Abstract:
A gasification plant and methods for producing ammonia, Fischer-Tropsch fuels, electrical power, and/or sulfur from carbon-bearing feedstocks including coal and/or petroleum coke. Methods for production of desired relative amounts of ammonia and Fischer-Tropsch liquid hydrocarbons by adjusting the amount of synthesis gas bypassing the Fischer-Tropsch reactor. The multi-product and integrated plants may be used to reduce the amount of CO 2  vented into the atmosphere during the production of these products.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application which claims the benefit under 35 U.S.C. §121 of U.S. patent application Ser. No. 11/874,741, filed Oct. 18, 2007, which is a continuation of U.S. patent application Ser. No. 11/004,036, filed Dec. 3, 2004, which claims priority to U.S. Provisional Application No. 60/526,515 filed Dec. 3, 2003, the disclosures of each of which are hereby incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates generally to the field of syngas generators, such as reformers and gasifiers of hydrocarbon fluids and solid carbonaceous materials, and Fischer-Tropsch (FT) units primarily for creating liquid hydrocarbons from syngas. Syngas generators, FT, and ammonia synthesis are combined to create an integrated plant for providing one or more of ammonia, carbon dioxide, electric power, and even sulfur when dealing with sulfur-containing raw material. 
       BACKGROUND 
       [0004]    Our modern civilization cannot be sustained without burning carbonaceous materials for primarily motive and electrical power within the foreseeable future. The carbon dioxide (CO 2 ) generated by such burning may be contributing to the gradual increase of the planet&#39;s temperature since 1900. This is occurring because CO 2  permits the sun&#39;s energy to pass through the atmosphere, but traps the longer wavelength energy radiated by the earth into the atmosphere. 
         [0005]    The integrated plants and processes of this invention can help reduce the amount of CO 2  currently vented into the air as a by-product of synthesizing the various products later discussed in the description of the manufacturing plant flow diagrams. Consequently, the reduction of CO 2 , which is a greenhouse gas, through the sequestration processes detailed herein, reduces the amount of greenhouse gases vented into the atmosphere. Further, the plants of this invention produce substantial energy savings by balancing exothermic and endothermic reactors as discussed below. 
         [0006]    U.S. Pat. No. 6,306,917 to Mark S. Bohn et al. teaches that hydrocarbons, carbon dioxide, and electric power can be manufactured at a plant using the Fischer-Tropsch (FT) reactors. It also suggests that urea can be produced from the carbon dioxide but no suggestion is given as to what facilities or processes are needed to manufacture the urea or the economic practicality of such a course. U.S. Pat. No. 6,632,846 to Sheppard et al. teaches that ammonia, carbon dioxide, hydrocarbons, electric power and urea can be manufactured using FT reactors. Urea is produced from reacting the ammonia with the carbon dioxide. 
         [0007]    In U.S. Pat. No. 4,886,651, Patel et al. describe an integrated system that produces methanol, ammonia, and higher alcohols from natural gas. Steam reformers are used to produce streams of gases rich in hydrogen. Nitrogen for the ammonia synthesis is obtained from an air separation unit. The process is not relevant to a coal or petroleum coke feedstock. 
         [0008]    In U.S. Pat. No. 6,248,794, Gieskes describes an integrated process for converting hydrocarbon gas to liquids. The tail gases from the Fischer-Tropsch reactor are used only as fuel. Also, the systems described are not relevant to systems using a solid carbonaceous feedstock. 
         [0009]    In U.S. Patent Application Publication No. 2002/0143219, Price et al. describe a system for converting natural gas to hydrocarbons and ammonia. Tail gases from a FT reactor are recycled to the front end to a reformer in one example, and tail gases are recycled back to a second autothermal reformer in another example. Here again, solid carbonaceous feedstocks requiring gasification cannot be used in this system. 
         [0010]    In U.S. Pat. No. 6,586,480, Zhou et al. describe an integrated system using synthesis gas derived from coal for producing hydrocarbon liquids and ammonia. In this system, the FT tail gas is shifted and hydrogen removed from the shifted tail gases is used in ammonia production. Reforming the gaseous hydrocarbons in the FT tail gases is not considered. 
         [0011]    The mentioned references deal with economic niches where tax incentives, regulatory penalties and other incentives must combine with other factors to make the processes commercial. A continuing increase in world temperatures or a firmer tie-in between the CO 2  in the atmosphere and increasing world climate temperatures could quickly result in such incentives. The plants can be of particular utility when sited at remote locations where there is a large surplus of natural gas, petroleum, coal or other carbonaceous materials which are presently unrecoverable because of transportation costs, etc. 
         [0012]    Increasing regulatory demands have limited, and, in some instances extinguished, the petroleum producers&#39; and refiners&#39; ability to flare waste gases. Further, there are often limitations on the amounts and kinds of other wastes that can be disposed of locally without harm to the environment, e.g., at an offshore crude oil producing platform. The multi-product plants of this invention provide a mechanism for packaging the various unit processes required for the utilization of this invention in a manner that the resulting plants can be utilized to supply electricity for a platform, eliminate the need for flares, convert the waste gases and liquids normally flared into liquid hydrocarbons and ammonia substantially eliminating local CO 2  emissions. Solid commercial products can also be produced for agriculture, e.g., sulfur. 
         [0013]    The unit processes of this invention are each individually well known and the economics of the processes have been commercially proven. However, the joining of these unit processes as taught herein provides a utility for environmental and other purposes that has heretofore been unforeseen. 
       SUMMARY 
       [0014]    With the present invention, cleaned syngas generated by gasification of a carbonaceous raw material with oxygen and produced in an Air Separation Unit (ASU) is introduced into a Fischer-Tropsch (FT) synthesis unit for production of liquid hydrocarbons. The tail gases from the Fischer-Tropsch reactor containing significant amounts of gaseous hydrocarbons are reformed in a steam reformer to produce additional amounts of hydrogen. The CO in the tail gas from the FT unit and in the bypassed synthesis gas is shifted to produce hydrogen (H 2 ) which, after extraction, e.g., in a hydrogen membrane, and purification, is combined with nitrogen (N 2 ) from the ASU in the correct ratio for ammonia production, typically around a molar ratio of H 2 :N 2 =3. This mixture is compressed and introduced into a standard ammonia synthesis loop. After extraction of the H 2 , the residual gas can be used for power generation, e.g., in a combined cycle power unit. The FT production relative to the ammonia production may be adjusted by bypassing more or less syngas around the FT synthesis unit. 
         [0015]    As a variation to the above, the FT tail gas may be combined with the by-passed synthesis gas and shifted. Hydrogen removed from the shifted gas is used in the ammonia synthesis reactor while the remaining tail gases may be used as fuel in a gas turbine combustor. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0016]      FIG. 1  is a simplified flow diagram of the disclosed process of producing ammonia and FT liquids. 
           [0017]      FIG. 2  is a simplified flow diagram of an alternative process for producing ammonia and FT liquids. 
       
    
    
       [0018]    Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangements shown, since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
       DETAILED DESCRIPTION 
       [0019]      FIG. 1  discloses a process for producing ammonia, FT fuels and power. Oxygen and nitrogen are separated from air in air separation unit  10 . Carbonaceous raw material and water from tank  15  and oxygen from unit  10  are introduced into synthesis gas generator  30  as slurry  20 . As shown in Examples 1 and 2, a slurry of coal and/or petroleum coke is used. Under synthesis gas forming operating conditions, synthesis gas  40  comprising hydrogen, carbon monoxide, carbon dioxide, methane, water, and sulfur compounds is produced. Although synthesis gas generator  30  is a gasifier in this example, other types of gas generators may be used. Inorganic slag  35  is exported for sale or other uses including disposal. 
         [0020]    Synthesis gas  40  is fed to process boiler  50  for steam heat recovery before it is introduced into syngas cleaning unit  60  for char removal. Boiler  50  produces high pressure steam  53  while reducing the temperature of the syngas. Char  63  is recycled to gasifier  30 . 
         [0021]    Reactor effluent gas, or cleaned syngas  65 , is cooled in unit  70  and then processed through acid gas removal (AGR) unit  80  to remove hydrogen sulfide and carbon dioxide. An amine scrubbing system or other AGR system known to one skilled in the art may be used. For cooling, a tubular heat exchanger or other known systems may be utilized. Process condensate water  71  and hot boiler feed water  73  are recycled respectively for plant uses. 
         [0022]    Essentially all of the sulfur in feedstock  20  is converted to H 25  during syngas generation. Having undergone acid gas removal in unit  80 , H 25  produced in generator  30  is contained in acid gas stream  83  and may be recovered by utilizing a sulfur recovery system  90 . For example, for large amounts of sulfur and relatively high H 2 S, a Claus unit may be employed. Since the amount of H 2 S produced depends on the sulfur content of a feedstock, the type of sulfur recovery system required would depend on the desired sulfur recovery efficiency, the quantity of sulfur to be removed, and the concentration of the H 2 S in the acid gas, other types of sulfur recovery systems should be evaluated to maximize the installation of best available control technology. Once recovered, sulfur  95  may be exported. Carbon dioxide  81  from acid gas removal unit  80  may be sequestered for sale or for other on-site or off-site uses. 
         [0023]    After acid gas removal, further cleaning to remove contaminants detrimental to the downstream FT catalyst is required. Synthesis gas  85  is passed through guard beds  100  to reduce contaminant levels in the synthesis gas before it is admitted to the FT reactor. A zinc oxide bed can be used to remove a few ppm of hydrogen sulfide. Other types of guard beds and various configuration of beds may be utilized. 
         [0024]    A portion  105  of synthesis gas  103  is introduced into Fischer-Tropsch reactor  110  where primarily aliphatic hydrocarbons and carbon dioxide are formed. Liquid hydrocarbons  112  from this reaction are separated from Fischer-Tropsch tail gas  117  comprising carbon dioxide, uncondensed hydrocarbons, unreacted hydrogen and unreacted carbon monoxide. Separated FT effluent  116  may be recycled to the slurry preparation tank  15 . Liquid hydrocarbons  112  undergo product upgrade in reactor  113  where hydrotreating allows products such as naphtha  114  and diesel  115  to be exported. 
         [0025]    A portion  106  of synthesis gas  103  is combined with Fischer-Tropsch tail gas  117  from FT reactor  110  whereby gas mixture  118  is formed. Gas mixture  118  is compressed to an elevated pressure using compressor  120 . Compressed gas mixture  125  is then introduced along with steam into one or more shift reactors  130  to convert a portion of the carbon monoxide in the FT tail gas and water to hydrogen and carbon dioxide. Shifted gases  135  are introduced into hydrogen membrane separator  150  to produce two gas streams-stream  151  comprising hydrogen-rich gases and stream  153  comprising hydrogen-lean gases. Optionally, absorption unit  140  may be used to remove carbon dioxide from shifted gases  135  before introducing the gases into hydrogen membrane separator  150 . Carbon dioxide from the absorption unit may be combined for sequestration with the carbon dioxide  81  from acid gas removal as denoted by  81   a.    
         [0026]    Stream  153  is burned in gas turbine combustor  160  exhausting into heat recovery steam generator (HRSG)  170 . Through HRSG  170 , high pressure steam  173  is directed through steam turbine/generator set  180 , e.g., a three-stage turbine mechanically coupled to a generator, during the production of electricity. Low pressure steam  181  from the turbine may be directed to export. Power  185  can be allocated as parasitic power  187  to feed the plant or exportable power  189 . Steam  171  from HRSG  170  is a source of plant steam. 
         [0027]    Stream  151  is compressed to an elevated pressure in compressor  190  and then introduced into pressure swing adsorption unit  200  to produce a stream  205  of high purity hydrogen. Stream  205  together with nitrogen from air separation unit  10  is introduced into reactor  210  to produce ammonia  215  for sale. A portion  206  of stream  205  is used for product upgrade of liquid hydrocarbons  112  from FT reactor  110 . 
         [0028]      FIG. 2  discloses an alternative process for producing ammonia, FT fuels and power. The processes before the introduction of synthesis gas into the FT reactor are similar to those of  FIG. 1 . A portion  105  of synthesis gas  103  is introduced into Fischer-Tropsch reactor  110  where primarily aliphatic hydrocarbons and carbon dioxide are formed. Liquid hydrocarbons  112  from this reaction are separated from Fischer-Tropsch tail gas  117 . Liquid hydrocarbons  112  undergo product upgrade in hydrotreater  113  wherein products such as naphtha  114  and diesel  115  may be produced, e.g., for export. 
         [0029]    In this alternative process, Fischer-Tropsch tail gas  117  from FT reactor  110  is compressed to an elevated pressure using compressor  310 . Compressed FT tail gas  315  is then introduced into steam methane reformer  330 . Steam methane reformers typically use natural gas comprising methane, ethane and smaller amounts of other gaseous hydrocarbons as a feedstock. In this embodiment, the methane, ethane, ethylene, propane, propylene, butane, butane and/or small amounts of higher hydrocarbons in the FT tail gas serve as feedstock. Hydrocarbons in FT tail gas  315  and water are converted to reformer effluent  335  comprising hydrogen, carbon monoxide, and carbon dioxide. Here, the portion of synthesis gas, which was previously combined with the Fischer-Tropsch tail gas from the FT reactor, is introduced into the ammonia plant train before shifting occurs. Thus, portion  107  of synthesis gas  103  is combined with reformer effluent  335  whereby the gas mixture is fed to shift reactor  340 . In the shift reactor, carbon monoxide is reacted with more steam to produce a mixture of carbon dioxide and hydrogen. Shifter effluent  345  is fed into carbon dioxide absorption unit  350  wherefrom CO 2  is removed. Carbon dioxide from the absorption unit  350  may be combined for sequestration with the carbon dioxide  81  as denoted by  81   b . The product  355  of the absorption unit contains traces of CO and CO 2  in a highly concentrated hydrogen stream. The carbon dioxide removal unit  350  may use an amine for absorption. Methanator  360  is used to convert the trace CO and CO 2  in stream  335  to methane. The methanator effluent  365  comprises high purity hydrogen and methane. Effluent  365  together with nitrogen from air separation unit  10  are introduced into reactor  370  to produce ammonia  375  for sale. Adiabatic pre-reformer  320  may be used to remove unsaturated hydrocarbons, which may form carbon in the reformer, from compressed tail gas  315  prior to introduction into steam reformer  330 . The ammonia loop comprising units  330 ,  340 ,  350 ,  360 , and  370  may be in an existing ammonia plant. 
         [0030]    Purge stream  371  is introduced into hydrogen membrane separator  380  to produce two gas streams-stream  385  comprising hydrogen-rich gases and stream  383  comprising hydrogen-lean gases. Stream  383  is burned in HRSG  390 . Through HRSG  390 , high pressure steam  393  is directed through steam turbine/generator set  400 , e.g., a three-stage turbine mechanically coupled to a generator, during the production of electricity. Low pressure steam  401  from the turbine may be directed to export. Power  405  can be allocated as parasitic power  407  to feed the plant or exportable power  409 . Steam  391  from HRSG  390  is a source of plant steam. 
         [0031]    Stream  385  is compressed to an elevated pressure in compressor  410  and then introduced into pressure swing adsorption unit  420  to produce a stream  425  of high purity hydrogen which is used for product upgrade of liquid hydrocarbons  112  from FT reactor  110 . 
         [0032]    Similar to  FIG. 1 , H 2 S produced in generator  30  is contained in acid gas stream  83  and may be recovered by utilizing a sulfur recovery system  90 . Once it is recovered, sulfur  95  may be exported. 
         [0033]    The following calculated examples are presented to further illustrate the process. Example 1 is based on  FIG. 1 . Example 2 is based on  FIG. 2 . 
       Example 1 
       [0034]    Two thousand (2,000) short tons per day (STPD) of petroleum coke containing 7% moisture are gasified to produce synthesis gas comprised of hydrogen, carbon monoxide, carbon dioxide, water, methane, nitrogen and impurities. After condensing the water and removal of impurities, the remaining gases are divided into two streams. One stream is fed to a slurry Fischer-Tropsch reactor utilizing an iron-based catalyst. The tail gases from the FT reactor after liquid product removal are comprised of hydrogen, carbon monoxide, carbon dioxide, nitrogen, ethane, ethylene, propane, propylene, butane, butene, pentane, pentene, and smaller amounts of higher hydrocarbons. These tail gases are combined with the other stream bypassing the FT reactor and the combined gases are fed to a shift reactor to produce hydrogen and carbon dioxide from carbon monoxide and water. The gases from the shift reactor are fed to a hydrogen membrane separator for recovering hydrogen. The hydrogen permeate from the membrane separator is compressed and refined to high purity using a pressure swing adsorption (PSA) unit. The purified hydrogen from the PSA unit is fed to an ammonia synthesis reactor where it reacts with nitrogen from the air separation unit to produce ammonia for export. A small portion of the purified hydrogen is used for upgrading the FT products. Off-gases from the hydrogen membrane separator are used for fuel in a gas turbine combustor. Flue gases from the gas turbine combustor provide heat required by the heat recovery steam generator (HRSG). Steam from the gasifier process boiler, the FT reactor cooling, and the ammonia synthesis reactor cooling are fed to the HRSG. Electrical power from both the steam turbine and gas turbine is used for plant requirements. 
         [0035]    Based on the process described above using 2,000 STPD of petroleum coke as the feedstock, calculations using in-house software programs show that the following amounts of FT products and ammonia can be produced for export: 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Synthesis Gas Bypassing FT Reactor 
               
             
          
           
               
                   
                 Products 
                 0% 
                 50% 
                 100% 
               
               
                   
                   
               
             
          
           
               
                   
                 FT Product, BPD 
                 3400 
                 1700 
                 0 
               
               
                   
                 Ammonia, STPD 
                 467 
                 1023 
                 1596 
               
               
                   
                   
               
             
          
         
       
     
       Example 2 
       [0036]    Five thousand one hundred and seventy (5,170) short tons per day (STPD) of Wyoming Powder River Basin (PRB) coal containing 30% moisture are gasified to produce synthesis gas comprised of hydrogen, carbon monoxide, carbon dioxide, water, methane, nitrogen and impurities. After condensing the water and removal of impurities, the remaining gases are divided into two streams. One stream is fed to a slurry Fischer-Tropsch reactor utilizing an iron-based catalyst. The tail gases from the FT reactor after liquid product removal are comprised of hydrogen, carbon monoxide, carbon dioxide, nitrogen, ethane, ethylene, propane, propylene, butane, butene, pentane, pentene, and smaller amounts of higher hydrocarbons. Approximately 25% of these tail gases are separated for use as fuel for the steam reformer described below. Approximately 75% of these gases are compressed and fed to an adiabatic pre-reformer for removal of olefins. The gases exiting the pre-reformer are combined with steam and fed to a steam reformer for producing hydrogen, carbon monoxide, carbon dioxide, methane and water. The other stream bypassing the FT reactor is combined with the effluent from the steam reformer and the combined gases are fed to a shift reactor to produce hydrogen and carbon dioxide from carbon monoxide and water. The carbon dioxide is removed from the shifted gases and combined with the carbon dioxide from the acid gas removal system. This concentrated stream of carbon dioxide can be sequestered. The remaining gases are fed to a methanator for removal of carbon monoxide. The remaining gases comprised of hydrogen, nitrogen and methane are combined with nitrogen from the air separation unit and fed to an ammonia synthesis reactor. Ammonia from the ammonia synthesis reactor is exported for sale. A small purge stream from the ammonia synthesis reactor is fed to a hydrogen membrane separator for recovery of hydrogen. The hydrogen permeate from the membrane separator is compressed and refined to high purity using a pressure swing adsorption (PSA) unit. The purified hydrogen from the PSA unit is used for upgrading the FT products. Off-gases from the hydrogen membrane separator and the PSA unit are used for fuel in the heat recovery steam generator (HRSG). Steam from the gasifier process boiler, the FT reactor cooling, reformer flue gases, and the ammonia synthesis reactor cooling are fed to the HRSG. The superheated steam from the HRSG is used in a steam turbine for generating electrical power for plant usage and for export. 
         [0037]    Based on the process described above using 5,170 STPD of Powder River Basin Coal as the feedstock, calculations using in-house software programs show that the following amounts of FT products and ammonia can be produced for export: 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Synthesis Gas Bypassing FT Reactor 
               
             
          
           
               
                   
                 Products 
                 0% 
                 50% 
                 100% 
               
               
                   
                   
               
             
          
           
               
                   
                 FT Product, BPD 
                 5000 
                 2500 
                 0 
               
               
                   
                 Ammonia, STPD 
                 666 
                 1652 
                 2636 
               
               
                   
                   
               
             
          
         
       
     
         [0038]    Although the present invention has been described with reference to various embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. Each apparatus embodiment described herein has numerous equivalents.