Abstract:
When odorant injection systems are inactive, they may accumulate unwanted vapors in the pump mechanism and associated tubing. In order to restart the odorant injection system, it is best to purge the unwanted vapors from the odorant pumps. The present pump purge system facilitates purging of unwanted vapors from odorant injection systems in an environmentally friendly fashion. The pump purge system purifies these vapors before they are vented to atmosphere. In addition, the pump purge system accumulates liquid odorant which is a byproduct of the purging process and stores it in a tank to reduce the likelihood of improper disposal. As an option, the pump purge system may also include a liquid odorant recapture system. The liquid odorant recapture system uses high pressure gas to return accumulated liquid odorant to the odorant injection system to be reused. This liquid odorant recovery system ensures environmentally responsible behavior.

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 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 6,208,913 which are owned by Y-Z Industries, Inc. Modern odorant injection systems are often controlled by a programmable logic controller (PLC), a personal computer (PC), a flow computer or some combination thereof. These automatic odorant injection systems often have audit features to confirm and document the odorant injection process. 
         [0002]    Those skilled in the art know that unwanted odorant vapors are sometimes vented to atmosphere without any filtration and that liquid odorant is sometimes disposed of using improper techniques. There is a need for an improved apparatus to deal with odorant vapors and to encourage proper disposal and/or reuse of odorant. 
       SUMMARY OF THE INVENTION 
       [0003]    The pump purge apparatus of the present invention is an environmentally friendly way to purify unwanted odorant vapors and encourage proper disposal or reuse of liquid odorant. If an odorant pump has been shut off it tends to accumulate unwanted odorant vapor in the pump mechanism instead of liquid odorant. The odorant pump may not function properly until the pump mechanism is full of liquid odorant. Prior to restarting odorant pumps, it is desirable to bleed off any unwanted odorant vapor from the pump mechanism and refill the pump with liquid odorant. 
         [0004]    In the present invention, liquid odorant is stored in a primary odorant storage container or tank, sometimes called an odorant tote, under about 25 psi of nitrogen blanket pressure. The tote may be a large metal container holding 50 gallons or more of liquid odorant. When empty, these totes are returned to the odorant supplier to be refilled. The odorant pumps are used to increase the pressure of the liquid odorant to several hundred psi or even more than a 1000 psi. But before restarting an odorant pump, it should be purged of any unwanted odorant vapor. 
         [0005]    To accomplish the purge, a downstream valve on each of the pumps is opened to direct the pump output into a downstream sight glass instead of an odorant injection conduit. To make it easier to see the clear odorant, some visual indicator may be added to the sight glass, such as a plurality of balls or a spinner wheel. When liquid odorant comes into contact with the visual indicator, the operator is given a visual confirmation that the pump mechanism has been refilled with liquid odorant because the sight glass is downstream of the odorant pumps. The valves are then actuated to redirect the pump output to the odorant injection conduit. The odorant injection system may then be restarted to odorize unscented natural gas and/or gasified LNG. 
         [0006]    When unwanted odorant vapor is passing through the sight glass with a visual indicator, the unwanted vapor does not turn the spinner wheel. If the visual indicator is a plurality of balls, the balls are stationary when unwanted vapor is passing through the sight glass. The unwanted odorant vapor then flows into the odorant accumulator bleed down tank. The unwanted odorant vapor then flows to a odorant exhaust filter which may be as large as a 55 gallon drum. The odorant exhaust filter is filled with filter media, such as activated charcoal which must be periodically replaced when it becomes contaminated. The odorant exhaust filter reduces the concentration of odorant in the unwanted vapors and the purified vapor is then vented to atmosphere. 
         [0007]    Over a period of time, the odorant accumulator bleed down tank may fill up with liquid odorant that accumulates as a result of the purging process. The odorant accumulator bleed down tank could be manually removed and replaced with an empty tank when it becomes full of odorant. In the alternative, the pump purge system could further include a liquid odorant recovery system. The liquid odorant recapture system includes a high pressure gas cylinder connected to the odorant accumulator bleed down tank. Valves and other conduits may be opened to allow high pressure nitrogen or some other inert gas into the odorant accumulator bleed down tank. The nitrogen is at about 2,200 psi. A regulator, not shown, is on the outlet of the high pressure gas cylinder. The outlet pressure of this regulator needs to be set to about 20 psi above the blanket pressure in the liquid odorant tank  12 . The pressurized nitrogen forces the liquid odorant out of the odorant accumulator bleed down tank and back into the primary odorant storage container for reuse. 
         [0008]    The odorant injection system, pump purge system and/or liquid odorant recapture system may be manually operated. Or in the alternative, the odorant injection system, pump purge system and/or liquid odorant recovery system may be operated by a PLC, a PC, a flow computer or any other electronic means. The odorant injection system, pump purge system and liquid odorant injection system may each have their own stand alone control system or there may be an integrated control system for any combination of these systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic of the pump purge system with flow arrows indicating the flow of odorant and unwanted vapors. 
           [0010]      FIG. 2  is a schematic of the odorant injection system injecting liquid odorant into the odorant injection conduits as indicated by the flow arrows. 
           [0011]      FIG. 3  is a schematic of the liquid odorant recapture system with flow arrows indicating the flow of liquid odorant from the odorant accumulator bleed down tank back into the odorant tank. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  is a schematic of the environmentally friendly pump purge system  8  with flow arrows indicating the flow of liquid odorant and unwanted vapors. Liquid odorant  10  is held in the primary odorant storage container or tank  12 . Odorant flows from the container  12  through a downcomer,  13 , a conduit  14 , a tee  15 , a valve  16 , a conduit  17 , an odorant pump  18 , a conduit  20 , a valve  22 , a tee  24  to a sight glass  26 . As an option, the sight glass may have a visual indicator, such as balls or a spinner wheel. Odorant also flows from the tank through the tee  15 , a valve  32 , a conduit  34  a second odorant pump  36 , a conduit  38 , a valve  40 , the tee  24  to the sight glass  26 . 
         [0013]    Unwanted vapors  51  and/or liquid odorant  10  exit the sight glass through the conduit  42  and pass through a valve  44 , a conduit  46 , and enter the odorant accumulator blow down tank  50 . Unwanted odorant vapors  51  exit the odorant accumulator bleed down tank via a conduit  52  and pass through a valve  54 , a conduit  56  into the odorant exhaust filter  58 . The odorant filter  58  is filled with at least one replaceable filter element, not shown, such as activated charcoal. The at least one filter element is changed periodically when it is contaminated by odorant. 
         [0014]    The concentration of odorant in the unwanted vapors  51  is reduced in the odorant exhaust filter and purified vapors  66  exit the filter via a conduit  60  and pass through a valve  62  before being vented to atmosphere via a conduit  64 , as indicated by the flow arrow. 
         [0015]      FIG. 2  is a schematic of the odorant injection system  78  injecting liquid odorant  10  into odorant injection conduits  80  and  82  as indicated by the flow arrows. In this figure, each pump mechanism has been filled with liquid odorant  10  from the tank  12  and valves  22  and  40  have been turned from the on to the off position. As odorant pump  18  continues to operate, liquid odorant flows from the tank  12  as indicated by the flow arrow and exits the pump into the odorant injection conduit  80  to odorize unscented natural gas or gasified LNG. As odorant pump  36  continues to operate, liquid odorant  10  exits the tank, as indicated by the flow arrow, and flows into the odorant injection conduit  82  to odorize unscented natural gas or gasified LNG. Those skilled in the art know that an odorant injection system can have multiple odorant injection conduits as shown in this figure, or both pumps may be injecting into a single odorant injection conduit, not shown. 
         [0016]      FIG. 3  is a schematic of the liquid odorant recapture system  88  with flow arrows in the opposite direction indicating the flow of liquid odorant from the odorant accumulator bleed down tank  50  back into the odorant tank  12 . In  FIG. 3 , the liquid odorant has reached a high level indicated by the line  104  in the odorant accumulator bleed down tank  50  which means tank  50  should be removed and replaced with an empty tank or in the alternative, it needs to be blown down to empty the liquid odorant back into the odorant tank  12  to be reused. In  FIG. 1 , the liquid odorant was at a relatively low level indicated by the line  102 . In  FIG. 3 , the amount of the liquid odorant has increased in the tank  50  and has risen to the line  104 . Over time liquid odorant accumulates in the tank  50  because each purge cycle allows a little liquid odorant to flow through the sight glass. This liquid odorant from each purge cycle accumulates in the tank  50 . 
         [0017]    In  FIG. 3 , valves  96  and  108  are in the open position. Valves  44  and  54  are in the closed position. Nitrogen gas  92  is stored in the high pressure nitrogen gas cylinder  90 . The pressure in the nitrogen gas cylinder is about 2,200 psi. A regulator, not shown, is connected to the outlet of the gas cylinder. The downstream side of the regulator may be set to about 20 psi above the blanket pressure in the liquid odorant container  12 . The nitrogen gas passes from the nitrogen gas cylinder  90 , the regulator, not shown, through a conduit  94 , the valve  96 , a conduit  98  and into the top of the odorant accumulator bleed down tank  50 . As the nitrogen gas enters the odorant accumulator bleed down tank  60 , the liquid odorant  10 , is forced out of the tank  50  into the downcomer  110 , the by-pass conduit  112  through the valve  108 , the conduit  114  and the downcomer  13  into the primary odorant storage container  12 . In this manner, the accumulation of liquid odorant  10  can be substantially reduced in the odorant accumulator bleed down tank  50 . The nitrogen gas pressure must exceed the blanket pressure in the primary odorant storage container  12  by about 20 psi in order to force the liquid odorant from tank  50  back into container  12 . 
       Method of Operation 
       [0018]    In  FIG. 2 , an odorant injection system is generally identified by the numeral  78 . The odorant injection system may be manually operated or it may have its own control system which may include a PLC, not shown, a PC, not shown, a flow computer, not shown, and combinations thereof. In the alternative, a single control system may operate both the odorant injection system  78 , the pump purge system  8  and/or the liquid odorant recapture system  88 . 
         [0019]    The odorant injection system will typically include at least one primary liquid odorant storage container  12  in fluid communication with at least one odorant pump  18  which is in fluid communication with an odorant injection conduit  80  and a plurality of valves and other conduits. As is well known to those skilled in the art, the liquid odorant is pumped from the primary odorant storage container, through the odorant pump into the odorant injection conduit to add a stinky smell to unscented natural gas or gasified LNG. From time to time, the odorant injection system will be turned off and the odorant pump will temporarily stop operating. 
         [0020]    Depending on the amount of time the system is off and other factors, unwanted vapor may accumulate in the pump mechanism and/or the associated conduits. When it is time to restart the odorant injection system, it is best to purge the pump mechanism and associated conduits of the unwanted vapors. 
         [0021]    Referring now to  FIG. 1 , the pump purge system  8  is generally identified by the numeral  8 . The pump purge system may be manually operated. In the alternative, the pump purge system  8  may have its own automated control system or be integrated with the odorant injection system  78  and/or the liquid odorant recapture system  88 . These control systems may include a PLC, a PC, a flow computer and combinations thereof, not shown. 
         [0022]    The purpose of the pump purge system  8  is to remove the unwanted vapors from the odorant injection system  78  and to fill the pump mechanism and associated conduits with liquid odorant, prior to restarting the odorant injection system  78 . The pump purge system typically includes at least one sight glass, at least one odorant accumulator bleed down tank, at least one odorant exhaust filter and a plurality of valves and conduits. 
         [0023]    When the pump purge system is actuated, the odorant injection lines  80  and  82  are closed, the odorant injection pumps are turned on so the unwanted vapors are captured, purified and vented to atmosphere. The pump purge system works as follows. The valves directing the unwanted vapors to the odorant exhaust filter are opened and the valves to the odorant injection lines  80  and  82  are closed. Then the at least one odorant pump  18  is turned on. The operator then looks at the sight glass  26  to determine when liquid odorant from the odorant tank  12  is passing through the sight glass. Because odorant is a clear liquid, it is helpful, though not required to have some visual indicator in the sight glass to make it easier to tell when liquid odorant is passing through the sight glass. Various types of visual indicators are known to those skilled in the art, including a plurality of balls, a spinner wheel or other apparatus. The unwanted vapors pass through the sight glass into the odorant accumulator bleed down tank  50  and through the odorant exhaust filter  58  which reduces the concentration of odorant in the unwanted vapor before it is vented to atmosphere. 
         [0024]    Some liquid odorant may also pass into the odorant accumulator bleed down tank  50  during each cycle of the pump purge system. For example, the line  102  in  FIG. 1  indicates a low level of liquid odorant in the tank  50 . Over time, the amount of liquid odorant will increase in the tank  50  as indicated by the line  104  in  FIG. 3 . When the tank  50  has accumulated a sufficient amount of liquid odorant, it may be simply replaced with an empty tank or it may be blown down with nitrogen or some other inert gas. 
         [0025]    Referring now to  FIG. 3 , the liquid odorant recapture system  88  is environmentally responsible because it encourages reuse of liquid odorant instead of disposal, which sometimes leads to inappropriate behavior. The liquid odorant recapture system may use nitrogen gas or any other inert gas that is approved for use in explosive environments. The liquid odorant recapture system  88  includes a high pressure gas cylinder  90  and associated valves and conduits to control the system and direct the flow of the gas to the top of the odorant accumulator bleed down tank  50 . 
         [0026]    Assuming the tank  50  is about full of liquid odorant as indicated by the line  104 , nitrogen gas from the nitrogen cylinder  90  may be fed into the top of the tank  50  as shown by the flow arrows in  FIG. 3 . This gas forces the liquid odorant through a downcomer  110 , a by-pass conduit  112 , through a valve  108 , through the downcomer  48  and back into the at least one primary odorant storage container  12 . This nitrogen recapture system  88  prevents spillage and ensures environmentally responsible behavior.