Environmental Engineering Reference
In-Depth Information
under stoichiometric conditions. Accordingly, the relatively low O
3
supply
economizes the power consumption. Therefore, the attention in this chapter is
initially focused on the sole NO
2
removal under traditional WFGD solution
conditions. Effects of the pH value and reductive substances in the solution on the
removal efficiency are studied, in addition to the determination of the optimal NO
2
removal conditions and a product analysis. Thereafter, the attention is focused on
effects of the excessive O
3
conditions on the removal efficiency increase and the
product species. Finally, a simultaneous NO
2
and SO
2
removal scheme combined
O
3
oxidation with a two-tower scrubber is presented.
4.2 Experimental Section
Fig. 4.1 shows the experimental setup that combines O
3
oxidation with a wet
scrubber. Oxygen flows into an ozone generator (CF-G-3-010g made by Guolin,
Qingdao, China) to generate ozone. One part of the ozone flows into an ozone
analyzer (IN2000, IN, USA) to show the ozone concentration. The other part
enters into the simulated flue gas. NO, SO
2
, and N
2
are supplied from each bottle,
the properties of which are shown in Table 4.1. Each gas flow is separately
controlled by a mass flow controller. The simulated flue gas, which is composed
of NO, SO
2
, and N
2
, reacts with O
3
and then flows into the bottom of a
27-cm-height and 28-mm-i.d. scrubber tower. Placed within a flume, a specific
solution (with the pH value and tetravalent-S concentration fixed) is pumped to
the top nozzle (1/4-WXD-1.0-SS, made by Aogong, GuangZhou, China) of the
scrubber tower by an acid/alkali-resistant pump (MG3004-W, made by Pasika,
Nanjing, China). The flue gas flowing from bottom to top mixes with the solution
before entering into a flue gas analyzer (Rosemount, NGA2000). The solution
sample acquired in the tower bottom follows several steps before determining
species concentrations: (i) adjusting the pH value into alkalescence; (ii) diluting
the high ion concentrations if needed; (iii) anchored in a low temperature
atmosphere; and (iv) analyzed by an ion chromatogram (792 Basic IC). Na
2
SO
3
,
HCl, and NaOH\Ca(OH)
2
\CaCO
3
were used to make absorption solutions with
different compositions. NO
2
is produced when the molar ratio of O
3
/NO is 1.
Under these circumstances, NO
2
gas, used to replace ozone and NO, was thus
employed directly to simplify the experimental setup. The total flow rate of the
simulated flue gas was 1.5 L/min under the standard conditions, and that of the
scrubber solution was fixed at 28 mL/min.
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