Patent Application
20140150402
The subject matter disclosed herein relates to burning vanadium-containing fuels, and, more particularly, to systems and methods for burning vanadium-containing fuels in gas turbine engines without the use of fuel additives.
Vanadium concentrations in petroleum fuels range from less than 0.5 ppm in distillate fuels to as much as 400 ppm in low-grade fuels. Low-grade fuels are inexpensive fuels and desirable for use in gas turbine engines. However, corrosion problems associated with vanadium-containing deposits on gas turbine engine surfaces limit the use of the cheaper, low-grade fuels. During combustion, vanadium forms vanadium oxides, including vanadium pentoxide (V2O5), which has a highly corrosive effect on gas turbine engine components.
Present practice is to treat low-grade fuels with vanadium oxide inhibitors, such as magnesium additives, that convert the vanadium contaminates into solid magnesium vanadates resulting in solid, non-corrosive ash deposits on the turbine blades. While these ash deposits are non-corrosive, the deposits can be detrimental to gas turbine engine operation. The use of magnesium as an additive results in the accumulation of these ash-like deposits on the interior gas turbine engine parts, which requires periodic shutdown and cleaning of the gas turbine engine to remove the deposits. In some instances, the gas turbine engine may need to be shut down and cleaned in a water wash process on a weekly basis. In addition to short waster wash cycles, higher efficiency gas turbine engines with high firing temperatures may depend upon nozzle and bucket cooling by injecting air across the surfaces of these parts. Solid magnesium vanadate deposits can plug the air cooling ports and lead to overheating. Thus, gas turbine engines capable of high efficiency operation on clean distillate fuels are generally de-rated for operation on low-grade, vanadium-containing fuels. Accordingly, it is desirable to decrease the formation of V2O5 when burning low-grade, vanadium-containing fuels without the use of magnesium additives and to remove vanadium oxides present in lower oxidation states from the exhaust gas.
In one aspect, a combustion system is provided. The combustion system includes a vanadium-containing fuel supplied to a combustor. The combustion system also includes at least one combustor configured to combust a reduced-oxygen mixture comprising the vanadium-containing fuel, ambient air, and at least a portion of a combustor exhaust gas, thereby facilitating the prevention of the formation of V2O5. The combustor is further configured to generate the combustor exhaust gas including at least one of V2O3 and V2O4 particles. The combustion system also includes a particle separator that is configured to receive the combustor exhaust gas from the combustor. The particle separator is further configured to remove substantially all of the V2O3 particles and/or the V2O4 particles from the combustor exhaust gas.
In another aspect, a method for combusting fuel is provided. The method includes channeling a vanadium-containing fuel to at least one combustor. The method also includes channeling at least a portion of a combustor exhaust gas to the at least one combustor to generate a reduced-oxygen mixture. Additionally, the method includes combusting the reduced-oxygen mixture in the at least one combustor to generate the combustor exhaust gas including at least one of V2O3 particles and vanadium tetroxide V2O4 particles, wherein combusting the reduced-oxygen mixture facilitates preventing the formation of vanadium pentoxide V2O5. The method further includes channeling the combustor exhaust gas to a particle separator and removing substantially all of the V2O3 particles and/or the V2O4 particles from the combustor exhaust gas.
In another aspect, a power generation system is provided. The power generation system includes at least one a gas turbine engine and a vanadium-containing fuel supply to the gas turbine engine. The gas turbine engine includes a rotatable shaft, at least one combustor, at least one compressor, and at least one turbine connected to the rotatable shaft. The combustor is configured to burn a reduced-oxygen mixture of the vanadium-containing fuel, air, and at least a portion of gas turbine engine exhaust gas, thereby facilitating the prevention of the formation of V2O5 particles. Additionally, the combustor is configured generate the combustor exhaust gas that contains at least one of V2O3 and V2O4 particles. The turbine is connected downstream of the combustor and is configured to receive and extract energy from the combustor exhaust gas, and discharge a turbine exhaust gas. Furthermore, the power generation system also includes a particle separator configured to remove substantially all of the V2O3 and V2O4 particles from at least one of the combustor exhaust gas and the turbine exhaust gas.
Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. Any feature of any drawing may be referenced and/or claimed in combination with any feature of any other drawing.
The features, functions, and advantages described herein may be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which may be seen with reference to the following description and drawings. As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
Approximating language, as used in the following specification and claims, may be applied to modify any quantitative representation that could permissibly 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 “approximately,” “about,” and “substantially,” is not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. In the following specification and the claims, range limitations may be combined or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
The systems and methods described herein relate to burning low-grade, vanadium-containing fuels without the use of vanadium oxide inhibitors, such as magnesium additives. In combustion systems burning low-grade, vanadium-containing fuels, the present systems and methods provide for generating solid vanadium trioxide (V2O3) and/or vanadium tetroxide (V2O4) particles in an exhaust gas, for removing the V2O3 and V2O4 particles from the exhaust gas, and for facilitating the prevention of vanadium pentoxide (V2O5) formation in the exhaust gas. Generating V2O3 and V2O4 while limiting the formation of V2O5 is desirable because the first two oxides, V2O3 and V2O4, can be considered refractory oxides (with melting points in excess of 3450 degrees Fahrenheit (° F.)). The melting point of V2O5, however, is about 1270° F. Thus, V2O5 is a liquid at typical gas turbine engine operating temperatures and has a highly corrosive effect on the engine components.
In an exemplary combustion system, a portion of the exhaust gas from the combustion system is circulated into the inlet of the combustion system, then mixed with ambient air before being introduced to the combustor of the combustion system. As a result, the mixture used for combustion has a lower percentage of oxygen than ambient air. This reduced-oxygen gas is burned in the combustor with the vanadium-containing fuel, resulting in an exhaust gas that is substantially oxygen-free. Additionally, the percentage of carbon dioxide (CO2) in the exhaust gas is higher as a portion of the exhaust gas is circulated to the combustion system inlet, which enhances the CO2 separation processes downstream. The exhaust gas is passed through a vanadium oxide particle separator to remove solid vanadium oxides, such as V2O3 and V2O4, before being circulated to the combustion system inlet. This separation process provides clean exhaust gas to the combustion system inlet, thereby preventing damage to the internal components of the combustion system.
In the above exemplary combustion system, it has been unexpectedly discovered that burning low-grade, vanadium-containing fuels without the use of vanadium oxide inhibitors, such as magnesium additives, and using high levels of exhaust gas recirculation (EGR) (ranging between approximately 30% and 70% by volume) facilitates preventing the formation of V2O5 by reducing the percentage of oxygen in the reduced-oxygen mixture burned in the combustor. By producing a substantially oxygen-free exhaust gas, i.e., limiting the concentration of oxygen in the exhaust gas to less than 1% by volume, it was discovered that the oxidation reactions of V2O3 and V2O4 to the corrosive V2O5 may be stopped.
A substantially oxygen-free exhaust from the exemplary combustion system may be accomplished by substantially stoichiometric burning in the combustor. That is, the oxygen-containing fresh air supply may be matched to the fuel flow such that combustion operates within slight deviations from stoichiometry. In other words, the amount of vanadium containing fuel and air mixed in the combustor may include a composition in which the mole ratio slightly deviates from the stoichiometric ratio.
Eliminating the formation of the corrosive V2O5 permits the use vanadium-containing fuels without the need for magnesium additives or other vanadium oxidation inhibitors, which in turn allows the exemplary combustion system to be operated at higher combustion temperatures thus increasing efficiency. The use of a high percentage of EGR provides additional benefits such as reducing nitrogen oxide (NOX) emissions and increasing the concentration of CO2 in the exhaust gas (thus significantly reducing the difficulty and cost to isolate and separate the CO2 using conventional means).
In the exemplary embodiment, the combustion system 10 further includes an EGR system 26. The EGR system 26 includes a vanadium oxide particle separator 24 (“particle separator”) configured to remove substantially all of the V2O3 particles and V2O4 particles present in the combustor exhaust gas 22 as the combustor exhaust gas flows through and contacts the particle separator 24. The combustor exhaust gas 22 may be split into at least two portions upon exit from particle separator 24. A portion of the combustor exhaust gas 18 is circulated to fluid transfer device 16. In one embodiment the remaining portion of the exhaust gas 28 is released to the atmosphere and in another embodiment, the remaining portion of the exhaust gas 28 is sent to a CO2 separation unit (not shown) to separate CO2 before being released to atmosphere.
The EGR system 26 may be used with the combustion system 10 to achieve a higher concentration of CO2 in the combustor exhaust gas 22 of the combustion system 10 and to limit the formation of V2O5 in the combustor exhaust gas 22. V2O5 formation may be stopped by decreasing the oxygen content percentage in the reduced-oxygen mixture burned in the combustor 12 as the ambient air 20 is mixed with a portion of the combustor exhaust gas 18, which includes reduced oxygen levels. In addition, the EGR system 26 may be used to increase CO2 levels in the combustor exhaust gas 22. In one embodiment, as discussed above, the remaining portion of the exhaust gas 28 is directed to a CO2 separation unit. Any CO2 separation technology may be utilized, e.g., amine treatment, PSA, membrane, etc. After separation, the CO2 rich gas may be directed to a CO2 conditioning system, including a CO2 compression system. The increase in CO2 concentration in the combustor exhaust gas 22 from the combustion system 10 enhances the efficiency of the CO2 separation process. In some embodiments, the oxygen level in the reduced-oxygen mixture burned in combustor 12 ranges between approximately 14% to approximately 16% by volume and the oxygen level in the combustor exhaust gas 22 from the combustor 12 ranges between approximately 0% and approximately 1% by volume. This low level of oxygen results in facilitating the prevention of the formation of V2O5 and the increase of CO2 concentrations up to approximately 10% by volume in the combustor exhaust gas 22.
In addition, during operation of the exemplary combustion system 10, the reduced-oxygen mixture in combustor 12 is combusted to generate the combustor exhaust gas 22 including at least one of V2O3 particles and V2O4 particles 206. In one embodiment, combustion of the reduced-oxygen mixture is performed substantially stoichiometrically to generate the combustor exhaust gas 22. The resultant combustor exhaust gas 22 may be substantially free of oxygen, e.g., containing less than 1% oxygen by volume. This low level of oxygen results in facilitating the prevention of the formation of V2O5 and the increase of CO2 concentrations up to approximately 10% by volume in the combustor exhaust gas 22.
Further, during operation of the exemplary combustion system 10, the combustor exhaust gas 22 is channeled to a particle separator 208. The particle separator removes substantially all of the V2O3 particles and the V2O4 particles from the from the combustor exhaust gas 210. The removal of substantially all of the V2O3 particles and V2O4 particles present in the combustor exhaust gas 22 is accomplished as the combustor exhaust gas 22 flows through and contacts the particle separator 24.
The particle separator 24 is useful in separating and removing vanadium oxide particles, such as V2O3 and V2O4, from at least one of the combustor exhaust gas 22 and turbine exhaust gas 36 (see generally,
In the exemplary combustion system, the particle separator 24 is generally located downstream of the combustor 12. The particle separator 24 may generally include a metal or ceramic substrate. The substrate may include any suitable structure, such as a monolith, honeycombed cells, a packed bed, reticulated foam, a long tube, multiple tubes, a grid or screen, a cylindrical shape, a plate, or the like. The substrate may be composed of or fabricated from high temperature materials such as metal alloys, ceramics, and the like. The structure of the substrate may generally be coated with an absorption material that operates to extract the vanadium oxides V2O3 and V2O4 from the exhaust gas. For example, the substrate may include a cylinder with a cross-section that includes honeycombed cells coated with an absorption material.
In other embodiments, the location of the particle separator 24 may vary. In one embodiment, the particle separator 24 may include an absorption material applied directly to the exhaust duct (not shown) between the turbine 46 and an HRSG 52 (see
The type of absorption materials useful for extracting vanadium oxide particles, such as V2O3 and V2O4, from the combustion exhaust gas 22 may vary based on the type of vanadium-containing fuel used. The absorption materials may include any suitable type of coating, e.g., elements such as titanium dioxide (TiO2), aluminum oxide (Al2O3), zirconium dioxide (ZrO2) (sometimes known as zirconia), silicon oxide (SiO2), zeolites, washcoats, mesospheres, and other metal oxides and nitrates like alumina, silica, blends thereof, and the like. Table 1 below lists some, but not all, potentially suitable materials that may be used alone or together in various combinations as one or more absorption materials.
Additionally, the absorption materials may be applied to the particle separator 24 as an easily removable coating to permit collection of the vanadium oxide particles after removal from the combustion exhaust gas 22. After removal of the coating for collection of the vanadium oxide particles, the particle separator substrate may be coated with a new layer of absorption material to further extract the vanadium oxides V2O3 and V2O4 from the exhaust gas.
In one embodiment, the absorption material may be chemically removed using a simple solvent, such as water, alcohol, ethanol, ethylene glycol, degreasers, detergents, or the like while remaining benign to combustion and turbine materials. In another embodiment, the absorption material may be mechanically removed by the application of mechanical forces, such as ultrasonic vibrations, pressure waves, and mechanical impact among others. If the absorption material is water soluble, the absorption material may be dissolved during an engine water wash. In another embodiment, a detergent or other simple solvent may be directed through the particle separator 24 to remove the absorption material. In certain embodiments, after use of a simple solvent other than water, a water wash may be performed to flush any remaining solvent from the particle separator 24. In some embodiments, ablation, ultrasonic vibrations, or a shockwave, etc. may be applied to the particle separator 24 to break up the absorption material. For example, the absorption material may be removed with mechanical vibration and/or pressure waves, e.g., by applying acoustic waves from an acoustic horn or speaker or by applying pressure waves from a combustion-driven device. By further example, the absorption material also may be removed with heat, e.g., by gradually thermally degrading the absorption material until it is completely removed over a limited period. After vibration, heat, mechanical, and/or other means for removal, a water wash may be applied to flush the fragments of the absorption material from the particle separator 24. After removal of the absorption material for collection of the vanadium oxide particels,
It is understood that the compressed reduced-oxygen gas 44 from the compressor 16 may include any suitable gas containing oxygen, for example, air, oxygen-rich air, and oxygen-depleted air. The combustion process in the combustor 12 generates the combustor exhaust gas 22.
In some embodiments, the power generation system 105 further includes an EGR system 26. The EGR system 26 includes a particle separator 24 configured to remove substantially all of the V2O3 particles and V2O4 particles present in the turbine exhaust gas 36 as the turbine exhaust gas 36 flows through and contacts the particle separator 24. In addition, the EGR system 26 may include a heat recovery steam generator (HRSG) 52 configured to receive the turbine exhaust gas 36 and generate steam. A steam turbine may be further configured to generate additional electricity using the steam from the HRSG 52, and the steam turbine may be connected to a steam generator. In some embodiments, the steam turbine may be arranged to be connected to the turbine shaft 48. A heat exchanger 30 may be configured to receive a portion of the exhaust gas 56. In some embodiments, the EGR system 26 may not contain an HRSG 52 and the turbine exhaust gas 36 may instead be introduced directly into a splitter 54 upon exit from the particle separator 24. In still other embodiments, the EGR system 26 may not include the heat exchanger 30.
As illustrated, the combustor exhaust gas 22 from the combustor 12 may be provided to the turbine 46. As indicated, the power generation system 105 includes a generator 50 attached to the gas turbine engine 40. In some embodiments, the turbine shaft 48 may be a “cold-end drive” configuration, meaning that the turbine shaft 48 may connect to the generator 50 at the compressor end of the gas turbine engine 40. In other embodiments, the turbine shaft 48 may be a “hot-end drive” configuration, meaning that the turbine shaft 48 may connect to the generator 50 at the turbine end of the gas turbine engine 40. The thermodynamic expansion of the combustor exhaust gas 22 fed into the turbine 46 produces power to drive the gas turbine engine 40, which, in turn, generates electricity through the generator 50. In the exemplary embodiment, the generator 50 may be connected to an electrical power grid such that electrical energy produced by the generator 50 is provided to the grid (not shown). The expanded turbine exhaust gas 36 from the turbine 46 may be fed to the particle separator 24 and then to the HRSG 52. The temperature of the turbine exhaust gas 36 discharged by the turbine 46 ranges between approximately 500 degrees Fahrenheit (° F.) to about 1300° F. and the exhaust gas 38 discharged by the HRSG 52 is at a temperature that ranges between approximately 60° F. to about 400° F.
In one embodiment, the EGR system 26 further includes a splitter 54 configured to split the exhaust gas 38 into at least two portions. A portion of the exhaust gas 56 is circulated to the compressor 16 through the EGR system 26. In one embodiment the remaining portion of exhaust gas 28 is released to the atmosphere and in another embodiment, the remaining portion of exhaust gas 28 is sent to a CO2 separation unit (not shown) to separate CO2 before being released to atmosphere. The portion of exhaust gas 56 may be sent to the heat exchanger 30. The heat exchanger 30 may be provided to reduce further the temperature of the portion of exhaust gas 56 to a range between approximately 60° F. to about 160° F. The heat exchanger 30 may be incorporated into the EGR system 26 anywhere downstream of the turbine 46.
The vanadium-containing fuel 14 may include any suitable vanadium-containing fuels, such as residual fuel oils. The combustor exhaust gas 22 from the combustor 12 may include vanadium oxides (VXOY), water, carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), nitrogen oxides (NOX), sulfur oxides (SOX), unburned fuel, and other organic compounds.
The EGR system 26 may be used with the gas turbine engine 40 to achieve a higher concentration of CO2 in the working fluid of the gas turbine engine 40 and to limit the formation of V2O5 formation. V2O5 formation from the combustor 12 is stopped by decreasing the oxygen content percentage in the compressed reduced-oxygen gas 44 as the ambient air 20 is mixed with the portion of exhaust gas 56, which includes reduced oxygen levels. In addition, the EGR system 26 may be used to increase CO2 levels in the exhaust gas 38. In one embodiment, as discussed above, the remaining portion of exhaust gas 28 is directed to a CO2 separation unit. Any CO2 separation technology may be utilized, e.g., amine treatment, PSA, membrane, etc. After separation, the CO2 rich gas may be directed to a CO2 conditioning system, including a CO2 compression system. The increase in CO2 concentration in the exhaust gas 38 from the gas turbine engine 40 enhances the efficiency of the CO2 separation process. In some embodiments, the oxygen level in the compressed reduced-oxygen gas 44 ranges between approximately 14% to approximately 16% by volume and the oxygen level in the combustor exhaust gas 22 from the combustor 12 ranges between approximately 0% and approximately 1% by volume. This lower level of oxygen facilitates preventing the formation of V2O5 and increases of CO2 concentrations up to approximately 10% by volume in the combustor exhaust gas 22 from the combustor 12.
Exemplary embodiments of systems and methods for burning low-grade, vanadium-containing fuels without the use of vanadium oxide inhibitors, such as magnesium additives, are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, operations of the methods and components of the systems may be utilized independently and separately from other operations or components described herein. For example, the systems and methods described herein may have other industrial or consumer applications and are not limited to practice with gas turbine engines as described herein. Rather, one or more embodiments may be implemented and utilized in connection with other industries.
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 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 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.
