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Biomass Conversion and Biorefinery

, Volume 2, Issue 3, pp 229–244 | Cite as

Cold flow model investigations of the countercurrent flow of a dual circulating fluidized bed gasifier

  • Johannes C. Schmid
  • Tobias Pröll
  • Hannes Kitzler
  • Christoph Pfeifer
  • Hermann Hofbauer
Original Article

Abstract

A novel fluidized bed gasification concept with enhanced gas–particle interaction combining two circulating fluidized bed reactors is proposed. Cold flow model results show the feasibility of the concept with regard to fluid dynamics. The aim of the design is to generate a nitrogen (N2) free product gas with low tars and fines contents. Therefore, the system is divided into an air/combustion and a fuel/gasification reactor. Two gas streams are obtained separately. The two reactors are interconnected via loop seals to assure the global circulation of bed material and to avoid gas leakages from one reactor to the other. The global circulation rate is driven by the gas velocity in the air/combustion reactor. Furthermore, the fuel/gasification reactor itself is a circulating fluidized bed with the special characteristic of almost countercurrent flow conditions for the gas phase and bed material particles. By simple geometrical modifications, it is possible to achieve well-mixed flow conditions in the fuel/gasification reactor along the full height. The gas velocity and the geometrical properties in the fuel/gasification reactor are chosen in such a way that the entrainment of coarse particles is low at the top. Due to the dispersed downward movement of the bed material particles and the feedstock input at defined locations of the fuel/gasification reactor, no volatiles are produced in the upper regions and the problems of insufficient gas phase conversion and high tar contents are avoided.

Keywords

Fluidization Circulating fluidized bed Dual fluidized bed Countercurrent gas–particle movement Gasification Sorption enhanced reforming 

Notation

Symbols

A

Free cross section, m2

AC

Constricted cross section, m2

AC/A

Aperture ratio, –

Ar

Archimedes number, –

D

Riser free diameter, m

DC

Constricted diameter, m

dp*

Dimensionless particle diameter, –

dp50

Particles mean diameter, m

Δp

Pressure drop, mbar

ε

Void fraction, voidage, –

(1 − ε)

Particle volume fraction, –

Fr*

Modified Froude number, –

g

Gravity constant, g = 9.81, m/s2

Gp

Particle mass flux, circulation rate, kg/(m2 s)

\( {{\dot{m}}_{\text{p}}} \)

Particle mass flow, kg/h

Re

Reynolds number, –

U

Superficial gas velocity, m/s

U*

Dimensionless gas velocity, –

Umb

Minimum bubbling velocity, m/s

Umf

Minimum fluidization velocity, m/s

Ut

Terminal velocity, m/s

\( {{\dot{V}}_{\text{g}}} \)

Gas volume flow, m3/h

ν

Kinematic gas viscosity, m2/s

ρg

Gas density, kg/m3

ρp

Particle density, kg/m3

(ρp − ρg)/ρg

Density ratio, –

Φ

Sphericity of particles, –

Abbreviations

APF

Absolute pressure fluctuations

AR/CR

Air/combustion reactor

CAGI

Compressed Air and Gas Institute

CFB

Circulating fluidized bed

CFM

Cold flow model

CLC

Chemical looping combustion

CLR

Chemical looping reforming

DCFB

Dual circulating fluidized bed

DFB

Dual fluidized bed

DPF

Differential pressure fluctuations

EPA

US Environmental Protection Agency

FR/GR

Fuel/gasification reactor

ILS

Internal loop seal

LLS

Lower loop seal

NBS

National Bureau of Standards

NIST

National Institute of Standards and Technology

SATP

Standard ambient temperature and pressure

SER

Sorption enhanced reforming

ULS

Upper loop seal

Notes

Acknowledgments

This work is part of the projects G-volution II and ERBA which are being conducted within the “New Energies 2020” research calls funded by the Austrian Climate and Energy Fund and processed by the Austrian Research Promotion Agency (FFG). The work has been accomplished in cooperation with TECON Engineering GmbH, voestalpine Stahl GmbH, and voestalpine Stahl Donawitz GmbH & Co KG.

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Johannes C. Schmid
    • 1
  • Tobias Pröll
    • 1
  • Hannes Kitzler
    • 1
  • Christoph Pfeifer
    • 1
  • Hermann Hofbauer
    • 1
  1. 1.Institute of Chemical EngineeringVienna University of TechnologyViennaAustria

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