US3416778A - Apparatus for thermal treatment of minerals - Google Patents

Description

Dec. 17, 1968 CHABAGLIYAN 3,416,778

APPARATUS FOR THERMAL TREATMENT OF MINERALS- Filed March 29, 1967 to 2 Sheets-Sheet 1 INVENTOR. HENRI FERNAND CHABAGLIAN Dec. 17, 1968 H. F. CHABAGLIAN 3,416,778

APPARATUS FOR THERMAL TREATMENT OF MINERALS Filed March 29, 1967 2 Sheets-Sheet 2 INVENTOR.

HENRI FERNAND GHABAGLIAN United States Patent 3,416,778 APPARATUS FUR THERMAL TREATMENT OF MINERALS Henri Fernand Chabaglian, Maisons-Laflitte, France, as-

signor to Poiysius G.m.b.H., Neubeckum, Westphalia, Germany Filed Mar. 29, 1967, Ser. No. 626,736 Claims priority, application France, May 6, 1966,

4 Claims. Cl. 26332) ABSTRACT OF THE DISCLOSURE Background of the invention The invention relates to apparatus for thermal treatment of minerals which have been sized or shaped by tumbling, pelleting, briqueting or any other process.

The known apparatus utilizes one or more traveling grills which transport the material toward a rotary kiln where the roasting itself is conducted, while on the grill, preceding the kiln, the material is heated by hot gases discharged from the kiln.

In certain apparatus the kiln is preceded with a traveling grill through which the gas makes two passes, i.e., the \grill is separated into two parts, the hot gases recuperated from the downstream part being supplied to the upstream part of the grill.

In other apparatus, the kiln is preceded by two grills in cascade, the first serving as a recuperator for the heat radiated from the kiln and from the cooler, and the second serving as recuperator for the heat of the gases discharged from the kiln. In this apparatus the circuit of the gas is independent and forms a simple gas passage.

These devices for thermal treatment have given good results in many cases, but they are nevertheless limited by the maximum dimensions which it is technically feasible to give to the traveling grill.

Moreover, when the hot gases are derived principally from the kiln, it is necessary to have a large volume of gas flowing through the kiln, so that because of the dimensions of the kiln and the intensity of the current of gas, clouds of dust are created with resultant danger of incrustation of the apparatus.

Summary of the invention The object of the invention is to provide a heat treatment apparatus of the type hereinbefore described in 'which the circulation and the recuperation of the hot gases permits greater flexibility of treatment by separating the functions of drying and preheating and assuring an improvement in the efficiency of heating on the grills, as well as an increase in capacity which is difiicult to obtain by merely increasing the dimensions of the grills.

The invention then comprises apparatus for thermal treatment of minerals characterized in that it comprises a first traveling grill for drying on which the material is heated by gases which have passed through a second preheating grill on which the material is heated partly by gases discharged from the kiln and partly by burners which are supplied with secondary air of combustion consisting of hot air discharged from a cooler which follows the kiln, a burner in the kiln being also supplied with secondary air consisting of part of the hot air discharged from the cooler.

Other auxiliary features of the invention will appear from the following detailed description, in which reference is had to the annexed drawings. It will be understood that the description and the drawings are given only by way of example and are not intended to limit the scope of the invention.

Brief description of the drawings FIGURE 1 is a schematic view of an apparatus according to the invention.

FIGURE 2 is a schematic view of a modification of the apparatus according to the invention which is shown in FIGURE 1.

Description of the preferred embodiments According to the invention, the apparatus for thermal treatment shown in FIGURE 1 comprises a conveyor 1 which conducts the material to be treated into a hopper 2 which distributes it upon a first traveling grill 3, which transports the material across a drying chamber 4 and discharges it into a hopper 5 which distributes the dry material upon a second traveling grill 6.

The role of this intermediate hopper 5 is to form a reservoir of material between the two grills 3 and 6 in order that the grill 6 may be suitably covered with the material.

Furthermore, this hopper 5 on the one hand tends to cause the material to be turned over in the course of its transfer, thus permitting better equalization of the temperatures in the mass of the material, and on the other hand tends to stir the material so as to cause segregation of the fine particles or small fragments of material, the elimination of which, When necessary, can be obtained by using a hopper wall 7 consisting of a screen.

This hopper 5 thus makes possible a speed of travel of the material which is different on the two grills, so that the thickness of the layer of the material may be different on each grill, the height of the layer upon the grill 6 being determined by an adjustable regulator 8, while a level detector 9, which may consist of a sound transmitter and a sound receiver, for example, permits the determination of the quantity of material in the hopper 5.

The difference in the speed of travel of the material on the two grills which is made possible by the hopper thus permits adjustment of the duration of treatment in accordance with the requirements of the material being treated.

Material on the grill 6 then passes through the precalcination chamber 10 and is transferred into a rotating kiln 11, where the actual roasting takes place, after which the material is discharged upon a grill 12 where it is cooled while passing through three successive chambers, 13, 14 and 15.

The air which is used for final cooling in the exit chamber '15 is discharged to the exterior at a temperature of about to 200 C.

The air which is used for intermediate cooling in the intermediate chamber 14 at about 200400 C. is withdrawn by a fan 16 and conducted to the chamber 10, where it is used as air of combustion for the burners 17.

Air which is used for the initial cooling of the material in the inlet chamber 13, at about 800-1 100 C., is discharged into the kiln 11 adjacent a burner 18, to serve as secondary air of combustion for the burner 18, which is also supplied with primary air, at the head of the kiln 11.

Gases at about 1000-1200 C. from the kiln 11 pass into the chamber 10, where they are mixed with the gases flowing from the burners 17, and pass through the bed of material to bring the material to an average temperature of 700 C. at which the principal reactions for changing the state of the material commence (between 500 and 900 0., according to the material) such as decarbonation, dehydration, oxidation or others.

In a chamber 19 under the grill 6, the gases at 200- 400 C., which have passed through the bed of material, are withdrawn through a dust collector 20 by a fan 21 which discharges them into the chamber 4.

The gases discharged by the fan 21 then pass through the bed of material disposed upon the grill 3, to penetrate into a chamber 22 at a temperature of 80120 C., from which they are withdrawn by a fan 23 which discharges them to the exterior by a stack 24.

It will be noted that upon the drawing the flow of the material is indicated by solid arrows, while the flow of the gases is indicated by dashed arrows.

The apparatus according to the invention permits great flexibility of the thermal treatment.

Because of the fact that the sensible heat which can be recovered in the cooler is extracted, it becomes useful to furnish the necessary combustibles for the entire process partly at the head of the rotary kiln 11, by means of the burner 18, and partly upon the precalcination grill 6 by means of the burners 17 when the thermal requirements in the kiln 11 are substantially less than those necessary in the chambers 10 and 14, for example:

For pelleting of a rich hematite, the requirements in the kiln 11 are of the order of 140 Th., and the thermal requirements in the chambers 4 and 10 are of the order of 310 Th.

For the pellting of a magnetite concentrate, the requirements in the kiln 11 are of the order of 128 Th. The thermal requirements in the chambers 4 and 10 are of the order of 200 Th.

For the pelleting of a calcareous minette of Lorain, the requirements in the kiln 11 are of the order of 190 Th., and the requirements in the chambers 4 and 10 are of the order of 540 Th.

Forthe roasting of an artifical cement, the requirements in the kiln 11 are of the order of 520 Th., and the requirements in the chambers 4 and 10 are of the order of 550 Th.

In the first three cases cited, the thermal requirements in the kiln are substantially less than those necessary in the chambers 4 and 10.

In accordance with the invention, it is desirable to furnish the combustibles partly at the head of the kiln by means of the burner 18, and partly at the chamber 10 by means of the burners 17. This distribution may vary between one-third and two-thirds of the total at each of the points 18 and 17, depending upon the material treated.

For the fourth case cited, the thermal requirements are substantially the same in the kiln 11 and in the chambers 4 and 10. The distribution makes it possible to limit the gas flow between the kiln 11 and the chamber 10, to prevent raising dust. When the treatment of the material requires high temperatures, and in order not to treat the material too long in the rotary kiln where the material is subjected to agitation which impairs the cohesion, one may carry the material on the second grill to an elevated temperature of about 1200" C., in which case it is desirable, for mechanical and economical reasons, to employ a second grill which is short. Also, the material arriving upon this second grill should already be at a temperature which is relatively high, about 600 to 900 C., so that it is desirable to employ a modification of the abovedescribed apparatus, which modification is represented by the form of the apparatus illustrated in FIGURE 2.

According to this form of the apparatus embodying the invention, shown in FIGURE 2, the first grill 3 is a grill which is subjected to two passes of the gas, and

which travels through two chambers, the drying chamber 4 followed by a preheating chamber 25 which receives the gases discharged from the chamber 19 under the second grill 6.

These gases, after having passed through the bed of material, pass into a chamber 26 under the grill 3, from which they are withdrawn through a dust collector 27 by a fan 28 which discharges them into the chamber 4.

Thus all of the relative advantages of FIGURE 2 are retained, while the cost of the installation is reduced substantially by comparison with continuous installations which employ only one grill.

The invention is not limited only to the modes of realization which have been described and shown, but covers all other variations thereof.

I claim:

1. Apparatus for thermal treatment of minerals comprising a rotary kiln preceded by traveling grills for drying and preheating, wherein the improvement comprises a first traveling grill for drying; a second traveling grill for preheating, the inlet end of which is arranged to receive material discharged from the exit end of the first grill, and the exit end of which is arranged to discharge material into the inlet of the kiln; an enclosed cooler arranged to receive material discharged from the exit of the kiln; two separate chambers adjacent to the two ends of the first grill, which are bounded by the upper surface of the grill; two separate chambers adjacent to the two ends of the first grill which are bounded by the lower surface of the grill; a separate chamber bounded by the upper surface of the second grill; a separate chamber bounded by the lower surface of the second grill; a burner in the kiln; an inlet for supplying air to the cooler; a recuperating system for withdrawing the air which has been heated in the cooler and supplying a portion thereof as secondary combustion air to the kiln and another portion thereof to one of the chambers associated with the second grill; said chamber containing a burner and having a connection through which it receives hot gases discharged from the kiln; and another recuperating system for withdrawing, from the other chamber associated with the second grill, gases which have passed through the grill, and for supplying such gases to one of the chambers adjacent to the exit end of the first grill; the other chamber adjacent to the exit end of the first grill being provided with a recuperating system for withdrawing from such chamber gases which have passed through the adjoining portion of the first grill and for supplying such gases to one of the chambers adjacent to the inlet end of the first grill to cause such gases to pass through the other portion of the first grill.

2. Apparatus :for thermal treatment of minerals comprising a rotary kiln preceded by traveling grills for drying and preheating, wherein the improvement comprises a first traveling grill for driving; a second traveling grill for preheating, the inlet end of which is arranged to receive material discharged from the exit end of the first grill, and the exit end of which is arranged to discharge material into the inlet of the kiln; an enclosed cooler which is divided into an inlet chamber arranged to receive material discharged from the exit of the kiln, an intermediate chamber which receives material from the inlet chamber, and an exit chamber which receives material from the intermediate chamber; a separate chamber bounded by the upper surface of each of the grills; a separate chamber bounded by the lower surface of each of the grills; a burner in the kiln; inlets for supplying cooling air to all three chambers of the cooler; a recuperating system for withdrawing, from the intermediate chamber of the cooler, air which has been heated to an intermediate temperature, and for supplying such air to one of the chambers associated with the second grill; such associated chamber containing a burner and having a connection through which it receives hot gases discharged from the kiln; and another recuperating system for withdrawing, from the other chamber associated with the second grill, gases which have passed through the grill, and for supplying such gases to one of the chambers associated with the first grill to cause such gases to pass through the first grill; the inlet chamber of the cooler having a connection through which air which has been heated in such inlet chamber to a temperature higher than such intermediate temperature is supplied as secondary combustion air to the kiln; and the exit chamber of the cooler having an outlet for exhausting air Which has been heated in such exit chamber.

3. Apparatus according to claim 2 wherein a hopper is arranged to receive the material passing from the first grill to the second grill, for controlling the thickness of References Cited UNITED STATES PATENTS 1,468,168 9/1923 Pike 26332 3,254,882 6/1966 Helming 26332 3,313,534 4/1967 Frans 26332 FREDERICK L. MATTESON, JR., Primary Examiner.

E. G. FAVORS, Assistant Examiner.

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