How to Consistently Blend Biomass

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Before 2020, Drax, a British power supplier, purchased fuel pellets based on volume. They learned during that time that not all pellets are created equal. The company was paying the same fuel price no matter its BTU value. This meant the company paid more per BTU in some shiploads than others, and the practice disincentivized suppliers from optimizing their pellets. Thus, in 2020 Drax changed how they’d purchase pellets going forward: they’d buy according to BTU value, not volume. This was a good move on Drax’s part, highlighting a reality in manufacturing: quality pays. Customers won’t pay the same price for a lower-quality product if they can help it. They want a good value.

BTUs are only one aspect to value. Consistency is another. In energy production, consistency affects the temperature in the boilers. It affects efficiency. It affects customers’ return on investment. It affects trust. In the grill pellet industry, consistency also affects flavor. If a pellet manufacturer cannot offer a consistent product, they cannot expect consistent sales.

To create consistent, high-quality pellets, manufacturers must take steps to ensure their feedstock meets their requirements. They can’t accept feedstock with a blend of 30 percent hardwood when their pellets have a lower-percentage blend of hardwood to softwood, for example. Each tree species has different characteristics, and pellets made from an off-blend feedstock will perform differently than pellets made to specification. Pellet manufacturers must demand their suppliers provide what the two parties have agreed upon. That agreement, of course, needs to be specific: “wood fiber” does not provide much definition. The supplier and purchaser need to define quantities, schedules, species, moisture levels, particle sizes, and acceptable contaminants if any.

Humans being what they are, though, suppliers will not always deliver what they said they will. Thus, the only way for a pellet manufacturer to ensure they’re getting what they want is to sample and test the fiber being delivered. Samples can be collected automatically, as is common in the pulp industry, or manually with a port such as BE&E supplies. To ensure accuracy, personnel should collect samples throughout the shipment. The more samples, the more accurate the tests. Tests will not be more accurate with larger, albeit fewer, samples, as the characteristics of the delivery will vary from one area to another. Samples taken at a trailer door, for example, may have more fines than other areas in the trailer. See Biomass Sampling on www.advancedbiomass.com for a detailed explanation of sampling procedures.

Suppliers may not intentionally deliver off-spec. Accidents happen. There will always be that worker who drops his hammer into the fiber supply or who tosses in a 2×4 with the waste shavings without understanding the consequences. Mishaps like these are common, and they can cause serious damage to processing equipment. This is why it is not only necessary to sample the material being received but to screen it to remove metal and oversized pieces. Doing so is not only prudent, it’s required by the NFPA® standards for wood processors to reduce the risk of fire and deflagration.

BE&E supplies disc screens (scalping screens) for this very purpose. We can also procure and install magnets to remove ferrous metal from biomass feedstock, and we can build systems to detect metal in whole logs and automate their removal from the line.

Storage

Besides screening and testing, manufacturers must also consider how they will segregate material if they receive more than one species or wood specification. It’s necessary to segregate material because there is no way otherwise to ensure each feedstock remains unadulterated or to ensure they are mixed consistently before being pelletized. Yes—materials must be stored separately to be blended well. This is because different materials will not blend in a pile or silo. Physics will not allow it: materials will stratify according to size and density. So, no two portions of material will be the same, and neither will any two bags of pellets from material “blended” in this manner.

Blending

 

Accurate blending takes planning, like any other step in producing pellets. Consider that just as the material will stratify in storage, it will stratify in the surge bin in front of the pellet mills. This must be considered in the design of the bin, along with the bin’s size and discharge method.

There are several ways manufacturers can accomplish accurate blending. SMART Containers from BE&E present one solution. SMART Containers are containerized, horizontal silos with stroker-based reclaim. These machines can store and meter dry materials into a common receiving conveyor, thereby mixing the material upon discharge. Manufacturers may also incorporate multiple surge bins from which they can feed materials so they’ll blend immediately before entering the pellet mill. Again, BE&E can provide this solution. We manufacture bins and augers for complete feed systems.

With pellet use on the rise and more mills being planned, competition will only increase. If pellet manufacturers want to earn top dollar for their products, they must position themselves as a top-quality supplier. This is only possible if they can produce pellets with consistent BTUs, flavor, and burn characteristics. Adding compliance procedures to test feedstock and investments into screening and proper blending will go a long way toward increasing pellet value—and potential price—for years to come.

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