published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

The labelling of methyl tertiary butyl ether (MTBE), an oxygenate additive used extensively in gasoline blending, as an environmentally harmful chemical has led to the banning and subsequent phasing-out of this additive in California (USA). In response, the global petroleum industry is currently considering replacement strategies, which include the use of tertiary amyl methyl ether (TAME) or ethanol. Subsequently, SASOL (South African Coal and Oil Limited), a local petrochemical company, in its capacity as an environmentally responsible player in the global petroleum and aligned chemical markets, has commissioned this investigation into the environmental fate of the fuel oxygenates: TAME, ethanol and MTBE. In order to evaluate the environmental fate of the oxygenates, this dissertation has formed a three-tiered approach, using MTBE as a benchmark. The first tier assessed the general fate behaviour of the oxygenates using an evaluative model. A generic evaluative model, developed by Mackay et al. (l996a), called the Equilibrium Criterion (EQc) model was used for this purpose. This fugacity based multimedia model showed MTBE and TAME to have similar affinities for the water compartment. Ethanol was demonstrated to have a pre-disposition for the air compartment. Parameterisation of the EQC model to South African conditions resulted in the development of ChemSA, which reiterated the EQC findings. The second tier quantified the persistence (P), bioaccumulation (B) and long-range transport (LRT) potential of the additives. This tier also included a brief toxicity (T) review. MTBE and ethanol were demonstrated to be persistent and non-persistent, respectively, according to three threshold limit protocols (Convention on the Long Range Trans-boundary Air Pollution Persistent Organic Chemical Protocol; the United Nations Environment Programme Global Initiative; and the Track 1 criteria as defined by the Canadian Toxic Substances Management Policy, as referred to by the Canadian Environmental Protection Act 1999). These protocols were not unanimous in the persistence classification of TAME. Further investigation of persistence was conducted using a persistence and long-range transport multimedia model, called TaPL3, developed by Webster et al. (1998) and extended by Beyer et al. (2000). TaPL3 reiterated the conclusions drawn from the threshold limit protocols, indicating that TAME's classification worsened from non-persistent to persistent on moving from an air emission to a water emission scenario. This served to emphasise the negative water compartment affinity associated with TAME. Using classification intervals defined by Beyer et al. (2000), TaPL3 demonstrated that the long-range transport potential of the oxygenates increased in the order of TAME, ethanol and MTBE; however, it was concluded that none of the oxygenates were expected to pose a serious long-range transport threat. Bioaccumulation was not expected to be a pertinent environmental hazard. As expected, the oxygenates were dismissed as potential bioaccumulators by the first level of a screening method developed by Mackay and Fraser (2000); as well as by the threshold limit protocols listed above. Simulation of biomagnification, using an equilibrium food chain model developed by Thomann (1989), demonstrated that none of the oxygenates posed a biomagnification threat. A review of toxicity data confirmed that none of the three oxygenates are considered particularly toxic. LDso values indicated the following order of increasing toxicity: ethanol, MTBE and TAME. The third tier focussed on oxygenate aqueous behaviour. A simple equilibrium groundwater model was used to analyse the mobility of the oxygenates in groundwater. TAME was found to be 21 % less mobile than MTBE. Ethanol was shown to be very mobile; however, the applicability of the equilibrium model to this biodegradable alcohol was limited. An analysis of liquid-liquid equilibria comprised of oxygenate, water and a fuel substitution chemical was performed to investigate fuel-aqueous phase partitioning and the co-solvency effects of the oxygenates. Ethanol was shown to partition appreciably into an associated water phase from a fuel-phase. Moreover, this alcohol was shown to act as a co-solvent drawing fuel chemicals into the water phase. MTBE was found to partition sparingly into the water phase from a fuel-phase, with TAME partitioning less than MTBE. Neither ether was shown to act as a co-solvent. It was concluded that TAME and ethanol pose less of a burden to the environment than MTBE. Ethanol was assessed to be environmentally benign; however, it was concluded that ethanol's air compartment affinity and the extent of its co-influence on secondary solutes justified the need for further investigation before its adoption as a fuel additive. This project showed sufficient variation in the environmental behaviour of TAME and MTBE to justify the abandonment of the axiom that MTBE and TAME behave similarly in the environment. However, as MTBE is a significant water pollutant, and TAME has been shown to share a similar water affinity, it is cautiously recommended that the assumption of environmental similarity be discarded, except for the water compartment. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.

No description available.

Motor fuel taxes have been collected as a principal source of highway funding for close to a century. They account for approximately two thirds of all the highway user fees and about half of all highway expenditures. Federal fuel taxes have not kept pace with the inflation in general and increasing traffic demand and resulting construction, maintenance and operation costs of the transportation assets in particular. Lack of political will, combined with rising anti-tax sentiment among the populace, has kept the federal tax level not only well below its initial intents, but also at a unsustainable level in future. Mileage based user fees are possibly an alternative to the fuel taxes, which have been the main mechanism for funding the transportation system. Mileage based user fees have been successfully utilized in many parts of the world with glowing results. Germany‟s “TollCollect”, a quasi government enterprise has utilized GPS technology in collecting the users‟ fee from the truck operators. The system has been a financial engine providing much needed funding for many major transportation projects. Oregon Department of Transportation, in a federally co-funded pilot project, examined the practicality of the mileage based user fee collection at the fuel pumps. According to the Oregon study, there are not any major technical difficulties in mileage based user fee collection at the pump. Study participants (general motorist) did not express any objection to the mileage based user fee collection. This dissertation evaluates revenue impacts of several pricing policies including: Current per gallon fuel taxes, conversion to a mileage based user fee, time of day user fee application, iv area type user fee and congestion priced user fees. State of Florida‟s years 2015-2035 fuel revenue forecast is used as a case study. A model is constructed to estimate annual vehicle miles travelled for the analyses period. Fuel efficiencies, current per gallon fuel taxes and their corresponding mileage-based user fee equivalents are the input to a financial model developed for comparisons. Results demonstrate that decrease in fuel revenues due to vehicles fuel efficiency improvements can be offset by replacing current per gallon fuel taxes with a mileage-based user fee. Pricing the user fee according to area type, roadway classification, time of day and congestion level can not only generate more revenues but also assist in demand management.

Atomization of fuel is an important pre-requisite for efficient combustion in devices such as gas turbines, liquid propellant rocket engines, internal combustion engines and incinerators. The overall objective of the present work is to explore air-assisted atomization strategies for high viscosity fuels and liquids. Air-assisted atomization is a twin-fluid atomization method in which energy of the gas is used to assist the atomization of liquids. Broadly, three categories of air-assisted injection, i.e., effervescent, impinging jet and pre-filming air-blast are studied. Laser-based diagnostics are used to characterize the spray structure in terms of cone angle, penetration and drop size distribution. A backlit direct imaging method is used to study the macroscopic spray characteristics such as spray structure and spray cone angle while the microscopic characteristics are measured using the Particle/droplet imaging analysis (PDIA) technique. Effervescent atomization is a technique in which a small amount of gas is injected into the liquid at high pressure in the form of bubbles. Upon injection, the two-phase mixture expands rapidly and shatters the liquid into droplets and ligaments. Effervescent spray characteristics of viscous fuels such as Jatropha and Pongamia pure plant oils and diesel are studied. Measurements are made at various gas-to-liquid ratios (GLRs) and injection pressures. A Sauter Mean Diameter (SMD) of the order of 20 µm is achieved at an injection pressure of 10 bar and GLR of 0.2 with viscous fuels. An image-based method is proposed and applied to evaluate the unsteadiness in the spray. A map indicating steady/unsteady regime of operation has been generated. An optically accessible injector tip is developed which has enabled visualization of the two-phase flow structure inside the exit orifice of the atomizer. An important contribution of the present work is the correlation of the two-phase flow regime in the orifice with the external spray structure. For viscous fuels, the spray is observed to be steady only in the annular two-phase flow regime. Unexpanded gas bubbles observed in the liquid core even at an injection pressure of 10 bar indicate that the bubbly flow regime may not be beneficial for high viscosity oils. A novel method of external mixing twin-fluid atomization is developed. In this method, two identical liquid jets impinging at an angle are atomized using a gas jet. The effect of liquid viscosity (1 cP to 39 cP) and surface tension (22 mN/m to 72 mN/m) on this mode of atomization is studied by using water-glycerol and water-ethanol mixtures, respectively. An SMD of the order of 40 µm is achieved for a viscosity of 39 cP at a GLR of 0.13 at a liquid pressure of 8 bar and gas pressure of 5 bar. It is observed that the effect of liquid properties is minimal at high GLRs where the liquid jets are broken before the impingement as in the prompt atomization mode. Finally, a pre-filming air-blast technique is explored for transient spray applications. An SMD of 22 µm is obtained with diesel at liquid and gas pressures as low as 10 bar and 8.5 bar, respectively. With this technique, an SMD of 44 µm is achieved for Jatropha oil having a viscosity 10 times higher than that of diesel.