The present invention is directed to a method and apparatus for extracting contaminants from soil, soil liquids, and/or soil gases, wherein vapor and/or liquid recovered from the ground are pretreated prior to final removal of contaminants. More specifically, the present invention is directed to processes and apparatus for pretreating contaminant-containing gases and liquids extracted from soil, followed by final treatment to remove contaminants. One embodiment of the present invention is directed to an apparatus for extracting contaminants from a stream comprising a contaminant-containing mixture of liquids and gases which comprises: (a) a contaminant-containing mixture input; (b) a vapor-liquid separator receiving the contaminant-containing mixture from the input and producing a liquid component stream at a first outlet and a gaseous component at a second outlet; (c) an optional first contaminant removal system receiving the liquid component stream from the vapor-liquid separator and producing a contaminant-free liquid stream; (d) a vacuum inducing device in fluid communication with the contaminant-containing mixture input and the vapor-liquid separator and receiving said gaseous component from the vapor-liquid separator; (e) a cooling element receiving the gaseous component at a first temperature from the vacuum inducing device and producing the gaseous component at a second temperature from a first outlet and a condensed liquid component from a second outlet, said second temperature being lower than said first temperature; (f) a heating element receiving the gaseous component from the cooling element at said second temperature and producing a reduced-relative-humidity gas component at a third temperature, said third temperature being higher than said second temperature, said heating element having a heating jacket surrounding a conduit through which the gaseous component passes through the heating element, said heating jacket receiving a heating fluid from a first heat fluid conduit into a heating jacket input and outputting said heating fluid from a heating jacket outlet into a second heating fluid conduit; and (g) an optional second contaminant removal system receiving the reduced-relative-humidity gas component from the heating element and producing a contaminant-free gas; wherein the apparatus necessarily includes either the first contaminant removal system or the second contaminant removal system. Another embodiment of the present invention is directed to an apparatus for extracting contaminants from a stream comprising a contaminant-containing mixture of liquids and gases which comprises: (a) input means for inputting the contaminant-containing mixture; (b) vapor-liquid separating means for separating the contaminant-containing mixture into a liquid component stream and a gaseous component; (c) means for inducing a vacuum in fluid communication with the input means and the vapor-liquid separating means, said vacuum inducing means receiving the gaseous component from the vapor-liquid separating means; (d) optional means for removing contaminants from the liquid component of the mixture; (e) cooling means for reducing the temperature of the gaseous component subsequent to exiting the vacuum inducing means, thereby condensing liquid materials from the gaseous component and separating said liquid materials from the gaseous component; (f) means for heating the gaseous component subsequent to condensation of the liquid materials therefrom, said heating means supplying heat generated by said vacuum inducing means; and (g) optional means for removing contaminants from said gaseous component exiting said heating means; wherein the apparatus necessarily includes either the means for removing contaminants from said gaseous component exiting said heating means or the means for removing contaminants from the liquid component of the mixture. Yet another embodiment of the present invention is directed to a process for extracting contaminants from a stream comprising a contaminant-containing mixture of liquids and gases which comprises: (a) providing a contaminant-containing mixture of liquids and gases in fluid communication with a vacuum inducing device; (b) separating the contaminant-containing mixture into a liquid component stream and a gaseous component; (c) optionally removing contaminants from the liquid component stream; (d) transporting the gaseous component through the vacuum inducing device; (e) subsequent to transporting the gaseous component through the vacuum inducing device, cooling the gaseous component from a first temperature to a second temperature, thereby condensing liquid from the gaseous component; (f) subsequent to cooling the gaseous component to the second temperature, heating the gaseous component to a third temperature, said third temperature being higher than said second temperature, thereby reducing the relative humidity of the gaseous component, wherein heating of the gaseous component is accomplished with heat generated by the vacuum inducing device; and (g) optionally removing contaminants from the gaseous stream subsequent to heating of the gaseous component; wherein contaminants are necessarily removed from either the liquid component stream or the gaseous component.
Contaminants can exist in subsurface soil and groundwater in the liquid or vapor phase as discrete substances and mixed with and/or dissolved in groundwater and soil gases. Various contaminants can be found in groundwater and soil, such as volatile compounds, including volatile organic compounds, nonvolatile materials, metal contaminants, and the like. Such contaminants can be found and dealt with in the vadose (unsaturated) zone found between the surface of the earth and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
At many industrial and commercial facilities and at waste handling and disposal sites, soil and groundwater are contaminated with suspended or water-soluble chemicals, or both. A variety of techniques have been used for removal of contaminants and remediation of affected soil. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. For example, in U.S. Pat. No. 4,323,122, it was proposed that a vacuum be applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is lighter than water, would float on the water table and present a layer that could be drawn off by vacuum applied to the liquid at or around that level. U.S. Pat. No. 4,323,122 (Knopik) discloses a system and method for recovering organic liquid such as gasoline which has settled on the water table in underground areas. The system comprises a conduit extending from the ground surface to a point just above the water table, a collection head fitted on the lower end of the conduit, a collection vessel connected to the upper end of the conduit, and an exhaust means for creating less than atmospheric pressure in the vessel. The collection head has a liquid impermeable end portion and a liquid permeable intermediate portion for permitting the passage of liquid. The process comprises providing an opening in the ground to a point beneath the surface of the water table, positioning the conduit with the collection head in place so that the liquid permeable wall of the collection head is just above the surface of the water table, connecting the conduit to the collection vessel intake, and exhausting air and other gaseous materials from the vessel to cause liquid to flow into the collection head through the conduit into the vessel.
Others have suggested the possibility of venting soil above the water table (i.e., in the vadose zone) to cause vaporization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Groundwater requiring treatment is in such processes conventionally removed by pumping from separate conventional water wells. In situations in which water does flow into vacuum extraction wells, it has been suggested that a second, liquid phase pump be placed either in the well or at the surface to remove the water through a second conduit. For example, U.S. Pat. No. 4,660,639 (Visser et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for the removal of volatile contaminants from the vadose zone of contaminated ground by extracting volatilized contaminants from the vadose zone by way of one or more vacuum extraction wells. The process entails drilling one or more wells into the subsurface media in the contaminated area, the well being constructed so that fluids in the vadose zone can flow into the well, whereas the liquid in the saturated zone below the water table cannot substantially flow into the well. The borehole and conduit of the well can optionally extend below the water table, in which case the vacuum applied to the upper portion of the conduit will be effective to draw contaminant from the vadose zone, but insufficient to draw a significant amount of water from the saturated zone into the conduit. If it is desired to remove groundwater from below the water table, this removal is accomplished either by a separate sampling device situated in the borehole or through a separate well.
In addition, Stinson, "EPA Site Demonstration of the Terra Vac In Situ Vacuum Extraction Process in Groveland, Massachusetts", Air & Waste Management Association, Vol. 39, No. 8, pages 1054 to 1062 (1989), the disclosure of which is totally incorporated herein by reference, discloses an evaluation of an in situ vacuum extraction process. The process entails removal of contaminants from the vadose zone by vacuum. Wells are installed in the contaminated vadose soil. A vacuum pump or blower induces air flow through the soil, stripping and volatilizing volatile organic compounds from the soil matrix into the air stream. Liquid water, if present in the soil, is also extracted along with the contamination. The two-phase stream of contaminated air and water flows to a vapor/liquid separator where contaminated water is removed. The contaminated air stream then flows through a treatment system such as gas-phase activated carbon to remove contaminants from the air stream. The clean air is exhausted to the atmosphere through a vent. U.S. Pat. No. 4,593,760 (Visser et al.), the disclosure of which is totally incorporated herein by reference, and U.S. Pat. No. Re. 33,102, the disclosure of which is totally incorporated herein by reference, also disclose processes for removal of volatile contaminants from the vadose zone of contaminated ground by pumping volatilized contaminants from the vadose zone using one or more vacuum extraction well.
"Forced Venting to Remove Gasoline Vapor from a Large-Scale Model Aquifer," American Petroleum Institute, Health and Environmental Sciences Department, API Publication No. 4431 (1984) discloses the results of experiments examining forced venting of air through the soil above a gasoline spill in a model aquifer. Various flow rates and geometries for the venting plumbing were used to determine the most efficient method of removing gasoline from the underground environment and lowering gasoline vapor concentrations in the unsaturated zone above the spill.
"Venting for the Removal of Hydrocarbon Vapors from Gasoline Contaminated Soil," J. Thornton and W. Wootan, J. Environ. Sci. Health, A17(1), 31-44 (1982) discloses the results of an experiment investigating the use of a venting strategy to remove gasoline vapors from contaminated soil strata. A contained gasoline leak was created in a large outdoor facility which simulates soil strata and a static water table. An air flow was established, and vapor samples taken before, during, and after venting were checked for hydrocarbon content.
U.S. Pat. No. 5,050,676 (Hess et al.) and U.S. Pat. No. 5,197,541 (Hess et al.), the disclosures of each of which are totally incorporated herein by reference, disclose apparatus and processes for two phase vacuum extraction of contaminants from the ground which entails vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluents. Two phase vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing.
U.S. Pat. No. 5,172,764 (Hajali et al.), the disclosure of which is totally incorporated herein by reference, discloses an apparatus and process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table which comprises providing a borehole in the contaminated area; placing in the borehole a perforated riser pipe inside of which is situated a vacuum extraction pipe with an opening situated near, at, or at any point below the water table within the perforated riser pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams.
U.S. Pat. No. 5,076,360 (Morrow), the disclosure of which is totally incorporated herein by reference, discloses methods and apparatus for vacuum extraction of contaminants from the ground which, in a preferred embodiment, entails vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluent. A primed vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing utilizing a priming tube which introduces air or other gas to the liquid collected at the bottom of a well. The method permits vacuum extraction of both liquids and gases from the subsurface by way of wells having a liquid layer which is more than thirty feet below the soil surface or in which a screened interval of the extraction pipe is entirely below the liquid surface.
U.S. Pat. No. 5,271,467 (Lynch), the disclosure of which is totally incorporated herein by reference, discloses methods and systems for recovering groundwater, gases and vapors from subsurface locations in a single, integrated operation by applying a vacuum to groundwater recovery wells. Selective recovery of specific contaminants from zones of interest containing high levels of those contaminants is achieved by manipulating the local water table level. Groundwater recovery systems may also utilize eductor systems having venturi nozzles that create a vacuum networked. A plurality of such recovery wells operated using eductor systems may be operated by a single pump at or above grade level. In this fashion, a network of recovery wells may be operated using a single pump and control system. The recovery methods and systems are preferably utilized in association with known contaminant removal systems to provide complete removal of contaminants and improved remediation efficiencies.
Copending application U.S. Ser. No. 08/056,349 (Mancini et al.), filed Apr. 30,1993, entitled "Improved Process and Apparatus for High Vacuum Groundwater Extraction," the disclosure of which is totally incorporated herein by reference, discloses a process and apparatus in which vacuum extraction is used to remove soil contaminants in both the saturated and vadose zones. One embodiment of the invention is directed to a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table, which comprises providing a borehole in the contaminated area to a depth below the water table; placing in the borehole to a depth below the water table a perforated riser pipe inside of which is situated a vacuum extraction pipe with a bottom opening situated within the perforated riser pipe, said vacuum extraction pipe containing groundwater prior to application of a vacuum thereto, said vacuum extraction pipe having at least one gas inlet situated below the groundwater level in the vacuum extraction pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a two-phase common stream; introducing a gas into the vacuum extraction pipe at a level below the groundwater level in the vacuum extraction pipe to initiate two-phase flow within the vacuum extraction pipe; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams.
Processes are also known for treating soil gases and/or liquids containing contaminants. In processes wherein both gaseous and liquid phase contaminant-containing materials are brought to the surface, the gaseous and liquid phases generally are separated and treated separately. For example, in two-phase extraction processes, such as those disclosed in U.S. Pat. Nos. 5,050,676, 5,197,541, 5,172,764, and 5,076,360, subsequent to extraction, frequently the contamination resides predominantly in the vapor phase, which requires vapor phase treatment prior to discharge to the atmosphere. Treatment performance can be affected significantly by the conditions of the vapor stream treatment process. For example, in a typical process, the gases and liquids are drawn from the ground with a high vacuum capacity pump, typically one with a vacuum capacity of over 20 inches of mercury, such as a liquid ring pump employing water as the seal liquid, and subsequent to separation of the liquid and vapor phases, the vapor phase is treated with carbon filters. Treatment efficiencies, however, frequently are poor. The vapor phase, which under vacuum exits the ground at a temperature of about 55.degree. F. and a relative humidity of about 100%, passes through the vacuum pump, where its pressure and volume are changed. The pressure and volume changes result in a change in saturation temperature (the temperature where the relative humidity is 100%) to a temperature typically above 100.degree. F. The vapor phase may be further heated to decrease its relative humidity to a value more favorable for carbon filter treatment, such as about 40 percent, to maximize carbon absorption efficiency. To achieve this relative humidity, however, the vapor stream typically is heated to temperatures of about 140.degree. F., which is significantly higher than the temperatures at which carbon absorption efficiency is maximized, typically about 70.degree. F. To overcome this difficulty, it has been proposed to situate the carbon filters in the treatment system such that the vapor phase stream passes through the carbon filters prior to passing through the vacuum pump, thereby taking advantage of the relatively low temperature of the vapor stream at this point in time. This approach, however, also results in reduced carbon absorption efficiency, since at this stage in the process the vapor stream is still under high vacuum conditions, and volatile organic compound contaminants tend to be stripped out of carbon filters under high vacuum conditions.
Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for extracting liquid contaminants, gaseous contaminants, or both from soil (including both particulate soil and bedrock). In addition, a need remains for processes and apparatus for pretreating contaminated liquids and gases obtained from soil with increased efficiency. Further, there is a need for processes and apparatus for pretreating gaseous materials containing contaminants extracted from soil (including both particulate soil and bedrock), soil liquids, and/or soil gases. Additionally, there is a need for processes and apparatus that enable control of the relative humidity and temperature conditions of gaseous materials containing contaminants extracted from soil (including both particulate soil and bedrock), soil liquids, and/or soil gases prior to final treatment to remove the contaminants. There is also a need for a system for treating soil, soil liquids, and/or soil gases containing contaminants wherein the processes and apparatus employed exhibit process flexibility, thereby rendering the apparatus and processes amenable to alternative treatment processes at optimum conditions. In addition, there is a need for processes and apparatus for pretreating gaseous materials containing contaminants extracted from soil, soil liquids, and/or soil gases which enable the use of carbon filters at enhanced efficiencies. Further, a need remains for processes and apparatus for recovering free phase contaminants from liquid and gaseous sources and reduce final treatment requirements. For example, recovery of free phase contaminants from liquid and gaseous sources can provide a recyclable process stream and reduce the quantity of contaminants requiring final treatment. In addition, there is a need for processes and apparatus for pretreating contaminated liquids and/or gases that exhibit process flexibility which enhances the performance of all existing vacuum based remediation technologies. There is also a need for processes and apparatus for pretreating contaminated liquids and gases obtained from soil with reduced energy requirements. Additionally, a need remains for processes and apparatus for pretreating contaminated liquids and gases obtained from soil which enable relative humidity conditioning of the gaseous phase at reduced cost. There is also a need for processes and apparatus for pretreating contaminated liquids and gases obtained from soil which employ relatively compact, reduced-space equipment. It is particularly desirable for the entire vacuum extraction system and vapor phase conditioning system to be combined onto a single skid unit that enables portability of the system without losing effectiveness, and which also enables reduced investment cost.
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