Patent Application
20160172954
The disclosure relates generally to power plants, and more particularly, to a power plant using magnetohydrodynamic generator exhaust to feed at least one stage of a gas turbine.
Gas turbines generate power in conjunction with a generator by extracting mechanical power from a combusted fuel using a set of turbines coupled to a generator by a rotating shaft. Steam turbines work in a similar fashion by extracting mechanical power from a steam flow. Magnetohydrodynamic (MHD) generators convert thermal energy and kinetic energy of a conductive plasma flow, e.g., very hot gases, directly into electric power. MHD generators are different from turbines in that they rely on moving a conductor in the form of the conductive plasma flow through a magnetic field to create electric power, and therefore have no moving mechanical parts.
MHD generators may be used in combination with gas turbines and steam turbines in a number of ways to improve overall power plant efficiency. In one approach, an MHD generator is used to generate electric power as a topping cycle for a steam turbine power plant. Here, the very hot MHD generator exhaust may be used to create steam for the steam turbine system to increase efficiency, e.g., using a heat recovery steam generator (HRSG). In another approach, the very hot MHD generator exhaust may be used to pre-heat an airflow used to feed a combustor that feeds combusted fuel back to the MHD generator and then to the gas turbine.
A first aspect of the disclosure provides a power plant comprising: a gas turbine (GT) for powering a rotating shaft, the gas turbine having a gas turbine exhaust; a magnetohydrodynamic (MHD) generator having an MHD exhaust; a combustor operatively coupled to the MHD generator for creating a flow with a working fluid for powering the MHD generator; a compressor for creating a compressor exit flow; a heat exchanger exchanging heat between the MHD exhaust and the compressor exit flow to cool the MHD exhaust using the compressor exit flow and heat the compressor exit flow using the MHD exhaust; a first conduit for delivery of the compressor exit flow exiting the heat exchanger to the combustor; and a second conduit for delivery of the MHD exhaust exiting the heat exchanger to at least one stage of the gas turbine.
A second aspect of the disclosure provides a power plant comprising: a gas turbine (GT) for powering a rotating shaft, the gas turbine having a gas turbine exhaust; a magnetohydrodynamic (MHD) generator having an MHD exhaust; a combustor operatively coupled to the MHD generator for creating a flow with a working fluid for powering the MHD generator; a compressor for creating a compressor exit flow and a compressor pre-exit flow; a first conduit for delivery of a mix of the MHD exhaust and the compressor pre-exit flow to at least one stage of the gas turbine; and a second conduit for delivery of the compressor exit flow to the combustor.
The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.
These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:
It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.
As indicated above, the disclosure provides a power plant including a magnetohydrodynamic (MHD) generator. In one embodiment, an MHD exhaust is cooled using a compressor exit flow to a temperature at which the MHD exhaust can be fed to at least one stage of a gas turbine. The heated compressor exit flow may be used to feed a combustor for the MHD generator. In an alternative embodiment, the gas turbine exhaust may be used in a heat recovery steam generator (HRSG) for a steam turbine system. In addition, in other embodiments, the gas turbine exhaust exiting the HRSG may be fed back to a compressor for the combustor to the MHD generator. In another embodiment, a power plant may include a compressor exit flow feeding a combustor for an MHD generator and an MHD exhaust may be mixed with a compressor pre-exit, extraction flow for feeding to at least one stage of a gas turbine. This latter embodiment may also include a combined cycle version and an exhaust gas recirculation version.
Referring to
In the embodiments described herein, load 106 has been described as a generator that is coupled to rotating shaft 104 to generate electric power from gas turbine 102. The generator may include any now known or later developed electric generator. It is understood that other forms of a load may also be employed within the scope of the invention, e.g., a machine transmission, other industrial machine, etc.
Power plant 100 may also includes a compressor 110 for creating a compressor exit flow 112, i.e., a flow having greater pressure than that entering the compressor. Compressor exit flow 112 includes a compressed gas flow that has been exposed to most, if not all, of the compression stages of compressor 110. Compressor 110 may use air as a working fluid and use conventional air intake systems, e.g., filters, noise reduction, moisturizing, etc. In an alternative embodiment, compressor 110 may be operatively coupled to, for example, an oxygen separation system 114 such that compressor exit flow 112 may include air with oxygen. Oxygen separation system 114 may include any now known or later developed system for generating purified oxygen. Oxygen separation system 114 can include, for example, a cryogenic unit including one or more distillation elements capable of supplying gaseous stream(s) including a majority of oxygen. In one particular embodiment, compressor exit flow 112 may include mostly oxygen. Alternatively, other gases may be used within power plant 100 in a closed loop, or open arrangement. For example, another gas may include carbon dioxide. Compressor 110 may be powered by rotating shaft 104. In alternative embodiments, compressor 110 may include a dual spool compressor, i.e., with two sets of turbines, or a main compressor 110 with a booster compressor 116 (shown in phantom). Booster compressor 116 may be driven by a transmission from rotating shaft 104 or another power source. An exhaust or flue gas vent 174 may be utilized to extract a portion of the working gases commensurate with the amount of air or oxygen brought into the cycle, wherein a desired pressure within the cycle is maintained. As will be described herein, in the
In contrast to conventional power plants, a combustor 130 is not coupled directly to gas turbine 102 but is operatively coupled to a magnetohydrodynamic (MHD) generator 140 for creating a flow with a working fluid in the form of, for example, a conductive plasma flow, for powering the MHD generator. Combustor 130 may create any now known or later developed conductive plasma flow for MHD generator 140. In one embodiment, combustor 130 receives a seed (or injected plasma) material flow 132 and a fuel 134 that is combusted in a conventional manner to create a conductive plasma flow 136. For example, conductive plasma flow 136 may be created by thermal ionization, in which the temperature of the gas is high enough to separate the electrons from the atoms of gas. Plasma flow 136 is electrically conductive because of the free electrons therein. Plasma flow 136 generation requires very high temperatures, the extent of which can be lowered by seeding or injecting with an alkali metal compound, e.g., potassium carbonate, which ionizes more easily at lowered temperatures. Seed material flow 132 may be recovered and recycled downstream of MHD generator 140 in a conventional manner. Fuel 134 may include any variety of combustible fuel such as but not limited to: natural gas, coal, oil, integrated gasification combined cycle (IGCC) fuel, etc. As will be described herein, a heated compressor exit flow 146 may also be fed to combustor 130.
MHD generator 140 may include any now known or later developed electric generator capable of converting thermal energy and kinetic energy of conductive plasma flow 136 directly into electric power without moving parts. For example, MHD generator 140 may include but is not limited to: a Faraday-type MHD generator, a segmented Faraday-type MHD generator, a Hall-type MHD generator, and a disk-type MHD generator. A segmented Faraday-type MHD generator may include, for example, a non-conductive duct having an acceleration nozzle (e.g., Venturi) through which conductive plasma flow 136 passes. Downstream of the acceleration nozzle, a set of segmented electrodes extends about the plasma flow path in the duct within a strong perpendicular, magnetic field. The magnetic field may be created, for example, by a number of solenoids. As the conductive plasma flow 136 passes through the magnetic field, it creates an electric flow in the segmented electrodes. There are no moving parts. A Hall-type MHD generator works similarly to the segmented Faraday-type device but places an array of vertical electrodes on the duct sides, some of which are shorted to reduce losses. A disk-type MHD generator, also known as a Hall affect disk generator, flows conductive plasma flow 136 between a center of a disk, and a duct positioned around an edge of the disk. A pair of Helmholtz coils may be used to create the magnetic field below and above the disk. Current can be pulled from ring electrodes near the periphery and center of the disk. It is emphasized that while a number of particular MHD generators have been briefly described that the teachings of the invention are applicable to any form of MHD generator now known or later developed. In any event, it is understood, MHD generators operate at very high temperatures, e.g., greater than 2480° C. Consequently, a conventional MHD exhaust cannot, as is, be used to power gas turbine 102, which typically operates at below 1540° C. In addition, as MHD generator 140 creates direct current electric power, an inverter 142 is typically provided to convert the electric power to alternating current. Inverter 142 may include any now known or later developed system for conditioning and inverting direct current to alternating current for feeding to conventional power distribution systems along with power generated by a generator, i.e., load 106.
In accordance with embodiments of the invention, power plant 100 includes a heat exchanger 120 exchanging heat between an MHD exhaust 144 and compressor exit flow 112 to cool MHD exhaust 144 using compressor exit flow 112 and heat compressor exit flow 112 using MHD exhaust 144. The result is a cooled, MHD exhaust 144 in the range of approximately 1050° C. to approximately 1540° C. The compressor exit flow is heated commensurate with the change in enthalpy of the MHD exhaust in the heat exchanger, thus reducing the amount of fuel needed in the combustor. Heat exchanger 120 can take any form capable of exchanging heat between the two streams, and may be integral or separate from MHD generator 140. Heat exchanger 120 does not allow intermixing of MHD exhaust 144 and compressor exit flow 112.
A first conduit 150 delivers heated, compressor exit flow 146 exiting heat exchanger 120 to combustor 130 for use in creating conductive plasma flow 136. In this fashion, a more efficient combustion using a heated, flow 146 can be obtained. In addition, a second conduit 152 delivers cooled, MHD exhaust 144 exiting heat exchanger 120 to at least one stage of gas turbine(s) 102 to power the gas turbine. Cooled MHD exhaust 144 can be injected to gas turbine(s) 102 in any now known or later developed fashion, and to all or any number of stages of the gas turbine. No other combustion flow needs to be provided. Power plant 100 thus takes advantage of MHD exhaust 144 in number of ways. First, the high pressure MHD exhaust 144, rather than simply being used as a heat source, is leveraged to directly power gas turbine(s) 102. For example, MHD exhaust 144 may exhibit a pressure in the range of approximately 0.4 MegaPascal (MPa) to approximately 3 MPa. Second, MHD generator 140 may be operated at a very high firing temperature, e.g., above approximately 2500° C., creating a very hot conductive plasma flow 136, thus improving efficiency thereof while also allowing excess heat to be advantageously transferred to compressor exit flow 112 for use by combustor 130.
Referring to
Power plant 200 may also include a heat recovery steam generator (HRSG) 260 receiving a gas turbine exhaust 262 to generate steam for steam turbine 202. HRSG 260 may include any now known or later developed system to recover energy from a hot gas stream so it can be used to produce steam. In this fashion, gas turbine exhaust 262 feeds a bottoming, Rankine steam cycle. The use of MHD exhaust 144 in gas turbine(s) 102 may result in a hotter gas turbine exhaust 262 providing higher efficiency steam generation in HRSG 260. A conventional condenser 270 may be coupled to LP sections to recuperate water to feed HRSG 260.
Referring to
With continuing reference to
Referring to
While use of gas turbine exhaust 262 to feed HRSG 260 and its recirculation via conduit 266 to compressor 110, 310 have been illustrated as being used together in
In the foregoing embodiments, the working fluid has been described, in most cases, as air, perhaps with a supplemental oxidant supply system, e.g., oxygen separation plant 114 (
While
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
