Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a process for the production
of a gas containing hydrogen, carbon monoxlde and liFht
hydrocarbons from a hydrocarbon(s)-containin~ fuel
by means of partial oxidation and thermal cracking.
In this specification hydrocarbon(s)-containing
fuel includes mineral oils or oil fractions, tar sand,
tar sand oil or shale oil. Carbon-containin~ particles,
such as soot or coal, may be present in the fuel.
Partial oxidation of such fuels is carried out
in a hollow reactor with air, with oxygen or with air
enriched with oxygen. The pressure may vary within wide
limits. Mostly, steam is added to the reaction mlxture.
Such a partial oxidation results in a stream of ~as
rich in hydrogen and carbon monoxide at a temperature
of at least 1200C. The gas may be used for various
purposes, such as combustion, reduction, hydrogenation,
synthesis. It is known in the art that the composition
of the gas can be adapted to the application concerned
by a proper choice of feedstock, oxidant, and process
conditions and by means of one or more after-treatments
or conversions.
~hermal cracking of organic material is carried
out in general by supplying heat to the material in
the absence of a catalyst. Partial oxidation of hydrocarbons
is an exothermic process and it has already been proposed
to utilize the heat content of the hot gases for the
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endothermic thermal cracking process. In this combination
cracking is carried out under hydrogenating conditions
because of the direct contact of the hydrocarbons with
the heat-carrier which contains free hydrogen. The
invention provides a flexible process with various
possibilities of optimization.
Accordingly the invention relates to a process
for the production of a gas containin~ hydrogen, carbon
monoxide and light hydrocarbons from a hydrocarbon(s)-containing
~uel by means of partial oxidation and thermal cracking,
in which process
a) 50-100% of the fuel is introduced into a cracking
zone together with the hot gas as obtained accordin~
to c), resulting in a stream of gaseous products
and a residue,
b) the residue is separated from the gaseous products,
c) the residue as obtained according to b) and
the remaining fuel, if any, together with oxygen
or an oxygen-containing gas are introduced
into a gasification zone, resulting in a stream
of hot gas.
According to this process at least 50% of the
fresh fuel is introduced into the stream of hot gas.
This implies that most of the heat content of the gas
is utilized and ir 100% of the~fresh fuel is introduced
into the cracking zone maximum use is made of this
heat at the degree of cracking concerned. Furthermore,
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the residence time Or the fuel in the cracking zone
is of importance with respect to type of products obtained.
The introduction of the major part, up to 100%,
o~ the fresh ~uel into the hot gas has the considerable
advantage that up to the maximum amount of hydrocarbon
material with a high H/C ratio is subjected to crackin~,
leading to the maximum yield of light products of the
type wanted. It does not matter in principle how much
material with the lower H/C ratio is obtained as residue
from the cracking zone. The residue is gasified, which
process may be carried out properly with any type of
fuel, irrespective of the H/C ratio. There are many
degrees of freedom in this process, such as temperatures,
fuel composition, residence time, fuel/oxygen ratio,
fuel/steam ratio, etc., allowing a large flexibility
as far as product composition and yield are concerned.
Introduction of up to 100% of the fresh fuel into the
hot gas increases this flexibility because of the abundant
availability of material with a high H/C ratio for
the cracking process.
Introduction of the residue as obtained according
to b) into the gasification zone is preferably carried
out with a stream of steam. Steam is often introduced
in a gasification process as referred to in this specification
in order to convert soot into C0 and H2. Gases of an
inert type such as N2 may be used as well.
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Separation of residue and gaseous products obtained
from the cracking zone may be carried out by any suitable
mean Mostly the residue will consist of non-sticky
particles, which may easily be separated by centrifugal
forces such as exist in cyclones or bend separators.
Still more flexibility with regard to products
~ormed is obtained by recirculation to the cracking
zone of part of the residue obtained according to b).
This leads to a further degree of cracking. The temperature
10at the exit of the cracking zone is 500-~00C. Without
recirculation this temperature is 800-1100C. The heat
aontent oP the hot gas is ~urther utilized. The product
composition is ~hifted towards more cracking products
and less gasification products.
15Recirculation of residue to the cracking zone may
be varied within wide limits. A constraint is formed
by the heat requirement in the cracking zone, dictating
the minimum amount of combustible material to be fed
to the gasification zone. The production of heat in
the gasification zone is further dependent on the type
oP oxidant used.
.
.
- The stream oP gaseous products Prom the cracking
zone may be introduced into a fractionation column,
;~resulting in one or more hydrocarbon fractions and
~25~ a stream of gas. At least part of one or several of
the hydrocarbon fractions may be recirculated to the
.
~ cracking zone. This may be the heavier part of the
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products of the column, such as the residue. The final
result is formation o~ hydrogen- and carbon monoxide-containing
gases and li~hter hydrocarbon fractions, varying from
methane and other light ones in the gas to li~uid products,
such as tops and naphtha~ The fuel is fully converted.
The process is self-supporting as far as heat reauirements
are concerned.
The invention will further be elucidated with the '
aid of some figures.
Figure 1 shows a flow scheme of a process according
to the invention.
Fi~ure 2 shows a flow scheme of such a process
with recirculation of residue in the cracking zone.
~ igure 3 shows a flow scheme of such a process
combined with a fractionation column.
In figure 1 a gasification zone is indicated by
1 and a cracking zone by 2. 50-100% of the fresh fuel
3 is introduced into the cracking zone at 4 and the
remaining part, if any, into the gasification zone at
5. Gaseous products and a residue leave the cracking
zone 2 and are introduced into a cyclone 6 at 7. The
- residue leaves the cyclone at 8 and is taken up in
a device 9 into a stream of steam 10, which dispersion
is introduced into the gasification zone at 11. Oxygen
or an oxygen-containing gas is introduced at 12. Hot
gas from the gasification zone 1 is fed to the cracking
zone 2 at 13. Gaseous products leave the cyclone S at 14.
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In figure 2 and in fi~ure 3 corresponding elements
of the schemes are correspondin~ly numbered. Addition
o~ steam and separation of gaseous products and residue
are not indicated in fig. 2. Part o~ the residue 15
from the cracking zone 2 is recirculated at 16 to this ,
zone 2. The remainder is fed to the ~asification zone
1 at 17.
In figure 3 the gasification zone 1 and the crackin~
zone 2 are combined in one vessel 18. In this example
100% of the fresh fuel 3 is introduced into the cracking
zone 2 at 20, together with the residue 19 of a column
21. Column 21 is a fractionation column which is fed
by the stream 14 of gaseous products from the cyclone
6. Dependin~ upon the operating conditions of the column
21 and upon the composition of' the gaseous products
14, a variety of,.liquid products may be obtai,ned. The
gas 22 leavi~ the column 21 contains hydrogen and carbon
monoxide and possibly nitrogen and furthermore, light
hydrocarbons, like methane, ethane, propane, butane.
Liquid products may be tops 23, light naphtha 24, heavy
naphtha 25 and a residue 19. In this example 100%
~ of the residue 19 is recirculated to the cracking zone
2.
At least part of one or more of the other fractions
25, 24 or 23 may be recirculated to the cracking zone.
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