Changes in redox potential (Eh), major sulfur species and the solubility of selenium and boron in reduced flue gas desulfurization (FGD) sludge, when exposed to atmosphere were studied in laboratory experiments. Also the effect of organic carbon and temperature on reduction of FGD sludge and changes in concentration of major S species was studied. Stable isotopic ratios of sulfur and carbon compounds were used to investigate the possible pathways of S transformation in FGD sludge disposal site. Oxidation of reduced sludge appears to be a two step process, a fast step of chemical oxidation followed by a slow step of biological oxidation and is significantly affected by moisture content and mixing of the sludge. With the addition of organic carbon Eh of the FGD sludge dropped exponentially and reduction of sulfate initiated at Eh of about -75 mV and was maximum in the range of -265 to -320 mV. Temperatur8e of the profile and organic carbon appear to be the key factors affecting the rate and extent of reduction in flooded FGD sludge. Selenium solubility decreased four times as Eh dropped from 215 mV to -350 mV while boron solubility was unchanged in this range of Eh. Stable isotopic ratio of sulfate and sulfide are typical of bacterial reduction and suggest that only aqueous sulfate was being reduced. The low δ³⁴S values of CaSO₄ from the upper layers of profile indicate the production and upward movement of hydrogen sulfide gas in the FGD sludge.

Power generation from coal combustion serves as a major source of energy however this process has detrimental environmental effects. SO₂ is a destructive pollutant and is oxidized with water vapour to form sulphuric acid which falls as acid rain causing corrosion to monuments, deforestation, soil erosion and destruction of the natural habitat. SO₂ emissions cause chronic respiratory diseases. The development and advancement in pollution control technologies is a pressing issue as environmental regulations become more stringent. The principal technology that is currently implemented is termed Flue Gas Desulphurization (FGD) and involves treating the flue gas before it is released into the atmosphere. Industries are constantly welcoming new research and development that would reduce their SO₂ emissions. As a result most companies are turning to sorbents to solve the major environmental crisis. In the work undertaken an effective test unit for sulphur dioxide capture was commissioned and recommended conditions for SO₂ removal were established. Four ESKOM sorbents were prepared and tested in the experimental set-up. These sorbents were then ranked according to their desulphurization efficiency. The effect of particle size on desulphurization efficiency was determined using four different size fractions and it was found that smaller particles have higher sulphur removal efficiency. The effect of the presence of CO₂ in the gas mixture was also determined by comparing the efficiencies obtained using two different flue gas mixtures. The chemical, physical and surface properties of each sorbent was also analysed and used to support the conclusions drawn from the ranking of the sorbents. A suitable model to represent the data set was also investigated and it was found that the simple shrinking core model best described the system investigated. / M.Sc.Eng. University of KwaZulu-Natal, Durban, 2013.

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.

No description available.

An experimental system was built to test the effect of various process parameters on the performance of the Modified Dry Limestone Process (MDLP) for flue gas desulfurization. Two types of limestone, one calcitic and one dolomitic, were used. These materials were characterized by ICP analysis, X-ray diffraction, optical microscopy, SEM, and electron microprobe before and after reaction. Performance was judged on the basis of the formation of a friable gypsum reaction product and the maintenance of a pH of about 4.84 or higher in water through which the exit gases were bubbled. Two primary and one secondary parameter were identified as the most important for optimum performance of the MDLP. The two primary parameters were temperature and water content. A temperature of 68°-70°C promoted reaction, while no reaction occurred at 31°C. The solubility of SO₂ in water was the controlling factor for water content. A maximum ratio of about 3.4 g SO₂/100 g water at 69°C was necessary. The secondary parameter was the type of limestone used. A dolomitic limestone with a reasonable amount of Fe performed better than either marble or a calcitic limestone, both low in Fe. A reasonable amount of Fe and an extensive pore structure seem to be the most important factors in limestone SO₂ absorption performance. / Master of Science

A Research Report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Engineering (MSc 50/50) School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa November, 2016 / The global focus on cleaner air has seen sulphur removal processes’ gaining popularity and adsorptive desulphurisation has been identified as an effective alternative. Adsorptive desulphurisation was used to simulate and evaluate the performance of the polymer supported imidation agent (Sodium N-chloro-polystyrene sulphonamide) as an adsorbent in the desulphurisation of diesel fuel. This study involved the development of a mathematical model for the adsorption process of sulphur on the polymer supported imidation agent, based on the mass balance on a continuous fixed bed column and pseudo second order kinetics. The developed model was solved using numerical methods, and the simulation of the process carried out varying different parameters; the inlet sulphur concentration, the adsorption column bed height and the particle size (radius) of the adsorbent. The simulation showed that the adsorption capacity of the studied adsorbent increased with increase in the inlet sulphur concentration; an increase in the adsorption bed height and a decrease in the adsorbent particle size. Validation of the simulation done was carried out by comparing the simulation data with experimental data. The proposed model fit experimental data and can be used to predict the inlet concentration conditions, bed height and particle size of the adsorbent. The overall research enhances the understanding of the adsorptive desulphurisation of diesel fuel using the polymer supported imidation agent and the mathematical modelling of the process. / MT2017

No description available.

D. Tech. Mechanical Engineering. / Investigates and/or rank the performance of locally available materials (i.e. limestone, dolomite, or calcrete) as sorbents in the capture of SO2 emissions from coal-fired power plants. Two experimental procedures were adopted in this work: the pH-stat method was used to simulate conditions encountered in wet flue gas desulphurisation (WFGD); and the fixed-bed reactor was used to simulate conditions encountered in the dry in-duct flue gas desulphurisation (DFGD) process. It is important to note that most studies of using calcium-based materials as sorbents for SO2 removal have been carried out in overseas countries. These studies were carried out using materials and research conditions prevailing in the particular countries. Furthermore, all South African coal-fired power stations burn low grade coal allowing the high grade coal to be exported. As a result, coal-fired power stations in South Africa emit higher emissions than the overseas power stations which are operated on high grade coals. Thus the results achieved internationally may not be directly translated to the South African conditions.

M. Tech. (Department of Chemical Engineering, Faculty of Engineering and Technology): Vaal University of Technology / Strict environmental regulation on flue gas emission has led to the implementation of FGD technologies in power stations. Wet FGD technology is commonly used because it has high SO2 removal efficiency, high sorbent utilization and due to availability of the sorbent (limestone) used. SO2 is removed by passing flue gas through the absorber where it reacts with the slurry containing calcium ions which is obtained by dissolution. This study presents the findings of the dissolution of a calcium-based material (limestone) for wet FGD process. This was done using a pH stat apparatus and adipic acid as acid titrant. Adipic acid was used because of its buffering effect in wet FGD process. The conditions used for this study are similar to what is encountered in a wet FGD process. The extent of dissolution was determined by analyzing the amount of calcium ions in solution at different dissolution periods. The dissolution kinetics were correlated to the shrinking core model and it was found out that chemical reaction at the surface of the particle is the rate controlling step. This study also investigated the dissolution of coal fly ash and bottom ash. Their dissolution kinetics showed that the diffusion through the product layer was the rate controlling step due to an ash layer formed around the particle. The formation of ash layer was attributed to pozzolanic reaction products which is calcium-alumino-silicate (anorthite) compounds were formed after dissolution. The effect of fly ash on the dissolution of rate of limestone was also studied using response surface methodology. Limestone reactivity was found to increase with increase in the amount of fly ash added and the pH was found to be strong function of the rate constant compared to other dissolution variables. The presence of silica and alumina in fly ash led to a significant increase in the specific surface area due to hydration products formed after dissolution. / Eskom