US2541630A - Sludge handling system and apparatus - Google Patents

Description

Feb. 13, 1951 c. Yl-:oMANs SLUDGE HANDLlNG SYSTEM AND APPARATUS Filed Aug. 19, 1946 IN V EN TOR.

Patented Feb. 13, *1951 OFFICE SLUDGE HANDLING SYSTEM AND APPARATUS Charles Yeomans, Hubbard Woods', Ill., assigner to Yeomans Brothers Company, Chicago, Ill'., a corporation of Illinois Applicationnugust i9, i946, serial No. 691,606l

(ci. 21o- 2) l1 Claims.

This invention relates to an improvement in gas" displacement pumping Ysystems, such as are used for pumping sludge from a sewage settling tankto a digester, in which thesludge is decomposed to form a combustible gas which is stored under pressure and delivered to various gas consuming appliances.

Thisapplication is a continuation-impart of my prior, co-pendihgapplication Serial Number 583,539, now Patent No..2f,481,894, Which Wasflled on March, 19, 19455,. and' which is assigned tov the assignee of the. present invention. Certain of the features of' the present invention. are directed to improvements in the pumping system disclosed in my co-pending application, and particularly, to. improvements in the control equipment for systems of that type..

Heretofore in the pumping of sludge inrdigester gas producing systems it has. been the practice to. use reciprocating pumps for moving the sludge fromI the settlingY tank to the digester. This has given rise to. serious problems in, maintaining the pumpingequipment in operable` condition, because the materials handled made it necessary that the pumps be4 cleaned andthe pumpvalves be reseated at frequent intervals. Such cleaning is not only an expensive, time-consuming, operation but itis also objectionable,` because. it subjects the Workmen who do the cleaning, to the dangers of serious. illness or even asphyxiation t d'ue toback ilow of gas from the digester. There is also the further danger that an explosive mixture of gas, and air may be producedin the pump pits due to leakage of the gas from. the line to theV digester.. Again, continuity of operation rcf quires the costly provision of duplicate alternate pumping equipment, each unit of which may be placed in operation when the, other is taken down for cleaning and adjustment. r

Most of these difficulties can be overcome by the use of pneumatio. or gas displacement type, ejectors for this purpose. However, prior to the development ofthe system disclosed in my said co-pending application thev use ofrf gas displace-- ment elector equipment for this purpose hasnot been considered feasible because of. the possibility that airfrom. the ejector equipment will become mixed4 with the gas' produced in the digester to form a highly explosive. gas mixture.

As above stated, the present invention` is an improvement of thesystem of my prior` application. It providesy an` arrangement whereby a gas displacement ejector may be employed for the automatic pumping of sludge from a settling tank to a digester', or like operations., without incurring any risk of producing an` explosive mixture of air and gasV in or about the system. n

A particular 4object ofthe invention is' to provide la sludge moving system which will beautematically operative for an extendedv period of time with a minimum of maintenance andother servicing, and which will, for these and: other reasons, be exceptionally low in costfof operation and nfiaintenance.A l y Other objects and advantages. of they invention Will be understood by reference' to: the following specification and accompanying drawings,J where'- Y in is. illustrated an exemplary embodiment of the improved control methodv and apparatus:`

In vthe drawings:

Fig; l is a diagrammatic illustration ofthe system and apparatus; k f f Fig.v 2 is anenlarged detail sectionall View of ofthe Weil" |13 into a trough from which it is in e turn conducted to other clarifying treatments or to al point' of disposal.

Sludge is drawn from the bottom portion of the tank by an outlet pipe I5' which preferably extends. from near the bottom of the Settling basin to near the top thereof; yThe discharge end of the sludge outlet pipe, in conventional practice, is connected to .the-suction side of the pump which discharges the'sludge through a suitablepipeline Elinto a digester Il. Usually the pumpis located' below the level of the bottom of the settling tank'or clarifier to provide gravityflow to the inlet side of the pump. In the-digester, the sludge isv decomposed and a combustible gas (methane) is formed which is drawn oirv by a compressor i9 which delivers the gas under pressure, for example, 30 pounds per square inch, through a check valve tl and` pipeline to a suitable gas holder 2l.. From the gas4 holder 2|, the ,gasv is conducted through a pipeline 2.3 to various. appliances wherein thegas is used. The compressor AI9' in the illustrated embodiment of theinventonis motor driven and is. controlledv byv an electrical control system acting through an electrical starting unit 2|).

According to the present invention, the sludge is conducted fromthersettling tank into the receiver of a gas displacement type ejector through a pipeline 26. The sludge enters the receiver through the inlet 21 communicating with the bottom vof the receiver and it is discharged from the receiver through the outlet 29 which communicates through a pipeline 3| with the digester |1. Suitable uniflow check valves'which may be of the flap type, as indicated at 33 and 35, are provided in the receiver inlet 21 and outlet 29 to prevent reverse ow of the sludge. Also, suitable valves, such as indicated at 31 and 39 respectively, are provided in the pipelines 26 and 3| for permitting closing thereof.

The receiver 25 has a top opening normally closed by a cover 4| which is equipped with a suitable stufng box 42 through which there is slidably mounted a shaft or rod 43 which actuates the ejector control means. The lower end of the rod 43 has connected to it downwardly and upwardly facing bells 45 and 41 respectively, which are spaced about as shown in the drawing, and so arranged that the weight ofv liquid in the lower bell will always tend to move the rod downwardly into the receiver while air or gas trapped inthe downwardly facing bell when the level of the receiver contents reaches the lower edge thereof will operate to lift Vthe bell and move they rod 43 upwardly through said stuing box.

It is desirable that the rod 43 be vertically movable without excessive binding by the stuling box 42 which must be provided to prevent leakage of gas from the receiver around the rod 43. To prevent the escape of gas without necessitating excessive tightening of the packing 40 around the rod 43, the arrangement illustrated in Fig. 2 is provided. As there shown, the packing gland 38 is provided with an annular shaped groove or chamber 44 around the rod 43 near the upper end of the gland. YThe chamber 44 communicates through a port 45 with a waste gas pipe 48, which is preferably vented to the amtosphere where the liberation of gas will not create a hazard.

Above ,the chamber 44, the gland is provided with an auxiliary packing filled recess 50, which is closed by a pressure plate 52. The auxiliary packing in the recessv 58 will, of course, be sufciently tight around the rod 43 to prevent the passage of any gas from the chamber 44 upwardly around the rod. The contact area of the packing in the recess 50 is small as compared with the contact area of the packing 4U, so that the auxiliary packing in the recess 50 will not aord an objectionable grip on the rod 43 to interfere with its Vertical movement. At the same time it reduces greatly the pressure which must be applied to the main packing 49 to obtain a satisfactory seal.Y

The upper end. of the rod 43 is connected by means of a link 48 to the arm 5| of the bell crank lever, the other arm 53 of which is connected to the piston 55 of a three-way, piston valve 51. The

valve 51 has one port 8| in communication with the interior of the receiver 25, another port 63 connected by means of pipelines 66 and 65 to the gas holder 2|, and another port 61 connected by means of a pipeline 69 to the compressor intake pipeline 1|. Surges of pressure are not desirable in the digester l1 as the optimum operating pressure is approximately 8 inches of water. To prevent such surges when the receiver is vented, a check valve 19 is included in pipeline 1|, allow- 4 ing flow only in the direction indicated by the arrow shown in the drawing.

The control system comprises a plurality of pressure responsive electrical switches and an electrical motor starting device 20 operable to energize the compressor ,|9, the system is energized by a source of electrical power entering the system by a line switch 18. A pressure responsive safety switch 9| is connected in series with the source of power and is designed to effect deenergization of the compressor upon the reduction of pressure in the digester to a predetermined critical value. The normally open pressure responsive switch 99 is designed to maintain the desired pressure in the gas holder 2|. The normally open pressure responsive switch 28 serves to energize the compressor upon admission of compressed gas to pipeline 15. An alternative pressure control means is introduced by a presfrom the digester. If the rate of gas withdrawal becomes excessive, the safety control switch 9| on the digester opens the circuit until the desired pressure is again reached. In order to start the operation of the ejector system, gas shut-off valve |8| is opened; the two position three-way valve 13 is opened so. as to simultaneously admit gas under pressure from t 'e gas holder 2| to the inlet valve port 63 and through pipeline 15 to the normally open pressure switch 28, which closes the circuit thus energizing the compressor I9; and, sludge valves 31 and 39 are opened. When the sewage level in the'receiver reaches a predetermined high point the piston 55 of valve 51 will be moved from the position shown to the righthand side of the valve opening intake port 63 and thus admitting compressed gas to the receiver. The gas being under pressure will force the sludge downwardly in the receiver and out through the discharge pipe 29 and through the pipeline 3| into the digester. When the sludge level is lowered sufficiently the weight of liquid in the bell 41 will restore the valve piston to the position shown, Iwherein the intake port 63 is sealed and the vent port 61 is opened. The gas trapped under pressure in the receiver will then escape through the vent port 61 and the pipeline 69 to the inlet side of the gas compressor, whereby the gas is re-compressed and forced through pipeline and unilow valve 81. As the vented gas discharged from the receiver is at a pressure of approximately 30 pounds per square inch, a uniflow check valve 19 is introduced into line 1| between the digester and the compressor. The valve 19 prevents a surge of pressure in the digester and the resultant rupture of the safety seal 8|, thus venting the digester gas to the sur-.- rounding atmosphere. The sludge will then now into the 'receiver through inlet 21 until bell 45, as before described, effects the admission of compressed gas, thus automatically restarting the pumping cycle.

In some cases it will be desirable to reduce the pressure more rapidly in the receiver than can be accomplished by the direct action of the compressor. In such cases an expansion tank 83 may be provided to absorb a portion of the presgester, a closed gas system for collecting and holding the gas produced in said digester, said system including a gas holder and a gas compressing unit operable to withdraw gas from said digester and deliver it under pressure to said gas holderga gas displacement ejector which includes a receiver and control means responsive to the level or" material contained in said receiver to admit pressure gas to said receiver at the beginning of each ejection operation and to vent said receiver at the conclusion of each ejection operation, said receiver having inlet and outlet connections, means for conducting material to be moved by said ejector into said receiver through said inlet connection, means connecting said outlet connection to said digester, pressure respony sive means operable to effect the energization of said compressor valve means operable to conduct gas under pressure from said holder to said receiver and to said pressure responsive means thereby to eiiect the energization of said gas compressing unit and the movement of material from said receiver to said digester, control means operable to (ie-energize said compressor unit upon the reduction of pressure in the digester to a predetermined critical value, and means operable, following each operation of said ejector to return the compressed gas to said holder without substantial dilution thereof and without increasing pressure in the digester.

4. In apparatus of the class described, a digester, a closed gas system for collecting and holding the gas produced in said digester, said system including Va gas holder and a gas compressing unit operable to withdraw gas from said digester land deliver it under pressure to said gas holder, a gas displacement ejector which includes a receiver and control means reponsive to the level of material contained in said receiver to admit pressure gas to said receiver at the beginning of each ejection operation and to vent said receiver at the conclusion of each ejection operation, said receiver having inlet and outlet connections, means for conducting material to be moved by said ejector into said receiver through said inlet connection, means connecting said outlet connection to said digester, means operable to conduct gas under pressure from said holder to said receiver to eiect movement of material from said receiver to said digester, means operable to energize said gas compressing unit upon the increase of pressure in the ejector gas exhaust system to a critical value, control means operable to deenergize said compressor unit upon the reduction of Ipressure in the digester to a predetermined minimum value, and means operable, following each operation of said ejector to return 'substantially undiluted gas to said holder Without increasing pressure in the digester.

5. In apparatus of the class described, a digester, a closed gas system for collecting and holding the'` gas produced in said digester,A said system including a gas holder and a gas compressing unit operable to withdraw gas from said digester and deliver it under pressure to said gas holder, control means therefor to maintain a predetermined pressure inssaid gas holder and means to prevent reduction of pressure in the digester below a critical value, a gas displacement ejector which includes a receiver having inlet and outlet connections, means for conducting material to be moved by said ejector into said receiver through said inlet connection, means connecting said outlet connection to said digester, means operable to conduct gas under pressure 8 l from said holder to said receiver upon the occurrence of predetermined conditions to effect movement of material from said receiver to said digester, and means operable, following each operation of said ejector to deliver said substantially undiluted gas to the inlet side of said compressor, whereby said gas is delivered to said gas holder and means including a uniow valve whereby substantially equal pressures are maintained in the digester.

6. In apparatus of the class described, a digester, a closed gas system for collecting and holding the gas produced in said digester, said system including a gas holder and a gas compressing unit operable to Withdraw gas from said digester and deliver it under pressure to said gas holder, control means therefor to maintain a predetermined pressure in. said gas holder and means to prevent reduction of pressure in the digester below a critical value, a gas displacement ejector which includes a receiver and control means responsive to the level of material contained in said receiver to admit pressure gas to said receiver at-the beginning of each ejection operation and to vent said receiver at the conclusion of each ejection operation, said receiver having inlet and outlet connections, means for conducting material to ybe moved by said ejector into said receiver through said inlet connection, means connecting said outletconnection to said digester, pressure responsive means operable to keffect the energization of said compressor, valve means operable to conduct the gas under pressure from said holder to said receiver and to said pressure responsive means, thereby to effect simultaneously the energization of said gas compressing unit and the movement of material from said receiver to said digester, and means operable, following each operation of said ejector to `vent said receiver and to deliver the gas so vented to the inlet side of said compressor without substantial dilution thereof,4 whereby said gas is returned to said gas holder, and means including a uniow valve whereby surges in the system resulting from the venting of said receiver are prevented from substantially changing the pressure normally maintained within said digester.

7. In a system of the class described, a gas producing digester, a gas displacement ejector including a receiver, having sludge inlet and outlet openings, a control device responsive to the level of material contained in said receiver for admitting compressed gas to said receiver at the beginning of each ejection operation and for venting said receiver at the conclusion of each ejection operation, and material conducting means for conducting sludge to the inlet of said ejector, means for conducting said sludge from the outlet-of said ejector to said digester, and a closed gas system for V`collecting and holding the digester gas under pressure, said gas system including a gas holder, a gas compressor, an eX- pansion tank connected to the inlet side of said compressor, the outlet of said compressor being connected,lthrough a uniow valve to said gas holder', Ythe inlet side of said compressor and said lexpansion tank being connected to said digester through a uniow valve, a pressure responsive safety control device connected to said digester and operable to de-energize said compressor upon reduction of pressurein the digester to a predetermined critical value, means for conducting gas vented Afrom the outlet of sad ejector by said ejector control device to said expansion tank, vmeans for conducting compressed gas from said gas holder to said ejector control device, said -last mentioned means including a control valve operable to simultaneously admit compressed gas to said ejector control device and to a pressure switch which is operable to effect the energizationof said compressor.

8. In a system of the class described a gas producing digester, a gas displacement ejector including a receiver, having sludge inlet and outlet openings, an ejector control device responsive to the level of material contained in said receiver for admitting compressed gas to said receiver at the beginning of each ejection operation and for venting said receiver at the conclusion of each ejection operation, and material Yconducting means for conducting sludge to the inlet of said ejector, means for conducting said sludge from the outlet of said ejector to said digester, and a closed gas system for collecting and holding the digester gas under pressure, said gas system including a gas holder, a gas compressor, the outlet of said compressor being connected, through a uniflow valve to said gas holder, the inlet side of said compessor being connected to said digester through a uniow valve, a pressure responsive safety control device connected to said digester and operable to de-energize said compressor upon reduction of pressure in the digester to a predetermined critical value, means for conducting gas vented from the outlet of said ejector by said ejector control device to said gas compressor inlet, means for conducting compressed gas from said gas holder to said ejector control device, said last mentioned means including a control valve operable to simultaneously admit compressed gas to said ejector control device and to a pressure switch which is operable to eiect the energization of said compresc sor.

9. In a treating system of the class described wherein material is delivered to a digester, in

which a combustible gas is formed, and wherein such gas is compressed by a compressor and de- `-livered to a gas holder for delivery to gas using appliances, the method of moving material into the digester which consists in delivering the material to be moved to the receiver of a gas diswhich consists in delivering the sludge to be moved to the receiver of a gas displacement ejector by gravity flow from the settling tank to the receiver, admitting gas under pressure from said gas holder to said receiver to effect movement of sludge from the receiver into the digester, and iinally venting the ejector receiver by returning the gas supplied thereto to said compressor for re-compression and re-delivery to said holder while simultaneously preventing the pressure gas vented from said ejector receiver from entering said digester.

11. In a sewage treatment system wherein sludge is settled out in a settling tank and delivered to a digester in which a combustible gas is formed, and wherein such gas is Withdrawn from the digester by a compressor and compressed therein and delivered to a gas holder, the method of moving sludge from the settling tank to the digester which consists in delivering the sludge to be moved to the receiver of a gas displacement ejector having inlet and outlet openings, which openings are respectively connected to the settling tank and the digester, admitting gas under pressure from said gas holder to said receiver when sludge has filled said receiver to a predetermined level, said gas under pressure serv-v ing to effect movement of the sludge from the receiver through said outlet opening and into the digester, and nally venting the ejector receiver by returning the gas supplied thereto to said compressor while simultaneously preventing the back-now of said returned gas into said digester, said venting occurring when the level of sludge in the receiver reaches a predetermined low level, thereby to permit sludge to again flow into the receiver.

CHARLES YEOMANS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 724,051 Scholl Mar. 21, 1903 948,725 Freeman Feb. 8, 1910 1,247,540 Jones Nov. 20, 1917 2,097,454 Fischer Nov. 2, 1937 2,190,598 Fischer Feb. 13, 1940 2,280,930 Reeves Apr. 28, 1942 2,348,670v Woodward May 9, 1944 2,383,834 Yeomans Aug.v28, 1945 2,481,894 Yeomans Sept. 13. 1949 OTHER REFERENCES "Sludge Pumping-a Better Way by Charles Yeomans, published in Water Works and Sewerage, Aug. 1945, pages 258 to 260.

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