US 3427252 A
Description (OCR text may contain errors)
Feb. 11, 1969 A ETAL 3,427,252
APPARATUS FOR THE CONTROL OF FOAM FORMATION DURING THE F LIQUIDS PROCESSING 0 Filed March 51, 1966 INVENTGR.
MAL/AM J HOLCOMB A7 TOR/V5 Y Feb. 11. 1969' P.J.GAUGHAN ETAL 3,427,252 APPARATUS FOR THE CONTROL OF FUAM FORMATION DURING THE PROCESSING OF LIQUIDS Filed March 31, 1966 Sheet g of 2 INVENTOR. PH/L/P J GAUGHAN BY GFORKE E UO/PWA/FT JOHN E. (0R0 United States Patent 3,427,252 APPARATUS FOR THE CONTROL OF FOAM FORMATION DURING THE PROCESSING OF LIQUIDS Philip J. Gaughan, Philadelphia, George E. Dorwart, Southampton, and John B. Lord, Abington, Pa., assignors to Betz Laboratories, Inc, Philadelphia, Pa., a corporation of Pennsylvania Filed Mar. 31, 1966, Ser. No. 539,085 US. Cl. 252-361 Int. Cl. B01d 19/04, 19/02 9 Claims ABSTRACT OF THE DISCLOSURE In a technique commonly referred to as a wet-process, phosphoric acid is prepared from phosphate rock by means of reaction with a strong mineral acid. In practice, the phosphate rock is added to the mineral acid, e.g., sulfuric, hydrochloric, nitric acid, etc., to form metal salts and phosphoric acid with the former being ultimately removed. The economical operation of commercial methods for the conduct of phosphoric acid wet processes requires large treating receptacles and a comparatively high throughput. Conventionally, the reaction is initiated in one receptacle or vessel by means of combining the phosphate rock and acid, and the resultant reaction medium is subsequently passed through a series of receptacles in which the further reaction, concentration and refining of the phosphoric acid, as well as the full or partial separation of reaction =by-products such as the previously mentioned metal salts, is achieved. These wet-process Synthesis are accompanied by excessive foam formation which yields problems in the form of the build-up of deposits upon the treating apparatus, and hazards to operating personnel when foam occurrence is so great as to result in overflow from the treating vessels. To combat this problem, anti-foam agents are conventionally added to the wet-process. A phosphoric acid wet-process and the use of anti-foam agents in the conduct of such a process, are disclosed by US. 3,044,855 to Young.
While a number of anti-foam agents including tall oil, kerosene, complex amides, and the like are commonly employed in the treatment of phosphoric acid wet-processes, their use is accompanied by a number of impediments. Specifically, the frequency and extent of foam occurrence during the acid synthesis is subject to drastic variations as the result of fluctuations in the organic and phosphate content of the rock, the size of the rock particles which are treated, the reaction temperature, throughput rates, and the like. As a consequence of such fluctuations, foam surges occur. While the constant feed of a quantity of antifoam agent calculated to combat the average foam forming tendency may be adopted, it is grossly uneeonomical to continually feed a quantity of anti-foam agent adequate to overcome periodic surges or peaks of foam occurrence. In addition, by the time such foam surges are noted, the quantity of foam to be dispelled may have exceeded the anti-foam efficiency of the anti-foam agent employed, unless large quantities of the agent are immediately added to the reaction medium, Normally, the anti-foam requirements during such surge periods are in excess of the capacity of conventional and economical pumps. Accordingly, a foam surge may necessitate an actual bucket brigade for the introduction of adequate quantities of the anti-foam agent. Even such drastic, ineflicient and uneconomical methods may not sufiice to quell the foam occurrence before damage to apparatus and personnel is experienced, or before it becomes necessary to stop the process in order to combat the foam. Furthermore, a foam surge frequently results in the overflow of foam to downstream receptacles which are normally not treated with an anti-foam agent for reasons of economy. In such instances, there is an obvious and unavoidable lag between the time of introduction of the anti-foam to the first reaction vessel, and its travel to downstream sites of foam occurrence. Such lags may result in damage to personnel and apparatus, or the necessity for shutting down the operation.
It is an object of the present invention to provide methods for the treatment of processes involving foam producing liquids with anti-foam agents, in which the antifoam agents may be economically employed in a system capable of efficiently dealing with the foam surges which occur during the conduct of such processes.
Another object is the provision of such methods for the treatment of phosphoric acid wet-processes with anti-foam agents.
A further object is the provision of such methods which also permit the sensing of downstream foam occurrence and automatically dispense anti-foam agent to the sites of such occurrence.
Another object is the provision of methods for successively sensing varying degrees of foam occurrence and progressively increasing the feed of anti-foam agent in response, and proportion, to the degree of such sensings.
An additional object is the provision of apparatus suitable for the conduct of the methods of the foregoing objects. These and other objects of the invention will be made apparent from an examination of the subsequent specification and claims in conjunction with the attached drawings in which:
FIGURE 1 is a diagrammatic cross-sectional side view of a phosphoric acid wet process employing the inventive methods and apparatus; and
FIGURE 2 is a cross sectional view through plane 2-2 of FIGURE 1.
It should be noted that the exposition of the present invention without the specification deals primarily with the use of the invention in conjunction with phosphoric acid wet processes. This results from the fact that these processes are highly illustrative and representative of processes involving liquids which produce pronounced problems in respect to the formation of foam. However, the inventive methods and apparatus are equally applicable to other processes involving a body or bodies of a liquid which is productive to foam. One of the primary characteristics of the inventive methods and apparatus is their flexibility and adaptability in respect to adoption for use with processes of divergent natures, foam forming characteristics and physical arrangements. This characteristic permits one skilled in the art relating to any process involving the formation of foam to readily utilize the invention in combatting that formation. Typical of other processes which are susceptible to, and benefitted by, the practice of the invention, are the processing of aluminum ore, the wet end of paper and pulp slurries, clay slurries, and the like.
The foregoing objects may be best described in relation to the treatment of a given process and are achieved in that context by means of the feed and an anti-foam agent to the phosphoric acid wet process in response to increases in the quantity of foam which occurs in or upon the surface of the reaction medium and intermediates formed during the process, with the attainment of an increase in the quantity and rate of anti-foam fed to the process in proportion to the foam occurrence and increases which are sensed. More precisely, the anti-foam agent is dispersed by a pump operating at a rate calculated to dispense a quantity of anti-foam agent adequate to combat the amount of foam which might be yielded by the treated system at times of peak foam occurrence. During normal or non-surge operation of the phosphoric acid process, all or a portion of the anti-foam agent is returned by means of a by-pass, to the original source of supply of the antifoam agent. Positioned in a graduatedly increased spaced relationship to the surface level of the phosphoric acid reaction medium are a plurality of foam contacts which are connected to, and capable of actuating, valves positioned in feed lines leading from the forementioned pump to the reaction medium. As a consequence, when foam occurs upon the surface of the reaction medium, it contacts the lowest of the foam contacts and opens a valve located in a feeder for the anti-foam agent, to introduce the anti-foam agent to the reaction medium at a predetermined rate. If and as the foam continues to rise it successively contacts additional foam contacts located at progressively increased distances from the normal surface level of the reaction medium to open other valves in additional feeders, and thereby further increase the flow of anti-foam agent to the reaction medium. It should be noted that the term reaction medium as employed throughout the present specification and claims is used to connote the liquid reaction medium, reaction intermediates, and the reaction product and by-products which are experienced in a given process, e.g., in the case described, a wet-process for the synthesis of phosphoric acid. Specifically, foam may occur in, or overflow to, the series of receptacles utilized in such processes, and the liquid upon the surface of which the foam occurs, may in some cases be more properly referred to as a medium for concentration, refining, separation, etc. However, for reasons of simplicity, the term reaction medium is herein employed to refer to all of those liquids which are realized during the synthesis of phosphoric acid by a wet process, upon the surface of which foam may occur.
In a preferred embodiment of the invention, a pump is employed to pump a quantity of anti-foam agent calculated to be at least adequate to effectively combat the maximum quantity of foam which might be expected to occur within the system to be treated under conditions most favorable to, foam formation. The pump output is divided into two flow systems, one of which comprises a return circuit to the original source of anti-foam supply, with the second circuit comprising a distribution system leading to the area of the phosphoric acid wet process reaction medium. The distribution system preferably includes a distributing header connected to a primary feeder provided with a flow control valve opened to a degree adequate to permit the passage of a quantity of anti-foam agent adequate to combat the foam occurrence of the system under normal conditions. The return circuit is provided with a restriction such as an adjustable, springloaded, relief valve which is opened by virtue of the fact that the quantity of anti-foam being pumped by the pump is in excess of the flow rate which is permitted by the valve opening of the valve in the primary feeder and any auxiliary feeders which may be open. As a consequence, the pressure generated by the pumping of a quantity of anti-foam agent in excess of the flow capacity of the valve in the primary feeder, displaces the spring-loaded relief valve to accomplish the return of the excess anti-foam agent to the anti-foam agent supply source. When foam occurs upon the surface of the reaction medium as the result of abnormal foam occurrence conditions, and despite the constant feed of a quantity of anti-foam agent,
the rising foam contacts a sensing element or foam contact which is preferably an electrode or spaced electrodes which completes a circuit designed to open a valve in an auxiliary feeder, and thereby increases the flow of antifoam agent to the reaction medium. This increased flow of anti-foam agent is subtracted from the quantity of anti-foam agent which would otherwise pass through the return circuit since the opening of the valve in the auxiliary feeder reduces the in-system back pressure against the spring loaded relief valve in the return line and thereby reduces flow through the relief valve. Preferably, a number of such auxiliary feeders are employed, with foam contacts or sensing elements located at gradually increased distances from the surface of the reaction medium. Accordingly, the quantity of anti-foam agent is gradually increased in response to the rise of foam upon the surface of the reaction medium. Such a system provides a more positive control over the addition of anti-foam agent to the reaction medium in direct response to the degree of foam occurrence.
In another embodiment of the invention, which is primarily useful in those processes in which foaming is normally a problem only during surges or peaks of foam occurrence, the anti-foam agent need not be fed continuously. In such an embodiment, all of the anti-foam feeders are provided with valves actuated by the contact of foam with the foam contact. Accordingly, anti-foam agent is not fed to the reaction medium until such time as the foam on its surface rises to a predetermined level. Antifoam agent is then fed to the reaction medium and may be increased by means of auxiliary feeders which are actuated in the event of the continued rise of the foam level.
Another embodiment of the invention is concerned with the supplying of anti-foam agent to receptacles located downstream of the zone of primary treatment. In such a. system, a single pump and supply source for the anti-foam agent may be employed with the previously described systems of distribution to the zone of primary treatment. However, additional sensing-actuating elements and addiditional primary and/or auxiliary feeders are provided at potential areas of foam formation located downstream from the zone of primary treatment. As a consequence, foam which overflows from the zone of primary treatment, or which is actually formed at the downstream locations, can be immediately sensed and appropriately treated with the anti-foam agent.
The first described method may be comprehended from a consideration of FIGURE 1 which diagrammatically depicts the utilization of this method in the treatment of a representative wet-process for the synthesis of phosphoric acid. As may be observed, anti-foam agent 10 is withdrawn from a supply source 11 by means of a pump 12, and is pumped into a main feed line 13. The main feed line 13 is connected to a relief line 14 and a distributing header 15. The relief line 14 is connected to an adjustable, spring-loaded relief valve 16 which is in turn connected to the supply source 11 by means of a return line 17. The distributing header 1-5 is provided with a primary feeder 18, and a plurality of auxiliary feeders 19, 20, 21 and 22. The primary feeder 18 is provided with an adjustable flow control valve 23 and the auxiliary feeders 19, 20, 21 and 22 are provided with solenoid Valves 24 which are actuated by foam contacts 25 which are shown, and preferably employed, in the form of electrodes.
The phosphoric acid wet-process depicted by FIGURE 1 is merely representative of a variety of such processes in which the size and nature of the reaction vessel, their physical relationship to one another, and the like, may be highly varied without diminishing or obviating the suitability and general applicability of the inventive methods and apparatus. In the process illustrated in FIGURE 1, a mineral acid is withdrawn from storage and continuously added to the primary reactor 26 through a conduit 27. At the same time, phosphate rock is continuously added to the primary reactor 26 from an overhead hopper 28. The combined acid and phosphate rock provide the reaction medium 29 which is treated by the inventive methods and apparatus. Due to the continuous addition of the acid and rock, the volume of the reaction medium 29 in the primary reactor 26 is constantly increased to result in a continued overflow through overflow outlet 30, to the downstream reactors 31 and 32. Some or all of the reactors may contain agitators and heating elements to increase throughput, reduce settling out, and accelerate the reaction of the acid and rock. In addition, the system may include recirculation of the reaction medium 29 from the downstream reactors 31 and 32 to the primary reactor 26.
It should be noted that the foam contacts 25 of auxiliary feeders 19, 20, '21 and 22, respectively, are located at gradually increased distances from the surface 33 of the reaction medium 29.
In a preferred practice of the invention, the pump 12 is operated at a capacity at least adequate to provide the quantity of anti-foam agent required to combat the maximum foam forming potential of the system treated, which includes the primary reactor 26 and all downstream reactors such as 31 and 32, which may experience foam formation. The determination of the quantity of antifoam agent 10 required for the effective control of foam under both normal and abnormal conditions may be based upon the experience of the operating personnel for the system treated. The valve 23 in the primary feeder 18 is opened to the extent necessary to permit the flow of a quantity of anti-foam agent 10 which is adequate to combat the foam formed during conditions normally experienced in the operation of the wet process, but less than the quantity of anti-foam agent 10 which is being circulated by the pump 12. Accordingly, a predetermined quantity of the anti-foam agent 10 is continuously fed to the reaction medium 29 through the primary feeder 18. Since the quantity of anti-foam agent .10 being introduced into the main feed line 13 is greater than that quantity which can be passed through the valve 23, the remainder of the antifoam agent 10 is returned to the storage container 11 through the relief line 1 4, the relief valve 16 and the return line 17.
However, when foam occurring on the surface 33 of the reaction medium 29 rises to a height whereby the lowest foam contact 25, i.e., that associated with auxiliary feeder 19 in FIGURE 1, is contacted, the solenoid valve 24 in auxiliary feeder 19 is opened to permit the passage of an additional quantity of the anti-foam agent 10 to the reaction medium 29. Similarly, if and when the foam occurring on the surface 33 of the reaction medium 29 rises to heights adequate to permit the contact of the foam with the foam contacts 25 of auxiliary feeders 20, 21 and 22, the solenoid valves 24 of these feeders are also opened to permit the addition of further quantities of the anti-foam agent 10 to the reaction medium 29. As previously stated, the pump 12 is operated at a capacity adequate to circulate at least that quantity of the antifoam agent which is required to overcome the quantity of foam formed during the maximum conditions of foam formation which can be experienced by the system treated. Similarly, the total flow capacity of the primary feeder 18, and the auxiliary feeders 19, 20, 21 and 22, is adequate to permit the introduction of that quantity of antifoam agent 10 which is required to combat the maximum foaming tendencies of the reaction medium 29.
It is readily apparent that the inventive methods and apparatus provide extensive flexibility in respect to the anti-foam treatment of phosphoric acid wet-processes having widely divergent foaming characteristics. For example, changes in the capacity of the pump 12, and the number and flow capacity of the primary feeder 18 and auxiliary feeders 19, 20, 21 and 22 and the distances between the foam contacts 25 and the surface 33, permit the quick adjustment of the system to meet variations within a given wet-process, or to permit the use of the system with only minor changes and adjustments, with a number of wet processes possessing highly divergent foaming characteristics, or different physical arrangements or relationships.
Similarly, the inventive methods and apparatus may be readily adjusted to meet day to day changes in the foaming characteristics of a given wet-process. For example, relatively minor changes in foaming characteristics may be compensated for by simple adjustments of the flow control valve 23 of primary feeder 18, while continuing to maintain the protection against sudden foam surges which is provided by auxiliary feeders 19-22.
In a preferred practice, the continuous feed of the antifoam agent 10 from the primary feeder 18, which is adequate to combat normal foaming conditions, involves only a fraction of the combined flow capacities of the primary and auxiliary feeders. The next actuated auxiliary feeders, e.g., auxiliary feeders 19-21, add further quantities of the anti-foam agent calculated to combat foam surges which exceed the norm by relatively minor amounts, and the last auxiliary feeder, i.e., auxiliary feeder 22, is adjusted to provide a large quantity of the anti-foam agent in the event of sudden foam surges. It must be realized that the spacing of the foam contacts 25, and the adjustment of the flow capacities of the primary and auxiliary feeders must be calculated to provide the desired anti-foam effect in respect to the foaming characteristics of the particular system to be treated. In reaching such determinations, it must also be realized that the time-quantity relationship between the quantity of foam and antifoam agent, and the time required for that quantity of anti-foam agent to dispel the extant quantity of foam, are to be considered. Accordingly, the flow capacity of a given auxiliary feeder must be such as to rapidly dispel the quantity of foam extant when the foam is present in a quantity adequate to achieve contact with the sensing-actuating element for that particular auxiliary feeder, when added to the quantity of anti-foam agent 10 which is currently being supplied by any of the other primary or auxiliary feeders.
To demonstrate the practice of the present invention, the treatment of a specific phosphoric acid wet-process is hereafter described. It was first determined that the foaming tendencies normally exhibited by the system to be treated could be eifectively combatted by means of a continuous feed of a specific liquid anti-foam agent at the rate of 40 cubic centimeters per minute. It was also found that the system experienced relatively frequent, but minor, foam surges which necessitated increasing the anti-foam agent addition rate by between 20-60 cc./minute. Less frequently, the system had experienced sudden and massive foam surges which required the addition of as much as 300 cc./minute of the anti-foam agent. It was further found that during normal operating conditions the foam which was formed upon the surface of the reaction medium did not exceed a height, i.e., vertical height from the surface of the reaction medium, of 2 inches. During the frequent but minor foam surges the foam normally rose to a height of no more than 4 inches. The described system was treated by a method and apparatus such as those shown by FIGURE 1. The flow capacity of flow control valve 23 in primary feeder 18 was adjusted to permit the passage of 40 cc./minute of the anti-foam agent 10. The flow capacity of auxiliary feeders 19-21 were each adjusted to permit the passage of 20 cc./minute of the anti-foam agent 10 through each of these auxiliary feeders, While auxiliary feeder 22 was similarly adjusted to permit the passage of 200 cc./minute of the anti-foam agent. The flow adjustment of the auxiliary feeders 19-22 was accomplished by means of flow control valves which are not shown in FIGURE 1 but which are shown in FIGURE 2 and subsequently discussed in respect to that figure. However, it should be noted that the adjustment of the flow capacity of the auxiliary feeders may also be achieved. by means of the 7 selection of the valve sizes of the solenoid valves 24, or by employing more expensive solenoid valves having an adjustable flow capacity. After adjusting the flow capacities of the primary and auxiliary feeders, the sensingactuatiug elements 25 of auxiliary feeders 19, 20, 21 and 22 were positioned above the surface 33 of the reaction medium 29 at heights of 2.5, 4.5, 6.5 and 8 inches, respectively. These distances represent the point of closest proximity of that portion of the sensing-actuating elements which are actuated by contact with the foam, to the surface 33 of the reaction medium 29. These heights were selected on the basis that during normal operations as much as 2 inches of foam could be expected to occur 1 upon the surface 33 without indicating the occurrence of a foam surge. However, the occurrence of 2.5 inches or more of foam indicated the onset of a foam surge and initiated the first increase in the feed of anti-foam agent 10 by means of auxiliary feeder 19. Similarly, the antifoam feed rate was increased at foam levels of 4.5 and 6.5 inches through auxiliary feeders 20 and 21. The rate of anti-foam agent 10 provided by the simultaneous operation of primary feeder 18 and auxiliary feeders 19-21, i.e., 100 cc./minute, was found adequate to dispel minor or moderate foam surges, e.g., involving foam levels of 2.5 to 6.5 inches. However, the achievement of a foam level of 8 inches normally indicated the occurrence of a massive foam surge and auxiliary feeder 22 was activated to increase the rate of anti-foam addition by 200 cc./min ute. In the operation of the above system, it was found that foam could normally be controlled during the operation of the process by means of the anti-foam agent 10 fed by primary feeder 18 at the rate of 40 cc./minute. However, several times during each day, one or more of the auxiliary feeders 19-21 were activated by minor to moderate foam surges which necessitated increasing the feed rate to 60100 cc./minute. At less frequent intervals, auxiliary feeder 22 was also activated to increase the feed rate to 300 cc./minute. It should be noted that in the latter event, the rate of anti-foam addition was 7.5 times as great as during normal operating conditions and 25 as great as the rate employed in respect to minor to moderate foam surges. It was found that the greatly increased treatment supplied by auxiliary feeder 22 was highly desirable in the achievement of the rapid dispelling of massive foam surges.
In the conduct of the above treatment, the pump 12 employed possessed a maximum capacity of 350 cc./minute but was adjusted to a capacity of 320 cc./minute. Consequently, even when the primary feeder '18 and all of the auxiliary feeders 19-22 were operating to reach the maximum flow capacity of the system, i.e., 300 cc./minute, 20 cc./minute were being recycled to the supply source 11 via relief line 14, relief valve 16 and return line 17. At other times during the operation of the system, between 220-280 cc./minute of the anti-foam agent 10 were being recycled to the supply source 1 1. As may be observed, the relief valve 16 had been adjusted to permit the unseating of the valve when the capacity of the pump exceeded the flow capacity of the primary and/or auxiliary feeders by as little as 20 cc./minute.
As an indication of the effectiveness of the present methods and the simplicity and compactness of the present apparatus, the foregoing treatment was achieved by means of portable apparatus which included the pump and distribution system mounted in a chest measuring approximately 17 x 20 x 22 inches and having a total weight of less than 175 pounds. The foregoing apparatus also included an event recorder which registered the periodic but sporadic increases in the quantity of anti-foam agent which was fed, and permitted a determination of optimal continuous and surge feeding of the anti-foam agent. Upon installation, the only requirements were the plugging in of the electric motor which operated the pump, the connection of the pump and the return line to the supply source, the connection of feed line extensions to the primary and auxiliary feeders, and the positioning of the electrodes in relation to the surface of the liquid which was treated.
Another embodiment of the invention, in which the anti-foam agent 10 is fed to the reaction medium 29 only upon the occurrence of a predetermined quantity of foam, may also be derived from an examination of FIGURE 1. In such an embodiment, the flow control valve 23 of primary feeder 18 is completely closed, or the primary feeder 18 is entirely removed from the system. During normal operating conditions, none of the anti-foam agent 10 is fed to the reaction medium 29, but is instead recycled to the supply source 11 via the relief line 14, relief valve 16 and return line 17. However, whenever foam occurring upon the sunface 33 of the reaetion medium 29 rises to a height adequate to bring about contact with the foam contact '25 of auxiliary feeder 19, the feed of the anti-foam agent 10 is initiated, and further implemented by means of auxiliary feeders 20'-22 in the event of continued foam rise. Obviously, in such a system the foam contact 25 located in closest proximity to the surface 33 of the reaction medium 29, must be positioned above the level at which foam can be tolerated without requiring the addition of the anti-foam agent 10.
Still another embodiment of the invention, involving the treatment of foam occurrences at sites downstream from the zone of primary treatment, may also be derived from further reference to FIGURE 1. In such a system, the primary treatment of the primary reactor 26 by means of primary feeder 18 and auxiliary feeders 19-22, is implemented by additional auxiliary feeders 34, 35 and 36, which are employed in conjunction with the downstream reactors 31 and 32. It should be noted that the downstream reactors which are treated may be located adjacent to the primary reactor 26, as in the case of downstream reactor 31, or remotely therefrom, as in the case of downstream reactor 32. In addition, the downstream sites which are treated may include digestors, concentrators, separators, refiners, coolers, etc., which are plagued by foam occurrence, as well as conduits and transport means such as overflow outlet 30. As may be noted, the downstream auxiliary feeders 34, 35 and 36 are also provided with solenoid valves '24 and foam contacts 25. It must also be realized that a primary feeder such as that employed in conjunction with primary reactor 26 may also be utilized in the event that foam occurrences at downstream sites are so excessive as to warrant the continuous addition of an anti-foam agent. Similarly, individual pumps may be utilized at sites of downstream treatment, or the entire system employed at the zone of primary treatment. Obviously, each feeder employed may be provided with a pump, but a single pump serving a plurality of feeders is preferred for simplicity, economy and ease of maintenance. In most applications the systems depicted by FIGURE 1 in conjunction with downstream reactors 31 and 32, will suflice. In such systems, one or more downstream auxiliary feeders 34, 35 or 36 are positioned over the downstream site of foam occurrence and are actuated when the foam level rises to a height adequate to achieve contact with the foam contacts 25. It should be noted that downstream foam occurrences may result either from in situ reactions at the downstream sites, or from foam carryover through conduits such as over-flow outlet 30. In either event, the system shown in respect to downstream reactors 31 and 32 permits the immediate treatment of the foam occurrence, without the necessity for waiting for anti-foam agent added at the zone of primary treatment to travel downstream.
In the practice of the invention, the pump employed is preferably a constant delivery pump such as a gear pump, since a continuous flow and a constant in-system pressure are preferred. Such flow and pressure are less abusive to the relief valve 15 which experiences greater abuse and wear when a pulsing or cyclic pump such as a piston or diaphragm pump is used. However, cyclic pumps may be used when a wear resistant relief *valve is employed, or frequent replacement or maintenance of the relief valve is acceptable. As previously mentioned, the capacity of the pump is selected to provide a flow of the anti-foam agent which is at least adequate to combat the foaming characteristics of the system to be treated. A pump with an adjustable capacity, e.:g., by means of current input or stroke adjustment, is preferred so that the pump capacity may be increased in the event that the foaming characteristics of the system treated are increased, e.g., due to the processing of phosphate rock with a high organic content. Naturally, the quantities of anti-foam agent which are added may be increased by enlarging the openings of the valves 23 and 24 in the primary feeder 18 and auxiliary feeders 19-22, but the pump 12 employed must have a capacity adequate to provide a capacity which is at least equal to, and preferably slightly in excess of, the flow capacity of all of the feeders which are employed, or which may be employed in future. For example, an increase in the foaming characteristics of the treated system may necessitate the addition of additional auxiliary feeders at primary or downstream sites. However, it must also be noted that a ravity feed from an overhead supply source may be employed if reduced efiiciency and the necessity for maintaining a relatively constant head can be tolerated.
As previously noted, the relief valve 16 is spring loaded and adjustable in respect to its ability to be unseated in response to pressures encountered within the system. More precisely, the relief valve 16 should be capable of being adjusted in relation to the smallest back pressure which is inherent in the particular system. It must also be realized that the relief valve functions primarily as a restriction which maintains the desired pressure Within the distribution system consisting of the distributing header 15, primary feeder 18 and the auxiliary feeders 19-22. Consequently other means of flow restriction can be employed in place of the relief valve. For example, a bore reducer or restrictor may be placed in the relief line 14. In such case, the aperture of the bore reducer mus-t be adequate to permit the passage of the total quantity of anti-foam agen transferred by the pump, in the event that the valves of all of the feeders are closed. At the same time, the back pressure or resistance of flow which is provided by the bore reducer must be adequate to maintain the desired constant delivery pressure within the distributing header and feeders when the valves of the feeders are open. Consequently, spring loaded diaphragm valves or vaned flow reducers are preferred if a relief valve is not employed. It should also be noted that the pressure realized within the distribution system may be adjusted or maintained to some extent by means of increasing the hydrostatic head by elevating the return line above the height of the distribution system. When such a measure is adopted the head created, in combination with any flow restriction imposed upon the relief or return lines operates to control and maintain the pressure realized within the distribution system.
While a V valve is preferred in the primary feeder 18, it should be noted that the valve 23 may comprise any adjustable flow control or throttling type valve, e.g., needle, gate, globe, angle and diphragm valves.
As previously mentioned, the valves 24 employed in the auxiliary feeders 19-22 and 34-36 are preferably solenoid valves, and the foam contacts 25 employed in conjunction Wth the auxiliary feeders are preferably electrodes which complete a circuit including the foam, a source of electrical current, a relay, and the solenoid coil of the solenoid valves 24. A preferred arrangement is depicted by FIGURE 2, which is a cross-sectional view taken through plane 2-2 of FIGURE 1, and includes the primary reactor 26, reaction medium 29, auxiliar feeder 22, solenoid valve 24, and distributing header 15. For the purpose of illustrating a preferred form of flow control in the auxiliary feeders, a flow control valve which is not detailed in FIGURE 1 has also been added. Referring to 10 FIGURE 2, one may observe that the foam contact 25 of FIGURE 1 is an electrode 43 attached to a terminal 44 of a circuit 45 containing a relay 46 and an electric motor 47. A second terminal 48 in the circuit 45 is attached to ground 49.
Also positioned above the surface 33 of the reaction medium 29 is the auxiliary feeder 22 containing a solenoid valve 24. When foam occurs upon the surface 33 and rises to contact the electrode 43, the circuit 45 is completed and the relay 46 is tripped. When the circuit 45 is completed, current supplied by the motor 47 energizes the solenoid coil 52 to draw the magnetic core plunger 53 within the solenoid coil 52, and in contact with the stationary core 54. As a consequence, the stem 55 is retracted to unseat the disc 56 from the aperture 57 and thereby permit the passage of the anti-foam agent in the direction indicated by the arrows. The anti-foam agent 10 then flows from distributing header 15 through the auxiliary feeder 22, to be added to the reaction medium 29. It should be noted that the exit end of the auxiliary feeder 22 may be positioned beneath the surface 33 of the reaction medium 29 or above an area of high agitation for more rapid dispersion of the anti-foam agent 10 within the reaction medium 29.
For ease of control, the auxiliary feeder 22 shown in FIGURE 2 is also provided with a flow control valve 61. Accordingly, the solenoid valve 51 need not be controlled in respect to flow capacity but is instead fully opened when the solenoid coil 52 is energized. Flow control is then achieved by means of the adjustment of the flow control valve 61. The flow valve 61 is preferably a V valve but any adjustable valve such as a needle valve, a gate valve, globe valve, angle valve, diaphragm valve, etc., may be used. The flow control valve 61 may be located either upstream, as shown, or downstream from the solenoid valve 24. As previously mentioned, the flow control valve 61 maybe obviated if the solenoid valve 51 is selected to provide the desired flow rate, or if an adjustable solenoid valve, e.g., through the positioning of stationary core 54, is employed.
It may also be noted that the solenoid valve 24 is normally maintained in a closed position with the disc 56 tightly seated in aperture 57 as a result of the urging provided by the spring 58 which engages the fixed spring retainer 59. The current provided by the motor 47 is adequate to energize the solenoid coil 52 to the extent required to overcome the force of the spring 58 and thereby withdraw the magnetic core plunger 53 wthin the axis of the solenoid coil 52.
It should be noted that while the electrode 43 of FIG- URE 2 is preferred as the foam contact, other elements may be employed. For example, two spaced electrodes may be substituted for the electrode 43 and ground 49 without modification of the circuit 45. In such case, the circuit 45 is completed upon the bridging of the two spaced electrodes by foam borne upon the surface 33 of the reaction medium 29 and the latter does not become a part of the circuit. However, in the use of two spaced electrodes care should be taken to provide adequate spacing. If the two electrodes are too closely spaced, foam trapped between them will be retained and will continue to bridge the electrodes and complete the circuit long after the anti-foam agent has succeeded in dispelling the foam occurrence and the foam on the surface 33 has receded. In the use of spaced electrodes, it is advisable to provide a foam and splatter shield about the electrodes since bridging may also result from the splashing of foam upon the spaced electrodes. Such a shield may simply comprise a cylinder coextensive with the spaced electrodes, which are then positioned in the longitudinal axis of the cylinder.
In the use of the above circuit it is desirable to reduce the voltage within the circuit formed by the sensing element and valve both for the protection of personnel, and to avoid polarization of the electrode or electrodes. T-his may be readily accomplished by means of the insertion of a transformer within the illustrated circuit.
It is apparent that the present invention provides methods and apparatus which permit a greatly improved control of foam occurrence in wet-processes for the synthesis of phosphoric acid. Such methods and apparatus are further characterized by an unusual degree of control and flexibility in enabling the combatting of sporadic foam surges, permitting the use of a quality of anti-foam agent which is constantly matched to the foam forming tendency of the system being treated, providing methods which may be readily adjusted to conform to changes in processing characteristics, and permitting the treatment of a plurality of sites within the wet-process by means of a single, automated system.
It is further obvious that various alterations, substitutions and modifications may be made in the inventive methods and apparatus without departing from the spirit of the invention which is defined lby the following claims.
1. A system for treating a process liquid to suppress foam formation by the addition of an anti-foam agent from a supply source, comprising means for transferring said anti-foam agent at a rate adequate to counteract the maximum foam forming potential of said liquid from said supply source to a distribution system comprising a plurality of feeders through which said anti-foam agent is dispensed to said liquid, said feeders having a flow capacity substantially equal to said rate, a plurality of valves controlling the flow of said anti-foam agent through said feeders, a plurality of sensing means located at graduatedly increased distances from the surface of said liquid and responsive to the level of said foam upon said surface to open said valves, a return line connecting said distribution system and said supply source, and a restriction of said return line to maintain a constant predetermined pressure within said distribution system.
2. A system as claimed by claim 1 in which said distribution system also contains means for continuously diverting a portion of said anti-foam agent to said liquid.
3. A system as claimed by claim 1 in which said feeders are located at different distant zones of said liquid.
4. A system as claimed by claim 1 in which said means for transferring is a gear pump.
5. A system as claimed by claim 1 in which said valve is a solenoid valve and said valve, said liquid (and said sensing means form an electrical circuit whch is completed by the contact of said sensing means with said foam.
6. A system as claimed by claim 5 in which said sensing means is an electrode.
7. A system as claimed by claim 1 in which said valve is a solenoid valve, said sensing means is a pair of spaced electrodes, and said valve and said sensing means form an electrical circuit which is completed by the bridging of said spaced electrodes by said foam.
8. A system as claimed by claim 1 in which said feeders also contain flow control valves in addition to said valves.
9. A system as claimed by claim 1 in which said restriction is a relief valve.
References Cited UNITED STATES PATENTS 1,916,614 7/1933 Harrison 252-321 1,984,789 12/1934 Everett 252-321 2,883,344 4/1959 McKinney 252-321 3,306,341 2/1967 Pugh et a1. 159-13 RICHARD D. LOVERING, Primary Examiner.
US. Cl. X.R.