Combustion turbine system with increased pressure ratio

Abstract

A method, device and system for operating internal combustion engines with an increased pressure ratio and vehicle with this system. Internal combustion engines have a technically restricted pressure ratio, which limits the thermal efficiency. Gas turbines have so far had a maximum pressure ratio of 33:1, diesel engines have compression ratios of up to 23:1. An oxidizer is fed into the combustion chamber in (cold) liquefied condition under very high pressure. The fuel is also supplied in liquid form under high pressure. The pressure ratio of the oxidizer pump is 200, 500 or more. In the combustion chamber, the oxidizer and fuel react and expand to more than a thousand times the liquid volume. Depending on the fuel used, an expansion machine with a pressure ratio of around π=500 or more or an equivalent expansion ratio of ε=85 or more can be implemented.

Claims

1. A method for generating energy from a liquid oxidizer and a liquid or gaseous fuel in a turbo-electric system, wherein the method comprising the steps of: providing only liquid oxidizer as an oxidizer in a turbine system for a combustion process, injecting the oxidizer in liquid form from an oxidizer pump directly into a combustion chamber of a turbine: pressurizing the oxidizer in liquid form in the oxidizer pump instead of in a compression phase; evaporating the oxidizer only in the combustion chamber, then the oxidizer is burned together with the liquid of gaseous fuel, the oxidizer being brought to an injection pressure below the critical temperature of the oxidizer and injected into the combustion chamber; expanding combustion gases with a total pressure ratio of 200 or more (π>>200) in the turbine; delivering mechanical shaft energy from the turbine to a generator, wherein the generator is capable of being switched to an electric motor operation to drive the turbine in a startup operation; converting electrical current from the generator as required; and passing the electrical current on directly from the generator.

2. A device for performing the method according to claim 1 the device comprising: a vacuum-insulated vessel for storing the oxidizer; a fuel vessel for storing the liquid of gaseous fuel; wherein the oxidizer pump, which is arranged downstream of the vacuum-insulated vessel, with connection to the turbine, or with connection to an electric motor of the oxidizer pump; a fuel pump, which is arranged downstream of the fuel vessel, with a connection to the turbine, or with a connection to an electric motor of the fuel pump; the combustion chamber, with an injection plate located therein, with connection to the oxidizer pump and connection to the fuel pump; the turbine, which is arranged downstream of the combustion chamber; the generator, with connection to the turbine; a voltage/frequency converter, which is arranged downstream of the generator; and wherein an intermediate storage being an accumulator or capacitor for the electrical current, the intermediate storage being arranged downstream of the voltage/frequency converter.

3. A vehicle with the device according to claim 2, which is part of a drive unit, the vehicle comprising: the device from claim 2 for generating drive energy; and an electric drive motor.

4. The vehicle according to claim 3 with a device for cooling a passenger compartment, wherein an amount of cold liquefied air is removed from the vacuum-insulated vessel in order to cool the passenger compartment, and an admixture to fresh air or to circulating air takes place via an atomizer, via an evaporation container, a nebulizer, via a surface wetted with liquid, or via a membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the cycle described here as a clockwise thermodynamic cycle in the T-s diagram. An ideal Joule cycle (dashed line) is given as a comparison.

(2) FIG. 2 shows the cycle described as a clockwise thermodynamic cycle in a p-V diagram. The ideal Joule cycle (dashed line) is given as a comparison.

(3) FIG. 3 shows the system of a turbo-electric machine with a turbine, which works according to the method of FIG. 1 and FIG. 2.

(4) FIG. 4 shows the schematic structure of a vehicle that is powered by the turbo-electric drive system from FIG. 3.

(5) FIG. 5 shows the general structure of a passenger compartment air conditioning with atomized cryogenic liquid air.

(6) FIG. 6 shows the general structure of an evaporation container for cryogenic liquid air.

(7) (FIG. 1 and FIG. 2) EXAMPLE in the T-s diagram, respectively in the p-V diagram of Air.

(8) Explanation of the Changes in State.

(9) 1-2 Isentropic Compression

(10) The pressure of the cold liquid oxidizer is increased from p1=1 bar to p2=500 bar by a liquid pump

(11) The temperature is increased from T1=80K to T2=91K

(12) Supply of the specific compression work wt12=60 kJ/kg

(13) The specific entropy remains constant

(14) The specific volume decreases from V1=1.15×10.sup.−3 m.sup.3/kg to V2=1.08×10.sup.−3 m.sup.3/kg

(15) 2-3 Isobaric Combustion

(16) The combustion takes place continuously in a flame zone

(17) No pressure change

(18) The temperature rises from T2=91K to T3=2250K

(19) Heat supply q23=2750 kJ/kg

(20) The specific entropy increases from s2=2.8 kJ/kg/K to s3=7.3 kJ/kg/K

(21) The specific volume increases from V2=1.08×10.sup.−3 m.sup.3/kg to V3=1.35×10.sup.−2 m.sup.3/kg

(22) 3-4 Isentropic Expansion

(23) Expansion in a turbine

(24) The pressure relaxes from p3=500 bar to p4=1 bar

(25) The temperature drops from T3=2250K to T4=466K

(26) Withdrawal of turbine work wt34=−2208 kJ/kg

(27) The specific entropy remains constant

(28) The specific volume increases from V3=1.35×10.sup.−2 m.sup.3/kg to V4=1.38 m.sup.3/kg

(29) 4-1 Isobaric Heat Removal

(30) The gas is released into the environment

(31) Removal of specific heat q41=−608 kJ/kg

(32) The invention proposes a clockwise cycle (FIG. 1, FIG. 2) in which the oxidizer (in this example air) is supplied in a cold liquefied state. This eliminates the compression cycle. Instead, the liquid oxidizer is brought to the injection pressure below its critical temperature and injected into the combustion chamber. Under real conditions, the injection pressure must be higher than the combustion pressure in order to overcome it.

(33) Compared to the classic cyclic processes from thermodynamics, the exhaust gas temperature is a few hundred Kelvin (4) lower. The graph shows that the useful work (area within 1-2-3-4-1) is very large in relation to the amount of heat dissipated. The ideal thermal efficiency is over 80%. The specific useful work is about 4 times as large as in a comparable Joule/Brayton cycle. Equation: η=W eff/Q supp (in which: η . . . efficiency; W eff . . . effective work; Q supp . . . supplied heat)

(34) All oxygen carriers that can be stored in the cold liquefied state or in the liquid state at standard temperature, even under increased pressure, are suitable as oxidizers. This includes, for example, liquid oxygen (LOX) or oxygen-enriched, cold-liquefied air. Cold liquefied air (LAIR) with natural oxygen, nitrogen and argon components is particularly suitable, as it is non-toxic and does not pose a direct risk to the environment if it escapes in low doses. In addition, it can be obtained anywhere from the ambient air and produced inexpensively.

(35) The oxidizer (11) can be stored in a vacuum-insulated vessel (35). These are double-walled—similar to a thermos flask—and shielded against radiation so that the stored liquid remains cold for as long as possible. A daily evaporation rate of 1% of the content is unavoidable due to heating. Small amounts of evaporation can be released into the environment without danger. Typically, cold liquefied air is stored at approx. −190° C. (80K) under a maximum tank pressure of 5 bar. Refueling can be done without pressure via a well insulated hose.

(36) A major advantage of using liquid air instead of liquid oxygen is the greater mass throughput when a turbine is used. (Equation: Q=Wt×m; in which: Q . . . heat quantity; Wt . . . technical work; m . . . mass). Higher mass throughput results in more useful energy. 1 kg of gasoline requires around 14.7 kg of liquid air for stoichiometric combustion. When burning gasoline with pure oxygen (O2), the ratio would be around 1 kg gasoline to 3.5 kg oxygen.

(37) Another advantage of a turbine is that there are no push-in and push-out losses due to gas exchange. There is also no compression work that needs to be done. Only relatively small losses are to be expected, which result from pressure loss in the injection device, efficiency of the oxidizer pump (s), combustion chamber efficiency and turbine efficiency.

(38) Far less energy is required to pump the oxidizer in the (cold) liquid phase to a higher pressure level than to compress it in the gas phase. In contrast to gases, liquids are almost incompressible and hardly heat up with isentropic pressure increases. The isentropic pressure increase of cold liquefied air from 1 to 500 bar causes a temperature increase of about 11 Kelvin. The density of the fluid increases by about 7%. The proportion of drive energy required for the injection pump (s) is wastefully small. In a conventional gas turbine, which sucks in air in a stoichiometric ratio and compresses it, around 33% of the mechanical shaft energy is lost as drive energy for the compressor. It is known that gas turbines have to suck in and compress more air than required stoichiometrically in order to ensure internal cooling of the combustion chamber and the turbine.

(39) The push-in work and the compression work that occurs in a conventional reciprocating piston engine or a gas turbine in the gaseous state of aggregation do not have to be performed. The compression work is done, e. g. in a stationary air liquefaction plant with a much higher efficiency. In a power plant, electricity can mainly be used at night in the cheap electricity phase when there is already overproduction. The resulting pressure energy is stored in the oxidizer (e.g. cold liquefied air). During the combustion in the combustion chamber, a large part of this pressure energy is released again. If the oxidizer is kept in the liquid state until it enters the combustion chamber, i.e. below the critical temperature, the flow rate remains low. As a result, throttle and flow losses also remain low. The insertion work required when injecting into the combustion chamber is extremely small due to the low specific volume. Equation: W=p×V (in which: W . . . work; p . . . pressure; V . . . volume)

(40) The oxidizer (11) releases its energy together with the fuel after ignition in the combustion chamber (15). The combustion temperature can be around 2000-2400K, depending on the fuel used, if cold liquefied air is used as the oxidizer. If oxygen (O2) is used, the combustion temperatures are considerably higher. The fuel can be supplied in liquid or gaseous form. For adiabatic compression, however, gases require more energy than liquids, which are almost incompressible. Since relatively little fuel is needed in relation to the oxidizer, the losses are manageable. The combustion pressure is at least 200 bar, better 500 bar, or more.

(41) The combustion of a cold liquefied oxidizer in a high pressure combustion chamber results in two effects that affect the combustion temperature. On the one hand, the cold liquefied oxidizer causes a reduction; on the other hand, the high pressure causes an increase in the combustion temperature—compared to the calculated adiabatic combustion temperature under standard conditions. This is due to the higher reactivity of the molecules under pressure.

(42) (FIG. 3) The combustion chamber (15) has a very similar structure to the combustion chamber of a liquid rocket. Rocket combustion chambers achieve efficiencies of 95%-99.5%. This is due to the good distribution, mixing and turbulence of the combustion gases. The injection plate (15b) consists of several interconnected perforated disks. At the same time, it represents the cover plate of the cylindrical combustion chamber and injects fuel and oxidizer over a large area through many small holes over its entire surface.

(43) (FIG. 3, FIG. 4) Then the expansion takes place in a turbine (16) with a pressure ratio of at least π=200, better π=500 or higher. This dispenses with a compressor and would have to be optimized for processing solely a cryogenic liquefied oxidizer (11) and a fuel (12). Compressorless turbines are commonly referred to as expansion turbines or turboexpanders. These usually have a total pressure ratio of at most n=25.

(44) Last generation turbo expanders have a single stage with a pressure ratio of 25 and more. In order to achieve such a ratio with the best possible degree of efficiency, the flow is accelerated in a nozzle to 1.5 to 2.5 times the speed of sound before entering the turbine. See WO002014175765A1. Two stages with n=25 in series would already result in a total pressure ratio of π total=625. The required total pressure ratio can be achieved in a compact machine with only two turbine stages and good efficiency. Equation: π total=π1×π2

(45) Such a turbine can easily be coupled to an electric machine (e.g. a high-frequency generator) (FIG. 3). Compare ‘turbo-electric drive’ in locomotives and large ships. The polarity of this generator (31) can be reversed during start-up operation or, if required, in an electric motor operating state and thus drive the turbine if required. After voltage-/frequency conversion (32), the electrical current generated in this way can be temporarily stored in an accumulator (33) or in capacitor(s) before the electrical current is passed to the drive machine(s). In such a combination, braking energy recuperation is also possible. The current can also be sent directly to the electric drive motor(s) (34). The turbine can thus be kept at an optimized operating point for the highest possible efficiency.

(46) Since the fresh gas volume and the turbine speed are not related to one another, as is the case with the single-shaft turbine, the dynamics are very high. The machine takes less time to reach a desired load point. In addition, the connected generator can be polarized as an electric motor when starting up or if necessary (for boosting).

(47) (FIG. 4) The weight of a 100 kW turbine should be well below 10 kg and have a gross volume of less than 10 liters, including auxiliaries. In general, size and weight are comparable to an exhaust gas turbocharger in today's cars or trucks, also in terms of manufacturing costs. In this way, the turbine can easily be placed in a car where the transmission tunnel is today. The large vacuum-insulated vessel (35) for the oxidizer can be placed in the front of the vehicle.

(48) A turbine inlet temperature of 2400K is a bit too high according to the current state of the art. The materials used cannot withstand such high temperatures over the long term. Up to 1900K are common in large gas turbines with curtain or film cooling. Therefore, four possible approaches are proposed.

(49) Variant 1: The turbine is operated with an excess of oxidizer, approximately with λ=1.2 to λ=1.7. Comparable to the curtain or film cooling in a gas turbine, additional air is supplied to the combustion chamber walls and turbine stator/rotor. The consumption compared to a stoichiometric combustion would be increased accordingly. The disadvantage of the lower turbine inlet temperature is roughly offset by the advantage of the increased mass throughput. The specific useful work is therefore approximately retained.

(50) Variant 2: Additional water is injected into the turbine with the aim of cooling (similar to variant 1). The water required for this can be recovered from the exhaust gas. Every time it is burned, a not inconsiderable amount of water is produced anyway. Example: Gasoline-air in the stoichiometric ratio results in approx. 8% water vapor in the exhaust gas. Due to the principle-related low exhaust gas temperature, condensed water could be recovered from the exhaust gas tract, possibly with the help of heat exchangers.

(51) Variant 3: The turbine is operated in two stages with a high and low pressure section. After the isentropic expansion in the high-pressure part, the combustion gas is passed past the outer wall of the combustion chamber or passed into a heat exchanger and will be reheated there. The heat exchanger can be fed from the combustion chamber or the stator(s). This leads to a lower turbine inlet temperature upstream of the high-pressure turbine and a higher turbine inlet temperature upstream of the low-pressure turbine. As a result of the reheating (compare Clausius-Rankine cycle), the overall efficiency drops only slightly. The pressure loss in the heat exchanger and the longer gas paths have a negative effect.

(52) Variant 4: High temperature-resistant composite materials with very low thermal expansion are already being used in rocket engines in the nozzle neck area. For the next generation of gas turbine blades, a fatigue strength of up to 2000K could be achieved in the coming years through the use of ceramic matrix composites. These could be used in places that are particularly exposed to high temperatures, such as combustion chamber walls and the first turbine stage. The cost factor is minor, as the affected parts are much smaller. The turbine runner of a 100 kW turbine is estimated to be a few centimeters in diameter.

(53) The high combustion temperature (3) is seen as an opportunity, as a result of which almost flameless combustion can be achieved. The formation of nitrogen oxide (NOX), for example, can be largely suppressed. The combustion is cleaner and more complete.

(54) Due to the high pressure ratio the exhaust gases are cooled down to a turbine outlet temperature (4) of about 400-500K, which is unusually low for internal combustion engines (FIG. 1). There are extremely low thermal losses. The residual heat in the exhaust gas can still be used to partially or completely heat up the passenger compartment in winter.

(55) Due to the high efficiency, the combustion of natural gas (consists mainly of methane), hydrogen or a mixture of both (hythane) could prevail alongside conventional gasoline or diesel fuel. In all cases, a significantly smaller pressure vessel would be required for the same range. So far, fuel cell vehicles have not caught on mainly because of the high manufacturing costs. The pressure tank has a large share of the manufacturing costs. The hydrogen consumption would decrease by at least 30% compared to the fuel cell.

(56) The fuel consumption of a turbo-electric drive system with a turbine was compared with a turbo-gasoline engine (car) and a turbo-diesel engine (car) of the latest generation. Fuel consumption and CO2 emissions could be reduced by 50-65%. This corresponds to a realistic gasoline consumption of around 1.85-2.1 kg and a liquid air consumption of 28-32 kg in a mid-range vehicle with a running weight of 1500-1700 kg. As a result, that's around 57-66g CO2 emissions per km in the vehicle. The energy consumption for the production of 1 kg of liquid air in a large power plant is around 300 Wh/kg.

(57) Further Advantage: Air Conditioning with Liquid Air

(58) A secondary, but not insignificant, advantage when using cold liquefied air as an oxidizer in the above-described method in a vehicle is the possibility of air conditioning the interior with little effort.

(59) The task is to present a system that is used to cool the passenger compartment. It should be possible to achieve this with little technical effort, low weight and compact dimensions. In addition, it should require little drive energy, manage without the use of a refrigerant and also be able to be operated when stationary. To solve this problem, a method according to claim 2 is shown.

(60) There is a need for cooling in a vehicle in the summer, which is conventionally provided by a condensation air conditioning system with poor efficiency. A drive power of 4-6 kW is typical for an air conditioning compressor. On average, however, only around 0.25 kW cooling capacity is required in a car. Such cooling is ensured by the evaporation of approx. 2.5-3 liters of cold liquefied air per hour.

(61) Open or closed evaporation systems operated with water are known, e.g. from DE10221191A1 and DE19729077A1. However, water cannot provide the cooling energy of cold liquefied air by far. In addition, an open system increases the humidity in the cooled room and thus worsens the well-being of the passengers.

(62) Closed cryogenic systems that are operated in a closed circuit, especially filled with nitrogen, are also known, e.g. EP611934B1. However, such a system is complex and requires drive energy for at least one (refrigeration) compressor. All closed systems that are operated in the reverse Rankine cycle require mechanical drive energy, which is usually provided by an internal combustion engine. The overall efficiency is relatively poor due to the long efficiency chain (combustion engine—mechanical drive—refrigerant compressor—evaporator—heat exchanger). This means that an above average amount of energy is required for cooling. The additional pollutant emissions/CO2 emissions are high.

(63) KR102005020448A shows the atomization of cold liquefied nitrogen in a parked vehicle in summer. The disadvantage of pure nitrogen in an almost closed passenger compartment is that if it is enriched in the air it can lead to hypoxia and, in the worst case, to death from asphyxiation. Therefore, such a system can only deliver higher amounts of the coolant into the interior when there are no people or animals in the passenger compartment. Ventilation must be provided before entry.

(64) (FIG. 5, FIG. 6) At summer temperatures it is proposed to enrich the outside air supply (41) or the circulating air (42) for the interior with cold liquefied air (11) supplied from the vacuum-insulated vessel (35). This can be done by atomization (43) or spraying of the liquid air. Alternatively, the targeted evaporation in an evaporation container (44), over a surface wetted with liquid air, or a moistened membrane can be used for cooling. As an alternative or in addition to the liquid supply, the amount of evaporation that is generated in the vacuum-insulated vessel anyway due to insulation losses can be fed (45) into the passenger compartment in a metered manner. In both cases, it would make sense to filter the gaseous air produced in this way, for example in a (activated carbon) filter (46), before it is fed into the interior. Such a system does not require any high pressure compressors or pumps. Under certain circumstances, the overpressure of the vacuum-insulated container alone is sufficient to convey and atomize the required cold-liquefied air. A small delivery pump ensures the delivery rate in any case.

(65) Some aspects of the present technology can include a method for generating energy from a liquid oxidizer and a liquid or gaseous fuel in a turbo-electric system, characterized in that: 1.1) only liquid oxidizer (11) serves as oxidizer in the turbine system for the combustion process, this being in liquid form via the injection plate (15b) directly into the combustion chamber (15) of the turbine (16), 1.2) instead of the compression phase, the oxidizer is pressurized in liquid form in a pump (13), 1.3) the oxidizer only evaporates in the combustion chamber (15), then is burned together with the fuel, the oxidizer being brought to the injection pressure below its critical temperature and injected into the combustion chamber, 1.4) the combustion gases (15c) are expanded with a total pressure ratio of 200 or more (π>>200) in a turbine (16), 1.5) the mechanical shaft energy is delivered from the turbine to a generator (31), which can also be switched to electric motor operation, 1.6) the electrical current from the generator is converted as required (32) and 1.7) the electrical current with or without intermediate storage (33) is passed on to the electric drive motor(s) (34).

(66) Wherein the device for performing a method according to the above, consisting of: 2.1) a vacuum-insulated vessel (35) for storing the oxidizer (11), 2.2) a suitable vessel (36) for storing the fuel (12), 2.3) an oxidizer pump (13), which is arranged downstream of the vacuum-insulated vessel, with connection to the turbine, or with connection to its own electric motor (19), 2.4) a fuel pump (14), which is arranged downstream of the fuel vessel, with a connection to the turbine, or with a connection to its own electric motor (19), 2.5) a combustion chamber (15), with the injection plate (15b) located therein, with connection to the oxidizer pump and connection to the fuel pump, 2.6) a turbine (16) which is arranged downstream of the combustion chamber, 2.7) a generator (31), with connection to the turbine, 2.8) a voltage/frequency converter (32), which is arranged downstream of the generator and 2.9) an accumulator (33) or capacitor(s) for electrical current.

(67) Wherein a vehicle with a device according to the above, which is part of the drive unit, consisting of: 3.1) a device according to the above for generating drive energy and 3.2) the electric drive motor(s) (34).

(68) Wherein the vehicle according to the above with a device for cooling the passenger compartment, characterized in that: 4.1) a small amount of cold liquefied air (11) is removed from the vacuum-insulated vessel (35) in order to cool the passenger compartment (40) and 4.2) the admixture to the fresh air (41) or to the circulating air (42) can take place via an atomizer (43), via an evaporation container (44), a nebulizer, via a surface wetted with liquid, or via a membrane.

REFERENCE SIGNS

(69) 11 Oxidizer 12 Fuel 13 Oxidizer Pump 14 Fuel Pump 15 Combustion Chamber 15b Injection Plate 15c Combustion Gases 16 Turbine 17 Exhaust Gas 19 Electric Motor for Pump(s) 30 Turbine System 31 Generator 32 Voltage-/Frequency Converter 33 Accumulator or Capacitor 34 Electric Drive Motor 35 Vessel for Oxidizer 36 Vessel for Fuel 37 Vehicle 40 Passenger Compartment 41 Fresh Air 42 Circulating Air 43 Atomizer 44 Evaporation Tray 45 Feed Line 46 Filter