US2069875A - Process of and apparatus for roasting ores - Google Patents

Description

Feb. 9, 1937.

.c. P. DEBUCH ET AL .PROCESS OF AND APPARATUS FOR ROASTING ORES Filed Sept. 11, 1934 Inventor: CARL PAUL DKBUGH ERNST MARKWORW 9 Patented Feb. 9, 1937 PATENT OFFICE raocnss OFAND APPARATUS Fon ROASTING ours I Carl Paul Debuch and Ernst Markworth, Frankfort-on-the-Main,

Germany,

assignors to American Lurgi Corporation, New York, N. Y., a corporation of New York Application September 11, 1934, Serial No. 743,510

, In Germany March 10, 1934 11 Claims.

, The present invention relates to the roasting of ores and more particularly to a process of roasting ores in rotary tube-furnaces and to an imin the interior of the furnace. As a result of the excessive heat and of the fusing of the charge,

the inside lining of the furnace and other parts of the furnace deteriorated rapidly. The agglom with the operations of the apparatus and required frequent and expensive shut-downs and repairs. I Various attempts were made to avoid the disadvantages noted hereinabove, but ,none, as far as it is known, wasv wholly successful and satisfactory in actual practice. Thus, forinstance, instead of introducing the entire amount of.the oxidizing air at one end of the furnace, the air distributed over the entire length of the furnace. While this procedure brought about a more uniform temperature distribution, it did not prevent excessive rising of the temperature and did not eliminate the fusing of the charge and the formation of 'agglomerations and incrustations. It was attempted to withdraw the excess heat from the ,.-furnace byincreasing the air supply above the normal amount essential for good roasting conditions, or by returning cooled exhaust gases to the furnace. This procedure, however, was found to be objectionable, because it detrimentally affected 'the roasting reactions and other conditions es sentialto good roasting. Furthermore, by increasing the volume of the outgoing gases, it also increased the dust carrying capacity thereof. In prior processes, it was necessary to operate the rotary tube-furnaces at low capacity, 50 and reduce the rate at which the material was being treated in orderto prevent excessive rises in temperature causing sintering and agglomeration of the charge.

. It is an object of the present invention to' provide a process which substantially eliminates the erations and incrustations, moreover, interfered was admitted through a number of nozzles evenly difficulties and shortcomings noted hereinabove, which is simple, practical and eflicient, and which is capable of being carried into practice satisfac torily and economically. I Itis another object of the invention to provide an improved process of roasting ores and other metallurgical materials in rotary tube-furnaces,

which substantially prevents detrimental fusing and agglomeration of the charge, and which permits the rotary tube-furnaces to be operated at a higher capacity than it has been possible heretof ore.

The invention contemplates a method of withdrawing excess heat developed in the roasting apparatus without substantially disturbing the conditions essential to good roasting.

A further object of the invention is to provide a process that will permit a higher concentration of SOz-gases in the furnace atmosphere than it has been possible heretofore in rotary tube-furnaces.

It is likewise within the contemplation of the invention to provide a simple and improved apparatus capable of carrying the present invention into practice successfully and economically.

The invention further provides special means for withdrawing heat developed in the roasting apparatus, according to the principle of the invention.

Other objects and advantages of the invention.

will become apparent from the following discussion taken in conjunction with the accompanying drawing in which:

Fig. 1 shows diagrammatically a side elevational view, partly in section, of apreferred form of an apparatus embodying the present invention; and

Fig. 2 illustrates alongitudinal section of an air nozzle on a'large scale.

In general, theinvention comprises withdrawing heat from the furnace atmosphere and balancing the heat thus abstracted by increasing thecharge of the material undergoing treat- ,ment. The heat is withdrawn in quantities sufficient to prevent substantially sintering andincrustations of the charge. According'to the invention, withdrawal of heat may be efiected by admitting the oxidizing air through a plurality of air-nozzles projecting into the furnace, and

in. addition by withdrawing heat from the walls of the nozzles. I

Referring more particularly to Fig. 1, the

drawing illustrates by way of example, a rotary.

tube-furnace comprising a shell I lined with refractory material 2. Inlet and outlet means for the material undergoing treatment are designat ed by reference characters 3 and 4 respectively."

An outlet for the furnace gases is provided by exhaust gas flue 5 at the feed end of the furnace. The apparatusis supported on track rings 6 and may be rotated through gear drive 'i by any conventional driving mechanism (not shown in the drawing).

A controllable amount of roasting air is admitted into the furnace through a plurality of air nozzles and distributed over the entire length of the furnace. 'The nozzles are mounted on shell I by means of an intermediate'member l4, and are extended into the furnace to a sufiicient depth to prevent the material treated in the furnace from reaching the outlet orifices of the nozzles. The nozzles consist substantially of an inner nozzle-tube H and a jacket tube In. Interspaced between the jacket and tube II is another tube l2 which preferably does not extend entirely to the outlet end of the nozzle. An inlet for the roasting air is provided at the nozzle head l5. Reference character I3 denotes a connection for a cooling medium for the air nozzle.

A suitable-cooling medium for the nozzlesmay be air, which may be supplied by a blower l9 through pipe I 8, distributor head l1 and pipes {6 which rotate with the furnace and are provided with control devices 9. The cooling air flows through connections 13 into the space between tubes II and 12 to the end of the nozzle where it is deflected into the outer jacket and flows back between tubes I2 and Ill to outlet 20 at the nozzle head. 7 i

The roasting air is admitted intothe turnace through pipe II. If the furnace operates under negative pressure, pipe ll may be open at'both ends and the roasting air is drawn in the furnace directly from the outside. In order to control the flow of air, the outer end of pipe II at the nozzle head may be provided with valves, dampor rivets. Fixed on intermediate member H, for

instance'by means of bolts is nozzle head l5, which may comprise annular members l5a, I59, 9. sealing-member I51) and an air damper l5c, assembled to form two annular spaces |5d and I5) which are not in direct communication with each other. .Damper 15c may be of the usual type employed for controlling the flow of air in I the nozzles hitherto in use.

The outer tube ill of the nozzle is suitably secured to intermediate member I, for instance by clamping the flared. end thereof between ring l5a and'interme'diate member I4. At the discharge end of the nozzle, tube H) is joined to the end of tube H to make a substantially air tight connection, for instance by welding. The other end of tube ll, however, is preferably not fastened ndmay be only made to fit closely into the central bore of annular member 15a, thereby allowing for free thermal expansion of the tubes.

At the intake end of the nozzle, inner tube l2 may be suitably joined to wall I-5g between annular spaces lid and I51. The other end of the dividual nozzles.

zones.

instance, iron, copper or heat resisting alloys. It

is preferable to use heat resisting steel or alloys, because, due to their excellent durability in service, thinner gauge material can be used,,and the nozzles will be lighter than if other material is used. It is to be observed, however, that it may be suflicient to have only outer tube lil madeof heat-resisting alloys while a less expensive material may be employed for tubes II and 12, which in service are usually maintained by the cooling to a substantially low temperature. In view of the fact that inner tube II is cooled to a lower temperature than tubes Ill and I2, it may be advisable to construct the nozzle so that tube ll takes up the principal mechanical stresses and also carry tubes I2 and ill. It is possible, however, to distribute the stresses in a suitable manner among all three tubes. 1 I

In carrying the present invention into practice," a proper amount of roasting air is admitted into furnace .l rotating at a suitable rate. A prede-' termined amount of the material tobe roasted, is

terial undergoing treatment travels toward outlet 4 at the other end of the furnace, it is ignited and subjected to the oxidizing action of the roastcharged through charging device 3. As the manature of the roasting. reaction, the temperature of the charge tends to be raised rapidly and, if left uncontrolled, some of the unroasted material will fuse together or matte causing agglomerations and incrustations of the mass, and-the roasting operation will be interfered with, perhaps stopped altogether.

It was found, however, that if the air nozzles projecting into the furnace are internally cooled according to the principle of the invention, the temperature can be controlled substantially to prevent fusing of the charge. The hereindescribed method employed for cooling the nozzles may extensively be controlled and adapted to suit the working conditions in the several zones of the furnace, by intensifying or diminishing the cooling, or by entirely suppressing the cooling of in- I If some of the furnace zones become too cold, the heated cooling air from other nozzles may be employed as roasting air in such The temperature of the furnace may be controlled to maintain substantially the desirable conditions in the furnace.

It is possible to abstract by the aforesaid method large quantities of heat which it is to be observed is withdrawn substantially all from the furnace gases. It has been determined that of the heat generated in the furnace by the roasting normal charge Fm some cases, however, it may be advisable to increase the charge so as to replace only 15% of the heatwithdrawn by cooling.

In this case, with the intensity of cooling a vented. Furthermore, the cooling air, which has been heated in passing through the nozzle, may be utilized for heating or drying, or similar purposes. I

It is to be observed that the present invention provides a process whereby ores and other metallurgical materials may be roasted efiiciently without substantially disturbing the desired conditions essential to good roasting, and whereby the efficiency of rotary tube-furnaces may be increased without, however, causing fusing and incrustations of the charge.

It is to be noted that since the heat is Withdrawn substantially all from the atmosphere of the furnace and not from the material undergoing treatment, substantially little adverse influence is exerted on the roasting reactions, and active roasting may thereby be maintained without, however, causing overheating of the charge.

It is also to be observed that the cooling is efsubstantially cool state, and balancing the heat thus abstracted by increasing the charge of the fected within the furnace without, howeve diluting, contaminating, or otherwise changing the composition or nature of the furnace atmosphere.

The amount of roastingair entering the furnace can thereby be controlled to give the most active,

roasting atmosphere, and other conditions such may be partly balanced by increasing the rate at which the material is being treated, thereby increasing the efficiency of the furnace. As more fully disclosed hereinabove, this also results in a higher concentration of sulphur dioxide in the furnace atmosphere than it has been possible heretofore in rotary tube-furnaces.

Although the present invention has been described in, conjunction with preferred embodiments, it is understood that modifications and variations may be resorted to without departing,

from the spirit of the invention, as those. skilled in the art will readily understand.

We claim:-- V

1. The process of roasting ores in a rotary tubefurnace and of controlling the reaction temperature in said furnace which comprises passing ore to be roasted through a rotary-tube-furnace, admitting'roasting air into said furnace as a plurality of jets at spaced intervals of the length thereof, discharging said roasting air substantially radially into zones adjacent to the axis of the furnace, circulating a cooling medium within the furnace in association with each of said jets of roasting air but independently thereof, and

roasting air isdischarged into the furnace in a substantially cool state.

2. The process of roasting ores in a rotary tube-furnace and of controlling the re action temperature in said furnace which comprises passingore to be roasted through a rotary tube furnace, admitting roasting air into said furnace as a plurality of jets at spaced intervals of the length thereof, discharging said roasting air substantially radially to the sides of said furnace into zones adjacent to the axis of the furnace, circulating cooling air within the furnace in association with substantially the entire length of each of said jets of roasting air but independently thereof, withdrawing said cooling air to withdraw heat from the gases inthe furnace and to discharge roasting air into the furnace in a substan,

tially 0001 state, and separately controlling the amount of cooling air circulated within separate zones of the furnace to control the temperature independently in said zones,

3. The process of roasting ores in a rotary tubefurnace and of controlling the reaction temperature in said furnace which comprises passing ore to be roasted through a, rotary tube furnace, admitting roasting air into said furnace as a plurality of jets at spaced intervals of the length thereof, discharging said roasting air s'ubstantially radially to the sides of said furnace into zones adjacent to the axis of the furnace, circulating cooling air within the furnace in asso ciation with substantially the entire length of each of said jets of roasting air but independently thereof, withdrawing said cooling air to withdraw heat from the gases in the furnace and to discharge roasting air into the furnaceyin a ore undergoing treatment.

4. The process of roasting ores in a rotary tubefurnace and of controlling the reaction temperature in said furnace which comprises passing ore to be roasted through a rotary tube furnace,

admitting roasting air into said furnace as a pluf rality of jets at spaced intervals of the length thereof, discharging. said roasting air substantially radially to the sides of said furnace into zones adjacent to the axis of the furnace, circulating cooling air within the furnace in association with substantially the entire length .of

each of said jets of roasting air but independently thereof, withdrawing said cooling air to withdraw heat from the gases in the furnace andto discharge roasting air into the furnace in a substantially cool state, controlling the amount of cooling air circulated within the furnace to withdraw substantially 50% of the heat contained in the furnace gases, and replacing heat thus abstracted from the furnace gases by increasing the charge of the ore undergoing treatment substantially 15%. I

5. A rotary tube furnace for roasting ores comprising a rotatable shell, means for charging material to.be treated into said shell and for withdrawing treated material therefrom, a plurality of air nozzles for supplying roasting air to the interior of said shell, said'air nozzles being distributed at spaced intervals over said shell and extending therethrough to a substantial depth in the interior thereof, an outer jacket in intimate heat exchange with the furnace gases surrounding substantially the entire length of each of said air nozzles, means for circulating a cooling fluid within said jacket forwithdrawing substantial quantities of heat from said furnace gases to maintain their temperature within preferred limits, and means for withdrawing Combustion gases from the furnace. I

6. A rotary tube furnace for roasting ores comprising a rotatable shell, means for charging material to be treated into said shell and for withdrawing treated material therefrom, a plurality of air nozzles for supplying roasting air to the interior of said shell, said v air nozzles being diswithin said jacket for withdrawing substantial maintain their temperature within preferred lim-' tributed at spaced intervals over said shell and extending therethrough to asubstanti'al depth in the interior thereof, an outerjacket in intimate heat exchange with the-furnace gases surrounding substantially the entire length of each of said air nozzles,means for circulating a cooling fluid quantities of heat from said furnace gases to its, means for supplying said cooling fluid to said jackets, and means for withdrawing combustion gases from the furnace.

7. Arotary tube furnace for roasting ores com-: prising a rotatable shell, means for charging material to be treated into said shell and for withdrawing treated material therefrom, a plurality of air nozzles for supplying roasting air to the interior of said shell, said air nozzles being distributed at spaced intervals over said shell and extending therethrough to a substantial depth in the interior thereof an outer jacket in intimate heat exchange with the furnacegases surrounding substantially the entire length of each of said air nozzles, means for, circulating a cooling fluid within said jacket for withdrawing substantial quantities of heat from said furnace gases to maintain their temperature within preferred limits, a blower for supplying cooling fluid to said jackets and conduit means mounted on said shell for connecting said blower to said jackets.

8. The process of roasting ores in a rotary tube furnace and of controlling the reaction temperature in saidfurnace which comprises introducing roasting air into the-interior of a rotarytube furnace through a plurality of 'air nozzles projecting into the furnace at spaced intervals, discharging said roasting air-substantially radially into zones adjacent to the axis of the furnace, circulating astream of a cooling fluid in indirect and' intimate heat exchange with each of said streams of roasting air and with said furnace "gases, and continuously withdrawing said cooling fluid whereby heat is withdrawn from said furnace gases and thejiemperature' of said roasting air and of said furnace gases is maintained within preferred limits.

9. The process of 'roasting ores in a rotary tube furnace and of controlling the reaction temperature in said furnace which comprises introducing roasting air into the interior of a rotary tube furnace in a plurality of streams at spaced intervals, discharging said roasting air substantially radially into zones adjacent to the axislof the furnace, circulating a stream of cooling fluid in indirect and intimate heat exchange with each of said streams of roasting air and with said furnace gases, independently controlling each of said streams of cooling fluid, and continuously withdrawing said cooling fluid whereby heat/is withdrawn from said furnace gases arid the tem- I perature of said roasting air and of said furnace gases is maintained within preferred limits.

10. The process of roasting ores in a rotary.

tube furnace and of controlling the reaction temperature in said furnace which comprises introducing roasting air into .the interior of a rotary tube furnace in a plurality of streams at spaced intervals, discharging said roasting air into zones adjacent to the axis ofthe furnace, circulating a stream of cooling fluid in indirect and intimateheat exchange with each of said streams of roast-' adjacent to the axis of the furnace, circulating a stream of cooling air-in indirect and intimate streams of roasting air and with said furnace gases, independently controlling each of said streams of cooling air, continuously withdrawing said cooling air whereby heat is withdrawn from said furnace, and reintroducing said withdrawn cooling air as roasting air into the cooler zones of said furnace to maintain preferred tem- CARL PAUL DEBUCH. ERNST MARKWORTH.

peratures therein.

' heat exchange with a selected plurality-of said

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