Recursos naturales

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

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 —

Inlet Zone Ca-1m Ca-1m Ca-1m Ca-1m Ca-1m Ca-1m — — Ca-1m

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.

– No mortar is applied to the kiln shell or the extrado side of the bricks.

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.

Figure 4 - Last closure brick installation

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

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

Max. 8 mm Max. 8 mm

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

Max. 8 mm Filled with mortar

Figure 8 - Brick Lining Adjustments For Distorted Kiln Shell (Radial)

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

80mm ^{Down Kiln}

50

50

retaining ring 180