Attrition (Eliminator) Mill
The attrition mill, or 'Eliminator', is the second and final milling stage of the processing system. Switchgrass enters the top of the eliminator and is pulverized using two horizontal side-by-side counter-rotating hammers. The mill's rotors are each powered by a 300 hp electric motor.
Pneumatic Transport Blowers & Transport Piping
Two positive displacement 100 hp rotary blowers force the switchgrass through the transport piping to opposing corners of the east fireball in the OGS boiler. The transport piping extends approximately 1,500 feet from the switchgrass process building to the OGS boiler.
The pulverized switchgrass that drops from the eliminator is transported to the primary cylone. The primary cyclone separates the larger constituents of switchgrass from the more fine and dust-like particles through taking advantage of rotational effects of air and gravity. The heavier material is dropped out into the surge bin. The finer, lighter materials are evacuated to the baghouse.
As switchgrass is dumped into the surge bin, the material is in final processed form and ready to be sent to the OGS boiler for firing. The surge bin is essentially a staging container that holds switchgrass before it enters the pneumatic transport system. Two screw feed conveyors at the bottom of the bin push the switchgrass into the rotary airlocks.
The rotary airlocks transport switchgrass from the surge bin into the pressurized pneumatic transport pipes. This equipment allows for the transfer of material into the pneumatic pipes without any loss of pressure.
A 20,000 cubic feet per minute centrifugal blower attached to the baghouse draws air from the eliminator exit, through the primary cyclone, and finally into the baghouse. Switchgrass that passes through the primary cyclone enters the baghouse through a tangential air duct. Due to its height, the baghouse is located on the outside of the process building. The baghouse works similarly to the primary cyclone, separating the material by size. The larger particles drop to the bottom while the smaller particles are forced onto a series of polyester bag filters. The dust that is collected on the bag filters is removed using a pulsed air jet on the clean side of the bags. All collected and filtered material exits through a rotary airlock at the bottom of the baghouse.