Pergamon

J. AemsoI Sci. Vol. 29, Suppl. 1, pp. S479-S480. 1998 0 1998 Published by Elxvier Science Ltd. All tights reserved

Printed in Great Britain C%?l-8502’98 $19.00 + 0.00

Application of Electrostatic Spraying to Reduce SO2 Emission in a Laboratory-Scale Spray Drying Absorber

Young-Cheol Byun, Jae-Yoon Jung, and Jungho Hwang

Department of Mechanical Engineering, Yonsei University, Seoul, 120-749, Korea

KEY WORDS

Atomization, SO, scrubbing, Electrostatic spraying, Slaked lime slurry

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 slaked lime slurry droplets (Ca(OH),) 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 and dispersion angle of the alkaline components.

Experiments were conducted to investigate the increase of SO, scrubbing efftciency in a laboratory-scale SDA with an application of high voltage to the nozzle/mesh electrodes (Fig. 1) and determine a charging system at the viewpoint of SO, scrubbing efficiency. For selected experimental conditions concentrations of SO, exited from the reactor were measured with various applied voltages and slurry flow rates. The applied

voltage varied from -10 to 1OkV. Configurations of conduction charging and induction charging were utilized.

air Compressed II

.

-10 -8 .6 4 3 0 2 4 6 6 10

Applied Wattage [Kvl

Fig. 1 System schematic Fig. 2 SO, concentration with respect to applied voltage

s479

S480 Abstracts of the 5th International Aerosol Conference 1998

Figure 2 shows the scrubbing efficiency of SO, for slurry flow rates of 15, 25, 35 ml/mm at the different charging systems. Consequently, the SO, scrubbing efficiency increased about 30% with the applied voltage of * 10 kV but independent of the polarity of the applied voltage. It was also found that the conduction charging system resulted in higher scrubbing efficiency of SO, than the induction charging system by 10 -20 %.

Especially for applied voltages greater than f 8 kV the rate of increase in the SO, scrubbing efficiency and current flowing was somewhat large. Difference of efficiency and current flowing between two charging configurations resulted from the difference of electric fields strength at charging zone, transport zone and deposition zone. For the conduction charging system, the electric field strength in charging zone might exert more sufficient Coulomb force on the liquid surface than that of induction charging system so that the force affected dispersion process itself to contact with more SO,.

Also the effect of slurry temperature on the SO, scrubbing efficiency was studied. It seemed that the temperature slightly influenced on both current flowing between the electrodes and SO, scrubbing efficiency, due to the relation between surface tension and threshold voltage.

Finally, 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 and physical properties of slaked lime slurry. For given slurry flow rate the droplet charge to mass ratio increased and the droplet diameter decreased as the strength of the applied voltage increased. To investigate the effect of electric field on spray characteristics, spray visualization was performed. Differences were distinct in droplet size and length of jet owing to the Coulomb force when high voltage was applied and these results approximately agreed with the droplet diameter by theoretical prediction.

ACKNOWLEDGEMENTS

The Korea Science and Engineering Foundation under grant 95-0200-05-01-3 has supported this work.

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