Advanced Membrane Systems: Recovering Wasteful and Hazardous Fuel Vapors at the Gasoline Tank
Source: DOE Success Story (
click here to go to the source)
Challenge
A typical gasoline station can release over 3,000 gallons of fuel as vapor each year. These vapors
represent an economic loss as well as pose a hazard for health, safety, and the environment.
One of the constituents of gasoline vapor (benzene) is a carcinogen, and hydrocarbon vapors
contribute to low-level ozone and smog formation.
Gasoline stations store fuel in underground storage tanks, which are filled from tanker trucks and
then emptied slowly as fuel is pumped into customer vehicles. Gasoline vapor escapes during
both filling and emptying, and Stage I and Stage II vapor recovery systems are used for these
operations. In Stage I systems, vapor displaced from the underground storage tank during filling
is directed to the tanker truck, so the truck leaves with a tank full of vapor that would otherwise
have been vented. In Stage II systems, vapor from refueling customer vehicles is directed back to
the underground storage tank.
As gasoline stations were installing Stage II vapor recovery systems, the California Air Resources
Board (CARB) and the Environmental Protection Agency (EPA) required new cars to be
equipped with another approach to solving the same problem: on-board refueling vapor recovery
(ORVR) systems to capture vapors at the vehicle. However, testing subsequently showed that
these ORVR systems caused Stage II systems to release more fugitive emissions through tank
vents.
In response to this problem, CARB required gasoline stations to reduce fugitive emissions using
equipment compatible with ORVR systems. It was believed that gasoline stations could meet the
regulations with vent processors that remove fuel vapor from the air passing out of tank vents.
However, fugitive emissions can also escape from other system leaks, so some vent processors
needed to be designed to maintain fuel tanks at a slightly negative pressure.
Any leak in a negative-pressure tank will draw air in rather than release emissions.
Innovating Solutions
CMS saw vent processors as a natural application for their proprietary fluorinated polymer
membrane. The CMS membrane is well suited for use with solvents and other aggressive
chemicals. It is also unique in that it lets air pass through and retains volatile or
ganic compound (VOC) vapor. Other membranes used for vent processors work in a reverse manner, permitting vapors to pass and retaining air, thus requiring systems that are more complicated.
CMS began research on VOC-air separation with EPA SBIR Phase I funding in 1993, followed
by a Phase II award the following year. This funding supported a feasibility study, initial testing,
and economic evaluation. DOE EERE SBIR funding, beginning in 2000, allowed CMS to
continue developing the membrane and improve its vapor recovery efficiency by about 75%.
The State of Delaware augmented DOE's Phase I and II funding.
During the DOE SBIR-funded work, CMS partnered with Innovative Membrane Systems, Inc.,
a subsidiary of Praxair, Inc., to develop the membrane and double its efficiency. CMS chose
Innovative Membrane Systems as a supplier for the membrane fiber because of their well-
established expertise in producing membranes for air separation and gas processing.
The DOE SBIR project also allowed CMS to develop the rest of the vapor processing system
in collaboration with Vapor Systems Technologies, Inc. This relationship began during the EPA
SBIR project when Vapor Systems contacted CMS and introduced them to the gasoline recovery
application. While developing the system with Vapor Systems Technologies during the DOE
SBIR project, CMS was again able to double the system's performance.
