Abstract:
An integrated gasification combined cycle power generation system ( 100 ). In one embodiment, shown in FIG.  1 , a gasifier ( 108 ) is configured to generate synthetic gas ( 117 ) from a carbonaceous material ( 106 ) and an oxygen supply ( 109 ) with a cleaning stage ( 120 ) positioned to receive synthetic gas ( 117 ) from the gasifier ( 108 ) and remove impurities therefrom. A gas turbine combustion system ( 2 ) including a turbine ( 123 ) is configured to receive fuel ( 128 ) from the gasifier ( 108 ) and a first air supply ( 131 ) from a first air compressor ( 130 ). A steam turbine system ( 4 ) is configured to generate power with heat recovered from exhaust ( 140 ) generated by the gas turbine system ( 2 ) and an ion transport membrane air separation unit ( 110 ) includes a second air compressor ( 114 ) for generating a second air supply ( 113 ). A first heat exchanger ( 118 ) is configured to cool the synthetic gas ( 117 ) prior to removal of impurities in the cleaning stage ( 120 ) by flowing the second air supply ( 113 ) through the first heat exchanger ( 118 ) so that the second air supply ( 113 ) receives heat from the synthetic gas ( 117 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to power generation systems, and more particularly, to integrated gasification combined cycle systems. 
     BACKGROUND OF THE INVENTION 
     Integrated Gasification Combined Cycle (“IGCC”) systems are an economically attractive alternative to conventional fossil fuel power plants. They present an opportunity to deploy coal, an abundant resource, in an economical and clean manner, bringing improved efficiency over conventional coal-burning steam turbine power generation. 
     In an IGCC system, a carbonaceous fuel such as coal is converted to a synthetic gas fuel, termed syngas, a mixture formed by partial oxidation at elevated temperatures. Syngas comprises carbon monoxide, hydrogen, and other gaseous constituents. Oxygen-blown gasifiers typically source oxygen from cryogenic Air Separation Units (ASUs) or from Ion Transport Membrane (ITM) Air Separation Units. Cryogenic ASUs employ a combination of compressors, heat exchangers, valves, and distillation columns to effect the separation of oxygen from air at very low temperatures. The cryogenic air separation process consumes significant quantities of electric power, reducing the net plant output and efficiency. 
     In an ITM air separation process, oxygen molecules in high temperature air, generally in the range of 1400°-1700° F. (760-927 C), are converted to oxygen ions on the cathode side of the membrane, and are transported through the membrane under an applied voltage or pressure differential relative to the anode side of the membrane. Oxygen ions lose electrons on the anode side, reforming into oxygen molecules, with the electrons migrating to the cathode side of the membrane to again ionize oxygen. The membrane elements, being manufactured from ceramic materials, are permeable to oxygen ions at elevated temperatures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of the invention will be best understood when the following detailed description is read in conjunction with the accompanying drawings, wherein  FIGS. 1-5  each illustrate an IGCC incorporating an ITM ASU according to an embodiment of the invention. 
       Like reference numerals are used to reference like features throughout the figures. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention comprises an IGCC system that integrates an air separation unit with recovery of sensible heat. In one embodiment a power generation system  100 , shown in  FIG. 1  comprises a gasification system  1 , a gas turbine system  2 , a Heat Recovery Steam Generator (HRSG)  3 , and a steam turbine system  4 , each of which may be configured in a conventional manner. The gasification system  1  includes a hydrocarbon fuel source  106 , such as a coal slurry, a gasifier  108 , an ITM air separation unit  110 , an air compressor  114 , a syngas cooler  118  and a gas cleaning stage  120 . The gas turbine system  2  includes an air-compressor  130 , a combustor  132 , a gas turbine  134 , and an electrical generator  136 . The HRSG  3  comprises an economizer  172 , a steam drum  174 , an evaporator  176  and a super heater  178 . The steam turbine system  4  includes a steam chest  152 , a steam turbine  160 , an electrical generator  162 , a condenser  164  and a feed-water pump  166 . 
     Oxygen  109  is provided to the gasifier  108  from the ITM ASU  110  which receives high temperature, high pressure air  113  from the syngas cooler  118 . The compressor  114  driven by a motor  116  intakes ambient air  115  to provide a source of high pressure air  113  to the syngas cooler  118 . The compressed air  113  may be delivered from the stand-alone compressor  114  shown in  FIG. 1 , or from a compressor  130  of the gas turbine system  2 , or from another source. The ITM ASU  110  produces the high purity oxygen  109  while operating in a temperature range of about 1400°-1700° F. (760-927 C) and with an oxygen partial pressure differential across the membrane of 200 to 400 psia (1378.6 kPa-2757.2 kPa). The membrane operating temperature is achieved by flowing the air stream  113  through the syngas cooler  118  so that sensible heat present in hot syngas  117  exiting the gasifier  108  heats the air stream  113 . After being separated from the air  113  in the ASU  110 , oxygen  109  is delivered to the gasifier  108  and oxygen-depleted air  127  may, as shown, be delivered to the fuel line  125  for addition to the fuel mixture  128 . Although not shown, the syngas cooler  118  may include an additional heat exchanger to generate steam from a portion of the feed-water  167  exiting the steam turbine system  4 . 
     In the gasifier  108 , the hydrocarbon fuel  106  undergoes partial oxidation to generate primarily carbon monoxide and hydrogen in an exothermic reaction, with the hot syngas  117  exiting the gasifier  108 , generally in the temperature range of about 2000°-2800° F. (1093-1538 C). To meet air quality requirements, impurities such as sulfur, nitrous compounds, and dust particles are removed in the gas cleaning stage  120 . The syngas cooler  118  reduces the syngas temperature before introduction of the syngas  117  to the gas cleaning stage  120 . The cleaned syngas  124  is mixed with steam  126  from the steam chest  152 . Steam  126  can be used to regulate the combustion process temperature, the internal combustor temperature profile, and the combustor exit temperature by varying the steam flow rate. The mixture  128  of steam  126  and syngas  124  flows through a fuel supply line  125  to the fuel manifold  123  and into the combustor  132  of the gas turbine system  2 . The mixture  128  may also include nitrogen or oxygen-depleted air  127  from the air separation unit  110  to reduce flame temperature and NO x  formation. 
     During operation of the power plant  100 , the compressor  130  inducts ambient air  129 , producing compressed air  131  which is directed to the combustor  132 . The compressed air  131  may be oxygen enriched. The fuel mixture  128  enters the manifold  123  and passes through multiple ports  133  thereof, into the combustor  132  where the fuel mixture  128  reacts with the compressed air  131  to produce a hot, pressurized gas  135  which enters the gas turbine  134  where it expands, thereby producing power in the rotor shaft  138  to drive both the compressor  130  and the electrical generator  136 . As a result of having been expanded in the turbine  134 , a low temperature, low pressure gas  140  is exhausted from the turbine  134 . The expanded gas  140  exhausted from the turbine  134 , typically in the range of 850°-1100° F. (454-593 C), is directed to the HRSG  3  for further recovery of heat. Feed-water  167  sent from the steam turbine system  4  by a pump  166  is heated in the HRSG  3  by the relatively hot gas  140  flowing therethrough. The cooled, expanded gas  140  exiting the HRSG  3  is then discharged to atmosphere via a stack  156 . The feed-water  167  first flows through the heat transfer tubes of the economizer  172 , where its temperature is raised to near the boiling point and is then directed to the steam drum  174 . The heated water is then circulated through the heat transfer tubes of the evaporator  176  where it is converted into saturated steam  177 . The steam temperature is further elevated as it flows through the superheater  178  prior to entry into the steam chest  152 . Steam  153  from the steam chest  152  is directed to the steam turbine  160 . Steam  126  from the steam chest  152  is injected to the fuel supply line  125  for entry to the fuel manifold  123  as a component of the fuel mixture  128 . 
     Within the steam turbine  160 , the steam  153  expands, thereby producing power in the rotor shaft  161  to drive the electrical generator  162 . In other designs, the steam turbine  160  may be coupled to the shaft  138  and generator  136  of the gas turbine system  2 . After passing through the turbine  160  the cooled, expanded steam  163  enters the condenser  164  for recycling as feed-water  167 . Fresh water  165  is supplied to the condenser  164  to compensate for loss of water in the system  100 . 
     In the embodiment of  FIG. 2  a power generation system  200  comprises a gas turbine system  2 , a HRSG  3 , and a steam turbine system  4  as described with respect to  FIG. 1 , and a gasification system  5 . In the system  200  compressed air being directed to an ITM ASU is preheated in two stages. 
     The gasification system  5  includes a gasifier  208  which receives a fuel source  206  and an oxygen supply  209  from an ITM ASU  210  to generate syngas  217 . The syngas  217  undergoes temperature reduction in the cooler  218  before entering a gas cleaning stage  220  for removal of impurities, e.g., sulfur, nitrous compounds, and dust particles. The cleaned gas  224  is mixed with steam  126  from the steam chest  152  to form a fuel mixture  228  which flows through a fuel supply line  225  to the manifold  123  and into the gas combustor  132  of the gas turbine system  2 . 
     In the gasification system  5  a compressor  214 , driven by a motor  216 , provides compressed air  213  from a source of ambient air  215 . The compressed air  213  may be delivered from the stand-alone compressor  214  shown in  FIG. 2 , or from a compressor  130  of the gas turbine system  2 , or from some other source. The compressed air  213  flows through an air pre-heater  212  to receive sensible heat from the hot gas  140  exiting the gas turbine  134  of the system  2 . The cooled gas  140  exiting the pre-heater  212 , still relatively hot (typically in the range of 482-583 C), is directed to the HRSG  3  for further recovery of heat. After being heated to a pre-determined temperature (typically in the range of 427-538 C), the compressed air  213  leaves the pre-heater  212  and enters a syngas cooler  218  to facilitate cooling of the syngas  217 . Heat transfer to the compressed air  213  occurring in the cooler  218  further elevates the compressed air temperature prior to entry into the ASU  210 . The compressed air  213  receives sufficient heat from the syngas  217  to elevate the temperature as required for the ITM process to occur in the ASU  210 . 
     After being separated from the air  213  in the ASU  210 , a supply of oxygen  209  is delivered to the gasifier  208  while oxygen-depleted air  227  may, as illustrated, be delivered to the fuel line  225  for addition to the fuel mixture  228 . Although not shown, the syngas cooler  218  may include an additional heat exchanger to generate steam from a portion of the feed-water  167 . 
     In the embodiment of  FIG. 3  a power generation system  300  provides a method of pre-heating compressed air prior to entering an ASU with a closed loop heat exchange system using an intermediate working fluid heated by gas turbine exhaust. The system  300  comprises a gas turbine system  2 , a HRSG  3 , a steam turbine system  4  as described with respect to  FIG. 1 , and a gasification system  6 . The gasification system  6  includes a gasifier  308  which receives a fuel source  306  and an oxygen supply  309  from an ITM ASU  310 . Hot syngas  317  generated in the gasifier  308  is cooled in a syngas cooler  318  using a portion  191  of feed water  167  exiting the steam turbine system  4  before the syngas enters a gas cleaning stage  320  for removal of impurities, e.g., sulfur, nitrous compounds, and dust particles. In the syngas cooler  318  the cooling water  191  is converted to steam  392  which is sent to the steam chest  152 . The cleaned syngas  324  is mixed with steam  126  from the steam chest  152  to form a fuel mixture  328  which flows through a fuel supply line  325  to the manifold  123  and into the gas combustor  132  of the gas turbine system  2 . 
     In the gasification system  6  a compressor  314 , driven by a motor  316 , provides compressed air  313  from a source of ambient air  315 . The compressed air  313  may be delivered from the stand-alone compressor  314  shown in  FIG. 3 , or from a compressor  130  of the gas turbine system  2 , or from another source. In the heat exchange system  11  the compressed air  313  flows through an air pre-heater  312  for heat exchange with a hot working fluid  394 . The  394  circulates in a closed loop between the air pre-heater  312  and a heat exchanger  342  with assistance of a pump  390 . The working fluid  394  may be pure water or may predominately comprise water. Other suitable fluids may include oils or glycol-based solutions. Some organics may be unstable and therefore unsuitable for the application due to operating temperatures. 
     In passing through the air pre-heater  312  the temperature of the compressed air  313  is elevated to effect oxygen separation when it passes into the ASU  310 . The ITM operation temperature is achieved by heating the air stream  313  in the air pre-heater  312  with one or more heat sources, including the sensible heat recovered from the hot exhaust gas  140  using the working fluid  394 . The fluid  394  receives sensible heat as it circulates in the heat exchanger  342  through which the hot exhaust gas  140  flows after exiting the gas turbine  134  of the system  2 . After being separated from the air  313  in the ASU  310 , the resulting supply of oxygen  309  is delivered to the gasifier  308  and oxygen-depleted air  327  may, as illustrated, be delivered to the fuel line  325  for addition to the fuel mixture  328 . Although not shown, the syngas cooler  318  may include an additional heat exchanger to generate steam from a portion of the feed-water  167  exiting the steam turbine system  4 . 
     With the cooled gas  140  exiting the heat exchanger  342  of the heat exchange system  11  still relatively hot, it is directed to the HRSG  3  for further recovery of heat. The exhaust gas  140 , being further cooled after flowing through the HRSG  3 , is then discharged to atmosphere via a stack  156 . 
     In the embodiment of  FIG. 4  a power generation system  400  provides a method of pre-heating compressed air prior to entering an ASU with a closed-loop heat exchange system using an intermediate working fluid heated by hot syngas. The system  400  comprises a gas turbine system  2 , a HRSG  3 , a steam turbine system  4  as described with respect to  FIG. 1 , and a gasification system  7 . The gasification system  8  includes a gasifier  408  which receives a fuel source  406  and an oxygen supply  409  from an ITM ASU  410  and generates syngas. Hot syngas  417  exiting the gasifier  408  is cooled in a syngas cooler  418  using a heat exchange working fluid  497  prior to entering a gas cleaning stage  420  for removal of impurities, e.g., sulfur, nitrous compounds, and dust particles. The cleaned syngas  424  is mixed with steam  126  from the steam chest  152  to form a fuel mixture  428  which flows through a fuel supply line  425  to the manifold  123  and into the gas combustor  132  of the gas turbine system  2 . 
     In the gasification system  7  a compressor  414 , driven by a motor  416 , provides compressed air  413  from a source of ambient air  415 . The compressed air  413  may be delivered from the stand-alone compressor  414  shown in  FIG. 4 , or from a compressor  130  of the gas turbine system  2 , or from another source. In the heat exchange system  12 , the compressed air  413  flows through an additional heat exchanger, air pre-heater  412 , for heat exchange with the hot working fluid  497  returning from the syngas cooler  418 . The syngas cooler  418  and the pre-heater  412  are coupled so that the working fluid  497  circulates in a closed-loop between the air pre-heater  412  and the syngas cooler  418  with assistance of a pump  493 . In passing through the air pre-heater  412  the temperature of the compressed air  413  is elevated to the ITM operating temperature of the ASU  410 . The membrane operating temperature is achieved by heating the air stream  413  in the air pre-heater  412  with one or more heat sources, including the sensible heat recovered from the hot syngas  417  exiting the gasifier  408  using the working fluid  497 . After being separated from the air  413  in the ASU  410 , the resulting oxygen supply  409  is delivered to the gasifier  408  and oxygen-depleted air  427  may, as shown, be delivered to the fuel line  425  for addition to the fuel mixture  428 . Although not shown, the syngas cooler  418  may include an additional heat exchanger to generate steam from a portion of the feed-water  167 . 
     In the embodiment of  FIG. 5  a power generation system  500  provides a method of pre-heating compressed air prior to entering an ASU with two closed-loop heat exchange systems recovering sensible heat from hot syngas and hot gas turbine exhaust. The system  500  comprises a gas turbine system  2 , a HRSG  3 , a steam turbine system  4  as described with respect to  FIG. 1 , and a gasification system  8 . The gasification system  8  includes a gasifier  508  which generates hot syngas in an exothermic reaction of a fuel source  506  and an oxygen supply  509  from an ITM ASU  510 . Syngas  517  exiting the gasifier  508  is cooled in a syngas cooler  518  prior to entering a gas cleaning stage  520  for removal of impurities, e.g., sulfur, nitrous compounds, and dust particles. The cleaned syngas  524  is mixed with steam  126  from the steam chest  152  to form a fuel mixture  528  which flows through a fuel supply line  525  to the manifold  123  and into the gas combustor  132  of the system  2 . 
     In the gasification system  8  a compressor  514 , driven by a motor  516 , provides compressed air  513  from a source of ambient air  515 . The compressed air  513  may be delivered from the stand-alone compressor  514  or from a compressor  130  of the gas turbine system  2 , or from another source. The compressed air  513  is heated in two stages, in a first air pre-heater  512  and in a second air pre-heater  515 , prior to entering the ASU  510 . In the first air pre-heater  512  the compressed air  513  is heated to a pre-determined temperature by heat exchange with a first hot working fluid  594  returning from a heat exchanger  542 . The fluid  594  receives sensible heat from the hot exhaust gas  140  exiting the gas turbine  134  of the system  2 . The fluid  594  circulates in the closed-loop system  13  between the air pre-heater  512  and the heat exchanger  542  with assistance of a pump  590 . The temperature of the compressed air  513  exiting from the first air pre-heater  512  is further raised to the ITM operation temperature when passing through the second air pre-heater  515 . The temperature of the air stream  513  is elevated with one or more heat sources, including the sensible heat recovered from the hot syngas  517  exiting the gasifier  508  using a working fluid  597 . The working fluid  597  circulates in a closed-loop heat exchange system  14  between the air pre-heater  515  and the syngas cooler  518  with assistance of a pump  593 . 
     The hot compressed air  513 , with its temperature raised to that required for oxygen separation, passes into the ITM ASU  510 . After being separated from the air  513  in the ASU  510 , the resulting supply of oxygen  509  is delivered to the gasifier  508  and oxygen-depleted air  527  may, as illustrated, be delivered to the fuel line  525  for addition to the fuel mixture  528 . The cooled gas  140  exiting the heat exchanger  542 , still relatively hot, is directed to the HRSG  3  for further recovery of heat. The gas  140 , being further cooled after flowing through the HRSG  3 , is then discharged to atmosphere via a stack  156 . Although not shown, the syngas cooler  518  may include an additional heat exchanger to generate steam from a portion of the feed-water  167 . 
     While example embodiments of the invention have been illustrated, the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the invention as described in the claims.