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Dynamic Modelling of Reactive Fluidized Bed Systems Using the Example of the Chemical Looping Combustion Process for Solid Fuels

  • Lennard Lindmüller
  • Johannes Haus
  • Ernst-Ulrich Hartge
  • Stefan HeinrichEmail author
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Abstract

The novel open-source flowsheet simulation software DYSSOL was used to simulate effects inside a system of interconnected fluidized bed reactors. The development of the needed models was done exemplary for the Chemical Looping Combustion process for solid and gaseous fuels. In CLC a solid oxygen carrier material is circulated between interconnected fluidized bed reactors. In the simulation, the focus is laid on the prediction of the dynamics of the whole system, especially the process start-up, shut-down and fuel load change. A dynamic model, which can be applied for bubbling beds and circulating fluidized beds was derived. Additionally, a cyclone was introduced for gas-solid separation. Loop seals ensure gas sealing between the reactors and were included into the modeling. Fluid mechanics inside the systems are modeled with empirical and semi-empirical, one-dimensional correlations, to enable fast calculations. These considerations allow real-time simulations of long-term effects in the system. The chemical reactions for gaseous and solid fuel combustions are included in the simulation. This has an effect on the solid oxygen carrier and so the oxidation and reduction of the carrier are regarded. The simulations were validated with experiments on a 25 kWth Chemical Looping Combustion facility at TUHH. The flowsheet models are able to predict the movement of the bed material between the units after operation changes as well as the time frames in which these changes occur. Besides, the gas and solids conversions in the fluidized bed reactors were simulated accurately.

Abbreviations

AR

Air Reactor

CCS

Carbon Capture and Storage

CFB

Circulating Fluidized Bed

CFD

Computational Fluid Dynamics

CLC

Chemical Looping Combustion

CLOU

Chemical Looping with Oxygen Uncoupling

CSTR

Continuously Stirred Tank Reactor

FR

Fuel Reactor

iG-CLC

In situ Gasification-CLC

OC

Oxygen Carrier

PFR

Plug Flow Reactor

S

Siphon/loop seal

SP

Standpipe

Nomenclature

a

Decay constant in the freeboard region (–)

Ar

Archimedes number (–)

Ar

Cross-sectional area of reactor (m2)

as

Share ratio of flow which is in inner cyclone vortex (–)

at

Ratio of interfacial area between bubble and suspension phase to the volume of a reactor element (1/m)

C

Weir coefficient (–)

Cb,l

Gas concentration of gas component l in bubble phase (mol/m3)

Cd,l

Gas concentration of gas component l in dense suspension phase (mol/m3)

Cf,l

Gas concentration of gas component l in the freeboard (mol/m3)

cv

Solids concentration (–)

cv,i,∞

Solids concentration above the transport disengagement height (–)

cv,mf

Solids concentration at minimum fluidization velocity (–)

cv,suspension

Solids concentration in the dense suspension phase (–)

D

Molar binary diffusion coefficient (m2/s)

Dc

Cyclone design parameter (–)

d*

Cyclone cut size diameter (m)

di,p

Average particle size in class i (m)

dp

Particle diameter (m)

dv

Bubble size (m)

dv,0

Initial bubble size (m)

Ea

Activation energy for the reaction (J)

Fg

Fd gravitational and drag force (kg m/s2)

g

Gravitational acceleration (m/s2)

Gs,i,∞

Solids circulation rate (kg/(m2s))

h

Height inside the reactor (m)

Hb

Height above the distributor where dense bottom zone ends (m)

Hw

Weir height (m)

\({\dot{\text{J}}}_{{{\text{Q}},{\text{l}}}}\)

Convective flow of gas component l (mol/m3)

k0

Pre-exponential factor (mol1−n Ln−1 s−1)

k1–k7

Reaction rate constant (mol1−n Ln−1 s−1)

kG

Gas diffusion resistance (mol/s)

Ki,∞

Elutriation rate for each particle interval i (kg/(m2 s))

KQ

Convective exchange rate of gas l (1/s)

Mass flow rate (kg/s)

mr

Total reactor inventory (m)

n

Reaction order (–)

p

Pressure (Pa)

ΔQ3,i

Particle size class fraction (–)

R

Universal gas constant (J/(K mol))

rg,l

Reaction rate of solid with gaseous component l (mol/m3)

T(ut,i)

Cyclone separation efficiency curve (–)

u

Superficial gas velocity (m/s)

ub

Bubble rise velocity (m/s)

ud

Velocity in dense suspension phase (m/s)

umf

Minimum fluidization velocity (m/s)

ut,i

Terminal velocity of particles in size interval i (m/s)

b

Visible bubble volumetric flow (m3/s)

or

Volumetric flow through a single orifice (m3/s)

W

Width of the standpipe/weir (m)

Xj,l

Solids conversion of component j with gas component l (–)

Greek letters

µ

Gas viscosity (Pa·s)

εb

Bubble volume fraction (–)

εmf

Minimum fluidization voidage (–)

ηf(d)

Cyclone separation efficiency (–)

θ

Scale dependent geometry parameter (–)

λ

Average bubble lifetime (s)

ρm,j

Molar density of solid reactant j (mol/m3)

ρsolid

Solid density (kg/m3)

Indices

0

Initial

b

Bubble

d

Dense suspension phases

f

Freeboard

i

Particle size class

j

Solid component

l

Gas component

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Copyright information

© Springer Nature Switzerland AG 2020

Authors and Affiliations

  • Lennard Lindmüller
    • 1
  • Johannes Haus
    • 1
  • Ernst-Ulrich Hartge
    • 1
  • Stefan Heinrich
    • 1
    Email author
  1. 1.Institute of Solids Process Engineering and Particle TechnologyHamburg University of TechnologyHamburgGermany

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