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 an ammonia decomposition facility is equipped with: a heating medium line through which a heating medium that is heated with heat generated in a gas turbine flows; an ammonia feeding line through which ammonia flows; an ammonia decomposition device; and an ammonia removal device.

<CIT> a gas turbine plant is provided with a gas turbine, a heating device, a decomposition gas line, and a decomposition gas compressor. The heating device heats ammonia and thermally decomposes the ammonia to convert the ammonia into decomposition gas (PG) including hydrogen gas and nitrogen gas.

<CIT> describes a method for operating a power device, the power device comprises a gas turbine and an exhaust gas system for treatment of exhaust gas, wherein the gas turbine comprises a combustion chamber and a turbine.

<CIT> describes a gas turbine power plant for generating useful energy, preferably electrical energy, with a gas turbine which has a compressor, a combustion chamber and a turbine on a shaft and which can be charged with a process gas , which is capable of reacting with air to release energy.

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 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 ammonia flow is communicated to the cracking device at a pressure between <NUM> atm (<NUM> psi) and <NUM> atm (<NUM> psi).

In a further embodiment of the foregoing, the ammonia flow is heated to a temperature at a temperature between <NUM> (<NUM> °F) and <NUM> (<NUM> °F).

In a further embodiment of the foregoing, the ammonia flow is heated to a temperature at a temperature above <NUM> (<NUM> °F).

In a further embodiment of the foregoing, the flow of component parts includes Hydrogen (H<NUM>) and Nitrogen (N<NUM>).

In a further embodiment of the foregoing, the compressor heat exchanger includes an exhaust heat exchanger that provides thermal communication between the ammonia flow and exhaust heat from the turbine section.

In a further embodiment of the foregoing, the compressor heat exchanger that provides thermal communication between the ammonia flow and compressed air from a last stage of the compressor section.

In a further embodiment of the foregoing, the compressed air from a last stage of the compressor section that is in thermal communication with the ammonia is subsequently in thermal communication with the combustor to provide combustor cooling.

In a further embodiment of the foregoing, the compressed air from a last stage of the compressor section that is in thermal communication with the ammonia is subsequently in thermal communication with the turbine to provide combustor cooling.

In a further embodiment of the foregoing, the compressor heat exchanger that provides thermal communication between the ammonia flow and compressor air from an intermediate stage of the compressor section.

In a further embodiment of the foregoing, a combustor heat exchanger that provides thermal communication from cooling air after it has cooled the combustor.

In a further embodiment of the foregoing, a combustor heat exchanger that provides thermal communication from cooling air after it has cooled the turbine.

In a further embodiment of the foregoing, the ammonia flow is heated prior to entering the cracking device.

In a further embodiment of the foregoing, the ammonia flow is heated in the cracking device.

In a further embodiment of the foregoing, the gas turbine engine further includes a turboexpander that receives the ammonia flow and the flow of component parts from the cracker. The ammonia flow and the flow of component parts are expanded through the turboexpander to drive a mechanical output.

According to an aspect of the disclosure, there is provided a method of operating an energy extraction system as recited in claim <NUM>.

In a further embodiment of the foregoing, the pressure is raised to between <NUM> atm (<NUM> psi) and <NUM> atm (<NUM> psi).

In a further embodiment of the foregoing, the heat exchanger heats the ammonia to a temperature between <NUM> (<NUM> °F) and <NUM> (<NUM> °F).

In a further embodiment of the foregoing, the heat exchanger heats the ammonia flow to a temperature above <NUM> (<NUM> °F).

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 an ammonia-based fuel flow <NUM> 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 ammonia-based fuel comprises decomposition products of ammonia (NH<NUM>) and/or a mixture of ammonia (NH<NUM>) and the decomposition products provided by 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 (<NUM> psi) and a temperature of <NUM> (<NUM> °F). Alternatively, ammonia is a liquid at a pressure of <NUM> atm and a temperature of -<NUM> (-<NUM> °F). 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 of ammonia 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, removal of nitrogen from the ammonia can reduce nitrous oxide emissions.

The disclosed fuel system <NUM> uses heat to decompose a flow of ammonia fuel <NUM> into mostly component parts of hydrogen and nitrogen. The component parts of hydrogen and nitrogen along with residual ammonia are communicated to the combustor <NUM> to produce the high energy gas flow <NUM>.

The ammonia fuel <NUM> is stored in a fuel storage tank <NUM> and pressurized by a fuel pump <NUM> to a higher level for communication into the combustor <NUM>. The pressurized ammonia fuel flow <NUM> is communicated to a cracker assembly <NUM> for decomposition into the component parts of hydrogen and nitrogen. The decomposition process utilizes thermal energy that is drawn from locations on the engine <NUM>.

Referring to <FIG>, with continued reference to <FIG>, the decomposition or conversion process of ammonia into component parts of hydrogen and nitrogen can reach an equilibrium point shown at <NUM> based on a temperature indicated at <NUM> and pressure indicated by lines <NUM>, <NUM>, <NUM> and <NUM>. Decomposition or conversion progresses toward the equilibrium value in the presence of a catalyst that sufficiently promotes the reaction with enough heat supplied for the reaction to proceed. At very low pressures, a very high percentage of ammonia can be converted into hydrogen and nitrogen in the cracker assembly <NUM> as indicated at <NUM>. The percentage of ammonia converted into component parts at pressures around <NUM> atm (<NUM> psi) can approach <NUM>% at temperatures above around <NUM> (<NUM> °F). However, higher pressures are needed to communicate the components of the fuel into the combustor <NUM>.

The degree of conversion decreases as the pressure of the ammonia fuel 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 needed to achieve <NUM>% conversion exceeds <NUM> (<NUM> °F) as indicated by line <NUM>. At a pressure of <NUM> atm (<NUM> psi), indicated by line <NUM>, the temperature needed to achieve <NUM>% conversion exceeds <NUM> (<NUM> °F). The example fuel system <NUM> uses thermal energy from the engine <NUM> to elevate the temperature of the ammonia fuel flow in view of the pressure required to generate the desired degree of decomposition.

Thermal energy is drawn from various heat sources including heat producing engine systems as is schematically shown at <NUM>, <NUM> and <NUM> in <FIG>. The heat drawn from the various heat sources is communicated to the cracker assembly <NUM> as is indicated by arrows <NUM> to aid and encourage the cracking and decomposition process.

In the disclosed example embodiment, heat is drawn from at least one of several locations within the engine assembly <NUM>. Heat from each location is communicated through a thermal transfer device such as schematically shown heat exchangers <NUM>, <NUM> and <NUM>. In this example, the heat exchanger <NUM> draws heat from the core airflow <NUM> after an intermediate or final stage of the compressor section <NUM>, and may draw heat from all or a portion of the core airflow. Cooled air exiting heat exchanger <NUM> is delivered as cooling air to engine components such as the combustor or turbine, or to portions of these components. The heat exchanger <NUM> draws heat from cooling airflow that has been heated after being used to cool portions of the combustor <NUM> and the turbine section <NUM>. Cooling airflow accepts heat from combustor <NUM> and parts of the turbine section <NUM> and therefore becomes heated. At least a portion of this now heated cooling airflow is utilized to heat the ammonia fuel flow <NUM>. The heat exchanger <NUM> draws thermal energy from gases exiting an intermediate or final stage of the turbine, or from gases exhausted through a nozzle <NUM>.

The heat exchangers <NUM>, <NUM> and <NUM> are schematically shown and can be of different configurations based on the location and source of heat, can be located inside or outside the engine, and can be located within or outside the core flow path. The heat exchangers, <NUM>, <NUM> and <NUM> may be air/fuel heat exchangers that place the heated airflow into thermal communication with the ammonia fuel flow <NUM>. The heat exchangers may be integral with one or more engine components; for example, ammonia may pass through a turbine vane to cool the vane and extract heat from the core flow. The example heat exchangers <NUM>, <NUM> and <NUM> may also include an intermediate thermal transfer medium to communicate thermal energy from the heat source to the ammonia fuel <NUM>. Moreover, although several example heat source locations are disclosed by way of example, other heat source locations within the engine <NUM> could be utilized and are within the contemplation of this disclosure.

The cracker assembly <NUM> uses the heat <NUM> communicated from the example heat sources <NUM>,<NUM>, and <NUM> in the presence of a catalyst to thermally decompose the ammonia fuel flow <NUM>. The higher heat energy aids decomposition of the ammonia fuel flow <NUM> depending on the pressure. The catalyst may be a nickel and/or nickel alloy material, iron, ruthenium, or any other catalytic material that provides for the decomposition of ammonia. The decomposition of the ammonia fuel into hydrogen and nitrogen occurs according to the chemical equation:.

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. In one example embodiment, the ammonia fuel flow <NUM> is elevated to a temperature above <NUM> (<NUM> °F) either before the cracking assembly <NUM> or within the cracking assembly <NUM>. In another disclosed embodiment, the ammonia fuel flow <NUM> is elevated to a temperature between <NUM> (<NUM> °F) and <NUM> (<NUM> °F) either before the cracking assembly <NUM> or within the cracking assembly <NUM>. In still another disclosed embodiment, the ammonia fuel flow <NUM> is elevated to a temperature above <NUM> (<NUM> °F) either before the cracking assembly <NUM> or within the cracking 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 example temperatures provide for cracking of the ammonia fuel flow <NUM> into component parts of hydrogen and nitrogen at levels that provide desired combustion properties and performance.

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

Because the cracking process is endothermic, the cracked fuel including hydrogen and nitrogen has increased fuel chemical energy and can therefore 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>), the resulting cracked gas occupies more volume and can provide more work output.

A turbo-expander <NUM> may be provided to receive a portion of the component fuel flow <NUM> to utilize the increased volume and energy provided in the cracked component fuel flow <NUM>. In this disclosed example, the turbo expander <NUM> drives a mechanical output in the form of a shaft <NUM> that drives an engine accessory device <NUM>. The engine accessory device can be an oil pump, generator and/or hydraulic pump as well as any other accessory component utilized to support engine or aircraft operation. Because the cracked gas is less dense and has a higher specific heat capacity it can produce more work as enthalpy is extracted during turbo-expansion.

Furthermore, the cracking process changes the chemical composition of the ammonia fuel and thereby also changes its vapor-liquid equilibrium properties providing greater turbo-expansion of the cracked gas. As appreciated, for a given pressure, the saturation temperature, where vapor begins to condense to liquid, is much lower for H<NUM> and N<NUM> than it is for NH<NUM>. As a result, the conversion of some or all of the NH<NUM> to H<NUM> and N<NUM> allows a larger temperature drop and more work extraction across the turbo-expander <NUM> without crossing the vapor-liquid equilibrium line than would be possible with pure NH<NUM> as the working fluid in the turbo-expander.

Thermal energy can be added to the ammonia fuel to aid cracking in different manners within the contemplation of this disclosure. Referring to <FIG>, in one disclosed example, thermal energy <NUM> is input into the ammonia fuel flow <NUM> prior to entering the cracker <NUM>. Without further heat addition in the cracker, a temperature gradient of the fuel flow through the cracker assembly <NUM> decreases with an axial distance from the inlet of the cracker assembly <NUM> as endothermic cracking progresses, as shown by graph <NUM>. Accordingly, the initial input temperature may be elevated to such a degree that the fuel achieves and maintains a minimum temperature upon being communicated away from the cracker assembly <NUM> as the component fuel flow <NUM>.

Referring to <FIG>, thermal energy is input into the cracker assembly <NUM> to provide a constant temperature as shown by graph <NUM>. In this example the cracker assembly <NUM> may be combined with a heat exchanger to provide more direct thermal communication between the heat source and the ammonia fuel flow.

Referring to <FIG>, thermal energy is input into the ammonia fuel flow <NUM> and to component fuel flows <NUM> at intermediate locations between segmented cracker assemblies 94A, 94B and 94C. In this example, the different segmented cracker assemblies 94A, 94B and 94C allow different heat sources to be utilized to input heat into the ammonia fuel <NUM> and the component fuel flows <NUM>. Moreover, the different fuel flows can be preferentially routed to vary thermal input into the fuel flow as needed to match cracking efficiencies with engine operation. Heat input between segmented cracker assemblies may also reduce the variation of temperature through the cracker (maximum to minimum) as compared to a single cracker unit as depicted in <FIG> for example, which may be desirable if temperature limits or variation are of concern.

The disclosed engine and fuel system provide for the advantageous use of ammonia fuel to improve engine efficiency and reduce carbon emission. The disclosed systems use advantageous properties of components of an ammonia fuel to improve combustion performance and engine efficiencies.

Claim 1:
A gas turbine engine comprising:
a cracking device (<NUM>) configured to decompose a portion of an ammonia flow into a flow of component parts of the ammonia flow;
a compressor heat exchanger (<NUM>) configured to heat the ammonia flow to a temperature above <NUM> (<NUM> °F);
a combustor (<NUM>) configured to receive and combust the flow of component parts of the ammonia flow to generate a high energy gas flow (<NUM>);
a compressor section (<NUM>) configured to supply compressed air to the combustor (<NUM>), wherein the compressor heat exchanger (<NUM>) draws heat from a core airflow after an intermediate stage of the compressor section (<NUM>) to heat the ammonia flow; and
a turbine section (<NUM>) in flow communication with the high energy gas flow (<NUM>) produced by the combustor (<NUM>) and mechanically coupled to drive the compressor section (<NUM>), wherein the core airflow from the compressor heat exchanger (<NUM>) is delivered to cool at least one of the combustor (<NUM>) and/or turbine section (<NUM>).