US3131919A

US3131919A - Multiple hearth refractory furnace

Info

Publication number: US3131919A
Application number: US143175A
Authority: US
Inventors: Henry J Hartley; Ashley J Hollingsworth
Original assignee: BARTLETT SNOW PACIFIC Inc
Current assignee: BARTLETT SNOW PACIFIC Inc
Priority date: 1961-10-05
Filing date: 1961-10-05
Publication date: 1964-05-05
Anticipated expiration: 1981-05-05

Description

1964 H. J. HARTLEY ETAL 3, 31,919

MULTIPLE HEARTH REFRACTORY FURNACE Filed Oct. 5. 1961 3 Sheets-Sheet 1 IE E L INVENTORS Henry J l/orf/ey 45/7/57 J. Ho/fl'nyswar/h 147' 7 ORA/E X5 United States Patent F MULTIILE HEARTH EIRACTORY Henry .I. Hartley, Les Angcles, and Ashley .I. Hollingsworth, Atherton, Caiifu, assignors to Bartiett-Snow- Pacific, ind, San Francisco, Calif, a corporation of Caiifornia Filed Get. 5, 1961, Ser. No. 143,175 5 Claims. (Ci. 263-22) This invention relates to furnaces and more particularly to furnaces or kilns of the multiple hearth construction.

In multiple hearth furnaces constructed in the past, the general arrangement has been a stacked plurality of stationary hearths each having a central opening through which a central shaft is rotatably passed. Each of the stationary hearths also includes openings in the floors thereof through which material to be processed may be passed downwardly from one hearth to the next. Rabble arms are afixed to the central shaft at the level of each hearth. Upon rotation of the shaft and rabble arms, the material to be processed is rabbled across the hearth toward the openings therein to pass downwardly to the next lower hearth.

Due to the strength required for the central shaft and rabble arms, the material used in the past for the construction of these elements has necessarily been steel. The use of steel has limited the maximum temperatures which may be employed in such furnaces. Although various means have been considered and utilized for cooling the shaft and the rabble arms. Such means usually comprise forcing cool air through central openings in the shaft and rabble arms. However, even with the cooling devices of the prior art, maximum temperature in furnaces of this type has been in the neighborhood of 1860" or 1900 F.

In view of the above it is an object of this invention to provide an improved multiple hearth furnace or kiln.

It is a more particular object of this invention to provide a multiple hearth furnace having improved maximum temperature characteristics.

It is still another object of this invention to provide a multiple health furnace with modular construction wher in the furnace capacity may be easily altered.

It is still another object of this invention to provide a multiple hearth furnace wherein the number of required burners per hearth is reduced.

It is still another object of this invention to provide a multiple hearth furnace wherein close temperature control may be operated.

It is a further object of this invention to provide a furnace having the above mentioned characteristics, wherein the gaseous atmosphere within the furnace can be easily controlled.

It is another object of this invention to provide a multiple hearth furnace wherein the interior of the furnace is sealed with respect to its exterior.

It is still another object of this invention to provide a multiple hearth employing rabble arms and rabble teeth which may be adjusted or replaced while furnace is in operation.

It is still another object of this invention to provide a multiple hearth furnace of the aforementioned characteristics whereby the rabbling speed of each individual hearth may be separately adjusted.

It is still another object of this invention to provide a multple hearth furnace of the aforementioned characteristics which employs overload protection for the forces exerted by the rabble arms themselves.

It is still another object of this invention to provide a multiple hearth furnace which incorporates a simple apron feed wherein material may be supplied to the furnace with an air seal.

3,131,919 Patented May 5, 1%54 It is still another object of this invention to provide a multiple hearth furnace wherein the rabble arms are secured at both ends, thereby providing increased strength.

it is still another object of this invention to provide a multiple hearth furnace of the aforementioned characteristics which may be disassembled and re-assembled rapidly in order to facilitate shipping, cleaning and repair.

These and other objects and features of the invention will become more clearly apparent upon a review of the following description in conjunction with the drawing, in which:

FIGURE 1 is an elevational view of a furnace in accordance with one embodiment of this invention;

FIGURE 2 is a top plan view of the furnace shown in FIGURE 1 with the roof member removed;

FIGURE 3 is a composite elevational cross sectional view of the furnace shown in FIGURES 1 and 2;

FIGURE 4 is a side elevational view of a rabble arm assembly in accordance with another embodiment of this invention;

FIGURE 5 is a sectional view taken along the line 5-5 of FIGURE 4;

FIGURE 6 is a side elevational view of a rabble arm in accordance with still another embodiment of this invention;

FIGURE 7 is a sectional view taken along the line 7--7 of FIGURE 6;

FIGURE 8 is a plan view of a rabble arm in accordance with a further embodiment of this invention; and

FIGURE 9 is an elevational view of a tooth used with the arms of FIGURE 8.

In general, the above objects and features of this invention are accomplished by providing alternate rotating hearth sections and stationary ring sections stacked to form a furnace which may have a variable number of hearths. Rabble arms with depending teeth, formed of refractory material, are supported by the stationary ring sections. The material to be processed is supported by the rotating hearth while the stationary arms and teeth serve to rabble the material across the hearths towards openings in the floor thereof through which the material is passed to the next lower hearth.

Referring particularly to FIGURES l, 2 and 3 of the drawing, upright support members 11 are secured to a base member on floor 13. Ring sections 15 are removably secured to thesupport members 11 by means of the flanges 17 and 19 which are secured to each other by means of bolts or the like, whereby they may be easily removable. Flanges 17 and 19 may be secured to the respective supports 11 and sections 15 by welding or other suitable means.

Each of the stationary ring sections 15 is annular in form and comprises an inner shell 21 of refractory material and an outer shell 23 of heat insulating material. In addition a thin annular band 25, which may be of steel, surrounds the shell 23.

Also secured to each of the stationary ring sections 15 are a plurality of rollers or bearings 31 about the outer periphery thereof. The rollers 31 may be omitted on the uppermost stationary ring sections for reasons which will become apparent hereinafter. Conveniently, the upper extremity of the rollers 31 may extend above its asso ciated ring section 15, although this is not entirely necessary.

Also secured to the upright supports 11 is a bottom member 33 secured to the support member by flanges similar to those associated with the stationary ring sections. The member 33, like the stationary section 15, includes a plurality of rollers or bearings 37.

The

rollers

31 and 37 serve to rotatably support the various hearth sections 39. The hearth sections 39 each include a hearth floor 41 formed or" refractory material surrounded by an annular formation 43 of insulating material.

' On the upper face and near the outer periphery of each of the stationary sections 15, bottom sections 33, and hearth sections 39, there is included an annular well 45 which is filled with a sealing material such as sand. Annular sealing members 47 are formed on the lower face of each of the ring sections 15 and hearth sections 39 in registry with the annular wells of the adjacent sections to form a gas seal between the inside and outside of the overall furnace. A plurality of plowing pins 48 are disposed about the annular sealing member'47 and serve to continually break up the sealing material such that a hardened or packed pocket cannot be formed. Thus, the sealing member and the sealing material form a continual and effective gas seal.

Each ofthehearth sections 39 includes an outer band 49 which may beof steel, to which is secured a radially extending annular flange E. The flange 51 cooperates with the

rollers

31 and 37 to provide spaced support for the hearth sections 39 with respect to the stationary ring sections 15. Thus, it is seen that the hearth sections 39 maybe rotated with respect to the ring sections onthe

rollers

31 and 37.

Means for rotating the hearth sections -3 include motive means 53 operatively coupled to a vertical shaft 55.

7 One of the upright support members 11 may rotatably re-,

tain the shaft 55 by means of the bearings 57. Drive gears or sprockets 5% may be secured to the shaft 55 by means of sheer pins 61 or by an overload slip clutch. Drive chains '63 cooperate with the sprockets 5? and extend about the rotatable hearth 39. The hearth member 3? may include radially extending pins or the like to provide a positive driving relationship between the chain 63 and the hearth sections themselves. it is apparent that the diameter of individual sprockets 59 may be varied whereby the relative rotational velocity of the individual hearths with respect to each other may be varied. In addition, overall speed adjustment may be accomplished by means of a variable speed drive 65 associated with the motive means 53 and the shaft 55.

It is apparent from the construction of the furnace thus far described that the number of hearths may be simply varied, even after the structure is completed, by adding or removing individual stationary ring sections 15 and associated hearth sections 3? to or from the upright I support members 11.

Upon the uppermost stationary ring section 15 there is placed a top or root member 67 which includes an un der surface'69 of refractory material as well as an annular portion 71 and top portion 73 of heat insulating material. Heat seal means is provided between'the uppermost, ring section 15 and the top of roof member '67 As noted'particularly in FIGURE 3 each of the hearth floors 41 includes at least one opening therein for passage of the material to be processed from one hearth to the next lower hearth. In the embodiment shown in FIGURE 3 the upper and lowermost hearth 'fioors ll include a central opening 75 while the central hearth iloor 41includes peripheral openings 77. If .additional hearths arev used central openings 75 and peripheral openings 77 will. be alternatively employed whereby rabbling may occur in one hearth from the periphery to the center and on the subsequent hearth from the center to the periphery etc.

It is convenient that the uppermost hearth employ a centralopening 75 whereby apron feed means may be employed at the periphery. Thus, a pipe 79 is located near the outer periphery of the uppermost hearth. The pipe 79 is passed through the roof section 67 and exends downwardly into the furnace in close proximity with the uppermost floor section 41. Thus, as the uppermost hearth floor 41 is rotated, it cooperates with the pipe 79 to form an apron feed. The material to be processed is passed through the pipe 79 and distributed about the periphery of the uppermost door 41. In addition, with the the removal means cooperates with the outlet 3 7 to form.

ary ring sections employs a plurality of rabble arms 81 I arranged as shown more clearly in FIGURE 2. Each of the rabble arms 81 is constructed of refractory material and includes a stem portion 83 and depending teeth 85. The arms may be inserted into the furnace through circumferentially spaced openings 87 in each of the stationary ring sections 15. The size ofthe openings 87 are proportioned such that the rabble arms may be passed through while the depending teeth are in a relatively horizontal plane. The arms are subsequently rotated such that the teeth 85 extend downwardly.

As notedparticularly in FIGURES 2 and 3 each of the rabble arms extend inwardly to the center of the'frame and is keyed as at 89 whereby they are joined together to form a relatively rigid armsupported at each end. In addition each of the stationary ring sections may include a burner 91. Since the hearths in this case are rotatable, a single burner may be' employed at each hearth to heat all of the material to be processed. In particularly large furnaces it maybe desirable to provide additional burners butin any case the number of burners required will be less than ordinarily required for station-' ary hearth furnaces since the material is continually passed beneath the stationary burners.

7 Doors 93 may be provided whereby inspection of furnace operation may be accomplished. Additionally a spudding tool may be easily used against the moving hearth through the door 93 without stopping the furnace. I V

A flue 95 isprovided in the top section 67 whereby the gases'developed in the furnace may be removed. Also a material outlet 97 is provided in the bottom section 33 in registry with the central opening in thelowernlost hearth floor 41. The material maybe received from the outlet 97 and distributed in a convenient manner Preferably,

an'apron outlet whereby a gas seal is provided by the processed material itself.

In the operation of the furnace, the material to be processed'is passed through the apron feed 79' onto the outer periphery of uppermost hearth floor 41. The rotation of the hearth causes the material to be spread about the uppermost door. with the uppermost floor cause the material to be removed centrally toward the opening 75 whereby it is dropped to the next lower hearth floor 4-1, at the next lower floor the rabble arms have teeth disposed at an opposite pitch to those associated with the first hearth and thus cause.

the material to be rabbled outwardly to the opening 77 where it is dropped to the next lower hearth floor 41.

. The cycle is repeated until the material is rabbled toward the lowermost opening 75 and through the outlet 7.

Referring particularly to the embodiment shown in.

FIGURES d and 5 therabble armsextend not only to the center of the hearth but completely across whereby it may be secured at each wall. With this construction a single arm may be employedfor each hearth. As seen in FIGURE 5 a pair of bars 101 are employedand may be extended entirely across the furnace and secured at the outer walls thereof. The bars rill are spaced so 'asto provide anopening 1% through which the rabble teeth Hi5 may pass. The teeth 1%5 include head portions 107.

which rest upon the bars 101 and may be of such dimension to provide the requ red spacing between teeth when in abutting relationship as shown at 199; Thus, it is seen that the teeth 1435 may be readily removed from the bars Trill. Broken teeth may be replaced by merely removing the same and sliding another tooth along the bars it'll.

Referring more particularly'to FIGURES, it is seen that the bars 161 may include a centrally disposed metal Stationary rabble arms associated pipe 111 surrounded by refractory material. The metal portion may provide additional strength and may be cooled by the passage of air therethrough. if desired the pipe can be eliminated and the entire structure fabricated from refractory material. in any event no metal surface is directly exposed to the furnace heat.

Referring to FIGURES 6 and 7 in the form of a tooth assembly, a rabble arm is shown. Here again, the arm extends entirely across the furnace and the ends are secured at the outer walls of the furnace.

In this case a plurality of teeth 113, each having lzeyed surfaces 115, are held together by axial compression of the tooth assembly. An opening 117 through each tooth may be used in conjunction with a rod (not shown) passed therethrough to hold the teeth in their assembled relationship when the axial compressi e force is removed. Thus, to replace a broken tooth, a rod is passed through the opening 117 of all the teeth, the compressive force is removed and a new tooth is passed along the rod into keyed relationship with the other teeth. The compressive force is returned and the rod subsequently removed.

Referring to FZGURES 8 and 9 another rabble arm is shown wherein a plurality of teeth 119 are mounted on a central shaft 121. As can better be seen in ElGUnE the teeth 119 are loca d on the shaft 121 at an acute angle with the shaft axis. Thus, the raobdng pitch of the arm is determined. Each of the teeth includes a mounting head 123 having a series of concentric grooves 125 on one face and a series of concentric ridges (not shown) on the opposite face in registry with grooves.

The shaft 1 1 includes a wedge shaped stop member 127 secured at one end by welding or otherwise, and the plurality of teeth 119 are fitted over the shaft in stacked relationship adjacent the stop member 127. One or more tapered Washers 129 of the Belville type are fitted next over the shaft and the assembly is tightened together by a threaded nut 131.

Due to the action of intermeshed grooves 125 and ridge the assembly is held intact even with wide temperature variations and the consequent cracking in the teeth themselves.

Thus, it is seen that an improved multiple hearth furnace is provided wherein high temperatures may be employed. Since the construction of the interior of the furnace is refractory material, particularly high temperatures may be employed in the neighborhood of 2500 to 2600 F. and above. If desired the rabble arms as described hereinabove may include central pipe portions for additional strength. Coolin fluids may be passed through the pipe portions to reduce the temperature destruction thereof.

The furnace retains the features of precise temperature control, even heat distribution and high heat recovery which are well known in rotary hearth furnaces. At the same time much higher temperatures may be employed which in the past have required rotary kilns.

Due to the combination of the improved temperature characteristic along with rabbling actions, processes never before achieved may be performed. One important process made feasible by this novel furnace is the recovery of lime [C210] from lime sludge [Ca(OH)]. Other processes include oxidation of certain metals requiring high heat. In addition, since the internal atmosphere of the furnace is controlled by sand seals between movable members, and by material seals at the apron feed and discharge, the reduction of metallic oxides is greatly facilifated.

We claim:

1. A multiple hearth furnace comprising a plurality of vertical support members, a plurality of stationary annular ring sections rigidly but removably secured to said support members in vertically spaced relationship, each of said ring sections defining a central opening, a hearth section rotatably supported below and extended across the opening of each of said stationary ring sections, said hearth sections being supported entirely externally of the hearth and said stationary ring sections, motive means for rotating said hearth sections relative to said stationary ring sections and rabble arm means supported by said stationary ring sections and extending inwardly thereof, said rabble arm means including a pair of transversely spaced bars extending entirely across the interior of the furnace, and teeth removably disposed between said bars.

2. A furnace as defined in claim 1 wherein said bars are formed entirely of ceramic refractory material.

3. A furnace as defined in claim 1 wherein said bars include a metal pipe and refractory material, the outer surface of said metal pipe being entirely surrounded by said refractory material.

4-. A multiple hearth furnace comprising a plurality of vertical support members, a plura ity of stationary annular ring sections rigidly but removably secured to said support members in vertically spaced relationship, each of said ring sections defining a central opening, a hearth section rotatably supported below and extended across the opening of each of said stationary ring sections, said hearth sections being supported entirely externally of the hearth and said stationary ring sections, motive means for rotating said hearth sections relative to said stationary ring sections, rabble arm means supported by said stationary ring sections and extending inwardly thereof, said rabble arm means comprising a tooth assembly, said tooth assembly including a plurality of separate teeth each having key means on opposed side faces thereof said teeth being disposed adjacent each other with the key means of adjacent teeth being keyed together, and means for compressively urging said teeth together whereby the teeth are retained in an assembled condition.

5. A furnace as defined in claim 4 wherein each of said teeth include a central opening communicating with each of said opposed faces, a rod adapted to be passed through said opening whereby temporary retention of the teeth in assembled condition may be maintained.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A MULTIPLE HEARTH FURNACE COMPRISING A PLURALITY OF VERTICAL SUPPORT MEMBERS, A PLURALITY OF STATIONARY ANNULAR RING SECTIONS RIGIDLY BUT REMOVABLY SECURED TO SAID SUPPORT MEMBERS IN VERTICALLY SPACED RELATIONSHIP, EACH OF SAID RING SECTIONS DEFINING A CENTRAL OPENING, A HEARTH SECTION ROTATABLY SUPPORTED BELOW AND EXTENDED ACROSS THE OPENING OF EACH OF SAID STATIONARY RING SECTIONS, SAID HEARTH SECTIONS BEING SUPPORTED ENTIRELY EXTERNALLY OF THE HEARTH AND SAID STATIONARY RING SECTIONS, MOTIVE MEANS FOR ROTATING SAID HEARTH SECTIONS RELATIVE TO SAID STATIONARY RING SECTIONS AND RABBLE ARM MEANS SUPPORTED BY SAID STATIONARY RING SECTIONS AND EXTENDING INWARDLY THEREOF, SAID RABBLE ARM MEANS INCLUDING A PAIR OF TRANSVERSELY