WO1995027572A1

WO1995027572A1 - Method and apparatus for cleaning contaminants from soil

Info

Publication number: WO1995027572A1
Application number: PCT/US1995/004379
Authority: WO
Inventors: Percy Greenberg; Peter S. Gross
Original assignee: TECHNOLOGY REMEDIATION Inc
Current assignee: TECHNOLOGY REMEDIATION Inc
Priority date: 1994-04-12
Filing date: 1995-04-10
Publication date: 1995-10-19
Anticipated expiration: 1996-10-12

Abstract

A method and apparatus for cleaning contaminants from soil is disclosed. The soil cleaning apparatus (10) includes a combining chamber (22), an aerator (24) and a separator (26). Contaminated soil (14) is combined with a solvent (46) from a solvent reservoir (28) to form a fluidized composition (70). The fludized composition (70) is then aerated such that the contaminants are volatized and removed from the fluidized composition (70) in a vapor form. The solvent (46) is separated from the fluidized composition (70), resulting in clean soil (72). The separated solvent (46) may be recycled for subsequent reuse in cleaning remaining contaminated soil (14).

Description

METHOD AND APPARATUS FOR CLEANING CONTAMINANTS FROM SOIL

BACKGROUND OF THE INVENTION

The present invention concerns a soil contamination removal method and apparatus. More particularly it relates to a method and apparatus for cleaning contaminated soil through aeration.

An unfortunate but all too common problem in industrial areas is the release of pollutants into the environment. More specifically, toxic materials, such as gasoline, oil, etc., are often spilled on to the ground, contaminating the contacted soil to unacceptable levels. This soil contamination can occur through leaking underground storage tanks or conduit systems, improper handling of receptacles containing toxic materials, operation of refinery and industrial sites using petroleum-based substances, etc. The failure to remove these dangerous contaminants from the soil can lead to spreading of the contaminant beyond the original spill area, thus endangering surrounding water supplies.

There are in existence a variety of systems for dealing with the above-described dilemma. For example, an obvious but expensive method is to isolate the soil spill site below the level to which the pollutant material has traveled. However, along with the great expense incurred in performing such an isolation, the contaminant will always remain within the soil.

Other systems have been developed which purportedly act to remove contaminant from soil. However, these systems are quite complex, involving the use of sensitive bacteria microbes, chemicals, or other colloidal agents. Additionally, these systems require tempered environments in which heat and pressure must be maintained at exact levels to achieve the cleaning effects desired. The complexity of these systems limits their effectiveness when any of the parameters involved are not maintained. Further, the use of bacteria microbes and chemicals places an added constraint and cost on the system in question.

For example, U.S. Patent No. 5,172,709 shows an apparatus and process for removing contaminants from soil. Contaminated soil is placed in a container and then subjected to steam under a pressure of between 1 and 100 psi and at a temperature of between 214° and 338°F. The steam wets the entire volume of soil, while the heat vaporizes the volatile fraction of the contaminant for removal in the vapor phase. The liquid fraction and steam migrate downward through the soil, with the contaminant being removed in both liquid and vapor form for disposal. This process and apparatus cannot remove all contaminants in vapor form and requires that specific temperature parameters be maintained to facilitate the removal of a steam fraction and liquid fraction of contaminant.

U.S. Patent No. 5,039,415 shows a method and apparatus of decontaminating soil by deploying hydrocarbon-consuming microbes into the contaminated soil. The soil is first pulverized into fine particles. These particles are then coated with a microbe-containing aqueous solution. The invention focuses upon the method by which the microbes are easily and accurately dispersed into the soil. The microbes are of a type which act to consume hydrocarbons, thereby eliminating pollutant levels in the treated soil. Successful decontamination as taught by the invention explicitly depends upon the use of bacteria or other biologically created microbes.

U.S. Patent No. 4,969,775 shows a process for dressing contaminated soils which separates contaminated soil into a relatively coarse fraction and a relatively fine fraction. To achieve this separation, the contaminated soil is placed in a drum containing an aqueous medium and loose pieces of material to grind and abrade the soil particles. Following this grinding, a relatively coarse portion of decontaminated soil is discharged as purified soil. The relatively fine fraction, still containing contaminated soil, is processed through various mechanical and chemical processes from which a liquid pollutant concentrate is ultimately withdrawn.

U.S. Patent No. 4,927,293 shows a method and apparatus for remediating contaminated soil. The contaminated soil is mixed with an absorbent material, including a chemical additive suitable for fostering a reaction which substantially decontaminates the soil. Additionally, an oxidizing material, such as hydrogen peroxide, is dispersed onto the composition while compressed air is employed to aerate the soil/absorbent material composition and drive the desired reaction between the soil and the absorbent material. This chemical reaction volatilizes the contaminants from the soil. Notably, the solid reagent and soil are thereafter returned into the environment, precluding any reuse of the solid reagent.

The above described systems have all been created to cleanse contaminated soil. However, each employs complex methods, such as the use of microbes, chemicals, additives, and temperature requirements, which greatly detract from the ease and effectiveness during actual use. Additionally, the contaminant is often removed only after a number of steps are followed and at different processing stages. Therefore, a substantial need exists for a simple yet effective contaminated soil cleaning method and apparatus, not requiring chemical additives or controlled heat parameters.

SUMMARY OF THE INVENTION The invention provides a method and apparatus for cleaning contaminated soil based upon the principles of aeration. The soil cleaning method and apparatus of the present invention will remove virtually all traces of contaminants from soil over a short period of time. With this method, contaminated soil is excavated from the spill site and transferred to a combining chamber. A predetermined volume of solvent, preferably water, is mixed with the contaminated soil to form a fluidized composition. To ensure the soil and solvent properly mix, an agitation device is employed. It is during this mixing stage that the majority of contaminant is transferred from the soil to the solvent.

Following the completion of the mixing step, the entire fluidized composition will assume a flowing, mud-like form. The fluidized composition is transferred to an aeration stage. Preferably, the aeration takes place within a single receptacle having a number of forced air diffusers. As the fluidized composition is aerated, the contaminants become volatized and are expelled from the fluidized composition in the form of a vapor. In other words, the aeration/volatilization step effectively strips or evaporates the contaminants from the mixture. The chemical composition of the chosen solvent varies from that of the contaminants such that the contaminants will evaporate before the solvent during volatilization or "cold boiling". The vaporized contaminants are then released from the fluidized composition into the atmosphere. If necessary, an additional treatment step may be provided to collect the contaminants and prevent their release.

The decontaminated fluidized composition is transported to a separation stage at which the solvent is separated from the soil. This separation takes place in a tank, centrifuge or settling basin, which allows the bulk of the solvent to be removed from the soil. Finally, the decontaminated soil is replaced at the site from which it was excavated. Notably, any solvent still remaining with the cleansed soil will be removed through natural evaporation. The previously separated solvent is then available for reuse in cleaning other contaminated soil.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a soil cleaning apparatus in accordance with the present invention.

FIG. 2 is a diagrammatic view of the system shown in FIG. 1 including a side sectional view of a combining chamber of the present invention. FIG. 3 is a top sectional view of a portion of the system of FIG. 1 showing an aerator of the present invention.

FIG. 4 is a side sectional view of a portion of the system of FIG. 1 showing an aerator of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the soil cleaning apparatus 10 of the present invention is shown in FIG. 1. An earth moving device 12 is used to deliver contaminated soil 14 to the soil cleaning apparatus 10. The soil cleaning apparatus 10 includes a storage bin 16, a first belt conveyor 18, and a mobile support frame 20 (which supports a combining chamber 22, an aerator 24, and a separa- - 26), a solvent reservoir 28 and a second belt conveyor 30.

The storage bin 16 has an opening (not shown) at which the first belt conveyor 18 is connected. The first belt conveyor 18 has a support structure 32 which is positioned to align an upper end 34 of the first belt conveyor 18 at a level above the combining chamber 22.

The combining chamber 22 has a hopper 36 above which the upper end 34 of the first belt conveyor 18 is positioned. At the lower end of the hopper 36 is a gravity feed inlet 38, which is attached to the combining chamber 22 at a bearing plate 39. Pressurized piping 40 is connected to the combining chamber 22 at a sealed inlet 42 on the bearing plate 39. The pressurized piping 40 is also connected to a pump 44. The pump 44 draws solvent 46 from the solvent reservoir 28 via tubing 48. Finally, the combining chamber 22 is connected to a transfer duct 50 by an outlet (not shown).

The combining chamber 22 is designed to rotate about an imaginary axis running from the transfer duct 50 to the center of the bearing plate 39. This rotation is imparted by a motor (not shown) which actuates a drive chain 51. The drive chain 51 is integrally attached to the combining chamber 22 such that movement of the drive chain 51 results in rotation of the combining chamber 22. Notably, the bearing plate 39 remains stationary during rotation of the combining chamber 22.

Aerator 24 is connected to the transfer duct 50 by an inlet 52. The aerator 24 contains a screw conveyor 54 and an exit vent 56. A manifold 58 directs forced air into the aerator 24 from an air compressor 60. A duct 62 is connected to the aerator 24 at an outlet (not shown).

The duct 62 enters the separator 26 at an inlet 64 on a bearing plate 65. The separator 26 has a centrally located solvent conduit 66 attached to the bearing plate 65 with an open end positioned above the solvent reservoir 28. Additionally, the separator 26 has an exiting trough 68 positioned above the second belt conveyor 30.

The separator 26 is designed to rotate about an imaginary axis running from the center of the bearing plate 65 to the exit trough 68. This rotation is imparted by a motor (not shown) which actuates a drive chain 69. The drive chain 69 is integrally attached to the outer perimeter of the separator 26 such that movement of the drive chain 69 translates into rotation of the separator 24. Notably, the bearing plate 65 remains stationary during rotation of the separator 26. Additionally, the exiting trough 68 is centrally positioned as to allow the separator 26 to rotate around it.

The preferred process of cleaning contaminated soil by the apparatus 10 shown in FIG. 1 and FIG. 2 begins with contaminated soil 14 being loaded into the storage bin 16 by an earth moving device 12. The contaminated soil 14 is delivered from the storage bin 16 to the hopper 36 by way of the first belt conveyor 18 or other similar mechanism capable of moving soil. The contaminated soil 14 is fed into the combining chamber 22 through the gravity feed inlet 38 from the hopper 36. Alternatively, the storage bin 16 and belt conveyor 18 may be omitted where the contaminated soil 14 is delivered directly to the hopper 36 by the earth moving device 12.

Once inside the combining chamber 22, the contaminated soil

14 is mixed or combined with a volume of solvent 46. The solvent 46 is drawn from the solvent reservoir 28 and is delivered to the combining chamber 22 by way of pressurized piping 40. The solvent 46 and contaminated soil 14 are mixed together within the combining chamber 22 to form a fluidized composition 70. Preferably, the solvent 46 is water, but can be any other fluid, such as steam, perchlorethylene (dry cleaning fluid), soap, acetone, etc., having the ability to facilitate aeration of contaminants contained within soil.

When properly mixed, the fluidized composition 70 will assume a mud-like form having the ability to flow. In this form, the fluidized composition 70 is delivered to the aerator 24 through the transfer duct 50. The fluidized composition 70 will traverse through the transfer duct 50 by way of gravity. However, any other method of moving fluidized material, such as a conveyor, auger or a pump, will suffice.

Once inside the aerator 24, the fluidized composition 70 is subjected to aeration or forced air flow. Forced air is delivered from the standard air compressor 60 and is directed through the manifold 58 to the aerator 24. The forced air in the aerator 24 causes the fluidized composition 70 to volatize or "cold boil". This volatilization drives the contaminates from the fluidized composition 70 in a vapor form. The vaporized contaminants are released from the aerator 24 via the vent 56. Where necessary, the vent 56 may be equipped with an additional treatment device, such as a filter, to prevent contaminants from entering the atmosphere.

Movement of the fluidized composition 70 through the aerator 24 is imparted by gravity and the screw conveyor 54. As the screw conveyor 54 rotates, the fluidized composition 70 is transported through the aerator 24 at a predetermined rate. Alternatively, any other device capable of forcing the fluidized composition 70 to traverse the aerator 24, such as a pump, etc, can be employed.

Upon removal of the contaminants from the fluidized composition 70 by the aerator 24, the fluidized composition 70 is delivered to the separator 26 by way of the transfer duct 62. Preferably, gravity will cause the fluidized composition 70 to pass through the transfer duct 62. However, any other method of moving fluidized material, such as an auger or pump, will suffice. The separator 26 acts to divide the fluidized composition 70 into solvent 46 and clean soil 72. This result is achieved by rotating the separator 26 about an imaginary axis which, via centrifugal dynamics, forces the soil 72 and solvent 46 to separate. The separator 26 is preferably a large centrifuge, but can also take the form of any other device having the ability to separate solvent from soil, such as a settling basin or dryer.

The removed solvent 46 is withdrawn from the separator 26 through the solvent conduit 66, and delivered to the solvent reservoir 28. This separated solvent 46 is then available for reuse in subsequent cleansing of any remaining contaminated soil 14. The cleaned soil 72 exits the separator 26 at the exit trough 68. The cleaned soil 72 is transferred from the apparatus 10 by the second belt conveyor 30 and returned to the earth. Any solvent 46 still remaining within the cleaned soil 72 will be removed through natural evaporation.

The overall layout of the soil cleaning apparatus 10 is such that a continuous material flow through the combining chamber 22, aerator 24, and separator 26 is provided in a simple yet proficient manner. By physically positioning the exit of the combining chamber 22 above the entrance to the aerator 24, and the exit from the aerator 24 above the entrance to the separator 26, the force of gravity will effectively result in continuous material flow. Additional augers and conveyors, 54 for example, are provided to supplement this gravity-induced flow. Alternatively, any mechanism capable of transporting the fluidized composition 70 from each processing stage, such as a pump, conveyor or additional augers may be employed.

While the soil cleaning apparatus 10 has been described to preferably sustain a continuous material flow, such a flow is not required for successful soil decontamination. In other words, the method and apparatus for cleaning contaminated soil as previously described will be equally effective where a volume of material is physically transported from the combining chamber 22, aerator 24 and separator 26 on a batch basis. Operation Of The Combining Chamber As shown in detail in FIG. 2, the combining chamber 22 is comprised of an enclosing wall 80, a bearing plate 39 and an auger apparatus 82 or any other apparatus which will assist in forcing the contaminated soil 14 to interact with the solvent 46. The combining chamber 22 is designed to function much like a cement mixer. The contaminated soil 14 enters the combining chamber 22 through the bearing plate 39 at the gravity feed inlet 38 via the hopper 36. While the gravity feed inlet 38 preferably passes through the bearing plate 39, it may also be located at any other position on the combining chamber 22. When so positioned, the hopper 36 will be disengaged from the combining chamber 22 and the gravity feed opening 38 closed when subsequent mixing takes place. The solvent 46 enters the combining chamber 22 through pressurized piping 40. The solvent 46 and contaminated soil 14 are thoroughly combined by rotation of the outer wall 80 in conjunction with the auger 82. Other agitation devices for combining the solvent 46 and contaminated soil 14, such as a propeller-type mixer or stirring rod, may be provided.

The auger 82 is comprised of a plurality of blades 84 radially extending inward from the outer wall 80. The auger 82 is driven by the rotational motion of the combining chamber 22. The blade 84 action of the auger 82 acts both to reduce any contaminated soil clumps into a uniform consistency and to mix the contaminated soil 14 with the solvent 46. Alternatively, any other device capable of breaking the contaminated soil 14 into fine particles can be used. For example a hammer mill can be provided externally from the combining chamber 22, which acts to pulverize the soil 14 prior to mixing with solvent 46.

Proper combining of the contaminated soil 14 with the solvent 46 in the combining chamber 22 will result in the formation of the fluidized composition 70. The fluidized composition 70 is transported through the combining chamber 22 by the auger 82 and exits the combining chamber 22 through the transfer duct 50. The transfer duct 50 is preferably located at the rotational center of the combining chamber 22. Alternatively, the transfer duct is connected to the combining chamber 22 at an additional bearing plate (not shown) which does not rotate upon operation of the combining chamber 22.

Operation Of The Aerator As shown in detail in FIG. 3 and FIG. 4, the aerator 24 is a container defined by an outer wall 100 being constructed of high strength, heat resistant material. In the preferred embodiment, polypropylene having a minimum thickness of 0.5 inches is used. However, any other material of appropriate thickness having the ability to withstand internal heat and pressure can be employed. The fluidized composition 70 enters the aerator 24 through the transfer duct 50 and is passed through the aerator 24 by way of gravity and the screw conveyor 54. The aerator 24 is divided into a plurality of aerated chambers 102, 104, and 106, and quiescent chamber 108. The aerated chambers 102, 104, and 106 and quiescent chamber 108 are defined by the outer wall 100 and baffle walls 110, 112 and 114. Each baffle wall is constructed of appropriately dimensioned high strength, heat resistant material. In a preferred embodiment, polypropylene having a minimum thickness of 0.25 inches is used. Each baffle wall 110, 112, and 114 has a strategically placed plurality of openings, each having a diameter of approximately three inches, to promote a serpentine-action fluid flow. For example, baffle wall 110 has openings 116 located on one end while baffle wall 112 has similar openings 118 located at an opposite end.

Forced air is directed into the aerator 24 through the manifold

58. The forced air is passed from the manifold 58 to a plurality of air diffusers 122, 124 and 126. The forced air diffusers are constructed of 304L stainless steel and are diamond in shape, but can assume any shape capable of properly diffusing air. Air is released from each diffuser 122, 124 and 126 by a plurality of ports contained on the diffuser. As the forced air passing through the diffuser 122, 124, or 126 interacts with the fluidized composition 70, the contaminates contained within the fluidized composition 70 are volatized. The volatized contaminants are expelled from the aerator 24 in vapor form through a vent 128.

The aerator 24 is designed to promote a surpentine fluidized composition 70 flow during aeration. As the fluidized composition 70 enters the aerator 24 at the entrance duct 50, forced air is released from the diffusers 122, 124 and 126, thus initiating the volatilization process. The fluidized composition 70 continues to enter the aerator 24, accumulating within the first aerated chamber 102. The level of the fluidized composition 70 will amass within the first aerated chamber 102 until the height of the openings 116 in the baffle wall 110 is realized. Once this height is obtained, the fluidized composition 70 flows through the openings 116, filling the second aerated chamber 104 where volatilization resumes. A similar cycle takes place within the second aerated chamber 104. The fluidized composition 70, while being volatized continues to accumulate until the height of the openings 118 in the baffle wall 112 is reached, thereby causing the third aerated chamber 106 to fill. Finally, after traveling through the third aerated chamber 106 into the quiescent chamber 108 via the openings 120 in the baffle wall 14, the fluidized composition 70 exits the aerator 24 through the exit duct 62. To assist in maneuvering solid particles, such as rocks, through the aerator 24, the screw conveyor 54 along with a tapered floor 130 is provided. Solid particles settle at the center of the aerator 24 along the tapered floor 130. The screw conveyor then forces the solid particles (not shown) through the aerator 24 after which they are removed through the exit duct 62.

The above-described aerator is similar to a commonly known stripping system manufactured by Aeromix Systems, Inc. In other embodiments, the use of a plurality of aerated chambers and a quiescent chamber is not required. Rather, a single chamber in which aeration occurs can be employed.

Example In order to demonstrate the effectiveness of the above- described process, a test was performed in which one gallon of gasoline (BTEX) was added to 5 cubic feet of generic garden soil and a first sample was taken. The contaminated soil was placed in a large tank and thoroughly mixed with water. The entire mixture was then placed in a commonly known aeration device and subjected to forced air flow for 10 minutes. Before the soil dried, a second sample was taken. The two samples of soil taken prior to and following cleaning by the above-described apparatus were tested for contaminant levels by mass spectrography. The following results were obtained:

COMPOUND NAME INITIAL CON.PPB* FINAL CON [:PPB* 9SREMOVED

Benzene 70,000 8.7 99.99

Ethylbenzene 7600 19 99.75

Toluene 130,000 33 99.97

Xyline 94,000 42 99.96 *PPB= parts per billion

Conclusion

The method and apparatus for cleaning contaminated soil of the present invention overcomes the deficiencies of prior systems. Namely, the use of bacteria consuming microbes or strict heat and pressure constraints have been eliminated in favor of a method and apparatus capable of decontaminating soil based upon the volatilization associated with aeration. Large amounts of soil can be cleaned with an effectively constraint-free system, which can be mobilized for transporting to the actual spill site.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the combining chamber can be replaced by any type of container in which soil and solvent are mixed. Similarly, the aerator can be any other type of container into which the fluidized composition is subjected to forced air flow. Finally, the separator, while described as a centrifuge, can assume the form of a variety of devices which promote the evaporation of solvent from soil, or could be eliminated completely.

Claims

WHAT IS CLAIMED IS:

1. A method of removing contaminant from soil, the method comprising: combining the soil with a solvent to form a fluidized composition; and aerating the fluidized composition to volatize the contaminant and remove the volatized contaminant from the fluidized composition.

2. The method of claim 1 further including: separating the solvent from the soil to yield cleaned soil.

3. The method of claim 1 further including: reducing the soil to a uniform consistency before combining with the solvent.

4. The method of claim 2 wherein the combining is performed in a first chamber, the aerating is performed in a second chamber and the separating is performed in a third chamber, the method further including: transporting the fluidized composition from the first to the second chamber; and transporting the fluidized composition from the second to the third chamber.

5. The method of claim 2 further including: recycling the solvent separated from the soil for subsequent combining with contaminated soil.

6. An apparatus for removing contaminant from soil, the apparatus comprising: means for combining the soil with a solvent to form a fluidized composition; means for aerating the fluidized composition to volatize the contaminant and remove the volatized contaminant; and means for separating the solvent from the soil to yield cleaned soil.

7. The apparatus for removing contaminant from soil of claim 6, further comprising: means for reducing the soil into a uniform consistency before combining with the solvent.

8. The apparatus for removing contaminant from soil of claim 6, wherein the means for reducing is an auger.

9. The apparatus for removing contaminant from soil of claim 6 further comprising: means for collecting the volatized contaminant removed from the fluidized composition.

10. The apparatus for removing contaminant from soil of claim 6, further comprising: transportation means for providing continuous transportation of the fluidized composition to the means for separating.

11. The apparatus for removing contaminant from soil of claim 10, wherein the transportation means is an auger.

12. The apparatus for removing contaminant from soil of claim 6, further comprising: means for recycling the solvent separated from the soil by the separating means.

13. The apparatus for removing contaminant from soil of claim 6, wherein the solvent is water.

14. The apparatus for removing contaminant from soil of claim 6, wherein the means for combining the soil with a solvent is a chamber having an auger.

15. The apparatus for removing contaminant from soil of claim 6, wherein the means for aeration is a container having a plurality of chambers.

16. The apparatus for removing contaminant from soil of claim 15, wherein at least one chamber has at least one forced air diffuser.

17. An apparatus for cleaning contaminant from soil, the apparatus comprising: a mixer for combining the soil with a solvent to form a fluidized composition; an aerator for aerating the fluidized composition to volatize the contaminant and remove the volatized contaminant; and a separator for separating the solvent from the soil to yield cleaned soil.

18. An apparatus for cleaning contaminant from soil, the apparatus comprising: an elongated frame; a conveyor for transporting contaminated soil to the frame; a sifter located on the frame for reducing the soil to a uniform consistency; a mixer located on the frame for combining the soil with a solvent to form a fluidized composition; an aerator located on the frame for aerating the fluidized composition to volatize the contaminants and remove the contaminants; and a separator located on the frame for separating the solvent from the soil to yield cleaned soil.