Note: Descriptions are shown in the official language in which they were submitted.
~13414
The increasing scarcity of ~luid fossil fuels such as
oil and natural gas is causing much attention to be directed
towards converting solid carbonaceous materi,als such as coal,
oil shale, tar sands, uintaite and solid waste to liquid and
gaseous hydrocarbons by pyrolysis. Pyrolysis can occur
under nonoxidizing conditions in a pyrolysis reactor in the
presence of a particul~te source of heat to yield as products
pyrolytic vapors containing hydrocarbons and a particul'~te
carbon-containing solid residue. The particulate source of
heat for eff`ecting the pyrolys,is of the carbonaceous material
can be obtaincd by oxidizing carbon in the particulate carbon-
containing solid residue in a combustion cllamber.
There are many problems associated with this use of a
pyrolysis reactor and a combustion chamber in co~nl~ination for
obtaining hydrocarbons from soli,d carbonaceous materials. One
of these problems i,s caking of coal along the walls of the
pyro],ysis reactor when the carbonaceous material is an
aggrlomerative coal, parti,cularly an Eastern Un;ted States
coal, which expe-rience shows to have a tendency to ag~omerate
in a reactor, especial]y along the walls oI' the reactor.
Anotller probleln concerns trar-sfe~cring the particulate
carbon-containing solid product from the pyrolysis reactor
to the combus-tion chamber while at the same time preveilting
oxygen that is present i,n the combustion cllalnber from enterillg
the r~yrolysis reactor. If oxy~elllnanages to leak i,ntc~ the
pyrolysis reacl,or, the value of tl3e hydrocarl~oll procluct is
reduced anc,ll;~ol-(?over, a ~iolent e~l)losion may occ,uv~.
A, th-ird prol>lem concc-~rns the rleed to 113'-~ ni~e product,i,on
~ ca-~boll dil-xic~ln and min:i,ln:ize prcd-~ct,i,on o,f o<irbon ~031C-~'i c,~e
- 30 i,n -tlle com'bus1;io~1 ~03ie i~ order -to nn'l~:i.mi7,(' l'C.`COVC`ry of l:]le
,~ _
~k~
1113~14
heating value of the carbon-containing solid residue during
oxidation. The kinetics and thermodynamic equilibria of the
oxidation of carbon favour increased production of carbon
monoxide relative to carbon dioxide at temperatures greater
than about 1200F. (650C.) at long residence times when there
is a stoichiometric deficiency of oxygen. Because pyrolysis of
carbonaceous materials often is conducted at temperatures greater
than 1200F. (650C.) and can approach temperatures higher than
2000F. (1100C.), it is necessary to form a particulate source
of heat having temperatures greater and often considerably
greater than 12000F. (650C.). Moreover, the particulate carbon-
containing solid residue is only partly oxidized in a stoichio-
metric deficiency of oxygen to form the particulate source of
heat. Thus production of carbon monoxide inevitably occurs
during the oxidation of the particulate carbon-containing solid
residue. The carbon monoxide formed represents a loss of thermal
efficiency of the process.
Therefore, there is a need for a process and an apparatus
for obtaining values from a solid carbonaceous material by
pyrolysis which are sueful for agglomerative coals; which, when
a particulate carbon-containing solid residue of pyrolysis of the
carbonaceous material is oxidized to form a particulate source of
heat to pyrolyze the carbonaceous material, prevent oxygen from
entering into the pyrolysis reaction; and which maximize pro-
duction of carbon dioxide while minimizing production of carbon
monoxide.
The present invention therefore provides a method in
which the fluidized bed is fluidized by a fluidizing gas contain-
ng oxygen.
Preferably there is provided a continuous process for
pyrolysis of particulate solid carbonaceous materials which
3 -
?
4~
comprises, in combination, the steps of:
a) subjecting a particulate solid carbonaceous material
to flash pyrolysis by continuously:
(i) transporting the particulate solid carbonaceous material
contained in a carrier gas which is substantially nondeleteriously
reactive with respect to products of pyrolysis of the particulate
solid carbonaceous material to a substantially vertically
oriented, descending flow pyrolysis reactor containing a
pyrolysis zone operated at a pyrolysis temperature below about
2000F;
(ii) feeding a particulate source of heat at a te~perature
above the pyrolysis temperature and comprising heated particulate
carbon containing solid residue of pyrolysis of the particulate
solid carbonaceous material to the pyrolysis reactor at a rate
sufficient to maintain said pyrolysis zone at the pyrolysis
temperature;
(iii) forming a turbulent mixture of the particulate source
of heat, particulate solid carbonaceous material and carrier gas
to pyrolyze the particulate solid carbonaceous material and yield
a pyrolysis product stream containing as solids, the particulate
source of heat and a particulate carbon containing solid residue
of pyrolysis, and a vapor mixture of carrier gas and pyrolytic
vapors comprising hydrocarbons;
b) passing the pyrolysis product stream from the
pyrolysis reactor to a first separation zone and separating at
least the bulk of the solids from the vapor mixture; and
c) forming the par~iculate source of heat by:
(i) transporting at least a portion of the particulate carbon
containing solid residue formed by pyrolysis of the particulate
solid carbonaceous material and separated from the vapour mixture
to a fluidized be~ around a substantially vertically oriented
- 3a -
~3~
open conduit in open communication with a substantially vertically
oriented riser, the conduit and riser comprising a first combust-
ion zone;
(ii) educting particulate carbon containing solid residue from
the fluidized bed upwards into the first combustion zone by inject-
ing a gaseous source of oxygen upwardly into the conduit to
oxidize carbon in the particulate carbon containing solid residue
thereby heating the particulate carbon containing solid residue
and to transport particulate carbon containing solid residue and
gaSeQus combustion products of the particulate carbon containing
solid residue, including carbon monoxide, to a second combustion
zone;
(iii) introducing a source of oxygen into the second
combustion zone in an amount at least equal to 50% of the molar
feed of carbon monoxide to the second combustion zone for
oxidation of such carbon monoxide in the second combustion zone,
the total oxygen fed to the first and second combustion zones in
combination being sufficient to generate the particulate source of
heat; and
(iv) passing the formed particulate source of heat and the
gaseous combuation products from the second combustion zone to a
second separation zone and separating the particulate source of
heat from the gaseous combuation products of the particulate
carbon containing solid residue and feeding the thusly separated
particulate source of heat to the pyrolysis reactor.
Preferably the invention provides a process for pyrolysis
of solid carbonaceous materials by heat transferred thereto by a
particulate source of heat to yield a particulate
- 3b -
~13~
carbon~colltaining solid residue as a product of pyrolysis,
t;he particulate source of heat being formed by oxidizing at
least a portion of the particulate carbon-containing solid
residue, characterised by transporting at least a portion
of the particulate carbon-containing solid residue formed by
pyrolysis of the solid carbonaceous material to a fluidized
bed around a substantially vertically oriented, open conduit
in open communication with a substantially vertically oriented
riser, the conduit and riser comprising a first combustion zons;
educting sol.id residue from the fluidized bed into the first
combustion zone by illjecting a gaseous source of oxygen
upwardly i.nto the conduit to oxidize carbon in the solid
residue for partly lleating the solid re-idue and to transport
solid residue and gaseous com~ustion products of the solid
residue, including carbon monoxide, to a second combustion
zone; and introdllcing a source of oxygen into the second
combustion zone in an amount at least equal to 50% of tho
molar feed of carbon monoxide to the second combustion zone,
t.he total oxygen ~eed to the :first and second combustion
zones being sufficient to generate the particulate source of
heat.
Prefera.bly the said conduit is spaced ~part from said riser
al~d the particulate carbon~conta.ining solid res.idue is ~luidized
: in the l`luidized bed by an upward flcw of a fluidlzing gas that
passes into the riser through the space between t;he riser and
tile COlldlli t . The ilui.dizing gas desirably contains oxy~en.
In prel`er3ed embodiments of the inventi.oll the pyrolysis
process is a so~c~li.ed flasll pyrolysi.s st;ep, performed by
cont;inuously tra]~sporti.ng pa:rt:iculate solid carbo1laceouc mater~
fee~ contaill.ed in a c.lrrieJ ~ras whi.ch ;s subst;al-l-li.ally
-- 4 --
1~13414
nondeleteriously reactive with respect to products of
pyrolysis to a vertically oriented, descending flow
pyrolysis reactor containing a pyrolysis zone operated at
; a temperature below about 2000 F. ( 1100 C. ); feeding the
particulate source of heat at a temperature above the
pyrolysis temperature to the pyrolysis reactor at a rate
sufficient to maintain said pyrolysis zone at the pyrolysis
temperature; forming a turbulent mixture of the particulate `
source of heat, particulate solid carbonaceous material feed
and the carrier gas to pyrolyze the solid carbonaceous material
feed and yield a pyrolysis product stream containing as solids,
the particulate source of heat and a particulate carbon-containing
solid residue of pyrolysis, and a vapor mixture of carrier gas
.
; and pyrolytic vapors comprising hydrocarbons; and passing the
;; pyrolysis product stream from the pyrolysis reactor to a first
separation zone to separate at least the bulk of the solids from -
the vapor mixture.
The first separation zone may be a cyclone separation zone.
; The formed particulate source of heat may be separated from
the gaseous combustion products of the second combustion zone
in a(secon~ cyclone separation zone. Alternatively, the
second combustion zone may comprise a cyclone oxidation-
separation zone.
The process is preferably performed with the use of a
pyrolysis reactor ha~ing a solids feed inlet for the solid
carbonaceous material feed and a vertically oriented chamber
surrounding the upper portion of the pyrolysis reactor, the
inner peripheral wall of said chamber forming ar overflow weir
to a vertically oriented mixing zone of the reactor, the
particulate solid carbonaceous material being transported
5 -
~134~4
in a carrier gas to the solids feed inlet and thence being
injected into the mixing zone, the particulate source of
heat being fed to the said vertically oriented chamber and
being fluidized in such chamber by a flow of a fluidizing gas
substantially nondeleteriously reactive with respect to the
products of pyrolysis, the fluidized particulate source of heat
discharging over said weir and downwardly into said mixing zone
to form a turbulent mixture with the particulate solid carbon-
aceous material, said mixture passing downwardly from the
mixing zone to the pyrolysis zone of the pyrolysis reactor to
pyrolyze the solid carbonaceous material.
The invention also provides an apparatus in which the
combustion chamber is a cyclone for separating formed particulate
source of heat from such formed combustion gas.
Such apparatus is particularly useful for combination
with a pyrolysis reactor utilising a particulate solid source
of heat. Accordingly, in another aspect the invention provides
an apparatus for pyrolysis of solid carbonaceous
,~
~f j
1~13~4
materials~ comprising a descending flow pyrolysis reactor;
means for forming a turbulent mixture of a particulate source
of heat and a solid carbonaceous material contained in a carrier
gas for introduction into the pyrolysis reactor to pyroiyze the
solid carbonaceous feed to form a pyrolysis product stream
containing a vapor mixture and, as solids, the particulate
source of heat and a particulate carbon-containin~ solid
residue of pyrolysis; a first separator for separating at least
th~ bulk of the solids from the vapor mixture in the pyrolysis
product stream; means for transferring the pyrolysis product
stream to the first separator fro~ the pyrolysis reactor; means . .
for f~ming the particulate source of heat, comprising a
vessel containing a fluidized bed of the separated solids
around an open, substantially vertically oriented conduit,
a substantially vertically oriented riser in open communication
. with the conduit, a combustion chamber in communication with the
riser, means for introducing a gaseous source of oxygen upwardly
into the conduit to educt solids from the fluidized bed into
the conduit, and means for introducing oxygen into the combustion
chamber to heat the solids to form the particulate source of
heat, means for passing the separated solids from the first
separator to the fluidized bed; means for transferring the
particulate source of heat from the second combustion chamber
to the second separator; a second separator for separating
the particulate source of heat from the gaseous combustion
~: product; and means for transferring the separated particulate
source of heat from the second separator to the pyrolysis
reactor, '
~referably the said conduit is spaced apart from said riscr
The first and second separators may con~eniently both be
7 --
1~ r;~L~1!4
cyclone separators although in a modified arrangement the
second combustion cha3nber and the second separator are
integrated and constituted by a cyclone oxidation-separation
device.
In a preferred embodi~ent of the apparatus, the pyrolysis
reactor contains a substantially vertically oriented mixing
section and a su~stal3tially ~ertically oriented pyrolysis
section, and has a solids feed inlet, a substanti.ally
vertically or;ented ch~nber surrounding the upper portion
of the reactor and ha~ing an inner peripheral wall that forms
an overflow weir to the vertically ori.ented mixing section,
- and the means for forming a turbu.lent mixture comprises means
for feeding par':iculate source o~ heat to t;he vertically
oriented chamber; means for introducing a fluidizing gas into
the cha1nber to maintain the particul.ate source of heat therein
in a fluidized state; and means for injectil~g the solid
carbonaceous feed contained in the ca.rrier gas from tthe solids
feed inlet into the mixi.ng section to form tlle resultant
turbulellt mixture.
Irl anotller aspect the invention provides an apparatus
for pyrol.ysis of agglomerati~re coals, comprising a descelldillg
flow pyrolysis reactor con1aining a substan~:ially vertically
orienled n~i~cingr section, a su1~stanttially vertically or.iented
pyrolysi.s section, a solids feed :in1.et, a1-lcl a su1~t;a1lt:ially
erticall.~ oriented cham1~er surrounding t}~c~ up~er por1;;on of
the reac-tor, t;he im-er pe1-i.pheral ~Tall of t1~e cl1an31~er formi1~r
an o~er~lo~r1~re:i.r to the mi.~i.ng section, ~lle:ce-in an ag~lo1~3erati~-r
coal feed containecl in. a ca-rri.er gas is combillec~ a
partici~l.c~..t;e SOUl~C.? of heat IllldCr l-Urb~lCllt f1O~r condii;ic-ns :in
tlle pyrolysis sect:i.on Or t:he p!T olysis ro<lc-t~ co yiel.d a
pyrolysis product stream containing as solids the particulate
source of heat and a particulate carbon containing solid residue
of pyrolysis, and a ~apor mixture; means for feeding the particulate
source of heat to the vertically oriented chamber; means for
introducing a fluidizing gas into the chamber to maintain the
particulate source of heat therein in a fluidized state; means
for passing a coal feed from the solids feed inlet into the
mixing section; a first cyclone separator in con~nunication with
the pyrolysis reactor for separating at least the bulk of the
solids in the pyrolysis product stream from the vapor mixture
in the pyrolysis product stream; means for forming the particulate
source of heat, comprising a vessel containing a fluidized bed
of the separat~l solids arour~d an open, substantially vertically
oriented conduit, a substantially vertically oriented riser in
open communication with the vertically oriented conduit and
separated therefrom, a second combustion chamber in communication
with the riser, means for introducing a gaseous source of oxygen
upwardly into the conduit to educt solids from the fluidized
bed into the conduit and to partially oxidize carbon in the
solids to heat the solids with attendant formation of combustion
products, means for introducing o~gen into the second combustion
ch~nber to further heat the solids to form the particulatc
source of heat; a dipleg I`rom the first cyclorle separator to
the fluidized bed for transferring the scparated soli~s from the
first cyclone separator to the fluidized bed, a second cyclone
separator in communica-tlon with the coml~usiion cham~Gr for
separatirlg tl~e particulate source of heat from tl~e ~cr~seous
com~ustion products, and a d:;ple~r from t~le second cyclone
separator to the cllamber surrounding l}le uI)per po:rt;oll of the
pyrol-ysis reaG-toJ J`or transferring t}le p.lrt3.cuL~te source of
~ g _
4~
heat to the pyrolyæis reactor. ~:
Further preferable features of the process of the
invention and of the apparatus thereof will be discussed
and described in the following, with reference to the
accompanying drawings in which:
~ IGURE 1 illustrates . diagrammatically a process
and an apparatus embodying features of this invention; and .-
FIGURE 2 is an enlarged and more detailed view of the
region marked 2 in ~igure 1.
The drawings illustrate a pyrolysis unit 8 comprising
a descending flow pyrolysis reactor 10 which has a substantially
vertically oriented mixing sectiosl or zone 12 and a
substantially vertically oriented pyrolysis section or zone
14 below the mixing section. Arrow 1~ shows the approximate
extent of the pyrolysis section. The reactor has an elbow
~, 18 towards the end of the pyroly~is section, by which it can
be supported. The lower end 20 of the reactor termînates in
. a separation zonè such as first cyclone separator 22.
A generally upright annular solids feed inlet 24
`t 20 terminating within the mixing section 12 and constricted
at its end to form a nozzle 26 is provided for introducing
a so1id carbonaceous materi.al into the mixing region.
-The upper end 28 of the reactor is open and of larger
diameter than the nozzle 26, thereby leaving an annular gap
30 between the upper end 28 of the reactor and the nozzle 26.
A vertically oriented fluidising chamber or well 32 surrounds
the upper portion of the reactor and is formed by a preferably
annular section 3~ which connects the wall 36 of the solids feed
: inlet above wllere the wall constricts to for.m the nozzle 26
and the upper portion 2~ of the reactor, The chamber 32
-- 10 --
~3~13~4
surrounds the nozzle 26 and a portion of the upper wall 28
of the reactor. The inner peripheral wall of the chamber
32 is formed by thè upper wall 28 of the reactor and serves
as an over~low weir to the mixing section 12 of the reactor
10.
A second vertically oriented solids inlet 38 terminates
in the annulàr fluidizing chamber 32, prefe~ably at a level
below the top edge 40 of the pyrolysis reactor 10,
There is a gas inlet 42 to the bottom of the fluidizing
chamber for a fluidizing gas. Means are provided such as
a cylindrical, horizontally oriented, perforated plate 44
positioned towards the oottom of the fluidizing chamber below
the end of the second inlet for distributing the fluidizing
gas so that the fluidizing gas flows u]~wardly through the
fluidizing chamber.
The first cyclone separator 22 serves to separate a
particulate carbon-containing solid residue of pyrolysis
from the gaseous products of pyrolysis.
The particulate source of heat for the pyrolysis reactor
is forméd by oxidizing at least a portion of the particulate
carbon-containi.ng solid re~idue in a combustion unit 50.
The combustion unit includes a vessel 52 containing a
fluidized bed 60 of a particulate carbon-conta.ining solid
residue around an open, substantially vertica]ly oriented
conduit or tube 54. There i.s a gas inlet 56 for a transport
gas at the base of the vessei 52 w13ich narrows down to form
a vertical]y oriented nozz.le 5~ for inJection of the tran~port
gas directly upwardly into the open conduit 5~1. The ~luidized
bed 60 of carbon-containing solid residue is fluidized by a
fluidi7ing gas entering the cbalnber througll a gas i.nlet 62 at
~ ~3~
the base of the vessel. The fluiclizing gas is distributed
throughout the fluidized bed by means of a second, horizontally
oriented perforated distributor plate 64.
The top 66 of the vessel 52 tapers upwardly and i-.-wardly
to connect to a vertically oriented riser 68. The riser and
conduit comprise a first combustion zone or chamber. The riser
couples the vessel 52 to a second combustion zone or chamber 70.
The conduit 54 is below the riser 68 and tlle top edge 72 of
the conduit is spaced apart from the riser so that an annular
gap of space 74 is formed between the inlet 76 to the riser
and the top edge 72 of the conduit. The top portion 71 of
the conduit can be tapered inwardly so that the diameter of
the conduit at its top edge is smaller than the diameter of
the riser.
A vertically oriented standpipe or dipleg 78 having
stripping gas inlets 122 extends from the bottom of the first
cyclone separator 22 into the ves.sel 52 below the top 80 of the
flu;dized bed of carbon-containillg solid residue. Solids
separated by the first cyclone separator are transferred
througll this dipleg into the vessel.
There is an inlet 82 at the upper portion of the riser
68 for introduction of a source of oxygell into the second
comb-lstion chamber 70. The second combustion chamber is in
open comm~lication with a second separa1;or such as cyclone
separator 84. This separator serves to separate a particulate
source of heat generated in the combus-tion unit 50 from any
combustion gases present in the com~ustion unit. The
particulate source o~ heat is transferred from the second
cyclone separa-tor 8ll to 1;1~e second inlet 38 of the pyrolysi,s
reactor throu~ll a vertica,,ly or:ienl;ed d;pleg or stancdp;pe 86
- 12 -
1~i3L?~'~4
originating at the bottom o~ the second cyclone separator 84
and terminating in the second inlet 38. The length of the -
standpipe 86 is chosen to balance the accumulation of
differential pressures throughout the remainder of -the
system. Inlets 88 for a stripping gas are provided along
the length of the standpipe 86.
In summary, what has' been described is an apparatus for
pyrolysis of a ~solid carbonaceous material comprising two
ntain units, a pyrolysis unit 8 and a combustion unit 50.
These t~o units are coupled by two cyclone separators 22, 84
and two vertically oriented stanclpipes or risers 78, 86 which
allow car~on-containing solid residue to be transferred from
the pyrolysis unit to the combustion unit and particulate source
of heat to be transferred from the combustion unit to the pyrolysis
unit, respectively.
In the proc~ss of this invention, a particulate solid
carbonaceous ~1aterial is subjected to flasll pyrolysis by
transporting the particulate solid carbonaceous material
feed containcd in a carrier gas through. the first feed i.nlet
24- to the feed no~le 26 and thus to the pyrolysi.s reactor 10.
The carri.er ~as is substantially nonde]eteriously reacti~e Wit~l
respect to the products of pyr.olysis and may sc~rve as a diluen-t
to pre~ent se].f-agg]o~neration of the carbonaceous ma-tericLl.
.As used hAl~ein, by a "nondeleteriously reacti.ve" gas
there is l~eallt a ~IS StreaT,Il WhiCh iS SUbStant~ 11Y free 0f
free OXYgel1. A1 l;hOUgh the gas ~nay con.-tain con.stituc~llts 1,llLt
reac-t uncler nonox.idizing conditions w-itll pyrolysis ~)rod~cts
to upgrade -thei.r ~T.-Llue, the gas sl-ould no'c conta;n
cons-tit,uents that dcgrade pyroly.5:i.s proc]ucts. T]le carri.or
3o gas may, ~or ~ st,al~ccT be -t.]le O:)~ -L.S prCldliCt O:l~ pyrolys
13 -
~3414
ste~2 which will react under suitable conditions with char
or coke formed from pyrolysis to yield, by water-gas shift
reactions, hydrogen that serves to react with and stabilize
unsaturates in the products of pyrolysis; any desired inert gas;
or mixtures thereof. The carrier gas can, for instance, be
synthesis gas, especially a hyTdrogen-enriched synthesis gas.
The carbollaceous material may be treated before it is
fed to the first fluidized bed by processes such as removal
of inorganic fractions by magnetic sepàration and classification,
particularly in the case of municipal solid waste. The
carbonaceous material also can be dried to reduce its moisture
content. The solid carbonaceous material is usually comminuted
to increase th<: surface area avai]able for pyrolysis.
Preferably a substantial portion of the carbonaceous
material is o~ a particule size of less than about 1000 microns
to pre~sent a large surface-to-volume ratio to obtain rapid
heating of the coal in the pyrolysis zone. Rapid heating
results in improved yields of hydrocarbons. For an
agglomerative coal, the partlcle size is preferably mainly less
than a~out 250 microns because aggLomerative coals are well
-known to plasticize and agglutinate at relatively low
temperatures i.e., 400 to 850 F. (200 - 450 C.). An
agglomerative coal should -therefore be rapidly hcated through
the plastic state be~ore it strikes the wall of a pyrolysis
reactor to prevent caking on the reactor waLl.s. Because thc
rate at ~Thich a coal particle can be lleated increases as
particle size decreases, it is important that an agglomerative
coal bc comminuted to 250 ~licrons or less, depending 031 the
si~e and conriguration of the pyrolys;s re~cl->r, so that
substantia31y all the coal particle3 have l~assccl thro~g}l t~le
~i3'~:~4
plastic state and have become non-tacky by the time the coal
particles stri~e a reactor wall, ~or example, when a
bituminous high-~ol.atile C coal which agglomerates at
temper~tures above 500 F. (260 C.) is pyrolyzed at a temperature
of 1075 F. (580 C.) in a 10 inch (250 mm) diameter pyrolysis
reactor of the design shown in Figure 1 and described below,
the coal should be comminuted to a size less than 250 mi.crons
in diameter to prevent caking on the reactor walls, Coal
parti.cles larger than 250 microns in diameter could strike
the reactor walls before passing through the plastic state.
The carbonaceous material introduced into the pyrolysis ,'
reactor is preferably substantially free of fines less tllan
about, 10 microns in di.ameter, because carbon-containing solid
residue fincs 3~esu~.-ting from pyrolysis of the carbonaceous
material have a tendency to be carried into and contaminate
the liquid hydrocarbon. products.
Simu].taneously with the introduction of the carbonaceous
materi.al ~eed, there is introduced. a particulate source of`
heat i,nto the fluid;zing cha1nber 32 through the second
vertically oriented inlet 38. Because in tll-_ preferred
embodiment the second inlet 38 terminates bel-)w the top edge
40 of the pyrolys:is reactor 10, incom;l-lg "art:ic~llatc? source
of heat bui.lds up in the fluidizing chaniber be3o~J the weir
28 to form a solids seal. The particula.te source of lleat
in chamber 32 is mainta.ined in a fluidized st~te in the chamber
~y introduction O:r a flu,idiz:ing gas st:ream -tllrc)~ l? tlle gas .inlet;
42~ The f`lu:i,di~ing gas is distributed b~r the d--stributor
plate 411 tC? maintai.n the particulat-e SOUl'Ce Or )leat in a -fluidiz(?cl
st~l1;e throughout l;h-' cl?amber. ~s addi t.. ,?nal I?arl~i CUlat;r? source
of heat is ini;~oAllced :illt~? tlle cl~ambe:r t~ .ll`tiCUlatC SOllrCC
- 15 -
of heat passes over the upper end 40 of the weir and through
the opening 30 between the weir and the nozzle 26, into the
mixing section 12 of the pyrolysis reactor 10 with aid of
fluidizing gas. An advantage of this weir-like configuration
is that substantially steady flow of fluidi~ed particulate
source of heat enters the mixing section because the mass of
the particulate source of heat backed up behind the weir of
the reactor damps minor fluctuations in the flow of the
particulate source of heat.
In the mixing zone of the pyrolysis reactor, the
carbonaceous material conta.ined in th~ carrier gas-is
discharged from the nozz]~ as a fluid jet 112 expanding
towards the reactor wall at an angle of about 20 or less
as shown by dotted lines 88 ~hich represent ths periphery of
the fluid jet. Once the particulate source of heat is inside
the mixing section, it falls into the path of the fluid jet 112
of the carbonaceous material feed stream and carrier gas coming
from the nozzle and is entrained thereby, yiel.ding a resultant
turbulent mixture of the particulate source of heat, particulate
solid carbonaceous materia] feed, and the carrier gas, The
jet has a frce core region 113 of carbonaceous material, as
delineated by the V~sha.ped dotted line 114s extending
considerably into the reactor, but as tlle jet expands, the
particula.te source of lleat present is entrained 1~ith mixing
of the carbonaceous material in -th.e pOl-tiOn of thc flui~ jet
112 arou.nd the free core re~i.on 113, The par-ticulate source
of heat along the ~eri.p~-Zery 88 of the f1a~:id 3et prefera~ly
he&ts the carbonaceous materi.al in the ca.se of an ag~lomeralive
coal to a temperature al~ove~ tho temperat;ure at whic}- t]!e coal
J S tacky. In tlle re~ion 116 ~et~een t~l react.o3 walls and
- 16 -
3~4
the fluid jet 112, there is unentrained particulate source
of heat.
This mixing of the particulate source of heat with the
solid carbonaceous material in the mixing zone 12 initiates
heat transfer from the particulate solid source of heat to
the carbonaceous material, causing pyrolysis in the pyrolysis
sect;ion 14 of the pyrolysis reactor 10. Pyrolysis is a
combination of vaporization and cracking reactions. As the
vaporlzation and cracking ractions occur, condensible and
noncondensible hydrocarbons are generated from the carbonaceolls
material with an attenc~ant production of a carbon-containing
solid residue such as coke or char. An effective pyrolysis
time i 9 le.ss tllan about 5 seconds, and -treferably from about
0.1 to about 3 seconds, to maximize yield of middle distillates,
Middle distillates are the middle boiling hydrocarbons, i.e.,
C5 hydrocarbons to hydrocarbons having a boiling end point of
about 950 ~. (510 C-)- These hydrocarbons are useful for the
production of gasoline, diese]. fuel, heating fuel., and the li~e.
As used herei.n, "pyrolysis timc" mealls the time from when
th.e carbonaceous material con-tacts the ~arti.cu]ate source of` heat
until the pyrolytic vapors produced by pyrolysi.s are separated
from the particulate source of lleat in the first sepa.ration
zone 22, as described below.
A convellient measure of pyrolysis ti.me ;s the average
residence tir~e of the carrier ~a3 in the p~rolysis section
14 of tlle pyrolysis reactor ancl. the first scp<trator 2~.
Snflicient pyrolysis time must ~e pro~ri~ed to heat tlle
carbon~cec-us rrlater;.al to the pyrolysis tcl.;peratll:re.
All advanta~;c-~ of t;he pyro:lysis react~ S~10~!11. -in the
clrawinp~s is tlla-t thc turbul.ent flow c<-uses -tll( s~.l.id
- ~-7 -
1~3'};~4
carbonaceous material feed to be heated rapidly, which improves
yields, In the case of agglomerative coals, buildups of
coal particles on the reactor walls are prevented by the
rapid heating and turbulent flow. Preferably the particulate
source of heat enters the mixing section 12 at a rate of flow
less than turbulent and the solid carbonaceous material enters
the mixing section through the nozzle under the turbulent
flow conditions at a rate sufficiently high for the resultant
mixed stream from these two inlet streams to be turbulent.
Turbulent flow results in intimate contact be-tweerl the solid
carbonaceous material and the particulate source of heat
particles, thereby yieldin~ rapid heating of the carbonaceous
material. In the case of an agglomerative coal, the
turbulence results in mixing o~ the particulate source of
heat with the coal particles in the inner portion of the fluid
jet, thereby quickl3r heating these coal particles through the
tacky/plastic state. As used herein, "turbulent" means that
the stream ~7s a Reynolds flow index Number greater than 2000
as calculated by the velocity of the carrier gas at operating
conditions. Laminar flow in the pyrolysis reactor tends to
severely limit the rate of heat transrer within the pyrolysis
zone. Process parameters such as the noz~le diameter ancl mass
flow ratc o~ the carbonaceous material and its carrier gas are
varied to maintain the flow rate of the particulate stream
entering the ~irst inlet in tlie turbulent region.
The end o~ the sc,lids feecl inle-t is pref`era7,1y cooled,
e.g. I~y water when pyrolyzing an agglomerati~re c~al because
othel^wise ths lnlet might be heated abo~c tlle point at which
the coRl becomcs tacliy, by hea-t transfer f`lom t]le ~articulate
source o~ heat s~urroundirlg the end of t}l~ solid~, feed inlet.
l8 -
9.3~i~i4:~
Although the drawings show a solids feed inlet 24
having a nozzle 26 at its end to achieve high inlet
velocities into the mixing region, a nozzle type inlet is
not required. Alternatively, the carbonaceous material
and its carrier gas can be supplied at a sufficient velocity
to the inlet 24 so that the resultant mixture is under
turbulent flow wit,hout need for a nozzle.
The hot particulate solid source of heat is supplied
at a rate and a temperature consonant with maintaining a
temperature in the pyrolysis zone suitable for pyrolysis.
Pyrolysis initiates at about 600 F, (315 C.) and may be
carried out at temperatures above 2000 F. (1100 C.).
Preferably, however, pyrolys;s is conducted at a temperature
ranging from about 900 F. (480 C.) to about 1400 F. (760 C.)
to maximize the yield of middle boiling point hydrocarbons.
Higher temperatures, by contrast, enhance gasification reactions.
The maximum temperature in the pyrolysis reactor is limited by
tl~e temperature at which the inorganic portion of the particulate
source of heat or carbonaceous material soft,ens wi.th resultan-t
fusi.. on or slag formation.
Dependlng upon pyrolysis temperature, tl~e we:igrht rat:io of
- particulate solid source of heat to carbGnaceous rnaterial ;.s
preferably in the range 2 to 20 at the entry to the reactor.
At these ratios w;thin this range, the particu3ate source of
heat is introducecl to the reactor at a tenlperal,ure from about
100 to about ~00 F. (~5 - 2~0 f',) above tl2e d^s:;red pyrolys:is
tel~perat,ure .
For economy the amount of fluidizing ~ras injecl;ed tJll`Oll~
inlet li2 into the flll;.di.zi.n~ chaml)er i.s mail~ta:i~ic?d at as 3.o~
a 3evel as poss~ Le sul)ject to t,he co~isl.:ra:iJ-It, i;]l~lt, l;he
_ ~9 _
~ ~ ~ 3L~ ~
particulate source of lleat be maintained in a fluidized
state.- Preferably at least a portion of the fluidizing
gas is ad,mitted into the mixing section of the reactor to
prevent eddy formations with r~sultant back-mixing of partly
spent particulate source of heat. The quantity of carrier
gas injected with the sol,id carbonaceous material is that
which maintains turbulent flow during the progress of the
solid carbonaceous material througll the plastic state in
the case of an agglomerative coal. Sufficient carrier gas
must be injected to preven-t undesirable pressure fluctuations
due to flow instabilities. The amount of gas employed to
transport the solid car~onaceous material is sufficient to
avoid plugging in the reactor, and normally in excess of that
amount to dilute the ~solid materials anl prevent self-
agglomeration in the case o~ an agg],omerative coal.
Generally high solids content in the pyrolysis feed
strearn is desired to minimize equipment size and cost.
However, preferably the resultant turbu],ellt mi~ture contains
su~ficient carrier gas for the mixture to have a solids content
2~ ranging from about; 0.1 to about 10~ by volume based on the
total vo]ume of t;he stream, to provide turbulence for rapid
heating of the carbvnaceous material and to ditute the
carbonaceous material and help prevent self-agglomeration,
particularly ~hen processing an agglomerat;~e coal. napid
heating res-ults in high yields and pre~eIlts agglutinat,ion
o~ agglomerative coals.
~lle si~e ~r.vt con~igurativn of tl~e pyrolysis reactor is
chosen to main~ain the desired residellce t;in}lc ror the pyrolysis
reaction. Generally, as the pyrol~sis t,e~ erclt;ure is reduccd,
longc-~r residence t;imes are used -to ma:i}lt-c~in -tll-- desirecl y-ie]d
- 20 -
L~
of volatilized hydrocarbons.
~or economy, the pressure in the pyrolysis reactor is
typically greater than atmospheric to compress the vapors
formed during pyrolysis so that low volume separation
equipment downstream of the reactor can be used.
A pyrolysis product stream is passed f'rom the end 20
of` the pyrolysis reactor 10 to the first cyclone separator
22. The pyrolysis product stream contains as solids, the
particulate source o~ heat and the particulate carbon-containing
solid residue of pyrolysis, and a vapor mixture of carrier
gas and pyrolytic vapors comprising noncondensible hydrocarbons
and eondensible hydrocarbons. Preferably the first cyclone
separator is in open communication with vhe lower end 20 of
the pyrolysis reactor so that a quick separation of the vapors
from the solids can be ef`fected to mini.~ize pyrolysis time
and so that the vapors can be quenched to prevent cracking
reactions f`rom occuring which tend to decrease the recovery
of middle distillates from the pyrolytic vapor. In tlle
cyclone separator 22 at least the bulk of the solids are
separated from the vapor mixture. The va.por mixture contains
pyrolytic vapors containing volati.lized hyclroca.rbons~ inert
carrier gases, and nonhydrocarborl components such as
hydrogen sulf`i,de which ]rlay be generated in the pyrolysis
reaction.
r~he vol~tiL;.zed h~idrocarbons prod~ced by pyrolysi.s
consist Or condensible hydrocarbon~s wh:ich Illcly ~e recoveled
l~y contacting the vol~t;,lized llydrocarbons sucll as met~lanc
and other hydrocarboJl gases which are not reco-c,eral:)ly by
or~ ~ r co~ldens~tjG~l meansO Conc~ c;ib~e l~y-<~ o(~al~bons C~til
~e separat,ecl and reco~rered by COllV-?~lt:i Ol1al Ill<`~llS SUC11 aS ~c`lit~lr:i
scrubbers, indirect heat exchangers, wash towers, and the like.
~he undesirable gaseous products can be removed from the
uncondensible hydrocarbons by means such as chemical
scrub~ing. Remaining uncondensed hydrocarbons can be sold
as a product gas stream and can be utilized as the carrier
gas for carrying the carbonaceous material to the pyrolysis
reaction zone.
The particulate source of heat is formed in the combustion
unit 50. The solids separated in the first cyclone separator
22 are passed down through the dipleg 78 into the fluidized
bed 60 contai}ling spent particula1;e source of heat and the
carbon-containing solid residue of pyro3ysis. As the solids
drop down through the dipleg, hydrocarbons on the surface of
the solids are stripped by an upward ~low of stripping gas,
nondclcteriously reacti~e with respect to pyrolysis products,
such as steam. The stripping gas is introduced through gas
inlets 120 on the side of the dipleg. The bed 60 is maintained
in a fluidized state by an upward flow of fluidizing gas stream
91 into the Yessel 52 through the gas inlet 62 and distributed
by the distributor plate 64. The fluidizing gas can be
nonreactive with respect to the solids in the fluidized bed,
being for instance the off gas product of pyrolysis, or the gas
may contain a portion of the oxygen required for oxidizing the
solids to form the particulate source of ~eat.
A transport gas is introduced upwardly through the gas
inlet 56 and nozzle 58 into the riser 54. The transport gas
preferably conta;lls free oxygen. Other reactan1,s which lea~
to the formation of carboll monoxide may be ~-resent~ These
include ste.~ and carbon dioxide, When steam is present,
3~ hydrogen also is formed.
~? -
In the preferred process, the transport gas contains,as indicated, some oxygen to generate a portion of the heat
necessary to raise the char to the temperature required for
feed to the pyrolysis reactor in the first combustion zone.
However, the amount of oxy~en is limited for if there is too
much oxygen in the transport gas, the carbon monoxide
generated in the transport line cannot be converted to
carbon dioxide in the second combustion zone without
introducing so much additional oxygen to the second
combustion zone that the char would be raised to a temperature
above the te~perature required for feed to the pyrolysis
reactor.
As indicat~d i.n ~igure 1, the transport gas can be an
air stream 90 introduced upwardly through the gas inlet 56
and nozzle 58 into the conduit 54. A sufficient supply of
this air stream at a.n appropriate oxygen content is maintained
to: 1) educt solids ~rom the fluidized bed into the conduit;
2) to oxidize a portion of the carbon in the solids to heat
the solids in tho conduit and riser; and 3) to transport the
solids and combustion products, including carbon monoxide, of
the solids upwardly through the verti.cal riser 68 into the second
combustion zone chamber 70. The fluidizing gas stream 91
passes through the annular or space gap 74 between the upper
edge 72 of the conduit and the vertical r;ser 68 to help carry
the solids vpwardly into the second combustion chamber 70
If the top portion 71 of tlle conduit is smaller in dia~neter
than the riser, the flow of gas and solids upwardly in-to t}le
riser from the conduit can serve to eduet t~e f]uidizing gas
into the riser t1lrough the annular gap 74,
The ve:locity of the transport gas is main1;ained s~^ficielltly
.3~1~
high to educt solids into the conduit and convey them into
the second combustion zone. For~example, when the transport
gas contains air as a source of oxygen, a diluent gas
subst~ntially free of free oxygen, e.g. nitrogen or flue
gas, can be combined with the air to provide an oxygen-lean
carrier gas having sufficient velocity to educt and transport
the solids without introducing too much oxygen to generate too
much carbon monoxide. By diluting the heated air stream,
a carrier gas stream containing less than about 20% oxygen
by volume is formed.
The amount of oxygen in the transport gas is controlled
to maintain the desired temperature in the riser. This is
always less tha-l the stoichiometric amount required to
completely oxi~lize the char. Because of this deficiency of
oxygen and the relatively high temperature in the riser,
which can range up to about 1100 F. (595 C) in the case of
a pyrolysis reaction zone maintained at a te]nperature ranging
up to over 2000 F. ( 1100 C. ) for a pyrolysis reaction designed to
enhance gasif;cation, appreciable amounts of carbon Tnonoxide
are formed.
Also, as the solids and combustion gases pass upwardly
through the riser 68, carbon dioxide introduced in the
~transport gas and carbon dioxide formed by oxidation of
char tends to react with additional carbon in the char to
rorm carbon monoxide according to the reaction:
C ~ C02 ~ 2CO
Thus generally,less than about halr, and usuall~- from about
20 to about 50C~ 0~ the oxygen required to form the particulate
3o source O:r heat 3 g in the transport gas. The remainder o~` the
- 2~ _
3~
oxygen required is introduced into the second combustion
zone to oxidize the carbon monoxide from the first combustion
zone to carbon dioxide.
Excess solids in the fluidized bed beyond what is
required for oxidation to form the particulate source of
heat represent the net solid product of the pyrolysis
reaction, and are withdrawn from the first chamber through
line 94.
The configuration of the combustion unit shown in the
drawings and described above has many advantages. Among
these is instant ignltion of the solids entering the
flui.dized bed 60. When exposed to a source of oxygen the
carbon in the carbon-containing solid residue is readily
oxidized. If the carbon~containing solid residue has poor
ignition properties oxygen can be introduced with the
fluidizing gas to oxidize carbon in the solids in the
fluldized bed to raise the temperature of the fluidized bed.
Duri.ng startup, a f.uel gas followed by air can be utilized as
a fluidizing ga.s to elevate the temperature of the solids in
the fluidized bed above the solids igniti.on temperature . .
Another advantage of the scheme shown in the draw:ings an.d
described above is that the temperature in the first combustion
chamber is easily controlled by controlling the amount of o~ygen
fed to the fluidized bed in the fluidizing gas stream 90,
Another advantage results from the large 1nass of soli.ds
in the fluidized ~ed. Because of this large mass, Jninor
system upsets are damped by changcs in t}le le~el of t11e
fluidized bed. As ~the le~rel i21 the flu:i~.izecl bed increases~
adclition~l solids are remo~ed through the ~ithdrawal line 94
and ~ddi.tional solids are educted by the tra~ls~c)rt g 3S becauso
1~.3L~14
of the higher differential pressure of the solids due to
the increase in height of the bed. Conversely, as the
level in the bed decreases fewer solids are withdrawrL as
product arLd less solids arc ed~1cted by the transport gas
because the differential pressure of the bed decreases.
If any additional controls on the level of the fluidized
bed are required, the jet flow of the source of oxygen can
be varied. Thus the fluidized bed is a self-compensating
system.
Another advantage of the configuration of the first
combustion ch~nber and vessel is that because the solids
are fluidized in the fluidized bed, withdrawl of solid
product is facilitated. As the level of the solids in the
fluidized bed rises, more solids are au1omatically withdrawn
through the solids outlet line 40. ~his line extends upwardly
into the vessel 52 and its height determines the average top
80 of the fluidized bed in the vessel.
A major advantage of the scheme shown in the drawings
is that it provides a comparatively "fail-safe" method of
preventing oxygen in the combustion unit 50 from entering
the pyrolysis scction 8. The hei~ht of the fluidized 1>ed
acts as a barrier against the backflow of oxyge~l through
the dipleg 78 inlo the pyrolysis reactor. In addition,
au-tomatic control means can be provided to scnse the level
of the fluidi~.ed bed, and ir t~-Le level drops too low,
automatically to cut off the fLow of the source of oxyge
into the firs-l combllstion cl1amber.
A source of oxy~erl is int:roduced throu~]l il1e ~s inlet
8~ into t;lle seeolLd co~nbustio-n ZOl.e. Tlle amc,~ Li; of free
oxygen introd~Lcec1 illtO tl]e SeCOrlCI Colnl);lStioll ~O~.C c~uals ca-t
_ ~6 -
l~i3'~4
least 50~ of the molar amount of carbon monoxide entering
the stage to completely oxidize carbon monoxide generated
in the first combustion zone so the total potential heating
value of the char oxidized in the first combustion zone is
obtained. In addition, oxygen above the stoichiometric
amount can be added to react with the carbon in the char
to heat the char to the temperature required to form
the particulate source of heat for introduction into the
pyrolysis zone. The total oxygen feed to the two oxidation
stages is at all times sufficient to raise the solids to
the temperature required for feed to the pyrolysis zone.
Typically the particulate source of heat has a temperature
from about 100 to 500 F, (55 - 280 C.) highcr than the
pyrolysis zone temperature.
Introducing oxygcn to oxidize carbon in the solid
residue in two combustion zones serves to obtain maximum
heating value from solid residue by oxidation. When the~
solid residue is oxidized where there is less than
stoichiometric amounts of oxygen and/or the residence
time is long, t;hen some of the carbon dioxide in the
reaction product gases tends to react with carbon in the
solid residue to produce carbon monoxide. This is
undesirable because more valuable carbon-cont;aining solids
residue has to be burned to achieve desired temperatures
than if carbon dioxide were the only product;. Net carbor
mono~ide formed is minimiæed and the carborl dioxide to
carbon monoxide ratio maximized to maximize tl-~e alllount of
heat generated per Ullit ~ree carbon combusted by using two
ca~bust;ion zones.
The formecl particulate source of hea-t and the gaseous
- 27 -
l~i34~4
;~ . ,
combustion products of the solids, as well as nonreactive
components of the source of oxygen such as nitrogen, pass
from the second combustion chamber to a second cyclone
separator 84. In the separat3r the particulate so~rce of
heat is separated from the combustion gases for feed to
the pyrolysis reaction zone. The gases 100 are discharged
through the top o~ the cyclone 84. Because most of the
c
carbon monoxide formed in the riser and conduit is oxidized
to carbon dioxide in the oxidation zone, the combustion gases
~0 can be directly released to the atmosphere. How-~ver, if
... . .
there are appreciable amounts of carbon monoxide or other `-
pollutants in the combustion gas stream 100 from the second
cyclone separator 84, these gases can be treated as by
chemical scrubbing before release to tha atmosphere.
,~
ÇJ ~ ~lthough the drawings show the second combustion zone
and the second cyclone separation zone oonstituted by oeparate
apparatus, it is possible to form the particulate source of
heat from the preheated solids and separate the particulate
source of heat from the gaseous combustion products
~` -20 simultaneously in a single cyclone oxidation-separation zone.
This modification has significant advantages. ~nong
these advantages are reduced capital and operating costs
for the process because a separator and a combustion zone
are replaced with a single cyclone separator. In addition,
production of car~on monoxide is minimized because short
reac~ion times, which favour production of carbon dioxide,
. , .
are obtained ~y using a cyclone vessel ~or oxidizing the
carbon-containing solid residue~ lt is preferred that the
residence times of solids in a cyclone oxidation-separatioll
zone be less than about 5 seconds, and more pre-r`erably~ from
- 28 -
4~ -
about 0.1 to about 3 seconds. This short residence time
favours production of carbon dioxide compared to carbon
monoxide. -
Another advantage of using a cyclone oxidation-separation
zone is that carbon-containing solid residue fines, which
are less valuable than larger particles are burned
preferentially because of the more efficient separation of
the larger particles from the fines in the cyclone.
The formed particulate source of heat separated from
the gases in the second cyclone separation zone is passed
through the standpipe 86 to the fluidized chamber 32
surrounding the inlet to the pyrolysis reactor. The
standpipe is fluidized by an aeration gas nondeleteriously
reactive with respect to pyrolysis products. The aeration gas
.
is introduced through the inlets 88 along the length of the
standpipe.
Although the invention has- been described in terms of
certain preferred embodiments other embodiments will be apparent
to those skilled in the art. For example, steam can be injected
along with the carbon-containing solid residue to the fluidizing
chamber 32 to react with the hot particulate source of heat
to form hydrogen gas by water-gas shift reactions. The
hydrogen so produced can hydrogenate the volatilized
hydrocarbons resulting from the pyrolysis of the carbonaceous
material to upgrade their value. In addition, one or more
cyclones in series or parallel as required can be used to
replace the cyclone separators 22, 84. The advanta~e of
using more than one cyclone in series is that a fines
frac*ion of the carbon containing solid residue and a fine~
fraction of the particulate source of heat can be removed
~ 29
. . ,
from the bulk of the particles so that the amount of
solids carried over with the vapor mixture to a product
recovery operation is minimized.
- 30 -
