In a production line used for drying aluminum hydroxide, the drying section employs a combined drying system consisting of a wedge-type paddle dryer followed by a rotary flash dryer. The feed system of the rotary flash dryer utilizes a stainless steel screw conveyor with dimensions of 300 mm × 3000 mm. Its primary function is to receive pre-dried material from the upstream wedge paddle dryer and convey it into the flash dryer for final drying. Material leakage occurs specifically at the shaft end seal of this screw conveyor.
Structure of the Feed System of the Flash Dryer:
Shaft End Sealing Condition:
Based on the drying process flow, the drying medium reaches temperatures up to 250 °C and enters the bottom of the flash dryer tangentially at high velocity due to the induced draft fan. The internal pressure inside the equipment is maintained at approximately 0.045 MPa (positive pressure).
Based on the drying process flow, the drying medium reaches temperatures up to 250 °C and enters the bottom of the flash dryer tangentially at high velocity due to the induced draft fan. The internal pressure inside the equipment is maintained at approximately 0.045 MPa (positive pressure).
Screw Shaft End Seal Structure:
To better illustrate this structure, a simplified schematic of the screw shaft end seal has been prepared:
To better illustrate this structure, a simplified schematic of the screw shaft end seal has been prepared:
1 – Gear reducer
2 – Bearing housing
3 – Screw conveyor
4 – Feed inlet
5 – Rotary flash dryer main body
6 – Shaft end seal
7 – Bearing support
2 – Bearing housing
3 – Screw conveyor
4 – Feed inlet
5 – Rotary flash dryer main body
6 – Shaft end seal
7 – Bearing support
Causes of Material Leakage in the Feed System:
As shown in the diagram, the elasticity of the conventional packing (gland packing) is limited. With repeated friction between the rotating shaft and the packing gland, the radial clearance rapidly increases over a short period. Under the influence of the internal positive pressure (0.045 MPa), this enlarged clearance leads to progressively worsening material leakage.
As shown in the diagram, the elasticity of the conventional packing (gland packing) is limited. With repeated friction between the rotating shaft and the packing gland, the radial clearance rapidly increases over a short period. Under the influence of the internal positive pressure (0.045 MPa), this enlarged clearance leads to progressively worsening material leakage.
Retrofit Solution for the Feed System:
Modifying the sealing structure of the feed system effectively mitigates severe leakage. According to the client, the retrofit process is straightforward, taking less than 7 hours to complete. Importantly, no modifications to the main equipment are required, and the total retrofit cost is approximately RMB 460. The specific retrofit measures are as follows:
Modifying the sealing structure of the feed system effectively mitigates severe leakage. According to the client, the retrofit process is straightforward, taking less than 7 hours to complete. Importantly, no modifications to the main equipment are required, and the total retrofit cost is approximately RMB 460. The specific retrofit measures are as follows:
