Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF ' E INVENTION
Field of the Inven~ion
This invention relates to a method of preventing
agglomeration of carbonaceous solid particles in a fluid
bed in coal conversion processes. More particularly, this
invention relates to improvements in a process for reacting
coal particles in a fluid-bed hydrocarbonization zone.
.. . . ..
Description of the Prior Art
Increasing energy needs have focused attentlon
on solid fossil fuels due to their availability in the United
States in a relatively abundant supply and their potential
value if converted into more useful forms of energy and feed-
stock. Processes such as carbonization, gasification9 hydro-
carbonization and hydrogasification, wherein synthetic fuel ` ~ .
products have been prepared by introducing a fluidized stream
of finely-divided coal particles into a fluid-bed reaction
zone and reacting the coal particles at elevated temperatures
in the presence of inert gasec, air, steam, hydrogen or the
like~ are well known. A major operating difficulty in such
processes has been the tendency of coal particles, especially
intensified in a hydrogen-rich atmosphere ? to agglomerate
at the elevated temperatures required for reaction.
Coal particles, especially caking, swelling or
agglomerating coals, become sticky when heated in a hydrogen-
rich atmosphere. Even non-caking, non-swelling and non- ~.
agglomerating coals become sticky when heated in such an
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atmosphere. Coal particles begin to become sticky at tem-
peratures in the range of about 350C to about 500C, de-
pending on the specific properties of the coal, the atmo-
sphere and the rate of heating. The stickiness results
due to a tarry or pla~tic-like material forming at or near
the surface of each coal particle, by a partial melting
or decomposition process. On further heating over a time
period, the tarry or plastic-like material is further trans-
formed into a substantially porous, solid material referred
to as a "char." The length of this time period, generally
in the order of m~nutes, depends upon the actual temperature
of heating and is shorter with an increase in temperature.
By "plastic transformation" as used throughout the speci-
fication is meant the hereinabove described process wherein
surfaces of coal particles being heated, particularly when
heated in a hydrogen atmosphere, develop stickiness and
transform into substantially solid char, non-sticky surfaces.
"Plastic transformation" is undergone by both normally ag-
glomerating coals and coals which may develop a sticky sur-
face only in a hydrogen-rich atmosphere.
Agglomerating or caking coals partially soften
and become sticky when heated to temperatures between about
350C to about 500C over a period of minutes. Components
of the coal particles soften and gas evolves because of de-
composition. Sticky coal particles undergoing plastic trans-
formation tend to adhere to most surfaces which they contact
such as walls or baffles in the reactor, particularly relati~ely
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cool walls or baffles. Moreover, contact with other sticky
particles while undergoing plastic transformation result
in gross particle growth through adherence of sticky particles
to one another. The ormation and growth of these agglomerates
interferes drastically with the maintenance of a fluid-bed
and any substantial growth usually makes it impossible to
maintain fluidization.
In particular, entrance ports and gas distribution
plates of equipment used in fluid-bed coal conversion pro-
cessesjbecome plugged or partially plugged. Furthermore,
even if plugging is not extensive, the sticky particles tend
to adhere to the walls of the vessel in which tha operation ;~
is conducted. Continued gross particle growth and the for-
mation of multi-particle conglomerates and bridges intereres
with smooth operation and frequently results in complete
stoppage of operation.
Agglomeration of coal particles upon heating de-
pends on operating conditions such as the heating rate,
final temperature attained, ambient gas composition, coal
type, partic:Le size and total pressure. When heated in a
hydrogen atmosphere, even non-agglomeratLng coals, such as
lignites or coals from certain sub-bituminous seams, are
susceptible to agglomeration and tend to become sticky in a
hydrogen atmosphere. Thus, agglomeration of coal particles
is accentuated in a hydrocarbonization reactor where heating
in the presence of a hydrogen-rich gas actually promotes for-
mation of a sticky surface on the coal par~icles reactedO
, ., .. , ; . - . , , . :.. .
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Moreover, in genPral, introducing any carbonaceous, com-
bustible, solid particles, even those that are normally
non-agglomerating, to a fluid-bed having an atmosphere
tending to induce agglomeration can result in agglomeration
and defluidization of the bed.
Heavy liquid materials are also fed at times to
the fluid-bed in coal conversion processes. They may be
recycled heavy tar products to be converted to lower molec-
ular weight products, light liquids and gases. Or they may
be heavy liquids from an external source added, for example,
to enrich the normal gas and/or liquid product, or as a
means of waste disposal. Feeding such liquids is known to
cause rapid loss of fluidization due to particle agglomera-
tion and plugging.
In an attempt to overcome the problems associated
with agglomeration, char as a recycle material from fluidized
bed processes has been mixed with an agglomerating type coal
feed at a ratio as high as 8 to 1. Also, tar has been ball-
milled with a great excess of adsorbent char before feeding
into the processes. However, since such procedures reduced
the unit throughput, they were wasteful of energy and there-
fore costly. Other attempts included a pretreatment step
wherein coal was oxidized and/or devolatilized superficially
in order to prevent sticklng and agglomeration of particles,
but this lowered yields of useful products and added costs.
Thus, it is highly desirable economically to avoid or at
least reduce the extent of such pretreatment or such
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char recyc le .
Summary of the Invention
It is an object of this invention to provide a
method of substantially preventing agglomeration of carbona-
ceous combustible, solid particles in a fluid~bed in coal
conversion processes. Another object is to provide improve-
ments in a hydrocarbonization process for the preparation
of fuel products. Still another object is to provide a
process whereby all types of particulate coal can be handled
in a continuous process without agglomera~ion and plugging
type problems.
Briefly, this invention relates to the discovery
that agglomeration of coal particles ln a fluidized bed may
be substantially prevented by introducing the coal particles
into a fluid-bed reaction zone at a high velocity. The
fLuid-bed is conventionally maintained by passing a fluidiz-
ing medium through finely-divided solid particles. "Intro-
duction velocity" as used throughout the specification means
the velocity of carrying gas through a device which causes
the solids or liquid velocity to approach the m~ximum theo-
retical ratio to gas velocity, i.e., 1 to 1. By a high velo-
city is meant a velocity sufficient to rapidly and uniformly
disperse fresh coal particles entering the fluid-bed at
temperature below the plastic transformation temperature
wlthin a matrix of non-agglomerating particles in the fluid-
bed. The non-agglomerating particles contained in the fluid-
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bed may include inert materials such as ash, sand recycledchar and the like which are inherently non-agglomerating.
However, preferably, the non-agglomerating particles are
hot, partially reacted coal particles and char particles that
have undergone plastic transformation and are situated w~th-
in the fluid-bed reaction zone at the reaction temperature.
Ordinarily, due to the difference of temperature between the
entering coal particles and the reaction zone, heat is trans-
ferred rapidly from the reaction zone to the entering coal
particles which then tend to undergo plastic transfonmation
and agglomerate. However, it has been fo~md that when in-
troduced in the fluid bed at a high velocity, the entering
coal particles rapidly and uniformly disperse within a
matrix of non-agglomerating particles within the fluid-bed
before undergoing plastic transformation.
Introduction of coal particles into the fluid-bed
at a high velocity as described hereinabove, promotes rapid,
turbulent mixing of the entering particles with the part-
icles circulating in the fluid-bed. This prevents their
coherence and defluidization of the bed. Instead, the
entering, sticky or potentially sticky coal particles are
rapidly distributed at a temperature below their plastic
transformation temperature and brought into int~mate assoc-
iation with non-sticky, hot particles situated within the
fluid-bed reaction zone. The entering particles donot ad-
here to these non-agglomerating hot particles which have
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passed through th.e plastic transrormation-temperature range
or are inherently non-agglomerat'Lng materials as described
above. The hot non-agglomeratlng particles or materials
at bed tempera.ture trans~er heat to the entering coa.l parti~
cles. This heat ~rans~er enables the entering coal particles
to traverse the plastic transforl~tion-temperature range
without con~acting significant numbers of other sticky coal
particles berorehand. Consequently, the ~resh coal particles
undergo plastic transformatlon wlthout a sign~ficant amount .
o~ agglomeration occuring in the fluid-bed reaction zone.
This invention is particularly a.ppllcable as an lm- :~
provement ln a hydrocarbonization process utilizing a dense
phase fluid-bed. By the term "hydrocarbonization" as employed
throughout the specification is mea.nt a pyrolysis or carbon-
ization ln a. hydrogen-rich atmosphere under such conditions
that significant reaction o~ hydrogen with coal and/or partl- -
ally reacted coal and/or volatile reactlon products of coal
occurs. By dense phase as used throughout the speclflcatlon
is meant a concentration of solids in ~luidizing gas o~ from
about 5 pounds to about 45 pounds of sollds per cublc foot o~
gas, more typically from about 15 pounds to about 40 pounds
o~ solids per cubic foot o~ gas. In a hydrocarbonizatlon
process employlng a dense phase ~luid-bed, the particles in
the bed are substantially backmixed, whlch ensures a near
uni~orm-composition of pa.rticles throughout the bed. Since
the fluid-bed is in dense phase, fresh coal partlcles
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should enter the bed at a velocity sufficient to penetrate
and spread rapidly throughout the bed.
A velocity rate useful in the method of this in~
vention may be obtained by any suitable means. For example,
an inlet means having a passageway whose cross~sectlonal
area is tapered, narrowed or necked down may be employed
to accelerate the coal particles to a high velocity. In
addition, process gas may be physically added to the
fluidized stream of fresh coal particles at a point before
the fluidized stream enters the inlet to the reactor. The
addition of process gas increases the flow ra~e o the
~luidized stream and hence the velocity of the coal particles. -
An amount of process gas suficient to achieve the desired
entrace velocity of coal particles should be used.
Since the fluidized coal particles are trans-
ported through the lines in a dense phase ~low~ a flow rate
velocity equivalent to the injection velocity in the reactor
is usually unnecessary and undesirabla due to the abrasive
characteristics of coal. A hîgh velocity flow of coal
particles ~h:roughout the lines would have required wear
plates to be installed throughout the lines to control
the otherwise rapid erosion rate of the llnes, such wear
plates being an undesirable expense. However, according
to the present invention, only a small surface area in
the immediate vicinity of the reactor, will be exposed
to abrasive wear and this part may be replaced readily
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and economically with little or no dowrLtime of the system.
For example, an inlet means comprising a material
having a wear-resistant surface may preferably be employed
in ~his invention as a means for increasing the velocity of
coal particles entering the reacti~L zone and as a means of
controlling the manner of entry. Use of such an inlet means
lengthens the wear time of the surface exposed to the high
erosion rate caused by the high velocity flow of coal parti-
cles. Suitable wear-resistant surface may be composed of
materials such as tungsten carbide, silicon carbide or other
wear-resistant materials knowTL in the art in any combination
or mixture thereof. For clarity and illustrative purposes
only, the description of this invention will be mainly
directed to the use of tungsten carbide as the wear-resistant
surface of the material that reduced erosion in the lines
although any number of other wear-resistant materials
can be used successfully according to this invention.
An inlet means such as a nozzle which comprlses a
transfer line having a reduced or constructed cross-sectional
area may be employed in the method of this invention. The
length to cross-sectional area ratio o~ the nozzle should
be sufficiently large enough so that the desired velocity
of injectiorl for the solid coal particles or non-vaporiz-
able recycle oil may be achieved. A length to cross-sect-
ional area o~ this section o transfer line of greater than
about 5 to 1 is desirable, greater than about 10 to 1 pn~rab~.
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This allows for a finite distance which the coal particles
and/or vaporizable recycle oil require for acceleration to
the velocity approaching that of the carrying gas.
According to this invention, it is preferable to
introduce a fluidized stream of coal particles into the
lower portion of a substantially vertical fluid-bed reaction
zone. More preferably, the particles are introduced into
the reaction zone through at least one inlet means in a
reactor in a vertically upward direction. l'he inlet Means
is situated substantially in the vicinity of the vertical
axis at or near the reactor bottom. The coal particles
are introduced at a velocity sufficient to mix the fresh
coal having a temperature below the plastic transformation-
- temperature rapidly with non-agglomerating particles such
as partially reacted coal and char particles in the reaction
zone at the reaction temperature thereby substantially pre-
venting agglomeration of the fluid-bed.
In the reactor, which is preerably substantially
vertical, the natural circulation of coal particles within
the fluid-bed reaction zone is a complex flow pattern. How-
ever, it may be described approximately by dividing the
reaction zone into two concentric sub-zones, an inner
sub-zone and an outer sub-zone surrounding the inner sub-
zone. In the inner sub-zone which is situated substantially
within the axially central portion of the reactor, coal
particles flow in a generally ascending path. In the
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outer sub-zone which is situated substantially near the
walls of the reactor, coal partic:les ~low in a generally
descending pa~h. Advantages of introducing the coal
particles into the fluid-bed through the bottom oE the
reactor in an essentially vertically upwards direction are
that the natural circulation of coal particles in the
fluid-bed is enhanced and that the coal particles get
at least a minimum residence time. Introduction of coal
particles into the fluid-bed through the bottom of the
reactor promotes a channeled circulation of particles
within the reaction zone along the natural circulation
path. Circulation eddies, are thus enhan~ and promote
the dispersion of the entering coal particles with a
matrix of non-agglomerating particles within the fluid-
bed reaction zone.
The fluidized coal particles should be introduced
into this inner sub-zone, the central upflow zone with-in
the reactor. The central upflow zone extends radially
from the vertical axis of the reactor to an area where
the outer sub-zone, the peripheral downflow zone begins.
It is essential that the coal particles be introduced
into the central upflow zone in order to avoid striking
the walls of the reactor or entering the p~ripheral down-
10w zone. Preferably, the coal particles are introduced
through the base or bottom of the reactor at one or more
inlets situated in the vicinity of thè point where the
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vertical axis of the reactor int:ersects the base of the
reactor.
It has been discovered that introducing a
fluidized stream of coal par-ticles into a dense phase, fluid-
bed reaction zone at a velocity of more than about 200 feet
per second in a manner described hereinabove substantially
prevents agglomeration or caking of the fluid~bed. When a
lower injection velocity, for example, about 100 feet per
second is used, agglomeration of the fluid-bed is not pre-
vented. In order to substantially prevent agglomeration ofthe fluid-bed reaction zone, coal should be introduced at a
high velocity into ~he zone in a high velocity stream, i. e.
at a velocity more than about 200 feet per second, and pre-
ferably more than about 400 feet per second in the manner
described h~reinabove. "Reaction zone" as used throughout
the specification is meant to include that area wherein
carbonaceous, combustible, solid and sometimes liquid
particles, are reacted to form char, liquid and/or vapor
fuel products in coal conversion processes such as carboni-
zation, gasification and dry hydrogenation (hydrocarboni-
zation). A zone of reaction can also be referred to by the
name of the process e.g., hydrocarbonization zone is the
reaction zone in a hydrocarbonization process.
This invention is applicable to ~he various coal
conversion processes mentioned hereinabove. For example,
a hydrocarbonization process can be improved to handle both
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agglomerating and/or non-agglomerating coals in a continuous
manner and maintain fluidization of the fluid-bed. In a
hydrocarbonization process, a dense phase flow of coal parti-
cles may be passed through a preheating zone before entering
a fluid-bed hydrocarbonization zone wherein the coal parti-
cles are rapidly heated in the presence of a hydrogen-rich,
essentially oxygen-free gas, to an elevated temperature above
about 500C where the desired reactions can occur. The im~
provement according to this invention comprises introducing
the preheated fluidized coal particles into the fluid-bed
through the bottom of a hydrocarbonization zone in an
essentially vertically upwards direction ~t a high velocity.
This rapidly brings the entering coal particles to a non-
sticky, high temperature, partially reacted state without
~heir contacting too many coal particles also traversing
the plastic transformation-temperature range. Preferably,
the preheated, particulate coal in a fluidized state is
introduced into a fluid~bed hydrocarbonization zone in a
vertically upwards direction as described hereinabove at
a velocity of more than about ~00 feet per second and more
preferably at a velocity of more than about 400 feet per
second.
Coals have been classified according to rank as
noted in the following table, Table A:
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TABLE A, Clas~ification of Coals by Rank.a
(Legend: F.C, ~ ixed carbon; V,M, 8 volatlle matter;
B,'c.u, ~ritish thermal units)
Class Group Limit8 of fixed
carbon or B.t.u., ~ .
ash free basi~
l, Meta-anthracite Dry F.C.,98% or more
(dry C ,M~, 2~, or le88)
l, Anthracite 2,Anthraci1:e Dry F,C,, 927. or more
and le3 ~ ~ch~n 98%
(dry V,M,9 8% or le~s
and more than 27.)
3. Semianthraciteb Dry F,C,, 86% or more
and less than 929/.
(dry V.M., 14% or
les~ and more ~chan
87~)
_ _ , .
1. Low-volatile Dry F,C., 78X or more
bituminou~ coal and less than 86%
(dry V,M,, 2270 or
less and more than
II, Bituminotlsd 1~%)
2, Medium-Volative Dry F.C. 9 69% or more
bituminous coal and le~s than 78
(dry V,M., 31% or
less and more than
22c/.)
3. High-volatile Dry F.C.9 le~s than
A bituminou~ 69Z (dry V,M., more
coal than 31%)
4. High volatlle MoistC B.t.u.,13,000
B-bituminou~ or more and le~s
coal than 14, oooe
5, Hlgh-volatile Moi~t B. t,u,, 11, ûO0
C bi~uminous or more and les~
~Oalr than 13, oooe
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Class Group Limit~i of fixed
carbon or B, t ,u.,
ash free basie
.. . . ..
1. Sub-bitumin,l~us Mois t B, t .u,, 11, l)OO
A eoal or mor0 ~nd les~
than 13, oOoe
20 Sub-bi~inou~ Moist B. t,u., 9, 500
B coal or more and less
th~n 11, oooe
III. Sub-
bituminous
3. Sub-bituminou6 Moist B,t.u,, 89300
C coal or more and le~s
than 9, 5ooe
...... ~
1. Lignite Moist B, t,u,, le~s
than 8, 300
IV. Ligflitic
2. Brown coal Mo~st B t u., les i
than 8 300 ::
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a - Thi~ clas~fication does not include a few coals that
that have ~nusual phy6ical and chemical propert~es
and that come within the limits of fixed carbon or
B.t,u. of the high-vola~ile b~tuminous and sub-
bituminous ranks. All of the~e coals either contain
less than 48% moisture ~nd ash free fixed carbon or
have more than 15,500 moist, ash free B,t,u.
b ~ If agglomerating, classiy in low volatile group of
the bi~umlnous claBs~
c - Moist B,t.u. refer3 to coal eontaining its natural bed
moisture but not including visible water on the ~urfaee
of the coal.
d - It is recognized that there may b~ noncaking varieties
in each group of the bituminous class,
e - Coals having Sg7. or more fi~ed carbon on the dry,
mineral-matter-free basis ~hall be classified aceording
to fixed carbon, regardle~6 of B.t,u.
f - There are three varieties of coal in the high-volatile
C bituminou~ coal group, namely, Variety 19 agglomer-
ating and non-wea~hering; Variety 2, agglomerating
and weathering; Variety 3> nonagglomerating and
non-weathering.
Source A,S,T.M. D388-38 (ref. 1). : .
15b
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As can be seen from Table A above, the preferred
coals which may be used according to the present invention
without any pretreatment step added to prevent agglomeration
comprise the lowest ranked coals, the non-agglomerating,
sub-bituminous and lignitic classes, III and IV.
Agglomerating coals, such as most bit~nlnous and
some sub-bituminous coals, are strongly agglomerating in a
hydrogen atmosphere. They can not be handled conventionally
even with a pretreatment step. These coals may now be
handled without an in~urious degree of defluidization by
the process of this invention alone or in combination with
a pretreatment step, if necessary. If a pretreatment step
is necessary, the needs for pretreatment are milder and
cost less. For example, at present even after heavy pre-
treatment, the use of a highly agglomerating coal such as
Pittsburgh Seam Coal in a hydrocarbonization process presents
the problem of agglomeration occurring in the fluid-bed.
However, it is beneficial to use the process of this in-
vention to overcome this agglomerating problem. Those
skilled in the art will recognize that any n~mber of suitable
pretreatment steps may be applied in combination with the
process of this invention for the handling of coals which
are either highly aggl~merating or highly agglomerating in a
hydrogen-containing atmosphere. These pretreatment steps
include, for example, but are not limited to, chemical pre-
treatment such as oxidation or mixing with inert solids suchas recycle char.
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The manner in which the invention is carried out
will be more fully understood from the following description
when read with reference to the accompanying drawing which
represents a semi-dlagrammatic view of an embodiment of a
system in which the process of ~his invention may be carried
out.
Figure 1 illustrates coal supply vessels 10 and 16,
a coal feeder 22, a preheater 30 and a reactor vessel
40. Lines are provided for conveying inely divided coal
through the vessels in sequence. A line 26 conveys the
coal from the pick up chamber 18 to the preheater 30.
A line 34 conveys the coal from preheater 30 into
the reactor vessel 40. A line 44 conveys devolatized coal
~termed "char") from the reaction vessel 40 for recovery as
solid product or for recycle. A line 42 is provided for
conveying liquid and vapor products from the reaction vessel
40 for further processing and/or recycle.
According to the process of this invention, the
feed coal is in particulate form, having been crushed, ground,
pulveriæed or the like to a size finer than about 8 Tyler mesh,
and preferably finer than about 20 Tyler mesh. Futhermore,
while the feed coal may contain adsorbed water, it is pref-
erably free of surface mois~ure. Coal particles meeting these
conditions are herein referred to as "fluidizable." Any such
adsorbed water will be vaporized during preheat. Moreover, any
such adsorbed water must be included as part of the inert
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carrying gas and must not be in such large quantities as to
give more carrying gas than required.
The coal supply vessels 10 and 16 each can hold a
bed of fluidizable coal particle~:, which are employed in the
process. Coal supply vessel 10 is typically a lock-hopper
at essentially atmospheric pressure. Coal supply vessel 16
is typically a lock-hopper in which fluidized coal can be
pressurized with process gas or other desired fluidization
gases.
Operation of vessels 10, 16, and 22 can be illus-
trated by describing a typical cycle. With valves 14 and 17
closed, lock-hopper 16 is filled to a predetermined depth
with coal from lock-hopper 10 through open valve 12 and line
11 at essentially atmospheric pressure. Then, with valves
12 and 17 closed, lock-hopper 16 is pressurized to a pre-
determined pressure above reaction system pressure through
open valve 14 and line 13. Valves 12 and 14 are then closed
and coal is introduced into fluidized feeder vessel 22 through
open valve 17 and line 20. The cycle about lock-hopper 16
is then repeated. A typical time for such a cycle is from
about 10 to about 30 minutes. With valve 17 closed, fluidized
coal is fed at a predetermined rate through line 26 to the
downstream-process units. Other variations of the feeding
cycle to the fluidized feeder are possible, of course, but
they are not illustrated herein since they do not form the
inventive steps of this process.
In fluidized feeder 22, a fluidizing gas passes
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through line 24 at a low velocity sufficient to entrain the
fluidizable coal and convey it in dense phase flow through
line 26 and into the bottom of coal preheater 30, or directly
to line 34 if no preheat is required. Alternately, additional
gas could be added to the line conveying the coal in a dense
phase flow through line 26 to assist in the conveyance. Any
non-oxidizing gas can be used as the fluidizing gas, e.g.
fuel gas, nitrogen, hydrogen, steam and the like. However,
it is preferable, in general, to use reaction process gas
or recycle product gas.
Coal preheater 30 is a means to rapidly preheat,
when desirable, the finely divided coal particles, under
fluidized conditions, to a temperature below the minimum
temperature for softening or significant reaction rangel
in the substantial absence of oxygen. The maximum allowable
temperature of heating is in the range of from about 325C
to about 400~C. The stream of gas-fluidized coal in dense
phase is heated upon passing rapidly through the heater
having a very favorable ratio of heating surface to
internal volume. The coal is heated in the heater 30
- to the desired temperature by any convenient means of heat
exchange, e.g., by means of radiant heat or a hot flue gas
such as depicted in Figure 1 as entering the bottom of heater
30 through line 28 and exiting at the top of the heater
30 through line 32.
Preheated fluidized coal particles exit the preheater
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30 through line 34 and enter at or near the bottom of
the reactor vessel 40 substantially near the center of the
bottom. According to this invention, the coal particles
are introduced into the fluid-bed reaction zone through
the reactor bo~om at a high velocity. This high velocity
may be achieved by acceLerating the fluidized stream of
coal particles to the desired velocity along a constricted
path of confined cross-section. A nozzle, narrow inlet
port, tapered channel or any inlet means which narrows,
constricts or necks down the cross-sectional area of the
passageway to the inlet where the fluidized coal particles
enter the reactor may be used to accelerate the fluidized
stream of particles to the desired velocity. The stream
of preheated, fluidizable coal particles is introduced -
into the central upflow zone of the fluid-bed within the
reaction vessel at the high velocity in an essentially
vertically upwards direction, preferably through the bottom
of the reaction vessel.
Recycle oil may also be fed into reactor 40 through
line 36. Injection of the recycle is also preerably at a
stream velocity o~ about 200 feet per second or greater, and
more preferably about 400 feet per second or greater into
the central upflow zone of the fluid-bed of the reactor
through the bottom of the reactor vessel in an essentially
vertically upwards direction. Like the entering coal
particles, the recycle oil stream follows a substantially
ascending path about a substantially axially central portion
of the reaction vessel. In the injection of the recycle oil
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and fluidizable coal particles, it is essential that they be
introduced into the reactor vessel in such a way that they
do not immediately and directly strike the walls of the
reactor vessel, a result which could lead to unnecessary
and undesirable agglomeration.
Only one inlet each for entry of the preheated
coal particles and the recycle oil is shown in Figure 1.
These inlets may also represent a multiplicity of inlets
for ease of operation of this process. A multiplicity of
inlets may be desirable, for example, where the reactor is
large, or when separate recycle streams of oil are being
injected into the reactor. The entry points for the coal
particles and/or recycle oil are preferably situated near
the point where the vertical axis intersects the reactor
bottom. Each stream of coal particles and/or recycle oil
is preferably introduced at a high velocity at each inlet
in an essentially vertically upwards direction, the inlets
situated in or near the reactor bottom substantially near
the point where the vertical axis intersects the reactor
bottom. In this manner, the separate streams of entering
carbonaceous materials are kept separate and apart until
rapidly mixed in the fluid-bed wlth partially reacted coal
and char particles.
The entering carbonaceous materials are reacted
with a sui~able reagent in the reaction zone at a temperature
above about 500C.
Char from reactor vessel 40 is cont~nuously removed
.. . .
,
g490
51.
through line 44.
Liquid and vapor products are removed from the
reactor vessel 40 through line 42. Fluidization gas is fed
into the reactor vessel 40 through line 38, the type gas
depending on the type process involved. For example, steam
or steam and oxygen are fed into a gasifier in a gasification
process; a non-reacting gas is fed into a carbonlz~r in a
carbonization process; and a hydrogen-containing, sub-
stantially oxygen-free gas is fed into a hydrocarbonizer in
a hydrocarbonization process.
The following examples are illustrative of the
concept of this invention, demonstrating the method of pre-
venting agglomeration of coal in fluidized bed processes
via the high velocity injection of coal particles into a
reaction zone.
EXAMPLE I
The apparatus employed, shown schematically in
the drawings, comprised two coal feed lock-hoppers (10, 16)
connected in parallel to a fluidized feeder 22, a preheater
30 and reactor 40. The entire coal conveying line was
constructed of 3/8-inch I. D. by 5/8-inch 0. D. tubing.
The two coal feed lock-hoppers (10, 16) that fed the flu-
idized feeder alternately each had a 7-inch I. D. and height
of 8 feet. The fluidized feeder 22 had a 24-inch I. D. and
height of 20 feet. The preheater 30, a lead bath heated
by "surface com~ustion" burners had a 24-inch I. D. and
height of 12 feet. The reactor 40 had an ll-inch I. D.
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. .
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5i~
fluid-bed, a bed depth of 17-1/2 feet an outside cross-
sectional area of 0.66 sq. ft.
The average velocity through the dense phase
coal feed l-ine was not particularly high, the maxlmum
velocity being approximately 40 feet per second at the
inlet to the reactor and only lS feet per second at the
outlet of the coal feeder, erosion of the pipe at thess
velocities still remaining at an acceptable level. Attempts
to feed the coal into the reactor at velocities of approx-
imately 100 feet per second resulted in agglomeration and
coking-up of the fluid-bed. A 15/32-inch diameter tungsten-
carbide nozzle was used to increase the rate at which the
fluidized coal-hydrogen stream was introduced into the
reactor to 200 feet per second and provide an erosion
resistance surface.
In operation, the reactor was filled wi~h coal and
slowly heated up toward the target conditions and gas flows
and pressures were established. Hydrogen was employed as
the gas phase. When the target co~ditions were established
the coal feed was begun. On the termination of the run the
reactor was opened up. No large agglomerates or coke parti-
cles were found. Operating condition~ during the hydro-
carbonization are shown in Table I below:
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l ~ 6~S~L 9490
, C~
; ,~ ~r ~ r~
~ O O U`l O ~ ~ O ~J-
I`~ Ir1 0 0 C~
.~
bO ~ 0 `
~ ~o o~ ~ ~ b
~ ~0~ ~ ~ o ~ W O ~ ¦ ¦ 4C~ ~
C ~ ~ ~ y ~ ~
~i O ~ r
1~ r ~ ~ ~
O O u~ o ~ In o oO .
~ ~ o O ~ ~ cO~ ~ ~u a
. __ , c, O ~d '
h ,3 c.l ~ h ~q O r
:, ~ ~1 a) a) ~ r-l
O 1~ ~ r ~ ,~ ~ :
r~
o ~ o W ~-1 .
h ~-1 N tl~ r-~
~ U U ~ ~ ~ ~
o a l¦ I
_ 2~
9~90
-
TABLE II-LAKE DE SMET COAL, WYOMING,
SUBBITUMINOUS C (AN
Moisture and Ash Free BasisWeight Percent
-
C 72.0
H 5.3
N 1.3
S 1.0
0 20.4
Ash 11.9 (dry basis)
Water 30 (as received)
EXAMPLE_II
Two additional runs were conducted employing appa-
ratus and procedures similar to those employed in Example I,
except that oil, the higher boiling fractions (all product
boiling above 235~C) of the liquid product, was recycled to
the reactor. These additional runs were conducted to de-
termine whether a high velocity injection of heavy oil could
be fed to the reactor without agglomerating the fluid-bed.
The oil recycle equipment added to the pilot plant apparatus
comprised a storage tank, to hold the recycle oil, an oil
preheater to preheat the oil prior to injection into the
reactor.
The main hydrogen stream to the reactor was split
into two roughly equal streams, each of which was preheated
to 300C to 350C. The heavy recycle oil was pumped into
one of these hydrogen streams and injected into the reactor
through a l/4-inch diameter tungsten carbide nozzle at ~ ~re~n
velocity of approximately 400 ~eet per second~ The no~zle9
which pointed vertically up the reactor; was located in the
center of the reactor bottom 5 ~eet above the coal inlet. The
other hydrogen ~tream wa~ mixed with preheated coal, and intro-
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duced into the bottom of the reactor through a 15/32-inch
diameter tungsten-carbide nozzle at approximately 160 feet
per second in a vertically upwards direction. The data for
these runs are summarlzed below ln Table III.
TABLE XII
.
Run 1 _ _ _
Coal Feed Rate 1000 lb./hr. 1000 lb/hr.
Coal Feeder Pressure 1100 psig. 1100 psig.
Reactor Pressure 500 psig. 500 psig.
Reactor Temperature 55o C 580 C
Reactor Fluidization
Velocity 3.5 ft./sec. 0.5 ft./sec.
Length of Run 5 hrs. 5 hrs.
Recycle Oil Feed Rate100 lb./hr 240 lb./hr.
Coal - H , Inlet Velocity160 ft./sec.160 ft./æec.
Oil - H2, Inlet Velocity420 ft./sec.420 ft./sec.
.
No problems were encountered in ma~ing these runs.
There was no evidence of agglomeration in the fluld-bed, even
when in~ecting oil at the 240 lb.Jhr. rate.
EXAMPL~ III '
-
The bench-scale apparatus employed in this example
comprised a pulverized solid hopper having a solid's capac-
ity of 4.5 liters and constructed from a 3-inch diameter by
4-foot high schedule 80 carbon steel pipe; a reactor was
made of l-inch I . D. by 9-inch high stainless steel tube
havlng a l/4-inch wall thic~ness and an expanded head 4-inches
high and 2 inches I.D.; sollds over~low line constructed of
1j2-inch Schedule 40 pipe; a vapor line constructed from
3/8-inch 0. D. stainless steel tubing; and a solids feeder.
_26-
... .
~ s~
Two liquid feed pumps, Lapp Micro~low Pulsafeeders were used,
one to feed the liquid belng invest-lgated and the other to
feed water for steam generation. Electrically heated liquid
and water vaporizers and superheaters constructed of l/4-inch
0. D. stainless steel tubing were installed between the feed
pumps and the feed in~ection nozzle to the reactor. Thermo-
couples located 3,6,8 and 11-inches ~rom ~he bottom of the
reactor were installed in a l/4-inch O.S. thermowell placed
axially in the center of the reactor. The lower three thermo-
well were in the fluidized bed while the upper thermocouple
was in the vapor space above the bed.
In operation, tars boilin~ about 235 C obtained
from hydrocarbonization of La~e de Smet Coal were employed
as the feedstoc~ to the reaction zone for conversion to oils
boiling below 230 C. The tars were distilled from the whole
liquid product obtained from the hydrocarbonization into
various distillation fractions and a blend o~ these di~-
tillation fractions used in this example had a nominal
atmospheric temperature range for 75~ of the tar between
235~C and 460 C. The remaining 25~ boiled above 460 C.
The solids feed hopper was filled with LaKe de
Smet hydrocarbonization char as descrlbed hereinabove. The
water and tar feed reservoirs were filled and heated to
operating temperature. During the heat up period, a pre-
determined flow of hydrogen passed through the empty reactor.
~s soon as operating conditions were approached, the char
feed and water feed (superheated steam by the time it
entered the reactor through the in~ection ori~ice) were
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. . , : , ,
~6~1
started. The three thermocouples located in the fluidized
bed, at the levels lndicated hereinabove, served as an
indication of bed behavlor. Attem~ to feed this tar
stream at velocities o~ 100, 200 and 300 ~eet per second
resulted in rapid agglomeration o~ the ~luidized react3r
bed, A 26-gauge hypodermic needle used was to achieve a
400 feet per second in~ection velocity of the whole tar
feed. Using this inlet velocity ~r the whole feed, co~ing
up of the fluldized bedwithin the reactor was prevented ~nder
the ~ollowing operatlng conditions contained in Table IV.
TABLE IV - OPERATING CONDITIONS -
LAKE DE SMET COAL
. .~....
Pressure 150 psig
Hydrogen Partial Pressure 115 psig.
Residence time o~ Vapors in Char Bed
Based on Superficlal Linear Velocity 1.33 sec.
Char Feed 250 g/hr.
Oil Feed Rate 2 ml/min.
Water (as steam) Feed 3 ml/min.
Hydrogen Flow to ~eactor 35 SCFH
Moles Hydrogen/Moles 011 ~5~1
Temperature 650 C
Super~lcial Linear Velocity of
Hydrogen 0.5 ft./sec.
Time of Run 5 hrs.
Fluidizing Gas Hydrogen
:, - - ----
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9490
EXAMPLE IV
100 pounds per hour of Pi~tsburgh No. 8 seam coal,
-20 mesh, are introduced into a low temperature, fluid-bed
reactor for pyrolysis at a reactor temperature of 540~C to
obtain liquid products, gaseous fuel and dry char. Pittsburgh
No. 8 seam coal is a highly swelling, agglomerating, high
volatile A bituminous coal. Nominal residence time of the
coal and the product char in the reactor bed is 15 minutes.
When the coal is introduced into the reactor bed with re-
cycled product gas at a coal and gas injection velocity of
20 feet per second, agglomeration of the reactor bed begins
immediately. Within 30 minutes, the bed is highly agglomerated
so that no fluidization occurs and no further coal can be
injected as a practical matter.
However, when fresh coal is introduced into thefluid-bed of the reactor at injection velocities of 200, 300
and 400 eet per second, respectively, a fluid-bed at a
reaction temperature between about 500C and about 700C is
maintained without substantial agglomeration. The fresh
entering coal rapidly mixes with the partially carbonized
coal (char) circulating in the bed, so that as the fresh coal
particles undergo plastic transformation and become sticky,
the fresh coal particles primarily see particles which have
already undergone plastic ~ransformation and are now non-
sticky. Carbonization products, gases, tars and other liquids,
water and char are continuously withdrawn from the carbonization
reactor.
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9490
EXAMPLE V
In an agglomerating ash gasifier of the type
described in U. S. Patent 3,171,369, 1000 pounds per hour
of fresh Pittsburgh No. 8 seam coal, -60 mesh, is gasified
at a tempera~ure between about ~16C and a~out 1000 C with
steam. Heat is provided by circulation to the gasifier of
about 12,000 pounds per hour of agglomerated ash particles
from a char fired, fluid-bed combustor. When the fresh
coal is injected into the fluid-bed of ash and partially
reacted coal, at a velocity of 20 feet per second with steam,
partial agglomeration occurs. Large aggregates of char are
formed which cannot be separated from the ash agglomerates
and poor fluidization and soon poor thermal efficiency results.
It is essential to the operation of the process that the coal,
as it carbonizes and gasifies, remains free-flowing and finely-
divided.
When the velocity of the injected Pittsburgh No. 8
coal and steam is increased to 400 feet per second, dispersion
within the fluid-bed is excellent. No significant agglom-
eration occurs and separation of the fine char formed and
~he larger denser particles of agglomerated ash is readily
accomplished. The introduction of the fresh coal into the
fluidized, generally descending bed of hot agglomerated ash,
at a velocity of 400 feet per second, occurs at a point near
the bottom of the bed, but somewhat above the bottom to avoid
carry-down of coal or char by the cycling ash. Injection is
in a generally vertical and upward direction. This promotes
.
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.,, . ", ,, . , . , . . . ~ . . .
i . .
. ' ' ,.. :' ., . .. :'': ' : . ~ ', .. '
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9490
great turbulence of ash~ coal and char near ~he points of
introduction, which disperses the coal throughout the bed
and effectively pre~ents agglomeration.
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