PULSE POWER ELECTROSTATIC TECHNOLOGIES FOR THE CONTROL OF FLUE-GAS EMISSIONS

The reduction of pollutant emissions (NOx, SO2 and solid particulate) from fossil fuel boilers has become a major objective in several industrialized countries. The removal of solid particulate from flue gas is accomplished mainly with electrostatic precipitators because of the high collection efficiency they ensure without requiring onerous operating procedures. The application of microsecond pulse voltage energization, instead of the conventional rectified a.c. voltage energization, substantially improves the collection efficiency, at a given specific collection surface; reduces the specific power consumption, from about 0.5 Wh/Nm3 to about 0.1 Wh/Nm3; and allows a flexible operation of the precipitator to attain the required efficiency values, up to 99.8%, in the presence of fly ash with different physical and chemical characteristics. Although the benefits of pulse voltage energization are more remarkable when the electrical resistivity of the fly ash is higher than 1011 ω cm, they are still noticeable even when the electrical resistivity is lower by several orders of magnitude. Recently the nanosecond pulse voltage energization has been successfully applied for the simultaneous dry removal of NOx and SO2 from flue gas. Experiments carried out with test reactors, having a design configuration like the conventional electrostatic precipitators, have evidenced a removal efficiency of 50% to 60% for the NOx and higher than 80% for the SO2 with an energy input to the gas of about 15 Wh/Nm3. An additional benefit of the technology consist in the end products, ammonia sulphates and nitrates, which could be used as fertilizers or soil conditioners. While microsecond pulse voltage technology has already reached full industrial demonstration and reliable equipment is available, nanosecond pulse voltage technology is still at the development stage and requires further investigation of the process as well as testing of the pulse power supply on a larger industrial scale. © 1990.