Note: Descriptions are shown in the official language in which they were submitted.
FUEL COMBUSTOR
BACRGROU~D OF THE INVEN ION
,
This invention relates generally to fuel com~
-~ bustor.s, and, more particularly~ to a slagging combustor
5 in which the fuel is pulverized coal. In the combustion
and gasification of coal, non-combustible ash and mineral
components cannot be allowed to accumulate within the
combustion chamber, or serious operatîonal problems will be
experienced. In a slagging combustor, the temperature in
10 the chamber is maintained high enough to allow the slag to
be removed in liquid form by the action of shear ~orces
and/or gravitational forces acting on the slag. This
slagging capability will also have benefits related to
operation of downstream equipment interacting with the
15 product flowstream.
A slagging combustor m~y have different re-
quirements, such as overall ~toichiometry, imposed on
--2--
it by the characteristics of a downstream process utilizing
the products of combustion. However/ regardless of these
different requirements an ideal slagging combustor should
have good slag recovery characteristi~s and should operate
5 at a relatively low temperature, to minimi~e heat losses and
maximize efficiency.
The degree of combustion of the coal in a slagqing
combustor will depend in part on the intended application of
the gaseous products of combustionO For exam~le, if the
10 combustor is to be employed to produce gas for use as a fuel
in a conventional power generation plant, or in chemical
processes~ the gases exiting from the combustion chamber
should still be relatively rich in combustibles. Accord-
ingly, if a coal combustor is to be used as such a gas
15 generator, the combustion process should take place in a
relatively fuel-rich environment. In terms of stoichio~
metry, a stoichiometric ratio as low as 0.3 might be
desirable for subsequent combustion in a boiler or use as
feed stock in a chemical process. If the gas were to be
20 immediately employed in a combustion or heat exchange
process, it might be desirable to provide a gas at a higher
temperature, but with a lower equivalent heat value in the
combustibles in the gas. This could be done by more
completely combusting the coal in the slagginy combustor,
25 i.e. at a higher stoichiometric ratioO
By way of further example, the desired stoi-
chiometry of a slag~ing combustor would be substantially
different if the output gases were to be used in a mag-
netohydrodynamic (MHD) electric power generator. An
30 MHD generator utilizes a high-temperature, high-velocity
--3~
plasma which is passed throuyh a magnetic field to generate
electricity directly, without the use of rotating machinery.
For such an application, the gaseous products from the
slagging combustion stage may be lower in combustibles
5 content and higher in temperature and heat contentO The
products of combustion may then be subject to further
combustion after le~ving the slagging combustor. Addi-
tional oxidi~er r and sometimes additional fuel, may be added
to the exiting g~ses for this purpose~ Regardless of the
10 end use to which the products of combustion are put, and
the different requirements thereby placed on the com-
bustor, the slagging combustor should still ideally provide
good slag recovery and relati~ely low operating tempera-
tures~
In any appl ication of a coal ~ombustor t the
desired stoichiometry of the combustion process will
depend on the requirements of the downstream application.
Acceptable combustor operation and combustion product
properties will also be dependent on the temperature and
20 composition of the oxidizer gas, and the type and size of
the coal particles. Selection of the appropriate para-
meters, to satisfy the requirements of the downstream
application, typically involves a number of practical
design trade-offs. For example, preheating the oxidi-
25 zer gas to a higher temperature and thereby permittingreactions at a lower stoichiometric ratio might still
meet the re~uirements of the downstream application,
but would obviously require either the consumption of more
energy in the preheating stage or the addition of a heat
30 exchanger. The first of these alternatives may or may not
comport with the overall energy requirements o~ the appli-
~ L~
,~ .
cation, and the second may not even be feasible.
Furthermore, appropriate choice of the s~oi-
chiometric ratio in a slagging combustor is of critical
importance to the rate of slag recovery. If the ratio is
5 too low, temperatures will also tend to be low, and the slag
may not liquify sufficiently to ~cilitate recovery.
Conversely, if the ratio is too high, the :~mperature may be
so high that a significant proportion of the slag is lost by
vaporization. In theory at least, the effective slagging
10 range has been thought to lie above 0.4 and up to 1.0 for
the combustor as a whole. However, the stoichiometry
desired to meet the requirements of the downstream appli-
cation may not fall within this theoretical slagging range.
Por example, if the combustor is to act as a gas yenerator,
15 a stoichiometric ratio as low as 0.3 might be preferred.
In any event, it will be appreciated that~a
coal combustor of this general type should ideally be
capable of matching the overall combustor stoichiometry, and
other characteristics of the slagging combustor, with the
20 require~ents of the downstream application of the com-
bustor. Furthermore, the slagging combustor should provide
a high rate of slag recovery, a relatively low heat loss,
and therefore a relatively high thermal efficiency. In
addition, there should be complete fuel utilization, i.e.,
25 no uncombined carbon should leave the combustor. In prior
art combustors, it has not been possible to satisfy all of
these objectives simultaneously. ~or example, good slag
recovery, in conv.entional combustors, is not ~onsistent with
a relatively low temperature and low stoichiometric ratio.
--5--
~ .S. Patent No. 4~217,132 to ~urge et al proposes
one solution to these problems by combining an axial and a
tangential flow of oxidizing gas, so that the combustion of
the fuel particles is essentially complete before the
5 particles impinge on the walls of the combustion chamber.
Although this technique is satisfactory in many respects, it
fails to address the particular problem~ outlined above. In
at least one respect, the Burge et al patent is typical of
prior art coal combustion techniques in that the oxidizer
10 gas flows in a continuous pattern in which there is an axial
velocity component directed from the head end to the exit
end. No combustors operating on this principle combine good
slag recovery, low heat loss and complete carbon burnout
under all operating conditions of interest.
There is, therefore, a significant need for
a coal combustor which can provide high thermodynamic
efficiency and acceptably high rates of slag removal, and be
adaptable to match the thermodynamic needs of a downstream
process or application. The present invention s~tisfies
20 this need.
SUMMARY O~ THE INVENTION
The present invention resides in a slagging coal
combustor, having a head end and an exit end, in which
oxidizer is introduced in such a manner that at least a
25 portion of it flows away from the exit end and toward the
head end, coal being introduced into the oxidizer flowing
toward the head end, to provide an initial phase of combus-
tion in the head end~ Combustion in this first phase can
take place at a stGichiometric ratio much less than that of
the combustor as a whole~
Although conceived for the purpose of solving
a problem experienced in coal combustors, the invention
has application as well to combustors of other fuels. The
5 essential elements of the invention in its broadest sense
are means for introducing oxidizer in such a manner that a
portion of it flows toward the head end, and means for
injecting fuel into this oxidizer portion to provide the
first phase of combustion in thle head end.
Basically, and in general te~ns, the invention in
its form as a pulverized coal combustor comprises a combus-
tion chamher having a head end and an exit end, means for
injecting pulverized coal into the head end, means for
injecting oxidizer gas peripherally into the chamber, means
15 for removing non-combustible slag from the chamber, and
means located at the exit end to provide an exit for the
essentially gaseous products of combustion. Most impor-
tantly, the means for injecting oxidizer gas and pulverized
coal are so configured that at least a portion of the
20 oxidizer gas stream flows toward the head end of the chamber
and is there reacted with the coal fuel in the first phase
of combustion. In one embodiment of the invention, gases
from the first phase of combustion are further combusted
with the remaining portion of the oxidizer gas, which flows
25 toward the exit end of the chamber. In this embodiment, the
stoichiometric ratio in the first phase of combustion in the
head end, which is approximately one half of the overall
ratio for the combustor, may; for example, be as low as
0.3 for some ~esigns. Contrary to generally accepted
30 practice with respect to effective slag removal, extreme-
_7~
ly good slag removal characteristics can be obtained inthis low stoichiometric range.
When used for supplying high-temperature gases to
an MH~ generator, the combustor of the invention operates at
5 an overall stoichoimetric ratio selected to provide the best
combination of slag recovery characteristics in the head end
and exit gas conditions matching the requirements of the M~D
generator. In a presently preferred embodiment, an overall
ratio of approximately 0.6 i used, with a ratio of ap-
10 proximately 0.3 in the head endO
The oxidizer gas, when introduced tangentiallyinto the combustion chamber, splits into two streams. One
stream has an axial velocity comp~nent directed toward the
exit encl of the chamber while the other portion has an axial
15 velocity component directed toward the head end J into which
the f~el is injectedO In one preerred embodiment of t~he
inventi~on, the tw~ streams are approximately e~ual in
volumetric flow rates. Because the fuel is initially
combusted with a relatively low volume of oxidizer, first-
20 phase combustion at the head end of the chamber takes placeat a relatively low stoichiometric ratio. Thére is a
correspondingly low reaction temperature and a relatively
high efficiency, because of the reduced heat loss a~
the lower temperature. Howeverr highly effective slag
z5 removal is obtained in these conditions. In short, the
slagging stage is more efficient thermodynamically, and
provides excellent slag recovery. Unburned gases from the
first combustion phase then react with the remaining or
exit-end stream of the oxidizer gas, and this second phase
30 of combustion takes place at a higher stoichiometric
--8
ratio. For example, if the downstream application of the
combustor is an MHD generatorl the overall ratio can be
approximately 0.6 to 0.9, with a corresponding head-end
ratio of 0.3 to 0.45. Because o~ a relatively high tem-
5 perature in the exit end, it may be ~ade relatively shorterin length than is possible in conventional combustor of
the same type. This reduces thle heat loss from the chamber
and improves the overall thermodynamic efficiency of the
combustor.
If the combustor is to be used as a gas genera-
tor, it may be operated at a relatively low overall stoi-
chiometric ratio by diverting all of the oxidizer gas toward
the head end of the chamber, and regulating the flow rate of
the oxidizer to provide the desired ratio~ In this case,
15 effective sla~ removal is still provided in the head end of
the chamber, but since no oxidizer is allowed to fl~w
directly toward the exit end, there is no second phase of
combustion to provide a higher overall stoichiometric
ratio. Consequently, the overall ratio for the entire
29 combustor in this embodiment is the same as the localized
ratio for the head-end combustion phase.
Coal injection into the first-phase combus-
tion zone can be effected by a pintle no7zle disposed
axially in the head end and directing fuel flow into that
25 portion of the oxidizer gas flowing toward the head end.
Alternatively, fuel can be injected through fuel inlets
disposed peripherally around the chamber, to direct the
flow into the head~end portiQn of the oxidizer gas flow.
Both horizontal and vertical config`urations
- 9 -
of the chamber are contempl~ted. In the horizontal con-
figuration, the means for removing slag from the chamber
includes a slag port disposed at the bottom portion of the
cylindrical wall of the chamber. In the vertical config-
5 uration, the head end qf the ch ~ber is the lowermost endand the exit is the uppermost. The slag port is located at
the head-end.
In terms of a novel method, the invention in
its broadest terms comprises the steps of injecting oxidizer
10 gas peripherally into a chamber having a head end and an
exit end, in such a manne~ that at least a portion of the
flow is directed towards the head end, injecting fuel, such
as pulverized coal, into the head end in such a manner that
combustion takes place initially at a relatively low stoi-
15 chiometric ratio and low temperature, regardless of the enduse of ~he gaseous products of combustion and regardl~ss of
the overall stoichiometry of the com~ustor, removing any
non-combustible slag from the chamber, and allowing the
essentially gaseous products of combustion to exit the
20 chamber. More specifically, the steps of injecting oxidizer
gas and injecting pulverized coal include injecting the
oxidizer gas ;tangentially into the chamber at a point
between the head end and the exit end of the chamber such
that the oxidizer gas flow splits into two approximately
25 equal portions having opposite axial components, and in-
jecting the pulverized coal into the oxidizer gas portion
flowing toward the head end, wherein a first phase of
combustion occurs in the head end at a stoichiometric ratio
of approximately one hal of the overall stoichiometric
30 ratio for the combustor. In accordance with another em
bodiment of the invention utilized as a gas generator,
--10-- ,,
substantially all of the oxidizer yas flow is directed
toward the head.end in such a manner that the head-end
stoichiometric ratio remains substantially the same as in
the embodiment not ~sed as a gas generator.
It will be appreciate,d from the foregoing that the
present invention represents a significant advance in the
field o~ coal combustion and gasification. In particular, a
novel coal combustor achieves qood slag removal rates while
attainillg high thermodynamic efficiency, low heat loss and
10 complete burning of carbon. Moreover, the combustor of the
invention allows for convenient matching of its thermo~
dynamic characteristics with those of a desired downstream
process. Other aspects and advantages of the present
invention will become apparent from the following more
15 detailed description, taken in conjunction with the ac
companying drawings~
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a simplified perspective view of a
coal combustor embodying the present invention, including
20 the slagginy combustor and slag removal apparatus, and also
showing an exit combustion stage which is not part of the
invention;
, FIG. 2 is a diagr~mmatic view o~ the slagging
combustor;
FI~. 3 is a fragmentary sectional view of a
pintle no~zle used to inject coal and, for MHD and other
selected applications, an additive material ~ into the
combustor;
FIGo 4 is a diagrammatic view ~howing typical
flow patterns of fuel~ oxidizer gas and combu~tion products
5 within the slagging combustor;
FIG. 5 is a diagrammatic elevational view
showins the configuration of a first embodiment of the
invention, having a tangential oxidizer inlet and a volute
exit port;
FIG. 5a is an end view of the embodiment shown in
~IGo 59 taken in the direction of the arrow Sa in FIG.
5;
FIG~ 6 is a dia~rammatic elevational view
showing a second embodiment of the inven~ion, having~ a
15 tangential oxidizer inlet, a symmetric exit port and a
shortened exit end portion;
FIG. 6a is an end view of the embodiment shown
in FIG. 6, ta~en in the direction of the arrow 6a in
FIG. 6;
FIG. 7 is a diagrammatic elevational view of
a third embodiment of the invention similar to the second
embodiment shown in FIG. 6 but having the slag tap located
in the head end rather than the exit end;
E'IG. 7a is an end view of the embodiment shown in
25 FIG. 7, taken in the direction of the arrow 7a in FIG.7;
-12-
FIG. 8 is a diagrammatic elevational view
showing a fourth embodiment of the invention having a
recessed volute oxidizer inlet, a symmetric exit port and a
head-end slag tap;
S FIGo 8a is an end view of the embodiment shown in
FIG~ 8, taken in the direction of the arrow 8a in FIG.
8;
FIG. 9 is a diagrammatic elevational view of
a fifth embodiment of the invention having two slagging
10 combustors, ea~h with a recessed volute oxidizer inlet, and
a head end with a fuel injector ~nd a slag tap, the two
combustors being matched to a common, centrally l~cated exit
port
FIG. 10 is diagrammatic elevational view showing
15 a sixth embodiment of the invention with a vertically
oriented combustion chamber, a recessed volute oxidizer
inlet t a symmetric exit port, peripheral coal injectors, and
a head-end slag tap;
FIG. lOa is a plan view of the embodiment shown
20 in FIG. 10;
.
FIG. lOb is a sectional view of the embodi-
ment shown in FIG. 10, taken substantially along line
lOb~lOb in FIG. 10;
FIG. 11 is a diag~ammatic elevational view
25 of a seventh embodiment of the invention having a vertically
orien~ed combustion chamber similar to that shown in FIG.
-13-
10, but including an inlet flow diverter to divert all of
the inle~ oxidizer flow ~o the head end of the chamber;
and
FIG. lla is a secti.onal view of the embodiment
5 shown in FIG. 11, taken substantially alc)ng line lla-lla
in FIG. llo
DESCRIPTION OF THE PREFERRED EM~ODIM~NTS
As shown in the drawing~ for purposes of illus--
tration~ the present invention is principally concerned with
10 a pulverized coal combustor, and more particularly with a
slagging coal combustor. In slagging coal ~ombustors, th~
non-combustible ash and mineral componentæ of the coal are
removed in li~uid ~orm, so that these constituents do not
remain in the gases produced by the combustor.
Designers of coal ~ombustors in the past have
striven for efficient slag removal, low heat loss, high
thermodynamic efficiency, complete burning of carbon, and
appropriate matching of the thermodynamic characteristics of
the combustor with the requirements of downstream processes
20 utilizing the products of combustionO Ideally, for example,
a coal combustor should be adaptable to provide gas to an
MHD generator, or to provide fuel gas for subsequent burning
in boilers or in other chemical processes, and still should
maintain a high rate of slag recovery and a high thermal
25 efficiency. Prior coal combustors have traditionally
employed an oxidizer flow patt~rn having an axial component
directed towards the exit end, and have not been able to
achieve the desired combination of ideal characteristics.
Lil~`J~
In accordance with the present invention, a
coal combustor is provided with f~el and oxidizer injection
means which cooperate in such a manner th~t combustion takes
place initially in the head end of the combustor at a
5 relatively low stoichiometric ratio, regardless of the end
use of the gaseous products of combus'cion and regardless of
the overall stoichiometry of the combustor. Extremely good
slag recovery is provided at. the relatively low local
stoichiometric ratio in the head end, and heat losses are
lO minimized, with a corresponding maximization of efficiency.
A second combustion phase may optionally be provided to
yield a higher overall stoichiometric ratio, for use in
conjunction with an MHD generator, for example. If the
second combustion phase is omitted, a relatively low overall
15 stoichiometric ratio is then provided, such as when the
combustor is operating as a synthesis gas 92nerator.
As shown in FIG. l~ the apparatus of the invention
includes a slagging coal combustor, indicated generally by
reference numeral lO, and having a tangential oxidizer inlet
20 12 and an axial coal inlet 14~ The combustor lO comprises a
~enerally cylindrical reaction chamber 16, shown as being
disposed with its longitudinal axis horizontal~ the cylinder
having an exit end 18 through which the products of combus-
tion leave the chamber, and a head end 20 into which the
25 pulveri~ed coal fuel is introduced~ As shown in this
illustrative configuration, the exit end 18 includes an exit
assembly 22 usually referred to as the symmetrical type. As
will be apppreciated from FIGS~ 6a and 7a, a symmetrical
exit is one in which the exit path followed by the products
30 of combustion is symmetrical with respect to the axis of the
combustor, i.e. the exit path extends from the center of the
.D~
--15--
exit assemhly, rather than being tangential or vol~lte. The
illustrative embodiment of FIG. 1 also include~ a further
exit combustion stage 24 into which further oxidizer and/or
fuel may be introduced, through the inlet 26. This exit
5 stage 24 is illustrative of a typical environment for the
combustor, but is not essential to the present invention,
since the slagging combustor will operate equally well
without the exit stage.
As best shown in FIG 2, unburned minerals or ash
10 are removed as liquid slag from the chamber 16, through
a slag port located low on the cylindrical wall of the
chamber close to the exit end 18. The port is connected to
a slag removal assembly 28, the details of which are not
critical to the present invention. The entire chamber
15 16 and the oxidizer inlet 12 are cooled by a fluid,,
such as water, passed through coolant inlets 30 on top
of the cylinder and emerging from coolant exits at the
bottom, some of which are shown at 32. Cooling of the
combustion chamber 16 produces a solidified layer of slag on
20 the chamber walls. The solid layer of slas protects the
chamber walls from erosion by liquid slag and by burning
fuel particles, and also provides a relatively low cond~c-
tivity insulating layer to reduce heat losses from the
chamber. To provide better adhesion of the solidified slag
25 layer to the chamber walls, the walls have a large number of
upstanding pins affixed to them, as shown at 34 in FIG. S.
In one embodiment of the invention the pins 34 are approxi-
mately 1/8 inch (3.2 mm) in diameter and 1/4 inch (6.4 mm)
long, welded to the chamber walls at approximately 3/4 inch
30 (19.2 mm) spacing. The exit combustion stage 24 is used
only in the event that it is required for matching the
~16-
thermodynamic characteristios of the combustor with some
downstream process, such a.s an MHD generator~
FIGn 2 shows in diagrammatic form the basic
configuration of the slagging combustor. Oxidizer gas
5 is introduced tangentially into the combustion chamber 16
through a rectangular port located between the head end 20
and the exit end 18. Fuel from the coal inlet 14 is dis-
persed along a generally conical spray having a substantial
radial velocity component. In a presen~ly preferred eM-
10 bodiment of the invention, a half ~ngle of approximately60 with respect to the central axis of the cylinder 16/
is used. As best shown in FIG. 4, air from the oxidizer
inlet 1~ diverges into two separate paths, with respect to
the axial componen~ of flow of the oxidizer. That portion
15 of the oxidizer flowing back towards the head end 20 will
encounter fuel from the coal inlet 14, and combustion will
take place in the head end at a stoichoimetric ratio of
approximately half the overall ratio for the entire com-
bustor. Fuel particles leaving the nozzle 14 will be
20 substantially heated as they traverse the head end to
meet the oxidi~er gas near the chamber walls. Thusr if the
overall stoichiometric ratio is 0~58, as in an M~D generator
application, the stoichiometric ratio in the first combus-
tion phase in the head end will be approximately 0.29~ For
25 this MHD application, additional oxidizer is added in the
inlet to the MHD generator ~not shown).
Gases from the first phase of combustion will then
move into a central region of the head end, near the axis,
and will move generally along and near the axis and toward
30 the exit end 18, where a further reaction will occur with
-17-
the remaining portion of the oxidizer gas flowing towards
the exit end. Combustion in this second phase of the
combustor increases the overall stoichiometric ratio, such
that the overal.l ratio is at the desired level. As shown in
5 FIG. 9~ there is also a small reverse core flow back
through the exit port~ It must be kept in snind, when
referring to ~IG. 4~ that it represents only the axial
and raclial components of gas f10WO Superimposed on this
flow pattern is the rotational flow induced by the tangen-
10 tial introduction of the oxidizer gas. This rotational orcyclonic flow is important in that it provides a relatively
long path over which burning of the fuel particles can take
place and slag can be formed. The swirling action enhances
fuel and oxidi2er mixing, and directs entrained material
15 outward to the wall surfaces.
An annular baffle 40 prevents, for all practical
purposes, any flow of slag beyond the exit end 18 of the
slagginq combustor. Liquified slag, principally from the
head enc3 20, flows towards the slag tap 28 under the effects
20 of gravitational force and shear force between the slag and
the adjacent moving combustion gases. ~or the MHD and other
selected applications of the combustor, an additive material
may be injected axially with the coal fuel, as indicated at
41 in FI~. 2, to increase the electrical conductivity of the
25 resultant exiting gases or to otherwise mod.ify the exhaust
gas species~ Flow of the additive material has no signifi-
cance in the present invention, however, except to the
extent that it may be injected with sufficient velocity to
avoid being captured in outfl~ing slag and to. react with
-lfl-
the hot exhaust gases.
~IG. 3 shows in sectional form a typical pintle
nozzle structure. The pintle 14 is cylindrical in shape and
has a number of annular elements defining an axial passage
5 42 for the additive material, two concentric annular pass-
ages 43 and 44 joined in fluid communication at the end of
the pintle, as shown at 45, to provide a cooling fluid path,
and a surrounding annular fuel passage.46. The annular
fuel passage 46 terminates in conical exit port 48 extending
10 in a continuous circle around the periphery of the pintle.
Coal is ejected in a conical sheet from the e~it port 48.
An additional annular cooling passage 49 is provided between
the fuel passage 46 and the outside surface of the pintle.
As shown in ~IGSo 5-11, the invention may be used
15 in a variety of embodiments, depending on the needs of the
associated downstream application~ First, in FIG. Sr the~e
is shown a basic configuration ~tilizing the principles of
the invention. Included are the coal .pintle nozzle for
injection of coal at 14, a tangential inlet 1~, slag tap 28,
20 and an exit shown at 22a. In this embodiment, and all
others to be described, the coal could be alternatively
injected by means of peripheral fuel inlet ports, such as
those shown at 60 in FI~S. 10 and 11. The only difference
between the embodiment shown in FIG. 5 and that discussed
25 with respect to ~IGS. 1-4 is that the exit 22a is a volute
exit shown in more detail in FIG. 5a. In a volute exit,
the radius of the exit assembly increases from a minimum
value to a maximum value, and, an exit duct merges tangen-
tially with the assembly at its point of maximum radius.
30 This is to be distinquished fro~ the symmetrical exit (FIG.
--19--
6a), wherein an exit duct merges with a cylindrical exit
assembly symmetrically, i.e. r along a radiusO In both types
of exit:~ the object is to provide a unifonm, non swirling
flow in the exit duct~
The embodiment shown in ~IGS. 6 amd 6a differx
from tilat of FIG. 5 in two respects. Pirst, a simpler
sylTmetrical exit ~2b is shown~. Secondly, and more impor-
tantlyr the exit 22b is locatled much closer to the inlet,
i.e., the overall length of the slagging stage is reduced.
10 This reduction is made possible because the second phase of
combustion, in th~e exit end 18 of the chamber 16l takes a
relatively short time t since it involves only gaseous
components at a high temperature, the solid fuel ha~sing been
practically completely combusted in the head end. The more
15 compac~ design of the FIG. 6 embodiment results in a further
reduced heat loss and increased efficiency, while still
maintaining good slag recovery.
The embodiment shown in ~IGS. 7 and 7a is similar
to that shown in FIG. 6; except that the exit end combus-
20 tion phase takes place in an even smaller volume, since theoxidizer inlet, referred to as 12c, is moved much closer to
the exit end 18 of the chamber 16, as a consequence of
locating the slag tap 28c at the head end. The coal in-
jector has been accordingly lengthened and effectively moved
25 toward the exit end with the inlet 12c. The head end volume
is correspondingly increased by relocation of the slag tap9
and, as in all of the embodiments shown, most of the slag
removal function is taking place in the first phase of
combustion, at the head end. In this manner, heat loss
30 through the slag tap 28c is reduced, because of the lower
-20-
temperature in the head end region~ Placement of the slag
tap 28c at the head end 20 also results in a higher slag
removal efficiency, since there should be reduced slag
volatilization because of the lower temperature of the head
5 end. Moreover, the slag deposited on the head-end walls
should be more easily convectecl ~oward the slag tap by the
axial
component of the inlet flow entering the head end 20.
The configuration shown in ~IGS. 8 and 8a repre-
10 sents a further refinement of the embodiment shown in FIG~
7. In particular, the tangential oxidizer ga~ inlet has
been replaced by a volute inlet 12d, usually referred to as
the recessed volute type. The same volume of oxidizer gas
can he introduced through the volute inlet as through
15 the tangential inlet, but with an effective reduction
in axial length of the inlet, since the volute inlet duct
can be largerr measured in a radial direction, than~a
tangential inlet to a cylinder of the same size. This
shorter axial length can reduce heat losses from the com-
20 bustor, and thereb~ lncrease efficiency. More importantly,however, the recessed volute 12d, shown in more detail in
~IG. 8a t introduces the oxidizer gas in a more symmetrical
fashion about the walls of the chamber 16. The oxidizer
circulating in the volute spills over the volute edges in a
25 fairly uniform way around the volute circumerence, rather
than spilling out into opposite axial directions in a
limited reyion close to the tangential inlet opening.
Stated another way, the volute inlet introduces oxidi2er
flow uniformly about the periphery of the chamber, rather
30 than at an ansularly limited region.
-21-
In the configuration shown in FIG. 9, there
is a double-ended slagging combustor, in which two head
ends 20 and 20 are disposed one on each side of a ~entral
exit region 50, there being two inlets 12e of the recessed
5 volute type shown in the FIG. 8 configuration. There are
also two slag taps 28e and two coal injectors 14 and 14 ~
The principal advantage of the configuration shown in FIG. 9
is further reduced heat loss, since the exit ends of the
FIG~ 8 configurations are eliminated. In the single-ended
10 configurtion of ~IG. 8I there is substantial heat loss from
the exit end 22a,~ but in the FIG. 9 configuration such
losses ~re minimi~ed by ~oining the exit ends at the central
region 507
FIG. 10 shows a vertically oriented combustion
15 chamber 16 having a recessed volute inlet 12f, a symmetrical
outlet 22f, coal lnjectors 60 disposed peripherally about
` the chamber 16 at a location slightly towards the head end
20f from the inlet 12f, and a slag tap 28f located in an
axial orientation in the head end. The principle of opera-
20 tion is the same as that of the basic configurations alreadydescribed. Coal i,s injected into the portion of the inlet
flow proceeding towards the head end 20f of the chamber 16,
and a first phase of combustion occurs at the head end at a
relatively low stoichiometric ratio. A'second stage of
25 combustion can then occur in the exit end of the combustor
before the products of combustion exit through the symme-
trical exit 22f.
Any of the aforede$cribed embodiments may be
modified for operation as gas generators by including
30 means for diverting the entire oxidizer gas flow towards the
-22-
head end 20 of the combustorO For example, as shown in
~IGS. 11 and lla, the vertically oriented embodiment
of FIG~ 10 is shown as having a head end 20g and a cylin-
drical baEfle 62 disposed in the oxidizer inlet 12g to act
5 as a flow diverter, ensuring that the oxidizer flow has an
axial component directed only toward the head end, ~s shown
by the arrows 640 The inlet flow is, of course, adjusted to
provide a desired stoichiometric ratio for generating
combustible gas. By this means, the second phase of com-
10 bustion described above as occurring in the exit end of thecombustor, is elirninated, and the overall stoichiometric
ratio of the combustor is reduced to the same relatively low
value that: obtains in the head end. Exit gases are thereby
provided with the thermodynamic properties characteristic of
15 suitable fuel gas~ It will be understood that any of the
other configurations could easily be modified to include the
flow diverter 62 shown in FIG. 11 for gas generator opera-
tion.
It will be appreciated from the foregoing that
20 the present invent;ion represents a significant advance in
the field of coal combustors. In particular, the invention
provides a slagging combustor operating with desirable slag
removal characteristics at a relatively low stoichiometric
ratio, and therefore providing for reduced heat losses and
25 increased efficiency. Furthermore, the combustor is
easily adaptable to match the requirements of various
downstream processes, such as MHD generators or processes
requiring synthetic fuel gas. It will also be appre-
ciated that, although speeific embodiments of the invention
30 have been described in detail for purposes of illustration,
various modifications may be made without departing from the
~ 2 3 r
spirit and ~cope of the invention. Accordingly, the inven
tion ic; not to be limited except a~ by the ~pp~nded claims.
