US2030021A - Method and apparatus for the production of sulphur dioxide - Google Patents

Description

H, o. c. 'INGRAHAM Feb. 4, 1936.

METHOD AND APPARATUS FOR THE PRODUCTION OF SULPHUR DIOXTDE Filed Sept. 15, 1952 xNvEN-roR H0. C. Inf/*ahum I BYZI/ ATTORNEY o o 0 a d e u n a b 0 n n n l o o n Patented Feb. 4, 1936 UNITED) STATES DIETHOD AND APPARATUS FOR THE PBO- DUCTION F SULPHUR DIOXIDE Harold 0. C. Ingraham, Greenwich, Conn., as-

signor to General Chemical Company, New York, N. Y., a corporation of New York Application September 15, 1932, Serial No. 633,251

8 Claims.` (CL 'i5- 60) This invention relates to methods and apparatus for roasting sulphide ores, and more particularly to methods and apparatus for roasting finely divided iron and zinc sulphides, flotation concentrates and the like for the purpose of desulphurizing the same and producing sulphur dioxide for use in the manufacture of sulphuric acid or other arts.

The practice most generally followed at present in roasting sulphide nes, involves the use of mechanically operated multiple hearth furnace constructions, such as the well-known Herresho and Wedge burners. Roasting furnaces of this type are effective, but their complicated structure and operation involve considerable initial and operating expense. Efforts have been made to provide other methods for roasting sulphide ores by which the ore might be roasted in a satisfactory manner, and at the same time to eliminate the employment of complicated and expensive apparatus. For this reason roasting of finely divided sulphide ores in gaseous suspension has been developed. In such instance, the fines are either injected into a roasting chamber in suspension in an oxidizing gas, or are showered downwardly into the roasting chamber wherein the fines encounter cross or counter currents of gases which tend to hold the ore particles in suspension and support the combustion thereof.

Suspension roasting is particularly desirable when the ore is in a very finely divided state, such as notation concentrates, and has the material advantage over the multiple hearth operation of lowering production costs by eliminating the expensive apparatus necessary for the construction and operation of hearth burners. However, in the practice of suspension roasting, operating difculties have been presented which tend to offset the theoretical advantages over hearth roasting. Iron pyrites have been successfully roasted by suspension methods largely on account of the presence inthe ore of relatively large amounts of available sulphur rendering the roasting operation comparatively highly exothermic and affording a source of heat by which the reaction is readily maintained self-sustaining and generating heat in quantities sullcient to produce a. satisfactory roast of the ore. In other situations, considerable dilculty has been encountered in suspension roasting of sulphide ores, such as zinc sulphide, usually requiring extraneous heat to effect emcient desulphurization. With this in view, suggestions have been made to furnish the necessary extraneous heat either by preheating the air or ore, or both. Notwithstanding such proposals, suspension roasting of sulphide ores requiring extraneous heat has met with indifferent success, principally because of inelcient methods of initially bringing the finely divided ore up to the ignition temperature and on account of losses of substantial amounts of heat actually developed in the reaction, which lost heat, if conserved,

would in most instances be of considerable assistance in facilitating substantially complete desulphurlzation of the ore. Y

It is, therefore, among the predominant objects of the invention, when applied to roasting ores, to provide a method and apparatus by which roasting of nely divided sulphide ores generally requiring the application of extraneous heat may be successfully carried out by suspension methods, and further to provide for the roasting of sulphide nes, such as iron pyrites usually not requiring extraneous heat, at higher temperatures if desired. The invention likewise contemplates the 'provision of improved apparatus for carrying out roasting and other operations.

According to that aspect of the invention directed to ore roasting, sulphide nes are roasted in suspension in oxidizing gas in a reaction generating heat which is utilized in initially bringing the nely divided ore up to the ignition temperature and in making the roasting operation selfsustaining. In carrying out the invention, the hot exit gases of the roasting process are caused, preferably after separation of the resulting cinder, to pass the reaction zone in indirect heat exchange relation therewith rst to reduce heat transfer outwardly from the lower hotter section of the reaction zone, thus conserving, to a large degree, heat generated in the roasting operation, and facilitating completion of desulphurization of the ore, and second, to cause heat transfer inwardly to the upper cooler section of the reaction zone, thus raising the temperature of this portion of the reaction zone and acting to hasten preheating of the ore particles and quick- 1y raise the temperature' thereof to the ignition point.

From the viewpoint of apparatus, the invention aims to provide a furnace for roasting sulphide ons, and carrying out similar operations, so constructed as to prevent, to a, large extent, heat losses by radiation from the more highly heated parts of the roasting chamber, and built in such manner as to effect heat transfer inwardly from the hot reaction gases to the cooler portions of the roasting chamber to raise the temperature thereof and bring the ore more rapidly to the ignition temperature Briefly considered a preferred embodiment of the roasting furnace of the invention comprises a vertically elongated reaction chamber provided at the upper end with feed mechanism for forming in the reaction chamber a suspension of finely divided ore in'an oxidizing gas. 'I'he roasting chamber is encased preferably throughout its length by a shaft or shell, the inner surface of which forms with the exterior wall of the roasting chamber a secondary chamber surrounding the reaction chamber. The secondary chamber and the roasting chamber communicate near the base of the furnace through openings in the lower ends of the Walls of the reaction chamber, and reacted gases discharged from the bottom of the roasting chamber are caused to flow upwardly through the secondary chamber. At the bottom of the shaft furnace, the hot gases in the secondary chamber 'tend to equalize the temperatures on opposite sides of the reaction chamber walls and prevent, to a large degree, heat transfer outwardly from the reaction chamber, thus serving to retain, in the reaction zone, heat generated in the roasting reaction. At the upper end of the furnace, the reaction gases in the secondary chamber are, generally speaking, hotter than the corresponding upper section of the reaction zone. Consequently, heat is transferred inwardly, and acts to a considerable extent to preheat the ore particles and raise the same quickly to the ignition tempera'ure. The roasting chamber and the secondary chamber are both provided with hearths serving to turn the course of the gases abruptly at the base of the furnace, effect separation of cinder from the gas stream, and provide means for discharging cinder from the furnace. Gas- Aeous products of the roasting operation are Withdrawn from the furnace through an outlet at the top of the secondary chamber. The invention also includesl particular features of construction of the furnace.

Additional objects and features of novelty of' I of Fig. l.

The roasting furnace ill is built upon a base il, and comprises principally an inner shell l2 and an outer shell i3, both constructed of refractory material. Shell l2 is preferably cylindrical, and, extending upwardly from base il, forms a vertically elongated roasting or combustion chamber i5. The top of the shell l is closed oi by a brickwork crown l, having an in let il through which projects the lower end of an ore-air feed mechanism indicated generally by reference numeral B8. The particular means for feeding a mixture of finely divided ore and air into the roasting chamber l5, and for forming therein a suspension of nely divided sulphides in an oxidizing gas constitute no particular part of the invention. The feed mechanism may be of any approved construction including a hopper I9 for feeding ore, and an inlet conduit 2l! for introducing air or other oxidizing gas into the feed mechanism to facilitate the formation in the roasting chamber of a suspension of finely divided sulphide ore in oxidizing gas. The specic construction of the feed device I8 may be advantageously the same as shown in United States Patent No. 1,758,188 to Burgoyne and Cordy.

The combustion chamber I5 may be provided at its lower and upper ends with Work- holes 22 and 23, having removable closures 24. As will be seen from the drawing, the cinder hearth 26, constituting the lower end of the combustion chamber I5, comprises inverted V-shaped brickwork the upper edge 21 of which extends diametrically across the reaction chamber. The underside of hearth 26, the inner surface of the lower end 29 of shell I2 and the upper side 30 of base II form an air inlet chamber 32 connected to an air inlet conduit, not shown. 1

As indicated, the diameter of the inner shell I2 is considerably less than that of the outer shell I3, thus providing a substantially annular, vertically disposed secondary chamber 35. Outer shell I3 extends upwardly to the top of the shell I2, the top of chamber 35 being closed off by an annular ring 36 lying between the top of shell I3 and the outer periphery of shell I2. The ring 36 is constructed so as to include therein a plurality of conveniently located work-holes 3l.

Settling and heating chamber 35 is terminated at the bottom by inclined hearths 40 and 4I the surfaces of which, as will be seen from an inspection of Figs. 1 and 2, are cot-extensive with the downwardly sloping surfaces of hearth 26 in the combustion chamber I5. Hearths 46 and 4l intersect in a horizontal line 42 which is in effect an extension of apex 2l of hearth 26. Annular chamber 43, beneath hearths 4U and 4l, is also in communication with the air duct, not shown, furnishing air to chamber 32.

The bottom of combustion chamber l5 communicates with the lower endpf secondary chamber 35 through diametrically positioned discharge openings 45 in the Walls of shell l2, substantially at the point of connection of hearths 25, lu and di. This arrangement is clearly indicated in the lower sectional portion of Fig. 2. Hearths 26 d@ and il are provided with a plurality of horizontally disposed openings l? which permit introduction of air from chambers 32 and d3 into the combustion. chamber l5 md the heating and dust settling chamber Conveniently, the lower section of the outer shell i3 may be square in cross-section as shown in FigfB. Cinder outlets 56, closed by gates 5l, pass through the walls of shell lil, and afford means for discharging cinder collecting on hearths d@ and lll. Gaseous products o the roasting operation are withdrawn from the furnace through a gas outlet 53 opening into the upper encl of the chamber 'The briciiworl of shell. i2 of the combustion chamber i5 is laterally supported by a plurality of wing walls 55 rigidly connected to outer shell I3 and extending radially1 toward the shell l2. The inner edges of the wing Walls may engage but are not connected to shell i2, this construction providing for free movement of the latter arising from temperature fluctuations.

Shell I3, which may be enclosed in a steel protective casing 56, may be constructed to include a plurality of suitably positioned work-holes 5l.

The operation of the method and apparatus of the particular sulphide ore to be roasted. Where, for instance, pyrites, zinc blend and pyrrhotite are to be desulphurized, the combustion chamber may be initially/'heated to temperatures of about 850 C. During the preheating operation, the cover 24 of work-hole 23 is removed to permit the escape of products of combustion.

Sulphide nes, which have been dried until the moisture content is not greater than about .3% and preferably between .1% and .2% and of a particle size such that 'about 100% will pass a 60 mesh screen, are then fed into the hopper I9 by any satisfactory conveyor mechanism not shown. A substantial body of finely divided ore is maintained in hopper I9 to prevent the escape of gas from the furnace. From hopper I9, the ore flows into the feed mechanism I8, and is therein admixed with the proper proportions of air or other oxidizing gas introduced through inlet conduit 20. The oxidizing gas may be either at atmospheric temperature or preheated to anyl desired temperature below the ignition point of the particular ore to be roasted.

The amount of the air introduced through inlet 20 will depend upon the amount of the sulphur to be desulphurized, the concentration of the sulphur dioxide desired in the exit gas, and other factors evident to those skilled in the art, and the regulation of the air supply may be accomplished in any suitable and well known manner. In practice, the determination of the sulphur dioxide content of the exit gas will usually indicate the amount of air introduced through inlet 20 necessary to provide the desired results, the sulphide nes being supplied from hopper I9 at a substantially constant rate. The pressure under which the air is introduced should be so regulated that a positive pressure very closely approaching atmospheric is obtained at the bottom of the combustion chamber I5.

Since the construction and operation Aof the feed mechanism I9 constitutes no particular part of the invention, it is suflcient to say that the operation of the latter effects the formation in the roasting chamber of a suspension of finely divided sulphide ore in an oxidizing gas.

As is known in the art, the oxidation of sulphide ores is exothermic, and after introduction of the ore into the roasting chamber, and raising the temperature of the ore to the ignition temperature, ignition of the ore takes place, and

desulphurization proceeds as the ore particles drop through the combustion chamber I5. In operation, the temperature will be quite high throughout the length of thecombustionichamber I5, and, generally speaking, in the lower portions of the shaft the temperature prevailing in the combustion chamber isv preferably around 1000 C.

The roasted ore particles fall on the V-shaped hearth 26, and are discharged from combustion chamber I5 through openings 45 onto hearths 40 and 4I. The slope ofthe surfaces of hearths 26, 40 and 4I is greater than the angle of repose of the ore particles, so that the cinder ilows readily through openings 45 and into the bottom` of chamber 35.

The sulphur dioxide gases formed by the roasting of thev ores likewise are discharged from the combustion chamber through openings 45 into the lower. end of chamber 36. On entering the latter, the gases are subjected to an abrupt 180 change in direction, and rise thence through chamber 35. This sudden turn in direction of the ow of the gases causes a large portion of whatever fine cinder particles may be retained in suspension to drop out of the gas stream and onto hearths 40 and 4I. The hot reaction gases iiowing upwardly through chamber heat the outer side of shell I2, and in the lower section of the shaft furnace tend to equalize temperatures on opposite sides of shell I2. Thus, at the bottom part of the furnace, it willbe seen that this blanket of hot gas surrounding shell I2 prevents, to a large extent, heat losses from the reaction chamber by radiation, and aids in retaining in the reaction chamber heat generated by the oxidation reaction taking place therein.

-The upper end of the reaction chamber, say the upper third, is relatively cool, particularly that section in which the ore particles are finally being heated to the ignition temperature. Since the reacted gases in the top of chamber 35 are of higher temperatures, heat is transmitted inwardly through shell I2, raises the temperature in the upper end of the reaction chamber, and serves to more rapidly bring the ore particles to the ignition temperature.

The sulphur dioxide gases produced by the roasting operation are nally discharged from the apparatus through outlet 53. 'I'his mode of operation is of considerable economic importance, By vsuch procedure, sulphide ores, such as zinc sulphides, and other ores usually requiring the utilization of relatively large quantities of extraneous heat, .may be satisfactorily roasted by suspension methods, and minimum amounts of extraneous heat are necessary. Whatever heat, other than that generated during the roasting operation, may be needed under particular conditions maybe supplied by preheating the fines or air or both as may be desired.

'In operation, limited quantities of cinder may be allowed to collect on hearths 40 `and 4I, and may thus for a short interval of time be per- 'mitted to remain in the hot roasting atmosphere, thereby ensuring a substantially dead roast of the ores. If the particular operating'conditions so require, regulated amounts of air may be admitted into the lower ends of combustion chamber I5 and chamber 35 through openings 41 in hearths 26, 40 and 4I to supply any additional amounts of oxygen which may be needed to aid in bringing about such dead roast of the cinder before the discharge thereof from the furnace through the outlets 50. Additionally, the amount of air admitted through openings 41 may be controlled so as to provide suiiicient oxygen in chamber 35 to effect oxidation of any minor quantities of unburned sulphur therein.

prising a reaction chamber, an inlet at one end of the reaction chamber, means associated with the inlet for introducing into the reaction chamber a suspension of finely divided material in an oxidizing gas, a wall forming the opposite 55. Since certain changes in carrying out the above end of the chamber, and a discharge opening ady jacent said opposite end whereby solid materials are separated from reacted gases, means adjacent said opposite end for. introducing supplemental oxidizing gas into the reaction chamber, and

means for causing reacted gases from the reaction chamberto flow along the outer walls of the reaction chamber.

2. An ore roasting furnace comprising a vertically disposed roasting chamber, an inlet at thel top of the chamber, means associated with said inlet for introducing into the reaction chamber a suspension of finely divided ore in oxidizing gas, a secondary chamber surrounding the reaction chamber, an opening in the wall of the reaction chamber near the base thereof affording communication between the reaction chamber and the secondary chamber, an outwardly sloping hearth at the base of the reaction chamber for discharging cinder therefrom, means for causing hot gases from the reaction chamber to flow upwardly through the secondary chamber, and a gas outlet at the top of the secondary chamber for withdrawing gases therefrom.

3. An ore roasting furnace comprising a Vertically disposed roasting chamber, an inlet at the top of the chamber, means associated with the inlet for introducing into the reaction chamber a suspension of finely divided ore in oxidizing gas, a secondary chamber surrounding the reaction chamber, an opening in the wall of the reaction chamber near the base thereof affording communication between the reaction chamber and the secondary chamber, a sloping hearth at the base of the reaction chamber for d ischarging the cinder from the reaction chamber into the secondary chamber, means for introducing supplemental oxidizing gas into the base of the reaction chamber and the secondary chamber, means for causing hot gases from the reaction chamber to flow upwardly through the secondary chamber, a gas outlet at the top of the secondary chamber for withdrawing gases therefrom, and means for discharging cinder from the secondary chamber.

4. Apparatus of the character described cornprising a vertically disposed reaction chamber, an inlet at the top of the chamber, means associated with the inlet for introducing' into the reaction chamber solid material and reactant gas, diametrically disposedA discharge openings in the. walls of the reaction chamber near the base thereof, a shell surrounding the reaction chamber and forming with the outer walls of the latter a secondary chamber, hearths forming the -bottom of the secondary chamber, a hearth at the base of the reaction chamber constructed to discharge solidmaterial through the openings onto the hearths in the secondary chamber, said latter hearths being positioned co-extensively with the hearth in the reaction chamber, means rigidly connected to the inner Walls of the shell and engaging the walls of the reaction chamber for supporting the latter, a gas outlet at the top of the secondary chamber, and means for discharging solid material from the secondary chamber.

5. The method of roasting sulphide oreswhich comprises introducing sulphide ore and oxidizing gas into a reaction zone, roasting the ore in the reaction zone the initial section of which is relatively cooler than the final section to produce hot sulphur dioxide gases and cinder, separating cinder and hot gases, retaining heat in the hotter section of the reaction zone and supplying heat to the cooler section of the reaction zone by passing the hot efliuent gases of the reaction zone in indirect heat exchange relation with the hotter section of the reaction zone and in indirect heat exchange relation with the cooler section of the reaction zone.

6. The method of roasting sulphide ores which comprises introducing sulphide ore and oxidizing gas into the top of a reaction zone, roasting the ore in suspension while passing the ore downwardly through the reaction zonethe initial section of which is relatively cooler than the final section to produce hot sulphur dioxide gases and cinder, separating the cinder and hot gases, retaining heat in the lower section of the reaction zone and supplying heat to the upper section of the reaction zone by passing the hot gases upwardly in indirect heattransfer relation with the reaction zone.

7. Apparatus of the character described comprising a reaction chamber, an inlet at one end of the reaction chamber, means associated with the inlet for introducing into and for forming in the reaction chamber a suspension of finely divided material in gas, a secondary chamber surrounding at least a major portion of the reaction chamber, an opening for the reaction chamber adjacent the opposite end thereof affording cornmunication between the reaction chamber and the secondary chamber, an outwardly sloping hearth forming the opposite end of the chamber, and arranged to effect discharge of solid residue therefrom, means for causing hot gases from the reaction chamber to fiow through the secondary chamber along the outer walls of the reaction chamber, and a gas outlet for the secondary chamber at the end remote from said opening.

8. The method of roasting sulphide ores which comprises introducing sulphide ore and oxidizing gas into a reaction zone, roasting the ore while in suspension in the oxidizing gas in the reaction zone the initial section of which is relatively cooler than the final section to produce hot sulphur dioxide gases and cinder, separating cinder and hot gases, retaining heat in the hotter section of the reaction zone and supplying heat to the cooler section of the reaction zone by passing the hot effluent gases of the reaction zone in indirect heat exchange relation with the hotter section of the reaction zone and in indirect heat exchange relation with the cooler section of the reaction zone.

HAROLD O. C. INGRAHAM.

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