Continuous Emission Measurements of PM from an In-use Uncontrolled Outdoor Hydronic Wood-fired Furnace (OWB) and the Influence of Burn Practices on Emissions

GEORGE ALLEN (1) Lisa Rector (1) Pete Babich (2)

(1) NESCAUM (2) CT Dept. of Environmental Protection

     Abstract Number: 393
     Last modified: November 9, 2009

Abstract
Stack PM Emissions from an in-use uncontrolled outdoor wood boiler (OWB) were measured over a four-week period using a continuous method. A Matter Engineering (TSI) rotating disk dilution system was used for the first series of tests, and an EPA method 5G dilution tunnel was used for the second series; a standard burn was conducted with both sample trains for comparison. Stack temperatures were measured continuously, and stack flows for damper open mode were estimated using tracer gas techniques. A model 1400ab TEOM ® at 30 degree C with fast response time settings was used for continuous PM measurements; short-term very low face velocity Teflon filter gravimetric collocated samples were also collected for comparison with TEOM data. Integrated 2-hour speciated PAH measurements were made on a subset of runs using an XAD trap back-end for total PAH (gas and particle phase).

Burn practices (type of wood, fuel charge, moisture levels) were varied across runs to assess their effect on PM emissions. An EPA method 28 test crib was burned for comparison with lab tests. A total of twelve 8-hour runs were conducted in the fall-spring of 2007-2008. Damper state (open/closed) was controlled manually, and emissions for each state were segregated. Damper closed PM emission rates were negligible compared to damper open rates. The type of wood was the largest factor in PM emissions across tests, with softwood having several times the PM emissions (grams/hour) than hardwood. Softwood emissions peaked at over 200 g/h. The EPA 300 lb. test crib (a dimensional hardwood structure) had emissions of 50 g/h, similar to cord hardwood burns and laboratory test data. Emissions also varied within a load of wood; the early burn phase of a large load had PM emissions several times higher than the same load once it had charred. It is clear from this work that simply burning seasoned split hardwood reduces PM emissions substantially relative to poor burn practices.

Limited sampling of speciated PAH showed naphthalene as the predominant species, with emissions peaking at 5 g/h. 20 ppm of SO2 was measured in the stack; a sample of wood showed 100 ppm sulfur. This wood was from southern New England, and the sulfur is presumably from wet deposition. Mercury was not measured, but as with sulfur would be expected to be present in wood from this area and thus in the combustion emissions. Future work will assess mercury in woodsmoke. Teflon filter samples were frozen immediately after sampling, weighed before and after 24-hour equilibration; average mass loss was 13%, was not moisture related, and was very consistent regardless of filter loading. The agreement between the filter PM samples and matching TEOM data was reasonable.