Investigation of Advanced NO Oxidation Process with the Delivery
of OH from Thermal Decomposition of H
2
O
2
Kaikai Kou,
1
Wei Zhou,
1
Yan Wang,
1
Haiqian Zhao
2
and Jihui Gao
1
*
1. School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, P. R. China
2. School of Civil Engineering & Architecture, Northeast Petroleum University, Daqing 163318, P. R. China
DevelopmentofanefficientandeconomicNOoxidationtechnologyisthekeystepforthesimultaneousremovalofNOx andSO
2
incoal-
firedpowerplants.Inthiswork,anoveladvancedoxidationprocessofNOwasproposed,whichdirectlydeliveredhighlyoxidativehydroxyl
radicals (OH)generatedfromthethermalactivationofH
2
O
2
vapourintofluegasflow.Theexperimentsweredemonstratedinalab-scale
device,measuringtheoxidationofNOastheindicatorofradicalformationanddelivery.Theinfluenceofvariousoperationalparameterson
NO oxidation was evaluated. Increasing the H
2
O
2
dosage, the temperature of the hot-nitrogen, the flow rate of the hot-nitrogen, and the
totalgasresidencetimegreatlyenhancestheNOoxidation.TheNOoxidationwasinhibitedobviouslywiththeincreasingoftheH
2
O
2
pH
andtheNOinitialconcentration.IncreasingtheH
2
O
2
pHandtheNOinitialconcentrationobviouslyreducedtheNOoxidation.Theresults
indicatedthatthethermalactivationofH
2
O
2
isfeasibletooxidizeNOandthattheH
2
O
2
homogeneousthermaldecompositionreactionis
essential, therefore, the temperature and the flow rate of the hot-nitrogen can significantly affect the conversion efficiency. Finally, a
potentialapplicationwasproposed,whereNOoxidationbygas-phaseH
2
O
2
canbecoupledwiththegeneralSCRsystemtomeetstringent
regulatory requirements and with a low operating cost.
Keywords: NO oxidation, H
2
O
2
vapour, thermal decomposition, hydroxyl radicals
INTRODUCTION
T
he emission of sulphur dioxide (SO
2
) and nitric oxides
(NOx) from coal-fired power plants has caused severe
effects on the environment and public health. The
impacts include acid deposition, regional haze, and photo-
chemical smog.
[1]
Due to its coal-dominated energy structure,
the Chinese government has to face enormous pressure to
reduce pollutant emissions and has issued a series of restriction
criteria, especially for coal-fired power plants (“Emission
Standard of Air Pollutants for Thermal Power Plants” (GB
13223–2011)). With the limit value in national standard
becoming increasingly stringent, the technologies for pollutant
control are developing. Currently, low NOx combustion and
ammonia-based selective catalytic reduction (NH
3
-SCR) pro-
cesses are common techniques for NOx emission reduction.
[2]
Treatment for SO
2
generally includes lime or limestone
scrubbing of flue gases.
As the public grows more concerned about the environment,
pollution control technology needs to be upgraded. The ultra-
low emission for NOx is 50 mg/m
3
, which will probably be the
next Chinese national standard. When the SCR process treats a
low concentration of NOx (<100 mg/m
3
), the dosage of
catalysts and NH
3
tend to dramatically increase, which will
increase the leakage of NH
3
and increase the operating costs.
[3]
Parties responsible for the emission sources are going to seek
economic methods to meet regulatory requirements, and this
method could be a promising way of further removing NOx and
SO
2
downstream the SCR unit.
[4]
However, NOx is difficult to
remove in wet scrubbers because its predominant form (NO)
has a remarkably low solubility.
[5,6]
In recent years, various advanced oxidation processes
(AOPs) have been developed to convert NO to the
more soluble higher oxidation states (NO
2
, HNO
2
, and HNO
3
)
for the simultaneous removal of NOx and SO
2
, such as low-
temperature plasma,
[7,8]
photocatalysis,
[9–12]
ozonation,
[13,14]
the liquid Fenton system,
[15–17]
etc. Nevertheless, there are
several problems related to their commercial application,
including high operating costs, unstable performance, and
the liquid phase mass transfer limitation.
[18]
Hence, an
economical and efficient method urgently needs to be
developed.
H
2
O
2
-based oxidation processes have been widely investigated
in the gas and liquid contamination treatment field, due to their
superiority in terms of their relatively lower cost and lower
secondary environmental impact.
[19,20]
H
2
O
2
iseffectivebecauseit
dissociates into OH, and this radical is extremely reactive (redox
potential of 2.8 V).
[21,22]
Some authors carried out the oxidation of NO by utilizing
various H
2
O
2
-based reaction systems. Liu et al.
[18]
developed an
oxidation removal process for the simultaneous removal of NO
and SO
2
using a vacuum ultraviolet activated O
2
/H
2
O/H
2
O
2
system, and it exhibited excellent simultaneous removal
capacity. Hao et al.
[23]
proposed a process that included UV
catalyzing H
2
O
2
vapour for the simultaneous removal of SO
2
and
NO. However, UV lamps directly in the flue gases can lead to
operating and maintenance problems.
[5]
H
2
O
2
can also be
activated homogeneously by thermal energy, in which the
H
2
O
2
molecule decomposes into two OH.
[24]
The hydroxyl
* Author to whom correspondence may be addressed.
E-mail address: gaojh@hit.edu.cn
Can. J. Chem. Eng. 9999:1–7, 2019
©
2019 Canadian Society for Chemical Engineering
DOI 10.1002/cjce.23482
Published online in Wiley Online Library
(wileyonlinelibrary.com).
VOLUME 9999, 2019 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING 1