Causes of Corrosion in Cement Plants:

1) Acid-alkaline corrosion

The pH value of cement dust is about 10-12, which is strongly alkaline, creating an alkaline corrosion environment in the dust collector. Due to the high humidity of flue gas and high dew point temperature, condensation is likely to occur when the temperature of the flue gas drops, especially when there is leakage or other defects in the dust collector. In addition to causing "bag sticking" problems, condensation can also lead to alkaline corrosion of the metal components of the dust collector.

2) High-temperature flue gas corrosion

Flue gas in cement plants typically ranges from 220°C to 350°C (extreme conditions may exceed 400°C). If the dust collector's steel structure is not protected from corrosion and oxidation, the oxidation and corrosion of the metal structure will be severe. Rust and debris from oxidation not only pollute the final product but also cause uneven oxidation and corrosion surfaces that can disrupt the normal flow of flue gas. This can lead to significant dust accumulation in localized areas, severely affecting the normal production of the cement plant.

To ensure that a transformer operates normally over its service life, its outer protective coating system must have good adhesion, weather resistance, water resistance, oil resistance, and heat resistance, as well as excellent corrosion resistance.

3) Ammonia corrosion

During the denitrification process in cement plants, ammonia water is commonly used as a reducing agent. When ammonia water is sprayed in excess, it directly pollutes the equipment. Ammonia has strong adsorption and corrosion properties, and it adheres to equipment such as flue ducts and dust collectors, which is difficult to remove. Over time, it gradually causes corrosion to the equipment. Furthermore, ammonia water decomposes into ammonia gas, which decomposes faster at higher temperatures. Ammonia gas can ionize into ammonium ions and hydroxide ions in a humid environment, forming an electrolytic solution that accelerates the corrosion of metals by promoting electrochemical reactions. Ammonia molecules can form complexes with many transition metal ions, making them easily soluble in water and stripping away the protective oxide layer on the metal surface. During the denitrification process, excessive ammonia water leads to ammonia gas formation, which causes corrosion to metal equipment such as dust collectors and ducts, requiring urgent anti-corrosion measures.

4) Erosion and wear

The flue gas velocity in cement plants is around 1.5 m/s, with a high dust concentration. The erosion and abrasion caused by the flue gas on the metal structures is severe, especially when the flue gas at the kiln head contains larger dust particles. Although the concentration is relatively low, the abrasion is more severe.

I. Reference Standards

Current national standards, relevant regulations, and mandatory standard provisions;

"Code for Construction and Acceptance of Building Anti-corrosion Engineering" (GB50212-2002)

"Standard for Corrosion and Rust Removal Levels of Steel Surface Before Coating" (GB8923-1988)

"Safety Regulations for Coating Operations and Safety Management Rules" (GB6514-1995)

"Quality Requirements for Anti-corrosion Coatings" (GB6514-1991)

"Safety Regulations for Coating Operations, Paint Process Safety, and Ventilation Purification" (DJ/T6931-1999)

"Code for Construction and Acceptance of Industrial Equipment and Pipeline Anti-corrosion Engineering" (HGJ229-91)

"Safety Regulations for Coating Operations and Safety of Surface Preparation Process" (GB7692-87)

"Noise Limits at Construction Sites" (GB12523-90)

ISO9001 Quality Management System Documents

ISO14001 Environmental Management System Documents

GB/T28001 Occupational Health and Safety Management System Documents

I. Design Basis

Environmental Conditions: The corrosion level of atmospheric environments on steel structures can be determined according to Table 1.

I. Industrial Fan

Fans are one of the most commonly used devices in factories and enterprises. They are essential for boiler air supply, smoke and dust removal, and ventilation and cooling. Cement plants, mines, chemical and environmental protection projects all rely on fans. The fan blades are one of the critical parts, and their lifespan directly affects the overall lifespan of the fan. The working environment of the fan blades is harsh and prone to abrasive damage. Therefore, high-quality protective coatings are necessary. The coating must provide corrosion resistance, extend the lifespan of the blades, and focus on impact resistance and wear resistance. It should also provide a smooth aerodynamic surface to increase the fan's conversion efficiency. The coating should have good adhesion, high wear resistance, weatherability, and resistance to atmospheric corrosion.

New dry-process cement production lines use high-pressure fans at six key locations: raw material mill circulation fan, coal mill circulation fan, kiln head exhaust fan, kiln tail high-temperature fan, kiln tail exhaust fan, and cement mill circulation fan. When these fans operate at high speeds, some dust particles are carried by the airflow into the fan, causing significant wear on the internal rotor. Over time, dust particles accumulate inside the fan, and the constant friction between the fan's internal rotor and casing under pressure and thrust causes widespread erosion and wear, severely damaging the fan's rotor and casing.

Fans are machines that convert mechanical energy from a prime mover into airflow, giving the air energy. They are essential equipment in cement plants and include supply fans, exhaust fans, primary fans, sealing fans, and others. In actual operation, particularly for exhaust fans, which operate under harsh conditions, failure rates are high. Quickly diagnosing the causes of faults and taking corrective measures ensures the continuous and safe operation of the factory. Fan faults are varied and complex, but common issues include bearing vibrations, high bearing temperatures, stuck moving blades, and incorrect activation of protective devices. The corrosion issue in fans is particularly prominent in the cement industry. For example, rough gas fans operate in harmful environments at high speeds, leading to corrosion. Rotor corrosion mainly occurs on the front and rear discs and blades, resulting in pitting, deep protrusions, and rusting. Severe rotor imbalance can lead to failure.

Table 1: Graphene Corrosion Protection Plan for the Interior of Industrial Fans

Table 2: Graphene Corrosion Protection Plan for the Exterior of Industrial Fans

I. Cement Factory Chimney

In the cement production process, the flue gas entering the chimney contains dust particles, escaping ammonia, sulfur compounds from coal combustion, chlorides from waste incineration, and other corrosive gases and humid solutions, which cause severe corrosion to metals, leading to significant chimney corrosion.

Corrosion Analysis: The gas temperature near the top is low, the gas flow speed is slow, and with the return of cold air, a large amount of water vapor condenses at the near-top position. The water and oxygen cause electrochemical corrosion of the steel. The alkalis, chlorides, sulfur, and other elements in the flue gas dissolve in water to form electrolyte solutions, accelerating the electrochemical corrosion. Rainwater and melting snow are also factors accelerating the corrosion. The upward gas flow and returning cold air create turbulence at the top of the chimney, increasing shear forces, which continuously peel off corrosion products from the metal surface, allowing the corrosion products to be blown into the air or fall to the bottom.

Table 1: Corrosion Protection Plan for Chimney <120℃

I. Preheater of Cement Plant

The preheater mainly consists of a cyclone and chute pipe to preheat the raw material. The equipment structure features high-temperature devices such as the cyclone, chute pipe, and tertiary air duct, all of which are lined with fireproof and heat-insulating materials. Whether during the construction of the preheater steel structure or the fabrication of the equipment, the corrosion protection process should never be neglected. This is reflected in poor structural pre-treatment and surface treatment, where welding slag, spatter, welding beads, and cutting burrs are not removed. Rough-cut slots that affect the appearance must be ground smooth, and the base material under the intact paint film must be treated. Additionally, the internal lining of fireproof and heat-insulating materials is uneven, and the detachment of partial insulating materials during operation leads to noticeable thermal corrosion. Furthermore, the uneven flow of raw materials in the pipes and cylinders during production can cause temperature differences at the same location at different times. On-site inspection detected significant temperature differences at the welded joints and surrounding areas, despite being less than 10 centimeters apart.

I. Cement Factory Preheater

Structure of the rotary kiln preheater: The preheater mainly consists of a cyclone, air ducts, discharge pipes, decomposing furnace, lock air valve, material spreading disc, inner tube hangers, decomposing furnace, and feeding chamber. The material enters the kiln through the bucket elevator and rises into the material bin at the top of the kiln. The rotating discharge feeder feeds the material into the kiln tail preheater from the feeding port of the air duct. With the rising airflow, the material in the air duct is carried into the cyclone. Inside the cyclone, the material is collected by the cyclone and flows into the discharge pipe. The discharge pipe is equipped with a spreading device at the outlet, ensuring the material is evenly distributed in the rising airflow, thus enabling full heat exchange between the material and hot gases. The processes above the cyclone are similar to those described above. The decomposing furnace is a core equipment in the preheater system, equipped with four sets of coal spraying pipes, spraying fuel into the decomposing furnace in both left and right rotations. About 55-65% of the total fuel burns in the furnace, providing the required temperature for material decomposition. The fully heated and decomposed material, along with the gas, enters the cyclone, and finally, the material enters the rotary kiln through the feeding chamber. In summary, the entire process involves the material moving from top to bottom, while the high-temperature gas moves from bottom to top, conducting material heating and decomposition.

1. What is a Cement Factory Bucket Elevator

A bucket elevator is a mechanical conveying device with a fixed installation, primarily used for continuous vertical lifting of powdery, granular, and small block materials. It is equipped with safety protection devices such as rope breakage protection, stop protection, buffer devices, upper and lower height limiters, and anti-loosening rope devices. The elevator mainly consists of a driving device (motor, reducer, etc.), head, tail, plate chain (or steel wire rubber belt), hopper, and electrical control and protection systems. It is a very important material transportation tool in a cement production line. The bucket elevator is a commonly used type of equipment in cement factories, fixed in the material transport position, responsible for material transportation. The bucket elevator can operate vertically, has low power consumption during operation, and offers clear advantages, meeting the basic material transport needs of a cement plant.

The bucket elevator has a sealed shell, but a large amount of dust can be generated at the material receiving point at the bottom of the elevator. Due to the large height of the elevator, air is drawn from the lower part to maintain negative pressure inside the shell. Because of the use of a reverse blowing bag dust collector, it is often affected by weather conditions such as rainy days and high material humidity, causing dust to accumulate inside the filter bags. Despite this, the dust phenomenon in the bucket elevator is not very significant.

Oil-based Corrosion Protection Coating Plan

Water-based Anti-corrosion Coating Solution

I. What is a Cement Plant Elevator?

A material elevator is a mechanical conveying device that is fixed in place, primarily used for the continuous vertical lifting of powdery, granular, and small-block materials. It is equipped with safety devices such as rope break protection, stop safety devices, buffer devices, height and limit positioners, and anti-loosening rope devices. The elevator mainly consists of a driving device (motor, gearbox, etc.), head, tail, plate chain (or steel wire rubber belt), hopper, and electric control and protection systems. It is an essential material transportation tool in cement production lines. The bucket elevator is commonly used in cement plants, fixed at the material transportation position, specifically responsible for the transport of materials in the cement plant. Bucket elevators can operate vertically, and while running, they consume relatively low power, which is a significant advantage, meeting the basic material transportation needs of cement plants.

The bucket elevator has a sealed outer shell, but a significant amount of dust tends to form at the receiving point at the bottom of the elevator. Considering the elevator's height, negative pressure is maintained within the shell by extracting air from the lower part of the elevator. Due to the use of a reverse-flow pulse bag filter, under the influence of rainy weather and high humidity materials, dust filters often experience a "swelling" phenomenon due to accumulated dust. Despite this, the dusting phenomenon in the elevator is not particularly severe.

Oil-based Anti-corrosion Coating Plan

Water-based Anti-corrosion Coating Plan

I. Corrosion Severity of Rotary Kiln

The rotary kiln, also known as a hollow kiln structure, mainly consists of the cylinder, riding ring, support rollers, stop rollers, drive device, sealing device, and cooling device. The cylinder is the main component of the rotary kiln. It is a steel cylinder, generally with a steel plate thickness of 18-50mm. The thicker the steel plate, the larger the diameter of the cylinder, and the cylinder is lined with 100-200mm of refractory material. Due to the gravity of the kiln body, refractory materials, and materials, the cylinder experiences axial bending between the two support rollers. In practice, deformation at the interface of the cylinder is also a major cause affecting the service life of the kiln lining. In addition, the combustion zone and firing zone inside the rotary kiln, the area covered by the flame is called the combustion zone. The middle region of the flame, where the temperature reaches its highest, can reach 1600-1800°C. At this point, the clinker is heated to 1300-1450°C, with 25%-30% of the material being transformed into a liquid phase. The adhered material formed on the refractory inside the kiln is called the main kiln skin. This area of the kiln is referred to as the firing zone. The formation of kiln skin can protect the refractory inside the kiln and extend the operational cycle of the rotary kiln.

In the cement production process, it is inevitable that certain chlorine, sulfur, sodium, potassium, and other chloride-containing substances are brought in with raw materials and fuels (especially from waste). When the concentration exceeds a certain limit and at an appropriate temperature, these substances directly cause corrosion reactions with the metal surface oxide film. Part of the corrosive gases inside the cylinder are eliminated through the material, while some corrosive gases come into contact with the cylinder through gaps in the refractory material, leading to corrosion of the cylinder. This causes thinning of the cylinder, pitting, and hydrogen embrittlement, which severely damage the cylinder. Rotary kiln cylinder fractures occur frequently in cement plants, and in severe cases, losses can exceed tens of millions of yuan. According to investigations, corrosion of the inner wall of the kiln body accounts for more than 30% of kiln body fractures.

1. Bag Dust Collector Corrosion Protection

Corrosion Issues of Bag Dust Collectors

In dry cement production lines, the kiln exhaust gas is used for raw material drying, raw material preheating, and waste heat power generation. The exhaust gas passes through the bag dust collector to collect dust. The bag dust collector is a dry dust filtration device. It is suitable for capturing fine, dry, non-fibrous dust. When dust-containing gas enters the bag dust collector, it passes through the filter bags, where dust particles are filtered out. Larger and heavier dust particles settle due to gravity and fall into the ash hopper. Gas containing finer dust is filtered as it passes through the filter material, thus purifying the gas. With increasing environmental and safety requirements, most cement kilns in China are equipped with the SNCR de-NOx system. However, due to the impact of the production process and desulfurization liquid, the bag dust collector usually experiences severe corrosion problems after 2-3 years of use, significantly shortening the service life of the equipment and severely affecting the normal production of the enterprise.