Method And Apparatus For Abating Fugitive Emissions From A Volatile Liquid Storage Tank

Abstract

A fugitive emissions abatement system for use a storage tank 4 with a floating roof assembly 10 comprises a roof structure 12, a first peripheral seal 70 slidably engaging an interior surface 4 A of the tank 4 to form an annular gas chamber 60 intermediate the first peripheral seal 70 and the liquid level 50 within the tank 4, and an aperture 78 in the first peripheral seal 70 coupled to the first end 82 of a fluid conduit 80. The second end 81 of the fluid conduit 80 may be coupled to the inlet of a gas mover 88 so that operation of the gas mover 88 draws gas from the annular gas chamber 60 through the fluid conduit 80 so that it can be delivered to a processing apparatus that may include, but is not limited to, a compressor, a vessel, a heat exchanger and/or an incinerator.

1 . A method of abating fugitive emissions from a volatile liquids storage tank comprising the steps of:
 providing a generally disc-shaped floating roof assembly having an annular recess within the volatile liquids storage tank;   disposing a seal about the floating roof assembly in a vertically spaced-apart relationship from a liquid interface on the floating roof assembly to define an annular gas chamber there between; and   disposing the annular gas chamber in fluid communication with an inlet to one or more gas movers through one or more fluid conduits to withdraw gas from the annular gas chamber.   
   
   
       2 . The method of abating fugitive emissions from a volatile liquids storage tank of  claim 1  further comprising the step of:
 disposing an outlet of the one or more gas movers in fluid communication with an inlet to a volatile liquids recovery process.   
   
   
       3 . The method of abating fugitive emissions from a volatile liquids storage tank of  claim 1  further comprising the step of:
 disposing an outlet of the one or more gas movers in fluid communication with an inlet to a volatile liquids incineration process.   
   
   
       4 . The method of controlling fugitive emissions from a volatile liquids storage tank of  claim 1  further comprising the step of:
 biasing the seal against an interior wall of the volatile liquids storage tank.   
   
   
       5 . The method of  claim 1  further comprising the step of coupling the gas mover to the floating roof assembly. 
   
   
       6 . A method of controlling fugitive emissions from a volatile liquids storage tank comprising the steps of:
 providing a generally disc-shaped floating roof assembly having an annular recess within the volatile liquids storage tank;   disposing a first generally circular seal about the floating roof assembly in a vertically spaced-apart relationship from a liquid interface about the floating roof assembly to define a first annular gas chamber there between;   disposing a second generally circular seal about the floating roof assembly in a vertically spaced-apart relationship from the first generally circular seal to define a second annular gas chamber there between; and   disposing at least one of the first annular gas chamber and the second annular gas chamber in fluid communication with an inlet to one or more gas movers through one or more fluid conduits.   
   
   
       7 . The method of controlling fugitive emissions from a volatile liquids storage tank of  claim 6  further comprising the step of:
 disposing an outlet of the one or more gas movers in fluid communication with an inlet to a volatile liquids recovery process.   
   
   
       8 . The method of controlling fugitive emissions from a volatile liquids storage tank of  claim 4  further comprising the step of:
 biasing the generally circular seal against an interior wall of the volatile liquids storage tank.   
   
   
       9 . The method of controlling fugitive emissions from a volatile liquids storage tank of  claim 1  further comprising the step of:
 periodically sampling the gas drawn from the annular gas chamber through the one or more fluid conduits to determine the performance of the first seal.   
   
   
       10 . The method of controlling fugitive emissions from a volatile liquids storage tank of  claim 9  further comprising the step of:
 containing at least a portion of gas emitted from a volume of volatile liquid stored in the storage tank using a seal disposed generally around a disc-shaped floating roof assembly;   withdrawing at least one sample of gas from a plurality of locations along an annular gas chamber disposed about the floating roof assembly; and   comparing gas samples drawn from a plurality of angularly distributed fluid conduits to assess the performance of identifiable portions of a seal.   
   
   
       11 . A method of controlling fugitive emissions from a volatile liquids storage tank comprising the steps of:
 withdrawing one or more streams of gas from an annular gas chamber around a floating tank roof assembly using a gas mover to maintain a vacuum within the annular gas chamber; and   processing the one or more gas streams to minimize emissions to the atmosphere from the tank.   
   
   
       12 . The method of  claim 11  further comprising sampling the one or more gas streams to determine the performance of identifiable portions of the seal. 
   
   
       13 . A floating tank roof assembly comprising: an annular recess about a first perimeter portion of a roof platform;
 a first seal about a second perimeter portion to form a first annular chamber there below; and   one or more fluid conduits having an inlet at the first annular gas chamber an outlet in and the suction of a gas mover to withdraw gas from the annular chamber.   
   
   
       14 . The floating roof tank assembly of  claim 13  further comprising one or more sampling ports accessing one or more fluid conduits. 
   
   
       15 . The floating roof assembly of  claim 13  further comprising a second seal about a third perimeter portion of the roof platform. 
   
   
       16 . The floating roof assembly of  claim 15  wherein the second seal forms a second seal forms a second chamber above the first annular chamber. 
   
   
       17 . The floating assembly of  claim 13  further comprising one or more tracer gas injection ports. 
   
   
       18 . The floating tank roof assembly of  claim 13  further comprising one or more automatic gas sampling devices. 
   
   
       19 . The floating tank roof assembly of  claim 18  further comprising a means for transmitting one or more signals indicating the content of gas withdrawn from the first annular gas chamber. 
   
   
       20 . The method of  claim 11  further comprising the steps of:
 providing at least one valve in fluid communication between the annular gas chamber and the gas mover;   sensing a condition of the annular gas chamber and generating a signal;   adjusting the at least one valve in response to the signal to modulate the rate of gas withdrawal from the annular gas chamber through the one or more gas streams.