Note: Descriptions are shown in the official language in which they were submitted.
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HUG~ L. CAMPBEII
FIX~D BE~ GASIFIER WITH GAS CLEA~ING MEANS
AND M~THOD FOR PRODUCING COMBUSTIBLE GASES
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The present invention relates to an improved fixed
bed9 single sta~e Raslfier. Fixed bed, sin~le stage gas,.fiers
are used to combust coal or other solid carbonaceous fuel. to
produce combustible gases. Generally, the gases produced are
collected at the top of the gasifier vessel, abov~ the fuel bed,
and are exhausted from the vessel through an offtake pipe. The
~ases are at an elevated temperature and contain particulate
matter. If the carbonaceous fuel being gasified ls a bit.uminous
coal or any coat of lower rank, the offtake gases also contai.n
1~ vaporized tars and oils.
In conventional practice, the offtake gases from a
fixed bed gasifi.er are passed ehrou~h a refractory-lined cyclone
which removes a portion of the particulates. In conventional
bituminous coal gasiflcation, the gases are then delivered to
15 ~ the burner in an insulated pipe so as to prevent the deposit:ion
of tars and oils on the internal surface of the delivery pipe,
which woulcl require subsequent removal. If the ~ases are to be
transported or any ~significant distance, it is customary
practlce to cool the gases in a scrubber, whlch causes condensa-
~n t~ on of the tAr~ ~nd o~ls And remov~l. from the tr~n.s~nrted~aseous stream.
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In situations where the hot gases containing tars and
oils are Le(i d.Lrectly to a burner, ~he constructlorl of
refractory-lined distribution piping is expensive~ and inter-
mittent operation of the gasifier will still resul~ in the need
for frequent cleaning of the gas distribution pipe.
In sltuatiorls where cooled gas is required, the
problem of rer.loving the tars and oils from the scrubbing water
requires the use of separation tanks and pumps which are both
costly and cumbersome. Also, cooling of the product ~ases, to
remove tars and oils, reduces the efficiency of the gasification
process.
In additiong in conventional fixed bed gasifiers the
space within the gas-ifier vessel, at the top of ~he vessel,
which must be pro-~.lded so as to allow the ~ases to flow to the
offtake pipe~ lowers the fuel reac~ion potenti~l at full losd by
imposing a limit on ~he contact time between the gas being
produced and the coal entering the ~asifier. .
A~tempts have been made to use the coal in the
gasifier for the purpose of removing some of the particulates
~0 ¦ from the gases~ In U.S. 4,165,970, there is dlsclosed a gasifier
for the high pressure gasification of coal, of a particle size
of 2-60 mm. A shielding wall is provided within the gasif.ier
through which coal is fed and the coarser particles are said to
accumulate near the shielding wall, while finer particles tend
to enrich the central portion of the bed. The shLelding wall is
eparate from the reactor wall and an Annular space is formed.
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IThe shiPlding wall has apertures through which gases will pass
¦ after flowing through the coal fed to the reactor. The passage
of gas through the coal bed havir~g a distribution of the
different particle siæes is said to tend to decrease the rate at
which dust is entrained by the produst gas leaving the reactor.
This is due to the gas entering the annular chamber at its lower
end as well as entering through ~he openings in the shielding
wall~ While some tangentlal flow of gases toward the discharge
from the vessel may result, no specific such tangential fJow is
discussed. While such an approach may remove some parEic~lates
from the gases to be exhausted from the gasifier since the coal
acts in the nature of a filter, it does not significantly reduce
the amount of vaporlzed tars and oils present in the gases that
are exhausted from the gasifier.
According to the present invention3 an appara~u and
process are provided which clean th~ gases produced ln a fixed
hed gasifier to remove particulate matter, tars, and oils from
the gases which may then be either immediately conlbusted or
transported to distinct locations for combustion.
It is an object of the present invention to increase
the contact surface and duration of an incoming coal charge to a
gasifier without increaslng the depth of the gasifier vessel.
This will result in the ability to operate the gasification unit
at high loads with less possibility of formation o~ blowholes or
other we~ nesses in the fire bed.
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nother object of the present invention is to coo] the
hot gases leaving the gasifier with the f]ow oE incomin~ coal to
the gasifier. .~uch coo]ing wi]l resul~- in ~he de~osition of some
tar and oil leaving the gasifier on the surEace of the incomin~
¦ coal, and reinlection of these tars and oils into ~he gasifier
vessel.
It is yet another object of the present invention to
provide a fue] feed configuration wn-ich will allow for the use
I of swelling and cak-Lng coals in the gasifier.
1~ ¦ It is a further obJect of the present invention to
impart a ro~atiorlal motion to the gases exhausted from the
gasifier at a poin'~ where particula~e matter separatecl by the
change in flow of the gases and the rotational motion will
return by gravity to the gasifier and be entrained in the
t5 incoming fuel stream.
I~ is yet a f,urther object of the presen~ invention to
cause a gradual blending of gases exhausted from the gasifier in
a manner which will -result in an exit gas from which ~.ar and oil
have been re~oved, but which will be heated to a temperature
2~ above the dew point o~ the exit gas so that deposition of
remainin~ tar and oil in the distribution pipes is minimized.
Brief_Summary of the Invention
A fixed bed, single stage gasifier for producing
combustible gases from a solid carbonaceous fuel, having a f~lel
~5 ¦ supply means and inlet means for supplyinR fuel to the upper
region of the gasifier vessel~ has at least one verticallY
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ex~ending coal feed tube of an inverted truncated cone design
which feeds coal from a fuel supply bin into the inlet of the
gasifier vessel. Preferably, a plurality of such tubes are
provided. The feed tubes have a smaller interior diameter at the
upper region thereof than at the lower region, and the tubes
have apertures therein for passage of gases therethrough. A
gaseous exhaust gas conduit surrounds each of the feed tubes.
¦Gases from the gasifier pass upwardly through countercurrently
descending c031 in .he feed pipes and out of the slots into a
chamber formed between the tubes and the gas conduit,, while a
minor amount of hot ~ases passes upwardly from the vessel
directly into the chamber. The gases are exhausted from the
chamber tangentially into an exit conduit with gases from the
exit conduits of ~ plurality of such conduits combined in a
common offtake conduit.
Upon passage of the ~ases through the descending coal
in the feed tubes, the tars and oils are condensed and returned
to the gasifier vessel, while the descending coal bed also
~ filters out particulates.
Brief Description of the Drawin~s
Figure 1 is a vertical sectional view of the upper
section of a fixed bed gasifier of the present invention; and
Figure 2 is a view taken along lines II-II o Figure
1.
De~ailed Description
Reerring now to the drawings, there is illustrated a
fixed bed carbonaceous fuel gas producer ~essel 1, hav~g a
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combustion chamber~ the vessel having a jacket 3, and a shaft 5
for an agitator which passes through the roof 7 of the vessel.
The roof 7 also has therein a plurality of openin~s g Eor the
introduction ~o the vessel of coal.
An elevated fuel bin 11 is providecl, above the vessel
1 from which coa] is to be charged, by gravity, to the vessel,
the bin having a valve 13 to effect flow of coal through an
opening 15 in the bin.
A feed tubeg in the form of an inverted, truncated
conical member 17~ ;s connected to the opening 15 of the coal
bin and con~rols tke flow of coal from the bin 11 into the
vessel 1, through openings 9, the terminus 19 of the conica]
member situated within the vessel 1. The term "conicaL member,"
as used hereln, is meant to include, in additiona' to a cone of
clrcular cross-section, a conlcal member of elliptical or
rectangular cross-sectional shape. A baffle 21 is provided,
depending from the roof 7 of the vessel 1 and spaced from the
terminus 1~ of the conical member 17. The conical member 17 is
constructed such that the terminus 19 has a ]~;ger interior
~ di~meter d th~n the interlor diameter d' of the upper region of
the conical member at the opening 15 of the fuel bin.
A conduit 23, which forms a gaseous exhaust sleeve, is
provided which is coaxial with, surrounds, and encloses the
conical member 17 while being spaced therefrom. The cond~ t 23
extends from the roof 7 of the gasifier vessel 1 to the elevated
feed bin 11.
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A plurality of slots or apertures 25 are provided in
¦¦~he conical. member 17 which provide access between the ;nterior
of the con;cal member 17 and the chamber 2i formed by the
conical member and the spaced condui L 2~. The apertures 25 are
sized and spaced such that gas from the gasifier l wi.ll flow
through the Euel feed and be gradually admitted ~hrough aper-
tures 25 into the chamber 27. The apertures are further design~d
such that most of th~ gas will flow through most of the Euel
flowing into the gasifier l, that is, most of the gas will exit
near the top of the conical member 17.
: A ~angetltial exi~ conduit 29 is connected tG and
communicates with the conduit 23 (Figure 2) and this conduit is
l in turn connected to a simi]ar exlt conduit 29' on an adjacent:
: conduit 23, both of which exit conduits discharge in~o a gas
offtake conduit 31.
In the operation of a fixed bed solid carbonaceous
fuel gasifier of the present lnvention, coal. from a fuel bin ll
flows through valve 13, through opening 15, into the upper
region of the conical member 17 and at substantially atmospheric
2n ~ pressures down~ardly by gravity through the opening 9 ln the
roof 7 of the vessel l. The larger interior diameter d at the
terminus l9 of the conical member 17~ relative to the upper
region interior diameter d', allows continued flo~ of coal c ,
despite swelling or caking which may occur when high swelling
bituminous coals are gasified. The baffle 21, extending down-
¦wardly into the gasifier vessel l, allows for a slight space
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between the underside of the roof 7 and ~he top of the fuel bed.
Gases generated in the combustion chamber flow upwardly through
the terminus 21 countercurrent to the flow of coat and di~fuses
into the chamber 27 formed between the conical member 17 and the
conduit 23, throu&h apertures 25 in the conical member 17. As
the gas flows upwardly through the descending coal, it is cooled
by the coal, and tar~ and oils contained in the hot gas condense
and are deposited on the surface of the descending coal. While
most o the gases flow throu~h the coal, a .mal] fraction of the
hot ~as stream flows through the annulus formed by the openin~at the bottom o~ ~he conical member 17 and ~he conduit 23. This
hotter gas blends in the chamber 27 with the ~ases flowing
through apertures 25 so as to keep the temperature of the exil:
gas stream above the dew point of the gas.
lS The amount of hot gases that is passed throu~h the
flnnulus directly into the bottom of the chamher 23 ls determined
by the temperatures required to keep the exit gas stream above
the dew point. The amount may vary dependent upon the type of
coal being gasified. Preferably, however, about 90 percen~, and
2~ up to about 95 percent, of the volume of the gases should be
passed upwardl~ through the descending coal in the ccnical
member and out ~hrough the apertures 25 into ~he chamber 27,
while the remaining volume of the ~as will pass throu~h the
annulus directly into the chamber from the gasifier vessel. I
Normally, tars and oils wlll condense from the ~ases when the
gases are ooled to temperstures oE below sbo~t 400F.
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Gases flo~ing to the top of the conduit 23 exi~ j
tangentially to the conduit through exit condu~ 29 which merges
with a similar conduit 29' connected to the ~op of a second
conduit 23 on the other side of the gasifior. The tangential
exit gas conduits 29 and 29' combine to form a gas offtake
conduit 31 which may be, in turn, connected to the conventional
cyclone for secon~ary removal of fines. I
The change in di.rection of fiow of the gases at the
top o the conduit 23 and the circular motion imparted to the
gases by the tangential exit gas condui~s 29 and 29' will ca~se
a primary separation of particulate matter from the ~as stream,
and such particulate matter will drop hy gravity through the
annulus back into the gasiier vessel 1 and be recombined with
the incoming coal~
The operation of the gasifier of the present i.nvention
will produce ~ gas that will be cleaner and have less ta-, oil,
and particulate matter than gases produced in conventi.onal fixed
bed gasifiers. Cooling of the gases with the incoming coal wil]
~ also reduce or eliminate heavy tars and pi~ch caused by
2~ "cracking" volati.les with hot offtake gas. The use of t:he
present invention will enable the use of fixed bed, single stage
gasifiers operating in a "hot raw gas" mode in more applications
than has hereto:fore been possible using conventi.onal technolog~y.
The present i.nven~ion provides the benefits claimed for two
stage gasifiers wlthout the capital expense or coal selecti.on ¦
restrictions inherent in such two stage gasifiers.
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