The Future of Brush

[Note: This post has been submitted for publication in a trade journal for arborists.]

The Future of Brush

Petroleum prices climb every year, with no end in sight. Eventually this unsustainable fuel will, by definition, no longer be available. How will this affect our business? 

Perhaps the problem is the solution. As arborists, we generate fuel every day, in the form of wood and chips. We use petroleum to process and dispose of this fuel as waste. Some of us have a firewood business on the side, or we screen and color wood chips for sale as mulch. Others have switched to plant-derived fuel, grown mushrooms, or milled lumber from logs. We can become more conservative and clever about our petroleum use. But what if we could use our own waste as fuel?

Wood as fuel

Burning wood has earned a bad name. Tar, soot, carbon monoxide and particulates in smoke cause health problems and death. Modern fireplaces are smoky and inefficient space heaters, and the chimneys frequently don't draw properly. Even an EPA certified low-emission stove puts out as many fine particulates in 2-1/2 days as a car does in a year.(1) Urban areas and valleys are especially vulnerable to smog. But about 80 percent of residential renewable energy comes from wood heat appliances (not including fireplaces), compared with 15% from solar.(2) And today we have wood burning alternatives, new and old, that can restore firewood's reputation and save arborists money. They would utilize our 'captive' fuel source to heat our shops and homes. And by promoting them to the public, we can develop a market for our waste.

Rumford fireplaces and wood stoves

Open fireplaces are not the most efficient heat sources, but so-called modern fireplaces are much worse than Rumford fireplaces, which first appeared in the 1700's. Rumfords radiate as much as 63 percent into the room, and the exhaust is invisible two minutes after lighting. There are many Rumford references online, but most of them misrepresent the original design. Here(3) is an accurate one. There are also new high-efficiency wood stoves that enable either cordwood or wood pellets to be burned more cleanly than before, dramatically reducing emissions. (4) [image]


Furnaces and boilers have also undergone significant improvement. These units deliver heat through pipes to a heat exchanger for space heat and hot water, using wood, pellets, or other fuels. Because they burn so cleanly, they are exempt from EPA regulation, although some manufacturers strive for voluntary compliance.

Rocket stoves

Rocket stoves are a cheap, massive DIY heat source using mostly recycled materials such as metal drums, brick, and 'urbanite' (broken concrete or similar material). Labor-intensive to build, they not only burn cleanly, but they capture nearly all the heat produced in the small firebox and radiate it into the living space over several days. (5)

Wood gas

Still more exciting are wood gas generators, which produce heat, electrical power and shaft (PTO) power. They generate electricity for $1-2 per watt, fit on a pallet, and can be tied to the grid. Carbon monoxide, tar and soot are consumed by the machine, eliminating pollution. Wood gas generators are far more powerful than solar systems. (6)

Charcoal and biochar

Charcoal has been made for centuries by pyrolysis of wood. Biochar is a special form of charcoal that can be added to soil to increase CEC and water retention. Biochar making equipment is just becoming available, and the potential market is huge. (7)

Torrefied wood

Pyrolysis can be halted before the wood changes color, which can then be ground to a fine powder that can be driven through a jet and ignited to burn like propane. This torrefied wood powder is also the substrate for gas-to-liquid technology to manufacture liquid fuel from wood gas — what some regard as the holy grail of biofuel. Both of these applications are still under development.

Torrefied wood powder has been the substrate for wood pellet manufacture since the 1930s, and the industry is growing rapidly. Pellets can be used in many boilers and furnaces. Rising petroleum prices have led to pellet mills being built to use chipped wood instead of sawdust, opening the door to arborists. (8)


Besides the usual waste from tree pruning and removal, many locales would benefit from a 'coppice' approach to wood production to assure a steady supply. Any species that resprouts from the base can be harvested on a 5- to 20-year cycle. Coppice has been practiced for centuries. Besides fuel, it yields usable materials and promotes wildlife. (9)


It's not likely there will ever be a fuel as versatile as petroleum, not to mention its other uses. Wood is solar energy, in a form that's safer than ever, increasingly economical, and available day and night. As petroleum gradually becomes more expensive, biofuel will become more profitable. Arborists have a captive source of biofuel. In addition to meeting in-house energy needs, wood waste is a growing profit center. We would do well to become informed about the alternatives and promote them, and some of us may pursue additional income streams from installing wood energy systems for others.








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Copyright 2013 by T. Gray Shaw