[OPINION] Biomass Facilities Play Important Role in Improving Air Quality
[Read the opposing view to this opinion piece, “Biomass Energy Facilities Can Worsen Air Pollution,” by Jana Ganion, Blue Lake Rancheria]
– by Bruce Springsteen, Compliance and Enforcement Manager, Placer County Air Pollution Control District
California biomass power plants provide an alternative to the open pile burning of woody forest and agricultural wastes as a means of disposal. By utilizing this significant renewable resource for clean and efficient power generation, biomass power plants avoid the significant air pollution from open pile burning and reduce reliance on fossil fuels.
Presently California’s 22 biomass power plants, with individual capacity ranging from 10-50 MW, produce 530 MW of renewable and reliable baseload (24/7) electricity. Much of the biomass fuel for these plants is woody waste that is the byproduct of the sustainable management of California’s highly productive: (1) fruit and nut orchards in the Central Valley, and (2) forested lands through the foothills and mountains.
Fruit and nut orchard wastes include annual tree prunings and periodic removal of over-mature trees. Forest wastes – small diameter tree stems, tops, limbs, branches, and brush – are the product of fuel hazard reduction, forest health and productivity improvements, and traditional commercial harvest. Of concern is the pending increase in forest waste supply as land managers accelerate the scale and pace of fuels treatments to reduce the risk of high severity wildfire and to return forests to fire-resilient conditions in response to tree mortality (Stevens 2016) and the overly dense fuel condition resulting from a century of successful wildfire suppression (North et al. 2015, Dombeck et al. 2004).
Leaving forest waste in piles, or chipped and scattered on the ground, where it is generated, will not meet fire hazard reduction objectives. Neither approach is yet a sustainably acceptable practice for orchard wastes (Cox 2015, Mohan 2015, Hecteman 2016). Use for compost or other low value products such as firewood or landscape cover are almost never economic. In many cases, use for energy is the most valuable option that can cover most or all of the cost for wood waste processing and transport.
Where there is no viable biomass energy facility that can utilize the material cost-effectively, woody biomass waste is piled and burned at the site of generation. This is especially critical today considering the drought conditions and high tree mortality in the central and southern Sierra Nevada range. With estimates of over 100 million dead trees in the Sierra Nevada, and many requiring removal to mitigate infrastructure or public safety hazards, there is a compelling need for disposal methods as an alternative to pile and burn.
Open pile burning of biomass waste adversely impacts regional air quality and human health through release of various air pollutants – including fine particulate matter (PM2.5), carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOCs), air toxics (including polycyclic aromatic hydrocarbons and aldehydes), and greenhouse gases of carbon dioxide (CO2), and short lived climate pollutants of methane and black carbon. Air Districts, with regulatory authority over open pile burning, issue burn permits to mitigate smoke impacts when meteorological conditions allow for favorable smoke dispersion; however smoke and its impacts can not be eliminated.
As an alternative to open pile burning, use in existing biomass power plants results in reductions of greater than 99% for PM2.5 and black carbon, 95-99% for CO and VOCs (including methane), 40-70% for NOx, and 30% for CO2(e). These benefits have been conclusively demonstrated in numerous comprehensive lifecycle assessments (Springsteen et al. 2015, Springsteen et al. 2011, Lee et al. 2010, Jones et al. 2010, Moyer and Pont 1997). Reductions result from a combination of: (1) utilization of wastes in power plants with efficient emissions control technology; (2) negligible emissions and energy requirements from well controlled and efficient processing and transport equipment and engines; and (3) production of renewable energy from wastes that are the product of harvesting that is unrelated to any potential biomass value and that replace nonrenewable fossil fuel-generated energy.
Interviews with biomass power plant fuel managers indicate that about 480,000 bone dry tons/year (650,000 green tons/year) of wood waste from agriculture and forest operations are currently diverted away from open pile/burn disposal for use as fuel to produce renewable power. This translates to overall California annual emissions benefits of approximately: PM2.5 of 2,000 tons, CO of 24,000 tons, NOx of 900 tons, VOC of 600 tons, and CO2(e) of 140,000 tons.
Comparison of emissions from open pile burning and biomass energy (adapted from Springsteen et al. (2011) and (2015).
Air pollutant emissions from biomass power plants are limited by Air District permits based on the use of “Best Available Control Technology” for criteria air pollutant and “Maximum Available Control Technology” for air toxics. Filters and precipitators achieve highly efficient removal of PM. Selective non-catalytic reduction is used for NOx control. Combustion controls effectively limit CO and VOCs. Toxic inorganic emissions (including mercury, lead, chromium, and chlorine) are inherently low as biomass contains these in trace amounts.
Newer operations are achieving even lower emissions through use of oxidation and selective reduction catalysts and scrubbers. The next generation of bioenergy technology, distributed gasification integrated with inherently clean internal combustion engines and eventually fuel cells, with co-production of biochar, will have still lower emissions, comparable to natural gas boilers and engines (Williams and Kaffka 2015).
Air pollution emissions from select biomass energy operations.
|Power plant||Combustor design||Air pollution control system||Electricity capacity (MW)||Air pollutant emissions (lb/MWhe)|
|SPI Lincoln||Stoker||ESP, SNCR||22||0.2||1.4||2.0||0.05|
|SPI Anderson||Stoker||ESP, SNCR||32||0.3||3.2||3.9||0.01|
|Burney Forest Power||Stoker||ESP, SNCR||30||0.2||2.0||9.0||0.08|
|Rio Bravo Rocklin||CFB||ESP, SNCR||25||0.3||1.4||0.1||0.00|
|Rio Bravo Fresno||CFB||ESP, SNCR||25||0.3||1.1||0.0||0.00|
|Woodland Biomass||CFB||FF, SNCR||25||0.2||1.0||0.1||0.01|
|DTE Stockton||Stoker||ESP, SCR, OC, WS||50||0.1||0.3||0.5||0.02|
|Tahoe Regional Power Cabin Creek, North Fork Community Power1||Dryer, gasifier, IC engine||WS, SCR||2||0.1||0.3||1.0||0.30|
1: Projected emission estimate, proposed power plants have permits but are not yet in operation.
CFB: Circulating fluidized bed; BB: Bubbling fluidized bed; IC: Internal combustion engine; ESP: Electrostatic precipitator; FF: Fabric filter; SNCR: Selective non-catalytic reduction; SCR: Selective catalytic reduction; OC: Oxidation catalyst; WS: Wet scrubber
As part of the permitting process, impacts are considered through detailed air toxics risk assessment and California Environmental Quality Act review. Emissions limits are ensured through permit requirements to use continuous stack monitors for CO, NOx, and opacity (as a surrogate to PM), process monitoring of fuel quality, feed rates, and control device operating parameters, annual stack manual source testing, and unannounced on-site inspections by Air District staff.
In limited situations, older-generation biomass power plants can contribute to an increase in localized air pollution from the use of inefficient and under- or improperly-designed combustion system and controls, unexpected variation in fuel composition, negligent operation, and/or flagrant disregard for permit requirements (Scheck and Dugan 2012). However, when properly designed and operated, biomass power plants provide irreplaceable air quality benefits, in addition to supporting rural community economies, and helping to provide support toward protecting critical forested land resources including recreation, wildlife habitat, and upper watershed health (water quality, quantity, and timing).
Cox J. 2015. Plant closure could force return to open ag burning. Bakersfield Californian, October 24.
Dombeck M, Williams J, Wood C. 2004. Wildfire policy and public lands: Integrating scientific understanding with social concerns across landscapes. Conservation Biology August 883-889.
Hecteman K. 2016. Orchard wood recycling offers disposal option. Ag Alert, The Weekly Newspaper for California Agriculture, October 19. http://agalert.com/story/?id=10245.
Jones G, Loeffler D, Calkin D, Chung W. 2010. Forest treatment residues for thermal energy compared with disposal by onsite burning: emissions and energy return. Biomass Bioenergy 34:737-746.
Lee C, Erickson P, Lazarus M, Smith G. 2010. Greenhouse gas and air pollutant emissions of alternatives for woody biomass residues. Stockholm Environmental Institute, Seattle, WA. http://data.orcaa.org/reports/all-reports-entries/woody-biomass-emissions-study/.
Mohan G. 2015. Solar is in, biomass energy is out—and farmers are struggling to dispose of woody waste. Los Angeles Times, December 31.
Moyer C, Pont J. 1997. Emission Benefit from Firing Orchard Residues at Delano Energy Company, Final Report Prepared for ThermoEcotek Corporation and Planning and Conservation League, December 10.
North M, Brough A, Long J, Collins B, Bowden P, Yasuda D, Miller J, Sugihara N. 2015. Constraints on mechanical treatment significantly limit mechanical fuels reduction extent in the Sierra Nevada. Journal of Forestry 113(1):40-48.
Scheck J, Dugan I. 2012. Wood Fired Plants Generate Violations. Wall Street Journal, July 23.
Springsteen B, Christofk T, York R, Mason T, Baker D, et al. 2015. Forest biomass diversion in the Sierra Nevada: Energy, economics and emissions. California Agriculture Journal July-September 142-149.
Springsteen B, Christofk T, Mason T, Clavin C, Storey B. 2011. Emission reductions from woody biomass waste for energy as an alternative to open burning. Journal of the Air and Waste Management Association 61:63-68.
Stevens M. 2016. California has 102 million dead trees – and no easy answers for what to do with them. Los Angeles Times, November 28.
Williams R, Kaffka S. 2015. California Biomass Collaborative, University of California, Davis. Biomass Gasification. California Energy Commission. Publication number: CEC-5-11.020.
Bruce Springsteen is Compliance and Enforcement Manager for Placer County (California) Air Pollution Control District