What is a plant-based fuel source and how do amendments benefit?
This is part one of a two part review. Part one shows our early determinations and part two addresses the alternative developed.
The prospect of creating combustion from plant resources started by an assumption that wood pellets were already being used successfully in Europe to produce electrical power generation. Other places in the US and abroad were grinding up wood pellets burned with coal or natural gas in flotation bed gasifiers. The solutions are far from emissions free but it provided a starting point for consideration.
The image to the left actually shows most of the reasons why wood pellet fuel is actually a very poor fuel source, due mostly to the astronomical capital and maintenance costs to produce them. As a result the quality and energy density of all wood pellets is well below a standard for a more advanced fuel solution. The random lengths, rough fractured ends and variations in material density all play a role adding to the unreliable nature of wood pellets.
The problems with this source began to show up almost immediately. At least 3% of the product is crumble right form the store as the bags are handled a minimum of six times from manufacturing to retail distribution, resulting in product damage to a fragile product.
Storing the bags in any closed area near humidity was a risk to carbon monoxide exposure from off-gassing in the bags which are required to be ventilated. Worse, within a week to ten days, the pellets had begun to swell and break apart as they arrive at 3% moisture to be stored in 20% humidity or higher. The pellets become hygroscopic, absorb ambient moisture, swell and fall apart. More pellets were acquired and stored to a sealed container to avoid this.
The next problem was trying to light the pellets to start a consistent burn. While our process did not call on a "pellet stove" per se, we soon learned those who have pellet stoves will generally purchase and use a treated starter material coated in paraffin wax to establish a small center burn with a drafting fan. This added complexity, cost and a need for start up intervention.
Our initial testing was done in a vented container reliant on updraft convection which would not be there until the pellets had begun to burn sufficiently. This was not all that surprising as we expected we would need to assist air flow, but the amount of air pressure to supply a large stack of pellets was a huge problem. During this start up time to reach temperature the pellets generated considerable smoke as a result of incomplete burning. If the pellet stack was too high, it didn't breath sufficient air through the pellets to continue the burn. This would be a totally unacceptable concern.
The cause of the crumble, water absorption and updraft resistance all stem from the manufacturing method conventional pellets are made by. The equipment requires huge capital investment for ring die particle extrusion mills. The wood first passes through three levels of grinding, dust separation then becomes auger fed, steam moisture added to 10% and finally conveyed to a pellet mill. The mill then forces the wood to pass through steel dies with hundreds of tapered holes to compress the moist wood particles. As the dies heat up the particles passing through the die are compressed and heat up, soften the lignin which then behaves like a water based glue as the particles are forced through hundreds of tapered holes. The pellets are sheared off at random lengths which must then pass through a conveyor oven to drive off the excess added moisture.
There also seemed to be a huge variation of properties and quality not just from different suppliers but even within the same supplier. On further investigation with pellet manufacturing it was learned that despite regulations on pellet content, pellet makers will put almost any form of wood into pellets they can find for lower price.
This might be fine but for the fact there is nothing in pellet burning that can account for these variations to insure clean or complete burning. Some pellets failed to burn completely and became glass "clinkers" others didn't want to keep burning. It was clear there was very little control over composition or manufacturing except for the more costly "premium" grade pellets which came with stated composition assurance. Even the premium grade pellets could be made from several species of hard wood, soft wood or combination of both.
In the end it had become painfully evident commercial wood pellets would NOT serve as a fuel source to satisfy the concerns we identified going in. Accordingly this meant having to move backward in time to before wood pellets which put us in the arena of other processes and or plant sources and to refine the manufacturing to remove complexity and create a more reliable solution.
See the solution developed at part two of our review.
