Browsing by Author "Wright, George Todd"

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    Application of synthetic molecular sieve zeolites and silica gel towards the separation of sulfur dioxide from combustion gases
    Wright, George Todd (Virginia Polytechnic Institute and State University, 1979)
    An evaluation of several commercial adsorbents for use as contacting media in a process for combustion gas desulfurization was performed. Linde Synthetic Molecular Sieves types 13X and AW500 and Davison Silica Gel were the materials studied. The motivation for this investigation was based on the premise that a suitable method for removing sulfur dioxide from combustion gas streams has not been realized. Sulfur dioxide adsorption capacities were obtained for equilibrium (non-flow) and dynamic flow conditions. Sulfur dioxide adsorption on the molecular sieves could be described by a modified Langmuir expression of the form q/qm = kc1/n/ 1 + kc1/n Calculated isosteric heats of adsorption were found to agree with measured data. Small scale dynamic studies consisted of contacting the adsorbents in a packed column with a simulated combustion gas. Evaluation of the adsorbent materials consisted of monitoring the effluent gas concentration after exposure to a step change in sulfur dioxide concentration. Sulfur dioxide loadings were greatest for the type 13X molecular sieve followed by AW500 molecular sieve. The effect of gas throughput was minimal which suggests that mass transfer was adsorbent side controlling. As gas temperature increased, sulfur dioxide adsorption decreased linearly for 100 percent sulfur dioxide concentration and non-linearly for low concentrations (0.003 percent). The effect of water vapor on sulfur dioxide adsorption capacity was determined by monitoring the effluent gas composition for specified sulfur dioxide-water vapor mixtures. Breakthrough time for sulfur dioxide was found to be an inverse function of the inlet water vapor concentration. For a typical combustion gas stream, (8 percent water vapor) the breakthrough time is roughly 10 percent of the water vapor free value. Based on the results obtained, a shallow bed (0.15m, 0.5 ft) of either type 13X or AW500 molecular sieve removed 5 to 3 times that of activated charcoal for a gas temperature of 57.2°C (135°F) and low gas pressure drop 4.6 cm H₂0 (1.85 in. H₂0). Adsorption degradation studies were performed to determine the loss in sulfur dioxide adsorption capacity after adsorbent regeneration. Both the 13X and AW500 molecular sieve could be regenerated, but the loss in adsorption capacity depended on the gas contacting conditions. X-ray spectroscopy was used to determine the homogeneity of the sulfur distribution within the adsorbents. The sulfur dioxide adsorption capacity for subsequent regeneration cycles was found to be a function of the Al₂O₃/SiO₂ ratio of the molecular sieve. Application of the molecular sieve adsorbents in a simulated combustion gas for sulfur dioxide removal was found to be superior to several adsorbents for the temperature range 21-76°C (70-170°F). However, as gas temperature increases, sulfur dioxide adsorption decreases. No adsorption of sulfur dioxide above 148°C (300°F) could be measured.
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    Conceptual design of an SOx scrubber system utilizing plant waste
    Wright, George Todd (Virginia Polytechnic Institute and State University, 1975)
    The use of ash pond water and cooling tower blowdown as possible SOx scrubber liquors has been studied. Information on analysis of ash pond water indicates that this method may be feasible. lt was found that ash from the furnace contained salts which could be used to absorb SOx in the scrubber. This would. significantly reduce the cost of lime or limestone addition to the scrubber water as presently proposed. Blowdown from cooling towers using sulfuric acid for calcium carbonate scale control does not appear to be an acceptable scrubber liquor. However, the makeup water may be passed through a flue gas cooler where a portion of the sulfur dioxide (SO₂) and sulfur trioxide (SO₃) are absorbed and the flue gas cooled before entering the scrubber. A scrubber design has been proposed which allows cleaning a portion of the scrubber packing while the scrubber is operating. A comparison of reheat versus fan power to assist in flue gas removal via the stack was made. A fan which would disperse the flue gas will be more economical if the maintenance costs of the fan and the saturated plume emitted from the stack at a high velocity are compatible.