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Optimization of the location of injector in urea-selective catalytic reduction system

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Abstract

Urea–water solution (UWS) has been widely used in selective catalytic reduction (SCR) system as reductant to generate ammonia. The position where UWS nozzle should be located is a concerned issue and worth a deep investigation. Although UWS droplet evaporates and decomposes once it has been sprayed from the nozzle, the decomposition of droplet may be still incomplete if the distance between nozzle and reactor is not long enough. Thus, the incomplete decomposed UWS droplets will collect at the entrance of reactor, which is not beneficial for droplet evaporation, system flow and SCR efficiency. This paper presents the position where UWS nozzle should be placed from the perspective of evaporation and decomposition of UWS droplet. A numerical model of UWS droplet evaporation and decomposition was established in this paper and the droplet displacement is solved by adding droplet motion equation to the simulation model. The results can provide a practical help for designing a urea-SCR system.

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Abbreviations

A :

Pre-exponential factor, kg/(s m)

B m :

Spalding mass transfer number

B T :

Spalding heat transfer number

C D :

Drag coefficient

c p :

Heat capacity, J/(kg K)

D :

Droplet diameter, m

D c :

Mass diffusion coefficient, m2/s

E a :

Activation energy, J/mol

F :

Force, N

g :

Gravitational acceleration, m/s2

H :

Enthalpy of reaction, J/kg

h :

Heat transfer coefficient, W/(m2 K)

L :

Latent heat of vaporization, J/kg

M :

Molecular weight, kg/kmol

m :

Droplet mass, kg

m d :

Mass transfer rate, kg/(m2 s)

\(\dot{m}\) :

Mass flow, kg/s

P :

Pressure, Pa

\(\dot{Q}\) :

Heat transfer rate, W

R :

Universal gas constant, J/(mol K)

r :

Droplet radius, m

T :

Temperature, K

t :

Time, s

u :

Velocity, m/s

x :

Displacement, m

X :

Mole fraction

Y :

Mass fraction

∞:

Ambient

s:

Droplet surface

g:

Gas phase

mix:

Exhaust and water vapor mixture

d:

Droplet

l:

Liquid phase

vap:

Vaporize

u:

Urea

th:

Thermolysis

D:

Drag

B:

Buoyancy

Sphere:

Spherical droplet

i, j :

Species index

sat:

Saturation

a:

Air

w:

Water

u:

Urea

film:

Gaseous film

ρ :

Density, kg/m2

λ :

Heat conductivity, W/(m K)

\(\Phi\) :

Physical property

Nu:

Nusselt number

Re:

Reynolds number

Pr:

Prandtl number

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Acknowledgments

This study was supported by National Natural Science Foundation of China (Grant No: 51109049) and China postdoctoral Science Foundation (Grant No: 2011M500641).

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Authors and Affiliations

  1. College of Power and Energy Engineering, Harbin Engineering University, Harbin, 150001, China

    Xinna Tian, Youhong Xiao & Wenping Zhang

  2. Department of Naval Architecture and Marine Engineering, University of Strathclyde, Glasgow, G4 0LZ, UK

    Xinna Tian & Peilin Zhou

Authors
  1. Xinna Tian
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  2. Youhong Xiao
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  3. Peilin Zhou
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  4. Wenping Zhang
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Correspondence to Youhong Xiao.

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Tian, X., Xiao, Y., Zhou, P. et al. Optimization of the location of injector in urea-selective catalytic reduction system. J Mar Sci Technol 20, 238–248 (2015). https://doi.org/10.1007/s00773-014-0267-0

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  • DOI: https://doi.org/10.1007/s00773-014-0267-0

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