Exhaust gas heat recovery from cryo-compression engines with cogeneration of cryo-working fluid

The present invention provides an energy recovery, phase change storage and prime mover system with co-generation and cryogenic compression of the working fluid for distributed electric generation and motor vehicle application.

FIELD OF THE INVENTION

The present invention relates generally to electric generation and motor vehicle prime movers, and specifically to those operating on the temperature differential between a heat source and a cryogenic heat sink. Recovered heat from a high temperature heat source such as a fuel gasifier, solar concentrator, nuclear reactor, fuel cell or combustion engine is further recovered from prime mover exhaust gas to provide power output including co-generation of liquefied air for cryo-compression of the working fluid.

BACKGROUND

Since the 1970's a high efficiency prime mover with renewable energy storage has been a goal of motor vehicle and distributed electric generation design to provide energy independence, conserve fossil fuels, and reduce emission of combustion products. This has led to an increased need for clean and reliable energy storage devices, which can store the power generated, and make it readily available when needed in a wide range of applications. As fossil fuels are consumed more rapidly than they can be produced, an “energy crisis” has emerged and there is a widely recognized need to develop new energy technologies. Moreover, the products of combustion are both unhealthy and dangerous for the environment, while the gradual increase in temperature of the earth's atmosphere, or “greenhouse effect”, advises development of energy technology that minimizes the release of heat and greenhouse gases. Some examples of technologies that exploit natural “clean” energy sources include solar photo-voltaic panels, wind turbines, motor vehicle regenerative braking, and fuel cells. Other, yet undeveloped technologies, include structure and motor vehicle draft recovery, advanced refrigerant liquefaction for heat sink cooling, and application of synfuel gasification to production of hydrogen and cryo-sink refrigerant.

Energy storage of solar, wind, and other intermittent sources, has in general, been dominated by advanced batteries. Batteries are resource intensive to manufacture; have a limited number of charge cycles; and present an unprecedented fire hazard. Other storage concepts under development, such as super capacitors, flywheels, and compressed air are too expensive, hazardous and/or inefficient. Renewable fuels, such as compressed hydrogen, liquid natural gas, and bio-fuels are useful for extended unavailability of intermittent energy sources, but are in limited use. Hydrogen is produced inefficiently by electrolysis of water or steam reforming of methane from natural gas, which is available via the environmentally controversial fracking process. Because hydrogen is burned in inefficient converters, on-board vehicle storage is problematic and high pressures must be employed. While carbon from production of synthetic fuels may be captured for sequestration, combustion of these fuels normally discharges carbon dioxide to the atmosphere.

Phase change of liquid air or nitrogen is a promising alternative storage means, for both electric generation and motor vehicles. Specific storage capacity is equal to fuel saved due to cryo-compression per unit weight or volume of refrigerant plus container. The liquid or solidified gas is referred to hereinafter as heat sink refrigerant produced by refrigerant liquefaction. A “liquid nitrogen economy” has been proposed [Kleppe, J. and Schneider, R., “A Nitrogen Economy”, ASEE, 1974] and some high pressure engines with phase change storage using cryogenic compression have been tested. These include a fired turbine [Kishimoto, K. et-al, “Development of Generator of Liquid Air Storage Energy System”, Mitsubishi Tech. Review Vol. 35-3, 1998] and two fuel-less reciprocating engines [Knowlen, C. et-al, “High Efficiency Energy Conversion Systems for Liquid Nitrogen Automobiles”, U. of Washington, SAE 981898, 1998] and [Ordonez, C. et-al, “Cryogenic Heat Engine for Powering Zero Emission Vehicles”, ASME Intl. Mech. Engineering Congress & Expo., 2001]. More recently, phase change storage is gaining acceptance in the United Kingdom as indicated by an operating 300 kW pilot plant and a fuel-less liquid nitrogen engine for compact urban vehicles [Center for Low Carbon Futures, “Liquid Air in the Energy and Transport Systems”, ISBN: 978-0-9575872-2-9, 2013]. In these prime movers, low compression work is attained by incompressible working fluid. Consumption of refrigerant is excessive in these high pressure engines (40 to 80 bar), which are not optimized, nor supplemented by recovered energy. Two improved cryo-compression engines have been proposed. These are a closed cycle with ambient heat source and quasi-isentropic cryo-compression sink [Ordonez, C., “Liquid Nitrogen Fueled, Closed Brayton Cycle Cryogenic Heat Engine”, Energy Conversion & Management 41, 2000], and an open cycle with over ambient heat source and quasi-isothermal cryo-compression sink as disclosed in the inventor's U.S. Pat. No. 7,854,278. Both concepts would economize refrigerant consumption and profoundly impact design and production capacity of refrigerant condensation facilities.

Refrigerant liquefaction to supply early stage cryo-compression engines is primarily by various standard expansion-cooling cycles. These are powered primarily from the electric grid at low cost off-peak time. Inherent disadvantages of this power source include transmission loss, transport of the refrigerant and perpetuation of the environmental downside of centralized fossil fuel and nuclear use. Large central expansion-cooling liquefiers are attaining efficiency of about 50%. This requires complex equipment with features, however, such as pre-cooling, multi-stage expansion and sub-cooling to a lower temperature sink, such as with liquid natural gas during distribution. These features are not economical in smaller distributed applications, leading to higher liquefier power requirements. On-board motor vehicle refrigerant liquefaction is considered to be impractical due to low liquefaction efficiency.

It is important to minimize refrigerant consumption. Moreover, it is recognized that advanced liquefier concepts are required for smaller scale distributed use in conjunction with universally available renewable energy to drive refrigerant liquefaction in both stationary and motor vehicle application. Two promising prior art liquefiers with application to cryo-compression engines are under development. These are magneto-caloric refrigeration, [Matsumoto, K. et al, “Magnetic Refrigerator for Hydrogen Liquefaction, J. of Physics: Conf. Series 150, 2009], and thermo-acoustic refrigeration [Wollan, J. et al, “Development of a Thermoacoustic Natural Gas Liquefier”, Los Alamos Natl. Lab., LA-UR-02-1623, AlChE, 2002]. An undeveloped prior art liquefier concept is sub-cooling of an air liquefier by available cryo-liquid from a gasifier, as disclosed in the inventor's U.S. Pat. Nos. 10,343,890 and 10,384,926 for examples, or liquefied natural gas facility during vaporization for distribution. Prior art renewable energy power sources adaptable to refrigerant liquefaction for general use include solar, wind and process heat and pressure recovery. Motor vehicle regenerative braking due to deceleration is a developed technology, potentially supplemented by photo-voltaic solar recovery, for on-board liquefaction. Regenerative braking potential is partially lost due to compression heating in reciprocating engines. Solar recovery to motor vehicles is limited by available capture area and photo-voltaic panel efficiency. Three undeveloped prior art liquefier power source concepts are energy recovery of wind, motor vehicles, and fuel synthesis for distributed and mobile applications, as disclosed in the inventor's U.S. Pat. Nos. 9,395,118; 7,854,278; and 10,343,890, respectively.

SUMMARY OF INVENTION

There are two main embodiments of the engine of the present invention for distributed electric generation and motor vehicle application. While one of at least ordinary skill in the art will recognize that some features of the main embodiments may be substituted, these are the preferred versions.

The object of the present invention is, therefore, to provide a prime mover (multiple expansion engines) with capability to recover heat and pressure from an originating energy source such as a fuel gasifier, solar concentrator, nuclear reactor, fuel cell or combustion engine to a cascaded arrangement of two or more expansion engines.

It is a further aspect of the present invention to provide a prime mover (multiple expansion engines) with capability to recover pressure from an originating energy source such as the fuel of a fuel cell or combustion engine to a cascaded arrangement of two or more expansion engines.

It is a further aspect of the present invention to provide phase change energy storage by co-generating liquefied air or re-liquefied (less specific energy) air, to cool heat sink working fluid, thus enabling cryo-compression and increasing overall operating temperature difference of a prime mover.

It is a further aspect of the present invention to recover exhaust heat discharging from an expansion engine to cryogenically compressed intake air entering an adjacent expansion engine.

It is a further aspect of the present invention to recover exhaust pressure discharging from a first expansion engine to drive cryo-compression of expansion engine working fluid.

It is a further aspect of the present invention to co-generate production of liquefied air by load shifting between a prime mover and the drive of an air liquefier of a stationary prime mover or a motor vehicle.

It is a further aspect of the present invention to co-generate re-liquefaction of liquefied air used to provide cryo-compression of the working fluid of a prime mover.

These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, accompanying figures and claims.

DETAILED DESCRIPTION

As a preface, it should be noted that all physical components are referred to with an even reference number and all fluid compounds that move amongst the physical components are referred to with an odd reference number. Components with heat exchange properties are depicted as bisected boxes, generally depicting colder pressurized and hotter non-pressurized flow paths. It will be understood from the description that these components gain heat from one fluid and provide heat to another fluid, where the fluids are not likely to mix. Dashed lines indicate an electrical communication between relevant components and do not include reference numbers. This is as opposed to lines between components where an arrow is labeled with a reference number, which indicates a specific fluid and that fluid's direction. InFIG.2b, cross-hatching indicates mechanical communication between two rotors. When it is noted that a component is disposed between two other components, this disposition indicates the position of the various components on the fluid's path, not necessarily the actual spatial position of the components. Finally, it is noted that when a specific model or distributor of a system component is included, this inclusion is merely exemplary and comparable components may be substituted. In addition, one of at least ordinary skill in the art will recognize that alternate fluids may be substituted.

Referring first toFIG.1, a schematic of the most basic form of energy recovery system100is provided. Energy recovery system100includes an air liquefier112; dewar114; first cryo-mixing junction120; first cryo-recuperator132; first cryo-compressor128; second cryo-mixing junction122; second cryo-recuperator134; second cryo-compressor130; at least one energy source102; engine138; engine recovery heat exchanger140; engine driven generator144; and electric regulator146. The at least one energy source102is preferably one of a fuel gasifier, nuclear reactor, or solar concentrator.

Cryo-recuperators are heat exchangers that recover heat internally from the intake to the discharge flow of an associated cryo-compressor. Cryo-compressors compress a mixture of liquid air and atmospheric air cooled by vaporizing liquid air. Two types of cryo-compressors are discussed herein, a turbine driven cryo-compressor and an electric driven cryo-compressor. Recovery heat exchangers transfer heat between components in external flow paths. Turbines are devices that transform rotational energy from a fluid that is picked up by a rotor system into useable work or energy. As specified herein for various embodiments of system100, a turbine may be, for example, a turbine-generator or a compressor drive turbine. A generator is a device that converts mechanical energy to electricity and may be, for example, an engine driven generator. An electric regulator, as used herein is a hub through which electricity is directed to various components.

The fluid that moves between the various components of energy recovery system100is air. As described below, several modifications of the term “air” will be provided, e.g., liquid air105, primary air111, secondary exhaust air113, and oxygen depleted air due to boil-off or chemical reaction. In addition, letters may be added to a designation to indicate different portions of the same type of air, e.g., first and second portions of liquid air105a,105b. It is understood that these various air designations merely distinguish the same basic working fluid in different states (e.g. liquid versus gas) and different production methods (e.g. primary air107as a product of mixing liquid air105aand atmospheric air103b), or primary exhaust air111as a product of primary air107through engine138.

A first portion of atmospheric air103ais provided to air liquefier112, which liquefies atmospheric air103ainto liquid air105. Liquid air105is provided to dewar114. Dewar114provides first and second portions of liquid air105a,105bto first and second cryo-mixing junctions120,122, respectively. Second and third portions of atmospheric air103b,103care provided to first and second cryo-recuperators132,134, respectively. The first portion of liquid air105aand the second portion of atmospheric air103bare mixed in first cryo-mixing junction120to produce primary air107, which has the temperature of liquid air105adue to isothermal vaporization. The second portion of liquid air105band the third portion of atmospheric air103care mixed in second cryo-mixing junction122to produce secondary air109, which has the temperature of liquid air105bdue to isothermal vaporization. Primary air107is compressed through first cryo-compressor128and provided to energy source102. Secondary air109is compressed through second cryo-compressor130and provided to engine recovery heat exchanger140. It is understood that, as illustrated, the provision of a fluid from one component to another may not always be direct. Primary air107may be provided from first cryo-compressor128to energy source102via first cryo-recuperator132, for example.

Complimentary flow paths are fed by the cryogenic working fluid. A first fluid flow path begins with the entry of primary air107into energy source102. Primary air107recovers heat from the energy source102, continues on to engine138where it expands in the form of primary exhaust air111; and continues on to engine recovery heat exchanger140. The second fluid flow path begins with entry of secondary air109into engine recovery heat exchanger140. Secondary air109recovers exhaust heat from primary exhaust air111in engine recovery heat exchanger140; and continues on to engine driven generator144where it expands. The first and second fluid flow paths compliment and facilitate one another with their fluid heat exchange.

Engine driven generator144produces secondary exhaust air113and delivers power to electric regulator146. As discussed below, in system200, exhaust air113is circulated back to a first pre-heater136that is one of the at least one energy sources102in that embodiment. InFIG.2b, exhaust air113is vented. Heat of secondary exhaust air113may be recovered for use, including recovery to an optional third flow path (not shown) fed by cryogenic working fluid and comprising a recovery heat exchanger and engine.

Electric regulator146provides power to at least air liquefier112and second cryo-compressor130. As discussed below, in system200, shown inFIG.2a, electric regulator146also provides power to cryo-compressor128, which is first electric driven cryo-compressor156in that embodiment. In system300, shown inFIG.2b, electric regulator146also receives power from energy source102, which is second engine driven generator170in that embodiment. It is understood that the short dashed line pointing down and out from electric regulator146indicated net power output.

Now referring toFIG.2a, a schematic of a preferred embodiment of the energy recovery system100of the present invention is provided. In this embodiment, system200is a heat recovery system for recovering energy of end product, exhaust, or circulating coolant from an originating heat source (in this case, primary heat source150, discussed in more detail below). In system200, first cryo-compressor128is first electric driven cryo-compressor152. Second cryo-compressor130is second electric driven cryo-compressor156. The engine138is first turbine driven generator154. The engine driven generator144is second turbine driven generator108. (Second turbine driven generator108is depicted inFIG.2aas a rectangle, which is unlike how turbines are usually depicted in the figures herein. This depiction is to show consistency withFIGS.1and2b.) This embodiment also includes a second pre-heater142disposed between engine recovery heat exchanger140and second cryo-recuperator134. Electric regulator146provides power to first electric driven cryo-compressor152in this embodiment.

In system200the at least one energy source102includes first pre-heater136and primary heat source150. First pre-heater136receives primary air107from first electric driven cryo-compressor152and heats primary air107. Primary heat source150is preferably one of a fuel gasifier, nuclear reactor, or solar concentrator. Primary heat source150includes source recovery heat exchanger158. A coolant131circulates between primary heat source150and source recovery heat exchanger158to transfer heat from source150to primary air107. The coolant131may be a circulating exhaust gas, such as a combination of hydrogen, carbon monoxide, carbon dioxide and char of an air blown fuel gasifier, helium of a nuclear reactor, or steam coolant of a solar concentrator, for examples. Secondary exhaust air113is provided from second turbine driven generator108to first pre-heater136and the heat of secondary exhaust air113is used to heat primary air107therein.

System200also includes first and second liquid air pumps160,162that receive first and second portions of liquid air105a,105b, respectively. First and second liquid air pumps160,162pump first and second portions of liquid air105a,105bto first and second cryo-mixing junctions120,122, respectively. First storage valve164is disposed between air liquefier112and dewar114and controls a flow of liquid air105there-between. Second storage valve166controls a flow of liquid air105out of system100. That is to say, that excess portions of liquid air105that are not used in the operation of system100may be removed from system100to storage (not shown) through second storage valve166. As noted above, first and second portions of liquid air105a,105b, are used in the operation of system100, which is why they are referenced separately from the liquid air105that leaves system100through second storage valve166. Although not shown so as not to overly complicate the illustration, electric regulator146may provide power to first and second liquid air pumps160,162and first and second storage valves164,166.

A first innovative feature of system200is recovery of heat from a high temperature external heat source150to energize first turbine driven generator154via source recovery heat exchanger158followed by recovery of exhaust heat from first turbine driven generator154to energize second turbine driven generator108. First stage heat recovery from primary exhaust air111of first turbine driven generator154is shown and may be replicated in parallel flow relation by additional cascaded flow paths (not shown) at diminishing temperature. Such optional additional flow paths, fed by cryogenic working fluid, include a recovery heat exchanger and engine.

A second innovative feature is feed of liquid air105into first and second electric driven cryo-compressors152,156via regulator146. The mixture of liquid air105and cryo-cooled atmospheric air103is a cryogenic heat sink providing least compression work, to increase thermal efficiency of system200.

In addition, an innovative operational feature, load shifting, provides liquid air105for cryo-compression. Relatively constant output at peak efficiency of system200is maintained during off-peak electric demand by shifting electric output of first and second turbine driven generators154,108to liquefier112via regulator146, as required. Advantages of load shifting are increased time-average thermal efficiency and reduced thermal transients.

Exemplary design point performance of the cryo-compression prime mover and air liquefier ofFIG.2ais described for recovery of heat from a high temperature [>427° C. (800° F.)] heat source to power an air turbine expansion system. The described turbine-generator arrangement will reduce minimum generating capacity of available micro-turbines from about 25 kWe to 12 kWe. The example is based on the lower end of micro-turbine-generator capacity range (˜25 kWe to 500 kWe), in which small units have higher incidence of off-peak operation, and illustrates the effect of the parallel arrangement of the two turbine generators on rotor speed limit, which is inversely proportional to capacity. Micro-turbine-generators are used for distributed generation, however turbine-generators of the present invention also increase the capacity of large central station generators. Two-stage heat recovery is considered, rather than a more complex and higher performance, multi-stage secondary recovery system. Equivalent fuel consumption is reduced, as compared to a fully recuperated turbine driven generator with ambient intake air, due to efficient heat recovery combined with cryo-compression of the working fluid. Estimated thermal efficiency of the cryo-compression air turbine driven generators is 70%, or ˜2.5 times as for other advanced recovery cycles. Cryo-compression alone reduces compression work of air turbines to about 14% of total generating capacity, as compared to 55% with ambient intake air. First turbine driven generator operating conditions are; pressure ratio=2.3 at air inlet temperature=838° C. (1540° F.) and rotor speed=100,000 rpm. Second turbine driven generator operating conditions are; pressure ratio=1.5 at air inlet temperature=615° C. (1140° F.) and rotor speed=100,000 rpm. Cryo-compressor inlet air temperature=−173° C. (−280° F.). Sufficient air is liquefied to meet the cryo-compression liquid air requirement of 2.6 kg/kWe (5.7 lb/kWe), based on an estimated specific power requirement of 1100 kJ/kg (475 Btu/lb) of an advanced air liquefier. Load shifting to the liquefier compressor during off-peak electric demand provides relatively constant turbine driven generator output at peak efficiency, in effect, reducing energy required for air liquefaction. In addition, thermal transients of system100are reduced.

Now referring toFIG.2b, a schematic of an alternate preferred embodiment of the energy recovery system100of the present invention is provided. System300pressurizes atmospheric air103and directly recovers energy in the form of pressure and heat from the energy source102, such as the fuel of a combustion engine or fuel cell. In system300, electric output for motor vehicle prime mover application is generated via an internal combustion second engine driven generator170.

In system300, first cryo-compressor128is turbine driven cryo-compressor168. Second cryo-compressor130is third electric driven cryo-compressor282. (It is understood that this is the sole electric driven cryo-compressor in system300, but has been designated the “third” so as to avoid confusion with first and second electric driven cryo-compressors152,156in system200). Engine138is compressor drive turbine174. Engine driven generator144is reciprocating engine driven generator176. Energy source102is second engine driven generator170with fuel supply172. (Second engine driven generator170is a separate component from engine driven generator144, which is reciprocating engine driven generator176in this embodiment.) Fuel supply172is preferably hydrogen.

In system300, air liquefier112is the preferred air re-liquefier288. Although air re-liquefier288is only shown inFIG.2b, it is understood that air re-liquefier288may be used in any embodiment of system100. Air re-liquefier288requires less energy to operate, as it does not have to process sensible heat and only absorbs and rejects the latent heat of the liquefying air to atmosphere. An example of a commercially sold air re-liquefier288is that sold under the trademark Cryomech, used for re-liquefying liquid nitrogen, the first stage coolant in production of liquid helium. An example of a commercially sold air liquefier112that does not include the additional benefits of air re-liquefier288is that sold under the trademark Nikkiso-Cosmodyne.

Unlike in system200, in system300, turbine driven cryo-compressor168is not powered by electric regulator146. Instead, turbine driven cryo-compressor168and compressor drive turbine174are in mechanical communication such that rotations of their respective rotors is synchronized.

Like system200, system300may also include first and second liquid air pumps160,162and first and second storage valves164,166that may be powered by electric regulator146.

System300may include first and second cryo-air extraction junctions278,280; first and second liquefier valves272,274; and liquefier junction276. First cryo-air extraction junction278is disposed between first cryo-recuperator132, to which the second portion of atmospheric air103bis provided, and first cryo-mixing junction120.

A portion227of the second portion of atmospheric air103bis extracted at first cryo-air extraction junction278so that not all of the second portion of atmospheric air103bis provided to first cryo-mixing junction120. Second cryo-air extraction junction280is disposed between second cryo-recuperator134, to which a third portion of atmospheric air103cis provided, and second cryo-mixing junction122. A portion229of the third portion of atmospheric air103cis extracted at second cryo-air extraction junction280so that not all of the third portion of atmospheric air103cis provided to second cryo-mixing junction122. First and second cryo-air extraction junctions278,280are in fluid communication with liquefier junction276. First liquefier valve272is disposed between first cryo-extraction junction278and liquefier junction276and controls a flow of portion227that is provided to liquefier junction276. Second liquefier valve274is disposed between second cryo-extraction junction280and liquefier junction276and controls a flow of portion229that is provided to liquefier junction276. Portions227,229of atmospheric air103are provided to air re-liquefier288for re-liquefaction. These additional components, first and second cryo-air extraction junctions278,280; first and second liquefier valves272,274, and liquefier junction276, are required for extracting and re-liquefying the cryo-air. As such, their inclusion is necessary only when air liquefier112is air re-liquefier288, as discussed above.

Complimentary fluid flow paths are fed by the cryogenic working fluid. A first fluid flow path begins with the entry of primary air107into engine driven generator170, where primary air107supports combustion of fuel from fuel supply172. Primary air107is heated and expelled from engine driven generator170as primary exhaust air111; continues on to compressor drive turbine174where it expands; continues on to engine recovery heat exchanger140in the form of primary exhaust air111; and is exhausted from engine recovery heat exchanger140in the form of primary exhaust air111. The second fluid flow path begins with entry of secondary air109into engine recovery heat exchanger140. Secondary air109recovers exhaust heat from primary exhaust air111in engine recovery heat exchanger140; and continues on to reciprocating engine driven generator176where it expands and is exhausted as secondary exhaust air113. The first and second fluid flow paths compliment and facilitate one another with their fluid heat exchange.

The first innovative feature of system300is recovery of engine exhaust gas pressure to drive turbine driven cryo-compressor168followed by recovery of exhaust heat from compressor drive turbine174via engine recovery heat exchanger140to energize reciprocating engine driven generator176. First stage heat recovery from primary air111discharging from compressor drive turbine174is shown, which may be replicated in parallel flow relation by additional cascaded flow paths (not shown) at diminishing temperature. Such optional additional flow paths, fed by cryogenic working fluid, would include a pre-heater, recovery heat exchanger and engine.

A second innovative feature is feed of liquid air105into cryo-compressors128,130via regulator146. The mixture of liquid air105and cryo-cooled atmospheric air103is a cryogenic heat sink providing least compression work, to increase thermal efficiency of system300.

A third innovative feature is recirculation and extraction of a portion of cryo-working fluid to re-liquefier288. Re-liquefaction enables rejection to atmosphere of only the latent heat of the extracted air227and229at saturation temperature of cryo-compression, thus eliminating rejection of sensible heat and reducing the specific energy requirement of liquefaction.

In addition, an innovative operational feature, constant load, combines engine driven generator load and liquefier load to store and dispense liquid air205during highway driving. Regenerative braking is sufficient to meet liquid air demand during urban driving. Higher engine driven generator efficiency with constant load operation supports the added re-liquefier power requirement. Advantages of constant load operation are increased time-average thermal efficiency and reduced thermal transients.

Exemplary design point performance of the cryo-compression combustion engine/air re-liquefier ofFIG.2is described for recovery of heat and pressure from engine exhaust to engine intake air and to a single stage reciprocating engine. Only single stage heat recovery is considered for motor vehicle application, rather than a more complex and higher performance multi-stage recovery system.

Fuel consumption is reduced as compared to a turbo-charged internal combustion engine with ambient intake air, due to efficient heat recovery and cryo-compression of the working fluid. Estimated peak liquid air consumption is based on net power output of a 1590 kg (3500 lb) car at highway speed of 120 km/h (75 mph). Equivalent gasoline mileage and liquid air consumption at this speed=18.7 km/L (44 mpg) and 16 lb liquid air/lb H2, respectively. Engine operating conditions are: net power output=30 HP, compression ratio=10, excess air ratio=1.0, exhaust temperature=615° C. (1140° F.) at 6500 rpm and pressure ratio to the turbine driven cryo-compressor=2 at 200,000 rpm. Reciprocating engine operating conditions are: pressure ratio=20 at air inlet temperature=560° C. (1040° F.) at 6500 rpm. Thermal efficiency of the spark ignition engine at 120 km/h (75 mph) is increased from ˜25% to ˜45% with cryo-compression and exhaust heat recovery. It is estimated that addition of a second recovery flow path would increase overall efficiency to 60%. Sufficient air is re-liquefied to meet the cryo-compression requirement based on regenerative braking in an urban driving cycle. For the highway driving cycle, higher engine driven generator efficiency due to combined load with the re-liquefier, supports the re-liquefier power requirement, while excess liquefied air is held in storage. Re-liquefaction improves the specific power requirement of air from 0.77 kWh/kg (1200 Btu/lb) liquefied to 0.52 kWh/kg (800 Btu/lb) re-liquefied.

Now referring toFIG.3, a block diagram illustrating the steps of the method of the present invention are provided. Understanding system100and its preferred embodiments of systems200and300, one of at least ordinary skill in the art will recognize that method400that is a method for cascaded energy recovery inherent in the operations of these systems. In its most basic form, the steps of method100are providing heat generated by a first heat source to an n prime mover402, wherein the n prime mover generates n prime mover exhaust heat when the heat is provided from the first heat source to the n prime mover; providing the n prime mover exhaust heat to an n+1 prime mover404, wherein the n+1 prime mover generates n+1 prime mover exhaust heat, and wherein steps402and404are achieved through fluid flow between the first heat source, the n prime mover, and the n+1 prime mover; and406providing cryogenic liquid working fluid to feed the fluid flow, wherein the cryogenic liquid working fluid provides cryogenic compression of working fluid to each of the prime movers. As used in reference to method400, n=first; n+1=second; n+2=third; etc. . . . . It is preferred that the method also include the step of repeating step404until the n prime mover exhaust heat is insufficient to cause the n+1 prime mover to generate n+1 prime mover exhaust heat408, wherein on each execution of this repeating step, n increases by 1. In other words, exhaust heat from the first prime mover is provided to the second prime mover. Exhaust heat from the second prime mover is provided to the third prime mover. Exhaust heat from the third prime mover is provided to the fourth prime mover, etc. . . . . This continues until the n prime mover cannot provide sufficient heat to the n+1 prime mover for the nth+1 prime mover to generate its own exhaust heat. In this way, the original heat generated by the first heat source is used as fully as possible. As described above, with reference to the systems of the present invention, the first heat source is preferably a fuel gasifier, a nuclear reactor, or a solar concentrator. Also as described above with reference to the systems of the present invention, the prime movers may be: generally, engine138and engine driven generator144(as shown inFIG.1) or, specifically first and second turbine driven generators154,108(as shown inFIG.2a) or compressor drive turbine174and reciprocating engine driven generator176(as shown inFIG.2b). Also as described above with reference to the systems of the present invention, the steps of providing heat or exhaust heat are preferably achieved through heat exchangers.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions would be readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the description should not be limited to the description of the preferred versions contained herein.