US2745274A - Means for discharging pulp from bleaching towers - Google Patents

Description

J. P. RICH May 15, 1956 MEANS FOR DISCHARGING PULP FROM BLEACHING TOWERS Filed Oct. 22, 1952 3 Sheets-Sheet 1 FIG. I.

I INVENTOR JOHN P. RICH ATTORNEY May 15, 1956 J, RICH 2,745,274

MEANS FOR DISCHARGING PULP FROM BLEACHING TOWERS FIG. 2.

INVENTOR ATTORNEY May 15, 1956 J. P. RICH 2,745,274

MEANS FOR DISCHARGING PULP FROM BLEACHING TOWERS Filed Oct. 22, 1952 3 Sheets-Sheet 3 FIG. 3.

INVENTOR JOHN P. men

United States Patent "ice MEANS FOR DISCHARGING PULP FROM BLEACHING TOWERS John P. Rich, Nashua, N. H., assignor to improved Machinery Inc., Nashua, N. H., a corporation of Maine Application October 22, 1952, Serial No. 316,117 4 2 Claims. '(Cl. 68-481) It is an object of this invention to improve the efliciency, mechanical, hydraulic and chemical, of high density downfiow, circulatory type, continuous pulp bleachers.

The above and other objects will be made clear from the following detailed description taken in connection with the annexed drawing, in which:

Figure 1 is a vertical section through a typical tower;

Figure 2 is a section on the line 22 of Figure 1;. and

Figure 3 is a detail of one of the valves controlling each dilution nozzle.

A bleaching tower of the type here under consideration may range from 8 to 20. feet in diameter and from to 75 .feet high, dependingon its intended capacity in tons per hour and the time during which the pulp is to remain in the tower, exposed to the bleaching action.

Inasmuch as chemical reaction is occurring throughout the time the pulp is in the tower, it is essential that so nearly as possible the pulp be removed from the bottom of the tower in the identical sequence in which it was added. There are certain other practical problems. Any particular tower is rated for a particular out-put but there is no guarantee that it will be operated always at that rate. In practice, for example, the tower must be capable of operating efiiciently down to as low as /2 of its rated out-put and up to as high as 25 percent above its rated out-put. .There are advantages in operating the tower at relatively high consistencies, e. g., from 10 to percent solids. To be removed by pumping action, however, it must be diluted to between 2% and 4 percent solids. The removal of the dilute stock should be uniform.

In the pat there have been provided hydraulic jets peripherally arranged around the tower which were intended to operate on the high density pulp mass much in the manner of hydraulic mining jets. The size and number of jets is arrived at by consideration of the water requirements under the most extreme conditions, that is: assume maximum density of the body of pulp in the tower and minimum density of the stock to be pumped out. This defines the rated capacity. percent above the rated capacity is usually selected. Such a computation will provide ample nozzle capacity to meet the worst conditions. Unfortunately, however, except during relatively brief periods of overload, such a nozzle system, for reasons which will appear hereafter, is operating below optimum elficiency.

In the past the typical nozzle has included a valve operating on the general principle of a needle valve, connected to a spring-pressed diaphragm or piston wherein the pressure of the water entering the valve moves the diaphragm or piston to withdraw the valve from its seat. Obviously the higher the pressure in the valve, the greater the opening, and vice-versa. Regulation for this type valve is accomplished by increase or decrease of header pressure as by manual setting of a throttle valve supplying the header from which all of the nozzles are fed. This means that at rates and flows less than maximum (overload conditions) the throttle valve leading to the header pressure cannot only remain 2,745,274 Patented May 15, 1 956 '2 header is partially shut down, reducing the pressure in the header and consequently. in the valves. Thus under most operating conditionsthe full pressure desirable for optimum hydraulic mining is not available.

There is herein proposed a new application whereby 7 full but actually increase under reduced flow p The. present invention combines features of the nozzle design 'with certain well known characteristics of centrifugal pumps to the end that the delivered pressure and therefore velocity increases as the flow demand of the system decreases.

The present, invention contemplates a control of the valves by means independent of line pressure so that velocity, which contributes so greatly to the effectiveness of the jets as hydraulic miners, is not only undiminished but actually increased even though by independent ad provided in the line feeding the header and the valvesso that full pump pressure available at all times.

.Referring now' to rFigure 1 there is shown a typical tower having ahcylindrical shell.10. Pulp is supplied through an inlet 12 by conventional pulp feeding means indicated generally at 13 andwill lieusualiy in a comically topped pile 14. The bottomof: the tower is a conical formation 16 and one or more agitators 18 are placed, adjacent'the base of the cone 16; Dilute pulpemerges through an outlet 29 while. dilution jets 22 supply the diluting and disintegrating effect.

As will be clearfrom Figure 2 the jets or nozzles are mutually identical. .Each controlled by a valve 24 and all are'supplied by a header 26. The header 26 receives dilution water through a line 27 from a substana I tially constant speed centrifugal pump 31. The valves are supplied, with operating pressure by a: line 28 and with control pressure by a line '30. The pressure in the control line 30 is manually set at acontrolpanel 32 by conventional means;

Referring now ,toEigure there generally illustrated a nozzle 22 in which is formed a groove or channel 34, theeifective area of which is adjusted by axial movementof a tongue'36v which slides on the underside 38 of the nozzle 22. Thetongue 36 is movedbya rod 4001 the opposite end .of which is mounted aconic alpoppet' valve 42 adapted when the tongue 36 is at its extreme leftward movement to seat on a conical member 44 for water-tight closure of the nozzle; The rod 40 and the valve 42 are secured to a shaft 46 which passes through a stuifing box 48. Water emerges from the header 26 into a chamber 50 through an orifice 51, the chamber 50 being closed by the stufiing box 48.

Rod 46 is secured to a frame 52 and springs 54 surrounding rods 56 bias the whole structure, that is frame 52, rods 46 and 40, tongue 36 and associated parts, toward closing position. At one end of the frame 52 is mounted a diaphragm 58 which is clamped between a fiange 60 formed in the frame 52 and a flange 62 of a cover plate 64 which, with the diaphragm 58, defines an air chamber 66. A rod 68 secures the diaphragm through a connection 70 with a substantial part of the machine. Actually the connection 70 is part of a frame similar to the frame 52. Itpasses through aligned openings 71 in the frame 52 and is bolted (without spring relief, however) to the member 57 which receives the bolts 56. The chamber 66 has an air inlet and outlet 72 which is connected by a line 74 with a pilot valve 76. Operating air comes to the pilot valve through a line 28 and is exhausted through a line 29. The pilot valve is actuated by air supplied thus to govern "the position c f"the"tbn gue 36.

the 'coiitrol line 30. In usual practice the operating 'lir1e: 28 would-carry-air at-about 100 p. s. i. (as =used herein, the abbreviation p; s. i. means pounds per square inch) while the control line 30 would carry air at eressnresbetween 3p. s." i. and'about 13p: s; i. At 3 'p. s. i., th valvewotild be 'cil'o'seil. At i5 pgs. i. it would be wideop'en and -'at about '9 p. s. i. it Would-"be half open.

In operation when, say, 9 358. i. is-suppneu to {the mini-o1 lin'e' th'e pildt *va'lve admits the main fline airthrough the line 74 to the vchanibc'a'r "6'6. Since the *position of "the diaphragm "583's fixed the entire assembly nibves to the right-urawing'the tongue 36 *to ah'alf open position; 6f the nozzles will be adjusted simhltan'eoilsly anae'qnal'ly. In general usage a -valve'istefme'd" a pilot valve if it is used to control the actibn'ofanothervalve. Here; the pilot vailve "76 'setsfthe valve "24 'to'pr'ovide aj-riroper inflow '-and outflow of air to the Chamber 7'0 insure proper pressure on "the diaphragm 58:an'd

67 bears on the right hand'endof fix'ed'rodfis and resists moy'ementof "the pilot valve 76.'-=:"Ihe spring 67 is 'calibrate'd -t'o yield to a predeter'mined positionfforeach piedetermined p. s. i. ofcontrol pressure supplied through theco'ntjrol pressure-finest). I v i J j The nozzles perform a number of ""functions among which, 'df-eo'urseji's the'simple supplying-of dilution water,

the demand for which-is quite variable as noted *earlie rl above. Theyalso s'e'rve'tocut awayand defiberthe bottom of the mass of high density stock and, "further; they con tribute' materially to'thecirculation of the stock ati'the'base of theftower. Both 'of these last twofunctions are functions of velocity 'or, rather; the energy of the jets; As

the "quantitative "demand fordilu'tion Water g down,

the fuhitions o'f defiberin'g and circulation become "increasinglyum mam and-bothof these functions, asjus't noted, are related to the energy ratlrer-"than'the quaritity of the jets. Obviously, as "the-total flow decreases, the mass "delivered byi'the'j'ets fd'ecrea'ses. "v elocityfhoweverfis fa' function "of head 'and "the energy bf'the jets is th roduct-of mass times the 'square' of*thevelocity. Accordingly, ifthe effective p'ressureofthe jets,"and'hence the effective-velocity; can be maintainedor inc'rease'd, the

energy of'the jets, being'responsive to the square'of the" velocity "and onlydirec'tly to the quantity or mass; may be maintained at, or near, optimum efiiciencysofaras fthe defitiering-and' circulating functions are concerned. 2Intlieoperation of centrijug'alpumps, fthefeflective headincreas'es as tliefiow decreases; :Bywontrolling'the v ailves' directly"andf indeperidently; fiill advantage 'is taken I 5 of characteristic,'*and the more the flow"is?reduced, thehigher thehead therefore, the fvelocit'y,"which A spring livered head at minimum flow is 22-5 ;p. s. -i.-while at maximum flow it is p. s. i., but the energy at minimum flow (0.5x225) is 66.5% of the enfifi at flow .(tl.'2S,- 135); In conventionalrpractice, vmaximum valve opening would occur at 135 p s i. on the pump.

This would be reduced by'throttling thedinefeedingthe header. The pumpipressurqito be;s,ur e, ,would increase, but the header pressure would decrease due to the throttle.- 'The energy at minimum flow (volumetrically 40% of maximum) would be far less than 40% of the energy of the maximum flow as compared with the above noted 665% -obtained-by thislinvention.

I claim:

' 1. Means "for bleachingwood pulp comprising Z a reaction tower having its 'axis'ver'tical; means at thetop -of the tower for continuously deliveringinto thetoweria high density mixture of pulp and a bleaching agent; said tower 'having an outlet adjacent its bottom; a plurality of "inwardlyflirected, peripherally spaced nozzles adja= cent thebottom of said tower but spaced vertically above said outlet; '21 substantially constant speed ;centrifu gal pump for delivering dilution'water'tor gsaid nozzles; means connecting said pump to each,ofysai'dfnozzles; cachet said "nozzles having an outlet opening and'a member.

movable within eachof'th'e nozzles'tjo adjust the area of said openings; eachfo'f said members having afluidpre'ssureresponsiverdevice connected ther'eto for inovingfth'e same; 'a source :of fluidpressure independent of said "2. Means'asset'forth inelaimd-in which'sa'id control mean's'applie'sfluid-pressure simultaneously-to all of said devices.

References Gitedin the fileof this -patent V UNITEDISTATES PATENTS

Claims (1)

1. MEANS FOR BLEACHING WOOD PULP COMPRISING A REACTION TOWER HAVING ITS AXIS VERTICAL; MEANS AT THE TOP OF THE TOWER FOR CONTINUOUSLY DELIVERING INTO THE TOWER A HIGH DENSITY MIXTURE OF PULP AND A BLEACHING AGENT; SAID TOWER HAVING AN OUTLET ADJACENT ITS BOTTOM; A PLURALITY OF INWARDLY DIRECTED, PERIPHERALLY SPACED NOZZLES ADJACENT THE BOTTOM OF SAID TOWER BUT SPACED VERTICALLY ABOVE SAID OUTLET; A SUBSTANTIALLY CONSTANT SPEED CENTRIFUGAL PUMP FOR DELIVERING DILUTION WATER TO SAID NOZZLES; MEANS CONNECTING SAID PUMP TO EACH OF SAID NOZZLES; EACH OF SAID NOZZLES HAVING AN OUTLET OPENING AND A MEMBER MOVABLE WITHIN EACH OF THE NOZZLES TO ADJUST THE AREA OF SAID OPENINGS; EACH OF SAID MEMBERS HAVING A FLUID PRESSURE RESPONSIVE DEVICE CONNECTED THERETO FOR MOVING THE SAME; A SOURCE OF FLUID PRESSURE UNDEPENDENT OF SAID PUMP, AND CONTROL MEANS FOR APPLYING SAID FLUID PRESSURE EQUALLY TO ALL OF SAID DEVICES.

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