Patent Application
20230382725
It is proposed that reversible endothermic and exothermic fluid thermochemical means be used for efficiently storing and utilizing H2 in the form of a thermochemical battery rather than an electrochemical battery. An example of an endothermic fluid is cyclohexane (C6H12). An example of an exothermic fluid is benzene (C6H6) plus hydrogen (H2). Since the process revolves around the use of benzene (C6H6) as a means of cyclically storing and giving off H2, the process is termed the “Benzene Battery” (BB) cycle. By reversible is meant that the elements of a BB cycle are completely contained in a cyclical process that requires only the input and removal of thermal energy to continually operate. By allowing H2 to be stored in a liquid state at Standard Temperature and Pressure (STP), the BB cycle is seen as useful for efficiently storing electricity and/or heat energy for later and/or distant use.
Essential to the function of a BB cycle is the Bland/Ewing (B/E) thermochemical heat engine cycle (B/E Cycle) proposed in U.S. Pat. No. 3,225,538, and in part in U.S. Pat. Nos. 3,067,594 and 3,871,179. The present invention proposes methods and apparatus for improving the technology disclosed in U.S. Pat. Nos. 3,225,538, 3,067,594, and 3,871,179, wherein techniques are detailed for creating a unique thermochemical cycle involving “molecular expansion” and “molecular compression”, termed the Bland/Ewing Cycle (B/E Cycle) after the co-inventors.
Also essential to the function of a BB cycle is the proposal to segment the B/E Cycle into endothermic and exothermic segments, proposed in US Patent Application #18-0954634. As shown in US Patent Application #18-0954634, a complete Bland/Ewing Combined Heat and Power (B/E-CHP) cycle or Bland/Ewing Combined Cycle (B/E-CC) is composed of an endothermic segment and an exothermic segment.
The various endothermic and exothermic segments described in US Patent Application #18-0954634 are referentially included herein.
It is proposed that reversible endothermic and exothermic fluid thermochemical means be used for efficiently storing and utilizing H2 in the form of a thermochemical battery rather than an electrochemical battery. By allowing H2 to be stored in a liquid state at STP, the BB cycle is seen as useful for efficiently and inexpensively storing electric and/or thermal energy for later and/or distant use.
The present invention proposes a thermochemical battery cycle. By allowing H2 to be stored in a liquid state at STP, the BB cycle is seen as useful for efficiently and inexpensively storing electric and/or thermal energy for later and/or distant use. The present invention is generally based on U.S. Pat. Nos. 3,225,538, 3,067,594, and 3,871,179, wherein techniques are described for creating a unique thermochemical cycle, termed the Bland/Ewing Cycle (B/E Cycle) after the co-inventors, involving “molecular expansion” and “molecular compression”. The present invention is also based on US Patent Application #18-0954634 which proposes optimizing endothermic and exothermic “segments” for the creation of either Combined Heat and Power (CHP) or Combined Cycle (CC) applications.
The invention will be illustrated in greater detail by description in connection with specific examples of the practice of it and by reference to the accompanying drawings, in which:
Several other means of constructing B/E endothermic and exothermic cycle segments capable of producing net work out are referentially included from US Patent Application #18-0954634.
It is proposed that reversible endothermic and exothermic fluid thermochemical means be used for efficiently storing and utilizing H2 in the form of a thermochemical battery rather than an electrochemical battery. An example of an endothermic fluid is cyclohexane (C6H12). An example of an exothermic fluid is benzene (C6H6) plus hydrogen (H2). Since the process revolves around the use of benzene (C6H6) as a means of cyclically storing and giving off H2, the process is termed the “Benzene Battery” (BB) cycle. By reversible is meant that the elements of a BB cycle are completely contained in a cyclical process that requires only the input and removal of thermal energy to continually operate. By allowing H2 to be stored in a liquid state at STP, the BB cycle is seen as useful for efficiently and inexpensively storing electricity and/or heat energy for later and/or distant use.
Additionally proposed is the use of a BB cycle as a means of making a Regenerating Fuel Cell (RFC) more practical. In an RFC system, water (H2O) is split by electrolysis. The resulting H2 and O2 are then stored. Later and or/distantly, the H2 and O2 are united in a fuel cell that regenerates the H2O and creates electricity, heat, and. An RFC is seen as useful as a means for storing electricity and heat energy. The stored components are H2O, O2 gas, and H2 gas. A BB RFC system differs in its ability to store the H2 in liquid form at STP, avoiding the need to store the H2 as either a highly compressed gas or as exceedingly cold H2. It is also advantaged over the use of storage by metal hydrides by the ability to store and/or transport H2 in liquid form at STP.
Additionally being proposed is the use of an Endothermic/Exothermic Reactor Exhaust Compressor or E.R.E.C. as a means of increasing the overall efficiency of a BB cycle. The concept of the E.R.E.C as applied to increasing the efficiency of a B/E-CHP or B/E-CC exothermic segment was proposed in US Patent Application #18-0954634. It is herein proposed as a means as well of increasing the efficiency of the endothermic segment of a B/E-CHP cycle, B/E-CC cycle or BB cycle.
Additionally proposed is the use of part or all the stored H2 as a fuel which is released by an endothermic fluid's conversion to exothermic fluid. The H2 fuel may be combusted as a means of supplying the endothermic thermal energy required for the release of the H2 from the endothermic fluid. This application of the BB cycle is seen as useful for allowing the release of H2 regardless of the local availability of a sufficiently high temperature source of thermal energy to drive he endothermic catalytic process. The H2-generated heat may be used directly or it may take the form of waste heat from an H2 combustion engine or process.
Additionally proposed is the use of heat proceeding from H2 fuel being combusted as a means of supplying the endothermic thermal energy required to drive a B/E-CC endothermic segment engine system.
The BB Cycle
In a BB cycle, H2 is generated at some location by some means. An exothermic segment, such as one described in US Patent Application #18-0954634, is used to store the H2 by the exothermic conversion of a fluid mix, such as C6H6+3H3, into an endothermic fluid, such as C6H12. The endothermic fluid is then stored until it is required. It may then be removed from storage and reconverted into the exothermic fluid by passing it over a catalyst at some pressure and temperature.
The BB cycle concept is defined by the following theoretically reversible chemical processes:
6H2O+energy=6H2+O2;6H2+2C6H6=2C6H12&energy;2C6H12+energy=2C6H6+6H2;6H2+3O2=6H2O&energy
Taken separately:
6H2O+energy=6H2+O2
That is, water is separated with energy (usually electrical) into hydrogen and oxygen.
6H2+2C6H6=2C6H12&energy
Hydrogen gas is thermo-chemically bound to benzene to produce cyclohexane and energy.
2C6H12+energy=2C6H6+6H2
Cyclohexane is thermo-chemically separated with energy to produce benzene and hydrogen.
6H2+3O2=6H2O&energy
Oxygen and hydrogen are electrically or thermo-chemically bound to produce water and energy.
Ignoring the energy constituent, the BB cycle can be written as
6H2O↔6H2+3O2↔(3O2)+2C6H6+6H2↔(3O2)+2C6H1
where↔indicates a theoretically reversible process.
Ignoring the O2, which might not require storage in all instances, the BB cycle can be written
6H2O↔6H2↔2C6H6+6H2↔2C6H12
which simplifies to
3H2O↔3H2↔C6H6+3H2↔C6H12
The critical stored components of a BB cycle are thus H2O, C6H6, and C6H12, all of which may be stored as liquids at STP. O2 gas must also be stored unless it is readily available, such as within Earth's atmosphere. Note that H2 is essentially thermo-chemically stored as a liquid at STP.
The 2009 NASA RFC Proposal
In February of 2009 or earlier, NASA proposed an RFC system for use on the lunar surface, as disclosed in a slide show available on the NASA website:
The NASA RFC systems may be generally defined by the following theoretically reversible chemical process:
2H2O+energy=2H2+O2;2H2+O2=2H2O&energy
Specifically, in the NASA RFC systems, water is split by electrolysis powered by solar energy over the two week long lunar “day”. The resulting H2 and O2 are then stored. Over the two week long lunar “night”, the H2 and O2 are united in a fuel cell that creates electricity and heat. The stored components are H2O, H2 gas, and O2 gas.
In the 2009 NASA analysis, five different approaches for storing the H2 and O2 gases for an RFC are discussed: four high pressure (NASA H P System), and two cryogenic (NASA Cryo RFC system). H2 and O2 are compressed in high pressure tanks in the NASA H P RFC system approach. In the NASA Cryo RFC system approach, H2 and O2 are stored as liquids, reducing the mass of the overall system by greatly reducing the tank mass. Per slide 51, the two systems, which are intended to produce ˜1,770 kWe of stored electrical energy for use during the 2 week long lunar night, will have a specific energy (power density) of 434, 509, and 598 W-hr/kg for the NASA H P RFC system versions, and 913 and 1,153 W-hr/kg for the NASA Cryo RFC system versions.
The NASA H P RFC system includes 3,238, 2,732, and 2,312 kg for tanks. The RFC NASA Cryo system reduces tank masses to 467 and 393 kg. The top end NASA Cryo RFC system also includes 104 kg for drying/liquification equipment, 267 kg for power for cryogenic storage, and 10 kg for additional radiator and piping mass, or a total additional mass of 381 kg. Total system mass is also given. Total mass for the NASA H P RFC system equaled 4,607, 3,931, and 3,347 kg. Total mass for the NASA Cryo RFC systems equaled 2,191 and 1,760 kg. The large difference in power density for the two NASA RFC systems clearly comes down to the greater mass of pressurized storage tanks, as shown on slide 51.
The proposed NASA RFC power plant was predicted to provide 6.4 kW-h of electricity on the lunar surface during periods of zero solar insolation. To convert H2 and 02 back into electricity will always yield significantly less than 100% electricity. For 6.4 kW-h of electricity output, a 70% fuel cell conversion rate was assumed in the 2009 NASA analysis (sheet 51). That would require (6.4/0.7=) 9.1 kW-h output of H2, assuming the low heat of H2 combustion or 33.3 kW-h/kg. That in turn equates to an H2 mass requirement of 0.273 kg/hour of H2. It is known that, for the NASA RFC, 87 kg of liquid H2 and 692 kg of liquid O2 was proposed for a total of 779 kg of “exothermic fluid”. That would equate to 318 hours or about 13.3 days of power, which would be about right for the approximately 2 weeks that most of the lunar surface goes without sunlight during the lunar night.
The BB RFC System
The operation of the a BB RFC would exactly match that of the BB cycle, with the additional requirement that the H2 generated would power an RFC. As a result, making comparisons between the two proposed systems is relatively simple.
Practicality Comparison:
If C6H6 is used to store H2 on one side and the H2 is directly released into an H2 oxidizer on the other side, the need to store H2 as either a very cold liquid or as a very high pressure gas is eliminated.
Specific energy (power density) comparison:
On the lunar surface, specific energy is extremely important. Assuming the SpaceX Starship is used, to put an object on the lunar surface requires approximately 300 times its mass on the Earth's surface. From above, the specific energy for the to produce 1,770 kWe of stored electrical energy for use during the 2 week long lunar night, will have a specific energy (power density) of 705 W-hr/kg for the NASA H P RFC system version and 1,153 W-hr/kg for the NASA Cryo RFC system version.
At Standard Temperature and Pressure (STP) (1 atm and 273.14 K (491.7° R)), C6H12 (liquid) has a mass of 84.16 g/mol. C6H6 (liquid) has a mass of 78.11 g/mol. The difference, or 6.05 grams, is essentially equal to 3 moles of H2, which has a mass of 2.02 g/mol.
The total mass of H2 required for electrolysis, as in the NASA RFC, equals 87 kg of H2. For a BB RFC system, that would require 43,000 moles of H2. At 3 moles per mol of C6H12, total C6H12 required equals 1,108 kg, or (1108/779=) 1.4× the mass of the NASA RFC exothermic fluid.
A comparison of the NASA H P RFC, NASA Cryo RFC, and a “BB Cryo RFC” system that takes into account the ability to store H2 as a liquid would essentially “borrow” from both NASA systems. For liquid O2 storage, a more massive tank would be required than for the C6H6 and C6H12 storage tank or tanks. Also, less mass would be required for the BB Cryo RFC system than for those systems required by the NASA Cryo RFC system but not required for the NASA H P RFC system.
It is known that, for the NASA RFC, 87 kg of liquid H2 and 692 kg of liquid O2 were proposed. The total mass for both H2 and O2 cryogenic storage tanks is estimated at 393 kg. The individual mass for the H2 and O2 tanks is not given. However, we know that liquid H2 has a density of 70.85 g/L and that liquid O2 has a density of 1.141 kg/L. For 87,000 g of liquid H2, volume would equal (87,000/70.85=) 1,228 L. For 692 kg of liquid O2, volume would equal (692/1.141=) 606 L. That is an H2 to O2 volume ratio of (1,228/606=) about 2 to 1. Since H2 must be far more extensively insulated than O2, and since pressure is not an issue, it is reasonable to assume that the H2 tank has twice the mass of the O2 tank, and is thus equal to about (393/3=) 131 kg. Assuming a single storage tank with a separator can be used to store both the C6H6 and the C6H12, and especially since it would not be necessary to store those liquids at cryogenic temperatures, it can be assumed that the tank would have about the same or less mass ratio as the liquid O2 tank. Since that ratio equals 5.28:1, the mass of the C6H12/C6H6 storage tank would equal about 354 kg.
For the BB Cryo RFC cryogenic O2 storage system, additional mass will be considered equal to about half of the NASA Cryo RFC system, or about 190 kg. Total tank and extra cryo system mass would thus equal: Liquid O2 tank mass+Liquid C6H12/C6H6 tank mass+incidental cryogenic mass, or (131+354+190=) 676 kg.
In all other respects, the mass for the “BB Cryo RFC” system (with cryogenic O2 storage) would equal the mass of the NASA H P RFP system. Replacing tank mass for the NASA H P RFP system leaves 1,369 kg. Adding BB Cryo RFC tank plus incidental cryogenic mass (676) and the C6H12 mass (1,108 kg) equals a total mass for the BB Cryo RFC system of 3153 kg.
How does that compare to the NASA Cryo RFC system? At 1.137 kW-h/kg and a 1,760 kg mass, total power output equals 2001.12 kW-h The BB Cryo RFC system therefore has a specific power of 0.631 kW-h/kg, or masses about 80% more than the NASA Cryo RFC system.
However, the BB Cryo RFC system requires something the NASA Cryo RFC system doesn't: It requires a heat source at a sufficient temperature to release the H2 from endothermic fluid. This is a critical difference, since there are times when a source of sufficiently high temperature thermal energy is not available to disassociate the endothermic fluid. In the application that NASA is considering, the H2 needs to be released during the lunar night.
The BB RFC Self-Heating System
It is proposed that combustion of part of the H2 released by the endothermic fluid's conversion to exothermic fluid be used to supply the endothermic thermal energy required to release H2 from the endothermic fluid.
Assuming the low heat of combustion, 1 kg of H2 has a combustion value of ˜120,000 kJ (33.33 kW-h), or 120 kJ/gram (0.0333 kW-hour, 0.000555 kW-minute). 1 mol of C6H12 can release 3 moles or 6.06 g or H2. The combustion of 6.06 grams of H2 can theoretically supply 727 kJ. Since the combustion of 6.06 grams of H2 can theoretically supply 727 kJ, it is feasible to combust 30% of the H2 released by the endothermic fluid's conversion to supply the endothermic thermal energy required to release H2 from the endothermic fluid, thus liberating 70% of the H2 in the exothermic fluid, or approximately 4.234 grams (2.1 moles) of H2 per mol of C6H12. For the C6H12>C6H6+3H2 reaction, the required chemical temperature of reaction at 1 atmosphere is about 820 K (1,476 R, 547 C 1,016 F). However, the combustion of H2 can release thermal energy at a far higher temperature than that, so achieving the required temperature for thermochemical conversion is not an issue.
Unfortunately, decreasing the amount of available H2 per kg of C6H12 has two direct negative impacts on specific energy. First, it will require 30% more C6H12 for a given power output. Second, it will increase the amount of solar energy required to create the electricity to create a 30% increase in H2. The first impact will essentially increase the relative mass and thus the specific energy by 30%. That will increase the calculated specific energy for the BB Cryo RFC to 4,099 kg.
The BB with B/E-CC Self-Heating System
It seems clear that combusting 30% of the H2 released would appear to add inefficiency to a BB RFC. However, there is an alternative approach that can theoretically maintain specific power, and that is through the use of a Combined Cycle (CC) power plant
From https://en.wikipedia.org/wiki/Combined_cycle_power_plant: “A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy.”
If 30% of the H2 released is used as fuel to release the other 70% of H2, the 30% of H2 can be used to power a combustion engine. A H2-powered diesel engine can achieve at least 45% thermal efficiency. If an H2 combustion engine produced work with a 45% efficiency, and the 55% “waste” heat from that engine powered a bottoming cycle engine that also produced work with a 45% efficiency, then the overall efficiency of the CC engine would equal 45% plus another 45% of 55%. That is, total overall efficiency would equal 69.75%.
In other words, since the engine was producing the same efficiency as the fuel cell, it would make sense to simply use a larger CC engine to convert 100% of the H2. Such a BB CC system could thus theoretically maintain specific energy of about 630 W-h/kg.
In US Patent Application #18-0954634, a novel B/E-CC engine was proposed. By looking at the original B/E cycle as a combination of two engines, one being based on an endothermic segment and one being based on an exothermic segment, a theoretical CC “bottoming” engine was examined with a theoretical efficiency of about 46%. Since then, it appears to be possible to increase that theoretical efficiency.
BB RFC with RFC-Powered Heating System
In the NASA analysis referenced above, a 70% fuel cell efficiency was indicated. In theory, 30% of the potential energy is still available as waste heat, which exactly equals the energy required to drive an endothermic catalytic reduction of C6H12 to C6H6+3H2. If the temperature of that waste heat is sufficient to drive the endothermic reaction, even if no net work were developed, then the overall efficiency would still equal 70%. If the reaction were to take place at a small fraction of 1 atmosphere of pressure, then the required temperature could be reduced. At 1/100th of an atmosphere, the endothermic temperature requirement for a 99% conversion would equal about 600 K, and even larger pressure drops would continue to drop the required temperature for conversion.
BB RFC with B/E Cycle Endothermic Segment Expansion
There is one other approach to maintaining specific energy which is directly attributable to the Bland/Ewing Cycle as proposed in U.S. Pat. No. 3,225,538. In addition, US Patent Application #18-0954634 proposes that an endothermic segment can be a stand-alone heat engine.
Per the concept of the Bland/Ewing Cycle, an endothermic conversion of, for example, C6H12 product to C6H6+3H2 reactant occurs at constant temperature and constant pressure but at expanding volume. In fact, with 100% conversion of a quantity of C6H12 product, the conversion in volume is exactly equal to 1:4. That represents work out.
Note that in US Patent Application #18-0954634,
It may also be shown that, theoretically, the latent heat of just the vaporous C6H6 reactant, if passed in heat exchange with the C6H12 product, can supply all the thermal requirements to raise the product to the temperature of the endothermic reactor, including the thermal requirement to vaporize the C6H12, assuming a negligible amount of work in by a device called an E.R.E.C.. And because, per US Patent Application #18-0954634, a simple pump may be used to pressurize the endothermic fluid, there is only a negligible amount of pumping work required.
Even more usefully, the H2, if it could be separated out, for example by the process shown in
There are other techniques for gaining efficiency, such as using uncooled expanders and low friction bearings. And there is the possibility, as suggested in U.S. Pat. No. 3,871,179, to use a constant volume heat exchange process rather than a constant volume heat exchange process.
Finally, note that the efficiency at which work is produced by any heat engine, including an endothermic segment engine system, is directly determined by the temperature at which the engine is operated, and the temperature at which H2 can be combusted is extremely high.
For all these reasons, there is reason to expect that, by using a BB RFC with B/E cycle endothermic segment expansion, a full conversion of endothermic fluid is possible and much of the decrease in specific energy due to the 30% combustion requirement can be reversed.
The BB cycle concept can be defined as
6H2O+energy=6H2+O2
That is, water is separated with energy (usually electrical) into hydrogen and oxygen.
6H2+2C6H6=2C6H12&energy
Hydrogen gas is thermo-chemically bound to benzene to produce cyclohexane and energy.
2C6H12+energy=2C6H6+6H2
Cyclohexane is thermo-chemically separated with energy to produce benzene and hydrogen.
6H2+3O2=6H2O&energy
Oxygen and hydrogen are electrically or thermo-chemically bound to produce water and energy.
The critical stored components of a BB cycle are thus H2O, C6H6, and C6H12, all of which may be stored as liquids at STP. O2 gas must also be stored unless it is readily available, such as within Earth's atmosphere. Note that H2 is thermo-chemically stored as a liquid at STP.
In addition to these components, a BB cycle requires a heat source at a sufficient temperature to release the H2 from endothermic fluid.
In
In
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In
In
In
In
In
In
In
To complete the cycle, the exothermic fluid (C6H6 in this example) is recharged with H2.
In the application of the E.R.E.C. to the exothermic segment as proposed in US Patent Application #18-0954634, Claim 4 (revised), the E.R.E.C. was used to compress C6H6 (an olefin/alkene) to a slightly higher pressure following vaporization, such that when the C6H12 (a paraffin/alkane) exiting the exothermic reactor was passed in heat exchange with the lower pressure C6H6, the C6H12 was able to condense at a higher temperature than the C6H6 required for vaporization, thus substantially reducing the thermal energy otherwise required by the exothermic segment.
In the proposed application, an E.R.E.C. is used to compress a paraffin/alkane (C6H12) to a slightly higher pressure following vaporization, such that when an olefin/alkene (C6H6) exiting the endothermic reactor is passed in heat exchange with the lower pressure paraffin/alkane the olefin/alkene is able to condense at a higher temperature than the paraffin/alkane requires for vaporization, thus substantially reducing the thermal energy otherwise required by the endothermic segment.
In US Patent Application #18-0954634, under “Specification—Operation—Fourth Embodiment—B/E-CHP-H”, steps for an endothermic half-cycle are given, referencing
Referencing
As stated above, in essence, a BB cycle may be generally defined as
3H2O↔3H2↔C6H6+3H2↔C6H12
In essence, an RFC system may be generally defined by the following theoretically reversible chemical process:
2H2O+energy=2H2+O2;2H2+O2=2H2O&energy
That is, water is separated with energy (usually electricity) into hydrogen and oxygen; hydrogen and oxygen are converted to water, generating energy. That is, water is separated with energy (usually electricity) into hydrogen and oxygen; hydrogen and oxygen are converted to water, generating energy.
Shown with energy removed, the cycle simplifies to
2H2O↔2H2+O2
Increasing the moles transferred in the standard RFC system equals
6H2O↔6H2+3O2
For a standard RFC, the stored components are H2O, O2 gas, and H2 gas.
Unfortunately, gases in general are difficult to store in quantity, and H2 is perhaps the most difficult of all gases to store. A BB cycle is proposed as a means of solving this storage problem. As shown above, the addition to
6H2O↔6H2+3O2
of
(3O2)+2C6H6+6H2↔(3O2)+2C6H1
equals
6H2O↔6H2+3O2↔(3O2)+2C6H6+6H2↔(3O2)+2C6H1
which equates to
6H2O+energy=6H2+O2;6H2+2C6H6=2C6H12&energy;
2C6H12+energy=2C6H6+6H2;6H2+3O2=6H2O &energy
Therefore, for a BB RFC, the critical stored components are H2O, C6H6, and C6H12, all of which may be stored as liquids at STP. O2 gas must also be stored unless it is readily available, such as within Earth's atmosphere. That is, the BB RFC system differs in its ability to store the H2 in liquid form at STP, avoiding the need to store the H2 as either a highly compressed gas or as exceedingly cold H2 liquid. It is also advantaged over the use of H2 storage in metal hydrides by its ability to easily store and/or transport H2 in liquid form at STP.
In the BB RFC system, the BB cycle H2 storage technique is proposed as an alternative to the high pressure gas or liquid H2 storage techniques proposed in the NASA RFC concept. For example, three molecules of H2 may be stored in one molecule of benzene (C6H6) as cyclohexane (C6H12). Since C6H6 and C6H12 are both liquids, this essentially stores H2 in a liquid form. The generation of C6H12 (the endothermic fluid) from the catalytic reaction of C6H6+3H2 (the exothermic fluid) is an exothermic reaction, evolving a set quantity of heat per mol at a temperature that is totally dependent on pressure, with higher pressure generating higher temperature.
While heat is released when the exothermic fluid is combined to create the endothermic fluid, the generation of H2 from the endothermic fluid requires a thermal source. It is also, like the C6H6 plus H2 capture process, a function of temperature and pressure. In U.S. Pat. No. 3,225,538, Table I, chemical heat of reaction changes for C6H12↔C6H6+3H2 are given. In Table I, chemical heat change equals approximately 52.3 kilogram-calories/mol (kcal/mol) (219 kJ/mol) of C6H12 for both endothermic and exothermic reactions. The information given is for 1 atm (14.7 psi) constant pressure, but since heat is chemically stored, it would essentially be the same at any pressure or temperature driving the reaction.
Finally, note that exactly as much thermal energy is required to catalytically dissociate a mol of C6H12 into a mol of C6H6 and 3 moles of 3H2 as is given up during a catalytic conversion of a mol of C6H6 and 3 moles of 3H2 into a mol of C6H12. At any given pressure, the difference is only in the temperature of the reaction. Likewise, at any given temperature, the difference is only in the pressure of the reaction.
In operation, the operation of the a BB-RFC would exactly match that of the BB cycle, with the addition that the H2 generated would power an RFC.
There are times when a source of sufficiently high temperature thermal energy are not available to disassociate the endothermic fluid. For example, in the application that NASA is considering, the H2 needs to be released during the lunar night.
It is proposed that combustion of part of the H2 released by the endothermic fluid's conversion to exothermic fluid be used to supply the endothermic thermal energy required to release H2 from the endothermic fluid.
As mentioned earlier, for C6H12>C6H6+3H2, the required chemical temperature of reaction is about 820 K (1,476 R, 547 C 1,016 F). At Standard Temperature and Pressure (STP) (1 atm and 273.14 K (491.7° R)), C6H12 (liquid) has a mass of 84.16 g/mol. C6H6 (liquid) has a mass of 78.11 g/mol. The difference, or 6.06 grams, is equal to 3 moles of H2, which has a mass of 2.02 g/mol. Assuming the low heat of combustion, 1 kg of H2 has a combustion value of ˜120,000 kJ (33.33 kW-h), or 120 kJ/gram (0.0333 kW-hour, 0.000555 kW-minute).
Since the combustion of 6.06 grams of H2 can theoretically supply 727 kJ, it is feasible to combust 30% of the H2 released by the endothermic fluid's conversion to supply the endothermic thermal energy required to release H2 from the endothermic fluid, thus liberating 70% of the H2 in the exothermic fluid, or approximately 4.234 grams (2.1 moles) of H2 per mol of C6H12. Assuming a 90% conversion efficiency, 1 mol of circulated C6H12 would thus produce 1.886 moles of H2 massing 3.811 grams for use elsewhere, leaving 0.1 mol of C6H12 and 0.9 moles of C6H6 for circulation out of the exothermic fluid.
In operation, the operation of the a BB-RFC self-heating system would exactly match that of the BB cycle as shown in
Clearly, combusting 30% of the H2 released would appear to add inefficiency to a BB RFC. However, it is possible to reduce that inefficiently if the thermal energy of combusting 30% of the H2 released is being directed specifically at converting an endothermic fluid into an exothermic fluid. In other words, if all source heat goes directly into the endothermic reaction, the full 30% of endothermic fluid is converted into exothermic fluid. At the same time, work out will still be generated by a Bland/Ewing Cycle endothermic segment engine, as discussed above. In addition, the efficiency by which the exothermic fluid is produced can easily be increased by raising the temperature at which the reaction is made to take place, and the combustion of H2 can create extremely high temperatures.
In the original Bland/Ewing cycle proposed in U.S. Pat. No. 3,225,538, it may be recalled that one molecule of C6H12 was to be compressed but 4 molecules of exothermic mix were to be expanded. In essence, a method is herein being proposed to take advantage of exactly that thermochemical expansion process.
In US Patent Application #18-0954634,
In operation, one possible version of a BB-RFC with B/E endothermic segment-powered self-heating system would resemble the BB cycle as shown in
Alternatively, it is possible that a fuel cell may itself produce exhaust heat at a sufficient temperature to drive a catalytic reaction such as is shown in
In the NASA analysis referenced above, a 70% efficiency was indicated. In theory, 30% of the potential energy is still available, which exactly equals the energy required to drive an endothermic catalytic reduction of C6H12 to C6H6+3H2, particularly if the reaction were to take place at a small fraction of 1 atmosphere of pressure. As noted above, at 1/100th of an atmosphere, the endothermic temperature requirement for a 99% conversion would equal about 600 K, and further pressure drops would continue to drop the required temperature for conversion.
In operation, the operation of the one possible version of a BB-RFC with B/E endothermic segment-powered self-heating system would exactly match that of the BB cycle as shown in
It is obvious that the BB cycle energy storage and delivery process has a potential usefulness beyond the lunar surface. In fact, it can easily be shown to represent a meaningful alternative to the present hydrocarbon-combustion processes that currently underpin much of the human race's energy generation and distribution network.
For example, a process can be envisioned whereby:
Other thermochemical cycles are possible, as disclosed in U.S. Pat. Nos. 3,225,538, 3,067,594, and 3,871,179, and therefore the C6H12+heat↔C6H6+3H2 cycle is used as a general example. Also, pressure and temperature define endothermic and exothermic processes of heat absorption and rejection. Accordingly, all calculations herein should be considered only useful as means of generally illustrating the larger findings herein.
This application claims the benefit of provisional patent application EFS ID 45714697, Application Ser. No. 63/342,093, filed 14 May 2022 by the present inventor, which is incorporated by reference in its entirety. This field is related to heat engine cycles based on U.S. Pat. Nos. 3,225,538, 3,067,594, and 3,871,179.
| Number | Date | Country | |
|---|---|---|---|
| 63342093 | May 2022 | US |
