WO2014197913A1 - Contaminated soil remediation and oil recovery process - Google Patents

Abstract

Disclosed are methods and systems for treating contaminated and salty soil(s), particularly those contaminated with heavy, weathered crude oil to provide for 1) recovery of the oil contained therein, 2) a substantial reduction in the salt content of the cleaned soil and 3) high water recycle rates to allow for economical use in arid regions of the world.

Description

CONTAMINATED SOIL REMEDIATION

AND

OIL RECOVERY PROCESS

STATEMENT OF PRIORITY

This application claims priority pursuant to 35 U.S.C. § 119 to U.S. Provisional Appl. No.

61/832,440, filed June 7, 2013, the contents of which are incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The invention is directed to remediation of salty soil contaminated with heavy, weathered crude oil and recovery of the oil contained therein, specifically a soil remediation and oil recovery process that can remove high levels of weathered crude oil from soil, and substantially reduce the salt content of the soil by utilizing a solvent based extraction technique combined with specific processing equipment.

BRIEF SUMMARY

The invention is directed to remediation of salty soil contaminated with heavy, weathered crude oil and recovery of the oil contained therein, specifically a soil remediation and oil recovery process that can remove high levels of weathered crude oil from soil, and substantially reduce the salt content of the soil by utilizing a solvent based extraction technique combined with specific processing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the invention are described more fully below with reference to the attached drawings in which:

FIG. 1 illustrates an overview of inputs and outputs of the various sub-processes incorporated in an embodiment of the process, specifically Soil Preparation, Soil Scrubbing, Liquid-Solid Separation, and Water Treatment, and further illustrates the relationship between these sub- processes;

FIG. 2 illustrates an embodiment of the Soil Preparation sub-process;

FIG. 3 illustrates an embodiment of the Soil Scrubbing sub-process;

FIG. 4 illustrates an embodiment of the Liquid-Solid Separation sub-process; and

FIG. 5 illustrates an embodiment of the Water Treatment sub-process.

As will be appreciated by those skilled in the art, additional process equipment will typically be required for successful operation of the disclosed process, but the selection and use of such equipment is within the ability of one of ordinary skill in the art and a routine part of designing an operating facility and bringing it online. As a consequence, detailed discussion of such routine equipment and operations is deemed unnecessary.

It should also be noted that these FIGURES are intended to illustrate the general characteristics of the methods disclosed and certain example embodiments of the invention in order to supplement the detailed written description provided below and should not, therefore, be applied to limit the scope of the invention unduly. DETAILED DESCRIPTION

As noted above, FIG. 1 is an overview of the four sub-processes. The sub-processes preformed sequentially, and include Soil Preparation, Soil Scrubbing, Liquid-Solid Separation and Water Treatment modules. Major inputs into the Soil Preparation module are an oil-contaminated soil characterized by an oil content that can be 500,000 mg/kg or even greater and a wash solution.

The contaminated soil and/or other material(s) may be further characterized by the type(s) and size distribution of particles found within the soil. These particles may range from clay particles of less than 1 micrometer in size to particles including, for example, agglomerates, as large as 10 cm in diameter.

The contaminated soil and/or other material(s) be further characterized by the nature of the contaminating species. For example, the contaminated material(s) may have been heavily weathered after the initial contamination, a process during which the more volatile components of oil (typically CI to C18 compounds, for example) have been evaporated or, in contrast, may represent a relatively recent deposit in which some, and possibly many, of the volatile components absent in weathered soil will still remain in the contaminated soil. As will be appreciated, in those contaminated materials that have been the subject of repeated episodes of contamination, the nature of the contamination will include both weathered and more recent exposures. This combination of contaminate exposures will, in turn, tend to complicate the hydrocarbon profile within the contaminated materials. The second major input is specialized surfactant/solvent mixtures that can be modified to some degree to improve the performance against a particular blend of contaminants. These surfactant/solvent mixtures can be mixed individually into an aqueous solution and/or may be added in one or more prepared compositions or "master batch(es)" during operation of the Soil Preparation sub-process. Certain example embodiments of these mixtures will be further described in the detailed discussion below.

The major outputs of the disclosed process(es) are cleaned soil and/or soil particles, recovered oil and a recycle water stream. When operating properly, the disclosed process(es) will produce cleaned soil and/or other materials that has/have been cleaned to a degree sufficient to meet the client's and/or relevant regulatory requirements. These requirements may include, for example, a substantial decrease in the residual oil concentration to, for example, a level of less than 2,500 mg/kg although lower levels of, for example, less than 1,000 mg/kg and even as low as less than 100 mg/kg may be achieved. As noted above, another major output of the disclosed process(es) is the recovered oil and other hydrocarbon components that have been removed from the soil. This recovered oil may be subjected to recycling and/or further processing. The outputs from the water treatment sub-process, however, include a recycle water stream and, when the mineral/salt content of the contaminated soil and sludge is elevated, a concentrated brine stream that can, in turn, be subject to additional processing to recover the salts.

DETAILED DESCRIPTION

SOIL PREPARATION

FIG. 2 illustrates an embodiment of the basic process in which the soil, sand, or other granular or particulate material contaminated with heavy oil(s) and/or salt can be treated. The soil or other granular or particulate matter (hereafter "soil") is first excavated using conventional methods. Then the soil is prepared for washing by screening out oversize debris including, for example, particles having a size in excess of 10 mm in size and/or ferrous debris, adding water and an appropriate washing chemical composition based on factors including, for example, the degree of weathering of the contaminated soil and the amount of oil in the soil to form a slurry. This slurry may then be subjected to a secondary screening for removing the larger of the cleaned particles, e.g. , those particles characterized by a size distribution falling between, for example, 4.75 to 10 mm in size. The relatively smaller surface area to volume of these larger removed particles tends to provide better contaminant removal than that achieved with the smaller particles removed. Accordingly, the cleaning of these larger particles is typically sufficient without the need for the additional processing to which the smaller particles must be subjected to obtain similar degrees of contaminant removal.

The washing chemical is selected based on the amount and type of oil in the soil and the degree of weathering of the oil. Since these two factors vary from location to location and may even vary month-to-month or week-to-week at a given location, empirical testing is routinely used to determine the washing chemical composition. The washing chemical composition must satisfy two criteria. First, it must not emulsify the type(s) of oil or other hydrocarbon contaminants found in the soil. Second, the specific gravity of the resulting combination of washing chemical composition and oil that is cleaned must be less than about 1.0. When these two conditions are satisfied, the oil removed from the particles during the washing operation will float to the surface of the slurry mixture where it can be skimmed off for reclamation and further processing.

For soils with relatively low amounts of oil contamination, e.g. , less than 20,000 mg/kg and negligible salt, a washing chemical composition consisting of, for example, 5 to 15% of one or more glycol ethers, 1 to 5% of one or more alkoxylated alkanolamides, 1 to 5% of one or more block co-polymer nonionic surfactants, and 0.1 to 2.0% of one or more oxide block co-polymers, all percentages being by volume, dispersed in 75 to 90% water is used. It is anticipated that successful cleaning may be achieved using a usage rate or application rate of from 1.0 liters/metric ton to 5.0 liters/metric ton. This application rate may be adjusted empirically during operation to attain the desired level(s) of cleanliness which commonly are less than 2,500 mg/kg petroleum hydrocarbon content, but may be as low as 100 mg/kg. This operation may also be conducted in several stages with different application rates and/or washing chemical

compositions to achieve improved cleaning performance.

For soils that can be described as sludge with oil contamination in the range of 20,000 mg/kg to 150,000 mg/kg and negligible salt, a chemical mixture consisting of 60 to 90% hydrotreated heavy naphtha, 15 to 30% of one or more glycol ethers, and 2 to 5% of one or more low foaming non-ionic surfactants, all percentages being by volume, may be used. The usage rate ranges from 1.0 liters/metric ton to 5.0 liters/metric ton and is adjusted empirically during operation to attain desired levels of cleanliness which commonly are less than 2,500 mg/kg petroleum hydrocarbon content, but may be as low as 100 mg/kg. As noted above, this operation may also be conducted in several stages with different application rates and/or washing chemical compositions to achieve improved cleaning performance.

For soils having a salt content from 1,000 mg/kg to 5,000 mg/kg and nominal oil contamination, a cleaning chemical composition consisting of 1 to 15% diethylenetriaminepentaacetic acid, 1 to 2 % of a blend of naturally occurring humus based acids, and 60 to 90% water, all percentages being by volume, may be used. For higher concentrations of salt in the range of, for example, 5,000 mg/kg to 10,000 mg/kg, the amount of humic based acids in the cleaning chemical composition can be increased to 2 to 3%. For extremely high salt concentrations, e.g. , those having a concentration in excess of 10,000 mg/kg, the amount of humic based acid is increased to 3 to 5%. The usage rate ranges from 1.0 liters/metric ton to 5.0 liters/metric ton and may be adjusted empirically during operation to attain desired levels of cleanliness which commonly are less than 2,500 mg/kg petroleum hydrocarbon content, but may be as low as 100 mg/kg. The residual salt content in the decontaminated soil is commonly desired to be less than 1000 mg/kg so as not to suppress the growth of vegetation. This operation may also be conducted in several stages with different application rates and/or washing chemical compositions to achieve improved cleaning performance.

For particularly heavily contaminated soils wherein, for example, the oil content is 20 to 60% or more, a booster chemical composition consisting of, for example, 60 to 95% of one or more methyl esters and 5 to 40% of one or more glycol ethers monoisopropanolamide alkoxylates, all percentages being by volume, may be used. In this situation, the booster chemical composition is added to the washing chemical composition in an overall proportion of 50% up to 100%, e.g. , volume ratios of 1 :2 to 1 : 1. For the most difficult situations, those situations in which the soil(s) has 60% or greater oil that has been heavily weathered by evaporation of carbon molecules smaller than C18, the booster chemical composition may be used in place of the usual washing chemicals. In such a case the amount of chemical used is adjusted empirically during operation to attain desired levels of cleanliness, commonly 2,500 mg/kg petroleum hydrocarbon residue in the soil, but as little as 100 mg/kg remaining oil content. This operation may also be conducted in several stages with different application rates and/or washing chemical compositions to achieve improved cleaning performance. In the case of exceptionally weathered soil wherein the soil is so contaminated and weathered that it is similar to a hard tar-like material, the tar- like material is first processed through a machine similar to a plow mixer or equivalent prior to further processing. The objective of this processing is to fractionate or physically disrupt the acquired structure of the tar- like material to obtain a smaller size distribution, e.g. , having a characteristic particle diameter of 2 mm or less. This is done in order to expose more surface area to the effect of the selected chemical(s), as well as to homogenize the distribution of the contaminant throughout the solids matrix and to further soften and dissolve the oil from the solid particle surfaces. It is noteworthy that this operation may be conducted without using heated components or heating processes, thereby tending to reduce the energy necessary to operate this process. This is particularly important because heating the oil/hydrocarbon contaminants tends to increase volatilization of compounds that are potential air pollutants unless condensed and removed or otherwise addressed prior to discharge to the atmosphere.

SOIL WASHING-SCRUBBING

The prepared soil together with washing chemical is then processed as depicted in FIG. 3. The soil first passes through an attrition scrubber which, using counter rotating action, causes the oiled solid particles to rub against each other. The effect of the rubbing friction, combined with the dissolving action of the washing chemicals, is to remove oil from the solids and entrain the oil into the liquid phase.

From the attrition scrubber, the oil, chemical, and solids are conveyed through a flotation process that allows the released oil to float to the surface of the mixture where it is skimmed off using conventional equipment and collected in a tank for recovery/recycling. The solid phase, which may still contain some oiled particles, is conveyed through hydrocyclones which separate the solid particles from the aqueous/chemical phase of the slurry. The liquid so removed is recycled to the beginning of the skimming process in order to collect additional oil for recycling. The solid particles separated by the hydrocyclones are directed to the soil washing machine.

As the solid particles, still containing some attached oil, flow through the soil washing machine, the particles are bombarded with 2 to 8 water jets at a pressure of approximately 700 bar and a flow rate of approximately 125 liters per minute. The optimal solids content of the flow through the soil washing machine ranges from 5 to 10% by volume. The effect of the resulting high- energy impact forces is to strip the remaining oil from the solid particles. The oil, water, and solid particles are now ready for the next major step in the cleaning process, liquid-solid separation.

LIQUID-SOLID SEPARATION

FIG. 4 illustrates the separation of the washed solid particles from the liquid phase using conventional means. The sub-process may consist, for example, of a series of hydrocyclones which are sized to successively remove particles larger than, for example, 150 microns, then particles larger than, for example, 75 microns, and finally particles larger than, for example, 37 microns. As will be appreciated, the number of hydrocyclones and the actual particle sizes removed at each step may be adjusted based on available equipment, recognizing that 37 microns is a currently considered a practical limit to the smallest particles that can be removed using this conventional technology. These size points may be varied depending on the size and density characteristics of the solid particles being cleaned. Speaking generally, particles less than 37 microns in size are difficult to recover using hydrocyclone technology. In all cases the recovered solids are collected for reuse. Particles smaller than 37 microns are processed through a conventional centrifuge after emerging from the final hydrocyclone. The centrifuge processing is intended to capture particles as small as 5 - 8 microns in size.

Depending on the particle size distribution of the incoming solids, it may be that a proportion consists of very fine clay particles in the range of 1 to 15 microns in size. If this is the case, up to 50% of the small particles may not be captured in the hydrocyclone/centrifuge process. It also may be that the extremely fine clay particles retain an amount of oil bound to their surfaces that exceeds the amount of residual oil that is allowed by the cleanliness standard being employed. In that case, the solid particles emerging from the 37 micron hydrocyclone step are directed to an apparatus first revealed in U.S. Patent No. 6,325,079 Bl, entitled Apparatus and Method for Removing Contaminants from Fine Grained Soil, Clay, Silt, and Sediment Particles, the contents of which are hereby incorporated by reference in their entirety. This apparatus uses collision forces to desorb the remaining oil from the fine clay particles and place the oil in the water phase. The resulting slurry stream is then centrifuged to finally separate the liquid and solid particles, with the solid particles being directed to recovery and the liquid stream being further directed to the last major process, water treatment.

WATER TREATMENT

FIG. 5 illustrates the process for treating the liquid phase of the treatment stream, for purifying the water for recycling, and for removing sludge for disposal. The general situation prior to treating the water is that the cleaned solid particles have been removed from the slurry stream down to approximately 5 to 10 microns in size. The remaining solid particles are then removed from the slurry stream using conventional water treatment technology consisting of polymer addition, clarifying, removing oil with a coalescing filter, filtering using a combination of filter presses and bag filters. The fine solids removed in this manner may be disposed as waste if they exceed a prescribed cleanliness level or, if the solids meet the prescribed cleanliness levels may be added to the reclaimed soil or used in other processes as a separate component.

Substantially all solids have now been removed from the slurry stream. In the case where the contaminated soil had high salinity, the salt is dissolved in the water stream and must be removed. This may be accomplished using conventional technology consisting of an ultrafiltration unit and a desalination unit. The outputs of the desalination unit are desalinated water and a concentrated brine from which the salt(s) may be recovered by evaporation.

It is anticipated that application of the processes, methods and systems disclosed herein may be operated in a manner to achieve: a. removing 90% to 99% of the oil from the soil particles and recovering the oil in a manner that will allow the recovered oil to be recycled through

conventional refining processes; b. cleaning the solid particles to a degree sufficient to render them suitable for reuse as part of a manufactured soil process or other use wherein solid soillike particles are required; and c. recovering the majority of the water used in the process for recycling

through the process and/or otherwise made available for reuse as clean water. It will be appreciated by those skilled in the art that various other modifications of the basic processes as detailed herein may be made to adapt the disclosed processes for specific applications without departing from the nature and spirit of this disclosure.

Claims

CLAIMS I claim:

1. A method for cleaning contaminated soils, the method comprising: screening the contaminated soil to obtain a first sized soil stream; combining the sized soil stream with a cleaning composition to prepare a slurry; removing a portion of the larger particles from the slurry to obtain a second sized soil stream; high energy cleaning of the second sized soil stream; recovering the separated oil; and concentrating residual salts into a brine solution.