Canbio Update: Hothouse of Opportunities
Heat has always been a major expense for greenhouses. With the recent steep rise in fossil fuels, many have considered lower cost biomass, but what type of biomass and equipment?
May 28, 2009 By Bruce McCallum
Heat has always been a major expense for greenhouses. With the recent steep rise in fossil fuels, many have considered lower cost biomass, but what type of biomass and equipment? With recession comes lower oil and gas prices, but they won’t last. It is sensible to move to lower cost and more stable biomass energy during this brief respite, and there are also environmental benefits from switching to clean, carbon-neutral biomass.
As a bioenergy consultant, I have often been asked about the various biofuels and biomass systems to cut energy costs. There are no simple answers. Most greenhouse operations are unique. They vary in size, crops or products grown, season of operation, and heat-load profiles. Daytime heat loads can be significantly lower than those at night. Some have relatively small winter bedding plant operations followed by much larger grow-out acreages. Existing and possible future heat requirements need to be considered.
Supply & Systems
There is also a variety of biomass available. In most forested regions, mill residues such as sawdust, shavings, and bark make sense. Yet in some regions they are in short supply, especially with so many sawmills down. A thorough search of local mills may still uncover enough fuel to meet your needs, especially if it is stockpiled during summer.
If mill residues are scarce, woodchips may work. They can be bought directly from forestry contractors, or you can buy low-grade roundwood and hire a contractor with a chipper, or buy your own chipper. This approach has been taken by Den Haan’s Greenhouse in Nova Scotia. Woodchips typically cost $45–50 per green tonne delivered.
The moisture content of green woodchips and mill residues is typically 40–50%. Several Canadian companies make fully automated industrial class (wet fuel) burners, most notably KMW Energy and Wellons FEI Corp. Usually these systems start at about 1 MW (3.4 million BTU/h) capacity. Grovewood Heat builds small-commercial burners that can handle fuels up to 45% moisture content.
Wet fuel burners tend to be larger, more capital intensive, and require more tending than dry fuel systems. It may make sense to pay a premium for drier biofuels that have greater energy content and increase system output. Dry chips can be produced from urban wood waste such as pallets and clean building debris if forestry fuels are unavailable.
Today, many greenhouse owners are turning to a more refined biofuel such as wood pellets. Pellet-burning appliances can offer a high degree of automation and are smaller and cheaper to buy than wet fuel systems of equal capacity. But pellets are generally at least double the cost of green woodchips on a dry matter basis (one tonne of pellets has the energy value equivalent of roughly two tonnes of green woodchips).
Wood pellets are produced in large volumes in BC, Quebec, and the Maritimes. Canadian pellet production surpassed two million tonnes in 2008 and is projected to grow to three million tonnes by 2010. Most are being exported to Europe where demand now exceeds 10 million tonnes. In Nova Scotia, pellets can be purchased in bulk for about $200 per tonne at the plant. One tonne of pellets displaces 450–500 litres of heating oil, depending on system efficiency. In BC, pellets can be purchased for less than $100 per tonne at the plant. Some regions, such as Ontario, currently lack adequate pellet production or distribution, but plants are being planned.
Several Manitoba companies have been building coal stokers that can burn pellets. Examples include Decker, Pelco, and Blue Flame, all of which are being used to heat Canadian greenhouses. European pellet burners are also starting to be sold in North America, and there will be many more to come. Canadian companies are also beginning to build pellet-burning appliances.
In farming regions, there are other options. Low-quality grains, including those of corn, wheat, rye, and barley, can be burned in multi-fuel burners. For example, more than 50 Danish Tarm Multi-Fuel boilers are burning low-grade grains, mostly in the Prairie provinces. Burning grains typically generates more ash and a lot of solid clinkers, but the savings can justify the extra time spent tending the burners. However, not all pellet or coal burners can burn grains. The Danes have used straw as a fuel for many years. They now have fully automated straw burners in sizes suitable for greenhouse operations.
Greenhouse owners may want to use more than one type of biomass system, depending on the length of the operating season. If you have a large core area that has a long operating season, woodchips or mill residues might be the best option. Pellets may be the best option for greenhouses that are only operated for a few months a year. The lower cost pellet systems are less of a burden if the system is sitting idle for part of the year.
Canada is rich in biomass resources. Biomass fuel prices are stable and competitive with fossil fuels in most regions of the country. Greenhouse owners need to determine which biomass fuels are available in their area and the bioenergy system or systems that best meet their long-term needs.
Bruce McCallum of Ensight Consulting wrote this article on behalf of CANBIO, specifically for Canadian Biomass. This CANBIO Update will be a regular feature in Canadian Biomass.
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