This study was undertaken on a refueling station using a Gilbarco Vapor-Vac Stage II vacuum assisted system to:
For the first two investigations conducted with the p/v valves ON and OFF, the PERMEATOR system was not actuated. For the mass balance measurements taken around the membrane module with PERMEATOR active, the vent line p/v valve was ON. The study was conducted during the period 14 February - 17 February 2005.
Summary
The results obtained with the p/v valves ON and OFF are compared with figures obtained in a 1999 CARB Study (California Air Resources Board) entitled, "Total Hydrocarbon Emissions from Two Phase II Vacuum Assist Vapor Recovery Systems During Baseline Operation and Simulated Refueling of On-Board Refueling Vapor Recovery (ORVR) Equipped Vehicles" (http://www.arb.ca.gov/vapor/orvr_report.pdf). As seen in the attached "Table 1 Field Test Data Summary," the results obtained from this test far exceed the results obtained in the above referenced study. The measured results with the p/v valve ON exceed the Gilbarco results reported by CARB by a factor of 1.53 - 2.60 and they exceed the Dresser/Wayne results reported by CARB by a factor of 22.90 - 38.77. With the p/v valve OFF, the measured results exceed the Dresser/Wayne results reported by CARB by a factor of 12.04.
ARID feels that the difference between the recent data and the historic CARB data are due primarily to fugitive leak sources that did not allow for an accurate accounting of the excess volumes generated. In addition, the large measured gap in the present study between the p/v ON and p/v OFF measurements also indicates the presence of fugitive leak sources that manifest themselves at elevated storage tank pressures. This assumption is confirmed by the information summarized in Appendix 1 -"Notes Regarding Field Test Leak Results." As seen in this summary, a large, persistent leak was observed in the overfill drain valve bucket of the premium gasoline storage tank, T3. Since the p/v ON measurements are taken at a large prevailing backpressure of +3 inches H2O, the fugitive leaks are relatively large contributors and significantly impact the observed flow-rates recorded by the flow-meters installed by Matus Technical Services. (Inches H2O is methodology of measuring the amount of pressure being exerted) Please note that the simple installation of a p/v valve in no way reduces or eliminates the prevailing excess vapor volume generation rates; thus, the difference must be due to leakages. It is also interesting to note that although the leak decay test was passed with a starting pressure of +2 inches H2O; the portable hydrocarbon detector showed that the drain valve bucket leaks became prominent at a pressure of about + 2.7 inches H2O. Since PERMEATOR maintains the average storage tank pressure less than 0.5 inches H2O, a level significantly below 2.7 inches H2O, the fugitive leak sources are minimized or altogether eliminated (PERMEATOR On vs Off GraphAppendix 2 - "PERMEATOR ON VS OFF" shows the pressure trace comparison with PERMEATOR ON versus OFF).
The measured results are also compared to values calculated by ARID's proprietary Evaporative Loss Model (ELM). As seen in Appendix 3 -"ELM.xls," the year 2005 predicted gasoline savings are 23.12 gallons per day. With reference to Table 1 Field Test Data Summary, the actual measured losses with the p/v OFF total 21.31 gallons per day, exhibiting excellent agreement with the ARID ELM. The ARID ELM also presents expected results for future years up to and including 2014 (Average values for the 10 year period are presented in bold font, at the bottom of the 2004 column). Please note that the savings expected in 2014, due solely to the increase in ORVR population, are tabulated at 58.04 gallons per day; a 250% increase over the 10 year period. The after tax internal rate of return (IRR) is shown to be 44%, yielding a slightly greater than two-year payback on invested capital while at the same time reducing emissions an average of 33.8 tons per year for a single refueling station.
With reference to Appendix 4 (Gasoline RVP Samples.pdf), the inputs used in the ELM were as follows: V/L ratio = 0.97 (average value derived from measured values), gasoline RVP = 11.1 psia (measured by The State of Florida, Department of Agriculture and Consumer Services Laboratory located in Port Everglades, Florida; Facility # SP0002), average storage tank temperature = 74 F (via tank gauge), altitude of refueling facility = 25 feet above sea level (estimated).
Of particular note, as seen in Table 1 Field Test Data Summary, the evaporative loss rate during times when the station is Closed (no dispensing of fuel) exceeds the evaporative loss rate when the station is Open. This fact confirms the presence and the importance of the resaturation of air comprising the primary mechanism of the evaporative losses at this relatively high throughput station.
Also of particular importance is the overall hydrocarbon recovery efficiency calculated as 99.27% in Table 2-1 (Page 4 of Matus Technical Report (MATUS_test_report_148.pdf)) for the PERMEATOR "ON" case. Matus technical services simultaneously recorded hydrocarbon concentrations in three streams: the feed (flow to the PERMEATOR), retentate (clean air exhaust), and permeate (enriched hydrocarbon stream returned to the storage tanks). Matus also recorded the flow rate of the clean air exhaust. These inputs were used to calculate an overall mass balance and subsequent overall recovery efficiency for the PERMEATOR in accordance with the equations described in the Matus report. Thus, instead of emitting 21.3 gallons of gasoline per day, the station equipped with a PERMEATOR will emit approximately 0.16 gallons of gasoline per day.
Acknowledgements: ARID wishes to thank Mr. Martin Costello, Department of Environmental Protection, Bureau of Air Monitoring and Mobile Sources, Tallahassee, Florida, for his oversight, inspection and assistance in conducting this test. ARID also thanks and appreciates the insights provided by Mr. Joe Kahn, Bureau Chief, Department of Environmental Protection, Bureau of Air Monitoring and Mobile Sources, Tallahassee, Florida. ARID also appreciates the oversight and test protocol assistance provided by Mr. Tom Driscoll, Senior Environmental Engineer, Office of Air Quality Planning & Standards, Emissions Factors & Policy Application Group, United States EPA, Research Triangle Park, North Carolina. In addition, ARID is grateful to the State of Florida, Palm Beach County Health Department's Mr. Selva Selvandran, Mr. Paul Kalamaras and Ms. Melinda Robinson for their collective assistance with our testing program.
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