Principle of Multi-Pollutants Removal Technology in Flue Gas by Ozone - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 41

discharge in generating ozone are summarized as follows: (i) Less energy is
needed when transforming a gas source into ions and neutral substances. A
sophisticated cooling system that used to cool electrodes is no longer needed in
the cooling system, thereby reducing the cost; (ii) High energy electrons are
produced; (iii) The dielectric existence eliminates the spread of charged particles,
resulting in the streamer evenly distributing on the dielectric surface; (iv) The
dielectric existence can also eliminate the emission of cathode electrons and
inhibit the occurrence of an arc discharge phenomenon, thereby promoting the
streamer discharge. The published experimental results [48-52] have indicated that
the aforementioned ozone generator system equipped with pulsed discharge is
promising. However, before the real application, a number of issues need to be
resolved, such as (i) the lifespan and cost of the high-voltage power that used to
generate the nanosecond pulse and (ii) applicable methods for increasing the
discharge power.
Samaranayake et al . [53,54] experimentally studied the ozone generation by
using streamer discharge. It was found that the in a dry-air atmosphere and
without dielectric material, the ozone concentration increased with the energy
input density, whereas under the circumstances with PVC as the dielectric, this
concentration initially increased but then decreased. With the pulse repetition
frequency, air gap, and gas flow rate of 25 pps, 11 mm, and 3.0 L/min,
respectively, the ozone production rate attained the maximum value of 202
g/(kWh). For a spiral-cylindrical pulsed discharge electrode without dielectric
material, results from Namihira's group [55-57] suggested with the pulse repetition
frequency below 500 pps, pulse width of 130 ns, and oxygen as the gas source, the
ozone production rate achieved 100 g/(kWh), accompanied by the ozone
concentration of 30 g/m 3 . Also in the field of pulsed discharge used for ozone
generation, Shimomura et al . [58] experimentally obtained the highest ozone
production rate of 350 g/(kWh), while Samaranayake et al . [59,60] numerically
investigated the ozone generation assisted by the pulsed discharge method.
Understanding well the streamer propagation mechanism facilitates to improve
the ozone production efficiency of the pulsed discharge. Accordingly, Tsukamoto
et al . [57] experimentally obtained a streamer propagation velocity of 4.7×10 7 cm/s,
whereas Namihira et al . [56] acquired a clearly higher measurement of 1.8×10 8 -
3.3×10 8 cm/s. Although the two mentioned levels are different from those reported
values (i.e., 1.1×10 6 , 4.4×10 7 , 9×10 7 , and 1.8×10 8 cm/s), it can be determined that
the streamer propagation velocity under different experimental conditions should