Lighting a tonne of wheat straw on fire produces much less energy than if it is allowed to smoulder under the right conditions.
That’s the physics lesson upon which Raymond Dueck is building his new business.
The Manitoba entrepreneur has developed a technology to extract a large amount of usable energy from a tonne of straw.
In scientific terms, the process is known as gasification. It uses raw organic material such as wood or straw as its base fuel.
“My short explanation isn’t very scientific,” said Dueck, president of Innovaat.com International in St. Adolphe, Man.
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“Basically, we burn straw at a very low oxygen level in the primary chamber. But, it’s not really burning. It’s just smoking and smouldering away. We say it cooks the straw. This forces the gases to escape from the biomass. It’s sort of a charcoaling effect. It’s not really considered to be combustion in the truest sense. The scientific term is pyrolysis. It’s these gases that hold the high energy you can use for other things.
“There have been all sorts of gasification projects over the years, but this project has a different twist,” said Dueck, who named his new company Biomass Energy System Technologies (BEST).
“We tend to shy away from calling this a gasifier. We call it a two-stage, close-coupled combustor because that’s what describes it. It’s not a gasifier in the normal sense of the word that everyone thinks of. We don’t try to capture the gas or clean it up or store it to sell later. We burn it immediately at the source to create immediate heat energy. And of course, heat energy can be converted into all kinds of viable work, such as electricity.”
Dueck is not a scientist. Instead, the project’s scientific expertise was supplied by Eric Bibeau of the University of Manitoba’s mechanical engineering department. Dueck said Bibeau has been instrumental in making the process clean and efficient.
“When we burn straw, we burn it clean, so we produce virtually no pollution in the creation of energy,” Dueck said.
“We say that straw is just sequestered solar energy. That’s really what it is. We take residual solar energy laying in the field, bale it, burn it and convert it into usable energy that produces work.”
The first stage in the process is pyrolysis, which is similar to other gasification projects.
The term pyrolysis comes from the Greek words for fire and decomposition. It happens in nature when a forest fire creates heat but uses up nearly all available atmospheric oxygen in the immediate area, preventing a total burn. Complete combustion is not possible for the remaining trees and biomass.
While Dueck’s system is geared specifically for straw from farm fields, similar systems around the world are fed by a variety of biomass materials, as long as moisture content is below 30 percent.
Fuel sources include sawmill and logging residue, fire and disease killed trees, urban waste and surplus hay stockpiles.
The BEST design feeds round straw bales into the primary combustion chamber on an automatic conveyor. A mechanical agitator on the chamber floor keeps the biomass turning for optimal decomposition. The rotating grate also makes ash removal easier.
Stage one biomass decomposition by heat occurs at temperatures of 260 to 540 C. Byproducts of the incomplete burn typically include carbon monoxide, hydrogen, methane, carbon dioxide and water. Solid char is sometimes formed, as well as liquid tar.
An open fire in nature lets those high-energy gases escape. Enclosing the smouldering fire in an airtight primary combustion chamber with controls for intake and exhaust makes it possible to harness the escaping gases.
“The gases we harvest from the straw go into what we call an afterburner. We add oxygen just as the gases go in,” Dueck said.
“Adding oxygen to the unburned gases is the key to creating a very strong afterburn or secondary combustion, and that is the energy we work with. That’s the energy that has commercial value.”
There are two ways to extract commercial value from the volatile gases:
- The most expensive and most efficient technology injects pure oxygen into the flow as it enters the afterburner. Pure oxygen in the mix creates the hottest and most efficient flame, but it costs more.
- The more common approach is to blow fresh atmospheric air into the gas flow entering the afterburner. Air contains about 20 percent oxygen, enough to create a strong burn in the secondary chamber.
This process is known as air-blown gasification or partial oxidation. Nitrogen in the atmospheric air dilutes the oxygen, so the resulting gas is classified as a low-energy gas. However, it also creates high temperatures.
A disadvantage of feeding straw into a gasification process is the byproduct silica.
Dueck said silica clogs up most straw-fueled heat exchanger systems and can’t be avoided because it’s the most abundant mineral on Earth.
His design manages the byproduct by condensing it against the walls of the afterburner. Liquid silica then drains into a collector at the bottom of the chamber, allowing it to be removed.
Dueck said this is possible because of high temperatures and design features within the afterburner.
“Temperatures in our secondary combustion chamber run from 1,100 to 1,650 C. We get a very clean burn. There’s very few emissions. The City of Winnipeg requires a burn of 1,800 F (980 C) to be considered a clean burn, so we’re well above that point.”
Dueck said heat always has value.
“Once you’ve harnessed a new source of clean, high temperature heat, you can do many things. You can generate electricity or you can heat homes and factories. Or you can apply this heat to the many manufacturing processes that require heat every day.”
What is …
Gasification dates back to 1699 when coal gas was first extracted in an experiment.
Pyrolysis is a form of incineration that chemically decomposes organic material through heat in the absence of oxygen.
Producer gases, as they were commonly known, were used during the Second World War to drive internal combustion engines in cars and trucks and for heating and cooking without petroleum fuel. Germany used the process to ensure independence from imported oil. When the war ended, petroleum fuel was cheap and plentiful and gasification became a historical footnote.
