Case Study

Retrofit Air Mizer® Shaft Seals Protect Plant Equipment and Personnel

Application: Screw Conveyors

Cement is made from a mixture of raw materials heated by a high-temperature kiln, often fueled by coal, to produce clinker. Clinker is then mixed with gypsum and ground into a fine powder to produce the final product.

In a cement plant located in the United Kingdom, several screw conveyors are used to transport coal throughout the facility. The screw conveyors, equipped with packing to seal the glands, were leaking coal dust into the atmosphere, coating the floor and neighboring equipment. The abrasiveness of the coal, excessive shaft movement, and frictional contact was causing the gland packing to quickly deteriorate, creating a leak path and allowing coal to escape into the atmosphere. Exposed coal dust is extremely hazardous. Inhaling large amounts can lead to significant health issues and a single spark can ignite the dust, causing an explosion. The coal dust would also migrate down the shaft into the support bearings, two on each shaft, causing them to fail within a few months. Replacing the bearings and packing was expensive, frequent, and ineffective. Several different types of packing and combinations of lantern rings, air, and grease purges, were attempted. No combination was successful.

Excessive Dust Creates Safety Concerns

Due to the coal dust in the air, a weekly cleanup up regime was required to ensure levels were acceptable. The weekly clean-up was carried out by a specialist outside contractor at a high cost. In addition to this operation, all workers were required to use extra health & safety protection.

Filter Screw Before Retrofit Side View_caption

A Permanent Solution

The cement plant turned to Inpro/Seal® for a permanent shaft sealing solution. The Inpro/Seal Air Mizer® is a non-contacting, non-wearing shaft seal that uses small amounts of air to create a positive purge along the shaft, forming a barrier that eliminates leakage. Because Air Mizer shaft seals do not use contact with the shaft to create a seal, the abrasiveness of the coal was not an issue. Also, unlike packing, Inpro/Seal Air Mizer shaft seals fully articulate to accommodate radial run-out, axial movement and angular misalignment simultaneously. Their unique, non-contacting design has no wearing parts and requires minimal maintenance, making them the perfect sealing solution for this challenging environment.

These screw conveyors presented a unique challenge. Their shafts became scored from the abrasiveness of the coal and contact with the packing. Due to tight clearances required between the seal and shaft, a clean shaft was needed for proper function of the Air Mizer shaft seal. Therefore, a simple sleeve was mechanically secured to the shaft. Oversized o-rings were then used to ensure a good internal shaft to sleeve seal.

Exposed Bare Shaft with Grooves_caption

Success Summary

Since 2015, Air Mizer shaft seals have been installed on six of the coal plant’s screw conveyors. Since installation, the seals are working flawlessly with no recorded seal degradation experienced. Because coal dust was no longer escaping to atmosphere, creating a hazardous environment, the facility’s insurance premiums were greatly reduced and weekly subcontractor cleaning costs were cancelled.

Advantages of Air Mizer Shaft Seals on Screw Conveyors

  • Provides a long-term maintenance free ATEX Certified seal system.
  • Prevents lost time injury and high-cost incidents.
  • Negates weekly cleaning costs.
  • Improves air quality for local workers.
  • Eliminates bearing replacement costs.
  • Increases plant availability.

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