Planning the Logistics of Woody Feedstocks
The logistics of feedstocks is critical for maintaining the biofuels supply chain as bio-oil is growing in recognition for sustainability.
Logistically, there are a number of complex steps involved that are for the most part standardized as the: harvesting, collection, processing, transportation, and storage of woody feedstocks to be converted into biofuel.
As in all things, there are a few factors that can affect the logistical costs for woody feedstocks such as the type of wood, particle size, moisture content, and the level of soil contamination.
From a logistical standpoint, when done effectively and efficiently the steps can be simple and cost effective (Bioenergy Alliance Network of the Rockies, 2021).
Harvesting and Collection
In mountainous regions it is typical for manual felling be the method used for the harvesting and collection of woody feedstocks. It is also common in areas where there isn’t space enough to maneuver machinery needed for mechanized harvesting and collection.
Mechanized harvesting of woody feedstock has been done with single-grip harvesters and ground based skidding and forwarding machinery. These kinds of machinery have a hydraulic arm that allow them of felling trees as well as process branches and stems small enough to be chipped or grinded into a smaller particle size (Keefe et al, 2014)
Processing
An optional step that’s not always added into the processing step is the drying of woody biomass. From a logistical standpoint, drying is an important step that should not be overlooked as it can lessen the cost of transportation and increase the efficiency of combustion at the end use location.
Drying can occur right after the harvest and collection of woody feedstock. The easiest, and common, way for drying to occur is through transpiration; the process of wood drying out through the foliage and any wood surfaces that are open.
Again, drying is optional as it is not a required step; however, logistically it can be an important part of the process as it can lead to reduced costs of the transportation and handling of woody biomass (Pre-processing and Drying Woody Biomass, 2019).
Comminution
Comminution of woody biomass is the last step before transportation to a conversion facility as it reduces woody biomass to smaller particle size; thereby simplifying the converting of woody biomass to bio-oil.
Comminution is done using a chipper, shredder, or grinder depending on the total woody biomass volume, customer requirements, haul distance, accessibility of the needed machinery for comminution, and the length of storage before being moved to a conversion facility (Pre-processing and Drying Woody Biomass, 2019).
Chippers– Making up the most common method for comminution, chippers are favored for their high-speed knives efficiently reducing the particle size of woody biomass. Most chippers are capable of blowing wood chips into transportation vehicles for hauling immediately after harvesting allowing for harvesting, collection, and processing to occur simultaneously.
The number one downside of using chippers is their susceptibility to knife wear from rocks, stones, and high soil content mixed in the woody biomass (Pre-processing and Drying Woody Biomass, 2019).
Grinders– This machinery repeatedly pounds woody biomass reducing woody biomass with a combination of compressive and shearing forces. A benefit of using grinders is that wider range of wood size can be placed in this machinery, such as: stumps, large branches, and brush.
Like chippers, the one setback is that high soil content mixed in with the woody biomass can damage and wear out the machine (Pre-processing and Drying Woody Biomass, 2019).
Shredders– This machinery is not often used for woody biomass operations as they are slower, have a higher cost, and because the woody biomass particle size is larger than that of a chipper and grinder.
The only time shredders are considered is when there is to significantly high soil contamination making slow comminution necessary to reduce the level of contamination during the processing phase (Pre-processing and Drying Woody Biomass, 2019).
Transportation
The final step in the logistics of woody feedstock would be the transportation from the collection site to either storage or the conversion facility. A major challenge in transporting woody biomass is the low bulk density if it is transported in its raw form. Majority of transportation volume for low bulk density woody mass is unfortunately air; therefore, processing can be an efficient cost-effective way to reduce the cost of transportation.
Also, something to keep in mind is that the processing of woody biomass decreases their longevity resulting in their unsuitability for being converted to bio-oil; a favorable oil for sustainability. For this reason, about 90 percent of woody biomass in the U.S. are transported by truck to a facility to be converted to bio-oil instead of being stored.
Tractor-trailers– These trucks are standard use as they range from six to ten-wheels with a tandem axle granting them road flexibility, and a greater capacity for large cargo holds. Some tractor trailers include hydraulic power allowing for the function of self-unloading floors for easy offloading (Biomass Transportation and Delivery, 2019).
Fixed trucks– These trucks aren’t as favorable for woody biomass transportation as tractor trailers due to its lesser amount of cargo space. These trucks are no more than 40 feet long, and are more suited for hauling cargo short distances. Despite their shortcomings in comparison to tractor trailers, fixed trucks are easier to maneuver in tighter areas (Biomass Transportation and Delivery, 2019).
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Read more about woody feedstocks.