Abstract:
The apparatus and method for venting and depressurization of an odorant injection system may be used on special LNG tankers that have onboard gasification equipment, on land or elsewhere. Odorant injection systems may operate at high pressures on an intermittent basis. On some occasions, the odorant is drained from a pressurized system and disposed of in inappropriate ways. The present invention depressurizes an odorant injection system and transfers the unwanted liquid odorant back into an odorant tank where it can be reused when the odorant injection system is restarted.

Description:
DESCRIPTION OF THE PRIOR ART 
       [0001]    Natural gas is a clear, odorless and tasteless gas as it comes from the ground. For safety purposes, odorant is commonly injected into the natural gas before it is distributed to customers. There are many prior art odorant injection systems including U.S. Pat. No. 6,142,162 owned by the assignee of the present application, which is incorporated herein by reference. Other odorant injection systems are disclosed in U.S. Pat. Nos. 5,406,970 and 6,208913 which are owned by Y-Z Industries, Inc. 
         [0002]    On land, natural gas is commonly transported in pipelines. In order to transport natural gas in a ship, it is first liquefied and stored in large land based tanks before it is loaded onto the ship. One cubic foot of liquefied natural gas (LNG) represents about 600 cubic feet of natural gas. Liquefaction saves space and makes LNG economical to ship on the high seas. 
         [0003]    Natural gas is typically liquefied in geographic areas of the world where natural gas is produced, but where there is little commercial market for the gas, such as Indonesia, Trinidad and the Middle East. LNG is commonly shipped on LNG tankers to markets where it is used, such as Japan, the United States and Europe. LNG it typically offloaded from these tankers to large tank based storage facilities on land where the LNG is gasified. Depending on local needs, the LNG may be gasified on a continuous or intermittent basis. 
         [0004]    Special LNG tankers have been developed which regasify the LNG onboard instead of offloading the LNG to a large land based storage tank. These special LNG tankers often moor offshore to a buoy and gasify the LNG which is injected into a pipeline for transport to the pipeline distribution grid onshore. This offshore gasification process may be continuous or it may be intermittent; it make take several days to gasify the LNG and empties the tanker. 
         [0005]    Odorant injection systems are used on some of these special LNG tankers with onboard gasification facilities. The onboard odorant injection systems need to depressurize between the intermittent periods of gasification to reduce the chance of leaks and stress on the system. Leaks in odorant injection systems tend to have an in terrorium effect among crew and officers because they sense a gas leak. There is a need for improved systems to depressurize and vent odorant injection systems when not in use, such as between the intermittent periods of gasification on special LNG vessels and elsewhere. 
       SUMMARY OF THE INVENTION 
       [0006]    In the past, unwanted odorant has not always been treated with respect. For example, there are rumors that unwanted odorant has been collected in a tin can or glass jug when an odorant injection system has been depressurized. Other rumors indicate that unwanted odorant has sometimes been thrown on the ground or disposed of in other inappropriate ways. 
         [0007]    The present invention is a system that returns unwanted odorant from a depressurized odorant injection system to an odorant tank(s) which is sometimes called an odorant tote in the industry. The odorant can thus be reused when the odorant injection system is restarted. The present invention also filters vapors from the odorant tank(s) before they are vented to atmosphere. If widely implemented, this system will reduce improper disposal of odorant when an odorant injection system is depressurized and it will reduce airborne discharge of stinky gas that has a high concentration of odorant. The present invention may be used onboard a LNG vessel and elsewhere. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic of an odorant injection system with flow arrows indicating the odorant flow from the odorant tanks to and odorant injection line. 
           [0009]      FIG. 2  is a schematic of an odorant injection system with flow arrows indicating the depressurization of the system and venting of filtered vapors to atmosphere. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]      FIG. 1  is a schematic of an odorant injection system  10  with flow arrows indicating the odorant flow from the odorant tanks  12  and  14  to the odorant injection conduit  16 . This odorant injection system may be located on a specialized LNG tanker, as previously described, or it may be located elsewhere. For purposes of this illustration, the odorant injection system  10  will be located on the specialized LNG tanker and will be used to odorize the gasified LNG before it leaves the tanker. The regasification activity is intermittent. 
         [0011]    A downcomer  18  is located in the first odorant tank and is in fluid communication with a valve  19 , a conduit  20 , a valve  22 , a conduit  24 , a valve  26 , a conduit  28 , a valve  30  and the first odorant filter  32 . During the injection process, as illustrated by the flow arrows in  FIG. 1 , liquid odorant  8  flows from the first odorant tank  14 , through the downcomer  18 , the valve  19 , the conduit  20 , the valve  22 , the conduit  24 , the valve  26 , the conduit  28 , the valve  30  to the first odorant filter  32 . 
         [0012]    A second downcomer  34  is located in the second odorant tank and is in fluid communication with a valve  36 , a conduit  38 , a valve  40 , a conduit  42 , the valve  26 , a conduit  46 , a valve  48  and the second odorant filter  50 . During the injection process, as illustrated by the flow arrows in  FIG. 1 , liquid odorant flows from the second odorant tank  14 , through the second downcomer  34 , the valve  30 , the conduit  38 , the valve  40 , the conduit  42 , the valve  26 , the conduit  46 , the valve  48  to the second odorant filter  50 . 
         [0013]    It is typical for an odorant injection system to have dual filtration of the odorant as it flows from the odorant tank to the odorant pumps. The first filter  32  is in fluid communication with valve  60 , conduit  62 , and the common odorant feed conduit  64 . The second filter  50  is in fluid communication with the valve  72 , the conduit  73  and the common odorant feed conduit  64 . During the injection process, as illustrated by the flow arrows in  FIG. 1 , liquid odorant flows through the first odorant filter  32  and the second odorant filter  50  through the common odorant feed conduit  64 , to the first odorant pump  70  and the second odorant pump  80 . 
         [0014]    As is well know to those skilled in the art, blanket pressure in the range of from about 20 psi to about 25 psi is kept on the first and second odorant tanks to help keep the conduits from the odorant tanks to the odorant pumps at least partially filled with liquid odorant. Tank blanket pressure from the system cabinet, not shown, enters the system through conduit  90  as indicated by the flow arrow. Blanket gas flows through valve  92 , tee,  96 , valve  98 , conduit  100 , valve  102  and into the top of the first odorant tank  12 . Blanket gas flows through the valve  92 , the tee,  96 , the valve  104 , the conduit  106  and the valve  108  to the top of the second odorant tank  14 . Because blanket gas is relatively low in pressure, leaks in the odorant injection system seldom develop between the odorant tanks and the injection pumps. However, downstream of the odorant pumps, the odorant may reach pressures in the range of about 1400 psi. These relatively higher pressures, especially those in the odorant injection conduit  16  may cause leaks; it is therefore desirable to depressurize the odorant injection conduit  16  when not in use. 
         [0015]    Odorant  8  is pressurized in the first pump  70  and exits the first pump at the outlet  120  and passes through conduit  122 , a valve  124 , a conduit  126 , a tee  128 , a valve  78  and enters a flowmeter  132 . Likewise, odorant  8  is pressurized in the second pump  80  exits the second pump  80  at the outlet  134 , and passes through a conduit  136 , a valve  138 , the tee  158 , the valve  130  and enters the flowmeter  132 . 
         [0016]    Odorant  8  exits the flowmeter  132  through a flowmeter outlet  142  and passes through a valve  144 , a conduit  146 , a check valve  148 , a conduit  150 , a valve  152  and enters the odorant injection conduit  16 . 
         [0017]      FIG. 2  is a schematic of an odorant injection system with flow arrows indicating the depressurization of the system and venting of filtered vapors to atmosphere. The structure depicted in  FIG. 1  and  FIG. 2  is the same, but the flow of odorant through  FIG. 1  is the opposite of the flow through  FIG. 2  as indicated by the flow arrows in each respective figure. In  FIG. 1 , the odorant injection system  10  is pumping liquid odorant into the odorant injection conduit  16 . In  FIG. 2 , the odorant depressurization system  160  is depressurizing the odorant injection conduit  16  and venting filtered vapors to atmosphere. The odorant depressurization system  160  is composed generally of the bypass conduit  162 , the vapor filter  164 , and valves which will be described in detail below. 
         [0018]    During depressurization odorant flows from the odorant injection conduit  16  through the valve  152 , a conduit  167 , a valve  166 , the bypass conduit  162 , a valve  168 , and into a tee  169  where the flow splits and passes through the valve  22 , the conduit  20 , the valve  19 , the downcomer  18  and back into odorant tank  1 . Odorant from the tee  169  also passes through the valve  40 , the conduit  38 , the valve  30  and the downcomer  34  into the second odorant tank  14 . 
         [0019]    Vapors  6  from the first odorant tank  12  pass through the valve  102 , the conduit  100 , the valve  98 , a tee  178 , a valve  170 , a conduit  172  and into the vapor filter  164 , as indicated by the flow arrows. Vapors  6  from the second odorant tank  14  pass through the valve  108 , the conduit  106 , a valve  104 , the tee  178  and merge with the stream from the first odorant tank. The combined flow of vapors passes through the valve  170 , the conduit  172  and into the vapor filter  164 . Filter media, not shown, fills the inside of the vapor filter. Activated charcoal is a suitable filter media. Other types of filter media may be used or several types of media may be used in the vapor filter. After passing through the filter media, the filtered vapors  175  exit the vapor filter  164  at the exit port  174  as indicated by the flow arrow. The filtered vapors  175  have a lower concentration of odorant than those exiting the odorant tanks,  12  and  14 . 
       Operational Description of FIGS. 1 and 2 
       [0020]    Referring to  FIG. 1 , the purpose of the odorant injection system  10  is to inject odorant  8  from the tanks  12  and  14 , under pressure into the odorant injection conduit  16 . In  FIG. 1 , the following valves are in the open position during injection of odorant:  19 ,  22 ,  26 ,  30 ,  32 ,  48 ,  60 ,  68 ,  72 ,  92 ,  98 ,  102 ,  104 ,  108 ,  124 ,  130 ,  144 ,  152 . In  FIG. 1 , the following valves are in the closed position during injection of odorant:  166 ,  168 ,  170  and  176 . Odorant flows from the odorant tanks, the odorant filters, the odorant pumps, the odorant flowmeter to the odorant injection line as indicated by the by the flow arrows in  FIG. 1 . 
         [0021]    Referring to  FIG. 2 , the purpose of the depressurization system  160  is to depressurize the odorant injection line  16 , transfer unwanted odorant back into the odorant tanks  12  and  14  and vent purified vapors to atmosphere. In  FIG. 2 , the following valves are in the open position during the depressurization of the odorant injection system:  19 ,  22 ,  98 ,  102 ,  104 ,  108 ,  152 ,  166 ,  168 , and  170 . In  FIG. 2  the following valves are in the closed position:  26 ,  130 ,  144  and  176  as indicated by the by the flow arrows in  FIG. 1 . The odorant flows from the odorant injection line, through the bypass line to the odorant tanks, as indicated by the by the flow arrows in  FIG. 1 . Vapors leave the odorant tanks, pass through the filter and are vented to atmosphere as indicated by the flow arrows in  FIG. 1 . 
         [0022]    As an example, the present invention is capable of depressurizing a ¾ inch odorant injection line that is approximately 600 feet long from the odorant injection system cabinet, not shown, to the point of injection into the gas being offloaded from the LNG ship. A typical odorant tote may hold 250 gallons of odorant so the tote may weigh more than 1700 lbs. Heavy items like the odorant tote need to be lifted from sea level to the deck of the LNG tanker by an on-board crane. Two totes are often used in the odorant injection system. The deck of the LNG tanker is about 3 stories from sea level. The odorant injection system cabinet needs to be near the totes, which need to be near the crane. This location necessitates a long odorant injection line that is several hundred feet in length. The present invention can reduce the pressure in the odorant injection line from about 1400 psi to about zero psig. After depressurization, it takes some odorant systems about 15 to about 20 minutes to build up the necessary pressure in the aforementioned odorant injection line, before offloading can begin. Odorant is not put in LNG because it can crystallize. 
         [0023]    Odorant injection systems are often controlled by a programmable logic controller (PLC), personal computer (PC), flow computer or other automated means that is often housed in the odorant injection cabinet, as is well know to those skilled in the art. The PLC, PC, flow computer or other automated means controls the operation of the odorant injection pumps, valves and other necessary components to control the injection system. The PLC, PC, flow computer or other automated means may also be used to control the valves in the present invention. In the alternative, the present invention may be manually operated.