Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the gasiication of
solid fuels by partial oxidation~ More particularly, it
is concerned with the recovery of ungasified solid uel
from the partial combustion products and the return of
the recovered ungasified solid fuel to the gasification
zone where with additional fresh solid fuel it is subjected
to partial oxidation~
Ordinarily in the gasification of solid fuel such
as coal or coke~ the fuel is subjected to partial oxidation
with airp oxygen~enriched air or substantially pure oxygen
in a gasificatio~ zone with the production of a product
ga3 containtn~ carbon monoxide and hydrogen and also con-
taining minor amounts of CO2 and CH4 and if the feed con-
tains sulfur, H2S and COS. However, since insufficient
oxygen is introduced into the gasification zone for complete
combustlon of the carbon in the solid fuel, some of the solid
fuel will proceed through the gasiication zone without
being converted to an oxide of carbon. When a hydrocarbon
liquid is subjected to partial oxidation the unconverted
carbon appears in the product gas as fine particles of soot
whereas when a solid fuel is subjected to partial oxidation
the unconverted carbon appears in the product as particles
of solid fuel. In addition, depending on the type of solid
fuel feed, ash also appears in varying amounts in the com-
bustion products. It will be appreciated, of course, that
few o the uncon~erted particles are purely ash or purely
carbon.
To cool the hot products of partial oxidation
leavin~ the gas generation zone and to remove particles of
ash and unconverted solid fuel entralned therein, the hot
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gas is contacted with a quench medium such as water in a
quench zone whereby the gas is cooled and entrained
particles are transferred to the quench medium~ Larger,denser
particles of ash or slag which are low in carbon tend to
settle to the bottom of the quench zone and are removed
~ut the ~ le~ d~nse particles form a suspension in the
quench medium. To control the concentration of solid
material in the quench medium, a portion is withdrawn
continuously or periodlcally and is replaced with fresh
quench medium. For economic and ecological reasons, it
is desirable to reuse the quench water and unconsumecl fuel.
As menttoned above, when the ~eed to the gas
generatton zone is a hydrocarbon liquidt the unconverted
carbon appears as fine particles of soot which are micro-
scopic in slze whereas when the feed to the gas generation
zone is a solid fuel the unconverted carbon is in the form
of discrete particles of solid fuel. The soot formed in
the gasification of the hydrocarbon liquid may be recovered
f.rom suspenslon in the quench water by admixture with a
hydrocarbon liquid as disclosed in U. S. Patent 2,992,906
issued July 18~ 13~1 to F. E. Guptill, Jr. and U. S. Patent
No. 3,917,569 issued November 4, 1975 to G. N. Richter,
W. L. Slater~ E. T. Chlld and J. C. Ahlborn.
Unfortunately, the unconverted particles of solid
fuel do not have the affinity for liquid hydrocarbon as do
the soot particles formed by the partial combustion of a
liqu~d fuel and the separation tecAnique used for soot
recovery ~s unsat~sfactor~ for the recovery of ~converted
solld fuel partlcles from the quench water.
I~ the g~s~ication o~ liq~id ~uels ~ any carbon
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ln the feed which is not converted to an oxide of carbon
appears in the product gas in the form of microscopic size
particles of soot~ When the hot product gas containing
entr~ined soot partlcles is quenched~ for example in water,
the soot particles are transferred to the quench water which
is heated and in turn the product gas is cooled. Ordinarily
the soot particles are reco~ered from the water by contac~ing
the ~ater ~ith a lo~ molecular weight hydrocar~on liquid
such as ~aphtha into which the soot particles ~igrate leaving
a suspension of soot in naphtha and clarified water, The
naphtha containing suspended soot particles may then be
contacted ~ith the liquid hyarocarbon feed to the gas
generator to ~orm a hydrocarbon liquid mixture containing
suspendad soot particles. The mixture is heated to distill
off the naphtha which is recycled to recover additional soot
partlcles from the quench water while the suspension of
soot particles in the heavy oil eed to the gasifier is
subjec~ed to partial combustion,
The soot formed during the conversion of liquid
2C hydrocarbon is quite different in character from the
particles of uncon~erted fuel which appear in t~e product
gas when the fuel to be gasified is a solid fuel. For
example~ the soot particles resulting from the gasification
of a licIuid fuel generally have a surface area in excess of
100 m2~cr and more usually in excess of 200 m2~c3 whereas par-
ticles of unconverted uel resulting fr~m the gasification of
a ~olid fuel generally have a surface area of 1ess than 50 m2/g.
The particles which appear in the product gas when
the fuel to be gasified is a solid fuel do not have the
afinity for hydrocarbon liqulds that the soot parkicles
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resulting from the gasification of a liquid fuel have.
As a resul~ the procedure used for the recovery of soo-t
particles ~rom the quench water is not effective for the
reco~ery of unconverted solid fuel particles from the
quench water. For this reason, ungasified solid fuel has
been recovered from the quench water by cooling the same
and allowing it to settle in open vats. Such a procedure
involvas the use of large and costly heat exchangers to
recover the sensible heat in the quench water. It also
means that all o~ the quench water is subjected to steam
stripping to remove undesirable noxious gases which must
be treated before emission to the atmosphere. Additionally
the quench water must then be repxessured pxior to its
return to the quench zone.
It is therefore an object of this invention to
recover unconverted solid fuel from the quench water.
Another object of the invention is to dispense with heat
exchange equipment ordinarily used during the recovery of
unconverted solid fuel from synthesis gas. Still another
o~ject is to minimize the amount of water which must be
treated for the presence of noxious gases contained therein.
Yet another o~ject is to conserve the energy present in the
quench water as it leaves the quench zone.
According to our in~ention there is provided a
process for the gasification of a solid carbonaceous fuel
which comprises subjecting said solid fuel to partial
oxidation in the presence of H2O and at a pressure of at
least 100 psig to produce a gas comprising CO and H2 and
containing particles of unconverted solid fue!l, quenching
3Q said pxoduct ~s ~e contacting same with wa~er in a quench
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zone to cool said product gas and to form a suspension of
said particles of unconverted solid fuel in the quench
water, passing said suspension to a settling zone maintained
at substantially the same temperature as said quench zone
and also malntained at a pressure not less than about 75
psig t allowins the suspension to settle in an upper clariied
portion and a lower more concentrated portion containing
settled unconverted solid fuel particles and re1;urning at
least a portion of said settled particles to the partial
oxidation zone.
The feed to the process of our in~ention comprises
any solid carbonaceous fuel containing ash-forming ingred-
ients such as coal t sub-bituminous coal, lignite, petroleum
coke, organic waste and the like.
The solid fuel ground to a particle size o less
than one-quarter inch and preferably ground so that at
least 95% passes through a 14 mesh sieve (U.S. Standard)
is introduced into the gas generation zone where it is
subiected to partial oxidation with a gas such as air,
oxygen-enriched air or substantially pure oxygen that is,
oxygen havin~ a purity of at least about 95~. The finely-
di~ided fuel may be introduced into the partia:L oxidation
or gas generation zone as a slurry in a liquid such as
water or oil or as a suspension in a gaseous or vaporous
medium such as steam~ carbon dioxide or mixtures thereof.
In the gas generation zone, the solid fuel is subjected
to parttal oxidation at a temperature between about 1600
and 3500F, preferably between 1800 and 3200F'. The
pressuxe in the gas generation zone may range between about
100 and 3000 psig pre~erably between about l50 and 2500 psig.
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The oxygen may be introduced into the gasification zone
at an oxygen to carbon atomic ratio of between about 0.7
and 1.6 preferably between 0~8 and 1.2. When the solid
fuel is introduced Into the ~asi~ication zone as a slurry
in water, the slurry should contaln less than 50 wt. %
water as a water content above that ~alue will affect the
the~mal e~ficiency of the r~action.
In a preferred embodiment hot product gases
containln~ entrained particles of unconverted fuel pass
downwaxdly throu~h a lower outlet at the bottom of the
gasiflcatlon chamber and are discharged into the quench
ch~mber under the surface of the watex contained therein.
Lar~ex particles,composed ~or the most part of ash free rom
carbon, ~or example less than 2.0 wt. ~ t descend gravita-
tionally into the lower part of the quench chamber where
they are removed periodically by means of a lock hopper.
The finer particles of unconverted solid fuel remain
suspended In the quench water due, at least in,part, to
the ag~tation supplied by the discharge of the ~ot gases
under the sux~ace of the water.
Separation o~ the solid particles from the water
is effected by transferring the suspension from the quench
chamber to a s~ttllng zone where the suspension is permitted
to settle substantially free ~m agitation into a clarified
upper portlon and a more concentrated lower portion. This
settling is conducted at elevated temperatures and pressures~
In a preferred embodiment the settling zone is maintaine~ at
substantLally the same pressure and temperature as the
quench zone, However~ good results are obtatned when the
settllng is efected at a temperature between about 100F~
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and 706F. and a pressure between about 50 psig and
3500 psig, preferably at a temperature between 200 and
668F. and a pressure between 100 and 2500 psig.
The residence time in the settling zone will
depend on the size o the particles of unconverted fuel
whi~h in par-t is dependent on how finely the feed fuel has
been ground. Ordinarily the residence time should be in
excess of three minutes with from five minutes to thirty
minutes being preferred.
The concentrated suspension in the lower section
of the settling zone, which may contain as much as 50 wt. %
solids, is recovered from the bottom of the settling zone.
If the solid fuel is introduced into the gas generator as
a water slurry, the concentrated suspension may be returned
directly to the mixing zone where a slurry of frash feed
and water is prepared. If the feed to the gas generator
is in the form of solid fuel suspended in a hydrocarbon
liquid advantageously the settled fuel may be subjected to
water removal treatment and then mixed with the fresh sQlid
fuel feed. The clarified water removed from the upper end
of the settling zone may be used for making additional
fresh feed slurry or may be returned to the quench ~one.
By making the separation at an elevated temperature
and pressure~ the settling time is considerably reduced o~er
the time for settling the suspended solid fuel in open vats
as in the prior art. In addition, since the separation is
made hot, it is not necessary to cool the suspension using
the large and costly heat exchangers of the prior art.
Furthermore dissolved gases are kept in the system which cuts
down on the amount of low pressure sour gas which must be
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subjected to treabment~
The follo~ing examples are submitted for illustra-
tive purposes only and it should not ~e considered that the
in~ention is restrlcted thereto.
E~MPLE I
This example represents conventional practice
where the suspended solids are permitted to settle at
ordinary conditions~
The charge to the gaslfication zone is a s:Lurry
or petroleum coke, ground so that 94% passes through a 40
mesh sieve (0.0165 inch opening) in a California Reduced
Crude oil, the coke forming 49~93 wt. % of the slurry. The
slurry is fed into a 2.15 cu. ft. unpacked gas generator
a-t a rate of 424 pounds per hour wi~h 4752 SCF~ of oxygen
and 240.6 pounds of steam per hour. This represents an
oxygen to carbon atomic ratio of 0.808. Temperature in the
gasifier is maintained at 2389F. and the pressure at 810
ps~
Quench water containing suspended solids is
withdrawn~ cooled by heat exchange and allowed to settle
in an open countainer. After a residence time of 3.1 hours,
analysis o~ the clarified water withdrawn from the top of
the settler shows a solids content of 0~005 wt~ %.
The solids content o~ the concentrated suspension
removed from the bottom of the settler is 37 wt. %.
Th~s run shows the xesults obta~ned by settling
in a conventional manner at 100F. and atmospheric
pressure .
*standard cubic ~eet per hour
t"~
EXAMPLE II
,
This example represents one embodiment o~ the
process o~ oux in~Jention.
The gasi~ication step here is similar to that of
Example I~ ThP feed to the ga~ifiex in this ca6e is a
slurry of petroleum coke ground as in Ex~mple I containing
47.7 wt. % coke in California Reduced Crude. Feed rates
are 5656 SC~H af oxygen, 428.8 pounds of slurry per hour
and 444.3 pounds of steam per hour, representing an oxygen
to carbo~ atomlc ratio of ~.943. Gasification temperature
is 2~77F.and pressure 810 psig.
The quench water containing suspended unconverted
solid fuel is transfe~red at 410F. to a continuous settler
whexe it is maintained at a pressure of 800 psig. After
a residence time of 12 minutes, analysis of the clarified
water remo~ed ~rom the top of the settler shows a solids
content of less than a~ ool wt. ~ solids. The solids content
of the concentrated supension withdrawn from the bottom of
the settler is 40.1 wt~ %.
It will be noted that by transferring the sus-
pensi~n without cooling from the quench zone to the
settllng zone at substantially the pressure of the gasific-
ation æone, superior settling is obtained at 15 times the
rate of settling in Example I.
The clarified-water i5 xecycled to the quench zone
~ith a minimum of repressuring; and the suspended solids
ater drying r are returned to the mixer where fresh slurry
feed is prepared.
Althaugh the ex~mples describe the gasification
3~ of coke in an oil slurr~, the process of our in~ention may
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be used equally well in the yasification of a coal in oil
slurry~ a coal in water slurry or a coke in water slurry,
for the separation of unconverted solid fuel particles
from the quench water. Qur pro~,ess may also be used when
the solid fuel feed Is suspendad in a gaseous or vaporous
medium~
In addition to being appli.cable to gasification
processes in which suspensions are formed by the direct
quench of synthesis gas, our invention is also applicable
to processes where the hot synthesis gas is partially
cooled by indirect heat exchange and then contacted with
quench or scrub water~
Various modi~ications of the invention as
hereinbefore set forth may be made without departing from
the spirit and scope thereo, and thereore, only such
limitations should be made as are indicated in the
appended claims.
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