Carbon-Negative Woodchip Furnace
Burt's Greenhouses, Kingston, Ontario
Alex English, a self-taught combustion engineer, learned gasification techniques from Dr. Tom Reed at the National Renewable Energy Lab.
In 2005, Burt's Greenhouses in Odessa, Ontario, Canada decided to convert their fuel oil heating system to a renewable, local, carbon-neutral fuel: woodchips. Burt's operates 15 large greenhouses to supply five retail nursery stores, plus a wholesale business. Every winter, this 1.5 acres of growing chambers must be heated, along with associated one acre of outdoor plant bedding terraces. Burt's contracted with Alex English to engineer, install and operate this new biomass heating system.
In summer 2006, Burt's fuel oil furnace was replaced with a Blue Flame Stoker woodchip furnace manufactured in Manitoba. The Blue Flame Stoker uses a chain grate to carry woodchips across the burn chamber and through the combustion zone. Several innovations were required to make this switch feasible. An intelligent, sophisticated augur and conveyor was needed to automatically move woodchips to the furnace. New sensors and computer software were designed to permit full control of the combustion chamber and other equipment.
In winter 2006-7, Burt's Greenhouses went from burning 120,000 litres of imported fuel oil to combusting perhaps 600 tons of woodchips, which included a somewhat longer heating season.
Then, in summer 2007, Alex took this project a step further: all the way to carbon-negative. Alex modified the Blue Flame Stoker recirculate combustion gases, and inject extra oxygen above the burn chamber. By manipulating the burn chamber environment, Alex could assure complete gasification and gas combustion, and bring particulates, soot and carbon monoxide emission nearly to zero. Using software he wrote for his laptop computer, and special sensors in the furnace and flue, Alex can run the furnace in two modes:
full-burn to ash, or
controlled-burn to biochar.
According to owner Brian Burt,
"Making charcoal with the system involves two variables:
1) strict control of under-fire air, and
2) strict control of grate speed
thus determining time duration material is exposed to high temperature. Other modifications included introduction of over-fire air, and special oxygen sensors to properly control toxic emissions. The system has run brief periods of time in this mode, proving it can be done with a unit in this configuration. We hope to continue work on the system to prove it can be operated routinely to produce biochar, and to do so economically, but we aren't there yet."
On cold winter nights, Alex runs the furnace at full bore to crank out maximum heat, and woodchips are oxidized completely to ash. But on milder nights and daytime, Alex can throttle back the burner and recirulate combustion gases to starve the burn chamber of oxygen and force the burn into full pyrolysis. Then, when fresh air is introduced in the over-fire, the pyrolysis gases released in primary combustion are burned, and carbon monoxide, smoke and soot emissions go to near-zero and carbon is captured as biochar. Using common sense, sound science and ingenuity, Alex has converted Burt's Greenhouses to carbon-negative operation, with a further bonus to produce a potentially valuable soil enhancement by-product.
A very nice video was produced describing Burt's Greenhouse's change to a renewable fuel for winter heating. The video details the various innovations and design features of the biomass burning system, but does not discuss the use of biochar. However, in 2009, Burt's Greenhouses began experiments using biochar in soil mixes and garden vegetables, and created a webpage about biochar.
In early February 2010, Burt's Greenhouses will hold a 1-day seminar and 2-day workshop on biochar with Dr. Hugh McLaughlin, director of biocarbon research for Alterna Biocarbon.
Recently, Alex English embarked on a new project to build a 400-gallon TLUD, a batch pyrolsis burner fashioned from a tank. This huge barrel has a 4-hour burn cycle time when loaded with dry woodchips. Alex will inject the TLUD pyrolysis gases into the Blue Flame Stoker combustion chamber along with woodchip feedstock. This should help starve the chamber of oxygen, force a more rapid onset of pyrolysis, and boost total heat output.
539 Maple Road
Odessa, Ontario, K0H2H0