U.S. patent number 3,803,022 [Application Number 05/318,209] was granted by the patent office on 1974-04-09 for retorting system.
This patent grant is currently assigned to Atlantic Richfield Company. Invention is credited to Yahia A. K. Abdul-Rahman.
United States Patent |
3,803,022 |
Abdul-Rahman |
April 9, 1974 |
RETORTING SYSTEM
Abstract
Hot porous pellets are cycled to a retort zone to mix with and
retort preheated crushed oil shale, thereby producing gas and oil
products, a combustible deposition on the pellets, and a mixture of
pellets and spent shale. The main source of heat for retorting is
derived from controlled burning of the deposition on the pellets in
a pellet deposition burning zone. The hot flue gas thus generated
is passed to a secondary preretort oil shale heating zone to
additionally preheat already preheated oil shale. Thereafter, the
hot flue gas is passed to a gas elutriation system where the
mixture of spent shale and pellets is processed to separate and
recover the pellets for return to the retorting process. From the
gas elutriation system, the hot flue gas is used to lift the
recovered pellets to the pellet deposition burning zone.
Thereafter, the hot flue gas is passed to an initial preretort oil
shale heating zone to preheat raw crushed oil shale before it is
fed to the secondary preretort heating zone. The hot flue gas from
the burning zone usually contains carbon monoxide and may, at any
desirable point in the system, be passed through a carbon monoxide
shift reaction zone.
Inventors: |
Abdul-Rahman; Yahia A. K.
(Plano, TX) |
Assignee: |
Atlantic Richfield Company (New
York, NY)
|
Family
ID: |
23237138 |
Appl.
No.: |
05/318,209 |
Filed: |
December 26, 1972 |
Current U.S.
Class: |
208/411 |
Current CPC
Class: |
C10G
1/02 (20130101); C10B 53/06 (20130101); C10B
49/16 (20130101) |
Current International
Class: |
C10B
53/06 (20060101); C10G 1/00 (20060101); C10B
53/00 (20060101); C10B 49/16 (20060101); C10G
1/02 (20060101); C10B 49/00 (20060101); C10b
053/06 () |
Field of
Search: |
;208/11 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3020227 |
February 1962 |
Nevens et al. |
3164541 |
January 1965 |
Linden et al. |
3565784 |
February 1971 |
Schlinger et al. |
3573197 |
March 1971 |
Gessner |
3617472 |
November 1971 |
Schlinger et al. |
3644193 |
February 1972 |
Weggel et al. |
|
Primary Examiner: Davis; Curtis R.
Claims
The embodiments of the invention in which an exclusive property
or
1. A method for retorting of crushed oil shale comprising
a. lifting pellets bearing a combustible deposition with lift gas
to a pellet deposition burning zone, said pellets being particulate
heat carriers in a size range between approximately 0.06 inch and
0.3 inch;
b. heating said pellets passed to said pellet deposition burning
zone to an outlet temperature of between 1,000.degree. F and
1,500.degree. F by burning said combustible deposition on said
pellets with a combustion supporting gas thereby producing hot flue
gas;
c. passing said lift gas from said pellet deposition burning zone
to an oil shale first preretort heating zone;
d. feeding crushed oil shale at a temperature lower than said lift
gas to said first preretort heating zone and heating said oil shale
by intimately contacting said oil shale with said lift gas to a
temperature below about 600.degree. F;
e. passing the heated oil shale from said first preretort heating
zone to a second preretort heating zone;
f. passing said hot flue gas from said pellets deposition burning
zone to said second preretort heating zone and heating at a
temperature higher than the heated oil shale passed thereto and
heating said oil shale by intimately contacting said heated oil
shale with said hot flue gas to a temperature below about
600.degree. F;
g. passing said heated pellets from said pellet deposition burning
zone and the heated oil shale from said second preretort heating
zone to a retort zone, said pellets having a surface area of at
least 10 square meters per gram, the ratio of said heated pellets
to said crushed oil shale entering said retort zone on a weight
basis being between 1 and 3, said ratio also being such that the
sensible heat in said pellets is sufficient to provide at least 50
percent of the heat required to heat said oil shale from its retort
zone feed temperature to a retort zone outlet temperature of
between 800.degree. F and 1,150.degree. F;
h. retorting in said retort zone gas and oil products from the oil
shale thereby forming particulate spent shale;
i. recovering said gas and oil products generated by retorting the
oil shale;
j. passing hot flue gas from said second preretort heating zone to
a separation zone;
k. passing a mixture of pellets and spent shale from said retort
zone to said separation zone at least one stage of which involves
subjecting said mixture to elutriate and separate spent shale from
the pellets in said mixture with elutriation gas, said elutriation
gas being comprised of said hot flue gas passed to said separation
zone;
l. passing separated pellets from said separation zone to a pellet
lift zone;
m. passing hot elutriation gas from said separation zone to said
pellet lift zone, said hot elutriation gas being comprised of said
hot flue gas passed from said pellet deposition burning zone to
said second preretort heating zone to said separation zone; and
n. using said hot elutriation gas passed to said pellet lift zone
as lift
2. The method according to claim 1 wherein prior to step (j), the
hot flue gas from said second preretort heating zone is passed
through a supplemental heating zone wherein said hot flue gas is
heated to a higher
3. The method according to claim 1 wherein the hot flue gas
contains carbon monoxide, and at some point in the method between
the pellet deposition burning zone and the end of step (d), said
hot flue gas is passed through a carbon monoxide shift reaction
zone.
Description
BACKGROUND OF THE INVENTION
This invention relates to a retorting system wherein hot porous
pellets are used to retort preheated crushed raw oil shale and are
separated and recovered from spent shale particles, are lifted to a
burning zone, reheated and recycled through the process, and
wherein the hot flue gas from the burning zone is sequentially
passed through several stages of the process.
As a preliminary stage in the production of petroleum oils and
gases, the solid carbonaceous organic solid matter or kerogen in
oil shale is pyrolyzed or retorted. Retorting denotes thermal
conversion of kerogen or organic matter to oil vapors and gas,
thereby leaving solid particulate spent shale and includes
separation of the oil vapors and gas from the spent shale. The
spent shale contains residual carbonaceous organic matter and
matrix mineral matter.
When the kerogen is retorted, a normally gaseous fraction, a
normally liquefiable vaporous fraction, and a combustible organic
residue are formed. The product distribution between gas, liquid,
and residue is important and relates to the distribution of the
various boiling point fractions in the liquid product. Copending
applications Ser. No. 284,288, filed Aug. 28, 1972; Ser. No.
285,732, filed Sept. 1, 1972; Ser. No. 304,074, filed Nov. 6, 1972;
and Ser. No. 308,136, filed Nov. 20, 1972, which are owned by a
common assignee and are incorporated herein, provide processes for
retorting oil shale using special pellets in a way which causes a
combustible organic carbon deposition to be formed on the pellets
during retorting of oil shale and improves the recovery of useful
components and liquid product distribution. Some or all of this
combustible deposition is burned in a pellet deposition burning
zone to heat and reheat the pellets. In such processes, the spent
shale is separated from the pellets prior to burning and the
pellets are recycled through the process. Preferably, separation
will involve hot gas elutriation in one or more stages.
In retorting processes, especially processes of the aforementioned
nature, fuel requirements and the amount of fuel used for heating
purposes should be kept as low as possible. Moreover, due to
restrictions on gas emissions and the costs and difficulties of
cleaning gas emission streams, it is highly desired that the number
of gas emission points be kept as low as is practical.
SUMMARY OF THE INVENTION
The retort system of this invention provides a method of retorting
using hot porous pellets and sequential passage of hot flue gas
through a secondary crushed oil shale preheating stage, a spent
shale separating zone using gas elutriation, a pneumatic pellet
lifting system, and an initial oil shale preheating stage -- all in
a way which conserves gas heating values, reduces fuel
requirements, and minimizes gas emissions.
Mined oil shale which contains solid carbonaceous organic matter
and other mineral matter and which has been crushed is preheated
and retorted in a retort zone with hot pellets at a temperature and
in an amount sufficient to provide at least 50 percent of the
sensible heat required to retort the oil shale. Retorting oil shape
produces gas and oil products which are recovered, and particulate
mixture of pellets and spent shale. The retorting process also
deposits a carbon-containing deposition on the pellets. The spent
shale is separated from the mixture of pellets and spent shale and
the pellets are recovered and passed to a pneumatic lift system
where the pellets are gas lifted to a pellet deposition burning
zone. The pellet deposition is burned to reheat the pellets to a
temperature of between 1,000.degree. F and 1,500.degree. F, thereby
producing hot flue gas which is sequentially passed in
aforementioned fashion.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a partly schematical, partly diagrammatical, flow
illustration of a system for carrying out a preferred sequence of
the process of this invention.
DETAILED DESCRIPTION OF THE INVENTION
A process for retorting crushed oil shale containing a carbonaceous
organic matter, commonly called kerogen, and other mineral matter
with hot pellets which are later separated and recovered from the
spent retorted shale is described having reference to the
drawing.
Pellets bearing a combustible deposition which was previously
absorbed or deposited on the pelets in an earilier stage of the
retorting system are passed through pellet return line 11 which
acts as an inlet line to pneumatic pellet lift system 12 where the
pellets are lifted by way of lift line 13 to pellet deposition
burning zone 14. Preferably, the pellets will be lifted to an
elevation which allows gravity feed of the pellets to a retort
zone. The pneumatic pellet conveying system operates in the
conventional manner to lift and convey the pellets except that the
lift gas which enters the lift system via line 15 and moves through
lift system 12 at a velocity sufficient to elutriate or lift the
pellets, for example, 25 to 60 feet per second, is at least in part
comprised of a hot flue gas which originated in pellet deposition
burning zone 14 as hereinafter shown.
As shown, pellet burning deposition burning zone 14 is comprised of
surge hopper 16 for collecting the lifted pellets and leveling out
fluctuations and from which the pellets fall into burning units 17.
The hot lift gas passes overhead of the surge hopper through exit
line 18 where the hot lift gas is passed to oil shale first
preretort heating zone 19 which may be comprised of one or more
heating units. Raw or fresh oil shale which has been mined and
pulverized, crushed or ground for the most part to a predetermined
maximum size for handling in a retort system by any suitable
particle diminution process and which is at a temperature lower
than the hot lift gas is fed directly from a crusher or from a
hopper or accumulator by way of shale inlet line 20 into first
preretort heating zone 19. In the zone, the hot lift gas lifts,
intimately contacts, and heats the cooler crushed oil shale to a
temperature not to exceed 600.degree. F in order to avoid retorting
or loss of oil values in the raw shale. The hot lift gas and
preheated oil shale pass overhead through exit 21 to collection
chamber 22 where the oil shale settles from the lift gas and is
gravity or mechanically fed through line 23 to second preretort
heating zone 24. The separated hot lift gas passes overhead of
collection chamber 22 through exit line 25 where the gas may be
passed to additional upstream preretort oil shale heating
units.
Crushing of the raw mined shale expedites more uniform contact and
heat transfer between the shale feedstock and hot lift gas and in a
retort zone between the shale and pellets. In normal practice, the
degree of crushing is simply dictated by an economic balance
between the cost of crushing and the advantages to be gained by
crushing when retorting the kerogen from the shale. Generally the
shale feedstock is crushed to about 1/2 inch and no particular care
is taken to produce or restrict production of finer materials.
In burning units 17, the combustible deposition on the pellets is
burned to provide at least 50 percent or more of the heat required
to reheat the pellets to the temperature required to effect
retorting of the shale. The combustible deposition is burned in a
manner similar to the way that catalytic cracking catalysts
particles are regenerated and which is controlled to avoid
excessive heating of the pellets which would excessively reduce the
effective surface area of the pellets to less than 10 square meters
per gram. A progressive bed burner is preferred. A combustion
supporting gas, for example air, a mixture of air and fuel gas
generated in the process, and flue gas with the desired amount of
free oxygen, is compressed or blown into the pellet deposition
burning zone at a temperature at which the deposition on the
pellets is ignited by way of combustion gas inlet 26. Steam may
also be used to control burning provided that the steam does not
excessively reduce the surface area of the pellets. The combustion
supporting gas may be preheated in heaters 27 by burning some of
the gases produced in the process to reheat the pellets to the
minimum ignition temperature. The quantity of combustion supporting
gas, e.g., about 2 to 3 pounds and higher depending on compression
pressure of oxygen per pound of carbon deposit, affects the total
amount of deposition burned and the heat generated by such burning
and in turn the temperature of the pellets. The bulk density of the
pellets is about 40 to 50 pounds per cubic foot and the specific
heat of the pellets varies between about 0.2 and 0.3 British
Thermal Units per pound per degree Farenheit. The gross heating
value of the carbon-containing deposition is estimated to be about
15,000 to 18,000 btu per pound. The amounts of carbon dioxide and
carbon monoxide produced in the flue gases created by burning the
pellet deposition indicate the amount of combustion supporting gas
required or used and the amount of carbon-containing deposit not
burned. Generally, it is desirable to attempt to free the pellets
of all of the combustible deposition. Other factors taken into
consideration during burning of the pellet deposition are the
pellet porosity, density, and size, the burner chamber size and
pellet bed size, residence burning time, the desired temperature
for the pellets, heat losses and inputs, the pellet and shale feed
rates to the retort zone and the like. The residence burning time
will usually be rather long and up to about 30 to 40 minutes.
Combustion of the deposition should be controlled in a manner which
does not heat the pellets to above 1,500.degree. F. Of course,
additional fuel material or gases may be used to supplement burning
of the pellet deposition if this is necessary.
The hot flue gases generated in the pellet deposition burning zone
are passed through lines 28 to second preretort heating zone 24,
which may be comprised of one or more heating units. Generally, as
previously indicated, the hot flue gases will contain carbon
monoxide which can be used in a conventional manner in a carbon
monoxide shift reactor wherein the carbon monoxide is changed to
carbon dioxide thereby exothermically producing additional heat.
Therefore, whenever additional heat is required or if at some point
an excess of heat is present, the hot flue gas may be passed
through an optional carbon monoxide shift reaction zone. If an
excess of heat is present, the heat can be used for boiler
operation or the like. The carbon monoxide shift reaction zone may,
as indicated, be located at any appropriate point along the path of
the flue gas from the pellet deposition burning zone to the last
stage of process wherein the flue gas is used. As shown, the hot
flue gas containing carbon monoxide is first passed through shift
reaction zone 29 before being passed to secondary preretort heating
zone 24.
If the hot flue gas contained an excess of oxygen, supplemental
fuel could be added to consume the oxygen or the oxygen converted
by other means.
The hot flue gases via line 30 entering secondary preretort heating
zone 24 are hotter than the preheated crushed oil shale entering
the zone from the first preretort heating zone. The hot flue gas
lifts, intimately contacts, and heats the oil shale to a higher
temperature which temperature does not exceed about 600.degree. F.
The hot flue gas and heated oil shale pass overhead through exit 31
to collection chamber 32 where the oil shale settles from the hot
flue gas and is gravity or mechanically fed through retort inlet
line 33 to retort zone 34. The separated hot flue gas passes
overhead of collection chamber 32 through exit line 35 where the
gas may be passed to additional preretort oil shale heating units
(not shown) or passed to a separation zone as hereinafter
described.
In the pellet deposition burning zone, there is produced a
continuous stream of hot pellets having a temperature above
1,000.degree. F and not exceeding 1,500.degree. F. As used herein,
the term pellets refers to subdivided or particulate heat-carrying
bodies having, when they leave the combustion zone, a minimum
relatively high effective surface area of 10 square meters per gram
and higher, a size range between about 0.06 inch and 0.3 inch,
including a narrower range therewithin, and a shape and density or
particle weight such that for a particular size the elutriation
velocity of a pellet of that size is significantly, that is,
measurably and usefully, higher than the elutriation velocity of
most of the particles of spent shale of that size. Preferably, the
average surface of the pellets will be between 10 and 150 square
meters per gram. The surface area is the average effective of the
pellets as they enter the pyrolysis zone. The surface area may be
determined by the conventional nitrogen absorption method. The
pellets may be cylindrical shape, approximately oval or spherical
shape, or purely spherical shape. The much preferred pellets have a
sphericity factor of at least 0.9 which shape gives the highest
particle weight and is particularly useful in separating the
pellets by elutriation and screening from spent shale produced in
the retort zone. The sphericity factor is the external or geometric
surface area of a sphere having the same volume as the pellet
divided by the external surface area of the pellet.
The pellets are made up of materials such as alumina or silica
alumina, which are not consumed in the process and which are
subdivided or particulate matter having significantly high internal
surface area. The pellets are sufficiently wear or breakage
resistant and heat resistant to maintain enough of their physical
characteristics under the conditions employed in the process to
satisfy the requirements of the process, to affect retorting of the
oil shale, and to permit controlled burning of a carbon-containing
deposition formed on the pellets during the process. More
specifically, the pellets do not disintegrate or decompose, melt or
fuse, or undergo excessive surface area reduction at the
temperatures encountered during such burning and the thermal
stresses inherent in the process.
The pellets do, of course, undergo gradual wear or size reduction.
Fresh pellets will usually be between 0.15 and 0.3 inch with a
range between 0.2 and 0.3 being initially sought. After wear or
attrition, the size range will increase, and great effort is made
to retain and recover all pellets above about 0.06 inch or plus 14
U.S. Sieve Series Screen size. Finer grain pellet-like particles
which were once part of the pellets may be present, but no special
effort is made to retain these finer grains and a large percentage
of substantially smaller finer grained pellets is undesirable.
The stream of hot pellets is fed by gravity or other mechanical
means to retort zone 34 by way of pellet inlet pipe 36. The pellets
and shale feedstock could be fed to the retort zone by way of a
common retort zone inlet. The hot pellets are at a temperature
ranging between 1,000.degree. F and 1,500.degree. F, which is about
100.degree. F to 500.degree. F higher than the designed retort
temperature within the retort zone. The most favorable practical
temperature range depends on other process variables. The quantity
of pellet heat carriers is controlled so that the pellet-to-shale
feedstock ratio on a weight basis is between 1 and 3. This ratio is
such that the sensible heat in the pellets is sufficient to provide
at least 50 percent of the heat required to heat the shale
feedstock from its retort zone feed temperature to the designed
retort temperature. The feedstock feed temperature is the
temperature of the oil shale after preheating, that is the
temperature of the shale upon entry into the retort. The average
retort temperature ranges between about 850.degree. F and
1,200.degree. F, depending on the nature of the shale feedstock,
the pellet-to-shale ratio, the product distribution desired, heat
losses, and the like.
The retort zone is any sort of retort which causes intimate contact
or mixing of the crushed oil shale and pellets. The preferred
retort is any sort of horizontal or inclined retorting drum that
causes the oil shale and pellets to undergo a tumbling action. This
sort of retort is herein referred to as a rotating retort zone.
This type of retort zone is quite flexible over a wide range of
conditions and has the advantages of causing rapid solid-to-solid
heat exchange between the pellets and shale feedstock thereby
flashing and pyrolyzing the oil and gas vapors from the shale in a
way which allows the vapors to separate from the solids without
passing up through a long bed of solids and which minimizes
dilution of the product vapors by extraneous undesirable retorting
gases, of allowing for a high shale throughput rate at high yields
for a given retort volume, of providing for greater control over
residence time, of aiding in preventing overcoking and
agglomeration of the pellets and shale, of facilitating formation
of a more uniform controlled amount of combustible
carbon-containing deposition on the surface area of the pellets,
and of causing flow of the pellets and shale through the retort
zone in a manner which aids in eventual separation of the pellets
from the spent shale.
The retorting process is carried out in concurrent or parallel flow
fashion with the hot pellets and the raw shale feedstock being fed
into the same end of the retort. The retort zone may be maintained
under any pressure which does not hamper efficient operation of the
retort, interfere with production of valuable retort vapors, or
cause excessive deposition of residue on the pellets. Generally,
pressurization of the pyrolysis or retort zone causes considerable
difficulties, especially if a rotating retort zone is used. The
pressure employed is, therefore, generally the autogenous
pressure.
In the retort zone, the hotter pellets and cooler crushed shale
feedstock are admixed and intimately contacted almost immediately
upon being charged into the retort zone. The shale particles are
rapidly heated by sensible heat transfer from the pellets to the
shale. Any water in the shale is distilled and the kerogen or
carbonaceous matter in the shale is decomposed, distilled, and
cracked into gaseous and condensable oil fractions, thereby forming
a valuable vaporous effluent including gas, oil vapors, and
superheated steam. Pyrolysis and vaporization of the carbonaceous
matter in the oil shale leaves a particulate spent shale in the
form of the spent mineral matrix matter of the oil shale and
relatively small amount of unvaporized or coked organic
carbon-containing material.
As the aforementioned vaporous effluents are formed, a combustible
carbon-containing deposition or residue will be formed or deposited
on the pellets if the effective surface area of the pellets has not
already been covered with all of the deposition that it can
sustain. The total amount of deposition formed or deposited on the
pellets upon one passage through the process is sufficient upon
combustion to provide at least 50 percent of the heat required to
reheat the pellets. The amount of combustible deposition deposited
on the pellets during the retorting stage is on an average less
than 1.5 percent by weight of the pellets, and the preferred range
is between 0.8 and 1.5 percent. The pellet surface area, size, and
amount coacts with other process conditions to accomplish the
desired amount of combustible deposition and product distribution.
If the surface area of the pellets is less than 10 square meters
per gram, either too little total deposition will be formed or the
burning of the deposition will not be sufficient to provide a major
portion of the heat required to heat the pellets to the desired
temperature and to carry out the retorting phase of this process.
This would necessitate the use of supplementary fuels which is
undesirable.
The mixture of pellets and shale moves through the retort zone
toward retort exit 37, and the gaseous and vaporous effluents
containing the desired hydrocarbon values separate from the
mixture. The residence time for the pellets required to effect
retorting and deposition of the pellet deposition is on the order
of about 3 to about 20 minutes with residence times of less than 12
minutes for the pellets being preferred. The shale residence time
depends on its flow or movement characteristics and since the shale
is not uniform in size and shape, the shale residence time
varies.
The mixture of pellets and spent shale exits from retort zone 34 at
a temperature between 800.degree. F and 1,050.degree. F by way of
retort exit 37 into recovery chamber 38 where the gaseous and
vaporous products, resulting from retorting the oil shale collect
overhead and rapidly pass to overhead retort products line 39 at an
exit temperature between about 750.degree. F and 1,050.degree. F.
The product vapors are usually subjected to hot dust separation,
and the dust thus collected may be combined and handled with other
spent shale. Hot dust or fines separation may be accomplished by
hot gas cyclones, quenching and washing, agglomeration with sludge
or a separately condensed heavy product fraction, centrifuging,
filtration, or the like.
The retort zone particulate mixture of pellets and spent shale are
passed through separation zone 40 for separation of the spent shale
from the pellets and for recovery and return of the pellets to the
pellet deposition burning zone. The separation zone may be any sort
of exiting and separation system accomplishing at least 75 percent
by weight separation of the total spent shale from the pellets and
at least 95 percent by weight separation of the spent shale that is
smaller than the pellets, provided that, at least one stage of the
separation zone involves gas elutriation of at least part of the
spent shale. The separation zone may be comprised of any number and
types of units of equipment. As shown, the mixture of pellets and
spent shale first passes through optional revolving screen or
trommel 41 extending into product recovery chamber 38 and which has
openings or apertures sized to pass the pellets and spent shale of
the same or smaller size than the pellets and screen out any spent
shale and agglomerates larger than the pellets. Most of the spent
shale and the pellets flow through the openings in trommel 41 and
drop to the bottom of recovery chamber 38 to exit via exit line 42.
Any spent shale, mineral matter, and agglomerates too large to pass
through the openings in the trommel, pass outward through exit 43
to spent shale disposal. This prescreening or initial separation of
spent shale larger than the pellets is optional and may also be
delayed until a later or final stage of the separation system. The
rotating retort makes initial screening easier.
The spent shale and pellets in the bottom of recovery chamber 38
are discharged via exit line 42 at a temperature between about
750.degree.F and 1,050.degree. F where these particulate solids are
passed or conducted by gravity or other means of conveyance to a
subsequent phase of the separation and recovery zone involving at
least one stage wherein the mixture of pellets and spent shale is
subjected to elutriation gas, preferably preheated or already hot,
to elutriate and separate a part of the spent shale from the
pellets. The elutriation gas is, at least in part, comprised of
flue gas which originated in pellet deposition burning zone 14 and
was used in secondary preretort oil shale heating zone 24. As
shown, the flue gas in line 35 is first passed through optional
heater 44, wherein, if desired, the flue gas can be reheated.
Heater 44 could be a carbon monoxide shift reaction zone as
previously discussed or could use other means of direct or indirect
heating including additional fuel burning. It should be noted,
however, that the flue gas will already be hot and the need for
additional fuel is, therefore, reduced. The hot flue gas then
passes through line 45 to elutriation zone 46. The elutriation zone
may be in one or more stages conducted in batchwise fashion or in a
combination of batch and separate units, or in two or separate
units or stages, as disclosed in Copending Application Ser. No.
318,190, filed Dec. 26, 1972 by the same inventor, entitled
"Separating Retorted Shale from Recycled Heat-Carrying Pellets,"
and owned by a common assignee. The internal operation and design
of gas elutriators is well known and depends on the properties of
the particles and such factors as free board height, bed height and
weight, gas type and velocity, column diameter and cross-sectional
area, and transport disengaging height. In this process, it is
highly desirable that the elutriating gas be maintained at a
temperature above 750.degree. F, and it is essential that
elutriation be accomplished in a way which retains the desired
amount of combustible deposition on the pellets; consequently, the
elutriating gas must be a noncombusting gas, that is, a gas that
will not burn the combustible deposition on the pellets.
The mixtures of pellets and spent shale in line 42 passes to
elutriation zone 46 where the mixture is subjected to gas
elutriation with gas entering the elutriation zone by way of line
45. As stated previously, at least a part of this elutriation gas
is hot flue gas from the pellet deposition burning zone. In the
elutriation zone, a major portion of the spent shale is elutriated
and separated from the pellets. For simplicity, only one
elutriation stage is shown and the spent shale and elutriation gas
pass overhead through line 47 to overhead separator 48, for
example, a cyclone, scrubber, or the like, to remove the spent
shale to disposal by way of bottom line 49 and to clean and allow
the elutriation gas to exit overhead through line 15 and pass from
the separation zone through line 15 to pellet lift system 12 as
previously described. If additional elutriation stages are used,
the elutriation gas may first be returned to such stages, if
desired. The mixture of remaining pellets and spent shale in
elutriation zone 46 is added to any other pellet return streams
(not shown) and passed through line 11 to pellet lift system 12,
where, as previously described, the pellets are relifted to the
pellet deposition burning zone by the hot lift gas from line 15 at
least part of which is comprised of hot flue gas originating in the
pellet deposition burning zone.
In a retorting system of the nature just described, it would be
highly advantageous to initially produce the hot flue gas at a
pressure which would eliminate or at least reduce the need for
subsequent pressure increasing or compession stages especially at
points where the gas contains entrained solids. This may be
accomplished in the illustrated process by raising the inlet
pressure of the combustion supporting gas in line 26 when the
combustion supporting is more or less solids free. It has
previously been pointed out that the pressure in the retort zone
may be the autogenous pressure. This retort zone pressure may be
below the pressure to which the combustion supporting gas is
compressed. If so, an appropriate conventional gas seal system will
be placed in the pellet feed system between the pellet deposition
burning zone and the retort zone. Preferably, the combustion
supporting gas will be compressed to a pressure high enough to
cause passage of the flue gas throughout the system as herein
described. For example, if the retort system involves one lift
heating unit in the secondary preretort heating zone, three stages
of elutriation, and two lift heating units in the first preretort
heating zone, the entry pressure of the combustion supporting gas
could be increased to about 6 to 19 pounds per square inch above
the atmospheric pressure.
The foregoing description of the conditions and variables of the
process illustrates a preferred method of conducting retort system
and how the system conserves gas heat energy, and reduces emission
points to accomplish the advantages and objectives herein set
forth.
Reasonable variations and modifications are practical with the
scope of this disclosure without departing from the spirit and
scope of the claims of this invention. For example, while the
disclosure of this process and the variables have been limited to
oil shale, the process concepts lend themselves readily to
retorting any solid organic carbonaceous material containing
hydrocarbon values which can be recovered by thermal vaporization
of the solid carbonaceous material, such as, for example, coal,
peat, and tar sands. By way of further example, while only a single
train of units and stages have been described, it is to be
understood that any stage or zone could be comprised of more than
one stage or zone.
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