DEVELOPMENT OF A NEW TEST METHOD USING SULFUR HEXAFLUORIDE TRACER GAS TO DETERMINE THE CAPTURE EFFICIENCY OF HOODS OR ENCLOSURES AROUND HOT PRESSES USED IN WOOD PRODUCTS PANEL MANUFACTURING

摘要

The information provided to and used by the US EPA to determine the control “floor” for the currently proposedPlywood & Composite Wood Panels MACT Standard includes some presses with enclosures and pollutioncontrolled devices. These press enclosures are believed to generally conform to the requirements of EPA Method204, however, it is not clear that these installations have been rigorously examined or if ventilation rates areadequate to maintain an acceptable workplace environment. Additionally, the majority of the enclosures included todefine the “floor” determination were installed around conventional multiple-opening and short continuous presses.New generation, long continuous presses (i.e., 90 to 120 feet long) are not included in the ‘floor” determination.The regulation as currently proposed with sole reliance on Method 204 will unduly increase costs, stifle innovation,and force some installations to contend with a clearly inapplicable provision.An Alternative Procedure to Determine Capture Efficiency from a Hot Press Enclosure in the Plywood andComposite Wood Products Industry using Sulfur Hexafluoride Tracer Gas has been developed to allowdetermination of capture efficiency of press enclosures. The proposed test method appears is included in theproposed rule as “Appendix A to Subpart DDDD - Alternative Procedure to Determine Capture Efficiency from aHot Press Enclosure in the Plywood and Composite Wood Products Industry using Sulfur Hexafluoride Tracer Gas.”This proposed method uses sulfur hexafluoride (SF6) as tracer gas to determine the capture efficiency of pressenclosures. A known mass of SF6 is continuously released at specific locations around the press operation withinthe enclosure. Concurrently, the mass emission rate of SF6 is determined in the captured gas stream. The resultingcapture efficiency data must meet the Data Quality Objectives (DQO) or Lower Confidence Limit (LCL) approach.Concerns have been raised concerning the precision and accuracy of the method when applied to press operations.The press operations are cyclic and may result in variable flow rates and SF6 concentrations of the capturedemissions. The sampling and analytical strategies allowed in the method must be able to account for these possiblevariations to obtain accurate capture efficiency results and meet the DQO and/or LCL precision requirements.To evaluate the accuracy of the method, a simulated test condition was created by spiking SF6 directly into thecaptured gas stream between the press hood and the SF6 sampling location thus yielding 100% capture of the SF6spike. Sampling techniques and sampling periods were also evaluated for both accuracy and precision during the100% capture simulation. After identification of the most suitable sampling and analytical methodologies, captureefficiency tests were then conducted on a partially enclosed press under actual operating conditions.Spiking the press manifold alone resulted in 96.8% capture, while spiking the side-unloader manifold alone resultedin 73.3% capture. Spiking through both manifolds resulted in 84.3% capture.