DEVICE FOR THERMALLY TREATING GRANULAR SOLID MATTER

DISPOSITIF POUR LE TRAITEMENT THERMIQUE DE MATIERES SOLIDES EN GRAINS

English Abstract

The invention relates to a device for thermally treating granular solid matter
for the purpose of carrying out endothermic reactions. CO2 and/or water is
removed from the solid matter in a reactor by burning fuel to generate a
combustion gas in the reactor, vortexing the solid matter with the combustion
gases in the reactor, using hot exhaust gas from the reactor to pre-heat the
solid matter and removing the solid matter from the reactor. The reactor used
is an approximately cylindrical, horizontal cyclone with an approximately
horizontal axis of symmetry and vortex. Fuel, solid matter and gases are
supplied in an inlet zone of the reactor while a rotation vortex is formed in
said inlet zone and solid matter and hot gas are removed from an outlet zone
of the reactor.

French Abstract

L'invention concerne un dispositif pour le traitement thermique de matières solides en grains, servant à réaliser des réactions endothermiques. Selon l'invention, le CO¿2? et/ou l'eau sont séparés des matières solides dans un réacteur. On fait brûler un combustible pour produire un gaz de combustion dans le réacteur, on crée un tourbillon entre les matières solides dans le réacteur et les gaz de combustion, on utilise les gaz brûlés chauds sortant du réacteur pour préchauffer les matières solides et on retire les matières solides du réacteur. Ce dernier se présente sous la forme d'un cyclone horizontal, pratiquement cylindrique, comportant un axe de symétrie et un axe de tourbillon pratiquement horizontaux. On achemine le combustible, les matières solides et les gaz dans une zone d'entrée du réacteur, en créant un écoulement tourbillonnaire dans cette zone d'entrée, et on retire les matières solides et le gaz chaud de la zone de sortie du réacteur.

Claims

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Claims
1. An apparatus for the thermal treatment of granular solids
for performing endothermic reactions, wherein CO2 and/or
water is split off from the solids, comprising a reactor
to which fuel, O2-containing gas and preheated solids
are supplied, wherein the fuel is burnt in the reactor to
produce combustion gas with temperatures in the range
from 600 to 1500°C, the solids in the reactor are brought
in fluidizing contact with the combustion gases, hot ex-
haust gas from the reactor is used for preheating the
solids, solids are withdrawn from the reactor with tem-
peratures in the range from 400 to 1200°C and the O2-
containing gas is preheated by means of the hot solids,
characterized in that the reactor constitutes an approxi-
mately cylindrical, lying cyclone with an approximately
horizontal axis of symmetry and swirling, where in an
inlet area of the reactor fuel, solids and gas are intro-
duced into the reactor, and from an outlet area of the
reactor disposed opposite the inlet area with a horizon-
tal distance solids and hot exhaust gas are withdrawn.
2. The apparatus as claimed in claim 1, characterized in
that at least one preheating cyclone is disposed before
the reactor.
3. The apparatus as claimed in claim 1 or 2, characterized
in that at least one cooling means is disposed subsequent
to the reactor, in which cooling means solids withdrawn
from the reactor are cooled in direct contact with O2-
containing gas.
4. The apparatus as claimed in claim 1 or any of the preced-
ing claims, characterized in that the reactor has a dis-
charge line for withdrawing hot exhaust gas, which dis-
charge line protrudes into the interior of the reactor by

a length T of 0.03 to 0.2 times the entire horizontal
length L of the reactor.
5. The apparatus as claimed in claim 1 or any of the preced-
ing claims, characterized in that the solids inlet open-
ing of the reactor is disposed at the periphery of the
reactor opposite the solids outlet.

Description

CA 02384957 2002-03-15
1
DEVICE FOR THERMALLY TREATING GRANULAR SOLID MATTER
Description
This invention relates to an apparatus for the thermal treat-
ment of granular solids for performing endothermic reactions,
wherein CO2 and/or water is split off from the solids, com-
prising a reactor to which fuel, Oz-containing gas and pre-
heated solids are supplied, wherein the fuel is burnt in the
reactor to produce combustion gas with temperatures in the
range from 600 to 1500°C, the solids in the reactor are
brought in fluidizing contact with the combustion gases, hot
exhaust gas from the reactor is used for preheating the sol-
ids, and solids are withdrawn from the reactor with tempera-
tures in the range from 400 to 1200°C.
Apparatuses of this kind are known and described for instance
in WO 97/18165 A1 and GB 2 019 369, wherein alumina is pro-
duced from aluminum hydroxide. WO 97/18165 proposes a circu-
lating fluidized bed for the reactor, and in accordance with
Gg 2 019 369 A1 the reactor is tubular with a vertical axis.

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It is the object underlying the invention to design the
above-mentioned apparatus in a simple way, so that a rather
small overall height of the plant will be sufficient.
In accordance with the invention this is achieved in that the
reactor constitutes an approximately cylindrical, lying cy-
clone with an approximately horizontal axis of symmetry and
swirling, where in an inlet area of the reactor fuel,
solids and gas are introduced into the reactor, and from an
outlet area of the reactor disposed opposite the inlet area
with a horizontal distance solids and hot exhaust gas are
withdrawn.
Expediently, at least one preheating cyclone is disposed be-
fore the reactor. In this case, preheating the solids can be
performed in~at least one cyclone by means of exhaust gas
from the reactor, the used exhaust gas being withdrawn
through a discharge line disposed in the cyclone in the man-
ner of a submerged tube. The discharge line designed like a
submerged tube reduces the overall height and at the same
time can be used for fixing the cyclone.
Expediently, a cooling means is disposed subsequent to the
reactor, so that solids withdrawn from the reactor are cooled
in direct contact with OZ-containing gas and the heated 02-
containing gas is introduced into the reactor, where it is
required for combustion.
The reactor may be used for the thermal treatment of various
solids; by way of example only aluminum hydroxide should be
mentioned here, which is converted to alumina. Furthermore,
e.g. carbonates may be used, from which COZ is thermally ex-
pelled, in order to recover oxides. Usually, it will be en-
sured that at least 50 wt-% of the solids supplied to the re-
actor have a dwell time of at least 5 seconds in the reactor,
where they are heated to the respectively required tempera-

' . ' CA 02384957 2002-03-15
_ _ 3 _
ture. To achieve a prolongation of the dwell time, the hot
exhaust gas should expediently be withdrawn from the reactor
through a discharge line which in the manner of a suspended
tube protrudes into the interior of the reactor by a length T
of 0.03 to 0.2 times the entire horizontal length of the re-
actor. This discharge line in the manner of a suspended tube
provides an additional fluidization in the gas, whereby the
dwell time thereof and hence also the dwell time of the sol-
ids in the reactor is prolonged.
Embodiments of the apparatus will be explained with reference
to the drawing, wherein:
Fig. 1 shows a variant of the apparatus in a view,
Fig. 2 shows a vertical longitudinal section through the re-
actor in a schematic representation,
Fig. 3 shows a section along line III-III of Fig. 2 through
the inlet area of the reactor as shown in Fig. 2, and
Fig. 4 shows a section along line Iv-IV through the outlet
area of the reactor as shown in Fig. 2.
The central element of the plant in accordance with Fig. 1 is
the reactor 1, which approximately has the shape of a lying
cylinder with a horizontal axis of symmetry and swirling.
The two preheating stages include the cyclones 2 and 3 with
associated rising pipes 2a and 3a, to each of which solids
are supplied in the base area. The solids to be treated, e.g.
aluminum hydroxide, are introduced into the rising pipe 2a
through line 4, in which rising pipe they are pneumatically
moved into the cyclone 2 by means of hot gas from line 5. The
exhaust gas leaves the cyclone 2 through line 2b, which ex-
tends downwards inside the cyclone 2 and opens in a gas
cleaning 6. The gas cleaning may for instance be designed as
wet cleaning or as electrostatic precipitator; cleaned gas is
withdrawn via line 7. In practice, any number of preheating
stages may be chosen.

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Solids preheated in the cyclone 2 leave the same through line
8 and are supplied to the base of the rising~pipe 3a. Hot ex-
haust gas from the reactor 1, which is supplied via line 9,
moves the solids to the cyclone 3, and preheated solids are.
supplied to the reactor 1 through line 10. Exhaust gas leaves
the cyclone 3 by flowing downwards in line 5 and is supplied
to the first preheating stage. If necessary, part of the sol-
ids coming from the cyclone-2 can be admixed to the hot sol-
ids of line 11, by-passing the hot area~of~the plant through
line 8a indicated in broken lines.
Through line 12, preheated, 02-containing gas (e.g. air) is
supplied to the reactor 1, and at the same time fuel is sup-
plied from line 13. To minimize the production of ash in the
reactor 1, gaseous fuel, e.g. natural gas, is normally used.
Usually, the combustion of the fuel with the o2-containing
gas already starts at the gas inlet la of the reactor 1, and
then a turbulent flow with a horizontal axis of fluidization
is formed in the inlet area of the reactor 1; details will be
explained below with reference to Figs. 2 to 4.
The hot solid product leaves the reactor 1 through the outlet
1b and is supplied to the cooling through line 11. Like pre-
heating, cooling can be effected in one or several stages. In
the present case, two cooling stages are represented, which
include the cyclones 15 and 16 and the associated rising
pipes 15a and 16a. Relatively cold, 02-containing gas is
supplied through line 17 to the base of the rising pipe 15a,
where it moves the solid product from line 11 into the cy-
clone 15. The gas leaves the cyclone 15 through line 12, and
the partly cooled solids reach the base of the rising pipe
16a through line 18. Relatively cold 02-containing gas, e.g.
ambient air, is supplied to this rising pipe 16a through line
19, and the solids are pneumatically moved into the cyclone
16. The gas then leaves the cyclone 16 through line 17, and

' CA 02384957 2002-03-15
cooled solids are withdrawn via line 20. Of course, any num-
ber of cooling stages may be chosen.
Figs. 2 to 4 show details of the reactor 1 with the gas inlet
la, a solids inlet lc, a gas outlet 9a and a solids outlet
1b. The preheated solids are supplied via line 10 and for in-
stance centrally supplied through the inlet lc to the inlet
area of the reactor 1, where they are entrained by the com-
bustion gases coming from the gas inlet la. It is-possible to
supply the solids from line 10 wholly or partly through line
10a indicated in broken lines also through the inlet la to
the reactor 1.
In particular by choosing the length L and the diameter Z of
the reactor 1 it should be ensured that at least 50 wt-o of
the solids supplied to~~the 'reactor have a dwell time of at
least 5 seconds and preferably at least 7 seconds in the re-
actor. The discharge line 9a is preferably designed so as to
protrude into the interior of the reactor in the manner of a
suspended tube preferably by a length T. This provides favor-
able flow conditions, which prolong the dwell times in the
reactor. The length T preferably is 0.03 to 0.2 times the re-
actor length L. An advantageous embodiment consists in that
the turbulence number, which is the ratio of axial momentum
to angular momentum in consideration of the solids momentum
and the quotient of inlet and outlet temperature, is larger
than 1.5.

Representative Drawing