An application of the electrostatic spray technology to increase scrubbing efficiency of SO$_{2}$ emitted from thermal systems

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Emission control of acid exhaust gases from coal-fired power plants and waste incinerators has become an increasing concern of both industries and regulators. Among those gaseous emissions, SO has been eliminated by a Spray Drying Absorber (SDA) system, where the exhaust gas is mixed with atomized limestone-water slurry droplets and then the chemical reaction of SO with alkaline components of the liquid feed forms sulfates. Liquid atomization is necessary because it maximizes the reaction efficiency by increasing the total surface area of the alkaline components. An experimental study was performed with a laboratory scale SDA to investigate whether the scrubbing efficiency for SO reduction increased or not with the application of a DC electric field to the limestone-water slurry. For a selected experimental condition SO concentrations exited from the reactor were measured with various applied voltages and liquid flow rates. The applied voltage varied from -10 to 10 kV by 1 kV, and the volume flow rate of slurry was set to 15, 25, 35 ml/min which were within the range of emission mode. Consequently, the SO scrubbing efficiency increased with increasing the applied voltage but was independent of the polarity of the applied voltage. For the electrical and flow conditions considered a theoretical study of estimating average size and charge of the atomized droplets was carried out based on the measured current-voltage characteristics. The droplet charge to mass ratio increased and the droplet diameter decreased as the strength of the applied voltage increased.