Fuel tank ullage pressure reduction

An apparatus for reducing the pressure in a fuel tank ullage comprising:

• a. a vapor extractor connected to the fuel tank ullage for pulling vapor therefrom,
• b. a pressure sensor adapted for mounting to detect the pressure in the fuel tank ullage,
• c. a separation module having
• 1) an inlet connected to said vapor extractor,
• 2) a separation membrane in said module,
• 3) a permeate outlet separated from said inlet by said separation membrane and adapted for connection to the fuel tank ullage, and
• 4) a retentate outlet not separated from said inlet by said membrane,
• d. a vapor pump connected to the permeate outlet for creating a lower pressure in said separation module near said permeate outlet than near said inlet so as to induce selected vapors to pass through said separation membrane,
• e. a vent in communication with said retentate outlet to vent retentate to atmosphere,
• f. a discharge valve associated with said retentate outlet,
• g. a hydrocarbon detector to detect hydrocarbon concentrations in said vent,
• h. a controller
• 1) for receiving inputs from said pressure sensor and said hydrocarbon detector and
• 2) outputting control signals to
• a) said vapor extractor to control said vapor extractor to extract vapor from said tank ullage at a slower rate than the maximum achievable by said extractor to provide a long residence time for hydrocarbon vapor molecules adjacent said separation membrane,
• b) said vapor pump to actuate said vapor pump and
• c) said discharge valve to open said discharge valve
• 3) in order to pull vapor from the ullage when the pressure exceeds a pressure threshold and return permeate to the tank and permit relatively hydrocarbon-free air to be released through said vent, thereby reducing the pressure in the ullage.

An apparatus for reducing the pressure in a fuel tank ullage comprising:

• vapor extractor connected to the fuel tank ullage for pulling vapor therefrom,
• a pressure sensor mounted in the fuel tank ullage for detecting the pressure therein,
• a separation module having
• an inlet connected to said vapor extractor,
• a separation membrane in said module,
• a permeate outlet separated from said inlet by said separation membrane and connected to the fuel tank ullage, and
• a retentate outlet not separated from said inlet by said membrane,
• a vapor pump connected to said permeate outlet for creating a lower pressure in said separation module near said permeate outlet than near said inlet so as to induce selected vapors to pass through said separation membrane,
• a vent associated with said retentate outlet to vent retentate to atmosphere, and
• a controller for receiving inputs from said pressure sensor and outputting control signals to said vapor extractor and said vapor pump to actuate said vapor extractor and said vapor pump to pull vapor from the ullage when the pressure exceeds a pressure threshold and return permeate to the tank and permit relatively hydrocarbon-free air to be released through said vent, said controller including a control routine that tracks the rate of decrease of pressure in the fuel tank ullage and outputs the control signals in a fashion to cause the rate of decrease of pressure in the fuel tank ullage to be less than the maximum of which the vapor extractor and vapor pump are capable, thereby reducing the pressure in the ullage.