Application of Flotation-Agglomeration method in soil remediation

EXECUTIVE SUMMARY 

The agglomeration-flotation method of soil remediation has been proven as one effective method of cleaning grossly contaminated soil of many different types, from beach sand, silty loam, to contaminated Kuwaiti soil. Our previous application of this method has successfully reduced the oil content of Sucarnoochee soil from Sumter County, Alabama, from 15-wt% crude oil to 170 ppm in the laboratory [1]. A model has also been developed that predicts the oil concentration in soil after remediation as a function of the process variables.

In order to study the applicability of this method on a commercial scale, the laboratory batch process that was previously modeled needs to be scaled-up to industrial size, and must be converted into a continuous and steady process so that more soil could be remediated and the capital and operating costs be reduced. With these two strategic goals in mind, our current plan is to procure further funding so that we can build and test a trailer-mounted field demonstration unit. Our student will design, cost, procure and build the unit, and participate with oil field operators and the Alabama State Oil and Gas Board in trial-run clean-ups at several sites in Alabama, including weathered sites.

Considering the cost of developing the project, we propose a budget that averages $100,000 per year for the 2000, 2001 and 2002 three-year period.

INDRODUCTION AND OBJECTIVES

Contamination of soils with crude or refined oil products is a problem often associated with production, refining, and distribution of petroleum hydrocarbons. In the gulf coast region, numerous oil production sites are covered with oil-soaked soil due to historically routine operations such as testing well deliverability by flowing to pits, dumping untreatable emulsions in pits, or due to leaky pumps and flow lines. There are now several technologies available for remediating grossly contaminated soil sites, such as bioremediation [2], hot-water washing or incineration [3,4], yet all have their limitations either in effectiveness or in cost.

The petroleum coke/fine coal agglomeration-flotation process has broken through the limitations of the aforementioned technologies. Researchers at the University of Alabama have remediated Sucarnoochee soil from Sumter County, Alabama, and reduced oil content from 15 wt% to 170 ppm. Recently, a model has been developed to predict the oil concentration in soil after remediation as a function of the process variables. One of our graduate students, Vencent Newbill, developed a model using Microsoft Excel that calculates the flow rate, composition, and temperature of all process streams [5]. It also calculates the size and energy consumption of each piece of equipment.   Cost studies have been also performed by Vencent Newbill to determine major cost sources. Compared to other remediation methods, agglomeration-flotation soil remediation was found to be lower in cost and more effective. Newbill concluded that the agglomeration-flotation method is an acceptable remediation method. It is recommended that a pilot-scale process be built so that the operation of an industrial-size unit can be further refined before it is built.

STATEMENT OF NEED

Contamination of soils with crude or refined oil products is a problem often associated with production, refining, and distribution of petroleum hydrocarbons. In the gulf coast region there are numerous oil production sites with oil-soaked soil due to historically routine operations such as testing well deliverability by flowing to pits, dumping untreatable emulsions in pits, or due to leaky pumps and flow lines. Bioremediation is effective only in lightly contaminated soils, since gross contamination kills the requisite bacteria. Gross contamination of soil must be handled by physical cleaning techniques such as hot-water washing or incineration. However, hot-water washing is effective only with large grain-size soils such as sand and the recovered oil is difficult to handle. Incineration of the soil is effective, yet expensive. Besides, the energy value of the oil is lost and air may be polluted. Therefore seeking an alternative oil cleaning method is of absolute necessity.

TECHNOLOGY TRANSFER PLAN

With the objectives of scaling up previous laboratory batch process and of converting it into a continuous and steady process, our immediate plan is to construct a trailer-mounted portable agglomeration-flotation soil remediation process field-test unit and conduct a soil remediation field-test in the oilfields of South Alabama. A trailer-mounted unit can be cheaply built with off-the-shelf components. This process is low cost, portable, applicable to a variety of soil types, capable of handling high levels of gross contamination with heavy hydrocarbons and recovers the oil in the form of an easily transportable fuel.

Approach

Since 1991 researchers at the university of Alabama have been working on cleaning-up of oil-contaminated soils with the method of agglomeration-flotation (Rahnama and Arnold, 1993; Narayanan et al., 1994; Narayanan and Arnold, 1997; Prasad and Arnold, 1997) [6, 7, 8, 1]. In this technique, fine coal or fine petroleum coke is blended with oil-contaminated soil in hot water slurry. The oil agglomerates with the fines and is then returned to the earth. The method has been successfully demonstrated with artificially contaminated beach sand, silty loam and Sucarnoochee soil.  Tim Dean (1997) [9] and Niraj Prasad (1997) [10] studied the optimization of one-step and two-step processes of this agglomeration-flotation method at the bench scale.   Ravi (1998) applied this method in soil sampling in south Alabama oil fields and remediated the contaminated soil from 34-wt% crude oil to 2000 ppm  Since the focus of this proposal is to design a continuous steady state process and scale-up to an pilot-sized unit, the model developed by Vencent Newbill will be used to calculates the flow rate, composition, and temperature of all process streams, as well as to calculates the size and energy consumption of each piece of equipment, and the major cost contributors.

Methodology

                Figure 1 is a schematic of the proposed continuous coke/coal agglomeration-flotation soil remediation process.

Figure 1. Process flow diagram of the continuous one-step process.

Once the characteristics of all streams and the size of equipment have been established, the cost of each piece of equipment can be determined.  Two methods are used to estimate the capital and operating costs. The first method is a quote from a vendor. If at all possible, a vendor can be found that sells the particular type of equipment. The vendor will then able to provide the exact up to date equipment cost. For some pieces of equipment, a vendor may not be found or is not very responsive. In that case, the cost curves from Peters and Timmerhaus(1991) is used. When using quotes for cost estimation, the size of the equipment that was quoted may not be correct. The cost must be adjusted under these circumstances. Equation 1 can be used if the cost needs to be scaled for equipment size (Peter & Timmerhaus, 1991)

Cost if equip a = cost of equip b      (1)

Figure1. Comparison of remediation costs of the competing soil remediation methods

Seven competing technologies have been studied. Figure 2 is a graph showing the remediation cost for each method as compared to the continuous one-step agglomeration-flotation soil remediation method. There are two methods, isolation/containment ($80/ton) and solidification/stabilization ($100/ton), with lower remediation costs than the agglomeration-flotation method ($116/ton). However, both of those methods do not remove the contaminants from the soil and may not be stable over a long period of time. The closest methods to agglomeration-flotation are high temperature thermal desorption and chemical extraction, each costs $170/ton. High temperature thermal desorption is not very effective in remediating heavy hydrocarbons such as crude oil since they are involatile. It also is a source of air pollution because it simply transfers contamination from the soil to the air. Soil washing is effective, but causes water pollution problems. Chemical extraction not only costs $250/ton, which is much higher than agglomeration-flotation, but also involves pollution transfer. The remediated soil is often contaminated with organic solvents after processing, and the solvent must be treated because itself is also contaminated. In situ verification ($370/ton) is much like solidification/stabilization in that the contaminants are trapped in the soil and not removed. Thermal treatment of incineration is the only method that can completely remove all hydrocarbons, but it destroys the soil. It also causes and air pollution problem because the contamination is only transferred from one place to another.

Agglomeration-flotation does not have any of these problems. It has a low remediation cost at $116/ton. The contaminants are collected by the petroleum coke and can be burned as fuel. The water stream from the process is not contaminated with surfactants or solvents. The residual oil concentration after remediation is as low or lower that the other methods except for incineration. Its benefits are:

1.        it makes use of petroleum coke that is otherwise a disposal problem.

2.        petroleum coke/oil agglomerates can be processed and used as fuel.

3.        it is an effective technique for remediation of gross, heavy crude oil contamination.

4.        it is quicker than most other physical cleaning methods.

5.        pollution not transferred to other areas (air or water).

Relationship to previously sponsored GCHSRC activities

Two projects of ours are currently sponsored by GCHSRC. One is “Soil Sampling in South Alabama Oil Fields”. The purpose of which was to find good candidate sites for applying the method of agglomeration-flotation. Samples from contaminated sites were cleaned in the laboratory to determine the effects of soil type, oil type and weathering on the effectiveness of the method. Six parameters were studied in the one-step process of field sample remediation by agglomeration with petroleum coke.  A statistical model was developed to process and evaluate data.  Experimental validation run at optimal conditions gave a residue oil concentration of 1950 ppm of, and the oil removal rate was 99.5%, a desirable result [11].

Another GCHSRC sponsored project is “Soil Remediation with Ultra-High-Efficiency Hydrocyclones”.  In this project, we constructed and tested small diameter hydrocyclones. Dewatering experiments on Sucarnoochee soil were carried out with a one-inch and a 10 mm diameter ultra-high-efficiency hydrocyclones, a more economical and efficient alternative to conventional dewatering devices in soil remediation. Hydrocyclones were found to have the capability of speeding up the rate limiting step of soil remediation, namely, dewatering process [12].

Both projects proved that agglomeration-flotation is an effective method for cleaning oil-contaminated soil. They also provided strong support for the two primary goals of our current proposal, i.e., scaling up the batch level process and converting the discrete process into a continuous process. Our findings and experience from previous studies will enable us to launch our research plan with more opportunities of successes.

QA/QC plan

The following is the outline of QA/QC plan prepared according the specifications of "Preparation Aids for the Development of Category IV Quality Assurance Project Plans," U.S. EPA, February, 1991. The detailed plan will be submitted to GCHSRC once the project is approved.

1.0     QA OBJECTIVES

The QA objectives are determined by the limits of the equipment available and previous work done on this topic.

Precision of tests will be reported by standard deviation results. Accuracy will be checked with standards when possible. Test procedures will be strictly adhered to and exceptions noted. Results will be carefully recorded and reported in a timely fashion.

1.1  QUANTITATIVE QA: ACCRUACY, METHOD DETECTION LIMIT, AND COMPLETENESS

Mass balances will be performed for each run and runs rejected for variations greater than+/- 5%. Replicates of several treatments will be done to establish the precision of the testing procedure. Precision for all critical measurements will be given as relative standard deviation. (Precision of each measurement is omitted here)

1.2  QUALITATIVE QA: COMPARABILITY OF AND REPRESENTATIVENESS

Each experiment will be run individually, one batch will constitute one run and yield one set of data, and each run is documented fully and only the appropriate variables are changed. Comparability will be demonstrated by a Central Composite Design (CCD) statistical model. The experiments will be run on a specific type of soil and will not be representative of many soil types. The characteristics of the soil type to be used will be documented.

1.3  OTHER QAs

Other QA criteria such as a laboratory standard operating procedure will be developed as the research progresses.

Routine QA matters will be discussed with the principal investigator and the QA Officer on a regular basis. The need for corrective actions will be discussed immediately with project management. The sponsor will receive QA information in quarterly progress reports and in materials for publication.

2.0     SAMPLING AND ANALYTICAL PROCEDURES (omitted)

3.0   INTERNAL QC

The analysis of replicate samples and blanks for each set of data is the primary approach of internal quality control.

3.1 DATA QUALITY AND HANDLING

Data calculation and preservation will be primarily processed by computer, preceded with proper manual data entry and recording.

3.2  DATA QUALITY INDICATORS

The experiments will all be performed within a CCD, which internally calculates the reproducibility of the methods. This formal statistical design will be heavily relied upon for the validation of experimental results.

3.2.1 Precision. Eqs. (2) and (3) on page 33 of the "Preparation Aids …” will be used to calculate STD for CCD.

3.2.2 Accuracy. Accuracy will be determined   by the calibration of instruments. Spikes will not be used.

3.2.3 Completeness The entire experimental process will be done manually, with careful measurements.

3.2.3   Method Detection Limit. Equation (8) on page 34 of the "Preparation Aids …” will be used.

4.0 Safety plan

The University of Alabama Health and Safety Plan will be followed in this work. The details of this section have been omitted due to lack o space

REFERENCES 

1.       Prasad, N., and Arnold, D. W., 1999. Optimization of two step process for remediation of Sucarnoochee soil with petroleum coke. Advances in Environmental Research, 3(2), 189-201. 

2.        Atlas, R. M. 1995. Bioremediation. Chemical Engineering News. 73, no. 14, 32-42. 

3.        Davis, E. L. and B. K. Lien. 1993. Laboratory study on the use of hot water to recover light oily wastes from sands. EPA/600/SR-93/021, Robert S. Kerr Environmental Research Laboratory, Ada, OK.  

4.        Vance, D. B. 1991. Onsite bioremediation of oil and grease contaminated soils. The National Environment Journal. 9,  26. 

5.        Vencent, N. 2000. Design and cost analysis of the agglomeration-flotation soil remediation method. A Thesis. 

6.        Rahnama, M. B. and D. W. Arnold. 1993. Soil remediation by agglomeration with blue creek coal. Journal of hazardous materials. 35,  89-102. 

7.        Narayanan, P.S., Arnold, D.W. and Rahnama, M. “Remediation of Sucarnoochee Soil by Agglomeration with Fine Coal,” Waste Management Vol. 14, No. 6, pp.539-548(1994). 

8.      Narayanan, P. S. and D. W. Arnold. 1997. Remediation of Sucarnoochee soil by agglomeration with petroleum coke. Advances In Environmental Research. 1, no. 1, 27-35. 

9.       Timothy, D., 1998. Soil remediation by agglomeration with enhanced surface petroleum coke. A thesis. 

10.    Prasad, N., 1999. Optimization of process variables for remediation of Sucarnoochee soil by agglomeration with petroleum coke. A thesis. 

11.    Ravindra, M., 2000. Remediation of soil from south Alabama oil fields using the agglomeration-flotation method. In progress. 

12.    Yao, T. 2000. Dewatering performance of small diameter hydrocyclones. A thesis.