Abstract:
A method for producing hydrogen from a light hydrocarbon gas with the hydrocarbon gas being converted to particulate carbon and hydrogen and thereafter quenched with liquid sulfur with the purified hydrogen being recovered as a product.

Description:
RELATED CASES 
       [0001]    This application is entitled to and hereby claims the benefit of the filing date of U.S. provisional application Ser. No. 61/198,099 entitled “Method for Producing Hydrogen” filed Nov. 3, 2008 by Peter D. Clark, Justin A. Lamar, and David K. Stevens. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the production of hydrogen from a light hydrocarbon gas with the hydrocarbon gas being converted to particulate carbon and hydrogen and thereafter quenched with liquid sulfur with the purified hydrogen being recovered as a product. 
       BACKGROUND OF THE INVENTION 
       [0003]    Recently there has been increased interest in the use of hydrogen as an automotive fuel and in many processes there is a requirement for hydrogen gas. These processes vary widely but particularly include refining operations. In most such operations, sour gas streams are also produced. These sour gas streams may be the result of other refining operations, such as desulfurization, crude oil distillation and the like. Further, natural gas streams containing acid gas components may be available to the refining operation. As a result of the removal of the acid gas components from such gases and the recovery of the acid gas components from other refinery streams, a considerable amount of sulfur is typically recovered by the use of Claus plants. 
         [0004]    Claus plants are considered to be well known to the art and basically comprise the partial oxidation of an acid gas stream to oxidize any hydrocarbons present in the stream and to convert the stream to a stream which contains hydrogen sulfide and sulfur dioxide in a 2:1 ratio. The sulfur dioxide and the hydrogen sulfide are then reacted over well known catalysts in the Claus process in successive stages to produce sulfur and an exhaust gas stream, which after processing in a tail gas clean up unit as well known to the art, comprises primarily carbon dioxide and water. Such processes produce sulfur but in many instances the amount of sulfur available from such processes exceeds the demand for sulfur. Further there is a need for hydrogen in refining and other operations and for fuel. 
         [0005]    Carbon black has been produced by a thermal carbon black process which consists of two furnaces which are used in alternate heating and production periods of about five minutes with each of the furnaces containing a network of heat resistant bricks. These are heated with natural gas and air. At a temperature of about 1400° C., the air is switched off and only natural gas is introduced for pyrolysis. Since this reaction is endothermic the temperature falls. At about 900° C. a new heating period is necessary. The products leaving the furnace are typically carbon black particles and nearly pure hydrogen gas.  Ullman&#39;s Encyclopedia of Industrial Chemistry  5 th    Ed., Vol. A 5, 1989. 
         [0006]    It is also well known that acetylene can be used to produce acetylene black, which has slightly different properties than carbon black, but also results in the production of hydrogen, although less hydrogen is produced with acetylene than with saturated light gases, such as methane. 
         [0007]    A further disclosure of thermal black processes is shown in Kirk-Othmer Encyclopedia of Chemical Technology, 4 th  Ed., Vol. 4, 1992, pp. 1053-1054. 
         [0008]    Such processes are considered to be well known to those skilled in the art and require the use of substantial heat input to thermally decompose methane or other light hydrocarbon gases into carbon particles and hydrogen gas. The use of such processes results in the production of a hydrogen gas stream which contains particulate carbon. This carbon is difficultly separated from such streams and accordingly an improved process has been sought whereby the carbon is readily removed from such streams. 
         [0009]    In view of the need for hydrogen and the excess capacity available for sulfur production, improved methods for the production of hydrogen utilizing the excess sulfur have been sought. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention comprises a method for producing hydrogen from a light hydrocarbon gas, the method comprising: passing the light hydrocarbon gas to a light hydrocarbon gas thermal decomposition zone to produce particulate carbon and hydrogen; separating the carbon particles from the hydrogen by contacting the carbon particles and the hydrogen with liquid sulfur to produce a liquid sulfur and carbon particle suspension and hydrogen; and, passing a portion of the liquid sulfur and carbon particle suspension; and, an oxygen-containing gas to combustion to produce a desired temperature in the thermal decomposition zone and produce a stream containing sulfur dioxide and carbon dioxide. 
         [0011]    The invention further comprises a method for producing hydrogen from a light hydrocarbon gas stream and an acid gas stream, the method consisting essentially of: passing the light hydrocarbon gas to a light hydrocarbon gas thermal decomposition zone to produce a particulate carbon and hydrogen; passing an acid gas steam to a Claus plant to produce a liquid sulfur stream and a carbon dioxide and water stream; passing the particulate carbon and hydrogen stream into contact with a portion of the liquid sulfur stream to produce a hydrogen stream and a liquid sulfur and carbon particulates suspension; and, combusting a portion of the liquid sulfur and carbon particles suspension with an oxygen-containing stream to produce heat for the thermal decomposition zone and a stream containing sulfur dioxide and carbon dioxide. 
         [0012]    The invention also comprises a method for producing hydrogen, sulfur, a sulfur dioxide and carbon dioxide stream and a carbon dioxide and water stream from a light hydrocarbon gas stream and an acid gas stream, the method consisting essentially of: passing the light hydrocarbon gas to a light hydrocarbon gas thermal decomposition zone to produce particulate carbon and hydrogen; passing an acid gas stream to a Claus plant to produce a liquid sulfur stream and a carbon dioxide and water steam; contacting the particulate carbon and hydrogen with liquid sulfur to produce a hydrogen stream and a sulfur and particulate carbon suspension; and, combusting a portion of the sulfur and particulate carbon suspension in a combustion zone to produce heat and a sulfur dioxide and carbon dioxide stream. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  discloses an embodiment of the present invention wherein a light hydrocarbon gas stream is passed to a thermal decomposition vessel with the exhaust stream from the vessel being passed to a sulfur quench to remove carbon particles with the sulfur being supplied by a Claus plant and a portion of the resulting sulfur/carbon suspension being used for a fuel to produce the desired temperature in the thermal decomposition vessel. The exhaust gas from the combustion of the sulfur/carbon suspension is passed to a Claus plant so that the products of the process are a sulfur stream, a hydrogen stream, a sulfur-carbon particulates suspension and a carbon dioxide and water stream; 
           [0014]      FIG. 2  shows a similar process wherein the product streams are a sulfur dioxide/carbon dioxide stream which is passed to injection into a subterranean formation or the like, a water/carbon dioxide stream and a hydrogen stream which is converted into energy; and 
           [0015]      FIG. 3  shows an alternate embodiment of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    In the description of the Figures, various pumps, valves, motors and the like required to achieve the described flows have not been shown since these articles of equipment are well known to those in the art and are omitted for conciseness. In the description of the Figures the same numbers will be used throughout to refer to the same or similar components in  FIG. 1  and  FIG. 2 . 
         [0017]    In  FIG. 1  a hydrogen production process  10  is shown wherein a methane or natural gas stream is charged through a line  12  to a light hydrocarbon gas disassociation vessel  14  which may optionally be a catalytic vessel. Vessel  14  is heated to a desired temperature (2300-2600° F.) by combustion of a liquid sulfur/carbon particulates suspension charged via line  18  with an oxygen-containing gas stream  16 , which may be air, oxygen-enriched air, or pure oxygen, which is combined with the suspension in line  20  and, as shown, combusted in vessel  14  to produce the desired temperature to thermally decompose the light hydrocarbon gas and produce a carbon dioxide/sulfur dioxide stream  22 . The light hydrocarbon gas is desirably natural gas and may contain hydrocarbon gases up to as high as propane. Desirably heavier hydrocarbon gases have been removed from this stream prior to passing it to vessel  14 . It will be appreciated that the methane stream in line  12  may have been treated for the removal of acid gases and the like which if removed, may be charged to a Clause plant  32 . 
         [0018]    The mixture of hydrogen and carbon particles is passed from vessel  14  through a line  24  to a sulfur quench vessel  26  wherein the stream is passed in intimate contact with a liquid sulfur stream to remove carbon particles from the hydrogen stream. The recovered hydrogen stream is then passed through a line  28  optionally with additional purification (not shown), as a product stream. The sulfur/carbon particle suspension is passed via a line  42  to a zone  44  from which it may be exported through a line  46  as a product or in which it may be solidified and marketed as a solid product. In either event, this material is desirable as a fuel and is particularly desirable for use as a fuel in sulfuric acid plants. 
         [0019]    The Claus plant  32  receives an acid gas feed stream through a line  34 , which may contain hydrogen sulfide, sulfur dioxide, light hydrocarbons and the like and optionally a carbon dioxide/sulfur dioxide stream through line  22 . In the Claus process, these materials are treated to produce sulfur and a gaseous stream  38  comprising carbon dioxide and water, which may be treated for venting to the atmosphere. The Claus plant produces sulfur, which is recovered through a line  30  and passed via line  30  to sulfur quench  26 . A sulfur product stream is also produced and recovered through a line  36 . By this process, a hydrogen stream and a sulfur/carbon particle suspension stream is produced along with a carbon dioxide and water stream and a sulfur product stream from light hydrocarbon gas and acid gases. This embodiment has effectively used a substantial quantity of the sulfur produced to produce another more valuable stream, i.e. the hydrogen stream. Further the sulfur recovered with the carbon suspension is a desirable fuel product and is readily marketed. 
         [0020]    The various types of and operation of the thermal decomposition vessel are considered to be well known, as is the operation of the Claus plant. The sulfur quench can be by any suitable contacting method which effectively contacts the liquid sulfur with the gaseous stream. Further the sulfur/carbon particle suspension may be marketed, as indicated, as a liquid or it may be solidified and marketed as a solid. Methods for converting such liquid streams to solids for marketing are well known to those skilled in the art and need not be discussed further. 
         [0021]    In  FIG. 2  a similar process  10 ′ is shown, but the sulfur dioxide/carbon dioxide stream recovered through line  22  is passed to disposal in a subterranean formation or the like in lieu of passing it back to Claus plant  32 . The stream charged through line  12  is a natural gas or pure methane stream and the operation of the decomposition vessel  14  is substantially the same as discussed above. The hydrogen stream produced through line  28  is passed via a line  48  to a fuel cell  50 , gas turbine or via a line  52  to any other suitable device, such as a turbine  54 , for converting the hydrogen into energy by the generation of steam, electricity or the like. This process produces, from an acid gas and a natural gas, an injection stream of sulfur dioxide and carbon dioxide, a product stream of sulfur, a sulfur/carbon particle suspension, energy and a stream comprising carbon dioxide and water. 
         [0022]    Many variations of the flow schemes shown above are possible to utilize the thermal decomposition reactor to produce the hydrogen and carbon particles with the removal of the carbon particles from the hydrogen by the use of a sulfur quench using sulfur produced by a Claus plant or other source of sulfur, which may utilize an acid gas waste stream to produce the sulfur. Both the sulfur and sulfur/carbon particle suspension are marketable as products as is the hydrogen stream with the sulfur dioxide and carbon dioxide being useful for injection into a subterranean formation for recovery of hydrocarbons. 
         [0023]    In  FIG. 3  a process  10 ″ is shown wherein an acid gas stream and a light hydrocarbon gas steam are converted into a hydrogen stream, a sulfur dioxide/carbon dioxide stream, a sulfur products stream and an exhaust carbon dioxide and water stream. In this process, a light hydrocarbon gas is charged through a line  112  to a thermal decomposition zone  114  which is heated to produce a desired temperature, which typically is from about 2300 to about 2600° F., to thermally disassociate the light hydrocarbon gas into a stream recovered through a line  120 , which includes carbon particulates and hydrogen. This stream is passed into a sulfur scrubber  122 , which includes a contact zone  124  wherein the gaseous stream containing the carbon particulates is passed upwardly through a downcoming stream of molten sulfur supplied to vessel  122  through a line  126 . 
         [0024]    A stream of hydrogen is recovered via a line  128  and passed through a heater  132  prior to passing to a hydrogenation vessel  134 . Hydrogenation vessel  134  may include a suitable hydrogenation catalyst. Hydrogenation vessel  134  is used to hydrogenate any sulfur compounds which may remain in the hydrogen stream is line  128 . The recovered stream from vessel  134  is passed through a line  136 , which includes a heat exchanger  138 , to an amine scrubber which comprises a first vessel  140  having a contact zone  142  wherein the hydrogen stream flows upwardly countercurrently to a downcoming aqueous lean amine stream  149  (regenerated amine) wherein the hydrogen sulfide is absorbed with the hydrogen stream being purified and discharged through a line  144 . 
         [0025]    The spent amine is recovered through a line  146  and passed to the upper portion of an amine regenerator  148  which includes a contact zone  150  where it flows downwardly, countercurrently to a stripping gas stream (not shown) to strip the hydrogen sulfide from the spent amine and produce a regenerated amine which is passed back to the top of vessel  140  as shown in line  149 . The acid gas steam in line  152  is desirably passed to the feedstream into a Claus process having a Claus combustor  190 . 
         [0026]    The stream of sulfur and carbon particulates recovered through a line  130  is passed to oxidation in a combustor  154 , which includes a heat recovery section  156 . An oxygen stream containing oxygen, oxygen enriched air or air is charged through line  155  to combustor  154  to produce sulfur dioxide and carbon dioxide which are passed through a line  162  to a heat recovery section  164  from which sulfur dioxide may be recovered and passed via a line  166  to Claus reactor  190  as desired. The amount of sulfur dioxide removed and returned to the Claus reactor  190 , is determined based upon the amount of sulfur dioxide necessary to produce the desired ratio of hydrogen sulfide to sulfur dioxide in the Claus process. The sulfur dioxide is used as desired to adjust the ratio of hydrogen sulfide to sulfur dioxide in the Claus process. The remaining constituents of the combustion stream in line  162  are then passed through a line  170 , which includes a heater  168  to cool the stream to a desired temperature with the stream of sulfur dioxide and carbon dioxide then being passed via a line  170  to injection into a subterranean formation or other disposal. 
         [0027]    An acid gas stream  178  may be passed to a first vessel  174  of an amine scrubbing system, which includes a contacting zone  176  to produce a desulfurized light hydrocarbon gas which is passed by a line  172  to combination with the natural gas stream or light hydrocarbon gas stream passed into the disassociation vessel  114  via line  112 . The acid gas constituents removed are removed by an amine solution which is passed through a line  186  to an upper portion of vessel  174  and contact the rising gas stream to remove the acid gas components from the stream for recovery through a line  180 , which contains spent amine solution. This stream is passed to an upper portion of an amine regeneration vessel  182 , including a reaction zone  184 . The regenerated amine is recovered through a line  186  and returned to the upper portion of vessel  174 . The acid gas constituents removed from vessel  182  along with a stripping gas, constitute an acid gas which may be used as a feedstream  188  to Claus reactor  190 . Further a second acid gas stream may be charged to the process through a line  152  as an additional acid gas feedstream to Claus reactor  190 . 
         [0028]    The acid gas streams fed to Claus reactor  190  are partially combusted with an oxygen-containing stream supplied via a line  192 , which may be air, oxygen, enriched air or oxygen, to produce a gaseous mixture having a ratio of hydrogen sulfide to sulfur dioxide of 2:1. These gases are at a relatively high temperature (typically, equal to or greater than 1500° F.) and are passed to a heat recovery zone  191  at a temperature from about 2200 to about 2800° F. from which heat values are recovered. The gaseous mixture is passed through line  196  to catalytic sulfur stages schematically shown at  198 . Molten sulfur is typically produced from heat recovery zone  191 , as shown through a line  194 , with additional sulfur being recovered from the catalytic Claus stages  198  as shown through a line  200 . These streams are combined to produce a product stream of sulfur in line  201 . A portion of the sulfur is passed through line  126  to sulfur quench in vessel  122 . 
         [0029]    The remaining components of the gaseous stream pass to the catalytic Claus stages and then via a line  202  to a conventional Claus tail gas treating process and then through line  206  to a Claus tail gas clean-up zone  204  an then to a stack  208  and to the atmosphere via a discharge as shown by line  210 . The heat produced in heat recovery  191  is shown as recovered by lines  118  and  160  and show the transfer of heat from heat recovery sections  156  and  191  to vessel  114  with the cooled stream from vessel  114  being recovered via lines  116  and  158 . The heat is thus transferred from heat recovery sections  191  and  156  to supply the heat required in thermal disassociation vessel  114 . 
         [0030]    This process results in the production of a hydrogen stream and a sulfur dioxide and carbon dioxide stream from an acid gas stream and a light hydrocarbon gas stream. The light hydrocarbon gas stream may be natural gas ad it may contain acid gases which may be separated as shown to produce desulfurized gas for charging to thermal disassociation vessel  114  by conventional amine scrubbing processes. In combination, the process produces a clean hydrogen stream, which may be at an elevated pressure if desired, a sulfur dioxide and carbon dioxide stream and a carbon dioxide and water stream with a product sulfur stream. The sulfur dioxide and carbon dioxide stream can be used as an injection stream for secondary or tertiary recovery of hydrocarbons or for other suitable uses. 
         [0031]    In all of its embodiments, this process has used sulfur constituents for the production of energy and for the separation of carbon particles from hydrogen gas to produce a hydrogen gas stream by the use of sulfur streams produced from sulfur which may be in excess of the demand for sulfur. In any event, even if the demand for sulfur is adequate to require the production of all of the sulfur available, the use of the sulfur on site as an existing process stream results in economies of operation since a locally produced stream is used as a reagent and does not require importation into the process. 
         [0032]    In summary, the present invention has been shown to be effective to produce hydrogen by heretofore unknown processes at units wherein Claus plants are present so that the hydrogen may be made available for other process requirements thereby avoiding the cost and inconvenience of importation of hydrogen into the plant. 
         [0033]    While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments.