Abstract:
Floating roof storage vessels including a vapor emission reduction system designed to be inserted into deck leg apertures, when the legs have been removed during hydrocarbon storage.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 61/613,399 filed Mar. 20, 2012 (20 Mar. 2012). 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention relate to systems and methods for reducing vapor emission from deck leg apertures of floating roof storage vessels. 
         [0004]    More particularly, embodiments of the present invention relate to systems and methods for reducing vapor emission from deck leg apertures of floating roof storage vessels, where the vessels include a deck leg aperture vapor reduction system. 
         [0005]    2. Description of the Related Art 
         [0006]    A large number of petroleum above ground storage tanks (AST&#39;s) were built prior to 1980 and prior to the EPA more stringent regulations regarding hydrocarbon vapor emission control. The latest emission control standards require the use of the best available control technology (BACT) to minimize the vapor emissions. The new standards have required companies with older storage tanks to find practical ways to retrofit existing tanks to achieve compliance. 
         [0007]    The purpose of a leg sleeve on an internal floating roof (IFR) storage tanks is to allow for the insertion of pipe legs in order to support the floating roof during maintenance activities. Normal out of service maintenance of the tank bottom is performed in the high leg position to allow safe entry under the roof. When the tank is returned to service the pipe legs are removed from the sleeves and placed on the floating roof until the next out of service maintenance is required. The remaining leg sleeve penetration in the roof is where vapor emissions can occur. In an effort to minimize the cost of taking tanks out of service and modifying each leg sleeve, most AST owners have adopted the simple approach of installing an impermeable bag or leg sock over the leg sleeve to minimize vapor emissions. 
         [0008]    The existing technology is able to achieve compliance; however, the devices are not as effective as the vapor plug design and are difficult to maintain. In some cases these bags or socks do not seal well around the leg sleeve and rip or tear from the installation process and material fatigue. These rips or tears in the bags or socks can be found during required inspections and can result in owners receiving Notice of Violation (NOV) from the governing Air District. These fines can carry stiff penalties in some cases. 
         [0009]    New technology is typically presented to the local Air Pollution Control District Agency, and after documented testing is confirmed, the Agency may consider it to be BACT and even establish a lower emission factor for the technology compared to other devices. A lower emission factor would create potential savings when purchasing emission credits for future processing and storage of petroleum products. 
       SUMMARY OF THE INVENTION 
       [0010]    Embodiments of this invention provide emission control systems for floating roof storage tanks having a plurality leg sleeves, where the emission control systems include vapor emission control apparatuses inserted into the leg sleeves. The vapor emission control apparatuses include a compressible member that when compressed forms an air tight or substantially air tight seal against an inner surface of the leg sleeves, where the seal is positioned below leg pin apertures that lock the legs in place during tank maintenance The emission control systems of this invention are designed to reduce, substantially eliminate or completely eliminate VOC emission from the leg sleeves. 
         [0011]    Embodiments of this invention provide emission control methods including providing a floating roof storage tank having a plurality leg sleeves and inserting a plurality of vapor emission control apparatuses of an emission control system of this invention into the leg sleeves, and forming an air tight seal or a substantially air tight seal between compressible members associated with the vapor emission control apparatuses below leg pin apertures in the leg sleeve, where the vapor emission control apparatuses reduce, substantially eliminate or completely eliminate VOC emission from the leg sleeves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention can be better understood with reference to the following detailed description together with the appended illustrative drawings in which like elements are numbered the same: 
           [0013]      FIG. 1  depicts an embodiment a vapor emission control apparatus of this invention. 
           [0014]      FIGS. 2A-C  depict other embodiments of vapor emission control apparatus of this invention. 
           [0015]      FIG. 3  depicts a perspective view of an open floating roof storage tank equipped with the vapor emission control apparatuses of  FIGS. 1 ,  2 A,  2 B, and  2 C. 
           [0016]      FIG. 4  depicts a plan view of an internal floating roof storage tank equipped with the vapor emission control apparatuses of  FIGS. 1 ,  2 A,  2 B, and  2 C. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The inventor has found that emission control systems may be designed for floating roof (FR) storage tanks having a plurality leg sleeves, where the emission control system includes a plurality of vapor emission control apparatuses inserted into the top end of the leg sleeves, where the apparatuses include a compressible member designed to form an air tight or substantially air tight seal with an inner surface of the leg sleeves below the leg pin apertures of the leg sleeves. The inventor has also found that methods may be implemented using the emission control system for floating roof storage tanks. The methods include inserting a plurality of vapor emission control apparatuses of an emission control system of this invention into the top end of the leg sleeves associated with a floating roof storage tank and compressing the compressible members to form an air tight or substantially air tight seal with an inner surface of the leg sleeves below the leg pin apertures of the leg sleeves. The vapor emission control apparatuses are designed to reduce, substantially eliminate, or eliminate vapor emissions from the leg sleeves. The emission control systems of this invention are ideally suited for internal floating roof (IFR) storage tanks and open floating roof storage tanks. 
         [0018]    The vapor emission control systems of this invention have a number of benefits (1) the systems reduce vapor emissions for FR, IFR or open floating roof storage tanks; (2) the systems are likely to be classified by agencies as having a lower emission factor compared to current technology resulting in cost savings for emission credits; (3) the systems are easy to maintain; and (4) the systems reduce the likelihood of permit violations. 
         [0019]    Embodiments of this invention broadly relate to emission control systems for floating roof storage tanks having a plurality leg sleeves, where the emission control systems include vapor emission control apparatuses inserted into the top end of leg sleeves associated with a floating roof storage tanks, where the apparatuses include a compressible member designed to form an air tight or substantially air tight seal with an inner surface of the leg sleeves below the leg pin apertures of the leg sleeves. The vapor emission control apparatuses are designed to reduce, substantially eliminate, or completely eliminate VOC emission from the leg sleeves. The vapor emission control apparatuses include a compressible member interposed between a top compression plate and a bottom compression plate. The compression or compressible member includes an aperture therethrough as do the plates. The apparatuses also include a threaded shaft inserted through the member and the plates. The shaft includes a head designed to engage a bottom surface of the bottom plate and a handle for rotating the threaded shaft at its tail end. The apparatuses also include a top, which is designed to rest on a top end of a leg sleeve of a floating roof of a floating roof storage tank. The apparatuses also include a locking assembly such as a nut with wings (a wing nut), two or more nuts, or other locking assemblies. The apparatuses also include a spacer interposed between the top and the locking member. The apparatuses also include a spacer tube interposed between the top and the top plate. The apparatuses are inserted into the leg sleeve so that the compressible member is situated below leg pin apertures in the leg sleeves and the seal is formed below the apertures. 
         [0020]    The apparatuses operate as follows. When the handle is turned one way, the plates move apart permitting the compressible member to relax so that the apparatus can be removed from the leg sleeve. When the handle is turned the other way, the plates move closer together compressing the compressible member to form a vapor tight or substantially vapor tight seal against the sleeve inner wall. 
         [0021]    Embodiments of this invention broadly relate to emission control methods including providing a floating roof storage tank having a plurality leg sleeves and inserting a plurality of vapor emission control apparatuses of an emission control system of this invention into the leg sleeves, where the vapor emission control apparatuses reduce, substantially eliminate or completely eliminate VOC emission from the leg sleeves. 
         [0022]    The term “substantially” mean in relationship to air tight seals that the seal prevents at least 95% of VOCs from venting through the seal. In other embodiments, the term means that the seal prevents at least 97.5% of the VOCs from venting through the seal. In other embodiments, the term means that the seal prevents at least 99.5% of the VOCs from venting through the seal. In other embodiments, the term means that the seal prevents at least 99.9% of the VOCs from venting through the seal. 
         [0023]    Suitable materials out of which the compressible member may be made include, without limitation, any rubber, cured or uncured, but preferably cured. Suitable rubbers for uses in the compressible members include, without limitation, butyl rubber, nitrile rubber (NBR), EPDM, styrene-butadiene rubber (SBR), styrene-isoprene rubber (SIR), styrene-butadiene-isoprene rubber (SBIR), silicon rubbers, polyurethane rubbers, fluorosilicon rubber, perfluoroelastomers, other types of rubbers, or mixtures or combinations thereof. The rubbers, which are made up of two or more monomers, may be random or blocked rubbers, may be hydrogenated, or treated in other ways. The rubbers may be compounded with fillers including, without limitation, carbon blacks, silicas, clays, other fillers, and mixtures or combinations thereof. The rubbers may also be compounded with antioxidiants and antiozoants, other stabilizing materials or mixtures or combinations thereof. The rubbers may also be and preferably are cured, where the curing may be sulfur based, peroxide based, radiation based, other curing or mixtures or combinations thereof, depending on the type of rubber compound out of which the compressible member is made. Due to the presence of VOCs, the preferred rubbers are rubber resistance to VOCs including, without limitation, nitrile rubber (NBR), Viton, polyurethane, fluorosilicone, tetrafluoroethylene-propylene copolymers (TFE/P), such as AFLAS®, a registered trademark of AGC Chemicals Americas, Inc., perfluoroelastomers such as KALREZ®, a registered trademark of DuPont, and mixtures or combinations thereof. 
       DETAIED DESCRIPTION OF THE DRAWINGS 
       [0024]    Referring now to  FIG. 1 , a simple embodiment of a vapor emission control apparatus for leg sleeves of a floating roof storage tank, generally  100 , is shown to include a compressible member  102  interposed between a top compression plate  104  and a bottom compression plate  106 . The compression member  102  includes an aperture  108  therethrough; the top plate  104  includes an aperture  110 , therethrough; and the bottom plate  106  includes an aperture  112 , therethrough. The three apertures  108 ,  110 , and  112  are designed to align. The apparatus  100  includes a threaded shaft  114  inserted through the apertures  108 ,  110 , and  112  in the member  102  and the plates  104  and  106 , respectively. The shaft  114  includes a head end  116  designed to engage a bottom surface  118  of the bottom plate  106 . Of course, the shaft  114  may also be integral with the lower plate  106  or welded to the bottom plate  106  as described herein. The shaft  114  also includes a handle  120  for rotating the threaded shaft  114  at its tail end  122 . The apparatus  100  also includes a locking member  124  having a nut  126  and wings  128 . The apparatus  100  is designed to be inserted into a top end  130  of a leg sleeve  132  of a roof  134  of a floating roof storage tank. The apparatus  100  is inserted into the leg sleeve  132  so that the compressible member  102  is disposed below leg pin apertures  136  in the leg sleeve  132  and the seal is formed below the leg pin apertures  136 . 
         [0025]    When the handle  120  is turned one way, the plates  104  and  106  move apart permitting the compressible member  102  to relax so that the apparatus  100  can be removed from the sleeve  132 . When the handle  120  is turned the other way, the plates  104  and  106  move closer together compressing the compressible member  102  to form a vapor tight or substantially vapor tight seal of the member  102  against an inner surface  138  of the sleeve  132  below the leg pin apertures  136  reducing or eliminating VOC emissions from the sleeves  132 . 
         [0026]    Referring now to  FIG. 2A , another embodiment of a vapor emission control apparatus for leg sleeves of a floating roof storage tank, generally  200 , is shown to include a compressible member  202  interposed between a top compression plate  204  and a bottom compression plate  206 . The compression member  202  includes an aperture  208  therethrough; the top plate  204  includes an aperture  210 , therethrough; and the bottom plate  206  includes an aperture  212 , therethrough. The three apertures  208 ,  210 , and  212  are designed to align. The apparatus  200  includes a threaded shaft  214  inserted through the apertures  208 ,  210 , and  212  in the member  202  and the plates  204  and  206 , respectively. The shaft  214  includes a head end  216  designed to engage a bottom surface  218  of the bottom plate  206 . Of course, the shaft  214  may also be integral with the lower plate  206  as shown in  FIG. 2B  or the head end  216  of the shaft  214  may be welded to the bottom plate  206  by a weld  206   a.  The shaft  214  also includes a handle  220  for rotating the threaded shaft  214  at its tail end  222 . The apparatus  200  also includes a top  224   a  having a top surface  224   b  and a bottom surface  224   c . The top  224   a  is designed to rest on a top end  226  of a leg sleeve  228  of a roof  230  of a floating roof storage tank. The apparatus  200  also includes a locking member  232  having a nut  234  and wings  236 . The apparatus  200  also includes a spacer  238  interposed between the top  224   a  and the locking member  232 . The apparatus  200  also includes a spacer tube  240  interposed between the top  224   a  and the top plate  204 . The apparatus  200  is inserted into the leg sleeve  228  so that the compressible member  202  is disposed below leg pin apertures  242  in the leg sleeve  228  and the seal is formed below the leg pin apertures  242 . 
         [0027]    When the handle  220  is turned one way, the plates  204  and  206  move apart permitting the compressible member  202  to relax so that the apparatus  200  can be removed from the sleeve  228 . When the handle  220  is turned the other way, the plates  204  and  206  move closer together compressing the compressible member  202  to form a vapor tight or substantially vapor tight seal against an inner surface  244  of the leg sleeve  228  below the leg pin apertures  242  reducing or eliminating VOC emissions from the sleeves  228 . 
         [0028]    Referring now to  FIG. 3 , an embodiment of an open floating roof storage tank, generally  300 , is shown to include a tank shell  302  having a open top  304  and a floating roof  306 . The floating roof  306  includes a solid guidepost  308 , a gauge float  310 , an access hatch  312 , gauge hatch or sample port  314  and an overflow drain  316 . The floating roof  306  further includes a rim seal  318 , a vacuum breaker  320  and a rim vent  322 . The floating roof  306  also includes a plurality of leg sleeves  324  equipped with the vapor emission control apparatuses  326  of  FIGS. 1-2D . 
         [0029]    Referring now to  FIG. 4 , an embodiment of a closed floating roof storage tank, generally  400 , is shown to include a tank shell  402  having a top  404  and a floating roof  406 . The tank  400  also includes a guide post  408  as in the tank  200  of  FIG. 2 . The roof  306  includes a plurality of deck leg sleeves  410  equipped with an equal plurality of the vapor emission control apparatus  412 . Of course, the tank  400  includes some or all of the other features of the tank  300  of  FIG. 3 . 
         [0030]    All references cited herein are incorporated by reference. Although the invention has been disclosed with reference to its preferred embodiments, from reading this description those of skill in the art may appreciate changes and modification that may be made which do not depart from the scope and spirit of the invention as described above and claimed hereafter.