Note: Descriptions are shown in the official language in which they were submitted.
31-0155/16085
SLAGGING COMBUSTION SYSTE~
Background of the InYention
Conventional coal-burning boiler plants and industrial
furnaces combust the coal in a reaction zone directly within the
furnace, wherein combustion temperatures ~re high enough to keep
~lag above its fusion temperature. They are normally operated at
an overall stoichiometry greater than 1, which results in
generation of substantial quantities of the oxides of nitrogen
and the oxide~ of sulfur, as well as relatively high emission of
particulates into the atmosphere. Such furnaces bave relatively
low energy release per unit-volume and count on the use of
refractories to protect against slag erosion. They commonly
operate at ~elatively very low power densities, requiring
large-volume ~fire bo~es~ for burning out the carbon content of
the fuel, collecting the residual slag and extracting energy from
the flame.
: In recent years, oil prices have increased by about a factor
of ten~ Many electric-utility boiler plants and industrial
furnaces are caught in a cost s~ueeze. Trona kilns, for example,
require vast quantities of thermal energy; operators of such
industrial processes have lar~e capital investments in facilities
that are not economically viable~at current oil and gas prices~
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Conversion of these boilers and furnaces, to burn coal rather
than oil or gas, would provide very substantial energy-cost
savinys and this can often avoid plant closing, abandonment of
capital investment and loss of jobs in the community. But,
attempting to burn coal in multi-megawatt boilers originally
designed and constructed for oil or gas presen~s several
difficulties that have been thought to be insurmountable: Slag
and fly-ash from conventional coal burning will coat the water
tubes, sharply reducing efficiency; Emission of sulfur oxides
(herein SOx) and/or nitrogeneou~ oxides (NOx) is not merely
objectionable socially but, under current clean-air regulations,
often prohibited in the urban and semi-urban locales where
electricity-generating boiler plants ~re commonly located. Most
often, the space available for installation of coal handling and
combustion equipment is severely limited. And, boilers
originally designed for oil and gas usually have no provision for
slag collection and disposal.
Thus, our society has developed a siynificant social and economic
need for a process and apparatus for conversion (retrofit) of
pre-existing boilers and furnaces to adapt them to burn coal.
Any such system, to be economically, technically and
environmentally acceptable should meet the following
requirements:
!o~ ~,a~E~ 3ity: - about 1.0 million Btuthour per cubic
foot of volume in the primary combustion chamber.
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~o~ ~o~: - Consistently less than 450 ppmv and, preferably,
less than 250 ppmv in the gases emitted into the ~tmosphere.
Lo~ SO~: - Substantially lower than heretofore achievable
with conventional combustors and~ preferably, reduction of
the sulfur-compounds content of the stack gases by about 50
to 90 percent.
Ra~o~able of ~o~o~bustibles: - Capture, and removal from
the gaseous products of combustion, of 70% to 90% of the
noncombustible-minerals content of the fuel before the
gaseous products are conducted to the end-use furnace or
boiler, depending on the requirements of the specific end
u~e.
~rLoo C e~vov~r: - Conversion of substantially all carbon
to oxides of carbon before the gaseous products pas5 to the
boiler or other heat-utilization equipment.
D~rabilit~: - Protection of the walls o the combustor such
that deleterious cvrrosion and/or eroslon of the walls is
kept within co~mercially-acceptable limits.
CCL~ 9l~8~- Delivery to the end-use equipment of a
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gaseous-products stream having about 85 to 90 percent of the
chemical potential energy of the carbonaceous fuel.
Preferably ~his energy ls delivered partly as sensible heat
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and partly in the form of carbon monoxide and hydrogen
contained in the gaseous-products and readily cornbust-
ible, to completion, in the end-use equipment.
The present invention provides a system meeting the
foregoing requirements.
U.S. Patent 4,217,132 to Burge et al describes an
apparatus for combusting carbonaceous fuels tha~ contain
noncombustible mineral constituents, separating such
constituents as liquid slag and conveying a stream of
hot combustion products to a thermal energy utiliæation
equipment, such as a boiler. In the Burge et al apparatus
solid carbonaceous fuel ~e.g. powdered coal) is injected
into a combustion chamber and, simultaneously, a stream of
oxidizer (e.g. preheated air) is introduced tangentially
into the chamber to produce high velocity swirling flow
conditions therein suitable for centrifugally driving most
of the liquid slag to the inside walls of the chamber. The
apparatus described in the '132 patent is a first-genera-
tion, high-power-density slagging combustor. The present
invention relates to improvements in slagging combustors,
resulting from extensive study and development including
recognition of requirements peculiar to adap~ing slagging
combustors to industrial furnaces and electric-utiIity
boilers originally designed and constructed to use oil
and/or natural gas. Our apparatus, described herein, is a
slagging combustor, belonging to the same general class as
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that disclosed by Burge et al. Our apparatus includesseveral
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improvements and is, to the best of our knowledge, the only
extant technology for simultaneously removing substantially all
sl~g, controlling NOx and Sx emissions, and avoiding carryover
of unburned carbon and other particulate, while operating at high
efficiency, having commercially-acceptable durability and being
small enough to be retrofitted into the limited space normally
available in commercial-sized industrial and utility plants.
Summary of our Invention
According to the present invention there is provided a
compact apparatus ~nd method ~or efficient combustion of
particulate carbonaceous materials at high energy output per unit
of volume while removing noncombustibles to the hi~hest levels
possible, at the same time minimizing the generation o~ nitrogen
oxides and removing a ~ajor portion of the fuel's sulfur content.
Our apparatus comprises, in combination, a precombustion
chamber having a first a~is; a primary combustion chamber having
a second a~is which is substantially normal to the first axis; a
baffle plate, at the exit end of said chamber, having a keyhole-
like aperture; a plenum for recovering slag from the gaseous
products of combustion; means to dispose of molten slag; means to
deliver produc~ gas to an end-use application; and means for
adding supplementary oxidizer to the product gas subs~antially as
it arrives at the end-use equipment.
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In a preferred embodiment, the precombustion chamber
comprises, first, a cylindrical oxidant addition chamber defined
by an end wall of the prec~mbustion chamber and a first apertured
baffle, spaced from ~he end wall. It includes ,also, means for
tangentially introducing oxidant to the first oxidant addition
chamber. A first combustion zone extends along the first axis
fro~ the baffle to a second oxidant introduction zone, which
comprises a plenum co~municating with a duct receiving the
effluent of the first combustion zone at the terminus thereof,
said duct including means for introduction of a second oxidant
stream for admixture with the effluent of the first co~bustion
~one. Nozzle means for introducing particulate fuel extends from
the end wall of the precombustion chamber, to approximately the
location of the aperture of the first apertured baffle. This
nozzle ~e~ns is adapted to inject particula~e carbonaceous
material into the first combustion zone at an angle of at least
about 45 degrees to the first axis. The second oxidant
introduction zone terminates in a duct extending to the primary
combustion ohamber and is attached thereto by a rectangular
openin~ positioned to enable introduction of oxidant and products
of combustion from the precombustion chamber tangentially and
adjacent to the walls of the primary combustion chamber. The
~xis of the precombustion chamber is positioned at an angle to
the horizontal suficient to cause substantially all of the
precombustor's products to flow into the primary combustion
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chamber.
A fuel injector for introduction of particulate carbonaceous
material extends into the primary combustion chamber from the end
wall thereof.
The primary combustion chamber provides an inner wall
surface, adapted to retain, and maintain thereon, a slag layer
resulting from combustion of the particulate carbonaceo~s
~aterial. The oxidizer inlet into the primary chamber is
positioned to divide effluent of the precombustor into two flows:
one directed towards the head end~ the other directed towards the
exit end. Preferably, the precombustion chamber includes a
damper at the rectangular opening, to control the velocity of
flow into the primary combustion chamber independently of mass-
flow rate and thereby to maintain the inflow tangential velocity
at a preselected level.
Products of combustion leave the primary chamber in a high-
velocity swirlîng flow through the keyhole~like aperture of the
apertured baffle plate. Also, liquid slag flows throuqh the
downwardly extending slot portion of the keyhole aperture. Thus,
these products of combustion pass rom the primary chamber into
an expansion chamber where the gaseous products expand and the
velocity of the swirling decreases. Larger lumps and droplets of
slag are, thereore, ~eparated from the gaseous combustion
products in this expansion chamber and flow, by gravity, ~o a
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~lag disposal subsystem. Gaseous products of combustion flowupwardly, at relatively low velocity, and are then conducted to
an end-use equipment, such as a boiler or furnace. As these
gases arrive at the interface between our apparatus and the end-
use equipment, ~uppl~mentary oxidizer is added to the gaseous
combustion products, in amounts sufficient to oxidize to
completion any as-yet unburned constituents (e.g., carbon
monoxide, ~oot and/or hydrogen) of the flow.
In operation, oxidant is introduced to the precombustor's
first mixing chamber and exits the aperture of the first
apertured baffle, swirling. The oxidant is mixed with from about
10% to 25~ of the total particulate carbonaceous material to be
fed to the system. The amount of oxidant introduced into this
mixing cha~ber is normally sufficient for stoichiometric
combustion of all the fuel fed to the precombustor. Products of
this combu~tion are diluted by a second oxidant in flow to form
an oxidant-rich effluent, e.g., from about 2 to about 5 times the
stoichiometry for the precombustor, suitable for injection into
the primary combustion chamber and use therein as the sole source
of oxidizer for combusting the primary input of carbonaceous
fuel. The balance of the particulate carbonaceous material is
fed by the fuel injector to the primary combustion chamber at an
angle of from about 45 to about 90 degrees to the axis thereof,
mixes with the oxidant-rich effluent from the precombustion
chamber, which is delivered at a temperature of from about 1200
to about 2000F. C~mbustion in this primary combustor is
substoichiome~ric with the total oxidizer fed to the primary
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combustion chamber being in the range from about 0.7 to about 0.9
of the stoichiometric amount that would be required for
combu~tion of all the combustibles in the fuel. In the primary
combustion chamber, combustion occurs substantially in flight
with conver~ion of substantially all noncombustibles to molten
slag which, by the whirling action of flow fields within the
primary combustion chamber, is centri:Eugally driven to the walls
of the pri~ary combustion chamber and collects thereon as a slag
layer whose surface is molten. In st~eady-state operation, slag
flows toward the primary chamberis appertured baffle, through the
slotted opening, to the slag-collection means. The hot oxidant
inflow from the precombustor is beneficial in deterring the
accumulation of frozen slag near the oxidant-inflow aperture.
Perhaps more importantly, it maintains a high temperature
environment, heated by radiant combustion products, throughout
the he~d-end portion of the primary chamber, thereby assurin~
prompt and stable fuel combustion closely adjacent the fuel
injection assembly and conversion of 85~ to 90~ of the carbon
before the fuel particles reach the wall of the primary
chamberO The gaseous products of combustion flow throu~h the
aperture of the baffle into the expansion chamber, wherein any
large size residue slag is separated from the gaseous product
before it is introduced to an end-use apparatus. Supplementary
oxidizer is introduced into the gaseous products at the interface
with the end-use equipment, so that final combustion of C0 and H2
produced in the substoichiometric primary combustor is
accomplished as the gaseous products enter the end-use equipment.
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In the particularly preferred embodiment of the invention,
the precombustion chamber has a length-to-diameter ratio of 3 to
l; the primary combustion chamber has a length-to-diameter ratio
of 1.5 to 2 to 1; the expansion chamber has a length-to-diameter
ratio of 1 to 1; and the primary chamber has a baffle area ratio
in the range from 2:1 to 4:1. As noted above, the total oxygen
fed to the primary chamber is, preferably, about 0.7 to about 0.8
of the amount that would be required for complete combustion, to
carbon dioxide and water, of all the carbon and hydrocarbons
contained in the fuel. Accordingly, the gaseous combustion
products leaving the primary combustion chamber contain
subs~antial amounts of carbon monoxide and hydrogen and,
therefore, are suitable for further combustion, to completion, in
an end-use equipment, e.g~, a boiler or industrial furnace. The
preferred carbonaceous feed is coal. A sulfur sorbent may be
introduced, in a direction opposite to the bulk flow of
reactants, into the primary combustion chamber, to enable capture
of sulfur-containing constituents of the carbonaceous fuel.
Brief Description of the Drawings
FIG. 1 is a perspective arrangement of tbe system in
relation to an effluent-consuming furnace.
FIG. 2 illustrates the precombustor.
FIG. 3 ;llus~ra~es the primary co~bustor, slag recovery and
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collection, combustion-products conduit and secondary burner,
FIG. 4 illustrates in more detail the interaction of
reactants and reaction products in ~he primary combustor and the
expansion chamber.
FIG. 5 illustrates the structural arrangement used to
provide thermal protection for the walls of the apparatus.
FIG. 6 shows details of tube-and-membrane construction for
the containment walls of the apparatus.
FIGS. 7 and 7A show the hot-sleeve injector assembly.
FIGS. 8 and 8A show a fuel injector assembly s~itable for
firing with slurry.
FIG. 9 shows a sectional view of a fabricated assembly at
the junction of the precombustor with the primary combustor.
Detailed Description
There is provided, in accordance with the present invention,
a system employing particular apparatus and methods for
efficiently combusting particulate carbonaceous materials and
removing solid noncombustibles to the highest levels possible, at
the same time mini~izing the generation of nitrogen oxides,
providing an eficient means to remove sulfur compounds, and
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collecting and removing 70 to 9o% of the molten slag before the
gaseous products are introduced into an associated thermal energy
utilization equipment.
The achievement of the~e improvements is brought about by
the u~e of methods and apparatu~ which prepare the particulate
carbonaceous materials and the oxidant used to combust them, for
rapid ignition and reaction in fluid dynamic flow fields. The
apparatus employed, consists of four mechanical units connected
together: a preco~bustor, a primary combustor, a slag-collection
unit and a conduit ~ith an integral secondary burner. All are
compact and produce an energy-release rate per unit-volume of
apparatus that is much larger than can be achieved in
conventional coal-burning furnace~.
By the term ~particulate carbonaceous fuel~ as used herein,
we mean carb~n-containing substances that include noncombustible
minerals and which can be provided as a fuel in a dispersed
state, either suspended in a carrier fluid as free particles, or
as a slurry. Representative carbonaceous materials include,
among others, coal, char, the organic residue of solid-waste
recovery operation6, tarry oils that are dispersible in liquid,
and the like. All that is required is, that the carbona eous
material ~o be at least partially oxizable in the primary
combustion chamber, and be amenable to dispersion within the
chamber as discrete particles in the carrier liquid. Typically,
the fuel is powderecl coal.
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By the term "oxidant" there is meant air or oxygen-enriched
air.
By the term ~carrier fluid" there is meant a gas or liquid,
which may be inert or an oxidant. An oxidant is a preerred
carrier gas, and water i5 a preferred carrier liquid.
Preconditioning of the oxidant is accomplished in a short
and compact cylindrical precombustor to which all the ~irst
oxidant is supplied. The first oxidant is u~ed to combust from
about 10~ to about 25% of the total carbonaceous feed to form a
first reaction product. A second portion of the oxidant enters
the precombustor and mixes with the first reaction product to
form a hot~ oxidant-rich gas stream which is directed in a
controlled fashion into the primary combustor. The oxidant-rich
gas stream also carries all the residual precombustor fuel and
noncombustibles, including still-burning carbonaceous particles
dispersed throughout its volume. As a result, pre-combustor exit
temperature may range from about 1200F ~o about 2000F.
The particulate carbonaceous material in the precombustor is
introduced, in most instances as solids, into an intense,
whirling gas flow field at the head end of the preco~bustor
chamber. Introduction is through a centrally-located injector
that produces a conical flow of particulate carbonaceous
material~ mixing into the oxidant whirling flow field. The
whirling flow field of oxidant and re~ulting reaction products
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produces a strong recirculation zone of hot gases and combusting
particles, once ignition is achieved. Precombu~tor geometry
provides self-sustaining combustion when air is used as the
oxidant and such air is introduced at temperatures of from about
300 to 500F or higher. The precombustor is preferably arranged
at an angle to the horizontal of about 22-1/2 degrees, with all
flows being ~ownward from the head end along this angle to a
rectangular exit, to assure that no solids or liquid slag remain
in the precombustor. The overall stoichiometry of the
pre-combustor i8 from about 2 to about 5 times the amount of
oxygen required for total oxidati~n of the carbon content of the
fuel being f0d to the precombustor. This stoichiometry is
controlled by adjusting the flow of particulate carbonaceous
materials into the o~idant flow to main~ain the above exit
temperatures.
The heated oxidant and reactants, generated in the
precombustor, movç through a rectan~ular exit to a primary
combustor of cylindrical geometry. This prec~mbustor-effluent
stream is introduced essentially tangential to the interior wall
of the primary combustion chamber. The rectangular exit from the
precombustor is sized such that the dimension parallel to the
primary combustor axis is larger than the dimension perpendicular
to the axis of the primary combustor A length-to-height ra~io
of 2.5 to 1 is preferred PreferablyO the centerline of the
rectangular exit is aligned with the longi~udinal axis of the
precombustor and is positioned, upstream from the mid point of
the primary chamber's longitudinal axis, i.e., about 1/3 to 1/2
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of tbe distance from the head end to the primary chamber's
apertured baffle.
By locating the rectangular exit of the precombustor in the
above-described manner, the precombustor effluent causes a
whirling motion to be imparted to the flow within the primary
combustor. We have found that, by controlling the precombustor
exit velocities to the order of 330 fps, through the use of
d~oper plates located within the rectangular exit region of the
precombustor, satisfactory co~bustion may be achieved over a wide
range of primary combustor fuel feed rates. The above-described
location also causes a division of the effluent into two nearly-
equal flows: one flow w~irls along the walls towards the head
end, while the other flow generally moves helically along the
wall of the primary combustor toward its exit. The axial
component of the whirling 10w toward the head end has a
relatively low velocity, in the order of S0 fps. This flow is
turned inward at the head-end wall of the primary combustor, and
then axially back towards the exit of the primary combustor, all
the while following whirlin~ or helical paths. The exit end of
the primary combustor is provided with a baffle plate which is
located perpendicular to the axis of the primary combustor and
which has a generally centrally-located aperture~
The major part of the solid carbonaceous fuel is introduced
into the primary caDbustor, approximately at the center of the
head end, through a fuel-injector assembly. ~his assembly causes
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the particulate carbonaceous material to be introduced as solids
in a gas or li~uid carrier, in a conical flow pattern, into the
whirling gas flow field. The injector assem~ly extends into the
primary chamber from the head end to a point slightly upstream of
the precombustor-exit rectangular opening.
As noted above, the oxidizer inflow to the primary chamber
divides into two streams, with about 50% of the precombustor
effluent flowing toward the head end, where initial ignition
occurs in a fuel-rich reaction zone, with an overall head-end
stoichiometry of from about 0.4 to about 0.5. The balance of the
incoming oxidizer flows tvwards the exit end of t~e primary
combustor. The interaction of the conical-pattern fuel injection
with the high-velocity whirling flow field provides intimate and
rapid mixing of the fuel, oxidizer and products of combustion.
As will become more ~pparent from the detailed description,
hereinafter, this provides precise and highly beneficial control
of the stoichiometry, compositions and accelerative forces in
several portions of the combustion zone and these characteristics
are important to achieving the objectives and requirements set
forth hereinabove. The bulk of the fuel's combustibles are
consumed in flight through the heated oxidi~er flow field, giving
up energy in the form of heat ~f reaction and further heating the
resultant combu~tion products. The particles in free flight
follow generally helical flow paths towards the exit end of the
primary chamber.
In typical operation, a small fraction, preferably not more
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than about 12% of the carbon content of the fuel reaches the wall
of the primary combustor in the form of unburned carbon, normally
a combustible char, which continues to be consumed. The liquid
slag layer flows helically along the walls of the primary
chamber, in response to aerodynamic d.rag and gravity, toward the
exit-end baffle. Typically, combustion of the fuel takes place
through a rapid heating of the particles, which causes a
gasification of volatile organics, which may be in the order of
from 50% to 80% by ~eight of the total combustibles. The
remainder is combusted essentially as particles of char,
primarily while in flight.
Fuel-rich gases generated in the head end of the primary
combustor, generally flow towards the exit-end baffle while the
whirling motion is maintained~ That portion of the p~ecombustor
effluent which initially divided from the head-end flow proceeds
towards the e~it-end baffle plate in an outer annular zone with a
whirling motion, is forced inward by the baffle plate, and mixes
and reacts with fuel and fuel-rich gases, to bring the overall
stoichiometry of the primary combustor, up to a level of from
about 0.7 to about 0.9, preferably from about 0.7 to about 0.8,
and yielding, as the output product of the primary combustor, a
stream of hot combustion products rich in CO and H2 and from
which most of the noncombustibles have been removed, as liq~id
slag.
The internal ~i~ing and reaction are further enhanced in the
primary combustor by a StrGng secondary recircula~ion flow along
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the centerline of the primary combustor, the flow moving
generally along the centerline towards the head end of the
primary combustor. This recirculation flow i~, also, whirling
and, therefore, substantially helical; but its axial component is
toward the head end of the primary combustor. It produces a
fuel-rich core portion within the prirnary co~bustion chamber.
The average diameter and mass-flow rate of this reverse-flowing
core portion is determined and contro:Lled by the pre~ombustor
exit-flow velocity and selection of the diameter of the primary
chamber's baffle aperture. Preferably, precombustor exit
velocity is about 330 fps, and a preferred baffle-opening-
diameter to primary-chamber-diameter ratio of approximately O.5
or more, produces ldeal secondary recirculation flows ~or
enhanced control of ignition and overall combustion in the
primary chamber.
From approximately the radius of the baffle aperture
inwardly, the tangential velocity decreases to a value of
essentially zero at the centerline of the primary combustor.
This whirling flow field accelerates the fuel particles radially
in their early consumption histories, and at the same time
enable~ burned-out particles, down to about 10 microns, to be
trapped within the primary combustor as molten slag.
The pri~ary chamber's fuel injector assembly is designed to
allow for molten slag flow along its exterior surface from the
head end, t~wards tlhe point of injection of the particulate
carbonaceous material~ This very hot ~molten slag) exterior
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surface on the injector assembly functions as a flame holder to
assure immediate ignition of fuel particles as they leave the
injector, thereby promoting and maximizing efficient
combustion. In operation, the flowing slag along the injector
strips off short of the point of solid particle injection, and
provides small-point centers of intense radiation and igni~ion of
the head-end-generated fuel-rich gase!s.
When a gaseous carrier fluid is used, the particulate fuel
is carried into the primary combustor in dense~phase transport,
wherein the solids-to-carrier fluid ratio at normal power levels
is in the range from about 3 to 1 to about 10 to 1 by weight.
When the fuel is fed as a liquid slurry, fuel to carrier fluid
weight ratios of about 2:1 or higher may be used. The primary
chamber's products of co~bustion are sufficiently hot to maintain
a molten slag layer at a temperature above the slag fusion
temperature. Accordingly, slag flow~ freely along the walls of
the primary chamber. Coolant flow to the metal walls is
controlled. Particulate fuel mass-flow rate is controlled~ The
mass flow rate and velocity of oxidizer from the precombustor are
controlled. Coordinated regulation of these independent
variable~ keeps the primary combustion zone temperature in a
range such that slag vaporization is avoided, a protective slag
layer is maintained on the metal walls and liquid ~lag flows
continuously, over tha~ slag layer, toward the slag disposal
subassembly. ~uel-rich combustion in the head-end region and the
core portion facilitate NOX control down to environmentally
acceptable levels.
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Preferably, the walls of the primary chamber are made
of water-cooled, tube-and-membrane constructions, with a
generally circumferentially-directed winding of the tubing.
The tube-and-membrane structure is further equipped with
slag-retaining studs. The containment walls are initially
lined with a sacrificial refractory, applied at a nominal
thickness of about 0.5 inch and maintained by s~uds. In
operation, the refractory employed causes the molten slag
to tightly adhere to the xefractory in a thin frozen layer,
with the remainder of the slag flowing over the frozen-slag
layer. After long periods of operation this refractory
material is eroded away, i.e. sacrificed. But any portion
thereof which is so eroded is immediately replaced by
congealing slag. This combination of refractory and frozen
and molten slag layers provide thermal and chemical protec-
tion ~o the welded tube-and-membrane wall structure. Local
slag flow provides for self-replenishment of any lost
refractory. Design of the cooling circuits pro~ides for a
metal wall temperature of from about 325 to about 600DF,
which precludes condensation of acidic compounds and thereby
minimizes corrosion.
The longitudinal axis of the primary combustion chamber
is positioned, preferably, at an angle of about 15 degrees
with respect to horizontal, to insure that proper slag flow
occurs,
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avoiding accumulation of excessive quantities at the bottom of
the chamber. The qlag generally is driven in a helical pattern
towards the exit-end baffle along the wall of the primary
combustor. As the slag flow builds up along the wall, a larger
portion of the molten slag flows to the bottom of the primary
co~bustor, since the gravity forces exceed the aerodynamic
forces. The bottom-collected slag fl~s toward the baffle. The
baffle plate has a centrally-located aperture and a rectangular,
keyhole-like opening extending from the aperture to the bottom
wall of the prlmary chamber. This rectangular slot en~ble~ slag
flow through the baffle plate, adjacent to the bottom wall of the
chamber. When burning 200-mesh co~l~ about B0% to 95% of the
noncombustible content of the coal is removed from the gaseous
product stream, captured as liquid slag, and disposed of by way
of a slag-tapping subsystem located downstream of the key-hole
slotted baffle.
By use of a primary combustor length-to-diameter ratio of,
nominally, 2 to 1; a baffle diameter-to-primary chamber diameter
ratio of 0.5 or more, and with essentially free-flight burning of
200-mesh coal, as described herein, virtually no loss (carryover~
of unburned carbon out of the primary chamber is experienced.
Tbe combustion products and liquid slag from the prim ry
combustor pass into a preferably cylindrical slag-recovery
chamber. The slag-recovery unit comprises a short length-to-
diameter chamber having diameter approximately equal to that of
th~ primary chamber~ At its bottom is a slag-tapping aperture.
At the top is a circular aperture, with a transition geometry
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22-
arranged at essentially perpendicular with respect to the
centerline of the slag-recovery chamber. From this aperture, at
the top of the slag-recovery chamber, extends,an exit flow
conduit to carry the fuel-rich gases on to their ultimate use.
This conduit leaves the slag-recovery section at an angle close
to vertical, and extends for about onle to two length-to-diameter
ratios ~one being preferred) before turning the combustion-
product~ stream horizontally towards its ultimate use. The slag-
recovery unit additionally provi~es a short distance between the
primary chamber's baffle and the vertical-exit aperture, such
that a large portion of any residual slag droplets in the
gaseous-products stream are captured on the walls of the slag-
recovery section~ The vertical exit enhances ~ravity settling of
any captured slag particles. Placing the slag-tap aperture
substantially opposite the vertical exit enhances internal
thermal radiation to the slag-tap ~o aid in maintaining good slag
flo~ through the slag-tapping aperture into the slag removal
tank.
The slag-recovery section, in ~onjunction with tbe baffle
plate, also provides the source of the hot recirculation gases
which flow helically back into the core portion of the primary
combustion zone. The diameter of this recirculation, hot-gas
core portion is normally about 70% to about 75% of the diameter
of the aper~ure of the primary chamber's baffle plate. This
results in increased tangential and axial velocity of the exiti~g
combustion-products ~tream at the baffle's aperture. Slaq
droplets which ~re in ~his flow are further accelerated towards
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the wall of the slag-recovery chamber for capture as molten
slag~ More importantly, this core portion provides a relatively
less turbulent region into which additives can be introduced for
capturing potential air pollutants, such as s~lfur compounds. It
provides for the optimum placing of an injector for sorbents for
6ulfur-emission control. Injection of sorbents into this
reverse-flow core portion, from a point along the centerline of
the primary combustor near the baffle aperture, provides
excellent thermal preconditioning, as well as chemical
preparation, of the sorbent. The reverse-flow flow field carries
a major portion of the sorbent into the core portion of the
primary combustion zone where the sorbent reacts with sulfur
compounds in a fuel-rich environment. Efficient use o~ sorbent
results in a recovery percentage as high as 60~ to 70~ of the
sulfur content of the fuel.
In the practice of our invention, operating at an overall
primary-chamber stoichiometry of about 0.75 produces
nitrogen-oxide emission levels in the range of 250 to about 300
ppm. This enables our system to conform ~o clean-air regula~ions
without resorting to expensive stack-gas cleanup measures.
Our invention utilizes fiuid and combustion-reaction
principles which make possible confident scaling from one power
si~e to another~ We have built apparatus having power capacities
up to 170 million BTU/hr., utilizing the same scaling
principles. As ~n lexample of these scaling principles, cross-
sectional di~ension~3 of the precombustor, ~he primary combustor,
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-24-
and the slag-recovery chamber scale approximately directly as the
sguare root of the desired power capacity. At sizes of
commercial interest, the length-to-diameter ratios are held
constant at about 3 to 1 for the precombustor, about 1.5 to 2 to
1 for the primary combustor, and about: 1 to 1 for the slag-
recovery unit. The nearly-vertical exit conduit has a length-to-
diameter of about 1 to 1 ~o provide for final slag capture and
conducting the hot eshaust gases to any specific end-use
apparatus. The precoMbustor's rectangular exit is designed such
that the exit~height to primary combustor-diameter ratio is from
about 0.2 to about 0~3, allowing the width of the rectangular
exit to be adjusted to produce a nominal inlet velocity of 330
fps, at a temperature of from about 1200 to about 2000Fo The
inlet with sli~ing damper system also aids in achieving ~urn-down
ratios of 3 to 1, in order to accommodate variable demands at the
point of use. Turndown is accompli~hed by throttling the oxidant
flow and particulate carbonaceous material flow in direct, or
nearly-direct, proportion in the precombustor and by throttling
of the particulate carbonaceous material flow into the primary
combustor.
For input air ~low, the system efficiently utilizes a
conventional fan syste~ providing input oxidant at an input
pressure of approximately 25 to 45 inches of w~ter~ This makes
our apparatus directly adaptable to e~isting end-use equipment,
such as industrial furna~es and electric: utility boilers
originally designed and sonstructed to burn oil or na~ural gas,
as well as for new designs of boller plants where atmospheric-
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pressure combustion is specified. Coal/water slurry ratios of
appro~imately 70% solids to 30% liq~id, have been successfully
combusted.
With reference now to Figs. 1, 2 and 3~ slagging combustor
10 is comprised of precombustor section 12, primary combustion
chamber 14, and slag recovery chamber 16 cooperating with a slag
collection ~ub~ystem 18. A carrier fluid which may be gas, vapor
or liquid, is used to transport particulate carbonaceous fuel
from reservoir 20 by line 22 to injector a~sembly 24 positioned
in endplate 26. In typical operation, from about 75~ to about
90% of the fuel is delivered to primary combustor 14 and the
balance to precombustor 12, by dense-phase transport means, not
shown.
Fuel is fed to precombustor 12 through nozzle 28.
Precombustar 12 is essentially a cylindrical structure closed on
one end by end-closure plate 30, and throu~h which no~zl~
as~embly 28 extends. An oxidant flow, preferably preheated to a
temperature of from about 300 to about 500F or higher, is
introduced into mixing zone 34 by way of duct 32, tangentially
attached to precombustor 12. The tangential introduction of
oxidant imparts a whirling motion in zone 34. The whirling
motion of oxidant flow ~ay b~ accentuated by a damper plate 36 to
increase o~idant velocity thr~ugh aperture 40 of baffle 44 into
combustion zone 38 of precombustor 12. The diameters of zones 34
and 38 are, typically, identical. ~uel-injection nozzle assembly
28 extends into precombustor 12 at least to, and preferably
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~hrough, aperture 40, to a position such that no reaction takes
place in zone 34. A suitable ignition system 42 is inserted
through end plate 30 and is positioned to provide initial
i~nition of oxidant and the particulate fuel. The particulate
car~onaceous material and oxidant are reacted in zone 38 tv an
initial overall ~toichio~etry of from about O.5 to about 1~5
times the amount of oxygen required to convert all carbon present
to carbon dioxide, thereby producing al stable reaction
temperature which is typically near the adiabatic ~lame
temperature for the mixture of oxidant and carbonaceous material.
Typical tangential velocities of oxidant flow in zone 34,
are in the order of about 150 fps. Damper plate 36, located in
duct 32, serves as a means for maintaining desired tangential
velocities in zone 34 as demanded power ratings change. The
diameter of aperture 40 in baffle 44 is preferably about one half
of that of precombustor 12~ The whirling motion continues into
combustion zone 38, and serves to stabilize the com~ustion
therein.
Additional oxidant is introduced into precombustor 12 via
duct 48, which opens into a surrounding plenum 50, which encloses
a distribution network 52. This additional oxîdant mixes with
~he hot reaction products hydrocarbon and residual oxidan~ from
zone 38, to produce a stream of reaction products that passes
through duct 56~ wh:ich changes the cylindrical cross-section to
rectangular cross-section. This stream flows through aperture 58
tangentially into p,rimary combustion chamber 14. To control the
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velocity of the precombustor's product stream, duct 56 is
equipped with two damper plates 60 and 62, which control the
effective opening of rectangular aperture 58. The mixing of
secondary oxidant with the reaction pro~ucts of zone 38, produces
an overall reaction product stream having a temperature of from
about 1200 to about 2000F. The ~tream is o~idant-rich,
normally containing from about 2 to about S times the amount of
oxygen neces~ary to fully oxidize ~11 of the fuel fed to nozzle
28.
The primary combustion rhamber 14 is closed at its head end
by end wall 26, and dafined at its exit end by apertured baffle
64. Particulate carbonaceous material, along with its carrier
fluid, is introduced through fuel injector 24, which is located,
preferably, on the axis of primary oombustor 14 in end wall 26.
Fuel injector 24 extends through end wall 26 to a position such
that the particulate fuel and its carrier fluid are injected into
combustion zone 70 at a location just upstream from the oxidizer
inlet aperture 58. The stoichiometry in zone 70 is con~rolled by
the flow rates of particulate carbonaceous ~aterial and carrier
fluidt and oxidizer flow from aperture 58. Combustion occurs
under conditions wherein the oxidant feed is from about 0.7 to
about 0.9 of balanced ~toichiometry, preferably from about 0.7 to
about 0.8. The tangentially introduced oxidizer stream~ flowing
in through tangential inlet ~8, provides a s~rong w~irling flow
in zone 70. ~perture 68 in baffle 64 is preferably a keyhGle-
like configura~ion to facilitate the flow of ~olten slag along
the bottom cha~ber 64, through the slot at the bottom of aperture
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58, and into the slag-recovery section. The area ratio of baffle
64 to aperture 68 i5 selected from a range of from about 2 to
about 4, and maintains a desired whirling and~centrifuging action
in ~one 70. A nominal tangential flow velocity for reaction
products into zone 70, of from about .250 to about 400 fps,
preferably about 330 fps, is also important to the ~hirling and
centrifugal flow fields to maintain desired operation. Whirling
flcw in zone 70 impart~ a strong cent.rifuging force on
noncombustible and nongaseous product~s created from the reaction
of the feed streamsO This forces substantially all liquid and
solid noncombus~ibles, and any noncombusted combustibles, to the
wall of primary chamber 14 in the form of molten slagO Molten
slag in pri~ary chamber 14 flows towards aperture 68, in response
to the combination of aerodynamic drag force and gravity. The
primary chamber is coupled to a slag-recovery section 18. Molten
slag, which enters section 16 via the keyhole-like aperture 68,
flows into duct 71 and through aperture 73 into slag collector
76. End wall 66 serves to collect free-flight large slag
particles for delivery to collector 76, as do the surfaces of
ducts 77 and 79.
Little, if any, co~bustion takes place in slag recovery
section 16. The stream of combustion products from primary
combustor 14, i~ further stripped of molten slag by passing
upwardly alo~g du~t 77~ which is ~ubstantially vertical and has a
diameter such that bulk flow velocity of the gas stream is on the
order of from abvut 100 to 150 fps, preferably about 125 fps.
These relatiqely low velocities assure that aerodynamic-drag
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-29
forces applied any large slag droplets are small enough to be
overcome by gravity. Also, molten slag flows d~wnwardly ~long
the walls 77 and 79 to the bottom o section 18, comprising slag-
tap aperture 73, located in short coupled duct 71 and
communicating with slag reservoir 76. The gaseous reaction
products now substantially cleaned of molten slag, ash and
particulates, flow nearly vertically up oonduit 77, for a
distance of approximately one to two diameters thereof, and are
then turned nearly hori~ontal by duct 81, through which the
gaseous combustion products are carried to their ultimate use
point in ~econdary combustion zone 72 of furnace 78. Depending
on the specific end-use, supplementary oxidant te.g. air) is
introduced into the combustor-effluent stream from plenum 80
through annular duct 83. Thus, combustion is completed in zone
72 of end-use furnace 78. The ultimate end use may be, for
example, an electric-utility boiler plant or an industrial boiler
or furnace for supplying process heat. The stoichiometry of the
overall product ~tream at conduit B5 is the same a5 that at the
exit end of primary combustor 14. All oxidant necessary to
complete combustion in zone 72 comes from plenum 80.
Wi~h reference again to Fig. 2, operation of precombustor 12
involves tangential flow of oxidan~ into zone 34, with the
injection velooity being, nominally, about 150 fps. The swirling
flow increases in velocity as the o~idant passes through aperture
40 in baffle ~4 and decreases again in 20ne 38. The particulate
carbonaceous fuel and carrier fluid are introduced into zone 3~
at an angle of from about 4~ to about 90 de~rees with respect to
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the centerline of precombustor 12. The injected fuel and
oxidizer flow fields cause a strong toroidal recirculation. This
carries hot c~mbustion gas toward injector nozzle 28, producing
an intense combustion zone in the head end of zone 38. While
fu~l conversion is high, it is not necessary that the combustion
be complete in precombustor 12. Inst~ead, it is preferred to
control the system so that the precombustor outlet temperature at
aperture 58 is from about 1200 to about 2000F. Oxidant
entering plenum 50 is radially bled into the transition zone
formed by o~idant distribution grid 52, as illustrated by the
~mall flow vectors, an~ mixes with the reactant flow from zone 38
into duct 56. Thus, the precombustor subassembly 12 feeds to
primary combustor 14 a high-temperature, high velocity stream of
oxidizer suitable for generating a swirling, quasi-helical flow
field adjacent to the walls in primary combustor 14.
Preco~bustor volume, diameter and length are selected such that
little, if any, slag is collected on the wall vf the
precombustor. Further, precombustor 12 is tilted at an angle
with respect to the horizontal to assure that all reaction
products in the form of solids and fluidS are discharged to
primary chamber 14.
The interaction of the flow fields in primary combustor 14
and slag-recovery chamber 16 is illustrated in greater detail in
Fig. 4. The flow fields are complex, vary as a function of time,
and s~mewhat turbulent; however, Fig. 4 illustrates
macroscopically the time-averaged conditions and performance.
The oxidizer stream from preco~bustor 12 enter primary combustor
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14 in a tangential flow through aperture 58 and create a
generally whirling flow 2. Superimposed on whirling flow field 2
are several important secondary flows~ The gaseous part of the
stream from aperture 58 divides into two ~ubs~antially-equal
halves: one portion flows more-or less helically, adjacent the
inside walls, toward baffle 64; the other portion flows generally
toward the head end 26, whirling near the walls and turning back
at the head end as indicated, general:ly, by vector 5. Powdered
uel and carrier fluid are injected from centrally-located fuel-
injector 24 in a ~ubstantially conical pattern having a nominal
angle of from about 45 to about 90 degrees with respect to the
longitudinal axis of primary combustor 14. The particulate
fuel/carrier gas ratio weight/weight, is in the range from 3 to
10; preferably close to ten when the system is operating at rated
power capacity. The input fuel and carrier gas flow velocity is
about 50 to 200 feet~Recon~. The oxidizer flowing from
precombustor 12 provides, at its introduction temperature, the
primary source of ignition for the injected fuel, normally
injected at a size distribution ranging from as small as a few
microns to as large as 150 microns for a typical 200-mesh coal.
Preferably, the mean ~e~h size is about 75 microns with a top
size of about 125 to 150 microns. The injected particulate fuel
and carrier fluid are quickly picked up by strong rotational flow
2, and are accelerated towards the wall of primary combustor
14. At the sa~e ti~e, the axial-flow component acts upon the
particulate carbonaceous materials~ Combustible v~latiles in the
order of from S0% to 80~ of the mass of typical coals are driven
off in the free-flight burning of the par~iculate carbonaceous
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materials. Smaller-sized particles burn nearly completely,
before they strike the walls, leaving unly droplets of molten
~lag. Only a small fraction of the fuel's carbon reaches the
walls, and burns there on the molten slag. The interaction of
flow vectors 2, 3, 4 and 5 with the injected particulate fuel,
ollectively denoted as 6, cause~ a dispersion of the solid
particles to take place, as illustrated. The strength of the
internal rotating flow 2 is determined by the velocity of the
injected oxidizing effluent and the ratio of the diameter of
baffle aperture 68 to the internal diameter of primary chamber
14. For a diameter ratio of 0.5, and a primary combustion
chamber length-to-diameter ratio of 2 to 1, the re~idual molten
~lag from no~inal 10-micron and larger fuel particles, is
captured at the baffle. All increasingly larger ~olid particles
are trapped at different impact points on the primary combustor
wall surface by other trajectories7 as illustrated. ~he
collected slag on primary combustor wall 14 also has its own flow
characteristics. In the outer or lower end, near baffle 64, the
slag flows as a thin liquid layer in a generally helical pattern
towards baffle 64a In the upper or head end of primary combustor
14, the slag flow~ in a thin layer, partly towards end-closure
26, and radially inward and axially along centrally-located
nozzle a~embly 24, where the axially flowing sl~g then strips
off and is driven radially ou~ward to the primary combustion
chamber wall, again as denoted by slag trajectory a. The
helical-surface slag flcw and radially-inward-flowing slag flow
at head end are aerodynamically ~hear-stress driven. When the
aerodynamic forces can no longer helically drive all the molten
,~,...
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slag flow, a portion of the slag flows along the bottom of
primary combustor 14 towards baffle 64. At baffle 64, a keyhole-
like slot allows the molten slag to flow into slag-recovery
section 16 and, finally, into slag co:Llection section 18. Also
at baffle 64, radially-inflowing combustion products cause an
aerodynamic shear drag inwardly on a part of the molten slag,
resulting in some slag being driven through aperture 68 along
with the gaseous products. The strong whirling flow ~, in
conjunction with baffle aperture 68, causes a reverse-
recirculation core portion to be created appro~imately within
boundary 9. This reverse flow originates at the central part of
slag-recovery section 16. Within the volume 70 of primary
combuQtor 14, the reverse flow gases diffuse across boundary 9,
as shown by flow vectors 11. On ~he average this core-portion is
relatively fuel-rich compared to the annular portion surrounding
it. As fuel-rich gases move across boundary 9, they mix with
oxidizer and are further combusted. When the gaseous product
flow 13 passes through baffle aperture 58, externally of reverse~
flow boundary 9, it has an increased whirling velocity,
determined primarily by the velocity of initial oxidant flow 2 in
the area of aperture 68. Gaseous product flow 13 also has an
axial velocity component that is determined by the amount of flow
which must pass through the annular area created by the diameters
of baffle aperture 68 and reverse flow boundary 9. ~n the
average, the diameter of reverse flow boundary 9 to the diameter
of baffle 68, is ab~ut 0.7, ~ith changes in operating conditions
causing this to range from about 0.50 to about 0.75.
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Preferablyt the longitudinal axis of the primary combustor
is inclined at an angle of about 15 degrees with respect to the
horizontal. This slope provides for satisfactory liquid-slag
flow fram primary ch~mber 14 through the keyhole-like aperture
68. Depending on the flow velocities, power levels and operating
temperatures chosen for a specific end-use application this
inclination may be as small as about five degrees. At greater
angles, the amount of slag flowing through the central part of
baffle aperture 68 might result in excessive molten slag carry-
over, resulting fro~ gaseous product flow stripping molten slag
from the edges of baffle 64.
The entire interior surface of the lower portion of slag-
recovery section 16, and at least a part of its upper portion, is
covered with a thin layer of flowing molten slag. The molten
slag flow in primary combustor 14 flows through the keyhole slot
in baffle 64 a~d continues on into slag-recovery section 16 and
thence into slag collector 18. The gaseous combustion product
exiting from chamber 14 is at its maximum velocity at the
aperture 68, and decreases in velocity as t~e flow e~pands in
slag-recovery section 16.
The division of reaction product flow 2 into two essentially
equal parts 3 and 4, results in a st~ichiometry in the head-end
zone con~aining the injector assembly 24 of apprvximately one-
half of the overall stoichiometry of primary combustion chamber
14. This low stoiclliometry inhibits the formation ~f nitrogen
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oxides as the reaction between the heated oxidant product stream
and the particulate fuel be~ins to take place in primary
combustor 14. Gaseous species are formed, such as NH3 and HCN,
thereby reducing the formation of nitxo~en oxides~ The overall
reducing stoichiometry of primary combustor 14 further inhibits
nitrogen oxide formation~ In addition, when the overall, space-
average stoichiometry within primary chamber 14 is kept within
the range from aboout 0.7 to about 0.8, the temperatures inside
zone 70 are su~ficiently high to keep the slag molten, but not so
high as to cause large vaporization of molten slag before it is
removed to slag-collection section 18. The overall stoichiometry
in slag-recovery æection 16 and exit conduits 81, 85 is the same
as that in the downstream end of zone 70, thus preserving the
low-nitrogen-oxide-emission system desiderata. Overall, this
results in reduction of ~Ox in the stack gases, after secondary
combustion, to the order of 250 to 450 ppmv.
During steady-rate introduction of fuel to precombustor 12
thr~ugh nozzle assembly 28, reaction product flow from opening 58
contains some still-burning particles and numerous burned-out
particles in the from of solid fly ash and slag. The fly ash and
slag are virtually uniformly distributed through the reaction
product and may be hotter than the average of the inflowing
oxidant stream~ As a result, the oxygen rich stream entering
primary combustor 14 functions as a radian~ body; and, therefore,
the entire head-end portion of zone 70 is exposed to intense
radiation from this radiating stream; ignition, combustion and
slag flow ln ~he head-end region, in and ar~und injector assembly
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24, are thereby enhanced. Similarly, throughout combu~tion zone
70, particulate loading of the gas flow causes intense thermal
radiation to occur; this promotes temperature uniformity within
zone 70 and aids in stablizing the ovlerall combustion.
Locating slag-tap aperture 73 di:rectly opposite nearly-
vertical ducts 71, 77, and 79, results in increased thermal
radiation to slag-tap aperture 73. This increased thermal
radiation helps to maintain a good fluid flow of molten slag to
slag collector 76.
Fig. 5 illustrates a preferred structure for providing
thermal and corrosion protection of the walls of the apparatus.
Cooling is provided by the flow of coolant 86 at a suitable
velocity insid~ a passage enclosed by surfaces 88 and 90. The
passage may be a tube, a double-walled membrane construction or
the like. When first constructed~ a suitable sacrificial
refractory clay ~2, such as Missouri Flint Clay, is placed on the
hot-gas side of surface 9~ in a nominal thickness of about 0.5
inch. In operation, gravitational forces and the hot gas
denoted by vector 94, cause several physical phenomena to
occur: ~olten slag 98 is deposited on the interior surface of
the clay 92; heat transfer to the slagging surface occurs by both
conve~tion and thermal radiation; the flowing ~a-~es 94
aerodynamically drag and shear part of the liquid slag along the
interior surfa~e; gravitational forces tend to cause the liquid
slag to run to the :Lowest point on the interior surface; heat
transfer ~o ~he coo'Lant cau~es the slag to also form a frozen
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37-
slag layer ~6 over the clay 92, and local heat transfer causes
the combination of liquid slag 98, frozen slag 96, and refractory
clay 92 to adjust in thickness to accommodate the local heat
flux. As time progresses, the original refractory clay i5
partially or completely replaced by the solid and liquid slag
layers. Thus, c~olant passage wall 90 is thermally protected,
while the coolant passage formed by walls 88 and 90 also operates
at an ideal temperature to prevent con~ensation of acidic
compounds and minimize corrvsion. Further, flowinq molten slag
98 provides a source of insulating material for curing and
replenishment for ~ny loss of thermal protection of wall surface
90. Coolant flow 86 is kept in a temperature range of from about
3254 to about 600F. Operating above 325 minimizes acidic
corrosion of ~urface 90~ Reeping it below 600~F guards against
hydrogen-sulfide corrosion. Water is preferahly utili3ed as the
coolant. Mis~ouri Flint Clay has been found to provide a ready
surface g2 for typical slags to adhere to in a tenacious manner,
such that the ~pparatus described herein may be started up and
shut down without concern for lo~s of thermal protection, so long
as clay layer 92 i8 initially properly bonded onto and retained
on cool~nt passage surface 90.
Fig~ 6 illustrates the presently preferred wall construction
and arrangement for securely retaining refactory and/or slag.
The coolant passage surfaces 90 and 88 are the interior and
exterior surfaces o.E a cylindrical metal tube through which
coolant flow ~6 ~oves~ Attached, by welding to surface 90, are
studs 100, which ~re staggered at nominal 1 1/4-inch centers
.. . .
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along the coolant passage length, in rows spaced about 7/8 inch
apart. The sacrificial clay 92 is initially formed into and
around the stud pattern.
Fig. 6 also illustrates the tube-and-membrane construction
utilized in the containment walls of ~precombustor 12, primary
combustor 14, and ~la~ recovery chamb~er 16.. Each tube, made up
of surfaces 88 and 90, is joined to the next tube by a full-
penetration weld at mid-diameter with membrane 102. The tube-
and-membrane construction maintains an adequate wall temperature,
even in the case of local loss of slag and/or refr~ctory thermal
protection.
Ignition and stability of the combustion in zone 70 of
prim~ry combu~tor 14, are enhanced by the use of an externally-
hot fuel injector, examples of which are depicted in Figs. 7, 7A,
8 and 8A. A hot exterior is achieved by placing the primary
in~ector assembly inside a sleeve 104. As shown in Figs. 7 and
7A, the injector is a coaxial device suitable for feeding dense-
phase powdered coal with carrier gas. In Figs. 8 and 8A, the
injector assembly is an ato~izer for carbonaceous particles
suspended in ~ liquid, for example coal-water slurry.
With reference to Figs. 7, 7A, 8 and 8A, sleeve 104 is shown
in longitudinal cross-section, while t~e injec~ors are shown in
partial cross-section. Sleeve 104 may, as shown in Fig. ~, ~e
notched with rectangular qrooves 106 t which form circular fins on
sleeve 104. Alternatively, pins 108 are shown in ~ig. 7. Sleeve
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104 is designed with a clearance of about 0.25 inch, to allow
pintle 110 or atomizer 112 to slide into sleeve 104. The end of
sleeve 104 is in turn positioned to within a range fro~ about
0.25 to 1.0 inch of injection orifice 114 of pintle 110 or ports
116 of atomizer 112, through which the particulate fuel and
carrier fluid flow. With reference to Fig. 8r rectangular slots
106 are preferably of nominal dimensions of 0.25 inch by 0.25
inch. Slag forms a frozen layer on the surface of sleeve 104
inside grooves 106 or, as shown in Fig. 7, ar~und pins 108.
Molten slag is aerodyna~ically dragged axially towards the end of
~leeve 104, and produces a hot boundary layer at the point of
fuel injec~ion that enhances combustion on injection to zone 70
in primary combustor 14.
Figs. 7 and 7A show a typical cro~s-section of pintle
injector 110. The particulate carbonaceous materials and carrier
fluid enter the injector assembly via annular duct llG and emerge
from in~ection slot 114 at an injection angle of about 60 degrees
over surface 118. The entire injector assembly is positioned in
end walls 26 and 30~ To preven~ undesirable caking and tarring
effects of the flswing particulate carbonaceous material and
carrier fluid, upon exposure to the heat of zones 38 and 70, i~
is necessary to internally cool injector nozzles 110 and 112
inside the hot reaction environment. With reference to Fig. 7,
coolant is provided by passa~es 124 on the outside of duct 116
and head manifolds 128, through use of supply-and-return duc~s
130 and 132. Sealing is provided between the external
environ~ent and zones 38 and 70 by means of a suitable gland seal
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(not ~hown) which is controlled in leak tightness by any suitable
adjustment means.
With reference now to Figs. 8 and 8A, atomizer 112 may be
used for introduction of a slurry fue:L in an atomized state. Its
operation and maintenance of combustion close to the point of
injection of the slurry into zones 38 and 70, are predicated on
the use of an atomizing gas, normally an oxidant such as air,
which intercepts the slurry in a direction sub~tantially normal
to slurry flow, and mixes with and atomizes the slurry to achieve
rapid expansion of atomized particles immediately upon ejection
from the injector. This promotes combustion immediately adjacent
the periphery of the injector.
Atomizer 112 is retained in sleeve 104. The slurry is
introduced to the injector through conduit 137 along an axis
substantially normal to the direction of ejection from nozzle
112. Ato~izing carrier gas~ normally the oxidi~er such as air
introduced by conduit 134, intersects the slurry at the juncture
of communicating port~ 136 and 138 in a direction ~ubstantially
normal to the point of traYel of the slurry from port 136 to port
138. This causes shear and atomization of the slurry into zone
38 or 70, at clo~e to right angles to their axis.
The introduced slurry is diverted by cone-~haped
pro~ection 140 to a plurality of conduits 135 feeding
ejector port 136. ~jector port 138 is preferably slightly
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divergent in the direction of flow, optimally at an angle of
divergence of about 5 degrees and of greater diameter than
mating ports 136, to account for shearing gas introduction.
A coolant such as water is supplied by conduit 140 to
manifold 142 and returns by conduit 144. This protects the
head of atomizer 112. ~ith reference to Figs. 7, 7A, and 8,
sleeve 104 is independently cooled with a fluid, such as
water, which enters by conduit 146 and exits by conduit 148.
This protects the pintle and/or the atomizer, and insures a
layer of frozen slag on the exterior surfaces of sleeve 104.
Typical injection velocities through slot 114 and curves of
channels 136, are of the order of from 50 to 200 fps.
Suitable life is obtained by using surfaces formed of
tungsten carbide, tantalum carbide, or an equivalent wear-
resistant material, where a change in flow dir ction occurs.
The structure, operation and advantages of the extern-
ally-hot fuel injectors shown in Figs. 7, 7A, 8 and 8A are
more fully described in co-pending Canadian Application
Serial No. 4959060, filed concurrently with this application
and assigned to the same assignee. Reference may be had to
this co-pending application for more specific understanding
of how the subject matter thereof may be used in conjunction
with our present invention.
Fig. 9 shows some detail of the tube-and-membrane
cooling system of Figs. 5 and 6, and, in particular, the
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structural arrangeme.nt coupling precombustor 12 to primary
combustor 14. Damper plates 60 and 62, which control the
velocity and mass flow rate of oxidizer flow into primary
combustor 14, are driven by suitable actuators 150 and
motors 152. The damper plates are driven in and out to
form rectangular opening 58 for introduction of the oxidize.r
stream from precombustor 12 to primary combustor 14.
The design principles embodied in this invention provide
a means for ready scaling to various power levels. Because
the reac~ion processes are essentially intense-volume
burning processes, wherein aerodynamic principles control,
the sizing is accomplished by the use of cross-sectional flow
areas while making minor adjustments on oxidant inlet
velocities. The basic scaling relationships are as follows:
1. Precombustor, primary combustor, and slag-recovery
cross-sectional areas:
Power of Unit 1 = ~Diameter of 1)~ that is
Power of Unit 2 ~Diameter of 2
as onP scales to larger sizes the power capacity
increases approximately as the square o~ the dia-
meter of the cylindrical combustion chambers.
2. Length-to-diameter requirements, L/D:
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Precombustor 3:1
Primary combustor (1.5 to 2~:1
Slag-recovery section 1:1
3. Baffle area ratio
for primary combustor (2 to 4):1
These rel~tionships are tempered only by hardware implementation
re~uirements.
Typical results for sizing of the hardware for a
nominal 50-million BTU/hour unit utilizinq Ohio ~6, 200-
mesh coal~ are as follows:
Precombustor
Diameter 17 inches
: Length 55 inches
Primary Combust~r
: Diameter 34 inches
Length 60 inches
Inlet aperture 2~ i~ches by 10 inches
Baffle aperture 17.125 inches
Baffle keyhole 3 inches wide by 8~417 inches ~igh
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Sla~ ecovery Section
Diameter 34 inches
Length 60 inches
Sl~g tap ;L8 inches
~ it Diameter Equivalen~c 30 inches
For a combustion appara~us of the size indicated above, the coal
used is prefer~bly 80% through ~00 Mesl~ or apparatus scaled up
to larger power capacities, one may use ~ ~osne what cozlrser fuel
while still realizing the several described ~dvanta~es of our
invention .
While we have shown and described a specif ic e~bod;Dent of our
invention, it i~ to be understood that varic)us ~3ific~tions may
be made t~7~rein witbout depar~ing from our invention; and it is,
therefore, our intent to cover all changes and modificatior~s as
fall within the true spirit and scope o~ our inven'cion.
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