Abstract:
A natural gas reformer system is provided. The natural gas reformer system includes a natural gas inlet configured to receive a natural gas slipstream. The natural gas reformer system also includes an air inlet configured to introduce a slip stream of air. The natural gas reformer system further includes a preconditioning zone configured to pretreat the natural gas slipstream. The natural gas reformer system also includes a mixing zone configured to mix the natural gas slipstream and the air in a rich proportion. The natural gas reformer system further includes a reaction zone configured to combust the natural gas and air to generate a syngas. The natural gas reformer system also includes a quench zone configured to mix the natural gas back into the syngas.

Description:
BACKGROUND 
       [0001]    The invention relates generally to fuel reformer systems and, more particularly, to fuel reformer systems for gas turbines. 
         [0002]    Fuel injection and mixing are critical to achieving efficient and clean combustion in gas turbine engines. In case of gaseous fuels, it is desirable to obtain an optimal level of mixing between air, fuel, and combustion products in a combustion zone. 
         [0003]    Exhaust gases from gas turbine engines contain substances such as Nitrogen Oxides (NOx) that are harmful regulated emissions. Hence, there has been increased demand in recent years for gas turbines that operate in partially premixed (PP) or lean, premixed (LP) mode of combustion in an effort to meet increasingly stringent emissions goals. Partially premixed (PP) and lean premixed combustion reduces harmful emission of Nitrogen Oxides without loss of combustion efficiency. 
         [0004]    However, combustion instabilities, also known as combustion dynamics, are commonly encountered in development of low emissions gas turbine engines. Combustion dynamics in the form of fluctuations in pressure, heat-release rate, and other perturbations in flow may lead to problems such as structural vibration, excessive heat transfer to a chamber, and consequently lead to failure of the system. 
         [0005]    Reforming the fuel is a solution to reduce combustion dynamics. One method employs a rich catalytic system to reform the fuel just prior to combustion and is further integrated into the combustion chamber. However, such a technique requires catalysts that have substantially high capital and operating costs. 
         [0006]    Therefore, a need exists for an improved fuel reforming system for controlling combustion dynamics that may address one or more of the problems set forth above. 
       BRIEF DESCRIPTION 
       [0007]    In accordance with one aspect of the invention, a natural gas reformer system is provided. The natural gas reformer system includes a natural gas inlet configured to receive a natural gas slipstream. The natural gas reformer system also includes an air inlet configured to introduce a slip stream of air. The natural gas reformer system also includes a preconditioning zone configured to pretreat the natural gas slipstream. The natural gas reformer system further includes a mixing zone configured to mix the natural gas slipstream and the air in a rich proportion. The natural gas reformer system also includes a reaction zone configured to combust the natural gas and air to generate a syngas. The natural gas reformer system further includes a quench zone configured to mix the natural gas back into the syngas. 
         [0008]    In accordance with another aspect of the invention, a method of operating a fuel reformer system is provided. The method includes introducing a slipstream of natural gas. The method also includes introducing a slipstream of air. The method further includes preconditioning the slipstream of natural gas. The method also includes mixing the natural gas and the air in a rich proportion a mixing zone. The method also includes reacting the natural gas and air in the reaction zone, to form a syngas. The method further includes quenching the syngas leaving the reaction zone with the natural gas. 
         [0009]    In accordance with another aspect of the invention, a retrofit unit for a gas turbine is provided. The retrofit unit includes a natural gas inlet configured to receive a natural gas slipstream. The retrofit unit also includes an air inlet configured to introduce a slipstream of air. The retrofit unit further includes a preconditioning zone configured to pretreat the natural gas slipstream. The retrofit unit also includes a mixing zone configured to mix the natural gas slipstream and the air in a rich proportion. The retrofit unit also includes a reaction zone configured to combust the natural gas slipstream and air to generate a syngas. The retrofit unit further includes a quench zone configured to mix the natural gas back into the syngas. 
     
    
     
       DRAWINGS 
         [0010]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0011]      FIG. 1  is a block diagram representation of a fuel reformer system in accordance with an embodiment of the invention; 
           [0012]      FIG. 2  is a block diagram representation of a regulated fuel reformer system in accordance with an embodiment of the invention; 
           [0013]      FIG. 3  is a block diagram representation of a regulated fuel reformer system including a heat exchanger in accordance with an embodiment of the invention; 
           [0014]      FIG. 4  is a block diagram representation of a regulated fuel reformer system including a carbon capture system in accordance with an embodiment of the invention; 
           [0015]      FIG. 5  is a schematic illustration of mixing and reaction zones of a fuel reformer system employing effusion cooling mechanism; 
           [0016]      FIG. 6  is a schematic illustration of mixing and reaction zones of a fuel reformer system employing an impingement cooling mechanism; 
           [0017]      FIG. 7  is a schematic illustration of mixing and reaction zones of a fuel reformer system including a ceramic liner; and 
           [0018]      FIG. 8  is a flow chart representing steps involved in an exemplary method for operating a fuel reformer system. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    As described in detail below, embodiments of the present invention provide a fuel reformer system and a method for providing the same. The system includes mixing and reacting a slipstream of natural gas or fuel with a slipstream of air to increase concentration of hydrogen. The introduction of hydrogen into the natural gas allows lowering of a lean blow out point and enables reduction in combustion dynamics. The term “combustion dynamics” used herein refers to fluctuations in air pressure, temperature, heat release and unsteady flow oscillations that effect operation of an engine, including a gas turbine. Further, the term ‘lean blow out point’ used herein refers to a point of loss of combustion in a combustor. Variations in fuel composition and flow disturbances result in a loss of combustion in sufficiently lean flames. It is hence desirable to operate systems with a highly reactive fuel component, such as hydrogen. As disclosed herein, embodiments of the invention include a fuel reforming retrofit unit that provides pretreatment of fuel via means of combustion. 
         [0020]    Turning to the drawings,  FIG. 1  is a block diagram representation of a fuel reformer system  10 . The fuel reformer system  10  includes a natural gas slipstream  12  that is pretreated in a preconditioning zone  14 . In a particular embodiment, the natural gas slipstream  12  is pre-mixed with water or steam. In another embodiment, the preconditioning zone  14  includes a natural gas swirler. In yet another embodiment, the swirler includes oxidant injection orifices on an outer wall or an inner wall of duct. In another embodiment, the swirler includes oxidant injection orifices in multiple vanes. A slipstream of air  16  is introduced to mix with the natural gas slipstream  12  that are mixed in a mixing zone  18  in rich proportions. As used herein, the term “rich proportions” refers to a stoichiometric ratio of the natural gas  12  and the air  16  of between about 1.5 and about 4. In an exemplary embodiment, the stoichiometric ratio of the natural gas  12  and the air  16  is about 2.3. In a particular embodiment, the slipstream of air  16  is supplemented with oxygen. 
         [0021]    Further, the natural gas  12  and the slipstream of air  16  are allowed to react in a reaction zone  20  to generate a gaseous mixture of synthesis gas  22 , commonly known as syngas, which typically consists of hydrogen and carbon monoxide. In a particular embodiment, the syngas includes at least about 20 percent of hydrogen gas. In another embodiment, the synthetic gas includes at least one hydrocarbon species. In yet another embodiment, the syngas includes hydrogen, carbon monoxide, nitrogen and water. In another embodiment, the syngas  22  has a temperature less than about 2000 degrees Fahrenheit. In a presently contemplated embodiment, the reaction zone  20  has a residence time of less than about 200 ms. The term “residence time” refers to a time period during which the natural gas  12  and the air  16  react in the reaction zone  20 . A natural gas supply  24  is finally directed back into a quench zone  26  to mix with the syngas  22  leaving the reaction zone  20 . A mixture  28  of the natural gas  24  and the syngas  22  is further directed into a downstream system such as, but not limited to, a combustor. In a particular embodiment, the fuel reformer system  10  includes an area equal to about 1/10 th to about 1/80 th of an area of a combustion system. 
         [0022]    In another illustrated embodiment of the invention as shown in  FIG. 2 , a block diagram representation of a regulated fuel reformer system  30  is depicted. The fuel reformer system  30  includes a natural gas supply  24 , as referenced in  FIG. 1  that is controlled by a metering and valve system  32  to generate a natural gas slipstream  12  that is passed into the preconditioning zone  14 , as referenced in  FIG. 1 . Similarly, a stream of air  34  is passed through a metering and valve system  36  to generate a slipstream of air  16 , as referenced in  FIG. 1 . The slipstream of air  16  and the natural gas slipstream  12  are mixed in the mixing zone  18  and allowed to react in the reaction zone  20 . The natural gas supply  24  regulated by the metering and valve system  32  may also be directed into the quench zone  26  to mix with the syngas  22  leaving the reaction zone  20 . 
         [0023]    In yet another illustrated embodiment of the invention as shown in  FIG. 3 , a block diagram representation of a fuel reformer system  50  is depicted. The fuel reformer system  50  includes a natural gas slipstream  12 , as referenced in  FIG. 1  and a slip stream of air  16  passed into a mixing zone  18  and a reaction zone  20 , thereby generating a syngas  22 . The natural gas  24  is regulated by a metering and valve system  32 , as referenced in  FIG. 2 , and directed into another metering and valve system  52  before passing into a first quench zone  54 . The natural gas  24  and the syngas  22  are mixed in the first quench zone  54  to form a syngas mixture  56 . The syngas mixture  56  is directed into a heat exchanger  58  that enables cooling of the syngas mixture  56 . A cooled syngas mixture  60  from the heat exchanger  58  is further directed into a second quench zone  62 , wherein the cooled syngas mixture  60  is quenched by the natural gas  24 . 
         [0024]      FIG. 4  is a block diagram representation of a fuel reformer system  70  including a carbon capture system  72 . After mixing a natural gas slipstream  12  and a slip stream of air  16  in the mixing zone  18  and reacting the mixture in the reaction zone  20 , a syngas  22  is passed into a first quench zone  54 , as referenced in  FIG. 3 , to quench the natural gas  24 . The syngas mixture  56  in  FIG. 3  is passed through the carbon capture system  72 . The carbon capture system  72  reduces the amount of carbon monoxide from the syngas mixture  56  resulting in a refined mixture. The mixture is further passed into a heat exchanger  58 , as referenced in  FIG. 3 . A cooled syngas mixture  60 , as referenced in  FIG. 3 , from the heat exchanger  58  is then directed into a second quench zone  62 , as referenced in  FIG. 3 , to quench the syngas mixture  60 . 
         [0025]      FIGS. 5 and 6  illustrate various cooling mechanisms that may be employed in the fuel reformer system  10  in  FIG. 1 .  FIG. 5  is a schematic illustration of a fuel reformer system  80  employing effusion cooling through natural gas to extract heat from walls  82  of a reaction zone  20  as referenced in  FIG. 1 . A natural gas slipstream  84  passing through an inlet  86  mixes with a slipstream of air  88  entering through an inlet  90  in a mixing zone  18  as referenced in  FIG. 1 . Multiple jets  92  of natural gas are injected into injection holes  94  on a wall liner  96  in a confined space  98 . A mixture of syngas is formed at the reaction zone  20  and passes through a quench  100  that provides rapid cooling prior to mixing with a stream  102  of natural gas and entering a downstream system such as, but not limited to, a combustion chamber  104 . A cooled syngas mixture  106  further enters the combustion chamber  104 . 
         [0026]      FIG. 6  is a schematic illustration of a fuel reformer system  110  employing impingement cooling through natural gas to extract heat from walls  82  as referenced in  FIG. 5  of a reaction zone  20  as referenced in  FIG. 1 . A natural gas slipstream  84 , as referenced in  FIG. 5 , passing through an inlet  86  mixes with a slipstream of air  88  entering through an inlet  90  in a mixing zone  18  as referenced in  FIG. 1 . Multiple jets  112  of natural gas at a very high velocity are impinged on a wall liner  114  through multiple cooling holes  116  in a confined space  118 . In a particular embodiment, the velocity may vary between about 10 m/sec to about 100 m/sec. A syngas is formed at the reaction zone  20  and passes through a quench  100  that provides rapid cooling prior to mixing with a stream  120  of natural gas and entering a combustion chamber  104 , as referenced in  FIG. 5 . A cooled syngas mixture  122  further enters into the combustion chamber  104 . 
         [0027]      FIG. 7  is a schematic illustration of a fuel reformer system  130  employing a ceramic liner  132  outside of walls  82  as referenced in  FIG. 5  of a reaction zone  20  as referenced in  FIG. 1 . A slip stream of natural gas  84  passing through an inlet  86  pre-mixes with a slip stream of air  88  entering through an inlet  90  in a mixing zone  18  as referenced in  FIG. 1 . A syngas mixture is formed at the reaction zone  20  and passes through a quench  100  that provides rapid cooling prior to mixing with a stream  134  of natural gas and entering a combustion chamber  104  as referenced in  FIG. 5 . A cooled mixture  136  further enters into the combustion chamber  104 . The ceramic liner  132  provides desirable resistance against corrosion and high temperatures. 
         [0028]      FIG. 8  is a flow chart representing steps involved in an exemplary method  140  of operation of a fuel reformer system. The method  140  includes introducing a slipstream of natural gas in step  142 . A slipstream of air is introduced in step  144 . The natural gas is preconditioned in a preconditioning zone in step  146 . In a particular embodiment, the natural gas is preconditioned using a swirler. Preconditioned natural gas and air are mixed in a rich proportion in a mixing zone in step  148 . In a particular embodiment, a stoichiometric ratio of the natural gas and the air is between about 1.5 and about 4. In an exemplary embodiment, the stoichiometric ratio of the natural gas and the air is about 2.3. Further, the natural gas and the air are allowed to react in a reaction zone forming a syngas in step  150 . The natural gas is quenched with the syngas leaving the reaction zone in step  152 . In a particular embodiment, a metering and valve system is employed to regulate flow of the natural gas being introduced. In another embodiment, the natural gas is directed into the syngas via multiple injection holes in the reaction zone. 
         [0029]    The various embodiments of a fuel reformer system for lowering of a lean blow out point as well as controlling combustion dynamics and a method for operating the same described above thus provide a way to achieve a sustained lean, premixed or partially premixed flame in the combustor without lean blow-out or combustion dynamics. These techniques and systems also allow for highly efficient gas turbine engines with a fuel reformer retrofit unit due to improved combustion in their respective combustors. 
         [0030]    Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0031]    Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. For example, an effusion cooling mechanism described with respect to one embodiment can be adapted for use with a carbon capture system described with respect to another. Similarly, the various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. 
         [0032]    While only certain features of the invention have been illustrated and described herein, modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.