Chalmers University of Technology

Assessment of Oxyfuel Circulating Fluidized Bed Boilers – Modeling and Experiments in a 5 MW Pilot Plant

2nd International Oxyfuel Combustion Conference September 13th, Queensland, Australia

Department of Energy and Environment Chalmers University of Technology

Metso Power Oy

Sadegh Seddighi David Pallarès Filip Johnsson

Mikko Varonen Irina Hyytiäinen Ville Ylä-Outinen Marko Palonen

sadegh.seddighi@chalmers.se

Chalmers University of Technology

Outline 1. Introduction

2. Modeling Fluid dynamics Combustion Heat Transfer

3. Experiment

Chalmers University of Technology

Why oxyfuel CFB?

General advantages of CFB : Fuel flexibility In-bed SOx removal Low thermal NOx

Particular advantages Oxyfuel CFB : Thermal flywheel of solid particles offers:

Efficient temperature control Potential for higher [O2] compact unit Capability of heat extraction external of furnace

Circulating Fluidized Beds (CFB):

Metso: 29 000 employees in 50 countries

Metso Power Main products: power & recovery boilers, evaporators, environmental systems

Introduction Modeling Experiment

Chalmers University of Technology

Aim 1. Model for: Design & scale-up of oxyfuel CFB Predicting Heat load distribution Gas/solid flow

Capable of handling Oxy/air 1D/3D Different FGR strategies Co-combustion (e.g. coal/biomass/waste)

2. Oxyfuel model validation 5 MW oxyfuel CFB experiments 100 KW oxyfuel CFB experiments

Introduction Modeling Experiment

Chalmers University of Technology

Background - CFB modeling at Chalmers

Existing model for air-fired CFB 6 year long model development Used for design scale up of CFB boilers 4 Journal paper published Validated against large scale(up to 550 MWth )

CFB boilers with good agreement

Introduction Modeling Experiment

-20

2

-5

0

5

5

10

15

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25

30

x [m]

z [m

]

800

850

900

950

1000

1050

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1150

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1250

1300

Chalmers University of Technology

Comprehensive model of CFB combustion

Fluid dynamics

Heat transfer Combustion

Introduction Modeling Experiment

Chalmers University of Technology

Comprehensive model of CFB combustion

Heat transfer

Introduction Modeling Experiment

Combustion

Char combsution

Volatile combsution

Disperse phase Dense bed Cluster phase

Convection

Radiation Fluid dynamics

Chalmers University of Technology

Solid circulation as a key parameter

Introduction Modeling Experiment

Air-fired

O2 [%mass]

Hea

t ex

trac

tio

n n

orm

aliz

ed

by

tota

l th

erm

al p

ow

er

Crucial design parameter for oxyfuel CFB

Chalmers University of Technology

5 MW CFB pilot tests Aims: To investigate Difference between air and oxy-combustion Safe operation of oxyfuel combustion(process control, interlocking system) Different test parameters

Introduction Modeling Experiment

Specifications: h= 13 m, Atop= 1x1 m2

52 tests in 4 weeks

Chalmers University of Technology

Features of test campaign

Introduction Modeling Experiment

Minimum Maximum

Thermal power MW 2.5 5.0

Average furnace temperature °C 770 920

Freeboard velocity m/s 3.0 5.5

O2 concentration in primary gas after mixing % 16.0 35.0

Fuel sulfur content % Low High

Ca/S ratio - 0 6

Chalmers University of Technology

Introduction Modeling Experiment

Schematic of test matrix

(Thermal power varying from 2.5 MW up to 5 MW) Selected test point in this presentation

Chalmers University of Technology

Oxyfuel case - Vertical distribution of pressure and solid concentration

Introduction Modeling Experiment

Oxyfuel case: [O2]primary = 25 % Ufreeboard = 4.8 m/s Pth= 4.2 MW • P = 7200 Pa

Chalmers University of Technology

Oxyfuel case - gas concentration

Experimental values which are shown here, are cross sectional averages (from three lateral positions). Model values are cross sectional averages.

Introduction Modeling Experiment

Chalmers University of Technology

Summary

A comprehensive model for CFB combustion has been developed to also apply to oxyfuel conditions. The work made so far shows that the model is Capable of describing different oxyfuel operational conditions Validated for Fluid dynamics and Combustion against experimental data

(Heat transfer validation ongoing)

Experimental runs in 5 MW oxyfuel CFB showed: Successful and safe operation under different operational conditions In furnace vertical temperature profile is smooth for all runs ([O2]primary =

16 - 35 % )

Chalmers University of Technology

Extra slides

Chalmers University of Technology

Thermal strategies

Thermal Strategies Inputs Outputs

given Tbb Tbb Tseal, Hseal

given Hseal Hseal Tbb, Tseal

given Hseal correlation Hseal=f () Tbb, Tseal, Hseal

Chalmers University of Technology

Fluid dynamics

Vertical Horizontal

Disperse phase

Core-annulus

Exponential decay

Core-annulus

Lateral differential flow

Cluster phase

Ballistic

Exponential decay Random-walk

Dense bed Perfect mixing

Introduction Modeling Experiment

Crucial design parameter for oxyfuel CFB

Chalmers University of Technology

Combustion

Volatiles combustion Combustibles: H2, CO, C1.16H4, C6H6.2O0.2 Non-combustibles: CO2 , H2O transport-controlled, mixing rate defined

Char combustion Both transport and kinetically controlled

Introduction Modeling Experiment

Chalmers University of Technology

Separate calculation of Radiation and convection

Convection: between gas-solids suspension heat extraction panels

Radiation: between Gas-solids suspension in core region Gas-solids suspension in wall layer Water walls Wing and division walls

qemittedi = •

i . A. • .T

i4

qabsorbed i = • • i,j qemittedi

qconv = hconv . A. • T hconv =25 . Cs 0.58

Optical factor

Heat transfer

Introduction Modeling Experiment

Chalmers University of Technology

Heat transfer – optical factor

i,j values are based on the following variables

Solids concentration Particle size Distance between radiating partners Geometrical disposition of each radiating partner

⋅⋅−=

s

v

d

lcF

5.1exp

Introduction Modeling Experiment

Chalmers University of Technology

1.5 radiation model • n radiative partners considered:

– Gas- solid suspension in core region – Gas- solid suspension in wall layer – Walls (including water walls and insulations) – Wing walls – Division walls

• Absorbed radiative heat by each partner is set by optical factors ( ) • An n*n matrix at each height is calculated

From\To layer core wall wgw1 wgw2 divw layer 0,0 0,3 0,5 0,1 0,1 0,0 core 0,8 0,0 0,0 0,1 0,1 0,0 wall 1,0 0,0 0,0 0,0 0,0 0,0 wgw1 0,2 0,8 0,0 0,0 0,0 0,0 wgw2 0,2 0,8 0,0 0,0 0,0 0,0 divw 0,0 0,0 0,0 0,0 0,0 0,0