A Better Bit for Biomass
Producers of woody biomass have always had a moving target to hit when it comes to end-product specifications. Depending on demand, biomass buyers used to accept a wide variety of ground material, but as biomass burning plants have aged, product specifications have become more stringent. In many locations around the country, a typical ground "hog fuel" is no longer accepted-biomass buyers want a product that will not plug or bridge their systems with inconsistent product.
Working closely with their customers, Peterson, a manufacturer of horizontal grinders and chippers, developed a Knife Edge Bit which has turned things around for several biomass grinding operations. These bits are forged from heat treated steel, adding strength to the overall design. When paired with Sharp Edge Bits in a horizontal grinder, the Knife Edge Bits produce woody material that is cleaner and chunkier compared to output produced using typical, carbon overlay bits. The benefits of using Peterson Knife Edge Bits include an increase in production, a denser, improved-quality product, and a reduction in fuel consumption.
Producing Biofuel and Benefits
The Peterson Knife Edge Bits work best with clean material: whole logs or slash that is free of dirt, rocks or other non-crushable debris. The bits work by cutting and tearing the wood across the grain, versus the shred-by-pummeling process, more common in grinding operations. The result is denser material and a cleaner product which stacks evenly, increasing the tonnage and payload in transportation. The machine ends up producing more in less time and this means an overall reduction in fuel consumption of 15-50%, depending on the material being processed.
In tests with Peterson machines using the Knife Edge Bit the benefits were instant:
- 5710C, 1050 hp, drum rotor, tan oak logs, Doug fir, pine, redwood
- Production increased 43%, from 20 minute loads to 14 minutes
- 10% increase in density
- 62% reduction in fuel consumption on tan oak, and 25% reduction overall with logs
- 4710B, 765 hp, drum rotor, full length jack pine and tamarack trees:
- Production increased 39% (from 60 to 99 tons/hour)
- 20% increase in density
- 43% reduction in fuel consumption (from .44 to .25 gal/hour)
- Total operating costs were reduced from $3.48 to $2.03 per ton
The effect has been particularly beneficial for some northwest coastal logging operations, where cedar and vine maple are being processed. This wood fiber tends to be stringy and elastic, making it difficult for grinding, and ending up with something that is not boiler-ready fuel. The solution is a set of Peterson Knife Edge Bits. These bits reduce wood by cross-cutting it for greater efficiency and with fewer strings and sticks.
“The Knife Edge Bits are of GREAT Value… The goal in trying these bits was to make a better product and we did. The unintended benefit was a large savings in production cost.” – Bill Herman of Herman Bros. Logging and Construction, Inc.
Other companies have switched to the Knife Edge Bits and reaped the rewards: Steve Morris Logging of California has seen the increase in production and savings in fuel; Godfrey & Yeager of Coos Bay were able to produce and deliver a product acceptable to the mill. And in Eugene, Lane Forest Products was awarded a contract by Seneca because the quality of their end product was preferred over others.
Peterson Knife Edge Bits are fitted with the bolts installed from the back of the bit holder. This provides another cost savings advantage, since it eliminates the need for washers and nuts. However, it is crucial to have the right size bolt so that, once installed, the end of the bolt is flush with the bit face. Otherwise, when it's time to rotate or change bits, an operator is going to have unnecessary downtime cutting off any part of the bolt exposed above the face. That's avoidable by ordering a kit from Peterson that includes the right size bolts and a tube of Never Seize, making bit removal a friendlier experience than breaking out the torch.
When installing the Peterson Knife Edge Bits it is crucial to have a bit holder and spacer that are even, so that the bit and spacer lay flat and flush against the holder. This way, most of the force of cutting is absorbed in the holder. Also, it is important to check the threads of the bits' bolt holes, making sure they are clean and free of any burrs or defections. This ensures an easier time with removal.
The bit life is not as long as the traditional bit – half that of the carbide overlay type – but, by taking one pass with a diamond pad grinder across the inside edge, you can extend the life up to another 40 hours.
Testing has shown that the best setup is to combine them with the Sharp Edge Bits on the outside of the rotor, and both types of bits alternating the middle positions: two of each type installed at 180 degree intervals. The Knife Edge Bits fill out the rest. With this configuration, there is less side wear on the machine and the engine is less likely to stall due to overaggressive processing.
As with all grinding operations, it is vitally important to maintain the entire machine according to OEM scheduled maintenance intervals.
Quality End Product
At the power plant, biomass fuel delivered to the boiler in a smooth, uninterrupted flow contributes to maximum combustion efficiency with reduced emissions. Stringy, fuzzy wood fragments can clump together, creating a product that can bridge, disturbing the delivery of fuel to the boiler. Feedstock containing fines, or "spears", also contributes to an undesirable fuel product, as this fragmented material builds up on chain conveyors and doesn't allow enough fuel to filter through screens to the boiler. For this reason, many plants running older conveyor systems are finicky about their fuel stock. They need a quality end product that flows better, allowing for a greater efficiency in feeding the boiler. The cross-cut wood chips produced with the Peterson Knife Edge Bits paired with the Sharp Edge Bits are that quality end product.