US2081421A - Furnace - Google Patents

Description

.May 25, 1937. J. o. BETTERTON Er AL FURNACE Filed Aug. 14, 1934 2 Sheets-Sheet 1 May 25, 1937. J. o. BETTERTON r AL FURNACE Filed Aug. 14, 1934 Patented vMay 25, 1937 UNITED STATES .PATENT `OFFICE FURNACE Application August 14,

13 Claims.

This invention relates to furnaces. 'I'he invention provides an improved furnace having a wide application in the chemical and metallurgical arts and is of particular importance in conducting volatilizing operations, especially those which are ordinarily effected only with difflculty. i

' Furnaces embodying the principles of the invention have, proved of signal importance in volatilizing a host of different compounds, materials and substances both pure and impure and in vaporizing and/or subliming many of the oxides, suldes, chlorides, etc. of arsenic, antimony, cadmium, lead, selenium, tellurium, zinc and the like, as well as various mixtures thereof. In such furnaces, remarkably improved results have been attained. Further, the invention permits such reactions as oxidation, reduction, halogenation and sulphatization to be readily practiced under precisely controlled conditions and any such reaction can' be readily inaugurated to be continued indefinitely or, if desired, changed at will.

In accordance with the invention, a furnace is provided having means for simultaneously heating atmosphere of'appropriate, controlled temperature and desired chemical composition.

Although the novel features whichare believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which'it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which Fig. 1 is' ,a longitudinal section through a furnace constructed `in accordance with the invention,

Fig. 2 is a cross-section of the furnace shown in Fig, 1, taken along the line 2--2,

Fig. 3 is a section through a modified form of furnace embodying the invention, and

Fig. 4f is-a section through a further modified form of furnace embodying the invention.

In the following description and in theclaims, various details wi-ll be identified by specific names for convenience, but they are intendedl to be as generic in their application as the art will permit.

Referring now to4 Figs. 1 and 2, Athere is shown a furnace. of the muilied-iiame type having re tubes 'I0 and II extending from the burner end of the furnace through a partition I2, which partition with end wall I3, defines chamber I4.

a charge and subjecting same to the action of an 1934, Serial No. 739,720

Burn'ers I5 (one shown) are operatively associated with re tubes IIJ and II the latter being composed of silicon carbide and set in asbestos cement I6 at the burner end and a suitable highly refractory cement Il in partition I2. Charge hoppers I8 and I9, equipped respectively with slide.

valves and 2|, open to the laboratory of the furnace 22 via feed ducts 23 and 24 respectively. Gas-tight work door 25 permits access to the laboratory of the furnace and a tap hole 26 equipped with removable plug 21 is provided at the lowest point of hearth 28. Pyrometer 29 extends through the side wall into the furnace laboratory. Positioned above the hearth of the furnace are inlet bale 30 and outlet baille 3I. Vent 32 of chamber I4 is equipped with damper 33, and inspection door 34, sampling tube 35 equipped withpressure gauge 36, and auxiliary gas inlet 31 are provided in wall I3. yPort 38 leads from chamber I4 to the laboratory of the furnace and outlet port 39 leads from the latter to the flue system 40. i

In the modified form of furnace shown in Fig. 3 the laboratory of the furnace is of increased dimension, the partition 4I serving both as an additional baffle and as a support for the joint between re tubes 42 and 43. In other respects the furnace structure is similar to that shown in Figs. 1 and 2 and the analogous parts are indicated by the reference characters bearing the suffix a. In the modified form shown in Fig. 4,

44 is` a kettle positioned over fire box 45 associated with burner 46 and ue 41. The superstructure of the furnace is carried by steel members 48' and 49 supported by I-beams' 50. Charge hopper 5I having screw conveyor 52 communicates with feed duct 53 via` slide valve- 54. The kettle 44 and fire box 45 are suitably mounted (not shown) for raising and lowering same into and out of operating position. In other respects the apparatus is similar to that shown in Figs. 1 and 2 as indicated by the analogous reference characters bearing the suffix b.

In operation the material to be treated is placed in hoppers I8 and I9 and supplied to the hearth of the furnace through feed ducts 23 and 24 by suitable manipulation of slide valves 20 and 2I. Obviously the feeding may be continuous or Iintermittent, the former, however, having been found more advantageous for most operations involving the use of the furnace as a volatilizing unit. Suitable fuel is supplied by burners I5 and burned in the fire tubes I0 and I I which produce a muiiled ame from which the gases comprising the products of combustion pass into'chamber I4.

By suitable regulation, the composition of the combustion gases may be accurately controlled over a Wide range from reducing through neutral to oxidizing. Further, their composition may be altered if necessary or desirable by the introduc-4 -action is of vital importance as will be later pointed out. In order to leave the furnace, the gases must pass under exit baille 3| with the result that the moving gas stream sweeps the charge during the entire duration of its passage through the laboratory of the furnace. The sweeping gases then pass out of the furnace through outlet port 39 into flue system 40 which may lead to a bag filter or other suitable recovery apparatus.'

In the modification shown in' Fig. 3 an additional baille is provided to insure the impingement of the sweeping gases upon the charge at all times during their passage through the furnace. In

Fig. 4 means for employing subsurface heating of the charge are shown which isvof advantage when working with some kinds of materials. Other modifications may be made in the construction of the furnace Within theV scope o f the invention. For example, a false arch may be substituted for the re tubes as the combustion chamber and it is even possible to substitute electrical heating units and supply the sweeping gases from an outside source.

The efliciency of the improved furnace of the inventionis well illustrated by the following comparative results obtained in the volatilization of antimony trioxide. In one instance a prior art furnace was used in which combustion gases were passed over the charge in the ordinary manner and the rate of volatilization was found to be 'one pound per hour for each-square foot of hearth area. In two other instances a furnace was used which was heated by means of tubes of silicon carbide suspended in the upper part of the furnace laboratory and the hot gases of combustion reversed and passed back through the laboratory above the charge of impure antimony oxide. In both of these cases the temperature was 900 C. but in the flrst'furnace which was not equipped lwith bailles the rate of volatilization was three 'area and the product was only of fair quality.

In the second furnace, equipped with inlet and outlet baffles as shown in the drawings, the rate of volatilization was sixteen pounds per hour for each square foot of hearth area and the product was of excellent quality.

It is believed that theimproved results attending the use of furnaces constructed in accordance with the invention are to be attributed 'in vthe main tothe heating of the charge by radiation while simultaneously sweeping the charge with the gases in the manner shown. In volatilizing substances in such furnaces, abundantheat is radiated directly to the very molecules passing from the condensed to the vapor state thus rendering the operation virtually independent of the high heat resistivity of surface films to convected,

heat which factor is the prime enigma of many of the prior art furnaces. .At the same time, the

unique manner in which the combustion gases are jetted or impinged against the charge enables more heat to be extracted therefrom than when the gases are merely passed through the laboratory of the furnace.

It is well known that heat is absorbed wheny substances, for example, arsenious oxide or antimony oxide, are volatilized and the transmission of heat from hot gases to a substance undergoing volatilization is more diicult than if the substance were substantially non-volatile. As the amount of heat of volatilization is of considerable magnitude, it is evident that unless sufficient heat can be constantly imparted to the substance, the rate of volatilization must necessarily be low. Inasmuch as furnaces in which the hot gases are simply passed through the furnace do unquestionably give low rates of volatilization as compared to the improved furnace of the invention, it is believed that the primary reason for such low rates is due to inadequate transmission of heat due mainly to the difiiculty of causing convected heat to travel downwardly in a furnace and to the fact that the Ivapors evolved from the charge flow against'the invention provides many advantages in the treat-4 ment of a great variety of chemical and metallurgical substances. While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the i port impinge upon the hearth of said main chamber.

2. In a furnace, a main chamber, re tubes positioned in the upper portion of said chamber interconnecting burners and a second chamber, an inlet port connecting said main and second chamber, an outlet port connecting said main 'chamber-with a suitable ue system, baffles associated with said inlet and outlet ports for deflecting gases onto the hearth of said chamber and an auxiliary gas inlet in saidsecond chamber.

I3. A furnace comprising a main furnace chamber having a hearth, charging means associated therewith, heating means in the upper portion of said chamber for burning fuel out of contact with the furnace charge, inlet and outlet ports inthe walls of said main chamber, baliles asso- .ciated with said ports and a second chamber adapted to receive combustion gases from said heating means and supply them to the inlet port.

4. In a furnace, a chamber having a solid hearth, inlet and outlet ports in the walls of said chamber, baffles associated with said ports, heating means for radiating heat to a charge on said hearth from fuel burned out of contact with said charge and means for circulating combusof said fire tubes, a port connecting said' main and second chambers and a baiiie disposed in the travel of gases from said port for directing them downwardly onto saidcharge.

6. A furnace comprising a main furnace chamber, fire tubes positioned in the upper portion of said chamber, a second chamber adapted to receive combustion gases from said re tubes, means for supporting a charge in the lower portion of'said chamber, an auxiliary heating appa; ratus for supplying heat 'to the charge, an inlet port for supplying combustion gases from said second chamber to the charge, an exit port connecting said main chamber to a flue and baiiles associated with said inlet and outlet ports to deect the combustion gases and cause same to sweep the charge.

l said hearth to supply heat to the charge by radiation, means for receiving the combustion gases and recirculating them through the laboratory of the furnace and baffles positioned to jet the gases against the charge yand sweep same during the entire passage of the gases through the laboratory of the furnace.

8. A furnace comprising a main chamber, a mixing chamber, re tubes in said main'chamber and communicating with said mixing chamber, an auxiliary gas inlet associated with said mixing chamber, an inlet port connecting said chambers, an outlet port leading from said main chamber to a fiue system and baffles in said main chamber so positioned that gases passed through the main chamber via said ports are jetted against the charge in said main chamber.

9. A furnace comprising a main chamber, a mixing chamber, means for burning fuel out of contact with the charge in the main chamber the gas exit from said means terminating in said mixing chamber, an auxiliary heatin'gelement for sub-surface heating of the charge in the main chamber, an inlet port connecting said chambers,

an outlet port leading from the main chamber to a suitable flue and means in said main chamber for deecting and impinging gases passed through said main chamber via said ports against 4 the charge in said main chamber.

10. A furnace of the muflled-ame type comprising the combination with a chamber defining a hearth for receiving a charge to be heated, of burners for the furnace, refractory conduit associated with the burners extending. through the hearth chamber of the furnace and'in the inte rior of which conduits combustion proceeds, an

auxiliary chamber communicating with the cons duits for receiving combustion gases therefrom, means for the auxiliary chamber enabling the composition and temperature of the combustion gases to be predeterminedly controlled and means for leading the said combustion gases from the auxiliary chamber into the hearth chamber.

11. A furnace of the muiiled-fiame type comprising ,the combination with a chamber having a hearth for receiving a charge of material to be heated, of an auxiliary chamber for receiving A v combustion gases, gas ports interconnecting the auxiliary chamber with the hearth chamber,

` heating means for radiating heat to a charge on the hearth from fuel burned out of contact with the charge, means for -circulating combustion gases from the heating means into the auxiliary chamber and thence into the hearth chamber through the said ports, and bafiies for directing the products of combustion into intimate contact with the charge on the hearth.

12. In the furnace treatment of volatile compounds, the improvement which comprises heat-v ing the charge predominantly with radiant heat by fuel burned out of contact with the charge and recirculating the combustion gases back over the charge in such manner that they impinge thereon thereby rapidly volatilizing the charge.

13. The process fortreating volatile substances vwhich comprises charging the material to the` hearth of a furnace and heating the material predominantly by radiation while simultaneously and continuously impinging hot gases against lsubstantially the entire surface of the charge whereby the material is volatilized at an extremely high rate.

JESSE O. BETTERTON. MELVILLE F. PERKINS.

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