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The fundamental design of wood biomass boiler systems commonly installed under the FFS&B program is fairly basic.  Basic system components include a fuel storage bin, fuel conveyance system, a firebox (combustion chamber or gasifier), an emissions control system including but not limited to a stack, and an attached water boiler.  Basic operation involves the wood fuel being conveyed to the firebox via an augering system.  In the firebox, the wood fuel is combusted and its heat transferred to heat the boiler water system which then distributes hot water or steam throughout the facility’s HVAC and/or hot water distribution systems.   

While basic system operation follows this general concept, different manufacturers design and build their systems in different ways which employ varied technologies and mechanisms.   Certain designs may better suit particular scenarios and applications and care should be taken to match the right system to meet your needs.  Variations of design may be determined by factors such as quality of wood fuel to be used, type of vehicles available for fuel delivery, facility space limitations, and compatibility with the existing HVAC distribution system.

Technology Resources

 Wood-Chip Heating Systems Guide, Tim Maker, Biomass Energy Resource Center (BERC), 2004 (1.56 MB PDF)

 Wood Pellet Heating Guide, BERC, June 2007 (1.04 MB PDF)

 Link to Manufacturers

Fuel Supply and Transport

 Wood biomass fuels sources can include residues from forest treatments and timber harvests, mill residues, clean urban wood waste from tree trimmings and construction site demolitions, and dedicated energy crops (short-rotation woody crops).   

 Assessing your local fuel supply

·    Identify local sources and estimated quantities available.  Find out who has residues and what they’re currently doing with them (mills, other wood product manufacturers, arborists, landfill, etc.)  For forest residues, local state and federal land management agencies may help to identify current and future forest management projects that will produce residues, and assist in identifying contractors in the area as potential suppliers. 

·    Identify potential suppliers in the area with equipment for processing material (chipper/grinder) and trucks for delivery.

·    Identify the type of wood fuel commonly available in your area.   Do this as you’re exploring different system designs and communicate that with the system engineers.  Determine whether the fuel will be chipped vs. ground wood material from forest or urban sources, soft- or hardwoods, a mix of both, sawdust, wood pellets or other material.  By doing this, the system manufacturer can design a conveyance and burner system that is compatible with the wood fuel you intend to burn.  

Factors that commonly affect the cost and availability of wood fuel include rates of material generation, ease of collection, competing users and haul distances.  It’s important to note that the cheapest wood fuel is not always the best.  Your wood fuel should meet certain standards and specifications as designated by the system manufacturer which provide for a few things: ease of conveyance, high heat value, and quality consistency.

To maximize flexibility in your suppliers it’s good to design your fuel storage facility to accommodate deliveries from a variety of locally available delivery vehicles (walking floor trailer, dump truck, potato truck, tractor, front-end loader, pneumatic systems, etc.).  

Fuel Supply Availability Resources

Biomass as a Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion Ton Annual Supply (“The Billion Ton Report”), USDA and DOE, April 2005

A Geographic Perspective on the Current Biomass Resource Availability in the United States, NREL, Dec. 2005 

TimberBuySell.com online Marketplace for Forest Resources and News

Managing Organic Debris for Forest Health: Reconciling fire hazard, bark beetles, wildlife and forest nutrition needs,  A Pacific Northwest Extension Publication, 2009.

Wood Fuel Transportation Resources

A Study of How to Decrease the Costs of Collecting, Processing and Transporting Slash, MCDC, et al., Dec. 2004

Options for Transporting Biomass, USFS

Forest Residue Transportation Costing Model (Trucking Simulator) Interactive spreadsheet calculator designed to compare costs of varied alternatives for slash collection, processing, and transportation methods.

Air Quality  

Using forest biomass for heat and energy production can offset air emissions from a number of activities—displacing open burning of slash piles; encouraging treatment of densely over-stocked forests at risk of damaging infestations by insects and disease and catastrophic wildfires, thus maintaining the forests ability to sequester CO2; and displacing CO2 emissions from the combustion of fossil fuels. 

Like other energy combustion sources, wood boilers emit pollutants, including particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), volatile organic compounds (VOC), sulfur dioxide (SO2), carbon dioxide (CO2), hazardous air pollutants and trace elements.  Particulate matter emissions can be minimized by choosing clean and efficient technology designs, proper systems operation and maintenance, and with the installation of pollution control devices.  As part of the FFS&B partners' commitment to ensuring good air quality, they have sponsored stack emissions testing on a variety of systems, regularly share lessons learned with the public at large, and continue to collaborate closely with regional and national air quality managers.

As you begin the design of a wood biomass energy system, consult your local, state, and national regulations as these will vary by location and project.

For national and regional information from the EPA.

Update on federal air pollution regulations for smaller commercial/institutional boilers, January 29, 2009  (PDF, 26 KB)

Information on Air Pollution Control Technology For Woody Biomass Boilers, March 2009 (PDF, 158 KB) - This document describes the types of control technology available and their effectiveness, and various aspects of designing and operating woody biomass boilers.

Emissions Test Reports from Fuels for Schools and Beyond Projects

Air Quality Presentations from 2007 Workshop

Emissions Consultants