Wood Chip Heating
Fröling wood chip fueled hot water boilers conveniently provide heat for larger applications such as process hot water, commercial, institutional, and industrial space heating applications.
Fröling chip boilers are ASME stamped boilers designed for indoor use. Fuel feeding, ignition, grate cleaning, heat exchange cleaning, and de-ashing are all automatically controlled. Combustion is actively controlled using variable induction fan speed, variable grate control, and motorized air controls. Fröling wood chip boilers respond to heating loads by ramping output up and down while minimizing on/off cycles. Use of properly sized thermal buffer and balancing flow in the system ensures smooth and successful boiler operation throughout a range of thermal demand.
Fuel storage is located adjacent to the boiler to minimize space and conveyance costs. Chips are usually stored in a flat bottomed bin. The fuel is generally moved to an auger with a rotary feeder or with a scraper floor. From the feed auger, fuel passes through a safety airlock into the stoker channel. The stoker is often an auger, but the Fröling Turbomat can utilize a hydraulic ram, which is used for larger chips or more inconsistent fuel.
Fröling engineers and supplies numerous chip feeding systems. Fuel handling integration is crucial for reliable operation.
The Fröling Turbomat can use wood chips up to 45% moisture content. The Fröling T4 can use wood chips up to 30% moisture content. The Turbomat has a much longer grate surface than the T4. The grate surface in the Turbomat moves chips horizontally. Chips enter unburned and exit seven feet away as ashes. The theory is that wood chip fuel can either be dried outside of the boiler or within the boiler. Boilers that can handle wetter chips generally have longer grates and very heavy, brick lined fireboxes, two attributes that allow the chips to dry within the boiler as they combust. Brick lining allows for an extremely hot environment (up to 900 C). Smaller and lighter boilers must have dry chips to ensure complete combustion because it is not possible to adequately dry the chips in relatively small combustion chambers surrounded by water. The result can be incomplete combustion.
Sometimes it makes sense to have smaller infrastructure at the boiler site and to use dry chips. Sometimes larger chip boilers and less expensive, wetter fuel makes better economic sense. Projected chip consumption, physical space, and initial capital costs will usually determine what type of wood chip boiler makes the most sense
Historically, heating with wood chips cost about 1/2 the cost of conventional fuels such as fuel oil and propane. The greater the volume of conventional fuel that is offset, the greater the savings.
Wood Chip fuel is produced by chipping whole trees or wood waste from forest management and land clearing. Wood chip fuel is less expensive than wood pellets. Wood chips come in various sizes, moisture contents, and qualities. Chipped wood allows for automatic and low maintenance boiler operation while using renewable wood fuel.
Wood chips (30% moisture content) have an average net BTU rating of 9,632,000 BTU/ton. When less bark and debris are present there will be less ash produced during combustion. Whole tree chips like those produced by roadside chipping are usually not used in wood chip boilers producing under 2 MM Btus/hr. High quality chippers and chip screens are generally required to produce a maintenance free fuel chip. The Fröling T4 150 burns dry chips (Less than 30% moisture content). Moisture content under 30% is achieved only by actively drying Eastern hardwoods.
American National Standards Institute (ANSI) has published a Wood Chip Heating Fuel Quality Standard officially titled ANSI/ASABE AD17225-4:2014 FEB2018 Solid biofuels -- Fuel specifications and classes -- Part 4: Graded wood chips. This standard describes qualities of wood chips such as wood chip feedstocks/origination, particle sizes, moisture content, and other qualities such as permissible contaminants.