US3479144A - Catalytic burner - Google Patents

Description

Nov. 18, 1969 H. F. BRosE CATALYTIC BURNER Filed sept. 22, 1964 United States Patent O 3,479,144 CATALYTIC BURNER Harlan F. Brose, Longmeadow, Mass., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Sept. 22, 1964, Ser. No. 398,449

Int. Cl. F23g 7/06; F23d 13/18; F24j 3/00 U.S. Cl. 2.3-288 10 Claims ABSTRACT F THE DISCLOSURE Catalytic burner in which a catalyst bed is centrally disposed in an enclosed container and a regenerative tubular-type heat exchanger surrounds the catalyst. Super insulation lines the container `and the regenerative heat exchanger is embedded therein.

This invention relates to apparatus for carrying out catalytic oxidation of gases and more particularly to a catalytic burner constructed to minimize heat loss conduction and/or radiation to the surrounding environment and, as a result of the air carrying the gases to be burned therethrough, leaving at a higher temperature than it entered.

In a sealed compartment of a manned spacecraft it is necessary to keep certain gases like methane, hydrogen and carbon monoxide at a tolerable level. As is well known in the art, these aforementioned gases can be chemically reacted in a catalytic burner forming carbon dioxide and water vapors. In a spacecraft it is of paramount importance that the power consumption be extremely low. I have found that I can fabricate a catalytic burner that requires extremely low power by maintaining the heat losses at a minimum level. This is `accomplished by imbedding a regenerative heat exchanger, heater and catalyst bed in a super insulator, providing maximum length of heat exchange in a given space and routing the contaminated airstream in a particular fashion through the catalytic burner.

It is therefore an object of this invention to provide in a catalytic burner as described, a vacuum chamber containing super insulating material mounted in a predetermined manner.

A still further object of this invention is to provide in a catalytic burner `as described, a particular regenerative heat exchange construction.

A still further object of this invention is to provide in a catalytic burner as described, a particular route for passing the gases through the catalytic burner.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention.

FIG. l is a cross-sectional View of the catalytic burner illustrating the details of this invention.

FIG. 2 is a view taken along lines 2`2 of FIG. l.

Referring to the drawings, the catalytic burner basically comprises an outer shell housing the regenerative heat exchanger 12, catalyst bed 14, heater 16 and super insulating material 18. The excavated chamber defined by outer shell 10 consists of an elongated cylinder bottom portion 20 closed at its bottom made from a suitable nonporous metal. An opening thereof at the top portion carries an inner threaded cap receiving member 22 rigidly secured thereto by weldment 24. Cap 26 having external threads engaging the internal threads of 22 forms the top closure member of the chamber. To avoid leakage into the chamber once evacuated, a suitable seal 28 is provided and may be a plastic or metallic O type of seal. A boss 30 extending from the top surface of cap 26 carries suitable electrical connector 32 for passing thereicc through heater wires 34 and 36. These heater wires extend into the chamber and are laid adjacent insulator material 18 and are routed adjacent the inner top and side surface of cap 26 to ceramic disc heater 16. As schematically shown, contact of switch 40 closes the circuit to energize heater 16. The catalyst container 44 formed from a cylindrical tube extending concentrically in the cylinder 20 is formed from any suitable nonporous material. The internally threaded heater support member 46 is firmly aixed by suitable means to the end of cylinder 44 and threadedly engages the external threads of heater retainer 48. To prevent leakage of fluid through these threads, a suitable seal 50 is mounted between members 46 and 48. Inasmuch as the catalyst does not react chemically, it will not have to be changed and it is contemplated within the scope of this invention that the cap portion and heater support members may be welded into place to form an integral unit eliminating the necessity of seals.

As noted from the drawing, heater retainer 48 is recessed on one side to receive the heater and a concave surface on the opposite side to provide an extended heating surface for the impinging inlet gas. The other part of the reactor is formed from cylinder 44, end cap 67 and the inlet tube 52 which is centrally disposed in and extends axially along the center line of the reactor. A suitable catalyst is retained and supported in cylinder 44 by a porous ceramic or Fiberglas material S4 and 56 disposed 0n either end which, in turn, is held in position by screens S8 and 60 respectively. Any catalyst which will promote oxidation is contemplated within the scope of this invention. Rhodium-alumina catalyst has been shown to be particularly eicacious as an oxidation promoter. The ends of the catalyst bed are then supported in position by opposing washers 62 and 64 disposed on either end around inlet tube 52. Washer 62 and screen 60 are spaced from end cap 67 by spacers 68 and 69. Washer 64 is locked to tube 52 with pin 66 thus retaining the catalyst.

Boss 70 iirmly secured to the outer surface of shell 20 contains a pair of openings for connecting the inlet and discharge ends of regenerative heat exchanger 12. Regenerative heat exchanger 12 is formed from brazing inlet coil 72 to adjacent outlet coil 74 which coils are helically wound to coaxially surround the catalyst bed and extend to the bottom of shell 10. Inlet coil 72 is connected to inlet tube 52 by suitable connecting member 76 and outlet coil 74 is suitably connected to outlet tube 78 by connector member 80. It will be appreciated that these coils are imbedded in suitable super insulating material as is the heater and reactor. The super insulating material is preferably formed from alternate layers of aluminum foil and Fiberglas sheets. It is important that the insulation be so placed that radiation from a hot surface to a colder surface is interrupted by the several alternate layers of foil and Fiberglas. It will be appreciated that the foil diminishes the potential radiation heat loss and the Fiberglas diminishes the conduction from alternate foils.

A suitable plugged opening 82 formed in boss 70 communicating internally with shell 10 may be provided to connect with an evacuator pump for evacuating thereof, or in a space application directly within the outer space atmosphere. Satisfactory operation of this catalytic burner has been evidenced when the vacuum was maintained at a level greater than one micron.

Now that the details of the present invention have been described, operation of the catalytic burner is described below. Air subjected to the exhalations of the occupants of the spacecraft and the gases given oif by equipment therein, first enters the heat exchanger through coil 72 Where it is heated by indirect heat exchange by the hot air emerging from the catalytic burner and passing through coil 74. This inlet air then passes through extended inlet tube 52 and is heated as it impinges on the inside of the heater retainer 48. The inlet air after striking the heater retainer then passes through the catalytic bed 14. Here, gases such as carbon monoxide, hydrogen, and methane contaminants in the inlet air are oxidized to carbon dioxide and water. The product air then passes out through exit tube 78 and coil 74 of the heat exchanger, where it is cooled, to reduce heat loss by transferring heat to the inlet air in coil 72.

The example below is given to merely illustrate the results of an experiment of one preferred embodiment using rhodium-alumina (approximately 1/10 inch diameter particle size) as the catalyst. The catalyst was formed by depositing rhodium on alumina pellets. In a five cubic inch catalyst bed, the following was evidenced: complete oxidation of 510 parts per million (ppm.) methane, 630 p.p.m. hydrogen, and 15 p.p.m. car-bon monoxide, in a stream of 0.4 pound per hour of oxygen at a pressure of 5 p.s.i.a., and at an average temperature of 485 F., and and the power consumption being approximately 4.5 watts.

The pressure drop through the entire catalytic burner was 0.5 p.s.i., as established by using nitrogen at 5 p.s.i.a. and 750 F. and a flow rate of 0.22 cubic foot per minute.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit or scope of this novel concept as defined by the following claims.

I claim:

1. A catalytic burner including outer and inner shells being in spaced relationship, heater means enclosing one end of the inner shell, means defining a catalyst bed in the inner shell but spaced from said heater, an elongated tubular member extending through said inner shell and terminating adjacent to said heater means, inlet and outlet tubes arranged in contiguous helical coils in said space and surrounding said inner casing, said inlet tube being connected to one end of said elongated tubular member remote from said heater means and the outlet tube communicating with said catalytic bed, insulating means including a` sealed evacuated chamber in said space defined between said outer and inner shells.

2. A catalytic burner as defined in claim 1 wherein said insulating means includes a low conductive material wrapped around said inner shell and said coil.

3. A catalytic burner as defined in claim 2 wherein said insulating means includes a low conductive material lining the inner walls of said outer shell.

4. A catalytic burner as defined in claim 1 wherein said insulating means includes sheets of aluminum foil and glass l'iber material mounted in juxtaposed relation.

5. A catalytic burner as defined in claim 1 wherein said elongated tubular member is centrally disposed in said inner shell.

6. A catalytic burner as defined in claim 1 including means for supporting said catalyst bed in spaced relationship relative to the end walls of said inner shell.

7. A catalytic burner construction, including a shell defining a chamber, inlet and outlet tubes within said chamber, said tubes arranged in contiguous cylindrical coils, a catalytic bed surrounded by said coils and a heater at one end of said bed, a connector tube discharging a gaseous stream from the inlet tube against said heater, a connection from the end of the bed opposite to the heater to the outlet tube, and insulating means between the coils and the shell and forming an enclosure for said coils and catalytic bed.

8. A catalytic burner construction as claimed in claim 7 including an outlet on one end of said catalytic bed remote from said heater, and connector means connecting said outlet and said outlet tube whereby said gaseous stream from the heater passes through said bed, said connector means and said outlet tube.

9. A catalytic burner construction, including a shell defining a chamber having an open end, an end cap closing said open end, inlet and outlet tubes within said chamber, said tubes arranged in contiguous cylindrical coils, a catalytic bed surrounded by said coils and a heater mounted in said end cap and located at one end of said bed, a connector tube discharging a gaseous stream from the inlet tube against said heater, a connection from the end of the bed opposite to the heater to the outlet tube, and insulating means between the coils and the shell and forming an enclosure for said coils and catalytic bed.

10. In a catalytic burner adapted to oxidize constituents contained in a gaseous stream by combustion in the presence of a catalyst comprising a cylindrical outer shell defining a chamber, a centrally disposed tube extending axially in said chamber, heater means at one end of said chamber adjacent the end of said tube for receiving the discharge gases `from said tube, a catalyst bed surrounding said tube, a regenerative heat exchanger having a first helically extending tube terminating adjacent a complementary opening in said outer shell and a second helically extending tube terminating adjacent a complementary opening in said outer shell adjacent to and in contact with said first helically extending tube, both of said tubes sur rounding but spaced from the catalyst bed, said first and second tubes being also spaced from the inner walls of said shell, first insulation means lining the inner walls of said shell within said chamber, second insulation means interposed between said catalyst bed and heater, and third insulation means between spaces between adjacent tubes of said first and second helically extending tubes, and means for permitting evacuation of the space between said catalyst bed and the inner surface of said outer shell.

References Cited UNITED STATES `PATENTS 2,668,692 2/1954 Hammell 165-15'6 MORRIS O. WOLK, Primary Examiner M. D. BURNS, Assistant Examiner U.S. Cl. XR.

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