- Time:Feb 22, 2023
Rotary kiln shell corrosion is a common technical problem in precalciner kilns at home and abroad.
I. Failure performance
Cylinder corrosion is the main reason cement plants replace cylinders. Many precalciner kilns have cylinder corrosion problems, which are generally found during equipment overhaul, kiln maintenance, and replacement of kiln lining refractory bricks. The flaky corrosion products removed from the inner wall of the cylinder have a multi-layer structure; close to the cylinder One side is reddish-brown and black, and the side close to the kiln lining is gray due to clinker. The middle layers are mixed with reddish-brown, black, and brass, and each layer has bright crystal points scattered or distributed on it.
Corrosion of the rotary kiln cylinder generally shows flaky peeling, and the rust flakes are loose and brittle. It can be found through the measurement of the ultrasonic thickness gauge that the cylinder has different degrees of thinning, and some also have circumferential unevenness on the inner surface of the cylinder. Grooves, such as the large gears in the front section of the kiln, often find grooves on the inside of the cylinder. The most severely corroded area of the cylinder is the cylinder near the large cone in the transition zone of the rotary kiln, and the annual corrosion rate is as high as 1~2mm.
II. Failure analysis
Analysis of the corroded flakes revealed that the main components of the rust layer were iron oxides and a small amount of chlorides and sulfides. Therefore, the corrosive substances on the inner wall of the kiln shell are oxygen, sulfur and chloride.
1. High temperature oxidation causes the inner wall of the cylinder to corrode
The rotary kiln shell is generally made of ordinary steel, and ordinary steel is not resistant to high temperature oxidation. At 200~300°C, a visible "protective" oxide film is produced. However, the structure of this oxide film is loose, and it is difficult to prevent the metal cylinder from being further oxidized, especially when the temperature is high. For example, the annual oxidation rate of A3 steel is 0.58mm at 400°C, and it is as high as 5.84mm at 600°C. The temperature of the cylinder in the transition zone of the rotary kiln is usually 300~400°C or even higher, so oxidation and corrosion on the inner surface of the cylinder is inevitable.
2. High temperature vulcanization causes the inner wall of the cylinder to corrode
High-temperature sulfidation corrosion is different from high-temperature oxidation corrosion. This corrosion can be carried out under the metal skin, and the subcutaneous corrosion products contain unoxidized metal. The hot corrosion temperature should be 600~950°C, but in Cl- and S-plasma strong corrosive media, high-temperature vulcanization may occur at about 400°C, resulting in corrosion of the inner wall.
3. High temperature chlorination causes the inner wall of the cylinder to corrode
In a high temperature environment, chlorine and chlorides have a particularly strong corrosion effect on steel. Under chlorination conditions, volatile FeCl with a low boiling point (324°C) will be formed, thereby aggravating the corrosion of the rotary kiln shell.
In the process of calcining cement clinker in the rotary kiln, the atmosphere in the kiln is very complicated, and various factors that cause the corrosion of the cylinder exist almost at the same time, and work together to make the cylinder of the rotary kiln "overwhelmed" and corroded.
III. Countermeasures
Corrosion of precalcined kiln shell is a relatively complicated technical problem, which needs to be comprehensively treated from various aspects such as process conditions, equipment operation, refractory material performance and shell material selection:
1. Improve the batching plan, reduce the content of harmful components in the raw fuel or adjust the matching of sulfur and alkali, reduce the enrichment of harmful components in the kiln, and then reduce the harmful components that can reach the inner surface of the cylinder, especially the content of chloride salts, Reduce barrel corrosion.
2. For the severely corroded cylinder, it needs to be replaced; for the slightly corroded cylinder, anti-corrosion treatment can be carried out on the corroded part of the inner wall of the cylinder.
3. In order to prolong the service life of the rotary kiln shell, anti-corrosion treatment can be carried out on the parts that are easy to corrode. The specific method is:
(1) Treat the inner surface of the cylinder to remove rust and stains, make it neat and clean, and reveal the metallic luster.
(2) Spray inorganic materials or brush cement slurry on the inner surface of the cylinder (which has been treated).
4. Reasonable selection of refractory materials, improvement of kiln lining quality and masonry methods. When selecting refractory materials, it is necessary to consider not only the durability, but also the heat insulation, and the matching of refractory bricks in the whole kiln system, so as to increase the shielding effect of the kiln lining. In sensitive parts with serious corrosion, it is advisable to use wet masonry to build kiln lining refractory materials. According to reports, after the wet kiln lining is built, the corrosion of the cylinder body is greatly reduced.
5. Improve the operating reliability of the main and auxiliary machines of the kiln system, avoid kiln shutdown, and reduce RCl moisture absorption and corrosion of the cylinder caused by kiln shutdown.
ZHENJIN REFRACTORIES has 38 years of experience in the refractory industry, and is committed to one-stop general contracting services such as R&D and manufacturing of refractory materials for cement, lime, nonferrous metals, steel and other industries, technical solution design, construction and supporting product provision. The service chain runs through the entire life cycle of the project, including preliminary consultation, scheme design, R&D and production, furnace construction and safety production. Through the optimized combination of various brand products, it can meet different process requirements and create value for customers.
