CIESC Journal ›› 2019, Vol. 70 ›› Issue (2): 450-459.doi: 10.11949/j.issn.0438-1157.20181129

• Process system engineering • Previous Articles     Next Articles

Impact of turbulence model in coupled simulation of ethylene cracking furnace

Chengzhen NI1(),Wenli DU1,2(),Guihua HU2   

  1. 1. School of Information Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
    2. Key Laboratory of Advanced Process Control and Optimization Technology of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China
  • Received:2018-10-08 Revised:2018-10-26 Online:2019-02-05 Published:2018-10-29
  • Contact: Wenli DU E-mail:779893036@qq.com;wldu@ecust.edu.cn

Abstract:

The ethylene cracking furnace equipped with the bottom burner and the side wall burner is more and more widely used. Different combustion modes affect the turbulent flow state in the furnace. Considering the turbulent flow in the cracking furnace and the gas injection, the combustion and heat transfer are strong. The nonlinear coupling effect, for this purpose, explores the influence of different turbulence models in the cracking furnace/reactor coupling simulation is critical for the precise design and optimization of the cracking furnace. In this paper, a coupling simulation for a 100000 t industrial ethylene cracking furnace was carried out for different turbulence models. The turbulent flow model established by the standard k-ε model, RNG k-ε and Realizable k-ε model was evaluated by CFD numerical simulation. The simulation results of the three turbulence models are compared with the industrial data. The distribution of velocity, temperature and turbulence capacity in the cracking furnace is analyzed. The results show that the Realizable k-ε model is superior to the other two models in flame stability and reaction efficiency. And based on the Realizable k-ε turbulence equation, the calculation results of the heat flux and the outer wall temperature distribution of the furnace tube are closer to the actual working conditions.

Key words: turbulent flow, CFD, numerical simulation, cracking furnace, reactor coupling

CLC Number: 

  • TQ 021.1

Fig.1

SL-II cracking furnace structure"

Table 1

Cracking furnace structure size and operating conditions"

ItemParameters
furnace segment
length (x-direction)/m18.94
width (y-direction)/m3.56
height (z-direction)/m13.707
number of floor burners36
number of wall burners48
firing condition
fuel gas ?ow rate in bottom/(kg/s)1.2439
fuel gas ?ow rate in side/(kg/s)0.2025
oxygen excess/% (vol)2
fuel composition/%(mass)
CH497.686
H20.516
CO0.897
C2H40.899
reactor coils
number of reactor tubes24
number of passes2
inlet tube diameter×103/m64
outlet tube diameter×103/m121
thickness of tube×103/m6.5
feed rate/(kg/s)11.11
steam dilution/(kg/kg)0.6
coil inlet temperature/K883
coil outlet pressure/kPa206

Fig.2

Flue gas z-velocity component along width of furnace in plane 0.525 m at different heights"

Fig.3

Temperature distribution of turbulence model in plane 0.225 m"

Fig.4

Turbulence intensity distribution of turbulence model in plane 0.525 m"

Fig.5

Turbulent flow energy of different turbulence models along height of furnace"

Fig.6

Turbulent dissipation rate of different turbulence models along height of furnace"

Fig.7

Turbulent viscosity of different turbulence models along height of furnace"

Fig.8

NO concentration distribution of turbulence model in plane 0.225m"

Fig.9

Distribution of NO mass fraction along height of furnace in different turbulence models"

Fig.10

Heat flux of different turbulence models and temperature distribution curve of outer wall of furnace tube"

Fig.11

Comparison of Prandtl numbers for different turbulence models"

Table 2

Comparison of simulated and industrial values between different turbulences"

项目工业值标准 k-ε模型Realizable k-ε模型RNG k-ε模型
出口油气温度/K11081102.81104.61099.6
最大管壁温度/K1247.61251.91253.51260.4
过剩氧含量/%(vol)21.811.901.90
炉管油气压降/MPa0.04330.03500.03660.0355
P/E0.680.720.680.0.74
乙烯收率/%(mass)30.14329.8629.74.29.46

"

Gk——由平均速度梯度引起的湍流动能
Ui——速度矢量
Yi*——时间τ*后细微尺度内组分i的质量分数
μt——湍流黏性系数
ξ*——细微尺度长度分数
ρ——流体密度
σε——湍流Prandtl数
τ*——反应时间尺度
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