US3790340A

US3790340A - Cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere under high pressure

Info

Publication number: US3790340A
Application number: US00367103A
Authority: US
Inventors: S Isaksson; H Larker; M Lindberg
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1972-06-13
Filing date: 1973-06-05
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05
Also published as: JPS4957421A; SE363957B

Abstract

In a cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere under high pressure, the furnace chamber is insulated from the walls of the pressure chamber by at least three tubular parts arranged one inside the other with insulating parts. At least one ring is provided attached to one of the tubular parts and having a downwardly and inwardly sloping similar part secured to the inside of this part and directed towards, but terminating short of, the opposed part.

Description

United States Patent 11 1 Isaksson et a1.

CYLINDRICAL ELONGATED FURNACE FOR TREATING MATERIAL AT HIGH TEMPERATURE IN'A GASEOUS ATMOSPHERE UNDER HIGH PRESSURE Inventors: Sven-Erik lsaksson; Hans Larker; Mats Lindberg, all of Robertsfors, Sweden Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: June 5, 1973 Appl. No.: 367,103

Assignee:

Foreign Application Priority Data June 13, 1972 Sweden 727781 U.S. Cl. 432/249, 432/251 Int. Cl. F23m 5/00 Field of Search 432/247, 249, 251, 252

j [451 Feb. 5, 1974 [56] References Cited UNITED STATES PATENTS 3,615,082 10/1971 Beck 432/251 X 3,682,457 8/1972 Hollingsworth 432/251 3,743,132 7/1973 Larker et al. 432/250 Primary Examiner.lohn J. Camby [57] ABSTRACT In a cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere under high pressure, the. furnace chamber is insulated from the walls of the pressure chamber by at least three tubular parts arranged one inside the other with insulating parts. At least one ring is provided attached to one of the tubular parts and having a downwardly and inwardly sloping similar-part secured to the inside of this part and directed towards, but terminating short of, the opposed part.

.7 Claims, 3 Drawing Figures PAIENIEU FEB 51914 SHEET 1 BF 2 Fig BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical elongated, preferably vertical furnace for simultaneous treatment of material at high temperature, up to 1500C, in a gaseous atmosphere under high pressure, preferably 500 bars and above.

2. The Prior Art The problems involved with furnaces of this type and also such a furnace have been described previously in US. Pat. No. 3,598,378.

ln furnaces of this type the furnace chamber must be insulated from the walls of a pressure chamber since these walls must be kept below a certain temperature for reasons of strength and because the heat losses must be kept down if it is even to be possible to achieve the desired temperature with reasonable power supply. The thickness of the insulation must also be kept down since the pressure chamber space is expensive and the cost of the pressure chamber increases sharply with increased diameter. The insulation is therefore an extremely important part of a pressure furnace.

Furnace insulation having a cylindrical insulating casing constructed'of a number of tubes placed one inside the other with insulating material in the gaps between the tubes has been found to provide extremely good insulation, thus enabling the thickness of the casing to be kept slight. However, it has been found that the difficulty of maintaining satisfactory insulation increases with increased furnace height, that is, with the length of the cylindrical insulation casing. The reason for this is that if the casing is long it is difficult to pack the insulating material in the annular space nearest the furnace chamber, that is, in the gap between the two inner tubes of the casing, where an extremely heatresistant insulating material must be used. Suitable types of material normally consist of A1 0 SiO and possibly Cr O When being packed the material is fibrous and soft, butit gradually hardens and becomes brittle. It must be packed uniformly and well for good heat-insulating capacity to be obtained. If the casing tubes are very long, there is also considerable risk that the tubes will be displaced with respect to each other when the insulating material is being packed in, so that they are no longer concentric. The thickness of the insulating layer will therefore vary around the circumference. Furthermore, if the furnace is tall, the convection will be considerable if cracks are formed in the insulating layer or if gaps are formed between the insulation and the casing tubes. The force'giving rise to the convection increases with increased height of the furnace.

By means of the present invention the convection is dampened if cracks or gaps are formed. Furthermore, it improves the chances of packing the insulating material uniformly and keeping a uniform gap between the two tubes on each side of the insulating layer. It also allows stabilization of the casing and this can be kept circular. It is characterised essentially in that, between two tubular parts in the casing, at least one ring is arranged having less radial extension than the gap be tween these tubular parts and is gas-tightly connected to one of them. The ring is constructed so that its generatrix, at least along a part of its length, is inclined with respect to a radial plane through the furnace. It is preferably gas-tightly joined to the outer of two tubular parts between which it is arranged. The generatrix of the ring is suitably directed downwardly in relation to the tube section to which it is sealed. Between the ring and the tube section, therefore, a space is formed which is closed at the top. The ring is thus normally funnel-shaped and may be constructed of a cylindrical or substantially cylindrical part and one or two conical parts. This construction increases the length of the bridge in the insulation in the gap between two tube parts, which results in making the heat dissipation in the ring material negligible. The ring or rings also make it easer to manufacture a tube part in the casing in several sections and join these as the casing is being built up and the insulating layer packed. The ring may constitute a stabilizing and centering element which facilitates jointing and welding.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying drawings.

FIG. 1 shows a pressure furnace,

FIG. 2, on a larger scale, shows an insulating casing in a furnace and H6. 3 shows a detail ofthis casing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings,.l designates a press stand which is movably arranged between the position shown in FIG.

chamber is attached to the pillar 9. The chamber has an upper end closure 15 which projects into the high pressure chamber tube 11. Between the tube and the end closure is a sealing ring 16. The actual furnace chamber 17, in which the charge 18 is inserted, is surrounded by an insulating casing 19 suspended in upper end closures l5 and gas-tightly connected to this. In the upper part of the casing 19 is an insulating lid 21 which is attached by an attachment ring 22 to the attachment ring 23 of the casing 19. In the upper end closure is a gas channel 24 for supplying pressure medium and a lead 25 for an electric cable 26. The gas channel 24 opens into the gap 27 between the tube 10 and the casing 19. In the furnace chamber 17 is a heating element 28 supported bya tube 30. Above the upper end closure is a pressure plate 31 with a groove for the electric cable 26. The pressure chamber has a lower end closure comprising an annular part 32 permanently arranged in the cylinder 10 and a bottom 33 projecting into the annular part, with an insulating bottom 34.

Between the tube 10 and the part 32 and between the part 32 and the btoom 33 are

seals

35 and 36. The bottom 33 is attached by a bracket 37 to a sleeve 38 running along a guide 40 which is attached to the pillar 9.

The bottom 33 can be raised and lowered with the help i of an operating cylinder 41, the piston rod 42 being attached to the bracket 43 on the sleeve 38.

. As shown in FIG. 2, the casing 19 comprises three

concentric tubes

44, 45 and 46, all suspended in the attachment ring 23. The tube 45 is firmly joined at its lower end to the ring 47, while the

tubes

44 and 46 can move freely in relation to ring 47 when the tubes expand or contract at different rates because of heating or cooling. The space between the

tubes

44 and 45 is filled with insulating material 48 which will stand high temperatures. Outside the tube 45 is a layer 50 ofa feltlike insulating material which abuts substantially only the tube 45. It is kept in position by helically wound, slightly springy strips 51. The compression of the insulating layer effected by the strips has a damping effect on the vertical gas circulation within the insulating layer. The insulating layer 50 may consist of a felt material which is sold under the name Fiberfrax, or of a felt material made of carbon fibers. The tube 45 may be made of stainless steel or an alloy sold under the name Hastaloy X. The strips are also preferably made of the materials mentioned. With a felt thickness of 12 mm, the distance between turns of the strip 51 should suitably be 10 15 mm. As can be seen in FIGS. 2 and 3, there is normally a clearance between the felt layer 50 and the tube 46. The friction between this layer and the tube and consequently the stresses in the tube 46 are therefore eliminated when the

tubes

45 and 46 alter in length.

FIG. 3 shows the positioning and design of a convection-reducing ring 52 in the insulating casing. In the embodiment shown, the ring comprises a flat ring 52a which is joined in a gas-tight manner to the center tube part 45 of the insulating casing by means of welds 55. A tube 52b having slightly smaller diameter than the tube 45 is gas-tightly joined by welds 54 and 53 to the ring 52a and the conical ring 52c which forms a part the generatrix of which is inclined with respect to a radial plane perpendicular to the longitudinal axis of the cylinder. Between the ring 52 and the tube 45 a pocket 56 -isformed. The conical ring 520 has a greater inner diameter than the tube 44 and a gap is therefore formed between these elements. This is necessary, among other things, because

tubes

44 and 45 are heated at different rates and will therefore be expanded to different lengths. The difference in extension can be limited but not completely eliminated by a suitable choice of material. "Ihe embodiment shown in FIG. 3 permits the tube .two

tubular parts

44,45.

45 to be constructed in several sections. One section is 7 passed over the tube 44, the insulating material 48 is then packed in the gap between the

tubes

44 and 45, after which a new section is passed over the tube 44 and welded to the first section by means of a weld 55. This considerably facilitates manufacture. It is an almost insuperable problem to pack insulating material satisfactorily into a gap 25 mm wide between tubes two meters in length. i

We claim:

l. Cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere under high pressure, comprising a cylindrical pressure chamber including a high pressure cylinder and end closures projecting into the high pressure cylinder, pressureabsorbing members which take up axial forces exerted on the end closures, and a furnace chamber arranged in the pressure chamber, a cylindrical casing insulating said furnace chamber from the walls of the pressure chamber, said cylindrical insulating casing having at least three tubular parts arranged one inside the other with insulating material between such parts, an insulating lid and an insulating bottom, at least one ring 52 arranged between two of said

tubular parts

44,45 having less radial extension than the radial distance between the said

tubular parts

44,45 and being gas-tightly connected to one of said tubular parts 45.

2. Furnace according to claim 1, in which the generatrix of the ring, at least along part of its length, is inclined with respect toa radial plane perpendicular to the longitudinal axis of the cylinder.

3. Furnace according to claim 1, in which the ring 52a is attached in a gas-tight manner to the outer of the 6. Furnace according to claim 5, in which the ring 52a comprises a substantially cylindrical part'52b and at least one funnel-shaped part 520.

7. Furnace according to claim 1, in which the tubular part 45 to which the ring 52 is connected is constructed in sections which are jointed at ring connections. i t III 4' i which the genera-

Claims

1. Cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere under high pressure, comprising a cylindrical pressure chamber including a high pressure cylinder and end closures projecting into the high pressure cylinder, pressure-absorbing members which take up axial forces exerted on the end closures, and a furnace chamber arranged in the pressure chamber, a cylindrical casing insulating said furnace chamber from the walls of the pressure chamber, said cylindrical insulating casing having at least three tubular parts arranged one inside the other with insulating material between such parts, an insulating lid and an insulating bottom, at least one ring 52 arranged between two of said tubular parts 44,45 having less radial extension than the radial distance between the said tubular parts 44,45 and being gas-tightly connected to one of said tubular parts 45.

2. Furnace according to claim 1, in which the generatrix of the ring, at least along part of its length, is inclined with respect to a radial plane perpendicular to the longitudinal axis of tHe cylinder.

3. Furnace according to claim 1, in which the ring 52a is attached in a gas-tight manner to the outer of the two tubular parts 44,45.

4. Furnace according to claim 3, in which the generatrix of the ring is directed downward in relation to the connection with the tubular part 45 to which it is gas-tightly joined.

5. Furnace according to claim 1, in which the ring 52a is at least partially funnel-shaped.

6. Furnace according to claim 5, in which the ring 52a comprises a substantially cylindrical part 52b and at least one funnel-shaped part 52c.

7. Furnace according to claim 1, in which the tubular part 45 to which the ring 52 is connected is constructed in sections which are jointed at ring connections.