Abstract:
A method and system for supplying fuel are provided. The fuel supply system includes a supply of a flow of fuel wherein the fuel includes an amount of moisture in a first predetermined range, a supply of a flow of gas wherein the gas includes an amount of moisture in a second predetermined range and wherein the second predetermined range is less than the first predetermined range. The fuel supply system further includes a vessel configured to receive the flow of fuel and the flow of gas, mix the flow of fuel and the flow of gas, and separate the flow of fuel from the flow of gas wherein moisture is transferred from the flow of fuel to the flow of gas.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to power generation systems and, more particularly, to methods and systems for providing fuel for an integrated gasification combined cycle power generation system. 
         [0002]    At least some known power generation systems humidify gases entering a gas turbine engine. The moisture in the humidified gas tends to increase the mass fed into the gas turbine engine such that an increase in the efficiency of the gas turbine engine is realized. The humidification of the gases uses energy for the vaporization of the water being added to the gas stream. Additionally, the power generation system may also dry the solid fuel being fed to the gasifier. Drying is typically performed by contacting an inert gas stream with the fuel prior to injection into the gasifier. The moisture in the fuel is vaporized using energy from the fuel. The energy used humidifying the gases and the energy used drying the fuel are lost to the system and the loss tends to decrease the efficiency of the system. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    In one embodiment, a fuel supply system includes a supply of a flow of fuel wherein the fuel includes an amount of moisture in a first predetermined range, a supply of a flow of gas wherein the gas includes an amount of moisture in a second predetermined range and wherein the second predetermined range is less than the first predetermined range. The fuel supply system further includes a vessel configured to receive the flow of fuel and the flow of gas, mix the flow of fuel and the flow of gas, and separate the flow of fuel from the flow of gas wherein moisture is transferred from the flow of fuel to the flow of gas. 
         [0004]    In another embodiment, a method of operating a fuel supply system includes receiving a flow of carbonaceous fuel, the fuel comprising a first amount of moisture and mixing the flow of carbonaceous fuel with a flow of a gas such that the first amount of moisture in the fuel is reduced and a second amount of moisture in the gas is increased. The flow of gas includes an amount of heat and at least some of the amount of heat is transferred to the flow of fuel during the mixing. 
         [0005]    In yet another embodiment, an integrated gasifier combined cycle power system includes a fuel dryer configured to receive a flow of fuel, receive a flow of fluid, transfer moisture from the fuel to the gas, and transfer heat from the gas to the fuel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1-3  show exemplary embodiments of the method and system described herein. 
           [0007]      FIG. 1  is a schematic diagram of an exemplary integrated gasification combined-cycle (IGCC) power generation system; 
           [0008]      FIG. 2  is a schematic block diagram of a portion of the integrated gasification combined-cycle (IGCC) power generation system in accordance with an embodiment of the present invention; and 
           [0009]      FIG. 3  is a schematic block diagram of a portion of the integrated gasification combined-cycle (IGCC) power generation system in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    The following detailed description illustrates embodiments of the invention by way of example and not by way of limitation. It is contemplated that the invention has general application to conserving energy by using waste heat from one part of the process to replace heat in another part of the process in industrial, commercial, and residential applications. 
         [0011]    As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
         [0012]      FIG. 1  is a schematic diagram of an exemplary integrated gasification combined-cycle (IGCC) power generation system  10 . IGCC system  10  generally includes a main air compressor  12 , an air separation unit (ASU)  14  coupled in flow communication to compressor  12 , a gasifier  16  coupled in flow communication to ASU  14 , a syngas cooler  18  coupled in flow communication to gasifier  16 , a gas turbine engine  20  coupled in flow communication to syngas cooler  18 , and a steam turbine  22  coupled in flow communication to syngas cooler  18 . In various embodiments, gasifier  16  and syngas cooler  18  are combined into a single integral vessel. 
         [0013]    In operation, compressor  12  compresses ambient air that is then channeled to ASU  14 . In the exemplary embodiment, in addition to compressed air from compressor  12 , compressed air from a gas turbine engine compressor  24  is supplied to ASU  14 . Alternatively, compressed air from gas turbine engine compressor  24  is supplied to ASU  14 , rather than compressed air from compressor  12  being supplied to ASU  14 . In the exemplary embodiment, ASU  14  uses the compressed air to generate oxygen for use by gasifier  16 . More specifically, ASU  14  separates the compressed air into separate flows of oxygen (O 2 ) and a gas by-product, sometimes referred to as a “process gas.” The O 2  flow is channeled to gasifier  16  for use in generating partially combusted gases, referred to herein as “syngas” for use by gas turbine engine  20  as fuel, as described below in more detail. 
         [0014]    The process gas generated by ASU  14  includes nitrogen and will be referred to herein as “nitrogen process gas” (NPG). The NPG may also include other gases such as, but not limited to, oxygen and/or argon. For example, in the exemplary embodiment, the NPG includes between about 95% and about 100% nitrogen. In the exemplary embodiment, at least some of the NPG flow is vented to the atmosphere from ASU  14 , and at some of the NPG flow is injected into a combustion zone (not shown) within a gas turbine engine combustor  26  to facilitate controlling emissions of engine  20 , and more specifically to facilitate reducing the combustion temperature and reducing nitrous oxide emissions from engine  20 . In the exemplary embodiment, IGCC system  10  includes a compressor  28  for compressing the nitrogen process gas flow before being injected into the combustion zone of gas turbine engine combustor  26 . 
         [0015]    In the exemplary embodiment, gasifier  16  converts a mixture of fuel supplied from a fuel supply  30 , O 2  supplied by ASU  14 , steam, and/or limestone into an output of syngas for use by gas turbine engine  20  as fuel. Although gasifier  16  may use any fuel, gasifier  16 , in the exemplary embodiment, uses coal, petroleum coke, residual oil, oil emulsions, tar sands, and/or other similar fuels. Furthermore, in the exemplary embodiment, the syngas generated by gasifier  16  includes carbon dioxide. Gasifier  16  may be a fixed-bed gasifier, a fluidized-bed gasifier, and/or an entrained gasifier. 
         [0016]    In the exemplary embodiment, syngas generated by gasifier  16  is channeled to syngas cooler  18  to facilitate cooling the syngas, as described in more detail below. The cooled syngas is channeled from syngas cooler  18  to a scrubber, and through additional cooling to a clean-up device  32  for cleaning the syngas before it is channeled to gas turbine engine combustor  26  for combustion thereof. Hydrogen sulfide (H 2 S) is separated from the syngas during cleanup and is sent to a processing unit where it is converted to products, typically sulfur or sulfuric acid. Carbon dioxide (CO 2 ) may also be separated from the syngas during clean-up and, in the exemplary embodiment, may be vented to the atmosphere. Gas turbine engine  20  drives a generator  34  that supplies electrical power to a power grid (not shown). Exhaust gases from gas turbine engine  20  are channeled to a heat recovery steam generator  36  that generates and superheats steam for driving steam turbine  22 . Power generated by steam turbine  22  drives an electrical generator  38  that provides electrical power to the power grid. 
         [0017]    Furthermore, in the exemplary embodiment, system  10  includes a pump  40  that supplies preheated water from steam generator  36  to syngas cooler  18  to facilitate cooling the syngas channeled from gasifier  16 . The boiled water is channeled through syngas cooler  18  wherein the water is converted to steam. The steam from syngas cooler  18  is then returned to steam generator  36  for use within gasifier  16 , syngas cooler  18 , and/or steam turbine  22 . 
         [0018]      FIG. 2  is a schematic block diagram of a portion of integrated gasification combined-cycle (IGCC) power generation system  10  (shown in  FIG. 1 ) in accordance with an embodiment of the present invention. In the exemplary embodiment, IGCC power generation system  10  includes a fuel dryer  200  in serial flow communication between fuel supply  30  and gasifier  16 . Fuel dryer  200  is also in serial flow communication between syngas cooler  18  and clean-up device  32 . Fuel dryer  200  is configured to receive a flow of relatively cool and wet fuel from fuel supply  30  and a flow of relatively hot and dry syngas from syngas cooler  18 . The flows of syngas and fuel are encouraged to mix in fuel dryer  200  such that the syngas and fuel come into close contact with each other. During the close contact, heat is transferred from the syngas to the fuel, drying the fuel before it is channeled out of fuel dryer  200  and on to gasifier  16 . Also during the close contact, moisture is transferred from the fuel to the syngas moisturizing the syngas before it is channeled out of fuel dryer  200  and on to clean-up device  32  and combustor  26 . In an embodiment, an auxiliary cleanup device  202  is provided in serial flow communication between fuel dryer  200  and clean-up device  32 . Auxiliary cleanup device  202  is configured to remove solids and particulates entrained in the syngas in fuel dryer  200  during the close contact between the fuel and the syngas. 
         [0019]      FIG. 3  is a schematic block diagram of a portion of integrated gasification combined-cycle (IGCC) power generation system  10  (shown in  FIG. 1 ) in accordance with another embodiment of the present invention. In the exemplary embodiment, IGCC power generation system  10  includes a fuel dryer  200  in serial flow communication between fuel supply  30  and gasifier  16 . Fuel dryer  200  is also in serial flow communication between air separation unit (ASU)  14  and combustor  26 . Fuel dryer  200  is configured to receive a flow of relatively cool and wet fuel from fuel supply  30  and a flow of relatively hot and dry nitrogen process gas (NPG) from ASU  14 . The flows of NPG and fuel are encouraged to mix in fuel dryer  200  such that the NPG and fuel come into close contact with each other. During the close contact, heat is transferred from the NPG to the fuel, preheating the fuel before it is channeled out of fuel dryer  200  and on to gasifier  16 . Also during the close contact, moisture is transferred from the fuel to the NPG, moisturizing the NPG before it is channeled out of fuel dryer  200  and on to combustor  26 . In an embodiment, an auxiliary cleanup device  202  is provided in serial flow communication between fuel dryer  200  and combustor  26 . Optional auxiliary cleanup device  202  is configured to remove solids and particulates entrained in the NPG in fuel dryer  200  during the close contact between the fuel and the NPG. In various embodiments, compressor  28  is positioned in serial flow communication between fuel dryer  200  and auxiliary cleanup device  202 , if used. Compressor  28  is used for compressing the NPG flow before being injected into the combustion zone of gas turbine engine combustor  26 . 
         [0020]    Although the source of preheat and drying of the fuel is described above as being syngas and/or NPG, it should be understood that any source of relatively dry gas may be used to dry and/or preheat the flow of fuel entering gasifier  16 . In addition, the fuel may be stored in a hopper or silo after drying and before being injected into gasifier  16 . In the exemplary embodiment, fuel dryer  200  comprises a stationary vessel. In an alternative embodiment, fuel dryer  200  comprises a movable vessel that may rotate about a longitudinal axis. 
         [0021]    The above-described embodiments of a method and system of power generation systems provides a cost-effective and reliable means increasing the efficiency of the power generation system by using heat that would otherwise be lost to the system to perform useful work. More specifically, the methods and systems described herein facilitate drying relatively wet fuel using relatively hot and dry gases in the process that will otherwise be cooled and humidified using energy from the system. In addition, the above-described methods and systems facilitate humidifying the gas using moisture that would otherwise be discharged from the system. As a result, the methods and systems described herein facilitate increasing the efficiency of the power generation system in a cost-effective and reliable manner. 
         [0022]    An exemplary methods and apparatus for drying fuel in a power generation system using gases being fed into the power generation system gas turbine engine to increase mass flow through the gas turbine engine are described above in detail. The systems illustrated are not limited to the specific embodiments described herein, but rather, components of each may be utilized independently and separately from other components described herein. Each system component can also be used in combination with other system components. 
         [0023]    While the disclosure has been described in terms of various specific embodiments, it will be recognized that the disclosure can be practiced with modification within the spirit and scope of the claims.