US2536952A

US2536952A - Apparatus for roasting ore

Info

Publication number: US2536952A
Application number: US782618A
Authority: US
Inventors: Kenneth D Mcbean
Original assignee: Teck Metals Ltd
Current assignee: Teck Metals Ltd
Priority date: 1947-10-28
Filing date: 1947-10-28
Publication date: 1951-01-02
Anticipated expiration: 1968-01-02

Description

Jan. 2, 1951 K. D. MOBEAN ,9

APPARATUS FOR ROASTING ORE Filed Oct. 28, 1947 4 Sheets-Sheet 1 KD. IV! Bea-n Inventor ATTORNEY K. D. M BEAN APPARATUS FOR ROASTING ORE Jan. 2, 1951 4 Sheets-Sheet 2 Filed Oct. 28, 1947 M a 6 m M D V w n e V V W 1 ATTORNEY Jan. 2, 1951 K. D. MOBEAN APPARATUS FOR ROASTING om:

Filed Oct. 28, 1947 4 Sheets-Sheet 3 K. D. MBeam l'Yl veYlToY ATTOB NEY 4 Sheets-Sheet 4 Jan. 2, 1951 K. D. M B EAN APPARATUS'FOR ROASTING ORE Filed Oct. 28, 1947 Inventor AT TO R NEY K. D. MBean nMMmuH n H Patented Jan. 2, 1951 2,536,952 APPARATUS FOR ROASTING our;

1 Kenneth D. McBean, Trail, British Columbia,

1 Canada, assignor to The Consolidated Mining and Smelting Company of Canada, Limited,

Montreal, Quebec, Canada, a corporation of Canada Application October as, 1947, Serial No. 782,618

4 Claims.

This invention relates to an apparatus for roasting ore and concentrates and is particularly directed to the roasting of mineral sulphides in gaseous suspension.

Methods and apparatus for roasting mineral sulphides in gaseous suspension are well known and are in relatively wide spread use. In general, the methods involve blowing a mixture of finely divided, dried mineral sulphide ore or concentrate particles into the upper part of a combustion chamber maintained by the heat of the combustion of the particles at a relatively high temperature, wherein the particles are disseminated concurrently with the air blast through it for the exposure of the surfaces of each particle to the oxidizing action of the hot combustion gases. The

conversion of the sulphides to oxides is effected by the combustion of the sulphur content of the charge supported by the air of the blast. The roasting temperature and the time of retention of the particles in the combustion zone are regulated in such a manner as to promote the oxidation of the charge without fusion or incipient fusion. The roasted material settling at the bottom of the combustion chamber is removed for further processing and the gaseous products of combustion are exhausted from the combustion chamber having ahigh concentration of sulphur dioxide. Such methods and apparatus are disclosed in 'U. S; Patent No. 1,884,348 and No. 1,963,282.

In roasting mineral sulphide particles in gaseous suspension according to known methods and apparatus, the sulphide particles have been dried on drying hearths placed above the combustion chamber or in separate drying apparatus outside the roasting furnace.

An important object of the present invention I is to provide an improved apparatus for roasting mineral sulphides in gaseoussuspension whereby the productive capacity of the roasting furnace is substantially increased with a substantial decrease in'capital and operating costs.

A further important object of the invention is to provide an improved roasting furnace which permits the arrangement of the apparatus asso-' ciated with the roasting furnace, such as the feed bins-fans, conduitsand conveyors, at a low level,

preferably adjacent to the floor level, which reduces the amount of heavy supporting structural steel required, and centralizes adjacent to that level the control of the process.

A- further important object is to provide a novel design of roasting furnace which may be readily modified to increase the capacity of the furnace. This may be accomplished by merely, extending the combustion chamber and burners upwardly without extensive dismantling and rearrangement of the furnace and associated parts.

An understanding of the manner in which the above and other objects of the invention are attained may be had from the following description, reference being made to the accompanying drawings in which:

Figure 1 is a plan view illustrating schematically a preferred arrangement of the furnace and associated apparatus;

Figure 2 is a plan view in section taken along the line 2-2 of Figure 6;

Figure 3 is a plan view in section taken along the line 33 of Fi ure 6;

Figure 4 is a plan view in section taken alon the line 44 of Figure 6;

Figure 5 is a plan view in section taken along 'the line 5--5 of Figure 6;

ent invention;

Figure 7 is a side elevation illustrating a, preferred arrangement for distributing dried ore particles to the burners; I

Figure 8 is a side elevation illustrating a preferred arrangement of the roasting furnace and associated storing and feeding apparatus; and

Figure 9 is a side elevation in section of the roasting furnace illustrating a preferred arrangement of conduits from the roasting chamber to the drying hearth and from the drying hearth to the intake of the burner fan.

Like reference characters refer to like parts throughout the specification and drawings.

A preferred embodiment of the invention is illustrated in Figures 1 to 9 inclusive and comprises, in general, a roasting furnace indicated by the numeral 20, a grinding mill 2|, such as a ball mill, for pulverizing the ore to a high degree of.

fineness, a classifier 22 for classifying the pulverulent ore particles from the grinding mill, and a blower 61 for distributing the ore particles to the burners, and associated fans, conveyors, ducts and storage bins, all of which are described in detail hereinafter.

The roasting furnace 20 is preferably a vertically disposed, elongated cylindrical metal shell internally lined with heat insulating material 30, such as refractory bricks, capable of withstanding the high temperature corrosive and erosive actions of the gases and the particles to which it is subjected. The outer surface of the shell is also covered with insulating material 3|, such as asbestos. to minimize heat losses through the shell.

The upper part of the furnace is in the form or an elongated, unobstructed combustion chamber 32 closed at the top by a steel cover 33 interhally lined with refractory heat-insulating material, and at the bottom by the uppermost collecting hearth 34. The combustion chamber is of a height sufficient to permit the substantially com plete oxidation of the particles as they fall to the uppermost collecting hearth 34 and of a diameter su'iilcient to permit the tho'rbugh dissemination of the particles therein.

The collecting

hearths

34 and 35 and the drying hearth 36 are positioned in the lower part of the furnace below the combustion chamber. The uppermost collecting hearth slopes slightly upwardly from the shell of the furnace towards a centrally disposed shaft 31 to terminate short of the shaft to provide between the shaft and the rim of the hearth an annular drophole 36 leading to the lower hearth 35.

The lower hearth 35 is similar in construction to the upper hearth 34 and extends downwardly from a point adjacent to the shaft 31 to the inner lining of the furnace shell. An outlet drophole 36 is provided in the hearth 35 and extends through the furnace shell for the discharge from the furnace of roasted particles collected on the hearth 35.

The particles collected on the lower collecting hearth 35 are moved by rabbles 61 attached to rabble arms carried by the shaft towards the periphery of the furnace and into the discharge outlet 39 which extends to a storage bin (not shown).

The chamber formed between the upper collecting hearth 34 and the lower hearth 35 is provided with an outlet 62 in the furnace wall for the combustion gas. This outlet 32 is located at a convenient place opposite the discharge outlet 39. The combustion gases are withdrawn through outlet 82 and preferably passed through a wasteheat boiler and cyclone (not shown).

The drying hearth 36 is positioned below the lower collecting hearth 35. The drying chamber 25 is defined by the underside of the lower collecting hearth 35 and the top of the drying hearth 36 and is isolated from the collecting hearths except for such minor leakage of gas as may occur through the small space between the shaft and the lower collecting hearth. Hot combustion gases are withdrawn from the combustion chamber through the conduit 44, Figure 9, and passed into the drying chamber 25.

The shaft 31 is in the form of a hollow rotatable steel shell externally covered with refractory heat-insulating material. The shaft extends from a point below the furnace to terminate a short distance above the uppermost collecting hearth 34. Rabble arms 46, 4i and 42 are carried by the shaft and extend radially outwardly from the shaft to move, on rotation of the shaft, over the collecting

hearths

34 and 35 and the drying hearth 36 respectively. The rabble arms are hollow and are adapted internally for cooling by a cooling medium, such as air, fed into the lower end of the shaft 31 through conduit 84 connected to a source of air under pressure, such as for example, a compressor (not shown) and discharged through conduit 65. The rabble arms are thus maintained at a temperature substantially below the normal operating temperature of the furnace. The shaft is rotated at a predetermined rate by means of a conventional driving mechanism 33, which may be a motor connected through a speed reduction gear box 4 to a pinion driving a ring gear mounted on the shaft below the furnace.

The associated parts of the roasting furnace for storing the moist ore, drying the ore, grinding the dried ore, delivering the finely com minuted, dried ore particles to the burners, and the circulation of combustion air and hot combustion gases are described hereinafter in con- Junction with the operation of the furnace and its associated apparatus.

Moist sulphide ore particles are stored in the bin 50, and are fed, preferably at a predetermined rate, such as by a screw conveyor 5!, to the periphery of the drying hearth 36.

The moist particles are advanced by the rabbles attached to the rabble arms 42, across the hearth 36 and during their passage across the hearth 36 the particles are exposed to the hot combustion gases fed into the drying chamber 25 from the combustion chamber 32 through the duct or conduit 44. The volume of the gas passing through the drying chamber 25 may be regulated such as by a valve 66, so that substantially all the moisture is removed by the time the particles have travelled across the hearth 36. The particles are moved toward and into the drophole 52, and into the conduit 53 which communicates with a conveyor 54. The conveyor 54 advances the dried particles to the grinding mill 2!, such as a ball mill, wherein any agglomerations are broken up and any coarse particles are ground to a finely comminuted state.

The dried, comminuted particles are carried from the grinding mill 2i in an air current generated by a fan or blower 26 through conduit 55, through the classifier 22 to a separator 56, such as a cyclone separator, in which the air and the dried comminuted particles are separated. The air on losing its burden of ore particles is returned through conduit 51 by the blower 26 to the grinding mill 21. Any excess air from the grinding circuit is preferably fed from the blower 26 through vent 53 to the burner fan inlet 16 to be used in the combustion of the sulphide particles.

The dried ore particles are arator 56 through a conduit storage bin 62, Figure 8. An 61 is provided in conduit 66.

The dried particles are fed at a predetermined rate by a conveyor 63 positioned below the storage bin 62. The conveyor 63 advances the ore particles to an air injector 64. The air injector 64 is connected to a source of high pressure air, such as a compressor (not shown) through conduit 65. The ore particles are carried in the air blast to the burner circuit.

The burner circuit preferably includes a conduit 66 connected at one end to a fan 61 and at the other end to a junction 66 at which the stream of dried mineral sulphide particles and air is divided for distribution to the burners. An opening in the conduit 66 is provided for the injected stream of ore particles from the injector 64, as indicated by the numeral 63. Excess air from the grinding circuit may be returned through vent 53 to burner fan inlet 16.

Combustion gas is drawn through the drying chamber 25 and withdrawn through conduit 1| and returned through the burner fan inlet 13 to the combustion chamber 32. Atmospheric air for supporting oxidation, or combustion, of the sulphide particles is drawn into the burner cir- 1cutit'ghrough the open end 12 of burner fan infed from the sep- 66 to a dry feed air sealing valve The stream of combustion pended dried mineral sulphide particles is divided at junction 68, into substantially equal streams for delivery to the burners l4 and 15,

each burner being supplied with approximately the same volume of the mixture of gas and sulphide particles.

In the preferred modification of the invention, two diametrically opposed burner nozzles 14 and 15 are extended angularly upwardly into the upper part of the furnace. The burner nozzles l4 and 15 are connected at their inlet ends to the conduits 16' and 11 respectively which; in turn, are connected to the junction 68. To ensure proper combustion of the particles and to avoid the formation of accretions on the furnace walls. the burner nozzles 14 and 15 are preferably gases and susdirected angularly upwardly. If more than two burner nozzles are used in the furnace, these are preferably spaced equidistantly around the combustion chamber.

A scraper 80, carried by a stationary arm 8|, preferably in the form of a water-cooledpipe, scrapes particles which have fallen on the top of the rotating shaft 31 and prevents their accumulation on the top of the shaft. I

The burner fan 61 forces a mixture of air and combustion gas into the conduit 66 for circulation to the burner nozzles 14 and 15. bustion gas is drawn from the combustion chamber through the conduit 44, and the drying chamber 25, and from the drying chamber through the conduit II to the burner inlet conduit 13 for Comnace. v

The embodiment of theinvention described in detail herein and illustrated in the drawings is capable of modification without departing from the scope of theinvention. For example,- in' 4 certain instances, it may be desired to discharge all or part of the gas from the drying chamber to the atmosphere, or into the hot combustion gases passed to the heat exchanger, or into the gases discharged :from the' heat exchanger,

rather than return it to the combustion chamber. Also, the gas from the drying chamber may be passed through a-separator, such as a cyclone separator for the removal of the entrained solids.

These entrained solids normally would include base of the furnace, the rotating shaft is exadmixture with atmospheric air and is delivered to the conduit 66 by fan 61. If desired, oxygen may be fed into the gas supplied to the burners to enrich the gas mixture. Additional air may be supplied to the burner circuit by by-passing air from the grinding circuit through conduit 58.

Hot combustion gases are withdrawn from the furnace through the outlet 82 in the furnace wall at a point adjacent to the periphery of the lower collecting hearth. The hot combustion gases withdrawn from the furnace are passed preferv ably through a heat exchanger, such as a wasteheat boiler, for the recovery of their heat value, and then passed through a separator, such as a cyclone separator, for the removal of the entrained solids.

The design of the furnace and the arrangement of the associated apparatus permit operation of the furnace to produce products of high quality at a highcapacity.

In operation, the dried mineral sulphide particles, on being blown into the furnace, are rapidly dispersed in the hot combustion zone and ,quickly reach their ignition temperature. The

roasted particles settle through the combustion chamber, on to the uppermost collecting hearth 34 whereon they are moved inwardly towards and into the annular drophole 38 to fall on to the lower collecting hearth 35. The particles on hearth 35 are rabbled outwardly towards and into conduit 39 through which they are removed from the furnace.

The rate of combustion and the temperature of the combustion chamber may be closely controlled by varying the rate of feed of mineral sulphide particles to the burner nozzles and the composition of the gaseous suspension medium, which may be easily varied by increasing or decreasing the rate of flow of atmospheric air or oxygen enriched air or combustion gases from the drying chamber or by returning cooled combustion gas from the exit of the heat exchanger.

tended only a short distance into the furnace leaving the combustion chamber free from any obstruction and thereby substantially increasing the capacit of the furnace. This design of furnace has a further important advantage in that it permits the thorough dispersion of the particles inthe hottest zone of the furnace to promote thorough combustion at a rapid rate and at the same time enables a relatively high concentration of sulphur dioxide to be obtained in the exit gas and diminishes the formation of zinc ferrates when the furnace is employed for roasting zinc sulphides containing iron compounds.

Also, further increases in furnace capacity may be obtained by an easily erected upward extension of the furnace and burners without major dismantling and reconstruction operations.

The design of the furnace makes possible the concentration of apparatus associated with the furnace at or adjacent to the floor level with attendant substantial reduction in capital cost and important savings in operating costs and facilitates close control over the operation of the apparatus.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. In a furnace for roasting mineral sulphides in gaseous suspension, a vertically elongated, unobstructed combustion chamber, an inlet for dried comminuted mineral sulphide particles in the upper part of said chamber, at least one collecting hearth below said combustion chamber, an outlet for roasted ore particles and an outlet for hot combustion gases from the collecting hearth, at least one drying hearth below the collectin hearth for drying the combustion chamber feed material, conduit means extending from the combustion chamber to a drying chamber defined by the collecting hearth and the drying hearth, an inlet for moist sulphide particles to the drying hearth. an outlet for dried sulphide particles from The air or oxygen enriched air isintroduced with the mineral. sulphide particles fed" to the burners l4 and 15 in the'upper part of the-fur.- nace chamber. It is not necessary to introducecombustion air or oxygen elsewhere in the= furthe drying hearth, an outlet for gases from the drying chamber, means for conveying dried sulphide particles from the drying chamber to the combustion chamber, a rotatable shaft extending from a point below the furnace to terminate a short distance above the uppermost collecting hearth, rabble arms carried by said shaft, and rabbles carried by said arms adapted to move on said hearths.

2. In a furnace for roasting mineral sulphides in gaseous suspension, a vertically elongated, unobstructed combustion chamber, means for injecting a mixture of oxidizing gas and dried, comminuted mineral sulphide particles into the upper part of the combustion chamber, at least one collecting hearth below said combustion chamber, an outlet for roasted ore particles and an outlet for hot combustion gases from the collecting hearth, at least one drying hearth below the collecting hearth for drying the combustion chamber feed material, conduit means extending from the combustion chamber to a drying chamber defined by the collecting hearth and the drying hearth, an inlet for moist sulphide particles to the drying hearth. an outlet for dried sulphide particles from the drying hearth, an outlet for gases from the drying chamber, means for conveying dried sulphide particles from the drying chamber to the combustion chamber, a hollow rotatable-shaft extending from a point below the furnace to terminate above but adjacent to the uppermost collecting hearth, rabble arms carried by said shaft, rabbles carried by said arms adapt-- ed to move on said hearths, and means for feeding a coolant through said shaft and rabble arms.

3. In a furnace for roasting mineral sulphides in gaseous suspension, a vertically elongated, unobstructed combustion chamber, means for in- Jecting a mixture of oxidizing gas and comminuted mineral sulphide particles into the upper part of the combustion chamber, at least one collecting hearth below the combustion chamber, an outlet for roasted ore particles and an outlet for hot combustion gases from the collecting hearth, at least one drying hearth below the collecting hearth for drying the combustion chamber feed material, a drying chamber defined by the collecting hearth and the drying hearth, means for feeding moist mineral sulphide particles to the drying hearth, conduit means extending from the combustion chamber to the drying chamber, an outlet for dried sulphide particles from the drying hearth, means for conveying dried sulphide particles from the drying chamber to the 8 combustion chamber. conduit means for returning gas from the drying chamber to the combustion chamber, a rotatable shaft extending from a point below the furnace to terminate a short distance above the uppermost collecting hearth, rabble arms-carried by said shaft, and rabblu carried by said arms adapted to move on said hearths.

4. In a furnace for roasting mineral sulphides in gaseous suspension, a vertically elongated, unobstructed combustion chamber, means for in- Jecting a mixture of oxidizing gas and comminuted mineral sulphide particles into the upper part of the combustion chamber, at least one collecting hearth below the combustion chamber, an outlet for roasted ore particles from the collecting hearth, a separate outlet for hot combustion gases adjacent to the collecting hearth, a drying hearth below the collecting hearth, a drying chamber defined by the collecting hearth and the drying hearth, means for feeding moist sulphide ore particles to the drying hearth, conduit means extending from the combustion chamber to the drying chamber, an outlet from the drying hearth for dried sulphide particles, means communicating with the last mentioned outlet for pulverizing said dried sulphide particles, means for advancing the dried comminuted sulphide particles to the combustion chamber, and conduit means for mixing an oxidizing gas with gas from the drying chamber'for admixture with the dried sulphide particles, a rotatable shaft extending from a point below the furnace to terminate a short distance above the uppermost collecting hearth.

, rabble arms carried by said shaft, and rabbles carried by said arms adapted to move on said hearths.

KENNETH D. McBEAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,929,308 Clarke Oct. 3, 1933 1,929,713 Queneau Oct. 10, 1933 1,963,282 Stimmel et a1. June 19, 1934 2,002,496 Freeman May 28, 1935 2,088,195 Ferguson July 2'7, 1937 2,104,091 Mullen Jan. 4, 1938 2,120,475 Stimmel et al. June 14, 1938 2,302,841 Connolly Nov. 24. 1942

Claims

1. IN A FURNACE FOR ROASTING MINERAL SULPHIDES IN GASEOUS SUSPENSION, A VERTICALLY ELONGATED, UNOBSTRUCTED COMBUSTION CHAMBER, AN INLET FOR DRIED COMMINUTED MINERAL SULPHIDE PARTICLES IN THE UPPER PART OF SAID CHAMBER, AT LEAST ONE COLLECTING HEARTH BELOW SAID COMBUSTION CHAMBER, AN OUTLET FOR ROASTED ORE PARTICLES AND AN OUTLET FOR HOT COMBUSTION GASES FROM THE COLLECTING HEARTH, AT LEAST ONE DRYING HEARTH BELOW THE COLLECTING HEARTH FOR DRYING COMBUSTION CHAMBER FEED MATERIAL, CONDUIT MEANS EXTENDING FROM THE COMBUSTION CHAMBER TO A DRYING CHAMBER DEFINED BY THE COLLECTING HEARTH AND THE DRYING HEARTH, AN INLET FOR MOIST SULPHIDE PARTICLES TO THE DRYING HEARTH, AN OUTLET FOR DRIED SULPHIDE PARTICLES FROM THE DRYING HEARTH, AN OUTLET FOR GASES FROM THE DRYING CHAMBER, MEANS FOR CONVEYING DRIED SULPHIDE PARTICLES FROM THE DRYING CHAMBER TO THE COMBUSTION CHAMBER, A ROTATABLE SHAFT EXTENDING FROM A POINT BELOW THE FURNACE TO TERMINATE A SHORT DISTANCE ABOVE THE UPPERMOST COLLECTING HEARTH, RABBLE ARMS CARRIED BY SAID SHAFT, AND RABBLES CARIED BY SAID ARMS ADAPTED TO MOVE ON SAID HEARTHS.