US2101249A - Pneumatic classifier - Google Patents

Description

Dec. 7, 1937.

M. FRISCH PNEUMATIC CLASSIFIER Filed March so, 1932 OVERS/Zf RETURN INVEN TOR 4/5 ATTORNEY Patented Dec. 7, 1.937

PNEUMATIC cms'smma Martin Frisch, New York, N. Y., assignor to Foster Wheeler Corporation, New York, N., Y., a corporation of New York Application March 30, 1932, Serial No. 601,916

6 Claims.

My invention relates to classifiers forclassifying finer or lighter particles of material from the coarser or heavier particles which may be suspended or carried in a current of air and more l particularly to classifiers for use in connection with coal pulverizers.

The primary object of my invention is the construction of an apparatus of the type above described which shall be adapted to continuously receive large volumes of air and pulverized material without any substantial interruption in flow therethrough while at the same time efiectlveiy eliminating heavier particles therefrom.

A second object of my invention is to provide 15 an apparatus of the type described which shall be adapted to be bolted or otherwise secured directly to the inlet of the exhauster or fan used to induce air through the pulverizer and classifier so that the classifier and fan may together 20 cooperate to form a self contained unit with no intermediate connections between them.

A further object of my invention is to so construct the classifier that the heavier particles which become separated do not pass through the 25 path of flow of the air and pulverized material during the separation process.

My classifier is particularly desirable for use with an air swept pulverlzing mill which is used for pulverizing coal to be supplied directly to a so furnace. To this end, I have provided means associated with the classifier for admitting additional air for combustion of the pulverized coal, as well as for controlling the velocity and volume of air sweeping the mill.

35 Other objects and advantages of my invention will be made clear upon consideration of the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawing, which forms a part of this spe- 40 cification and of which:

c Fig. 1 is a side view, partly in elevation and partly in cross-section, of a preferred embodiment of the invention;

Fig. 2 is a cross-sectional view taken along line 45 2-2 of Fig. 1;

Fig. 3 is a diagrammatic view showing the arrangement of the classifier at the discharge en of a ball type pulverizing mill; and Fig. 4 is a diagrammatic view showing the clas- 50 sifier attached directly to the fan casing.

The classifier, designated generally by numeral I 0, is mounted on the floor or foundation l2 by means of supports II. The classifier includes an outer casing comprising vertical end walls l9 and i 20 between which extend an upper curved wall portion l1 which is essentially semi-cylindrical 'and is curved on a given radius about the center line a, which center line constitutes the axis of the classifier, and which is horizontal, An upwardly directed inlet I4 is formed by wall por- 5 tions 4|, 42, 43, and a part of end wall l9. Wall portions 4! and l1 are continuations of each other, wall portion 4| being tangential to wall portion IT. A pocket 32 is formed by downwardly converging wall portions 44, 45, 46, and 41. The 10 wall portion 45 meets wall portion 42, and wallv portion 44 is tangential to and a continuation of wall portion l1.

Within the outer casing is an inner wall member 1a with respect to which wall portion 42 is a continuation and is. tangential. Wall member I8 is drawn about'the axis a concentric with the outer side wall portion ll. A part of wall member I8 is pivoted at 48 and forms a damper 26 presently to be explained. Wallmember l8 extends from wall portion 42 over the top of the center line a and terminates short of a complete circle providing a lower opening for the central partial cylindrical chamber 50 formed by member I8 and the end walls. 26

Between the outer wall portion I1 and the inner wall member is formed a partial annular passage 2! extending over the top of the inner wallmember l8. Just above the bottom 32 is what may be termed an expansion chamber 22. In the end of chamber 50 is an opening to which is connected a discharge conduit l6 concentric with the classifier axis a. This discharge conduit leads to a fan which conducts air laden with pulverized coal to a furnace or to storage.

On the top of the classifier is a port 29 over which is a plate 30. A damper or plate valve 3| is pivoted at one side of this port or opening at 52 and is arranged to be swung downwardly so as to extend across passage 2|. In its uppermost position, member 3| closes port 29. Port 29 affords connection with the atmosphere for introducing fresh air into the classifier. The position of member 3| is controlled manually by means of a lever 53 and a set screw or wing nut 54.

The damper 26 is adjustable by means of lever 21 and wing nut 28. As can be seen from Fig. 1,

this member can be swung upwardly so as to close or substantially close the passage 2|. It will be seen that, as this member is moved upwardly, it aflfords a restricted outlet from passage 2| into the expansion chamber 22. If, on the other hand, this-member is swung to the left of the position shown in foil lines in Fig. 1, it 5 serves to vary the effective volume of chamber Pocket 32 discharges downwardly into an air lock 33. This is a device for permitting coal or other pulverized material to pass therethrough while preventing, or substantially preventing the passage of air. The air lock may be constructed as shown with a plurality of vanes 35 mounted on a shaft in a cylindrical casing and driven from an electric motor 43 and reduction gearing 56. The air lock discharges into a conduit 33 which is connected with the coal inlet side of the pulverlzing mill.

Referring to Fig. 3, which shows one organization view including my improved classifier, air is supplied to the mill by conduit 53 and coal at 3L- The supply of air may be controlled by a damper $2. Auxiliary air may be supplied at 63.

The air passes through the mill, leaving by the conduit 65 which connects to the inlet I 4 of the classifier. The operation of the classifier is as follows:

Assuming that the valve members 3!, 26, and 23 are in the positions shown in full lines in Fig. 1, the fan F acts to draw air laden with pulverized coal from the mill through conduit 35 and into the inlet I3. Thence the air laden with coal passes through the passage 2!! and into a smooth passage, as shown, this is not necessary chamber 22. The passage 3i is arcuate and the curvature of this passage gives a centrifugal force effect to the coal. However, while I prefer so long as the air passage over the top of the member forming the central chamber is given a curved path. The coal being directed downwardly as it enters the expansion chamber 22, the heavier particles will keep on going downwardly while the air will carry the lighter particles upwardly into chamber lit and thence into the fan which may deliver the pulverized coal and air to a furnace. It will be noted that the heavier particles are given a direction away from the main stream and that the heavier particles do not cross the main stream in-passing to the pocket 32. It will be seen that the inlet l4 istangential to the passage 2| which affords a smooth entry of fluid into the classifier and avoids separation until the stream reaches the expansion chamber. It will be noted that the flow is spiral, working inwardly toward the center a, and that the discharge is axial at the center line.

If, now, the valve member 3| is moved to the position shown in dash-and-dot lines in Fig. 1, will beseen that flow from the mill through conduit B5 is cut off and the fan may draw only fresh air through the port 29. Consequently, it will be apparent that by adjusting the valve member 3! to any intermediate position, any desired ratio of fresh air to coal laden air may be obtained.

It will be understood that the member 31 will vary the proportion of coal laden air to fresh air, but it willnot control the amount of air passing through the fan. This, however, may be accomplished by the valve member 26 which is adapted in the position shown in dash-and-dot lines in Fig. 1 to substantially close the passage M. This member may be placed in an intermediate position so as to give a high restricted discharge into chamber 22 along the wall portion 4 4,

of the coal and the air and will cause a larger degree of precipitation of coal particles. Thus, the fineness can be regulated. The plate 23 may bemoved to control the effective volume of the chamber 22 and by moving this plate upwardly and fixing the damper 26 in a more inward position, the mixture can be made to contain more of heavier particles.

The change of velocity and directionof flow of the air and pulverized material as it enters the expansion chamber 22 are the factors which cause separation of the oversize therein. The particles of desired fineness float out through the central discharge conduit It to the point of use, while the heavier particles or oversize drop into the chamber 32.

The oversize which collects in chamber 32 is returned by gravity through conduit 33 to the feed end of the mill i5 for further pulverization. Obviously, however, the oversize may be returned to any part of the mill. An air lock or trap 33 has been inserted in conduit 33 to improve the efficiency of the classifier and to facilitate the operation of the gravity return. It is obvious that by merely adjusting the elements 23, 26, and 35 it is possible to get any desired degree of separation without altering the speed of the exhaust fan.

One of the important features of my invention is that at no time does the oversize, which has been separated out, have a chance to reenter or cross the path of the moving stream. This fact aids materially in improving the efficiency of my classifier since no power is wasted in pulling the cloud of dust through a screen formed by oversize dropping through the stream. Furthermore, the separation is more efiective since there is no chance for the oversize to be picked up again and carried out of the classifier.

It-isalso important to observe that the fiow of pulverized material and air through the classifier is smooth and substantially uninterrupted, which fact makes it possible to sweep the pulverlzing mill with large volumes of air without excessive power consumption by the fan and without making the classifier unduly large in size.

Fig. 4 shows the preferred combination of fan F and classifier Ill wherein the fan is immediately adjacent the classifier, the outlet of the classifier being attached directly to the inlet of the fan as by bolts 68. In this case the fan may be said to be supported on the classifier or in any event there is a rigid connection with a short conduit between the classifier and the fan whereby the two are in effect one unitary structure. This arrangement is advantageous in saving space.

Suitable access doors may be advantageously provided in the side wall of the classifier.

While my invention involves various novel features, it is to be understood that in some cases certain features of my invention may be used to advantage without a corresponding use of other features and yet fall within the scope of the invention, and that the invention is not movable to vary fiow therethrough and to vary flow through said auxiliary opening.

2.-A classifier comprising a casing including end walls and an outer curved wall portion connecting the end walls, an innerwall member, said outer wall portion and said inner wall member being curved about a horizontal axis and providing a central chamber open at the bottom and a curved passage extending over the top of the inner member, means to supply fluid to said curved passage tangentially of said classifier, an auxiliary air supply opening in said curved passage, a member in said curved passage movable to vary flow therethrough and to vary flow through said auxiliary opening, and a movable member for controlling the relation of flow into said pocket and said central chamber.

3. A spiral centrifugal classifier having its axis horizontal and comprising an upwardly extending inlet, a partial annular passage connected therewith for directing flow downwardly, an expansion chamber for receiving flow directed downwardly by said passage, means in said passage for varying the proportion of pulverized Vmaterial to air flowing therethrough, a damper for varying the velocity of flow into said expansion chamber, means for varying the effective volume of said expansion chamber, and a central discharge conduit having an axis coinciding with the axis of the classifier. I

4. A classifier comprising a casing arranged to provide a smoothly curving passage about a horizontal axis discharging in a vertically downward direction into an expansion chamber in the casing the classifier having an outlet disposed above the expansion chamber, the walls defining the curving passage being arranged so as to prevent the collection of material in flow- ,ing through the passage to the outlet and to prevent the passage of separated material into or through the normal path of flow through the classifier to the outlet, one of the walls defining the passage having an air opening, means comprising a damper operative to control said air opening and the flow area of the passage to vary the proportion of material and air flowing through the passage, and means comprising a damper conforming substantially to the curvature of a wall of the passage for controlling the flow area of said passage to control the velocity of fiow of material therethrough and into the expansion chamber to thereby control ,the degree of separation of material from the stream flowing through the passage.-

5. A classifier comprising a casing arranged to provide a smoothly curving passage about a horizontal axis discharging in a vertically downward direction into an expansion chamber in the casing, the classifier having an outlet disposed above the expansion chamber, the walls defining the curving passage being arranged so as to prevent the collection of material in flowing through the passage to the outlet and to prevent the passage of separated material into or through the normal path of flow through the classifier to the outlet, one of the walls defining the passage ,having an air opening, means comprising a damper operative to control said air opening and the flow area of the passage to vary the proportion of material and air flowing through the passage, and means comprising a damper in the expansion chamber for controlling the efiective volume of the expansion chamber to control the fineness of the particles of material separated from the stream of material flowing through the passage.

6. A classifier comprising a casing arranged to provide a smoothly curving passage about a horizontal axis discharging in a. vertically downward direction into an expansion chamber in the casing, the classifier having an outlet dis posed above the expansion chamber, the walls defining the curving passage being arranged so as to prevent the collection of material in flow-- ing through the'passage to the outlet and to prevent the passage of separated material 'into or through the normal path of flow through the classifier to the outlet, one of the walls defining the passage having an air opening and means comprising a damper operative to control said valr opening and the fiow area of the passage to vary the proportion of material and air flowing through the passage, means for controlling the flow area of the passage to control the velocity of flow of material therethrough and into the expansion chamber, and means for control ling the efiective volume of the expansion chamber.

MARTIN F'RISCH.

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