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

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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.

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Abbreviations

A :

Free cross section, m2

A C :

Constricted cross section, m2

A C/A :

Aperture ratio, –

Ar:

Archimedes number, –

D :

Riser free diameter, m

D C :

Constricted diameter, m

d p*:

Dimensionless particle diameter, –

d p50 :

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

G p :

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, –

U mb :

Minimum bubbling velocity, m/s

U mf :

Minimum fluidization velocity, m/s

U t :

Terminal velocity, m/s

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

Gas volume flow, m3/h

ν :

Kinematic gas viscosity, m2/s

ρ g :

Gas density, kg/m3

ρ p :

Particle density, kg/m3

(ρ p − ρ g)/ρ g :

Density ratio, –

Φ:

Sphericity of particles, –

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

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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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Authors and Affiliations

  1. Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060, Vienna, Austria

    Johannes C. Schmid, Tobias Pröll, Hannes Kitzler, Christoph Pfeifer & Hermann Hofbauer

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  1. Johannes C. Schmid
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  2. Tobias Pröll
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  3. Hannes Kitzler
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Correspondence to Johannes C. Schmid.

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Schmid, J.C., Pröll, T., Kitzler, H. et al. Cold flow model investigations of the countercurrent flow of a dual circulating fluidized bed gasifier. Biomass Conv. Bioref. 2, 229–244 (2012). https://doi.org/10.1007/s13399-012-0035-5

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