Refractory Installation Techniques In: Complete Guide & Down

The refractory lining is the protective armor of every hot process vessel in the cement plant: the preheater cyclones, the riser ducts, the calciner, the kiln shell, the hoods, the kiln inlet and outlet, and the clinker cooler all depend on their refractory to contain the process temperatures, resist the chemical attack of the clinker and the gases, and protect the steel structure. Yet the most carefully selected refractory material will fail prematurely if it is installed poorly: the installation quality, the joint control, the curing and the drying determine a large share of the lining life, and the installation techniques are therefore a complete engineering discipline in their own right. This article presents the complete technical treatment of the refractory installation techniques used in the cement industry: the material selection, the preparation of the installation, the brick installation methods for the rotary kiln, the castable installation by pouring and pumping, the gunning techniques, the ramming and the patching repairs, the curing, the drying and the heating procedures, the quality control of the finished lining, and the safety of the installation work. It is written for refractory engineers, maintenance managers, contractors and plant personnel who plan and execute refractory installations.

1. Refractory Materials and Their Installation Requirements

The cement plant’s refractory systems use three principal material families, each with its own installation technology: the shaped refractories, the bricks, which are laid with mortars or dry joints; the monolithic refractories, the castables, which are mixed with water and installed by pouring, pumping, gunning or ramming; and the special materials, such as the plastics and the ceramic fiber products, which serve specific zones. The selection of the material determines the installation method, and the selection is driven by the service conditions of each zone: the temperature, the chemical atmosphere, the abrasion, the mechanical load and the thermal cycling.

The principal refractory zones of the plant and their material and installation requirements are:

• The preheater cyclones and the riser ducts: abrasion-resistant castables and dense bricks, installed by pouring and gunning, with the emphasis on the abrasion resistance and the airtightness.
• The calciner: dense castables with the high alumina content, installed by gunning or pouring, resistant to the temperature and the meal abrasion.
• The kiln inlet and the transition zones: high alumina and magnesia-spinel bricks, laid with the mortar or the dry joints, with the emphasis on the alkali resistance and the thermal shock resistance.
• The burning zone: magnesia-spinel bricks, laid with the dry joints and the steel plates, designed to work with the coating and the thermal cycling.
• The kiln outlet and the nose ring: high alumina castables and bricks, resistant to the temperature and the mechanical loads.
• The kiln hood and the cooler feed end: dense castables and high alumina materials, installed by gunning and pouring.
• The cooler zones: high alumina and silicon carbide castables and bricks, with the abrasion resistance and the thermal shock resistance.

The installation technique must respect the material’s specific requirements: the bricks must be laid with the correct joints and the expansion allowances, the castables must be mixed with the correct water content and placed within the working time, and the gunning mixes must be applied with the correct velocity and the layer thickness. The material manufacturer’s instructions, the application datasheets and the installation standards form the basis of every installation procedure, and the deviation from these instructions is the most common cause of the premature lining failure.

2. Planning and Preparation of the Installation

The refractory installation is a major campaign that is planned in detail before the kiln stop: the scope is defined from the lining inspection, the materials are ordered with the delivery lead times, the installation crew and the equipment are scheduled, and the procedures and the acceptance criteria are prepared. The planning must also account for the production schedule: the installation time inside the kiln is on the critical path of the plant’s annual stop, and the sequence of the work is optimized to minimize the total duration.

The preparation of the installation site and the equipment includes:

• The delivery and the storage of the materials: the bricks are stored dry and protected from the weather, the castables in their sealed bags with the shelf life verified, and the consumables, the mortar, the plates and the anchors, are staged at the work location.
• The preparation of the shell: the surface is cleaned, the old lining and the anchors are removed, the shell is inspected for the damage and the deformation, and the repairs are completed before the new lining starts.
• The preparation of the installation equipment: the mixers, the pumps, the gunning machines, the scaffolding, the platforms and the lifting equipment are checked and positioned.
• The ventilation and the access: the kiln is ventilated, the lighting is installed, and the access platforms and the working levels are prepared.
• The training and the briefing: the installation crew is briefed on the procedures, the quality requirements and the safety rules for the specific work.

The quality of the preparation determines the quality of the installation: the well-prepared site allows the crew to work continuously at the required quality, while a poorly prepared site causes delays, improvisations and quality defects. The installation supervisor is responsible for the preparation checklist, and the completion of the preparation is verified before the lining work begins.

3. Brick Installation in the Rotary Kiln

The brick lining of the rotary kiln is the most critical installation in the plant, because the kiln bricks work under the highest temperatures, the mechanical loads and the thermal cycling. The kiln is lined in rings, each ring consisting of a number of bricks that form the complete circle, and the bricks are laid with the radial joints aligned to the kiln axis and the circumferential joints staggered between the rings. The installation is performed with the kiln stationary, using the ring installation machines, the bricking rigs, or the manual installation with the air-powered bricking machines.

The principal installation methods for the kiln brickwork are:

• The full circle ring installation with the bricking rig: the rig is positioned at the ring location, the bricks are placed around the full circle, and the last brick, the key brick, is driven into place to lock the ring.
• The partial circle installation: for the repair work, the new bricks are placed over a segment of the circle, and the ring is completed against the existing lining.
• The manual installation: in the smaller kilns and the difficult locations, the bricks are placed by hand with the bricking machines or the pneumatic hammers.
• The spiral or herringbone patterns: used in some designs to improve the stability of the lining, with the bricks laid at an angle to the kiln axis.

The quality requirements of the kiln brick installation are:

• The correct joint thickness: the radial joints are kept to the minimum, typically 1 to 2 millimeters for the dry-jointed bricks, and the circumferential joints are controlled within the specified limits.
• The correct keying: the key brick completes the ring with the correct fit, and the rings are keyed in the staggered positions to distribute the joints.
• The correct expansion allowance: the bricks expand thermally, and the design provides the expansion allowance through the joint arrangement and the flexible plates; the incorrect allowance causes the buckling of the lining at the operating temperature.
• The alignment of the rings: the rings are laid perpendicular to the kiln axis, and the deviation is controlled with the ring guides and the checks.
• The final compaction: the bricks are seated with the controlled force, ensuring the full contact of the joints and the uniform pressure around the ring.

The bricking machines and the rigs are the standard equipment of the kiln relining, and their correct operation is a trained skill: the rig is advanced ring by ring, the bricks are fed to the workers, and the quality of each ring is checked before the rig moves on. The modern installation uses the semi-automatic rigs that significantly reduce the installation time and improve the consistency, and the installation crews are trained and certified by the material suppliers and the specialist contractors.

4. Mortar Joints and Dry Joints in Kiln Brickwork

The joints of the kiln brickwork are either mortar joints, in which the bricks are bedded with a refractory mortar, or dry joints, in which the bricks are placed without the mortar and the sealing is achieved by the steel plates inserted in the joints. The selection between the two is a material and a zone decision: the magnesia-spinel bricks of the burning zone are typically laid dry with the steel plates, because the mortar does not match the brick chemistry and the plates provide the required flexibility and the thermal expansion control; the high alumina bricks of the transition zones are laid with the alumina-rich mortars, which bond the bricks and seal the joints against the gas penetration.

The mortar preparation and the application follow the material specification: the mortar is mixed with the exact water content, the working time is respected, and the joints are filled completely without the voids. The dry-joint installation uses the thin steel plates, typically 0.5 to 1.5 millimeters thick, inserted between the bricks to take up the thermal expansion and to stabilize the ring; the plates are placed at the specified positions, and their correct placement is part of the quality inspection. The choice of the plate material, the carbon steel for the moderate temperatures and the stainless or the alloy plates for the hot zones, follows the service temperature.

The joint control is one of the most important quality parameters of the kiln lining: the joints are the weakest points of the lining, and the gas penetration through the open joints attacks the brick faces and the shell. The inspection of the joints during the installation is performed continuously by the supervisor, and the completed lining is inspected with the joint measurement and the torch test, in which a light source is placed behind the joints to detect the open joints. The rework of the defective joints is performed immediately, because the correction is impossible once the kiln is back in service.

5. Castable Installation: Pouring and Pumping

The monolithic refractories, the castables, are installed in the preheater, the calciner, the hoods, the cooler and the many irregular shapes of the plant, where the brickwork is impractical. The castable installation by pouring is the basic method: the castable is mixed with water in the mixer, transported to the location, and poured into the forms, where it is vibrated to remove the air and to fill the form completely. The pouring method is used for the accessible, open locations, and its quality depends on the mixing consistency, the water content and the vibration.

The pumping method extends the pouring to the difficult locations: the mixed castable is pumped through the pipes and the hoses to the point of placement, where it is poured and vibrated in the forms. The pumping requires the castable formulation designed for the pumping, with the appropriate flow characteristics, and the pump equipment with the correct settings. The pumping reduces the handling and allows the placement of the large volumes in the confined locations, but it requires the careful control of the pumping pressure, the hose routing and the working time of the material.

The quality requirements of the castable installation are:

• The correct water content: the castable is mixed to the manufacturer’s specification, and the excess water weakens the material and increases the shrinkage; the water content is verified with the flow test or the consistency measurement.
• The complete filling: the forms are filled completely, the corners and the details are filled by the vibration, and the voids are prevented.
• The correct formwork: the forms are tight, the anchors are positioned correctly, and the form release is prepared.
• The anchor system: the stainless steel anchors, welded to the shell, hold the castable in place, and their spacing and the design follow the material and the temperature requirements.
• The control of the placement temperature: the castable is placed within the allowed temperature range, and the hot or the freezing conditions are managed with the procedures.

The castable installation is performed with the trained crews, and the sampling and the testing of the material, the cube strength tests and the density checks, verify the quality of the installed lining. The records of each pour, the material batch, the water content, the placement time and the test results, form the quality documentation of the installation.

6. Gunning Techniques

The gunning is the installation method in which the dry or the pre-mixed refractory is conveyed through a hose and mixed with water at the nozzle, then applied to the surface at high velocity. The gunning is used for the large areas of the preheater, the calciner and the cooler, and for the repairs of the existing linings, because it can apply the material quickly to the vertical and the overhead surfaces without the formwork. The gunning quality depends on the machine settings, the material consistency, the nozzle technique and the layer application.

The two gunning technologies are:

• The dry gunning: the dry mix is conveyed by the compressed air, and the water is added at the nozzle; the water content is controlled by the nozzle operator, and the method requires the experienced nozzleman to achieve the correct consistency.
• The wet gunning: the mix is prepared with the water in the mixer and pumped to the nozzle, where the accelerator is added; the wet method gives the better consistency control and the lower rebound, but requires the specialized equipment.

The key parameters of the gunning operation are:

• The air pressure and the material feed rate, which determine the application velocity and the compaction of the material on the surface.
• The water addition at the nozzle, which controls the consistency of the applied material; too little water gives the dusty, poorly compacted material, and too much water gives the weak, runny material.
• The nozzle distance and the angle: the nozzle is held at the correct distance from the surface, typically 0.5 to 1.5 meters, at the right angle, so that the material impacts and compacts properly.
• The layer thickness: the material is applied in the layers of the specified thickness, and the thick sections are built up in the successive passes with the appropriate time between the passes.
• The rebound control: the rebound, the material that bounces off the surface, is minimized by the correct settings and technique, and the rebound material is not reused.

The gunning is a skilled operation, and the nozzleman’s experience determines the quality of the lining. The quality control of the gunned lining includes the density and the strength testing of the cores and the panels, the visual inspection of the surface, and the thickness verification with the drilling or the measurement. The modern gunning systems include the continuous mixers and the automation that improve the consistency of the material delivery, but the human skill of the nozzle application remains the decisive factor.

7. Ramming, Plastics and Repair Techniques

The ramming is the installation method for the plastic refractories and the ramming mixes, in which the material is placed in the layers and compacted by the pneumatic rammers or the vibrating hammers. The ramming is used for the special shapes, the burner blocks, the damper areas and the localized repairs, where the material must be packed into the form by the mechanical compaction. The quality of the rammed material depends on the layer thickness, the compaction energy and the continuity of the work, and the material must be rammed before it stiffens.

The repair techniques of the refractory lining form a complete toolbox for the maintenance of the hot equipment:

• The patching: the application of the repair castables or the gunite material over the localized damaged areas, after the removal of the loose and the contaminated material.
• The gunning repairs: the large-area repairs with the gunning, used when the remaining lining is sound and the worn surface is rebuilt.
• The injection: the injection of the refractory or the sealant materials into the cracks and the joints, restoring the airtightness and the bond.
• The ceramic welding: the repair technique in which the refractory material is applied by the thermite reaction, bonding to the hot lining without the shutdown; used for the localized repairs during the short stops.
• The shotcreting: the application of the castable with the wet process at high velocity, used for the repairs of the large vertical surfaces.

The preparation of the repair surface is the key to the repair quality: the loose material, the dust and the old coating are removed, the surface is cleaned and, where required, the anchors are added, and the repair material is applied with the correct bond to the existing lining. The repairs are documented with the sketches and the photographs, and the repair locations are recorded in the lining life database for the future inspection and the planning.

8. Curing, Drying and Dry-Out Procedures

The newly installed monolithic linings must be cured and dried before they can be heated to the operating temperature. The curing is the process in which the castable gains its strength: the water in the mix hydrates the cement bond, and the castable must be kept moist for the specified period, typically 24 to 48 hours, depending on the material, to develop the full strength. The curing is performed by the water misting or the covering with the wet cloths and the plastic sheets, and it is followed by the drying, in which the free water is removed from the lining.

The drying and the dry-out are the controlled heating of the lining to remove the water and to prepare it for the service:

• The drying: the slow heating of the lining to the boiling point of the water, with the holding periods that allow the moisture to escape through the ventilation and the drains.
• The dry-out curve: the temperature is raised according to the defined curve, typically with the holding periods at 110 to 150 degrees Celsius, where the free water evaporates, and at 250 to 350 degrees Celsius, where the chemically bound water is released.
• The heating rate: the heating rate is limited to prevent the spalling, the explosive failure of the lining caused by the steam pressure inside the material; the rate of 10 to 30 degrees Celsius per hour is typical for the dense castables.
• The ventilation: the drying creates large quantities of steam, and the kiln or the vessel is ventilated to remove the moisture and to prevent the condensation in the cold parts.
• The duration: the dry-out of the large monolithic installations takes several days, and the kiln start-up schedule must include this period.

The dry-out procedures are documented for each installation, with the temperature curve, the holding times and the verification points, and the process is monitored with the temperature measurements and the moisture indicators. The premature heating of the undried lining is one of the most destructive errors in the refractory practice, and the discipline of the dry-out is a mandatory part of the installation procedure.

9. Heating Up and the First Service

After the dry-out, the lined vessel is heated to the operating temperature according to the start-up procedure. The heating of the kiln after a relining is performed with the burner at the minimum rate, with the kiln rotated slowly on the auxiliary drive, and the temperature is raised according to the refractory heating curve, which respects the thermal expansion and the thermal shock limits of the new lining. The shell temperatures are monitored continuously during the heating, and the coating is allowed to form gradually as the burning zone reaches the operating temperature.

The first service period of the new lining requires the special attention:

• The coating formation: the burning zone bricks are protected by the coating, which forms over the first days of the operation; the operating conditions are managed to build the uniform coating before the full production rate is applied.
• The expansion accommodation: the lining expands as it heats, and the designed expansion allowances are taken up; the shell temperature and the kiln ovality are monitored for the signs of the lining movement.
• The inspection after the first stop: the new lining is inspected after the first operating period, typically after the first few weeks, to verify the condition of the joints, the anchors and the localized areas, and the defects found are corrected.
• The documentation: the installation records, the dry-out records and the first service inspection are filed in the lining database, forming the baseline for the future condition monitoring.

The first service period is the test of the installation quality: a well-installed lining settles into a stable, uniform condition, while a poorly installed lining shows the early signs of the joint opening, the anchor failure or the localized overheating, which the monitoring detects and the corrective action addresses.

10. Quality Control of the Refractory Installation

The quality control of the refractory installation is organized at three levels: the material quality, the installation quality and the finished lining quality. The material quality is verified at the delivery: the certificates, the batch testing and the storage conditions. The installation quality is controlled during the work: the supervisor checks the joints, the water content, the anchor placement and the technique continuously. The finished lining quality is verified after the installation: the thickness measurements, the joint inspection, the density and the strength testing of the samples, and the final acceptance by the inspection team.

The standard quality control measures are:

• The material testing: the verification of the chemical and the physical properties of the delivered materials against the specification, with the sampling and the laboratory testing.
• The installation records: the daily records of the installation, the material batches, the quantities, the water contents and the working conditions.
• The joint inspection: the measurement of the joint thicknesses, the torch test for the open joints and the verification of the keying and the expansion allowances.
• The anchor verification: the inspection of the anchor welds and the spacing before the castable placement.
• The sample testing: the cubes and the panels of the installed castables are tested for the strength and the density, and the results are compared with the specification.
• The final inspection: the completed lining is inspected and the defects are documented and corrected before the acceptance.

The quality control is performed by the plant’s refractory engineer or the independent inspector, and the installation contractor works to the agreed acceptance criteria. The quality documentation of each installation, the material certificates, the installation records and the test results, forms the basis of the lining life management and the warranty claims.

11. Safety of the Refractory Installation Work

The refractory installation work is performed in the hot equipment, the kilns, the preheaters and the vessels, with the confined spaces, the heavy materials, the dust and the mechanical equipment, and the safety program is therefore an integral part of the installation planning. The principal hazards and the control measures are:

• The confined space entry: the permit system, the atmospheric testing, the ventilation and the standby personnel for the work inside the kiln and the vessels.
• The heat stress: the work in the still-warm equipment and in the summer conditions, with the hydration breaks, the cooling and the monitoring of the crew.
• The dust: the refractory dust is a respiratory hazard, and the dust control and the respiratory protection are mandatory.
• The heavy lifting: the bricks and the materials are handled with the lifting equipment, and the manual handling limits are respected.
• The mechanical equipment: the mixers, the pumps, the gunning machines and the bricking rigs are guarded and operated by the trained personnel.
• The working at height: the access platforms, the scaffolding and the fall protection for the work at the elevated locations.
• The housekeeping: the work areas are kept clean, the materials are stacked safely and the access ways are clear.
• The emergency procedures: the rescue plans for the confined spaces, the first aid and the communication in the event of an incident.

The safety briefing before the work, the daily toolbox talks and the supervision of the execution are the practices that protect the installation crews, and the plant and the contractors share the responsibility for the safe execution of every campaign.

12. Frequently Asked Questions

Q1: What is the most common cause of premature refractory failure?
The installation errors: the incorrect water content in the castables, the open joints in the brickwork, the insufficient curing or the premature heating, and the incorrect expansion allowances. The material selection and the operating conditions are the next most common causes, but the installation quality is the first line of the lining life.

Q2: How long does the curing and the dry-out of a castable lining take?
The curing typically takes 24 to 48 hours, and the dry-out follows with the heating curve that takes from one to several days, depending on the thickness and the material. The full dry-out of a large preheater lining can take three to five days before the operating temperatures are reached.

Q3: Why are the burning zone bricks installed dry with the steel plates?
The magnesia-spinel bricks of the burning zone do not bond with the mortar, and the dry joints with the steel plates provide the required flexibility for the thermal expansion and the kiln ovality. The plates also stabilize the rings and prevent the relative movement of the bricks.

Q4: What is the difference between the dry and the wet gunning?
In the dry gunning, the dry mix is conveyed and the water is added at the nozzle; in the wet gunning, the mix is prepared with the water and pumped, with the accelerator added at the nozzle. The wet gunning gives the better consistency control and the lower rebound but requires the specialized equipment.

Q5: How is the quality of the installed lining verified?
Through the joint measurements, the torch test for the open joints, the density and the strength testing of the sample cubes and the cores, the thickness verification and the final visual inspection. The records of the material batches and the installation parameters complete the quality documentation.

Q6: When should the ceramic welding be used instead of a normal repair?
The ceramic welding is used for the localized repairs during the short stops, because it bonds to the hot lining without the cool-down and the formwork. For the larger damage, the conventional repair with the brick replacement or the gunning is preferred, because it restores the lining structure completely.

13. Final Summary

The refractory installation techniques are the engineering discipline that determines the life and the performance of the entire hot equipment of the cement plant. The discipline covers the material selection and its installation requirements, the planning and the preparation of the campaigns, the brick installation in the rotary kiln with the joint and the expansion control, the castable installation by pouring and pumping, the gunning with its skilled nozzle application, the ramming and the repair techniques, the curing, the drying and the dry-out procedures that prepare the lining for the service, the controlled heating and the first service period, the quality control at every level, and the safety of the installation work. The plant that applies these techniques with the discipline and the quality control described in this article achieves the maximum lining life, the minimum refractory cost and the highest availability of the pyro line, and this article has provided the complete technical foundation for the refractory installation practice in the cement industry.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.