Energy recovery by gasification of agricultural and forestry wastes in fluidized bed reactors and in moving bed reactors with internal recycle of pyrolysis gas

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

Description

Process development and reactor modelling
Energy research

Informations

• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 9
• Langue: English
• Poids de l'ouvrage: 9 Mo

Extrait

Commission of the European Communities
energy
ENERGY RECOVERY BY GASIFICATION
OF AGRICULTURAL
AND FORESTRY WASTES
IN FLUIDIZED BED REACTORS
AND IN MOVING BEDS
WITH INTERNAL RECYCLE
OF PYROLYSIS GAS; PROCESS DEVELOPMENT
AND REACTOR MODELLING
Report
EUR 10012 EN
Blow-up from microfiche original Commission of the European Communities
energy
ENERGY RECOVERY BY GASIFICATION
OF AGRICULTURAL
AND FORESTRY WASTES
IN FLUIDIZED BED REACTORS
AND IN MOVING BEDS
WITH INTERNAL RECYCLE
OF PYROLYSIS GAS; PROCESS DEVELOPMENT
AND REACTOR MODELLING
F.G. VAN DEN AARSEN, H. SUSANTO, A.A.C.M. BEENACKERS
W.P.M. VAN SWAAIJ
LABORATORY OF CHEMICAL REACTION
Engineering and Industrial Processes and Products
Twente University of Technology
P.O. Box 217
NL-7500 AE Enschede
Contract No. ESE-R-029-NL
FINAL REPORT
Directorate-General Science, Research and Development
1986 EUR 10012 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of then is responsible for the use which might be made of the following
information
© ECSC—EEG—EAEC Brussels - Luxembourg, 1986 in
ABSTRACT
A modified co-current moving gasifier bed has been developed which
substantially reduces product gas tar content compared to conventional
down draft gasifiers and allows for a better scale-up of the reactor.
These improvements have been realized by installing an ejector in the
air inlet which sucks the pyrolysis gases into the gasifying air stream
and allows for subsequent combustion of the pyrolysis products in a
separate combustor. Results have been published in refs. (1, 2).
In relation to the modelling of a fluidized bed biomass gasifier, we
studied the fast pyrolysis of beech wood particles and the
char-carbondioxide gasification kinetics in a bench scale fluidized bed
reactor.
A 30 cm diameter fluidized bed biomass gasifier has been constructed and
the reactor performance on wood and rice husks has been studied. Those
experiments (at 50 kg biomass/hr) revealed that a good gas quality is
produced if the reactor is operated above 800eC, in the co-current mode
(bottomfeed) (3, 4, 5).
Ongoing research is on mass transfer and flow behaviour in the fluidized
bed reactor; a mathematical model of the fluidized bed gasifier is under
development. CONTENTS PAGE
I. Introduction
II. Summary of fluidized bed reactor research 3
III.y of research on the moving bed reac­
tor with internal recycle ?
IV. Publications resulting from contract
ESE-R-029-NL 10
A I. Introduction3
A II. Wood pyrolysis and carbon dioxide char gasi­
fication kinetics in a fluidized bed 25
A III.Bubble to dense phase mass transfer kinetics
in gas solid fluidized beds 51
A IV. Modeling of a fluidized bed wood gasifier 8
Β I. Introduction 165
Β II. Literature review on gasification and pyro­
lysis of wood '69
Β III.Experimental work in a pilot plant gasifier 200
Β IV. Thermodynamic analysis of recycle system 220
B V. Pyrolysis zone model 246
Β VI. General conclusions 265
Β VI. Literature section B.7
Β VI. Appendices to Section B.A. till Section
B.P. 27I. INTRODUCTION
During the past 5 years about: 40 companies in Europe alone
have been founded for production of small scale co-current
moving bed gasifiers using woodchips as the principal feed­
stock. Capacities offered vary between 10 and 1000 kg wood
per hour. Twente University started research on the co-cur­
rent gasifier as early as 1975. It published design rules
for this type of reactor under E.C. Contract 662-78-IESN.
One of the disadvantages of the co-current moving bed is its
poor flexibility with respect to feedstock. Specially small
particles as raw dust and high ash containing particles (e.g.
municipal solid wastes and rice hulls) often cause flow and
sintering problems.
For such difficult feedstocks a fluidized bed gasifier may turn
out to be a prospective alternative because of its rather om­
nivorous character with respect to feedstock specifications.
We therefore decided to develop a fluidized bed pilot plant
reactor and to derive a chemical reaction engineering model
for scale-up purposes and for predicting reactor performance
as a function of reactor design and both operating and feed­
stock parameters.
Part A of this report gives the results of this part of the
project.
An alternative solution for high ash containing fuels may be
found in a modified co-current moving bed reactor design in
which the pyrolysis gases are sucked to the air inlet, pré
mixed with the gasifying agent and then prë-combusted in a
separate combustion chamber yielding combustion products which
then subsequently act as the gasifying agent for converting
the char left from the pyrolysis process. This way, the local hot spots usually observed in conventioal co-current designs
possibly can be avoided thus providing a solution for low
melting, high ash containing, feedstocks.
Additionally this method is expected to prevent any slip
of unconverted pyrolysis gases to the reactor outlet thus
yielding extremely low tar producer gas. The latter property
would be an advantage in internal combustion engine applica­
tions.
In section Β we report on the development of this new type of
gasifier, the practical performance data observed and a model
describing the internal reactor processes as a function of
particularly the recycle ratio.