Patent Application
20240102657
This invention relates to engines, and more particularly to systems and methods for powering engines using ammonia as a source of fuel, and most particularly to using ammonia as a source of hydrogen fuel used by engines, especially aircraft, marine vessel, and other vehicle engines or stationary gas turbines for power generation.
Engines are used to produce mechanical energy that may be used to drive vehicles such as aircraft, ships, and locomotives, or to drive a generator for electrical power generation, relying on combustion of a fuel that is frequently and commonly hydrocarbon or fossil fuel.
At the same time, there is worldwide concern that the levels of CO2 in the atmosphere are producing climate change that will be potentially catastrophic, and that combustion of carbon-containing fuels contributes to the problem. There is a consequent desire in many quarters to reduce atmospheric concentration of CO2 by reducing human production of CO2 by carbon-based fuel usage that releases CO2 into the atmosphere, a large sector of which is transportation.
One area of particular consideration is aircraft transport. There are more than 5,400 airplanes in the air during peak hours and more than 45,000 daily flights in the U.S., totaling more than 16 million flights per year in pre-pandemic times based on FAA data. According to the U.S. Department of Transportation, the annual transportation of over 1 billion passengers generates more than 10.8 million jobs and constitutes 5.2% of the U.S. GDP.
Currently, aviation accounts for 2.5% of the global CO2 emissions, but, given increased globalization and the interconnected lifestyle of people worldwide together with the ongoing development of many countries, aviation's share of global CO2 emissions is expected to rise to 3.5%. That rise would account for roughly 1 billion metric tons of CO2 per year despite the improved fuel efficiency of newer aircraft.
This growth in aviation CO2 emissions has fueled the industry's desire to decarbonize as soon as possible. In 2009, the aviation industry agreed to ambitious carbon reduction goals that included stabilizing emissions from 2020 onwards with carbon-neutral growth, and reducing emissions to half of 2005 levels by 2050. Meeting those goals without substantially leaning on offsets will require development of alternative non-carbon based fuels.
Turbofan engines and turbine-based auxiliary power units (APU) are the two major aircraft systems that generate emissions due to their reliance on hydrocarbon fuel, i.e., fossil fuel-based Jet-A fuel. Accordingly, decarbonization of aircraft focuses on the use of carbon-neutral hydrocarbon fuels like drop-in biofuels or sustainable aviation fuels (SAF), or on replacement of the fossil fuel-based Jet-A with other energy carriers such as hydrogen or batteries.
Drop-in biofuels are a near-term way to reduce carbon emissions because they can be incorporated into a global aircraft fleet without requiring major aircraft or infrastructure changes, but the scaling up of manufacturing capability to provide cost-competitive drop-in jet fuels for the global fleet has presented substantial difficulties.
The other alternatives to hydrocarbon-based fuels are batteries and hydrogen. While both electrical and chemical storage can potentially be used in aviation to provide propulsive power, the required thrust-to-weight ratios limit the usage of electrical batteries for small aircraft and short-duration flights.
Hydrogen, sometimes called e-H2 when obtained by electrolyzing water, therefore appears to be the only e-fuel that will work. Hydrogen has an unmatched gravimetric energy density (LHV) of 120 MJ/kg, which is much higher than 46 MJ/kg for kerosene and makes it a seemingly attractive fuel to burn.
However, hydrogen storage comes with additional complexities, and its volumetric energy density of 8.5 GJ/m3 is far lower than 38 GJ/m3 for kerosene. Owing to its low volumetric energy density, hydrogen needs to be stored as a cryogenic liquid at 20 K in a well-insulated tank or as a gas at very high pressure (700 bar) in a heavy pressure vessel. Either of these hydrogen storage alternatives comes with complexities that are challenging for the commercial air transportation sector. In addition, the smaller molecular size of hydrogen and its wide range of auto-ignition and flammability lead to higher leakage potential and safety risks. Many countries in developing or under-developed parts of the world do not have the infrastructure for safe and reliable hydrogen storage and fueling, which is a serious concern for the safety-conscious aviation industry. Difficulty in the safe and easy handling of hydrogen has limited its widespread usage outside of the space and chemical industries, after decades of efforts, and that raises doubts about the feasibility and practicality of a global infrastructure and supply chain for refueling airplanes worldwide with liquid hydrogen. Also, cryogenic storage leads to thermal shock during refueling, posing increased fatigue failure risks.
Beyond those concerns, although hydrogen combustion does not produce CO2, the higher flame temperatures in hydrogen combustion also raise concerns about higher NOx emissions and higher amounts of water vapor in the exhaust that can lead to increased contrails.
Essentially, hydrogen is touted as the energy carrier of the future as it burns without carbon emissions and can be easily created from water. However, a main challenge associated with hydrogen is its storage. Either heavy compressed air cylinders at 700 bars have to be used or a cryogenic liquid at 20 degrees K. Both of those approaches appear unfeasible in the context of aviation, or other applications where weight or space constraints are of concern.
Other areas of transportation also may be decarbonized to reduce CO2 emissions. For example, it may be desirable to reduce CO2 emissions by decarbonizing gas turbine engines in marine vessels used to transport goods or passengers across oceans. Similarly, decarbonizing of turbine or internal combustion engines used for transport on land of goods or people, such as by locomotives in trains, or by other vehicles, may be desirable, as is decarbonization of stationary engines burning fuel to generate electricity However, in all these sectors, similar issues to those described above arise with respect to decarbonizing of those engines.
It is therefore an object of the invention to reduce CO2 emissions in vehicles by providing a system for powering vehicle engines that relies on the combustion of hydrogen or blends of hydrogen that avoids the above-described storage problems.
It is also an object of the invention to provide a system for powering an engine by combustion of hydrogen that reduces NOx emissions.
These objectives are accomplished in the invention by using liquid ammonia (NH3) as a carrier for hydrogen fuel.
In contrast to hydrogen, ammonia does not burn well. However, ammonia is an excellent H2 -carrier that can be catalytically cracked to provide H2 gas before combustion, and that can significantly reduce all forms of emissions. Also, ammonia is inherently safer to handle than liquid hydrogen, and does not require cryogenic liquefaction or high-pressure storage like liquid H2. Ammonia is a denser liquid and is liquid at much higher temperatures. Especially in the context of aviation, no cooling is required at cruising altitudes.
According to an aspect of the invention, ammonia is used as a carrier of electricity-derived, green hydrogen for aviation, with near-zero emissions. Ammonia is used as both a carrier of hydrogen as fuel, and also to provide cooling for compressor intercooling and cooled cooling air for NOx elimination and condensation of water vapor in the exhaust to reduce contrail formation.
Ammonia remains in a liquid state over a much wider temperature range than hydrogen, which enhances safety and reduces airport integration hurdles, and ammonia already has a robust and mature supply chain relative to H2. Relevant property comparisons are listed in Table 1. Thus, while e-H2 may be the theoretically best fuel to burn in decarbonized aviation, ammonia may be the best means to carry that hydrogen. In addition, there are significant advantages of ammonia over kerosene and hydrogen, in that ammonia offers superior endothermic fuel characteristics over kerosene because it is stored as a liquid at −33° C., it absorbs significant energy when releasing H2, and it does not form coke.
Interestingly, liquid ammonia carries more hydrogen per unit volume than liquid hydrogen itself, thus providing benefits for storage, for example, within the wings of an aircraft.
According to an aspect of the invention, a power system for a vehicle, comprises a storage tank containing ammonia. An engine supported on the vehicle is configured to operate using hydrogen gas or blends of ammonia and hydrogen as fuel. A conversion device receives ammonia from the storage tank and heat from the engine, and it uses the heat from the engine to dissociate the ammonia to produce hydrogen gas, nitrogen gas, and uncracked ammonia gas. The conversion device supplies the hydrogen gas mix to the engine wherein combustion of the hydrogen gas mix takes place, producing energy that drives the engine so as to generate thrust or move the vehicle, or drives a generator for conversion to electricity and the subsequent powering of an electric motor for moving the vehicle.
According to another aspect of the invention, an aircraft has a storage tank holding ammonia (NH3) in liquid form in its wing or fuselage and an engine, e.g., a turbofan engine adapted to run on hydrogen gas as fuel, connected with the storage tank. The ammonia is transmitted from the tank to a cracking module that exposes the ammonia to heat, preferably derived from operation of the engine, in the presence of a catalyst, as will be described further below. The cracking module causes the ammonia (NH3) to dissociate into N2 and H2 by the endothermic catalyzed reaction:
2NH3+heat→N2+3H2
According to one embodiment of the invention, the resulting gas mixture of H2, N2, and some amount of surviving NH3, which constitutes less than 10% of the gas mixture, is optionally carried to a separation membrane unit that has a selectively permeable mesh that permits passage of H2 but not N2 or NH3. The separation membrane unit outputs two separate gas streams, one H2 and the other a mixture of H2, N2, NH3. The H2 is transmitted to a combustor of the engine where it is combusted with air from the environment, resulting in a combustion product, which is essentially water. The combustion of the hydrogen drives one or more turbines of the engine as is well-known to those of skill in the art, resulting in thrust that propels the aircraft.
According to another embodiment, the cracking module receives the NH3 and cracks only a portion of the NH3 into H2, yielding a mixture of NH3 and H2 which is 30% to 70% H2 and 30% to 70% NH3. That mixture is supplied to the engine of the vehicle without separation, and the lesser percentage of H2 in the blend makes the combustion compared to pure NH3 or H2 combustion more manageable in the combustor, and reduces NOx created during combustion.
The engine preferably includes a low pressure compressor (LPC) that compresses air from outside the engine followed by a high pressure compressor (HPC) that further compresses that air to be used for combustion. The compression steps increase the temperature of the air in addition to its pressure, and that heat is preferably used in the system of the invention to derive H2 from NH3.
The heated air from the LPC is used to vaporize liquid NH3 to produce gaseous NH3 that flows through the cracking module so as to contact surfaces of catalyst material. That air then flows to the HPC where it is further compressed and heated. Removing heat from the air as it is compressed is referred to as compressor intercooling, and compressor intercooling has the benefit of reduced compressor work, which increases the core efficiency of the engine.
The heated air from the HPC is used for combustion, but a portion of that high-pressure air is a separate stream of cooling air for cooling the turbines of the engine. That cooling air is first directed to the cracking module where it is cooled by releasing heat that heats the catalyst surfaces of the cracking module. That heat provides the endothermic energy that drives the dissociation reaction of the ammonia into N2 and H2. The cooler cooling air then leaves the cracking module and is directed to the turbine to cool it. Cooler cooling air has the potential to increase the cooling efficiency in the turbine airfoils. Better cooling efficiency permits for improved core efficiency through either reduced coolant mass flow rate or higher turbine inlet temperatures.
The H2, N2, NH3 gas mixture from the separation membrane unit contains NH3 in a concentration that may be less than 10% of the mixture, which is the part of the ammonia that passes through the cracking module but is not dissociated, for whatever reason. The H2, N2, NH3 mixture or a portion of it may be mixed with air drawn in to the LPC where it is compressed with the ambient air and transmitted with that compressed air to the combustor and is combusted with the pure H2 gas stream, where the presence of the trace amount of NH3 reduces the formation of NOx in the combustion products.
The combustion of the H2 in the combustor produces heat, and alternatively to, or parallel with, using heat from the compressor, the combustor may be configured to use some of that heat from combustion to crack the NH3, by incorporating the cracking unit in or adjacent the combustor wall.
It is advantageous to also derive energy from the heat of the exhaust gases. For that purpose, the exhaust gas from the turbines of the engine is exposed to a heat exchanger that extracts heat that would otherwise be wasted, and a supercritical CO2 system uses a Rankin cycle to extract the heat and converts it to electrical power for use in the aircraft.
In addition, the exhaust is acted upon to reduce NOx emissions by a Selective Catalytic Reduction (SCR) system in which ammonia products are injected into the exhaust gas stream and reduce NOx to N2 and H2O. This process is enhanced by a catalytic surface.
Because ammonia is stored as a fuel in systems of the invention, parts of the stored ammonia fuel can be used for this purpose. That ammonia is evaporated from liquid to gas for this purpose, and the heat for this process comes from condensing the water in the exhaust, which reduces contrail emissions.
The use of ammonia as the hydrogen carrier offers multiple benefits, as will be seen from this disclosure, beyond the desirable use of NH3 for hydrogen generation. It is also beneficial for intercooling between the low and high pressure compressors, for cooling of air used for turbine cooling, for elimination of NOx from the exhaust, and for condensing water from the core exhaust to limit contrail formation. These features are enabled by the non-coking properties of NH3 (in contrast to Jet A or SAF), the ability of NH3 to reduce NOx to N2 in the presence of a selective catalyst (again, as opposed to both Jet A and H2), and its significantly lower explosion potential (as opposed to H2).
According to another aspect of the invention, cracking ammonia is performed within the combustion liner, which reduces the coolant requirement of the system, improving performance and durability, while providing high levels of heat at elevated temperatures for cracking.
Engines used in marine transport, i.e., ships on water, or various land-based transport systems, especially locomotives or large cargo vehicles, as well as gas turbine engines used in stationary power generation, and even internal-combustion reciprocating-piston engines, can also benefit from using ammonia as the source for H2 gas burned in those engines. The general principle shared by these engines is that ammonia is supplied to a cracking unit that receives heat from either a compressor that compresses intake air to the engine, creating heat, or from the combustor portion of the engine itself so as to use the heat from compression or combustion to produce the cracking of the NH3 to form H2 that is subsequently burned in the engine.
Even in ground transport, use of ammonia presents fewer problems in transporting fuel than does H2 gas, as was set out previously, and ammonia can be the form in which hydrogen is moved in bulk. This means that pipelines can pump ammonia instead of hydrogen, and ships can transport liquefied ammonia over oceans (similarly to LNG) instead of hydrogen. Ammonia can be stored on bases or depots instead of H2, so that NH3 is readily available as a fuel and no external cracking prior to use is required.
Other objects and advantages of the invention will become apparent from this specification.
A variety of vehicles that are powered by combustion of fuel may rely on combustion of H2, and engines for those vehicles may advantageously make use of a system supplying H2 fuel derived from ammonia.
Referring to
In one embodiment, the engine may be the engine of an aircraft.
Hence, a system as depicted in
The system may be used for any aircraft, but it is believed that a particularly desirable airframe for application of the system is a narrowbody aircraft. Narrowbody passenger aircraft account for a larger proportion of CO2 emissions in aviation than wide-body aircraft, and market forecasts through 2040 show that narrowbody aircraft deliveries are projected to outpace widebody by a factor of 4.25.
A suitable aircraft for the application of the system is a Boeing 737-8 (737 MAX 8). A Boeing 737-8 seats up to 220 passengers (typically 178-193 in a two-class cabin) and has a rated range of 3,550 nautical miles. The Boeing 737-8 accounts for nearly 50% of 737 MAX sales. It is powered by the CFM LEAP-1B high-bypass ratio turbofan engine, or possibly by its predecessor design engine, the CFM56-5B2 engine.
A schematic of one of these engines is shown in
Referring to
The ammonia is stored in the storage tank of the airframe as LNH3. One major advantage of ammonia over hydrogen is the higher temperature at which it goes into the liquid phase at standard atmospheric pressure, which is −33° C. (240K) compared to hydrogen at −252.9° C. (20K), respectively. Consequently, the cooling and insulation requirement is reduced, which results in less weight and reduced cooling power during flight. In-cruise cryo-cooling for ammonia is not required as it remains in a liquid state above 25,000 feet altitude due to the low ambient temperature in the atmosphere with increasing height, as shown in the graph of
Ammonia does not coke like kerosene. As a result, stored liquid ammonia on the aircraft can be used for various thermal management duties, such as compressor intercooling, cooling of cooled cooling air (CCA), and cooling of aviation electronics, which significantly improves core efficiency and specific fuel consumption (SFC) and/or minimizes extraction of power and compressed air from the core for non-propulsion purposes. These thermal management tasks could not be accomplished with kerosene (or with e-ethanol or e-methanol) because of its coking or thermal degradation, nor could they be accomplished easily with hydrogen because of its leakage and flammability potential. In fact, improved core efficiency as noted here can partially negate the lower gravimetric energy density of ammonia.
The LNH3 is initially used for intercooling the air compressed by the LPC 17 before the HPC 19 at step 27. The use of NH3 for intercooling between the LPC 17 and HPC 19 significantly reduces the power consumed by the HPC 19, thus improving overall core efficiency. This improvement can be significant, increasing the core efficiency from a typical value of ˜40% to more than ˜50%. A low level of continuous intercooling can also be added by cooling the stationary casing, with an additional reduction in compressor work.
A significant fraction (˜20% or higher) of air is extracted from the compressor as TCLA (total cooling and leakage air). If the extracted air is first cooled using NH3, as indicated in
Another potential emission from the engine is water vapor from H2 combustion, which potentially leads to contrail formation. However, H2 combustion does not create soot particles that could act as nucleation sites for condensation/ice-formation, so contrails are reduced. In addition, the NH3 needed for selective catalytic reduction (SCR) can be routed, while still in a liquid state at approximately −33° C., through a heat exchanger (
The primary purpose of the NH3, however, is to provide H2 gas to the engine as fuel. The initial step of that process is that the LNH3 is heated by the heat exchanger (step 29) to derive heat in the air introduced by the LPC 17, raising the temperature of the LNH3 to a higher temperature, such as, for example, 300 degrees C., and this temperature elevation also converts the LNH3 to gaseous NH3. The heating of the LNH3 to this temperature requires approximately 0.78 MJ for each kilogram of NH3.
Once the NH3 is gaseous, it is transmitted to a catalytic cracking module in step 31. The catalytic cracking module receives heat from the HPC or the engine of approximately 7.36 MJ per kg of NH3, and with that input energy cracks the NH3, causing it to dissociate into H2 and N2, which are output as a mixture of those gases, plus some NH3 that is not disassociated as less than 10% of the output mixture.
According to the embodiment shown, the output mixture is then separated by a separation membrane into two gas streams, one of which is essentially pure H2 gas that can pass through the membrane, and the other which is a mixture of primarily N2 with undisassociated NH3 and a residual amount of H2 that did not pass through the separation membrane. The H2 is sent to the combustor and burned, releasing 21.4 MJ per kg of NH3, and driving the turbines, and creating thrust. The other gas mixture is carried to a point upstream of the LPC and there mixed with the air that is passing through and being compressed in the LPC and the HPC, in some part bypassing the combustion part of the process to reduce NOx and use of NH3.
Alternatively, instead of separating the H2 and the other mixed gases from cracking, to reduce NOx and to control the combustion of the H2, the mixture of gases output from the cracking module may be supplied, without any separation, directly to the combustor of the engine as a fuel mixture. This reduces the temperature of the combustion and its energy output, which is very high for the combustion of H2 compared with hydrocarbon fuels.
After combustion, the exhaust is combusted gas products at high temperature, and a waste heat recovery system (WHR) 35 extracts heat from the exhaust gases using supercritical CO2 as a working fluid, and converts that heat to electrical energy for use in the other aircraft systems. In addition, the heated exhaust gases are cooled (step 37), as described previously, using the LNH3 as coolant, and, in a step 39, some NH3 is sprayed into the exhaust gas stream that subsequently flows through a selective catalytic reduction (SCR) screen that causes a reaction with the exhaust gas that removes NOx from the exhaust.
The fan 15 and LPC 17 have a bypass conduit 41 between them. The bypass line 41 is the air that bypasses the core as it is extracted after the fan. The bypass air's purpose is to provide a heat sink for the waste heat recovery unit (WHR unit) 43. The heat for the unit is transferred through the primary heat exchanger (PHX) 9, which is located after the LPT 13 so as to contact the engine exhaust gas. The WHR unit 43 is a sCO2 fluid system that has the capability to generate electric power that can support the APUs (in cruise mode of the aircraft) or can replace engine-mounted generators.
In addition, the aircraft is provided with liquid NH3 tank 45, which at altitude is allowed to cool to the ambient temperature to below −33 degrees C., maintaining the NH3 in its liquid state without pressurization, but which also maintains pressure of at least 16 atm to preserve the liquid state where ambient temperatures rise to as much as 40 degrees C. A heat exchanger or intercooler 47 is provided that uses the LNH3 to cool air output from the LPC 17. The cooled air flows on to the HPC 19, while the heat evaporates the LNH3 to form gaseous NH3 (GNH3) that flows though conduit 49 to catalytic cracking unit 51.
Catalytic cracking unit 51 also receives heated air from the HPC 19 through conduit 53. An exchange of heat occurs in the cracking unit, as the catalytic cracking of GNH3 to H2 is endothermic. The endothermic cracking reaction is a heat sink that cools the air from the HPC 19 for cooling the HPT 11, thereby also enabling better turbine blade cooling performance. The heated air heats the operative portions of the catalytic cracking unit, which cracks the NH3 so as to generate H2 and N2. The catalytic cracking unit then separates the H2 and supplies that and some or all of the output gases from the cracking process to combustor 21 via conduit 55, where combustion takes place, driving the turbines, i.e., HPT 11 and LPT 13. In addition, the now-cooled air from the HPC 19 is transmitted via conduit 57 to cool the high pressure turbine HPT 11.
Tubes 48 are connected in parallel to a supply line from the LNH3 tank that supplies liquid NH3 to flow through them. The tubes 48 extend circumferentially around the turbine shaft 16 in the annular space 50 defined between it and the outer shroud 10, and are supported in a baffle or other support structure in the air flow. The tubes 48 carry the LNH3 through them so as to cool the air flowing through space 50, and they are configured to maximize the surface-to-volume ratio of the tubes 48 to optimize heat exchange with the air from the LPC.
The heat imparted to the LNH3 causes it to become gaseous NH3, and the tubes 48 of the heat exchanger 47 all combine to connect to supply the gaseous NH3 to conduit 52 (
After being cooled by the heat exchanger 47, the air flows rearward to HPC 19, which comprises blades 20a mounted on rotatable second turbine shaft 12, and vanes 20b mounted on stationary shroud 10. Blades 20a and vanes 20b co-act to impart more pressure to air flowing through HPC 19, which also heats the air to about 500 degrees K.
The air from the HPC flows to plenum 54 where it is divided into a first stream of about 75% or more of the pressurized air from HPC 19, which is directed to the combustor 21 and used to burn the H2 fuel derived from cracking. The remaining 25% or less of the air bypasses the combustor and is at least partially routed through conduit 53 to the cracking unit 51 (
Operative parameters for the exemplary aircraft engine, the CFM56-5B2 engine, provided with the ammonia-based fuel system of the invention are set out in Table 2.
The engine operates in four different modes, namely (1) ground, (2) cruise, (3) landing, and (4) take-off, which have various fuel operating parameters and the various stages of a flight mission. Six cases are shown from the operational modes. Mode (1), ground, is split into three cases 1 to 3 corresponding to varying temperatures at the ground simulating summer and winter conditions. Cases 4 and 5 are for landing mode (3) and take-off mode (4), and, finally, case 6 is for cruise mode (2).
Referring to
The heat exchanger has a core flow rate that may be varied to achieve a target NH3 outlet temperature. Limiting the core flow in this manner enables the heat exchanger to achieve a very low air-side pressure drop (ΔP/P<0.5%). A variable flow rate can be achieved in practice using a thermostatically controlled inlet ramp for the core flow entering the heat exchanger. Operating conditions for the heat exchanger are set out in Table 3.
In another embodiment, the heat exchanger 47 may be an intercooler in the form of an annular plate-fin heat exchanger in a cross-flow arrangement. LPC discharge temperatures are typically less than 450 degrees K, which enables the use of a 6000 series aluminum alloy in the intercooler. The intercooler structure has offset-strip fins that provide heat transfer enhancement for the hot (engine core) and cold (NH3) flow paths.
As best shown in
The catalytic cracking unit 61 has in it passageways with a surface that is coated with a catalyst that promotes the cracking from ammonia to hydrogen. This is an endothermic process, meaning that heat is adsorbed, and the heat is provided by heated air supplied via conduit 53 from the HPC 19 so that the surfaces are heated to about 300 degrees C. The passage through which the air flows has a surface topology that is configured to optimize, or at least facilitate to at least some degree, heat transfer from the air flow to the body of the cracking unit, and therein to the catalyst surfaces in the module over which the NH3 flows and has contact. That heat provides the energy required for the endothermic cracking process, and the result is that the catalytic cracking unit 61 outputs a gas mixture of H2 and N2, together, in this embodiment, with a relatively low amount of NH3, preferably less that 10% or less than 5% that is not cracked because the cracking process is not 100% efficient.
In addition, the air from the HPC loses heat and is cooled during its passage through the cracking unit 61, and leaves through conduit 57 to go to cool the high-pressure turbine. The first turbine stage experiences extreme temperatures after combustion and is actively cooled by bleed air from the compressor. Typically, though, the HPC compressor exit temperature of the compressed cooling air is high. Cold cooling air improves the turbine performance and hence the core efficiency of the engine, and the cooled cooling air is cooled by exchanging heat with cracking process. In summary, the system provides a heat sink for improved turbine cooling by providing the required endothermic task of ammonia cracking.
A variety of catalysts may be used to effectuate the cracking process in the various cracking apparatus described herein. The most commonly used catalyst for cracking ammonia is iron and nickel, ruthenium, or boron nitride.
The Haber-Bosch process uses an iron-based catalyst to produce ammonia from nitrogen. This reaction is reversible, and the catalyst mass composition must be tailored to improve ammonia yields. Poor iron-based Haber-Bosch catalysts allow the realization of the reverse reaction. Previous work in this area has shown that high surface area iron particles supported on a silicate matrix have good hydrogen yields from ammonia. See W. C. Tucker, “Strong catalytic activity of iron nanoparticles on the surfaces of reduced olivine,” Icarus, 299, pp. 502-512 (2018).
The surface area and the support for the iron greatly affect the efficiency of this process. It was shown that the common mineral olivine (Mg2+, Fe2+)2SiO4 could be reduced to produce 10-50 nm diameter iron nanoparticles on a forsterite (Mg2SiO4) surface. This composition displayed strong catalytic activity not seen in powders without Fe nanoparticles with a rapid decomposition of NH3 to hydrogen and nitrogen observed. The energetics of catalytic decomposition of ammonia into hydrogen is comprehensively described in I. Dincer, Comprehensive energy systems, Elsevier (2018).
The gas mixture of H2, N2, and NH3, produced by the catalytic cracking unit 61 flows to the separation membrane unit 63 where it meets a separation membrane 65. Preferably, this membrane is composed of palladium coated vanadium. That membrane material is permeable to hydrogen but not to nitrogen, hence enabling the separation, and H2 passes through the membrane and out of the separation membrane unit through H2 conduit 67. The N2 and NH3, as well as a small amount of H2, do not pass through the membrane 65, and the gas mixture of those components flows to a different outlet conduit 69.
Generally, as ammonia is cracked into hydrogen and nitrogen, both gases have to be separated, with nitrogen being ejected to the atmosphere and hydrogen being routed to the combustion system via conduit 67. The NH3, N2, and H2 gas mixture separated from most of the H2 may be transferred via conduit 69 harmlessly to the bypass flow, with the NH3, N2, and H2 gas mixture being mixed with the compressed air passing through the LPC and HPC, which reduces the weight penalty of carrying extra NH3 would be needed for Selective Catalytic Reduction (SCR) if ammonia were not the fuel source for the aircraft.
Alternatively, the NH3, N2, and H2 gas mixture may be supplied with the compressed air from the LPC and HPC to the combustion chamber, as the inclusion of at least a portion of these gases may be beneficial in terms of addressing NOx issues, because the presence of ammonia in the combustion reduces the temperature of the combustion and reduces the production of NOx.
As another alternative, it may be desirable, in order to reduce NOx and also to reduce the very exothermic nature of the H2 combustion in the engine, that the separation unit be removed, and that the output of the cracking unit be a mixture of H2, N2 and a substantial amount of NH3 that is transmitted to the combustor of the engine to be combusted together. The presence of the NH3 reduces the NOx, and the presence of NH3 and N2 in the combustor reduces the temperature of the combustion of the H2, which may be beneficial to the engine components or to the operation of the engine. For those purposes, H2 is present in the gaseous mixture in a range of 30% to 70% by volume, and NH3 is present in a range of 30% to 70% by volume.
Thermal NOx considerations are important at high temperatures in the presence of ambient nitrogen, but when NH3 is used as a fuel or hydrogen carrier, the fuel-bound nitrogen can lead to fuel NOx. For this reason, the cracking of NH3 is ideal to make H2 available for combustion, while the highly stable N2 byproduct will inhibit the NOx formation. Standard practice for NOx control in power plants is to use NH3 for selective catalytic reduction (SCR) to reform NOx back to harmless N2 and O2, with a dramatic reduction of NOx to ˜3 ppm. Thus, the onboard NH3 can be used to nearly eliminate the NOx emissions, which would not be possible with other fuels.
Referring to
The outer cylinder and the inner cylinder 71 define between them an annular volume in which planar heat transfer walls 85 extend radially between the cylinders 71, 73, dividing the annular volume up into passages 87 extending the length of the unit 61, all of which communicate with air conduits 53 and 57 so that heated air from conduit 53 flows into all of the passages, heats the walls 85 and inner cylinder 71, and then flows out of the unit through outlet conduit 57. The configuration is intended to facilitate heat transfer from the air flow, through the inner cylinder wall 71 and to the catalyst surfaces, so as to provide heat for the endothermic ammonia cracking process.
The system of the invention operates using heat derived from its operation to crack the ammonia to derive hydrogen to fuel its operation. Accordingly, to start the engine, battery power is used to heat the catalytic cracking unit to the point that it can generate hydrogen fuel or to drive the HPC so that it produces heated cooling air that heats the catalytic cracking unit to operational temperature, and to also turn the rotor shaft of the engine. The hydrogen when generated is then combusted, starting fuel driven operation of the engine.
It should be noted that the NH3 can be pumped in the liquid phase, and not as a gas, to minimize pumping power requirements, in order to provide the pressure head necessary for all operations.
The foregoing embodiment uses heat derived from the operation of the engine, and in particular from the LPC and HPC compressors of the engine, both of which heat the air as they compress it. Specifically, in the foregoing embodiment, the heat from the LPC is used to convert the liquid NH3 to gaseous NH3, and the heat from the HPC is used to provide the endothermic energy that cracks the NH3 into H2 and N2 in the cracking module.
In addition to the heat from the compressors, however, heat from the operation of the engine also includes combustion of the fuel in the combustor 21, and heat from that part of the operation of the engine may be also used for cracking the ammonia.
The combustion liner is a crucial part of the combustion system. It contains the flame and is exposed to some of the highest temperatures within gas turbine system, and the combustion liner is actively cooled using compressor bleed air. The combustor liner itself may be made from a high-temperature alloy such as Inconel, and it may be coated with a ceramic thermal barrier coating, or the liner may be fully ceramic. It can be conventionally machined or additively manufactured.
The tubes 97 extend through or adjacent the liner of combustor 21 and absorb heat from the combustion. The absorbed heat provides the energy that causes cracking of the NH3 into N2 and H2 in the tubes 97, yielding a gas mixture of H2, N2, and some uncracked NH3 in each of the tubes 97. The cracking products from the tubes 97 are combined by a combining structure 99 that mixes the gas output from all of the tubes 95 in a common outlet conduit as a mixture containing N2, H2, and, if cracking is not complete, NH3, that flows out to a conduit 101. Conduit 101 carries the products of the cracking process to a separation unit 63 (
The channels 97 are coated internally with a catalyst to act as cracking-promoting surfaces while cooling the combustion liner. For the catalyst, most commonly used are iron and nickel, ruthenium, or boron nitride. The catalyst may be applied to the surface or in the channel together with a catalyst support to allow for gas flow. The channels 97 may be additively manufactured, and may have turbulence-promoting features such as ribs, pins, or other engineered surface roughnesses inside them to improve the cracking process. For example, the channels 97 may have one or more properties of the following: straight, wavy, triply-periodic-minimal surfaces (TPMS), staggered, and may have other internal features that increase surface area and promote turbulence.
As best shown in
In the embodiment shown, each channel 97 extends almost completely around 360 degrees of circumference of the cylindrical liner 103. Depending on acquired heat appropriate for a given engine or application, however, the circumferential tubes may go around the cylinder of the liner one quarter of the circumference (i.e., arranged as four separate channels of 90 degrees of the circumference distributed around the circumference), a third of the circumference (i.e., three separate channels of 120 degrees of the circumference distributed around the circumference), or one or two complete circumferences (360 degrees or 720 degrees).
Referring to
There are a variety of configurations of combustion chambers, and embodiments of these cracking channels may be used in can, can-annular, or annular style combustion chambers of a gas turbine engine.
Furthermore, the apparatus and methods of using ammonia as a source of fuel described herein can be applied to gas turbines in general, independent of their use. The engines can include engines for aircraft, as described above, but also engines used for marine vessels, engines for land vehicles, e.g., railroad locomotives, or engines for stationary power generation, or for any other application for which hydrogen fuel combustion may be considered desirable, or for which provision of fuel using NH3 is desirable. Engines that may be used advantageously in the invention herein include the engines sold under the trade names LM 6000, LM 2500, and LM 2500XPRESS by the GE Gas Power division of General Electric.
In addition to application to turbine engines, the apparatus and methods can also be used in an internal combustion engine burning hydrogen derived from ammonia.
In that context, an internal combustion engine may not have initial compressors such as the LPC or HPC found in the turbine engines described above. The heat to be used for cracking the ammonia to yield the H2 fuel gas is best derived from the heat of combustion in the cylinder of the reciprocating piston engine.
Referring to
The cylinder wall 125 is provided with catalyst-lined channels 131 surrounding the interior of the cylinder, with an arrangement in the cylinder wall the same as or similar to the channels shown in the combustion liner in
The channels in the cylinder wall may alternatively be of the configurations of
The terms used herein should be viewed as terms of description rather than limitation, as those of ordinary skill in the art with this disclosure before them will be able to make changes and modifications thereto without departing from the spirit of the invention.
This application claims the benefit of U.S. provisional application 63/409,609 filed on Sep. 23, 2022, and U.S. provisional application 63/537,438 filed on Sep. 8, 2023.
This invention was made with government support under NASA Cooperative Agreement No. 80NSSC22M0067 (NASA ULI). The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63409609 | Sep 2022 | US | |
| 63537438 | Sep 2023 | US |
