Liquid purification or separation – Processes – Including geographic feature
Reexamination Certificate
2000-02-16
2002-05-14
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Including geographic feature
C210S758000, C210S763000, C210S170050, C210S908000, C405S128700, C405S128750
Reexamination Certificate
active
06387278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the removal of organics such as oils, including petroleum crude oil and products thereof, shale oils, oils from tar sands and the like, and organic contaminants, from underground accumulations of organics, such as natural subsurface formations and sites of hydrocarbon contamination. The invention is particularly useful for removal of residual organics, particularly constrained organics (those that can not be readily removed, e.g., residual organics) during enhanced oil recovery and soil remediation. The invention further relates to an in situ hydrous pyrolysis/oxidation process useful for partial in situ oxidation of the residual organics to generate surfactant molecules within subsurface water to enhance the mobility of the remaining bulk organic accumulations.
2. Description of Related Art
Subsurface formations that contain accumulations of organics, such as oils or contaminant hydrocarbons trapped therein, can be referred to as reservoirs. Removal of such organics from reservoirs by naturally occurring forces such as expanding high pressure gas and buoyant forces from encroaching water or gravity, is considered a primary recovery technique. Constrained organics are residual subsurface organic compounds retained in the subsurface after oil recovery or contaminant remediation techniques have been applied. These organics are normally in regions of relatively low permeability, or where such compounds remain tightly adsorbed onto surfaces of various mineral phases, or where moderate to low concentrations of the compounds remain behind as dissolved components in the groundwater phase. Such constrained organics are most often the difficult-to-remove residual compounds resulting from leakage or spills of organics, i.e., contaminant hydrocarbons or contaminants, or the difficult-to-produce naturally occurring oils, e.g., petroleum, shale oil, tar sands, bitumen, and the like.
In the former instance, underground fuel storage-tank leakage and industrial spills have posed a serious environmental problem. Fuel leaks contribute significantly to the contamination of groundwater by gasoline, aviation fuel, and other refined petroleum derivatives. Industry, such as electronic, chemical and chemical cleaning plants, are responsible for contamination of ground water with halogenated, typically chlorinated solvents. Many chlorinated hydrocarbons and components of fuels are of particular concern because they are confirmed or suspected carcinogens.
Many systems and methods have been developed to address the problems posed by such contaminated sites. Examples include systems for containment of the contaminants, pump-and-treat technology, methods for enhanced removal such as in situ dynamic underground stripping followed by ex situ treatments of contaminants, and methods for in situ treatments using various chemical and biological agents. Such systems or methods, however, do little for removing all contamination and cannot actually complete the remediation. The methods are unable to destroy or degrade the substantial residual amounts of hydrocarbon contaminants, i.e., constrained hydrocarbons, attached to the rocks, gravel, sand, clay or soil after the major decontamination efforts. A serious problem results because the remaining bulk phase organic contaminants continue to serve as slow release sources for sustained groundwater contamination. Capillary forces hold this free organic liquid tightly in the smaller pore spaces of the rock or soil, resulting in a “residual saturation” of organic liquid, i.e., that which cannot be removed by pumping. This can amount to up to 20% of the liquid present. Thermal remediation methods address this residual contaminant principally by attempting to volatilize it and transport it in the vapor form, a process which is not effective for high-boiling point organics.
Current methods offer only incomplete remediation essentially because much of the subsurface contamination is deeply embedded into soils through diffusion and sorption. When there is free organic liquid present, its release to the aqueous phase may also be limited by solubility. These sorts of limitations are known as mass-transfer limitations. Many of the cleanup methods mentioned above would work if not for these mass-transfer limitations. Thermal methods overcome these mass-transfer limitations by viscosity reduction, accelerating the rates of diffusion and sorption/desorption and by increasing the solubilities and volatilities of the contaminant compounds. Although other oxidative methods have been proposed utilizing permanganate salts, Fenton's reagent, ozone, or other oxidants, they too suffer from the mass-transfer limitations. In addition, they present problems stemming from the inability to mix the reagent with the contaminant in the subsurface.
Attempts to design permanent containment systems for underground contaminants are not practical as such systems need to be properly and continuously maintained and monitored for indefinite periods of time. These systems may hold the contaminants within the system, but they do not remove or degrade them. Consequently, when using this approach, the problem is never solved, but merely postponed. Any major natural disaster, such as an earthquake, may destroy these containment systems and the instant release of large amounts of constrained contaminant may be potentially extremely hazardous to the environment. Clearly, it would be advantageous to have a method available for the removal of these water and soil fuel hydrocarbon and chlorinated hydrocarbon contaminants which overcomes problems currently encountered with containment systems and in situ and ex situ treatments.
Several in situ methods for cleaning-up volatile organic compounds (VOC) involve the application of either heat alone or heat plus water and/or steam to mobilize volatile contaminants. This approach is essentially based on the physical properties of the VOCs. As the name implies, under appropriate conditions these contaminants volatilize. A good example of major efforts for fuel spill decontamination is a recently developed method for in situ dynamic underground stripping (DUS). The method, which is useful for removal of large amounts of volatile contaminants, is described in the Interim Progress Report, DOE publication UCRL-ID-109906 (1991), and in UCRL-1D-118187 (1994). During dynamic underground stripping, a targeted site is heated to vaporize the volatile contaminants. Once vaporized, the contaminants are removed from the spill site by vacuum extraction and treated ex situ. Dynamic underground stripping seems to be the best technique currently available to treat the large fuel spills. The lowest cost for treatment is associated with contaminant recovered as free-product liquid, due to its low total volume for handling. The dynamic underground stripping method alone is highly superior to conventional vacuum recovery. In combination with the current process of the invention, almost complete decontamination can be achieved in a very short time.
One of the major problems facing the remediation of volatile contaminants and solvents is the remaining low concentration of volatiles which, while volumetrically insignificant, can render water undrinkable. The difficulty in removing these residual contaminants (constrained organics), owing to the limitations posed by mass-transfer at low temperature, makes it nearly impossible to remove volatiles from most aquifers down to maximum contaminant levels of the drinking water standards. The cost of the process, and the time to accomplish it, are prohibitive and prevent remediation of low-level contamination using the mass-transfer limited methods.
Another trend in contaminant removal utilizes biological agents such as existing biota, bacteria, etc. For example, U.S. Pat. No. 5,279,740 describes a process for improved removal of contaminants from ground waters. The process utilizes simultaneous introduction of steam and specific nutrients effectively enhancing th
Aines Roger D.
Eaker Craig
Knauss Kevin G.
Leif Roald N.
Newmark Robin L.
Carnahan L. E.
Hoey Betsey Morrison
Thompson Alan H.
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