A search of the Internet with the key words “gasifying wood boilers” bounces back 19,800 hits. When you Google just “wood boilers,” you get about 289,000 hits, so it is apparent that this new classification of boiler is relatively new to the world market.
The majority of the gasifying wood boilers are from Europe. That can be a good thing or a bad thing depending upon your perspective. It's a good thing because the Europeans are much more conservation minded than the North American market. They also have had much more stringent standards as it pertains to operating efficiencies and visual pollution.
Remember, it was not that long ago (1970s) that the Germans realized the tops of all of their forests were dying off due to man made air pollution. That was the beginning of the efficient boiler revolution. It is really unfortunate that it took an environmental disaster to get the ball rolling, but that's the way we work — reactively.
The bad part of buying European boilers at present is cost. The dollar is relatively weak against the euro right now, so it requires a fairly large investment of pocket green to be environmentally green. There are more and more wood gasifying boilers being manufactured on the North American continent, with more on the horizon, and that is a good thing.
Certainly, keeping the jobs and the money in our part of the world is a good thing to do. The Europeans do have the edge on us technology wise, as is obviated by high efficiency modulating condensing boilers.
This new class of boiler is different on some fronts. In order to maintain a good clean burn, the burn must occur at full blast, happening at a temperature high enough to completely combust the gas by-products that are produced when the wood is burned. This means that under most situations, the charge of wood will be efficiently converted to heat in a short period of time.
Most of the high efficiency boilers are low water content but are tied to large, super insulated storage tanks for mass retention and later use of the thermal energy produced in a short time frame. This requires the use of immersed heat exchangers for transferring the heat from the heat generator to the water, as well as extraction of heat from storage to the final destination.
This storage tank can be pressurized or it can be open/atmospheric. Remember, if it is an open atmospheric storage medium, it needs to be treated as an “open” heating system, which requires special consideration (non ferrous components) as it pertains to fluid transporting devices. This industry doesn't need any more rusty train wrecks to deal with in the future.
At present, there appears to be three basic classes of wood conversion biomass units. There are the “cord” wood units, which can basically burn any type of wood (new, old or recycled) of varying sizes. These units are manually (key word MAN) fed and must be loaded between one and two times per day depending upon the load being imparted.
If the man forgets to load the wood or is on vacation, then it is obvious there needs to be some provisions for a backup plan of maintaining heat. There also needs to be some provisions for the storage of cordwood inside the dwelling or right near the entrance to the dwelling, and there also should be easy egress for the ash content, which is significantly less than its predecessors.
Although it is a somewhat labor-intensive proposition, the monetary and environmental operating benefits well outweigh the labor expenses. Besides, splitting cordwood can be a good physical exercise program. There are not many fat loggers around. But, as we get older, it may not be a viable option, and purchasing pre-split, delivered wood can add to the operational costs.
In addition to the cordwood units, there also are pellet burners and chip wood burners. These units also require space for fuel storage. However, their needs are somewhat different in that these fuels can be automatically fed into the appliances with an auger system but require the fuel to be stored in a vertical silo/storage bin system in order to facilitate the auger feed system.
Not everyone has the necessary space to accommodate this vertical storage system. The residual ash content is relatively low due to the extremely high operating temperatures seen during conversion from wood to heat but still needs to be taken into consideration.
One of the system's advantages over the hand-feed system is that (barring an auger jam), it is completely automatic. Once the fire is started, other than hauling ash (and some have an automatic ash removal system at an additional expense) the appliance is fairly low on human maintenance.
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at firstname.lastname@example.org or by phone at 303/778-7772.