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Determination of phase equilibria for long-chain linear hydrocarbons by Monte Carlo simulation.Du Preez, Nicholas Bruce. January 2005 (has links)
The focus of this study was to determine the coexistence phase equilibria for three groups of long-chain linear hydrocarbons (n-alkanes, 1-alkenes and 1-alcohols) using Monte Carlo simulation. Three common transferable united-atom force fields were used in the simulations: OPLS-UA (Jorgensen et al., 1984), TraPPE-UA (Martin and Siepmann, 1998) and NERD (Nath, Escobedo, de Pablo and Patramai, 1998). Isothermal phase equilibria was calculated over a temperature range from approximately the normal boiling point up to just below the critical temperature. The liquid and vapour densities and vapour pressures were determined from the simulations. The density results were then fitted using least-squares regression to the scaling law and the law of rectilinear diameters in order to estimate the critical properties. The vapour pressure data were fitted using least-squares to the Clausius-Clapeyron equation to estimate the normal boiling points. The NVT-Gibbs ensemble method was used to simulate the pure-component coexistence of the vapour and liquid phases. The NPT-Gibbs ensemble was used to simulate the n-alkane binary mixtures. Two forms of configurational-bias Monte Carlo (standard CBMC and coupled-decoupled CBMC) were used to increase the number of swap moves accepted during the simulations. Dual-cutoff CBMC was implemented with a second cut-off of sA in order to speed up the CBMC calculations. Minimum image and a spherical potential truncation after 14A were implemented with standard tail corrections. BICMAC and TOWHEE were the two Fortran-77 codes used to simulate the hydrocarbon compounds. BICMAC was used in the simulations of non-polar molecules and TOWHEE was used in the simulations of polar molecules. System sizes ranged from 300 (for the CB'S) down to 100 molecules (for the Czo's). The simulations were typically equilibrated for at least 30000 cycles and production runs ranged from 50000 to 120000 cycles for the different hydrocarbon groups. Standard deviations of the calculated thermophysical properties were between 1-3% for the liquid densities and 10-20% for the vapour densities and vapour pressures. It was found that the coexistence density curves were generally in good agreement with experiment for all the hydrocarbon groups investigated (the OPL5-UA force field being the exception). The chain-length appeared to have littl e effect on the quality of the calculated thermophysical properties. The chain-length did however increase the time required to perform the simulations substantially. The va pour pressures were consistently over-predicted by NERD and TraPPE-UA. The normal boiling pOints were typically under-predicted by 2-5%. The critical tempe ratures and densities were predicted to within 1-5% of experimental values. The n-alkane mixtures were satisfactorily predicted using the NPT-Gibbs ensemble. While both the NERD and TraPPE-UA force fields were shown to be substantially more accurate compared to the OPLS-UA force field, there was little difference between their predictions. Thus, it is likely that the added complexity of using the bond-stretching potential (used by NERD) is unnecessary. The results of this study show that Monte Carlo simulation may be used to predict vapour-liquid coexistence properties of long-chain hydrocarbons and to approximate critical properties. However, current force fields require more refinement in ord er to accurately predict the hydrocarbon thermophysical properties. Plus, faster computing speeds are required before Monte Carlo simulation becomes an industrially viable method. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.
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High pressure vapour-liquid equilibrium data of fluorochemical systems for various temperatures using a new static apparatus.Tshibangu, Mulamba Marc. January 2010 (has links)
The thermodynamic knowledge of accurate phase equilibrium data plays an important role in the design and optimization of separation processes in chemical and engineering industries. Vapour-liquid equilibrium data are essential for the design of efficient separation processes such as distillation. The presented research study is mainly focused on the vapour-liquid equilibrium data measurement of fluorochemical and hydrocarbon binary systems at various temperatures and at high pressures. A new static analytical apparatus was constructed and commissioned for the measurement of accurate and precise vapour-liquid equilibrium data at temperatures and absolute pressures ranging from low temperatures to 323.15 K and 0 to 10 MPa respectively. The new apparatus incorporates the ROLSI TM sampler, a sampling technique developed by the CEP/TEP laboratory in Fontainebleau, France. Isothermal high pressure VLE data were measured for three binary systems comprising of hexafluoroethane (R116) + propane, HFPO + propane and ethane + octafluoropropane (R218). The R116 + propane system at 263.15 K was measured as a test system using the new static apparatus. These measurements helped to confirm the functioning of the experimental apparatus. The reliability and the reproducibility of the experimental procedure were also checked. The data obtained were in excellent agreement with data in the literature. Thereafter, measurements of previously unmeasured systems were undertaken. Isothermal vapour-liquid equilibrium data measurements for the ethane + octafluoropropane system were performed at five isotherms with temperatures and pressures ranging from 264.05 to 308.04 K and 0.298 to 4.600 MPa respectively. The five isotherms constitute new experimental data. The HFPO + propane system was also investigated and vapour-liquid equilibrium data were measured at three isotherms (283.05, 303.05 and 323.05 K) with pressures ranging from 0.437 to 2.000 MPa. The data measured also constitute a set of a new HPVLE data. The uncertainties in the measurement for both systems were within ± 0.09 K, ± 0.0016 MPa and less than 2% for temperatures, pressures and mole fractions, respectively. All experimental data were correlated via the direct method using the Peng-Robinson equation of state with the Mathias-Copeman alpha function and the Wong-Sandler mixing rules incorporating the NRTL activity coefficient model. The consistency of the measured VLE data was tested using the Van Ness point test which yielded few points of difference between the measured and calculated data, suggesting a low error rate. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.
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The design of two apparati to measure solid-liquid and liquid-liquid equilibria data.Tadie, Margreth. January 2010 (has links)
Two new apparati have been developed to measure solid-liquid and liquid-liquid equilibria via a synthetic visual method by determination of thermal signatures. One apparatus adopts a technique of using Peltier modules for cooling, and the other is a well-known design that uses a cryogenic fluid in a thermostatted glass cell for cooling of the sample. The Peltier design is for small sample volumes, with a 10 cm3 aluminium equilibrium cell and has a minimum operating temperature of 253.15 K. The glass design is developed to complement the Peltier and has a larger volume of 140 cm3 and a minimum operating temperature of 223.15 K. Both apparati have been semi-automated in order to increase the accuracy and improve the efficiency of data measurements. Therefore the experimenter no longer has to wait for many hours for the determination of equilibrium. This was done by incorporating software, which was specially designed for the apparati using Labview8TM, for controlling the cooling and heating rates. The uncertainty of the temperature measurements was found to be ±0.03 K for the Peltier apparatus and ±0.02 K for the Glass apparatus. Liquid-liquid equilibria data has also been measured on the Peltier apparatus, to demonstrate its versatility. This was done using a digital camera, controlled through the Labview software to identify cloud points. The results have been found to be comparable with literature values.
For solid-liquid equilibria new systems of n-alkyl carboxylic acid binary mixtures have also been measured: heptanoic acid + butyric acid and heptanoic acid + hexanoic acid. These systems were measured using both apparati and both systems exhibited eutectic behaviour. All eutectic temperatures were measured on the Glass apparatus. Experimental data for these systems was modelled using the local composition models: Wilson, NRTL and UNIQUAC models. The NRTL model was found to give the best results for both systems with root mean square deviations (RMSD) of 2.16 K and 1.27 K and absolute average deviations (AAD) of 0.61 K and 0.49 K, between temperature measurements of this work and those calculated from the models, for the heptanoic acid + butyric acid and heptanoic acid + hexanoic acid systems, respectively. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.
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Modification and commissioning of a static high pressure apparatus and phase equilibria measurements for fluorinated hydrocarbons.Chiyen, Kaleng Jim. January 2010 (has links)
Modifications were undertaken to a static high pressure vapour-liquid equilibrium (VLE)
apparatus described by Naidoo [2004]. The alterations were made to improve the sample
analysis technique. These modifications included the incorporation of the ROLSITM sampling
device into the equilibrium cell, a re-design of the air bath which improved the temperature
profile and further alterations described in the text.
The equipment has an operating temperature range of 278.15 K to 473.15 K and pressure range
of absolute vacuum to 150 bars. The apparatus consisted of an agitated cell in an air-bath. The
uncertainties in the temperature and pressure measurements were ±0.02 K and ±4 kPa
respectively. A Shimadzu Gas Chromatograph, Model 2010 was used for sample analysis.
An initial test of the apparatus was carried out to measure the pure component vapour pressure
data for propane and ethane in the temperature range of 279.24 – 360.18K and the results
concurred with literature data (absolute relative deviation <0.153%)
The experimental procedure used in this study was developed from the technique used by
Ramjugernath [2000], with some minor changes implemented only to achieve some
requirements for problems encountered during the project.
Isothermal binary measurements for the hexafluoroethane (R116) + propane system were used
as test system to investigate the accuracy and reliability of the equipment. Three binary
isotherms were measured at 291.22 K, 296.23 K and 308.21 K. The measured data compared
well with literature data.
Particular attention was placed on the fluorinated hydrocarbons. Specific properties of
fluorinated hydrocarbons give them many applications in industry, such as solvents,
refrigerants, propellants, anaesthetics, etc. Hence, a phase equilibria study of a fluorinated
hydrocarbons system was carried out in this project.
The commissioning of the equipment was successfully undertaken and the equipment was
found to be efficient and reliable. As a consequence measurements were made on the
hexafluoropropylene oxide (HFPO) + ethane system. No data has been previously published in
literature for this system. Measurements were undertaken at five different temperatures, 283.15 K, 290.15 K, 298.15 K, 308.15 K and 318.15 K. The isotherms were chosen in order to have
measurements below and above the critical temperature of ethane, in order to see the transition
at the critical temperature.
The experimental data were modelled via the direct (phi-phi) method. The Peng-Robinson
equation of state was applied, including the Mathias-Copeman alpha correlation with the Wong-
Sandler mixing rules incorporating the NRTL activity coefficient model. Good agreement was
found between the correlated and the measured data. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.
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Carbon dioxide capture methods for industrial sources.Osman, Khalid. January 2010 (has links)
In order to reduce the rate of climate change, particularly global warming, it is imperative that
industries reduce their carbon dioxide (CO2) emissions.
A promising solution of CO2 emission reduction is Carbon dioxide Capture and Storage (CCS)
by sequestration, which involves isolating and extracting CO2 from the flue gases of various
industrial processes, and thereafter burying the CO2 underground.
The capture of CO2 proved to be the most challenging aspect of CCS. Thus, the objective of this
research was to identify the most promising solution to capture CO2 from industrial processes.
The study focussed on capturing CO2 emitted by coal power plants, coal-to-liquids (CTL) and
gas-to-liquids (GTL) industries, which are common CO2 emitters in South Africa.
This thesis consists firstly of an extensive literature review detailing the above mentioned
processes, the modes of CO2 capture, and the various CO2 capture methods that are currently
being investigated around the world, together with their benefits and drawbacks in terms of
energy penalty, CO2 loading, absorption rate, capture efficiency, investment costs, and operating
costs. Modelling, simulation, and pilot plant efforts are also described.
The study reviewed many CO2 capture techniques including solvent absorption, sorbent capture,
membrane usage, hydrate formation, and newly emerging capture techniques such as enzyme
based systems, ionic liquids, low temperature cryogenics, CO2 anti-sublimation, artificial
photosynthesis, integrated gasification steam cycle (IGSC), and chemical looping combustion
The technique of solvent absorption was found to be the most promising for South African
industries. Vapour-liquid-equilibrium (VLE) measurements of solvent absorption using amine
blends were undertaken, using blends of methyl-diethanol amine (MDEA), diethanol amine
(DEA) and water (H2O) with composition ratios of 25: 25: 50 wt% and 30: 20: 50 wt%
respectively, and with CO2 and N2 gases at CO2 partial pressures of 0.5 to 10.5 bar. Experiments
were conducted under system pressures of 5 to 15 bar and temperatures of 363.15 and 413.15 K,
using a static analytic apparatus. CO2 liquid loading results were analysed and discussed.
The experimental data were regressed in Matlab (R2009b) using the Posey-Tapperson-Rochelle
model and the Deshmukh-Mather model. The Matlab programmes are presented along with the
regressed binary interaction and model parameters. The accuracy of model predictions are
discussed.
Thereafter an Electrolyte-NRTL model regression and simulation of the absorption process was
conducted using Aspen Plus V 7.1. for flue gas compositions, solvent compositions,
temperature, and pressure conditions similar to that of process operating conditions. CO2
loading, design factors, CO2 recovery, and CO2 purity results were analysed and compared where appropriate, with experimental results. Finally a general preliminary energy efficiency
and cost analysis was conducted based on the simulation results.
The main conclusions reached are that the amine solvent blend containing 25:25:50 wt% of
MDEA:DEA:H2O, produced higher CO2 loadings for its respective system conditions than other
solvents studied and those found in literature. However, absorption of CO2 was found to be
highly dependent on system temperature and pressure.
The Deshmukh-Mather model provided higher accuracy than the Posey-Tapperson-Rochelle
model, producing CO2 loading predictions with a relative error not exceeding 0.04%, in 1.5 to 3
minutes using a dual core processor.
Aspen absorption simulations provided significantly lower CO2 loading results than those
experimentally obtained, due to the low contact time achieved and higher temperature
dependence in the proposed absorption process. Process improvements were highlighted and
implemented to increase CO2 recovery and purity. Energy penalty values were found to be
higher than those found in literature, but room for process and design improvement was
identified and recommendations were given. Investment cost estimates were found to be
justifiable and within reason. Limitations of the simulation were also identified and discussed. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.
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Fluidised bed gasification of spent soda and sulphite liquors from the paper industry.Sewnath, Pravesh. January 2004 (has links)
The pulp and paper industry uses pulping chemicals for the treatment of bagasse, straw and wood chips. Spent liquor or effluent liquor, with high carbon content is produced and sent to chemical recovery to recover pulping chemicals. In addition, energy from the spent liquor is recovered and utilised to generate steam for electricity supply, thereby reducing fossil fuel power consumption. Spent liquor is destroyed using conventional incineration technology, in a recovery furnace or recovery boiler, which is the heart of chemical recovery. These units have over the past few decades been prone to numerous problems and are a major concern to the pulp and paper industry. They pose a threat to the environment, are expensive to maintain and constitute a safety hazard. Thus the pulp and paper industry is now looking at a replacement technology; an alternative that will effectively regenerate pulping chemicals and recover energy for generating electricity, ultimately to make the plant energy self-sufficient. Gasification technology may be the chosen technology but is yet to be applied to the pulp and paper sector. However, this technology is not new. It has been integrated and used successfully in the petroleum industry for decades, with applications in coal mining and the mineral industry. The overall objective of tills study is to develop a better understanding of gasification using a pilot-scale fluidised bed reactor which was designed and developed at the University of Natal. The reactor, "the Gasifier", is operated at temperatures below the smelt limits of inorganic salts (<750°C) in the spent liquor. In this investigation, spent liquor is injected
directly into an inert bed of alwninium oxide grit, which is fluidised by superheated steam.
The atomized liquor immediately dries when it contacts the grit in the bed, pyrolyses and the
organic carbon is gasified by steam. Pyrolysis and steam gasification reactions are
endothennic and require heat. Oxidised sulphur species are partially reduced by reaction
with gasifier products, which principally consist of carbon monoxide, carbon dioxide and
hydrogen. The reduced sulphur is said to be unstable in the gasifier environment, and reacts
with steam and carbon dioxide to form solid sodium carbonate and gaseous hydrogen sulphide. (Rockvam, 2001). The focus of this study will be to determine the Gasifier's ability to gasify spent liquor, from soda and sulphite pulping of bagasse, at different operating conditions. In addition, the fate of process and non-process elements will be investigated. The product gas generated in the gasification of spent soda and sulphite liquors consisted of
hydrogen, carbon dioxide, carbon monoxide and methane. In the gasification of spent sulphjte liquor, hydrogen sulphide was also produced. The water-gas shift reaction, which
was the main reaction, was found to be temperature dependent. In adilition, organic carbon
conversion increased with temperature. Furthermore, most of the sulphur in the bed
predominated in the form of hydrogen sulphide with very little sulphur in the form of sulphate. This indicated that gasification would reduce sulphate levels, which are responsible
for dead load in a chemical recovery cycle. Finally, an important result was that the aluminium oxide grit was successfully coated. It was previously speculated that this would not be possible. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.
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Development of a group contribution method for the prediction of normal boiling points of non-electrolyte organic compounds.Nannoolal, Yash. January 2004 (has links)
Physical properties are fundamental to all chemical, biochemical and environmental industries. One of these properties is the normal boiling point of a compound. However, experimental values in literature are quite limited and measurements are expensive and time consuming. For this reason, group contribution estimation methods are generally used. Group contribution is the simplest form of estimation requiring only the molecular structure as input. Consequently, the aim of this project was the development of a reliable group contribution method for the estimation of normal boiling points of non-electrolytes applicable for a broad range of components. A literature review of the available methods for the prediction of the normal boiling points from molecular structure only, was initially undertaken. From the review, the Cordes and Rarey (2002) method suggested the best scientific approach to group contribution. This involved defining the structural first-order groups according to its neighbouring atoms. This definition also provided knowledge of the neighbourhood and the electronic structure of the group. The method also yielded the lowest average absolute deviation and probability of prediction failure. Consequently, the proposed group contribution method was then developed using the Cordes and Rarey method as a starting point. The data set included experimental data for approximately 3000 components, 2700 of which were stored in the Dortmund Data Bank (DDB) and about 300 stored in Beilstein. The mathematical formalism was modified to allow for separate examination and regression of individual contributions using a meta-language filter program developed specifically for this purpose. The results of this separate examination lead to the detection of unreliable data, the re-classification of structural groups, and introduction of new structural groups to extend the range of the method. The method was extended using steric parameters, additional corrections and group interaction parameters. Steric parameters contain information about the greater neighbourhood of a carbon. The additional corrections were introduced to account for certain electronic and structural effects that the first-order groups could not capture. Group interactions were introduced to allow for the estimation of complex multifunctional compounds, for which previous methods gave extraordinary large deviations from experimental findings. Several approaches to find an improved linearization function did not lead to an improvement of the Cordes and Rarey method. The results of the new method are extensively compared to the work of Cordes and Rarey and currently-used methods and are shown to be far more accurate and reliable. Overall, the proposed method yielded an average absolute deviation of 6.50K (1.52%) for a set of 2820 components. For the available methods, Joback and Reid produced an average absolute deviation of 21.37K (4.67%) for a set of 2514 components, 14.46K (3.53%) for 2578 components for Stein and Brown, 13.22K (3.15%) for 2267 components for Constantinou and Gani, 10.23 (2.33%) for 1675 components for Marrero and Pardillo and 8.18K (1.90%) for 2766 components for Cordes and Rarey. This implies that the proposed method yielded the lowest average deviation with the broadest range of applicability. Also, on an analysis of the probability of prediction failure, only 3% of the data was greater than 20K for the proposed method. This detailed comparison serves as a very valuable tool for the estimation of prediction reliability and probable error. Structural groups were defined in a standardized form and the fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2004.
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A study of the factors affecting the size distribution of micro-capsules for carbonless copy paper.Chetty, Ezekiel. January 2002 (has links)
The process of micro-encapsulation by emulsifying a solution in a stirred tank has been accepted as
the most suitable method for the production of microcapsules for carbonless copy paper and is
currently used by Mondi Paper in Merebank. The focus of this project was to obtain a more
uniform size distribution of the microcapsules so that oversize capsules would not smudge when
they are coated on paper. There was also concern that the formation of very small ink/oil droplets
was consuming wall material unnecessarily and was not contributing to the formation of an image
on paper. The reduction of these tiny droplets would result in a saving of the cost of the wall
material.
Mondi currently produces microcapsules with an average diameter between 4 and 5 microns. The
amount of capsules produced above 10 microns, the oversize, is less than 1 per cent (v/v) and the
amount of capsules produced below 2 microns, the undersize, is between 25 and 30 per cent. Mondi
wishes to reduce the amount of undersize capsules, thereby producing a narrower size distribution.
This could result in large savings, as discussed above. It could also lead to the production of a six-sheet
set of carbonless papers instead of the four-sheet set, which is currently produced. The
production of microcapsules by emulsification was investigated in a 2.5-1iter laboratory tank, using
an impeller measuring 45 mm in diameter.
A range of agitation speeds was investigated and it was seen that at the lowest speed that formed
emulsions, 6600 rpm, 15.03 per cent of undersize capsules was produced and an average capsule
diameter of 7.57 microns, after 40 minutes of agitation. At the highest impeller speed, 8000 rpm,
the average capsule diameter was reduced to 1.93 microns and 67.02 per cent of undersize capsules
were classified as "undersize". No oversize capsules were observed. These capsule specifications
were not favourable. Further experimentation showed that at 7500 rpm, an average capsule
diameter of 5.12 microns and an undersize of 24.20 per cent were observed. The proportion of
oversize capsules was 1.63 per cent. Since these results were similar to the results obtained from
the plant, 7500 rpm was used accepted as the "standard" speed for the experiments. A reduction in
the impeIler speed from 7500 rpm to 7200 rpm after the first 20 minutes of emulsification was one·
way on reducing the proportion of undersize particles further. The proportion of undersize particles was reduced from 20.20 per cent to 19.71 per cent at standard conditions. The average capsule
diameter and the oversize were not affected significantly.
The effect of the emulsification temperature on the particle size distribution was investigated with
temperatures ranging from 22 to 40°C, in increments of 2 QC. A temperature of 30 °c was used as a
standard temperature as this temperature was being used at the plant. A decrease in the proportion
of undersize capsules to 17.12 per cent was seen at temperatures below 30°C and an average of
23.87 per cent was noticed above 30 QC. Although the proportion of undersize capsules decreased,
the average capsule diameter increased beyond the specified range to an average of 7.77 microns at
temperatures below 30°C. At temperatures above 30 °c the average size was reduced to 5.59
microns. Hence the selection 000 °c as the optimum temperature was confirmed.
Experimentation with the emulsification time showed that there were times when a unimodal size
distribution was produced. However, these were at times just after the polymerisation had begun,
and the reaction was not complete at this stage. A bimodal distribution was always noticed after 40
minutes of emulsification, i.e. after the completion of the reaction.
The effects of the baffle widths on the microcapsules were also investigated. Baffle sizes of 5, 10
and 15 mm were used. It was shown that with an increase in baffle width, there was a decrease in
the amount of undersize capsules produced. However, the average capsule diameter became too
large. A baffle width of 5 mm was shown to produce desirable capsule sizes, although the
undersize did not improve, or worsen. Too much of air was trapped in the emulsion when no
baffles were used in the tank.
Alternatives to the current surfactant, called "Lupasol" were tested so that Mondi could produce the
capsules independently instead of relying on the original raw material supplier. This investigation
was done based on limited informa.tion on Lupasol. Results from these experiments were
inconclusive since more data on Lupasol was required.
Samples of the microcapsule emulsion were sent to different companies, in South Africa and
abroad, to determine whether the particle size analyser used at Mondi was giving correct results.
The results obtained from the companies in South Africa differed by a small amount from that
measured at Mondi. However, results obtained from companies abroad varied considerably and it is
recommended that Mondi change their particle analyser settings. The power absorbed by the emulsion, in the laboratory-scale equipment was also found. This was
determined by monitoring torque. The power was found to be 141.97 Wand the power number was
calculated as 0.357. It was noted that the power per unit volume in the laboratory equipment was
significantly higher than the plant data (47 kW/m3 vs. 12 kW/m3).
The design of the impeller was not changed but the effect of baffle spacing was investigated. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.
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The evaluation of ozone technology to reduce the concentration of polychlorinated biphenyls (PCBs) in contaminated soil.Moodley, Shanita Jeewan. January 2011 (has links)
Polychlorinated Biphenyls (PCBs) are hazardous and toxic chemicals to both humans and
animals. In the late 1960’s PCBs were discovered to be a harmful pollutant which could cause
environmental contamination due to its slow degradation and even trace amounts of PCBs were
regarded as toxic to both human and animals.
Oil spills are a frequent occurrence at Eskom substations which could contain PCBs. The
contaminated sediments which are easily carried away by rain and wind can further
contaminate the environment and aquatic bodies. Eskom currently disposes of soil and ballast
stones contaminated with PCBs by thermal destruction. This is a costly process as PCBs are
regarded as hazardous materials and needs to be safely transported and disposed of at a licensed
disposal facility.
Based on literature, ozone has been used on a laboratory scale to treat soil contaminated with
PCBs with the addition of chemicals such as hexane and acetone which assist in breaking down
PCBs. The objective of this study was to evaluate whether ozone without the addition of
chemicals could reduce the levels of PCBs present in contaminated soil. In this study, two soil
samples and one ballast stone sample were contaminated with 50 ppm, 200 ppm and 600 ppm
of PCBs and then exposed to 0.4, 0.5 and 0.6 l/min of ozone for a period of 60 minutes to
examine the effects of increasing ozone flow rates on PCB destruction in soil.
The results of the experimental tests showed that ozone gas reduced the concentration of PCBs
in the soil and ballast stone samples for the different total gas flow rates. The literature study
identified that the final products of the ozonation of PCBs are carbon dioxide and water and that
any products formed after this process could possibly be degraded by the soil natural
microorganisms.
Calculations based on the Shin et al. (2004) model proved that ozone was in excess after the
ozonation process. The results of the experiments also confirmed this, as the PCB residuals
were similar for all three total gas flows, which showed that there was no dependence on the gas
flow rates hence, ozone was in excess. The experimental data was then trended with zero, first
and second order reaction equations, which showed that the best fit was obtained with the firstorder
reaction equation. It is recommended that ozone be used for the treatment of PCB
contaminated soil at Eskom substations. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.
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Investigation of the effects of polychlorinated biphenyl (PCB) dechlorination on the natural inhibitors and oxidation stability of uninhibited naphthenic based mineral oils.Nassiep, Sumaya. January 2010 (has links)
PCBs are persistent organic pollutants that have intentionally and unintentionally (through
contamination) been added to mineral insulating oil to improve its insulating and cooling
properties within electrical equipment. The Stockholm Convention on Persistent Organic
Pollutants (2001) orders the eradication of PCBs from use by 2025.
Sodium based dechlorination is a PCB destruction process that is non-thermal, relatively cost
effective and allows for the recovery of a reusable end product. A comparative benefits
study, contained in chapter 2 of this dissertation, describes the increased financial and
environmental impact associated with incinerating large volumes of PCB contaminated
mineral oil. The results of the comparative analysis indicate a cost ratio of 1: 2.5, in favour of
sodium dechlorination.
In addition to the financial benefit, the sodium based PCB dechlorination process is versatile
and can be either batched or skid mounted and is typically combined with an oil regeneration
step, allowing for transformers to be treated onsite and whilst energised. Eskom is currently
considering obtaining the mobile dechlorination unit for the purpose of conducting
dechlorination and regeneration on its PCB contaminated transformers while energised.
Mineral insulating oil is considered a strategic asset within most industries. Eskom uses
mainly uninhibited mineral oil in its older transformers and the effects of PCB dechlorination
on the natural inhibitor content of the oil is uncertain.
The objective of this study was to investigate the effects of sodium dechlorination on the
oxidation stability and thereby indirectly the natural inhibitor content of uninhibited
naphthenic based mineral oil. The study involved the dechlorination, regeneration and
subsequent chemical analyses of PCB contaminated oils in the PCB ranges <50ppm, 50 to
500 ppm and >500 ppm as stipulated by the Stockholm Convention on Persistent Organic
Pollutants (2001).
The study confirmed the reduction in oxidation stability and thereby the natural inhibitor
content of the mineral oil after sodium dechlorination. Based on the results obtain a
preliminary algorithm was established to predict the reduction in oxidation stability after
sodium dechlorination, as a function of the PCB concentration prior to dechlorination. This
will provide an indirect indication of the rate of natural inhibitor depletion of the oil, based on
its exposure to the sodium dechlorination reagents and process conditions. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.
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