Wang F.,University of Florida |
Annable M.D.,University of Florida |
Schaefer C.E.,CBandI |
Ault T.D.,CBandI |
And 2 more authors.
Journal of Contaminant Hydrology | Year: 2014
Simplified analytical solutions, developed as source strength functions (SSFs), are capable of describing the temporal dissolution of nonaqueous phase liquids in groundwater, which is useful for predicting source longevity and can serve as a guide for remedial activities. Here, SSF parameters were estimated by fitting enhanced aqueous dissolution data from a flow cell consisting of three injection and four extraction wells to analytical dissolution models (power law model (PLM) and equilibrium streamtube model (EST)) at a trichloroethene (TCE) contaminated site, Alameda Point, California. Both the PLM and the EST model were able to characterize the observed aqueous TCE dissolution during enhanced water flooding. Additional field activities conducted at the site included soil core collection, a recirculated partitioning tracer test, passive flux meter transects, and push-pull tracer tests. The additional site characterization data were used to independently estimate the observed SSF parameters using information such as the TCE mass, distribution and porous media heterogeneity. The exponential decay model (a subset of the PLM) accurately predicted the enhanced dissolution, likely because the site was significantly aged (most of the mass in the plume rather than in the source zone) or middle stage, and the mass in the source zone could be approximately estimated. The EST tracer-based model, when combined with data from the recirculated partitioning tracer test, soil cores, and the push-pull tracer test, was capable of accurately predicting the observed aqueous dissolution. The mass in the source zone and the fraction of contaminated flowpaths were the most important site characteristics, requiring the greatest accuracy to predict aqueous dissolution. Establishing steady state dissolution was essential to provide a more accurate estimate of the fraction contaminated and high resolution data from soil cores in the source zone were needed to estimate the mass present. © 2014 Elsevier B.V.
Schaefer C.E.,CBandI |
Towne R.M.,CBandI |
Lippincott D.R.,CBandI |
Lazouskaya V.,University of Delaware |
And 3 more authors.
Environmental Science and Technology | Year: 2013
Laboratory experiments were performed using minimally disturbed sedimentary rocks to measure the coupled diffusion and abiotic reaction of trichloroethene (TCE) through rock core samples. Results showed that, for all rock types studied, TCE dechlorination occurred, as evidenced by generation of acetylene, ethene, and/or ethane daughter products. First-order bulk reaction rate constants for TCE degradation ranged from 8.3 × 10-10 to 4.2 × 10-8 s-1. Observed reaction rate constants showed a general correlation to the available ferrous iron content of the rock, which was determined by evaluating the spatial distribution of ferrous iron relative to that of the rock porosity. For some rock types, exposure to TCE resulted in a decrease in the effective diffusivity. Scanning electron microscopy (SEM) indicated that the decrease in the effective diffusivity was due to a decrease in the porosity that occurred after exposure to TCE. Overall, these coupled diffusion and reaction results suggest that diffusion of TCE into rock matrices as well as the rate and extent of back-diffusion may be substantially mitigated in rocks that contain ferrous iron or other naturally occurring reactive metals, thereby lessening the impacts of matrix diffusion on sustaining dissolved contaminant plumes in bedrock aquifers. © 2013 American Chemical Society.
Winning H.K.,CBandI |
Coole T.,Dr Buckinghamshire New University
Flow, Turbulence and Combustion | Year: 2013
The implicit Colebrook-White equation is the accepted method for accurately estimating the friction factor for turbulent flow in pipes. This study reviews 28 explicit equations for approximating the friction factor to integrate both the accuracy to the implicit Colebrook-White equation and the relative computational efficiency of the explicit equations. A range of 901 Reynolds numbers were selected for the review between Re ≥ 4 ×103 and ≤ 4 × 108 and 20 relative pipe roughness values were selected between ε/ D ≥ 10 -6 ≤ 10-1, thus producing a matrix of 18,020 points for each explicit equation, covering all the values to be encountered in pipeline hydraulic analysis for turbulent flow. The accuracy of the estimation of the friction factor using the explicit equations to the value obtained using the implicit Colebrook-White equation were calculated and reported as absolute, relative percentage and mean square errors. To determine the relative computational efficiency, 300 million friction factor calculations were performed using randomly generated values for the Reynolds number and the relative pipe roughness values between the limits specified for each of the explicit equations and compared to the time taken by the Colebrook-White equation. Finally, 2D and 3D contour models were generated showing both the range and magnitude of the relative percentage accuracy across the complete range of 18,020 points for each explicit equation. © 2012 Springer Science+Business Media Dordrecht.
Shumake G.,CBandI |
Hydrocarbon Engineering | Year: 2010
The reformer is the most important piece of equipment in the hydrogen plant. The primary design margin for the reformer is the temperature margin between the design temperature of the reformer tubes and the maximum calculated tube wall temperature. The Larson-Miller is used to design the reformer tubes, based on a minimum required tube life. It may be possible to add an additional reformer to increase the overall plant capacity on low capacity hydrogen plants that use smaller cylindrical reformers. A method to debottleneck the reforming capacity of the hydrogen plant is to increase the feed preheat temperature of the feed gas and steam mixture to the reformer. This decreases the absorbed duty of the reformer, thereby allowing additional capacity for firing. The addition of a prereformer to an existing hydrogen plant can also increase the capacity of the plant. In modern hydrogen units, the final product purification is fulfilled by the use of a pressure swing adsorption unit (PSA). A thorough evaluation should be performed on each piece of equipment for a successful hydrogen plant.
AIChE Ethylene Producers Conference Proceedings | Year: 2014
This presentation covers first the fundamentals and basic principles of radiant decoking and the impact of coke deposition in cracking heaters. It addresses various problematic issues, difficulties, and possibilities in cracking heater radiant decoking. Some of the highlighted possibilities include minimizing feed withdrawal temperature swings, setting burner pattern for optimal coke combustion, setting air dampers to prevent convection overheating, selecting air/steam flow rate to minimize erosion while maximizing firing load, ensuring complete coke removal using appropriate criteria, and incorporating appropriate safeguard techniques. Lastly, the techniques of polishing, transferline exchanger decoking procedure, and additional automation and control issues in decoking are reported. This is an abstract of a paper presented at the 26th Ethylene Producers Conference 2014 (New Orleans, LA 3/30/2014-4/3/2014).
Neil C.W.,Washington University in St. Louis |
Yang Y.J.,U.S. Environmental Protection Agency |
Schupp D.,CBandI |
Jun Y.-S.,Washington University in St. Louis
Environmental Science and Technology | Year: 2014
Managed aquifer recharge (MAR) is a water reuse technique with the potential to meet growing water demands. However, MAR sites have encountered arsenic mobilization resulting from recharge operations. To combat this challenge, it is imperative to identify the mechanisms of arsenic mobilization during MAR. In this bench-scale study, arsenic mobilization from arsenopyrite (FeAsS) was characterized for conditions relevant to MAR operations. Experimentally determined activation energies for arsenic mobilization from FeAsS under aerobic conditions were 36.9 ± 2.3 kJ/mol for 10 mM sodium chloride, 40.8 ± 3.5 kJ/mol for 10 mM sodium nitrate, and 43.6 ± 5.0 kJ/mol for secondary effluent from a wastewater treatment plant. Interestingly, the sodium chloride system showed higher arsenic mobilization under aerobic conditions. In addition, secondary mineral precipitation varied among systems and further affected arsenic mobilization. For example, the wastewater system inhibited precipitation, while in the sodium chloride system, faster phase transformation of iron(III) (hydr)oxide precipitates was observed, resulting in hematite formation after 7 days. The phase transformation to hematite will result in less available surface area for arsenic attenuation. These new observations and activation energies can be useful to develop improved reactive transport models for the fate of arsenic during MAR, and develop strategies to minimize arsenic release. © 2014 American Chemical Society.
Industrial and Engineering Chemistry Research | Year: 2015
A two-step method for the solution of dynamic optimization problems with state inequality constraints using iterative dynamic programming (IDP) is presented. In the first step, a preliminary control policy along with approximate values for the start and end points of the state-constrained arc is obtained. The final solution is obtained in the second step by using the preliminary control policy as an input along with an analytical expression for the control during the constrained portion of the state trajectory. The use of flexible stage lengths in IDP helps in accurately locating the start and end points of the state-constrained arc. For the examples considered, the method results in better values of the performance index than those previously reported in the literature. It also results in a significant reduction in computation time as compared to the existing method for the solution of problems with a single active state constraint and a single control using IDP. © 2015 American Chemical Society.