Note: Descriptions are shown in the official language in which they were submitted.
s~L~s 0
BACKGROUND OF THE INVENTION
_
Field of ~he Invention
This invention relates to a method of avoiding
excessive agglomeration of carbonaceous solid particles
so as to prevent defluidization in a fluid-bed reaction
zone. More particularly, it is an improved method for
injecting fresh carbonaceous particles into a fluid-bed
hydrocarbonization, gasification or carbonization reaction
zone.
Description of the Prior Art
Increasing energy needs have focused attention 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 feedstock. Processes such as carbonization,
gasification, hydrocarbonization and hydrogasification,
wherein synthetic fuel products have been prepared by
introducing a fluidized stream of finely-divided coal or
other solid carbonaceous particles into a fluid-bed
reaction zone and reacting the said particles at
elevated temperatures in the presence of air, steam,
hydrogen or inert gases are well known. A major
operating difficulty in such processes has been the
tendency of coal or other carbonaceous particles,
especially intensified in a hydrogen-rich stmosphere, to
agglomerate at the elevated temperature 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
, ", - '
~ 5 5 ~ O-i,
and non-agglomerating coals become sticky when heated in such
an atmosphere. Coal particles begin to become sticky at
temperatures in the range of from about 280C, commonly from
about 350C to about 500C, depending on the specific
properties of the coal, the atmosphere and the rate of
heating. Such stickiness is due to a tarry or plastic-like
material forming at or near the surface o~ each coal particle,
by a partial melting or decomposition process. On further
heating over a period of time, the tarry or plastic-like
material is further ~ransformed into volatile products and
a substantially porous, solid material referred to as a
"char." The length of this time period depends upon the
actual temperature of heating an~ is shorter with an in-
crease in temperature. The term "plastic transformation"
as used herein refers to such tendency of the surfaces
of coal or other carbonaceous particles being heated,
particularly when heated in a hydrogen atmosphere, to
develop stickiness and transform into substantially solid
char, non-sticky surfaces. "Plastic transformation" is
undergone by both normally agglomerating coals and coals
which may develop a sticky surface only in a hydrogen-rich
atmosphere.
Agglomerating or caking coals partially soften and
become sticky when heated to temperatures between about 280C,
commonly from about 350C, to about 500C. The duration
of stickiness depends on the temperature of the coal, being
on the order of minutes at the lower end of said range and
being exponentially shorter, i.e. down to seconds, at the
upper limits of said range. Components of the coal par-
ticles soften and gas evolves because of decomposition.
Sticky coal particles undergoing plastic transformation
tend to adhere to most surfaces which they contact such as
walls or bafles in the reactor, particularly relatively cool
55'~3 9~ o~
walls or baffles. Moreover, contact with other sticky
particles while unde~going plastic transformation results
in gross particle growth through adherence of sticky
particles to one another. The formation and growth of
these agglomerates interferes drastically with the
maintenance of a fluid-bed and excessive growth can make it
impossible to maintain fluidization.
In particular, entrance ports and gas distribution
plates of equipment used in fluid-bed coal conversion
processes become plugged or partially plugged Furthermore,
e~en if plugging is not extensive, the sticky particles
tend to adhere to the walls of the reaction vessel, with
continued gross particle gro~th and the formation of
multi-particle conglomerates and bridges interfering with
smooth operation and frequently resulting in complete
stoppage of operation as a result of defluidization of
the bed.
Agglomeration of coal particles upon heating depends
on operating conditions such as the heating rate, final
temperature attained, ambient gas composition, coal type,
particle size and total pressure. Even non-agglomerating
coals, such as lignites or coals from cer~ain sub-bituminous
seams, are susceptible to agglomeration and tend to
become sticky when heated 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 formation of a
sticky surface on the coal particles reacted.
Introducing any carbonaceous, combustible, solid
particles, even those normally non-agglomerating, to a
~3
S5~'9 ,~ff/,-~
fluid-bed ~aving an atmosphere tending to induce
agglomeration can, moreover, 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
molecular weight products, light liquids and gases. Or
they may be heavy liquids added from an external source
to, for example, 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 excessive particle agglomeration 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
absorbent char before feeding into a fluid-bed reaction
zone Such procedures reduce the unit throughput,
are wasteful of energy and are, therefore, costly.
Other attempts have included a pretreatment step wherein
coal is oxidized and/or devolatilized superficially in
order to prevent stic~ing and agglomeration of par~icles,
but this lowers the yield of useful products and adds to
the overall cost of the operation. Thus, it is highly
desirable economically to avoid or at least reduce the
extent to which such oxidation pretreatment or such
char recycle is employed.
An alternate approach is that suggested by
Knudsen et al, US 3,927,996, in which the fines carried
1 1 ~ S 5'~9 ~ G'-~
overhead by gas from a fluid-bed are monitored and the
injection velocity of fresh feed material is regulated
in response to changes in the fines content of the gas to
produce controlled attrition of agglomerated particles in
the fluid-bed. In this approach, a caking coal or other
similar carbonaceous solid is introduced into a fluidized
bed containing char particles maintained at a temperature
in excess o~ the coal resolidification point by entraining
coal particles in a gas stream preheated to a temperature
in excess of about 300F, i.e. about 150C, but below the
initial softening point of the coal, For the gasification
of bituminous coals, preheat temperatures up to about
550F, i.e. about 285C, are said to be preferred. A
fluid-cooled nozzle 16 is employed for feeding the stream
of carrier gas and entrained coal particles into the
gasifier zone. The injection velocity is regulated
between superficial gas velocities as low as 15 feet/
second and as high as 1,000 feet/second in response to
variations in the fines content of the overhead gas.
Such a system necessarily requires continual processing
adjustments that are not desirable in continuous,
commercial scale operations. In addition, the
intermittent high injection velocities of the fresh coal
introduced into the fluid-bed under the indicated
conditions would generally be considered as having a /
potential for injection nozzle erosion that, if severe,
could lead to a need for premature shutdown for nozzle
replacement, adversely affecting the overall effective-
ness of the coal conversion operation being carried
out in the fluid-bed reaction zone.
~S5~9 ~ a-~
A need thus exists in the art for improved methods ~or
treating agglomerating coal or other solid carbonaceous
partlcles in fluid-bed reaction zones. This need resides
with respect to the effective injection of fresh particles
of such coal or other carbonaceous materials under
conveniently controlable conditions capable of avoiding
excessive agglomeration of feed particles and thus
preventing defluidization of the bed. Such improved
methods would desirably avoid the necessity for
pretreatment oxidation of the feed particles and/or their
admixture with recycle char particles prior to being
introduced into the fluid-bed reaction zone. The
improvements required for technically and economically
feasible coal injection operations must not, on the other
hand, in~roduce peripheral processing disadvantages, such
as undue injection nozzle wear, that would adversely
affect the overall coal or other solid carbonaceous
particle conversion operation.
It is an object of the invention, therefore, to
provide a method of preventing excessive agglomeration
of carbonaceous feed material in fluid-bed conversion
operations.
It is another object of the invention to provide a
method of avoiding defluidization in fluid-bed reaction
zones employed in coal or other solid carbonaceous con-
version operations.
It is another object of the invention to provide
a method for employing caking coals on a continuous
basis in a continuous fluid-bed reaction zone wi~hout
defluidization and/or undue equipment plugging problems.
1 1 ~ 5 5~ G~
It is a further object of the invention to ~rovide
a method ~or avoiding excessive feed particle agglomeration
while, at the same time, avoiding undue injection nozzle
erosion.
It is a further object of the invention to provide
improvements in the hydrocarbonization process for the
preparation of fuel products from coal.
With these and other objects in mind, the invention
is hereinafter described in detail, the novel features
thereof being particularly pointed out in the appended
claims.
Summary of the Invention
Fresh coal or other solid carbonaceous particles are
preheated to a temperature within the plastic transfor-
mation temperature range of the particles and are injected
rapidly and directly into a fluid-bed of non-agglomerating
particles at an injection velocity in excess of about
200 ft/sec. Nozzle erosion is thereby minimized without,
at the same time, causing undue agglomeration of the
fresh feed particles.
Brief Description of the Drawings
The invention is hereinafter described in detail
with reference to the accompanying single figure drawing
constituting a schematic diagram illustrating particular
embodiments of the fluid-bed coal conversion system in
which the process of the invention is employed to prevent
defluidization due to excessive agglomeration of the solid
carbonaceous feed material.
Detailed Description of the Invention
The objects of the invention are accomplished by
55~9 77'~
injecting solid carbonaceous feed particLes to a
fluid-bed reaction zone at high injection velocities and
at preheat temperatures within the plastic transformation
range of the particles. Upon being preheated to said
range, the particles are thus rapidly and directly injected
into the reaction zone containing a fluidized bed of
non-agglomerating particles. ~s described above, the
particles form a tarry or plastic-like material at or near
the surface of the individual particles upon being heated
to a temperature within their plastic transfor~ation
temperature range Particles are not preheated to said
range in conventional operations because the stickiness
resulting from such formation of a plastic-like material
causes undesired agglomeration and the possibili~y
of plugging the en~rance ports and gas distribution plates
of the equipment, adherence of the sticky particles to the
walls of the reaction vessel with the formation of
multi-particle conglomerates and bridges interfering with
the operation of the bed, and eventual defluidization or
bed failure as a result of excessive agglomeration.
It has now been found, surprisingly and contrary to
the conventional wisdom of the art, that feed particles
may be preheated to a temperature within the plastic
transformation temperature range and, at said preheat
temperature, rapidly and directly injected into the fluid-
bed of non-agglomerating particles at a high injection
velocity without excessive agglomeration and resultant
defluidization. The lubricity of the thus preheated
fresh feed particles, in addition, has been found to
minimize nozzle erosion that might be expected at high
_g_
SS4~3 7~f~-~
injection velocities. The hi~h velocity injection of the
preheated particles into the reaction zone achieves the
desired rapid and uniform dispersion of the feed particles
within the fluid-bed of non-agglomerating particles before
the stickiness of the particles can result in undue
agglomeration. The lubricity of the particles nevertheless
results from the formation of said plastic-like material at
the particle surface, thereby permitting the high speed
iniection of the fresh carbonaceous feed material in a
carrier gas with little or no erosion of the injection
nozzle. As the injection method of the invention obviates
the need for admixture of the fresh feed with recycle char
to avoid agglomeration, fresh feed injection without
recycle char avoids the abrasiveness of the char at high
injection velocities and avoids the nozzle erosion that
results when a fresh feed-recycle char mixture is
injected into ~he fluid-bed. The invention, therefore,
achieves the highly desirable result of avoiding
excessive agglomeration leading to defluidization of the
bed while, at the same time, minimizing nozzle erosion
that would otherwise cause a premature shutdown of the
flu-d-bed operations for nozzle replacement purposes.
The invention can be employed in the practice of any
known fluid-bed coal conversion process in which
defluidization and bed failure due to excessive
agglomeration may seriously interfere with, or even
prevent, effective utilization of such technology on a
continuous, commercially feasible basis. One such
process is the hydrocarbonization process in which the
gaseous reagent for fluidizing the bed and for reaction
-10- -
ll~S5~9
with fresh solid carbonaceous particles at reaction
temperatures of from about 450C to about ~50C, pre-
ferably from about 500C to about 600C, is a hydrogen~
rich, oxygen-free gas, Another such process is the
carbonization process in which the reagent comprises
carbonization product gases and vapors and essentially
inert carrier gas at reaction temperatures of from about
450C to about 700C. A third such process is the
gasification process in which solid carbonaceous particles
are reacted with steam to form synthesis gas at
temperatures generally from about 815C to about 1,100C.
It will be appreciated by those s~illed in the art that
the invention may advantageously be employed in the
practice of other such known processes or those subsequently
developed so as to avoid excessive agglomeration upon the
feeding of fresh carbonaceous solids to a fluid-bed reaction
zone.
The fluid-bed reaction zone is conventionally
maintained by passing a fluidizing medium through finely-
divided solid particles. "Introduction velocity'l as usedthroughout the specification means the superficial velocity
of carrying gas. By a high velocity is meant a velocity
sufficient to rapidly and uniformly disperse fresh coal
particles entering the fluid-bed at a temperature
below the plastic transformation temperature within a
m trix of non-agglomerating particles in the flùid-bed.
The non-agglomerating particles contained-in the
fluid-bed may include inert materials such as
-11-
~ff
~5S~
ash, sand, recycled char and the Like which are inherently
non-agglomerating. The non-agglomerating particles are,
however, preferably hot, partially reacted coal particles
and char particles that have undergone plastic
transformation and are situated within the fluid-bed
reaction zone at the reaction temperature, e.g generally
above about 450qC. Due to the difference of temperature
between the en~ering coal particles and the reaction zone,
heat is ordinarily transferred rapidly from the reaction
zone to the entering coal particles, accelerating the
plastic transfor~ation process increasing the agglomerating
tendency of the feed coal for a brief period of time
It has been found that when the preheated coal is rapidly
introduced in the fluid-bed at a high velocity, however,
the entering coal particles rapidly and uniformly disperse
within a matrix of non-agglomerating particles within the
fluid-bed without excessive particle agglomeration.
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 particles circulating in the fluid-bed. This prevents
their coherence and defluidization of the bed by imparting
sufficient mechanical energy to the reaction zone to break
the weaker bonds of thecoarser agglomerates, thereby
limiting the extent of agglomeration and substantially
avoiding defluidization resulting from exce~sive
- agglomeration. The entering, sticky or potentially
sticky coal particles are rapidly distributed with and
brought into intimate association with non-sticky, hot
particles si~uated within the fluid-bed reaction zone.
-12-
~3
5S~9 '~ c-~
The feed particles, in accordance with the invention, are
preheated to a temperature within their plastic transformation
range prior to injection into the fluid-bed reaction zone.
The hot non-plastic particles or materials at bed temperature
transfer heat to the entering feed coal particles. The molten
feed coal particles form partial bonds with these dry, hot
particles that have previously passed through the plastic
transformation temperature range as well as bonding with one
another. The extent of average bed particle growth is
determined by a dynamic equilibrium in which particle growth
is balanced by particle withdrawal and deagglomeration. Coal-
to-coal bonds are relatively strong whereas coal-to-char bonds
are relatively weak, depending on the extent of solidificat~on
which occurs prior to contact of the particles. Two freshly
molten coal particles tend to fuse into an indivisible agg-
lomerate, whereas fresh coal would be linked to a char
particle by a weaker bond.
With high velocity, high energy injection, rapid
dispersion of the entering coal particles occurs, and the
fresh particles thus traverse the plastic transformation
temperature range with a minimum number of sticky particles
contacting one another and at an overall mechanical or kinetic
energy input level sufficient to break up the weaker bonds
of the coarser agglomerated particles. Consequently,
agglomerating or caking coals can be injected into the fluid-
bed reaction zone and devolatilized without defluidization
occurring as a result of e~cessive particle agglomeration.
This invention is particularly applicable as an
improvement in a hydrocarbonization process utilizing a
dense phase fluid-bed. 3y the term "hydrocarbonization" as
~ 5 ~ 9
employed throughout the specification is meant a pyrolysis
or carbonization in a ~ydrogen-rich atmosphere under such
conditions that significant reaction of hydrogen with coal
and/or partially reacted coal and/or volatile reaction
products of coal occurs. By dense phase as used
throughout the specification is meant a concentration
of solids in fluidizing gas of from about 5 pounds to
about 45 pounds of solids per cubic foot of gas. In a
hydrocarbonization process employing a dense phase fluid-bed,
the particles in the bed are substantially backmixed, which
ensures a near uniform-composition of particles throughout
the bed. Since the fluid-bed is in dense phase, fresh coal
particles should enter the bed at a velocity sufficient to
penetrate and spread rapidly throughout the bed.
The overall mechanical or kinetic energy level necessary
and sufficient to prevent exce~sive particle agglomeration
will vary for each particular coal or carbonaceous feed
material. The minimum energy required for any particular
coal can readily be determined by incrementally decreasing
the high injection velocity to the point of bed failure. For
such purposes, the bed velocity will conveniently be
maintained at a constant rate, with shroud gas being passed
through the shroud passages of the injection nozzle at
a conventional velocity, e.g. about 35-100 ft./sec., to keep the
nozzle-tip clean and for temperature control purposes.
The particular high velocity injection-hot coal conditions
employed in the practice of the invention for any such
coal may be varied, as will be appreciated by those skilled
in the art, depending on the overall energy input of the
injection gas, the shroud gas, the bed fluidizing-reagent
gas and any attrition jets employed. It will be further
-13-a-
~3
~55~9 C/ ~ o -~
appreciated that the energy-to-coal ratio and the gas-to-
coal ratio of the overall plant design can be adjusted by
a variation of such energy and gas input factors to achieve
efficient overall technical and economic perfor~ance. The
invention, at the particular high velocity coal injection
employed, minimizes nozzle erosion by the preheating of the
fresh feed to a temperature within its plastic transformation
range without, at the same time, causing undue agglomeration
of the fresh feed particles.
A velocity rate useful in the method of this invention
may be obtained by any suitable means. For example, an
inlet nozzle means having a passageway whose cross-sectional
area is tapered, narrowed or necked do~n may be employed
to accelerate the coal particles to a high velocity. In
addition, process gas may be physically added to the
fluidized coal stream as it enters the inlet to the reactor.
The addition of process gas increases the flow rate of the
fluldized stream and hence the velocity of the coal particles.
An amount of process gas sufficient to achieve the desired
entrance veloci~y of coal particles should be used.
Since the fluidized coal particles are transported
through the lines in a dense phase flow, a flow or
transport rate velocity equivalent to the injection
velocity in the reactor is usually unnecessary and
undesirable due to the abrasive characteristics of coal.
A high velocity flow of coal particles throughout the
lines would have required wear plates to be installed
throughout the lines to control the otherwise rapid
erosion rate of the lines, such ~ear 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
-14-
~55~9
wear and this part may be replaced readily and
economically w$th little or no downtime of the system.
For example, an inlet means comprising a material
having a wear-resistant surface may preferably be employed
in this invention as a means for increasing the velocity
of coal particles entering the reaction 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
particles. Suitable wear-resistant surface may be
composed of materials such as tungsten carbide, silicon
carbide or other wear-resistant materials known 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 use of tungsten
carbide as the wPar-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 comprises 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 of
the nozzle should be sufficiently large enough so tha~
the desired velocity of injection for the solid coal
particles or non-vaporizable recycle oil may be
achieved, A length to cross-sectional area of this
section of transfer line of greater than about 5 to 1
is desirable, greater than about 10 to 1 preferable.
This allows for a finite distance which the coal
particles and/or vaporizable recycle oil require for
-15-
3Z~
13L~55'~9
acceleration to the velocity approaching that of the
carrying gas. The feed particles may be introduced into
the reaction zone in any convenient clirection, i.e.
upward, downward, sideways or otherwise. For example,
~he ~eed particles may be introduced into the reaction zone
from the side thereof in a substantially horizontal,
sideward direction. The feed may, furthermore, be
intzoduced into the reaction zone through two or more
injection points or nozzles positioned vertically along
the side of the reaction zone, including embodiments in
which the par~icles are introduced into the reaction zone
through injection points located in essentially opposed
positions on the wall of the reaction zone. In certain
embodiments, a multiplicity of injection points may be
employed. It may lso be desirable to withdraw~particles
from the bottom of the reaction zone.
In particular embodiments of this invention, it
~s feasible to introduce a fluidized stream of coal feed
particles into the lower portion of a substantially
vertical fluid-bed reaction zone. More particularly, the
feed particles are introduced into the reaction zone through
at least one inlet means in a reactor in a vertically
upward direction. The inlet means is situated substantially
in the vicinity of the vertical axis at or near the reactor
borrom. The coal particles are introduced at a velocity
sufficient to mix the fresh coal, in some embodiments having
a preheat 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 substan-
tially preventing agglomeration of the fluid-bed.
-16-
~1~5~
In a vertical reactor, the natural circulation of
coal particles within the fluid-bed reaction zone is a
complex flow pattern. However, 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 outer sub-zone
which is situated substantially near the walls of the
reactor, coal particles flow in a generally descending path.
Advantages of introducing the co~l particles into the fluid-
bed through the bottom of the reactor in an essentially
vertically upwards direction are that the natural circul-
ation of coal particles in the fluid-bed is enhanced and
that the coal particles get at least a minimum residence
time. Introduction o_ coal particles into the fluid-bed
through the bottom of the reactor promotes a ch,a,nneled
circulation of particles within the reaction zone along
the natural circulation path. Circulation eddies, are thus
enhanced 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 within
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 æone begins.
It is essential that the coal particles be introduced into
the central upflow zone in order ~o avoid stri~ing the
-17-
1 ~ ~ 5 5 ~
walls of the reactor or entering the peripheral down-
flow zone. The coal particles may be introduced through
the base or bottom of the reactor at one or more inlets
situated in the vicinity of the point where the vertical
axis of the reactor intersects the base of the reactor.
To minimize injection nozzle erosion without,
at the same time, causing excessive particle agglomeration,
the coal or other carbonaceous feed particles are preheated
to a temperature wiLhin the plastic transformation tem-
perature range, which varies for diferent feed materials
but is generally in the range of from about 280C
to 400C, commonly in excess of about 325C, e.g. from abGut
340C to about 375C. The reaction temperature within the
fluid-bed reaction zone is generally maintained above about
450C for known coal conversion processes with such temper-
atures being generally from about 500C to about 750C,
commonly from 500C to about 600C in hydrocarbonization.
At high injection velocities, particularly in excess,of
about 400 ft./sec., the mechanical energy input is suffi-
cient to break down the weaker bonds of the coarser
agglomerates, thereby substant~lly preventing excess
agglomeration and defluidization despite the preheating
-18-
l~lS~49
of the feed particles to a temperature within their plastic
transformation tempexature range prior to being rapidly and
directly injected into the reaction zone at such high
injection velocitie~.
It has been discovered that introducing a fluidized
stream of coal particles into a dense phase, fluid-bed
reaction zone at a velocity of more than about 200 ~eet per
second in a manner described hereinabove substantially pre-
vents excessive agglomeration or caking of the fluid-bed by
the imparting of sufficient mechanical energy to the reaction
7one to break up the coarser agglomerates and to rapidly and
uniformly disperse the fresh particles within the bed. When
a lower injection velocity, for example, about 100 feet
per second is used, without other modifications from con-
ven~ional practice, agglomeration of the fluid-bed is not
prevented. In order to substantially prevent agglomeration
of the fluid-bed reaction zone, coal should be introd~ced at
a high velocity into the zone in a high velocity, high kinetic
or mechanical energy stream, i.e. at a velocity more than
about 200, and preferably more than about 400, feet per
second, corresponding to an energy-to-coal ratio of at least
about 10 x 10 4, prefer~bly at least about 40 x 10-4,
horsepower-hours per pound of coal introduced. The energy-
to-coal ratio, as referred to herein, is the ratio of the
kinetic horsepower (in the injection jet as calculated
by the adiabatic expansion of the feed mixture) to the coal
feed rate. "Reaction zone" as used throughout the
specification is meant to include that area wherein carbon-
aceous, combustible, solid and someti~es liquid particles,
are reacted to form char, liquid and/or vapor fuel products
in coal conversion processes such as carbonization,
-19-
1~55~9 ~;~/v--~
gasification and dry hydrogenation (hydrocarbonization). 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.
-l9-a-
i5'~9 9,~9~
This invention is applicable to the various coal
conversion processes mentioned hereinabove. For example,
a hydrocarbonization process can be improved to handle
~oth 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 particles may be passed through a preheating zone
before entering a fluid-bed hydrocarbonization zone
wherein the coal particles are rapidly heated in the
presence of a hydrogen-rich, essentially oxygen-free gas,
to an elevated temperature above about 450C where the
desired reactions can occur. The improvement 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 or otherwise as herein
provided, at a high velocity. This rapidly brings the
entering coal particles to a non-sticky, high temperature,
partially reacted state without their contacting too many
coal particles also traversing the plastic transformation-
temperature range. The preheated, particulate coal in a
fluidized state is introduced, in some embodiments, into
a fluid-bed hydrocarbonization zone in a vertically
upwards direction as described hereinabove at a velocity
of more than about 200 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:
-20-
554~
9490-2-C
TABLE A. Classification of Coals by Rank.
(Legend: F.C. = fixed carbon; V.M. = volatile matter;
B.t.u. = British thermal units)
Class Group I.lmits of fixed carbon or
1. Meta-an~hracite Dry F C., 98% or more (dry
V.M., 2% or less)
2. Anthracite Dry F.C., 92% or more and
less than 98% (dry V.M.,
I. Anthracite b 8% or less and more than 2%)
3. Semianthracite Dry ~.C., 86% or more and
less than 92% (dry V.M.,
14% or less and more than 8%)
1. Low-volatile Dry F.C., 78% or more and
bituminous coal less than 86% (dry V.M.,
22% or less and more than 14%)
2. Medium-volatile Dry F.C., 69% or more and
bituminous coal less than 78% (dry V.M.,
31% or less and more than 22%)
II. Bituminous 3. High-volatile A Dry F.C., less than 69% (dry
bituminous coal V.M., more than 31%)
4. High-volatile B MoistC B.t.u., 13,000 or
bituminous coal more and less than 14,000
5. High-volatile C Moist B.t.u., 11,000 or
bituminous coal more and less than 13sO00
1. Sub-bituminous A Moist B.t.u., 11,000 or more
coal and less than 13,00Oe
III. Sub- 2. Sub-bituminous B Moist B.t.u., 9,500 or more
bituminous coal and less than ll,OOOe
3. Sub-bituminous C Moist B.t.u., 8,300 or more
coal and less than 9~500e
1. Lignite Moist B.t.u., less than 8,300
IV. Lignitic 2. Brown coal Moist B.t.u., less than 8,300
a - This class ification does not include a few coals that have
unusual physical and chemical properties and that come within
the limits of fixed carbon or B.t.u. of the high-volatile
bituminous and sub-bituminous ranks. All of these coals either
contain less than 48% moisture and ash free fixed carbon or
have more than 15,500 moist, ash free B.t.u.
b - If agglomerating, classify in low volatile group of the
bituminous class.
c - Moist B.t.u. refers to coal containing its natural bed moisture
but not including visible water on the surface of the coal.
d - It is recogni7ed that there may be noncaking varieties in each
group of the bituminous class.
e - Coals having 69% or more fixed carbon on the dry, mineral-
matter-free basis shall be classified according to fixed
carbon, regardless of B.t.u.
f - There are three varieties of coal in the high-volatile C
bituminous coal group, namely, Variety 1, agglomerating and
non-weathering; Variety 2, agglomerating and weathering;
Variety 3, nonagglomerating and non-weathering.
Source: A.S.T.M. D388-38 (ref. 1).
-2]-
~1 ~55~9 ~ o -~
Agglomerating coals, such as most bituminous and
some sub-bituminous coals, are strongly agglomerating in a
hydrogen atmosphere. They can not be handled conventionally
without a pretreatment step. These coals may now be
handled withou~ an injurious 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
pretreatment, 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 invention to overcome this agglomerating problem
Those skilled in the art will recognize that any number
of suitable pretreatment steps may be applied in
combination with the process of this invention for the
handling of coals which are either highly agglomerating or
highly agglomerating in a hydrogen-containing atmosphere.
These pretreatment steps include, for example, but are not
limited to, chemical pretreatment such as oxidation or
mixing with inert solids such as recycle char.
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
c -
~ S5'~
drawing which represents a semi-diagrammatic view of an
embodiment of a system in which the process of this invention
may be carried out.
Figure 1 illustrates coal supply vessels 10 and
1~, a coal feeder 22, a preheater 30 and a reactor vessel 40.
Lines are provided for conveying finely divided coal
through the vessel 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 pro-
cessing an~/or recycle.
According to the process of this invention, the
feed coal is in particulate form, having been crushed,
ground, pulverized or the like to a size finer than about
8 Tyler mesh, and preferably finer than about 20 Tyler mesh
for lower rank coals whi~e finer sizes, elgl -60 mesh U~, are
employed for bituminous coals. Furthermore, while the feed
coal may contain absorbed water, it is preferably free of
surface moisture. Coal particles meeting these conditions are
herein referred to as "fluidizable." Any such absorbed water
will be vaporized during preheat. Moreover, any such absorbed
water mus~ be included as part of the inert 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 particles, which are employed in
the process. Coal supply vessel 10 is typicàlly a
lock-hopper at essentially atmospheric pressure. Coal
55~ 9~jo^æ
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
illustrated 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 predetermined 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
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,
-24-
1~5549
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 range,
in the substantial absence of oxygen. The maximum
allowable temperature of heating is in the range of from
about 325C to about 400C, depending on the feed material
employed where preheating to below the plastic transforma-
tion temperature range is employed. Preheating to below
about 300C is common in such embodiments. 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 con-
venient means of indirect 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
30 through line 34 and enter at or near the bottom of the
reactor vessel 4Q substantially near the center of the
bottom. In this il1ustrated embodiment~ the coal particles
are introduced into the fluid-bed reaction zone through
the reactor bottom at a high velocity. This high
velocity may be achieved by accelerating
-25-
l~S~9 ~
o-~2
the fluidized stream of coal particles to the desired
velocity by addition of an accelerating gas
and/or 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 preferably at a
stream velocity of 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 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
-26-
~ss~ ~
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 introducsd 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 yertical 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 with partially reacted
coal and char particles.
The entering carbonaceous materials are reacted with
a suitable reagent in the reaction zone at a temperature
above about 450C or 500C.
Char from reactor vessel 40 is continuously removed
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
carbonizer in a carbonization process; and a hydrogen-
containing, substantially oxygen-free gas is fed into
a hydrocarbonizer in a hydrocarbonization process.
55'~3
As disclosed herein, further advantages unappreciated
heretofore in the art are obtained by preheating fluidized
coal particles in preheater 30 to a temperature essentially
within the plastic transformation temperature range of the
particles. The thus preheated particles exit preheater 30
through line 34 and pass rapidly and directly to the bottom
of reactor vessel 40 substantially near the center of the
reactor bottom in the embodiment shown in the drawings~
The coal particles are introduced into the fluid-bed
reaction zone at a high injection velocity, the lubricity of
the fresh feed material at the higher than conventional
preheat temperature tending to minimlze undesired nozzle
erosion while the rapid and direct injection of the
particles into the reaction zone precludes excess
agglomeration of particles and resultant defluidization.
As noted above, it will be appreciated in the art that,
in other embodiments of the invention, the fresh feed
particles can be introduced into reactor 40 in any other
direction, as by injection from the side thereof in a
substantially horizontal, sideward direction through one
or a series of injection points positioned along the side
of reactor 40. In particular embodiments, the injection
points may be located in essentially opposed positions
on the wall of reactor 40 for further turbulent mixing.
In other embodiments, the feed material may be passed
through line 34 for downward injection into reactor 40.
It will also be understood that reactor 40 may be
constructed with a lower reaction zone, an enlarged
upper zone and a cone-like transition zone, the upper
zone having a lower bed velocity facilitating separation
-28-
~ 3l, i~ 5 5 L~9
of gaseous materials from the bed and minimizing undesired
carry-over of fines in the gaseous effluent stream. It will
be Eurther understood that the feed inlet nozzle means will
be positioned substantially at the wall of the reaction
vessel, e.g. substantially at the bottom of the reaction
zone in the embodiment shown in the drawing, but may extend
somewhat into sa~d zone. In the illustrated embodiment, inlet
nozzle means 46 may extend, for example, 2 ft. or more
upward into the reaction zone. The injection point need not
extend appreciably into the interior of the fluid-bed region,
however, as is required in the Phinney patent, U.S. 2,709,67S
which relates to low speed coal injection, preferably in
conjunction with a draft-tube positioned within the fluid-
bed reaction zone. Shroud gas is passed in a conventional
manner through shroud passage 48 to maintain the nozzle tip
clean and free of clogging problems and to prevent over-
heating of the coalO
The following examples are illustrative of the
concept of this invention, demonstrating the method of
preventing agglomeration of coal in fluidized bed processes
via the high velocity injection of coal particles into a
reaction zone.
EXAMP~E I
The apparatus employed, shown schema~ically 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.
-29-
9~
~ 1 ~ 5 5~
The two coal feed loc'~-hoppers (10, 16) that fed the fluidized
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 h
height of 20 feet. The preheater 30, a lead bath heated
by "surface combustion" burners had a 24-inch I. D, and
height of 12 feet. The reactor 40 had an ll-inch I. D.
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 line was not particularly high, the maximum velocity
being approximately 40 feet per second at the inlet to
the reactor and only 15 feet per second at the outlet of
the coal feeder, erosion of the pipe at these velocities
still remaining at an acceptable level. Attempts to feed
the coal into the reactor at velocities of approximately
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 with 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 conditions
were established the coal feed was begun. On the
termination of the run the reactor was opened up. No
lsrge agglomerates or coke particles were found.
Operating conditions during the hydrocarbonization are
shown in Table I below:
-30-
?~ S549
u u ~ 9 ~jO-?
. U~ C ~ OJ 1
L~ D O O
C~ ~ 6
o
O O ~ O ~ ~ O
O ~ ~ O --
r~ o ~ ~ CJ`
.
~D o o
_~ O ~ r~
~ U ~ :1. Ll .
P U~ C
o~ C 5~ ~ _1 .C a
O O _ O C~ JJ 1
O ~ U o ~ :) _
r~l O ~ O O O ~ ~O 3 ~O
C ~ ~ ~ C
g ~ ~ o ~ ~ o O~ o
O ~O ~ O r~ O
. . .S: ~ C ~ 3
`D I ~ ~ O
h ~ 51 ,C
.~ o ~ D U g \r~
~s: . u
O ~0u, o C ~ a~ E
_ o ~ :~ _ o7 o
V~ O ~ .,
C C~ ~ -, o
C ~ ~ I ~ I ~ o
~ O o ou~ o ~o ~7 o co E ~ u E~
V~_/ o r~ o ~ ~ o _~
V ~ ~ o o 5~ ~ oO
~ ~ _I
a ~ _ :: u JJ v
~ o O~
Y ~ o 3 ~
c v o r
_~ U 02 .C
C~ 0 o~
o~ o _ v
I ~ C~ O D ~C~ ~ ~ w o~
cs: o-- ~ U _~ ~J C 07 0
_~ _ o ~ ,
E-~ I -I O ~n o
~D I_ O ~ ~ _ 1
CD O V ~ U O
, ~ l O '- ~ ~ C ~ ~ JJ
o I S~ I--~ ~ C U
O ~U~ O ~ 1~ 0 # ~ ~ 0 t~
O l-- O ~ ~ O _l
~ ~J O O _ ~ C
_~ ~ CO 0
_ C~
~, ~I CL V O
O ~ O
S-~ ,~ U I~ ~ v ~0~
O ~ ;~
,~ v :~ 5)
L~ U ~ ~
C",.~ ~,5 ~ a~ C
~ U
C) v ~ ~ vu ~ v
~ 0 ~ :: ~ O
'~ r --
07 ~ v u C ~ ~ ~
~ 6 CO _ O ~ ~ ~ It
~ C *
i.~ N
O O_~ ~ U vU~ C
, v u ~ E3
U
c ~ u ~~ E v
3 Ql 5~ _I O~ o
- c~ ~ z ~
-31-
5 5 L~ 9
TABLE II-LAKE DE SMET COAL, WYOMING,
_ SUBBITUMINOUS C (ANALYSIS)
Moisture and Ash Free BasisWeight Percent
C 72,0
H 5.3
N 1.3
S l.C
20.4
Ash 11.9 (dry basis)
Water 30 (as received)
EXAMPT.F. II
Two additional runs were conducted employing apparatus
and procedures similar to those employed in Example I,
except that oil, the higher boiling fractions (all product
boiling above 235C) of the liquid product, was recycled
to the reactor. These additional runs were conducted to
determine 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 thece hydrogen streams and injected
into the reactor through a l/4-inch diameter tungsten
carbide nozzle at a stream velocity of approximately
400 feet per second. The nozzle, which pointed
vertically up the reactor, was located in the center of
the reactor bottom 5 feet above the coal inlet. The
other hydrogen stream was mixed with preheated coal, and
introduced into the bo~tom of the reactor through a
-32-
~S549 c~o^~
15/32-inch diameter tungsten-carbide nozzle at approximately
160 feet per second in a vertically upwards direction. The
data for these runs are summarized below in Table III.
TABLE III
Kun L
.
Coal Feed Rate1000 lb,/hr. 1000 lb. /hrO
Coal Feeder Pressure1100 psig.1100 psig.
Reactor Pressure500 psig. 500 psig.
Reactor Temperature550 C 580 C
Reactor Fluidization
Velocity 0.5 ft./sec. 0.5 ft./sec.
Length of Run 5 hrs. 5 hrs.
Recycle Oil Feed Rate100 lb /hr.240 lb./hr.
Coal - H2, Inlet Velocity 160 ft /sec. 160 ft./sec.
Oil - H2, Inlet Velocity 420 ft./sec. 420 ft./sec.
No problems were encountered in making these runs.
There was no evidence of agglomeration in the fluld-bed,
even when injecting oil at the 240 lb./hr. rate.
EXAMPL~ III
The bench-scale apparatus employed in this example
comprised a pulverized solid hopper having a solid's
capacity of 4.5 leters 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 having a l/4-inch wall thickness and
an expanded head 4-inches high and 2 inches I. D~; solids
overflow line constructed of l/2-inch Schedule 40 pipe;
a vapor line constructed from 3/8-inch 00 D. stainless
steel tubing; and a solids feeder~ Two liquid feed
pumps, Lapp Microflow Pulsafeeders were used, one to feed
the liquid being investigated and the other to feed water
for steam generation. Electrically heated liquid and
water vaporizers and superheaters constructed of l/4-inch
-33-
55~9 ~7~d -~--
0O D. stainless steel tubing were installed between the
feed pumps and the feed injection nozzle to the reactor.
Thermocouples located 3, 6, 8 and ll-inches from the
bottom of the reactor were ins~alled in a l/4-inch O.S.
thermowell placed axially in the center of the reactor.
The lower three thermowells were in the fluidized bed while
the upper thermocouple was in the vapor space a~ove the
bed.
In operation, tars boiling about 235C obtained from
hydrocarbonization of Lake de Smet Coal were employed as
the feedstock to the reaction zone for conversion to oils
boiling below 230C. The tars were distilled from the whole
liquid product obtained from the hydrocarbonization into
various distillation fractions and a blend of these
distillation fractions used in this example had a nominal
atmospheric temperature range for 75% of the tar between
235C and 460C. The remaining 25% boiled above 460Co
The solids feed hopper was filled with Lake de Smet
hydrocarbonization char as described hereinabove. The
water and tar feed reservoirs were filled and heated to
operating temperature. During the heat up period, a
predetermined flow of hydrogen passed through the empty
reactor. As soon as operating conditions were approached,
the char feed and water feed ~superheated steam by the
time it entered the reactor through the injection orifice)
were started. The three thermocouples located in the
fluidized bed, at the levels indicated hereinabove, served
as an indication of bed behavior Attempts to feed this
tar stream at velocities of 100, 200 and 300 feet per
second resulted in rapid agglomeration of the fluidized
-34-
11f~55'q~9 ~f~-~-
reactor bed. A 26-gauge hypodermic needle used was to
achieve a 400 feet per second injection velocity of the
whole tar feed. Using this inlet velocity for the whole
feed, coking up of the fluidized bed within the reactor
was prevented under the following operating conditions
contained in Table IV.
TABLE IV - OPERATING CO~DITIONS -
LAKE DE SMET COAL
Pressure 150 psig.
Hydrogen Partial Pressure 115 psig.
Residence time of Vapors in Char Bed
Based on Superficial 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 Reactor 35 SCFH
Moles Hydrogen/Moles Oil 45/1
Temperature 650 C
Superficial Linear Velocity of
Xydrogen 0.5 ft./sec.
Rim of Run 5 hrs.
Fluidizing Gas Hydrogen
-35-
11~55~9 ~ ~ f~
~XAMPTF IV
100 pounds per hour of Pittsburgh No. 8 seam coal,
-20 mesh, are introduced into a low temperature, fluid-bed
reactor for pyrolysis at a reactor temperature of 540C 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 recycled 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 the fluid-
bed reactor at injection velocities of 200, 300 and 400
feet per second, respectively, a fluld-bed at a reaction
temperature between about ~00C 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 transformation and
are now non-stic~y. Carbonization products, gases, tars
and other liquids, water and char are continuously
withdrawn from the carbonization reactor.
-36-
55~3 c,~
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 temperature between about 816C and about 1000C 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 agglomer~tion occurs and separation of the
fine char formed and the 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 recycling ash.
Injection is in a generally vertical and upward
direction. This promotes great turbulence of ash,
coal and char near the points of introduction, which
-37-
5'~9 9~f ~fo -~
disperses the coal throughout the bed and effectively
prevents agglomeration.
E~YAMP~E VI
The advantages of the noveL high injection velocity-
hot coal embodiments of the invention were demonstrated
by introducing ILLinois No. 6 coal, without recycle char
and without pretreatment oxidation, upwardly into a
fluid-bed hydro-carbonization reaction zone at an injection
velocity of from about 400 to about 480 ft./sec , said
feed coal having been preheated to a carrier gas/coal
mixture temperature of about 390-400C., i_e. within the
plastic transformation temperature range of said coal.
The initial softening point of the coal was about 325-
350C. The coal particles, which were ~0-70% - 200 mesh,
were fed to the reaction zone over a 3-4 hr. period, with
the coal feed rate being slowly increased from 10 to
22 lb. of coal/hr. The injection gas/coal rate decreased
from 67 to 34 scf tstandard cubic feet) of gas per pound
of coal Gas was passed through the shroud passage of the
injection nozzle at about 70 ft./sec., corresponding to
a kin~tic energy/coal ratio of 0.1 x 10 4 hp-hr /lb. of
coal. The injection nozzle was located 20" above the grid
at the bottom portion of the reaction zone. No attrition
jets were employed. The bed velocity at the bottom of
the reaction zone was varied from about 1.6 to about
2.0 ft./sec., the bed density at this portion of the zone
varying from about 13 to about 7.3 lb./ft3 over the range of
the coal feed rate given above. Three inches from the
top of said zone, the bed velocity varied from about 2.3 to
about 2.8 ft./sec., with the bed density being in the
-38-
~æ
~ 1 ~ 5 5 ~ 2,
range of 8 to 11 lbs./ft3. The reactor employed had anenlarged upper zone and a cone-like transition zone, with
the upper zone having a lower bed velocity to facilitate
separation of gases from solids without excessive carry-
over of fines. The bed velocity in said upper zone
ranged from 0.60 to 0.68 ft./sec. with the bed density
being 13-14 lbs./ft3. No defluidization or bed failure
was encountered. Rapid dispersion of the feed particles
with the char in the fluid-bed reaction zone, together
with deagglomeration due to the mechanical or ~inetic
energy supplied to the reaction zone, served to maintain
the average bed size in a range suitable for fluidization.
The kinetic energy of the high velocity injection gas
was sufficient, therefore, to avoid excessive agglomeration
and to control particle size within the reaction zone to a
range that could be 'luidized. Despite the high injection
velocity, no observable erosion of the injection nazzle
- occurred. By contrast, a run carried out at 600 ft./sec.
with a feed comprising 1/2 part recycled char per part of
fresh coal was observed, at an entrance gas plus coal
mixture temperature of about 323C., to cause a 0.005"
nozzle erosion after 1 1/2 hr. at said injection velocity.
~ozzle erosion is a point of concern, therefore, particularly
when recycle char is mixed with the fresh coal. As indi-
cated above, however, nozzle erosion and the premature
shut-down of operations for nozzle replacement can be
avoided by employing high velocity fresh coal injection,
substantially without recycle char, at temperatures
within ~he plastic transformation temperature range of the
particles. The hot coal has a lubricity when heated to
-39-
3_
5 5 L~9
such range, thereby minimizing abrasion and resulting
nozzle erosion. The fresh, preheated particles are injected
r~pidly and directly into the fluid-bed reaction zone
and into direct contact with the non-agglomerating particles
therein. Under such conditions, undue or excessive agglom-
eration of the fresh feed particles is avoided despite the
operation at preheat temperatures avoided in the art
because of the agglomeration that would occur at conventional
operating conditions.
EXAMPLE VII
In operations utilizing the reactor system of
Example VI above, the indicated Illinois No. 6 coal was
injected into the hydrocarbonization reactor at an initial
injection velocity of 392 ft./sec. at a gas plus coal
injection temperature of 375C., which is within the
plastic transformation temperature range of t~ coal
particles. The coal feed rate was about 24-27 lbs./hr., with
the injection gas/coal feed rate being reduced from an
initial 31 to 21 scf of gas per pound of coal. The
injection velocity was thus decreased incrementally from
said 392 to 295 ft./sec. No attrition jets were employed.
Injection nozzle shroud gas was employed at a shroud gas
velocity of 55 ft./sec., having a shroud kinetic energy
of 0 1 x 10-4 hp.-hr./lb. of coal, to keep the nozzle tip
clean and to avoid overheating of the feed particles. The
bed uelocity at the bottom of the reaction zone was 1.5 ft./
ft./sec. with a bed density of 13 lbs./ft3. 3" from the
top of said zone, the bed velocity was about 2.0-2.1 ft./sec.,
with the bed density at this point ranging from about 7.9
to about 9.8 lbs./ft3. In the enlarged upper zone, bed
-40-
55~ ~'fff~ ~
velocity was reduced to 0 55 ft./sec. at a bed density of
14 lbs./ft3. Excessive agglomeration was avoided under
such conditions and no noticeab~e erosion of the injection
nozzle occurred. Bed failure resulted, due to defluidization
caused by excessive particle agglomeration, when the
injection velocity was reduced tobelow 300 ft./sec.
It should be noted that excessive agglomeration and
defluidization are not prevented simply bya high fresh
feed injection velocity, but by such a high injection
velocity of carrier gas and fresh coal or other carbonaceous
particles at such quantities, or loading levels, as to
provide sufficient mechanical or kinetic energy to assure
that excessive agglomeration and resulting defluidization
are prevented. Under the conditions of EXAMPLE VII,for
example, bed failure occurred when the injection velocity
was reduced to below 300 ft./sec. and the available power
- for controlling the siæe of particles was inadequate at
the loading level pertaining to the fluid-bed reaction zone
in this instance. The invention has been employed, in
other examples, with Pittsburg No. 8 as the feed coal to
achieve the desirable and unique combination of
results herein disclosed and claimed.
The invention represents a highly significant advance
in the art of feeding caking coals or other carbonaceous
materials to fluid-bed coal conversion operations. The
invention enables high velocity injection of such materials
to be carried out while nozzle erosion is minimized.
Despite the avoidance in the art of preheat temperatures
within the plastic transformation temperature range of the
particles, the in~ention enables such temperatures to be
-41-
.~
~1~ S 5 ~9 ~ 5~
used to advantage to minimize nozzle erosion leading to
premature shut-down of operations. Such unique preheat
temperatures are employed in conjunction with high velocity
coal injection, without the necessity for admixture with
recycle char and/or oxidation pretreatment, at kinetic
energy levels such as to suhstantially prevent defluidization
in the reaction zone despite the preheating of the feed
particles to their p~astic transformation temperature range.
Sufficient mechanical energy is thus imparted to the reactlon
zone to break up the coarser agglomerates that may form and
to rapidly and uniformly disperse the fresh feed particles
within the fluid bed of non-agglomerating particles within
the reaction zone. In addition to the minimizing of nozzle
erosion while substantially avoiding agglomera~ion, the
invention provides desirable operating flexibility and
advantages overcoming the economic disadvantage of high gas/
coal ratios associated with high injection velocity opera-
tions. At the temperature of the coal and gas injection
mixture as restricted to below the initial softening point,
i.e. below the plastic transformation range, of the coal in
conventional practice, addition of gas in excess of that
required to convey the coal to the reactor, as in high
velocity injection, would impose a thermal burden on the
reactor sys~em. Thus, the thermal energy balance around the
reactor in such circumstan~es would require a hotter feed
temperature for the remaining gas, such as the fluidizing-
reagent gas as more of the total gas input to the system
would be used to provide the dilute, easily dispersible,
high velocity fresh coal injection jet. This consideration
would be of particular importance in hydrocarbonization
-42-
Gj~f C~
~ 5 5 ~ 9
where the heat of reactîon is only slightly exothermic.
As the relative ra~io of the relatively cold
injection gas to hot gas is increased, a point is reached
at which the additional heat that the hot gas is required
to supply will call for temperatures that camnot be handled
without the use of expensi~e alloys for the hot gas
preheater and the transfer line to the reaction zone.
Operating with ~he injection mixture above the initial
softening point temperature of the coal and at the high
injection velocities employed in the practice of the inven-
tion, the advantages associated with a diluter injection
jet, both in terms of dispersion and deagglomeration
efficiency, can be achieved while minimizing the thermal
burden on the reactor. The process of the invention enhances
the technical and economic feasibility of desirable coal
conversion operations, provides advantageous flexibility
in meeting the overall heat and material balance limitations
of commercial plan~ designs, and constitutes a major
advance in the important efforts to develop practical
technologies for the use of caking coals in meeting the
ever-increasing energy requirements of modern industrial
societies.
-43-
