Principle of Multi-Pollutants Removal Technology in Flue Gas by Ozone - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 30

2

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

2.1 Introduction

NO x , which are a significant threat to the environment, usually consist of 95% NO
in coal-fired flue gas. NO is characteristic of an extremely low water-solubility.
Thus, a process similar to that used to remove sulfur content from flue gas is
barely applicable for NO x removal. On the contrary, compounds with a high N
valence (i.e., NO 2 , NO 3 , and N 2 O 5 ) have a high solubility in water to produce
HNO 3 . This means that when initially oxidizing to these compounds and then
using an alkaline solution process, NO can be removed together with other acid
gases (such as SO 2 , HCl, and HF) in flue gas [1] . Similarly, 80% - 90% of Hg 2+
(i.e., HgO, HgCl 2 , and Hg 2 Cl 2 ) can be eliminated by WFGD even though Hg is
hardly soluble in water [2,3] . Table 2.1 shows the water solubilities of main
pollutants in flue gas.
Due to the oxidized compounds with higher solubilities, all of NO, SO 2 and
Hg attend to be initially oxidized into the oxidized species by ozone and then
eliminated successfully by an alkaline solution integrated with WFGD. As a result,
a technology characterized by the simultaneous removal of SO 2 , NO, Hg, HCl,
and VOCs in flue gas by ozone oxidation, has been examined to be applicable in
both bench-scale and pilot test facilities.
Fig. 2.1 presents the typical multi-pollution control technology that utilizes
ozone. This system consists of the following main steps:
1)

Oxygen production. Oxygen is produced in an air separation unit.

2) Ozone generation. The ozone generation technology has been