Note: Descriptions are shown in the official language in which they were submitted.
6~
6~312-175
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_ESSURIZED CYCLONIC COMBUSTION METHOD
AND BURNER FOR PARTICULATE SOLID FUELS
B~CRGROUND OF XNVENTION
_
Thi~ invention pertains to a pres~uriæed cyclonic
combustion method and burner ap~aratu~ for effective com-
bu6tion of particulate ~olid fuels to produce ~lean pres-
~urized hot effluent gases. It pertain~ particularly to a
cylindrical pressurized. burner which utilizes helical flow
patterns ~o prnvide prolonged combustion of the fll~l solids
and uses an intermediate choke zone and an air quench ~ep
to ~mprove combustion and con~rol temperature of the effluent
lo gases produced.
Various types of burnerfi for particulate solid fuels
have been previou~ly proposed 6uch a~ dlsclo6ed by U.S.
Patent 2,614,573 to Miller et al; U.S. Patent 2,769,411 tG
Simmons; and U.S. Patent 2,881,720 to Lotz which utilize
tangential ~wirling flow pattern~ and a restricted exit
opening intended to retain ~olids ~n the burner longer for
more complete combustion, U.S. 3,199,4i6 to Nettel discloses
a s~milar burner for coal having dua~l tangential inlet for
the small and coarser coal particles, a restricted throa~
exit for combustion gases and a lo~er drain port for ~lag
removal. Other similar burner~ have been disclosed by U.S.
3,244,220 to Kloecher; U.S. 3,453,976 and U.S. 3,472,1~5 to
Burden et al, but they do not have re~tricted outlets and
~re not intended for pressurized operation~. U.S. 3,777,678
and ~.5. 4,053,505 to Lutes et ~1 di6close a horizontal
cyclonic type burner for combu~tible ~olid material3 in
which the fuel is introduced tangentially into the combustion
chamber at its inlet and combustion air is introduced tangen-
tially along the length of the burner, which has a restricted
choke outlet. Also, U.S 4,422,388 to Raskin dificlose~ a
ho~lzontal cylindri~al burner for ~olid fuel introduced
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tangential~y a~ one end, but maintains a fluidized bed of
fuel in its lower portion. In addition, ~croll or dual
re~is~er horiz~n~al fired type burners such as the Coen DAZ
burner have been used for ~he combustion of ~he air conveyed
solid fines. Such burners have dual registers with concen-
tric louvers which in effect divide the air stream into two
counter-rotating concentric streams which ~crub against
each other and provide turbulent mixing action for the fuel
introduced into the annular space between the dual air
streams.
It is noted that these prior ar~ burners are useful for
burning parti ulate solids at essentially atmospheric
pressure for incineration and also for ~he recovery of heat
ener~y. However, further improvements are needed in combus-
tion of particulate solid fuels at above atmospheric pressure
and in burner design for achieving higher throughputs for
the fuels and higher heat release rates in the burner to
produce relatively solids-free pressurized hot effluent
gases suitable for power recovery applications.
Burning solid fuels, unlike burning vaporous and volatile
liquid fuels, require increased reaction time constants which
are orders of magnitude longer for complete combustion,
i.e., mass diffusivity is rate con~rolling in the rapid oxi-
dation of solid fuels Historically, this longer combustion
time requirement has been minimized by solids size reduction,
a~ in firing pulverized coal instead of chunk or briquette
coal. While such size reduction is beneficial, it still
does not permit the firing of solid fuel materials at
combustion rates which approximate ~hose attained for non-
solid fuels. This difference is most apparent when volume-
tric energy releases for various heat generators are compared.
In order to increase the fuel particle retention time
in a burner, which time varies inversely with combustor size
for a given heat release, a new method for achieving in-
creased dual phase residence time for the solid fuel par-
ticles has now been developed. In this method, the solid
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fuel particles having higher mass are ret~ined for very long
periods of time relstive ~o the lower mass combustible
volatiles and gaseous materials in a cylindrical combustion
chamber having an aspect ratio of longitudinal length more
than about twice that of ~he chamber inside diameter. In~o
this combustion chamber the particulate solid fuel is intro-
duced tangentially in lean phase transport near the inlet
end. The fuel tangen~ial velocities in ~he burner are
sufficient ~o that very high centrifugal forces are imposed
on the fuel particles which are swirled around the inner
periphery `the burner, while the gaseous material not as
subject to such centrifugal forces and moving by molecular
motion is free to move along the burner longitudinal axis
while rapidly combusting, and then escape through a modula-
ting restriction opening at the burner exit end.
The 601id fuel particles are maintained in this helical
~low pattern, trapped by their relatively high mass and high
rotational ~elocity, slowly moving helically and at high
Re~molds number condition toward the outlet end of the
combustion chamber. This extended combustion pa~h is signi-
ficantly prolonged by the tangential injection of combustion
air along the longitudinal axis of the burner at a high
velocity. This combustion air is introduced under conditions
of high tangential velocity and associated high Reynolds
number, so as to impart an additional tangential acceleration
to the fuel particles ~uficient to overcome any reduction
in velocity due to flowing resistance of the orbiting parti-
cles. Accordingly, this combustion process is continued
under high Reynolds number conditions until the fuel particles
are sufficiently destructed to produce gaseous products
which escape the centrifugal forces in the combustion chamber
and pass out at the burner exit end.
The gas residence time in the combustion chamber is a
function of the volumetric throughput only, however, the
fuel ~olids residence time is pathway dependent and is
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determined by the combus~ion chamber circumference and the
number of revolutions divided by the velocity of the parti-
cles. Therefore, a particle can be retained in Lhe burner
to destruction for a much longer time than can volatile
uels and products of combustion which accompany the particle.
This improved combustion method also promotes more
rapid combustion of solid fuels by forcing the circulating
particles closely adjacent to the ho~ radiating interior
surfaces of the eombustion chamber. This radiating surface
is quite large relative to the particle and served to sustain
the reactior ~y constantly providing ~he threshold energy
needed for combustion. The addition of the acceleration air
along the helical path of the fuel particle promotes rapid
o~idation by continually supplying fresh oxygen very near
the particulate fuel solids undergoing reac~ion.
The addition of combustion air tangentially along the
length of the combustion chamber also provides an additional
benefit to the mechanical integrity of the burner by buffer-
in~ and tempering the surface of the heat resistant refrac-
tory insulation material lining the in~erior of the burner
cha~ber from the very hot products of combustion. This air
addition prevents the insulation surface from reaching
reaction temperatures which would be deleterious to the
insulation. This air-s~eep is enhanced by the design and
installation of the air inlet tuyeres.
Accordingly, it is an object of the present invention
to provide a pressurized cyclonic combustion method and
burner apparatus for particulate solid fuels which provides
for prolonged combustion of the fuel particles at conditions
of high tangential velocities, high centrifugal forces, and
high Reynolds numbers. Another object is to provide such a
burner which operates at highly turbulent eonditions and
high Reynolds numbers and provides very hi~h volumetric heat
release rates approaching those for liquid and gaseous
uels. Another object is to prov.ide a burner for solid
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64312-175
particulate fuels such as wood chips which produces a clean hot
pressuri7.ed effluent yas stream suitable for use in power
producing processes.
SUMMARY 0~ TRE INVE}~TIOl~
The present invention provides an improved combustion
method and burner apparatus for the pressurized combustion of
particulate solid materials to produce hot pressurized effluent
gases having low solids content.
Different aspects of the invention are claimed. For
example, according to one aspect the invention provides an
apparatus for burning particulate combustible fuel to produce a
pressurized gas, comprising: a house having side wall means
forming a cylindrical shaped primary combus~ion chamber, a
cylindrical shaped secondary combustion chamber, and a choke
opening of reduced size between said primary and secondary
combustion chambers, said secondary combustion chamber being in
fluid communication with said primary combustion chamber through
said choke opening, the end of said primary combustion chamber
opposite said choke openlng being closed by end wall means, the
end of said secondary combustion chamber opposlte said choke
openlng having an outlet opening for the passage of hot gas to a
utilization means, a fuel opening formçd through said side wall
means of sald primary combustion chamber near said end wall means
for introducing a particulate fuel under presæuxe therein
tangentially to the inner wall of said primary combustion chamber
and transverse to its axis such that the particulate fuel travels
toward said choke opening in a helical path around the inner wall
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6~312-175
of said primary combustion c~amber for burning therein for the
produc~ion of hot gas under pressure for flow ~hrouyh said choke
opening to said secondary combustion chamber~ a plurality of
tuyere openings formed throuyh said side wall means of said
primary combustion chamber between said fuel opening and said
choke opening for introducing a combustion supporting gas under
pressure in$o sald primary combustion chamber tangentially to the
inner wall thereof and transverse to its axis such tha~ the
combustion supporting gas travels in the same helical path as that
of the particulate fuel, the helical pa~h of the particulate fuel
and combustion supporting gas resulting in the particulate fuel
making a large number of revolutions in said primary combustion
chamber prolonging the time of the particulate fuel therein to
enhance burning thereof, the reduced size of said choke opening
also being effective to prolong the time of the particulate fuel
in said primary combustion chamber to enhance burning thereof, and
at least one quench gas opening formed through said side wall
means of said choke opening for introducing a quench gas into said
choke opening for cooling the hot gas flowing through said choke
~0 openlng to said secondary chamber to a temperature suitable for
use by a utilization means.
According to another aspect, the invention is a method
of operating the novel apparatus comprising the steps of,
introducing a particular fuel under pressure into said primary
combustion chamber through said fuel opening tangentially through
the inner wall of said primary combustion chamber and ~ransverse
to its axis such that the particular fuel travels toward said
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~ 312-175
choke opening in a helical pa~h around the inner wall of said
primary combustion chamber for burning therein for the production
of hot gas under pressure for flow through said choke opening ~o
said secondary combustion chamber, introducing the combustion
supporting gas under pressure through said tuyere openings inko
said primary combustion chamber tangentially to the inner wall
thereof and transverse to its axis such that ~he combustion
supporting gas travels in the same helical path as ~hat of the
particulate fuel, flowing the particulate fuel in the helical path
around the hot inner wall of said primary combustlon chamber such
that the particulate fuel makes a plurality of revolutions in said
primary combustion chamber prior to reaching said choke opening
for substantially complete combustion therein for the production
of hot gas for flow through said choke opening, the helix angle of
the helical path of the particulate ~uel in said primary
co~bustion chamber being only slightly less than 90 relative to
~he axis of said primary combustion chamber, and introducing a
quench gas into said choke opening through said quench gas opening
for cooling the hot gas flowing through said choke opening to said
secondary chamber to a temperature suitable for use by a
u~ilization means.
In a specified embodimenk of the method of the
invention, a particulate solid fuel having particle size smaller
than about 0.70 inch major dimension is pressurized and
pneumatically fed tangentially into the burner primary combustion
chamber opera~ed at a pressure at least about 3 atm. absolute and
usually not exceeding about 20 atm. pressure. The superficial gas
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64312-175
velocity for fu~l transport into the burner primary combu.stion
chamber should be at least about 80 ~t/sec and preferably about
90-120 ft/secO An oxygen-containiny combus~ion yas is also
supplied into the combustion chamber tangentially through mul~iple
tuyeres at a hiyh tangen~ial velocity exceeding about 100 ft/sec
and at a Reynolds number relative to the tuyere openings exceeding
about 900 rO. The fuel particles and combustion gas ln the
combustion chamber flow in a swirling helical motion or flow
pattern at high tangential velocity exceeding about 100 f~sec, so
as to provide high centrifugal forces on khe particles exceeding
about 1~0 gravitational or 'g' units. Because of the rotational
motion and the high centrifugal forces yenerated on the fuel
particles, the burner accordiny to the present invention retains
the fuel particles in the burner combustion chamber near the hot
wall for a substantially longer ti.me than occurs for conventional
prior art burners, so that the fuel solids are more rapidly and
completely combusted. Also, this high rotational velocity and
hlgh centrifugal force flow pattern not only retains the
particulate solids in the burner longer for more complete
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combustion, but a~di~ionally achieves flows at very high
Reynolds numb~rs exceeding about 150,000 and provides for
very high volumetric heat release rates in the burner ex-
ceeding about 400,000 Btu/hr ft3 chamber volume, which
substantially exceed the heat release rates provided by
conventional solid fuel burners. ~urthermore, the present
burner advant~geously provides heat release rates for burning
particulate solid fuels comparable to those for burning
liquid or gaseous fuels in gas turbine and internal combus-
tion engines.
Accordingly, it is an important feature of the present
invention that the fuel particles remain near the hot
radiant wall of the combustion chamber until all volatile
matter is continually evolved from the fuel particles, which
steadily diminish in size until the particles are substan-
tially completely combusted into gas. Also, because the
burner inside length to diameter ratio is at least about 2.5
and can advantageously be up to about 10, this cylindrical
configuration contributes to the fuel particles remaining in
the burner primary combustion zone significantly longer for
more complete combustion than for prior burner configurations.
The hot pressurized effluent gas produced in the primary
combustion zone is usually at temperature of about 2100-
~800 F and is cooled by mixing it with a quench gas such as
additional air or steam in a quench zone ~o reduce the gas
temperature to a lower temperature as desired, such as
limited only by the characteristics of a power recovery
turbine, and usually to about 1400-2000 F. Any remaining
solids in the effluent gas can be removed in a gas-solids
separation step prior to expansion in a gas turbine for
producing useful power.
In the embodiment disclosed any remaining particulate
solids in the effluent gas leaving the burner are mechanically
separated from the gas in a cyclone separator, after which
the clean gas is then expanded to a lower pressure through
a gas turbine for driving a compressor to provide the pres-
surized combustion air required in the burner. The gas
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turbine provides net shaft power output for driving a load,
which is usually an electric power generator.
The present invention also provides a burner apparatus
for pressurized combustion of particulate solid fuels to
produce a hot pressurized effluent or product gas. The
burner includes an elongated cylindrical shaped pressurizable
outer metal casing, an inner refractory lining located
adjacent the casing inner wall to provide an elongated
cylindrical shaped primary combustion chamber, a tangential
opening located near the burner inlet end for feeding a
particulate fuel tangetially into the primary combustion
chamber, a plurality of tangentially oriented openings each
having an aspect ratio at least about 2:1 and spaced apart
longitudinally along the length of the burner for intro-
ducing a combustion gas tangentially into the combustion
chamber, a choke opening located at the combustion chamber
exit end, and at least one aperture located tangentially in
the choke opening, the aperature being preferably oriented
opposite to the tangential opening in ~he combustion chamber
inlet end, whereby the particulate fuel is combusted rapidly
at high rotational velocity and high volumetric heat release
rate and the resulting hot effluent gas is quenched and
cooled to provide a lower temperature pressurized product
gas. Downstream from the choke, a secondary cylindrical
combustion chamber is connected pressure-tightly to the
outer casing of the primary combustion chamber. The choke
zone between the two chambers is tapered ou~wardly into the
secondary chamber, so as to minimize irrecoverable pressure
differential for the product gas flowing ther~through.
The burner of the present invention is useful for
burning various combustible particulate solid materials,
such as sawdust, wood chips, trim and shavings, petroleum
coke, and mixtures thereof. The burner is particularly
useful for combusting wood chips smaller than about 0.70
inch and preferably smaller than about 0.130 major dimension.
It is an advantage of the present pressurized combustion
method and burner apparatus that because of ~he greater
length/diameter ratio provided in the burner and the high
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rotational veloci~ies and centrifugal forces achieved for
the fuel particles, the particulate solids are retained in
~he burner for a significantly longer time for achieving
more complete combustion, thereby producing higher volume-
tric heat release rates and a cleaner product gas. Because
of the high rotational velocity of the combustible particles
in the burner and the resulting high centrifugal forces
developed, the burner is substantially unaffected by gravity
and can be operated while oriented in any direction. Also
because the resulting hot effluent gas is effectively
quenched with air, steam or mixture thereof, the effluent
gas is provided at a controlled lower temperature which is
advantageous for subsequent power recovery from the gas in
an engine or turbine.
BRIEF DESCRIPTION OF DRAWINGS
. . ~
The inven~ion will be further described with reference
to the accompanying drawings, in which:
Fig. 1. shows a longitudinal cross-sectional view
of a cyclonic burner assembly according to the present
invention, including the primary and secondary combus-
tion chambers;
Fig. 2 shows a cross-sectional view of the burner
feed inlet taken along lines 2-2 of Fig. l;
Fig 3 shows a cross-sectional view taken through
the burner choke section along~ lines 3-3 of Fig. 1:
Fig 4 is a graph showing the cen~rifugal forces
plotted vs. tangential velocity for fuel particles in
the burner, compared to similar conventional burners;
Fig. 5 is a graph showing volumetric heat release
rate plotted vs. internal pressure or the burner of
the present invention compared to similar conventional
burners; and
Fig. 6 is a schematic diagram of a system incor-
porating the burner of Fig. 1.
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I)ETAILED DESCRIP~10~ INVEl~l,rl()~;
A pressuri2ed cycl~nic burner ~r providing pr~l~n~ed
pressurized c~mbustion ~f particula~e 6c~1isl fUe~ nd
c~ns~cructed and ~perated in ~ccordance ~ith lthe present
inven~ion i~ 6hc>wn ~n ~ig. 1. In ~che illus~ra~ed p~eerred
emb~dimen~, ~che burner a~embl~y 10 ha~ ~ cylindric.sl ~haped
pres~uri2able ~u~er meeal casing 12 and a head 13 ~ whieh ~re
ret~ined tl~,ether by b~lted flange 12a. A refrac~Dry linin~,
material 14 i~ losated adjacent ~he inner wall of casing 12
and ~ithin head 13 and defines ~ primary ct)mbustic:n chamber
15, ~ith the lining material being ~uitable for wi~chstandi~,
~emper~Gture6 up to ~b~ut 30~0D ~.
~ he particulate ~lids combustible fuel material, ~uch
wood chips preferably ~maller ~han about 0.130 inch major
dimension~ is uni:l'DImly fed by 6uitable means (nc>t shown)
in~t) $he burner primary eombustit>n ehamber ~5 st tangential
inlet connecti~n 1~ located near the inle~ end head 13 ~f
the burner. In the chamber, the ~olid~ are ~ir entrâined ~t
t~n~,enticl ~el~city at least about ~0 ft/~c &nd prefer&bly
100-20~ ft/~ec. If de~ired, ~o improve igni~cion of the
p~r~icul&te 601ids feed entering th~ e3mbustion chamber, the
end ~11 14a of refr~ct~ry lining 1~ can be m2d~ convex
shaped ~nd extend axiall~7 into the combustion chamber to c
loc~ti~n not Ir.or~ thcr, ~bout (). S th~ burn~r in~ernc~ oicr.~t~r
p~st the pl&n~ c)f the fu~l in~et 16, a~ ~Chc>~ in d~tted
lines in ~ig. 1. This ~rr~n~ement ~esults in the solids
feed meterial moving eloser to the hot refractor~ ur:f~ce
14~ to provide for more effective ~diant heatin~ of ~he
feed .
Multiple t~ngential inlet openings ~r tuyeres 18c" 18b,
18c , etc ., are provided ~hrough c~sing 12 and lining 14 and
spaced ~par~ alc~ng the length ~f the burner for ~upplyin,~
combustiDn air ints~ the combustit)n chamber, The tl~yere
opening~ 18, 18a, e~c., are preferably prcvided as double
ro~.~s, as shown in Fig. 2 ~ectiona1 dr~ing, ~ith at least 3
.
....
~nd u~ually not En~re ehan 2~ ~uch ltuyere c)penin~ ~n e~h
ro~n The ~uyere openin~,~ 18, 1~ tc., ~re ~aade elDn~ed
~n 6h~pe ~n a direc~ion par~llel ~ th~ lDn~i~udin~l ~xi~ of
~he burner. ~he tuyere ~peninE,~ preferably 6h~uld hav2
len~,th/width ~peclt r~t~o exceedin~, ~bc)u~ nd prefer~bl
:Ln a ran~e of 3 :1 t~ 5: 1.
The combu~tit~n a~r 1~ 6upplied thr~u~h ~he ~yer~
opening~ ~t B veloc~ty exceeding ~b~ û f~/~ee ~nd ~t
Re~mold~. number relative ~o ~he tuyere ~penings es~ceeding
sb~ut 9~0, 000. The c~mbustion ~ir i~ pre~erably ~upplied
~hrou~h ~he guyeres a~ ~angent~l vel~ci~y of laO- 150 ~/~ec
and ~t Reynolds number of 1,000,000-3, E)~O,~)D0. A fl~nged
clean-~ut opening 17 i~ provided through ~che le~wer pc~r~ion
of head 13 and ~ncludes ~ remoYable refractory plu,~ 17~
Also, a ~ighc ~ube 19 i~ provided through She upper pc)rtion
of head 13 ~r viewing ~che combu~cion proce~s within chamber
15 .
~ he combustion chamber lS i~ oper~ted ~t internal
pressuræ of ~hout 3-20 a~m. abs~lute and prefer&bl~~ 4-1
~cm. The ufieful wei~ht rstio ~f cvmbuFtivn air to the
particulate :c'uel feed range6 frorn abc)ut 1. 0 to 4 . 0 times the
~oichiometric ~ralue.
At the exi~ end of ~che burner combusti~n chambi r 15, h
centrally~ cated choke element 20 i~ prDviàed ~hich has a
generally cylindrical openin~ 20a therethrou~h, and h~s a
cross~sectional ~re~ apprecifibly smaller ~han ~chat for the
combu6tion chamber 15. The opening 2ûa in choke 20 ~h~uld
~e made small enc~u~h tt~ help ret~in the circula~in~, c~mbust-
in~ solids in the primary combusti~n chamber, s~ ~s t~
prolong ~he solid~ re~iderlce ltlme for ~ub~tantially complete
combustion therein, but the opening i~ not made $0 small
that undesired diferentisl pres~ure for the ~ffluen~ E~a6e~
flowing through the choke iL~ appreciably irlcre~ed. The
cros~-sectional ~rea ~f the choke 20 ~hDUld be at least
ab~ut 30% that of the combustaon chamber 15, ~nd u~u~lly i~
40-SD% the cro~-sectivnal area of the combu~tion chamber.
:
Al~o, ~ de~ired ~ ~acili~ate the pas~ge ol ~sh ~rom the
primary combust~on chamber, th~ ch~ke ~penin~ 2~a can be
lo~ated near the l~er port~n o~ ~he chamber, ~r alter-
n~tively, ~he openin~ can be made no~-circular ~h~ped with
p~rtion ~f the ~penin~ exeendi~ do~w~rdly t~ rds ~he
l~wer ~all of ~he chamber. Thi~ eh~ke 20 i~ usually made
snnul~r shaped and i~ preferably formed as ~ castabl~ re-
frac~ory ma~erial ~hat i~ m~re ~bra6ion~lesi~tant than ~he
refract~ry lining 14. ~he choke 20 pre~er~bly hss a curved
inlet surf~c~ 20b and a tapered outer 6urface 20c to ~ssi~t
in retaining it in place in the ~urrounding refr~c~ory
material 24. Al~o, if desired, ~ refr~c~ry ce~ent material
~1 can be used between the choke element 20 ~nd th~ surround-
in~ refractory material 24 to help hcld th~ choke in place.
~ cr the burner ~f the present invention, visual obser-
vations made of the 601id fuel pareicles in ~he burner
during combustion c~peration indica~e ~Lhat the particle~
mo~e in 8 helical flo~ pa~ch t~hich is nearl~ perpendicular to
th~ lonitudinGl c,xis of t~l~ burn~, thus ir~oiectin~ that
the helix angle ~ the particle path relctive t~ the burner
axis is ~nly ~lightly less than 9~ hi~ flo~ p~ttern
indic~tes that the fuel particles m~ke a great n~mber of
re~olutions in the burner primcr~ combustior, ch~ber ~ntil
th~ ar~ com~let~l~ d~ lc~ d end cons~-.~c. ~.lsc, b~ccus~
c~f the p~rticle sot~tional velc>cit~, th~ pcrticulc,te ~olidc
r~spond to hi~h centrifug&l forces produced in the burneY
and the gaseous pr~duct~ of combu~tion respond t~ ~eynolds
number~ ~hich ~re very high. B~ using the burner configu-
rfiti~n of thi~ invention, ~he volumetric heat release rates
for pressurized burnin~ ~f partic~l~te ~olid fuels are
si~nificantly higher than ~or con~en~ion~l type burners, and
approach hea~ ~elea~e ~ates which ~ccur for burning liquid
~r gaseou~ fuel~ ~n internal combusti~n ængines.
Because ~f the high ~angential velocity and high eentri-
fu~al forces genera~ed on the sQlid fuel particles in the
burner primary combu~tion zone 15, ~he part~cula~e ~oliBs
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~c~ke very many rev~lutiDns ~therein ~nd ~re ~h~as re~ined in
the cDmbusti~n ~ne ~d~cent the h~t r~fractory lininE 14
for ~ ~ubst~n~ially lon~,er ~e6idence ~i~e unt~ he
lid~ h~ve been dev~ 2ed ~nd c~mbu~ted~ ~hereby achiæ~-
~n~ the ~ery h~gh ~l~ne~ric 3hea~ rele~ce ~tes~ The centri-
fu~,al f~rce produced ~n ~he ~p~r~icul~e 6t)1id~ being bu~ned
exceeds ~b~ut 14~ times earth &~r~vi~y 'g ' ~nd i~ pr~fgr~bly
ab~ut 150-3~ nd Reyn~ld~ n~mber for ~he hot ef~luent
~a~es i~ ~t least ~b~ut 150~0~û ~nd preferably 2ûO,ODû-
50û, 000. The vc~l~De~ric heat rele~e r~e~ in oche burner
primary c~mbu~ n chamber i~ < le~t ~ ut 4~, OD~ Btulh~
ît3 prim~ry c~mbu~ti~n chamber ~Dlume, snd ~ prefer~bly
5~û, 000 to 3, 9û~. 00~ Btu/hr ft3.
A sec~nd~ry cyllndric~l ~haped c~mbustion chsmbe~ 25 i~
preferably p~oYi~ed d~m6tr~am frc~m ~he pri~ary cham~ber 1
~nd cho3te 20, and ab~ut 25~ f the tot~l c~mbustic>n
occur in the secQndary chamber. Sec~ndary cc>mbu~io~
cha~.be:r 25 h~s a c~lindrie~l ~h~ped ~,e~l c~in~ 22 ~u~r~und-
refrsctory linin,~ 24. The ca~in,g 22 i6 connected
pressure-tightly to the ¢asin,~ 12 c)f primary combusti~n
~ha~ber 15 by b~lted flaa~e 26, and c~n be c~nnested pre~sure-
~i~h~l~ t~ d~3tream ductin~, ~s desired b~ flan~e 27.
.ls~ fract~r~ lininE 24 ~buts ~ainst th~ actc~s~
lininE 14 ~t ~ loc~ti~n ~adaally c)ut7~rdl~ from ch~k~ 2QA A
reduced diameter inter~ediate ~one 2B iE prt~id~d immedi~t~l~
d~ tream from ch~ke 20 ~nd ~ually h&~ ~ lerl~th: diame~er
rati~ of abDut 1:1 to 1.5:1. The ~nteraedi~e zone ~ ii6
followed by ou~wardly ltspered ~one 29 connecting ltO 6 full
diameter ~ne ~ ~eeond~ry ehamber 25 hav:in~ an in~ide
di~meter ~ppr~xima~ely the ~aD~e ~ fo~ the prim~ry c~mbu~tic~n
chamber 1 g .
A quench ga~ ~uch a~ add~t~on~l pre6~ur~2ed ~ir c>r
~team ~6 provided ~nto ~ec~ndary chamber 25 througll ~t le~t
one ~peni~g 30 through refr~etory 24 located i~edi~t~ly
down~tream from ch~e 20 for quenching ~nd cDc~ling ~he h~t
-13-
effluent gas flowing from ~he choke. Vsually two openings
30 are provided ~nd ~re preferably orien~ed in a ~angenti~l
directi~n opposite to thAt for the fuel inle~ l& and multiple
openings 18 for the combustion air in ~he primary combus~i~n
chamber 15, Thus, the eounter ~r ~ppo~itely ~lowing guench
gas ~tream flowin~ tangentially from conduit 32 through
openings 30 pro~ides a high velocity æhear type mixing flow
pattern for the quench gas and ~he hot effluent gas upstream
from ~ecoIIdary combustion chamber ~4, ~hereby advant~geou~ly
achieves highly effective mixing of the hot effluen~ gas find
the qu nch gas 80 as to lower the hot effluent gas temp-
erature from abou~ 2700 F to a lower ~emperature, ~uch as
1500-1800D ~ suitable for passing to a gas turbine. ~he
preferred quench gas is pressurized air because of its
general availability~ The useful weight ratio ~f the
quench air to the combustion gas upstream of choke 20 is
from about O.B to about 1.5. If ~team is used as the quench
gas, the 6team conditions and amount used ~hould be ~uch
that no condensate is provided in the gas turbine exhaust.
Also, to facilitate transfer of ash from the lower portion
of the primary combustion chamber 15 into the fiecondary
combustion chamber 25, a passageway is provided which
bypasses the choke 20.
The pressurized cyclonic combustion method and burner
apparatus of this invention will be further described with
reference to ~he following example, which 6hould no~ be
construed as limiting the ~cope of the invention.
EXAMPLE
A cylindrical 6haped cyclonic type pressurizable test
burner was con~ructed to have ~tructural feature~ and
performance characteri6tic~ according to the present inven-
tion, as li~ted below in Table I, which provides a compari-
son with twn 6imilar conven~ional horizontal burners and a
pro~otype cylindrical ~haped cyclonic ~urner used for burning
-14-
particulate solid fuel~ and havin~ simil~r nominal or total
heat release ratings. This new test burner was operated by
burning wood chips having particle size ~maller than about
0.125 inch, which were fed tangentially into the burner
under pressurized operAting conditions ~s liGted in Table 1.
For this burner compariæon, the particulate fuel is intro-
duced into each burner at es6entially ambient temperature.
Numerous observations of the burner operation by viewing
through ports ~ndicated that the ~olid particles in the
primary combustion chamber swirled around in a helical flow
path about the periphery of ~he burner until consumed.
Table I also æhows the tes~ burner operating results achieved
as compared to performance characteristics o ~he other
similar conventional non-pressurized burner~.
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~ r~m ~h~ e cDml-ari~n D ~he bu3rne~ ~trc~ural
~eature~ ~nd per~rmance eh~r~cteri~tic~, it i~ 6een ~h~
the pri~ary cDmbusti~n cha~ber :1 ~r th~ improved p~e~suri2ed
cycl~n~e burner c~ the pre~ent ~nvent~c~n he~ e ~,reater
~spec~ reti~ ~nd lar~ger chc)ke res~ric~i~n ~Btir:~ ~han ~r th~
6i~ilar kn~n cycl~nic type ~ d fuel b-lrner~. Al~, it
n~ted that ~he pre~en~ burner proYide~ e ~i~nif~e~ntly
hi~her Reync~lds number fc)r the cc~mbus~i~n ~ir ~nltering ~che
primary cDmbustiDn char~ber, en~ als~ pr~vide~ grecter
tsn~æntial fl~ Yel~ci~ie~ ~nd ~ignificantly gre~er centri-
fu~al fvrces on t~e helic~l flowing ~olid fuel particl~
bein~ combu~ted, ~s iB ~dditi~nally sho~ by ~i~. 4. ln
~dditi~n, it i~ ~een ~hat ~he pre~ent burner pr~ideE
~ubst~ntially higher volumetric hea~ rele~e ~tes ~nd
hi~her Reyn~lds number~ for the h~t effluent ~as mâ~erial
fl~in~ fr~m the pre~suri2ed burner prlmary ~nd ~ec~ndary
c~mbu~;tion chamber~ ~han d~ the ~imil~r conventional burners.
A compari~n ~f ~he ~lumetric he~t release r~in~ is ~ls~
s~ rcphiccll~ in ~ . Such i~.p~vveo burn~ perf~r-
m~n~e at pressurized ~per~tin~ conditi~ns ~s unexpected ~nd
th~ present in~enti~n ~d~nta~ec~usl~ pr~id~E th~ c~m~ustion
industr~ ~ith ~ nific~nt and un~bviouc impro~e~,en~ in
burner desi~n and perform~nc~ f~r pressuri~ed burnirE of
c~liG ~crticu~ct~ , cuch ~E ~ uc~ in p~ T ~rDdUCinE
pr~cesses~
:
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Referring now to Fig. 6, there will be described
the system incorporating the burner 10 of Fig. 1.
A source 110 provides wood chips having size smaller
than about 0.70 inch major dimension, and preferably smaller
than about 0.130 inch, which chips are collected at 111 in
the hopper 112 maintained at substantially atmospheric
pressure. The chips 111 are fed from the hopper 112 by
a variable speed screw conveyor 114 driven by motor 114a
into a vPrtically oriented chute 115, and are then passed to
a suitable feeder means 116 for delivering the wood particu-
late solids material into pressurized conveying conduit 118.
Feeder 116 preferably consists of two rotary valves 116a and
116b connected in series and arranged for transferring the
particulate solids material by gravity flow from the chute
115 into the conduit 118 at a pressure of about 3-20 atm.
absolute, and preerably at 4 15 atm. pressure. The pres-
surized transport air from condui. 117 flows in conduit 118
at 40-120 ft/sec superficial velocity and preferably at 60-
100 ft/sec velocity and pneumatically conveys the particulate
solids material tangentially to the pressurized burner 10.
The particulate solids fuel material is fed pnuemati-
cally into burner 10 at near its inlet end through ~angential
inlet port 16 at superficial gas velocity exceeding about 80
ft/sec and preferably at 90-150 ft/sec into primary combustion
chamber 15. Additional combustion air is introduced tangen-
tially into the primary combustion chamber 15 at superficial
velocity exceeding about 100 ft/sec, and preferably 110-150
ft/sec, through multiple spaced-apart openings or tuyeres
18a, 18b, 18c, etc., located axially along the length of
chamber 15. I preheating or drying the solids in conduit
118 is desired, such preheating can be provided in heat
exchanger 119 using any convenient source of heat such as
turbine exhaust gas flowing through a jacket surrounding an
elongated heat exchanger.
In the combustion chamber 15, the fuel solids are made
to swirl around at high rotational velocity exceeding about
80 ft~sec and preferably at 100-150 ft/sec and produce high
centrifugal forces exceeding about 140 gravitational units
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-19-
~gl, while the particles are rapidly heated by the ho~
chamber walls and progressively devolatized and burned to
produce a hot pressurized effluent gas at a temperature of
about 2100-2800 F. The particles are also advan~ageously
retained in the primary chamber lS for prolonged combus~ion
therein, not only by the high centrifugal forces but also by
the effect of choke opening 20a, located at the exit end of
the primary chamber 15. The choke opening 20a has a
smaller cross-sectional opening area than the combus~ion
zone 15 so as to prolong the particle solids combustion time
therein and thereby provide for more complete combustion of
the particulate fuel solids and produce very high volumetric
heat release rates exceeding about 400,000 Btu/hr ft3
of primary chamber volume ~nd prefersbly 500,~00-3,000,000
Btu/hr ft .
It has been found advantageous that the primary com-
bustion chamber 15 should have a length/diameter aspect
ratio for the chamber at least about 2.5:1 and usually need
not exceed about 10:1 to provide for adequate combustion
time for the solids. The combustion chamber inside diameter
should be at least about 1.5 ft. for achieving a reasonable
throughput rate for the combustible solids material and
usually should not exceed about 3 ft. diameter to achieve
adequate rotational velocity for the solid particles therein.
In the choke section 20 of chamber 15, the hot effluent
gas is mixed with additional combustion air provided through
conduit 32, to quench and cool the hot effluent gas to lower
temperature such as 1500~1800 F suitable for extended use
in a gas turbine.
The secondary or quench air is introduced in the choke
zone through dual openings 30 oriented in a tangential di-
rection opposite to that for tuyeres 18 in the primary com-
bustion chamber 15, thereby producing highly turbulent shear
type mixing of the two streams in the choke zone leading to
secondary combustion zone 25. The flow of supplementary
air at conduit 32 is controlled relative to combustion air
. . .
.. ~ ,.
-20-
in conduits 123a, 123b, 123c, etc. to the tuyeres 18a, 18b,
18c, etc. by controller 132, which monitors the air flows
at flow meters 131a, 131b, and operates control valve 129
in condiut 32.
The resulting cooled effluent gas in the secondary com-
bustion chamber 25, which may still contain a very small
concentration of incombustible particulate solids, is passed
through a cyclone type separator device 34 for substantially
complete removal of such fine solids. The cyclone separator
34 preferably uses an axial flow type element 35 to provide
for a more compact separator overall arrangement. From
separator 34, a clean hot effluent gas stream at 1500-1800
F temperature is removed at 36, while the particulate solids
removed are withdrawn through valve 37 for suitable disposal.
The cleaned effluent gas at 36 at 3-10 atm. pressure is
then passed through conduit 38 to the inlet of gas turbine
40, which is connected to drive air compressor 42 for
supplying pressurized air source at 44 for the combustion
air at tuyers 18 and the quench air at 32. Also, a portion
of the compressed air stream at 44 is cooled at 45 against
stream 45a sufficient to avoid combustion of the particulate
solids such as to about 200 F, usually by heat exchange
with ambient air. The air at 47 is further compressed at
46, preferably by a positive displacement type compressor,
to a differential pressure such as 2-10 psi and preferably
4-8 psi to provide the pressurized air at 117 required in
conduit 118 for pneumatically conveying the wood chips into
the burner 10.
Turbine 40 also rotatively drives a load device 50,
which is usually an electric generator for generating
electric power. From turbine 40, exhaust stream 41 at near
atmospheric pressure and at 900-1000 F temperature can
be passed to a heat recovery step at 52 and used as a heat
source for generating steam, for heating another fluid used
for heating purposes, or as a hot gas for preheating and/or
drying the particulate feed material in heat exchanger 119.
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-21-
The gas turbine unit 40 can be divided into two sepa-
rate turbines each operating at different rotational shaft
speeds, with the first tur~ine ~Oa used for driving the
compressor 42 at a high rotational speed, and the inter-
mediate exhaust gas stream at 41a from the first turbine 40a
being passed to second turbine 40b which is gear-connected
to an electric generator 50 for driving the generator at a
lower rotational speed. Alternatively, a single shaft type
turbine-compressor unit can be used in which bo~h the com-
pressor and electric generator are driven by a single t~rbine.
During start-up of the process, an auxillary burner
(not shown) using a hydrocarbon fuel source such as propane
is used to initially heat the refractory walls of primary
combustion chamber 10 to a temperature sufficient ~o ignite
the particulate solid fuel introduced at 16. Also, an
auxillary drive motor 54 is used to drive compressor 42 to
provide the hot air source initially needed for combustion.
Also, air further compressed by compressor 46 is used for
initially pneumatically conveying the particulate fuel
solids through conduit 118 into the burner 10.
The solid fuel pressurized combustion and power gene-
ration process of this invention will be further described
with reference to the following example of operations, which
should not be construed as limiting the scope of the in-
vention~
EXAMPLE
Wood chips and shavings, such as produced from a wood
processing mill source and having nominal size of about 1/8
inch, were transferred from an atmospheric pressure col-
lection hopper through tandem rotary feeder valves into a
pressuri~ed transfer pipe operating at about 5 atm. pressure.
The wood chips were pneumatically conveyed at superficial
gas velocity of about 80 ft/sec and fed tangentially into
the inlet end of a horiæontally oriented cylindrical cy-
clonic burner primary combustlon chamber having dimensions
, ~:
.
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-22-
as shown in Table II below. Pressurized combustion air was
also supplied tangentially into the combustion chamber
through 6 sets of dual tuyeres spaced-apart axially along
the chamber length and at superficial gas velocity of about
100 ft/sec. Numerous observations of burner opera~ion made
through viewing ports indicated that the particulate solids
were circulated in a swirling helical flow pa~h in the
combustion chamber at calculated tangential ~elocity of
about 100 ft/sec until consumed.
In the primary combustion chamber, the wood particles
being circulated at the high rotational velocity developed
high centrifugal forces of about 200 'g', which provided for
prolonged total combustion of the particles at high Reynolds
number and produced high volumetric heat release rates of
about 1,800,000 Btu/hr ft3. Thus, the solid fuel particles
were rapidly devolatized and combusted to produce a hot
effluent gas at 2700-2800 F temperature, which passed
~hrough a restricted choke opening at the exit end of the
combustion chamber.
The resulting hot effluent gas at about 2700-2800 F
temperature was quenched by additional pressurized secondary
air injected tangentially into the throat portion of the
choke opening. The quench air was injec~ed tangentially in
a direction opposite to that of the swirling effluent gas
rom the primary combustion chamber, thus producing highly
turbulent shear type mixing o the two gas streams so that
the hot effluent gas was effectively cooled to about 17004 F
and then passed into a secondary combustion chamber located
immediately downstream from the choke.
From the secondary combustion chamber, a portion of the
cleaned effluent gas containing about 250 ppm (wt.) fine
particulate solids was then passed through a centrifugal
type gas-solids separator in which the fine particulate
solids in the gas were substantially all centrifugally
separated and removed.
The resulting cooled and cleaned gas at about 16004 F
~26a~6~
temperature is then expanded through a gas turbine driving
a rotary air compressor to provide the pressurized transport
and combustion air, and also driving an electric generator
to produce net electric power. Based on burner operating
data and related experience, the projected continuous oper-
ating period for this process is in excess of 30,000 hours.
Performance data obtained for the pressurized combus-
tion step and typical performance for the power-producing
process of this invention are provided in Table II below:
, ~ . .,
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-24-
TABLE ~I
Solid Fuel Pressurized Combustion and Process Ch~racteristics
Test ~nit Prototy~
Primary combustion chamber:
Inside di~meter, in. 20 27
Length/diameter, ratio 3 ~3
Choke diameter, in. 6 6.5
Wood Chip feed rate, lb/hr 2020 6100
Transport and combustion
air flow rate, lb/hr 26,300 85,5C)n
Combustor pressure, psia 66 95
Combustor pressure, ~tm. abs. 4.5 6.5
Volumetric heat release rate,
Btu/hr ft3 1,866,0001,900,000
Quench air flow rate, lb/hr 9,000 ~5,000
Secondary combustion chamber
effluent:
Gas Temperature, ~F 17~0 1780
Solids concentration, ppm (~t.) 250 250
Solids concentration o~ separator
effluent, ppm (wt.) 3~ 30
Gas turbine:
Inlet temperature, CF . 1700
lnlet pressure, psia G
Exhaust temperature, CF 900
Exhaust pressure, pSia 15
Gas flow rate, lb/hr 17~"600
~et power produced, kw 3000
~ ~, - , . . . .
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.
-25-
From the above data, is is seen that the present
process utilizes improved pressurized combustion of wood
chips or other particulate solid combustible material to
provide high volumetric heat release rates in the burner.
The process also utilizes effective quenching and cooling
of the hot effluent gas together with gas-solids separation
to provide a clean pressurized effluent gas suitable for
extended use in a gas turbine to produce electrical power.
Although the present invention has been described
broadly and also in terms of certain preferred embodiments,
it will be understood that various modification and varia-
tions can be made within the spirit and scope of the inven-
tion, which is defined by the following claims:
.
::. .......
.
