Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
K 9374
PROCESS AND BURNER FOR THE GASIFICATION OF SOLID FUEL
The present invention relates to a process for the gasificat-
ion of a finely divided solid fuel and to a burner for carrying
out such a process.
Gasification of a solid fuel may be defined as a process
wherein solid fuel is partially combusted with a substoichiometric
amount of pure oxygen or an oxygen containing gas, such as air,
to form product gas consisting mainly of carbon monoxide and
hydrogen. Depending on the composition of the combustion medium
the productgas further contains other substances which may be
10 useful or may be considered as pollutant3.
Although the present invention will primarily be described
with reference to pulverized coal, it should be noted that the
burner and process according to the invention are also suitable
for other types of solid fuels which can be gasified, such as
lignite, wood, bitumen, soot and petroleum coke.
According to a well known gasification process solid fuel in
a finely divided state is passed with a carrier gas to a reactor-
zone via a burner, while the combustion medium is either added to
the solid fuel flow inside the burner or is separately introduced
into said reactorzone. Great care must be taken that the reactants
are effectively mixed with one another. If the reactants are not
brought into intimate contact with each other, the oxygen and
solid fuel flow will follow at least partially independent tra-
jectories inside the reactor. Since the reactor zone is filled
with mainly hot carbon monoxide and hydrogen, ~he oxygen will
rapidly react with these gases instead of with the solid fuel.
The so formed very hot combustion products carbon dioxide and
steam will also follow independent trajectories having poor con~
tact with the relatively cold solid fuel flow. This behaviour of
the oxygen will result in local hot spots in the reactor, thereby
possibly causing damage to the reactor refractory lining and in-
creased heat ~luxes to the burner(s) applied.
~,.
e~
. . .
:
:.,
~z~
Sufficient mixing of the solid fuel and the oxygen can be
attained by adding the oxygen to the solid fuel flow in the burner
itself. A disadvantage of this method consists, however, therein
that - especially at high pressure gasification - the design and
operation of the burner are highly critical. The reason for this
is that the time elapsing between the moment of mixing and the
moment the fueltoxygen mixture en~ers into the reactor zone should
be invariably shorter than the combustion induction time of the
mixture. Moreover, the velociey of the mixture inside the burner
should be higher than the flame propagation velocity in order to
avoid Elashback. However, the combustion induction time shortens
and the flame propagation veloci~y inceases at a rise in gasificat-
ion pressure. Further, if the burner is operated at a low fuel load
or, in other words, if the velocity of the fuel/oxygen mixture in
the burner is low, the combustion induction time or flashback con-
dition might easily be reached in the burner itself, resulcing in
overheating and possibly severe damage to the burner.
The above-mentioned problem of the premature combustion in
the burner itself will not occur if the Euel and oxygen are mixed
outside the burner in the reactor space itself. In this case
special measures are, however, ~o be taken to ensure a sufficient
mixing necessary for an effective gasification of the fuel as
discussed in the above. To promote an intimate mixing of fuel and
oxygen it has already been proposed to introduce the oxygen as
high velocity jets into the fuel flow. Applicant's copending Can-
adian patent application No.437,057 relates to such a systemfor gasification of solid fuel in which a core of solid fuel is
introduced into a reactor space and oxygen in the form of high
velocity jets are directed towards the core of solid fuel for
breaking up the solid fuel flow so that all fuel particles can
be contacted with oxygen for the purpose of gasification. This
' already proposed method for contacting the solid fuel with oxygen
- is attractive if the ~re of solid fuel can be kept rather small
~ or, in other words, if a rather low capacity gasfication process
. ~
~ t7~ ~
_3_ 3293-2~12
is aimed at. Problems may occur when high throughputs of solid
fuel are to be processed. In -the latter case the solid Euel
should be supplied as a relatively thick core into the reactor
space. Increase of the thickness of the core, however, has an
adverse influence on the possibility of breaking up the solid
fuel flow. The oxygen should then be supplied to the solid
fuel flow with extremely high velocities necessary for a suffi-
cient penetration into the solid fuel. Such high velocity jetsmay easily cause suction of the already formed reactor gases
along the burnerfront with the risk of overheating of the latter.
In the above-mentioned previous patent application it is there-
fore proposed to surround the high velocity oxygen jets with
shields of relatively low velocity steam for suppressing SUCti
of reactor gases.
Thus the present invention seeks -to provide a process
for the gasification of in particular high quantities of solid
fuel wherein the solid fuel flow can be properly broken up by
oxygen jets having a relatively moderate velocity.
Thus this invention provides a process for the gasifi-
cation of a finely divided solid fuel, comprising -the steps of
supplying finely divided solid fuel as an annulus into a reactor
space and introducing oxygen or an oxygen containing gas into
said reactor space, allowing the oxygen or oxygen containing gas
to react with the finely divided solid fuel for gasification of
the latter, wherein at least part of the oxygen or oxygen
containing gas is introduced into the reactor space as a
plurality of moderate velocity jets arranged to intersect the
3293-2~12
-3a~
annulus of finely divided solid fuel r and wherein said moderate
velocity jets are substantially uniformly distributed relative
to the said annulus of finely divided fuel.
Since in the above process the solid fuel is supplied
to the reactor space as an annulus, the thickness of the solid
fuel flow can be kept rather moderate even at high fuel through-
puts. The solid fuel can be easily penetrated by the oxygen
jets for a proper breaking up of the fuel flow.
The oxygen jets are preferably uniformly distributed
with respect to the annular solid fuel flow, to ensure a
substantially uniform breaking up to the solid fuel flow. The
number of oxygen
.
,
.
7~i~
jets which should be applied depends, among other things~ on the
diameter of the annulus of solid fuel, on the width of the annulus
and on the behaviour of the solid fuel itself. If the solid fuel
flow is relatively compact, a relatively large amount of oxygen
jets will be required for attaining a proper breaking up of the
solid fuel flow. Care should, however, be taken that the oxygen
jets are sufficiently spaced apart from one another to avoid
reduction of the oxygen jet momenta due to interference between
the oxygen jets.
In a suitable embodiment of the invention the oxygen jets
are arranged to intersect the annulus of finely divided solid
fuel fr the outside. For substantially eliminating the risk of
escape of non-conver~ed solids, it may be advantageous to arrange
the oxygen jets in such a manner that they form a substantially
closed shield around the annular solid fuel flow without, however,
interfering with one another. It is also possible to reach the
above objective by applying shielding means separate from the
oxygen jets for breaking up the solid fuel flow. It is preferred
to apply a low velocity flow of oxygen or oxygen containing gas
for forming said shield around the arrangement of solid fuel flow
and oxygen jets for break-up.
In a preferred gasification process according to the invent-
ion, combustion medium is not only supplied via the high velocity
jets intersecting the annular solid fuel flow from the outside
but also via a futher supply source substantially centrally
arranged inside the annular solid fuel flow. This further combust-
ion medium, formed by oxygen or an oxygen-containing gas, serves
apart from the combustion aspect a plurality of purposes. This
central gas flow will keep the flame formed after ignition of the
combustible mixture of solid fuel and oxygen, away from the burner
front thereby reducing the risk of overheating of the burner. It
further serves as a support of the annular solid fuel flow pre-
venting collapse of the fuel flow upon exposure to the oxygen
jets.
-- 5 --
In a further suitable embodiment of the invention the oxygen
jets are grouped in pairs, wherein the jets of each pair are
arranged at opposite sides inside and outside of the annular solid
fuel flow in such a manner that these jets intersect one another
substantially in the annulus of solid fuel. This arrangement of
the oxygen jets is particularly suitable for high capacity operat-
ion in which the annulus of solid fuel should necessarily have a
rather large width. The groupwise positioning of the oxygen jets
ensures that the solid particles remain in the annulus of fuel and
are not pushed away from the desired trajectory by the oxygen jets
operating from the inner side of the solid fuel annulus. The last-
mentioned process according to the invention may be further opti-
mized by the supply of low velocity gas in the annulus, preferably
in the centre, for further support;ng the annulus of solid fuel.
As already indicated in the above with reference to the process in
which the oxygen jets are all located outside the annulus, the low
velocity gas preferably consists of oxygen or an oxygen containing
gas, serving not only as a support for the fuel annulus but also
as further combustion medium completing the amount of oxygen
required for a proper gasification of the fuel.
The groups of oxygen jets are preferably substantially
uniformly distributed relative to the annulus of finely divided
solid fuel in order to obtain a substantially homogeneous mixture
of solid fuel and oxygen, resulting in a stable operation and high
quality gasification products. In a suitable embodiment of the
latter process the annular solid fuel flow and the groupwise
arranged oxygen jets are surrounded by a shield of low veIocity
gas, preferably oxygen or oxygen containing gas. The velocity of
the shielding gas flow is suitably chosen in the range of about 5
to 20 m/sec.
As already mentioned in the above, the important feature of
the invention consists herein that it makes it possible to attain
high throughputs of solid fuel at acceptable velocities of the
oxygen jets without impairment o~ the quality of the gasification.
~:
37~3
-6- 3293-2412
The velocities of the oxygen jets may be chosen in the usual
range of about 60 to 100 m/sec. These velocities can be
easily reached in the available burners without damaye o-f the
burnerwalls.
The invention further xelates to a burner for the
gasification of a finely divided solid fuel~ comprising an
annular outlet channel for finely divided solid fuel and a
plurality of outlet passages for oxygen or an oxygen containing
gas, the axes of said outlet passages being arranged to inter-
sect the extension of the annular outlet channel in the down-
stream direction, and wherein the outlet passages for oxygen
or oxygen containing gas are substantially uniformly distrib-
uted with respect to the annular outlet channel.
The oxygen outlet ports are preferably substantially
uniformly distributed rela-tive to the annular outlet channel.
~ In a first suitable embodiment of the above burner
the outlet passages are arranged around the annular outlet
channel. In a further suitable variant, the outlet passages
are grouped in pairs, the outlet passages of each pair being
arranged at opposite sides inside and outside of the annular
outlet channel and having their axes arranged to intersect one
another substantially in the extension of the annular outlet
channel.
~ or supplying oxygen or oxygen containing gas inside
the annular solid fuel flow issuing from the annular outlet
channel, the burner may optionally be provided with a central
oxygen outlet channel ~eing substantially c~axially arranged
: `
: ,
3293-2412
-6a-
in the annular outlet channel.
The burner according to the invention may suitably
be further provided with an annular outlet channel substantially
coaxially surrounding the annular outlet channel for supplying
a shield of low velocity oxygen or oxygen containing gas :~
around the solid fuel and oxygen jets during operation of the
burner.
The invention will now be further described by way
oE example only with reference to the accompanying drawings, in
which
Figure 1 shows a longitudinal section of the front
part of a first burner according to the invention;
E'igure 2 shows the front view of the burner depicted
in Figure l;
~.~
i. ~,' ,
5~3
-- 7 --
Figure 3 shows a longitudinal section of the front part of a
second burner according to the invention; and
Figure 4 shows the front view of the burner depicted in
Figure 3.
It should be noted that identical elements shown in the
drawings have been indicated with the same reference numeral. It
is further noted that the invention is by no means limited to the
description based on these drawings.
Referring to Figures 1 and 2, the front part of a burner,
generally indicated with reference numeral 1, for the gasification
of a finely divided solid fuel, such as pulverized coal, is shown
which burner comprises a cylindrical hollow wall member 2 with an
enlarged end part forming a front face 3 which extends substantial-
ly normal to the longitudinal axis 4 of the burner. The interior
of the hollow wall member 2 is provided with a substantially con-
centric partition wall 5 having an enlarged endpart 6 arranged
near the burner front face 3. The partition wall 5 divides the
interior of the hollow wall member 2 into passages 7 and 8 for
the circulation of a cooling fluid therethrough. The hollow wall
member 2 surrounds an annular oxygen supply channel 9, at the
- downstream end provided with a plurality of inwardly inclined
oxygen outlet passages 10 with outlet ports 11 in the burner ~ront
face 3. As clearly shown in Figure 2 the oxygen outlet ports are
uniformly distributed over a circle with the centre on the Long-
itudinal burner axis 4.
The annular oxygen supply channel 9 surrounds a smallerannular outlet channel 12 intended for the supply of solid fuel.
Finally, a substantially cylindrical channel 13 for the supply of
oxygen is arranged in the centre of the burner. The oxygen chan-
nels 9 and 13 may be supplied with oxygen via a common source. Forthe control of the burner operation, it is advantageous to connect
the oxygen channels 9 and 13 with separate supply sources.
The operation of the burner for the gasification of for ex-
ample pulveriæed coal is as follows. Pulverized coal suspended in
a carrier fluid is passed through the annular outlet channel 12
into a reactor space downstream of the burner outlet. Simultane-
ously the blast, mainly containing oxygen, is passed through the
annular oxygen supply channel 9 and the outlet passages 10 and
enters into said reactor space as a plurality of high velocity
jets issuing from the oxygen outlet ports 11. The radial compo-
nents of the momenta of the high velocity oxygen jets, directed
towards the annular coal flow, cause a breaking up of the coal
flow and an intensive mixing of the coal with the oxygen. At a
given inclination of the oxygen outlet passages lO, the velocity
of the oxygen jets should be chosen such that the oxygen can
penetrate into the coal flow without substantially re-emerging
therefrom. Suitable velocities of the oxygen jets are for example
in the range of between 60 and 90 m/sec. The annular coal flow is
at its inner side supported by oxygen supplied via the central
oxygen channel 13. This central oxygen flow forms moreover an
additional combustion medium source for the gasification of the
coal. In order to obviate constriction and thus compaction of the
coal annulus at the location where ~he high velocity oxygen jets
penetrate into the coal flow. The annular coal flow preferably has
a rather ~oderate velocity.
In the embodiment of the invention shown in the Figures 3
and 4, the burner is not only provided with oxygen outlet passages
having outlet ports around the annular coal channel 12 but also
with oxygen outlet passages 20 having outlet ports 21 arranged
within said channel 12. The outlet passages 20 are outwardly
inclined towards the annular coal channel 12 and are arranged
opposite to the outlet passages lO, so that during operation of
the burner the oxygen jets from opposite oxygen outlet ports meet
one another in the annular coal flow. The oxygen outlet passages
20 are connected to an annular oxygen supply channel 22 surrounded
by the annular outlet channel 12.
During operation o~ the burner shown in Figures 3 and ~, the
oxygen jets issuing from the outlet por~s ll and 21 will attack
~2~ 7~1
the flow from the annular channel 12 from both sides, causing a
breaking up of even relatively thick solid fuel flows. As the
inner ports are arranged opposite to the outer oxygen outlet
ports, escape of solid particles due to the energy of the inner
oxygen jets is prevented by the outer oxygen jets.
-
