By Gary Rondeau
(Update: 6/28/10 — The Seneca co-generation plant is presently under construction. As far as I know, they have no plans to make biochar. This is too bad. I wrote the following article about a year ago when their plans were less fixed in concrete. GR)
Future energy needs should be met with an eye to reducing atmospheric fossil carbon emissions and increasing regional energy independence by using locally produced power. The proposed Seneca plant does this in a way that is clean compared to the burning of imported fossil fuels. The plant could also be operated to produce biochar, a potentially valuable soil amendment and carbon sequestration product that could prove to be as valuable as the plant’s electricity.
The proposed Seneca cogeneration facility has generated substantial controversy concerning its true “greenness.” Although the power plant will utilize a renewable wood byproduct for fuel, the plant will emit some pollutants, and the fuel source calls into question the entire timber industry’s true “sustainability.” The debate over forest policy has been polarized for decades. How can it be possible for a major timber company and ardent supporter of conservative politics in the region to do anything really “green?”
In assessing the merits of the Seneca proposal, let’s start by looking at the mix of power and energy sources that we rely on in our community. Like most of the world, Eugene runs on oil for transportation fuel, natural gas for heating, and largely imported hydro electricity. Almost none of this mix is locally produced. The economic costs of buying essentially all of our energy from outside the region are an enormous drain on our local economy – not to mention destabilizing from an energy security standpoint. As fossil fuels become depleted and climate change issues become paramount, there will be ever more incentive to move away from fossil fuels, and hydroelectric power is already fully developed. This leaves a big gap to fill for our energy needs. As global supplies shrink, we are left with providing for our own local sources of energy. In our bio-region it makes sense to utilize biomass as part of the energy mix. The abundant rainfall means that things grow well around here, so let’s look carefully at the Seneca proposal and see how green it really is.
EWEB and SUB – the largest local utilities, have a combined peak capacity of about 740MW and average production of about 410MW. Seneca’s 18MW facility could contribute to about 4% of our present local electric needs. The output of the Seneca plant represents about $10 million worth of energy produced locally, so those dollars don’t immediately leave the region. This is a significant contribution from a single private business.
How Clean, How Dirty?
There has been concern that the proposed plant will generate large amounts of pollution. Let’s look carefully at the nitrous oxide (NOx) emissions, since this pollutant is a major problem in congested areas as a prime contributor to smog. The plant is expected to produce about 185 ton/yr of NOx emissions. Seneca is fortunate to be burning largely wood waste which has a very low nitrogen content in the fuel (0.1%). Fuel nitrogen is the source for most NOx emissions.
Petroleum products generally have higher nitrogen content. Hence, before the days of pollution equipment on automobiles, NOx coming out of tail pipes gave rise to the brown haze of smoggy skies common in congested regions. Current EPA regulations require emissions less than about 0.5gm/mi of NOx for light autos. One solution to further reducing auto emissions is to move to electric vehicles that don’t emit pollutants. We can compare the Seneca plant’s expected emissions with those that would be removed by converting to electric vehicles powered by Seneca’s electricity. Will Seneca-powered electric vehicles be cleaner than EPA regulated autos – or not?
A typical electric vehicle requires about 0.2kWH/mi; Seneca will generate about 150GWH/year, equivalent to 750 million electric vehicle miles per year. Ordinary EPA regulated autos would generate about 400 tons/year of NOx if they were driven those miles. If we compare this to Seneca’s projected emissions of 185 tons/year, we see that Seneca could potentially reduce overall pollution in our valley if a significant number of vehicles were converted from gasoline to the locally produced electric power.
How about forestry practices? Will we scour the forests clean and deplete the soils for future generations by burning woody biomass? Is Seneca a foot-in-the-door for widespread environmental destruction of our forests?
The Seneca plant will require about 175,000 BDT/y (Bone Dry Tons per year) of biomass. The lumber mill cuts about 600,000 m3/y of finished goods, which translates into about 350,000 BDT/y of biomass as finished lumber. The company says that 75% of the cogen plant fuel will come from the existing lumber mill byproduct stream, or about 131,000 BDT/yr. Hence, total extracted forest matter will go from about 481,000 BDT to 525,000 BDT. Clearly the issue of sustainability should focus on total extraction of forest material rather than the relatively small increase associated with biomass for energy production.
Seneca’s lands consist of 165,000 acres of forest, largely in Lane and Douglas counties. If Seneca was suppling all of its own material for its mill from its own lands, it would be need to extract around 3 BDT/acre-yr. This rate is doubtfully sustainable; production of 1 to 2 BDT/acre-yr is probably more typical of forest lands. Seneca also purchases timber from public lands, so their potential biomass pool extends beyond their own boundaries. A community based biomass energy study used 1.4 BDT/acre-yr as the sustainable harvest rate for their proposal, where reducing forest under-story fuels and selective thinning for fire resistance was one goal. Presumably timber production would add to their biomass production figure. There has been much discussion of utilizing fire hazard forest fuels in Oregon. Studies done by OFRI suggest that there is available about 0.25 BDT/yr-acre with a harvest period over the next twenty years, on over 4 million acres of forest land in need of thinning, while improving forest health and timber productivity. This is not part of Seneca’s proposal, probably because of the transportation cost associated with this biomass. About half the private land in Lane county is owned by private timber companies – totaling 597,000 acres. There is another 1,300,000 acres of public forest land in the county. If we were to assume typical sustainable production of 2 BDT/acre-yr, we would only have enough private timber holdings in the county to support two mills of Seneca’s size. It needs to be emphasized that Seneca’s forest demands are large, but the added burden of the cogeneration plant is just a small fraction of total biomass utilization.
Economics of Cogeneration
Seneca happens to be well positioned to benefit from a cogeneration facility largely because it has a need for the process heat from the plant and it has a zero-cost source of fuel in the form of mill waste. Some people have expressed the fear that the Seneca plant is the start of the burning of our forests for fuel. This is pretty unlikely today because it would be very hard to generate a profit from biomass power generation in the absence of any of the factors Seneca has in its favor.
It is estimated that procuring biomass through fire abatement thinning costs from $50 to $300 per BDT. One BDT of biomass can generate about 1MWH of electricity, which until recently you could sell wholesale in the Pacific Northwest for less than $35. The legislative mandate for 25% renewable energy for utilities by 2025 has pushed the price to about $87/MWH for qualifying power. It’s not a great business plan if it costs $300 for the fuel to make $87 of electricity with a $45 million facility.
Climate and Biochar
The “green” claim for sustainable biomass energy is based on their renewable nature and the replacement of fossil fuel sources. Carbon dioxide released when burning biomass is taken up yet again by growing trees that will be harvested in the future. However, the chainsaws, logging trucks and the people in our fair city still drive cars and burn tons of fossil carbon that ends up in the atmosphere. Peak oil may be here, but peak CO2 is not likely for another 50 years with potentially horrendous environmental consequences. The Seneca plant could provide the community with the first taste of a paradigm-altering “green” technology in the form of biochar. The combustion process can be controlled so that the feed stock is not completely burned – yielding a carbon-rich char rather than just ash at the furnace discharge.
There is great potential to use the biochar as an agricultural soil amendment. In many cases biochar can improve crop yields while reducing the need for chemical fertilizers. The biochar is not a plant nutrient per se, but rather has been shown to reduce leaching of nutrients from soils and improve the uptake of nutrients in the plants through modification of soil texture, pH, and a soil property known as the cation exchange capability of the soil. Many of these benefits come from the large surface area associated with aromatic carbon structures found in char. Once the biochar is mixed in the soil, it seems to remain there for very long periods of time compared to the carbon found in organic matter. The decay rate can be measured in centuries rather than the few years for carbon found in normal compost. This property of black carbon leads to the potential to use biochar systems as a means of sequestering carbon for climate restoration.
Trees and other biomass crops take up CO2 from the atmosphere as they grow. Only about half of the carbon in the biomass fuel is consumed in combustion and returned to the atmosphere. The other half of the carbon is converted to biochar and eventually sequestered in the soil for long periods of time. (The actual char fraction will depend upon the moisture content of the fuel and the particular combustion process.) This process is truly “carbon-negative”, removing carbon from the atmosphere and returning it to the soil.
The Seneca plant could be a leader in this technology. The Wellons furnaces called for in their plans will make biochar with little modification. Local industries exist that could utilize and market the biochar such as Lane Forest Products and Rexius. Biochar could be incorporated into planting mixes and composts. These industries now purchase mill waste from Seneca, so they will need to modify their businesses anyway, once the raw biomass is unavailable. Much more research on biochar still needs to be done. Adding biochar to soils may be a way of putting back the carbon and some of the nutrients that are normally removed in agricultural and forest extraction operations. Truly sustainable bio-fuels systems must include preservation and improvement of soils and minimal fertilizer inputs. Char systems offer this potential for agricultural, valley forest plantation lands, and possibly for commercial forest lands as well – all the while sequestering carbon from the atmosphere.
Economics of Biochar at Seneca
A large fraction of the capital cost for the Seneca plant is the electrical machinery and the pollution control technology. Adding biochar as a plant product in addition to the combined heat and power effectively increases the total throughput capacity of the plant. Total heat and power output need not be reduced, but rather the input rate could be increased to accommodate the biochar output stream. Alternatively, you could consider the plant’s planned input rate as fixed and consider the marginal value of the biochar compared to the value of the heat and power otherwise produced by the material turned to char. The moisture content of the fuel source will have a large effect upon the amount of char that can be produced. For dry feed stock, <10% moisture content, char yields can be ~30% of the feed stock. With moisture about 60% it is doubtful that any char could be produced. The unburned char has a residual energy density of about 24MJ/kg compared to the dry feed stock at about 18MJ/kg. Hence the removal of char depletes the thermal quality of the fuel by more than just the reduced mass of material. We will use estimates of char yield at 20% fuel moisture to be 20% char, and at 40% fuel moisture to be 12% char. These are my best estimates which yield the expected plant capacities shown in the table below. If char production were to be taken seriously, it would probably be a good idea to add further fuel drying facilities to the proposed plant.
|Overall Capacity Limited byInput Fuel Handling as presently planned||Overall Capacity Limited byOutput Electrical Generating Capacity as presently planned|
|Fuel requirements (BDT/y)||175,000||203,000 to 223,000|
|Biochar Fraction with 20% fuel moisture (better)||20% = 35000 T/y||20% = 40600 T/y|
|27% less energy produced||27% more fuel required|
|Biochar Fraction with 40% fuel moisture (planned)||12% = 21000 T/y Yield||12% = 24300 T/y Yield|
|16% less energy produced||16% more fuel required|
|Electricity Produced (GWH/y)||109 to 126||150|
35000T Char costs 41 GWH electric @ $87/MWH ==> ~$100/T char cost in lost electric generation 40600T Char costs 48000T more fuel @ $50/BDT ==> ~$60/T char cost in additional fuel
If you can sell the biochar for more than twice the cost of the raw fuel you will make a profit on the char when just pushing more material through the system.
Char Production and Plant Emissions
Char-producing pyrolysis systems are known to be very clean burning compared to more conventional combustion methods. The pyrolysis off-gases and the char are two very different fuels. Optimizing the combustion for just the off-gases is much easier than optimizing for the combined gas and char fuel with very different combustion temperatures and characteristics for the two components.
The Seneca plant is a significant step toward local energy independence. It’s cleaner to use Seneca’s electricity than to use imported oil and gasoline for transportation, so it passes the test of being at least as clean as what we have now. Seneca’s demand for forest biomass is large, but most of that demand does not come from the power facility but from the lumber mill. Looking at sustainable forest practices is an important topic for further policy debate, but largely unrelated to Seneca’s cogeneration facility. Seneca does have the opportunity to provide leadership with new biochar technology and production in the Pacific Northwest. They are well situated to produce biochar with the proposed plant. In conjunction with local biomass compost companies, Seneca could market biochar products effectively. Providing an abundant source of biochar would aid in the early adoption and development of a potentially planet-saving technology. The long term benefits to our community and the planet could be enormous. Let’s not miss the opportunity!
Selected Bibliography on biochar
Glaser, Bruno: Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century, Philosophical Transactions of the Royal Society, 362, 187-196 (2007)
Lehmann J 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387 DOI10.1890060133.
Lehmann J, Gaunt J and Rondon M 2006 Bio-char sequestration in terrestrial ecosystems – a review. Mitigation and Adaptation Strategies for Global Change 11: 403-427. DOI: 10.1007/s11027-005-9006-5.
Gaunt J and Lehmann J 2008 Energy balance and emissions associated with biochar sequestration and pyrolysis bioenergy production. Environmental Science and Technology 42: 4152-4158.
Lehmann J and Joseph S 2009 Biochar for Environmental Management: Science and Technology. Earthscan Ltd, London, UK, 404p
The International Biochar Initiative (IBI) website is a good starting point for further investigation of biochar.
Gary Rondeau, Ph.D., is an organic gardener, beekeeper, and autodidact of economics and environmental science. He works as Technical Director at Applied Scientific Instrumentation, Inc., in Eugene, Oregon.