US3743598A

US3743598A - Apparatus and process for mixing chemicals

Info

Publication number: US3743598A
Application number: US00177367A
Authority: US
Inventors: J Field
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-09-02
Filing date: 1971-09-02
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03

Abstract

AN APPARATUS FOR MIXING CHEMICALS COMPRISING A TANK HAVING FIRST AND SECOND INLETS CONNECTIBLE TO SOURCES OF FIRST AND SECOND CHEMICALS, RESPECTIVELY, AND AN OUTLET. THE CHEMICALS ARE CHANNELED WITHIN THE TANK SO THAT THEY COME INTO INTIMATE CONTACT, AND THE PATH FROM THE INLETS TO THE OUTLET IS ELONGATED THROUGH THE USE OF BAFFLES. MIXING OF THE TWO CHEMICALS IS ACCOMPLISHED WITHOUT MOTOR DRIVEN MEANS BY USING THE TWO CHEMICALS TO CREATE TURBULENCE WITHIN THE TANK. A SENSOR ADJACENT THE OUTLET MEASURES A CHARACTERISTIC OF THE MIXTURE OF CHEMICALS AND CONTROLS THE SUPPLY OF AT LEAST ONE OF THE CHEMICALS IN ACCORDANCE WITH THE VALUE OF THE MEASURED CHARACTERISTIC TO THEREBY CONTROL SUCH CHARACTERISTIC OF THE MIXTURE.

Description

July 3, 1973 J. P. FIELD 3,743,593

' I APPARATUS AND PROCESS FOR MIXING CHEMICALS Filed Sept. 2, 1971 2 Sheets-Sheet 1 v 1/ If?! 7 lNllfA/TOR: J Paul Field 53: M4, 621251 #Paod' A TTOQA/EYS United States Patent O 3,743,598 APPARATUS AND PROCESS FOR MIXING CHEMICALS J. Paul Field, 2508 Holly Lane, Newport Beach, Calif. 92660 Filed Sept. 2, 1971, Ser. No. 177,367 Int. C1. C02?) 1/34 US. Cl. 210-49 15 Claims ABSTRACT OF THE DISCLOSURE An apparatus for mixing chemicals comprising a tank having first and second inlets connectible to sources of first and second chemicals, respectively, and an outlet. The chemicals are channeled within the tank so that they come into intimate contact, and the path from the inlets to the outlet is elongated through the use of baffies. Mixing of the two chemicals is accomplished without motor driven means by using the two chemicals to create turbulence within the tank. A sensor adjacent the outlet measures a characteristic of the mixture of chemicals and controls the supply of at least one of the chemicals in accordance with the value of the measured characteristic to thereby control such characteristic of the mixture.

BACKGROUND OF THE INVENTION Many industries in the normal course of carrying out their business produce an acid waste. One such industry is the newspaper publishing industry. Ecology laws require that acid waste be neutralized before it can be disposed of.

Present systems for neutralizing acid employ large holding tanks. The acid waste and a suitable base are introduced into the tank, and the solution is held in the tank for a long period of time until the mixture reaches a pH of about 7 at which time the mixture can be disposed of. These holding tanks are expensive and require substantial time to accomplish the neutralizing function.

SUMMARY OF THE INVENTION The present invention employs a mixing apparatus and method which significantly reduces the time required for neutralization. With the present invention the acid waste is not held in a holding tank, but rather is continuously fed through a tank at a rate commensurate with a reasonable drain rate of the acid waste from the chamber in which it is held. Although the mixing apparatus is particularly adapted for acid waste neutralization, it can be readily used for other controlled mixing functions including acid injection.

A mixing apparatus constructed in accordance with the teachings of this invention includes a tank having an acid waste inlet, a base inlet and an outlet. Acid waste is typically in the form of a liquid although it may have undissolved solids, and it may be heavy or sludge-like. The acid waste enters the tank and fills the tank to a predetermined level.

To obtain some turbulence and mixing of the acid waste and base, the base is preferably introduced into .the tank below liquid level. The base can advantageously take the form of a gas such as ammonia (NH which is soluble in the acid waste and which bubbles up through the acid waste.

A feature of this invention is that the injection of the base into the tank is not modulated, but is controlled solely by an on/olf valve in response to the pH of the mixture adjacent the outlet. One advantage of this system is that digital operation simplifies valve and controller construction, and this produces a corresponding cost savings.

A second advantage of this construction is that it proacid and the base. With the gas under pressure and with on/off control, the gas is spurted or forced at relatively high velocity into the liquid each time the valve opens. These bursts of gas, at least at the outset, produce turbulence and intimate mixing of the gas and the liquid within the tank. Burst duration will depend on different factors including acid and base concentration. Providing bursts of base is not essential as in some instances base may be supplied continuously.

For optimum mixing, an injector is provided within the tank. The injector has a plurality of apertures through which the bursts of gas can pass. The use of multiple apertures distributed along a preselected region provides multiple inlet orifices for the gas with a consequent improvement in mixing. The apertured member can advantageously take the form of an elongated tube having apertures in the wall thereof.

To further provide for intimate contact between the acid and the base, the acid Waste is channeled across the injector. This can be accomplished by a bafiie and/or a plate which define a relatively confined passage through which the acid waste must flow. By restricting or confining the passage, intimate contact between the acid waste and the base is assured. The portion of the tank upstream from the baflle may be considered as an inlet zone and the apertured tube preferably extends for substantially the full length of the inlet zone.

To elongate the flow path between the inlet and outlet of the tank, a plurality of bafiies can be provided to thereby provide a tortuous flow path. In addition to elongating the flow path, the baffles create turbulence in the liquid as the liquid passes around each of the bafiles.

Another turbulence creating concept employed by this invention is a plurality of small apertures through one or more of the baflies. This creates a second flow path (the first flow path being around the bafiie) so that when the liquid travelling along the two flow paths meet, additional turbulence is created.

Preferably the baflle which assists in defining the restricted passage is not perforated thereby forcing or channeling all of the acid waste over the injector. The region of the tank which contains the baffles may be considered as an intermediate or a mixing zone of the tank.

Acids and bases are inherently difiicult to mix. One feature of this invention is that acid waste and a base are thoroughly mixed without employing power driven devices or movable mechanisms. In addition the present invention is adapted for gravity feed through the tank.

The zone of the tank adjacent the outlet is the outlet zone. The outlet zone contains a pH sensor which senses the pH of the mixture adjacent the outlet. The sensor transmits a signal to a pH controller which in turn operates an on/ off valve such as a solenoid valve which controls the flow of the base to the tank. Because on/olf control of the base is utilized, the pH of the mixture at the outlet will fluctuate between allowable tolerances. However, the average pH over any time span of reasonable length will be substantially neutral. This is acceptable in that short periods of some pH other than substantially neutral can be tolerated by disposal systems so long as the long period average is approximately neutral.

With the pH sensor located adjacent the outlet of the tank, it obviously cannot call for addition of base to the tank until the pH of the mixture at the sensor changes accordingly. This means that at start up there is a period of time during which acid is being fed into the tank and no base is being added. This produces a brief, but acceptable, period during which acidity of the mixture leaving the tank may be relatively high.

While this is not objectionable for many applications,

it may be desirable at least in some applications to eliminate the brief period of relatively high acidity. One way to accomplish this would be to provide a second pH sensor adjacent the inlet of the tank. However, pH sensors are relatively expensive instruments and the addition of a second pH sensor would significantly increase the cost of the mixing apparatus.

The present invention teaches that substantially the same results can be achieved much less expensively by utilizing a conductivity cell closely adjacent the acid Waste inlet to the tank. A conductivity cell is a relatively inexpensive instrument which measures the conductivity of a liquid. Acid waste is conductive primarily because of the dissolved solids contained therein whereas ordinary tap water is relatively nonconductive.

When the conductivity cell indicates a level of conductivity indicative of acid waste, it initiates the injection of the base into the tank. This eliminates the relatively high acid spike which would appear without the conductivity cell. Thereafter, injection of the base into the tank is under the control of the pH controller and the pH sensor.

An optional, but advantageous, feature of the present invention is that of water injection. Water can be injected into the inlet zone of the tank by a nozzle which directs a stream of water generally toward the stream of acid waste entering the inlet zone through the inlet. Water injection has four important functions. First, it dilutes the acid Waste. Second, it creates turbulence which further intimately mixes the acid waste with the base. Third, the acid and base react exothermically toelevate the temperature within the tank, and the water serves to reduce that temperature. Fourth, when ammonia gas is used as the base, it assures that the ammonia gas will be thoroughly dissolved even in the event of a malfunction which might otherwise allow the gas to escape to the atmosphere or to back flow into the acid waste inlet line.

Another optional, but advantageous, concept of the present invention is that of recycling the mixture from the outlet back to the inlet zone, or a location upstream thereof, if the pH of the mixture is not within the alowable tolerances. For example, if the supply of base should become exhausted, the pH of the mixture may fall below the allowable level. In this event, the pH controller would operate a three-way valve and energize a pump which would recycle the mixture back to the inlet of the tank until the supply of base could be replenished.

Another advantage of the present invention is that the tank and many of the components of the apparatus can be constructed of an inexpensive plastic material which will not react with the chemicals passing through the tank. For example, in many instances the tank can be constructed of polyvinyl chloride which is lightweight and inexpensive. The baffles, the injector, and the valves and fittings may also be constructed of plastic material.

The invention can best be understood by reference to the following description taken in connection with the ac companying illustrative drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view in elevation illustrating a mixing apparatus construced in accordance with the teachings of this invention with portions of the apparatus being shown diagrammatically.

FIGS. 2a, 2b and 2c are sectional views through the tank illustrating three of the baffles in the tank.

FIG. 3 is a representative curve of pH values versus time at the outlet of the tank.

FIG. 4 is an enlarged fragmentary sectional view taken generally along line 4-4 of FIG. 1 illustrating the injector or sparge.

FIG. 5 is a diagrammatic elevational view partially in section of a second form of mixing apparatus constructed in accordance with the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an apparatus 11 constructed in accordance with the teachings of this invention. The apparatus 11 is particularly adapted for mixing acid waste and a base to thereby neutralize the acid waste. However, the apparatus 11 may be utilized for other mixing operations and is not restricted to an acid neutralization function. Moreover, depending upon the setting of the instruments employed, the acid and base could be mixed to provide an average pH other than 7, if desired.

The apparatus 11 includes a tank 13 which, in the embodiment illustrated, is constructed of a polyvinyl chloride pipe 15 of cylindrical configuration and a pair of polyvinyl chloride end caps 17, each of which is in the form of a plate. While plastic is preferred because it is inexpensive and relatively lightweight, obviously other materials may be utilized for the tank 13. Similarly, the tank need not be of cylindrical configuration. The end caps 17 are suitably retained on the pipe 15 as by a plurality of elongated bolt assemblies 1 9 which clamp the end caps against the opposite ends of the pipe 15.

The tank 13 is divided into an inlet zone 21, intermediate or mixing zone 23 and an outlet or sensing zone 25. The inlet zone 21 is supplied with acid waste in substantially liquid form through an acid waste inlet 27 formed in the end cap 17. Acid waste is supplied to the inlet 27 from a source (not shown) through a conduit 29, a manual valve 31 and a check valve 33.

A base is supplied to the inlet zone 21 from a source 35 through a conduit 37, an on/oif automatic control valve such as a solenoid valve 39 and an injector 41 which, in the illustrated embodiment of the invention, is a sparge. The injector 41 in the embodiment is an elongated tube having two rows of circumferentially offset apertures or base inlets 43 therein (FIG. 4), with the apertures of the two rows being axially olfset. To improve mixing the apertures 43 open generally downwardly, e.g., at a 45 angle relative to the vertical.

The apparatus 11 is not limited to use with any particular kinds of acids and bases. The apparatus '11 is particularly adapted, however, to neutralize acid of the type typically produced in publishing newspapers. This acid is typically nitric acid. However, virtually any acid including sulfuric acid and hydrochloric acid can be neutralized.

Although various bases can be utilized, a gas is preferred because no pump is required to supply it and because of the agitation elfect which it has when it is discharged through the apertures 43. Ammonia gas can be used to advantage as it is readily soluble in the acid Waste and in water.

A nozzle 45 is suitably mounted on the tank 13. The nozzle 45 is supplied with water from a source (not shown) through a conduit 47, a manual valve 49' and an on/off automatic control valve such as a solenoid valve 51. The nozzle 45 is arranged at an angle to direct a stream of water in a pattern 53 which passes just beneath the inlet 27. This assures that the water from the nozzle 45 will not be directed into the inlet 27, but will be directed primarily at the acid waste exiting from the inlet. This water stream agitates the acid base mixture, dilutes the acid, provides a cooling effect on the exothermic reaction in. the inlet zone 21 and assures that the ammonia gas will be fully absorbed in the liquid phase within the inlet zone 21 and not allowed to escape as a gas.

The inlet zone 21 extends from the end cap 17 on the left as viewed in FIG. 1 to an imperforate baffle 55. As shown in FIGS. 1 and 2a, the bafile 55 is in the form of a part circular plate suitably affixed to the interior of the tank 13 and generally perpendicular to the axis of the tank. The baffie 55 closes the tank 13 except for a restricted orifice 57 through which the liquid in the inlet zone 21 must pass en route to an outlet 58 of the tank 13.

Another feature of the invention is that the injector 41 extends for substantially the full length of the inlet zone 21 to thereby distribute the ammonia gas throughout the full length of the inlet zone. The injector 4'1 terminates closely adjacent the restricted orifice 57.

A plate 60 is mounted on the battle and extends toward the inlet end of the tank 13 to thereby define along with the baffle 55 a restricted passage 62 in which the sparge 41 is positioned. The baffle 55 and the plate 60 cooperate to completely close ofi the tank 13 except for the passage 62. Accordingly, all of the acid waste is routed over the sparge 41 in close proximity thereto to thereby achieve good initial mixing of the acid and the base. The plate 60 also elongates the flow path through the tank 13.

The bafile 55 and two

additional baffles

59 and 61 are in the intermediate or mixing zone 23 with the bafiles 55 and 61 defining the extremities of the intermediate zone. The

bafiles

59 and 61 are suitably mounted on the tank 13 in generally perpendicular relationship to the axis of the tank and define with the tank restricted

orifices

63 and 65, respectively. The

bafiles

55 and 61 are mounted so as to provide the restricted

orifices

57 and 65 at the lower region of the tank and the bafiie 59 is positioned so as to provide the restricted orifice 63 at the upper end of the tank. The flow path through the

orifices

57, 63 and 65 is as shown by the arrows in FIG. 1. The baflies are preferably constructed of sheets of plastic and any suitable number of the baflies may be provided.

The

bafiies

59 and 61 have

small openings

67 and 69, respectively, therein. Although various numbers and patterns of the

openings

67 and 69 may be provided, manufacture of the

bafiies

59 and 61 is facilitated if the openings in both baffles are identical as to size and position. As shown in FIGS. 2b and 2c, the

openings

67 and 69 lie entirely Within the regions of their

respective baffles

59 and 61 which directly confront each other. Stated differently, all of the

openings

67 and 69 in both of the

bafiies

59 and 61 lie above a horizontal plane which includes the lowermost edge of the baflie 61 and below a horizontal plane which includes the uppermost edge of the baffle 59.

The

bafiies

55, 59 and 61 serve several important functions. First, the bafiie 55 assists in channeling all of the liquid in the inlet zone 21 across the injector 41 in passing from the inlet zone to the intermediate zone 23. Second, the bafiies provide

disaligned orifices

57, 63 and 65 to thereby provide an elongated flow path through the tank 13 so that the flow path through the tank is longer than the distance between the inlet 27 and the outlet 58. Third, the elongated flow path provided by the bafiies is tortuous, i.e., requires the fluid to make several changes of direction with consequent production of turbulence and agitation which improves mixing.

Fourth, the openings ,67 and 69 allow some of the liquid in the intermediate zone 23 to pass directly through one or both of the

baffles

59 and 61. This means that fluid which flows through the restricted

orifices

63 and 65 flows along a different path, Le, a generally axial path than fluid which flows directly through the

openings

67 and 69. The impingement of these two streams flowing in different directions further agitates the mixture with consequent thorough mixing. Thus, thorough mixing of the acid waste and the base is accomplished without any mechanical agitation or power driven agitators.

A pH sensor 71 is located in the outlet zone 25 closely adjacent the outlet 58 and beneath the liquid level in the outlet zone. With the pH sensor 71 so located, the pH of the liquid at the sensor is substantially identical to the pH of the liquid at the outlet 58 and downstream thereof. The mixture in the outlet zone 25 is continuously removed and allowed to tlow through a conduit 73 and a three-way control valve 75 to an open drain 77.

The apparatus 11 is controlled by a pH controller 79 which may be of conventional design. An electrical input signal is provided to the pH controller by the sensor 71 with a characteristic of such signal varying with the pH of the mixture of liquid adjacent the outlet 58. The pH controller 79 opens and closes the control valve 39 to thereby control the flow of ammonia from the source 35 into the tank 13 in accordance with the pH of the liquid at the sensor 71. For example, the control valve 39 may be opened by the pH controller 79 as long as the sensor 71 senses a pH of less than a preselected value and may be closed when the pH sensed is greater than such preselected value. The preselected value of pH may be adjusted as necessary to produce the desired results, and the valve 39 can be opened at one pH and closed at another, if desired. With this type of control and with normal flow rates through the tank 13, the valve 39 will be opened and closed periodically to supply bursts of pressurized ammonia gas through the apertures 43 of the injector 41. Regardless of the duration of the burst, the beginning of each burst further contributes to the agitation of the acid waste and base in the inlet zone 21.

With this type of control, the pH of the liquid fed to the open drain 77 may vary generally in accordance with the curve shown in FIG. 3. As shown in FIG. 3, the pH of the liquid at the outlet 58 varies generally in sawtooth fashion between an upper level a and a lower level b with the average pH being at an intermediate level 0. For example, the pH of the levels a, b and 0 may be 9, 5 and 7, respectively. Over a period of time, the pH of the liquid at the outlet averages out at the average level 0 which, in the specific embodiment disclosed herein, is 7. However, the pH controller 79 can be adjusted to maintain the average pH at other values.

The pH controller 79 has a second set point or alarm point so that if the pH of the liquid at the outlet 58 drops below" a preselected value d which is the minimum acceptable value, an electrical control signal is fed to the control valve 75 so that further fiow from the outlet 58 is through a conduit 81 and a pump 83 back into the conduit 29 just upstream of the inlet 27. With the control valve 75 in this position, there is no flow into the open drain 77. This recycling or bypassing of the liquid from the outlet 58 will continue until the pH of the liquid at the outlet 58 rises so as to be above the acceptable minimum d. The pH level represented by d in FIG. 3 can be adjusted to any suitable value by the pH controller 79.

In operation of the apparatus 11, the three-way control valve 75 is normally open to the drain 77. It is contemplated that the control valve 75 will recycle liquid back through the conduit 81 only in situations where there is a malfunction or in other extraordinary circumstances such as when the source 35 of ammonia is depleted, or when an unusually highly concentrated acid waste is supplied to the tank 13, etc. Thus, the control valve 75 serves as a. safety device to positively prevent dumping of a liquid into the drain 77 which has a pH below the acceptable minimum value d.

When the liquid is recycled, the pump 83 is operative to supply the necessary pressure to accomplish the recycling. In addition, the valve 51 is closed by the pH controller 79. So long as the pH of the liquid adjacent the outlet 58 is within acceptable tolerances, the pH controller 79 has no effect on the solenoid valve 51, in which event the valve 51 can be opened to supply water to the nozzle 45 by merely closing of a manual switch 85. If desired, a recorder 87 can be coupled to the pH controller 79 to make a permanent record of the variation in pH at the outlet 58 with time.

The tank 13 should be installed in a position so that a residual of liquid will remain in the tank when the apparatus 11 is not in use. For example, with the outlet 53 located in the end cap 17 as shown in FIG. 1, the tank 13 can advantageously be installed with the longitudinal axis horizontal or inclined slightly toward the outlet. The residual level should be sufiicient so that the sensor 71 remains submerged.

In operation of the system, the residue in the tank is sufiicient so that the sensor 71 is always submerged. The switch 85 is first closed to cause the nozzle 45 to supply water to the tank 13, and the manual valve 31 is opened to allow acid waste to be fed into the inlet zone 21. This addition of acid waste to any liquid residue left in the tank 13 will ultimately bring the pH at the sensor 71 below the average level to thereby cause the pH controller 79 to open the control valve 39. A burst of ammonia gas is then supplied through the valve 39 and the apertures 43 to mix with the incoming acid waste in the manner described hereinahove. The liquid from the inlet flows through the intermediate zone 23 as described hereinabove to the outlet zone 25. After a period of time the pH at the sensor 71 rises above the level 0, at which time the control valve 39 is closed by the controller 79. The flow through the tank 13 is continuous and under the influence of gravity. The flow of liquid through the outlet '58 is also continuous. Accordingly, there is no holding time absent an alarm condition which would actuate the control valve 75 to cause recycling.

In the above-described operation of the apparatus 11, it is assumed that operating conditions will cause the solenoid valve 39 to be cycled open and closed repeatedly so that ammonia gas is periodically supplied through the apertures 43. While the apparatus 11 is capable of functioning in this manner, it should be understood that the opening and closing of the solenoid valve 39 is controlled by the sensor 71 and the pH controller 79 in accordance with the pH of the mixture adjacent the outlet 58. Accordingly, the solenoid valve 39 may cycle on and off infrequently, or may remain open continuous- 1y, or be otherwise controlled by the pH controller 79 to achieve preselected pH conditions adjacent the outlet.

FIG. 5 shows a second form of apparatus 11a which is identical to the apparatus 11 (FIGS. 1-4) in every way not specifically shown or described herein. Portions of FIG. 5 corresponding to portions of FIG. 1 are designated by corresponding reference characters followed by the letter a.

The apparatus 11a does not have the three-way control valve 75, the pump 83, nor the conduit 81 all of which were shown by way of example in FIG. 1. In all other respects, the apparatus 11a is identical to the apparatus 11 except for the manner in which the apparatus 11a is controlled.

The apparatus 110 includes a conductivity cell 101 located adjacent the inlet 27a. In the embodiment illustrated, the conductivity cell 101 is within the conduit 29a near the location at which the conduit dumps into the tank 13a. Of course, the conductivity cell 101 may be located at various locations in the path of fluid which enters the tank 13. As will become apparent, the conductivity cell 101 could be located within the tank anywhere upstream of the sensor 71a. However, optimum results can be obtained by locating the conductivity cell 101 in the stream of fluid entering the tank.

The conductivity cell @101 is of conventional design and provides a signal to a relay controller 103. A characteristic of the signal is proportional to the conductivity of the liquid in which the conductivity cell 101 is immersed. The relay controller 103 is operative to open and close a relay 105 in response to predetermined signals, respectively, from the conductivity cell 101. The relay controller 103 is adjustable so as to respond to different signal values.

The sensor 71a provides a signal which varies in accordance with the pH of the mixture adjacent the outlet 58a. This signal is received by the pH controller 79a which operates a low pH relay i107 and a high pH relay 109. A suitable power source 111 is coupled into the circuit to operate the solenoid 39a.

The relay 109 remains closed so long as the pH of the liquid adjacent the outlet 58a remains below a preset value such as 9. The low pH relay 107 remains open so long as the pH of the liquid adjacent the outlet 58a remains above a pH value such as 6. The relay remains open so long as the liquid at the conductivity cell 101 has a conductivity below a preselected value. It is apparent from FIG. 5 that the solenoid valve 39a will be energized and therefore open if (1) both of the relays 105 and 109 are closed or (2) the relay 107 is closed as these two sets of relays provide parallel conductive paths.

Acid waste is typically much more conductive than ordinary tap water. This is due in large part to the presence of a relatively larger amount of acid ions in the acid waste. By way of example, if ordinary tap water were run through the conduit 29a to flush the conduit or for other purposes, the signal from the conductivity cell 101 would not operate the relay controller 103, and the relay 105 would remain open. In this event, assuming the pH of the liquid adjacent the outlet 58a to be greater than 6, the solenoid valve 39a would remain closed. However, if acid waste is run through the conduit 29a, the conductivity thereof is sufiiciently high so that the signal from the conductivity cell 101 causes the relay controller 103 to close the relay 105. Ordinary tap water would not have sufficient conductivity to cause closing of the relay 105. A circuit is then completed through the relays 105 and 109 to the solenoid valve 39a thereby opening the valve to supply base through the injector 41a. The relay 105 remains closed so long as the conductivity cell 101 is in acid waste. Thereafter, the system is under the control of the sensor 71m and the pH controller 79a. For example, if the pH rises above a certain value such as 9, the relay 109 opens to close the solenoid valve 39a. As the relay 107 is normally open under these conditions, the solenoid valve 39a closes.

The relay 107 operates primarily as a safety device in the event that the relay 105 should fail to close. For example, if for any reason the relay 105 should fail to close, the addition of acid to the tank 13 would ultimately cause the pH adjacent the outlet 58 to drop below a preset value such as 6. At this instant, the relay 107 is closed to provide a path around the relay 105 to thereby open the solenoid valve 39a giving the pH controller 79a and the pH sensor 71a overriding control of the apparatus.

Although an exemplary embodiment of the invention has been shown and described, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.

I claim:

1. A mixing apparatus for mixing a plurality of chemicals comp-rising:

a tank having first and second inlets for receiving a first and a second of said chemicals, respectively, said tank having an outlet, said tank defining a flow passage between said inlet and said outlet, said chemicals flowing through the flow passage from their respective inlets to said outlet;

at least one baflie in said flow passage to assist the mixing of the first and second chemicals to thereby provide a chemical mixture adjacent the outlet;

sensing means for measuring a characteristic of the mixture; and

means responsive to the measured characteristic of the mixture for controlling the amount of the first chemical which is received by said tank whereby said characteristic of the mixture is controlled.

2. A mixing apparatus as defined in claim 1 wherein said last mentioned means includes an on/off valve for controlling the amount of first chemical which is received by the tank.

3. A mixing apparatus as defined in claim 1 including a nozzle at least partially in said tank for directing a stream of liquid against the incoming second chemical, said'stream of liquid creating turbulence which assists the mixing of the first and second chemicals.

4. A mixing apparatus as defined in claim 1 including means responsive to said measured characteristic being of predetermined value for conducting the mixture flowing through the outlet to a location upstream of said bafile.

5. A mixing apparatus as defined in claim 1 including means responsive to the conductivity of the second chemical for initiating How of the first chemical into the tank.

6. A mixing apparatus as defined in claim 5 wherein said sensing means and said means responsive to the measured characteristic can override said means responsive to the conductivity of the second chemical.

7. A mixing apparatus as defined in claim 1 wherein said batfie includes a first baifie, said mixing apparatus including a second bafile, said first and second bafiies projecting from opposite sides of the tank to provide a tortuous fiow path, one of said baffles having at least one aperture therein to create turbulence which assists the mixing of the first and second chemicals.

8. A pH controlling apparatus for a plurality of chemicals including first and second chemicals in substantially fluid form wherein said chemicals have different values of pH, said apparatus comprising:

a tank having an inlet and an outlet, said inlet being connectible to a source of the first chemical;

an injector within the tank connectible to a source of the second chemical for supplying the second chemical to the tank;

means for channeling the first chemical across the injector as the first chemical flows from the inlet toward the outlet;

means for creating turbulence as the chemicals move toward the outlet to mix said chemicals to provide a mixture of the chemicals;

sensing means for measuring the pH of the mixture;

means responsive to the pH of the mixture for controlling the quantity of at least one of said chemicals which is supplied to the tank;

said channeling means including means for providing a restricted region in the fiow path between the inlet and the outlet of said tank, at least a portion of said injector being closely adjacent the restricted region; and

said injector having a plurality of apertures, said first chemical being a liquid and said second chemical being a gas, said injector being submerged in the liquid, said means responsive to the pH of the mixture including an on/off valve for controlling the amount of the gas which is received by the tank, said on/olf valve causing the gas to be periodically spurted through the apertures of the injector to thereby create turbulence which assists mixing of the chemicals, said means for creating turbulence including a plurality of baflles, at least some of said bafiies having apertures therein through which the chemicals can pass to create turbulence to thereby assist mixing of the chemicals.

9. A pH controlling apparatus as defined in claim 8 wherein said tank includes a pipe constructed of a plastic which is not reactive with said chemicals and end caps for closing the ends of said tank.

10. A pH controlling apparatus for a plurality of chemicals including first and second chemicals in flowable form wherein said chemicals have difierent values of pH, said apparatus comprising:

a tank having an inlet and an outlet and defining a chamber, said inlet being connectible to a source of the first chemical;

means for defining a restricted passage in said chamber of said tank which is of lesser cross sectional area than said chamber;

said injector extending into said restricted passage 10 jector as the first chemical flows from the inlet toward the outlet;

sensing means for measuring the pH of the mixture;

and

means responsive to the pH of the mixture for controlling the quantity of at least one of said chemicals which is supplied to the tank.

11. An apparatus as defined in claim 10 wherein said means defining a restricted passage includes first and second members extending generally transverse to and longitudinally of the direction of flow between the inlet and the outlet, respectively.

12. An apparatus as defined in claim 10 wherein said turbulence creating means includes at least one bafiie in said chamber to assist the mixing of the first and second chemicals.

13. A method of neutralizing acid waste comprising:

providing a neutralizing tank having an inlet zone, an outlet, a flow passage between the inlet zone and the outlet, and a bafile in said flow passage;

introducing acid waste into the inlet zone;

introducing a base into the tank to mix with the acid waste, said base being chemically reactive with the acid;

causing the acid waste and the base to flow in the flow passage toward the outlet with the bafile assisting the mixing of the acid waste and the base whereby a mixed solution is formed;

continuously removing some of the mixed solution from the tank through the outlet whereby fiow through said tank is continuous;

sensing the pH of the mixed solution; and

controlling the addition of the base in accordance with the pH of the mixed solution to at least substantially neutralize the acid waste.

14. A method as defined in claim 13 including providing a restricted region in said flow path and channeling the acid waste through said restricted region, and said steps of introducing a base including introducing at least some of the base at said restricted region.

15. A mixing apparatus for mixing an acid and a base wherein the acid and base are in flowable form, said apparatus comprising:

a tank having first and second inlets for receiving the acid and the base, respectively, said tank having an outlet, said tank defining a flow passage between said inlet and said outlet, said acid and base flowing through the flow passage from their respective inlets to said outlet and mixing as they flow toward the outlet to thereby form a mixture;

sensing means for measuring the pH of the mixture;

means responsive to the pH of the mixture for controlling the amount of the base which is received by said tank whereby the pH of the mixture is controlled; and

means responsive to the conductivity of the acid fed to the tank for initiating the flow of the base to the tank.

References Cited UNITED STATES PATENTS 3,521,752 7/1970 Lindman 21096 1,324,118 12/1919 Hottinger 21049 3,301,779 1/1967 -Kovacs 21061 X 2,666,740 1/ 1954 Gordon 21015 3,391,789 7/1968 Zievers et a1 21061 X 3,541,008 11/1970 Spinola 21049 3,238,128 3/1966 Gustafson 210--96 X MICHAEL ROGERS, Primary Examiner US. Cl. X.R.

whereby the first chemical is channeled over the in- 23285; 137-5, 93; 21060, 96, 198