Heating mantle with a porous radiation wall

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ates heat from its surface facing the retort to the surface

HEATING MANTLE WITH A POROUS of the retort. Because of the large contact surface be RADATION WALL tween the porous wall and the gases, the porous wall is

BACKGROUND OF THE INVENTION

heated at a high heat transfer rate and can radiate to the 5 retort wall at a high heat transfer rate. More specifi 1. Field of Invention cally, the face through which the gases enter the wall is This invention pertains to a gas-fired heating mantle heated to a temperature substantially equal to the tem for heating a retort furnace, and more particularly to a perature of the combustion gases entering through the heating mantle with a porous wall disposed in the path 10 face of the porous wall. Since the convective mecha for the combustion gases for raising the efficiency of nism of heat transfer, which is usually the rate limiting heat transfer to the furnace. step, has been increased in rate by the large area of 2. Description of the Prior Art contact in the surface of the porous wall, it permits the Gas-fired heating mantles are used extensively in the series mechanism of convection/radiation to proceed at metal processing industry for treating and processing 15 a significantly higher overall rate of heat transfer. Thus metals and alloys, as well as in the inorganic chemical in the present invention, a two step heating process industry in reactors. However present mantles are se takes place. In the first step, combustion gases pass verely deficient in a number of areas which limits their through the porous wall heating it, and specifically its use in commercial applications. The primary deficiency surface, by high rate convection. In a second step, the of present heating mantles is limited heat transfer rate porous wall surface heated by the gases radiates heat at from the mantle to the retort. 20 characteristically high rates, particularly at tempera

Typically, a gas-fired heat mantle surrounds a furnace tures above 1200' F., to the retort thereby improving retort vessel, and is constructed to provide a high rate the overall heat transfer characteristics of the mantle. of heating in a small space. This process is termed a porous wall radiation process Typically, the mantle is made of a steel shell with an or principle and its results in a heat transfer capability in inside lining of insulating refractory and must be shaped 25 the range of 25-60 BTU/hr-sq.-ft- degree F. to direct combustion flames away from the retort vessel to avoid damaging it. In this configuration, heat is trans

BRIEF DESCRIPTION OF THE DRAWINGS

ferred to the retort primarily through two mechanisms: FIG. 1 shows a side elevational cross-sectional view one, by convective heat transfer from the combustion of a mantle constructed in accordance with this inven

gases to the interior mantle wall and the retort vessel wall, and two, by radiation from the interior mantle tion, and shown as applied to the configurations of wall to the retort vessel wall. In a gas-fired heating heatingFIG.

a cylindrical retort vessel;

2 shows a plan cross-sectional view of the man mantle, at temperatures below 1200' F., the radiation heat transfer rates are low due to lower temperatures, tleFIG. of FIG. 1; and 3 is a partial detailed side view of the gases and the convective heat transfer rates are generally low 35 traversing the porous wall of the mantle in FIG. 1. due to low gas velocities. This combination results in low overall heat transfer rates. DETAILED DESCRIPTION OF THE At temperatures above 1400" F., heat transfer by INVENTION radiation from the mantle wall occurs at high rates, Referring now to the drawings, a heating mantle 10 however, the convective rates to the heating mantle constructed in accordance with this invention com wall remain low and becomes the rate limiting step in the overall heat transfer process. This keeps the overall prises a housing 12 made of an insulation material inside heat transfer rates low. a steel shell 24. The housing defines an interior chamber Typically, present heating mantles have a heat trans 14 with an outer wall 16.

fer rate in the range of 5-15 BTU/sq. ft.-hr.-degree F. 45 The chamber 14 is closed off at the top by a cap 18 depending upon temperature level and gas flow rates. with an opening 20. The chamber also has a floor 22 formed by lower housing 27. The lower housing 27

OBJECTIVES AND SUMMARY OF THE forms a cylindrical protective wall 32. Protective wall INVENTION 32 and outer wall 16 define an annular passageway 34 to In view of the above disadvantages of the prior art, it 50 a lower chamber 36. One or more burner systems 38 are is an objective of the present invention to provide a arranged and constructed to inject combustion gases heating mantle with an improved overall heat transfer into the lower chamber 36.

rate, in the range of 15-60 BTU/sq. ft.-hr. degree F., Supported on floor 22 within protective wall 32 there depending upon temperature level and gas flow rates. is a retort vessel 40 for holding the materials that are to The objective is accomplished by providing a heating 55 be treated. The interior of the retort vessel 40 is in con mantle with an innovative geometric configuration for munication with pipe 26 for receiving and/or discharg improved heat transfer by a combined convection and ing materials to be treated in the retort. The pipe 26 radiation process. passes through the lower housing and out through the Other objectives and advantages of this invention opening 28 in the shell. A packing gland seal 30 is pro shall become apparent from the following description of 60 vided between the opening 28 and pipe 26 to prevent the invention. A heating mantle constructed in accor heat and combustion gases from escaping from chamber dance with this invention comprises a housing having a 14.

chamber surrounding a retort or furnace holding the The retort extends through the opening 20 past cap material to be heated. Between the retort and the cham 18. The opening is sealed around the retort at 44. The ber there is a porous wall disposed in the path of the 65 retort has an outer wall 46.

combustion gases used to heat the mantle. The porous In chamber 14, between retort outer wall 46 and the wall is arranged and disposed so that it is convectively wall 16 there is a porous cylindrical wall 48 defined heated by the gases passing through the pores and radi between an inner face A directed toward the retort

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vessel 40, and an outer face B directed toward surface said material holding means, and a second chamber 16 which effectively divides chamber 14 into two annu section defined by said porous wall means and said lar sections: a first section 14 defined between the retort housing.

wall 46 and porous wall 48, and a second annular sec 3. The heating mantle of claim 1 wherein said porous tion 14" concentrically disposed around the first section wall means is constructed and arranged in said path 14 and defined between the porous wall 48 and outer with said gases flowing through said porous wall means. wall 16. An exhaust opening 50 is in connection with the 4. The heating mantle of claim 1 further comprising a second section 14". Preferably, porous wall 48 is termi passageway for leading said hot gases into said chamber nated with a groove 54 which is formed in cap 18. Con and protective wall means disposed adjacent said pas struction of housing 12 and cap 18 is facilitated by 10 sageway for protecting said material holding means flange 52 which connects these two sections. from said hot gases.

The heating mantle operates as follows. After mate 5. A method of heating materials comprising: rial is disposed in retort vessel 40, the burner system 38 a providing a porous member defined between a first is started up which causes high temperature combustion face and a second face; gases to flow into lower chamber 36. The combustion 15 b. passing hot gases through said porous member gases in this chamber are typically between 1000' F. and from said first to said second face for heating said 2700' F. These combustion gases flow from the lower first face to a high temperature by convection; chamber 36 through annular passsageway 34 into the c. heating said material by radiation from said first inner or first chamber section 14. At the point of entry face;

into this chamber section 14, these gases are very hot 20 d. disposing said porous member concentrically and therefore the retort wall is protected from extreme around said material;

temperatures by protective wall 32. From the inner e. passing said gases from a space between said mate chamber section 14 the combustion gases pass through rials and said porous wall through said porous wall; porous wall 48 into the second chamber section 14' and and are then exhausted through flue opening 50. As the 25 f. exhausting said gases after said gases passed gases pass through the inner face A of the wall directed through said second face. toward the retort 42, the face gets heated to a tempera 6. A heating mantle comprising: ture substantially equal to the temperature of the com a. a housing defining a chamber; bustion gases. This porous wall face A radiates heat to b. retort means disposed substantially coaxially the retort wall. 30 within said chamber;

Preferably wall 48 is made of porous ceramic, for c. a furnace system for providing hot gases into said example silicon carbide. For a mantle having an inner chamber in a hot gas path; chamber with a diameter of 34 inches, and a height of 48 d. a porous wall defined between an inner face di inches and a retort of 24 inches outside diameter, the rected toward said retort means and an outer face, wall 48 may be for example 1 inches thick. 35 and disposed in said hot gas path said hot gases Shell 24 is made preferably of steel. The housing 12, entering said porous wall through said inner face cap 18 and lowerhousing 27 are made preferably of cast for heating said inner face, said inner face radiating refractory. The retort is typically made of a high nickel heat toward said retort means wherein said hot alloy steel or high thermal conductivity ceramic. gases flow from said inner face to said outer face; Obviously numerous modifications may be made to and the present invention without departing from their e. means for exhausting said hot gases after said hot scope as defined in the appended claims. gases passed through said outer face. What is claimed is: 7. The heating mantle of claim 6 wherein said cham 1. A heating mantle for heating materials comprising: ber is cylindrical and said retort is disposed along a a. material holding means for holding said material; 45 longitudinal axis of said chamber.

b. a housing defining a chamber which substantially 8. The heating mantle of claim 7 wherein said porous surrounds said material holding means; wall is disposed around said retort. c. a source of hot gases constructed and arranged for 9. The heating mantle of claim 8 wherein said porous supplying hot gases through said chamber in a wall divides said chamber into a first and second cham preselected path; 50 ber section, and wherein said gases flow from said first d. porous wall means defined between a first face to said second chamber section through said porous directed toward said material holding means, and wall.

an opposed second face and disposed in said cham 10. The heating mantle of claim 7 further comprising ber in said path with said gases entering said porous a combustion chamber connected to said furnace for wall means through said first face for receiving 55 burning gases, and a passageway connected between heat from said hot gases, said first face radiating said combustion chamber toward said porous wall. heat toward said material holding means wherein 11. The heating mantle of claim 6 wherein said hous said gases flow from said first face to said second ing includes a cap for closing said chamber, and face; and wherein said porous wall is compressed by said cap to e. means for exhausting said gases after said gases form a seal to flowing gases.

passed through said second face. 12. The heating mantle of claim 11 further comprising 2. The heating mantle of claim 1 wherein said porous a sealing gasket disposed between said cap and said wall means divides said chamber into a first chamber porous wall.

section, defined between said porous wall means and t k k