Magister Commercii - MCom / In order to comply with the Air Quality Act 2010, Eskom will have to install flue gas desulphurisation (FGD) plants for both new and old power stations. Wet-flue gas desulphurisation (wet-FGD) is adopted world-wide as an effective flue gas treatment technology and therefore will be adopted by Eskom. During the process of desulphurisation, the flue gas is stripped of SO2 but gains a substantial amount of water. Sustaining this process requires a continuous supply of fresh water, a scarce resource in many places where power stations are built. This research investigates the economic feasibility of technologies capable of recovering water from flue gas. The following technologies were considered to capture water vapour from flue gas taking Eskom’s Medupi Power Station as a case study; condensing heat exchanger technology, desiccant drying systems and membrane technology using membrane modules developed by other students in this project. The water vapour selective membrane technology turned out to be superior.

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Large scale biofuel production from microalgae is expected to be integrated with point source CO2 sources, such as coal fired power plants. Flue gas (CO2) integration represents a required nutrient source for accelerated growth while concurrently providing an environmental service. Heavy metals inherent in coal will ultimately be introduced into the culture system. The introduced heavy metals have the potential to bind to microalgae cells, impact growth due to toxicity, and negatively impact the quality of biofuel and other microalgal derived products. Heavy metals As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Sn, V and Zn, commonly present in coal, were introduced to the microalgae growth medium at a concentration expected from a 7 day growth period using coal flue gas. Experimentation was conducted with Nannochloropsis salina cultivated in photobioreactors at a light intensity of 1000 μmol m-2 s-1. Heavy metals negatively impacted the growth with the average productivity being 0.54 ± 0.28 g L-1 d-1, corresponding to a decrease of 52% in biomass yield compared to control growths. Heavy metal analysis showed significant binding of the majority of the heavy metals to the biomass. A lipid content analysis found a decrease in lipid content from 38.8 ± 0.62% to 31.58 ± 0.50% (percent dry biomass). Control and heavy metal contaminated biomass were processed into biofuel through one of two different in-situ transesterification techniques, either acid-catalyzed or supercritical methanol conversion. The acid-catalyzed conversion resulted in an average crude biofuel production decrease from 0.31 ± 0.03 grams biofuel/gram microalgae for the control algae to 0.28 ± 0.02 grams biofuel/gram microalgae for the heavy metal algae, representing a 9.7% reduction. Supercritical methanol conversion exhibited a similar trend corresponding to a 15.8% reduction. Compared to the control, the total production of biofuel from the contaminated system was decreased by 51% for the acid-catalyzed conversion and 55% for the supercritical methanol conversion. Heavy metal analyses were performed on the biofuel, lipid extracted algae, and other biofuel conversion byproducts. Biochemical methane potential testing was performed on the lipid extracted algae to determine the effect of heavy metals on the generation of biogas. The effects of heavy metals in combination with the effects of acid catalyzed transesterification were found to have a positive effect on the amount of methane produced with an average productivity of 105.89 mL g-COD-1 from the heavy metals contaminated LEA compared to the control microalgae biomass which produced 53.25 mL g-COD-1.

The hybrid Zero Valent Iron (hZVI) process is a novel chemical treatment platform that has shown great potential in our previous bench-scale tests for removing selenium, mercury and other pollutants from Flue Gas Desulfurization (FGD) wastewater. This integrated treatment system employs new iron chemistry to create highly reactive mixture of Fe^0, iron oxides (FeOx) and various forms of Fe (II) for the chemical transformation and mineralization of various heavy metals in water. To further evaluate and develop the hZVI technology, a pilot-scale demonstration had been conducted to continuously treat 1-2 gpm of the FGD wastewater for five months at Plant Wansley, a coal-fired power plant of Georgia Power. This demonstrated that the scaled-up system was capable of reducing the total selenium (of which most was selenate) in the FGD wastewater from over 2500 ppb to below 10 ppb and total mercury from over 100 ppb to below 0.01 ppb. This hZVI system reduced other toxic metals like Arsenic (III and V), Chromium (VI), Cadmium (II), Lead (II) and Copper (II) from ppm level to ppb level in a very short reaction time. The chemical consumption was estimated to be approximately 0.2-0.4 kg of ZVI per 1 m^3 of FGD water treated, which suggested the process economics could be very competitive. The success of the pilot test shows that the system is scalable for commercial application. The operational experience and knowledge gained from this field test could provide guidance to further improvement of technology for full scale applications. The hZVI technology can be commercialized to provide a cost-effective and reliable solution to the FGD wastewater and other metal-contaminated waste streams in various industries. This technology has the potential to help industries meet the most stringent environmental regulations for heavy metals and nutrients in wastewater treatment.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vii, 42 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 33-34).

Thesis (Ph.D.)--New Jersey Institute of Technology, Dept. of Chemical Engineering, Chemistry and Environmental Science, 1994. / Includes bibliographical references (leaves 167-174). Also available via the World Wide Web.

Thesis (MTech. degree in Mechanical Engineering)--Tshwane University of Technology, 2009. / South Africa produces 41.3 GWe per year of which 90% is coal-derived. During combustion of coal, sulfur contained in the fuel is converted to SO2. The gas poses a serious danger for the human and environmental health. The health hazards associated with SO2 include hair loss, throat inflammation, impaired vision and respiratory illnesses. Sulfur dioxide is also forms acid rain, which leads to acidification of soils, waterways and forests. The main objective of this investigation is to explore methods of increasing lime utilization using South Africa calcium/siliceous-based sorbents for the purposes of removal of SO2 in the Flue Gas Desulfurization (FGD) system. Consequently, this study presents experimental findings on the preparation, characterization and sulfation of locally available fly ash, calcium oxide (CaO) and bottom ash. CaO was obtained from calcination of limestone in a laboratory kiln at a temperature of 900 °C and CaO/fly ash sorbent prepared using an atmospheric hydration process.

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CO2 absorption behaviour of four commonly used cement based building products: cement paste, concrete block, expanded polystyrene bead (EPB) and cement-bonded cellulose fiberboard are studied. Cement products are manufactured following industry formulation and process, and carbonation curing takes place in a chamber under a pressure of 0.5 MPa, at ambient temperature, for durations of mostly 2 to 8 hours with both pure carbon dioxide gas and flue gas. The flue gas of 13.8% CO2 content is collected from a typical cement kiln without separation. Influencing factors on carbon uptake, long-term strength as well as microstructure development are studied. / It is found that the CO2 uptake ability of those cement-based products follows the same order when exposed to either pure gas or flue gas: fiberboard has the highest uptake capacity, followed by cement paste, bead board and concrete. For fiberboard, the best CO2 uptake in flue gas is 8.1%, it reaches 23.6% if pure gas used. Introduction of cellulose fiber in the fiberboard significantly increases voids volume and cement paste surface area through dispersing the paste onto fiber surface, effectively increasing carbonation reaction sites and thus CO2 uptake. / For pure gas carbonation with high reaction rate, it takes longer time for carbonated products to further develop strength from subsequent hydration, due to the high water loss during carbonation, the densified cement matrix structures and even fast decalcified cement minerals. Fast carbonation with pure gas is detrimental to cement paste in its long-term strength. For flue gas carbonation, both immediate strengths and long-term strength of the products are comparable with those by pure gas carbonation, although with less CO 2 uptake ability. / Five CO2 uptake determination methods are evaluated. Weight gain method is suitable for both pure gas and flue gas carbonation systems. Mass curve method is more suited for pure gas carbonation. For flue gas carbonation, CO2 concentration method agreed well with the weight gain method. Pressure drop method is relatively less accurate because of water vapor generation during carbonation.

Carbon dioxide CO₂capture through hydrate formation is a novel technology under consideration as an efficient means of separating CO₂from flue/fuel gas mixtures for sequestration and enhanced oil recovery operations. This thesis examines post-combustion capture of CO₂from fossil-fuel power plant flue-gas streams through hydrate formation in a silica gel column. Power plant flue-gas contains essentially CO₂and nitrogen (N2) after suitable pre-treatment steps, thus a model flue-gas comprising 17% co₂and 83% N2 was used in the study. Previous studies employed a stirred-tank reactor to achieve water-gas contact for formation of hydrates; recent microscopic studies involved using water dispersed in silica gel to react with gas, showing potential for improved hydrate formation rates without the need for agitation. This study focuses on macroscopic kinetics of hydrate formation in silica gel to evaluate hydrate formation rates, CO₂separation efficiency and determining optimal silica gel properties as a basis for a CO2 capture process. Spherical silica gels with 30.0 and 100.0 nm pore sizes and 40-75 and 75-200 μm particle sizes were studied to determine pore size and particle size effects on hydrate formation. 100.0 nm pores achieved higher gas uptake and CO₂recovery over the 30.0 nm case. Improved CO₂separation was obtained when 75-200 μm particles with 100.0 nm pores were used. The two effects observed are due to improved gas diffusion occurring with larger pore and particle size, favouring increased hydrate formation. Compared to stirred-tank experiments, results in this study show a near four-fold increase in moles of gas incorporated in the hydrate per mole of water, showing that improved water-to-hydrate conversion is obtained with pore-dispersed water. At similar experimental conditions, CO₂recovery improved from 42% for stirred-tank studies to 51% for the optimum silica (100.0 nm 75-200 μm) determined in this study. Finally, effects of tetrahydrofuran (THF) - an additive that reduces operating pressure were evaluated. Experiments with 1 mol% THF, the optimum determined from previous stirred tank studies, showed improved gas consumption in silica but reduced CO₂recovery, indicating that the optimum concentration for use in silica is different from that in stirred-tank experiments.