In modern cement production, the smooth operation of air slide conveyor is crucial. Recently, a cement plant encountered several blockage incidents during trial operations. These issues severely impacted normal production. This article explores the causes of these blockages and the solutions implemented.
What is an air slide conveyor?
An air slide conveyor is a bulk material handling system that uses a layer of air to transport dry, powdery materials along a sloped channel. It features a porous surface that allows air to flow through, creating a fluidized bed that enables smooth and gentle movement of materials. This system is energy-efficient and commonly used in industries like cement and food processing.
How Air Slide Conveyors Work
Air slide conveyors transport dry, powdery materials using a layer of air along a sloped channel. They feature a porous surface that allows air to flow through, creating a fluidized bed. This design reduces friction and enables the smooth movement of materials without mechanical components. Consequently, air slide conveyors operate efficiently and are commonly used in industries like cement and food processing to ensure gentle handling of bulk materials.
Material Impact
The moisture content of the raw materials significantly contributes to blockages. For instance, clay can have a moisture content of 8% to 10%. The cement plant uses a single-chamber air-swept drying mill. When airflow is too strong, the moisture content of the milled material can exceed 1%. High-temperature, sticky materials can clog the pores of the aeration layer, leading to uneven airflow and causing blockages in the air slide conveyor. Additionally, during shutdowns, materials left in the conveyor can cool and condense, worsening the blockage. To address these issues, the plant implemented the following measures:
- Strictly Control Material Moisture: The moisture content of incoming clay is kept below 6%. The gas temperature from the mill is controlled between 90 and 100°C, ensuring the moisture content of the milled material does not exceed 0.8%.
- Emergency Cleaning Measures: In the event of unexpected long shutdowns, operators must open the conveyor cover and manually clear the material.
Mill Impact
During the initial trial of the cement mill, the spacing of the discharge grate was too wide, and issues with the rotary screen allowed iron scraps, small steel balls, and coarse materials to mix into the milled cement. These materials entered the air slide conveyor via the bucket elevator and accumulated in the aeration layer. When enough material builds up, the injected air cannot fluidize it properly, leading to blockages. To combat this, the workshop took the following actions:
- Adjust the Mill Discharge Grate Spacing: This ensures smooth discharge and prevents coarse materials and impurities from entering the conveyor.
- Set Up Monitoring Points: Monitoring devices were installed at the bucket elevator outlet and the conveyor entrance. Regular checks help clear any accumulated iron scraps and coarse materials.
Conveyor Impact
(1) Sealing Issues
The lower conveyor body was not sealed properly, causing air leaks. This reduced the pressure difference across the aeration layer, preventing proper fluidization of materials and making transport difficult. Upon discovery, the following actions were taken:
- Enhance Sealing: Additional clamps or sealing tape were used to address air leakage.
(2) Aeration Layer Damage
Damage to the aeration layer can cause air to short-circuit, leading to air jets that obstruct the material flow. As a result, blockages occur. To resolve this, the plant took immediate action:
- Regularly Inspect the Aeration Layer: Any damage should be addressed promptly with repairs or replacements.
(3) Exhaust Design Problems
The upper conveyor should maintain a zero or slight negative pressure. However, the plant's design connected the conveyor's exhaust to the bucket elevator housing, which was not linked to the dust collection system. This caused inadequate exhaust and positive pressure in the upper conveyor, making it difficult for materials to fluidize. To fix this issue, the plant implemented the following solutions:
- Redesign Exhaust Outlets: The conveyor's exhaust was connected to relevant equipment to ensure smooth airflow.
- Control Air Inflow: The opening of air valves was adjusted based on material characteristics to ensure even airflow and reduce blockage risks.
(4) Weather Impact
The plant's outdoor air slide conveyors were exposed to rainwater, which seeped through gaps and caused material to become sticky, leading to blockages. To mitigate this, the plant took the following steps:
- Install Rain Protection: The outdoor conveyors were modified with protective measures to prevent rain from entering and affecting material properties.
In conclusion, through thorough analysis and effective solutions for air slide conveyor blockages, the cement plant has improved its operating procedures and established preventive measures. After over a year and a half of production, the operation of the air slide conveyors has stabilized, ensuring smooth cement production.
For more information or technical support, please feel free to contact us. We look forward to collaborating with you to enhance the efficiency and safety of cement production.
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