Abstract:
A probe mounted directly to a conduit conveying a process stream of gas to be analyzed, which can condition a continuous sample of the gas before it is analyzed by removing undesirable vapor components of the sample through interaction with a heat exchanger conduit which condenses these components into a liquid such that they precipitate under the force of gravity back into the process stream. The probe uses a Venturi device to motivate the gas through a flow cell chamber where it interacts with light shown through the chamber before ejecting the sample back into the process stream through a sample return conduit.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority as a non-provisional application of U.S. provisional patent application Ser. No. 61/143,876; filed on Jan. 12, 2009. 
     
    
     BACKGROUND 
       [0002]    This invention relates to a probe for conditioning a fluid sample to be analyzed having one or more undesirable components entrained therein. In particular, it relates to a system that can very precisely cool the sample to remove just the undesirable components through condensation. In a process gas stream it is often desirable to know the concentration of one or more compounds that make up the process stream. This concentration knowledge allows feedback to be sent to an operator(s) or equipment in the process that can make changes based on the information obtained. For example, in a Claus sulfur recovery process H 2 S and SO 2  are reacted to produce elemental sulfur and water. By analyzing the concentration of H 2 S leftover in the tail-gas from the reaction, feedback can be provided that can be used to adjust the amount of H 2 S being supplied to the reaction. However, analysis of the tail-gas is complicated by the presence of elemental sulfur vapor which distorts the readings obtained from a spectrometer, and which can solidify on the analyzing equipment&#39;s interior surface. Therefore it is an object of the present invention to provide an in-situ probe that can remove sulfur vapor from a process gas stream by condensing the vapor into a liquid such that it precipitates into the process stream before it can accumulate on the analyzing equipment&#39;s interior surface. 
       SUMMARY OF THE INVENTION 
       [0003]    A sample of a process gas steam, which contains at least one undesirable component such as sulfur vapor, is conveyed by means of a Venturi device into a sample chamber where it interacts with a heat exchanger conduit. The heat exchanger conduit conveys a cooling fluid, such as steam, through a separate chamber that is not in fluid communication with the sample chamber as to preclude mixing of the cooling fluid and sample, but allows for heat transfer from the process gas steam sample to the cooling fluid through the wall of the heat exchanger conduit. The temperature of the cooling fluid is precisely controlled—in the case of steam this is accomplished by regulating the pressure of the steam—so that the undesirable component of the process gas steam sample will condense into a liquid. The undesirable component of the process gas steam sample precipitates out of the sample and falls under the force of gravity back into the process gas stream. In the case of sulfur being the undesirable component, it is of paramount importance that the temperature of the cooling fluid be very precisely controlled, because the pressure in a Claus process tail-gas line is kept below atmospheric pressure to prevent the possibility of gas leaking from the pipes, and at this sub-atmospheric pressure sulfur only exists in a liquid state within a very narrow temperature range. The reason pressure control is important is because if the temperature of the cooling fluid were to be too low, sulfur vapor will solidify on the surface of the heat exchanger conduit and insulate it such that the process gas steam sample will be able to pass by without its sulfur vapor content being removed, conversely, if the temperature of the cooling fluid is too high sulfur vapor will not condense leading to the same problem. Therefore, it is a critical aspect of this invention that the system can be adjusted such that sulfur can be condensed to a liquid through interaction with the heat exchanger conduit. After interaction with the heat exchanger conduit the process gas steam sample travels through an orifice in the bottom of a probe head manifold and into a flow cell chamber. The flow cell chamber is cylindrical with an inlet and outlet orifice for the process gas steam sample to enter and exit the flow cell chamber which is aligned perpendicular to the longitudinal axis of the sample chamber, and an optical inlet and outlet orifice with one in each and of the flow cell chamber aligned parallel and concentrically with and the longitudinal axis of the flow cell chamber such that a beam of light can be shown through the flow cell chamber entering through the optical inlet orifice and exiting through the optical outlet orifice. In this way some wavelengths of light being shown through the chamber will be absorbed by the sample in accordance with Beer-Lamberts law, and the light exiting the chamber can be analyzed by a spectrometer to identify the components of the process gas steam sample in the flow cell chamber. 
         [0004]    The flow cell chamber is also in close proximity to a demister which conveys a heating fluid, such as steam, through a serpentine channel. The serpentine channel is positioned in such a way that it is not in fluid communication with the flow cell chamber, which precludes mixing of the heating fluid and the process gas steam sample, but allows for heat transfer from the heating fluid to the process gas steam sample through the wall of the flow cell chamber. The demister further comprises a heating fluid inlet and outlet orifice to allow the heating fluid to enter the serpentine channel through one end and exit through the opposite end. This heating fluid system allows the temperature of the flow cell chamber to be held at a point above the condensation temperature of all components of the process gas steam sample so that liquids and solids do not accumulate in the chamber and block the flow of the process gas steam sample and light through the chamber. 
         [0005]    After the process gas steam sample exits the flow cell chamber it passes through the Venturi device where it mixes with an aspirating fluid, such as air, and is conveyed through a sample return conduit, which is housed in the sample chamber but not in fluid communication therewith, before being ejected back into the original process fluid downstream of the inlet of the sample chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  depicts the preferred embodiment of the present invention. 
           [0007]      FIG. 2  shows a detailed view of the Venturi device of  FIG. 1  shown in circle  2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    In reference to the drawing, it is to be understood that the depiction therein is for illustration of a preferred embodiment of the invention, and the invention is not limited thereto. 
         [0009]    As shown in  FIG. 1 , an in-situ gas analyzer probe  1  is mounted to a process pipe  2  carrying tail-gas  3  in a conventional Claus sulfur recovery operation (represented by box  99 ). The tail-gas is made up of multiple components including H 2 S, S 2 , and H 2 O, and is held at a pressure below atmospheric pressure and a temperature where all components exist in a vapor form. The tail-gas passes by the bottom end of a sample chamber  4  which extends, preferably approximately  2 / 3  of the way, into the process pipe  2 . The bottom end of sample chamber  4  is cut at an angle of approximately  45  degrees to the longitudinal axis of the process pipe  2  and oriented to form an opening  98  that faces the oncoming flow. The opening  98  is cut at an angle in order to increase the opening&#39;s area that is perpendicular to the flow in the process pipe  2  to facilitate the flow of a sample  5  of the tail-gas  3  into sample chamber  4 . 
         [0010]    The tail-gas sample  5  is motivated through the sample chamber  4 , a flow cell chamber  6 , and a sample return conduit  7  by a Venturi device  8 . Referring now to  FIG. 2 , the Venturi device  8  comprises an aspirating fluid inlet orifice  9 , a sample inlet orifice  10 , and a common outlet orifice  11 . The Venturi device  8  operates by flowing an aspirating fluid  12 , such as air, into the aspirating fluid inlet orifice  9  where it is conveyed through a bottleneck constriction area  13 . The bottleneck constriction area increases the velocity of the aspirating fluid  12  and consequently lowers the pressure within the bottleneck constriction  13  in accordance with Bernoulli&#39;s principal. The sample inlet orifice  10  is located near, but preferably at, the midpoint of the bottleneck constriction area  13 , such that when sized properly the pressure in the bottleneck constriction area  13  is lower than that of the tail-gas sample  5  upstream of the sample inlet orifice  10 . That pressure differential causes the tail-gas sample  5  to flow through the sample inlet orifice  10  into the bottleneck constriction area  13  wherein the tail-gas sample  5  mixes with the aspirating fluid  12  and exits the Venturi device  8  through the common outlet orifice  11 . 
         [0011]    Reverting to  FIG. 1 , the sample chamber  4  houses a heat exchanger conduit  14 . Heat exchanger conduit  14  is comprised of an inner tube  15  and an outer tube  16  of different diameters such that the inner tube  15  fits inside the outer tube  16 , and of different lengths such that the inner tube  15  is shorter than the outer tube  16 . Both the inner tube  15  and the outer tube  16  are aligned such that one end of each is coplanar with the end of the sample chamber  4  opposite the end through which the tail-gas sample  5  is entering, and the coplanar end of the inner tube  15 , outer tube  16 , and sample chamber  4  are flush against the flat bottom side of a probe head manifold  17 . 
         [0012]    The circumference of inner tube  15  on the coplanar end encircles a cooling fluid inlet orifice  18  in the bottom of the probe head manifold  17 ; such that a cooling fluid  19 , such as and not limited to steam, can be conveyed from a cooling fluid source  97 . The cooling fluid source  97  provides the cooling fluid  19  into the probe head manifold  17  through a connection inlet orifice  20 , the inlet orifice then directs the cooling fluid  19  through the interior volume of the inner tube  15 . The cooling fluid  19  can then pass out of the bottom end of the inner tube  15  opposite the coplanar end, and enter the space encapsulated by the outer tube&#39;s  16  inside diameter and the inner tube&#39;s  15  outside diameter. The cooling fluid  19  then passes through a cooling fluid outlet orifice  21  in the bottom of the probe head manifold  17  that is encircled within the outer tube&#39;s  16  circumference but not the inner tube&#39;s  15  circumference. The cooling fluid  19  exits the probe head manifold  17  through a cooling fluid connection outlet orifice  22 . The end of the outer tube  16  opposite the coplanar end is, obviously, sealed so as to preclude the mixing of the cooling fluid  19  with the tail-gas sample  5  in the sample chamber  4 , and allows for heat transfer between the tail-gas sample  5  and the cooling fluid  19  through the wall of the heat exchanger conduit  14 , in particular the outer tube&#39;s  16  walls. 
         [0013]    The tail-gas sample  5  in the sample chamber  4  flows past the heat exchanger conduit  14  where thermal energy is exchanged between the tail-gas sample  5  and the cooling fluid  19 . In normal operation the temperature of the cooling fluid  19  is kept below the tail-gas sample&#39;s  5  temperature so that heat is transferred from the tail-gas sample  5  to the cooling fluid  19 . In the preferred embodiment of the present invention the cooling fluid  19  is steam in which case the temperature of the cooling fluid  19  can be adjusted by regulating the pressure of the steam within a conventional pressure regulator  96 . 
         [0014]    The pressure of the cooling fluid  19  (preferably steam) must be precisely controlled such that the temperature of the steam will cool the tail-gas sample  5  to a point where the S 2  component will condense into a liquid, and not to a point that it will freeze into a solid. The liquid sulfur  23  then precipitates under the force of gravity against the flow of tail-gas sample  5  and passes back through the bottom end of a sample chamber  4  and into the process pipe  2 , as illustrated in  FIG. 1 . 
         [0015]    The tail-gas sample  5  exits the sample chamber  4  though a sample supply orifice  24  in the bottom side of the probe head manifold  17 , and flows through a sample inlet orifice  25  into flow cell chamber  6 . 
         [0016]    The flow cell chamber  6  is cylindrical with an optical inlet orifice  26  on one end of the flow cell chamber  6  and an optical outlet orifice  27  on the opposite end. Both optical inlet orifice  26  and optical outlet orifice  27  are aligned parallel to, and concentrically upon, the longitudinal axis of the flow cell chamber such that a beam of light (depicted by broken arrows) can be shown through the flow cell chamber  6 . Optical inlet orifice  26  and optical outlet orifice  27  each contain a lens  28  which allows the light to pass through the flow cell chamber  6 , but precludes the tail-gas sample  5  from escaping. 
         [0017]    The light is generated by a conventional light source  90 , that radiates specific wavelengths, or specific ranges of wavelengths that are required to properly analyze components and concentration of components in the tail-gas sample. In this way some wavelengths of light being shown through the flow cell chamber  6  will be absorbed by the sample in accordance with Beer-Lamberts law. The light exiting the flow cell chamber  6  can be analyzed by a conventional spectrometer  92  to identify the components of the process gas steam sample in the flow cell chamber  6 . 
         [0018]    Flow cell chamber  6  is in close proximity to a demister  29 . The demister  29  comprises a heating fluid inlet orifice  30 , a heating fluid outlet orifice  31 , and a serpentine channel  32 . A heating fluid, such as steam, from a heating fluid source  95 , enters the serpentine channel  32  through the heating fluid inlet orifice  30  and is conveyed through the convoluted path of the serpentine channel  32  above the flow cell chamber  6 . The heating fluid then exits through the heating fluid outlet orifice  31 . The heating fluid is hotter than the vaporization temperature of each component of the tail-gas sample  5  in the flow cell chamber  6  and keeps the tail-gas sample entirely in vapor form such that condensation will not form on the lenses  28  and solid particulates will not form and impede the flow of tail-gas sample  5  through the system. 
         [0019]    The tail-gas sample  5  exits flow cell chamber  6  through a sample outlet orifice  34  and passes through the Venturi device  8 . After passing through the Venturi device  8 —which is described in detail above—, the tail-gas sample is then conveyed through sample return conduit  7  before being ejected back into the process pipe  2  through sample ejection orifice  36 . 
         [0020]    The probe head manifold  17  is comprised of three concentric discs of approximately the same diameter. The probe head manifold  17  is split into discs for manufacturability, maintainability, and to allow each part to be replaced without having to replace the entire probe head manifold. Despite this objective of the instant invention, those skilled in the art will recognize the probe head manifold can be made from one solid piece, or further divided into more than three discs depending upon the particular application in which it is used. 
         [0021]    The bottom most disc  37  is directly connected to the coplanar ends of the inner tube  15  and outer tube  16  of the heat exchanger conduit  14  as well as the sample chamber  4 , and comprises the cooling fluid connection inlet orifice  20 , the cooling fluid connection outlet orifice  22 , the cooling fluid inlet orifice  18 , and the cooling fluid outlet orifice  21 . 
         [0022]    The middle disc  38  is directly connected to the top of the bottom most disc  37 , and comprises the Venturi device  8  as well as an aspirating fluid connection inlet orifice  39 . The aspirating fluid connection inlet orifice  39  is interconnected to an aspirating fluid source  88 . The aspirating fluid source  88  provides the aspirating fluid  12 , such as air, and pushes the aspirating fluid  12  into the aspirating fluid inlet orifice  9  as described above. 
         [0023]    The top most disc  40  is directly connected to the top of the middle disc  38  and comprises the flow cell chamber  6  as well as the demister  29 . 
         [0024]    Over time a small amount of S 2  vapor will make it past the heat exchanger conduit  14  and freeze into a solid form elsewhere in the system. Therefore it is desirable to periodically raise the temperature of the cooling fluid  19  higher than the vaporization temperature of S 2 . By occasionally raising the cooling fluid&#39;s temperature in the fluid inlet orifice  20 , the heated cooling fluid temporarily heats the tail-gas sample  5  so that as the tail-gas sample  5  passes through the rest of the system it vaporizes any accumulated S 2 , and in doing so effectively cleans the system without having to remove and disassemble the probe. 
         [0025]    Although the present invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the spirit and scope of the claimed invention.