Clinker burning is an important link in cement production, which affects the output, quality, various consumptions of cement clinker, and cement manufacturing costs, and ultimately affects the economic benefits of the enterprise. The rotary kiln is the main thermal equipment for clinker burning. Therefore, it is necessary to analyze and study the damage of refractory fire bricks at the cold end of the rotary kiln, so as to help us solve this problem well.
1 Analysis of the causes of damage to refractory bricks at the cold end of the rotary kiln
1.1 Compressive stress damage Compressive stress damage mainly refers to the deformation of the cylinder due to unreasonable design of the gap between the wheel belt and the pad, installation errors, etc., which leads to damage to fire bricks. The larger the gap, the less contact area between the wheel belt and the cylinder, and the smaller the reinforcement effect of the wheel belt on the cylinder, the greater the compressive stress, which increases the welding stress between the pad and the cylinder, produces cracks, and even breaks the pad. At the same time, the ovality increases, causing the refractory firebricks to burst.
1.2 Unreasonable setting of the retaining brick ring Due to the inertia of the rotary kiln during operation, the refractories bricks have a tendency to move downward. In order to prevent or reduce this tendency, retaining brick rings are often set at different positions in the kiln. From the perspective of force, the wheel belt is subject to the greatest force. If the brick retaining ring is set inside the wheel belt or close to it, the cylinder body is subjected to greater force and deformation. The brick retaining ring itself is often easily damaged, causing the weld to crack, which in turn damages the refractory bricks. In addition, the form of the brick retaining ring is also crucial. The earliest designed brick retaining ring was welded with angle steel, which had low strength, was easily damaged and deformed, and affected the stability of the bricks. Later, square steel brick retaining rings were widely used, and the strength was guaranteed, but the welding quality was often poor, which eventually caused bricks to fall off.
1.3 Irregular refractory fire brick masonry In the process of refractories brick masonry, the relevant national standards were not followed or not strictly implemented, resulting in dislocation, tilt, uneven mortar joints, climbing, opening, cavity dislocation, serpentine bending, etc., or the processed bricks were uneven, with corner drop, cracks, missing edges, etc., or when locking the seams, the joint steel plate was too thick, clamped too tightly or too loosely, etc.
1.4 The process operation system is not strict. The main reason is that the heating and cooling speed is too fast during the kiln opening and cooling process, which causes the bricks to be damaged by excessive thermal stress (rapid cooling and heating).
2 Countermeasures
2.1 Reduce compressive stress damage Select a suitable gap between the wheel belt and the pad. For the cold end of the rotary kiln, the gap should be 3~4mm. Too large or too small will easily damage the refractory bricks. It is best to choose an adjustable pad to ensure the best gap. The thickness of the cylinder under the wheel belt is moderate and the structure is proper. Too thin, it is easy to deform, too thick, the contact area between the wheel belt and the cylinder is reduced, the local pressure is increased and the wear is aggravated. The relative thickness δ/D under the wheel belt (δ is the thickness of the cylinder under the wheel belt, D is the diameter of the cylinder) is generally 0.012~0.015. The upper limit is taken for large kiln diameter and the lower limit is taken for small kiln diameter. The wheel belt should have sufficient rigidity. Small reaction force, not thin cylinder thickness, and small (very small) gap are all conducive to reducing cylinder deformation. However, if the rigidity of the wheel belt is too small, the kiln body will still be deformed, and the cycle of the refractory bricks will be very short.
2.2 The setting of the retaining brick ring should be scientific and reasonable. The retaining brick ring should be set 2.0m away from the center line of the wheel belt to prevent the elliptical force generated by the elliptical process from damaging it. It is best to use square steel for the retaining brick ring, and chamfer the parts to be welded, which can not only ensure the welding quality, but also facilitate the inlay of refractories bricks. The retaining brick ring cannot be set at the circumferential weld of the cylinder to avoid damage and strain to the cylinder. The refractories bricks protecting the retaining brick ring should be inlaid below the retaining brick ring to avoid the damage of the special-shaped bricks.
2.3 Bricklaying should be standardized and strictly follow the national standards. The refractory bricks should be close to the kiln body, the bricks should be close to each other, the brick joints should be straight, the intersection should be accurate, the brick joints should be firm, not misaligned, and not sagging or falling. The circumferential seams must be aligned, not climbing, not deviating, and avoiding misalignment or serpentine bending. The lock seam bricks must be complete and constructed strictly according to the lock seam regulations. The steel plate used for locking seams should preferably not exceed 2mm, and must be flat, without curling, twisting, or burrs. 2.4 Strict kiln drying and cooling system The kiln drying system is to carry out kiln drying operations according to a certain heating curve. Special attention should be paid to wet masonry to ensure that free moisture is discharged to prevent the explosion of refractories bricks due to excessive heating, and the heating rate should be strictly controlled; the cooling kiln process must ensure a certain insulation time, and the insulation (natural cooling) should be at least 8 hours after the kiln is stopped after unloading. For rotary kilns using insulation materials, the insulation time should be appropriately extended. At the beginning of the forced cooling stage, the air door should be closed and then gradually opened.
