Bland/Ewing Cycle improvements

Abstract

The present invention proposes methods and apparatus for improving the technology disclosed in U.S. Pat. No. 3,225,538, U.S. Pat. No. 3,067,594, and U.S. Pat. No. 3,871,179, wherein are detailed techniques 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 advantage of the B/E Cycle is best exemplified in FIG. 3 and FIG. 4 of U.S. Pat. No. 3,225,538, where P/V and T/S charts indicate the potential for increased power density. This power density is a result of the reduced compression work following exothermic conversion of a single mole of gas relative to the increased expansion work following endothermic conversion of multiple moles of gas. The present invention improves power density and/or overall heat engine thermal efficiency by capturing otherwise-waste heat in the exhaust of a B/E Cycle heat engine.

Claims

1. A method similar to the transfer of heat comprising the steps of claim 1 in U.S. Pat. No. 3,225,538 and adding the steps of (1) vaporizing a pre-pressurized quantity of liquid or solid paraffin/alkane reactant at the preferred pressure regime of the endothermic reactor, (2) converting said vaporized and preheated paraffin reactant within the endothermic reactor to olefin/alkene and hydrogen product at constant pressure and temperature, (3) adjusting said olefin and hydrogen product pressure and temperature to the preferred pressure and temperature regime of the exothermic reactor, (4) converting said olefin and hydrogen product back to the original paraffin at constant temperature and pressure, (5) cooling the resulting paraffin back to a liquid or solid state, and (6) compressing said resulting paraffin to the preferred pressure regime of the endothermic reactor.

2. The method of claim 1, where a portion of the heat evolved by an earlier cycle of olefin and hydrogen product passing through an exothermic reactor is used to vaporize the pre-pressurized liquid or solid paraffin.

3. A method similar to the transfer of heat comprising the steps of claim 1 in U.S. Pat. No. 3,225,538 and adding the step of using a portion of the heat evolved by a cycle of olefin and hydrogen product passing through a high pressure exothermic reactor to add source heat to a second much lower temperature and pressure thermochemical cycle comprising the steps of claim 1 in U.S. Pat. No. 3,225,538.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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 drawing, in which:

[0012] FIG. 1 is based on FIG. 1 in U.S. Pat. No. 3,225,538, which details a cyclical cyclohexane/benzene+hydrogen (C6H12<=>C6H6+3H2) catalytic process, with temperatures in degrees Kelvin and pressure in atmospheres measured logarithmically to the base 10 (an insert graphs the base 10 into the righthand bottom of the figure).

[0013] FIG. 2 and FIG. 3 illustrate one approach to constructing a B/E-L Cycle. FIG. 2 is based on a pressure/volume/temperature/BTU/entropy chart from FIG. 70, Marks Mechanical Engineers 'Handbook, 1st edition, 9-148, Internal-combustion engines, which is incorporated herein by reference.

[0014] FIG. 3 is a schematic illustration of a Bland/Ewing Liquid Cycle (B/E-L) engine. A positive displacement piston-and-cylinder configuration is assumed in the specification below. Other approaches such as other positive displacement equipment or multiple turbine blade expanders are clearly also possible.

[0015] FIG. 4 and FIG. 5 are similar to FIG. 1 and FIG. 2. However, in FIG. 4 and FIG. 5, a dual thermochemical cycle heat engine is illustrated.

DETAILED DESCRIPTION

DescriptionFirst Embodiment

[0016] One improvement to the foundational invention relates to a method and apparatus for improving the efficiency of a B/E Cycle heat engine. In a B/E-L Cycle, much as in a steam engine, power density can be greatly increased by first pressurizing the exothermic fluid in a liquid or solid state and then converting the fluid into a vapor at constant pressure or volume.

[0017] In addition, one beneficial means for supplying the heat energy for vaporizing the exothermic fluid following pressurization is to use the exhaust heat liberated by the exothermic reaction. Since a B/E Cycle's exhaust heat is essentially equal to the heat liberated by the exothermic reaction, it is clear that to the degree the liberated heat can be used to vaporize the heat engine's exothermic fluid the thermal efficiency of the Cycle will be improved.

OperationFirst Embodiment

[0018] The cyclical and reversible hydrocarbon reaction of 1 mol of cyclohexane (C6H12) generating 1 mol of benzene (C6H6) and 3 mols of hydrogen (H2) will be used to illustrate the proposed inventions. Per FIG. 1, a C6H12<=>C6H6+3H2 catalytic process at a given temperature and pressure will be either endothermic or exothermic. In the proceeding example, FIG. 1 indicates points (shown as the intersection of thin red lines) where, at 5 atmospheres, the temperature for a 90% endothermic conversion equals 950 K, while, at 1 atmosphere, the temperature for 99% exothermic conversion equals 600 K. These two points will represent the intake and exhaust temperatures and pressures (and endothermic and exothermic reaction temperatures and pressures) for a theoretical B/E-L Cycle heat engine

[0019] The chart in FIG. 2 is used to indicate a first order estimate of a prototype B/E-L Cycle heat engine. Note that FIG. 2 temperatures are measured in degrees R. The colored lines show the proposed B/E-L Cycle superimposed on the chart, with most of the chart removed for clarity and labeling purposes.

[0020] Table 1 below indicates the steps represented by the letters shown in FIG. 2:

Table 1

[0021] AC6H12 isobaric & isothermal endothermic expansion.

[0022] BC6H6+3H2 isobaric exhaust at 75 psi & 1,710 R.

[0023] CIsobaric cooling via heat exchanger #1, dropping C6H6+3H2 to 1,180 R.

[0024] DIsobaric expansion completes, isentropic expansion begins.

[0025] EIsentropic expansion ends at 750 R.

[0026] FIsobaric reheating of C6H6+3H2 to 972 R via heat exchanger #2.

[0027] GC6H6+3H2 isobaric and isothermal exothermic compression (972 R).

[0028] HIsobaric cooling/condensation of the C6H12 via heat exchanger #3.

[0029] IPressurization of liquid C6H12 to 75 psi.

[0030] JPreheating of liquid C6H12 to 972 R via heat exchanger #3 & vaporization of liquid C6H12 at 75 psi via heat exchanger #4.

[0031] KPreheating of C6H12 to 1,560 R) via heat exchanger #1.

[0032] LHeat source preheating of C6H12 to 1,710 R via heat exchanger #5.

[0033] Since it was important to keep the cycle elements roughly within the chart's shown boundaries, for this initial analysis, a maximum endothermic temperature is assumed of 1,710 R, (950 K, 677 C., 1,250 F.). By lowering the degree of endothermic conversion (in this example to 90%), the required temperature input at a given pressure has been lowered. A maximum pressure of 5 atm (75 psi) is assumed. An exothermic pressure of 1 atm or 15 psi (shown as 0 in FIG. 1) is likewise assumed. For 99% exothermic conversion, that would equal a temperature of 972 R (540 K, 267 C., 512 F.).

[0034] Note that, in lowering the degree of endothermic conversion, the cycle's theoretical power density and hence potential real world thermal efficiency is lowered. That is, after the 90% conversion of 1 mol of C6H12, there will be 0.1 mol of C6H12, 0.9 mol of C6H6, and 2.7 mol of H2, resulting in a molecular expansion of 1-to-3.7 rather than 1-to-4.0. Recall that the model is only a general analysis for purposes of illustrating the larger findings herein. Thus, for this analysis, a positive displacement piston-and-cylinder configuration is assumed. Other approaches such as other positive displacement equipment or multiple turbine blade expanders are clearly also possible.

[0035] Following the flow process illustrated in FIG. 2, FIG. 3, and Table 1:

[0036] A. C6H12 will be converted to C6H6+3H2 in the endothermic reactor at a temperature of 1,710 R.

[0037] B. The product (C6H6+3H2) will undergo a molecular expansion of about 3.7:1.

[0038] C. In counterflow heat exchanger #1, the hot C6H6+3H2 (1,710 R) mixture will exchange heat with cool inflowing C6H12 gas (972 R), dropping the C6H6+3H2 mixture to 1,180 R (process B, C).

[0039] D. Work will be generated by a 75 psi, 1,120 R, constant pressure and constant temperature expansion. Prior to TDC, the exhaust valve will have closed. At very near TDC, the expander inlet valve will be opened by pre-compression of remnant gas. Since the clearance space is minimized above the piston, some recompression of the remnant gas will assist the intake valve process by increasing pressure within the expander. Shortly after TDC, the expander inlet valve will be quickly closed, for example by solenoid, having charged the expander cylinder with a quantity of gas at 75 psi.

[0040] E. An isentropic expansion will then occur as the piston travels to BDC, dropping the gas to 750 R and one atmosphere or 15 psi.

[0041] F. Following isentropic expansion, the exhaust valve will be opened and the expansion piston will exhaust, at constant pressure and temperature (15 psi and 750 R), the C6H6+3H2 mixture into radiant heat exchanger #2, located external to to the exothermic reactor, receiving heat from and partially cooling the reactor, and raising the C6H6+3H2 mixture to 972 R. Simultaneously, a previous charge of the C6H6+3H2 mixture at 15 psi will exhaust through the exothermic reactor, converting the gases to C6H12 at a constant pressure and undergoing a molecular compression of about 1:4.

[0042] G. Simultaneously, the previous charge of 15 psi C6H12 vapor at 972 R will exhaust into counterflow heat exchanger #3, which will ideally cool it to less than 600 R. If necessary, a charge of the cooled C6H12 vapor will simultaneously exhaust into a simple cooler to achieve final condensation into liquid C6H12 (point H). Any H2 gas entrained in the stream leaving counterflow heat exchanger #3 or the cooler will be separated from the liquid and directed back to the exhaust stream leaving the expander.

[0043] H. The liquid C6H12 will then be pumped up to a pressure of 75 psi.

[0044] I. The 75 psi liquid C6H12 will then be warmed by the 15 psi C6H12 flowing into counterflow heat exchanger #3. The 75 psi C6H12 liquid/vapor mix will then be used to further cool the exothermic reactor in radiant heat exchanger #4, simultaneously converted any remaining liquid into vapor at a temperature of 972 R.

[0045] J. The 75 psi C6H12 vapor will then be partially raised in temperature (1,560 R) by counterflow heat exchanger #1 from the C6H6+3H2 exiting the endothermic reactor.

[0046] K. The 75 psi C6H12 vapor will then use heat source radiant heat exchanger #5 to reach the required maximum temperature (1,710 R) just prior to being fed to the endothermic reactor.

[0047] L. And thus back to the initial state.

[0048] Looking at the C6H12 <=>C6H6+H2 reaction, benzene is chemically highly active. Therefore, parts of the engine that will come in contact with benzene such as the pistons, connecting rod, cylinder head, cylinder base, valves, connecting manifolds, seals, etcetera, will need to either be fabricated or plated from non-reactive materials such as stainless steel, teflon, or nickel.

[0049] The B/E Cycle creates unique challenges in the area of engine seals. Stainless seals are possible, but seal lubrication becomes an issue. Lubrication is generally important as a means of reducing friction losses and increasing engine durability, but lubricants in the working fluid could seriously impact the quality of a thermochemical cycle. Ideally, a non-reactive material that doesn't require lubrication such as teflon would be used where required. However, in the example of the C6H12<=>C6H6+3H2 cycle engine operating with a peak temperature of 1,710 (FIG. 2), that temperature is far in excess of the temperature teflon can support. Teflon seals will work up to about 1,000 R, but no commonly known low friction, non-lubricated, chemically inert seal can handle a constant temperature of 1,710 R.

[0050] One partial solution to the reducing seal temperature is to create a positive displacement blended expansion cycle. That is, work is done initially at constant pressure with the entry of the working fluid into the positive displacement expander via an inlet valve. After some expansion, the inlet valve is closed and an isentropic expansion process continues, thus dropping the average temperature of the working fluid that seals need to be subjected to per cycle. However, with an inlet temperature of 1,710, it will be difficult to achieve a temperature sufficient to protect the teflon piston seals with a simple isentropic expansion.

[0051] For the prototype, an additional solution is to exchange heat between the cooler C6H12 constant pressure reactant stream entering the endothermic reactor and the hotter constant pressure C6H6+3H2 product stream exiting the reactor. Of course, such a thermal exchange will significantly lower the potential thermal efficiency of the engine by reducing the peak temperature seen by the expansion process. For advanced versions, alternative high temperature pre-expanders such as turbo-expanders are an obvious solution to regain thermal efficiency.

[0052] One well known technique for exchanging heat between two gas/vapor streams is the use of a counterflow heat exchanger. The gas exhausting from the endothermic reactor flows through a manifold in immediate physical proximity to a manifold with gas entering the endothermic reactor, said manifolds thus exchanging heat and simultaneously heating the inflowing reactants while cooling the outflowing products. Note that this is normally done at constant pressure in the gas/vapor streams, and that the two gas/vapor streams don't necessarily need to operate at the same pressure.

DescriptionSecond Embodiment

[0053] In FIGS. 4 and 5, a cycle substantially below atmospheric pressure is shown. The red lines in FIG. 4 show the variance in pressures and temperatures for endothermic and exothermic reactions for the the high temperature B/E-CC engine, and the green lines in FIG. 4 show the variance in pressures and temperatures for endothermic and exothermic reactions for the low temperature B/E-CC engine. For the high temperature B/E-CC, endothermic temperature at about 90% conversion equals about 950 K, while exothermic temperature at 99% conversion equals about 550 K. For the low temperature B/E-CC engine, at a temperature of about 550 K, a 90% endothermic reaction will occur at a pressure of about 0.0075 atmospheres (0.11 psi). At a pressure of 0.001 atmosphere (0.015 psi) and a temperature of about 375 K, a 99% exothermic reaction will occur. The expansion ratio of the low temperature engine would equal (0.11/0.015=) 7.3 to 1.

OperationSecond Embodiment

[0054] The reason there may be a chance for such a cycle to actually be functional is due to the thermochemical expansion process of the B/E heat engine concept, which greatly increases power density for a given pressure regime. One place where there may be a meaningful application for such a cycle is in space, where a near-perfect vacuum exists.

[0055] As a result, there is no need to deal with external atmospheric pressure in the mechanical design. Thus, walls of chambers can be exceedingly thin and low mass, as can positive displacement elements such as pistons. And at the low temperatures, teflon seals would be adequate throughout, aiding in reducing friction. Volumes of positive displacement equipment can thus be very large, compared to terrestrial systems, yet very low in mass.

[0056] The possibility of an exceedingly low pressure engine also raises the possibility that a low temperature B/E-CC Cycle can actually produce useful work. One intriguing potential application is to use a B/E-CC cyclohexane thermochemical cycle on the lunar surface. Note that the final exhaust temperature of 375 K is sufficient to boil water at 1 atmosphere pressure or less. Hence, if lunar regolith which contains entrained water molecules can be brought to that temperature and pressure, the lunar regolith should release most of the entrained water molecules. Importantly, an exothermic catalytic chamber or chambers can be created inside an object requiring low temperature heating, such as a tool for mining lunar soil containing ice, such as can be found in the super-cold environment of a PSR found in the vicinity of the lunar poles, allowing excess exothermic heat to be used to good effect. This is a direct and very efficient alternative to electrical heating of such tools.

Conclusion, Ramifications, and Scope

[0057] Other thermochemical cycles are possible, as disclosed in U.S. Pat. No. 3,225,538, U.S. Pat. No. 3,067,594, and U.S. Pat. No. 3,871,179, and therefore the C6H12<=>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.