Oil shale retorting process utilizing indirect heat transfer

Carbon-containing solids such as oil shale or coal are pyrolyzed or retorted in an apparatus constructed in such a manner that the heat required for pyrolysis is supplied by burning residual organic material in the pyrolyzed solids in an external combustion zone and in an internal combustion zone that is situated with respect to the pyrolysis or retorting zone such that the heat of combustion is transferred through the walls of the internal combustion zone into the pyrolysis or retorting zone. The pyrolyzed solids are passed from the retorting zone to either the external combustion zone or the internal combustion zone wherein a portion of the organic material in the solids is burned. The partially burned solids exiting this zone are then passed to either the external combustion zone or the internal combustion zone where all or a portion of the remaining organic material is burned. The heat carried into the internal combustion zone with the hot solids produced by burning the organic material in the external combustion zone and the heat of combustion produced in the internal combustion zone are transferred through the walls of the internal combustion zone to supply substantially all or a major portion of the heat required to pyrolyze the carbon-containing feed solids in the retorting zone. None of the solids or flue gases produced in either the internal combustion zone or the external combustion zone are passed directly into the retorting zone.

BACKGROUND OF THE INVENTION 
This invention relates to the pyrolysis of solids containing organic 
material and is particularly concerned with a process and apparatus for 
retorting oil shale or coal in which the heat required for the retorting 
process is supplied indirectly to the retorting zone by burning the 
residual organic material left in the retorted shale or coal. 
Because of a dwindling supply of petroleum liquids from underground 
reservoirs, attention has recently been focused on the recovery of 
hydrocarbon liquids and gases from solids such as oil shale, coal, 
industrial and municipal solid wastes and the like. Work by both 
governmental agencies and private industry has demonstrated that the 
organic material in such solids can be converted with varying degrees of 
difficulty into volatile hydrocarbonaceous fluids such as combustible 
gases, motor fuels, heating and fuel oils, and various by-products which 
have value in chemical and petrochemical industries. In general, the more 
attractive of the recovery techniques previously proposed involve the heat 
treatment of such solids in a manner sufficient to distill or otherwise 
decompose the organic material into the above-mentioned volatile 
hydrocarbonaceous products. Such techniques, which are commonly referred 
to as retorting or pyrolysis processes, take on a multitude of forms, 
including batch or continuous schemes utilizing fixed, moving or fluidized 
beds wherein either a portion of the solid organic material itself is 
combusted to supply the pyrolysis heat, or the pyrolysis heat is generated 
externally and supplied to the process via a gaseous, liquid or solid heat 
carrier. 
Oil shale is considered to be one of the best candidates of all 
carbon-containing materials for processing in such a retorting or 
pyrolysis scheme since it comprises a mixture of a minor amount of solid 
organic matter called kerogen and a major amount of mineral matter. 
Because of the physical and chemical compositions of oil shale, its 
organic content has not been found to be economically recoverable by any 
technique other than the application of heat via pyrolysis or retorting. 
When mined oil shale is retorted, the solid organic matter undergoes 
destructive pyrolysis and a large percentage of the organic matter is 
converted to liquid and light gaseous hydrocarbonaceous products with the 
remainder staying as a carbon-rich residue in the mineral matrix. 
Processes for recovering hydrocarbonaceous products from raw oil shale are 
generally classified into four categories according to the method in which 
the heat is supplied. These categories are as follows: (1) heat is 
transferred from an external source through the walls of the retorting 
vessel; (2) heat is supplied by direct combustion in the retorting vessel; 
(3) heat is supplied by passing an externally heated gas into the 
retorting vessel; or (4) heat is supplied by introducing externally heated 
solids into the retorting apparatus. The known processes which fall in 
category (1) have a major disadvantage in that there is a substantial 
amount of organic matter left in the retorted oil shale and this in turn 
substantially decreases the economics of the overall process. The 
processes encompassed by category (2) in which combustion is carried out 
in the retort itself avoids the problem of not converting a substantial 
amount of the organic material present but have disadvantages in that the 
product is diluted by the combustion gases produced, the naphtha yields 
are lower because the light vapors burn and there is a tendency for the 
shale to overheat and form clinkers in the retort. 
The indirectly heated retorting processes of categories (3) and (4) while 
having advantages over the processes in categories (1) and (2) still have 
major disadvantages. The use of an externally heated gas to supply heat 
enables the gas and solids residence times to be independently controlled 
and may result in greater than Fischer Assay yields. Unfortunately, such 
processes require high gas rates, result in a product diluted by the 
externally added gas, leave unconverted organic material in the retorted 
shale, and pose a high potential for solids carryover. The processes of 
category (4) in which the raw shale is contacted with externally heated 
solids, preferably produced by combusting spent shale produced in the 
retort, avoid dilution of the product gas but have disadvantages which 
include the requirement for additional expense of solids handling 
apparatuses and procedures, and a decrease in product yield caused by the 
adsorption of pyrolysis products on the heat carrier solids. Some of the 
processes which fall in categories (3) and (4) often yield a spent shale 
which contains as much as 30 percent of original feed carbon. This results 
in low thermal efficiency and poses potential waste disposal problems. 
SUMMARY OF THE INVENTION 
The present invention provides a process for the retorting or pyrolysis of 
oil shale, coal and similar carbon-containing solids which at least in 
part obviates the disadvantages of the processes referred to above. As 
used herein the phrase "carbon-containing solids" refers to any solids 
that contain organic material. In accordance with the invention, it has 
now been found that carbon-containing solids can be retorted or pyrolyzed 
without diluting the product and without introducing externally heated 
solids into the retorting or pyrolysis zone while at the same time 
obtaining a high conversion of the organic material contained in the 
solids. The carbon-containing solids are pyrolyzed in a fluidized bed 
retorting zone located inside a retorting vessel and situated in relation 
to a combustion zone also located in the same vessel such that heat 
generated in and introduced into the combustion zone can be transferred 
through its walls into the retorting zone to supply all or a majority of 
the heat required to carry out the pyrolysis. The carbon-containing feed 
solids are contacted with a fluidizing gas in the fluidized bed retorting 
zone under pyrolysis conditions to produce pyrolysis products and 
pyrolyzed carbon-containing solids. Liquid hydrocarbons are recovered from 
the pyrolysis products and the pyrolyzed solids are passed to an external 
combustion zone. Here the pyrolyzed solids are contacted with an 
oxygen-containing gas under conditions such that at least a portion of the 
residual organic material remaining in the solids is burned to produce hot 
combusted solids. These hot solids are then passed from the external 
combustion zone to the internal combustion zone where they are contacted 
with an oxygen containing gas under conditions such that at least a 
portion of any remaining organic material in the solids is burned to 
produce heat and this heat of combustion along with the sensible heat in 
the hot solids passed into the zone are transferred through the walls of 
the zone into the fluidized bed retorting zone thereby supplying the heat 
required to pyrolyze the carbon-containing feed solids. Substantially none 
of the combusted solids or the flue gas produced in either the external or 
internal combustion zones is passed into the retorting zone. Preferably, 
the fluidizing gas utilized in the retorting zone is a recycle gas 
recovered from the pyrolysis products. 
Normally, the solids exiting the internal combustion zone are recycled to 
the external combustion zone where they are reheated and then passed back 
to the internal combustion zone thereby serving as a heat carrier. 
Preferably, both the external and internal combustion zones contain 
fluidized beds. 
In an alternate embodiment of the invention, the pyrolyzed solids exiting 
the fluidized bed retorting zone are first passed into the internal 
combustion zone where only a portion of the organic material in the solids 
is burned to produce heat, the partially combusted solids are then passed 
to the external combustion zone where at least a portion of the remaining 
organic material is burned to produce hot solids and the resultant hot 
solids are returned to the internal combustion zone where their sensible 
heat and the heat of combustion generated in the zone are transferred 
through the walls of the internal combustion zone into the fluidized bed 
retorting zone to supply all or a major portion of the heat required to 
pyrolyze the carbon-containing feed solids. By utilizing both an internal 
and an external combustion zone to burn the organic material remaining in 
the pyrolyzed solids exiting the retorting zone, the velocity of the 
oxygen-containing gas which is introduced into the internal combustion 
zone can be controlled in such a manner to yield optimum heat transfer 
between the internal combustion zone and the retorting zone. In a system 
where only an internal combustion zone is utilized, the velocity of the 
oxygen-containing gas is set such that enough oxygen is present in the 
zone to burn the amount of organic material in the solids that is required 
to supply the heat for pyrolysis. The gas velocity set in this manner may 
not result in optimum heat transfer between the combustion zone and the 
retorting zone. The use of the external combustion zone in addition to the 
internal combustion zone overcomes this disadvantage by allowing the 
velocity of the oxygen-containing gas through the internal combustion zone 
to be set for optimum heat transfer because the portion of the organic 
material not burned in the internal combustion zone can be burned in the 
external combustion zone and the resultant heat passed with the hot solids 
produced therein to the internal combustion zone for transfer to the 
retorting zone. 
The process of the invention provides many advantages over processes 
proposed in the past for retorting oil shale and other carbon-containing 
solids. Residual organic material in the retorted solids is utilized to 
provide the heat required for retorting in such a way that the flue gas or 
hot solids do not contact the pyrolysis products. Clinker formation is 
minimized by combustion of organic material in a relatively dilute phase 
fluid bed and by improved heat transfer afforded by fluidization. Optimum 
heat transfer to the retorting zone is obtained by adjusting the flow of 
oxygen-containing gas in the internal combustion zone and the flow of 
fluidizing gas in the retorting zone. Fines which are generated by the 
loss of structural and particle integrity in the combustion portion of the 
process are not mixed with pyrolysis products. The use of the process of 
the invention results in greater heat utilization and higher thermal 
efficiency than can be obtained by the use of other retorting processes 
now known.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The systems shown in FIGS. 1 through 3 are designed for retorting or 
pyrolyzing carbon-containing solids in accordance with the process of the 
invention in order to efficiently recover hydrocarbon gases and liquids. 
Although the systems are preferably used to process oil shale, it will be 
understood that they may also be used to retort or pyrolyze bituminous 
coal, subbituminous coal, lignitic coal, solid organic waste, liquefaction 
bottoms, petroleum coke, tar sands and other carbon-containing solids in 
accordance with the process of the invention. 
The retorting system shown in FIG. 1 includes retort 10 and external 
combustor 12. Retort 10 includes a vertical vessel or shell 14 having a 
plurality of elongated, hollow tubular members or combustion tubes 16 
suspended within the vessel between end plates 18 and 20. The combustion 
tubes, which are fabricated from heat conductive materials, are open at 
each end and the open ends of each tube extend through end plates 18 and 
20, respectively. Nozzle 22, located near the top of the space external to 
the combustion tubes between end plates 18 and 20, serves as a means of 
removing the pyrolysis products produced in the retort. Nozzle 24, located 
near the middle of vessel 14, is used for introducing the 
carbon-containing feed material into the retort at a point near the top 26 
of fluidized bed retorting zone 28. 
The bottom portion of the retort 10 contains a distribution tray 30 located 
just above end plate 20. This device serves to distribute a fluidizing gas 
upwardly into fluidized bed retorting zone 28, which occupies a portion of 
the space inside of vessel 10 that is external to combusion tubes 16 and 
extends upward from distributor tray 30 to end plate 18. The fluidizing 
gas is introduced into the retort through nozzle 32. Distribution tray 30 
is preferably a sieve tray but can also be a pipe distributor, a bubble 
cap tray, or similar distribution device. 
When the system depicted in FIG. 1 is in operation, the carbon-containing 
feed solids are introduced through nozzle 24 into fluidized bed retorting 
zone 28 at a point near the top 26 of the zone. The carbon-containing 
solids pass downwardly through the fluidized bed in countercurrent contact 
with an upwardly flowing gas introduced into the retorting zone through 
nozzle 32 and distribution tray 30. This fluidizing gas serves to maintain 
the solids in a fluidized state and may be steam, an inert gas, a recycle 
pyrolysis gas obtained by processing the pyrolysis products removed from 
retort 10 and the like. Preferably, a recycle pyrolysis gas is utilized as 
the fluidizing gas. 
As the carbon-containing solids flow downwardly through retorting zone 28, 
they are subjected to a temperature between about 700.degree. F. and about 
1400.degree. F., preferably between about 900.degree. F. and about 
1000.degree. F. Although any pressure may be utilized in the retorting 
zone, it is preferred to maintain the zone at atmospheric pressure. Under 
the conditions in the retorting zone, the organic material in the 
carbon-containing solids is decomposed and volatilized to produce 
pyrolysis products containing vaporous and gaseous hydrocarbons. These 
pyrolysis products are stripped from the solids by the fluidizing gas and 
pass upwardly with the gas from the top 26 of fluidized bed retorting zone 
28 through the upper portion of retort 10 and out of the vessel 14 through 
nozzle 22. These pyrolysis products are then passed through line 33 to 
cyclone separator or similar device 34 where dust and other fine 
particulates are removed through dip leg 37. The vaporous and gaseous 
hydrocarbons from which the fines have been removed are withdrawn overhead 
from separator 34 through line 36 and passed to condenser 39 where the 
vapors are condensed. Liquid hydrocarbons are removed from condenser 39 
through line 41 and passed to downstream units, not shown in the drawing, 
for upgrading. Gaseous hydrocarbons are removed from the condenser through 
line 43 and passed to downstream processing units, not shown in the 
drawing, where gases are recovered as products and for recycling to retort 
10 through nozzle 32. 
After the carbon-containing solids have undergone pyrolysis in retorting 
zone 28, they are mixed with the fine particulates in dip leg 37 and 
passed through transfer line 38 into fluidized bed 40 in external 
combustor 12. The fluidized bed 40 consists of hot solids which extend 
upward above nozzle 42. The pyrolyzed solids introduced into fluidized bed 
40 are contacted and fluidized with an oxygen-containing gas which is 
introduced into the external combustor through bottom inlet nozzle 42. A 
sufficient amount of the oxygen-containing gas, which is preferably air is 
introduced into the external combustor such that at least a portion of the 
residual organic matter in the pyrolyzed solids fed to the combustor 
reacts exothermally with oxygen to form carbon dioxide, carbon monoxide, 
sulfur oxides, nitrogen oxides and combusted solids which comprise the 
majority of the fluidized bed. The temperature in the external combustor 
will be greater than the temperature in retorting zone 28 and will 
normally be maintained between about 900.degree. F. and about 2000.degree. 
F., preferably between about 1100.degree. F. and about 1400.degree. F. The 
pressure in the external combustor will be essentially the same as the 
pressure in retorting zone 28. The concentration of oxygen in the 
oxygen-containing gas will normally range between about 5 volume percent 
and about 25 volume percent. The combustion taking place within the 
combustor is normally controlled so that all of the organic material in 
the pyrolyzed feed solids is not burned away. A portion of the organic 
material is normally allowed to remain in the solids so that the 
carbon-containing solids produced in the combustor can be further burned 
in a combustion zone internal to retort 10. 
The gas leaving fluidized bed 40 in external combustor 12 passes through 
the upper section of the combustor, which serves as a disengagement zone 
where particles too heavy to be entrained by the gas leaving the vessel 
are returned to the bed. If desired, this disengagement zone may include 
one or more cyclone separators or the like for the removal of relatively 
large particles from the gas. The gas withdrawn from the upper part of the 
combustor through line 46 will normally contain a mixture of carbon 
monoxide, carbon dioxide, sulfur oxides, nitrogen oxides, unreacted 
oxygen, nitrogen and entrained fines. This hot flue gas is introduced into 
cyclone separator or similar device 48 where the fine particulates are 
removed via line 50. The raw, hot flue gas from which the fines have been 
removed is withdrawn overhead from separator 48 through line 52. This hot 
flue gas can be passed to a waste heat boiler or other device where its 
heat can be utilized to generate steam for some other purpose, or it may 
be used to preheat the carbon-containing solids that are fed into retort 
10 through nozzle 24 by passing the hot gas to a preheater where it is 
contacted directly with the incoming carbon-containing feed solids. 
A portion of the heat generated in external combustor 12 by burning a 
portion of the organic material in the solids fed into the vessel through 
line 38 is absorbed by the solids in fluidized bed 40. This heat is 
utilized, in accordance with the invention, to supply a portion of the 
heat necessary to pyrolyze the carbon-containing feed solids introduced 
into retort 10 through nozzle 24. This is accomplished by passing the hot 
solids from external combustor 12 into the combustion tubes 16 in retort 
10 so that the sensible heat in the solids can be transferred through the 
walls of the combustion tubes into retorting zone 28. The hot solids in 
fluidized bed 40 flow downward through standpipe 54 into transfer line 56 
where they are entrained in an oxygen-containing gas, preferably air, 
introduced into the transfer line through line 58. The hot solids are 
carried with the oxygen-containing gas through transfer line 56 into the 
bottom of retort 10 where they are introduced into internal fluidized bed 
combustion zone 60 which extends from the bottom of retort 10 upward 
through combustion tubes 16 to nozzle 62, which is located near the top of 
the retort. 
In the fluidized bed in internal combustion zone 60, the organic material 
remaining in the solids fed to the retort through line 56 reacts with the 
oxygen in the fluidizing gas to produce carbon monoxide, carbon dioxide, 
sulfur oxides, nitrogen oxides and large quantities of heat. The heat 
generated in the combustion zone and the sensible heat carried into the 
combustion zone with the solids from external combustor 12 are transferred 
through the walls of combustion tubes 16 into retorting zone 28 to supply 
substantially all or a major portion of the heat required in the retorting 
zone to pyrolyze the carbon-containing feed solids. Normally, the only 
other source of pyrolysis heat is the heat in the fluidizing gas 
introduced into the retorting zone through nozzle 32 and distribution tray 
30. In some cases, however, it may be desirable to supply additional heat 
into the retorting zone by burning a supplementary fuel, such as a fuel 
gas, in external combustor 12, internal combustion zone 60, or in both. 
The temperature in internal combustion zone 60 is normally maintained at a 
level substantially higher than the temperature in retorting zone 28 and 
normally ranges between about 900.degree. F. and about 2000.degree. F., 
preferably between about 1100.degree. F. and about 1400.degree. F. The 
pressure in combustion zone 60 will be essentially the same as the 
pressure in retorting zone 28. The concentration of the oxygen in the 
oxygen-containing gas introduced into the retort through lines 58 and 56 
will normally range between about 5 volume percent and about 25 volume 
percent. 
As the carbon-containing feed solids pass downwardly from inlet nozzle 24 
through fluidized bed retorting zone 28, they are heated to increasingly 
higher temperatures by countercurrent heat transfer from the hot gases and 
solids which flow upwardly through combustion tubes 16. This 
countercurrent heat transfer is a highly thermodynamically reversible 
process and results in greater heat utilization and higher thermal 
efficiencies than are possible with other methods of heat input. The 
optimum heat transfer from the portion of the internal combustion zone 
contained within combustion tubes 16 through the walls of the tubes into 
retorting zone 28 can be obtained only by varying the velocities of the 
gases flowing through the internal combustion zone and through the 
retorting zone in accordance with conventional heat transfer calculations. 
It has been found that the use of an external combustion zone in addition 
to the internal combustion zone will allow flexibility in selecting the 
amount and therefore the velocity of the oxygen-containing gas that flows 
through the internal combustion zone. Thus use of an external combustion 
zone allows optimum heat transfer to be obtained between the internal 
combustion zone and the retorting zone to efficiently supply the heat 
necessary to pyrolyze the raw carbon-containing feed solids without the 
need to supply external heat to the retorting zone in the form of added 
hot solids or hot gases. 
Referring again to FIG. 1, the number of combustion tubes 16 utilized in 
retort 10 will depend upon the amount of heat required to be transferred 
from the internal combustion zone 60 into retorting zone 28. The greater 
the number of combustion tubes utilized, the greater the area of heat 
transfer available and the more heat that can be provided to the retorting 
zone for pyrolysis of the carbon-containing feed solids. Also, a greater 
number of combustion tubes can be used to minimize circulation and mixing 
so that the carbon-containing feed solids and fluidizing gas introduced 
into the retorting zone flow countercurrently to each other in a 
relatively plug flow manner. 
The spent solids exiting the top of combustion tubes 16 will have given up 
a substantial amount of their heat content through the walls of the tubes 
into retorting zone 28 and will be relatively cool. These cool solids are 
removed from the upper portion of the retort through nozzle 62 and passed 
through line 64 into the upper portion of external combustor 12 at a point 
above fluidized bed 40. In order to maintain a desired bed level in 
external combustor 12, a portion of these spent solids are removed from 
the entire system as a purge through line 66. The relatively cool, spent 
solids that are introduced into external combustor 12 are continually 
circulated between the combustor and internal combustion zone 60 in retort 
10 until they are purged from the system through line 66. The continuous 
circulation of these spent solids allows the temperature in external 
combustor 12 to be maintained at a level such that high temperature alloys 
are not needed for vessel construction and undesirable high temperature 
mineral reactions do not take place. The cool, spent solids entering the 
combustor through line 64 absorb a portion of the heat generated in the 
combustor thereby maintaining the temperature at a relatively low level, 
preferably between about 1100.degree. F. and about 1400.degree. F. The 
temperature in the combustor can be lowered by increasing the circulation 
rate of the spent solids. 
The gas leaving the fluidized bed in internal combustion zone 60 passes 
through the upper section of retort 10, which serves as a disengagement 
zone where particles too heavy to be entrained by the gas leaving the 
vessel are returned to the bed. If desired, this disengagement zone may 
include one or more cyclone separators or the like for the removal of 
relatively large particles from the gas. The gas withdrawn from the upper 
part of the retort through line 68 will normally contain a mixture of 
carbon monoxide, carbon dioxide, sulfur oxides, nitrogen oxides, unreacted 
oxygen, nitrogen and entrained fines. This hot flue gas is introduced into 
cyclone separator 70 where the fine particulates are removed through line 
72. The raw, hot flue gas from which the fines have been removed is 
withdrawn overhead from separator 70 through line 74 and can be passed to 
a waste heat boiler or other device where its heat can be utilized to 
generate steam or for some other purpose. Alternatively this flue gas can 
be used to preheat the carbon-containing solids fed to retort 10. 
It will be understood that the process of the invention can be carried out 
in an apparatus which differs from that shown in FIG. 1 as long as the 
internal combustion zone is situated with respect to the retorting or 
pyrolysis zone in such a manner that the sensible heat in the combusted 
solids passed to the internal combustion zone from the external combustion 
zone and the heat of combustion generated in the internal combustion zone 
can be transferred through the walls of the internal combustion zone to 
the retorting or pyrolysis zone. In the embodiment of the invention 
depicted in FIGS. 2 and 3, the retorting and internal combustion zones are 
reversed. Thus, the tubes that contain a portion of the internal 
combustion zone in the apparatus of FIG. 1 contain the retorting zone in 
the apparatus of FIGS. 2 and 3. Similarly, the space external to 
combustion tubes 16 and encompassed by the walls of vessel 14 that 
contains the retorting zone in the apparatus shown in FIG. 1 contains the 
internal combustion zone in the apparatus depicted in FIGS. 2 and 3. 
Referring specifically to FIGS. 2 and 3, retort 76 is comprised of vertical 
vessel 78 and a plurality of open-ended pyrolysis tubes 80 mounted inside 
vessel 78 between end plates 82 and 84. Vessel 78 contains nozzle 86 for 
the introduction into the retort of the carbon-containing feed solids, 
nozzle 88 for withdrawing the pyrolysis products, nozzle 90 for 
withdrawing spent burned solids and nozzle 92 for introducing an 
oxygen-containing gas into the retort. Retort 76 communicates with 
external combustor 94 via connecting line 96, loop transfer line 98 and 
lift pipe 100. 
The bottom of retort 76 contains distribution tray 102 for the introduction 
of the oxygen-containing gas into fluidized bed internal combustion zone 
104, which comprises the space inside the retort encompassed by the walls 
of vessel 78 and extending upward from distribution tray 102 to connecting 
line 96. Also located at the bottom of retort 76 are gas distribution 
pipes 106. As shown in FIG. 3, these pipes enter vessel 78 from manifold 
108 and line 110. Each distribution pipe 106 contains a sufficient number 
of nozzles 107 such that the bottom of each pyrolysis tube 80 has a nozzle 
extending vertically into it from a distribution pipe. The distribution 
pipes and nozzles serve to introduce a fluidizing gas into fluidized bed 
retorting zone 112, which is partially contained within the pyrolysis 
tubes 80. 
When the embodiment of the invention depicted in FIGS. 2 and 3 is in 
operation, the carbon-containing feed solids are introduced into the top 
of retort 76 through nozzle 86 and passed into fluidized bed retorting 
zone 112, which extends downwardly into each pyrolysis tube 80. The 
carbon-containing solids flow downwardly through the pyrolysis tubes in 
contact with a fluidizing gas passed upwardly into the bottom of each 
pyrolysis tube 80 through nozzles 107 and distribution pipes 106. The 
fluidizing gas may be steam, an inert gas, a recycle pyrolysis gas 
obtained by processing the pyrolysis products exiting retort 76 through 
nozzle 88 or the like. As the solids flow downward through the pyrolysis 
tubes, they are subjected to a temperature between about 700.degree. F. 
and about 1400.degree. F., preferably between about 900.degree. F. and 
about 1000.degree. F. Normally, the pressure in the pyrolysis tubes is 
maintained at or near atmospheric pressure. Under such conditions, the 
organic material in the carbon-containing solids is decomposed and 
volatilized to form hydrocarbon gases and vapors that flow upwardly 
through the pyrolysis tubes toward the top of fluidized bed retorting zone 
112. 
The hydrocarbon vapors and gases that leave the fluidized bed in retorting 
zone 112 pass through the upper section of the retort, which serves as the 
disengagement zone where particles too heavy to be entrained by the vapor 
and gases leaving the vessel are returned to the bed. If desired, this 
disengagement zone may include one or more cyclone separators or the like 
for the removal of relatively large particles from the vapors and gases. 
The vapors and gases are withdrawn from the upper part of the retort 
through line 114 and passed to cyclone separator or similar device 116 
where dust and other fine particulates are removed through dip leg 118. 
The hydrocarbon vapors and gases from which the fines have been removed 
are withdrawn overhead from separator 116 through line 120 and passed to 
downstream processing units, not shown in the drawing, for the recovery of 
liquid and gaseous hydrocarbon products. 
The pyrolyzed solids flowing downwardly through pyrolysis tubes 80 exit the 
tubes and continue to pass downwardly around nozzles 107 and pipes 106 and 
out of the retort through line 122. The pyrolyzed solids pass from line 
122 into lift pipe 100 where they are entrained in steam or another inert 
gas introduced into the lift pipe through line 124. The inert gas and 
pyrolyzed solids are then mixed with fine particulates of pyrolyzed solids 
introduced into lift pipe 100 through dip leg 118 and the resultant 
mixture of solids entrained in the gas is passed into fluidized bed 126 of 
hot solids extending upward within external combustor 94 above nozzle 130. 
The pyrolyzed solids introduced into fluidized bed 126 are maintained in a 
fluidized state within the external combustor by means of an 
oxygen-containing gas, preferably air, introduced into the combustor 
through bottom inlet nozzle 130. The oxygen in the gas introduced into the 
bottom of the combustor reacts with at least a portion of the residual 
organic material in the pyrolyzed solids fed to the combustor through lift 
pipe 100 to form carbon dioxide, carbon monoxide, sulfur oxides, nitrogen 
oxides, combusted solids, which comprise the majority of the fluidized 
bed, and a substantial amount of heat. The temperature in the combustor is 
maintained at a level higher than the temperature in retorting zone 112 
and will normally range between about 900.degree. F. and 2000.degree. F., 
preferably between about 1100.degree. F. and 1400.degree. F. The pressure 
in the external combustor is essentially the same as the pressure in 
retorting zone 112. The combustion which takes place in fluidized bed 126 
is normally controlled so that all of the organic material in the 
pyrolyzed solids fed to the external combustor is not burned away. A 
portion of the organic material is normally allowed to remain so that the 
particles produced in the combustor can be further burned in internal 
combustion zone 104. 
The flue gas leaving the fluidized bed in external combustor 94 passes 
through the upper section of the combustor through a disengagement zone, 
which may include one or more cyclone separators or the like, for removal 
of relatively large particles from the gas. The gas withdrawn from the 
upper part of the combustor through line 132 will normally contain a 
mixture of carbon monoxide, carbon dioxide, sulfur oxides, nitrogen 
oxides, unreacted oxygen, nitrogen and entrained fines. This hot flue gas 
is introduced into cyclone separator or similar device 134 where the fine 
particulates are removed and withdrawn through line 136. Hot flue gas from 
which the fines have been removed is withdrawn overhead from the separator 
through line 138 and can be passed to downstream processing units for 
recovery of its heat content. 
The heat of combustion produced in external combustor 94 by burning the 
organic material in the particles fed into the external combustor through 
lift pipe 100 is absorbed by the solids in fluidized bed 126. These hot 
solids, which include partially burned particles containing residual 
organic material, are passed from fluidized bed 126 through loop transfer 
line 98 into the fluidized bed of solids in internal combustion zone 104, 
which extends upward above distribution tray 102 in retort 76. The solids 
are maintained in the fluidized state within internal combustion zone 104 
by an oxygen-containing gas, preferably air, introduced into the 
combustion zone through nozzle 92 and distribution tray 102. 
As the hot particles pass upward from loop transfer line 98 through 
internal combustion zone 104, the organic material remaining in the 
partially burned particles reacts with oxygen in the oxygen-containing gas 
to produce carbon monoxide, carbon dioxide, sulfur oxides, nitrogen oxides 
and additional quantities of heat. The heat thus generated along with the 
sensible heat in the hot particles introduced in the zone through loop 
transfer line 98 are transferred through the outer walls of each pyrolysis 
tube 80 into retorting zone 112 to supply substantially all or a major 
portion of the heat required to pyrolyze the carbon-containing solids that 
are introduced into the retort through nozzle 86. Normally, the 
temperature in the internal combustion zone will be maintained between 
about 900.degree. F. and about 2000.degree. F., preferably between about 
1100.degree. F. and about 1400.degree. F. The pressure in the combustion 
zone will be essentially the same as the pressure in retorting zone 112. 
In the embodiments of the invention described above and depicted in FIGS. 1 
and 2, the heat of pyrolysis is supplied by burning at least a portion of 
the organic material remaining in the pyrolyzed, carbon-containing feed 
solids. This heat is obtained by burning the residual organic material in 
both an external combustion zone and an internal combustion zone and the 
heat is supplied to the retorting zone indirectly through the walls of the 
internal combustion zone so that it is not necessary to pass hot combusted 
solids or flue gases directly into the retorting zone. The use of an 
external combustion zone in addition to the internal combustion zone 
yields substantial advantages over retorting systems which utilize only an 
internal combustion zone to supply indirect heat to the retorting zone. In 
the latter system, the amount of oxygen-containing gas supplied to the 
internal combustion zone is set by the amount of heat required for the 
pyrolysis and therefore the velocity of the oxygen-containing gas through 
the internal combustion zone is set to supply this required heat. This 
predetermined velocity, however, may have a deleterious effect on the heat 
transfer taking place between the internal combustion zone and the 
retorting zone. Ordinarily, it is desirable to set the velocities of the 
gases in the combustion zone and the retorting zone to obtain optimum heat 
transfer. The use of an external combustion zone in addition to the 
internal combustion zone allows the velocity of the oxygen-containing gas 
in the internal combustion zone to be set such that optimum heat transfer 
can be obtained. Any additional heat that ordinarily would have to be 
supplied by burning the residual organic material in the internal 
combustion zone can be supplied by burning the organic material in the 
external combustion zone and passing the resultant hot solids into the 
internal combustion zone where their sensible heat can be transferred to 
the retorting zone. 
Referring again to FIG. 2, the amount of the oxygen-containing gas 
introduced into internal combustion zone 104 through nozzle 92 and 
distribution tray 102 is controlled in order to obtain optimum heat 
transfer between combustion zone 104 and retorting zone 112. The amount of 
oxygen-containing gas introduced into external combustor 94 through bottom 
inlet 130 is determined by the amount of heat that must be generated in 
external combustor 94 to supply the additional heat required in internal 
combustion zone 104 to supply the heat requirements of retorting zone 112. 
If the amount of heat generated in both external combustor 94 and internal 
combustion zone 104 is insufficient to supply all of the heat required for 
pyrolysis, a supplementary gaseous or solid fuel may be added directly to 
the combustor to generate the additional heat required. This fuel may be a 
fuel gas, coal, coal liquefaction bottoms, or similar solid carbonaceous 
materials. 
The relatively cool, spent solids exiting the top of internal combustion 
zone 104 are passed with the flue gas generated in the combustion zone 
through connecting line 96 into external combustor 94. A portion of these 
spent solids is purged from retort 76 through nozzle 90 in order to keep 
them from building up within the system. When the cool, spent solids enter 
fluidized bed 126 in external combustor 94, they absorb a portion of the 
heat generated therein and can therefore be used to control the 
temperature in the external combustor. As the circulation rate of the 
spent solids is increased, the temperature in the combustor will decrease. 
In the embodiments of the invention described above and depicted in the 
figures, the pyrolyzed, carbon-containing solids exiting the retorting 
zone are first passed to an external combustion zone where a portion of 
their residual organic material is burned and the resultant hot, partially 
burned or combusted solids are passed to an internal combustion zone where 
all or a portion of the remaining organic material is burned. The heat 
generated in both zones is indirectly transferred from the internal 
combustion zone into the retorting zone. It will be understood that the 
invention is not limited to the situation in which the pyrolyzed, 
carbon-containing solids are passed into the external combustion zone 
first, but is equally applicable to the case where the pyrolyzed solids 
are first passed to the internal combustion zone and the resultant 
partially burned solids are then passed to the external combustion zone. 
If it is desired to practice such a procedure, the embodiment of the 
invention depicted in FIG. 2 may be altered by eliminating lift pipe 100 
and allowing the pyrolyzed solids exiting retort 76 through line 122 to 
pass directly into loop transfer line 98. This alteration in the system 
depicted in FIG. 2 will allow the pyrolyzed solids to flow directly with 
solids from external combustor 94 into internal combustion zone 104 where 
a portion of the residual organic material in them will be burned. The 
partially combusted or burned solids will then exit internal combustion 
zone 104 through connecting line 96 and pass to external combustor 94 
where all or a portion of the remaining organic material is burned. In 
this embodiment of the invention the solids in the internal combustion 
zone will be rich in organic material and the maximum amount of heat will 
therefore be generated in the internal combustion zone where the 
fluidizing rate of oxygen-containing gas is set to obtain optimum heat 
transfer to the retorting zone. The external combustor can then be 
operated in any way desired without fear of burning too much organic 
material. 
It will be apparent from the foregoing that the invention provides a method 
in which carbon-containing solids are pyrolyzed or retorted in such a 
manner that the heat of pyrolysis is supplied by burning the pyrolyzed 
solids in two combustion zones and the heat of combustion is indirectly 
transferred through the walls of one of the combustion zones into the 
retorting zone. As a result, it is not necessary to supply the heat 
required for pyrolysis by passing externally heated gases or solids 
directly into the retorting zone and it is possible to optimize heat 
transfer to the retorting zone by controlling the velocity of oxidizing 
gases in the combustion zone through whose walls the heat is transferred 
to the retorting zone.