Patent Description:
Turbine engine manufacturers continue to seek further improvements to engine performance including improvements to reduce environmental impact while improving propulsive efficiencies.

<CIT> describes a system for supplying a hydrogen-containing fuel, used for supplying the hydrogen-containing fuel to a plant including a steam turbine, the system.

<CIT> describes an offshore energy generation system comprising an offshore platform, a liquid ammonia storage vessel associated with the offshore platform, and an ammonia cracking reactor mounted to the offshore platform and arranged to crack ammonia thereby producing hydrogen to be supplied onshore via hydrogen pipeline.

According to an aspect of the disclosure, there is provided a gas turbine engine as recited in claim <NUM>.

In a further embodiment of the foregoing, the cracking device and the first separation device are combined in one device.

In a further embodiment of the foregoing, the gas turbine engine further includes a hydrogen compressor that is configured to receive the hydrogen flow from the first separation device. The hydrogen compressor is configured to increase a pressure of the hydrogen flow and communicate the pressurized hydrogen flow to the combustor.

In a further embodiment of the foregoing, the gas turbine engine further includes a turboexpander that is configured to receive the residual flow from the first separation device. The residual flow is expanded through the turboexpander to drive a mechanical output.

In a further embodiment of the foregoing, the second separation device is configured to receive the residual flow that is exhausted from the turbo-expander.

In a further embodiment of the foregoing, the second separation device is configured to communicate hydrogen and nitrogen separated from ammonia to the combustor.

In a further embodiment of the foregoing, the gas turbine engine further includes a pump that is configured to increase a pressure of the ammonia flow to a pressure above <NUM> atm (<NUM> psi) at the cracking device.

In a further embodiment of the foregoing, the gas turbine engine further includes a thermal transfer device that is configured to heat the ammonia fuel flow for decomposition of the ammonia flow in the cracking device.

According to an aspect of the disclosure, there is provided a method of operating a gas turbine engine as recited in claim <NUM>.

In a further embodiment of the foregoing, the method further includes heating the ammonia flow with thermal energy that is communicated from a heat source of the gas turbine with a thermal transfer device.

In a further embodiment of the foregoing, the method further includes expanding a residual flow from the first separation device using a turboexpander to drive a mechanical output.

In a further embodiment of the foregoing, the method further includes removing ammonia from a flow that is exhausted from the turboexpander in the second separation device.

In a further embodiment of the foregoing, the method further includes increasing a pressure of the flow that is communicated from the first separation device to the combustor with a hydrogen compressor.

Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations.

<FIG> schematically illustrates an example alternate fueled turbine engine assembly <NUM>. The engine assembly <NUM> uses a hydrogen (H<NUM>) fuel flow <NUM> generated from decomposition of ammonia (NH<NUM>). The hydrogen fuel flow <NUM> is mixed with a core gas flow <NUM> in a combustor <NUM> to generate a high energy gas flow <NUM> that expands through a turbine section <NUM> to drive a compressor section <NUM>. It should be appreciated, that the engine <NUM> is shown schematically and that other structures and engine configurations such as <NUM>-spool, <NUM>-spool and geared turbofan engines would benefit from this disclosure and are within the contemplation and scope of this disclosure. Moreover, a land based turbine engine would also benefit from application of the features of this disclosure. The disclosed hydrogen fuel flow is generated by decomposition of ammonia (NH<NUM>) provided by a decomposition assembly <NUM> of a fuel system <NUM>.

Ammonia (NH<NUM>) does not contain carbon, but does have a fuel energy similar to alcohols such as methanol. Ammonia can also be transported and stored in liquid form at moderate pressure and temperature. For example, ammonia is a liquid at a pressure of about <NUM> atm and a temperature of <NUM>. Alternatively, ammonia is a liquid at a pressure of <NUM> atm and a temperature of -<NUM>. Moreover, because ammonia does not contain carbon it may be heated to temperatures above that of a hydrocarbon fuel without forming carbon deposits on portions of a fuel system. The increased temperature capabilities provide an increased heat sink capacity that can improve engine efficiency. Ammonia can be decomposed into hydrogen and nitrogen component parts. Hydrogen provides improved combustion properties and a desirable clean burning fuel that does not generate undesirable exhaust products. Additionally, conversion of the ammonia fuel to a hydrogen fuel can reduce nitrous oxide emissions by eliminating the presence of fuel-bound nitrogen atoms, which are inherent to ammonia as a fuel.

The disclosed fuel system <NUM> uses heat to decompose a flow of ammonia <NUM> into mostly component parts of hydrogen and nitrogen. The component parts of hydrogen and nitrogen are separated from any residual ammonia and communicated to the combustor <NUM> to produce the high energy gas flow <NUM> via combustion. The removal of ammonia from the fuel communicated to the combustor can help to reduce the formation of nitrogen oxide emissions. Moreover, the reduction of ammonia from the fuel communicated to the combustor maximizes the amount of hydrogen burned to improve combustion efficiency and flame holding stability.

The ammonia <NUM> is stored in a fuel storage tank <NUM> and pressurized by a fuel pump <NUM>. The fuel pump <NUM> increases the pressure of the ammonia <NUM> to a higher level for communication into the combustor <NUM>. The pressurized ammonia <NUM> is communicated to a decomposition assembly <NUM> that includes a cracker device <NUM> and a first separation device <NUM> for decomposition of the ammonia into the component parts of hydrogen and nitrogen. The decomposition process utilizes thermal energy indicated by arrows <NUM> that is obtained from heat sources and locations of the engine <NUM>.

The pressure of the ammonia <NUM> can be adjusted depending on engine operating conditions and available thermal energy to provide desired combustor operation. In one disclosed embodiment, the ammonia <NUM> is pressurized to at least <NUM> atm (<NUM> psi) at the cracker device <NUM>. In another disclosed embodiment, the ammonia fuel is pressurized to between <NUM> atm (<NUM> psi) and <NUM> atm (<NUM> psi) at the cracker device <NUM>. The pressure of the ammonia fuel flow <NUM> may be more prior to entering the decomposition assembly <NUM> to accommodate pressure drops encountered within the cracker device <NUM> and separation device <NUM>, or in other components between the cracker and the combustor. Moreover, the pressure within the decomposition assembly <NUM> may be higher or different to provide a desired final pressure of the component fuel flow <NUM> for communication into the combustor <NUM>.

Referring to <FIG>, with continued reference to <FIG>, the decomposition or conversion process of ammonia into component parts of hydrogen and nitrogen is performed in the presence of a catalyst at a given pressure and temperature. The catalyst is typically a nickel, nickel alloy material, iron, or ruthenium, however other catalysts as are known are within the contemplation of this disclosure. The conversion process is limited by an equilibrium point based on pressure and temperature, and therefore some residual ammonia remains that is not decomposed. At very low pressures, a very high percentage of ammonia can be converted into hydrogen and nitrogen as indicated by line <NUM>. The percentage of ammonia converted into component parts at pressures around <NUM> atm (<NUM> psi) can approach <NUM>% at temperatures above around <NUM>. However, higher pressures are preferred to communicate the components of the fuel into the combustor <NUM>.

The degree of conversion decreases as the pressure of the fuel flow increases as is shown by graph <NUM>. At pressures of around <NUM> atm (<NUM> psi), the degree of conversion is reduced to below <NUM>% at <NUM> as is indicated at <NUM>. The degree of conversion at the same pressure increases with an increase in temperature. In this example, the conversion increases to over <NUM>% at temperatures above around <NUM>. Higher pressures require higher temperatures to achieve conversions above <NUM>%. At a pressure of <NUM> atm (<NUM> psi), the temperature to achieve <NUM>% conversion exceeds <NUM> as indicated by line <NUM>. At a pressure of <NUM> atm (<NUM> psi) the temperature to achieve <NUM>% conversion exceeds <NUM>. The lower conversions result in some quantity of residual ammonia that does not decompose and remains in the mixture downstream of the decomposition assembly <NUM>. As decomposition progresses, the accumulation of hydrogen as a decomposition product slows the decomposition process until equilibrium is reached and decomposition stops; after this point decomposition can only proceed if hydrogen is removed from the mixture.

The example fuel system <NUM> uses thermal energy <NUM> from the engine <NUM> to elevate the temperature of the ammonia fuel flow in view of the pressure required to generate decomposition levels. Thermal energy is drawn from various heat sources including heat producing engine systems including hot air from after the last stage of the compressor section <NUM> as indicated at <NUM>, heated cooling air exhausted from the combustor <NUM> and/or turbine as indicated at <NUM>, and the high energy exhaust gas flow <NUM> flowing through the exhaust section or nozzle <NUM> as is schematically shown at <NUM>. The heat drawn from the various heat sources is communicated to the cracker device <NUM> through a thermal transfer device <NUM> as is indicated by arrows <NUM>.

In one example embodiment, the ammonia fuel flow <NUM> is elevated to a temperature above <NUM> (<NUM> °F) before the decomposition assembly <NUM> or within the cracker device <NUM>. In another disclosed embodiment, the ammonia fuel flow <NUM> is elevated to a temperature between <NUM> (<NUM> °F) and <NUM> (<NUM> °F) before the decomposition assembly <NUM> or within the decomposition assembly <NUM>. In still another disclosed embodiment, the ammonia fuel flow <NUM> is elevated to a temperature above <NUM> (<NUM> °F) before the decomposition assembly <NUM> or within the decomposition assembly <NUM>. It should be understood that the above temperatures are provided as examples and that other temperature ranges could be utilized within the contemplation of this disclosure.

The decomposition of ammonia into its component part of hydrogen occurs according to the according to the chemical equation: <MAT>.

Depending upon the final temperature and pressure and the rate of decomposition in the presence of a catalyst, all of the ammonia or some portion of the ammonia may become cracked to form nitrogen and hydrogen. The cracking process is endothermic and therefore the cracked fuel has increased fuel chemical energy and can provide increased engine work output or thrust output without increased fuel flow and thereby improves engine fuel efficiency. The cracking process is endothermic and therefore additional heat absorption capacity becomes available at a given fuel temperature, thereby providing greater heat absorption before the fuel temperature approaches the temperature of the heat source.

The cracking process increases the number of moles, with one mole of ammonia NH<NUM> becoming two moles of cracked gas, per NH<NUM> → ½ N<NUM> + <NUM>(½ H<NUM>), such that the resulting cracked gas occupies more volume than the ammonia alone. Some portion of ammonia is not cracked as is shown in the graph <NUM>. The accumulation of hydrogen as a decomposition product can slow the decomposition reaction and limit the amount of hydrogen fuel produced. The example decomposition assembly <NUM> further includes the first separation device <NUM> that removes hydrogen from the residual ammonia, so the hydrogen can be used as a fuel that reduces or does not contain fuel-bound nitrogen and therefore provides lower NOx emissions. The first separation device <NUM> includes a hydrogen permeable membrane <NUM> that separates at least some hydrogen from the residual ammonia to create a hydrogen-rich permeate stream which when delivered to the combustor minimizes the amount of residual ammonia that is burned. The hydrogen permeable membrane <NUM> may be formed from Group V metals such as palladium, alloys of palladium with other metals such as silver or copper, or other materials with high permeability of hydrogen as compared to ammonia and nitrogen.

A flow of residual ammonia along with some quantity of nitrogen and hydrogen is exhausted from the first separation device <NUM> as a residual flow or retentate stream indicated at <NUM>. The residual flow <NUM> is communicated to a second separation device <NUM> to separate any remaining ammonia from the component parts of hydrogen and nitrogen. The remaining hydrogen and nitrogen in the retentate stream from the second separation device <NUM> are communicated to the combustor <NUM> as indicated at <NUM>, as a fuel mixture that reduces or does not contain fuel-bound nitrogen and therefore provides lower NOx emissions; this retentate stream can be mixed with the hydrogen-containing permeate stream from separation device <NUM> before delivery to the combustor, or it can be delivered directly to the combustor as an independent fuel stream. The separated ammonia indicated at <NUM> is returned to the fuel storage tank <NUM>. The second separation device <NUM> includes an ammonia permeable membrane <NUM> that separates at least some of the residual ammonia from the residual flow <NUM> exhausted from the first separation device <NUM>. The ammonia permeable membrane <NUM> may be formed from polymers, zeolites, or other materials with high permeability of ammonia as compared to hydrogen or nitrogen.

The hydrogen flow indicated at <NUM> from the separation device <NUM> is communicated to the combustor <NUM>. The hydrogen flow <NUM> can proceed directly to the combustor <NUM> if the pressure is maintained at a level required for entering the combustor <NUM>. However, if the hydrogen flow <NUM> is of a reduced pressure, all or a portion of the hydrogen flow <NUM> may be pressurized by a compressor <NUM>.

<FIG> illustrates the cracker device <NUM> and the first separation device <NUM> as distinct devices, however, the cracker device <NUM> and the first separation device <NUM> may be one single unit that integrates the cracking and separation processes. It is also possible to interleave the cracking and separation processes, or the cracking and separation devices by using multiple devices or units, to provide hydrogen separation before the completion of ammonia decomposition. When hydrogen separation occurs before the completion of ammonia decomposition, the accumulation of hydrogen during the decomposition process is reduced and further decomposition is promoted. As a result, the separation device <NUM> enhances decomposition by removing accumulating hydrogen and allowing a higher rate of decomposition and a higher degree of ammonia decomposition before the equilibrium limit is reached.

It should be appreciated, that the hydrogen flow <NUM> may include some residual portions of ammonia and nitrogen. However, a majority of the hydrogen flow <NUM> is comprised of hydrogen. Moreover, the residual flow <NUM> may include residual portions of hydrogen and nitrogen, together with the residual ammonia that remains after incomplete decomposition in the cracking device <NUM>.

Referring to <FIG> with continued reference to <FIG>, another example fuel system <NUM> is shown and includes a turbo-expander <NUM> in communication with first separation device <NUM>. The pressure of the residual flow <NUM> from the first separation device <NUM> is elevated to pressures required for communication of the hydrogen flow <NUM>, which is the permeate stream from the first separation device <NUM>, with the combustor <NUM>. The higher pressure and temperatures of the residual flow <NUM>, which is the retentate stream from the first separation device <NUM> and therefore at higher pressure than the permeate stream, are reclaimed through the turbo-expander <NUM>. The residual flow <NUM> is communicated to the turbo-expander where it is expanded to drive a mechanical output <NUM>. The mechanical output <NUM> in this example is a shaft that is coupled to drive an accessory device schematically shown at <NUM>. The accessory device <NUM> in this example can be a pump, generator or accessory drive gear train as well as any other system utilized to support operation of the engine <NUM> and/or aircraft.

The expanded residual flow comprising ammonia, nitrogen, and residual hydrogen, is exhausted from the turbo-expander <NUM> and communicated to the second separation device <NUM>. The second separation device <NUM> includes an ammonia permeable membrane <NUM> that separates ammonia from hydrogen and nitrogen. The separated ammonia is returned to the fuel storage tank <NUM> and the hydrogen and nitrogen components are communicated to the combustor <NUM>.

The elevated pressure and temperatures of the hydrogen fuel flow <NUM> may also be captured and utilized during operation where the flow <NUM> exceeds pressures required for communication into the combustor <NUM>. In this example, a second turbo-expander <NUM> receives the hydrogen fuel flow <NUM> at an elevated pressure and temperature. The pressurized hydrogen flow <NUM> expands through the second turbo-expander <NUM> to drive an output <NUM>. In this example, the output <NUM> is a shaft coupled to drive a device <NUM>. The device <NUM> may be any accessory device utilized to support operation of the engine <NUM> and/or aircraft. Moreover, the turbo-expander <NUM> provides a drop in hydrogen fuel pressure for operational instances where little pressure drop is encountered through the decomposition assembly <NUM>.

Accordingly, the disclosed assemblies provide for the advantageous use of ammonia fuel to improve engine efficiency and reduce carbon emission. The disclosed systems use advantageous properties of ammonia to maximize decomposition of ammonia into hydrogen fuel to reduce undesirable combustor emissions and improve engine efficiencies.

Claim 1:
A gas turbine engine comprising:
a cracking device (<NUM>) configured to decompose an ammonia flow into a flow containing more hydrogen (H<NUM>) than ammonia (NH<NUM>);
a first separation device (<NUM>) including a hydrogen permeable membrane (<NUM>) for separating hydrogen downstream of the cracking device (<NUM>), wherein residual ammonia and nitrogen are exhausted as a residual flow (<NUM>), the separated flow is exhausted separately as a hydrogen flow (<NUM>) that contains more hydrogen than ammonia and nitrogen;
second separation device (<NUM>) configured to receive the residual flow (<NUM>) exhausted from the first separation device (<NUM>), the second separation device (<NUM>) including an ammonia permeable membrane (<NUM>) configured to separate ammonia from hydrogen and nitrogen and communicate the separated ammonia to a fuel storage tank (<NUM>);
a combustor (<NUM>) configured to receive and combust the hydrogen flow (<NUM>) from the separation device and hydrogen and nitrogen from the second separation device (<NUM>) to generate a gas flow (<NUM>);
a compressor section (<NUM>) configured to supply compressed air to the combustor (<NUM>); and
a turbine section (<NUM>) in flow communication with the gas flow (<NUM>) produced by the combustor (<NUM>) and mechanically coupled to drive the compressor section (<NUM>).