Patent Description:
Gas turbine engines are known, and typically include a supply of air being delivered into a compressor. The air is compressed and then delivered into a combustor where it is mixed with a fuel and ignited. Products of this combustion pass downstream over a turbine rotor, driving it to rotate. The turbine rotor in turn rotates the compressor.

So-called "bottoming cycles" are known, and utilize the heat downstream of the turbine to drive a supplemental cycle. The cycle provides additional power for various applications associated with the gas turbine engine, or associated with other systems, such as aircraft systems.

In a bottoming cycle, a heat exchanger is positioned downstream of the turbine. The heat exchanger heats a working fluid associated with the bottoming cycle. The working fluid may be downstream of a bottoming compressor, and passing toward a bottoming turbine rotor. Thus, the working fluid approaching the turbine has a greater heat load, and provides additional power to the overall system.

Other types of engines besides gas turbine engines utilize bottoming cycles.

It is further known to have a secondary bottoming cycle heat exchanger capturing the heat downstream of the bottoming cycle turbine. Since the temperature of the working fluid downstream of the bottoming cycle turbine may be relatively low, an ambient working fluid typically may not have a large temperature difference. Thus, the bottoming cycle secondary heat exchangers have typically been relatively large, or have not effectively captured the remaining heat.

<CIT>, <CIT> and <CIT> are prior art documents useful to understand the invention.

According to an aspect of the present invention, a system is provided according to claim <NUM>.

Optionally, and in accordance with the above, the temperature of the fuel is below -<NUM> °F (-<NUM>).

Optionally, and in accordance with any of the above, the fuel is a liquid fuel.

Optionally, and in accordance with any of the above, the fuel is one of liquid hydrogen, liquid oxygen, or liquid natural gas.

Optionally, and in accordance with any of the above, a third heat exchanger is positioned to exchange heat between the products of combustion downstream of the first heat exchanger, and the fuel downstream of the second heat exchanger.

Optionally, and in accordance with any of the above, a top shaft is configured to drive a generator.

Optionally, and in accordance with any of the above, the bottoming cycle includes a bottom shaft configured to drive a generator.

Optionally, and in accordance with any of the above, the second heat exchanger also receives a second bottoming fluid for removing heat from the first bottoming cycle working fluid. A first stage valve controls the flow of the second bottoming fluid to the second heat exchanger. A control controls operation of the first stage valve such that the second bottoming fluid flow is increased when the heat reduction capacity of the source of fuel at the second heat exchanger is less than desirable to cool the first bottoming cycle working fluid.

Optionally, and in accordance with any of the above, the bottoming cycle work is used, at least in part, for driving a fan which is included in said top cycle to deliver air into the top compressor.

According to an aspect of the present invention, a gas turbine engine is provided according to claim <NUM>.

Optionally, and in accordance with any of the above, the temperature of the fuel is below -<NUM> °F (-<NUM>).

Optionally, and in accordance with any of the above, the top shaft is configured to drive a generator.

Optionally, and in accordance with any of the above, the bottoming shaft is configured to drive a generator.

Optionally, and in accordance with any of the above, the second heat exchanger is further configured to receive a second bottoming fluid for removing heat from the first bottoming cycle working fluid. A first stage valve controls the flow of the second bottoming fluid to the second heat exchanger. A control controls operation of the first stage valve such that the second bottoming fluid flow is increased when the heat reduction capacity of the source of fuel at the second heat exchanger is less than desirable to cool the first bottoming cycle working fluid.

Optionally, and in accordance with any of the above, the further use of the captured power includes at least driving a fan which is included in said top cycle to deliver air into the top compressor.

A gas turbine engine <NUM> is illustrated in <FIG>. A base gas turbine engine could be called a top cycle <NUM>. The top cycle <NUM> includes a shaft <NUM> which may be associated with a motor or generator <NUM>. The motor <NUM> may provide boost energy to the shaft <NUM>, while the generator <NUM> may capture rotational power of the shaft <NUM>, and utilize that power for any number of applications <NUM>. A top compressor <NUM> receives air, and compresses the air, and delivers it into a combustor <NUM>. The air is mixed with a fuel from line <NUM>, and ignited. Products of this combustion pass downstream over a top turbine rotor <NUM>, driving the rotor <NUM> to rotate. The rotor <NUM> in turn drives the compressor <NUM>.

It is known that in practice the top cycle <NUM> may include a number of other components. As an example, there may be a low pressure compressor and a high pressure compressor, and a high pressure turbine and a low pressure turbine associated with the compressor <NUM> and turbine <NUM>.

In addition, a fan shown schematically at <NUM> may deliver the air into the compressor <NUM>. The gas turbine engine <NUM> may be associated with an aircraft if a fan <NUM> is utilized. On the other hand, the fan <NUM> need not be utilized if a gas turbine engine <NUM> is associated with a land based power generator system.

Downstream of the turbine <NUM> the products of combustion pass through a heat exchanger <NUM> in this embodiment. The heat exchanger <NUM> is associated with a so-called bottoming cycle <NUM>. As shown, an amount of heat Q1 is extracted from the products of combustion that reach the heat exchanger <NUM>. This heat passes to a bottoming cycle working fluid as described below. The bottoming cycle <NUM> includes a shaft <NUM> which may drive a generator <NUM> such that rotational power of the shaft <NUM> may be captured and utilized for applications <NUM>.

In the illustrated embodiment, the bottoming cycle <NUM> is a Brayton cycle. However, other bottoming cycles such as a Rankine, an ORC, a supercritical CO2 cycle, or any number of other refrigerant cycles may be utilized.

The bottoming cycle <NUM> has a bottoming compressor <NUM> and an associated bottoming turbine <NUM>. A bottoming cycle refrigerant, or working fluid, downstream of the bottoming compressor <NUM> passes through the main heat exchanger <NUM>. The working fluid in line <NUM>, downstream of the compressor <NUM> is heated by the products of combustion in the heat exchanger <NUM>. Thus, when the working fluid <NUM> reaches the bottoming turbine <NUM> it has increased energy, and provides additional work.

The working fluid downstream of the bottoming turbine <NUM> passes into a line <NUM>, and then through a second heat exchanger <NUM>. The second heat exchanger <NUM> interacts with a fluid in a line <NUM> which is received by a tank <NUM> (e.g., fuel source). As shown, there is an amount of heat Q2 in the bottoming working fluid downstream of the turbine <NUM> at the heat exchanger <NUM> which passes to heat fuel <NUM>. The fluid may be fuel for the top cycle <NUM>. A pump <NUM> may drive the fuel from the tank <NUM> through the heat exchanger <NUM>.

Downstream of the heat exchanger <NUM> the fuel may pass through a supplemental heat exchanger <NUM> where it is also heated by the products of combustion downstream of the heat exchanger <NUM>. That heated fuel then passes into a line <NUM> where it is delivered into the combustor <NUM>.

Products of combustion downstream of the heat exchanger pass into a nozzle <NUM>. The products of combustion then exit at <NUM>.

While a particular bottoming cycle is disclosed, other types of bottoming cycles may benefit from this disclosure. As an example, the bottoming cycle need not have a compressor or turbine, but may instead have some other way of producing work from the captured heat.

In embodiments of this disclosure, the fuel in the tank <NUM> is preferably a cryogenic fuel, but may include any fuel or oxidizer that is stored below ambient temperature. As an example, liquid hydrogen, liquid oxygen or liquid natural gas may be utilized. Such fuel examples typically have a temperature between about -<NUM>°F (-<NUM>) and <NUM> °F (-<NUM>). In embodiments, the fuel has a temperature below <NUM> °F (-<NUM>) and in further embodiments the fuel has a temperature below -<NUM> °F (-<NUM>). More generally, the fuel has a temperature less than about -<NUM> °F (-<NUM>). As a lower end, the fuel may have a temperature greater than about -<NUM> °F (-<NUM>).

By utilizing such cold fuel, the heat differential between the working fluid in line <NUM>, which heats the fuel in line <NUM> is greater. Thus, the heat exchanger <NUM> may be much smaller than in the prior art. Moreover, the combined top and bottoming cycle efficiency is improved beyond the prior art by recapturing the heat rejected from the heat exchanger <NUM>.

A further feature is shown at a heat exchange portion <NUM> that receives the bottoming cycle working fluid downstream of the heat exchanger <NUM>. A fan <NUM>, or other fluid moving component, passes a secondary fluid across the heat exchanger portion <NUM> to remove additional heat Q3 that may remain in the bottoming cycle working fluid downstream of the heat exchanger <NUM>. The fan <NUM> may be selectively operated such as to be used when the volume, or quality, of the fuel in line <NUM> is insufficient to remove all of the heat Q2, and further cooling would be desirable before the bottoming cycle working fluid reaches bottom compressor <NUM>.

<FIG> shows the top cycle as a gas turbine engine. However, other engine types may benefit from a bottoming cycle as disclosed above.

For example, <FIG> shows an engine embodiment <NUM> where top cycle <NUM> is an engine type other than a gas turbine engine. As one example, it may be a hydrogen Otto cycle engine.

Any engine type that produces hot products of combustion may be used with bottoming cycle <NUM>. Again, the fuel entering the heat exchanger <NUM>, and heading for combustor <NUM>, is cold similar to the above embodiment described with respect to <FIG>.

As illustrated schematically in <FIG>, the top cycle provides work <NUM>, whereas a typical bottoming cycle <NUM> provided a first quantity of work, with the cryogenic fuel recaptured providing additional work in the bottoming cycle as shown at <NUM>.

<FIG> shows a claimed embodiment <NUM> having a top cycle <NUM> which is somewhat distinct from the <FIG> top cycle <NUM>. Here the system is generally as in the <FIG> embodiment other than the presence of a motor <NUM> (e.g., an electric motor) controlled by a controller <NUM>. The motor <NUM> drives an exhaust compressor <NUM>, and a nozzle <NUM> is downstream of the exhaust compressor <NUM> such that an exhaust <NUM> of the engine leaves the nozzle <NUM>.

The exhaust compressor <NUM> compresses products of combustion downstream of the heat exchanger <NUM>. The use of the compressor <NUM> can increase the amount of work provided by the top cycle <NUM> relative to the amount of work provided by the bottoming cycle <NUM>.

The speed of the motor <NUM>, and thus the amount of compression by the compressor <NUM> is controlled by control <NUM> based upon the operation of the top cycle <NUM> or key parameters in the bottoming cycle such as a target temperature entering the bottoming cycle turbine. Applicant has recognized that the amount of fuel delivered into line <NUM> is dependent upon the operation of the top cycle <NUM>, and thus the capacity for heat rejection to the fuel in line <NUM> at heat exchanger <NUM> is limited by the amount of flowing fuel. In high fuel flow situations, there may be sufficient fuel in line <NUM> to efficiently capture the bulk of the heat available in the heat exchanger <NUM>.

On the other hand, at low fuel operation, such as idle condition of an associated engine, there will be relatively less fuel. Under such condition, the control <NUM> may operate the motor <NUM> to increase the work provided by exhaust compressor <NUM>, which will in turn increase the efficiency of the top cycle <NUM> and require less heat rejection into the fuel through heat exchanger <NUM>.

Control <NUM> may be a main control for the entire system <NUM>, or may be a standalone control.

The motor <NUM> can be utilized to draw down the pressure downstream of the turbine <NUM> such as at takeoff to reduce the Q2 temperature at the heat exchanger <NUM>.

This optimizes the efficiency of the combined cycle at multiple operating points by controlling the compressor pressure ratio. Also, it ensures excess waste heat is sent to the top cycle exhaust instead of overheating the bottoming cycle. When the exhaust compressor receives more power, less heat is sent to the bottoming cycle. The bottoming cycle is a smaller portion of the total power, and less heat needs to be rejected to the fuel because more of it went out of the top cycle exhaust.

Such a system including the motor <NUM> and/or exhaust compressor <NUM> may be utilized with the <FIG> type system.

An optional feature <NUM> is illustrated in <FIG>, and can be incorporated into the systems of either <FIG>, or <FIG> or <FIG>. The heat exchanger <NUM> from <FIG>, <FIG> and <FIG> may be replaced by a two stage heat exchanger <NUM>. The first bottoming fluid <NUM> passes through the heat exchanger <NUM> as in the prior embodiments. Fuel at <NUM> also passes through the heat exchanger <NUM> and cools the bottoming fluid heading to compressor <NUM>. However, at times, there may be inadequate fuel cooling capacity to adequately cool the bottoming fluid in line <NUM> prior to it reaching the compressor <NUM>. As such, a second bottoming fluid is selectively passed through the heat exchanger <NUM>. In particular, a source of fluid <NUM> passes through a valve <NUM> to a line <NUM> that passes across the heat exchanger <NUM>. Fluid <NUM> may be air. A control <NUM> controls the valve.

If there is inadequate cooling capacity from the fuel flow alone, then the control <NUM> opens valve <NUM> to supply supplemental cooling fluid through the heat exchanger <NUM>. This allows the system to maintain the heat in line <NUM> downstream of heat exchanger <NUM> within acceptable limits.

<FIG> shows yet another embodiment engine <NUM>. In embodiment <NUM>, the generator <NUM> driven by rotation of shaft <NUM> is utilized to power a fan <NUM>. In this embodiment <NUM>, the compressor <NUM> is separately powered by the turbine as in the earlier embodiments. However, some of the power generated at generator <NUM> may be used to power the fan <NUM>.

While the top cycles are shown somewhat schematically, it should be understood there could be more than one gas turbine engine spool in the top cycle. As an example, there could be another turbine driving a fan. Moreover, a typical twospool engine could be utilized.

A system under this disclosure could be said to include a top cycle and a bottoming cycle. The top cycle is an engine having a combustor. The combustor receives a fuel. The combustor is capable of igniting a mix of fuel and a gas, and creating products of combustion. The products of the combustion pass downstream through a first heat exchanger. The bottoming cycle has a bottoming cycle working fluid receiving a first amount of heat through the first heat exchanger. The bottoming cycle produces work from the first amount of heat. The bottoming cycle working fluid then passes through a second heat exchanger and rejects a second lesser amount of heat. A source housing fuel to be delivered to the combustor via the second heat exchanger, such that the bottoming cycle working fluid provides heat to the fuel being delivered to the combustor. The source is configured to maintain fuel at a temperature equal to or below <NUM> °F (-<NUM>).

A gas turbine engine under this disclosure could be said to include a top cycle and a bottoming cycle. The top cycle includes a top compressor having an associated shaft. A top turbine drives the associated shaft to in turn drive the compressor. A combustor is positioned intermediate the top compressor and the top turbine. The combustor receives compressed air from the top compressor and receives a fuel. The combustor is capable of igniting a mixed fuel and air, and passes products of this combustion downstream over the top turbine to drive the top turbine and the associated shaft. Products of the combustion pass downstream of the top turbine through a first heat exchanger, and then to an exhaust nozzle. The bottoming cycle has a bottoming compressor and a bottoming turbine. The first heat exchanger exchanges heat between the products of combustion downstream of the top turbine and a fluid line with a bottoming cycle working fluid. The first heat exchanger receives the bottoming working fluid downstream of the bottoming compressor and upstream of the bottoming turbine such that the products of combustion heat the bottoming cycle working fluid. Downstream of the bottoming turbine the bottoming cycle working fluid passes through a second heat exchanger, and then returns to the bottoming compressor. A bottoming shaft is driven by the bottoming turbine to drive the bottom compressor, and power from rotation of the bottoming shaft is captured for further use. A source housing fuel to be delivered to the combustor via the second heat exchanger, such that the bottoming cycle working fluid provides heat to the fuel being delivered to the combustor. The source is configured to maintain the fuel at a temperature equal to or below <NUM> °F (- <NUM>).

Claim 1:
A system (<NUM>;<NUM>;<NUM>) comprising:
a first heat exchanger (<NUM>);
a second heat exchanger (<NUM>);
a top cycle (<NUM>; <NUM>; <NUM>), said top cycle (<NUM>; <NUM>; <NUM>) being an engine having a combustor (<NUM>; <NUM>), the combustor (<NUM>; <NUM>) receiving a fuel and being capable of igniting a mixture of fuel and a gas and creating products of combustion, the products of the combustion passing downstream through the first heat exchanger (<NUM>);
a bottoming cycle (<NUM>; <NUM>) having a bottoming cycle working fluid receiving a first amount of heat (Q1) through the first heat exchanger (<NUM>), the bottoming cycle (<NUM>; <NUM>) producing work from the first amount of heat (Q1), and the bottoming cycle working fluid then passing through the second heat exchanger (<NUM>) and rejecting a second lesser amount of heat (Q2); and
a source (<NUM>) housing fuel to be delivered to the combustor (<NUM>; <NUM>) via the second heat exchanger (<NUM>), such that the bottoming cycle (<NUM>; <NUM>) working fluid provides heat to the fuel being delivered to the combustor (<NUM>), wherein the source (<NUM>) is configured to maintain the fuel at a temperature equal to or below <NUM> °F (- <NUM>), characterised in that:
the system further comprises:
an exhaust compressor (<NUM>) which receives the products of combustion downstream of the first heat exchanger (<NUM>);
an electric motor (<NUM>) configured to power the exhaust compressor (<NUM>); and
an exhaust nozzle (<NUM>), said exhaust compressor (<NUM>) being upstream of the exhaust nozzle (<NUM>), and said electric motor (<NUM>) being provided with a control (<NUM>) that controls the speed of the electric motor (<NUM>) dependent on conditions of the engine.