Process And Apparatus For Destroying Hexavalent Chromium In Solution

Abstract

An apparatus and method for precipitating and/or destroying a chemical material comprising a source of material connected in series with an acidification unit, a reduction unit, and a pH adjustment unit and with detention chambers between each unit and a container to allow settling of the newly formed material. This apparatus provides a circuit through which the reaction takes place within engineered volumes of piping surrounding the unit.

Description

GENERAL DESCRIPTION OF THE INVENTION

The apparatus disclosed herein operates on the principle of acidification, reduction and then pH adjustment to allow settling of the newly formed material. The chemical reactions take place within engineered volumes of piping surrounding the module. The final settling of sludge takes place within the main holding vessel.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a destruction unit which is continuous and automatic in operation.

Another object of the invention is to provide a continuous chemical reaction unit.

GENERAL DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the machine according to the invention.

FIG. 2 is a front view of the machine.

FIG. 3 is a right side view of the machine.

FIG. 4 is a left side view of the machine.

FIG. 5 is a top view of the machine.

FIG. 6 is a back view of the machine.

FIG. 7 is a schematic view of the apparatus.

FIG. 8 is a schematic view of the tank.

FIG. 9 is a schematic view of the proportioning pump circuit.

DETAILED DESCRIPTION OF THE DRAWINGS

The circuit shown in FIG. 7 is made up of the three detention chambers 17, 25 and 32, which are connected in series with the sight-glasses 14, 18, 26 and 33. These are, in turn, connected in series with the sump 11 and the holding tank 38.

A pump 13 circulates liquid from the sump 11 through the line 12 and through the system.

Acid is added by means of a proportional acid injection pump 41 through line 16 and check valve V to the acid injection point 15 in line 12. The detection chamber 17 is sufficiently large in cross section and is internally baffled in such a manner to provide approximately one minute of turbulent detention in a typical example.

A pH cell 19 senses the pH of the liquid after it passes through sight-glass 18 and controls a valve 20 so that when the pH is above a predetermined value, the liquid is recirculated through line 21 back to the sump 11. If the pH is at or below the proper value, it proceeds into line 22. pH cell 19 passes an electrical signal to proportional controller 44 which, in turn, transmits a signal to proportional acid injection pump 41. The controller 44 will balance the pump 41 output rate such that said rate will stabilize at the desired setpoint to obtain correct pH at pH sensing cell 19. The liquid thence passes through line 22 to the reducing agent addition point 23 where a reducing agent injection pump 42 feeds reducing agent through check valve V and valve 24 and line 24'. The liquid then continues through the detention chamber 25 where it is held and mixed for a period of five minutes in a typical installation, thence through sight-glass 26 to the oxidation reduction potential detector 27. If the ORP reading is above or below the proper oxidation reduction potential range, the fluid is diverted through valve 28 into line 21 which recycles to sump 11. If the oxidation reduction potential falls within the acceptable range, the fluid will continue into line 29. ORP cell 27 passes an electrical signal to proportional controller 45 which, in turn, transmits a signal to reducing agent injection proportional pump 42. The controller 45 will balance the pump 42 output rate such that said rate will stabilize at the desired setpoint to obtain correct ORP at sensing cell 27. The liquid thence passes through line 29 to the caustic addition point 30 where caustic is added by way of a proportional caustic injection pump 43 through check valve V and through line 31 and valve 31'. The liquid then continues through the detention unit 32 where it is held and mixed for a period of one minute in a typical installation, thence through sight-glass 33 and pH sensor 34 and into detention tank 38 primary chamber 35. If the pH is below a predetermined level, the liquid is recirculated through pump 36 and line 37 to a point of injection in line 29 prior to caustic injection point 30. If the liquid is within the desired limits of pH, the liquid passes undisturbed from primary chamber 35 into sump 38. pH cell 34 passes an electrical signal to proportional controller 46 which, in turn, transmits a signal to proportional caustic injection pump 43. The controller 46 will balance the pump 43 output rate such that said rate will stabilize at the desired setpoint to obtain correct pH at pH sensing cell 34. The newly formed solids in the fluid are allowed to settle, for example, for 2 hours thence clear water is discharged through a pH cell and recorder 39 which will indicate the pH of the water discharged from the unit.

EXAMPLE

A typical example of operation will be hexavalent chrome of 1,200 ppm Cr.sup.+.sup.6 at tank 11 which will be pumped by pump 13 at a rate of 5 gallons per minute through sight-glass 14, chrome liquid will be yellow in color, and will have 60 cc. per minute of 66.degree. Be.sup.- Sulfuric Acid injected at 15 and it will be detained for a period of one minute at 17 where its color will become a reddish-orange, which may be observed at sight-glass 18. If the pH is below 2.5 at pH cell 19, the liquid will proceed past point 23 where 12.6 pounds per hour of 98 percent purity sodium bisulfite will be injected and shall be detained and mixed for a period of five minutes at 25 thus changing the color of the fluid to emerald green which can be observed at sight-glass 26. If the oxidation reduction potential at ORP cell 27 is less than 210 mv and greater than 190 mv, the liquid shall then proceed past point 30 where 6.8 pounds per hour of 98 percent sodium hydroxide will be injected and shall be detained and mixed for a period of one minute at 32 thus changing the color of the fluid to powder blue which can be observed at sight-glass 33. If the pH of the liquid at pH cell 34 is greater than 8.0, it shall pass into tank 38 where it shall be held for two hours to allow the chrome hydroxide to settle and allow the clear supernate to pass through pH recorder 39. Periodic removal of settled sludge will be accomplished through blowdown port 40.

Typical chemical reactions that will occur within the above circuitry are as follows:

Circuit 1:

2na.sub.2 Cr0.sub.4 + 2H.sub.2 SO.sub.4 .fwdarw.H.sub.2 Cr.sub.2 O.sub.7 + H.sub.2 O + 2Na.sub.2 SO.sub.4 .fwdarw.2H.sub.2 CrO.sub.4 + 2Na.sub.2 SO.sub.4

Circuit 2:

6naHSO.sub.3 + 3H.sub.2 SO.sub.4 + 4H.sub.2 CrO.sub.4 .fwdarw.2Cr.sub.2 (SO.sub.4).sub.3 + 3Na.sub.2 SO.sub.4 + 10H.sub.2 O

Circuit 3:

cr.sub.2 (SO.sub.4).sub.3 + 6NaOH.fwdarw.2Cr(OH).sub.3 .uparw. + 3Na.sub.2 So.sub.4

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for destroying hexavalent chrome comprising,

a series circuit including a first circuit element,

a chrome source,

a first pump,

an acid injection means,

a first detention and chemical reaction chamber,

a pH sensor means,

a pH correction means,

a means of diverting unacceptable material,

and a second detention chamber connected in series with said first detention chamber,

said pH sensor being connected to control means on a diversion valve actuated by said pH sensor whereby said material is recirculated to said chrome source when the pH of said material is above a predetermined value,

said pH sensor being connected to a proportional controller whereby exactly the amount of acid required is injected to achieve desired pH.

2. The apparatus recited in claim 1 wherein a reducing agent additive unit is connected in series with said first detention unit, a means of detecting oxidation, reduction potential, and a means of correcting amount of reducing agent additive by means of a proportionate controller in order to achieve exactly the correct amount of reduction agent,

and said second detention unit is connected in series with said reducing agent additive unit and said sensing and controlling means.

3. The apparatus recited in claim 1 wherein a third series of circuit elements is connected in series with said mentioned elements,

said third circuit elements comprising a caustic additive unit,

a third detention chamber and a second pH sensing unit,

said second pH sensing unit having means thereon for selectively directing material from said third detention chamber to said settling chamber and to recirculate said material to said caustic unit if the pH is below a predetermined level,

said second pH sensing unit being connected to a third proportional controller whereby regulation is achieved to inject exactly the correct amount of alkaline material to obtain desired pH.

4. The apparatus recited in claim 2 wherein a third series of circuit elements is connected in series with said mentioned elements,

said third circuit elements comprising a caustic additive unit,

a third detention chamber and a second pH sensing unit,

said second pH sensing unit having means thereon for selectively directing material from said third detention chamber to said settling chamber and to recirculate said material to said caustic unit if the pH is below a predetermined level,

said second pH sensing unit being connected to a third proportional controller whereby regulation is achieved to inject exactly the correct amount of alkaline material to obtain desired pH.

5. The apparatus recited in claim 3 wherein a first sight-glass, a second sight-glass, a third sight-glass, and a fourth sight-glass are disposed in said circuit, said first sight-glass being disposed prior to said acid injection point,

said second sight-glass being disposed following said first detention chamber,

said third sight-glass being disposed in circuit adjacent said second detention chamber,

and said fourth sight-glass being disposed adjacent said third detention chamber.

6. The apparatus recited in claim 3 wherein a reducing agent injection means is connected in series with said circuit between said acid addition unit and said third circuit element,

and a second retention chamber is provided and an oxidation reduction potential unit is connected to said circuit and means connected to said oxidation reduction potential unit whereby said material will be diverted when the oxidation reduction potential is at a predetermined value.

7. An apparatus for removing a chemical ingredient from a solution comprising,

a source of said solution,

a settling tank,

a plurality of large pipes and a plurality of small pipes connected in series with each other and disposed around said tank,

said pipes each being disposed generally in the form of a helix around said tank,

means for adding materials to said solution within said large pipes,

each said large pipe having a diameter and length sufficient to provide a predetermined detention time during which said solution is in the particular said large pipe,

said large pipes having sufficient volume to provide said detention time of a predetermined interval for said liquid flowing in said circuit,

said material being adapted to precipitate solid material whereby said solids will settle in said tank.

8. A chromate destruction module comprising a raw waste source,

a treated waste sump,

a circuit connecting said treated waste sump to said raw waste source,

said circuit comprising a first detention means and a second detention means, and a third detention means,

means connecting said detention means in series with each other,

and said means connecting said detention means in series comprising a first pH sensing device for selectively recirculating said liquid to said raw waste source when said pH is above a predetermined value and connecting said circuit to said second detention means when said pH is below a predetermined value and continuously adjusting volume of pH adjusting additive such that proper pH is obtained,

said circuit further comprises means to inject caustic into said circuit between said second detention means and said third detention means and means for recirculating said liquid from said circuit between said third detention means and said second detention means when the pH of said liquid at said treated waste sump has a pH below a predetermined value and transferring said liquid from said circuit between said third detention means and said treated waste sump when the pH of said liquid has a pH above a predetermined value.

9. The circuit recited in claim 8 wherein said circuit comprises a second detention means between said first detention means and said third detention means,

and means to inject a reducing agent into said circuit at the end of said first detention means adjacent said second detention means.

10. The circuit recited in claim 9 wherein means is provided to recirculate said material from said second detention means to said chrome source when the ORP thereof is outside of a predetermined range and a means of continuously adjusting the volume of ORP adjustive additive such that stabilized proper oxidation reduction potential is obtained and a means of circulating said material from said second detention means to said third detention means when the oxidation reduction potential thereof is within a predetermined range.

11. The circuit recited in claim 8 wherein said circuit comprises enlarged size pipes connected by reduced size pipes,

and said enlarged size pipes comprise a retention chamber.

12. The circuit recited in claim 11 wherein said pipes are connected to a tank and said pipes are arranged generally in the form of a helix around said tank.

13. A process of destroying hexavalent chromium in solution comprising circulating said solution from a source through a series of lines and detention chambers,

and adding acid and caustic to said solution in predetermined amounts to said solution comprising,

sensing said solution in said lines at a point subsequent to a first detention chamber and recirculating said solution when the pH varies above a predetermined value,

passing said solution to an electrical signal means to proportionally control an acid injection pump controlling the acidity of said solution,

passing said solution through a reducing agent addition point and adding a reducing agent to said solution,

passing said solution through a detention chamber to a pH detector and recirculating said solution when the pH thereof downstream of the point where said caustic is added is below a predetermined amount and allowing said liquid to pass through said line when the pH thereof is between predetermined limits.

14. The method recited in claim 13 wherein said liquid is passed from said caustic addition unit through an electrical signal to a proportional controller which transmits the signal to said caustic injection means whereby the rate of addition of caustic to said solution is controlled.