US2446140A - Apparatus for pneumatically separating relatively moist comminuted material - Google Patents

Description

July 27,Y 1948. J. M. McGEE 2,446,140 y APPARATUS FOR PNEUMATICALLY SEPARATING RELATIVELY MOIST COMMINUTED MATERIAL Filed Feb. 16,v 1945 JESSE M. McGEE ATTORNEY A Patented July-27,1948

RATING RELATIVELY MOIST COMMI- NUTED MATERIAL Jesse M. McGee, oak Park. nl, assigner tu" Roberts and Schaefer Company, Chicago, lll., yn. corporation of Illinois Application February' 1c. 1945, sensi No. 518,201

This invention yrelates to the art df separating materials, and is particularly concerned with a new process and apparatus for separating relatively moist comminuted material in accordance with the specic gravities'of its particles.

The invention is especially adapted to and will be` described herein in connection with the dry cleaning or separation of'raw' coal containing a relatively large amount of lines vand vcarrying an amount of excess surface moisture that would normally cause diiliculties in dry cleaningv or might even prohibit the economical and eiiicient use of dry cleaning equipment.

Coal of such character, which now represents for the industry a problem of considerable magniture, is produced in relatively large quantities, e. g., by modern mining methods including those which require water spraying at the face, and also due to the growing necessity of mining relatively poor deposits. The amount of fines in such coal is too large for economical wet cleaning, e. g., by float-sink methods, and the excessive moisture a clam. (ci. aos-s) of coarser particle size content stands in the way of emcien'tly employing pneumatic or dry cleaning apparatus. The troublesome aspects become manifest with materials having a particle size of approximately V2" x 0" land containing excess' surface moisture about 1% to 3% above normal.

The difficulties which must be considered will be apparent from the following brief discussion of the principal conditions that arise in the dry cleaning of coal containing relatively large amounts of nes:

l. Particles which are smaller than 48 mesh are troublesome and impede eilicient dry cleaning even in the absence of excess surface moisture. This is pointed out in detail in my. Patent 2,350,625, issued June 6, 1944. The troubles with such material `may be overcome, as proposed in this prior patent, by removing the fines of critical particle size and subjecting the remaining coarser material to dry cleaning. v

2. Excess surface moisture of about 1% to 3% above normal contained in the raw material introduces difficulties in the removal of the undeto dry cleaning, in the presence of a heated air stream which is circulated through the dry cleaner in a closed circuit.

Either one of the principal procedures noted in the preceding paragraph may be applied independently of the other. That-is to say, the raw material may be subjected to the action of a heated air stream for the purpose of facilitating the removal of fines of predetermined size preparatory to pneumatic separation, and the separation may be carried out in the usual way; and. alternatively, the preparatory treatment of the raw material may be carried out without the use of a heated air stream or may be omitted if de sired, and the operation of the dry or pneumatic cleaner may be facilitated by circulating a heated air stream therethrough in a closed circuit. The

features` may also be combined as stated before.

Other objects of the invention are concerned with humidity and temperature control of the air stream circulating through the system.

The various objects and features are described below in detail with reference to the accompanying drawing, showing in diagrammatic form an organization of apparatus for use in carrying out the invention. I

Referring now to the drawing, numeral I indicates a feed or storage bln from which the rela--- tively moist raw coal is fed by suitable means.

i e. gr, a conveyer 2' to the feed conduit comprising the surge bin V3. The latter in turn feeds the raw material to the mechanical air separator I which may be of the general type disclosed in U. S. Patr ent No. 1,783,357, dated December 2, 1930.

The mechanical air separator 4 receives the material from the surge bin through the connecting conduit Il. The separator comprises an outer shell which is cylindrical at the top and of inverted conical shape in its bottom portion. The outer shell contains an inner conical shell,

. a revolving distributor plate for receiving the sirable lines, and causes trouble in the dry cleaner even in the absence of such critical fines, due to the tendency of the small particles to lump, consequentiy causing fouling, packing and clogging of the material bed. Y l

' This invention proposes to overcome these and other drawbacks by removing from the raw material, preparatory to dry cleaning, lines which are smaller than 48 mesh, in the presence of a heated air stream, and subjecting the remaining material raw material, and a fan for creating a circulating .air current. The raw material within the separator is projected'laterally by centrifugal.

force from the distributor plate across the pathV of rising air currents created by the fan which picks up and carries away in suspension only the finer particles, whereas the heavier particles gravitate outv of the air stream into the inner conical shell or interior cone.

The operation ofthe mechanical air separator 4y is facilitated, andtroubles which may otherwise result from. the excess moisture content of the raw material are eliminated by cirduit dated in conduit I2 is chilled and has taken .ing bled on through conduit;

versely aiect the operation of the current-of controlled temperature and humidity.

The invention provides for this purpose a heater indicated at which may be a furnace or other suitable equipment. `Fresh air is supplied to the heater at 6, and heated air is conducted to the air separator 4 through suitable conduits which may be heat-insulated if desired or necessary, and which include the branches `I-l -8-I0. Conduits 1, 8 and 8 are part of the heated airsupply circuit taking care of the mechanical air separator'4 as well as of the dry or pneumatic cleaner I8, while the conduit branches III and Illa shown in dot-dash lines are provided specifically for supplying heated air to the raw material on its way through the feed conduit 3 and connecting conduit II to the air separator 4. Valves may be included in the branch lines III and Illa at any suitable or desired point. As shown in the drawing, the con- II) may terminate in the neck or connecting conduit Il, or it may terminate, as indicated at Ita, in the upper part of the surge bin or feed conduit I. In either case, the heated air is supplied to the relatively moist raw material about to enter the air separator and eects partial drying of the coal. The heated air is thus supplied to the air separator 4 together with the raw material.

lThe heavier and coarser particles (in this case 1/2" to 48 mesh) emerge from the mechanical air separator 4 laterally at an angle through the conduit intermediate I2 for separation in the air controlled gravity separator or dry cleaner I8. The fines, that is, in this speclnc embodiment, particles of a size smaller than 48 mesh, emerge for disposal from the mechanical air separator 4 centrally at the bottom through a valve I3 positioned in the discharge conduit and are disposed along the line I4. The valve I3 may be a double iiap valve forming an air. lock. The two flaps form in the discharge conduit an intermediate chamber which alternately lls and empties, ythus permitting discharge of the lines while preventing escape 'of substantial amounts oi' air.

The pneumatic gravity separator or dry cleaner II may be of the type shown in Patent 2,245,942, June 1T, 1941. The description of some of its salient features is included in the explanations which follow.

The separator I6 is provided with a bottom air chamber and with a perforated trough-like inclined deck for receiving the raw feed from the intermediate conduit I2 for stratification and separation in accordance with the speciilc gravities oi' its particles.

-The conduit 38 shown in dot-dash lines and including the valve 40 bleeds air from the intermediate conduit I2 to mix with the exhaust air from the separator I6 flowing through the exhaust conduit I8. Residual fines carried with the air inthe intermediate conduit I2 are thus shunted away from the separator I6. The air up moisture on its way through the air separator 4, and be- 38, cannot adseparator I6. Air impulses are injected into the air chamber of the separator I6 by means of a i'an I1. The air injected is clean and dry air maintained at about 350 F. The impulses go through the pertorated deck and through the layer of material thereon, which moves along the deck. keeping the material bed mobile and causing stratificagravities and middli'ngs 4 tion of its particles in accordance with the SIM!-v ciiic gravitiesthereof. The clean .coal is discharged at the opposite end of the separator as indicated by the arrow marked Clean coal." The refuse, that is, particles of :heavier specific consisting of particles of intermediatespecic gravities, may be discharged from the separator I6 along the lines marked Refuse and Middlings, respectively. The previously noted patent may be consulted for further details concerning the structure and operation of the separator I6.

The separator I6 is provided with a dust hood I8 which conducts the dustladen exhaust air into the conduit 20, and thence into a so-called cyclone collector the conduit 2G is substantially clean air 2|. The valve 20 may be part of the intake-conduit oi' the cylone collector. The air injected into the cyclone collector carries residual nes from the conduit 38 and'nes produced by attrition in the separator I6. It also carriesa certain amount of moisture taken up from the material.

'Ihe cyclone collector may be of the general type described in U. S. Patent No. 1,985,947, dated January 1, 1935. Its shape, as indicated in the drawing, is exteriorly somewhat similar tofthat of the mechanical air separator 4. The internal mechanism is, however, somewhat different. The collector is provided in its upper part with a cylindrical interiorly downwardly depending extension forming in the upper cylindrical portion an annular channel. The dustladen air from the conduit I9 is injected into the collector tangentially so a's to create a rotating air stream whichgyrates downwardly along the inner walls thereof. 'I'he eiciency of the collector is a. function ofthe inlet velocity and the neness and the particles to be separated from the dustladen air Acoming from the separator I6, and it will be apparent that the inlet velocity can be effectively regulated by properly positioning the inlet valve 20. -The entering dustladen air stream is directed tangentially along the inner surface of the outer wall of the collector lso that the maximum whirling or cen-trifugal effect is imparted to the suspended material which is deposited or concentrated adjacent the inner closed walls of the collector housing. The smaller lower end of the housing may be equipped with an upwardly and inwardly projecting conical bottom, as4 described in detail in the previously mentioned patent, and is provided with an outlet leading substantially tangentially from one side of the housing to connect with the outlet conduit indicated at22.A This outlet or exhaust conduit discharges the nes concentra-ted in the collector 2|A through a valve 23, which may be of the double nap airlocktype described in connection with dischargevalveIl` of the air separator 4. Therefore, suhstantiallyL only the lconcentrated exhaust nes .varejdischarged through valve 23 and conduit 22. .v y

The above described operationofthe cyclone collector, details of which may be hadfrom consulting the prevoiusly mentioned yPaten-t 1,985,947, is improved in the present case by recirculating a certain amount, say 19%, of the vmaterial fed inrto the collector. This is done through the conduit 24 shown in dottedtlines by a suitable fan or blower 25. A valve 26 may be included in conduit 24, for the purpose of regulating the amount of material for recirculation. l i l The air escaping from the collector 2-I` through which is -This clean air and 2l. which free of fines and dust particles. is conducted through conduits 21 I8, provided with a suitable valve character of may be heat-insulated, if desired 'or necessary. back to the blower or fan I1.

There is thus provided a closed circuit for circulating air through the pneumatic separator I6 which is in general in accordance with the disclosure in my previously mentioned Patent 2,350,625. The mere circulation of air in the closed circuit, throughthe separator. however, is insufficient in the presence of raw material containing a substantial amount of iines and excess surface moisture. In order to take care of this condition, I have provided means for heating the circulating air and for conducting it through the separator in a closed circuit in such a manner that the temperature of the air injected into the separator will always be substantially 350 F. and its humidity a predetermined minimum.

s The heating means includes the previously mentioned heater 5 and the conduits land 8 which connect with the return conduit 28. A

temperature control device, for example, a ther-l mocouple 30, is provided just ahead of the fan I1. The thermocouple governs the operation of the valve control device 3l which in turn ls adapted to operate the valve 32 in the auxiliary air supply conduit 33 which connects with the conduits 1-8 coming form the heater 5. If thetemperature just ahead of the fan I1 exceeds the maximum desired temperature of 350 F., the thermocouple will cause operation of the valve control device 3l which then opens the valve 32 so as to admit into conduit 33 atmospheric air until such time when the temperature is reduced to the desired 350 F. On the other hand, if the temperature is just right'or if it should drop slightly below 350 F., the valve control device 3l will react under the control of the thermocouple 30 to close the valve 32 so as to inhibit inlet of atmospheric air into the system.

Numeral 35 indicates a moisture control device which may be of any suitable, desired and approved type, including a recorder or wet and. dry bulb type adapted to indicate to the operator the humidity of the circulating air coming from the cyclone collector 2|. The humidity of the air coming from the collector should be ma-intained below the dew point. A vent fan 36 connected with `the conduit 28 through a valve 31 is provided for this purpose and allows the operator to regulate the humidityof the airas desired. If the humidity of the circulating air is too high, the operator will open the valve' 31 and exhaust air from the closed circuit, which is then replaced by dry heated air from the heater 5 until the desired humidity is restored. v

The operation of the system will be apparent from the above description, but may be summarized as follows:

Raw materialv containing a relatively large amount of fines and excess surface moisture above 1% to 3% of normal is first subjected to the drying action of heated air tapped off from the conduit 28 through the branch pipesl or conduits l0. Th'e raw material is then dropped into the mechanical air separator l together with the heated air. The separator effects removal of most ofthe critical iines, that is, particles smaller than 48 and feeds the remainder of the material, consisting of coarser particles, to the pneumatic separatorl. The operation of this separator is facilitated by the'current of heated air of controlled temperature and controlled humidity which circulates in a closed circuit from the fan or blower I1 through the separator, dust collector,

a ,-149 I l 6 and back' to the fan I1. circulating air and the temperature thereof are under constant control, the temperature being kept substantially about 350 F. and the humidity below the dew point.. In other words, dry, heated air is circulated throughfth'e separatorl. The temperature control is automatic by means 'of a thermocouple 30 which` governs the operation of the valve control device 3i and the latter in tiun governs the operation of the valve 32 controlling the amount oi' atmospheric air to be introduced into the closed circuit at anyone time for the purpose of temperature correction. The moisture control may likewise be automatic by providing suitable operating means for the valve 31 under the control of the humidity measuring device '35.

The exhaust air from the separator I5 is subjected in this closed circuit to the operation oi the cyclone collector 2l which collects and concentrates the residual fines and dust contained in it. The circulating air is thus automatically puried, and clean air of a controlled temperature and humidity is returned to the pneumatic separator.

The invention contributestoward the solution of the difilcult problem of cleaning relatively moist material, particularly material containing relatively large amounts of fines, and using th'erefor in an eicient manner dry cleaning apparatus which heretofore was considered unsuitable for the purpose. As a matter of fact', it is believed that the invention actually constitutes a solution for this important problem.

It is understood, of course, thatV the invention is not limited to the cleaning of coal, but may likewise be used in connection with the separation of materials exhibiting different properties but posing similar problems.

Changes may be` made within the scope andl spirit of th'e appended claims which denne what is believed to be new and desired tohave protectel by Letters Patent of the United States.

I c aim:

1. Apparatus for pneumatically separating raw' coal containing a relatively large amount of, nes and a substantial amount of surface moisture comprising a feed conduit for conveying a stream of such raw coal, means for injecting into said feed conduit heated air ata temperature of about y 350 F. to abstract moisture from the raw coal moving therethrough, a connecting conduit for receiving the stream of raw coal from said feed conduit together with the heated air injected thereinto, an air separator for receiving said raw coal stream fromrsaid connecting conduit t0- gether with the air th'erein and for removing from such coal stream lines Iwhich are smaller than about 48 mesh. an intermediate conduit for receiving fron1 ,said air separator the remaining coarser raw coal particles together with the air Y 2. The structure and combination dened in claim l., together with. means for withdrawing from said pneumatic separator air together with residual nes and discharging such' residual fines The humidity of the the iines together with removed with the air Number l Name Date from said intermediate conduit. 3.012.115 Woodruii' Aug. 20, 1935 2,181,500 Bird et al. June 6. 1939 .mssE M. Meow. magnus? Elben June e, 1944 REFERENCES CITED OTHER, REFERENCES The following references are of record in the Mitchell: "Coal Preparatmm" published' 1943' by the American Institute of Mining and Metalme of this patent: iurgicai Engineers, New York, N. Y. Copy in Div.

UNITED STATES PATENTS 10 25. Pages 624, 625, 626.

Perry, Chemical Engineers' Handbook." second m22 Byrgff Decffems edition. Published. 1941,11 McGraw-m1111001: Apr' 6 l con New York, NPY in Div- 25. Page 1850'756 Lessing Mar. 22: 1932 Berrisi'ord et al.: "The Pneumatic Dedusting of .118701042 narran Aug. 2' 1933 u Coal." 'Transactions ot the Institute of Mining ifs'zolsw nager sem 1933 www. vl 89. pases 328. 329 (sept. 192s).

2,000,131 Lessing my 7, was. CPY mmv' 25' 39132

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