Growing interest in wood boilers

January 17, 2008
Written by David Schmidt
32Regardless of the type of boiler or feedstock being used, wood boilers can be beneficial for greenhouse growers.

Bruce Bakker of Koch Greenhouses in Langley, British Columbia, has been using wood boilers to heat his greenhouse since 1986. Over those 20-plus years, he has used all types of boilers and all types of feedstocks but now uses wood pellets, what he describes as the “Cadillac” of wood biomass systems.

“It’s all about the fuel,” he told fellow growers at a biomass workshop. “Everything goes from there. You’re going to tune your system to the wood you’re using.”

Bakker switched to pellets because of convenience and ease of use. They are more expensive than wood waste, shavings or sawdust, but still offer significant savings over natural gas if the user can arrange a steady low-cost supplier.

Before using any feedstock, users should check its moisture content.

“You can’t burn water,” Bakker points out. That is another reason to choose pellets, as he says one unit of pellets has the same moisture content as four units of green shavings. “Using green shavings results in four times the emissions and four times the storage and transportation costs.”

Species is also a factor, as different woods have different BTU values and different emission levels. Bakker recommends pine, saying it has a high BTU value and very low nitrogen and ash content.

Another Langley greenhouse grower, Leo Benne of Bevo Farms, installed his first wood boiler, a
4.5-megawatt unit, in December 2002, and added a 6-MW unit 18 months later. Benne uses an ElectroStatic Precipitator to reduce emissions. Although an ESP system adds cost, Benne believes it is worth it to avoid potential complaints from neighbours.

Even with the extra maintenance cost involved in a wood boiler system, his heating cost, using primarily wood shavings, is still only about $4/gigajoule (compared to $6-10/GJ for natural gas systems). Bevo burns about 200,000 GJ/year. As a result, the $3 million cost of the two boilers, feed systems, silos and storage plant “is paid for.”

“We have a natural gas boiler as a backup but it hasn’t run for two years,” Benne said. While most growers using wood heat still maintain a natural gas boiler to provide CO2 for the greenhouse, Bevo has always relied on liquid CO2.

Even that could become unnecessary. Greenhouse consultant Hubert Timmenga is beginning a research project at Rainbow Greenhouses in Chilliwack to assess whether flue gases from wood pellet burners can be used as a source of greenhouse CO2.

“The biggest question growers ask when considering biomass boilers is what about CO2,” Timmenga said, noting 40 per cent of the natural gas used by greenhouses is to generate CO2.

Timmenga’s project is sponsored by the B.C. Greenhouse Growers Association, the United Flower Growers Co-op, the Wood Pellet Association of Canada, and the Agriculture Environment Initiative. It will assess whether flue gases are clean, whether they cause plant damage and what the quality of the fly ash and sludge is.

Testing of the flue gases has already begun, with plant assessments conducted from January to May.

Results should be available mid-year.

A similar project is underway at Agriculture and Agri-Food Canada’s Greenhouse and Processing Crops Research Centre in Ontario, but Dr. Xiuming Hao does not expect results for one to two years.

The Harrow project will use a flue-gas scrubbing system and compare it to liquid CO2.

Rainbow currently has two Binder boilers, which operate on wood waste. While wood waste is the most inexpensive biomass available, it can be more difficult to manage and often comes with unwanted extras.
 
“We are getting things like steel and concrete in the fuel,” Rainbow’s Stan Vander Waal said, adding industry is hoping to get standards in place to ensure users get a cleaner waste. Because of the large particle size and unwanted pieces, Rainbow uses a chain conveyor, rather than an auger, to feed the boiler.

While a cyclone keeps air emissions to about 100 ppm, Vander Waal is considering an ESP system. (Bevo’s ESP system limits their emissions to less than 25 ppm.)

He reminded potential users they will need plenty of storage space. “As the fuel supply tightens, it is critical to have a good three-month supply.”

To avoid ash and dust issues, Rainbow cleans the boiler room weekly and uses a pressurized air system to keep dust out of the electrical cabinet.

The primary workshop speakers were Fernando Preto and Irene Coyle of Natural Resources Canada in Ottawa. NRC is actively promoting biomass boilers in the greenhouse industry and the B.C. workshop followed five workshops for Ontario greenhouse growers. Preto said the biggest concerns regarding the use of biomass are economics and emissions.

While Preto said NRC is working with the Ontario government to make sure emission rules don’t adversely affect biomass users, “I’m not sure that’s possible in B.C.,” he admitted.

Most of B.C.’s greenhouse industry is located in the heavily populated Greater Vancouver/Fraser Valley area. While the federal government promotes the use of biomass, B.C. greenhouse growers are subject to intense local public and political pressure to reduce or eliminate their use of wood boilers. The Greater Vancouver Regional District is drafting a new Air Quality bylaw that will require all greenhouse growers who use wood boilers to obtain permits and pay fees based on their consumption levels.

“What we will allow will probably equal what you can achieve with natural gas,” GVRD regulation and enforcement division manager Ray Robb told growers in late 2005, flatly telling them “what we will have in the bylaw will be so far away from what you need.

(The GVRD) sees wood as back sliding and it will result in more emissions and more hazardous air pollutants,” he insists, “I don’t think the (GVRD board of directors) will be able to sign into law a bylaw which would allow burning wood which is not as good as gas.”

Although greenhouse growers have managed to avoid the permits to this point, that could soon change.

Recently, the NDP provincial opposition has raised the issue in the legislature and the media, claiming officials have no idea what the burners are emitting.

They are capitalizing on a public perception of biomass boilers as beehive burners spewing huge clouds of ash pouring out of old smokestacks.

Preto says the reality of today’s efficient systems is much different, insisting the only systems with harmful emission levels are those that “aren’t operating or designed properly.”

If there is good combustion through use of low moisture fuels and proper air staging coupled with a cyclone, ESP or bag filter, emissions can be kept to minimum. “Current commercial biomass combustion systems burning uncontaminated wood fuels can meet ‘reasonable’ emissions guidelines,” Preto insisted.

Because of the high capital cost of the boilers and fuel storage systems, biomass boilers may not be economical for small operators but should be cost-effective for larger operations.

“The economic advantage comes from five-acre-plus greenhouses,” Preto stated.

In addition to the savings in heating costs, biomass boilers may also offer opportunities for additional income through cogeneration and/or trigeneration.

“Cogeneration is a very attractive option,” Coyle said, particularly in Ontario, which offers 11 to 14 cents/kwH for power generated from biomass. The opportunity may not be as great in B.C., which offers only a two cent/kwH premium for electricity from cogen projects, and then only if the power is provided continuously. Since most B.C.

greenhouses do not run their boilers continuously and many even shut them down completely for a month or more, this may prove to be uneconomical.

If the research projects in Chilliwack and Harrow prove biomass boilers are able to generate usable CO2 for the greenhouse, this will also improve their cost-effectiveness.

Finally, use of a biomass boiler may generate carbon credits. Although government is still developing its policy on carbon credits, Keith Driver of Calgary’s Baseline Emissions Management says his company is already trading “renewable energy” credits between Canadian companies.

“We sell things which don’t exist,” he proudly claimed, saying Baseline has developed its own protocols (about 100 pages) and has already completed several domestic bilateral transactions. He notes such Large Final Emitters as B.C. Hydro and Duke Energy know some greenhouse gas emission reductions will be required regardless of what the eventual policy is.

“Large investors therefore want to know what credits they have available to them,” he said.

The source of biomass is the greatest determinant of the value of the credits. “You get the biggest credit if you use biomass which would otherwise go to a landfill,” Driver said.

Baseline is looking for projects of at least 10,000 tonnes/year. This may be too much for a single greenhouse but could be achieved if several greenhouses aggregate their amounts.

While the credits have traded for as little as $2/tonne, Driver says the average price will likely be much higher. Offsets in Europe are trading at about $7/tonne CDN.

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