
Polymerization
Unfired bricks, ramming mixes (especially fire clay and high alumina products)
Firing
- Liquid sintering
Eutectic bond (melts) (ceramic bond) (conventional bond) Primary bond (spinel)
Bonding during liquid phase
“fritting”
Primary bond “sintering”
All ceramically bonded (mixtures and mortars), basic products and special product Spinel forming induction Furnace mixtures - Dry sintering (periclase spinel)
(polymer bond) (active oxide)
SECTION 3
REFRACTORIES PROPERTIES
3.1 Properties of Refractories
The significant of any refractory - including its high temperature strength - depend on its mineral makeup and the way these minerals react to high temperatures and furnace environments.
Unfired or green refractories consist of a mixture of refractory particles varying from coarse to extremely fine sizes. Coarser particles may be 1/4 inch in diameter, and the fines may pass a 200-mesh screen.
After the refractory has been fired, the fines form the ceramic bond between larger particles. The fired refractory consists of bonded crystalline mineral particles and glass or smaller crystalline particles, depending largely on the composition of the refractories.
Most refractories contain a small amount of accessory oxides such as soda, lime, potash and iron oxide. These “impurities” promote formation of low-melting glasses, and so for many years considerable research has gone into elimination or control of these accessory oxides in refractories.
The physical properties of refractories most readily determined are bulk density, porosity and strength at room temperature.
Bulk density, usually expressed as pounds per cubic foot or grams per cubic centimeter, is an indirect measure of any refractory’s capacity to store heat. Technically, it is the ratio of weight or mass to volume.
The porosity of a refractory indicates its ability to resist penetration by slags and fluxes and permeation by gases as well as influencing its thermal conductivity. Insulating refractories are lightweights with a porous structure.
The cold crushing strength of refractories indicates ability to withstand handling and shipping without damage and impact or abrasion in low temperature operations. However, it provides little or no indication of their strength at furnace operating temperatures.
The most significant properties of refractories are those which enable them to stand up under conditions found in an operating furnace. Refractories must withstand the maximum service temperature of the furnace. In most applications the reheat, load and hot modulus tests, should play an important part in the choice of refractories for high temperature applications. These tests indicate the strength of refractories in service conditions.
Refractories must often resist spalling effects of rapid temperature changes. They may be called on to resist heavy loads, abrasion and impact, or the corrosion and erosion caused by liquids and gases. In general, the refractories that are strongest at operating temperatures show the best resistance to impact and abrasion.
The standard ASTM Reheat Test, method C113, tests brick for changes in dimensions. In this test, the bricks are placed in a furnace and gradually heated to a predetermined temperature, depending on their composition. The test temperature is held five hours and the bricks are cooled. Then they are measured to determine changes in linear dimensions and volume.
The Load Test, a standard laboratory procedure, measures the ability of a brick to carry a load at high temperatures, the temperature depending on the quality of the brick. In this test, two 9-inch straight are set on end in a furnace and a vertical load of 25 pounds per square inch in applied. Under ASTM Method C16, the temperature is gradually raised and held on a prescribed schedule. The load test is an accelerated test. In service loads are usually less than 25 psi.
In the Hot Modulus of Rupture Test, refractory samples are brought up to temperature in a testing furnace. They are placed in the testing machine, supported at both ends across a 7-inch span and broken in the middle (ASTM C583-76). The machine measures the forace in pounds required to break the specimen.
Thermal spalling is caused by stresses developed by unequal rates of contraction or expansion in different parts of the refractory, usually associated with rapid changes in temperature. The brick with greatest resistance to thermal spalling have the lowest average thermal expansion and do not expand sharply within any narrow temperature range.
The Panel Spalling Test, applicable to fireclay, some high-alumina and some basic brick, is designed to measure comparative resistance to thermal spalling. ASTM Method C38 calls for 14 brick laid in a movable panel to form a section about 18 inches square. One side of the panel is backed by insulation; the other, subjected to heat. After a 24-hour preheat, the panel goes through a thermal shock treatment, alternately heated and cooled according to a specified pattern. Results are reported in terms of average percentage loss in weight.
In most furnaces, chemical reaction contributes to the ultimate destruction of refractory linings. Refractory materials can react with the furnace charge, with slags or other furnace products, with fuel ash, fumes or dust and in some cases with other refractories. Absorption of liquids or penetration by gases or fumes into the refractories can change the size and orientation of crystals, form new minerals or glass and thus alter the physical and chemical characteristics of the refractories.
Erosion, washing away grains of refractory after the bond has been destroyed, in a physical process. Corrosion is the chemical process that destroys the bond.
Dense refractories, low in apparent porosity, generally can be expected to demonstrate greater resistance to corrosion and erosion. It is a natural assumption and generally true that basic refractories should be used where basic fluxes come into contact with the furnace lining, and acid refractories with acid processes. However, there are some exceptions to this general principle due to differences in operating and reaction temperatures, reaction rates, viscosities of reaction products and the formation of protective coatings on linings.
Chemical composition represents a guide to the ingredients of the mix. In the fireclay and high-alumina refractories, the high-alumina-silica ratio roughly indicates the refractoriness of the composition - the higher the alumina content, the greater the refractoriness. Accessory oxides also play a part in the quality of the refractory. Lime may be present as a result of the binder in monolithic refractories.
Iron oxide becomes important in refractory compositions when the process carried out in the refractory-lined vessel involves a reducing atmosphere. At certain temperatures, carbon monoxide can react with iron oxide in a refractory causing deposition of carbon within the lining. If the reaction continues, it will crack the lining. A hydrogen atmosphere will reduce iron oxide, sometimes producing volatile compounds that can be harmful to a process.
The Pyrometric Cone Equivalent (PCE) provides a standard for evaluating the high temperature softening behavior of some fireclay refractories.
In this test, a ground sample of the material is molded into test cones and mounted on a ceramic plaque with a series of standard pyrometric cones. The plaque is heated at a specific rate until the test cone softens and bends. The number of the standard cone whose tip touches the plaque at the same time as the tip of the test cone is reported as the PCE value of the test cone.
PCE does not indicate a definite melting or fusion point, but simply offers a comparison of thermal behavior in terms of standard cones. It is, however, widely used for quality control tests on fireclay products during mining and manufacturing.
SECTION 4
BRICKS SELECTION
4.1 Refractories Selection 4.2 Selection Criteria
4.1 Refractories Selection
Materials
Many suppliers
– Subtile and non-subtile differences
Installation Methods
“Know-how” with bricks
– Different with monolithics
Operating Conditions
“IPC Concept”
The “Integrated” Approach
A First Example
First Step, zoning, and installation methods (KIV)
Second Step, definition of the constraints – Causes and effects
– Thermal-mechanical-chemical
Stresses due to… causing such phenomena…
– Definition of the “properties” required Le cahier des charges par zone
Third Step, variability of the operation
– Key input variables - Key output variables The IPC… 1 to 4
Fourth Step, correlation-diagnostics – Post-mortem analysis
Fifth Step, new testing - back to first step
4.2 Selection Criteria
Thermal factors incomplete combustion of fuel, flame characteristics
variations in dosing of fuel, especially when coal is used, overheating
displaced, i.e. not adequately oriented, adjusted, burner pipe
secondary combustion
Chemical factors
use of fuel rich in sulphur and chlorine
use of high-ash coal
frequent change of fuel
disturbance of the SO3 / (K2O + Na2O) - equilibrium
high concentration of chlorides (KCI!) in kiln atmosphere (raw meal)
sulphatizing and/or addition of fluorspar
variations in cement raw material
grain size of SiO2 - component
change between reducing and oxidizing atmosphere
4.3 Guidelines
Coating formation With coating No coating
Temperature too
Unstable Stable Low high (seldom)
Chemical stresses
- clinker melts
- alkali salt components
- reduction (redox) — —
Thermal stresses
- heat load (overheating) — —
- thermal shocks
- thermal fatigue —
Mechanical stresses
- squeezing
- erosion —
Key: = very high, = high, = medium, = low, = very low, — = absent
Effected kiln areas Normal cases Special case
- transition zone — — —
- sintering zone —
- discharge zone — —
SECTION 5
MONOLITHICS
5.1 Monolithics for Preheater
5.2 Monolithics for Kiln
5.3 Monolithics for Burner Pipe
5.4 Monolithics for Hood
5.5 Monolithics for Grate Cooler 5.6 Monolithics for Planetary Cooler
5.1 Preheater
5.1.1 Material Selection There are many different ways to make a 60% alumina low cement castable, and also different ways to put it in place. With so many variables at hand, it is not very difficult to make selection mistakes. Although easier and faster to install than bricks, monolithic products cannot compete with bricks in performance. That makes material selection a simple task if longevity is the main factor, use bricks; if installation time is more important, then choose a monolithic product such as castables or plastics. In the upper stages of preheaters, mechanical stability should be the main concern in material selection. The temperature profile of a modern 6stage preheater shows maximum gas temperature of 1620° F for stage 6, and only 545° F for stage 1. Therefore a good quality fireclay castable is all that is required from stages 3 to 5, a 50 or 60% alumina low cement castable for stage 6, and a siliconcarbide alumina low cement castable for the flashcalciner, alkali bypass, riser duct and feed shelf. The purpose of the siliconcarbide grains is to minimize sulphur and alkali buildups in the area. For maximum performance, all these linings must be castvibrated in place. Gunning should only be used to install the backup insulation. Suspended roof in the cyclones and flashcalciner can be lined with refractory plastic rammed in place around brick anchors. The most common mistake in choosing materials for preheater application is to put the speed of installation ahead of material suitability. This difficult decision must be made at a plant level, with or without the installer’s input. If the preheater lining is supposed to last from 2 to 5 years, without major repairs, then the installation time should never dictate how the material will be installed. Day after day refractory manufacturers develop new products aimed at “speeding up” the installation. As a consequence, gunning, selfflow, freeflow and pumpables became more important than alkaliresistant, low permeability, thermal shock resistant products. The results are mixed and many plants are learning the hard way, by trial and error.5.1.2 Insulation Although the total heat loss by radiation in the preheater is less than 2% of the total heat input, most preheater vessels and ducts are insulated to protect the steel shell. The use of refractory fiber boards in the hotter sections of the preheater may induce premature lining failure if the fiber fails behind the dense lining. Fiber boards contain a certain amount of organic matter that, when exposed to moderate temperatures, burns out with emission of fumes. The damaged product lacks both mechanical strength and insulating properties, and exposes both the steel shell and the anchor stem to higher temperatures. The resulting relative movements damage the anchoring system and induce cracks on the dense lining. To avoid problems like this, chose an insulating material with the minimum amount of loss on ignition such as calcium silicate, diatomaceous earth or vermiculite boards, or insulating castables that can be cast, gunned, sprayed or pumped in place. 5.1.3 Lining Thickness The ideal lining thickness for any area of the preheater is the minimum thickness required to attain the specified shell temperature. If the lining is too thin, the shell and the anchoring system are exposed to temperatures that accelerate metal corrosion, scaling and fatigue. Once the anchor is “burned out” the lining collapses. Also the insulating layer may fail at its interface with the dense material, creating gaps where dust will accumulate and compromise the lining integrity. If the lining is too thick, high thermal gradients develop within the dense lining, causing it to crack or spall off. If the insulation is too thick, the dense lining operates at higherthannormal temperature and results destroyed by chemical attack or melting. This is particularly true for the flash calciner equipped with solid fuel burners. Over insulating also brings up the interface temperature between the two layers, with consequent damage to the anchors and to the insulating material.
material, and keep the dense layer constant. A good reason for our success in several installations is exactly the strict observance of this rule.
5.1.4 Dust Infiltration This is one of the most common failure modes in preheater applications: red hot kiln dust infiltrates behind the dense castable or brick and cause one or several of the following damages: anchor shearing or breaking insulation sintering and shrinking lining pushing in from behind In all three cases the lining in the affected area collapses in a short time. Since kiln dust particles are in average smaller than 48 microns, they behave like a fluid and find their way through any open joint, crack or hole in the lining. In cases where the insulation shrinks, dust deposits build up between the shell and the lining, or between the insulating lining and the dense lining, creating a tremendous head pressure that, in some instances, pulls the anchor away from the shell. The best remedy in this type of failure is to airtighten seal the entire lining at junctions, corners, ceilings and expansion joints. Metal trays supported by cantilevers or dust traps must be used at the beginning and at the end of each section. If brick is used, the entire lining must be installed with a good quality mortar, and brick anchoring must be used to bond the lining from time to time. Special attention must be given to inspection doors and peepholes. The flanks of the insulating layer cannot be exposed in those areas. Instead, use the dense material around doors and holes. 5.1.5 Sulphur Attack Sulphur penetrates the lining and reacts with the calcium aluminate phases according to:
The formation of anhydrite and gypsum weakens the lining and increases its tendency to promote and stabilize preheater buildups.
In order to minimize sulphur attack, choose castables with a minimum amount of calcium aluminate cement (check the CaO content) and increase the lining density. If possible, balance the sulphur to alkali ratio in the system to decrease the amount of free SOx.
On new linings, apply a protective ceramic coating to seal the open pores and prevent sulphur penetration.
5.1.6 Potassium Attack
Alumina containing castables, mullite based or bauxite based, are very sensitive to potassium oxide, chloride, sulphide and sulphate. It reacts with the castable according to:
3Al2O3.2SiO3 + 3K2O 3K2O.Al2O3.2SiO3 + 2 Al2O3
KCl, NaCl + 11 Al2O3 + 1/2 O2 (Na,K)2 Al22O34 + Cl2
During kiln shutdown, the products of reaction undergo a 30% volume expansion inside the castable, causing an alkali bursting and lining destruction. In the second reaction above, the product of reaction is a powerful flux that softens the castable in service.
This problem can be minimized using bauxite-based castables, as opposed to mullite-based or corundum-based materials. Although bauxite also reacts with potassium, the volume expansion is not as severe as with mullite. Another measure to minimize the problem is to reduce the alumina content in the product, if the service temperature allows.
Other ways to minimize potassium attack is to decrease the amount of back up insulation and to seal the finished lining with an alkali-resistant ceramic coating.
5.1.7 Thermal Overload
Thermal overload is becoming a common reason for lining destruction inside the flash-calciner and at the bottom part of the kiln riser. This trend is a consequence increased synthetic or waste fuels utilization in the back end of the kiln. Being a process problem, it must be solved at an operational level.
What causes the thermal overloading are unexpected variations in the heating value of waste-derived fuels. In those cases, the fuel mass input is constant, but not the amount of energy
released during fuel combustion. If this problem cannot be solved by the fuel supplier or by the kiln operator, then serious consideration should be given to a more refractor, magnesia-spinel lining.
In some other cases the thermal load is normal but buildups formed in the riser or inside the flash-furnace direct the hot gases to the wall and destroy it in a short time. The solution is to replace the lining with an anti-buildup silicon carbide-alumina castable.
5.1.8 Thermal Shock
Lining destruction by thermal shock is becoming more frequent with the trend in waste-fuel burning in the back end of the kiln. The main source of thermal shock is the frequent opening of inspection doors to air-blast or worse, water blast buildups formed on the walls. The secondary source are defective fuel feeding systems that introduce large volumes of cold air in the system in a cyclic way. Thermal cycling destroys not only the lining but also the anchoring system.
In order to eliminate the need for water-blasting, install a low coatability silicon-carbide alumina castable in the entire riser and flash calciner sections. In parallel, balance the sulphur to alkali ratio in the system to help minimize buildup formation. Before the dryout, seal the entire lining with a rare-earth oxide ceramic coating.
5.2 Kiln
5.2.1 Material Selection
Inside the rotary kiln, three types of monolithic products are used, according to the installation method: castables, pumpables and plastics. Gunning materials are not recommended inside a kiln because of their naturally higher porosity and lower strength at kiln temperatures.
Pumpables and self-leveling castables should be limited to the chain section where temperatures are moderate and the casting volumes are large. When pumping material into the chain section, especial care must be used in metering the amount of water. Too much water will render the lining abrasion-sensitive in a zone where abrasion resistance must be maximized.
For the nose-ring, a more refractory, higher alumina product can be used, provided there is no severe alkali attack in the area. In planetary cooler kilns, a 95% corundum low-cement castable is recommended around the satellite inlets.
No monolithic product should be used at or in the burning zone because of the limited hot-strength of castables and plastics, and the impossibility to properly anchor the product in place.
5.2.2 Insulation
Back up insulation is not recommended under monolithic products in the kiln. The insulation lacks compressive strength and could collapse under the dense lining causing its failure. Moreover, it has a tendency to overheat and destroy the anchoring system. In rotary driers, roasters and lower temperature kilns, however, back up insulation can be safely used provided the product modulus of rupture is above 250 p.s.i.
5.2.2 Eutectic Melting
The refractoriness of monolithic products is usually expressed in the manufacturer’s data sheet as “maximum service temperature”. Following that simple orientation, a 60 or 70% alumina castable could be used in service temperatures exceeding 3000° F. However, when installed in the rotary kiln, these products melt at temperatures as low as 1600° F.
Most castables, plastics and gunning materials contain mostly alumina and silica in their composition, and the minimum melting temperature in the pure system is in fact 3300° F. The addition of iron, sodium, potassium, calcium, sulphur and magnesium to the system, all elements present in the clinker melt, drastically reduce the melting temperature of the refractory through the formation of eutectic combinations. This phenomenon limits the application of monolithic products to areas of the kiln where clinker melt or salt concentrations do not occur.
5.3 Burner Pipe
5.3.1 Material Selection
The main reason for refractory failure in the burner pipe is differential expansion. Usually most materials prescribed for burner application are adequate, if they stayed in place.
Material selection for burner pipes must take into account a multiplicity of factors that require conflicting properties in the material:
- thermal cycling - alkali attack - sulphur attack - high abrasion
- low thermal conductivity - high refractoriness
Since it is impossible to take all these variables into consideration in the same product, a compromise solution must be found. Therefore, material selection must be done on a per-case basis when it comes to burner pipes. A good starting point is the wear mechanism. If we know what is causing lining destruction then material selection becomes a simple task.
5.3.2 Insulation
Since the main purpose of the lining here is to reduce heat transfer to the metal pipe, a low k-factor material is a must. Another option is to wrap the metal pipe with insulating felt, to a final thickness of 1/2 in., and fill the balance with the dense castable.
5.3.3 Lining Thickness
The size of the opening in the kiln door limits the lining thickness on the burner pipe to 1-4 in. A thicker lining has the advantage of better insulating, but it has the disadvantage of additional weight on the pipe. A 3 in. lining with 1/2 in. insulation can be advantageously applied to most cases.
In some kilns the burner lining only wears at the bottom tip, due to high heat radiation from the clinker and hard sandblasting with clinker fines carried with the secondary air. In this area the addition of 2% w/w stainless steel needles to the castable will help.
5.3.4 Differential Expansion
This is the main reason for refractory failure on burner pipes. The pipe, the lining and the anchors are constantly shrinking or growing, sometimes in the same direction, during normal operation, sometimes in opposite directions during kiln upsets. Therefore it is very important to thoroughly coat the pipe and all the anchors with a thin layer of any combustible material such as paraffin wax or bitumen. Upon burning, these materials leave gaps than can accommodate at least part of the differential expansion. Another way to minimize the consequences of expansion is to use articulated or floating anchors that allow free castable movements. Any type of rigid anchors induces stress in the lining and cause it to crack.
5.3.5 Potassium Attack
In certain kilns an alkali cycle is formed between the cooler and the burning zone. Potassium salts, mostly KCl, K2O and K2SO4 become trapped inside large clinker balls. As these balls enter
the cooler, they burst open under thermal shock and the red-hot core releases potassium vapors that end up in the burner lining where it reacts with alumina and silica to form feldspars. The castable becomes weak and as the feldspars crystallize they burst the castable in layers parallel to the hot face. In order to minimize potassium attack, low porosity, low alumina or no-alumina low cement castables are recommended. Coating the burner lining with a high temperature ceramic coating also helps seal the open porosity and deter alkali infiltration. Insulation plays a negative role by increasing the depth of alkali penetration. Potassium attack is particularly severe in kilns burning charcoal fines, lignitic fuels or insufflating high-alkali dust in the burning zone. Burning high moisture fuels also enhances the problem because water increases the vapor pressure of potassium.
5.3.6 Expansion Joints
The burner pipe expands in service and shrinks during kiln shutdown. So does the castable, but to a lesser extent. Therefore, radial and longitudinal dry joints are installed in most pipes. The problem with the open joints is clinker dust penetration and subsequent lining destruction. If joints are truly necessary in a given pipe, care must be taken to build it staggered or shiplapped so that dust cannot infiltrate. By using articulated or floating anchors and by properly coating the pipe and the anchors as described earlier, expansion joints can be avoided without any serious damage to the lining.
5.3.7 Clinker Blasting
The burner tip is constantly blasted by the secondary air stream. At burning zone temperatures, most castables lose strength and result severely abraded by the impinging particles. In planetary cooler kilns the same happens in the mid-section of the pipe. The best way to solve this problem is to zone the lining, using an extremely abrasion resistant material in these specific areas. Silicon carbide or corundum low cement castables are the most suitable products for the application.
5.3.8 Clinker Impact
In grate cooler kilns, when the burner pipe is positioned inside the kiln, past the nose ring, large lumps of clinker and coating constantly fall on the upper half of the pipe, damaging the lining by impact. To solve this problem, a v-shaped piece of Inconel can be welded to the pipe, forming a roof that will divert the falling pieces away from the castable underneath. The same applies to burner pipes in satellite cooler kilns at the satellite ;inlets. The best solution here is to create a tray on the upper side of the burner, exactly in the area where the clinker impacts. This metal tray or box is then filled with loose clinker nodules that can absorb the impact. The box is built over the regular lining.
5.4 Hood
5.4.1 Material Selection
For lining purposes the kiln hood must be divided in at least two areas: the upper half, towards the burner pipe, and the lower half towards the cooler. The upper half side walls and ceiling work under high temperature and high heat radiation. It is often subject to thermal spalling during clinker and coating avalanches, or during temporary kiln shutdowns when the hood door is open. The lining in this area is constantly exposed to alkali and sulphur coming from the cooler with the secondary air. These conditions are getting worse with the advent of the high-efficiency coolers that elevate the secondary air temperature a couple hundred degrees. The best lining in those circumstances is a 50 or 60% alumina, low cement castable. If the secondary air temperature is above 1650° F and loaded with potassium, then the best alternative is to line the hood with MAGKOK bricks backed up by insulating fire brick or calcium silicate board.
The lower half of the hood can be advantageously lined with a non-wetting silicon-carbide alumina or zircon-alumina low cement castable. Non-wetting properties are desired to minimize showman formation in the cooler.
Independently of which material is used in the application, pre-cast, pre-fired modular blocks should always be preferred to cast or gunned in place materials.
5.4.2 Insulation
The kiln hood must always be insulated due to the high heat concentration in the area. As the work lining thins down by wear, the insulation keeps the shell from overheating and warping. Moreover, there are always people circulating around the hood and a hot shell poses a safety problem to the workers and visitors.
The integrity of the insulation is critical to the work lining integrity. If hot clinker dust penetrates the insulating layer behind the dense castable or brick, it quickly damages the anchoring system and pushes the lining away from the shell until it collapses. Most insulating materials shrink at hood temperatures and make the situation even worse.
When choosing an insulating material for hood application, make sure it contains no organic binders, its limit service temperature is above 2000° F and it retains its full integrity at that temperature.
Our recommended choices are 2000 degrees calcium silicate boards or 2300 degrees insulating castable gunned in place.
5.4.3 Lining Thickness
The lining thickness is a function of the hood design and the desired temperature on the hood shell. It is always better to have a highly abrasion-resistant lining in a thin layer, than a conventional material in a thick layer.
The dense lining in the hood is usually a medium to high alumina castable or plastic. For such materials the dense layer should not be thicker than 8 in., and the backup insulation should not be thicker than 3 in. If the insulation is too efficient, the dense, work lining can be severely infiltrated and destroyed by alkali attack. Thicker linings also are subject to higher thermal gradients and, consequently, more prone to crack.
If lining the hood walls with RefrAmerica’s modular blocks, the dense layer will be 7 in. thick, and the insulation will be 2 in. thick.
5.4.4 Potassium Attack
In certain kilns an alkali cycle is formed between the cooler and the burning zone. Potassium salts, mostly KCl, K2O and K2SO4 become trapped inside large clinker balls. As these balls enter
the cooler, they burst open under thermal shock and the red-hot core releases potassium vapors that end up in the burner lining where it reacts with alumina and silica to form feldspars. The castable becomes weak and as the feldspar crystallize they burst the castable in layers parallel to the hot face. In order to minimize potassium attack, low porosity, low alumina or no-alumina low cement castables are recommended. Coating the burner lining with a high temperature ceramic coating also helps seal the open and deter alkali infiltration. Insulation plays a negative role by increasing the depth of alkali penetration. Potassium attack is particularly severe in kilns burning charcoal fines, lignitic fuels or insufflating high-alkali dust in the burning zone. Burning high moisture fuels also enhances the problem because water increases the vapor pressure of potassium.
5.4.5 Sulphur Attack
Sulphur penetrates the lining and reacts with the calcium aluminate phases according to:
in operation: SO3 + 2 (CaO.Al2O3) CaO.2Al2O3 + CaSO4
SO3 + CaO.Al2O3 2Al2O3 + CaSO4
during shutdown: CaSO4 + xH2O CaSO4.xH2O
The formation of anhydrite and gypsum weakens the lining and increases its tendency to promote and stabilize preheater buildups.
In order to minimize sulphur attack, choose castables with a minimum amount of calcium aluminate cement (check the CaO content) and increase the lining density. If possible, balance the sulphur to alkali ratio in the system to decrease the amount of free SOx.
On new linings, apply a protective ceramic coating to seal the open pores and prevent sulphur penetration.
5.5 Hood
5.5.1 Material Selection - Side Walls
Gunnables, pumpables, self-flow, self-leveling and shot-crete materials follow the FIFO RULE in this application: Fast-In-Fast-Out. Since we want the cooler lining to last at least three years, with minor repairs, the installation velocity should never dictate which materials will be employed. The best alternative to line cooler walls is still brick, but, unfortunately, this technology is dead in the U.S. The acceptable options left are conventional or low cement castables cast-vibrated behind forms and held in place by a combination of metal and ceramic anchors. A 60% alumina product is sufficient for most applications.
Another interesting alternative, finding more and more acceptance in cement plants, is the modular lining which offers the advantages of both bricks and castables. In this alternative the castable is pre-cast and pre-fired into blocks that have the insulation and the anchoring system pre attached.
5.5.2 Material Selection - Roof
The cooler roof lining works under high heat radiation, thermal cycling, tensile stress, gouging abrasion from clinker fines and a constant risk of dust collecting behind the lining.
High alumina plastic held by a combination of ceramic and metal anchors is recommended, but it requires a perfect dryout before the kiln starts. A second option is a low cement gunning mix, gunned over a lightweight material also gunned in place.
5.5.3 Material Selection - Back Wall
The main wear mechanism in the back wall is heavy impact from hot clinker balls bouncing from the bed of material. A corundum or silicon carbide low cement castable can be advantageously used in the area of impact.
Another common problem in modern coolers, with high secondary air temperature, is the formation of snowman that raise to the kiln level. The use of a non-wetting silicon carbide-alumina, silicon carbide or alumina-zirconia low cement castable should address the problem. These materials are available in modular blocks for prompt installation.
5.6 Planetary Cooler
5.6.1 Material Selection - Inlet and Elbow
Mechanical stress, clinker abrasion, clinker impact, high temperature and varying temperature are the main factors in this area of the kiln. Mullite based or corundum based, coarse grained low cement castables should be used in this application, with or without 2% w/w steel reinforcement. The anchoring design and the expansion joints design are critical for good material performance.
5.6.2 Material Selection - Tubes
Abrasion and impact are the main wear factors here. The cam lining should preferably be in mullite brick, and base lining in fireclay brick or low cement castable.
SECTION 6
REFRACTORIES INSTALLATION IN A ROTARY KILN
6.1 Introduction
6.2 We must look at general requirements when we start a new installation or a repair job
6.3 Different methods of installation in a rotary kiln 6.4 Kiln cleaning (kiln coating removal)
6.5 Drilling (thickness of the brick lining) 6.6 What refractory should be stripped
6.7 Installation of the individual brick grade (zoning suitable for the different burning process)
6.8 Installation
6.9 Nose-ring
6.0 METHODS OF REFRACTORY INSTALLATION IN A ROTARY KILN. 6.1 Introduction
The lifetime of the refractory lining in rotary kiln is base on different conditions: The operating conditions of the plant
The condition of the kiln shell ovality in the tyre area and the procedure of heating-up and cooling down the kiln
The choice of refractory materials in respect of its quality and its positioning (zoning) in the kiln
A proper and efficient installation of the refractory lining will not only help to increase lifetime and eliminate some stresses. It will prevent premature wear.
6.2 We must look at general requirements when we start a new installation or a repair job Safety for workers (they have to be well instructed and we must give them the
appropriate tools).
Installation quality. The lining must be installed in such a way that it will fit the most perfectly and tightly against the kiln shell that will increase lifetime to the refractory.
Acceptable bricking progress. A good planning, a good supervision and appropriate tools will help to reach this goal.
6.3 Different methods of installation in a rotary kiln
The following methods will be demonstrated in the Baker brick installation video
Screw Jack method
Glueing method
Hydraulic and pneumatic method
6.3.1 Screw Jack Method
Advantages
– Low investment in equipments
– Possibility to rotate the kiln during the job
Disadvantages
– A slow method of installation
– Necessitate to turn the kiln very often (slow down the job) – Can be used only in small kiln, not more than 4.5 Ø
– It is not a very safe method for the workers
6.3.2 Glueing Method
Advantages
– Kiln can be rotate at all time during the lining work – Low investment in equipment
– Easy access to the lining work (no scalfoling or platform required) – Fast method of installation
Disadvantages
– Storability and used (critical temperature has to be respected) – Requires to turn the kiln very often
– When gluening bricks over welding seams, corrections can not be made with mortar on the extrado side of the bricks
– That method is not save for the working personnel. The shell must be very clean and free of rust and specified temperature has to be respected. That is why this method is only use on specific job for example in very narrow area.
6.3.3 Hydraulic and Pneumatic Jig (mul-o-ring method)
Advantages of this method
– The rig can be moved easily along the kiln, so that there is no need for the platform to be continually rebuilt compare to some other method
– The kiln does not have to be rotated. There is no time lost to modify access paths and electrical wiring, etc.
– This method is reliable and safe.
– The bricking progress is very good, 6 to 8 hours per tonnes of bricks install. It is about half the time of the other method.
Disadvantages of that method
– With this method, the possible kiln turns have to be scheduled many hours in advance, so that enough time is allowed to close all the open rings.
– It is more difficult to install bricks with mortar in the upper section of the kiln. The equipment get dirty and it may cause malfunction of the cylinders.
– High investment costs for equipments.
– When lining a long section, all keys are in the same area. It may cause a weakness in that area.
6.4 Kiln Cleaning (kiln coating removal)
Kiln with diameter Ø bigger than 4.0 m has to be free of his coating and clean. Completely from the nose-ring to the inlet.
To protect the workers from the falling coating
To permit a good inspection of the bricks lining
Kiln with smaller Ø don’t loose easily its coating, thus it is possible to leave the coating in place, as long you are sure of the good condition of the bricks lining.
6.5 Drilling (thickness of the brick lining)
Make drilling at 3 points equally distribute on the kiln circumference and at every meter along the kiln. Keep these informations as records for the follow-up of the lining refractory. You will need these informations to decide witch sections of bricks lining should be stripped and also for the planification of the next shut-down.
6.6 What refractory should be stripped
Each plant has to establish its own criteria in regard of their past experience taking in consideration their constraints.
Most plants consider that a lining thickness of 125 mm in the sintering zone is acceptable for a regular campaign (normally for 1 year).
In case of a very difficult lining section, like transition zones, the use of a brick consumption factor may be very useful.
6.6.1 Defining a brick consumption factor
For a specific linear meter of brick in the kiln, calculate the factor which consist of the grams of brick consumed per ton of clinker produced
Make a relationship between that factor and the thickness of the bricks left.
Use that figure to find out the thickness of bricks lining you will normally need for your next campaign for that specific section of lining.
6.7 Installation of the individual brick grade (zoning suitable for the different burning process)
The choice of the brick grade must be suitable for the individual zone in different burning process (wet, semi-dry, dry, preheater and calciner). The brick grade should be selected to meet the special requirements of each individual rotary kiln.
Table 1 - Kiln Zoning
Zone Preheater Great Cooler Preheater Planetary Cooler Dry Process Kiln Wet Process Kiln Precalciner Kiln < 4.0 m Ø > 4.0 m Ø < 4.0 m Ø > 4.0 m Ø
With Great
Cooler PlanetaryWith Cooler
With Great
Cooler Planetary;With Cooler With Great Cooler > 4.0 m Ø Outlet Zone 4-1x Ø 4-1x Ø 1-1.5x Ø 1-1.2x Ø * 1-1.5x Ø * 1-1.5x Ø * Lower Transition Zone Burning Zone 1 1x Ø 1-2x Ø 1x2 Ø 1x2 Ø 1-2x Ø 1-2x Ø 1-2x Ø 2x Ø 1-2x Ø Burning Zone 2 3x Ø 4x Ø 3x Ø 4x Ø 3x Ø 3x Ø 3x Ø 3x Ø 6-8x Ø Upper Transition Zone Burning Zone 3 2-3x Ø 3x Ø 2-3x Ø 3x Ø 3x Ø 3x Ø 2-3x Ø 2-3x Ø 2-4x Ø Safety Zone 2x Ø 2x Ø 2x Ø 2x Ø 2x Ø 2x Ø 2x Ø 2x Ø 2x Ø Preheating Zone 5-8x Ø 5-8x Ø 5-8x Ø 5-8x Ø Difference with respect to overall length of kiln From 12-16x Ø
Chain Zone — — — — 4-6x Ø 4-8x Ø 4-8x Ø 4-8x Ø —
6.8 Installation
6.8.1 The following are to be followed when installing the brick
a) No change of material in the tyre area
A change of material in the tyre area, from magnesie-chromite or magnesia-spinel bricks to alumina bricks should be avoided, as due to different thermel conductivity and coating behaviour of different refractory bricks installed on both side of the tyre. That will cause differential tyre clearances. The tyre will not run on the whole surface, resulting in increased ovality and higher stresses to the refractory lining, thus resulting in damages to the refractory of that zone.
The same applies to the change from alumina to MgO bricks.
b) No use of different MgO brick grade in the burning zone
If small parts, of magnesia-chromite bricks are installed in the coating-free transition zone between high-alumina and magnesite-spinel bricks, the magnesia-chromite bricks are exposed to high mechanical load due to their different refractoriness under load as a consequence there is often caused a premature wear of the refractory lining.
6.8.2 Installation with mortar, clench-laid or metal shims
a) Installation with mortar
Advantages
– Refractory bricks installed with mortar form a gas-tight monolithic unit. Any mechanical loads occurring due to kiln shell ovality, are distributed more uniformly over the entire lining, so that brick hot face spalling is rare.
– Differences in brick dimensions can be compensated for, by means of mortar, so that it is easier to follow the mixed lining ratio.
b) The following points must always be observed
The mortar must be mixed in accordance with the manufacturer’s instructions. There is three basic types of mortar available for rotary kilns:
– High-alumina mortar – Magnesia mortar – Fireclay mortar
It is recommended to use the product pure undiluted to avoid premature setting. – The mortar should be spread uniformly to give a maximum joint thickness of 1 to
1.5 mm.
c) Clench lining (V.D.Z. ISO)
The method is coming more and more adopted in recent years. The following details should be noted.
– It is recommended to depart from the theoretical mixed brickwork and to adapt the mixed brickwork to the kiln shell requirements.
– The extrado side of the bricks must be completely in contact with the kiln shell and the horizontal joint must point in the direction of the kiln axis.
– For this purpose, it is necessary to adapt the mixed brickwork to the kiln shell requirements.
– Sometimes the brickwork become stepped, particularly near the welding seams. To compensate for this, thin mortar joints may be applied between the bricks and, in the case of larger welding seams beneath the bricks. In no case any metal shims should be used as to compensate for this.
– In the case of a kiln with large ovality and big shell deformation, it will be wise to use mortar.
d) Installation with metal shims
– Some of the magnesia bricks, are still laid with metal shims. From our experience, these shims get oxidized during the operation, take volume specifically on the hot face and cause premature wear to the refractory lining. – Like the other method, the bricks must be completely in contact with the kiln shell
and the horizontal joint must point in the direction of the kiln axis.
– When closing the rings, avoid by all means the insertion of two metal shims into one brick joint.
6.8.3 Expansion joints in brickwork
– Because of the different thermal expansion behaviour of refractory materials, the increased expansion in the case of magnesia bricks must be compensated for, by the insertion of cardboard spacers.
– Alumina bricks do not need any additional joints, since the expansion of this material is slightly greater than the expansion of the entire rotary kiln axially and vertically.
– With basic brick grades, expansion joints of 2 mm are inserted between the individual ring (2 mm is the equivalent of 1% of the brick length).
6.8.4 Ring Closure
Correct closure of the brick ring is very important to secure the brick work (Figure 3).
– Use only the original brick to close the rings. Never use cut bricks to fit the closure.
– Never use key bricks side by side, alternate them with standard VDZ or ISO shapes. Same with ASTM.
– The metal shims used for the closure, should have a thickness of not more than 2 mm.
– Never use more than one metal shim per joint. If more than one shim is needed for keying the closure bricks, they should be distributed over the entire closure area.
– Sharpening of metal shims makes insertion much easier.
Figure 3 - Keying of ring
Correct installation Key bricks Keying shims max. 2 mm Correct installation Keying shims max. 2 mm Key bricks
a) Installation of the last closure brick
The final brick of the ring must be inserted from above because it is impossible from the side as in the case of other rings (Figure 4).
– Make sure that the last bricks are tightly pressed against kiln shell and that the horizontal joint extends in the direction of and parallel to the kiln axis.
– Make the opening for the last brick such that a standard VDZ or ISO shape brick fits. Do not use any cut bricks. Same for ASTM. The ring is secured by knocking in keying shims which should be distributed over the entire closure zone.
6.8.5 Important points to take care of during the bricking work
One of the important thing for a good lining lifetime is the installation of the refractory bricks in separate ring without any entangle of the ring to one another. This can be achieved if the ring are place exactly parallel to the vertical seams (Figure 5).
– Reference lines are drawn on the kiln shell parallel to the welding seams at every 1.5 m. These lines must be strictly followed for the lining work.
– If only a section of the lining refractory has to be repaired, take the nearest welding seam as a reference line. An uncut ring should be laid to secure the older lining. Cut the following ring of new brick to adapted with the new alignment. – The last ring have to be adapted to the old lining. You need to have at least 100
mm brick length to join the old lining. If impossible, cut the two last consecutive rings. By doing so, this shall respect the minimum length of brick recommended (some companies provide bricks 250 mm, that avoid to cut on two rings of bricks).
– As a guideline for the brickwork, the long axis of the kiln is to be determined. Two point needs to be located. The lowest point in the kiln is determined at the start of the section to be lined, using a spirit level parallel to a vertical welding seam. The same is done at the end of the section to be lined. These two points are then connected by a line. A timber batten or steel angle is placed along this line and fixed to prevent it from shifting. This gives a straight brickwork end, which subsequently facilitates closing of the ring.
Figure 5 - Alignment of brickworks
Parallel alignment
Horizontal welding joints of kiln shell
Auxiliary line e.g. chalk line
Vertical welding joint of kiln shell Axial joint
Parallel alignment Radial joint
a) Brick lining over welding seams
– A welding seam higher than 8 mm the bricks should be cut to fit the shell (Figure 6).
– A welding seam lower than 8 mm the bricks are backed with mortar. So the brick can be installed parallel to the other brick rings.
– With the glueing method, the brick have to be cut out above the welding seams.
Figure 6 - Brick Lining Adjustment of Welding Seams
To be filled with mortar
Kiln shell To be cut on installation
More than 8 mm
Kiln shell To be filled with mortar
Kiln shell To be filled with mortar Kiln shell To be filled with mortar
6.8.6 Installation of bricks lining over distorted kiln shell is possible but it has to be done very carefully
– Like usual, the extrado side of the brick must fit tightly against the kiln shell (Figure 7).
– The horizontal joints must be laid with mortar. The maximum mortar joint thickness between the bricks should not exceed 1.5 mm.
– Mortar is use to compensate for irregularities between the extrado side of the bricks and the kiln shell. Maximum thickness 8mm.
– It is advisable to position these deformed kiln area in the lower half of the kiln before starting bricking.
Figure 7 - Brick Lining Adjustments For Distorted Kiln Shell (Axial)
Filled with mortar Max. 8 mm
A
6.8.7 Retaining rings
– Because of the kiln’s inclination of 2.5 to 4% and refractory expansion, a pressure is done towards the kiln outlet. A way to compensate this is the use of retaining rings in several places in the kiln. Usually, the retaining ring is installed at every 35metres apart. Never install a retaining ring in the burning zone, the transition zone , over the tire or the kiln drive. In these zones, the basic brick expansion (1.6 to 1.8% and mechanical stress causes high pressure against retaining rings resulting in damaged brick. Thus leading to hot spots.
6.8.8 Types of retaining rings
We have found that a successful retaining ring is made of a pair of rings separated by 80 mm. Each ring from the pair has a square section of 50 mm by 50mm and is made from 8 to 10 segments depending on the kiln size diameter. The retaining ring is designed such that a brick of 198 mm can be laid on top of them. The other type of recommended retaining ring is the triangle shape one as shown below. Like the other one, it is made from 8 to 10 segments. The lower retaining ring should be place at least 800 mm up-hill of the nose-ring.
Figure 9 - Retaining Rings
10mm 80mm 80m m Down Kiln 50 50 retaining ring 180
6.9 Nose-ring
The most two types of lining used for nose-ring construction: bricks or castable.
6.9.1 Bricks construction
Quality of bricks required:
High abrasion resistance
Good thermal shock resistance
Good resistance to mechanical stresses
Good resistance to alkalies
a) Advantages
– Easier and faster to install
– Heating up procedure much faster than the castable lining – Can be installed without regard of temperature
– Quality of the lining remain constant all around the brickwork – Easier to replace compare to castable
Some nose-rings are builted with special bricks shapes. Other are builted with bricks cut from standard shapes. The manufacturers can not produce special shape bricks that correspond to the required quality, because of the complicated production technic. The experience has proved that the use of regular bricks shape has done better results.
