Abstract:
A nuclear density gauge has an elongated transmission chamber adjacent to an elongated source chamber so that they can both be installed through a single nozzle on a high pressure vessel, making an airtight seal with the nozzle. The shape and position of the source chamber allows the positioning of a radiant energy source inside the vessel, a distance from one end of the transmission chamber. The radiation emitted by the radiant energy source travels through contents of the high pressure vessel and then through the elongated transmission chamber to a detector. The method of use of the gauge or multiple gauges, and the adaptation of vessels for such gauges, are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is a Continuation-in-part of application Ser. No. 12/242,177 filed on Sep. 30, 2008, the entirety of which is hereby incorporated by reference in this application as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The current invention relates to measuring properties of the contents in a vessel, more specifically with a nuclear density gauge. 
       BACKGROUND OF THE INVENTION 
       [0003]    Nuclear density gauges are often used to measure liquids (the term liquid, when used in this application for patent, includes slurries) in a vessel at places such as oil refineries. As illustrated in prior art  FIG. 1 , a nuclear density gauge  10 P has two parts that are separated with the liquid to be measured located between them. The first part is a sealed source of radiation  14 P, commonly referred to as a “source.” The second part is a detector  16 P, for example, a scintillation detector. When radiation leaves the source, the amount reaching the detector aligned with the source decreases as the distance between them increases, even if there is only a vacuum between them. When passing through a liquid  18 P in a vessel  20 P, the mass of the liquid absorbs some of the radiation. In addition to the liquid, if the source, the detector, or both, are located outside the vessel, the radiation must also pass through at least one of the vessel walls  22 P. Since the absorption of the radiation by the walls  22 P is constant, and the distance between a source  14 P and a detector  12 P is constant, the amount of radiation reaching the detector is indicative of the density of the liquid  18 P it passes through. As the density of the liquid changes, the amount of radiation reaching the detector changes. The greater the density of the liquid, the less radiation reaches the detector. The detector typically provides density measurement in the form of a current output. 
         [0004]    It should also be noted, that to keep a detector cool, and make it easier to maintain, detectors  12 P are almost always located outside the vessel  20 P. The source  14 P, however, is durably packaged, and may be placed inside the vessel to be operated in extremes of pressure and temperature safely, using insertion tubes. 
         [0005]    In installations where the vessel walls  22 P are thin, and the distances across the vessel  20 P are small, for example less than two to three feet, a source  14 P can be on one side of the vessel, and the detector on the other side as schematically shown in prior art  FIG. 1 . Such an arrangement is also often used to measure density inside a pipe. Then radiation passes through a first vessel wall, the entire length of liquid, and a second vessel wall before reaching the detector. This works best when the vessel walls are thin and the path through the liquid is short. For liquid density measurements, for example, this arrangement is typically used when the path through the liquid is not greater than two or three feet. For thick walls or long paths, more radiation is absorbed, decreasing measurement sensitivity. Larger sources may be used, but compensating with ever larger sources of radiation becomes impractical. 
         [0006]    For larger vessel sizes or greater wall thicknesses, there are ways to decrease the material that must be penetrated. For larger vessels or thicker walls, what is known as an “internal solution” can be used as shown in prior art  FIG. 2 . An internal solution entails placing the source  14 P inside the vessel, and the detector  16 P, outside the vessel. This decreases the distance of liquid  18 P the radiation passes through, and decreases the number of vessel walls  22 P from two to one. 
         [0007]    There are also limits on the size of vessel for which the configuration of  FIG. 2  is a desired solution. Distance, steel thickness, and liquid density all play a role. A general rule is that 4 inches of water, and ½ inch of steel, have about the same affect on the radiation. However, liquids being measured are not usually only water. As a general rule, if a distance is greater than 2 feet, or steel thickness greater than 2 inches, configurations other than  FIG. 1  or  FIG. 2  are necessary. 
         [0008]    Another internal solution is schematically illustrated in prior art  FIG. 3 . In this Figure, the vessel wall  22 P is thick. At the top of the figure, the wall is locally thinned at  24 P. One way of doing this is to drill a hole  26 P starting at the exterior, but stopping before reaching the interior. This hole  26 P is often called a “detector well” in the industry. The area around the hole  26 P is reinforced (not shown) as necessary, for example by welding on additional metal plating. A source  14 P is placed in line with the detector. This is done by drilling a hole  28 P through the vessel wall and welding in place a nozzle that can accept a sealed tube  30 P that can contain the source. The area around the hole  28 P is reinforced (not shown) as necessary, for example by welding on additional metal plating. This sealed tube  30 P is known as a “source well” and is often referred to as a “dry well.” Radiation leaving this source will pass through liquid near the vessel wall and a thin wall  24 P to reach the detector. 
         [0009]    Another type of detector well  32 P is shown in  FIG. 3  at the left side of the figure. This detector well fully penetrates the vessel wall through a nozzle with a welded in place sealed tube positioned interior to a detector. Another source well  29 P is used to place a source in line with the detector well  32 P. Radiation leaving this source will pass through a liquid path close to the center of the vessel, through a relatively thin well wall  33 P, through a distance of air  34 P, and reach the detector. 
         [0010]    The prior art of  FIGS. 1 ,  2 , and  3  all have disadvantages, some of which are explained in the following: 
         [0011]    As already stated, the configuration of  FIG. 1  is limited to smaller vessels and thinner vessel walls. 
         [0012]    In  FIG. 2 , alignment of the sources with the detectors can be difficult to achieve and maintain. It also does not accommodate thick walls. In addition, as vessel pressure and temperature change the vessel expands and the relative position of the sources and detectors changes. Large vessels intended for high pressure and high temperature operation may change length as much as 10 inches when going from ambient to operating conditions. Further, the source well inside the tank is subject to buffeting that may move its location relative to the detector. The detector, mounted outside the tank, may be inadvertently moved relative to the source. In short, the detector and the source are not coupled to one another, and therefore they are subject to different conditions that can move them out of alignment, creating significant measurement errors. 
         [0013]    In  FIG. 3 , the internal solutions, each of which require two holes in the vessel, are undesirable for at least three reasons. First, especially when dealing with high temperatures and pressures, it is preferred that vessel walls not be modified and be left in their full un-cut state, to maintain maximum integrity, without the addition of reinforcements. Second, drilling two precisely aligned holes, for example  26 P and  28 P, through a thick wall is very difficult. Even if aligned correctly at the start of the drilling, the drill can deflect off course while passing through thick metal. And third, even if the source and detector have a known geometric relationship to one another in a cool vessel, this can change as the temperature and pressure in the vessel changes. This may be further exasperated by the reinforcements placed around the holes that may cause non-uniform metal expansion, and thwart attempts to predict movement. 
         [0014]    The need for higher temperature and pressure vessels, and their thick walls, is increasing for a variety of reasons, including processes developed by the refining industry for upgrading heavy-oils. An example of this process is EST (Eni Slurry Technology) being developed by Eni corporation of Italy, as at least partly described in US Published Patent application 2006/0163115. Another example is VRSH (Vacuum Resid Slurry Hydrocracking) developed by Chevron Corporation, as partly described in U.S. Pat. Nos. 7,238,273 and 7,214,309. 
         [0015]    Thus, there exists the need for a nuclear density gauge configuration for more accurately and easily measuring the density of a liquid in a thick walled vessel at high temperature and pressures. Such a gauge also has advantages in less severe applications. 
       SUMMARY OF THE INVENTION 
       [0016]    In a first embodiment, a contents measuring gauge has an elongated transmission chamber adjacent to an elongated source chamber so that they can both be installed through a single nozzle on a high pressure vessel, making an airtight seal with the nozzle. The shape and position of the source chamber allows the positioning of a radiant energy source inside the vessel, a distance from one end of the transmission chamber. The radiation emitted by the radiant energy source travels through contents of the high pressure vessel and then through the elongated transmission chamber to a detector. 
         [0017]    A second embodiment is a system of gauges of the first embodiment installed in an array of locations varying in longitudinal location, angular location, and radial depth, to determine homogeneity of the contents of the vessel. 
         [0018]    A third embodiment is a vessel adapted for single-hole measurement of content density. The vessel has a wall, at least one nozzle in the wall having an elongated transmission chamber and an adjacent elongated source chamber. The elongated source chamber is configured to position a radiant energy source a distance from a one end of the elongated transmission chamber inside the high pressure vessel. The radiation emitted by the radiant energy source travels through contents of the high pressure vessel and then through the elongated transmission chamber to a detector. 
         [0019]    A fourth embodiment is a method of measuring a property of contents in a vessel at a particular location in the vessel. In the method, a gauge is installed through an opening of the vessel so that an airtight seal is made. A radiation source is within a portion of the gauge inside the vessel so that the radiation source is in alignment with a transmission chamber of the gauge. The transmission chamber has one end adjacent the contents at the particular location and a second end outside the vessel. The radiation source emits radiation through the contents at the particular location and into the transmission chamber. The emitted radiation that reaches the second end of the transmission chamber is measured, and a signal is created indicative of the property of the contents. 
         [0020]    A fifth embodiment is a method for measuring inside of thick tanks having walls that would substantially completely absorb a radiant energy signal of a particular strength radiant energy source. The method includes installing a nuclear density gauge through a single hole in the wall. 
         [0021]    In each of the noted embodiments, a reflector may be aligned relative to the source and transmission chamber to redirect radiant energy from the source into the transmission chamber after reflection from the reflector. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0022]      FIG. 1  is a schematic illustration of the prior art for smaller thin walled vessels. 
           [0023]      FIG. 2  is a schematic illustration of the prior art for larger thin walled vessels. 
           [0024]      FIG. 3  is a schematic illustration of the prior art for thick walled vessels. It is a cross-section through a cylindrical vessel, although it could also be representative of a spherical vessel. 
           [0025]      FIGS. 4 and 4A  are a schematic illustration of an embodiment of the current invention for comparison to  FIGS. 1 ,  2 , and  3 . 
           [0026]      FIG. 5  schematically illustrates an embodiment of the current invention installed in a filled vessel. 
           [0027]      FIG. 6  is an enlarged view of an embodiment in  FIG. 5 , in partial cross-section, with a radiation path illustrated. 
           [0028]      FIG. 6A  is an exploded cross-section view as indicated in  FIG. 6 . 
           [0029]      FIGS. 7 ,  8 , and  9  are an overview of loading a source into the embodiment of  FIG. 5 . 
           [0030]      FIGS. 10 and 11  are schematic illustrations of an embodiment of the current invention used to determine level. 
           [0031]      FIG. 12  is another embodiment of the current invention. 
           [0032]      FIG. 13  is another embodiment of the current invention. 
           [0033]      FIG. 14  is another embodiment of the current invention. 
           [0034]      FIG. 5  is another embodiment of the current invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    With reference to  FIGS. 4 and 4A , a vessel  10  containing a liquid  12  has a plurality of content gauges each installed through a single hole  14 . In this embodiment, the content gauges are nuclear density gauges  16 , but the single-hole concepts of the current invention may also be used for other gauges. Each nuclear density gauge  16  has a source  18  located at a smaller end  20  inside the vessel, and a detector  22  at a larger end  24  outside the vessel. Alternatively, the detector may be installed at a position inside the boundaries of the vessel  10  if the temperature is suitable, but positioning it outside makes it more accessible for maintenance and cooling. Gauges  16  are installed at various heights and angular locations corresponding to desired density readings of the liquid  12  at particular locations in the vessel  10 . There are two different length gauges illustrated. This will be further explained with reference to other figures. 
         [0036]    In  FIG. 5 , a vessel wall  26  has a nozzle  28  comprising a cylindrical nozzle body  30  and a nozzle flange  32 . The nozzle body  30  is welded to the vessel wall  26 , usually by the vessel manufacturer. Outside the vessel wall  26  is a layer of insulation  34 . Inside the vessel wall is the liquid  12 . In the example of the EST process, for which this gauge  16  is well suited, the contents are a liquid or slurry that may be at high temperature 420° C. (788° F.) and pressure 165 bar (2392 lbs/in2). One vessel for this process is approximately 150 ft. tall, 16 ft. in diameter and has 12″ thick steel walls. These parameters preclude the use of conventional instruments including conventional nuclear density gauges as described in prior art  FIGS. 1 and 2 . 
         [0037]    A gauge  36  is longer and extends nearer the center of the vessel than does a gauge  38 . Gauge  36  measures an inner measurement zone  40 , and gauge  38  measures an outer measurement zone  42 . Zone  44 , Zone  46 , and Zone  48  do not get directly measured, although with a greater number of gauges, or with gauges of different lengths, they could be measured. That is an advantageously flexible aspect of this invention. By installing longer or shorter gauges, different zones can be measured. Differently drilled pairs of holes, as needed in prior art  FIG. 3 , are not required to change the zone of liquid  12  that is being measured, or to redefine the size or quantities of measurement zones. The lengths of the gauges define concentric rings, for example  40  and  42 , labeled in  FIG. 5 . This will be understood in more detail from the description that follows of gauge  38  with reference to  FIG. 6 . In addition, angular locations as depicted in  FIG. 4 , and height location as depicted in  FIG. 4A , further pinpoint the area of liquid measured by a particular gauge. The locations of  FIGS. 4 and 4A  are representative only, of the ability to measure any location in a vessel that a nozzle is aligned with. By this method, the discreet data can be used to develop a map of the measurements, averages, etc. 
         [0038]    As seen in  FIG. 6 , gauge  38  has a transmission chamber  50  comprising a transmission wall  52 , a transmission outer tube  54 , and an end cap  56  secured to the transmission tube  54  by a weld  58 . Adjacent the transmission chamber is a source chamber  60  comprising a source tube  62  and an end cap  64  secured to the source tube by a weld  66 . Although welded end caps are used for both the transmission tube  54  and the source tube  62 , other variations that make a strong sealed tube may be used. Inside the source chamber  60  is a source cable  68 , a source carrier  70  comprised of a source shielding rod  72  made of tungsten, a source spacer  74 , a source  76  that produces gamma rays in all directions, and a guide nose  78 . As seen in  FIG. 6 , the source tube is not along the center axis of the transmission tube, but is instead to one side (the top, as drawn.) Further, the source tube  62  is straight both inside the transmission chamber  50  and immediately outside the transmission chamber  50  for a considerable distance, but has a radius  80  to align the source  76  over an empty part  82  of the transmission chamber  50 . This geometry creates a radiation path  84  comprising three components. Two of these components: a tip path  86 , and a chamber path  88 , are unaffected by changes in the liquid  12 . The third, a process path  90 , is affected by changes in the liquid  12 , specifically in the outer measurement zone  42 . This will be further explained. 
         [0039]    The tip path  86  extends from the source  76  in a straight line toward the detector  22 , ending outside the wall of the source tube  62  at a point  92 . Note that the tip path  86  would be longer if the radius  80  were greater (a larger value), and this difference would mean that the radiation would pass through a longer distance of metal in the wall of the source tube  62 . When designing and manufacturing a gauge, this longer distance of metal could lead to a calculated need for a greater source  76  size (strength). If the radius  80  changes during tank heating and cooling, the radius  80  change can lead to erroneous measurements. Therefore, the source tube  62  has a stable and constant radius  80  so that the absorption of gamma rays in the tip path  86  remains constant. 
         [0040]    The process path  90  extends from point  92  to the transmission wall  52 , and defines the outer measurement zone  42 . The absorption of gamma rays along the process path  90  varies with the density of the liquid  12 . The measured absorption averages any localized density difference along the process path  90 . For this reason, a gauge having a longer process path  90  may measure a different average than one having a shorter process path. The length and location of the process path, and therefore the measurement zone  42 , is chosen to match customer needs. The length of the process path may be changed by changing the length of the straight portion of source tube  62 . Because the process path  90  is a function of the gauge construction and is not dependent upon vessel dimensions and successful mounting on the vessel, the gauges of the current invention may be calibrated without being installed in the vessel. 
         [0041]    The chamber path  88  includes the metal of the transmission wall  52  and the air in the empty part  82  of the transmission chamber  50 , as well as any intersected metal used to mount and protect the detector  22 . To minimize the size of the needed source  76 , the metal intersected by the chamber path  88  is kept to a minimum, however the transmission wall  52  must be thick enough to withstand the pressure within the vessel  10 . Further, since radiation intensity decreases with distance, the longer the chamber path, the greater the calculated source required, even if the radiation is passing through a vacuum. 
         [0042]    As seen in  FIG. 6 , a primary flange  94  is welded to the transmission tube  54 , and fastened to the nozzle flange  32  in an appropriately strong and sealing arrangement. This connection seals the vessel  10 . The high pressure liquid  12  is free to move into a gap  96  between an outside  98  of the transmission tube  54  and an inside  100  of the nozzle tube  30 , but is stopped by the primary flange  94 . 
         [0043]    Referring to  FIGS. 6 and 6A , the transmission tube  54  has a secondary flange  102  that is thinner than the primary flange  94  and does not need to withstand pressure. Secondary flange  102  aligns the detector, as well as devices used to install and remove the source  76  from the source chamber  60 . As such, the secondary flange  102  has two alignment pins  104  and bolt holes (not shown) for mounting the detector  22 . A water-jacket housing  106  cools the detector  22 . 
         [0044]      FIGS. 7 ,  8 , and  9  illustrate the general process of loading the source  76  into the source chamber  60 . It is not the intent here to fully describe the safe storage and insertion of the radioactive source  76 . Systems such as a source housing  108  already exist to shield and transport the source carrier  70  until it is placed in its working position away from personnel. The presentation of these figures merely serve to show that the radius  80  does not prevent source carrier  70  insertion. In  FIG. 7 , a gauge  36  or  38  is represented schematically, as it would be when it is installed in the nozzle  28 , but not yet loaded with the source carrier  70 . A locking screw  110  is prevented from opening by a padlock  112 . In  FIG. 8 , the padlock  112  is removed and the locking screw  110  released so that the detector  22  and its housing  106  may be rotated away from a stationary plate  114 . In  FIG. 9 , the source housing  108  has been installed for the purpose of inserting the source carrier  70  to the bottom of the source chamber  60  by pushing it with the source cable  68 . After this operation, the source housing  108  is removed but the source cable  68  and source carrier  70  remain, ensuring that the source  76  is kept in its fully inserted position. The gauge  36 ,  38  is then operational, as shown in  FIG. 6 . 
         [0045]      FIGS. 10 and 11  illustrate a method of using a gauge  200  to measure level. In previous figures, the process path  90  was fully submerged in the liquid  12 , therefore any change in measurement indicated a change in the average density of the liquid  12  in the process path. By positioning the gauge  200  so that its process path includes a boundary  208  between liquid  204  and vapor  206  (or air), the gauge can be used to measure a level as in  FIG. 11 , or an absence of liquid as in  FIG. 10 . Either of these measurements can be taken by a gauge installed from either a bottom or a top of the vessel. Similarly, a side nozzle  28  could be used, if that side nozzle were in the vessel angled upwardly or downwardly. 
         [0046]      FIG. 12  illustrates another embodiment of a gauge  300 , to a level of detail showing differences to gauges  36 ,  38 . In this embodiment, the portion of the source chamber  60  inside the transmission chamber  50  is eliminated, as seen at  302 . This embodiment may be used with alternative methods of installing sources. For example, the entire gauge  302  may be removed from the vessel  10  and manipulated vertically to get the source  76  in and out of the source chamber  60  by using gravity. 
         [0047]      FIG. 13  illustrates an embodiment  400  of the invention in which a transmission chamber  402  and a source chamber  404  are made part of a nozzle  406  of the vessel  10 . This eliminates the need for the nozzle flange  32  and primary flange  94  to contain the pressure of the vessel  10 , and reduces material costs. An area  408  at an end cap  410  is shown right angled, rather than with a radius  80 . This is for the purpose of illustrating that the concept of this invention, having a single-hole gauge, is not limited to a radiused source tube. A radiused source tube is simply one way to achieve a source installation and removal consistent with currently available methods. This right angled configuration is not limited to any particular embodiment. The right angle provides a smaller tip path length  412  having less metal than the tip path  86  of radiused source chamber. 
         [0048]      FIG. 14  illustrates an embodiment  500  of the invention in which the radiant energy from the source which is at the interior end of the source chamber, is reflected back through the transmission chamber by operation of a reflector  502 . This embodiment has the potential advantage that the source chamber does not need to be curved at its interior end to form a straight line path from the source to the detector through the transmission chamber, as radiant energy is reflected into that chamber by the right angle reflector  502  attached to the end of the source chamber. 
         [0049]      FIG. 15  illustrates a still further embodiment  600  of the invention in which radiant energy from the source is reflected back to the detector. In this embodiment, there are dual transmission chambers on opposite sides of the source chamber, and dual reflectors  602  and  604  which reflect radiant energy back through the respective transmission chambers to the detector. This embodiment has the possible advantages of the embodiment of  FIG. 14  and the potential further advantage of providing redundant detection within the vessel by virtue of the dual radiant energy paths and dual transmission chambers. 
         [0050]    A specific design of a density gauge serves as an example of the invention described. In the specific design, a source tube  62  made of 1 and ¼ inch 0.382 wall 347 stainless steel pipe has a radiation path  84  that passes through 1.532 inches of wall as part of the tip path  86 . The process path  90  is 18.752 inches long, ending at a transmission wall  52  0.674 inches thick that is part of a transmission chamber  50  made of 4 inch diameter double extra heavy 0.674 wall 347 stainless steel pipe. For the gauge  38  measuring the outer measurement zone  42  the source size will be 50 mCi (milliCuries) Cs-137. The source will be 100 mCi (milliCuries) Cs-137 for gauge  36  measuring the inner measurement zone  40 . Even though these two process paths  90  and tip paths  86  are the same, the differing lengths of the chamber paths  88  lead to using sources  76  of different strength. Although Cesium is used in the specific example just described, the invention does not preclude using other sources, for example, Cobalt. For nuclear density measurements Cesium and Cobalt gamma radiation are often used, but the invention may have broader applications using other forms of radiant energy from other sources, measuring properties other than density or level. 
         [0051]    While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.