US3873809A

US3873809A - High temperature gas furnace

Info

Publication number: US3873809A
Authority: US
Inventors: Thorbjorn Skogland
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-09-27
Filing date: 1973-09-27
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25

Abstract

A circulation heater for heating to a high temperature gas under high pressure. The furnace includes an inner container and an outer container with gas pervious insulation positioned between the two containers. Electric heating elements extend into the inner container for heating gas received in the inner container. The inner container has openings, including openings around the electric heaters so that the insulation between the containers is in communication with the gas in the inner container. In the preferred embodiment, the insulation between the side walls of the containers is in the form of an insulation insert: including radially inner and outer walls with insulation held between the walls. The inner wall is shorter than the outer wall and the insulation to provide a communication path for the gas to the insulation. The insulation between adjacent walls at one end of the containers may be in the form of a plug of porous insulation brick which serves the dual purpose of providing insulation and physically supporting the inner container.

Description

Skogland United States Patent [1 1 1 HIGH TEMPERATURE GAS FURNACE [75] Inventor: Thorbjorn Skogland, Shelbyville,

[73] Assignee: General Electric Company,

Indianapolis, Ind.

22] Filed: Sept. 27, 1973 211 Appl. No.: 401,250

219/381. 390, 400, 401,408, 406; 126/110 R, 91 A, 99 A, 116 C; 137/341 [56] I References Cited UNITED STATES PATENTS 1,540,401 6/1925 Kelly et ul 219/406 1,946,262 2/1934 Adams 219/379 1,949.658 3/1934 Remseth et 111.... 219/380 1,985,280 12/1934 Carleton 219/380 2,462,746 2/1949 lnman 219/379 2,711,473 6/1955 Mahaffy et al.. 137/34] 2,768,277 10/1956 Bucket a1 13/20 X 2,836,696 5/1958 Ratchford t 219/390 3,109,912 11/1963 Cerulli ..2l9/381 3,226,467 12/1965 Kienel et a1 219/400 X l W f Mar. 25, 1975 3,383,495 5/1968 Laube et a1 219/380 X Primary Examiner-Volodymyr Y. Mayewsky [57] ABSTRACT A circulation heater for heating to a high temperature gas under high pressure. The furnace includes an inner container and an outer container'with gas pervious insulation positioned between the two containers. Electric heating elements extend into the inner container for heating gas received in the inner container. The inner container has openings, including openings around the electric heaters so that the insulation between the containers is in communication with the gas in the inner container.

in the preferred embodiment, the insulation between the side walls of the containers is in the form of an insulation insert: including radially inner and outer walls with insulation held between the walls. The inner wall is shorter than the outer wall and the insulation to provide a communication path for the gas to the insulation. The insulation between adjacent walls at one end of the containers may be in the form of a plug of porous insulation brick which serves the dual purpose of providing insulation and physically supporting the inner container.

3 Claims, 3 Drawing Figures PATENTEBHARZSIBYS SHEET 1 [IF 2 BACKGROUND OF THE INVENTION The presentinvention relates to furnaces for heating gas and, more particularly, to circulation heaters for heating to high temperatures gasesunder' high pressure.

It often is desired to heat various gases to high temperatures. The problems involved in furnaces for this purpose become much more complicated when the gas being heated is under high pressure. The strength of materials used in constructing gas furnaces lessens as their temperature is increased. Therefore, the furnace walls must be much thicker to withstand the pressure at high temperature. By way of example, a typical furnace material may be a Grade 332 stainless steel which is a high nickel, high chromium content stainless steel. A 3 inch thick plate of this material at 350 Farenheit will successfully withstand a pressure in the range of I75 pounds per square inch. However, if the temperature of the material is raised to 1700 Farenheit, the plate would have to be over 20 inches thick in order to successfully withstand a pressure of 175 pounds per square inch.

Because of the combined temperature-pressure effect it is very difficult to construct furnaces for heating high pressure gases to high temperatures which have reasonable size and cost relative to the volume of gas to be heated.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved furnace.

Another object of the invention is to provide such an improved furnace particularly adapted for heating to high temperatures gas under high pressure.

Yet another object of the present invention is to provide such an improved furnace which makes economic use of material used in construction of the furnace.

Yet another object of the invention is to provide a high temperature-high pressure gas circulation heater having an optimum size for the volume of gas to be heated.

The present invention, in accordance with one embodiment thereof, provides a gas furnace which includes an outer container and an inner container for receiving gas to be heated. Heating means is provided for heating gas received in the inner container. The inner container is mounted within the outer container in spaced relationship thereto and gas pervious insulation is positioned between the inner and outer containers so that the operating temperature of the outer container is substantially lower than the operating temperature of the inner container. The inner container has at least one opening communicating with the gas pervious insulation so that the inner container is subjected to a low pressure differential.

The above mentioned and other features and objects of this invention, as well as one manner of obtaining them, will become more apparent and the invention itself will be better understood by reference to the following description of a preferred embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat simplified and schematic plan view ofa furnace incorporating one form of the present invention.

FIG. 2 is a cross-sectional view of the furnace of FIG. 1, as seen along a longitudinal axis of the furnace.

FIG. 3 is an enlarged, fragmentary view as taken along 3-3 in FIG. 1, showing certain details of construction of one of the conduits utilized in providing gas to the inner container.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and particularly to FIGS. 1 and 2, there is shown, in somewhat schematic form, a furnace or circulation heater particularly adapted to heat to a high temperature gas which is under a high pressure. The furnace includes an inner container 11 and an outer container 12. The inner container 11 conveniently may be cylindrical in shape having

end walls

13 and 14 joined by a generally cylindrical side wall 15 by some suitable means such as weldmg.

The outer container 12 also is cylindrical in shape having end walls 16 and l7joined by generally cylindrical side wall 18. Conveniently the end wall 17 and side wall 18 may be welded together as indicated at 19 while the end wall 16 is removably connected to side wall 18. To this end, a collar 20 is welded around the upper end of the side wall 18. The end wall 16 is attached to the collar 20 by a number of bolts and nuts such as those shown at 21 and 22 with a gasket 23 sandwiched therebetween. With this arrangement, the end wall 16 may be removed to provide access to the interior of the furnace.

The inner container 11 is substantially smaller than the outer container 12 and is mounted within the outer container in spaced relationship thereto. To this end, a plug 24 of porous insulation brick material is positioned between the end walls 14 and 17. The furnace normally is mounted with the end walls 14 and 17 positioned downwardly. The plug 24 serves dual purposes of insulating the wall 17 from the wall 14 and providing physical support for the inner container 11. Conveniently the plug may be made of a aluminum silicate.

The annular space between

side walls

15 and 18 is filled by an insulating insert including an outer cylindrical wall 25 and an inner cylindrical wall 26 which sandwich a body 27 of fibrous insulation material between them. The outer wall 25 fits snugly along the inner sur-' face of wall 18 while the inner wall 26 is spaced slightly outwardly of the wall 15. The wall 25 extends the full distance from the plug 24 to the gasket 23 as does the body 27 of insulating material. The wall 26, however, is shorter than the wall 25 and is positioned so as to stop above the insulating plug 24. This exposes the lower portion of insulation body 27 to inner container 11.

A collar 28 is attached to the inside of wall 26 in a position spaced somewhat above the end wall 13 of the inner container and supports a plate 29. The space between the plate 29 and theupper end wall 16 of the outer container is filled with insulating material generally indicated at 30. Conveniently, the

bodies

27 and 30 of insulating material may be composed of the same 3 material and conveniently may be of aluminum silicate fiber.

Gas received in the inner container 11 is heated by means of elongated electrical heating elements such as those indicated at 31. Each of the heating elements is generally U-shaped in con-figurationand extends from a terminal box 32 through the end wall 16, insulation 30, plate 29 and end wall 13 into the inner container 11. The openings in the end wall 16 fit tightly about the heating elements 31. In fact the heating elements may be welded to the end plate 16 as indicated at 33. Contrary to this, the openings 34 through plate 29 and the openings 35 through the end wall 13 are larger than the heating element 31.

In order to provide for the passage of gas through the inner container 11, so that it may be heated by the heating elements 31, the furnace includes a pair of conduits generally indicated at 36 and 37. The conduit 36 conveniently may be provided at the end of the furnace opposite the terminal box 32. The conduit 36 includes a pipe 38 which extends from the interior of container 11 through an opening 39 in end wall 14, an opening 40 in the insulation plug 24 and an opening 41 in the end wall 17 to the exterior of the outer container. The

openings

39 and 40 are only slightly larger than the outside diameter of the pipe 38 while the opening 41 is substantially larger. The opening 41 is filled with insulation material 42 which extends beyond end plate 17 and also fills a short pipe 43. One end of the pipe 43 is welded to the outside of end plate 17 while the other end of pipe 43 is welded to one end ofa smaller diameter pipe 44 which fits tightly about pipe 38. The other end of the pipe 44 is welded to the outer end, of pipe 38 and to a collar generally indicated at 45. The various weld connections between the pipes and collar provide gas tight seals so that no gas may leak from the outer container 12 even though it leaks from the inner container. With this arrangement, the pipe 38 is firmly held into position in the lower portion of the container 12. lt is desirable that the outer surfaces of the furnace be at somewhat lower temperatures than the high temperature to which the gas isheated. A coil 46a is positioned around pipe 43 and is connected to a suitable cooling unit, not shown, so as to maintain the exposed portions of conduit 36 relatively cool even though the gas flowing through the pipe 38 is at a very high temperature.

Additional details of the conduit 37 are shown in FIG. 3 and are quite similar to the conduit 36. The conduit 37 includes a pipe 47 which extends from the interior ofinner container 11 through an opening 48 in side wall and then through the insulation insert, including

walls

25 and 26 and insulation material 27, and the cyclindrical wall 18 of the outer container 12. Another pipe 49 fits in the opening in outer wall 18 around the pipe 47 and is welded to the wall 18. The space between the

pipes

47 and 49 is filled with insulation material 50. Another pipe 51 fits tightly about the pipe 47 beyond the pipe 49 and is welded to the pipe 49. A collar 52 fits around the pipe 51 and is welded to it. The outer end of pipe 47 is formed as an outwardly extending flange 47a and fits within the opening of the collar 52. When another device or conduit is attached to the collar 52 a gas tight seal is formed at the outer end of the pipe 47. With this arrangement the pipe 47 may be pulled out of the furnace sufficiently to allow the insulation

insert including walls

25 and 26 and insulation 4 material 27 to be removed from the furnace axially. A coil 46b is positioned about pipe 49 and may be connected to the same coolingsource as coil 46a.

A pair of purgeoutlets generally indicated at 53 and 54 are provided at the axially opposite ends of the outer container. These purge outlets enable the air between the inner and outer containers to be evacuated and replaced with a suitable gas such as nitrogen prior to operation of the furnace.

In operation the gas to be heated is admitted to the inner container through conduit 37 and is heated by the heating elements 31. The heated gas exits through the other conduit 36. Thisgas may be at a very high temperature and pressure. By way of example, in one application, a mixture of methane, carbon monoxide and hydrogen has a furnace entrance temperature of approximately 1300 Farenheit and a furnace exit temperature of about l700 Farenheit as it leaves the furnace. The gas is under a pressure of pounds per square inch. Asingle wall furnace to serve this purpose constructed of a high grade stainless steel would require extremely thick walls, particularly the end walls.

By means of the present invention, it is possible to greatly reduce the size of the walls. This provides savings in both material and space. As previously described, the openings 35 in the end wall 13 of the inner container are larger than the heating elements and the opening 39 about pipe 38 is larger than the pipe 38. Also as previously described, the wall 26 is spaced from the wall 15 and terminates above the insulation plug 24. Additionally, the openings 34 in plate 29 is larger than the heating elements 31. With this arrangement, the space and thus the insulation, between the containers is in gas communication with the interior of the inner container 11. Additionally, all of the insulation is gas pervious. Therefore. if the gas within the inner container 11 is at 175 PS1, by way of example. then the pressure in the area between the inner-and outer containers will also be approximately 175 PS1. This means that the inner container is required to withstand little or no pressure differential.

Since the temperatures and pressures within the furnace will quickly reach an equilibrium there is little or no gas flow through the insulation from one portion of the inner container to another portion of the inner container and therefore there is no conviction heat transfer to the various portions of the insulation. This means that, even though the pressure present in the insulation is quite high, its insulation characteristics are not adversely affected and the insulation is effective to maintain the temperature of the outer container, including end walls 16 and 17 and side wall 18, at a much lower temperature. For instance, in the application described briefly above, the outside surface temperature of the outer container is maintained at about 350.

With this arrangement, the inner container 11, which is subjected to an extremely high temperature, is subjected to little or no pressure differential and may be constructed of thin material. On the other hand while the outer container is subjected to a high pressure its temperature is maintained at a much lower level than the inner container and it also may be constructed of thin material.

While in accordance with the patent statutes, 1 have described what, at present, is considered to be the preferred embodiment of my invention, it will be obvious to those skilled in the art that numerous changes and modifications may be made therein without departing from the invention, and it is therefore claimed in the appended claims to cover all equivalent variations as fall within the true scope and spirit of the invention, What I claim is new and desire to secure by Letters Patent in the United States is:

1. A furnace for heating gas, including: an elongated, generally cyclindrical inner container for receiving gas to be heated; heating means extending into said inner container for heating gas therein; conduit means communicating with said inner container for supplying gas to said inner container and for removing gas from said inner container after the gas has been heated; an elongated, generally cyclindrical, gas tight outer pressure container positioned around said inner container in spaced relationship thereto; gas pervious insulation substantially filling the space between said inner and said outer containers so that the operating temperature of said outer container is substantially lower than the operating temperature of said inner container; said insulation including an insulation insert removably received between the side walls of said inner and outer containers; said insert including coaxial, radially spaced apart cyclindrical members separated by a body ofgas pervious insulation; the inner of said members being spaced outwardly of the side wall of said inner container and axially shorter than said body of gas pervious insulation so that said body of gas pervious insulation is in communication with said inner container; and

said inner container having at least one opening communicating with said insulation so that said inner container is subjected to no more than a low pressure differential.

2. A furnace as set forth in claim 1, wherein: said heating means includes at least one electric heating element extending through one wall of said inner container; said one wall of said inner container being spaced from said at least one heating element,

3. A furnace as set forth in claim 1 wherein; said inner and outer containers include spaced apart end walls and a brick plug of porous insulation material is positioned between corresponding end walls of said inner and outer containers.

Claims

1. A furnace for heating gas, including: an elongated, generally cyclindrical inner container for receiving gas to be heated; heating means extending into said inner container for heating gas therein; conduit means communicating with said inner container for supplying gas to said inner container and for removing gas from said inner container after the gas has been heated; an elongated, generally cyclindrical, gas tight outer pressure container positioned around said inner container in spaced relationship thereto; gas pervious insulation substantially filling the space between said inner and said outer containers so that the operating temperature of said outer container is substantially lower than the operating temperature of said inner container; said insulation including an insulation insert removably received between the side walls of said inner and outer containers; said insert including coaxial, radially spaced apart cyclindrical members separated by a body of gas pervious insulation; the inner of said members being spaced outwardly of the side wall of said inner container and axially shorter than said body of gas pervious insulation so that said body of gas pervious insulation is in communication with said inner container; and said inner container having at least one opening communicating with said insulation so that said inner container is subjected to no more than a low pressure differential.

2. A furnace as set forth in claim 1, wherein: said heating means includes at least one electric heating element extending through one wall of said inner container; said one wall of said inner container being spaced from said at least one heating element.