Patent Publication Number: US-2002006969-A1

Title: System and method for converting light hydrocarbons into heavier hydrocarbons and for treating contaminated water

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims priority to previously filed provisional Application No. 60/207,812 filed in the United States Patent and Trademark Office on May 30, 2000. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates to the conversion of hydrocarbons such as through the FischerTropsch reaction, and more particularly relates to a system and method for converting light hydrocarbons into heavier hydrocarbons and for treating water such as desalinating salt water.  
       BACKGROUND OF THE INVENTION  
       [0003] The synthetic production of hydrocarbons by the catalytic reaction of synthesis gas is well known and is generally referred to as the Fischer-Tropsch reaction. The Fischer-Tropsch process was developed in early part of the Twentieth Century in Germany. It was practiced commercially in Germany during World War II and later in South Africa.  
       [0004] The Fischer-Tropsch reaction for converting synthesis gas (primarily CO and H 2 ) has been characterized by the following general reaction:  
                 
 
       [0005] The hydrocarbon products derived from the Fischer-Tropsch reaction range from single carbon methane to higher molecular weight longer chained paraffinic waxes containing more than 100 carbon atoms.  
       [0006] Numerous Fischer-Tropsch catalysts have been used in carrying out the reaction, including cobalt, iron, and ruthenium, and both saturated and unsaturated hydrocarbons can be produced. The synthesis gas may be made from natural gas, gasified coal, and other sources. Three basic techniques have been employed for producing the synthesis gas (“syngas”), which is substantially carbon monoxide and molecular hydrogen. The three include oxidation, reforming, and autothermal reforming.  
       [0007] Fischer-Tropsch hydrocarbon conversion systems typically have a synthesis gas generator and a Fischer-Tropsch reactor unit. The synthesis gas generator receives light, short-chain hydrocarbons such as methane and produces synthesis gas. The synthesis gas is then delivered to a FischerTropsch reactor. In the F-T reactor, the synthesis gas is converted to heavier, longer-chain hydrocarbons. Recent examples of Fischer-Tropsch systems include U.S. Pat. Nos. 4,883,170; 4,973,453; 5,733,941; and 5,861,441 all of which are incorporated by reference herein for all purposes.  
       [0008] For water to be used as potable water or to adequately treat water to allow for its disposal in some instances, water is frequently treated. Such water treatments may involve boiling the water for set periods, aerating it, or removing salt and other contaminants. In certain parts of the world, the need to desalinate water is particularly valuable given the shortage of clean water. Through the application the term-contaminated water will be used to include salt water, brine, or other water with contaminates that are to be removed.  
       [0009] Salt water, sometimes referred to as “brine,” typically is desalinated by a thermal or membrane process. The thermal technique employs a distillation technique with the salt water being boiled and the resultant steam being collected and condensed into desalinated water. A widely used thermal process is the multistage flash distillation (or MSF) units. In a MSF unit, the heated salt water is fed into a flash chamber in which the pressure if lowered to allow the salt water to boil at lower temperatures. The resultant steam is condensed on tubes that carry the incoming salt water into the system. The steam heats the cooler incoming salt water and the vapor condenses to form desalinate. The remaining salt water, which is now more concentrated, goes to a second chamber that is at a lower pressure and the steam/condensation process is repeated there. Numerous chambers may be used in a plant.  
       [0010] Because of the need to avoid the formation of calcium sulphate salts through precipitation on surfaces in the water treatment facility, the temperature of the boiling salt water is limited to about 120 C. This typically increases the energy requirement of the system. In the past, this energy has been provided in some circumstances by combining a desalination plant with an electrical power plant; see e.g., U.S. Pat. No. 5,346,592 and 5,622,605. Such systems usually take the steam from the power plant and use it as the thermal source for a MSF.  
       SUMMARY OF THE INVENTION  
       [0011] Therefore, a need has arisen for a system and method that addresses shortcomings of prior systems and methods. According to an aspect of the present invention, a process for converting light hydrocarbons into heavier hydrocarbons and for treating water includes the steps of preparing a synthesis gas; converting the synthesis gas to heavier hydrocarbons; removing heat generated in the steps of preparing and converting synthesis gas by generating steam; treating a water stream to remove contaminants with a water treatment unit that uses thermal energy; and using the steam generated in the heat removal to provide thermal energy for the treating of the water.  
       [0012] According to another aspect of the present invention a system for converting light hydrocarbons into heavier hydrocarbons and for treating water that includes a hydrocarbon conversion system having a synthesis gas subsystem for receiving an oxygen-containing gas and light hydrocarbons and producing a synthesis gas, a synthesis subsystem coupled to the synthesis gas subsystem for receiving synthesis gas and converting the synthesis gas to heavier hydrocarbons, and wherein the hydrocarbon conversion system is operable to produce steam; and a water treatment subsystem coupled to the hydrocarbon conversion system for receiving thermal energy therefrom and using the thermal energy to treat water.  
       [0013] According to another aspect of the present invention, a process for converting light hydrocarbons into heavier hydrocarbons, treating water, and producing electricity includes the steps of converting light hydrocarbons into heavier hydrocarbons; using energy produced in the conversion to power an electrical generator; treating a water stream to remove contaminants; and using thermal energy from the conversion step to provide the thermal energy for the water treatment step.  
       [0014] The present invention provides numerous advantages and a number of examples follow. An advantage of the present invention is that the combination of a water treatment subsystem with a hydrocarbon conversion subsystem allows for greatly improved thermal efficiency of the combined system. Another advantage of the present invention is that the chemical process generating steam for this system generates more steam than co-generation systems by several orders of magnitude—in some embodiments, the quantity steam generated could power ten or more desalination units. Another advantage is that the quantity of water treated can be readily expanded by adding stages in one embodiment that uses an MSF. Another advantage is the system allows better economic performance when compared to a separate hydrocarbon conversion plant and a separate water treatment plant (e.g., desalination plant). As another advantage, the system and method are able to utilize the large volume of low-pressure steam produced by a Fischer-Tropsch conversion system. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features, and wherein:  
     [0016]FIG. 1 is a schematic diagram of one embodiment of a system according to an aspect of the present invention for converting hydrocarbons and treating water;  
     [0017]FIG. 2 is a schematic diagram of a second embodiment of a system according the present invention showing an integrated conversion system and water treatment system;  
     [0018]FIG. 3 is a schematic diagram of third embodiment of a system according to an aspect of the present invention for converting hydrocarbons and treating water;  
     [0019]FIGS. 4A and 4B present a schematic diagram of fourth embodiment of a system according to an aspect of the present invention for converting hydrocarbons and treating water; and  
     [0020]FIG. 5 presents an alternate embodiment of the system in which tail gas may be combusted to generate additional steam. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0021] The present invention and its advantages are best understood by referring to FIGS.  1 - 5  of the drawings, like numerals being used for like and corresponding parts of the various drawings.  
     [0022] Referring to FIG. 1, a system  10  for converting light hydrocarbons into heavier hydrocarbons and treating water is presented. The water is treated to remove contaminates, such as salt, to produce a purified water. A prominent example used in the embodiments is to treat salt water to remove the salt. Fresh water may also be treated to remove other contaminants or with sufficient temperature to kill microorganisms.  
     [0023] The system  10  preferably includes a synthesis gas subsystem  12 , a synthesis subsystem  14 , and a water-treatment subsystem  16 . The system  10  may further include a product upgrade subsystem  18 . The synthesis gas subsystem  12  and synthesis subsystem  14  together form a hydrocarbon conversion system that takes light hydrocarbons and produces heavier hydrocarbons.  
     [0024] The synthesis gas subsystem  12  includes a synthesis-gas-generator. The synthesis gas generator (not explicitly shown) can take numerous forms such a partial oxidation unit, a catalytic partial oxidation unit, a steam methane reformer or an autothermal reformer (ATR), but is preferably an autothermal reformer unit with a quench cooler for the ATR exhaust. The synthesis gas subsystem  12  receives an oxygen-containing gas (e.g., air, oxygen, enriched air, etc., but preferably compressed air), light hydrocarbons, and steam through conduits  13 ,  15 , and  17  and makes synthesis gas and makes a high pressure (on the order of about 600 psi) steam. The high-pressure steam is delivered by conduit  20  to turbine  22 . Turbine  22  may power generator  24  or a synthesis gas booster compressor or some other item. The low-pressure steam (e.g., on the order of 25-50 psi) exiting the turbine  22  is delivered by conduit  26  to the water-treatment subsystem  16 . The low-pressure steam of conduit  26  might be atmospheric or even a vacuum to provide for optimum temperatures in the heat exchangers associated with desalination subsystem  16  to prevent plating and other associate problems. Boiler feed water is delivered to the synthesis gas subsystem  12  through conduit  28 . The synthesis gas generated in subsystem  12  is delivered by conduit  30  to synthesis subsystem  14 .  
     [0025] The synthesis subsystem  14  receives the synthesis gas from conduit  30  and also boiler feed water from conduit  28 . The boiler feed water is used to cool within subsystem  14  and it exits in conduit  34  as a medium pressure steam (preferably on the order of 150 psi) and is delivered—depending on pressure—to another turbine, a topping turbine  36 . Turbine  36  can just be a stage of turbine  22 . The turbine  36  may be used to drive a generator  38  or other equipment. The resultant low-pressure steam from turbine  36  is delivered to conduit  26  that delivers it to the water-treatment subsystem  16 . The synthesis subsystem  14  receives the synthesis gas and makes Fischer-Tropsch products that are preferably delivered through conduit  40  to product upgrade subsystem  18 .  
     [0026] The product upgrade subsystem  18  is used to form various products from the raw FT product such as by hydrogenating and hydrocracking. The product upgrade subsystem  18  generates considerable low-pressure steam (preferably on the order of about 50 psi) that is delivered through conduit  42  to conduit  26  and to water-treatment subsystem  16 . The product upgrade system further processes the Fischer-Tropsch products for a variety of uses and/or stores the product.  
     [0027] The thermal energy of the hydrocarbon conversion system (e.g. subsystems  12  and  14  and optionally  18 ) is used in the water treatment subsystem  16 . In FIGS. 1 and 3, the thermal energy of the hydrocarbon conversion system is converted to steam and the steam used in water treatment subsystems. The thermal energy may also be used by transferring the thermal energy to water that is to be treated and sending the water to the water treatment subsystem as illustrated in the embodiments of FIGS. 2 and 4 which are described further below.  
     [0028] The water-treatment subsystem  16  receives the low-pressure steam through conduit  26  and contaminated water to be treated, which may be a variety of types such as salt water in this example, through conduit  44 . Then using any of a number of water-treatment techniques known in the art (e.g., for desalination, it may be a multistage flash (MSF) unit or multi-effect distillation (MED) unit or a combination unit), the subsystem  16  produces a treated water stream, which in this example is a desalinate, that exits through conduit  46 . The desalinate may be chlorinated or otherwise treated before use as potable water. The non-desalinated contaminated water exits through conduit  48 . The non-desalinated, concentrated contaminated water of conduit  48  may be used in other systems or plants or may be exhausted back to sea or an ocean or other source assuming proper conditions. The boiler feed water exits through conduit  28  for use elsewhere in system  10 . System  10  is essentially a “tri-Gen” plant in that it generates the Fischer-Tropsch product, electricity, and treated water.  
     [0029] Referring now to FIG. 2, another system  100  for converting light hydrocarbons into heavier hydrocarbons and desalinating contaminated water is presented. System  100  has a synthesis gas subsystem  102 , a synthesis subsystem  104 , a product upgrading subsystem  106 , a desalination subsystem  108 , and a boiler feed water deaerator subsystem  110 .  
     [0030] The synthesis gas subsystem  102  receives an oxygen-containing gas, light hydrocarbons (e.g., methane), and steam through conduits  112 ,  114 , and  116 , respectively. The subsystem  102  produces synthesis gas that is delivered through conduit  118  to synthesis subsystem  104  and a high-pressure steam that is delivered to conduit  120 . Boiler feed water is delivered to synthesis gas subsystem  102  through conduit  117  and used to cool with high-pressure steam being generated. The high-pressure steam is delivered through conduit  120  to a turbine  122  that is driven thereby and from which boiler feed water exits having been condensed. Turbine  122  may drive a generator  123  or be used for shaft horsepower for another purpose. The expanded steam/water exists and is condensed by exchanger  126  and the resultant boiler feed water is delivered to conduit  124  and then to conduit  144 . As will be described further below, the boiler feed water exiting the turbine  122  is used to further heat pre-heated contaminated water to at or near its flash point temperature in heat exchanger  126  although it does not flash there because it is under pressure.  
     [0031] The synthesis subsystem  104  receives the synthesis gas  118  and preferably produces Fischer-Tropsch products that are delivered through conduit  128  to storage or to the product upgrading subsystem  106 . Boiler feed water is supplied through conduit  117  to subsystem  104  for cooling and a medium pressure steam in generated thereby. The medium pressure steam is delivered through conduit  130  to turbine  132 . The turbine  132  typically is used to drive a generator  133  or other device. The steam/water is delivered to heat exchanger  136  and the resultant condensed boiler feed water is delivered into a portion conduit  134  and then to conduit  144 . Conduit  134  includes the heat exchanger  136  that is used for further heating pre-heated contaminated water to at or near its flash point (although it does not flash because its under pressure) as will be described further below. The heat exchangers  126  and  136  are shown as separate devices from the turbines  122  and  132 , but can be an integral part of the turbine itself as many designs are possible; this is suggested in the drawing by the broken-line boxes around the turbines and heat exchangers.  
     [0032] The Fischer-Tropsch (“FT”) products are delivered through conduit  128  to the product upgrading subsystem  106 . Subsystem  106  takes the raw Fischer-Tropsch products and modifies them into various desirable products. The subsystem  106  receives boiler feed water through conduit  117  and produces large quantities of low-pressure steam that is delivered to conduit  140 . Conduit  140  contains a heat exchanger  142  that is used to further heat pre-heated contaminated water to at or near its flashing point, although it does not flash because it is under pressure as will be described further below. Conduits  124 ,  134 , and  140  deliver boiler feed water to conduit  144 .  
     [0033] Conduit  144  delivers the water to boiler feed water deaerator subsystem  110 . After deaerating the water, the deaerator subsystem  110  delivers the boiler feed water to conduit  117  for use in the system as previously described. Process water from the synthesis gas subsystem or synthesis subsystem may be delivered through conduit  201  to deaerator subsystem  110 .  
     [0034] Referring now to the de-salination subsystem  108 , contaminated water is introduced through conduit  146  to a heat rejection portion or stages  148  of subsystem  108 . Stages 1 through N are shown for heat rejection portion  148 . The contaminated water rejects heat as it travels through portion  148  and then is delivered to conduit  150 , which connects with conduit  152  and  154 . The contaminated water in conduit  152  is combined with waste contaminated water delivered through conduit  156  before exiting subsystem  108 . The salinity of the waste contaminated water in conduit  156  is adjusted to be safe for disposal in any oceans, lakes or seas. A side stream is pulled off of the contaminated water in conduit  146  and delivered by conduit  154  to a chemical injection drum  158  before being delivered by conduits  160  and  162  to contaminated water pump  164 . Drum  158  serves as a deaerator and allows injection of pretreatment chemicals. Conduit  166 / 172  is a contaminated water recycle. Conduit  168  maintains a vacuum. Contaminated water pump  164  motivates the contaminated water through conduit  172  to the heat recovery portion or stages  174 . Conduit  170  allows a vacuum to be pulled on all stages and removes non-condensables.  
     [0035] Heat is recovered by the contaminated water delivered by conduit  172  in stages  174  such that preheated contaminated water is delivered into conduit  176 . Conduit  176  delivers the pre-heated contaminated water to heat exchanger  142  and then to conduit  182 . Conduit  180  delivers pre-heated contaminated water to conduits  184  and  186 . Conduit  184  delivers the heated contaminated water to heat exchanger  136  and then to conduit  188 . The contaminated water in conduit  186  is delivered through heat exchanger  126  to conduit  188 . Conduit  188  delivers the heated contaminated water to conduit  182 . Generally, it is desirable to keep the contaminated water delivered by conduit  182  below 195° F. to avoid problems with precipitates in the contaminated water. Hotter temperatures are possible but more frequent cleaning and chemicals will be required. Conduit  182  delivers the heated contaminated water to heat recovery portion  174 . Heat exchangers  126 ,  136 , and  142  further heat the preheated contaminated water to the point that the contaminated water is ready to flash once the pressure is reduced at the first stage of the heat recovery portion  174 . The first stage is at a reduced pressure (sub-atmospheric) such that the contaminated water delivered by conduit  182  flashes, and stage  2  is at still a further reduced pressures such that the contaminated water again flashes and so forth to stage N. The contaminated water is evaporated and then condensed in heat recovery stages  174 . The contaminated water flashes and gets condensed on coils  189  and collected in the trough  190 . The desalinate in trough  190  migrates towards conduit  196  because of the pressure gradient between stages.  
     [0036] The desalinate is shown continuing between the heat recovery portion  174  and the heat rejection portion  148  by conduit  192  and similarly the contaminated water is transported between stages by conduit  194 . Large quantities of contaminated water are brought through conduit  146  to provide a one pass cooling of the contaminated water delivered through conduit  194  to the heat rejection stage  148  before the waste contaminated water is removed from system.  108 . Upon reaching the n-th stage of the heat rejection portion  148 , the wasted contaminated water is delivered to conduit  156 . The cumulative desalinate is delivered to conduit  196  from it where it may be used for any purpose desired for the desalinated water. A portion of the desalinate is removed from conduit  196  by conduit  198  to be used a make-up water for other portions of system  100 . The water in conduit  198  is delivered to the boiler feed water deaerator subsystem  110 .  
     [0037] Steam eductor  200  receives low pressure or medium pressure steam through conduit  202  which receives the steam from conduit  140 . Steam eductor  200  also receives inputs from conduits  170  and  168 . Steam eductor  200  is used to adjust the pressures within the various stages and devices of desalination subsystem  108  and to remove non-condensables.  
     [0038] Referring now to FIG. 3, a system  300  for converting light hydrocarbons into heavier hydrocarbons and for desalinating sea water is presented. System  300  is analogous in most respects to system  10  of FIG. 1, but notably has the addition of turbine  350  having combustor  352  and economizer or heat recovery steam generating (HRSG) unit  354  added on a front portion. In another embodiment, a gasifification unit could be substituted for combustor  352 .  
     [0039] Turbine  350  receives an oxygen-containing gas, preferably air, through inlet or intake conduit  356  which is compressed by compressor section  358  of turbine  350 . The compressed air is delivered by conduit  360  to combustor  352 , but a portion of the compressed air is removed from conduit  360  and delivered by conduit  362  to conduit  313  after passing through economizer  354 . Economizer  354  is associated with combustor  352  and is used to recover heat therefrom. Thus the compressed air of conduit  313  is compressed heated air that is delivered to the synthesis gas subsystem  312 . The economizer  354  also receives medium pressure steam through conduit  364  and super heats it before delivery to conduit  366 . If any super heated steam in conduit  366  is not needed for the synthesis gas subsystem  312 , it is delivered by conduit  368  to the high pressure steam of conduit  320 . Light hydrocarbons such as natural gas are delivered by conduit  370  to economizer  354  where the gas stream is heated and then delivered to conduit  315 .  
     [0040] Combustor  352  preferably is fueled by a low-BTU tail gas (for example 100 BTU/cu. ft. or less) that is delivered through conduit  372  after having been generated in the synthesis subsystem  314 . The BTU content of the tail gas in conduit  372  can also be higher than 100 BTU and further in some instances it may be desirable to further enrich BTU content by adding methane or other enriching gases through conduit  374 . The gas delivered by conduit  372  to combustor  352  is combusted and the exhaust is delivered through conduit  380  to expansion section  382  of turbine  350  and then exhausted through exhaust conduit or outlet  384 . Turbine  350  may be used to drive a generator  386  or other device.  
     [0041] Referring now to FIG. 4, another embodiment of a system  400  for converting light hydrocarbons into heavier hydrocarbons and for desalinating salt water is presented. System  400  is analogous to system  100  of FIG. 2 in most respects, but notably, turbine  510  with associated combustor  512  and associated economizer or heat recovery steam generator  514  have been added on a front portion. To conveniently present the analogous components and aspects of FIG. 4 as compared to FIG. 2, corresponding parts and subsystems have been identified with reference numerals related in that FIG. 2 starts with reference numeral  100  and carries through reference numeral  202  and the corresponding parts of FIG. 4 begin with reference numeral  400  and carry through reference number  502  with the last two digits being identical for corresponding parts.  
     [0042] An oxygen-containing gas is supplied to inlet or conduit  516  that is compressed in compressor section  518  of turbine  510 . The compressed gas is delivered at least in part by conduit  520  to combustor  512 . A portion of the compressed gas in conduit  520  is removed by conduit  522  for use in the hydrocarbon conversion subsystems. The compressed gas of conduit  522  is heated in economizer  514  to supply compressed heated air (or other oxygen containing gas) to conduit  412 . Light hydrocarbons such as natural gas are supplied through conduit  530  to economizer  514  where the gas is heated and then delivered to conduit  514 .  
     [0043] Steam, preferably a medium-pressure steam, is delivered to conduit  532  which is then delivered through economizer  514  where super heated steam is produced and delivered to conduit  534 . The super heated steam is delivered to synthesis gas subsystem  402 , but if not all of the super heated steam is needed, the excess is delivered by conduit  536  into conduit  420 . Synthesis subsystem  404  produces a Fischer-Tropsch product stream delivered to conduit  428 , but also a tail gas such as a low BTU tail gas (less than 100 BTU/cu. ft.) that is delivered to conduit  540  which in turn delivers the gas to combustor  512 . A richer BTU content tail gas may be used and in addition in some instances it may be desirable to enrich the tail gas by adding a fuel gas such as methane through conduit  542 . The exhaust products of combustor  512  are delivered by conduit or inlet  550  to the expansion section  552  of turbine  510  and then exhausted through outlet or conduit  554 . Turbine  510  may drive generator  560  or other devices.  
     [0044] In FIG. 5, an additional embodiment of the invention is shown in which all or part of the tail gas may be combusted in a relatively low BTU combustor to generate additional steam in the system. In this embodiment, the combustor takes on the form of a steam boiler, which may be fitted with low BTU burners. The low BTU combustor may burn pure tail gas or a mixture of tail gas and other higher BTU fuels. The higher BTU fuel may be blended with the tail gas, burned in dedicated burners, or a combination of the two methods may be used.  
     [0045] The system  600  includes a synthesis gas (“syngas”) subsystem  602 , a synthesis subsystem  604 , a product upgrading subsystem  606 , a desalination subsystem  608  and a tail gas combustor  610 .  
     [0046] The synthesis gas subsystem  602  receives an oxygen-containing gas, light hydrocarbons (e.g., methane), and steam through conduits,  611 ,  612 , and  613  respectively. The subsystem  602  produces synthesis gas that is delivered through conduit  614  to the synthesis (syngas) subsystem  604  and high pressure steam that is delivered to conduit  615 . Boiler feed water is delivered to synthesis gas (syngas) subsystem  602  through conduit  616  and is used for cooling in the subsystem, with high pressure steam being produced. The high pressure steam is delivered through conduit  615  to a module  617  that is used to extract work from the steam. The work module  617  may take on the form of a steam turbine that in turn is used to drive an electrical power generator, a compressor, or in other cases is another piece of equipment designed to perform other mechanical work. The steam may also be used for other types of work such as heating/cooling or other thermal or mechanical processes. In the process of performing work the high pressure steam is converted to low pressure steam and/or condensate which is delivered from the work module  617  to the desalination subsystem  608  through conduit  618 .  
     [0047] The synthesis subsystem  604  receives the synthesis gas from conduit  614  and also receives boiler feed water through conduit  619 . The boiler feed water is used for cooling within the subsystem with medium pressure steam being produced. The medium pressure steam (preferably on the order of 150 psi), is delivered to work module  622  through conduit  621 . Work module  622  can take on the form of a steam turbine for producing mechanical shaft work such as work module  617  previously described or can in fact form a part of work module  617  by injecting the lower pressure steam into a suitable stage of a larger steam turbine. The medium pressure steam can also be used for other thermal work such as heating or cooling and to supply other process needs such as the steam required by the synthesis gas module  602 . The resultant low pressure steam is delivered to conduit  618  which then delivers it to the water treatment subsystem  608 . The synthesis subsystem  604  receives synthesis gas and makes Fischer-Tropsch products that are preferably delivered through conduit  623  to product upgrading subsystem  606 . Synthesis subsystem  604  produces a low BTU tailgas (preferably on the order of 60-100 BTU/SCF) and delivers it to low BTU combustor  610  through conduit  620  where it is combusted. It should also be noted that the synthesis subsystem  604  can be operated in a multitude of ways so as to produce tailgas that can range in heat content from 50 BTU/SCF or below to 300 BTU/SCF or above. This may be advantageous under certain economic conditions in which there is little or no monetary value placed on certain Fischer-Tropsch products but there is a relatively large value placed on the work that can be realized from steam generation (e.g., electrical power generation or additional treated water capacity).  
     [0048] Fischer-Tropsch products are delivered through conduit  623  to product upgrading subsystem  606 . Subsystem  606  takes the raw Fischer-Tropsch products and modifies them to various desirable products. Subsystem  606  receives boiler feed water through conduit  624  and produces low pressure steam that is delivered to the water treating subsystem through line  699  and on through conduit  618 . Subsystem  606  also produces tailgas that is relatively small in amount but relatively high in BTU content when compared to tailgas produced in the synthesis section. This tailgas is preferably blended with the low BTU tailgas produced in subsystem  604  and delivered to the tailgas combustor  610  through conduit  625 .  
     [0049] Tailgas combustor  610  receives boiler feed water through conduit  626  and receives tailgas through conduits  620  and/or  625 . The tailgas is combusted to and the resulting energy release may be used to raise high pressure steam which is delivered to work module  628  through conduit  629 . Work module  628  extracts work from the steam in a similar manner and by a similar variety of mechanisms as do work modules  617  and  622  previously described. The resultant low pressure steam is delivered to water treatment subsystem  608  through conduit  618 . In addition to steam generation, there are a number of other methods by which the heat generated by combusting the tailgas can be used. This includes superheating steam, and/or preheating the oxygen-containing as and light hydrocarbon streams used in synthesis gas subsystem  602  or other process heating purposes. By including multiple heating coils in tailgas combustor  610  it is possible to simultaneously provide several process heating services to system  600  in one device.  
     [0050] Desalination subsystem  608  receives contaminated water (i.e.: brine) through conduit  630  and low pressure steam through conduit  618 . It produces purified water which is exported through conduit  632  and a portion of the produced water is made available to the various subsystems as boiler feed water through conduits  633 ,  616 ,  619 ,  626  and  624 . The embodiment of the water treating system and various configurations thereof are as previously described.  
     [0051] In general, the hydrocarbon conversion and product upgrading aspects of the present invention may be used to make numerous longer-chain hydrocarbons, e.g., the full spectrum of C 5+  products through the Fischer-Tropsch reaction (but other reactions might be used in some situations) and may be adapted to accommodate numerous environments and applications. The longer-chain Fischer-Tropsch products that may be made directly or with downstream processing include numerous products for numerous uses. A number of examples are presented below.  
     [0052] The Fischer-Tropsch products may include synthetic alpha olefins adapted for many applications, including, without limitation, PAO feedstock (alpha olefins in the range of C 6  to C 12  and preferably C 10  are used to produce poly alpha olefins); alpha olefins for laundry and other detergents (preferably C 12 -C 16 ); chlorination stock to be used in textiles, pharmaceuticals and transportation lubricants/hydraulic fluids (preferably C 18 -C 24 ); alpha olefins used to produce particle board emulsions and poly vinyl chloride lubricants (C 24 -C 28 ); and alpha olefins used to manufacture decorative and industrial candles, particle board emulsions and PVC lubricants (C 30 + alpha olefins, which are considered a synthetic paraffin wax and therefore used in many of the markets where paraffin waxes are used). The Fischer-Tropsch products are also well suited for use as a synthetic white oils because Fischer-Tropsch liquid normal paraffins meet FDA specifications governing their use in direct food contact applications, which gives them a wide range of potential markets to enter, including markets which traditionally use food grade mineral oils. Similarly, the Fischer-Tropsch products may be used for technical grade mineral or white oils that are used to produce paints, stains and inks, among other end-use products and may be used as a pharmaceutical (USP) grade white oil to be used to produce cosmetics and healthcare products. In these applications, Fischer-Tropsch products are better because the liquid or hydroisomerized product can probably satisfy ASTM standards with little effort.  
     [0053] The Fischer-Tropsch products may also be used for synthetic liquid n-paraffins in numerous applications. The Fischer-Tropsch product may be used as a chlorination feedstock to be used, for example, to produce chlorinated normal paraffins for use in textiles and industrial lubricants. The product may also be used as a linear alkyl benzene (LAB) feedstock (C 10  to C 13 ) which may be used for laundry detergents. The Fischer-Tropsch product may also be used as an aluminum rolling oil (C 14  to C 17 ), e.g., for cold rolling oils for aluminum foil. Further the Fischer-Tropsch product N-paraffin may be used for “liquid” candles.  
     [0054] The Fischer-Tropsch product may be used as a synthetic wax in numerous applications. For example, the product may be used to make thermostat wax, which is used primarily to control automobile thermostats. The wax is particularly suitable for this since it must be uniform in molecular weight, carbon number distribution and molecular structure. The Fischer-Tropsch wax may be used to make hotmelt adhesives, i.e., used as a viscosity modifier for industrial hotmelt adhesives. The synthetic wax may be used in printing inks . In that case, the wax is used as an antiscuff surface modifier for fine grade web offset and gravure inks. It may also be used for paints and stains. The wax is used to enhance water repellency of water-based paints and stains. The Fischer-Tropsch product may be used to make corrugated board in which the waxes are used to add strength and water repellency to the corrugated board. Similarly, the Fischer-Tropsch product may also be used as a wax for packaging and food additives.  
     [0055] The synthetic wax may be used as a PVC lubricant/extrusion aid; the high melting point waxes are used as internal/external lubricants for PVC extrusion. The wax may be used as a flushing compound, to impart the dripless quality to decorative candles, with cosmetics as a viscosity modifier and melting point enhancer, to bind various drugs which are in powdered form into tablet form (they also impart a slippery surface to tablets such as aspirin, etc.). Waxy Fischer-Tropsch products may also be used as plasticizers and extrusion aids for various plastics such as high density polyethylene, PET linear low density polyethylene and polypropylene. Another use is as anti-ozone additives to protect the outside surfaces of rubber products from packing and ozone damages.  
     [0056] Fischer-Tropsch product in the form of synthetic lubricants may be used in numerous additional applications. For example, the synthetic lubricants may be used as environmentally friendly drilling fluids. Fischer-Tropsch oils may be used to produce highly stable high temperature operation automatic transmission fluids. They may also be used as a hydraulic fluid that is very stable at high temperatures and ideally suited for use in vehicular and industrial hydraulic compounds. The synthetic lubricants may also be used as vehicular lubricants (PCMO and HDD). The Fischer-Tropsch product in the form of a synthetic lubricant may be used as a quenching oil or cutting oil. Further they may be used for a plurality of specialty lubricants such as for two-cycle, marine lubricants, or baroil. They may also be used as a vehicle for lubricant-additives.  
     [0057] Products that may be made from or as part of the Fischer-Tropsch products are synthetic fuels and blends, including Fischer-Tropsch compression ignition fuels, Fischer-Tropsch spark ignition fuels, fuels for fuel cell systems, aviation fuel (turbine, spark-ignition, and compression 5  ignition) and railroad fuels. The sulfur-free clean nature of the synthetic fuels thus made are advantageous. The Fischer-Tropsch products may also be used as synthetic solvents. As such, the uses of the synthetic solvents include as printing inks, paints, stains, drying agents, dye transfer agents, synthetic heptane, hexane, and de-waxing agents.  
     [0058] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of invention as defined by the appended claims. For example, portions of one embodiment may be adapted and used with other suggested embodiments. Although the term desalination subsystem is used it is to be understood that it encompasses the broader water treatment system in that even waters from such sources as oil field waters could be cleaned up via these subsystems. While MSF units are presented for illustrative purposes other treatment subsystems may be used in a like manner such as a MED 20  type desalination unit. Process water from the synthesis unit and synthesis gas unit may be used throughout the systems as well and may be treated by the water treatment system.