As you have learned, using screw conveyors with hanger bearings on stringy biomass causes material flow problems from the material hanging-up on the hanger bearings. In over 30 years of designing conveyors for biomass systems, I try to avoid screw conveyors except where the material size is small and uniform, such as with sawdust, wood chips, or wood pellets. And, I never use screw conveyors equipped with hanger bearings when handling dusty fibrous materials. If I can't use a shaftless screw conveyor, then I use a screw conveyor with a pipeshaft large enough to span span between the outboard bearings without excessive deflection. The longest hangerless screw conveyor I have used is ~12m long, but it had a 36" dia. pipeshaft. My preferred solution for handling stringy biomass would be to utilize a drag chain conveyor. However, if you must use screw conveyors for stringy biomass, then either use a shaftless screw or screw with a large diameter pipeshaft.

I work for Ausenco Sandwell, an international engineering company, and I am located in Vancouver, BC Canada. I specialize in the design of biomass handling systems for energy plants, pulp and paper mills, sawmills, pellet plants, etc.

Paul Janze

Senior Specialist, Wood and Biomass Handling

Ausenco Sandwell

Vancouver, BC Canada

604-638-4628 ■

Hanger bearings are a perennial problem and it is good practice to avoid where possible, except on the simplest duties. A cascade arangement is usually the best way for long transfer duties but, as an expedient, you may try removing the hanger bearing and fitting liner plates or bearing straps under the joint. Fill the screw flights to form as smooth a flight face continuation as possible and remove any joint bolts and replace them with pins that just project for a tack weld to hold. Run the screw as slow and as full as possible, as the material in transit will give support to the screw and reduce the bearing contact force. ■