Hammer mill

Wood Hammer Mill

A Wood Hammer Mill grinds straw, wood chips, and other biomass to size before putting it through a pelletizer. If you have timber chunks, you may need to chip them before putting them through the hammer mill.

Chipping needs to reduce your material into smaller, uniformly sized portions. When the material thickness is larger than 10 mm (7/16“) or size is greater than 50×50 mm (2”), a wood chipper is needed to chip these materials into smaller pieces. If you have large branches, tree trunks, or split timber, the cost of a chipper will be pretty high as these are serious bits of equipment.

The hammermill further crushes these small pieces into particles of less than 3 mm or 1/8 inch diameter. The small-scale hammer mill seen above is a steel drum containing a vertical or horizontal cross-shaped rotor with pivoting hammers.  The hammers are free to swing on the ends of the cross.  These high-speed hammers essentially beat the biomass apart until it fits through the openings of a metal screen. The size of the openings in the screen determines the final size of the processed biomass.  They have a reasonably high throughput and are very simple to operate.  They are also very noisy and can create a significant amount of dust with most dry biomass. The Nanjing Pellet Mill Co. Ltd in China makes the hammer mill pictured here Nanjing Pellet Mill Co. Ltd in China.

Making pellets can be quite an investment in the machinery required to generate fuel. Anyone considering manufacturing their own pellets and a wood hammer mill would need some hard cost analysis to ensure you are not over-capitalizing. Other options include purchasing from a large supplier or forming a cooperative to share the costs.