US20100307754A1

US20100307754A1 - Aerosol injection into vadose zone

Info

Publication number: US20100307754A1
Application number: US12/802,358
Authority: US
Inventors: Brian D. Riha; Lawrence C. Murdoch; Richard J. Hall
Original assignee: Clemson University; Savannah River Nuclear Solutions LLC
Current assignee: Clemson University; Savannah River Nuclear Solutions LLC
Priority date: 2009-06-04
Filing date: 2010-06-04
Publication date: 2010-12-09

Abstract

An apparatus and process for delivering aerosol-based amendments into a subsurface region is provided. The apparatus used to form the aerosol has an ability to restrict the aerosol particle size to a preferred particle size range such that undesired particle sizes are not introduced. By maintaining a proper ratio of aerosol particle size to subsurface pore size, the efficiency of an aerosol introduction can be enhanced.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application 61/217,805, filed on Jun. 4, 2009 and which is incorporated herein by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under Contract No. DE-AC09-08SR22470 awarded by the United States Department of Energy. The Government has certain rights in the invention.

FIELD OF THE INVENTION

This invention is directed towards an apparatus and method for introducing amendments into unsaturated subsurface zones. The invention is more particularly directed to the use of specific sizes and ratios of liquids and solid aerosol particles suspended in an injection gas stream. The invention provides a method and apparatus for delivering compounds to the vadose zone to improve remediation. The concept involves delivering compounds by creating small particles, or aerosols, that can be suspended in a flowing gas and injected into the vadose zone. This concept is implemented in a method that involves a device to produce particles of liquid or solid, remove particles above a certain size, and then suspended the remaining smaller particles in a stream of gas. This size fractionated aerosol is then injected into pre-existing vadose zone wells or through a tool pushed into the ground. The aerosol particles flow through pores in the formation along with the gas until they are deposited on the pore walls. Injection is continued until the desired amendment saturations are obtained. This technology has potential application for aerobic and anaerobic biostimulation and bioaugmentation, reactive barrier emplacement, chemical oxidation remediation and vapor intrusion abatement. The invention provides for a useful approach for aerobic and anaerobic biostimulation, bioaugmentation, reactive barrier layers and placement, and chemical oxidation remediation.

BACKGROUND OF THE INVENTION

This invention relates generally to techniques used to introduce amendments into a subsurface region. Conventional methods for introducing amendments into the saturated subsurface do not work well in the unsaturated zone. The inability to distribute amendments in contaminated unsaturated zones has limited the approaches that can be taken towards remediation.
It is known in the art as set forth in U.S. Pat. No. 5,560,737, which is incorporated herein by reference, to create pneumatic fractures within the soil and fill the fractures with aerosols. However, the process set forth in the patent requires a fracturing technique which is time and labor intensive, adds greatly to the cost, and has not been widely used or adopted.
U.S. Pat. No. 7,300,039, which is incorporated herein by reference, discusses generally that aerosols may be injected into a subsurface. However, the general teachings of this patent result in rapid clogging of available pores and thereby limits the distance of penetration of aerosols into the subsurface formation.
Accordingly, there remains room for improvement and variation within the art.

SUMMARY OF THE INVENTION

It is one aspect of at least one of the present embodiments to provide an apparatus and process for delivering to a subsurface liquid and/or solid amendments in the form of aerosols.
It is a more particular object of the present invention to provide a process and apparatus in which a suspension of micron to sub-micron particles suspended in a gas may be introduced into a subsurface zone.
It is yet a further and more particular object of the present invention to provide a process of providing particles that are retained in suspension by Brownian motion, which thereby increases the useful dispersion properties of the particles.
It is yet a further and more particular object of the present invention to provide an apparatus and process in which a liquid phase amendment may be introduced into a subsurface region as an aerosol, the injected aerosol retaining the ability to migrate radially from an injection point such that an injected material may be distributed vertically upward as well as downward and lateral directions.
It is still a further and more particular object of the present invention to provide for an apparatus and process for introducing an aerosol amendment into the vadose zone in which the distribution profile of the injected aerosol is more uniform while avoiding aggregation of introduced materials at a point of injection.
It is a further and more particular object of at least one aspect of the present invention to provide for an apparatus and process in which undesired large particles are segregated during aerosol formation, thereby preventing the introduction of large aerosol particles into the subsurface that may otherwise block the efficient flow of the aerosols through the subsurface pores.
It is yet a further and more particular object of at least one aspect of the present invention to provide for a method and apparatus that allows selection of a desired particle size for introduction into a subsurface. More particularly, it is an object of one aspect of the present invention to select a particle diameter for introduction via an aerosol that is smaller than the size of average subsurface pores within the targeted injection zone.
The following method and apparatus is designed to effectively deliver and distribute amendments to unsaturated subsurface formation materials for the purpose of enhancing remediation of contaminants. The process involves delivering liquid or solid amendments in the form of aerosols as suspensions of micron to sub-micron particles in gas. The particles are retained in suspension by Brownian motion, which decreases the effect of gravity that causes particles to settle out of suspension. Therefore, the transport characteristics of the small particles are similar to that of a gas. Gas containing amendment aerosols is injected into the subsurface, causing each aerosol particle to flow along with the gas until it impacts the solid surface of a soil grain. The injection process continues until the desired amendment concentrations or saturations are achieved. The result is a broad distribution of injected compounds lining pores in the vadose (unsaturated) zone.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A fully enabling disclosure of the present invention, including the best mode thereof to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings.

FIG. 1 is a diagram showing basic properties of an aerosolizer and a fluid that allows control of an average particle size produced.

FIG. 2 is a diagram showing an aerosolizer configuration that allows effective separation and collection of larger particles from flowing gas.

FIG. 3 is a graph showing injection distance of a vegetable oil substrate within a sediment.

FIG. 4 is a graph showing a mass of trichloroethylene (TCE) that can be biodegraded to ethene per mass of vegetable oil

FIGS. 5A and 5B are graphs showing A) the oil and water content of sediments following aerosol injection and B) the particle distributions measured for each corresponding fluid.

FIGS. 6A and 6B are graphs showing A) the water content of sediments following aerosol injection using two aerosolizer configurations and B) the particle distributions measured for water aerosols produced from each corresponding aerosolizer.

FIG. 7 is a graph showing results of particle counts from samples taken at the end of a sand filled column during a transient aerosol injection study.

FIG. 8 is a graph showing A) Water aerosols that initially penetrate through 1 inch of dry sand and B) Water aerosols that initially penetrate through 1 inch of sand that has been coated in vegetable oil.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.
In describing the various figures herein, the same reference numbers are used throughout to describe the same material, apparatus, or process pathway. To avoid redundancy, detailed descriptions of much of the apparatus once described in relation to a figure is not repeated in the descriptions of subsequent figures, although such apparatus or process is labeled with the same reference numbers.
The basic principle behind the jet aerosolization process is to introduce a liquid into a high velocity gas jet (FIGS. 1 and 2). As seen in FIGS. 1 and 2, an aerosolizer 10 which defines the gas inlet 12 is in communication with the gas conduit and a liquid inlet 14 which collectively function together to produce an aerosol 16. As seen in FIGS. 1 and 2, an impaction plate 18 can be positioned in the lower aerosol stream 16. Plate 18 can direct large aerosol particles in an opposite direction from smaller size target particles which can be directed toward an injection well or other below ground injector for delivery into a vadose zone. Various attributes of the aerosolizer construction can be adjusted in an effort to achieve desired resulting particle distribution. Under some circumstances, average aerosol particle size will decrease with increasing gas velocity (function of gas orifice diameter and pressure of gas feed), with decreasing liquid orifice diameter, with decreasing liquid feed rate, with decreasing liquid surface tension, and with decrease in distance between aerosol outlet and impaction place (FIG. 1). The impaction plate is placed in line with the aerosol jet such that larger particles with greater momentum will impact the plate and deposit whereas smaller particles with lesser momentum will flow around the plate along with the gas.
A regulator is used to control the gas pressure feed to the aerosolizer while a positive displacement pump, such as a peristaltic pump, is used to control the liquid feed. The liquid feed may include aqueous solutions, oils, and may also have additives in the form of various chemical additives, microbial additives, and other useful amendments that can facilitate chemical and biological processes in a vadose zone. The aerosolizer is installed onto a chamber such that the smaller particles produced are allowed to flow vertically upward along with the gas while the larger particles are removed and allowed to flow vertically downward to accumulate in the bottom as a liquid (FIG. 2). The chamber can serve solely as a point of liquid accumulation or can be used as a reservoir for liquid that can be pumped out and recirculated through the aerosolizer. Aerosol production is induced by providing constant gas and liquid mass flow rates simultaneously.
The apparatus described above is used to produce aerosols on-site at the ground surface. The gas-feed pressure to the aerosolizer can be adjusted to achieve a desired gas velocity within the aerosolizer. The resulting volumetric gas flow rate and gas velocity through the aerosolizer is then a function of gas orifice diameter, which will tend to range from 0.03 to 0.1 inches depending on injection conditions. Liquid orifice diameter is selected based on desired aerosol particle size distribution, and will tend to range from 0.01 to 0.07 inches or larger.
The pressurized gas used to produce the aerosol can be used to directly inject the aerosols into the vadose zone, or the aerosol-laden gas can be diluted with extra carrier gas if a lower aerosol concentration is desired. The flow rate, aerosol concentration, amendments within the aerosol, droplet size, and timing during injection can be modified based on desired aerosol distribution within the vadose zone and specific vadose zone soil properties. The aerosols can be injected into pre-existing vadose zone wells, or can be injected through a tool pushed into the ground.
The size of liquid droplets created by the aerosolizer can be adjusted by controlling various combinations of gas injection pressure, gas backpressure, liquid feed rate, liquid rheology and position of the impaction plate. The total mass rate of amendment delivered in the carrier gas will then be controlled by implementing the appropriate number of aerosolizers operating simultaneously.
The apparatus and process described above was used to create aerosols of vegetable oil and air, which were injected through a 1.5-meter-long sand-filled column constructed using 2-inch PVC pipe. Samples were taken along the length of the column to determine the distribution of oil. Results from tests involving oil injection at a mass rate of 0.26 g/min for periods of 1 hour and 5 hours showed that oil content within the sediment increases with injection time as seen in FIG. 3. Further, as set forth in FIG. 4, oil concentrations were established that are appropriate for anaerobic biodegradation of chlorinated solvents such as TCE at distances of up to 1.5 meters. This data establishes that oil saturations useful for remediation may be established at significant distances from an injection point.
The present invention has established the importance of controlling aerosol particle size during amendment injection. Water has a higher surface tension than oil, therefore a larger average particle size would be expected when water aerosols are produced from an aerosolizer operated under similar conditions. This tendency is observed in results plotted in FIG. 5B. Water aerosol injection experiments were conducted using configurations identical to those used to generate results for oil aerosol injection. Fluid content analysis indicate that, as compared to oil aerosols, the water aerosols tend to deposit closer to the point of injection with little deposition observed along most of the rest of the column (FIG. 5A). This behavior would be indicative of a greater average particle size distribution for water aerosols, a fact that is confirmed by sampling aerosols of the two fluids using a particle size analyzer (FIG. 5B).
An aerosolizer was constructed with the purpose of producing an aerosol with a smaller average particle size. This aerosolizer (Small Orifice Aerosolizer-SOA) has 0.03 inch diameter gas and liquid orifices and is operated at a smaller liquid flow rate than the aerosolizer used during previously described experiments, which has 0.07 inch diameter gas and liquid orifices (Large Orifice Aerosolizer-LOA). Samples taken using a particle size analyzer show that the SOA produces a particle size distribution with a smaller average size as compared to that of the LOA (FIG. 6B). Injection experiments conducted similarly to previously described experiments also show that water aerosols produced from the SOA tend to penetrate further into the column prior to deposition as compared to aerosols produced from the LOA.
Maximizing the efficiency of aerosolized amendment delivery requires that aerosols are produced within a size range that is deposited with the desired deposition in the subsurface. This size range will be a function of average grain size along with other formation properties, and can be investigated for by conducting aerosol injection experiments. Aqueous aerosols were injected through a sand-filled column while taking samples at the end of the column 1.5 m from the point of injection (FIG. 7). Results from this experiment show that the number of particles reaching the end of the column decreases with time, which is most likely indicative of accumulated deposition near the point of injection. However, the particle size that reaches the end of the column with the highest frequency does not change with time and is estimated to be approximately 0.8 microns by the particle detector. The aerosols in this particular study ranged up to 5 microns in diameter and it is likely that these larger areosols account for the majority of accumulation near the point of injection. An ideal particle size for distribution oil in the column experiment is believed to be up to 3 microns. This range will vary depending on formation properties, fluid properties, and desired aerosol penetration behaviors. However, it appears that under most subsurface conditions it will be important to limit the number of aerosol particles that are greater than approximately 3 microns in diameter to avoid rapid deposition in the vicinity of the point of injections. In coarse grained sands or gravels, the maximum size of aerosol particle may range up to 10 microns
The present invention also has established the importance of considering the affinity that the injected aerosols have for the surfaces of the porous media. Subsurface materials such as quartz sand will tend to be hydrophilic. The comparatively greater affinity of the sand surface to water results in greater deposition rates of water aerosols as compared to vegetable oil aerosols. Coating the sand grains with vegetable oil effectively creates more hydrophobic sand grain surfaces.
This behavior is illustrated in results from tests that involve using the particle analyzer to characterize the water aerosols that initially penetrate through 1 inch of sand (FIG. 8). A greater portion of the particles produced from the aerosolizer penetrate through oil coated sand as compared to the aerosols that penetrate through the dry sand (FIG. 8). The order in which amendments are delivered (Oil aerosols followed by water aerosols for instance), or preparation of subsurface materials for receiving a particular aerosol composition is therefore an important consideration in the delivery process.
Application of this technology in vadose zone formation materials provides important advantages when compared to traditional delivery techniques, which involve injection of continuous liquid-phase amendments. Liquid injected into sandy material in the vadose zone tends to flow vertically downward and so it only affects a small region around the injection point. Amendments injected as aerosols follow the path of the gas flow which are radial patterns in most cases. Injection of liquids in the vadose zone also tends to completely saturate the pore space within the affected volume, whereas distribution from aerosol injection would be more uniform and create lower fractions of liquid saturation that are more effective for remediation.
The same apparatuses could be used to create aerosols from many other liquids, including but not limited to water, oxidants, surfactants, or other liquids that could be useful for remediation. The technique could also be used to deliver small particles of solid compounds by suspending them in the carrier liquid. For example, suspensions of bacteria could be used to create aerosols of bacteria. Solid grains of reactive chemicals, including lime, permanganate, Portland cement, clay, or related materials could be mixed with a carrier liquid and injected as aerosols into the vadose zone.
The present invention offers improvements to the introduction into a vadose zone of materials when compared to traditional delivery techniques, particularly continuous liquid phase amendments. Injected liquids tend to flow vertically downward and will only affect a small region around an injection point. Amendments injected as aerosols can, upon careful selection of aerosol particle size, distribute radially and vertically to affect a much greater area of the vadose zone. The improved distribution of an aerosol injection also maintains a more uniform gradient of introduced materials and at lower saturations. Such distribution and lower saturations provide for a more effective remediation and avoid clogging an injection point or bio-fouling in an injection point from an over concentration of amendments.
It is also recognized that an important aspect of the process and apparatus involves establishing a proper ratio of the particle size of the aerosol relative to an average pore size within a vadose zone. By determining the vadose zone pore size and selecting an appropriate aerosol particle size, the ability of an aerosol to be successfully deployed within a vadose zone is greatly improved.
A variety of carrier gases along with various liquids may be aerosolized and used for injection. The carrier gas and liquid may be selected based upon the particular needs of the application, but the apparatus and process lends itself to any remediation approach that requires distribution of a liquid or a fine-grained solid phase amendment within a vadose zone.
For instance, with respect to a bioremediation process, the carrier gas may be selected based upon the metabolic environment. Atmospheric air or oxygen may be used for aerobic conditions whereas a nitrogen or nitrogen-hydrogen mixture may be used to produce or maintain anaerobic conditions. Likewise, water content may be adjusted or enhanced by injecting aerosolized water.
Biostimulation may be achieved by introducing a pH buffer; an electron donor such as lactate, corn syrup, or vegetable oil; a terminal electron acceptor such as a source of oxygen, nitrate, or sulfate; along with various trace nutrients such as nitrogen, phosphorus, and various metals. Further, bioaugmentation may be achieved by introducing useful microorganisms into the metabolic environment by incorporating microorganisms into the introduced aerosol.
Additional applications include the formation of a reactive barrier within a vadose zone region. By strategic placement of amendments, it is possible to effectively create a barrier to the intrusion of hazardous vapors into buildings, or to prevent contaminate migration downward into ground water. For instance, some contaminants have a tendency to partition into organic fluids, in particular food grade edible oils, and the placement of these materials causes an immediate decrease in vapor phase contaminant concentration. Further, the migration of contaminants into an introduced organic fluid provides an ideal environment for biological activity that can bring about a remediation of the contaminants.
The apparatus and process described herein may also be used to carry out a chemical oxidation by the emplacement of reagents such as potassium, permanganate, or hydrogen peroxide so as to induce an in situ oxidation of contaminants. Similarly, one may maintain a preferred pH level for oxidation by introducing buffers and pH altering reagents into the contaminated zone.
The above-described processes take advantage of the method and apparatus which allows for the introduction of liquid or solid amendments into an aerosol which may be maintained as suspensions of the micron to sub-micron size. The introduced particles are retained in suspension by Brownian motion, which allows for a radial distribution within the soil relative to an injection site. By controlling the aerosol particle size relative to pore size, an optimal level of distribution within the subsurface is possible. Aerosol particles will flow within the gas stream until the particle eventually impacts a solid surface of a soil grain. By using small particle sizes, clogging is avoided and the injection process may continue until there is a broad distribution of the injected materials within the vadose zone.
Although preferred embodiments of the invention have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged, both in whole, or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.

Claims

1. A process of introducing an aerosol into a vadose zone comprising the steps of:

providing an aerosolizer;

using said aerosolizer to select a desired aerosol particle size, said aerosol containing at least one of an edible oil, a bacteria, or a reactive chemical; and,

introducing said component containing aerosol into a vadose zone, said aerosol being distributed in a radial pattern relative to an injection zone site.

2. The process according to claim 1 wherein said step of selecting an ideal aerosol particle size further includes selecting the aerosol particle size based on the size of an average sub-surface pore within a targeted injection zone.

3. The process according to claim 1 wherein said step of selecting a desired aerosol particle size further includes blocking the delivery of particle sizes greater than the desired particle size during the aerosol formation step.

4. The process according to claim 1 wherein said component containing aerosols released into a vadose zone has a particle size distribution that can range from about 0.1 to about 10 microns.

5. An apparatus for generating an aerosol for introducing materials into a vadose zone comprising:

a gas inlet in communication with a gas conduit;

a liquid inlet being in communication with said gas conduit, said gas conduit adapted to receive a liquid from said liquid inlet thereby generating an aerosol stream;

an impaction plate placed within said aerosol stream, said impaction plate directing aerosol particles above a certain target size in a first direction whereas aerosol particles within a target size are directed toward an outlet, said outlet in communication with a conduit for release of the aerosol into a vadose zone.

6. The apparatus according to claim 5 wherein the size of said liquid inlet is adjustable.

7. The apparatus according to claim 5 wherein the pressure of the gas introduced into said gas inlet is variable.

8. The apparatus according to claim 5 wherein a position of said impaction plate relative to an aerosol stream is positionable.

9. The process according to claim 1 wherein said at least one of an edible oil, a bacteria, or a reactive chemical is selected for an ability to remediate a contaminant in situ in a vadose zone.

10. The process according to claim 1 wherein said aerosol containing at least one of an edible oil, a bacteria, or a reactive chemical establishes a barrier layer within the vadose zone to reduce migration of contaminants within said vadose zone.