Numerical modelling of CO2 enhanced coal

gasification in a pressurized circula-

ting fluidized bed reactor

Joanna Bigda1, Adam Klimanek2, Tomasz Chmielniak1, Wojciech Adamczyk2, Andrzej Szlęk2

1Institute for Chemical Processing of Coal, Zabrze, Poland

2Institute of Thermal Technology, Silesian University of Technology, Gliwice, Poland

12-16 June, Cologne, Germany

8th International Freiberg Conference

on IGCC & XtL Technologies

…beyond standards! 2

Introduction

• The work carried out within the frame of strategic project "Development of coal

gasification technology for high-efficiency production of fuels and energy"

Gasification of coal is one of the promissing `clean coal technologies’. This

includes gasification in CFBs

Growing popularity of FB utilization in the World

Modeling of dense particle laden flows in large systems is still challanging

Variety of modeling approaches can be used: from lumped models to

detailed DNS/DEM

Lack of comprehensive approaches in combustion/gasification modeling

Coupling of the hydrodynamics of reactive particles and gas

A few approaches are applicable to simulate medium and large scale

industrial facilities with detailed flow information in reasonable time

Motivation

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Introduction

Using of CO2 during pressurized gasification in circulating

fluidized bed

Attractive method of CO2 management removed during conversion of

fossil fuels – chemical recycling.

Reduction of consumption of hard coal and technical oxygen for the

same gas production.

Increasing efficiency and decreasing emission from the process.

Residence time of particles in the reaction zone promoting Boudouard

reaction.

„In situ” char.

Filling a market gap for gasification rectors with a capacity of 50-150

MW.

Increased reactor efficiency.

Increase of conversion degree of coal as a result of pressure influence

on the process kinetics.

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Classification of multiphase models for fluidized beds

1 μm 1 mm 0.1 m 10-50 m 1 m

Micro scale Meso scale Macro scale Lumped models

Unsteady

Steady and

quasi-steady

Correlation

models

0D

Global scale

Empirical and

semiempirical

1D/1.5D/3D

Euler-Lagrange

DEM/DPM-CFD

2D/3D

Averaged CFD

2D/3D

Euler-Euler

CFD-TFM

2D/3D

Particle scale

DNS, LBM,

DEM/DPM 2D/3D

1 μs

1 ms

1 s

1 h-1 d

1 year

Reproduced from: K. Myohanen, T. Hyppanen, 2011

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ANSYS Fluent vs. CPFD Barracuda

• General purpose software pakages

• It is an extended DPM approach for dense

systems with single particle or particle

groups (parcels) tracking

• Particle-particle interactions taken into

account by KTGF

• PSD taken into account in a natural way

• Heterogeneous reactions can be easily

implemented

• Limitations on the mesh size (parcels

should be smaller than cell volumes –

difficult balance)

• Designed to be focused on chemical reacting

particle dense flows

• MP- PIC approach for dense systems with

particle groups (parcels) tracking. Strong

coupling between fluid and particle phases

• Particle-particle interactions determined on

the Eulerian grid

• PSD taken into account in a natural way

• Heterogeneous reactions can be easily

implemented

• Detailed interphase momentum transfer can

be computed through the solved particle

distribution function

and taking into account contributions of

particles of different velocities and sizes

• LES turbulence model

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Geometry of the model

Gasification of solid fuels in CO2 in the pressurized circulating fluidized bed Parameters: Pressure: 1,6 MPa Coal stream: 100 kg/h Gasification agents: O2, CO2, steam Pilot scale gasifier, IChPW, Zabrze, Poland

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Geometry of the model

coal inlet char

recilculation

oxidizer

inlet

outlet

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Geometry of the model

Fluent mesh

135 000 elements

Barracuda mesh

100 000 elements

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Gasifying agent

Mass flow rate, kg/h 72.04

Composition, g/g

O2 0.164

N2 0.158

CO2 0.678

Temperature, K 421

Coal

Mass flow rate, kg/h 32.46

Coal inlet temperature, K 287

LHV, MJ/kg 27.5

Moisture (ar), % 10.7

Volatiles (ar), % 44.6

Fixed carbon (ar), % 35.7

Ash (ar), % 9.0

Operating conditions

Mass fraction, %

C 67.42

H 5.01

O 26.67

N 0.71

S 0.20

Ultimate analysis (AR)

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Operating conditions

• Coal density – 1200 kg/m3

• Char density – 650 kg/m3

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000

Cu

mu

lati

ve w

eig

ht,

%

Particle radius, mm

Coal

Char

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Coal gasification model

Volatiles release and breakup

• Constant rate devolatilization model

• Volatiles composition based on CPD model

VOL → 0.175𝐶𝑂 + 0.232𝐶𝑂2 + 0.048𝐶𝐻4 + 0.150𝐻2𝑂 + 0.0𝐻2 + 0.394𝑇𝐴𝑅

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Coal gasification model

Homogeneous reactions

𝐶𝑂 + 0.5𝑂2 → 𝐶𝑂2

𝐻2 + 0.5𝑂2 → 𝐻2𝑂

𝐶𝐻4 + 2𝑂2 → 𝐶𝑂2 + 2𝐻2𝑂

CO, H2 and CH4 oxidation - Eddy dissipation model/finite rate

𝑇𝐴𝑅 + 𝑎𝑂2 → 𝑏𝐶𝑂2 + 𝑐𝐻2𝑂 + 𝑑𝑁2

𝐶𝑂 + 𝐻2𝑂 ↔ 𝐶𝑂2 + 𝐻2

Water gas shift (kinetics from Bustamante et al., 2004)

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Coal gasification model

Heterogeneous reactions

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Results Average particles volume fraction (log scale)

Barracuda Fluent

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Results Gas Species Mass Fraction

Barracuda Fluent H2 CO

Barracuda Fluent

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Results

0

10

20

30

40

50

60

70

CH4 CO CO2 H2 N2 TAR

mo

le f

ract

ion

%

experiment

simulation - Barracuda

simulation - Fluent

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Results

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

mo

le f

ract

ion

of

com

po

ne

nts

, %

mole fraction of components (experiment), %

Barracuda

Fluent

CO2

CO

N2

H2

TAR

CH4

…beyond standards! 18

Conclusions

• Developed models corespond to changes in process

parameters and give results with a similar degree of

agreement

• The gas composition at the gasifier outlet using both

CPFD Barracuda and ANSYS Fluent models are

comparable with experimental data. The relative error

of mole fraction is lower than 20% besides H2 in Fluent

simulation

• The three-dimensional models and simulations provide

a promising way to simulate the coal gasification in

fluidized beds

• There are still challanges in the modeling framework

…beyond standards! 19

Thank you!

…beyond standards! 20

The investigations have been supported by the National Centre for

Research and Development in Poland as a research project Developing a

technology of coal gasification for high efficient production of fuels and

electric power.

www.zgazowaniewegla.

agh.edu.pl

www.ncbir.pl www.itc.polsl.pl www.polsl.pl www.ichpw.zabrze.pl