Abstract:
A tank mass measuring assembly ( 10 ) for monitoring an amount of a fluid ( 20 ) stored in a tank ( 12 ). The monitoring assembly includes a mass measurement chamber ( 42 ) adapted to be located remotely of a tank and adapted to be coupled in fluid communication with the tank to receive a portion of a fluid stored in the tank. The monitoring assembly further includes a sensor assembly ( 16 ) at least partially disposed in the mass measurement chamber, the sensor assembly adapted to measure a mass of the fluid disposed in the mass measurement chamber. The sensor assembly is adapted to relay the measured mass to a computation device ( 90 ) for determining the amount of the fluid in the tank based upon the measured mass of the fluid disposed in the mass measurement chamber.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to tank mass measurement assemblies, and more specifically, to tank mass measurement assemblies having a mass measurement chamber located externally of the tank.  
       BACKGROUND OF THE INVENTION  
       [0002]     Storage tanks for hydrocarbon products, a few suitable examples being LPG products such as butane and propane, present special problems for the installation of tank mass measuring assemblies. LPG storage tanks are classified as explosion hazards by the National Fire Protection Association (hereinafter “NFPA”), requiring special care in the design and installation of any ancillary equipment. The LPG Code (NFPA 58) defines the area within five feet of any tank, fill opening, or point where liquefied petroleum gas is dispensed, loaded, vented, or the like, as a Class I, Division 1, Group D hazard. Thus, special safeguards are in place, severely restricting the modification of a tank storing LPG products. The regulations surrounding the modification of a tank storing LPG products drastically increases the difficulty of installing a tank mass measuring assembly to the tank. This is especially true when components of the tank mass measuring assembly must be installed within the tank.  
         [0003]     For instance, in previously developed tank LPG gauges, such as the one illustrated and described in U.S. Pat. No. 6,662,643, the disclosure of which is hereby expressly incorporated by reference, require the pressure vessel portion of the tank to be penetrated during installation. More specifically, portions of the mass measuring sensor assembly must be installed within the tank. Installing the mass measuring sensor assembly within the tank requires the tank to be opened. Since the fluid is volatile and contained within the tank at a pressure above atmospheric pressure, the tank must be purged prior to opening of the tank.  
         [0004]     Further still, most tanks do not have an appropriate opening or openings able to accommodate the mounting and installation of the mass measuring sensor assembly within the tank. Thus, to accommodate the mounting of the mass measuring sensor assembly, an opening must be field welded upon the tank. The welding of the opening is an expensive operation, requiring a certified welder and the shutting down and purging of the tank for the work.  
         [0005]     Even if an opening is present on the tank able to accommodate the insertion of the mass measuring sensor assembly within the tank, the tank be must shut down and be purged during the installation procedure, adding great expense to the installation operation. Further, even if a suitable opening is present on the tank, the opening is virtually never located in the optimum location, i.e., equidistant from the ends of the tank to negate inaccuracies caused by the effects of “slope” when the tank is not oriented perfectly horizontal.  
         [0006]     Additionally, due to the complexity of inserting the mass measuring sensor assembly in the tank and the liability associated with modifying the tank, the installation of the tank mass measuring assembly requires highly trained individuals for proper installation further increasing the cost of installation.  
         [0007]     Further still, previously developed load cell type mass measuring sensor assemblies use a mass probe which is suspended in the tank. However, the mass probe may suffer in accuracy since the mass probe cannot extend in length the full height of the tank since a clearance space must be present at the bottom end of the mass probe to prevent interference between the bottom end of the mass probe and the tank bottom or debris accumulating thereon. Thus, the accuracy of the mass measuring sensor assembly suffers, especially when the fluid level in the tank is at a very low level.  
         [0008]     Therefore, there exists a need for a mass measuring sensor assembly and method of installation which permits the mass measuring sensor assembly to be installed without requiring the tank to be shutdown and purged, that may be installed without opening the tank to the atmosphere, that does not require the mass measuring sensor assembly to be installed equidistant between the ends of the tank for accurate results, and/or that can allow a mass probe having a length equal or greater than the height of the tank for improved accuracy.  
       SUMMARY OF THE INVENTION  
       [0009]     One embodiment of a tank mass measuring assembly formed in accordance with the present invention for monitoring an amount of a fluid stored in a tank is disclosed. The tank mass measuring assembly includes a mass measurement chamber adapted to be located remotely of a tank and adapted to be coupled in fluid communication with the tank to receive a portion of a fluid stored in the tank. The tank mass measuring assembly also includes a sensor assembly at least partially disposed in the mass measurement chamber. The sensor assembly is adapted to measure a mass of the fluid disposed in the mass measurement chamber. The sensor assembly is also adapted to relay the measured mass to a computation device for determining the amount of the fluid in the tank based upon the measured mass of the fluid disposed in the mass measurement chamber.  
         [0010]     An alternate embodiment of a tank mass measuring assembly formed in accordance with the present invention for monitoring an amount of a fluid stored in a tank is disclosed. The tank mass measuring assembly includes a tank having a fluid stored in the tank. The tank mass measuring assembly further includes an outlet passageway for permitting the fluid to exit the tank for use by a device requiring the fluid and an inlet passageway. The inlet passageway permits the fluid to be returned to the tank. The tank mass measuring assembly also includes a mass measurement chamber located externally of the tank and coupled in fluid communication with both the outlet and inlet passageways of the tank. The tank mass measuring assembly further includes a sensor assembly at least partially disposed in the mass measurement chamber. The sensor assembly is adapted to measure a mass of the fluid disposed in the mass measurement chamber and to relay the measured mass to a computation device for determining the amount of the fluid in the tank.  
         [0011]     One embodiment of a method performed in accordance with the present invention for installing a tank mass measuring assembly to a tank storing a pressurized fluid within the tank without purging the tank of the fluid is disclosed. The method includes closing an outlet valve on a fluid outlet line of the tank, closing an inlet valve on a fluid inlet line of the tank, and mounting a mass measurement chamber remotely of the tank. The method also includes coupling the mass measurement chamber in fluid communication with the fluid outlet downstream of the outlet valve and with the fluid inlet line upstream of the inlet valve. The method further includes installing a mass measuring sensor assembly at least partially within the mass measurement chamber for measuring a mass of the fluid in the mass measuring chamber and opening the inlet and outlet valves to permit fluid from the tank to freely enter and exit the mass measurement chamber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing aspects and many of the attendant advantages of this invention will become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0013]      FIG. 1  is an elevation view of one embodiment of a tank containing a fluid having a tank mass measuring assembly installed in accordance with the present invention;  
         [0014]      FIG. 2  is a cross-sectional view of the tank and tank mass measuring assembly of  FIG. 1  taken substantially through Section  2 - 2  of  FIG. 1 ;  
         [0015]      FIG. 3  is a partially exploded perspective view of an upper portion of a sensor assembly shown in  FIG. 1 ; and  
         [0016]      FIG. 4  is an elevation view of a mass probe shown in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Turning to  FIGS. 1 and 2 , one embodiment of a tank mass measuring assembly  10  formed in accordance with the present invention is shown. The tank mass measuring assembly  10  includes a tank  12  for storing a fluid  20 , a piping assembly  14 , and a sensor assembly  16 . The tank  12  of the illustrated embodiment includes a pressure vessel  18  able to store the fluid  20  at an elevated pressure, i.e., a pressure above atmospheric pressure. The tank  12  is preferably adapted for storing a liquefied hydrocarbon product, a few suitable examples being butane and propane, wherein the fluid  20  is stored within the tank  12  as a mixture of a liquid  22  and a vapor or gas  24 .  
         [0018]     The piping assembly  14  includes a liquid line  26  and a gas line  28 . The liquid line  26  couples the sensor assembly  16  in fluid communication with the tank  12  for permitting the transfer of the liquid  22  between the tank  12  and the remotely located sensor assembly  16 . Likewise, the gas line  28  couples the sensor assembly  16  in fluid communication the tank  12  for permitting the transfer of the gas  24  between the tank  12  and the remotely located sensor assembly  16 .  
         [0019]     The liquid line  26  and gas line  28  are coupled to a liquid outlet line  30  and a gas return line  32 . The liquid outlet line  30  is a section of pipe which penetrates the pressure vessel  18  of the tank  12 , terminating at a bottom of the tank  12 . The liquid outlet line  30  collects the liquid  22  in the tank and provides a passageway for the liquid  22  to be drawn out of the tank  12  as needed and used or manipulated by a device  33  requiring the liquid  22 , such as a transfer pump or other piece of machinery wherein the fluid  20  is combusted or used in some other process. The liquid line  30  also permits the fluid  20  to freely flow to and from the tank  12  to equalize the weights of the mass column in the remotely located sensor assembly  16 . An outlet valve  34  is disposed in the liquid outlet line  30 . The outlet valve  34  is adapted to be closed to impede flow of the liquid  22  through the outlet valve  34  and isolate the tank  12  or opened to permit a flow of the liquid through the outlet valve  34 . The liquid line  26  is coupled to the liquid outlet line  30  downstream of the outlet valve  34  such that the outlet valve  34  can be closed to isolate the tank  12  from the liquid line  26  during installation, removal, safety protection, or maintenance of the tank mass measuring assembly  10 .  
         [0020]     The gas return line  32  is a section of pipe which penetrates the pressure vessel  18  of the tank  12 , passing through a riser  36  vertically disposed within the tank  12 . In an alternative embodiment, the gas return line  32  may enter the tank  12  through topside piping when openings and valving are available. The riser  36  terminates near a top of the tank  12 , above a maximum liquid  22  level in the tank  12 . The gas return line  32  provides a passageway for unused fluid  20 , typically in a gaseous state, to be returned to the tank  12  as needed. An inlet valve  38  is disposed in the gas return line  32 . The inlet valve  38  is adapted to be closed to impede flow of the gas  24  past the inlet valve  38 , thereby isolating the tank  12 . The gas line  28  is coupled to the gas return line  32  upstream of the inlet valve  38  such that the inlet valve  38  can be closed to isolate the tank  12  from the gas line  28  during installation or maintenance of the tank mass measuring assembly  10 .  
         [0021]     Turning to  FIG. 2 , this detailed description will now focus upon the sensor assembly  16 . The sensor assembly  16  is a device for measuring a mass of a fluid  20  disposed in a mass measurement chamber  42  so that an amount (i.e., a level, a weight, and/or a volume) of the fluid  20  stored in the tank  12  can be determined. The sensor assembly  16  may measure the mass of the fluid disposed in the mass measurement chamber  42  in any number of ways, a few suitable examples being through ultrasonic, magnetostrictive, SONAR, and RADAR technologies. The sensor assembly  16  of the illustrated embodiment utilizes a float system for determining the mass of the fluid within the mass measurement chamber  42 , however it should be apparent to those skilled in the art that other methods for determining the mass of the fluid are within the spirit and scope of the present invention, including, but not limited to, those methods mentioned above.  
         [0022]     The mass measurement chamber  42  includes a riser pipe  44  having a top end and a bottom end. Coupled to the bottom end of the riser pipe  44  is a bottom cap  50 . Coupled to the bottom cap  50  is a piping connection  52  permitting the liquid line  26  to be coupled in fluid communication with the mass measurement chamber  42 . Coupled to the top end of the riser pipe  44  is a top cap  46 . Coupled to the top cap  46  is a piping connection  48  permitting the gas line  28  to be coupled in fluid communication with the mass measurement chamber  42 . Coupled to the top of the piping connection  48  is a control assembly  84  for calculating a mass or a volume of the contents of the tank  12  as will be described in more detail below. A conventional pressure-proof (and fire proof) electrical cable pass-through (not shown) passes axially through the piping connection  48  thereby permitting electrical signals to pass between the electronics located in the pressurized mass measurement chamber  42  and the control assembly  84 .  
         [0023]     Turning to  FIGS. 2 and 3 , a hanger bracket  54  is provided for suspending the in-tank elements of the apparatus. The sensor assembly  16  also includes a well-known circuit board  56  mounted on the hanger bracket  54 . The circuit board  56  is provided with a connector  58  for connecting the cable pass-through from the control assembly  84  in signal communication with the circuit board  56 . The circuit board  56  includes a first temperature sensor  60  for measuring the air temperature in the upper portion of the mass measurement chamber  42  and a pressure sensor  62  for measuring a pressure in the mass measurement chamber  42 . Although the first temperature sensor  60  and the pressure sensor  62  are illustrated and described as being present on the circuit board  56 , it should be apparent to those skilled in the art that they may be located in alternate locations without departing from the spirit and scope of the present invention.  
         [0024]     A universal joint assembly  64  is suspended below the hanger bracket  54 . The universal joint assembly  64  may be any suitable commercially available universal joint assembly, one suitable example being Part No. 64565K1 from McMaster-Carr Supply Company. One end of the universal joint assembly  64  is secured to the hanger bracket  54 . The other end of the universal joint assembly  64  is coupled to a sensor, which in the illustrated embodiment is a load cell  66 , of the sensor assembly  16  by a pivot pin  68 . Suspended from the load cell  66  by a clevis pin  70  is a mass probe  40 . The universal joint assembly  64  permits the mass probe  40  to hang vertically within the mass measurement chamber  42  even if the mass measurement chamber  42  is out of vertical plumb.  
         [0025]     The load cell  66  is able to measure the weight of the mass probe  40  when the mass probe  40  is suspended within a fluid contained in the mass measurement chamber  42 . In other words, the downward force applied by the mass probe  40  upon the load cell  66  is converted into an electrical signal proportional to the downward force applied. The downward force applied to the load cell  66  is in turn proportional to a buoyant force applied to the mass probe  40  by the mass of the fluid  20  present in the mass measurement chamber  42 . The electrical signal from the load cell  66  is sent to the circuit board  56  for processing.  
         [0026]     An additional benefit of the universal joint assembly  64  is that the load cell  66  is oriented horizontally. This eliminates the need for measurement and correction for any variation of the load cell  66  from the horizontal. Were the load cell  66  permitted to be oriented out of horizontal, its measurements of force would be reduced by the sine of the angle of deviation. The universal joint assembly  64  eliminates this source of error, and the necessity of compensation.  
         [0027]     Turning to  FIG. 4 , the mass probe  40  may be a hollow tubular aluminum extrusion having lightening passages, such as a vertically extending central passage  74  to lighten the mass probe  40  and increase its buoyancy. End covers  76  and  78  are secured to each end of the mass probe  40  to close the ends of the mass probe  40  while leaving the central passage  74  open to the liquid contents of the mass measurement chamber  42 .  
         [0028]     The sensor assembly  16  further includes a flexible temperature probe string  80 . The mass probe  40  houses the flexible temperature probe string  80  within the central passage  74  of the mass probe  40 . A plurality of temperature sensors  82  are spaced along the temperature probe string  80  for measuring the temperature of the liquid contents at spaced levels. In the preferred embodiment, the temperature sensors  82  are spaced so that they are suspended at approximately 5%, 35% and 65% of tank height levels within the tank  12 . Each temperature sensor  82  is coupled in signal communication with the circuit board. The temperature probe string  80  includes a connector  86  for coupling the temperature probe string  80  in signal communication with the circuit board via connector  88  on the circuit board  56  (see  FIG. 3 ).  
         [0029]     Referring to  FIGS. 2 and 4 , the data conveyed from the load cell  66 , pressure sensor  62 , temperature sensors  60  and  82 , and circuit board  56  is communicated externally of the pressure containing portion of the mass measurement chamber  42  to a microprocessor  90  of the control assembly  84 . The microprocessor  90  calculates the volume of contents in the tank from: (1) the apparent weight of the mass probe  40  as determined by the load cell  66 , compensated for air temperature surrounding the load cell  66  as measured by temperature sensor  60 ; (2) the liquid temperature data from temperature sensors  82 ; and (3) the specific gravity curve for the stored liquid  22 . The control assembly  84  also houses a radio frequency transmitter/receiver  92  which can transmit the data to a master computer. This eliminates the need for a power hook-up within the hazardous area of the tank, as the microprocessor and radio may be conveniently operated on safe battery power. Although the above illustrated and described embodiment is described as having the microprocessor  90  and control assembly  84  as coupled directly to the mass measurement chamber  42 , it should be apparent to those skilled in the art that microprocessor  90  and/or the control assembly may be located remotely of the mass measurement chamber  42  without departing from the spirit and scope of the present invention.  
         [0030]     Although the above described and illustrated embodiment measures the suspended weight of the mass probe, it should be apparent to those skilled in the art that the sensor assembly may determine the weight of the mass probe in any number of ways without departing from the spirit and scope of the present invention, a few suitable examples being by supporting the mass probe by a well known load cell or pressure sensor placed underneath the mass probe to determine the weight of the mass probe or measuring the amount in which the mass probe displaces a biasing member, such as a spring, that either supports or suspends the mass probe within the fluid contained in the mass measurement chamber.  
         [0031]     Further still, although the sensor assembly is illustrated and described as utilizing a single mass probe, it should be apparent to those skilled in the art that the sensor assembly may utilize two or more mass probes for determining the mass of the fluid disposed in the mass measurement chamber. One suitable example of a multiple probe configuration suitable for use with and that is within the spirit and scope of the present invention is disclosed in U.S. Pat. No. 5,157,968, the disclosure of which is hereby expressly incorporated by reference.  
         [0032]     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.