US 3350176 A
Description (OCR text may contain errors)
Oct. 31, 1967 R. B. GREEN ET AL 3,350,176
HYDROGEN GENERATOR Filed March 24, 1964 Pare/V2 Gene/*afar l! INVENTORS Habe/2" B. Greer; Haga Gersser 5mn/ey S. /wz'z United States Patent O 3,350,176 HYDROGEN GENERATOR Robert B. Green, Chatham, Hugo H. Geissler, Edison,
and Stanley S. Kurpit, Newark, NJ., assgnors to Engelhard Industries, Inc., Newark, NJ., a corporation of Delaware Filed Mar. 24, 1964, Ser. No. 354,476 3 Claims. (Cl. 23-281) This invention relates to apparatus for the production of hydrogen. More particularly, the invention concerns novel compact hydrogen generating apparatus which can be readily designed as a selfcontained hydrogen generator useful in connection with commercial and industrial processes to supply hydrogen. The invention is especially concerned with apparatus for hydrogen generation which is completely self-contained and may be employed as a portable hydrogen generator having significant commercial and military value.
In co-pending application Ser. No. 217,012, filed Aug. 15, 1962, methods and apparatus for hydrogen production employing steam reforming of hydrocarbon fuels as a source of hydrogen, and diffusion purification of hydrogen produced thereby, have been described. In that application, advantages of removal of hydrogen from a steam reforming reaction by means of diffusion coupled with utilization of 11n-diffused gases as combustion fuel gas for supplying heat to maintain the endothermic reforming reaction are set forth. That application is incorporated herein by reference.
The present invention constitutes improvements in the method and apparatus of the aforesaid application. An important feature of the present invention is the utilization of the residual undiffused gases separated from the reforming reaction zone as a source of providing the total energy requirements of the system. Heat obtained by the combustion of such unditfused gases provides the heat required for vaporization of fuel and water, as well as providing the heat required for the endothermic hydrocarbon steam reforming reaction. It may also exert the driving force for pressurizing the system by using the vaporization of the water for such purpose. A Ifurther advantage of the present invention resides in the utilization of a unique compartmented Water-fuel vessel wherein steam generated by use of such waste combustion gases provides the pressure necessary to feed fuel under pressure to the system. A further aspect of the present invention is the utilization of the pressure and/or temperature of the steam generator to control the amount of heat transferred from the Waste combustion gases to the steam generator, so as to provide positive control of the over-all system at any desired operating level. A further feature of the present invention is the utilization of the pressure of the steam generator operating through regulators and feed orifices against a nal effluent orifice to control the overall operation of the hydrogen generator. Another aspect is the aspiration of the required combustion air into the combustion chamber by means of the pressure of the reactor.
Hydrogen generators, in accordance with this invention can be built with capacities of about 1 to 2 s.c.f.h. and greater. As a matter of practicality, with units of about 6-10 s.c.f.h. capacity, the surface to volume relationship of the steam boiler and the start-up time associated with heating the large mass of water in such boiler may indicate the desirability of using other means of providing pressurization and conducting the vaporization. In such case, a hand pump or miniature pumps or other suitable means may be used for pressurization, still utilizing the heat obtained from the residual gases for vaporizat'ion.
In the practice of thepresent invention, hydrocarbon '3,350,176 Patented Oct. 31, 1967 r ICC fuel and water, in an appropriate ratio, are reacted in the presence of a steam reforming catalyst. The reforming reaction produces hydrogen, carbon monoxide, carbon dioxide and methane. The hydrogen is partially withdrawn through a diffusion element, and the remaining hot reactor gases, when used directly as a fuel, supply the heat requirements for the process including steam generation and a sufficient allowance for radiation and convection losses and losses in the ue gas. As described above, the heat may also provide the driving force for pressurizing .the system. In addition, because only hydrogen diffuses through the diffusion element, no further purification or processing of the product hydrogen stream is required. The resulting apparatus therefore can be extremely compact as well as highly efficient, and lends itself well to miniaturization.
Briefly, the apparatus of .the present invention operates as follows: Fuel and steam flow from their respective tanks, are metered, pre-mixed and pass through a vaporizer-preheater coil before entering the reformer. Flue gases passing over the underside of the water-fuel tank, which may be finned to improve heat transfer or, alternatively, through a heat exchange coil which may be positioned in the water tank, provide sufficient heat to generate the steam. The liquid fuel is pressurized by means of auxiliary air pressure or, preferably, by a exible diaphragm disposed between the fuel and steam chambers.
Flue gases passing over the vaporizer preheater coil supply the heat to complete the vaporizat-ion of fuel and preheat the fuel-steam mixture to reactor entry temperature. 'Ihe fuel-steam mixture enters the reactor, where, in the presence of steam reforming catalyst, and utilizing heat transferred from the combustion zone, it is reformed to carbon dioxide, carbon monoxide, hydrogen and methane. The product hydrogen is removed through the diffusion elements and passes to the hydrogen delivery line, optionally through a final cooling coil.
The residual fuel gas enters an operational burner where it is burned. Air is -aspirated into the combustion zone by the pressure energy of the residual -fuel gas passing through an aspirator orifice which maintains the system pressure. The combustion products ow through the reactor, the preheating coil, steam generator and out the exhaust. I
Specific features and advantages of the invention will become apparent from a consideration of the following detailed description and from the drawings, in which the sole figure accompanying this specification is a cross section of one embodiment of the present invention, showing schematic flow lines and associated controls.
Referring to the figure, a unitary hydrogen generator 11 is shown, consisting of a reactor-diffuser vessel 12 and a fuel, water and steam generator tank 13 mounted within the generator and in heat exchange relationship with central flue 14 of the reactor-diffuser.
As shown in the ligure, reactor diffuser 12 consists of annular concentric compartments. The inner compartment is a reaction zone 21 which is sealed from the hydrogen collection zone 17 by wall 20 and header 16. Diffusion element 15 is positioned in hydrogen collection zone 17. In a preferred embodiment, diffusion element 1S is in the form of a suspended coil. Diffusion element 15 lin the reactor, separated by permeation through the diffusion tubes and collected in chamber 17, exits'by line 18.
Line 18 is provided with pressure relief valve 19 and valve 22 which is of the open-closed type.
Catalyst 24 which is effective in steam reforming hydrocarbons, for example gasoline, kerosene, JP-4, to a mixture containing hydrogen, is provided in reaction zone 21.
The outlet of diffusion coil communicates with outlet line 27 through which residual gases from the reforming reaction after being depleted of product hydrogen (by diffusion into diffusion chamber 17) pass to aspirator 28. Aspirator 28 comprises an orifice which provides the back pressure against which the entire H2 generator is operated. Further, the llow of gases through this aspirator provides the motive power to inspirate the combustion air into the system. The combustion then takes place in combustion chamber 14. Combustion of these gases in flue 14 provides heat for maintaining the catalyst bed at the desired reforming temperature and provides necessary heat for preheating feed in coil 53 and generating steam in tank 13 hereinafter more fully described. Insulation 25 surrounds the reactor-diffuser.
Turning now to fuel, water and steam generating tank 13, it will be understood that this tank is mounted within the unitary generator in heat exchange relationship with the hot combustion gas produced in the reactor-diffuser. As shown in the figure, a suitable embodiment provides for the steam generator tank to be so placed in the generator that hot flue gas impinges on the underside 31 of the tank 13 which, if desired, may be of finned construction to provide heat transfer characteristics. Openings are provided in the generator wall as at 32 by which llue gas passes to the atmosphere. Alternatively, hot flue gases from flue 14 can be passed by conduit through a coil (not shown) disposed within water chamber 33 of the steam `generator in order to heat the water and provide necessary steam pressure. The degree of heat transferred to tank 13 is controlled by temperature sensing device 78 which operates damper 77. When the temperature rises above a predetermined set point, some of the flue gas is bypassed. Alternately, a temperature sensing device 78 could be a pressure sensing device positioned inthe vapor space of tank 13.
The fuel-water-steam generator tank 13 is divided into two compartments, water compartment 33 and fuel compartment 34, by a flexible diaphragm 36 which is impervious to steam and resistant to the action of gasoline or kerosene-like fuels. Suitably, flexible diaphragm 36 is composed of metal, eg., thin stainless steel sheet, plastic such `as Teflon or the like, or hydrocarbon-resistant rubber, e.g. neoprene. Fuel compartment 34 is provided with -fuel fill nozzle 37 and with pressure-resistant closure 38. Water chamber 33 is provided with water fill-nozzle 39 for introducing Water to the chamber, and with pressureresistant closure 41.
Depending upon the hardness and brackishness of the water used, the combination water-steam generator tank will have to be emptied periodically by spilling out the residue of water left in it. This emptying is preferably done at the end of every run. If the quality of the water is poo-r, scale will lay down on the sides and bottom of the steam generator over along period of time. When the scale deposit is of such magnitude as to reduce the elliciency of the hydrogen generator below a tolerable level, the scale is removed from the steam generator. This is easily accomplished by removing the quick fastening closure 42 that holds the upper and lower chambers together and removing the upper chamber and diaphragm, which will expose the lower chamber for cleaning.
Steam generated in chamber 33 during operation of the -generator passes by line 43 provided with pressure indicator 44 and valve 45 to pressure control valve 46 which can be manually adjusted to provide desired steam pressure in the steam exit line. Steam then passes by line 47 provided with pressure gauge 48 to fixed calibrated ori- `c 4.9 'through which the desired flow of steam is metered by controlling the pressure drop across the orifice, and then to mixer 51, from which an admixture of steam and fuel passes by line 52 to preheater coil 53 disposed within flue 14. Preheated mixture of steam and fuel is introduced to the reaction chamber by line 54 for distributing the fuel-steam mixture throughout the reaction zone. Pressure gauge 56 on line 52 is provided to monitor the pressure of the input stream to the reactor.
Referring to fuel chamber 34, it will be seen from the figure that line 61 is provided for passage of fuel in liquid form and under pressure to pressure control valve 62 which valve can be manually controlled. Line 61 is further provided with on-off valve 63. Fuel under controlled pressure as indicated by pressure indicator 64 passes by line 65 to precalibrated orifice 66 and thence by line 67 to fuelsteam mixer 51.
The hydrogen generator of the figure is further provided with auxiliary or start-up burner 71 which is of the blow-torch type, provided with manual piston 72 for pressurizing auxiliary fuel 73 of the hydrocarbon type therein, and having fuel feed orifice 74 and adjustable air inlet means 76.
A typical hydrogen generator of the type described herein can be operated as a portable back-pack type generator designed to deliver approximately 4 s.c.f.h. of hydrogen (referred to 1 atm. and 60 F.). Such a unit has been designed having an over-all volu-me of 2 cubic feet and weighing about 20 pounds. Fuel and water for start-up and 10 hours operation weigh approximately 6 pounds.
It will be understood that such a unit can be manufactured from material of construction known to be suitable, in terms of pressure and temperature requirements, by those skilled in the art. In one apparatus of the type described herein, the combustion chamber is fabricated from an Inconel X-750 tube having a 12" length and 0.0322 inch wall thickness. A 3-ineh O.D. tube of 304 stainless steel having a wall thickness of 0.05 inch positioned concentric to the inner combustion chamber provides the annular reaction chamber. The coiled diffusion tubes of 1/sinch O.D. comprised palladium-silver alloy of 4-mil wall thickness. The reactor-diffuser is insulated with 2-inch Kaowool designed to provide the required insulation at a minimum weight and volume. In the apparatus constructed in accordance with the invention, a flexible diaphragm of plastic-coated elastomer Fairprene is employed.
Operation and control of the apparatus described herein is simple and versatile. Initial start-up is provided by pressurizing start-up fuel in start-up burner 71 by means of manual piston 72. It should be understood that alternate methods of start-up can be provided, e.g. by providing a fuel line from the fuel compartment of the fuel-steam pressure generator to the start-up burner.
The burning of fuel in the start-up burner provides heat to bring the reactor up to the start-up temperature of between about 1000'l and 1500 F. During the start-up period, water in the steam generator tank 33 is vaporized and is passed by lines 43, 52 and 54, in the absence of fuel, to the reforming catalyst. Thus, the apparatus permits a brief steam (and air from pressurization) cleaning of the reforming catalyst to remove carbon deposits from previous operations and to thus regenerate the activity of the catalyst.
As pressure is transferred to the fuel in fuel compartment 34, and upon opening of valve v63, fuel is forced into the reactor in admixture with steam. The fuel-steam feed, preheated to vaporize the fuel in coil 53, passes to the catalyst by line 54 whereupon the reforming reaction is initiated. Residual fuel gas passes through the aspirator 28 by line 27, and is ignited in combustion chamber 14 by the flame from the start-up burner. When substantial hydrogen product gas is being produced, for example after 5-15 minutes of operation after initial start-up, depending on the fuel charge, the start-up burner is shut off and the self-contained unit is on stream.
During operation of the unit, reactor pressures of the order of 150 p.s.i.g. are used. With the reactor pressurelixed in this manner, a suflcient ow of fuel and the proportionate ow of steam to maintain the reactor pressure are admitted to the unit. This is done by controlling the pressure drop across calibrated xed area orices 49 and 66. The quantity of hydrogen delivered by the generator can be manually throttled by reducing the pressure drops across the fuel and steam feed orifices. With less material flowing into the reactor and through the eluent orice, a lower reactor pressure and hence a lower hydrogen delivery rate will result. In normal operation at a reactor pressure of p.s.i.g., the steam feed is provided at a pressure of about 160 p.s.i.g. (as indicated by pressure indicator 48), and the fuel feed at a pressure of 160 p.s.i.g. (as indicated by pressure indicator 64). At these pressures, and in view of the selection of calibrated orices 49 and 66 and in aspirator 28, the rate of steam ow to the generator will be in the range of 3 to 4 pounds per hour per pound of catalyst at a steam/fuel ratio of about 3:1.
The hydrocarbon fuel employed in the practice of the present invention may comprise normally liquid hydrocarbons, as well as liquiable natural gas hydrocarbons, such as propanes and butanes. Liquid hydrocarbon boiling in the gasoline, kerosene and gas oil boiling ranges, for example, BTX-Udex raflnate, JP-4 fuel, kerosene. and the like can be used as fuel.
Suitable catalysts for the production of hydrogen by catalytic steam reforming of hydrocarbon feeds are Well known and, in general, should possess high activity and good physical strength. Platinum group metal catalysts, e.g. Pt, Pd, Rh, Ru, Os, Ir, particularly Pt and Rh and combinations thereof have been found to be eifective catalysts. The catalyst metals are supported on refractory oxides, e.g. alumina, silica, thoria and combinations thereof. Calcium and magnesium oxides may be added to secure catalysts of greater strength at higher temperatures. It has been found that precious metal catalysts are particularly desirable because of the low steam/carbon ratios that can be used, thus further enabling the use of compact light-weight equipment.
In operation of the apparatus described herein, the choice of operating pressure will be dictated by the specification for delivery pressure of the hydrogen product.
This condition is determined by the hydrogen partial pressure driving force necessary for diffusion, In general,
the apparatus is employed at any operating pressure of 100 to 200 p.s.i.g., to provide a pure hydrogen eluent delivered at atmospheric to about 50 p.s.i.g.
What is claimed is: 5 1. Apparatus for the generation of hydrogen comprising in combination (a) a fuel source and steam generator contained in a compartmented unitary vessel, the fuel compartment being separated from the steam compartment by a flexible diaphragm impervious to steam,
(b) a combustion chamber disposed in indirect heat relationship with,
(c) a compartmented reactor consisting of a reaction chamber containing reforming catalyst and a hydrogen diffusion chamber, wherein a diffusion element permeable only to hydrogen is positioned,
(d) means for introducing fuel and steam to the reaction chamber for conversion to a gaseous mixture containing hydrogen,
(e) means for removing hydrogen from the diffusion chamber,
(f) means for removing residual gaseous products from the reactor,
(g) means for introducing said residual gaseous products into said combustion chamber, and
(h) means for supplying heat from the combustion chamber to the steam generator whereby steam pressure generated in said steam compartment exerts pressure on said flexible diaphragm.
2. Apparatus of claim 1 further characterized in that means are provided for controlling the supply of heat from the combustion chamber to the steam generator.
3. Apparatus of claim 2 wherein said means for controlling the supply of heat to steam generator comprises 35 a flue gas damper, the position of said damper being controlled by temperature and/or pressure of the steam generator.
References Cited UNITED STATES PATENTS 5/ 1916 Snelling 48-224 FOREIGN PATENTS 3/ 1927 Great Britain.