US2672946A - Hopper washing - Google Patents

Description

March 23, 1954 4 SheetsSheet 2 l -5| 52 f 53 -l INVENTORS Er:

ALEXANDER N- CROWDER ATTORNEYS March 23, 1954 s. RABKIN ET AL HOPPER WASHING Filed Dec. 5, 1950 4 Sheets-Sheet 3 loo INVENTORS.

-SAMUEL RABKIN 8. ALEXANDER N. CROWDER BY jwwdwm ATTORNEYS March 23, 1954 s RABKlN ET AL 2,672,946

HOPPER WASHING Filed Dec. 5, 1950 4 Sheets-Sheet 4 us we I07 "0 SAMUEL RABKIN 8. ALEXANDER N. CROWDER ATTOR N E Y5 Patented Mar. 23, 1954 Samuel Rabkin,

Union, and Alexander Crowder, Bound Brook, N.;.L, assignorsto Research Corporation, New York, N. Y.,' a corporation of New York ApplicationDecember 5, 19511,,Serial No..199,184

.7 Claimfi,

I This invention relates to the washing of hoppers of electrical precipitators, especially the hop-- pers-of ,precipitators employed to collectash from the gasesresultingfrom the burning of black liquor in thesulfate paper making process. The invention is particularly concerned with apparains r pp y n a d apply g W s in liqu d to; theinterior surfaces of the hoppers to maintain them in a clean condition and 'to'flush out collectedlmaterial.

Anobject of the invention is tov P d HDD ratus for washing or flushing the hoppers of electrical precipitators -efiectivel y,. simply and economically.

Ano.ther-object:o.f the, invention-is to provide ai-honper washing System wherein the washing liquid -not only-Jflushes the interior surfacesof the -.hopper but also flushes those parts of the washing system that are exposed to .dust fall within the hopperand thus are prone to collect dcn itsc precipitated material.

Another object is to provide in such a wash ing systema sealing .device whereby flushingliquidand collected material :is removed from the h ppers without escapeof gas through the liquid outlet.

Still another object is to provide av hopper washingsystemfor electrical precipitators that greatly improves thecollection and disposition .of water soluble precipitated material such as ashborne in gases from recovery furnaces in which black liquor is burned.

These and other objects of the invention, asmayappear hereinafter, are realizedin-an electrical-prcc pitator having theusual casing, com, plementary high tensionand extended surface electrodes in the casing, andzgas inlet and gas, outlet means in the casing directing a streamof gas to be-cleaned between the electrodes, a hopper in thebottom of the casing receiving'precipitated material removed from the electrodes and discharge means in the hopper, washing means'for the hopperincluding ailiquid conduit extending substantially along an upper edgeof the ,hopper, the conduit having liquid :outlet means positioned to discharge washing liquid against "anupper interior surface of the hopper, and means supplying washing liquidto the con.- duit.

The '{liquid conduit and liquid outlet means there'for may take a variety of forms. For exr ample, the liquid conduit may be an open top trough, the lips of which form liquid outlet means spilling washing liquid over the .outside of the trough and overthe hopper surfaces. to be washed.

2 Or, the liquid conduit may be a pipe extending around the top of the inside of the hopper and having holes or nozzles directing sprays of wash? ing liquid over the surfaces to be cleaned.

The sealing device of the invention includesa discharge conduitleading from the hopper'of the precipitator to a tank through which liquid flows by gravity. The discharge conduit terminates .in the tank below the normal level of liquid therein whereby escape of gas from the precipitator through the hopper and the discharge conduit is prevented.

These and other features of the invention will bedes cribed with particularity-in the following detailed description of several embodiments as shown in the drawings in which:

Fig. 1 is a diagrammatic illustration of a black liquor recovery system employing an electrical ip tatcr and Was i g ys m i ac rdance with the invention;

Fig. 2 is an enlarged, vertical, partial sectional view of an electrical precipitator and hopper washing apparatus suitable for use in the system o Fig. 1;

Fig. .3 is a partial vertical sectional View of.an-. other ,precipitator according to the invention;

Fig. 4 is a view similar to Fig. 3 of another form of the invention;

Fig, 5 is a vertical sectional view through the lower portion of still another form of precipitatcr; and

Fig, 6 is a sectional view taken along the line 6- 6 of Fig, 5,. y

The invention will be described by way of example with reference to a, black liquor recovery system forming an important part of a sulfate process paper mill. Such a recovery system is shown in Fig. 1 in which a weak black liquor storage tank It receives weak black liquor through the pipe II .from the pulp digesters (not shown) after the usual filtration operation. The weakblack liquor is an aqueous solution containing about 15% solids, a large part of the solids content being organic in nature, including sodium sulfate. In the recovery system, the weak black liquor is concentrated to a solids content of about 58% and burned in a furnace to oxidize and drive ofi most of the organic material, to evaporate the water and to reduce the sodium sulfateto sodium sulfide which is purified and reusedin the Pulp digesters.

Initial concentration of the weak black liquor is done in a multiple effect evaporator 2 to which the .weakblackliquor .flows through a pipe 13 acres is under control of a valve I4. The evaporator I2 is of well-known design and has a steam line l5 supplying steam to the calandria of the last effect and a condenser, such as the barometric condenser I6, receiving vapors from the first effect. The weak black liquor flows through the efiects from right to left, as seen in Fig. 1, in countercurrent relation to the vapor flow, the latter being indicated by the arrows at the top of the effects. Preliminarily concentrated black liquor issues from the last efiect of the evapator l2 into the line I! and is forced by the pump l8 through pipes I9, 20, 2| and 22 to a conventional disc evaporator 23. Valve 24 in the line 2! controls the flow of black liquor to the disc evaporator.

In the disc evaporator, the preliminarily concentrated black liquor is concentrated to a further extent by evaporation of water and the heavy black liquor so produced flows through the pipe 24a to the heavy black liquor storage tank 25.

Heavy black liquor from the tank 25 is forced by a pump 25 through the pipe 21 to a recovery furnace charging tank 23 from which it flows through the pipe 25 to a furnace charger 3!] that delivers the combustible heavy black liquor to the recovery furnace 3|.

The black liquor is burned in the furnace 31 to ash consisting chiefly of sodium sulfide and sodium carbonate, which ash is discharged from the furnace into a dissolving tank 32 wherein it is dissolved in water and from which it is forced by a pump 33 to a point of disposition. After purification, the solution of sodium sulfide is reused in the pulp making process.

Furnace gases that contain a heavy burden of moisture and not inconsiderable amounts of sodium sulfate and. sodium carbonate in suspension are passed at high temperature through a waste heat boiler 34 in the furnace 3! where some of the sensible heat is recovered. The partially cooled furnace gases then are passed through the disc evaporator 23 where some of the additional heat thereof is utilized to evaporatively concentrate black liquor flowing from the multiple effect evaporator [2 to the storage tank 25.

A fan 35 blows the furnace gases through an electrical precipitator 36 and thence through the exhaust duct 31 to atmosphere. In the precipitator, the furnace gases are substantially cleaned of their ash content, as will be explained in detail hereinafter, and the precipitated ash is returned to the process.

Referring to Fig. 2, the precipitator 36 is shown in enlarged detail together with certain components of the washing system. Gas flows through the precipitator from left to right in the direction of the arrows, entering the precipitator through the duct 38 and leaving through the duct 31. Within the precipitator there are extended surface collecting electrodes 39 and complementary discharge electrodes 40 in the form of fine wires insulatedly suspended in parallel relation to the collecting electrodes. The discharge electrodes are supplied with high voltage current, usually direct current, by means of a high tension cable M to which the wire electrodes are conventionally connected. Thus a high electric potential is maintained between the fine wire electrodes 40 and the collecting electrodes 39 whereby corona discharge occurs at the fine wire electrodes. The gas to be cleaned of ash passes between the curtains of discharge electrodes and the collecting plates and in these 4 zones the suspended particles become charged and are attracted to and deposited upon the collecting electrodes. Precipitated ash is removed from the electrodes by any suitable electrode cleaning device, such as a rapper (not shown).

Beneath and communicating with the precipitating zone is a plurality of hoppers 42 and 43 into which falls the ash dislodged from the electrodes. This ash, as has been indicated, is soluble in water or black liquor. It is removed from the hopper by hopper washing devices, three forms of which are shown by way of illustration in Fig. 2.

As seen in Fig. 2, the hoppers 42 and 43 have outlet openings 44 and 45 communicating with a discharge header 43 conveying discharged material to a tank 47. The tank receives preliminarily concentrated black liquor from the evaporators I2 through a pipe 48 under control of automatic valve 43 and a manually controlled valve 50 shown in Fig. 1.

The tank has an agitator 5i, driven by conventional means (not shown) and a heating coil 52. An outlet pipe 53 conducts liquid from the tank to a pump 54 that forces liquid through the line 55 to the hopper washing devices.

One such hopper washing device is shown in the hopper 43. It has troughs 56 supported on brackets 51 carried by the precipitator casing structure. Leveling screws 58 are threaded in the brackets, bear on the bottoms of the troughs, and are adjusted to level the troughs. The edges of the troughs that run parallel to the sides of the hopper are bent downwardly to provide overflow lips 59. Lying along or close to the bottoms of the troughs 55 are header pipes 60 connected at one end with washing liquid supply pipe 55 and being capped at the other end. The header pipes have spaced holes through which washing liquid is introduced into the troughs.

In operation, the troughs fill with washing liquid which flows over the edges of the troughs, down the lip portions 59 and is spilled upon the sides of the hopper. The liquid flows down the walls of the hopper washing them free from precipitated material that has fallen thereon, and the washings are returned to the tank 41 through the pipe 46.

It is seen that the flushing liquid washes not only the sides of the hopper but also the lips and sides of the troughs. The tops of the troughs present a horizontal free liquid surface. Thus it is evident that substantially all of the surfaces upon which falling precipitated material can impinge are subjected to the action of washing liquid.

If, as in the exemplary case, the precipitated material is soluble in the washing liquid, such liquid becomes more concentrated in solute as washing progresses and the concentration of solute in the tank 4? is also progressively increased. When the concentration of the solution in the tank reaches a desired value, some of the solution is drawn of! through the outlet pipe 6! to a pump 62 that forces it through a pipe 63 to the disc evaporator 23, as seen in Fig. 1.

The level of the liquid in the tank t? is maintained constant by the automatic admission of fresh liquor through the inlet pipe 43. Such admission of liquor is controlled by a liquid level sensitive device 64 in the tank actuating a control motor 55 that operates a valve actuating motor 65 through the usual connection 5'! to admit treahfiliquorrras .i'equiredrandiltd.istop Ftheiinfiux orlfresh diquor whenathesdesiredlevelin the tank' is attained. i

As best seeniinfi li'g. .2,Ythe':hopper discharge headenflfi has a. downturned leg 68 extending into the pool of liquid in the tank 4! and discharging therein at the open end 6 9 =locatedsubstantiallyrbeneathitheisurface ofiatheliquid pool. The precipitator 36 operates at superatmospheric pressures of from a fractionofpninch-to a few ihchesiofjwater and'the'subinerged outlet of the dischargeheader provides a liquid seal wherebyfs'uch operating 'pressurelisTmaintained while permitting outflow of washings' from theihop- IOthe'r' .iforms' of' hopper washing devices are shownin'the hopper '42 sting. 2. One form comprises a horizontal-pipe 10 extending over the side qof athe hopper to bewashed. This pipe is onnectedwith :a. source. of washing liquidiunder pressure through the pipe H. The horizontal pipe 10 has a plurality of longitudinally spaced holes providing jets directing sprays 12 of washing liquid upwardly a short distance into the air. At least a substantial part of the upwardly projected spray falls back upon the pipe HI thereby flushing the outside of the pipe as well as the hopper surface.

Another form of flushing device is also shown in the hop-per 42 of Fig. 2. This form has a trough I3, similar to the trough 56 described hereinbefore, supported on brackets '14 on the precipitator casing structure. The side wall 15 of the trough that is adjacent the wall of the precipitator or hopper is higher than the side wall 16 that faces the center of the hopper. Liquid fed to the trough from the header 1'! thus flows over the top of the Wall 16 only. An apron 18 having a hook-shaped upper portion 19 is engaged over the top edge of the trough wall 16 and hangs downwardly substantially into engagement with an inner surface of the hopper 42. This apron extends for substantially the full length ofothe trough wall 16 and provides a surface down which the washing liquid flows and from which the liquid is distributed to the hopper surface.

From a consideration of Fig. 1, it is seen that sulfate ash recovered in the precipitator 36 is returned to the system in solution in black liquor. This recovered ash is carried to the furnace 3| and again reduced to sulfide form.

It will be understood that the black liquor employed for washing the precipitator hoppers may be drawn not only from the evaporators l2 but also from any other convenient source. such as the weak black liquor storage tank In, from the disc evaporator 23 or from the heavy black liquor storage tank 25. A mixture of black liquors from these sources also may be used as make up liquor for the hopper washing tank 41. Also, black liquor discharged from the washing tank 4'! may be conveyed directly to the recovery furnace 3| or to the heavy black liquor storage tank 25 instead of being conducted to the disc evaporator 23.

A somewhat modified form of hopper washing system is shown in Fig. 3. Referring to this figure, the precipitator hopper 80 has walls 8| and 82 that slope at a small angle towards the center where there is located a drain pipe 83 emptying into a mixing tank 84 having an agitator 85. Washing liquid is circulated to spray pipes 86 and 8'! that extend along -the hopper walls 8| and 82 through the pipe 88, the pump 89 and iii) '6 pipes 'fiu winds!) l; .ithe, i latter ibeinguncler-= control of vaaval-ve 9.2.. Spray-pipes Stand-8'1 are provided with. spaced ho1es;93 that, direct jets of iwashing liquid against the sides iofthe precipitator and down over the hopper surfaces Bl-and. 82. A branch pipe '94 under control of a valve 954s used lto bleed-ofiffortified liquor. Makeup liquor is supplied-imequal volume to theonixing tank' iil' through 'apipemi. I i The washing system shown in Fig. 4 is simila'r to that shown in 3. It-differs essentially from-thesys'tem of Fig. -3 :in that' the liquid level in the mixing-tank 91 is automatically ma n tained at a predetermined level by means- Off a control system including a level sensing device 98 in *the tank controlling a valve 9-9 in themake upliquid' supply pipe 100. "The sensing-device operates through conventional motors lliland "12 to admit iliquid ithrough valve 99 as needed tozrestoreiliquidilevel:inithe tank. .J'

In Figs. 5 and 6, still another form of hopper arrangement and washing device is shown. The lower portion of the precipitator IE3 is divided into two similar hoppers H14 and I05 by a vertical wall 306. The bottoms ID! of the hoppers have substantially plane surfaces sloping downwardly from one side I08 to the other side 39. At the lower ends of the hopper surfaces I01 are located transverse troughs H0, the bottoms of which slope towards drain pipes l l I. At the upper ends of the sloping surfaces I07 there are positioned transverse header pipes H2 having nozzles H3 positioned to direct jets of washing liquid down and over the bottoms of the hoppers. Washing liquid is supplied to the headers through pipes 4.

In the washing system of Figs. 5 and 6, a copious flow of washing liquid is maintained over the surfaces I01 of the hoppers whereby they are maintained in clean condition.

We claim:

1. In an electrical precipitator including a casing, complementary discharge and extended surface dry electrodes in said casing and gas inlet and gas outlet means in said casing directing a stream of gas to be cleaned between said electrodes, a hopper spaced from said electrodes in the bottom of said casing receiving precipitated material removed from said electrodes, and discharge means in said hopper, washing means for said hopper comprising a liquid conduit extending substantially along the top edge of said hopper, said conduit having liquid outlet means positioned to discharge washing liquid against an upper interior surface of said hopper, and means supplying washing liquid to said conduit.

2. In an electrical precipitator includinga casing, complementary discharge and extended surface dry electrodes in said casing and gas inlet and gas outlet means in said casing directing a stream of gas to be cleaned between said electrodes, a hopper spaced from said electrodes in the bottom of said casing receiving precipitated material removed from said electrodes, and discharge means in said hopper, washing means for said hopper comprising a liquid conduit extending substantially along the top edge of said hopper, said conduit having liquid outlet means positioned to discharge washing liquid over said conduit and against an upper interior surface of said hopper, and means supplying washing liquid to said conduit.

3. An electrical precipitator as defined in claim 2 wherein said liquid conduit comprises a horizontal trough open at the top and said liquid outlet means is provided by a lip of said trough.

4. An electrical precipitator as defined in claim 3 wherein said trough has lips on opposite sides thereof positioned at the same level.

5. An electrical precipitator as defined in claim 2 wherein said liquid conduit comprises a horizontal trough open at the top thereof and having an overflow lip along one side, and apron means extending from said overflow lip into substantial contact with a wall of said hopper.

6. An electrical precipitator as defined in claim 2 wherein said liquid conduit comprises a pipe and said liquid outlet means comprises spaced holes located in the upper portion of said pipe.

7. An electrical precipitator as defined in claim 1 wherein said hopper has not more than two interior walls having substantial horizontal area components, each of said walls sloping downwardly towards said hopper discharge means,

8 said liquid conduit comprises a pipe, and said liquid outlet means comprises nozzle means spaced along said conduit.

SAMUEL RABKIN. ALEXANDER N. CROWDER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 768,450 Hardie Aug. 23, 1904 1,103,995 Murray July 21, 1914 1,250,088 Burns Dec. 11, 1917 2,031,437 Vincent Feb. 18, 1936 2,083,468 Nahigyan June 8, 1937 2,095,597 Drylie Oct. 12, 1937 2,217,345 McGraw Oct. 8, 1940 FOREIGN PATENTS Number Country Date 266,466 Italy July 29, 1929

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