Advanced Multiphase Simulation of Rotary Kilns: Coupling of ...

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emissions). ▫ Overview of the simulation challenges. ▫ Solution: Coupling of ANSYS Fluent and. KilnSimu by VTT. ▫ Samples and illustrations. ▫ Benefits of the ...

Advanced Multiphase Simulation of Rotary Kilns: Coupling of ANSYS Fluent and a Third Party Solver Eero Immonen Process Flow Ltd Oy

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Introduction to rotary kilns Why simulate?  Optimization (energy consumption, emissions) Overview of the simulation challenges Solution: Coupling of ANSYS Fluent and KilnSimu by VTT Samples and illustrations Benefits of the coupled solution

Rotary kilns in industrial processes 

Rotary kilns are huge (!) pyroprocessing devices used to raise materials to a high temperature Primary uses include:   

Manufacturing of pigment, cement, oxides, ... Lime calciner in the recovery cycle of chemicals (pulping) Roasting of sulfide ores prior to metal extraction

Slow rotation along primary axis ~ 1 rpm

Example: Rotary kilns in cement making

Schematic by Prosperity Minerals Holding LTD

Characteristics of rotary kilns 

A critical part of the manufacturing process  The kiln capacity defines the overall plant capacity  The main energy-consuming and greenhouse-gasemitting stage of production  Significant need for understanding the process and its parameters (e.g. heat transfer to the bed feed along kiln)  Significant optimization potential (e.g. burner section) Extreme operating conditions  High temperatures Challenging environment for measurements  simulate!  Vibration  Corrosion

Simulation challenges 

True multiphysical environment 

Solid phase phenomena (bed feed)  Particulate motion, erosion, heat transfer, chemical reactions (calcination), ... Gaseous phase phenomena  Combustion, turbulent flow, multitude of fuels Coupling of the solid and gaseous phase  Heat transfer from gas to the walls and bed feed  Transfer of reaction products (e.g. CO2, H2O, ...) from the bed feed to the gaseous phase

Introducing KilnSimu by VTT 

KilnSimu is a generic 1D multiphase simulator for rotary kilns 

State of the art resolution of bed chemistry using ChemApp Cell1

Gas out


Gas in eq.

Mass transfer of gas species between bed and gas. Convection and diffusion between gas and bed.


Gas in eq.

Gas in eq.

Gas in

Bed in

convection+ diffusion

convection+ diffusion

convection+ diffusion

dust+ volatiles

dust+ volatiles

dust+ volatiles


Bed in eq.


Bed in eq.

Mass transfer of condensed species between bed and gas. Dusting of solid particles and formation of liquid phases.


Bed out

Bed in eq.

Issue: Need a priori information on the combustion conditions (e.g. flame position) in order to obtain a realistic overall solution

Solution: Coupling of ANSYS Fluent and KilnSimu 

Gaseous and solid phase simulation in 1D in KilnSimu 

Gaseous phase simulation in 3D in ANSYS Fluent 

General-purpose solver for any rotary kiln application High-performance multi-phase CFD modeling environment hosting a leading selection of combustion sub-models Chemical reaction modeling, especially in turbulent conditions, has been a hallmark of Fluent since its inception

Coupling of Fluent and KilnSimu: KS  Fluent  KS  ...   

Unit conversions and front-end code for rapid simulation setup 1D  3D  1D geometry interfacing routines with interpolation Heat and mass transfer treatment on solid-gas interfaces  - Automated setup of b.c’s and c.z.c’s in Fluent Built-in postprocessing features

Schematic flow chart of the coupled solution Geometry and mesh


Fluent Set-up Fluent and KilnSimu or read parameters

Parameter files *.dat

Simulation parameters

Read interface fluxes

Export interface fluxes

Solve gas domain

Export interface heat fluxes


Solve KilnSimu domains

Read interface heat fluxes


KilnSimu solution loop

Fluent solution loop

Global solution loop

Illustration of the coupling: KilnSimu  Fluent Initial data calculated by KilnSimu are transferred to Fluent A.



Bed feed surface: Temperature boundary condition Gas volume: CO2 sources on bed feed surface Drum wall (lining): Temperature boundary condition



Drum shell Drum lining Gas volume Feed volume


Ilustration of the coupled solution

Resulting gas temperature profile

Benefits of the coupled simulation 

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Fewer a priori assumptions about combustion needed in KilnSimu to obtain realistic results Enhanced accuracy in estimating the gas-volume phenomena compared to the 1D treatment in KilnSimu Facilitates a detailed analysis, and optimization, of the burner area - this is not possible in a 1D solution More accurate description of radiation heat transfer Possibility of studying a large variety of chemical states in the feed, and, simultaneously, analyzing the associated gas volume phenomena

The coupled simulation helps reduce energy consumption and control emissions in rotary kilns!

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