N.C. Department of Environment and Natural Resources
 Welcome to the North Carolina Division of Air Quality
Estimating Emissions From Generation and Combustion Of "Waste" Wood



DRAFT



Some conventions and assumptions used by NC DAQ in evaluating permit applications and emission inventory submittals.



July 15, 1998 First Draft



Prepared for NC DENR Division of Air Quality by Wood Waste and Furniture Emissions Task Force







Table of Contents



Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 NOTICE: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Logging and Other In-Forest Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Sawing, Planing and Woodworking (Lumber) Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 General Description and Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Emission Factors and Assumptions for Lumber and Woodworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Kiln Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 General Description and Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Emission Factors and Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Burning Waste Wood in Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 General Description and Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Emission Factors and Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Burning Wood Waste in Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 General Description and Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Emission Factors and Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Open Burning of Wood Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 General Description and Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Emission Factors and Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Appendix of Miscellaneous Wood Related Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6





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Background



North Carolina is blessed to have an abundance of natural resources and a number of important related industries. One of these is the forest products industry which is closely related to furniture making, paper manufacure and lumber used for home construction, either in it's natural form or in manufactured products such as oriented strand board, chip board, etc. Due to the nature of the processes, air pollutants may be emitted as a consequence. These emissions begin at the harvesting stage and may continue through the manufacture of the final consumer products. Many of these operations are of a nature that makes the estimation of emissions from them very difficult. Many of the processes and operations are covered in EPA's Compilation of Air Pollutant Emission Factors (AP-42), which stands as the basic reference. However, from time to time that document may not adequately address process, specific practices and assumptions or may not include the latest information needed. In such cases, guidelines for assumptions and exceptions may need to be defined. This is the purpose of this document. This document may be updated from time to time as needed to reflect the dynamic process of improving emission estimates as new information and data are generated or otherwise become available for public use. This report is is intended to provide increased consistency among various offices of DAQ. Other documents may be developed if needed. Please provide any comments and critiques or recommendations on this document, or similar other needs to the Planning Section, Division of Air Quality, PO Box 29580, Raleigh, NC 27626-0580 or to jim_southerland@aq.enr.state.nc.us. NOTICE: Emission factors are guidelines that may provide reasonable estimates for groups of facilities, but which may not always be accurate for individual facilities or processes. The guidelines and assumptions presented here are intended for use by staff of the NC Division of Air Quality, along with other information that the Division may aquire, for review and evaluation of emission estimates and information submitted by point sources in NC for purposes of permit application and/or emission inventory requirements. This document is provided to the public as an indicator of the nature of what the Division uses in such evaluations. This collection of guidance and assumptions (including such information that is also provided in spreadsheets and/or the Division's Internet web pages) does not relieve an individual or company from the legal responsibility for using the best available information at the time of submittal for estimation of emissions. Inclusion of information herein does not mean that it is indeed the latest information at any time in the future.



Logging and Other In-Forest Operations General



Currently there is little to no information or data on air emissions from logging and other related operations, nor is there reason to believe that these are a significant air emissions problem. The only possible exception might be fugitive dust from logging roads and other transport operations. This topic is



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mentioned here only for completenes, consistency and clarity. Biogenic emissions from growing plants (including trees) are considered separately and are identified as a significant contributor to ozone in the Southeast, but are also not intended to be covered by this document. From the logging operations, wood may be transported to conventional saw mills, chippers, pulp operations, plywood manufacturing mills and other such facilities. Some of these operations are discussed below.



Sawing, Planing and Woodworking (Lumber) Operations General Description and Comments



Sawing, planing and woodworking cover a wide range of operations. Basic saw mills may be set up temporarily in the field near logging operations or be permanent complex facilities. Woodworking operations generally refers to those which take planed and sized wood to final products through fine sawing, joining, milling, etc. which generate finer sized dusts.The emitting processes however are similar in a general sense. Unfortuantely, there is no current section in AP-42 which covers even basic lumber operations, partially due to the general lack of test data and related information. The discussions below define some of the assumptions and crude extrapolations that are used in lieu of better and more definative literature or test information. Some common woodworking/lumber terms and definitions1: AIR-DRY: (1) Solid wood products: Dried (seasoned) by exposure to the open air without artificial heat. Moisture content of air dried wood depends upon relative humidity, temeprature and length of drying period. Lumber thoroughly air dried is commonly considered to have a moisture content of approximately 12% (O.D. wt. Basis). Air-dried wood fiber is commonly considered to be about 5 to 8% m.c. (O.D. wt. Basis). (2) Pulp and paper: Composed of 90% solidand 10% water. AIR-DRY TON: (A.D.T.) For wood pulp, an air dry ton is usually defined as a quantity of pulp which weighs 2000 lbs, 90% of which is wood fiver and 10% of which is moisture. Thus an air diry ton contains 1800 of pulp (ovendry basis) and 200 lbs. Of water. In terms fo wood bfiber content, one air dry ton equals 0.9 ovendry tons. Moisture content of an air -dry ton is 10%. BOARD FEET: (bd. Ft.) Nominally, a rough-sawn, green board 1 in. X 12 in. X 1 ft., or equivalent. Used as a log measure and measure of sawn lumber. BONE DRY: Having zero percent moisture content. Also: Ovendry. BONE DRY TON: (B.D.T.) A quantity of wood pulp or residue which would weigh 2000 lbs. at zero percent moisture content. Also: Ovendry ton. BONE DRY TON: (B.D.U.) - A quantity of wood residue which would weigh 2400 lbs. at zero percent moisture content. CORD: A measure of roundwood or pulpwood representing a stack of such wood 4 ft. X 4 ft. X 8 ft. or 128 cubic feet. CUNIT: (CCF) One hundred cubic feet of solid wood. Used as a log measure or as a measure of solid wood content. HOGGED FUEL: A mix of wood residues such as sawdust, planer shavings, and sometimes coarsely broken-down bark and solid wood chunks produced in the manufacture of wood productrs and normally



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used as fuel. KILN-DRY: Dried (seasoned) wby exposure to artificial heat and humidity under controlled conditions in a kiln. American lumber standards specify that seasoned lumber must have no more than 19% moisture content (m.c.). Lumber dried to 15% m.c. or less is grade stamped "MC 15". Veneer is commonly dried to about 2-5% m.c. All moisture contents are on an ovendry weight basis. ROUNDWOOD: Logs, poles,piling, and cordwood of any size with or without bark. WANE: Presence of bark or absence of wood, due to any cause, on the edge or corner of a piece of lumber. YIELD: (1) Forest Products Industries: The quantity of product recovered from a given quantity of raw material input. (2) Forest Mensuration: An estimate of the amount of wood which may be harvested from a particular type of forest stand (by species, site, stocking and management regime) at various ages.



Emission Factors and Assumptions for Lumber and Woodworking



Planing and other Woodworking: An April 26, 1995 memo from Laura Butler through Alan Klimek to the Regional Air Quality Supervisors and others, an April 18, 1996 memo from Laura Butler, similarly addressed, along with a July 15, 1997 memo from Tammie Watkins of the Mooresville Regional Office are basic references considered valid for DAQ assumptions for woodworking operations. A summary of the main technical points of those memos is provided below: ! 80% of sawing and planing emissions generated are >100 micrometers in aerodynamic particle size and not considered regulated. ! PM-10 replaced PM as the regulated pollutant October 16, 1995 for Title V review and billing purposes. PM-100 is still considered for 2Q.0102 purposes and 2D emission standards. ! Plant-specific PM-10 information normally takes precedence over generalized emission factor types of information, but all such information should be used in recognition of the other. ! Knife planers generate larger particles than abrasive planers, abrasive planers being more appropriately grouped with sanders. ! Knife planers used on "green wood" (>19% moisture)generate chips or emissions that are not considered regulated, even if a device is used to capture the chips, and does not need to be permitted. ! Knife planers used on dry wood (<19/5 moisture):For the uncontrolled emission stream into the control device, = 2.6% of inlet loading to control device is assumed to be PM. Apply appropriate control device efficiency to the 2.6% result when developing permit estimates (Cyclone may be up to 95% efficient on the very largest particles, but much less, perhaps even lower than 50% on smaller particles; bag filter assumptions of 99% are generally acceptable estimates, but determination of control efficiency must be determined on a case by case basis considering all the variables at the facility.). Typical percentages of wood waste: ! Rough sawing = 20% ! Fine sawing = 30% ! Sanding = 20% ! Molding (hog) = 40% ! Total = 100%



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Other Assumptions addressed in the memos are as follows:



Woodworking Process



Sanding Fine Sawing (band saws, etc) Rough Sawing (saw milling, etc.) Milling (hog) Molding Planing Wood Shaving



% of Wood Dust Regulated as PM (<100 micrometers) 76 31 18 10 5.2 2.6 0.56 % of Wood Dust* Regulated as PM-10 (PM-44, as a surrogate) 23.8 0.37 1.89 Not Included- assume 0 0 0 Not Included, assume 0



*Note that PM 2.5 is generally expected to be a small portion of the PM-10. Efforts to measure these fine particles from these operations are desperately needed, especially if areas of the state are monitored to be in non-attainment status. Related common assumptions accepted but not in the formal memos include: ! 1 Board foot = 2.6 pounds (pine). ! 1 Board foot = 3.4 pounds (hardwood). ! Frame shop has 20% waste. ! Case Goods shop has 65% waste. ! Yield is the amount of raw lumber received that actually becomes finished product. For typical furniture operations, this will be about 45%. However this figure is generally tracked very carefully by plant management and is probably available within tolerances of a percent and thus should be determined on a case by case basis. Additionally, some have made calculations based on width of saw blades and linear feet sawed, which can generate some idea of volume and weight of wood sawdust that is generated. These procedures, while crude can give an approximation of the total volumes generated and are useful for such purposes. Regions and reviewers are cautioned about "blind acceptance" of typical control efficiencies being applicable in all situations. Approximate particulate matter control efficiencies (PM - 95%, PM10-95%, PM2.5 -80%) were provided by Michael Koerschner of the ARO at the request of David Stout, Broyhill Furniture Industries, Inc., during a 2/4/98 telephone conversation regarding control efficiencies by multicyclones, and have become sited on many occasions. The efficiencies quoted by Mr. Koerschner are from Table C.2-3 "Typical Collection Efficiencies of Various Particulate Control Devices" of AP-42 for a "multiple cyclone w/o fly ash reinjection." During the elephone conversation, Mr. Koerschner expressed his opinion that these numbers appeared to be high (based on data we've seen) and do not apply specifically to wood-fired boilers. Therefore, the DAQ does not blindly accept the application of "typical control efficiencies. This was restated to the AFMA in Keith Overcash's May 27, 1998 letter to Andy



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Counts of the AFMA which was authored as a result of questions in AFMA's March 31, 1998 letter on how to estimate emissions, assumptions, etc..



Kiln Drying General Description and Comments



Wood is often kiln dried. This process is not currently described by AP-42, but is basically a process which results in green or (semi-)air dried wood being stacked into large rooms or containers which are then raised to high temperature (>212 degrees F) to drive off the moinsture in the wood. See various definitions of terms in the Lumber/Woodworking section preceeding. During the drying process, Volatile organic compounds (VOCs) are also expelled. Thus the process results in the emission of VOC from the kiln and the emissions from the fueling operation which is often gas or distillate oil. Estimates should be made, therefore, for both of these pollutants. However, if the operation is a small isolated kiln operating on a random schedule, the emissions may well be below the threshold requiring a permit.(????)



Emission Factors and Assumptions



This process has been handled inconsistently in North Carolina, largely because there has not been a good set of accepted and standardized information widely available. The main two sources of different data to date have been from WSRO and WaRO efforts. EPA and NCCASI are currently working on developing emission factors for lumber kiln operations, but, there appear to be little to no data that can be used for such a process.Currently, in Keith Overcash's May 27, 1998 letter to AFMA, previously cited, we indicate an effort is underway to come up with some better information that we would use, presumably, until the EPA efforts are completed. His September 3 memo further elaborated on the position and indicated that in the interim before these studies were done, we would accept 2.11 for pine and 0.211 for hardwood initially, for 1997 submittals, but afterward, if the studies were not completed by the end of 1998, DAQ would insist upon consistent use of 3.4 pounds of VOC per thousand board feet for steam heated kilns, based on limited tests of a plant in WaRO. This was intended to be improved upon and expanded by us in the mean while and one of the improvements is to get the VOC on an actual mass basis, instead of "as carbon." Betsy Huddleston spoke with David Word with NCASI at a conferencein July about the VOC as carbon problem. Their study results of VOC emissions from kilns is due to be published in a report by the end of 1998. He noted that right now if we were to be converting to total VOC using a surrogate, we should probably use alpha-pinene, which has been suggested before to me. Alpha pinene makes up to 50% of the VOC content. Note that this is for SOFTWOODS only. David said there is NOTHING to his knowledge out there to pick a surrogate for hardwoods. Would be a task for sure.It would be a good idea to wait until the report is published before implementing the big clean up on kiln emissions. There was a scheduled talk on this subject for today and Richard Lasater is there to take notes. I'll make sure they get forwarded to you as well



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Burning Waste Wood in Boilers



Burning of "waste" wood in boilers is somewhat of a misnomer or oxymoron in that when it is burned to supply heat or other useful form of energy, it is no longer a waste. This section, however, is intended to address the use of wood in such a manner to provide process steam or space heating. This transforms what might otherwise be a waste into a valuable commodity.



General Description and Comments



Wood is burned in many kinds of units. These units range from small homemade boxes with grates and an heat exchanger (usually air to water) to provide space heating, to large well designed units with baffles, reburn chambers, precisely controled combustion air and highly efficient heat extraction mechanisms. The type and quality of the wood waste that is burned depends largely upon the main operation taking place at the facility. If it is a crude lumber (e.g. sawmill) operation, the waste may be soft woods, hard woods or mixed, in the form of chunks, chips, bark, slabs or various combinations and may include significant quantities of dirt and other trash. Wood waste at the other end of the spectrum will likely be generated by furniture plants and other similar wood finishing operations. In this category of facility, the waste may be small chips, slivers with some shavings, but mainly sander dust and fine saw dust, probably from hardwoods, and a significantly "cleaner" dust in terms of foreign matter. Obviously, these different waste streams will have different burning characteristics and require different design considerations to achieve complete combustion and maximum efficiencies. For this reason, one must be careful when making emission estimates so that the assumptions and calculations fit the situation.



Emission Factors and Assumptions



AP-42 Section 1.6 addresses "Wood Waste Combustion in Boilers." This document contains details on firing practices, design and other cosiderations that do not need to be repeated here. Although, considerable informaiton is presented here, data do not exist in quantity and quality to allow reliable emission factors to be provided for all operations. This section was last updated in February of 1998, but EPA's CHIEF internet site should be monitored regularly to determine when additional improvements are made in this dynamicly updated document. Changes that are made on the CHIEF internet information are "in effect" when the final document is posted there and one does not need to wait till the paper copy is printed to obtain and use the information. The site has a "subscribe" feature which will automatically notify those who desire that changes are made by sending an e-mail message indicating what the changes are. Also, no-cost independent web services may be utilized which will automatically notify those who sign up of changes made in specific web pages. The major controversy in North Carolina over the accuracy and use of these AP-42 (combustion) emission factors stems from how to treat moisture content and Btu content in estimating emissions from wood dust and other waste from furniture plants, of which North Carolina has many.. There is a serious and urgent need for more test data to allow adjustments and improvements to be made in the ability to estimate these emissions.



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Burning Wood Waste in Incinerators



.



General Description and Comments



!



Emission Factors and Assumptions Open Burning of Wood Waste



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General Description and Comments



!



Emission Factors and Assumptions Appendix of Miscellaneous Wood Related Facts Approximation of Boiler Capacity/Rating



Many times wood waste is burned in boilers or other units that do not have "boilerplate" ratings. Since some rules require the determination of an approximate rating for their application, a means to accomplish this is needed. In Tom Reeder's (NC DAQ) July 13, 1998 memo, a citation of Mark's Mechanical Engineer's Handbook establishes the following Rule of Thumb: For a boiler to generate/release 2,000,000 Btu/hour (60 boiler horsepower), it must have a firebox size of approximately 350 to 400 cubic feet, equivalent to a cube of about 7 to 7.5 feet on each side. Beware that this is very approximate and will vary by specific details of design and qualities of fuel.



Ultimate Analysis of Bark



Sometimes it is necessary to utilize information on the general qualities of wood bark. Many sources of information such as this are available, but the table below provides a sample of typical analyses.



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Ultimate Fuel Analysis of Wood Bark - Avg % by Weight, Dry Basis Wilcox)



Component/Type Carbon Hydrogen (H2) Sulfur Nitrogen Oxygen Ash Total Heat Value-Dry, MF, Btu/lb Heat Value- Dry, ash-free MAF, Btu/lb Moisture range Pine 55.3 5.5 0.1 0.3 37.3 1.5 100 9170 9300 40 - 60%



(Babcock & Hardwood 49.7 5.4 0.1 0.2 39.3 5.3 100 8370 8840 40 -60%



Miscellaneous Wood Moisture and Btu Information



Wood fuels may vary considerably in their heat content and in their moisture content which effects the heat content. Such fuels are often termed as dry (air dried or kiln dried),or green. "Dry wood" is generally defined as wood which is < 19% moisture. Thomas A Glover, Pocket Ref Wood moisture is also determined by what industry the information applies to. For the pulp and paper industry (total weight basis), Moisture % = {Weight of Water in Sample}  {Total Weight of Sample} x 100 For other industries and applications (ovendry weight basis), Moisture % = {Weight of Water in Sample}  {Ovendry Weight of Sample} x 100 Conversion Factors for the Pacific Northwest Forest Industry, Institute of Forest Products,



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Characteristics for Some Typical North Carolina Wood Species.



Species Name Density (lb/cf) Hardness



American Elm Hickory Maple Oak, Red Oak, White Pine Spruce 35 40-55 35-44 45 47 25-27 28 Med Hard Hard Med Hard Hard Hard Soft Med



Million Btu/cord (dry) Assume 100% Eff.* 29 27 20 32



Comments



20 to 27 18



Medium Smoke Low Smoke Low Smoke Low Smoke Low Smoke Medium Smoke Medium Smoke



*Many wood burners are only 50-60% efficient.



1Board Foot = 1/12 cubic foot 1 Cord = 128 cubic feet. 1 Cord = 1536 board feet (a useless conversion) 1 Horsepower (mechanical) = 2542.48 Btu (mean)/hour. 1 Horsepower (boiler) = 33,445 Btu (mean)/hour 1 Horsepower (electric) = 2547.16 Btu/hr. Note that when you convert between units, there are a lot of variations and opportunities to make errors and wrong assumptions. 1. David A. Hartman, et. al., Conversion Factors for the Pacific Northwest Forest Industry, Institute of Forest Products, University of Washington



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