Abstract:
The present subject matter is directed to plasma dissociation of fluidic hydrogen sulfide to hydrogen and sulfur. A reactor is configured to have a plasma discharge and a vortex flow pattern. The plasma discharge provides energy to the hydrogen sulfide disassociation reaction and the vortex flow pattern helps to cause the condensation of sulfur molecules. The condensation of sulfur molecules helps to reduce the amount of energy input required to disassociate a certain amount of hydrogen sulfide. Additionally, the reactor may be configured to have a vortex flow pattern that provides for a recirculation zone in which relatively warm reaction products may exchange their heat energy with relatively cool input fluids.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Application No. 60/916,562, entitled, “HYDROGEN PRODUCTION FROM HYDROGEN SULFIDE”, filed May 7, 2007 (Atty. Docket No. DREX-1083USP), the entire contents of which are hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention pertains to the disassociation of hydrogen sulfide. The field of the invention may also be related to a chemical transformation using plasma. 
       BACKGROUND 
       [0003]    Greenhouse gas emissions are a recognized cause of global warming and pose a serious threat to the preservation of the environment. Scientists have been endeavoring to develop new scientific and technological innovations and approaches that can lead to the reduction of these emissions. Preliminary studies indicate that plasma dissociation of hydrogen sulfide may be a particularly promising technology for reducing greenhouse gas emissions. Hydrogen sulfide may be generated as a by-product in certain chemical processes, such as oil refining industry, as well being present in natural sources such as natural gas. In conventional methods of H 2 S processing, such as the Claus method, all hydrogen from H 2 S is transformed into water. 
       SUMMARY 
       [0004]    The present subject matter is directed to plasma dissociation of fluidic hydrogen sulfide to hydrogen and sulfur. A reactor is configured to have a plasma discharge and a vortex flow pattern. The plasma discharge provides energy to the hydrogen sulfide disassociation reaction and the vortex flow pattern helps to cause the condensation of sulfur molecules. The condensation of sulfur molecules helps to reduce the amount of energy input required to disassociate a certain amount of hydrogen sulfide. Additionally, the reactor may be configured to have a vortex flow pattern that provides for a recirculation zone in which relatively warm reaction products may exchange their heat energy with relatively cool input fluids. Again, this may reduce the required energy input to disassociate a certain amount of hydrogen sulfide and may also provide for an increased purity of the output streams. 
         [0005]    In one exemplary and non-limiting embodiment, fluidic hydrogen sulfide (H 2 S) is introduced into a reactor configured to establish a reverse-vortex flow pattern. Through chemical and physical energy imparted on the fluidic H 2 S, the H 2 S is disassociated to hydrogen and sulfur. 
         [0006]    For the purposes of the present subject matter, fluidic hydrogen sulfide, sulfur or hydrogen may be a liquid, gas, or supercritical fluid. Fluid may be a substance that continually deforms under an applied shear stress without regards to the magnitude of the applied stress. Further, although the subject matter may be discussed in terms of pure substances, i.e. pure hydrogen sulfide, it should be understood that impurities or other compounds or elements may be present in one or more of the fluid streams discussed below. 
         [0007]    Accordingly, in one aspect of the present invention there are provided reactors for dissociating hydrogen sulfide, comprising: a reaction chamber of generally cylindrical shape; at least one fluid inlet configured to introduce an input fluid into the reaction chamber in a direction generally tangential to a central axis of the reaction chamber, wherein the input fluid is comprised of hydrogen sulfide; at least one first outlet configured for outputting a first outlet fluid, wherein the first outlet and the fluid inlet are further configured to cause a reverse-vortex flow in the reaction chamber; a first electrode; and a second electrode connected to a power source, wherein the first electrode and the second electrode are disposed within the reaction chamber to provide for the generation of a plasma discharge within the reaction chamber. 
         [0008]    Other aspects of the present invention provides methods for dissociating hydrogen sulfide, comprising: providing a plasma reactor, said plasma reactor comprising: a reaction chamber; at least one fluid inlet configured to introduce an input fluid into the reaction chamber in a direction generally tangential to a central axis of the reaction chamber; at least one first outlet configured for outputting a first outlet fluid, wherein the first outlet and the fluid inlet are further configured to cause a vortex flow in the reaction chamber; an optional second outlet configured for outputting a second outlet fluid; a first electrode; and a second electrode connected to a power source, wherein the first electrode and the second electrode have surfaces exposed within the reaction chamber to provide for the generation of a plasma discharge within the reaction chamber; and introducing hydrogen sulfide into the reaction chamber through the fluid inlet. 
         [0009]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0010]    Other features of the subject matter are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The summary, as well as the following detailed description, is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings exemplary embodiments of the invention; however, the invention is not limited to the specific methods, compositions, and devices disclosed. In addition, the drawings are not necessarily drawn to scale. In the drawings: 
           [0012]      FIG. 1  is an exemplary and non-limiting illustration of a gliding arc discharge reactor using reverse-vortex flow; 
           [0013]      FIG. 1   a is a topside illustration of the reactor of  FIG. 1 , showing an exemplary and non-limiting example of how an input fluid may be introduced into the reactor; 
           [0014]      FIG. 1   b  is a side view illustration of the reactor of  FIG. 1  to further illustrate a reverse vortex-flow; and 
           [0015]      FIG. 2  is an alternate exemplary and non-limiting illustration of a gliding arc discharge reactor using reverse-vortex flow. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, applications, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention. 
         [0017]    Also, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. The term “plurality”, as used herein, means more than one. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable. 
         [0018]    The term “gliding arc” is used in the present subject matter as is understood by those skilled in the art. It should be understood that a plasma discharge in the present subject matter may be generated in various ways, for example, glow discharge. In a reactor implementing a glow discharge, a cathode current may be controlled mostly by the secondary electron emission, as occurs in glow discharge, instead of thermionic emission, as occurs in electrical arcs. 
         [0019]    It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, references to values stated in ranges include each and every value within that range. 
         [0020]    In the present disclosed subject matter, a gliding arc discharge plasma source is used to cause the dissociation of hydrogen sulfide, preferably into hydrogen and sulfur. A gliding arc discharge reactor is configured to cause a high-voltage electrical discharge to glide over the surface of one or more electrodes. The properties of the plasma discharge may be adjusted depending upon the configuration of the reactor. The reactor is further configured to utilize a reverse-vortex flow pattern. Reverse vortex flow means that the vortex flow has axial motion initially from a swirl generator to a “closed” end of reaction chamber. A reverse-vortex flow pattern may provide for, among other benefits that may not be specifically disclosed, the extraction of sulfur clusters due to the centrifugal effect of the spinning fluid, thus possibly increasing the efficiency of the reactor. 
         [0021]    Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to  FIG. 1 , a schematic view of an exemplary reactor, reactor  10 , is illustrated. Reactor  10  includes reaction chamber  12 . At or near top  34  of reactor  10 , there is a swirl generator, one or more nozzles  14   a,    14   b,  that cause rotation of the fluids in reaction chamber  12 . Rotation of the fluids in reaction chamber  12  may be caused by various ways. In the present embodiment, nozzles  14   a  and  14   b  may be tangential nozzles that introduce input fluid  2  into reaction chamber  12  tangentially. This present embodiment is for illustrative purposes only, as the rotation may be caused by other means, such as baffles inside of reaction chamber  12 . Further, in some embodiments, input fluid  2  may be introduced into reaction chamber  12  at or near sonic velocity having mostly the tangential component of the velocity vector. 
         [0022]      FIG. 1   a  further illustrates the rotation of the fluids inside reaction chamber  12 . Reactor  10  reaction chamber  12  has axis “A” that extends from the top (not shown), such as top  34  of reactor  10  to the bottom (not shown), such as bottom  36 , of reactor  10 . In the present embodiment, a rotational flow is generated by nozzles  14   a  and  14   b  introducing input fluid (not shown) into reaction chamber  12  tangential to axis “A”. A general flow pattern is caused whereby the fluids in the reactor rotate about axis “A”, shown by exemplary fluid flows  50  and  52 . 
         [0023]    It should also be understood that, although the reactor  10  of  FIG. 1  is shown as having top  34  and bottom  36 , reactor  10  may be arbitrarily oriented in space, and the significance of the spatial orientation of top  34  and bottom  36  are merely to provide reference points to illustrate the exemplary embodiment of reactor  10 . 
         [0024]    In one embodiment, input fluid  2  may be gaseous hydrogen sulfide. In another embodiment, input fluid  2  may be liquid hydrogen sulfide. In other embodiments, input fluid  2  may be supercritical hydrogen sulfide. It should be understood that input fluid  2  may also have substances or compounds other than hydrogen sulfide. The present subject matter is not limited to input fluid  2  being a pure fluid input, but rather, discusses the dissociation of the hydrogen sulfide component of input fluid  2  into hydrogen and sulfur. 
         [0025]    Referring back to  FIG. 1 , nozzles  14   a,    14   b  that help to generate a rotation of the fluids in reactor  10  may be located about a circumference of vortex reactor  10  and are preferably spaced evenly about the circumference. Although two nozzles,  14   a,    14   b,  are illustrated in  FIG. 1 , it should be understood that this configuration is an exemplary configuration and that reactor  10  may have one nozzle or more than two nozzles, depending upon the configuration. In other embodiments, additional nozzles, not shown, may be placed in various locations on reactor  10 . 
         [0026]    Additionally, although the presently disclosed subject matter shown input fluid  2  to be the same fluid, it should be understood that one or more nozzles may be used to introduce one or more input fluids into reaction chamber  12 . In the present embodiment, reactor  10  has input fluid  2  and two output streams, output stream  22  and output stream  24 . Output stream  22  is preferably a hydrogen-rich stream primarily composed of hydrogen and output stream  24  is preferable a sulfur-rich stream primarily composed of sulfur. It should be understood that output streams  22  and  24  may not be pure hydrogen or sulfur, respectively, but may contain non-disassociated hydrogen sulfide and other compounds because of impurities in input fluid  2  or the mixtures of fluids in input fluid  2 . 
         [0027]    Input fluid  2  is introduced to reaction chamber  12  via nozzles  14   a,    14   b,  the outputs of which are preferably oriented tangential relative to wall  13  of reaction chamber  12 , as shown by  FIG. 1   a,  which is a topside illustration of reactor  10 . As shown in  FIG. 1  a, reactor  10  has nozzles  14   a  and  14   b.  Input fluid  2  exits nozzles  14   a  and  14   b  and enters reaction chamber  12  in a generally tangential direction about an axis, such as axis “A” as illustrated in  FIG. 1   a.    
         [0028]    By introducing input fluid  2  in this manner, as discussed above, a rotational force is imparted upon the fluids in reaction chamber  12 , thus causing a rotation of the fluids in reaction chamber  12  in a clockwise direction in this embodiment. Thus, the velocity at which input fluid  2  enters reaction chamber  12  effects the rotational speed of the contents in reaction chamber  12 . It should be noted that the input direction may be in a direction reverse to that shown in  FIG. 1   a.  Further, it should be understood that one or more nozzles may be configured to introduce the input fluid in a direction dissimilar to other nozzles. 
         [0029]    Referring back to  FIG. 1 , in an embodiment of the present subject matter, flange  30  and circular opening  32 , located substantially at the center of flange  30 , assist to form a vortex flow. In the present embodiment, the vortex flow is a reverse vortex flow, though it should be understood that the vortex flow may be a forward vortex flow. 
         [0030]      FIG. 1   b  is provided to illustrate a reverse vortex flow pattern. Reactor  10  has top  34  and bottom  36 . Reaction chamber  12  has two general flow patterns, exemplary fluid flow  50  and exemplary fluid flow  52 . It should be understood that these flow patterns are one component of the flow of fluids in reaction chamber  12 , with the rotational flow pattern being the other component. Generally in reactor  10 , fluids flow in a downward motion from top  34  to bottom  36  outside near the outer wall of reactor  10  and in an upward motion from bottom  36  to top  34  near the center of reactor  10 , as shown in Figure lb. It should be understood that other flow patterns may be used. 
         [0031]    Referring back to  FIG. 1 , opening  32  in flange  30  is preferably circular, but may be other shapes such as pentagonal or octagonal. The size of circular opening  32  may be varied to configure reactor  10  for various flow patterns in reaction chamber  12 . In this present embodiment, for example, the diameter of opening  32  in flange  30  may be from approximately 70% up to 95% of the diameter of reaction chamber  12  to form the reverse vortex flow. 
         [0032]    The diameter of opening  32  may also be configured to establish, or prevent, a recirculation zone from forming. Reactor  10  may be configured to provide a way in which relatively hot fluids flowing from plasma region  40  may exchange a portion of their heat with fluids flowing to plasma region  40 . For example, exemplary fluids  38   a - c,  which are flowing generally towards plasma region  40  receive heat from exemplary fluid  42   a,  which is flowing from plasma region  40 . Exemplary fluid  42   a,  after exchanging heat with exemplary fluids  38   a - c,  may than flow back to plasma region  40 , as shown by exemplary fluid  42   b.  Thus, a portion of the reaction heat generated in plasma region  40  and a portion of fluids in reaction chamber  12  recirculate within reactor  10 . In one embodiment, if a recirculation zone is desired, the diameter of opening  32  in flange  30  may be approximately 10% up to 75% of the diameter of reaction chamber  12 . 
         [0033]    As discussed above, reverse vortex flow as used herein means that the vortex flow has axial motion initially caused by nozzles  14   a  and  14   b  along wall  13  of the chamber and then the flow turns back and moves along the axis to the “open” end of the chamber towards opening  32 . An example in nature of this flow pattern may be similar to the flow inside a dust separation cyclone, or inside a natural tornado. Input fluid  2  travels in a circular motion, traveling in a downward and inward direction towards plasma region  40 , as shown by exemplary fluids  38   a - c.    
         [0034]    In a suitable reactor, the dissociation reaction occurs in plasma region  40 . Disassociated sulfur travels outward from plasma region  40  towards wall  13  of reactor  10  in an exemplary direction illustrated by flow direction labeled “Sulfur” whereas the hydrogen travels upwards to opening  32  in an exemplary direction shown by output stream  22 . A portion of the disassociated sulfur condenses on wall  13  and travels downward along wall  13 , shown by sulfur output stream  24 , towards bottom  36  of reactor  10  outlet  18 . 
         [0035]    A reverse vortex flow in reaction chamber  12  causes the contents of reactor  10  in reaction chamber  12  to rotate around plasma region  40 , while output stream  22  travels in a direction upwards from the bottom of reactor  10  to opening  32 . Along with other benefits that may not be explicitly disclosed herein, the rotation may provide necessary time for the heating of the contents flowing to and in the relatively hot plasma region  40  as the contents move downwardly around central core region  40 . Another benefit of the rotation may be that the reverse vortex flow may increase the residence time of reactants and products, for example, sulfur clusters, inside reaction chamber  12 . Increased residence time may help to improve sulfur separation. In other words, as residence time increases, the molar percentage of hydrogen in output stream  22  may increase as well as the molar percentage of sulfur in sulfur output stream  24 . 
         [0036]    A vortex flow, such as the reverse-vortex flow described in  FIG. 1 , may provide for several benefits, some of which may not be explicitly described herein. For example, the flow may cause one two or more zones inside chamber  12 , one being plasma region  40 , the other being the remaining volume of reaction chamber  12 . For example, in the present subject matter, a temperature differential is established between plasma region  40  to wall  13  of reactor  10 . A central axis in plasma region  40  may have the highest temperature in reaction chamber  12 , and as the radial distance from that central axis increases to wall  13 , the temperature may decrease. 
         [0037]    In the present embodiment, the temperature of input stream  2  defines the temperature near or at wall  13  of reaction chamber  12 . In the dissociation of hydrogen sulfide, the temperature variance means that either most or a significant portion of the dissociation reaction occurs in relatively hot plasma region  40 , depending upon the configuration and efficiency of reactor  10 . Thus, in the present embodiment, the temperature at or near wall  13  is configured to be at or below the condensation temperature of sulfur output stream  24 . 
         [0038]      FIG. 2  is an illustration of a further embodiment of a gliding arc discharge reactor configured to have a reverse-vortex flow. In the present embodiment, reactor  100  has input stream  116  of hydrogen sulfide introduced into reactor  100  using a rotational flow pattern at near sonic speeds in a manner similar to that described in relation to  FIG. 1 , above. As previously mentioned, the introduction of input stream  116  imparts a rotational motion on the contents of reactor  100 . This causes a centrifugal separation of hydrogen, shown by output stream  128 , from sulfur, shown by output stream  122 . 
         [0039]    The dissociation process effectively commences in high temperature plasma zone  114  with hydrogen sulfide dissociating, or decomposing, to form sulfur molecules. Depending upon the conditions inside of reactor  100 , the dissociated sulfur may form primarily sulfur dimers, S 2 , while other sulfur clusters of varying formations occur, such as S 3 →S n . The sulfur clusters condense in the lower temperature areas of reactor  100 . In the present embodiment, reactor  100  is configured so that plasma zone  114  creates a high enough temperature to dissociate at least a portion of the hydrogen sulfide in input stream  116 . After the dissociation occurs, sulfur clusters form and begin to condense in the relatively lower temperature regions of reactor  100 . 
         [0040]    Without being bound by any theory of operation, it is believed that the condensation of sulfur clusters and a vortex flow pattern, such as the reverse-vortex flow of  FIG. 1 , may help to reduce the energy consumption of the reactor by allowing recovery of the energy of sulfur condensation. Depending upon the configuration of reactor  100 , the centrifugal force may cause sulfur molecules and clusters to migrate to wall  102  of reactor  100  radially towards wall  102 . The reverse-vortex flow may force the hydrogen sulfide to migrate radially towards the center of chamber  118 , or plasma zone  114 , of reactor  100 . 
         [0041]    A fluid stream is generated that rotates in the reactor  100 , which may be cylindrical, and additionally travels downwards along the cylindrical wall, then radially towards the axis, then upwards along the axis. The sulfur migrating towards wall  102 , shown as the flow labeled “Sulfur”, may condense and exchange its heat energy with the hydrogen sulfide, shown as the flow labeled “H2S” migrating towards plasma zone  114 . A nearly 100% heat exchange efficiency occurs when the heat of condensation of the sulfur (85,520 kJ total) is completely absorbed by the incoming H 2 S. It should be understood that the present subject matter is not limited to 100% efficiency. 
         [0042]    The construction materials of reactor  100  may vary. In one embodiment shown in  FIG. 2 , wall  102  may be constructed of insulating material, such as quartz. Other configurations may include partial or complete metallic construction using materials such as stainless steel or Inconel®. The present subject matter is not limited to any particular material of construction, but rather, the subject matter may be applied using various construction materials. 
         [0043]    Continuing with the construction of reactor  100 , reactor  100  has wall  102  defining reaction chamber  118 . Reactor  100  further has first electrode  104 , which in the present embodiment is a high voltage electrode, connected to a power supply (not shown) via electrical connection  106 . Reactor  100  also has second electrode  110 , which in the present embodiment may be grounded or may have a different potential than first electrode  104 . Plasma zone  114  may be initiated by evacuation of chamber  118  to a low enough atmospheric pressure as to cause the breakdown between first electrode  104  and second electrode  110 . After the breakdown occurs, gas may be injected to gradually increase the pressure in chamber  118 , along with current adjustment between first electrode  104  and second electrode  110 , until desired conditions are reached. It should be understood that the electrodes may be constructed using various construction materials and may be shaped and sized in various manners to create plasma zone  114 . 
         [0044]    The properties of plasma zone  114  may be further altered and, more specifically, tuned by modifying the relative electrical potentials that may be found throughout reactor  100 . For example, wall  102  of reactor  100  may be grounded in the present embodiment if wall  102  is constructed of metal, or be at a floating potential if it is made from a material such as quartz, but other embodiments may have an electrical potential applied to wall  102 . The electrical properties of reactor  100  may be further modified by applying an electrical potential to other parts of reactor  100 . 
         [0045]    Reactor  100  further has a rotational flow generator, input nozzle  120 , that introduces input fluid  116 , which is a stream of hydrogen sulfide in this embodiment, into chamber  118 . As discussed earlier in regards to  FIG. 1  and  FIG. 1   a,  preferably nozzle  120  is configured so that input fluid  116  is introduced into chamber  118  in a generally tangential direction, imparting a rotating force on the contents of chamber  118 . Additionally, although one input nozzle is shown, nozzle  120 , other configurations of reactor  100  may have more than one nozzle. As discussed previously, a rotational flow may be generated by various ways, such as a set of blades in chamber  118 . 
         [0046]    After dissociation, a fluidic output stream, stream  128  flows upwards out of reactor  100  through opening  130  and output stream  122 , which in this embodiment is condensed sulfur, flow downward out of reactor  100  to collection tank  124  to form sulfur output  126 . 
         [0047]    While the embodiments have been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function without deviating therefrom. Therefore, the disclosed embodiments should not be limited to any single embodiment but rather should be construed in breadth and scope in accordance with the appended claims.