Internal-combustion engines – Combined devices – Generating plants
Reexamination Certificate
1999-09-14
2001-04-03
Kwon, John (Department: 3747)
Internal-combustion engines
Combined devices
Generating plants
C123SDIG001
Reexamination Certificate
active
06209494
ABSTRACT:
FIELD OF THE INVENTION
This is a procedure for producing mechanical power and a hybrid power generation unit for practicing such a process. In particular, the procedure uses a thermal or catalytic cracker to crack or to pyrolyze (partially or completely) a liquid or gaseous petroleum fuel to produce a primary gaseous stream primarily containing hydrogen (and likely methane or other short-chain hydrocarbons) and a second intermediate stream. The hydrogen may be used in a fuel cell to produce electricity, which electricity is used in a linear or rotary electric motor. The second intermediate stream, a liquid fuel under low temperature operation, or preferably carbon monoxide-rich gas under high temperature operation, may be introduced to an internal or external combustion engine for further production of mechanical power.
For partial pyrolysis at low temperatures (below 650° C.), the second intermediate stream exits the fuel processor as a partially dehydrogenated gas and is then condensed primarily to a liquid and possibly some non-condensable gases for use in the engine.
For total pyrolysis at high temperatures (above 650° C.), carbon coke from the input petroleum fuel is deposited in the reactor, e.g., on the catalyst bed, during pyrolysis. This carbon coke is removed by introducing an oxygen carrying gas such as steam, carbon dioxide or other suitable gas or mixture thereof to form a carbon monoxide-rich gas to fuel the engine.
Most preferred of the combustion engines is one having high thermal efficiency. This combination of pyrolysis, fuel cell, and high efficiency heat engine results in a procedure and device which is significantly more efficient in terms of utilizing the energy present in the feedstock hydrocarbon fuel. Additionally, under high temperature operation when the fuel to the engine is a carbon monoxide-rich gas, the emissions from the system will be substantially lower than for conventional power systems. Finally, when some portion of the process heat required by the pyrolysis and de-coking operations is obtained from waste heat from the engine, an increase in the total thermal content of the fuel can be realized, further increasing the overall fuel economy of the hybrid system.
BACKGROUND OF THE INVENTION
The vast majority of all engine-driven vehicles in operation today use internal combustion engines using either a Diesel cycle or the Otto cycle. A very few automotive vehicles are powered by external combustion engines such as gas turbines, Stirling cycle engines, or steam engines. A relatively small number of vehicles are powered by electric motors.
Each class of motor vehicle propulsion system has its benefits and detriments. The Diesel cycle engines are simple and robust while utilizing significant amount of the energy found in its hydrocarbon fuel. The exhaust from most such diesel cycle engines is high in nitrogen oxides and carbon particulates. The Otto cycle engines are probably the most highly engineered mechanical device existing on earth. Although the efficiency of Otto cycle power plants as used in automotive vehicles has significantly improved since their first use in the latter part of the 19th century, their efficiency (based on the potential energy content of the fuel) is not high because of the low compression ratios associated with gasoline engines. In general, these engines can be made into quite lightweight packages for use in a variety of vehicles.
Vehicles using electric motors are currently not as flexible and practical as are those using one of the internal combustion engine power plants. Although acceleration and top speed of such electric vehicles may match those of internal combustion-engined vehicles, electric motor-powered vehicles have a significant detriment because of their need for batteries. A variety of different battery systems have been proposed for use in such vehicles. Lead-sulfuric acid batteries remains the primary choice for such vehicles as other, more advanced technology, batteries are being developed. Obviously, lead-acid batteries are quite heavy and often have a lengthy charging cycle. Such cars have a short vehicle range. Unlike the internal combustion-engined vehicles, those powered with electric motors have few if any vehicular emissions. Obviously though, the utility power plants which provide electric power to battery-powered electric cars will be responsible for some type of emission.
The motive engines discussed above are traditionally used for vehicular power. More recent approaches include hybrid electric and fuel-cell power systems. Hybrid electric systems generally make use of internal combustion units to recharge batteries. Fuel-cell systems often require very large hydrogen storage vessels. An alternative to hydrogen storage systems is the use of a continuous partial oxidation or steam reforming on board the vehicle. Our invention is an alternative to these.
Steam Reforming
Petroleum fuels may be reformed using steam to yield hydrogen. The procedure requires two moles of water and heat to decompose thermally the hydrocarbon according to the following reaction:
CH
x
+2H
2
O→CO
2
+(
x/
2+2)H
2
Using methane as a feedstock, x=4 and the theoretical hydrogen yield is four moles of hydrogen for each mole of methane fed to a reactor. The reaction is endothermic so that the theoretical heat required is 61.8 Kcal/gm-mole, the heat of combustion of methane is 191 Kcal/gm-mole, and the hydrogen efficiency is 91%. At equilibrium conditions, only about 2.55 moles of hydrogen is produced and therefore the hydrogen efficiency is reduced to 76%.
For a typical liquid petroleum fuel such as heptane, x=2.29, the theoretical hydrogen yield is 3.15 moles of hydrogen per mole of heptane, the heat required is 53.8 Kcal/gm-mole, the heat of combustion of heptane is 153 Kcal/gm-mole, and the hydrogen efficiency is 88%. However, at equilibrium conditions, the hydrogen production is reduced to 2.6 moles, and the corresponding hydrogen efficiency is reduced to 74%. This approach results in the highest hydrogen efficiency since some of the hydrogen is supplied by the steam which is broken down in the reforming reaction.
Partial Oxidation
In the partial oxidation of petroleum fuels, a portion of the fuel is burned to provide heat to decompose the fuel and water in an oxygen-starved environment, thus:
CH
x
+(1.5
−x/
8)H
2
O+¼(1+
x/
4)H
2
→CO
2
+(1.5+3
x/
8)H
2
+heat
For methane:
CH
4
+H
2
O+½O
2
→CO
2
+3H
2
+29.48 Kcal/gm-mole
The theoretical hydrogen efficiency for methane is 78% and at equilibrium conditions expected hydrogen efficiency at 64%. Using heptane as a feedstock, x=2.29 and the resulting equation is:
CH
2.29
+1.21H
2
O+0.39O
2
→CO
2
+2.36H
2
+25.1 Kcal/gm-mole
The theoretical hydrogen efficiency is 77% and at equilibrium the hydrogen efficiency falls to 60%.
Partial oxidation has a moderately high hydrogen efficiency since some portion of the hydrogen contained in the feedstock is combusted in this reaction scheme.
Pyrolysis
Pyrolysis is the direct thermal decomposition of petroleum according to the following equation:
CH
x
+heat→C+
x/
2H
2
For methane it is simply:
CH
4
+heat→C+2H
2
The heat required to decompose methane is about 18.9 Kcal/gm-mole and the corresponding theoretical hydrogen efficiency is 55%. Under equilibrium conditions, one could expect to extract about 90% of the hydrogen contained in the methane and the hydrogen efficiency is therefore reduced to 50%.
Using heptane, the reaction becomes the following:
CH
2.29
+heat→C+1.14H
2
The heat required in this reaction is 18 Kcal/gm-mole and the theoretical efficiency based on hydrogen is 40%. Experiments have shown that 90% of hydrogen can be recovered, thus reducing the overall hydrogen efficiency to 36%.
The pyrolysis process has the lowest hydrogen efficiency since only the hydrogen contained in hydrocarbon feedstock is available. It, however, has the advantage o
Manikowski, Jr. Ambrose F.
Noland Gary M.
Kwon John
Morrison & Foerster / LLP
Procyon Power Systems, Inc.
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