US3053919A

US3053919A - Furnace construction

Info

Publication number: US3053919A
Application number: US861287A
Authority: US
Inventors: Poole Henry Gordon; Allen D Abraham
Original assignee: Oregon Metallurgical Corp
Current assignee: Oregon Metallurgical Corp
Priority date: 1959-12-22
Filing date: 1959-12-22
Publication date: 1962-09-11
Anticipated expiration: 1979-09-11

Description

Sept. 11, 1962 H. G. POOLE ET AL FURNACE CONSTRUCTION 2 Sheets-Sheet 1 Filed Dec. 22, 1959 HllenDHbraham Heru 6.1 0018 P 11, 1962 H. G. POOLE ET AL FURNACE CONSTRUCTION 2 Sheets-Sheet 2 Filed Dec. 22, 1959 HIIenDHbraham Henry CiPoole NVENTORS Hf? s.

United States Patent Office 3,053,919 Patented Sept. 11, 1962 3,053,919 FURNACE CONSTRUCTION Henry Gordon Poole, Golden, Cold, and Allen D. Abraham, Albany, reg., assignors to Oregon Metallurgical Corporation, Albany, Greg, a corporation of Oregon Filed Dec. 22, 1959, Ser. No. 861,287 16 Claims. (Cl. 13-8) This invention relates to a novel furnace construction, and more particularly to a furnace for producing within a confined zone relatively high temperatures. The furnace is characterized by a number of novel features contributing to easy charging of the furnace, high thermal efiiciency, close control over operating temperatures, ease of repair without extensive shut-down time, control of atmospheric conditions Within the furnace, etc.

Commonly in various heat-treating processes it is desit-able to produce in a thermal reactor relatively high temperature within a confined treating zone, and maintain such temperature over long periods of time. Frequently controlled atmospheric conditions are also necessary, as areaction within the furnace may have to be carried out in the presence of an inert gas, or a gas mixture that excludes gases reactive with material being treated at furnace temperatures. Illustrative of various applications wherein the furnace or thermal reactor of this invention may be employed are simple heat treatments with helium, hydriding reactions, the Pidgeon process for magnesium, tin reduction of moly bdenite, thermal dissociation of molybdenite at high temperatures, and hydrogen reduction of molybdenum oxide. The invention is described hereinbelow in detail in connection with tin reduction of molybdenite although such should not be construed as a limitation in view of the wide range of uses for the furnace partially indicated above.

Furnace constructions are known that comprise furnace walls of refractory material defining a furnace chamber and a heater for the furnace comprising electric re sistance wire Wrapped around the outside of the filrnace Walls. The resistance Wire is in contact with the furnace walls and supported thereon. While satisfactory in some uses, the type of construction just outlined has a number of disadvantages. The provision of a heater wire around the outside of the furnace walls detracts from the efficiency of heat transfer to the inner furnace chamber. Further, the contact of the heater wire with the furnace walls makes necessary long Warmup and cooldown periods, in order to prevent excessive cracking of the furnace walls. In certain applications the heater wire itself frequently will burn out, particularly if certain gases came in contact with the wire to cause oxidation. When such a heater wire fails, its replacement is a lengthy and diflicult operation with conventional furnace constructions, and almost impossible if controlled atmospheric conditions within the furnace are to be maintained.

According to this invention, the furnace construction in an embodiment of the invention comprises an elongated, hollow, ceramic member provided with openings at opposite ends accommodating the circulation of gas therethrough. The interior of the hollow member constitutes a furnace chamber in the construction. A removable electric heater is mounted within the furnace chamber, and when this is energized, heat is transferred from the element to the circulating gas passing thereover and thence to the material being treated. Around the exterior of and adhered to the ceramic member is a covering of a cementitious refractory material that holds the walls of the member in place in the event that some cracking of the walls should occur. Around this covering is a covering of insulating material, and the whole is enclosed in a metal shell or casing.

Adjacent an opening at one end of the hollow member (the outlet for the furnace) and functioning to close it oif whereby controlled atmospheric conditions may be maintained Within the furnace chamber is a condenser section having wall structure defining a condensing chamber that receives the gases passing out of the furnace chamber. Similarly, adjacent the other of the openings and closing it off is a charging section having wall structure defining a manipulating chamber that communicates with the inner furnace chamber. The heater is proportioned to enable its removal from the furnace chamber through the inlet, and placement in the manipulating chamber. The furnace is constructed so that this can be done without opening up the furnace chamber and destroying any regulated atmospheric conditions set up therein. Thus glove-closed ports are provided that include glove memibers enabling an operator to reach in from the manipulating chamber and pull any defective heater from out of the furnace chamber. Once removed, a faulty heater may be replaced using the same ports.

From the above brief introduction it will be seen that faulty elements may be replaced rapidly without extensive shutdown time or loss of atmospheric conditions. Cracking of the furnace walls is minimized, and if such does occur it has little effect on furnace operation. Fast warmups are possible, as are maximum efliciencies in heat transfer, since heat is generated directly Within the interior of the furnace and thence transferred to the furnace charge.

Thus it is a general object of the invention to provide a furnace wherein relatively high temperatures may be produced within a confined zone by a heater disposed within the confines of a hollow member defining the zone.

Another object is to provide an improved thermal reactor where heat energy is introduced by heating a circulated gas.

Another general object is to provide an improved furnace having a heater that may be easily replaced in case of failure, without disrupting established atmospheric conditions.

Another object of the invention is to provide an improved furnace construction having a confined furnace chamber wherein additional chambers are provided at the inlet and outlet for the furnace chamber, one of which operates to collect and condense reaction products produced in the furnace and the other of which enables re moval of the heater without opening up the interior of the furnace.

Still another object is to provide a furnace construction that includes a furnace shell or casing housing the furnace walls, and wall structure joined to the shell defining condensing and manipulating chambers, wherein cooling of the casing is effectively done adjacent where such wall structure joins with the casing.

Still another object is to provide an improved construction for the heater, whereby it is readily moved in and out of a furnace chamber.

Another object is to provide a novel construction for the resistance element of an electric heater, whereby it is readily attached and detached to supply leads therefor.

Another object is to provide a furnace construction wherein a manipulating chamber is included to enable removal of the heater, and wherein means are provided the manipulating chamber accommodating the insertion of material into the chamber without disrupting atmospheric conditions established therein.

Another object is to provide a furnace that is easily cleaned and inspected between and during intervals of use.

Other objects and advantages are attained by the invention, which is described hereinbelow in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side view of a furnace constructed according to an embodiment of this invention, with portions broken away;

FIG. 2 is an end view of the right end of the furnace illustrated in FIG. 1, also with portions broken away;

FIG. 3 is a section view along the line 33 in FIG. 1; and

FIG. 4 is an enlarged view of the hollow tube that defines the furnace chamber, and a construction for a heater element that is supported within the interior of the furnace chamber.

Referring now to the drawings, and in particular to FIG. 1, the furnace construction shown comprises a central furnace section, indicated generally at 113, including a metal furnace casing or shell 11 encompassing a hollow, open-ended ceramic tube or tube portion indicated at 12 extending through the furnace casing. The walls of tube 12 constitute furnace walls defining within the tube a furnace chamber 13. At the charging or inlet end of tube portion 12, or to the right in FIG. 1, is wall structure 16 of a charging section defining a hollow manipulating chamber 15 communicating with inlet 17 of the tube portion. To the left of easing or shell 11 is wall structure 18 of a condenser section defining a hollow condensing chamber Ztl communicating with outlet 22 of tube portion 12. The furnace construction, comprising the central furnace section and the condenser and charging sections may be supported above the floor on suitable frame structure 24.

7 Considering now specific details of construction of the furnace section, tube portion 12 may be made of alundum or similar material capable of withstanding high temperatures. Casing or shell 11 comprises center, box-like portion 25 closed off at its ends by

opposed end walls

26, 28. These end walls are provided with openings 39, 32 that snugly receive and thus mount the protruding ends of tube portion 12. Surrounding tube portion 12 is a layer of refractory material at least partially comprised of a cementitious material, indicated at 36, and surrounding the latter and confined within casing 11 is a layer of insulating material which may take the form of insulating firebriek, indicated at 38. Layer 36 may take the form of a mixture of alundum and mortar, and is adhered to the periphery of ceramic tube 12, so that the walls of the tube portion are held in place regardless of any cracking of the tube that may occur by reason of heating and cooling. The walls of the tube portion, refraetory layer 36, and firebrick insulation 38 together provide insulation for the high temperatures generated within the furnace chamber.

In the form of the invention shown, end wall 26 of casing 11 is secured in fixed position to center portion 25 as by welding, whereas end wall 28 is detachable from center portion 25 to enable repair of the furnace in the event such should be necessary. The connection of end wall 28 with center portion 25 is by screw connections 48. As indicated earlier, the furnace is used often under vacuum conditions or under controlled atmospheric conditions. Thus it is important that shell 11 be airtight. To this end, end wall 28 is placed in sealing relationship with box-like center portion 25 by O ring seal 50. Cooling of the end wall 28 and box-like center portion 25 adjacent the location of the ring seal is provided for by including a tube 52 about the outside of casing 11 for the circulation of a coolant.

Considering now more specifically the wall structure 18 defining the condenser section, this comprises an elongated, substantially upright casing structure 54 of substantially square cross-section. The casing structure includes side walls indicated at 55, 56-, 57 and 58. A top 60 bounds the top of the casing structure, and at the bottom of the casing structure is a frusto-pyramidal or hopper portion 62. The walls of the casing structure are made of metal, and thus have heat dissipating properties. In operation of the furnace, hot gases and reaction products leave furnace chamber 13 and collect in the condenser section where they are cooled and condensing solids drop to the base of the casing structure and collect in hopper portion 62. To accommodate removal of material from the condenser section, the bottom of hopper portion 62 is provided with an opening 63 normally closed by a cover 64. The latter is secured to the hopper portion as by screw assemblies 66.

Condenser section 18 further includes a view port 7% adjacent the top of side wall 55. The view port is closed by a cover '72 that includes a transparent window portion enabling the inspection of the interior of the condenser section. Cover 72 is secured over the view port by screw assemblies '74. At the top of the condenser section is a light port 76 closed by a cover 78 provided with a transparent window section as is cover 72 and secured in place by screw assemblies 80. Completing the description of the condenser section, projecting into side wall below view port is a tube portion 82 integral with the side wall that receives an elongated rod 84 used in cleaning the interior of furnace chamber 13 and positioning a charge in the chamber. A suitable seal (not shown) is provided between the rod and tube portion 32 whereby the interior of the condenser section may be maintained sealed off from the outside of the furnace.

Casing structure 54 of the condenser section is secured to end wall 26 of shell 11 by screws 90. Wall 56 of the casing structure has an accommodating aperture receiving a protruding portion 92 of end wall 26 and the outlet end of ceramic tube portion 12. An airtight seal is produced between side wall 56 and end wall 26 by means of an O ring $1. The walls of shell 11 and the condenser section are cooled adjacent the location of the O ring by circulating a coolant through a manifold 96.

Considering now the wall structure 16 defining manipulating member 15, and referring to FIGS. 1 and 2, this comprises top and bottom walls 93, 99 and side walls 1%, 191, 132, 1 63. These walls also are metal in order that heat may be dissipated through the walls. The wall structure is joined to end wall 28 of shell 11 through a sleeve assembly generally indicated at 196. This includes a sleeve portion 103 integral with end wall 23 and a sleeve portion 11b integral with side wall 1% of structure 16. Sleeve portion nests within sleeve portion 108, and an 0 ring 112 is provided that is clamped between the sleeve portions to seal the two together when the sleeve portions are drawn together by means of screws 1114. Cooling coils 116 for circulating a coolant extend around the periphery of sleeve portion 168 and cool the sleeve assembly and the O ring that is part of the sleeve assembly. The coils 116 also aid in inhibiting heat transfer to the manipulating chamber 15.

Wall structure 16 defining the manipulating chamber '15 of the charging section further comprises a light port 120 provided top Wall 98 that is closed by a cover 122 provided with a transparent window portion and secured in place by screw assemblies 124. Side wall 102 is provided with a sight port 128 closed by cover 13%} and provided with a transparent window portion 132. Side wall 1111 is provided a port 136 closed by a cover 138 secured by screw assemblies 14!). Cover 133 is provided with a tube portion 142 receiving a rod 143. The latter rod is similar to rod 84 and is used for positioning a charge within the furnace and for cleaning purposes. Cover 133 also has integral therewith a tube section 144 having a cap 146 including a window 145 enabling inspection of the interior of furnace chamber 13.

An advantage and feature of the furnace construction of the invention is that a heater may be removed from within the furnace chamber in the event it need be replaced, with a minimum of shut-down time. Substitution of a new heater for a faulty one is accomplished within the manipulating chamber 15 defined by structure 16.

Thus within the chamber there may be provided a shelf 14-8 to carry spare heaters and repair equipment.

To facilitate the manual removal of a heater from furnace chamber 13 and other adjustments, a pair of gloveclosed port assemblies are included in side wall 132, indicated generally at 150 and illustrated in FIGS. 1, 2 and 3. The two are substantially the same in construction and thus only one is described. Referring to the figures mentioned, each comprises a port 151, and a flexible glove member 152 of rubber or other synthetic material adapted to receive a persons hand and secured in sealing relation with an annular flange portion 154 partially defining port 151. Over the outside of flange 154 is a cover 156 which may be secured in clamped relationship over the end of the glove member by screw assemblies 153. Within the interior of manipulating chamber 15 is a closure plate 160 slidable up and down and guided in guide rails 162. Closure plate 161 is held in a raised position wherein port 151 is opened by a latch ring 164 that fits over a catch 165. Cam 163 is for releasing the latch ring from the catch (through sharp up and down movement of plate 160) when it is desired to close port 151. The inner closure plate confines the glove member from the inside of the manipulating chamber when, for instance, sub-atmospheric pressures are present in the furnace. The outer cover 156 is for closing and sealing each port assembly. When it is desired to manipulate inside the manipulating chamber, the outer covers 156 are detached, a persons hands are inserted in the glove members, the inner closure plates are lifted and latched in place, and the manipulating chamber is then accessible Without disrupting any controlled atmospheric conditions existing within the furnace. Adjacent bottom wall 99 of wall structure 16 is a loading assembly, indicated generally at 1761 and illustrated best in FIGS. 1 and 2. Specifically, and with reference to these figures, bottom wall 99 of the wall structure is provided with an aperture 172 rimed by an angular flange 174. Securedto this angular flange and sealed thereto by seal 1'76 is a cover section 178 provided with a central port 1811. Integral with cover section 178 and at opposite sides thereof extending downwardly therefrom are the legs of a U-shaped member 182. These legs through their connection with cover section 178 and bottom Wall 99 are held in fixed position. Alongside each leg is a toggle link mechanism 184, each comprising toggle links 184a and 18412. Toggle links 184a, 18417 of each mechanism are connected at adjacent ends by a pivot connection 185. The bottom end of each toggle link mechanism is pivoted adjacent the bottom of a leg of member 182 by a pivot connection 186 and the top end of each toggle link mechanism is connected by a pivot connection 187 to a hollow loading bucket or receptacle, indicated at 190. Receptacle 1911 has its top placed in sealing relationship with cover section 178 by O ring seal 192.

Port 180 constitutes an entrance port for the manipulating chamber. The interior of receptacle 19% opens to port 181). Receptacle 1911 is moved away from the entrance port when it is desired to place material therein prior to placing it within chamber 15. Thus a handle portion 194 is connected to the bottom links 184a of the toggle link mechanisms 134. This handle may be pulled to the left (viewing FIG. 2), with the toggle links moving from the over-center position shown to an angular position with respect to each other, and this movement of the links is accompanied by movement of bucket 19% downwardly from port 130, to the position shown by the dotted outline in FIG. 2, where further movement of the receptacle is limited by stop 1% (which is secured to the receptacle) striking bracket 182. Ears 197 on the handle are provided with suitable bores receiving studs 198 with the bucket in a raised position, and nuts screwed onto these studs secure the bucket in a raised position. Within the manipulating chamber, a cover 200 is provided that is pivoted to the bottom Wall by pivot connections 202.

This cover closes the top of entrance port (thus constitutes a closure means for the entrance port), and is sealed to cover section 178 by seal 204. Cover 200 is secured in place by wing nuts 206. Note that cover 200 may be opened from within chamber 15 with receptacle 1% in operative position and secured in covering relation over the bottom of port 131).

The furnace construction of the invention enables the heating of materials under regulated atmospheric conditions. Thus there is provided means for circulating specific gases in the furnace, such as an inert gas, hydrogen and the like, and for removing air from the furnace. Referring to FIG. 1, wall structure 16 defining manipulating chamber 15 is provided with a conduit 210 connecting with the chamber, and wall structure 18 of the condenser section is provided With a conduit 212 connecting with chamber 21 These conduits may be connected to a suitable cleansing system, in the event that it is desired to recirculate specific gases in the furnace. Note also that the loading receptacle is provided with means for purging gas therefrom and for introducing a specific gas or gas mixture into the interior thereof, by including at the base of the

receptacle conduits

214, 216.

A form of heater means employed for heating the interior of the furnace is illustrated in FIG. 4. Specifically, and with reference to this figure, 220 indicates the heater means generally. This comprises a ceramic cylindrical block or mount 222 mounting a pair of elongated electrical lead elements or rods, indicated at 224, 226. Ceramic block 222 preferably has a cylindrical shield such as shield 22% secured about its periphery, to reduce sliding friction between the block and the inner surface of ceramic tube portion 12 during positioning of the heater. The shield and rods are made of suitable metal, and in a molybdenum reduction reaction the shield and rods ordinarily would be made of molybdenum.

Secured to the left ends of the rods in FIG. 4 is an electric resistance element indicated at 232. This may also be made of molybdenum and is bent in the form of a double loop. The resistance element is secured at its ends to the left ends of

rods

224, 226 by fitting the ends into clamp portions 234 of the rods. A central portion of element 232 is supported by fitting it within a clamp member 235 that has an end 235a supported in a tube 236. End 235a is a relatively thin portion curved semicylindrically and contacting snugly the inner wall of tube 236, and thus the inner bore of tube 236 is left substantially open whereby gas may flow through the tube and thence through furnace chamber 13. A resistance element is detached from block 222 by pulling it on. from clamp portions 234 and clamp member 235. Power is supplied element 232 by flexible conductors 240 and supply conductors 242.

In the reduction of molybdenite in a hydrogen atmosphere, a molybdenite-tin charge may be placed in a boat indicated at 244, shaped as a semi-cylindrical shell open at the top (the side shown in FIG. 4) and closed at its ends. A charge, such as that indicated at 248-, is placed within the interior of the boat. The charge may take the form of a sintered mixture of tin and molybdenite shaped as a cylindrical pellet, such pellet having an outer diameter only slightly less than the diameter of the inside of boat 244. Pellet 248 may be provided with a center bore 250 for the circulation of gas through the center thereof. The boat holds the charge and any part thereof that may melt out of contact with the furnace walls defining chamber 13.

Explaining the operation of the furnace in connection with the reduction of molybdenite, a charge is placed in boat 244, and the boat inserted into chamber 13 using push rod 143. Heater means 220 is then inserted Within the furnace chamber between the boat and manipulating chamber 15. With the boat and heater positioned, hydrogen may be passed through the furnace, at a flow rate, for example, of 200' to 300 cubic feet per hour.

7 Current may then be supplied the heater, with temperatures in the range of 15002500 C. quickly obtained, the specific temperature resulting in a given case depending upon the power input and the rate of gas flow. The specific flow rate and temperature mentioned are by Way of illustration.

During the reaction, hydrogen gas flows through the chamber 13, and through its heating before reaching the charge, transfers heat from the electric resistance element to the charge. As heat is applied the charge, volatile reaction products form, and these are carried off in the gas stream into condensing chamber 20. While the central ceramic tube portion 12 is heavily insulated within casing or shell 11, the walls 18 of the condenser section dissipate heat and thus the interior of chamber 20 is substantially cooler than the interior of chamber 13. Reaction products are condensed in chamber 2%, and drop to the hopper portion at the base of the chamber. Hydrogen gas with certain impurities is drawn off through conduit 212, whence it may be cleaned and recirculated.

The manipulating chamber 15, by reason of cooling coils 116 around sleeve assembly 106, since it is on the upstream side from the heater means, and since its walls also dissipate heat, ordinarily remains at approximately room temperature. In the event a heater element burns out, the power to the heater may be cut off and the heater removed by pulling block 222 and the element 2 32 connected thereto out through the inlet to tube portion 12. An operator removes the heater by opening the gloveclosed port assemblies 15H and inserting his hands into the glove members, which enables him to manipulate within the chamber. A new resistance element is readily positioned on

rods

224, 226 and the heater subsequently inserted into the furnace in an elapsed time of only minutes. The furnace then may be started and furnace temperatures reinstated. Note that throughout the entire operation regulated atmospheric conditions are maintained, and purging of the furnace after replacement of a heater is unnecessary.

It should be noted that the heater is carried out of contact with the walls of the ceramic tube. This enables fast warmup periods, without excessive cracking of the tube walls. Should some cracking of the tube occur, however, the layer surrounding the tube portion containing cementitious material holds the tube portion together and the operation of the furnace is not affected. The entire furnace is sealed, and should gases escape into the insulating material, operation of the furnace is not impaired.

Summarizing important aspects of the invention, what has been disclosed is a thermal reactor wherein heat is introduced to the charge in a reaction zone by heating a circulating gas, such gas then traveling over the charge. The gas may be purified and recirculated. The means for heating the gas in the embodiment shown is a resistance element, although in other embodiments are heaters or other forms of heaters may be practicable.

Fast reaction rates are possible, because of the type of heat exchange between the heated gas and the charge in the reactor. With a constant energy imput, the rate of gas flow controls the amount of heat transfer and the reaction temperature. With a constant flow, gas temperature and reaction rate may be adjusted by varying the energy imput. As a corollary of the above, both the flow of gas and the energy imput may be changed simultaneously to control temperatures. The provision of means for varying the pressure within the furnace or reactor provides another means for varying the rate of reaction within the reaction zone.

It should be noted that the circulated gas may function solely as a carrier, as When an inert gas is used. In some applications the gas may function as a reactant, as in carbon monoxide reduction or hydriding reactions. Certain normally solid reactants may be introduced into the gas stream as a vapor.

While there has been described an embodiment of the invention, and its operation in connection with a particular type of reaction, it should be obvious to those skilled in the art that changes may be made in the construction and its use without departing from the invention. It is intended not to be limited by the specific embodiment described, but to cover all modifications and variations that would be apparent to those skilled in the art and that come within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A furnace comprising furnace Walls defining a furnace chamber and spaced openings formed in the furnace walls accommodating the flow of gas therethrough, one of said openings constituting an inlet and the other of said openings constituting an outlet in the furnace, insulating means surrounding the furnace walls, means ad jacent the inlet and outlet of the furnace chamber closing them off whereby controlled atmospheric conditions may be maintained within the furnace chamber, and means for circulating gas through the furnace from said inlet to said outlet and heater means mounted within the furnace chamber having a size small enough to enable its removal through one of said openings and operable when energized to heat the chamber and any gas flowing thereover, said heater means being removable through said one opening.

2. A furnace comprising furnace Walls defining an elongated furnace chamber having openings disposed approximately at either end of the furnace chamber constituting an inlet and an outlet therefor, and accommodating the flow of gas through the furnace chamber, insulating means surrounding the furnace Walls, wall structure having heat-dissipating properties defining a condensing chamber communicating with the outlet for the furnace chamber for collecting gas leaving the furnace chamber and cooling the same, removable heater means supported within the furnace chamber removable through the inlet of the furnace chamber, and wall structure defining a manipulating chamber communicating with the furnace chamber inlet and proportioned to receive the heater means, the Wall structure defining the condensing and manipulating chambers closing off the inlet and outlet of the furnace chamber whereby controlled atmospheric conditions may be maintained within the furnace chamber during operation thereof.

3. A furnace comprising furnace walls defining a furnace chamber for receiving material for heating and having spaced openings accommodating the flow of gas through the chamber, one of the openings constituting an inlet and the other an outlet for the furnace chamber, respectively, removable heater means supported within the furnace chamber and constructed to be removable from the chamber through one of said openings, and means closing oif the inlet and outlet enabling the maintenance of regulated atmospheric conditions within the furnace chamber, said means including wall structure defining a manipulating chamber communicating with said one opening and proportioned to receive the heater means .on removal of the same through said one opening.

4. A furnace comprising furnace walls defining a furnace chamber for receiving material for heating, spaced openings provided the furnace chamber accommodating the flow of gas through the chamber, one of said openings constituting an inlet and the other constituting an outlet, removable heater means supported within the furnace chamber and constructed to be removable through said inlet, and means closing off the inlet and outlet openings enabling the maintenance of regulated atmospheric conditions within the furnace chamber, said means including wall structure defining a manipulating chamber communicating with said inlet and proportioned to receive the heater means on removal of the same through said inlet.

5. A furnace comprising furnace walls defining an elongated furnace chamber having openings at opposite ends accommodating the flow of gas through the chamber, an

electric heater disposed within the furnace chamber and mounting means supporting the electric heater out of contact with the furnace walls, said heater and the mounting means therefor being constructed so as to enable their removal from said furnace chamber through one of said openings, Wall structure covering the openings whereby regulated atmospheric conditions may be maintained in the furnace, said wall structure including wall structure defining a manipulating chamber communicating with said one opening and proportioned to receive the heater and mounting means on their removal from said furnace chamber.

6. The furnace of claim 5, wherein said manipulating chamber includes glove-closed ports provided the wall structure defining the chamber equipped with glove members in sealing relation with the wall structure and having interiors open to the outside of the manipulating chamber, said glove members enabling manual removal of the heater and mounting means from the furnace chamber.

7. The furnace of claim 5, wherein the manipulating chamber is provided with an entrance port formed in the wall structure defining the chamber for placing material in the chamber, closure means for sealing off said entrance port, and a hollow loading receptacle that in one operative position is detachably secured in covering relation over the entrance port, said loading receptacle having an opening that communicates with said entrance port in said one operative position, said closure means being openable with said loading receptacle secured in said one operative position.

8. The furnace of claim 5, wherein the wall structure covering the openings includes over the other of said openings wall structure defining an enlarged condensing chamber having a port accommodating the removal of material from the condensing chamber and closure means for the port.

9. A furnace comprising a furnace section substantially enclosed by a furnace shell, said furnace section having furnace walls defining an elongated hollow furnace chamber open at its ends that extends through the furnace section between a set of opposed sides of the furnace shell, condenser section and a charging section having walls defining a condensing chamber and a manipulating chamber, respectively, joined to said opposed sides of said furnace shell, said condensing chamber communicating with one open end of said furnace chamber and said manipulating chamber communicating with the other open end of said furnace chamber, and means for cooling the furnace shell and condenser and charging sections adjacent where the latter two join with the former.

10. A furnace comprising a furnace section substantially enclosed by a furnace shell, said furnace section having furnace walls defining an elongated hollow furnace chamber open at its ends that extends through the furnace section between a set of opposed sides of the furnace shell, a condenser section and a charging section having walls defining a condensing chamber and a manipulating chamber, respectively, joined to said opposed sides of said furnace shell, said condensing chamber communicating with one open end of said furnace chamber and said manipulating chamber communicating with the other open end of said furnace chamber, sealing means interposed between the condenser and charging sections and the shell of the furnace section whereby the former two are in sealing relation with respect to the latter, and cooling means adjacent where the sealing means are located for cooling the sealing means.

11. A furnace comprising an enlongated hollow member of ceramic material open at its ends and having inner walls defining a furnace chamber, a refractory covering about the exterior of the hollow member at least partially comprised of cementitious material adhered to the exterior of the hollow member, a covering of refractory material about said first-mentioned covering, a metallic furnace shell about said second-mentioned covering, a condenser section and a charging section having walls defining a condensing chamber and a manipulating chamber, respectively, joined to the furnace shell with the chambers communicating with the ends of the furnace chamber, means for cooling the walls of the furnace shell adjacent where the condensing and charging sections join with the furnace shell, and means for heating the furnace chamber, the latter comprising an electric heater disposed within the furnace chamber and held substantially out of contact with the walls defining the chamber.

12. The furnace of claim 11 wherein the electric heater is movable and of a size to accommodate its removal through an open end of the furnace chamber into said manipulating chamber.

13. A furnace comprising furnace Walls defining a furnace chamber for receiving material to be treated, said furnace chamber having spaced openings accommodating the flow of gas through the chamber, one constituting an inlet and the other an outlet, a heater supported Within the furnace chamber movable through said inlet, said heater comprising an electric resistance element, a support, and electrical leads carrying the resistance element mounted in said support, means closing off the openings of the furnace chamber whereby controlled atmospheric conditions may be maintained therein, said means including wall structure defining a manipulating chamber communicating with said inlet proportioned to receive the heater means on its removal through said inlet, said electric resistance element being easily detached from said electric leads.

14. In a furnace, furnace walls defining an elongated hollow furnace chamber with openings at opposite ends, and electric heater means fitted within the furnace chamber and removable through one of said openings, said heater means comprising a slidable mount, an electric resistance heater element, and electric leads completing an electric circuit for said heater element supported on said mount, said electric resistance heater element being detachably connected to said leads and held by the leads out of contact from the walls defining the furnace chamber.

l5. A thermal reactor for heating a charge comprising furnace walls defining a furnace chamber having open infeed and outfeed ends, means for circulating a gas through the chamber with the gas traveling from the infeed to the outfeed end, and means adjacent the infeed end for heating such gas whereby such gas may function as a carrier for the transfer of heat to the charge, said means comprising an electric resistance heater and leads completing an electric circuit thereto supported within the furnace chamber and substantially out of contact with said furnace walls.

16. A thermal reactor for heating a charge comprising furnace walls defining a furnace chamber having openings at opposite ends accommodating the flow of gas through the chamber, an electric heater disposed within said furnace chamber, mounting means supporting the electric heater out of contact with said furnace walls and constructed so as to enable removal of the heater from said furnace chamber through one of said openings, and means for maintaining regulated atmospheric conditions within the furnace and for circulating gas from said inlet over said heater and out of said outlet.

References Cited in the file of this patent UNITED STATES PATENTS 1,239,178 Grosvenor Sept. 4, 1917 2,325,521 Lambert July 27, 1943 2,328,479 Mathieu Aug. 31, 1943 2,330,751 Shaub et a1. Sept. 28, 1943 2,708,156 Paoloni May 10, 1955 2,952,723 Garmy Sept. 13, 1960