Patent Application
20130145773
The field of the invention relates generally to turbine engine systems, and more particularly, to turbine engine systems in power generation plants.
Turbine engines produce mechanical energy using a working fluid supplied to the engines. More specifically, in known turbine engines, the working fluid may be air that is compressed and delivered, along with fuel and oxygen, to a combustor, wherein the fuel-air mixture is ignited. As the fuel-air mixture burns, its energy is released into the working fluid as heat. The temperature rise causes a corresponding increase in the pressure of the working fluid, and following combustion, the working fluid expands as it is discharged from the combustor downstream towards at least one turbine. As the working fluid flows past each turbine, the turbine is rotated and converts the heat energy to mechanical energy in the form of thrust or shaft power connected to a generator.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from at least some gas turbines are subject to government standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), carbon monoxide (CO), and carbon dioxide (CO2). Air has been used as a working fluid because it is readily available, free, and has predictable compressibility, heat capacity, and reactivity (oxygen content) properties. However, because of the high percentage of nitrogen in air, during the combustion process, nitrogen oxides are formed. In addition, carbon contained in the fuel may combine with oxygen contained in the air to form carbon monoxide and/or carbon dioxide.
To facilitate reducing NOx emissions, at least some known gas turbine engines operate with reduced combustion temperatures and/or Selective Catalytic Reduction (SCR) equipment. However, operating at reduced combustion temperatures reduces the overall efficiency of the gas turbine engine. Moreover, any benefits gained through using known SCR equipment may be outweighed by the cost of the equipment and/or the cost of disposing the NOx. Similarly, to facilitate reducing CO emissions an oxidation catalyst may be used. To facilitate reducing CO2 emissions, at least some known gas turbine engines channel turbine exhaust through a gas separation unit to separate CO2 from nitrogen (N2), the major component when using air as the working fluid, and at least one CO2 compressor. Again however, the benefits gained through the use of such equipment may be outweighed by the costs of the equipment.
In one aspect, a method of separating carbon dioxide (CO2) from nitrogen (N2) and oxygen (O2) in a turbine engine system is provided. The turbine engine system includes a first compressor coupled to a turbine expander by a rotatable shaft, and a combustor coupled in flow communication to the compressor and the first turbine. The method includes directing an air stream into an air separation unit (ASU), separating N2 from the air stream in the ASU to form an oxygen (O2) rich air stream, and directing the O2 rich air stream to the combustor to mix with a fuel for combustion forming hot combustion gases, containing O2 and CO2, which are used to rotate the turbine. In some embodiments, the method also includes directing turbine exhaust gases to a heat recovery steam generator (HRSG) to create steam, directing exhaust from the HRSG to a condenser to separate water from a mixture of O2 and CO2 gases, and directing the mixture of O2 and CO2 gases to a separation system, where the CO2 is separated from the O2 gases and removed from the separation system.
In another aspect, a system in separating CO2 and N2 in a turbine engine apparatus is provided. The system includes an air separation unit (ASU) for separating N2 from an air stream that forms an oxygen (O2) rich air stream, a heat recovery steam generator (HRSG), and a condenser to separate water from a mixture of O2 and CO2 gases from the HRSG. The system also includes a separation system where the CO2 is separated from the O2 gases and removed from the separation system.
Novel methods of producing a carbon dioxide (CO2) rich stream and a nitrogen (N2) rich stream from combustion of a hydrocarbon fuel source (natural gas, oil, coal) are disclosed. Applications of the novel methods involve electricity production, enhanced oil recovery, carbon capture, and sequestration. The methods disclosed provide separation of CO2 and N2 gases which are products of a combustion process. Methods and systems for separating N2 and CO2 from the working air and/or exhaust in turbine engine systems in power generation plants are described below in detail. In addition, oxygen (O2) is separated from a CO2 and O2 mixture in the exhaust of the turbine engine system, and may be recycled back to the oxyfuel combuster of the turbine engine system. Removing the N2 from the working air reduces NOx emissions. Also, the CO2 removed from the exhaust may be sequestered for use in enhanced oil recovery. A stream of removed CO2 may contain no O2 or less that 1 percent of O2. Advantages of the methods and systems described below include removing O2 from a CO2 stream with lower energy and lower costs than known methods. With O2 removed from a CO2 stream, the CO2 stream may be used for injection in an oil well for enhanced oil recovery. Streams of CO2 that do include O2 can be detrimental to oil recovery because of the reactivity of O2. In addition, advantages of the methods and systems may include improved flexibility of operation of a power generation plant, a safer power generation plant because of reduced CO emissions and a reduced need for the use of CO oxidation catalysts.
Combustor 24 is also coupled in flow communication with at least one fuel source 32 and receives fuel from the fuel source, for example, natural gas. The air and fuel are mixed and combusted within combustor 24 which produces hot combustion gases. Turbine expander 16 is coupled in flow communication with combustor 24, and turbine expander 16 receives the hot combustion gases via a combustion gas conduit 34. Turbine expander 16 converts the heat energy within the gases to rotational energy. The rotational energy is transmitted to generator 20 via rotor 36, wherein generator 20 converts the rotational energy to electrical energy for transmission to at least one load, including, but not limited to, an electrical power grid.
In the exemplary embodiment, plant 10 also includes a steam turbine engine 40. More specifically, steam turbine engine 40 includes a steam turbine 42 coupled to a second electrical generator 44 via a second rotor 46. Power plant 10 also includes a steam generation system 48. In the exemplary embodiment, system 48 includes a heat recovery steam generator (HRSG) 50 that is coupled in flow communication with turbine 16 via at least one conduit 52. HRSG 50 receives exhaust gases from turbine expander 16 via exhaust gas conduit 52. The exhaust from turbine includes O2, H2O, and CO2. HRSG 50 is coupled in flow communication with steam turbine 42 via a steam conduit 54.
Conduit 54 channels steam from HRSG 50 to steam turbine 42 which converts the thermal energy in the steam to rotational energy. The rotational energy is transmitted to generator 44 via rotor 46, wherein generator 44 converts the rotational energy to electrical energy for transmission to at least one load, including, but not limited to, the electrical power grid. The exhaust steam from turbine 42 is directed to a condenser 56 where the exhaust steam is condensed to water. A pump 58 is coupled in flow communication with condenser 56. Pump 58 pumps the condensed water through a conduit 60 that is coupled in flow communication with HRSG 50.
In addition, the exhaust of the HRSG 50 is directed to a condenser 62 through a conduit 64 that is that is coupled to HRSG 50 and condenser 62. Exhaust from HRSG 50 includes O2, H2O, and CO2. Water is removed from condenser 62 through an outlet conduit 66. A portion of CO2 is recirculated back to compressor 14 through a conduit 68. A separation system 69 is used to separate the excess O2 from CO2 by compressing the mixture of CO2 and O2 and cooling the compressed mixture. Separation system 69 includes a compressor 70, a heat exchanger 74, and a separator 78.
The remainder of the CO2 and O2 is directed to compressor 70 through conduit 72 to compress the CO2 and O2 mixture. The compressed CO2 and O2 mixture is directed to heat exchanger 74 through a conduit 76 to cool down the mixture to temperatures of between about minus 60° C. to about minus 120° C. The cooled CO2 and O2 mixture is directed to separator 78 through a conduit 80 where the CO2 is separated as either a liquid or a solid. A non-condensable O2 rich stream is recycled to combustor 24 from separator 78 through a conduit 82. The liquid/solid CO2 is pumped from separator 78 through conduit 84 by pump 86 for sequestration.
In another embodiment, a CO2 and O2 separation system 90 replaces separation system 69 described above. Referring also to
Combustor 126 is also coupled in flow communication with at least one fuel source 132 and receives fuel from the fuel source, for example, natural gas. The air and fuel are mixed and combusted within combustor 126 which produces hot combustion gases. Turbine expander 122 is coupled in flow communication with combustor 126, and turbine expander 122 receives the hot combustion gases via a combustion gas conduit 134. Turbine expander 122 converts the heat energy within the gases to rotational energy.
SEGR 110 also includes a heat recovery steam generator (HRSG) 136 coupled in flow communication to turbine 122 by an exhaust conduit 138. HRSG 136 receives exhaust gases from turbine 122 via exhaust gas conduit 138. The exhaust from turbine 112 includes N2, H2O, and CO2. HRSG 136 is coupled in flow communication with second compressor 118 via a conduit 140. The exhaust gases may be recirculated to second compressor 118 through conduit 140 Water collected in HRSG 136 is removed through outlet conduit 142.
A portion of the exhaust gases from second compressor 118 is directed to a high pressure HRSG 144 via a conduit 146. A separation system 147 is used to separate the excess N2 from CO2 from the exhaust gases by compressing the exhaust gases and cooling the compressed gases. Separation system 147 includes HRSG 144, a compressor 148, an intermediate cooler 150, and a separator 152. The exhaust gases are directed from HRSG 144 to a compressor 148 via a conduit 154 where the gases are compressed to about 1000 psi to about 2000 psi (about 6,895 kPa to about 13710 kPa).
The compressed gases are directed to intermediate cooler 150 through a conduit 156 to cool down the gases. The cooled gases are directed to separator 152 through a conduit 158 where the CO2 may be separated using a physical solvent, for example dimethyl-ether-polyethylene-glycol (DEPG) or methyl alcohol, by absorption. A non-condensable N2 rich stream is removed from separator 152 through a conduit 160 to a compressor 162 for sequestration. The CO2 is removed from separator 152 through conduit 164 to a compressor 166 for sequestration.
In another embodiment, intermediate cooler 150 cools the gases to temperatures of between about minus 60° C. to about minus 120° C. The cooled gases containing CO2 and N2 is directed to separator 152 through conduit 158 where the CO2 is separated as either a liquid or a solid. A non-condensable N2 rich stream is removed from separator 152 through a conduit 160 to a compressor 162 for sequestration. The liquid/solid CO2 is pumped from separator 152 through conduit 164 to a compressor 166 for sequestration.
As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, includes the degree of error associated with the measurement of the particular quantity). “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, or that the subsequently identified material may or may not be present, and that the description includes instances where the event or circumstance occurs or where the material is present, and instances where the event or circumstance does not occur or the material is not present. The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. All ranges disclosed herein are inclusive of the recited endpoint and independently combinable. As used herein, the phrases “adapted to,” “configured to,” and the like refer to elements that are sized, arranged or manufactured to form a specified structure or to achieve a specified result.
Exemplary embodiments of a system for separating O2, CO2 and N2 from a turbine engine are described above in detail. The system is not limited to the specific embodiments described herein, but rather, components of the system may be utilized independently and separately from other components described herein. Although specific features of various 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.
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.
