Abstract:
A sealing device for a sulfur trap includes a float, a counterweight, and a cleaning rod. The density of the sealing device allows flotation of the device in molten sulfur. The counterweight includes a surface to mate with an upwardly extending hollow cylinder in the sulfur trap through which molten sulfur may flow. The sealing device engages the upwardly extending cylinder in a first position and floats in the molten sulfur contained in an upper chamber of the sulfur trap in a second position. The cleaning rod and counterweight contact the sides of the upwardly extending cylinder to prevent buildup of solid sulfur.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to equipment for separating molten sulfur from associated gases in industrial operations producing molten sulfur, such as oil refineries. More specifically, this invention relates to a seal for a sulfur trap. 
     2. Description of the Related Art 
     Gaseous compounds containing sulfur, such as hydrogen sulfide, mercaptans, carbonyl sulfide, carbon disulfide, exist in natural gas. Such gaseous compounds are produced as by-products in petroleum refining operations. 
     In industrial applications, gas streams containing sulfur compounds are processed to remove sulfur (primarily in the form of hydrogen sulfide). The gas streams are then further processed to form liquid sulfur in sulfur recovery units. 
     Conventional sulfur recovery units include a seal leg or trapping device to separate molten sulfur from the gas stream. The molten sulfur is condensed from the remaining gas stream. 
     The discharge into the atmosphere of residual tail gases associated with such molten sulfur, such as sulfur dioxide and hydrogen sulfide, is environmentally unacceptable. It is therefore necessary to separate the elemental sulfur from the tail gases associated therewith. 
     Sulfur traps associated with sulfur recovery units, as historically designed, include two concentrically arranged vertical pipes. The vertical pipes may extend approximately twenty feet to twenty-five feet into the ground. The outer pipe is capped at its lower end. The inner pipe lower end is displaced above the capped lower end of the outer pipe allowing molten sulfur to flow from the inner pipe to the annular space between the pipes. Molten sulfur is received into the inner pipe, flows downwardly from the inner pipe and upwardly in the annular space between the inner pipe and the outer pipe to a discharge pipe connected to the outer pipe. The discharge pipe transmits the sulfur into a sulfur storage tank where the sulfur may be maintained until pumped out for shipping or other disposition. A jacket is provided outside the outer pipe, with steam circulated between the jacket and the outer pipe to maintain the temperature of the sulfur trap above 250 degrees Fahrenheit and accordingly to maintain the sulfur in a liquid phase. The annular arrangement of the inner pipe and outer pipe provides a liquid trap preventing tail gases from being transferred in the storage tank. 
     Kuvasnikoff et al U.S. Pat. No. 4,185,140, Sims U.S. Pat. No. 4,255,408 and Singleton et al. U.S. Pat. No. 4,085,199 disclose processes for removing sulfur and sulfur compounds from sulfur bearing gases. 
     Stothers U.S. Pat. No. 4,504,459 discloses process and apparatus for extraction of elemental sulfur from sulfur compound gases. 
     Mori et al. U.S. Pat. No. 4,341,753 and Hellmer et al. U.S. Pat. No. 4,117,100 disclose processes and apparatus for converting sulfur dioxide and gas to sulfur. 
     Scott et al. U.S. Pat. No. 4,035,158 discloses a process and apparatus for burning hydrogen sulfide and other combustible fluids to recover sulfur. 
     Conventional in-ground sulfur traps require ground excavation and buried lines to install the concentric piping, the steam jacket and steam lines. In operation, the inner pipe or the annulus may become blocked or partially blocked from time to time by materials such as contaminated sulfur, carbon, catalyst dust, etc. To remove the blockage it is often necessary that the trap be partially disassembled and the inner pipe or annulus rodded out to restore circulation. 
     Operating pressures upstream of the conventional in-ground sulfur traps must be limited due to the nature of the liquid trap. Other disadvantages of conventional sulfur seal systems are that they extend 20′ or more into the earth, and that they are not easily cleaned. 
     U.S. Pat. No. 5,498,270 by this inventor discloses a sulfur trap that includes a sphere that engages an upwardly extending cylinder in a first position and that floats in the molten sulfur contained in the upper chamber in a second position. 
     The sulfur trap disclosed in U.S. Pat. 5,498,270 provided improved sealing over the prior art sulfur separation systems while allowing the process to operate at relatively high pressures upstream of the seal. Additionally, it did not require deep excavation and was relatively easy to clean. 
     The present invention comprises an improvement to the art by providing a self-cleaning mechanism on the trap enhancing the sealing interface. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a system that effectively separates elemental molten sulfur from associated tail gases and that has an improved sulfur sealing system. 
     It is also an object of the present invention to provide a self-cleaning mechanism to reduce solid sulfur build-up in the sulfur trap. 
     The sulfur trap of the present invention comprises generally a vertically-elongated upper chamber for receiving molten sulfur together with sulfur containing gases, a lower chamber disposed below the upper chamber, a wall segregating the lower chamber and the upper chamber, an orifice provided in the wall for fluid transfer from the upper to the lower chamber, an upwardly extending hollow cylinder adjacent the orifice wall, a spherical device in said upper chamber, a sealing device attached to said spherical device, said device engaging the upwardly extending cylinder in a first sealing position and said device floating in the molten sulfur contained in the upper chamber in a second sulfur-flowing position. The sealing device includes a counterweight extending from the lower outer surface. A beveled surface on the counterweight engages a beveled surface around the top of the upwardly extending cylinder. When the sealing device is in a first position, the beveled surface of the counterweight nests with the beveled surface of the upwardly extending cylinder and a portion of the counterweight is contained within the upwardly extending cylinder. A cleaning rod extends below the counterweight, further into the upwardly extending cylinder. Upon introduction of the molten sulfur into the upper chamber in sufficient quantities, the hydrostatic pressure of the molten sulfur displaces the spherical device upwardly to allow molten sulfur to flow through the orifice into the lower chamber. When the molten sulfur displaces the sealing device into the second position, the counterweight maintains the device orientation and the cleaning rod keeps the device aligned with the upwardly extending cylinder. The cleaning rod and counterweight reduce solid sulfur accumulations from the side of the cylinder and interface surface. 
     A discharge is fluidly connected to the lower chamber. An external shell is provided around the upper and lower chambers for circulating steam in the annular space between the shell and the upper and lower chambers to maintain the sulfur in a liquid phase. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   FIG. 1  depicts a cross-sectional view of the sulfur trap of the present invention. 
         FIG. 2  depicts a partial cross-sectional view of the sealing device engaging the cylindrical member in a first closed position. 
         FIG. 3  depicts a cross-sectional view of the dividing wall segregating the upper and lower chambers. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Referring first to  FIG. 1 , the sulfur trap  10  of the present invention is depicted in a cross-sectional drawing. The sulfur trap  10  includes an elongated, vertically oriented, cylindrical wall  12  having a segregating plate  14  horizontally disposed therein, segregating plate  14  defining an upper chamber  16  and a lower chamber  18  within cylindrical wall  12 . An orifice  20  is provided centrally of plate  14 . An upwardly extending, cylindrical member  22  is attached to the plate  14  with the hollow center of cylindrical member  22  aligned with the orifice  20  provided in segregating plate  14 . Cylindrical member  22  is provided with edges beveled outwardly along an upper edge  23 , shown in  FIG. 3 . Upwardly extending rods  24  are fixedly attached to plate  14  between the cylindrical member  22  and cylindrical wall  12 . 
     A sealing device  120  is disposed on the upper end of cylindrical member  22 . In the preferred embodiment, sealing device  120  includes a sphere  26 , a counterweight  110  and a cleaning rod  114 . Counterweight  110  is affixed to the underside of sphere  26 . Counterweight  110  has a beveled surface  112 , depicted in  FIG. 2 . Cleaning rod  114  extends downwardly from counterweight  110  through orifice  20 . As depicted in  FIG. 2 , beveled surface  112  engages upper edge  23  of cylindrical member  22  when sealing device  120  is not floating in the molten sulfur. 
     Counterweight  110  is provided with an arcuate lower surface  118 . The arcuate lower surface  118  facilitates centering of counterweight  110  in cylindrical member  22 . 
     When sealing device  120  is pushed upwards from cylindrical member  22 , counterweight  110  serves to maintain sphere  26  in an orientation such that counterweight  110  is always below sphere  26 . The flow of molten sulfur can cause sphere  26  to float slightly from side to side. As sphere  26  shifts, cleaning rod  114  scrapes the inside of cylindrical member  22 , thereby removing sulfur solids (not shown) that may have accumulated. Cleaning rod  114  also keeps sphere  26  aligned with cylindrical member  22  so that when the flow of molten sulfur stops, sphere  26  will come to rest with beveled surface  112  interfacing with beveled edge  23  on cylindrical member  22 . 
     In the preferred embodiment, counterweight  110  extends into cylindrical member  22  when sealing device  120  is seated against cylindrical member  22 . As the flow of molten sulfur pushes sealing device  120  upwards, the portion of counterweight  110  within cylindrical member  22  disengages sulfur solids that may have accumulated. Beveled surface  112  also scrapes upper surface  23 , removing sulfur solids (not shown) that interfere with the seal between sealing device  120  and cylindrical member  22 . 
     Referring to  FIG. 1 , an inlet orifice  28  is provided near the upper end of chamber  16  in cylindrical wall  12 . Inlet orifice  28  is connected to inlet pipe  32 . Inlet pipe  32  is connected to an inlet pipe flange  34 . Inlet pipe flange  34  is connected to a condenser (not shown) or other source of molten elemental sulfur and associated sulfur-containing gases. Inlet pipe  32  provides fluid communication between upper chamber  16  and the condenser. 
     Still referring to  FIG. 1 , a second upper chamber orifice  30  is provided near the upper end of upper chamber  16  in cylindrical wall  12 . Said second orifice  30  is connected to connecting pipe  36 . Connecting pipe  36  is connected to connecting flange  38 . As depicted in  FIG. 1 , connecting flange  38  is connected to a blind flange  40 . 
     As depicted in the preferred embodiment, molten sulfur inlet to the sulfur trap  10  may be introduced into the sulfur trap  10  through inlet orifice  28  and inlet pipe  32 . However, orifice  30  and connecting pipe  36  are provided for alternate inlet means of molten sulfur or for cleaning the sulfur inlet line connected to inlet pipe  32  of any solids deposited therein by using a straight rod. 
     A screen assembly  42  is disposed horizontally in upper chamber  16  below orifices  28  and  30 . The screen is above and remote from segregating plate  14 . 
     Still referring to  FIG. 1 , a rounded cap  44  is provided at the upper end of cylindrical wall  12 . Cap  44  is hingedly attached to cylindrical wall  12 . 
     A discharge orifice  52  is provided in cylindrical wall  12  near its lower end at lower chamber  18 . A discharge pipe  54  is connected to discharge orifice  52 . Discharge pipe flange  82  is connected to discharge pipe  54  at its end distal from discharge orifice  52 . 
     Shell members  66 ,  76 ,  78  and  80  are provided around the cylindrical wall  12 , inlet pipe  32 , connecting pipe  36  and connecting pipe  54 . 
     Referring now to  FIG. 3 , details of construction of the segregating plate  14  are depicted. Segregating plate  14  comprises a generally circular plate connected to the interior surface of cylindrical wall  12  throughout the exterior circumference of the plate  14 . Orifice  20  is centrally located in connecting plate  14 . Cylindrical member  22  extends upwardly from plate  14  into upper chamber  16 . 
     Cylindrical member  22  is provided with upper edges beveled outwardly. The beveled edges create an upper edge  23  of outer wall  22 . Absent an obstruction such as sealing device  120 , the orifice  20  and the interior of hollow cylindrical member  22  provide fluid communication between upper chamber  16  and lower chamber  18 . 
     Still referring to  FIG. 3 , a plurality of rods  24 , are connected to plate  14 , said rods extending upwardly into upper chamber  16 . Four rods  24  are provided in the preferred embodiment shown. Rods  24  are provided with rounded upper ends. Rods  24  are inclined outwardly at the upper ends. Rods  24  serve to center the sphere  26  over cylindrical member  22  and are sized and spaced accordingly. 
     OPERATION 
     Referring to  FIG. 1 , the operation of the present invention is depicted. Molten sulfur is received into upper chamber  16  through inlet pipe  32 , the molten sulfur containing tail gases including gaseous compounds containing sulfur, such as hydrogen sulfide, mercaptans, carbonyl sulfide, and carbon disulfide. Such molten sulfur is induced by gravity to flow through the screen assembly  42 , where large particles, including coagulated clumps of sulfur and sulfur compounds, are segregated from the molten sulfur. As a volume of sulfur accumulates in the upper chamber  16 , the sealing device  120  is displaced upwardly from its resting place at the upper edge  23  of cylindrical member  22 . The sealing device  120  is constructed with such an average density to float in molten sulfur. Such displacement of sealing device  120  allows molten sulfur to flow through the orifice  20  into lower chamber  18  and thence through discharge pipe  54  to a storage tank or other receptacle. 
     The flow of molten sulfur into the lower chamber  18  continues during the period that sphere  26  is displaced from upper edge  23 . A liquid seal is maintained during such flow by the liquid sulfur, preventing process gas from escaping with liquid sulfur to the lower chamber. As sealing device  120  is displaced from cylindrical member  22 , counterweight  110  maintains sphere  26  in an orientation relative to cylindrical member  22  with counterweight  110  below sphere  26 . Variations in the flow of molten sulfur cause sphere  26  to rotate and move slightly from side to side. As sphere  26  rotates and moves, cleaning rod  114  scrapes solid sulfur build up from the inside surface of cylindrical member  22 , thereby keeping it free of solid sulfur accumulation that can inhibit the flow of molten sulfur to lower chamber  18 . Counterweight  110  also scrapes the top inner portion of cylindrical member  22  and upper edge  23 , reducing solid sulfur build up that compromises the integrity of the seal between counterweight  110  and cylindrical member  22  when the flow of molten sulfur decreases. 
     Upon reduction of volume of molten sulfur in upper chamber  16 , sphere  26  with counterweight  110  drops to its original position at upper edge  23  of cylindrical member  22 . Arcuate lower surface  118  facilitates centering of counterweight  110  in cylindrical member  22 . Further flow of molten sulfur through orifice  20  is thereby terminated. The centering of sphere  26  on upper edge  23  is facilitated by rods  24 , said rods  24  being so located and sized as to direct sphere  26  to the center of chamber  16 . Further, cleaning rod  114  facilitates the centering of counterweight  110  over cylindrical member  22 . Beveled surface  112  interfaces with upper edge  23  to provide an effective seal against such flow of molten sulfur. 
     Steam is continually circulated through the annular spaces between shell members  66 ,  76 ,  78 , and  80  and cylindrical wall  12 , inlet pipe  32 , connecting pipe  36  and discharge pipe  54  to maintain the temperature within sulfur trap  10  above 250 degrees Fahrenheit. The sulfur contained within sulfur trap  10  is thereby maintained in a liquid phase. 
     As required for cleaning and to remove coagulated sulfur material, cap  44  may be rotated to an open position. The screen assembly  42  may then be removed from the upper chamber  16 . 
     The foregoing description of the invention illustrates a preferred embodiment thereof. Various changes may be made in the details of the illustrated construction within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the claims and their equivalents.