Introduction to Woody Biomass
Biomass energy can utilized in the form of heat or power or a combination of both. Heat and power are created through the combustion or the gasification of living carbon-based matter. While biomass includes a wide variety of resources, this page, and the listed biomass projects primarily focus on woody products, which are the most commonly used form of biomass fuel in Alaska, other sources include grasses and grains. Other sources, such as fish oil and municipal waste, are used to make biofuels. These sources are discussed in more detail on our alternative fuels page. Some common forms of biofuels include municipal waste, fish oil, and biodiesel.
Woody biomass can be directly used as firewood, processed into wood chips or densified into pellets or bricks, depending on technology and the resources that are available. While woody biomass is a widely distributed resource, finding, acquisition, gathering, and storage can create significant challenges to feasibility of projects.
How Biomass Works
Biomass has been a traditional source of energy for thousands of years. Our ancestors used biomass to heat their homes, to provide light, and to cook food. Most people living in the United States no longer have such a heavy reliance on biomass, but In Alaska, many still rely on woody biomass to heat their homes. Alaskans still use wood stoves to heat their homes especially in many rural areas, although only around 4% of Alaskans still use wood as their primary heat source, many Alaskans, up to almost 60% in south central and over 60% in interior Alaska, still use wood as their secondary or backup heat source.1
Many modern biomass systems and almost all of the large scale biomass systems in Alaska, use hydronic (hot water) furnaces and boilers that combust fuel to heat water or another fluid, which can then be transported and used nearby as district heating for buildings. Water effectively stores the energy produced by the combustion of biomass, making these systems much more efficient than the wood stoves that are used in many private homes.
Different boilers utilize a variety fuels from a variety of sources. This has the benefit of designing biomass projects specifically to use the resources that are accessible in a community. biomass offers more opportunities for communities wishing to lessen their reliance on expensive fossil fuels that have to be trucked or barged in. Some boilers burn wood that has been chucked into log rounds or wood that has been chipped, the technology for these methods is readily available, common and inexpensive . The wood used is often locally harvested which benefits local economies. Other boilers can use the waste products generated from sawmills, such as wood chips, sawdust, or hog fuel. Waste products can be cheap sometimes only costing the community transportation expenses to move fuel from the sawmill to the boiler location.2
Some boilers require the use of processed fuel. Most of these fuels are manufactured from pulverized wood, but they can also be made of other carbon based material, such as cardboard or paper.3 Processed fuel sources offer a variety of benefits for biomass use. These products are uniform in size; density and moisture content, which can improve the efficiency of boilers.4However, significant challenges also arise when using a processed product. These products are not readily available, and generally cost more than waste products from sawmills or cordwood, and require potentially expensive manufacturing. If communities don’t have their own pellet mill, fuel may have to be shipped great distances, adding cost to a project.
Biomass Energy in Alaska
Alaska has nearly 12 million acres of available forested land, with an estimated 1.9 million cords (3.7 million tons) of annual growth. On average, over 1.5 million acres per year of forested land are subject to wildfires and beetle-kill. Some of the wood on these affected lands is salvageable as biomass fuel, additionally culling trees to protect communities from wildfire is already a commonly used mitigation method which could provide a viable fuel source to many communities. Despite the obvious opportunities for biomass projects in Alaska, there are also significant challenges related to the deployment of biomass energy devices in Alaska’s urban and rural communities. Some of these challenges are common in installations in any location, others are specific challenges to certain communities.
To see what woody biomass fuel sources are available1 in your region of Alaska, please visit the Cooperative Extension page on the availability wood resources. [http://www.alaskawoodheating.com/availability.php].
Challenges in Biomass Energy
While biomass energy has the benefit of reducing fossil fuel use in Alaska, offering significant benefits to rural communities with readily available wood resources, it also has potential challenges, including environmental issues and inhibiting cost and transportation issues.
Like fossil fuels and other biofuels, woody biomass has the potential of being a pollutant. when incompletely burned, it creates black carbon which is one of the largest contributors to greenhouse gas pollution. This means that if biomass is to be used as an alternative fuel for the purpose of reducing one's carbon footprint, the proper infrastructure and combustion equipment is required.
Another consideration needed when developing new biomass projects is the availability of resources and very detailed information on quantity available for use. Sustainability of biomass supplies requires planning and coordination, and it will vary widely by area. Regional facilities that gather and process biomass could become a feasible option for upriver, forested communities to supply fuel to downriver communities. Mobile equipment for processing fuel could be shared by several villages in a region on a rotational basis. Road system communities could also benefit from medium-scale regional facilities.The high capital cost and projected operation and maintenance costs of Co-Heat and Power (CHP) systems will likely be feasible only in larger communities with high power demand, high diesel prices, and a way to use the substantial amount of heat from the system. As the technologies are refined and costs are reduced, smaller-scale applications may become feasible.
Over time biomass technology has improved, and is still doing so. While many Alaskans still use wood stoves to heat their homes, wood-fired furnaces and boilers have been on the market for many years. Many older-style outdoor wood boilers (OWBs) are used to heat water, but like most wood stoves, these tend to be inefficient burners and cause significant air pollution from incomplete combustion and convert only 35% of the energy available in the wood to heat energy Newer, more efficient boilers convert more than 70% of the energy in the wood to heat in the form of hot water or steam.
Heat and power is produced when biomass and the gasses these materials produce are burned. For example, wood is composed of several chemical components that react differently when they go through the combustion process. In a wood fire approximately 80% of the solid wood or volatile matter converts to gas before it burns. This gas made up of carbon monoxide and hydrogen and is commonly called producer gas or wood gas. About 20% of wood is in the form of fixed carbon. Fixed carbon is converted to charcoal or char when heated. The charcoal does not convert to gas, but burns in direct contact with air. Charcoal burns at much higher temperatures than wood gas, so it is preferred as a cooking fuel around the world. With devices that make gas or oil, the char is recovered or burned to provide heat to make producer gas. In a stove or furnace the charcoal burns once the gases have evolved and air is available for direct combustion. If it is burned directly in a stove or furnace, its heat is transferred directly to the living space or to water where its heat can be distributed to buildings by means of hot water or steam.5
Biomass technologies appropriate for Alaska fall into three categories:
Biomass furnaces require a fuel handling system, a combustion vessel (furnace, boiler, or gasifier), ash removal, and general maintenance. The simplest furnaces require manual loading, and equipment to gather, cut, and store the wood. These systems require an operator who loads the unit regularly so heat can be provided. More complicated units that use processed fuel have automated feeding systems eliminating the need for manual loading.
As the volatile components of producer gas cool some condense to form tars and oils. These oils can be converted to pyrolysis oil, also known as bio-oil, which can be used as a transportable liquid fuel. Technologies for making bio-oil are still in development. To learn more about producing fuel from woody biomass, please visit the Alternative Fuels page.
Community-scale heat and power systems are usually based on boilers that convert the heat to hot water or steam for distribution to surrounding buildings. Some large boilers can produce steam at a high enough temperature and pressure to generate power in a steam engine or turbine to make electricity. Steam engines and small turbines are generally very inefficient, so other fluids and generating devices such as Organic Rankine Cycles and Stirling engines are being considered for use. Chena Power is installing a co-heat and power unit that will utilize ORC technology, and use waste heat and Co2 emissions to provide heat to greenhouses.6
|TECHNOLOGY SNAPSHOT: BIOMASS|
|Installed Capacity (Worldwide)||Globally, biomass is the fourth largest energy resource after coal, oil, and natural gas. Uses: heating, cooking (biomass), transportation (biofuels), and electric power generation (biopower). NREL estimates 278 quadrillion BTUs of worldwide installed biomass capacity. EIA estimates >2.8 quadrillion BTUs of U.S. biomass energy consumption (2004)|
|Installed Capacity (Alaska)||Biomass – (heat & cooking) widely used; Biopower - 0 kWe (currently no commercial installations); Biofuels – (biodiesel, ethanol) demo projects|
|Resource Distribution||Potentially available to communities in all regions of Alaska with adjacent or transportable biomass resources. Alaska has >10 times more unused biomass energy resource potential than needed to offset all its diesel fuel used for power production in rural Alaska.|
|Number of communities impacted||100+ SE Alaska and Interior|
|Technology Readiness||Biomass – commonly deployed (heat); Biopower – Pre-commercial to early commercial; Biofuels – limited deployments (fish oil/biodiesel)|
|Environmental Impact||With proper management, impact on local forest land and species is generally considered to be positive. 1.5 million acres are lost annually to wildfire in Alaska, and thinning reduces fire risk.|
|Economic Status||High confidence in cost savings and localization of benefits for heat. O&M creates local jobs and savings. Bio-Power has high projected cost with limited potential at this time.|
|Case Studies||Tanana (Heating System), City of Craig (Heating System), Village Power CCHRC 25kW Gasifier, Community CHP Fairbanks 400 kWe ORC, Sealaska’s wood pellet fired boiler|
|Biomass Working Group|
There are a variety of different biomass systems that are, or could be utilized in Alaska. From woodstoves used as both primary and secondary heat sources, to Hydronic (hot water) systems. Some of these are very basic and inexpensive, while the more complicated add the costs of water or other fluid tanks, temperature and pressure control systems, insulation, and piping to end-users. While the optimal fuel source may be different, many of the boilers use some of the same technology such as gasification processes.
Gasification in wood boilers refers to burning the gasses like carbon monoxide and hydrogen that are released during normal combustion. In old boilers these gases, which contain up to 80% of the heat available, are not fully combusted and are released as emissions. In modern boilers, these gases are burned, utilizing that energy and eliminating emissions. To make gasification effective, temperatures of 700 degrees or more must be reached. Some boilers create temperatures this high in the main firebox. Others have a secondary chamber that reaches these temperatures and utilizes the gasses.7
Many of the systems currently utilized in Alaska burn cordwood. These systems require less fuel processing than more complicated systems, but generally require manual loading of the firebox. One such type of boiler that has been widely used in Alaska are Garn Water heating systems. These boilers are a proven technology, having been in use for over 30 years.8. Garn boilers, along with other cordwood are simple units with fewer complex operating systems that could fail. Garn units have three moving parts, the most sophisticated of those is the airblower, the boilers are unpressurized, so integrating them into a pressurized system requires the use of a heat exchanger system which could add additional costs to a project. Garn boilers do offer significant benefits, they can burn a variety of fuels, including cordwood, pallet wood, other waste wood, as well as processed woody bricks, and dried corn cob. Garn boilers have a firebox and a secondary gasification unit, fresh air is moved through the system using a blower.
Wood Chip Systems
Chip-fed systems require more infrastructure than chord wood boilers. This infrastructure includes a chipper to process fuel, a front-end or other loader to move wood chips, and a bin to store fuel and feeder such moving floor or auger which provides fuel to the boiler automatically, eliminating the need for manual loading. While there are are many advantages to using a wood chip system, such as automated loading, wood chips are more vulnerable to moisture than logs, and as such, require protection from weather. In many systems the wood chips require screening for oversized or undersized material, and they are subject to bridging, which is a resistance to flow in the automated feeding system when irregular sized or shaped chips get jammed. In Craig, a Chip Tec gasification boiler was installed to provide district heating to various community buildings. The unit in Craig, is fueled by a mix of pure wood chips and hog fuel.
Pellet and compressed wood systems
Pellet-fed and compressed wood systems are among the most sophisticated types of biomass boilers. Because they require more ‘upstream’ processing in addition to the actual boiler technology, they tend to be more costly than other systems. Pellets require a manufacturing facility with the proper equipment to make appropriate fuel. Communities that wish to use a pellet or compressed wood system would have to either produce their own pellets or purchase them, limiting pellet boiler use to communities that have reliable access to a fuel source. While pellets do have some infrastructure issues, they do have some very significant benefits. Like woodchip boilers, pellet boilers are fed via an auger, however, unlike wood chips or hog fuel, pellets are of a uniform size, and do not have the propensity for jamming. Pellets and other processed fuels, if stored correctly, also have the benefit of more predictable behavior during combustion as they have consistent moisture content. This helps the improve the efficiency of a unit and mitigate emissions issues that may affect other systems. Sealaska Native Corporation received funding from the Denali Commission EETG grant to install a commercial scale pellet boiler in their headquarters in downtown Juneau, to demonstrate the viability and use of this technology commercially in urban areas.
Co-heat and power and ORC systems
Co-Heat and Power gasification systems are the most complex of the biomass systems, as they are being used for more than supplying a heat source and are being used to produce electricity. These systems require more complex temperature, pressure, and electrical control systems than the more simple systems. They also require wood ash cleanup equipment; a generator, turbine or fuel cell and fail-safe switching. Additionally, they must be connected to the electrical grid and/or battery bank. As the fuel combusts, producer gas can be separated from the solids and burned as a fuel gas for turbines or engines. Producer gas must be used close to the source because of it has a low heating value and low energy density compared to more conventional fuels like natural gas; it has only 15% of the heating value of natural gas. but it can be burned directly in boilers, as a fuel in engines, or externally to heat other devices such as organic Rankine Cycle (ORC) fluids or Stirling engines attached to generators.9
CHP units have been in operation in operation in Europe for some time, however these are relatively large-scale power generators usually based on wood boilers that can operate at sufficient steam temperature and pressure to make electricity efficiently. A small power boiler, 10 MW, would be enough to power a sizeable town. The size of these systems are not suitable for small villages with moderate heat and power loads and limited technical expertise. Chena Power has been developing a biomass ORC unit that will utilize paper and wood waste that has been pelletized which could be used to determine whether these systems would be suitable for use to small rural communities.10
There are several options for heating, fewer for power generation. Listed below are some examples of high efficiency boilers and some new designs for small-scale power generation being used or considered for use in Alaska.
The following list includes developers who, at a minimum, have built a prototype device.
|Manufacturer||Device||Website||Location||Level of Development|
|Garn||High efficiency Hydronic Wood Fired Heaters||www.garn.com||Dot Lake, Tanana, Ionia, Homer (private individual)||Commercial 25 years, high fuel efficiency (75.4%), low emissions|
|Chiptec||Gasifier-boiler||www.chiptec.com||Craig||130 installed, 1 - 30 MMBtu|
|Decton||Chip and sawdust boiler||www.decton.com||Dry Creek, Kenney Lake Regal Saw Mill||Industrial and community use|
|Crorey Renewable Resources||25 kW gasifier||www.croreyrenewable.com||CCHRC Fairbanks||Prototype in development, not yet delivered|
|UTC Power||200 kW Purecycle ORC||www.utcpower.com||Chena Hot Springs||Commercial demonstration with geothermal, biomass demo under development|
|Danish Stirling||35 kW Stirling||www.stirling.dk||Denmark||Demo|
Biomass Projects in Alaska
Large scale wood-fired power systems are quite common throughout Europe, the United States, and Canada, especially at wood product manufacturing facilities that have the basic components for economic and technical feasibility: large demand for power, heat required for lumber drying or other processes, and plentiful wood waste that needs to be disposed or used. Conventional biomass-fired plants totaling over 60 MW in capacity operated at pulp and sawmills in Ketchikan, Sitka, Metlakatla, Haines, and Klawock into the 1990s. Retrofitting and re-permitting existing coal power plants to co-fire wood and other biomass represents another use in the Lower 48. In Alaska, Eielson Air Force Base’s power plant supplemented coal with densified paper separated from the Fairbanks borough waste until 2007.
Stand-alone, small combined heat and power (CHP) technology is generally considered pre-commercial in the U.S. While European and Asian firms have commercial experience and demonstration projects abound in the Lower 48, most systems are complex and have significant technical and economic challenges.
Cordwood is commonly used for heating throughout Alaska. Cordwood-fueled community scale heating systems have been demonstrated in several communities in Alaska. This technology has been used Dot Lake and Tanana, for example. A woodchip-fired school and community pool heating system was recently installed in Craig, and that heating system has been considered for other communities as well.
- EETG: Commercial Scale Wood Pellet Fired Boiler
- Tanana Heating System
- Craig Sawmill Waste fired Boiler
- Dot Lake Community Heating
- Delta Junction Biomass
- Gulkana Biomass
- Woody Biomass Crops
Links and Resources
- Biomass: A great .pdf detailing the idea behind biomass technology and energy production. A good introduction for beginning research.
- DOE, Energy Efficiency & Renewable Energy: Biomass Program Home Page.
Biomass Availability in Alaska
- Woody Biomass Availability In Alaska, Cooperative Extension: [http://www.alaskawoodheating.com/availability.php].