US3010215A - Gas-solids heat exchanger - Google Patents

Description

Nov. 28, 1961 KARL-HEINZ KAYATZ 3,010,215

GAS-SOLIDS HEAT EXCHANGER Filed June 29, 1959 2 Sheets-Sheet l ,M3-xl /I sumas .1. fl MATERIAL 1l l l ll s l RscvcLE l l MATemL 1 2. l, ,I l 19 l//nn//f/l,

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INVENTOR. KARL H. KAYATZ WW ad NOV- 28, 1951 KARL-HEINZ KAYATZ 3,010,215

GAs-soLIns HEAT EXCHANGER 2 Sheets-Sheet 2 Filed June 29, 1959 un... "a

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INVENTOR. KARL H. KAYATZ BY 2f@ MVT United States Patent O 3,010,215 GAS-SOLIDS HEAT EXCHANGER Karl-Heinz Kayatz, Hamburg-Nienstedten, Germany, assignor to Fuller Company, a corporation of Delaware Filed June 29, 1959, Ser. No. 823,668 13 Claims. (Cl. 34-11) YThe present invention relates Ito gas-solids heat exchangers such as for roasting, burning, or sintering operations, and is more particularly concerned with sealing between the chambers of material preheaters having a material-drying and a material-heating chamber, through which la single' bed of material is progressively moved, while gases discharged from the furnace are passed successively first through `the material in the heating chamber and then through the material in the drying chamber.

-It has been proposed to preheat materials bypassing them over a traveling grate through a first drying compartment and a subsequent heating compartment before delivering the material into a furnace or kiln. The exit gases of the kiln are, in certain cases, passed downwardly through the material layer in the heating compartment and then upwardly through the material layer in the drying compartment.

However, such prior expedients have not proved entirely satisfactory, and have been particularly prone to short-circuiting of hot gases between the compartments without passing through the materials, and to non-uniform treatment of the material resting without agitation on ythe traveling grate.

In general, the apparatus of the present invention, as embodied in ya preheater for hydraulic cement raw-materials, comprises a chamber having therein an assembly of movable grates alternating with fixed grates, a gas inlet adjacent one end of the grate assembly for receiving hot gases from the `cement kiln, and a gas outlet adjacent the opposite end of the grate yassembly for exhausting the gases to the atmosphere, or as the case may be, a dust collector.

Intermediate lthe ends of the grate assembly, a pair of Walls extend downwardly from the upper wall of the chamber to divide the chamber into an upstream drying compartment and a downstream heating compartment. The lower ends of the walls are spaced from the grate assembly andthe intermediate walls themselves are spaced apart fro each other to form la third compartment therebetween of a width at least equal to twice the depth of the slot between the grate assembly and the bottom edge of the wall adjacent the heating compartment.

A feed hopper is positioned adjacent the upstream end of the gratelassembly, which is yadjacent the gas outlet, and feeds material to the grate assembly through a slot substantially equal in dimensions to the depth of the slot between the grate assembly and the intermediate wall adjacent the heating compartment. Means are provided for transferring heated material from the downstream end :of the grate assembly into the kiln.

The space between the paired walls is kept at least partially filled by suitable means and preferably contains relatively stable material such as heated material from the downstream end of the grate assembly.

A fan or other suitable means is provided to cause a llow of gases from the gas inlet downwardly through the material in the heating compartment, adjacent the gas inlet, and then upwardly through the material in the drying compartment and through the drying compartment to the atmosphere.

A better understanding of the invention m-ay be derived from Athe accompanying drawings and description in which:

FIG. l is a sectional side View of a cement preheater embodying the invention;

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FIG. 2 is an enlarged view of a portion of FIG. 1 showing the sealing chamber; and

FIG. V3 is aplau View on line 3-3 of FIG. l.

As shown in the drawings, the invention, as embodied in a preheater for nodules or pellets of cement raw materi-als, comprises an elongated chamber 1 having a gas inlet 2 .communicating with the gas outlet of a rotary kiln 3 and a gas outlet 4 communicating with the atmosphere through a fan 5.

A Ilongitudinal conveying-grate assembly 6 divides the chamber 1 into an upper material chamber 7 and a lower gas chamber 8. The grate assembly comprises a series of perforated grates including fixed grates 9 and movable grates 1G alternating with and overlapping each other stepwise on an incline sloping downwardly toward the end of 'the chamber having the gas inlet 2. Where desired, the grate assembly may be larranged on a slope diiferent from that shown, or may be horizontal.

The particular means for driving the movable grates 10 forms lno part of the present invention and may be of any suitable form producing positive agitation and mixing of the material as it is conveyed, such as reciprocation or tipping of the movable grates. The grate assembly shown is substantially in accordance with the disclosure of latent No. 2,431,799 to l. B. Gainey, in which the movable grates 10 are mounted on a common frame and are lthereby reciprocated simultaneously on a plane parallel to the overlapped portions of the xed grate 9. Preferable, the driving means employed is to be variable in speed to permit regulation of the conveying capacity of the grate assembly.`

The chamber 1 has a material inlet -aperture or slot 11 adjacent its end having the gas inlet. The slot 11 is rectangular and extends the full width of the grate assembly 6 to distribute material uniformly thereon from a supply hopper 12.

The material chamber 7 is divided by a pair of intermediate walls y13 yand 14, respectively, into a drying compartment 15 adjacent the gas outlet, "a heating compartment 16 adjacent the hot gas inlet, and a sealing compartment 17 between the walls themselves. The sealing compartment 17 has `an aperture 18 at its upper end which opens `to the exterior of the chamber 1. The aperture 18 receives material feeding means such as a conduit 19 which delivers material from any suitable source, as discussed more fully hereinafter. While Vthe intermediate walls 13 'and 14 have been shown in vertical arrangement, it is to be understood that they may be arranged on a slope, if desired.

The lower edge of the transverse wall 13 is spaced from the grate assembly and carries a swinging gate 22 which extends the full width oi the grate assembly and is rotationally mounted on a shaft 23 to ride on the upper.

surface of material passing along the grate assembly.

The lower edge of the transverse wall 114 is spaced from the grate assembly and Iforms therewith and with the side walls of the chamber a metering aperture or slot 21. The slot 21 preferably is exactly equal in each dimension to the slot 11 at the upstream end of the lgrate assembly to provide a bed of material in the heating zone equal in dimension to the bed of material in the drying zone. f

The walls 13 and 14 preferably are spaced fromeach other a distance at least equal to twice the depth of the slot 21, and therefore at least equal in width to the sum of the two material beds in the drying and heating chambers.

In operation, the fan 5 is started and draws air through the kiln 3 and the chamber 1. The kiln 3 is then tired ina known manner, and the combustion gases therefrom are similarly drawn through the chamber .1.

When the ow ofV hot gas has been established the movable grates 10 are set into motion and nodules of cement raw material are delivered to the hopper 12,

l grates fromextreme temperatures.

and are'continuously delivered thereto during operation of the preheater. 'I'he nodules pass from the hopper 12 through the slot 11 as a relatively thin, evenly distributed bed onto the upper end of the grate assembly. The action of the movable'grates 10 passes the material bed along the upper surface of the grate lassembly and toward; the lower end thereof.V The agitation caused -by the grates prevents the material from forming a staticlayer, and causes a continuous shifting and mixing of the material for more uniform contacting of the gas with the' material.

As the advancing material passes under kthe transverse wall 13, the swinging gate 22 rides on theupper surface of the material and serves to insure the uniform distribution of material on the grate assembly. When the material bed passes through the restricted intermediate zone between the transverse wall 14 and the gate, the com-V 1 partment |17 is then lled with material to a depth above 'Y the. underlying grates at least three times the depths of the slot 21 and is thereafter maintained at or above that depth by any, suitable means (not shown) such as a bucket elevator controlled by a material-level indicator. The material delivered into the compartment may comprise heated nodules recycled from the discharge end of the grate assembly, iinished clinker or product particles from the discharge end of the kiln, or any material not detrimental to the process conducted within the kiln. If the original material is in a relatively stable physical form, particularly in processes -other than cement burning and` such as calcining of crushed lime rock, the chamber Y 17 may be fed with such raw material.

Where material is recycled from the downstream end of the grate assembly or from the kiln, similarly suitable means such as bucket elevators, screw conveyors orbelt conveyors may be employed, preferably under the control of a material-level indicator to insure the proper material depth. The choice of the conveyor will be at least partia1- "f ly dependent on the temperatures encountered.

When the compartment 17 has been lilled to the reyquired depth, the sealing elect of the material body thereinforces the gases being drawn from the kiln rst to pass downwardly through the material bed and perforated grates in the heating compartment 1-6, then through the gas chamber 8 and ultimately through the perforate grates Vand. the material in the drying chamber 15. The

Y hottest gases thus meet the nodulized material `in the heating chamber 16 and are reduced in temperature before passing through the grates, thereby protecting the rfhe continuously agitated material passing over the grate assembly is uniformly permeated by the gases; dried in the drying compartment A15, and preheated in the heating chamber 16 before being delivered into the kiln.

The pressure drop or differential between the two chambers 15 and 16 is substantial, such as, for example, 1Z0-140 m-m. water gauge. However, the maintenance of the proper level of the material body 20 prevents the gases from short-circuiting under the compartment 17 and washing away material Vat thatpoint. Since the smallest dimension of the body of material 20 is at least twice the combined depths of the equal slots 11 and 21 and the consequently equal depths of the material beds in the chambers 1'5 and 16, respectively, its resistance to gas ow therethrough is at least equal to the sum of the resistance of the two portions of the material bed in the drying and heating chambers, respectively. Therefore, with the added resistance to gas flowof the transverse wall 14 and the swing gate 22, the easiest path for the gases is the desired ow downwardly through the material in the heating zone 16 and upwardly through thematerial in the drying zone 15.

Although a small portion of the material in the compartment 17 is gradually and continuously lost through the slot 21, the constant maintenance of the desired level within the compartment insures continued adequate resistance to Short-circuiting of the gas.

Y their lower edges spaced from the grate assembly to penV Various changes may be made in the details of the disclosed invention without sacrificing the advantages thereof or departing from the scope of the appended claims.

I claim: y i A 1. A heat exchanger comprising a chamber having a gas inlet and a gas outlet, a grate assembly in the chamber having opposite ends thereof in the regions of the gas inlet and the gas outlet, feeding means forV delivering material torbe treated to the upstream region of the grate assembly, a pair of intermediate walls over the grate assembly and dividing the chamberrinto a plurality of compartments Yincluding a tirst compartment and -a second compartment adjacent opposite'ends of the grate assembly, the intermediate walls beingl spaced from each other to form a sealing compartment therebetween and having mit material ow therebetween in sealing contact with and through the material and grates underlying the Vsecond compartment in the opposite vertical direction.

2. A heat exchanger comprising a chamber having a gas inlet and a gas outlet, a grate assembly in t-he chamber having a downstream' end in the region of the gas inlet, said grate assembly comprisinga plurality of alternating xed grates'and movable grates, feeding means for delivering material to be treated to the upstream region,

of the grate assembly, means'for actuating the movable grates to ldeliver material over the grate assembly to the discharge end thereof, a pair of intermediate Walls over the grate assembly and dividing thechamber into a plurality of compartments including a first compartment adjacent the gas inlet and a second compartment adjacent the gas outlet, the intermediate walls being spaced from each other to form a third compartment therebetween and having their lower edges spaced from the grate assembly to permit material tiow therebetween in sealing contact with both the grate assembly and the lower edge of the downstream intermediate wall, and means for causing a ow of gas through the material and grates underlying the tirst compartment in one vertical direction, and through the material and grates underlying the second compartment in the opposite vertical direction.V Y

3. Heat exchange apparatusaccording to claimZ in which the movable grates are reciprocated longitudinally of the grate assembly.

4. Heat exchange apparatus according to claim 2 including means for maintaining a body of material in the third compartment.

5. Heat exchange apparatus according to claim 2 including means for maintaining a body of material in the third compartment at least equal in depth to twice the distance between the grate assembly and the downstream intermediate wall.

6. Heat exchange apparatus Vaccording to claim 2 in which the space between the grate assembly and the downstream intermediate wall defines at least in part a metering aperture equal in dimension to said inlet aperture. Y

7. Heat exchange apparatus according to claim 5` in` cluding means vfor recycling a portion of material yfrom beyond the downstream side of the downstream intermediate wall to the third compartment.

8. Heat exchange apparatus according to claim 2 in which the intermediate walls are spaced apart a distance at least equal to twice the distance between the 'grate assembly and the downstream intermediate wal-l, whereby the resistance to gas flow over a bed of material moving along said grate assembly beneath said third chamber will be at least as great as the combined resistance to` gas ilow through the bed of material moving under said irst and second chambers.

9. Apparatus according to claim 8 in which said feeding means includes an inlet aperture adjacent the upstream end of the grate assembly and said aperture is substantially equal in dimension to the space between the grate assembly and the downstream intermediate wall.

l0. A preheater for cement raw material comprising a chamber having a gas inlet and a gas outlet, a gas-pervious conveyor in the chamber having a downstream end in the region of the gas inlet, feeding means for delivering material to be treated to the upstream region of the conveyor and including a metering aperture adjacent to the upstream end of the conveyor, a pair of transverse intermediate walls over the grate assembly and dividing the chamber into a plurality of compartments including at least a drying compartment adjacent the gas outlet and a heating compartment adjacent the gas inlet, the intermediate walls having their lower edges spaced from the conveyor to permit material ilow therebetween in sealing contact with both the conveyor and the lower edge of the downstream intermediate wail, the space between the conveyor and the lower edge of the downstream intermediate wall forming at least in part a metering aperture substantially identical in dimension to the aperture of the feeding means, the intermediate walls being spaced from each other a distance at least equal to twice the depth of the aperture beneath the downstream intermediate wall and forming a third compartment therebetween, means for maintaining a body of material in the third compartment above the material passing therebeneath, and a fan communicating by way of its inlet with the gas outlet of the chamber.

11. A preheater according to claim 10 including means for maintaining the body of material in the third compartment at a depth at least equal to twice the depth ot' the aperture beneath the downstream intermediate Wall.

12. A method of thermally treating loose discrete particles of material which comprises passing a relatively thin bed of the material through a defined Zone including upstream, intermediate and downstream portions, passabove, said thin bed immediately above said intermediate portion of the zone, whereby said bed will pick up, when passing through said intermediate portion of the zone,

sufficient particles of the sealing material on the upper t surface thereof to form a barrier preventing gas iiow along the upper surface of the bed at said intermediate portion of the zone and diverting the gas ow downwardly through the bed at one side of the intermediate portion of the zone and for iiow upwardly through the bed at the other side of said intermediate .portion of the zone.

13. The method of claim 12 in which a portion of the material from the downstream portion of the bed is recycled to maintain said body of discrete particles of sealing material.

References Cited in the ile of this patent UNITED STATES PATENTS 1,322,143 Singmaster et al Nov. 18, 1919 1,538,192 Leach May 19, 1925 1,712,132 Breyer et al. May 7, 1929 2,209,636 Schubert July 30, 1940 2,363,037 Arnold Nov. 21, 1944

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