Abstract:
Methods and systems for generating power using syngas created using biomass gasification are provided. Exemplary power generation systems include a biomass dryer for receiving biomass, a biomass conversion reactor (either a biomass gasifier or a steam-biomass reformer) for receiving the dried biomass and generating syngas therefrom, and an external combustor for combusting the syngas and heating a working fluid to drive a turbine connected to an electrical generator. The external combustor includes a heat exchanger element for transferring heat from combustion of the syngas into the working fluid, while maintaining the working fluid isolated from the syngas and from syngas combustion products.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present disclosure relates generally to integrated gasification combined-cycle (IGCC) power generation systems, and more specifically to turbine power generation systems incorporating fuels generated from biomass materials. 
         [0002]    At least some known IGCC systems include a gasification system that is integrated with at least one power producing turbine system. Many of these IGCC systems incorporate a gasifier that creates a combustible gas, or a combustible gas precursor, which undergoes further processing into a combustible gas (referred to as “syngas”). Such IGCC systems often further incorporate a gas turbine in which the syngas is combusted and/or which is driven by the combustion byproducts of the burning of the syngas. 
         [0003]    A desirable source of syngas or syngas precursor feedstock is biomass material, as the use of biomass material reduces dependency on other sources of syngas feedstock, such as fossil fuel-based feedstocks like coal, coke, etc. However, the use of biomass material as a feedstock for syngas presents challenges for a number of reasons. Syngas produced from biomass material typically is contaminated with tar, ash, particulates or other contaminants, which contaminants are potentially damaging to the internal components of gas turbine engines. Furthermore, in order to be burned in a gas turbine engine, syngas typically must be compressed and/or cooled prior to injection into the gas turbine engine. Compression of the syngas requires expenditure of energy, thus lowering the efficiency of the IGCC system. Cooling of the syngas, typically by water scrubbing, likewise requires expenditure of energy, with a corresponding loss of efficiency. 
         [0004]    Accordingly, it would be desirable to provide an IGCC powerplant system and method that uses biomass material as a feedstock for the production of syngas to take advantage of the benefits of deriving power from biomass material, including the reduction in dependency on fossil fuel-based feedstocks. It would also be desirable to provide an IGCC powerplant system and method that is fueled by syngas that has improved efficiency by reducing or eliminating the need for compression or cooling of the syngas. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    In one aspect, a power generation system for use in generating power from biomass feedstock is provided. The power generation system includes a biomass conversion reactor coupled to a source of biomass feedstock, the biomass conversion reactor configured to produce syngas. The power generation system also includes a combustor coupled to the biomass conversion reactor. The power generation system also includes a first heat exchanger element coupled in the combustor in flow communication with a source of working fluid that receives heat from combustion of syngas while the working fluid flows through the first heat exchanger element, wherein the working fluid is isolated from the syngas and from products of combustion. The power generation system also includes a turbine coupled in flow communication downstream from the first heat exchanger element, the turbine driven by the heated working fluid. 
         [0006]    In another aspect, a method for generating power from biomass feedstock is provided. The method includes channeling biomass feedstock from a source of biomass feedstock to a biomass conversion reactor coupled to the source of biomass feedstock. The method also includes converting the biomass feedstock into syngas. The method also includes channeling the syngas to a combustor coupled to the biomass conversion reactor. The method also includes channeling working fluid from a source of working fluid through a first heat exchanger element coupled in the combustor. The method also includes transferring heat from combustion of the syngas into the working fluid while the working fluid flows through the first heat exchanger element, such that the working fluid is isolated from the syngas and from products of combustion. The method also includes channeling the heated working fluid to a turbine coupled in flow communication downstream from the first heat exchanger element, the turbine driven by the heated working fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic diagram of an exemplary system for generating power using biomass-generated syngas. 
           [0008]      FIG. 2  is a schematic diagram of another exemplary system for generating power using biomass-generated syngas. 
           [0009]      FIG. 3  is a schematic diagram of another exemplary system for generating power using biomass-generated syngas. 
           [0010]      FIG. 4  is a schematic diagram of another exemplary system for generating power using biomass-generated syngas. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Although specific features of various exemplary embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
         [0012]      FIG. 1  is a schematic diagram of an exemplary system  100  for generating power using biomass-generated syngas. System  100  includes a biomass dryer  102 , which receives biomass from a source  104 . A biomass conversion reactor  106  receives dried biomass  108  from biomass dryer  102 . Biomass conversion reactor  106  may be any suitable device that may be used to convert biomass into a syngas that will enable the systems described herein to function as described. For example, biomass conversion reactor  106  may be a biomass gasifier or a steam-biomass reformer. Biomass conversion reactor  106  discharges a syngas  110 . Syngas  110  is comprised chiefly of hydrogen (H 2 ), carbon dioxide (CO 2 ) and carbon monoxide (CO). Syngas  110  is channeled into an external combustor  112 , where syngas  110  is combusted with air  114  (typically ambient air) supplied by a blower  116 . In an alternative embodiment, a compressor (not shown) may be used in place of blower  116 . External combustor  112  discharges an external combustor exhaust  136 , which is channeled through an exhaust gas cleanup device  135 . External combustor  112  includes a heat exchanger element  118 , which is coupled in flow communication with a compressor  120  and a turbine  122 . Compressor  120  is rotationally coupled to turbine  122  by a transmission structure  132 . System  100  further includes an electrical generator  124 , which is rotationally coupled to turbine  122  by a transmission structure  123 . 
         [0013]    Ambient air  126  is channeled into compressor  120 , which discharges a compressed air  128 , which is, in turn, channeled into external combustor  112 . External combustor  112  discharges a heated compressed air  130 , which is channeled to turbine  122 , and subsequently discharged from turbine  122  as a turbine exhaust  134 . Heated compressed air  130  is expanded in turbine  122 , causing rotation of turbine  122 , and in turn, rotation of electrical generator  124 . Turbine exhaust  134  is combined with external combustor exhaust  136  to supply exhaust gases  138  for biomass dryer  102 . After flowing through a heat exchanger  140 , cooled gases  142  are then discharged through a vent  144  coupled to biomass dryer  102  to be released to atmosphere, or to be channeled to such additional gas cleaning equipment (not shown) as may be required. 
         [0014]    In system  100 , syngas  110  and external combustor exhaust  136  are isolated from compressor  120  and turbine  122 . Accordingly, compressor  120  and turbine  122  are protected from the damaging effects of tar, ash and other particulates, and other contaminants found in biomass-generated syngas and the combustion products therefrom. In addition, biomass-generated syngas  110  is channeled to external combustor  112 , without the requirement for any specific provisions for cooling or contaminant removal. 
         [0015]      FIG. 2  is a schematic diagram of an alternative exemplary system  200  for generating power using biomass-generated syngas. System  200  includes a biomass dryer  202 , which receives biomass from a source  204 . A biomass conversion reactor  206  receives dried biomass  208  from biomass dryer  202  and discharges a syngas  210 . Biomass conversion reactor  206  also includes a heat exchanger element  250 , which is coupled in flow communication with a compressor  220  and with a turbine  222 . Syngas  210  is channeled into an external combustor  212 , where syngas  210  is combusted with air  214  (typically ambient air) supplied by a blower  216 . In an alternative embodiment, a compressor (not shown) may be used in place of blower  216 . External combustor  212  discharges an external combustor exhaust  236 . External combustor  212  includes a heat exchanger element  218 , which is coupled in flow communication with compressor  220 , heat exchanger element  250 , and turbine  222 . Compressor  220  is rotationally coupled to turbine  222  by a transmission structure  232 . An electrical generator  224  is rotationally coupled to turbine  222  by a transmission structure  223 . 
         [0016]    Ambient air  226  is channeled into compressor  220 , which discharges a compressed air  228 , which in turn is channeled into biomass conversion reactor  206 . Specifically, compressed air  228  is channeled through heat exchanger element  250  in the biomass conversion reactor  206 , acquiring heat released during the gasification process. Biomass conversion reactor  206  discharges a heated compressed air  229 , which is channeled to external combustor  212 , where heated compressed air  229  acquires further heat while flowing through heat exchanger element  218 . 
         [0017]    Heat from the combustion of syngas  210  is transferred to heated compressed air  229 , resulting in a further heated compressed air  230 . Further heated compressed air  230  is channeled to turbine  222  and expanded, causing rotation of turbine  222 , and in turn, rotation of electrical generator  224 . Turbine  222  discharges a turbine exhaust  234 . External combustor  212  is coupled in flow communication with heat exchanger  252 . External combustor exhaust  236  is channeled to heat exchanger  252  to release heat to a boiler feed water  254 , creating a heated boiler feed water  255 . External combustor exhaust  236  is then channeled to an exhaust gas cleanup device  235 . Heated boiler feed water  255  is channeled to a heat exchanger  256  coupled in flow communication with turbine  222 , where heated boiler feed water  255  acquires further heat from turbine exhaust  234 , and is converted into a steam  258 . Steam  258 , in turn, is then channeled to a steam turbine (not shown) to generate further electrical or mechanical power, or is exported for other purposes. Turbine exhaust  234  and external combustor exhaust  236  are combined to supply exhaust gases  238 , which are channeled through a heat exchanger  240  coupled to biomass dryer  202 . Afterward, cooled gases  242  are discharged through a vent  244  coupled to biomass dryer  202  to be released to atmosphere. 
         [0018]    Similarly to system  100  described herein, in system  200 , syngas  210  and external combustor exhaust  236  are isolated from compressor  220  and turbine  222 . Accordingly, compressor  220  and turbine  222  are protected from the damaging effects of tar, ash and other particulates, and other contaminants found in biomass-generated syngas and the combustion products therefrom. In addition, biomass-generated syngas  210  is channeled to external combustor  212 , without the requirement for any specific provisions for cooling or contaminant removal. 
         [0019]      FIG. 3  is a schematic diagram of another alternative exemplary system  300  for generating power using biomass-generated syngas. System  300  includes a biomass dryer  302 , which receives biomass from a source  304 . A biomass conversion reactor  306  receives dried biomass  308  from biomass dryer  302 , and discharges a syngas  310 . Biomass conversion reactor  306  also includes a heat exchanger element  350 , which is coupled in flow communication with a compressor  320  and with a turbine  322 . Syngas  310  is channeled into an external combustor  312 , where syngas  310  is combusted with air  314  (typically ambient air) supplied by a blower  316 . In an alternative embodiment, a compressor (not shown) may be used in place of blower  316 . External combustor  312  includes a heat exchanger element  318  coupled in flow communication with compressor  320  and turbine  322 . External combustor  312  discharges an external combustor exhaust  336 . Compressor  320  is rotationally coupled to turbine  322  by a transmission structure  332 . An electrical generator  324  is rotationally coupled to turbine  322  by a transmission structure  323 . 
         [0020]    Ambient air  326  is channeled into the compressor  320 , which discharges a compressed air  328 , which in turn is channeled into biomass conversion reactor  306 . Specifically, compressed air  328  is channeled through heat exchanger element  350 , acquiring heat released during the gasification process. Biomass conversion reactor  306  discharges a heated compressed air  329 , which is channeled to external combustor  312 , where heated compressed air  329  acquires further heat while flowing through heat exchanger element  318 . A resulting further heated compressed air  330  is channeled to turbine  322  and expanded, causing rotation of turbine  322 , and in turn, rotation of electrical generator  324 . Turbine  322  discharges a turbine exhaust  334 . 
         [0021]    External combustor  312  is coupled in flow communication with a heat exchanger  352 , which is also coupled in flow communication with turbine  322  to receive turbine exhaust  334 . External combustor exhaust  336  is channeled to heat exchanger  352 , wherein external combustor exhaust  336  transfers heat to a boiler feed water  354 . Turbine exhaust  334  also releases heat to boiler feed water  354  while flowing through heat exchanger  352 . Turbine exhaust  334 , being essentially only heated air, is channeled through a vent  360  to atmosphere. External combustor exhaust  336  is channeled through an exhaust gas cleanup apparatus  362 , for removal of particulates and other contaminants. Cleaned external combustor exhaust  336  is then channeled to a vent  364  to be released to atmosphere. Boiler feed water  354 , having flowed through heat exchanger  352 , is converted to a steam  366 . A portion  338  of steam  366  is channeled to biomass dryer  302  for use in drying the biomass feedstock. Another portion  368  of steam  366  is channeled to a steam turbine (not shown) for the generation of additional electrical or mechanical power, or otherwise exported to other locations where a supply of steam is needed. Steam portion  338  is channeled through a heat exchanger element  340  coupled to biomass dryer  302 . Cooled steam  342  is subsequently channeled to a vent  344  to be released to atmosphere or to be channeled to other equipment (not shown). 
         [0022]    Similarly to systems  100  and  200  described herein, in system  300 , syngas  310  and external combustor exhaust  336  are isolated from compressor  320  and turbine  322 . Accordingly, compressor  320  and turbine  322  are protected from the damaging effects of tar, ash and other particulates, and other contaminants found in biomass generated syngas, and the combustion products therefrom. 
         [0023]      FIG. 4  is a schematic diagram of another alternative exemplary system  400  for generating power using biomass-generated syngas. System  400  includes a biomass dryer  402 , which receives biomass from a source  404 . A biomass conversion reactor  406  receives dried biomass  408  from biomass dryer  402 , and discharges a syngas  410 . In the exemplary embodiment, biomass conversion reactor  406  is a steam-biomass reformer, and includes a shell  407  and a heat-exchanging coil  488  that extends through biomass conversion reactor  406 , through which biomass  408  is channeled. Syngas  410  is channeled into an external combustor  412 , where syngas  410  is combusted with air  414  (typically ambient air) supplied by a blower  416 . In an alternative embodiment, a compressor (not shown) may be used in place of blower  416 . The external combustor  412  includes a heat exchanger element  418  coupled in flow communication with a compressor  420  and a turbine  422 . External combustor  412  discharges an external combustor exhaust  436 . Compressor  420  is rotationally coupled to turbine  422  by a transmission structure  432 . An electrical generator  424  is rotationally coupled to turbine  422  by a transmission structure  423 . 
         [0024]    Ambient air  426  is channeled into compressor  420 , which discharges a compressed air  428 , which in turn is channeled into external combustor  412 , where compressed air  428  acquires heat while flowing through heat exchanger element  418 . A resulting heated compressed air  430  is channeled to turbine  422  and expanded, causing rotation of turbine  422 , and in turn, rotation of electrical generator  424 . Turbine  422  discharges a turbine exhaust  434 . 
         [0025]    In the exemplary embodiment, a portion  496  of external combustor exhaust  436  is channeled to biomass conversion reactor  406  to supply heat for a steam-biomass reformation reaction. Portion  496  may supply all heat requirements for biomass conversion reactor  406 . In an alternative embodiment, portion  496  may supply only part of the heat requirement of biomass conversion reactor  406 . In such a situation, a fuel  490  from a source  492  and an air  494  from a source  495  are channeled via blower  497  into shell  407  and combusted to supply the remainder of the heat requirement. In another alternative embodiment, a compressor (now shown) may be used in place of blower  497 . In another alternative embodiment, combustion of fuel  490  and air  494  provides all of the heat required by biomass conversion reactor  406 , and none of external combustor exhaust  436  is diverted to biomass conversion reactor  406 . In an embodiment in which external combustor exhaust  436  is not used to provide heat for biomass conversion reactor  406 , combustion products from the combustion of fuel  490  and air  494  are vented  500  as flue gas. In an embodiment in which portion  496  of external combustor exhaust  436  is used to provide heat to biomass conversion reactor  406 , cooled portion  499  is channeled through exhaust gas cleanup device  502  prior to being vented  504  to atmosphere, to ensure that syngas contaminants are removed prior to release to atmosphere. If a combination of external combustion exhaust gas portion  496  and combustion of additional fuel  490  and air  494  are used to supply heat to biomass conversion reactor  406 , the combustion of additional fuel  490  and air  494  acts as a second combustion stage for portion  496 , facilitating complete combustion of syngas contaminants present in portion  496 . 
         [0026]    In the exemplary embodiment, external combustor  412  is coupled in flow communication with a heat exchanger  452 . A boiler feed water  454  from a source  456  of boiler feed water is channeled to heat exchanger  452 . If portion  496  amounts to less than all of external combustor exhaust  436 , a portion  460  of external combustor exhaust  436  is channeled to heat exchanger  452 , through heat exchanger element  458 , wherein portion  460  transfers heat to boiler feed water  454  to produce a steam  462 . Turbine exhaust  434  is channeled to a heat exchanger  464 , through a heat exchanger element  466 . A boiler feed water  468  from a source  470  is channeled through heat exchanger  464 , such that heat from turbine exhaust  434  is transferred to boiler feed water  468  to produce a steam  472 . Steams  462  and  472  are combined to form steam flow  478 . 
         [0027]    A portion  480  of steam flow  478  may be used as excess export steam. Another portion  482  of steam flow  478  is supplied to biomass dryer  402  as steam portion  484 , and to biomass conversion reactor  406  as steam portion  486 . In the exemplary embodiment, steam portion  482  may be superheated steam. In alternative embodiments, other types of steam may be present in steam portion  482 . Steam portion  484  is channeled through heat exchanger element  506 , to transfer heat to biomass  408 , after which steam portion  484  is vented  508  to atmosphere. Steam portion  486  is mixed with biomass  408  and channeled through a coil (or other heat-exchanging conduit)  488 , coupled through biomass conversion reactor  406 , towards channeling syngas  410  to external combustor  412 . Heat generated from the combustion of fuel  490  and air  494 , and from the heat contained within a portion  496  of external combustor exhaust  436 , if present, is transferred into biomass  408  and steam portion  486  flowing through coil  488 . 
         [0028]    Similarly to systems  100 ,  200 , and  300  described herein, in system  400 , syngas  410  and external combustor exhaust  436  are isolated from compressor  420  and turbine  422 . Accordingly, compressor  420  and turbine  422  are protected from the damaging effects of tar, ash and other particulates, and other contaminants found in biomass generated syngas, and the combustion products therefrom. 
         [0029]    In contrast to known integrated gasification combined-cycle (IGCC) power generation systems, the biomass conversion reactor power generation systems described herein enable biomass-generated syngas to be used for generating power, while protecting sensitive compressor and/or turbine components from the potentially destructive effects associated with syngas generated from biomass materials. This is accomplished by segregating the flow path of the biomass-generated syngas from the flow path of the working fluid used in the compressor and turbine. In addition, the biomass conversion reactor power generation system as described herein eliminates the need for cooling and/or compressing the syngas, which measures are required when syngas is combusted and the syngas combustion products are added directly to the working fluid in a compressor and turbine, as in combustion turbine applications. 
         [0030]    Exemplary embodiments of a method and a system for generating power using biomass-generated syngas are described above in detail. The method and system are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods and systems described herein may also be used in combination with other power generation schemes, and are not limited to practice with only the components as described herein. 
         [0031]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
         [0032]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.