Hongna Wang

Nov. 28, 2012

Journal Report

About CFD

Investigation of hydrodynamics, heat transfer

and cracking reaction in a heavy oil riser with

bottom airlift loop mixer Jian Chang , Fandong Meng

Luoyang, SINOPEC

Chemical Engineering Science

78 (2012) 128–143

This paper aims at CFD investigation and optimization of hydrodynamics, heat transfer and cracking reaction in a heavy oil riser together with a bottom airlift loop mixer, which is operated with the new operating mode of low temperature contact and high catalyst-to-oil ratio. By extending a validated gas–solid two-phase flow model (Zheng et al., 2001) to incorporate the feedstock vaporization and a 12-lump heavy oil reaction kinetics model (Wu, 2009), a three-phase CFD model is estab- lished .

Introduction

[1] Wu, F.Y., 2009. Study on Lumped Kinetic Model for FDFCC. (Doctor Thesis). East China University of Science and Technology, China. [2] Zheng, Y.,Wan,X.,Qian,Z.,Wei,F.,Jin,Y.,2001.Numericalsimulationofthegas- particle turbulent flow in riser reactor based on k–e–kp–ep–y two-fluid model. Chem. Eng.Sci.56,6813–6822.

12-lump kinetics model (Wu, 2009) is used to describe the

cracking reaction of heavy oil in the current riser reactor.

Modelling

[1]Lan, X.Y., Xu, C.M., Wang, G., Wu, L., Gao, J.S., 2009. CFD mdeling of gas-particle flow and cracking reaction in two-stage riser FCC reactors. Chem. Eng. Sci. 64, 3847–3858. .

Validation

Drastically non-uniform in the axial and radial directionDeteriorating the gas-solid contact and then the cracking reaction

Drastically non-uniform in the axial and radial directionDeteriorating the gas-solid contact and then the cracking reaction

Hydrodynamics in riser

Well mixed in mixerComplex in the nozzle region

Heat transfer characteristics

Injection angle----60°is superior

Optimization of operating parameters

Reaction time --- a short time i.e. 3.02s is favorable.

Optimization of operating parameters

Catalyst-to-oil ratio --- 7-8 is more suitable.

Optimization of operating parameters

Conclusions

Extending a validated gas–solid flow model and 12-lump kinetic model, a three-phase flow and reaction model is established.The bottom airlift loop mixer causes the hot and the cool catalyst well mix and obtains a uniform catalyst temperature at riser inlet. Preferable condition for a higher light liquid yield: injection angle of 60°; catalyst-to-oil ratio of 7-8; and a shorter reaction time of 3.02 s .

Steady-state simulation of core-annulus flow

in a circulating fluidized bed (CFB) riser Xi Gao, Li-Jun Wang

Zhejiang University

Chemical Engineering Science 78 (2012) 98–110

Introduction

A steady-state multiphase CFD model is proposed for the simulation of core-annulus flow in a circulating fluidized bed (CFB) riser.There is no demonstration in the literature that the unrealistic sensitivity of steady models is well settled. The main objectives are: (1) to develop a new steady-state model to simulate the core-annulus flow, which can eliminate the unrealistic sensitivity while consuming less computational resources compared with transient models; (2) to conduct comparative analysis of the effects of inlet boundary conditions on the simulation results; (3) to investigate sensitivity of model parameters on simulated results.

Modelling

A CFD model based on Eulerian–Eulerian approach and

modified k-e turbulence model.

Second-order scheme was used for all variables except the

volume fraction equations, for which the QUICK discretization

scheme was used.

Results and discussion

The steady-state model can simulate the core-annulus flow more efficiently, which can eliminate the unrealistic sensitivity and consumes less computational resources .

The steady-state model can simulate the core-annulus flow more efficiently, which can eliminate the unrealistic sensitivity and consumes less computational resources .

Inlet boundary conditions

Results show that in the fully developed region, the steady-state model is not sensitive to the three different inlet boundary conditions. So C is used for simulation

Results show that in the fully developed region, the steady-state model is not sensitive to the three different inlet boundary conditions. So C is used for simulation

These sensitivity analysis were investigated in this section, in which four key parameters including particle–particle restitution coefficient (es), particle-wall restitution coefficient(ew), specularity factor(ψ) and kinetic energy transfer coefficient(Cs) were considered.

Sensitivity study

Conclusions

The steady-state model can simulate the core-annulus flow more efficiently, which can eliminate the unrealistic sensitivity.In the fully developed region, the steady-state model is not sensitive to the three different inlet boundary conditions.The sensitivity of the model predictions with respect to four parameters indicates that ew and ψ has weak influence on the correctly prediction of core-annulus flow, while the model remains a certain of sensitivity to es (1)and Cs(0.85).