CA1165259A - Staged burning of retorted carbon-containing solids - Google Patents
Staged burning of retorted carbon-containing solidsInfo
- Publication number
- CA1165259A CA1165259A CA000399028A CA399028A CA1165259A CA 1165259 A CA1165259 A CA 1165259A CA 000399028 A CA000399028 A CA 000399028A CA 399028 A CA399028 A CA 399028A CA 1165259 A CA1165259 A CA 1165259A
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- Canada
- Prior art keywords
- fine
- coarse
- solids
- preburner
- zone
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G1/00—Production of liquid hydrocarbon mixtures from oil-shale, oil-sand, or non-melting solid carbonaceous or similar materials, e.g. wood, coal
- C10G1/02—Production of liquid hydrocarbon mixtures from oil-shale, oil-sand, or non-melting solid carbonaceous or similar materials, e.g. wood, coal by distillation
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Gasification And Melting Of Waste (AREA)
- Processing Of Solid Wastes (AREA)
- Combustion Of Fluid Fuel (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Residual carbon in pyrolyzed solids burned by combusting a fine fraction separating in a first dilute phase combustion zone and mixing the fine fraction and the bulk of the pyrolyzed solids in a second dilute phase combustion zone.
Residual carbon in pyrolyzed solids burned by combusting a fine fraction separating in a first dilute phase combustion zone and mixing the fine fraction and the bulk of the pyrolyzed solids in a second dilute phase combustion zone.
Description
~L~65'~59 Certain naturally occurring materials contain a carbonaceous component which, upon heating, will release a hydrocarbon product which is useful as a feedstock in petroleum processing. These "carbon-containing solids," such as oil shale and tar sands, including diatomite, may be pyrolyzed in reactor vessels having various designs. Following the pyrolysis of the carbon-containing solid to extract the volatile compon-ents, a "pyrolyzed solid" remains which contains a carbonaceous residue which may be burned to yield heat energy. The heat recovered from this carbonaceous residue may be used to supply heat for the pyrolysis of fresh carbon-containing solids during the process.
The inorganic residue that remains after the combustion of the carbonaceous residue is called "ash," or in the case of oil shale, "burned sha}eO" This material is recycled in some retorting processes as "heat carrier material," iDe., the hot burned shale from the combustion is mixed with fresh oil shale and the heat provided is used for pyrolyzing the fresh shaleO United States Patent Nos, 4,199,432 and ~,183,800 describe processes in which the oil shale or other carbon-containing solid is pyrolyzed in a downward moving bed containing a mixture of recycled hot burned shale (used as heat carrier material) and ; 20 particulate fresh oil shaleO A countercurrent flow of gas passes upward through the bed removing the product vapors and entraining the finer particulate fractions of the oil shale. The fine particles and product vapors are drawn off the top of the reactor vessel, and the fine shale particles are r~moved from the gas stream by a separation device, such as a cycloneO Processes such as this present some problems in designing an ; efficient combustor for burning the pyrolyzed oil shade which is recycled ,,, as the heat carrier materialO
During combustion of the carbonaceous residue in the pyrolyzed oil shale to produce heat, the physical integrity of the shale particles - is changed and a substantial amount of fine grained burned shale is produced which is not suitable for use as recycled heat carrier particles.
Therefore, it is usually necessary to separate this fine material prior to recycling the coarser grained particlesO
In process schemes us mg a liftpipe combustor to burn the carbonaceous residue in the pyrolyzed oil shale, sufficient residence time is required to complete combustion and to assure a thermal equilibrium between the hot burning particles and the cooler recycle particlesO Typically, a minimum residence time of 2 to 3 seconds in the combustion zone is requiredO If the fine shale and coarse shale particles are combusted in a liftpipe, the pipe must be of sufficient length to provide adequate residence time for all particles.
The present invention is advantageous for efficiently burning particulate pyrolyzed oil shale or other partlculate carbon-containing solids where the fine grained material and the coarser grained material are separated prior to combustion and the burned shale serves as heat transfer material in the process.
In its broadest aspect, this invention concerns a process for burning pyrolyzed solids containing a carbonaceous residue to provide heat for the pyrolysis of a particulate carbon-containing solid, wherein said pyrolyzed solids contain both a fine fraction and a coarse fraction and at least part of said fine fraction is contained in a separate feed-stream from the coarse fraction of the pyrolyzed solids, said process ~65~5~
comprising:
(a) burning at least part of the carbonaceous residue in the fine fraction contained in said separate feedstream in a dilute phase preburner by entraining the fine fraction in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the particles in the fine fraction;
(b) mixing the entrained, partially burned fine fraction from the preburner with the remainder of the pyrolyzed solids in a second entraining gas stream having a velocity greater than the terminal velocity of the coarse and fine fractions; and (c) burning the unburned carbonaceous residue in the entrained fine and coarse fractions in a second dilute phase combustion zone through which the second entraining gas and entrained solids are directed, said second dilute phase combustion zone containing sufficient oxygen to burn all of the unburned carbonaceous residue in the fine and coarse - fractions.
The process that is the subject of this invention is particularly advantageous when the carbon-containing solid is oil shale and the ash ~or burned shale in the case of oil shale) is used as heat carrier mate-rial. In such a process scheme, means are usually provided for separating the fine ash leaving the second dilute phase combustion zone from the coarse ash. This is because ash particles smaller than about 100 mesh (Tyler Standard) are generally not suitable for recycling as heat carrier material. Various means for such a separation are known to those skilled in the art and include a solids disengaging zone, cyclones, sifting devices, etcO It should be understood that the terms "fine" and "coarse,"
~6S2S9 when applied to both pyrolyzed solids and ash, are relative terms and the precise size of particle may vary in different embodiments of the invention or with the retorting process employed. However, for most purposes, a cut size of about 100 mesh represents a reasonable division of particle size between coarse and fineO
The present invention is further directed to a process for producing heat from retorted oil shale containing residual carbonaceous material, wherein said retorted oil shale contains both fine and coarse grained material and at least part of said fine grained material is contained in a separate feedstream from the coarse grained material, said process comprising:
.~- (a) burning at least part of the residual carbonaceous material in the fine grained material present in said separate feedstream in a fine preburner by entraining said fine particles in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the fine particles;
~b) burning part of the carbonaceous residue in the coarse grained material in a coarse preburner containing less than a stoichiometric amount of oxygen;
~c) mixing the entrained partially burned fine grained material from the fine preburner and the partially burned coarse grained material from the coarse preburner in a second entraining gas stream having a velocity greater than the terminal velocity of the mixture of fine and coarse particles and containing at least a stoichiometric amount of oxygen; and ~d) burning the carbonaceous residue remaining in the entrained ~ 652~9 fine and coarse grained material in a vertical combustion zone through which said second entraining gas is directed.
This invention also concerns an improved combustion device for burning particulate retorted oil shale separated into a flne particulate feedstream and a coarse particulate feedstream which comprises:
(a) a generally vertical main combustion chamber having an upper zone closed at the top, a middle zone, and a lower zone open at the : bottom, said lower zone having means for pneumatically entraining solids entering said lower zone, said middle zone being an elongate tubular zone adapted for the combustion of entrained particulate solids, said upper zone being adapted for the disengagement of entrained coarse particles and for the collection and removal of the disengaged coarse particles, said : upper zone further having an outlet for the removal of combustion gases - and fine entrained particles;
~ b) a generally vertical tubular fine solids combustion chamber adapted for burning pneumatically entrained fine solids, said fine solids combustion chamber having an open upper end communicating with the lower zone of the main combustion chamber, said fine solids combustion chamber further having a lower end having an inlet for the introduction of ~0 the fine particulate feedstream and means for pneumatically entraining the fine particulate material and conveying it the length of the fine solids combustion chamber; and ~ c) a coarse solids preburning chamber having an inlet for the introduction of the coarse particulate feedstream, means for fluidizing a burning bed of the coarse particulate material, and means for communication with the lower zone of the main combustion chamber.
~65ZS~
As used herein, the phrase "terminal velocity" refers to the maximum velocity attained by a particle falling in a very long column of stagnant air. A particle will become entrained in a flow of gas when the velocity of the gas exceeds the terminal velocity of the particle. Thus, an entraining gas is a gas having a velocity in excess of the terminal velocity of a given size of particle.
In the accompanying drawings:~
Figure l is a schematic representation of an oil shale retorting process of the type in which the present invention may be used most advantageously;
Figure 2 illustrates a cross-sectional view of one design for a - combustor which may be used in the process;
Figure 3 illustrates a cross-sectional view of an alternative design for a combustor which may be used in the process; and Figure 4 illustrates a cross-sectional view of a preferred embodiment of the combustion device of this invention.
Referring to Figure l, fresh crushed oil shale enters retort 2 via conduit 4 where it is mixed with the hot heat carrier material tburned shale) entering the retort through conduit 6. The mixture of hot burned shale and fresh shale moves downward in the retort 2 through a series of dispersing elements 8, lO and 12 which prevent substantial vertical bachmixing of the solidsO A substantially oxygen free stripping gas enters retort 2 through gas inlet 14 creating a countercurrent gas flow through the retort in opposition to the downward moving bed of shaleO Gas from the gas inlet 14, product vapors, and pneumatically entrained fine particles of shale move upward and leave the retort via conduit 160 The gas and .. .
5~S9 product vapors are separated from the entrained fines in cyclone 18;
the gaseous material exits by conduit 20 and the fines are carried away .- by conduit 22.
The coarse material containing particles of both burned oil shale and pyrolyzed oil shale leaves the bottom of retort 2 via solids conduit 24 and is conveyed to the combustor 26. Air entering the combustor via air conduit 28 is mixed with the coarse particles of shale, and the residual carbonaceous material present in the pyrolyzed material is ignitedO In this particular processs&heme, the fine particulate oil shale . 10 material separated by cyclone 18 enters the combustor as a separate feedstream from the coarse particulate material from the retort. The advantages of this scheme will be discussed in detail later. The fine material carried by conduit 22 is pneumatically entrained by air from conduit 30 and enters the combustor at the bottomO Following combustion of the carbonaceous residue, the coarse particles of burned shale and fine particles of burned shale are separated in the top part of the combustor, The coarse particles of burned shale leave the combustor via common conduit 320 Hot burned shale serving as heat carrier material is recycled to the retort via conduit 6 while excess burned shale is drswn off through outlet 34~ Flue gases and entrained fines leave the combustor via conduit 36 and are carried to cyclone 380 Fines are disposed of through conduit 40. Flue gases are carried off via conduit 42 for venting or recycling as stripping gasO
Turning to Pigure 2, a combustion device suitable for use in the retorting process described above is illustratedO Fine particles of shale separated from the product vapors and stripping gas enter the engaging ~P65Z59 chamber 104 at the bottom of the combustor via conduit 1020 Air enters chamber 106 by way of air line 108. The fine particles of shale are entrained by the air stream and carried upward through the fine shale preburner 110 where they are ignited and partially burnedO The burning fines exit the open upper end 112 of the fine shale preburner 110 and enter the main liftpipe engaging area 114 for the main combustion liftpipe Pyrolyzed shale from the bottom of the retort enters the main liftpipe engaging area 114 via conduit 1180 This feed may contain some fine particles but will consist mostly of coarser grained shale particles of a large enough size to not be entrained by the stripping gas passing through the retortO Shale entering via conduit 118 along with fine shale from the preburner 110 are entrained in additional air entering through air conduit 120. Both coarse and fine particles are carried upward by the gas stream and burned in the main combustion liftpipe 116.
The burned particles of oil shale enter the enlarged disengaging chamber 122 of the combustor which serves as a coarse solids disengaging area.
The coarse particles of burned shale settle out in collection zone 124 while the burned fines and flue gases leave the combustor via outlet 126, Coarse particles of burned shale for recycling to the retort or for disposal are removed via outlet 1280 An alternate embodiment for a combustor which may be used in carrying out this process is shown in Figure 3O In this design the fine shale enters the vertical fine preburner 202 via conduit 204. Air enters the preburner and entrains the fines by way of a venturi throat 206~ The burning fines enter plenum chamber 208 where they are mixed with .,.~ .
~. ~65'~59 secondary air entering via conduit 210. The bulk of the retorted oil shale enters the combustor through conduit 212 and is mixed in the engager 214 with the fines entering from the plenum chamber. The velocity of the primary and secondary air is sufficient to entrain both the coarse and fine particles which are carried up the main liftpipe combustor 216 where the coarse material is burnedO An adjustable seat 218 controls the size of opening ;220 between the engager and the main liftpipe combustor 216~ Tertiary air may be introduced as needed via conduit 222 to maintain sufficient velocity to prevent choking of the liftpipe, iOeO, collapse of the solids due to insufficient velocity to maintain entrainment, or to introduce additional oxygen for combustion. The burned shale and flue gas leave the combustor via outlet 224 and pass to a solids disengaging zone (not shown).
A particularly preferred way of operating the process which is the subject of this invention is by inclusion of a preburner for the coarse shale to partially burn the carbonaceous residue therein prior to mixing with the fine shale in the second dilute phase combustion zone.
Such an embodiment is shown in Figure 4.
As shown in Figure 4, fine particles of shale from the retort are carried to the combustor by fine shale inlet line 102. Air entering air inlet 104 is distributed around the open end 106 of fine shale liftpipe 108 by air plenum 110. The pneumatically entrained fines are ignited and carried upward through fine shale liftpipe 108. The burning fines exit the open upper end 112 of the fine shale liftpipe 108 and enter the liftpipe engaging area 114 for the main combustion liftpipe 116.
Coarse shale from the retort enters the annular coarse shale i9 preburning area 118 via inlet 1200 A fluidized bed of coarse shale is supported by perforated plate 122 and burned with a fluidizing gas containing a substoichiometric amount of oxygen introduced via inlet 124. Coarse particles from the fluidized bed in the preburner 118 spill over into the liftpipe engaging area 114 of the main combustion liftpipe where they, along with fine shale from fine shale liftpipe 108, are ~ entrained in a gas stream containing excess oxygen entering through primary air inlet 126. Both coarse and fine particles are carried upward by the gas stream and burned in the main combustion liftpipe 116.
The burned particles of oil shale enter the enlarged upper zone 128 of the combustion device which serves as a coarse solids disengaging area~
The coarse particles Gf burned shale settle out in collection zone 130 while the burned fines and flue gases leave the combustion device via outlet 132. Coarse particles of burned shale for recycling to the retort are drawn off Yia outlet 1340 Excess burned coarse shale is removed via outlet 136 for disposalO
As used herein, the phrase "fine particles of burned shale"
refers to particles of a size unsuitable for recycling as heat transfer material. Usually particles smaller than aboui 100 mesh size tTyler standard) are not suitable for use in the retorting process. Therefore, particles below this range are preferably removed with the flue gas as entrained fines. The separation of the fine and coarse particles is inherent in the design of the upper disengaging area of the combustion deviceO By exclusion "coarse particles of burned shale" refer to particles larger than about 100 mesh size. It should be understood that the terms fine and coarse are relative terms, the size of which may vary ' ` ~652~9 somewhat depending on the exact details of the process scheme. Thus in process schemes where particles smaller than 100 mesh may be tolerated, the term fine may include particles of a smaller diameter. Likewise, under other circumstances particles of a larger minimum mesh size may be required and the definition of "fine" may be adjusted accordingly.
In carrying out the process that is part of this invention the fine particles of retorted oil shale are preferably burned in the fine shale liftpipe with a substoichiometric amount of oxygen, iOe., insuffic-ient oxygen to allow complete combustion of the char. An air to fuel ratio in the range of from about 0O2 to about 0O9 would be suitable for operation This is to prevent excessive carbonate decomposition.
Usually temperatures in both the fine shale liftpipe and the coarse preburner are kept below about 1500F.
To insure entrainment of the fine particles in the fine shale liftpipe a minimum gas velocity of about 4 to 6 feet per second is required to prevent choking, i.eO, collapse of the solids in the pneumatic pipeO Preferably the velocity of the entraining gas is in the range of from about lO feet per second to about 20 feet per secondO In the preferred embodiment of this invention the fine particles have a residence time of about 105 to 2 seconds in the fine shale liftpipe which results in about 25% of the carbonaceous residue being burned in that zone (air/fuel mole ratio = o25)~
The coarse preburner is also operated in the substoichiometric mode and is usually designed to contain a bed of burning coarse material fluidized by a flow of gas from below.
The flow of gas through the main combustion liftpipe must be ~ ~5259 sufficient to entrain both the fine and the coarse particles of shale.
Usually a gas velocity in the range of from about 50 feet per second to about 150 feet per second is employed, with a preferred range of from about 80 feet per second to about 100 feet per second. It should be noted the velocity of the gas in the main combustion liftpipe is usually higher than that in the fine shale liftpipe to insure entrainment of particles entering from the coarse preburner. Combustion in the main liftpipe is carried out with at least a stoichiometric amount of oxygen present, and usually an excess of oxygen is employed. In the preferred embodiment of this invention the velocity of the gas in the main combustion liftpipe is greater than that in the fine shale liftpipeO
The combustion device and process described herein has the advantage of minimizing the height of the liftpipe required to completely burn the particles of retorted oil shaleO By preburning the coarse and fine shale in separate zones taking advantage of the relative sizes of both feeds, the total residence time required for combustion is satisfied in a shorter liftpipeO
Although the process of this invention is most advantageously used in an oil retorting process using recycled burned shale as the heat transfer material, the invention should not be limited to that retorting method. One skilled in the art can easily devise schemes by which other types of heat transfer material, such as for example ceramic compositions, sand, alumina, iron, steel or the like, are employed. In such an instance the heat transfer material may be simply mixed with the coarse shale feedstream to the combustor~ Even in processes using spent shale as the principal heat transfer material, it is often necessary to add supplemental ~ -12-~6~'~59 heat transfer material to the systems. Likewise, it is possible to devise other embodiments of the invention which could utilize the hot flue gas in retorting the raw oil shale or even use the combustor to heat water to produce steam.
In addition, if the carbonaceous residue in the pyrolyzed solids is insufficient to provide the necessary heat for maintaining the temperature in the reactor vessel at pyrolyzing levels, a supplemental fuel, such as granular coal or oil, may be added to the solids entering the combustor. Such a mode of operation may be necessary when the carbon-containing solid is of a low grade or where large amounts of supplemental heat carrier material are employed, thus lowering the percent of carbonaceous residue present in the feedO
The inorganic residue that remains after the combustion of the carbonaceous residue is called "ash," or in the case of oil shale, "burned sha}eO" This material is recycled in some retorting processes as "heat carrier material," iDe., the hot burned shale from the combustion is mixed with fresh oil shale and the heat provided is used for pyrolyzing the fresh shaleO United States Patent Nos, 4,199,432 and ~,183,800 describe processes in which the oil shale or other carbon-containing solid is pyrolyzed in a downward moving bed containing a mixture of recycled hot burned shale (used as heat carrier material) and ; 20 particulate fresh oil shaleO A countercurrent flow of gas passes upward through the bed removing the product vapors and entraining the finer particulate fractions of the oil shale. The fine particles and product vapors are drawn off the top of the reactor vessel, and the fine shale particles are r~moved from the gas stream by a separation device, such as a cycloneO Processes such as this present some problems in designing an ; efficient combustor for burning the pyrolyzed oil shade which is recycled ,,, as the heat carrier materialO
During combustion of the carbonaceous residue in the pyrolyzed oil shale to produce heat, the physical integrity of the shale particles - is changed and a substantial amount of fine grained burned shale is produced which is not suitable for use as recycled heat carrier particles.
Therefore, it is usually necessary to separate this fine material prior to recycling the coarser grained particlesO
In process schemes us mg a liftpipe combustor to burn the carbonaceous residue in the pyrolyzed oil shale, sufficient residence time is required to complete combustion and to assure a thermal equilibrium between the hot burning particles and the cooler recycle particlesO Typically, a minimum residence time of 2 to 3 seconds in the combustion zone is requiredO If the fine shale and coarse shale particles are combusted in a liftpipe, the pipe must be of sufficient length to provide adequate residence time for all particles.
The present invention is advantageous for efficiently burning particulate pyrolyzed oil shale or other partlculate carbon-containing solids where the fine grained material and the coarser grained material are separated prior to combustion and the burned shale serves as heat transfer material in the process.
In its broadest aspect, this invention concerns a process for burning pyrolyzed solids containing a carbonaceous residue to provide heat for the pyrolysis of a particulate carbon-containing solid, wherein said pyrolyzed solids contain both a fine fraction and a coarse fraction and at least part of said fine fraction is contained in a separate feed-stream from the coarse fraction of the pyrolyzed solids, said process ~65~5~
comprising:
(a) burning at least part of the carbonaceous residue in the fine fraction contained in said separate feedstream in a dilute phase preburner by entraining the fine fraction in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the particles in the fine fraction;
(b) mixing the entrained, partially burned fine fraction from the preburner with the remainder of the pyrolyzed solids in a second entraining gas stream having a velocity greater than the terminal velocity of the coarse and fine fractions; and (c) burning the unburned carbonaceous residue in the entrained fine and coarse fractions in a second dilute phase combustion zone through which the second entraining gas and entrained solids are directed, said second dilute phase combustion zone containing sufficient oxygen to burn all of the unburned carbonaceous residue in the fine and coarse - fractions.
The process that is the subject of this invention is particularly advantageous when the carbon-containing solid is oil shale and the ash ~or burned shale in the case of oil shale) is used as heat carrier mate-rial. In such a process scheme, means are usually provided for separating the fine ash leaving the second dilute phase combustion zone from the coarse ash. This is because ash particles smaller than about 100 mesh (Tyler Standard) are generally not suitable for recycling as heat carrier material. Various means for such a separation are known to those skilled in the art and include a solids disengaging zone, cyclones, sifting devices, etcO It should be understood that the terms "fine" and "coarse,"
~6S2S9 when applied to both pyrolyzed solids and ash, are relative terms and the precise size of particle may vary in different embodiments of the invention or with the retorting process employed. However, for most purposes, a cut size of about 100 mesh represents a reasonable division of particle size between coarse and fineO
The present invention is further directed to a process for producing heat from retorted oil shale containing residual carbonaceous material, wherein said retorted oil shale contains both fine and coarse grained material and at least part of said fine grained material is contained in a separate feedstream from the coarse grained material, said process comprising:
.~- (a) burning at least part of the residual carbonaceous material in the fine grained material present in said separate feedstream in a fine preburner by entraining said fine particles in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the fine particles;
~b) burning part of the carbonaceous residue in the coarse grained material in a coarse preburner containing less than a stoichiometric amount of oxygen;
~c) mixing the entrained partially burned fine grained material from the fine preburner and the partially burned coarse grained material from the coarse preburner in a second entraining gas stream having a velocity greater than the terminal velocity of the mixture of fine and coarse particles and containing at least a stoichiometric amount of oxygen; and ~d) burning the carbonaceous residue remaining in the entrained ~ 652~9 fine and coarse grained material in a vertical combustion zone through which said second entraining gas is directed.
This invention also concerns an improved combustion device for burning particulate retorted oil shale separated into a flne particulate feedstream and a coarse particulate feedstream which comprises:
(a) a generally vertical main combustion chamber having an upper zone closed at the top, a middle zone, and a lower zone open at the : bottom, said lower zone having means for pneumatically entraining solids entering said lower zone, said middle zone being an elongate tubular zone adapted for the combustion of entrained particulate solids, said upper zone being adapted for the disengagement of entrained coarse particles and for the collection and removal of the disengaged coarse particles, said : upper zone further having an outlet for the removal of combustion gases - and fine entrained particles;
~ b) a generally vertical tubular fine solids combustion chamber adapted for burning pneumatically entrained fine solids, said fine solids combustion chamber having an open upper end communicating with the lower zone of the main combustion chamber, said fine solids combustion chamber further having a lower end having an inlet for the introduction of ~0 the fine particulate feedstream and means for pneumatically entraining the fine particulate material and conveying it the length of the fine solids combustion chamber; and ~ c) a coarse solids preburning chamber having an inlet for the introduction of the coarse particulate feedstream, means for fluidizing a burning bed of the coarse particulate material, and means for communication with the lower zone of the main combustion chamber.
~65ZS~
As used herein, the phrase "terminal velocity" refers to the maximum velocity attained by a particle falling in a very long column of stagnant air. A particle will become entrained in a flow of gas when the velocity of the gas exceeds the terminal velocity of the particle. Thus, an entraining gas is a gas having a velocity in excess of the terminal velocity of a given size of particle.
In the accompanying drawings:~
Figure l is a schematic representation of an oil shale retorting process of the type in which the present invention may be used most advantageously;
Figure 2 illustrates a cross-sectional view of one design for a - combustor which may be used in the process;
Figure 3 illustrates a cross-sectional view of an alternative design for a combustor which may be used in the process; and Figure 4 illustrates a cross-sectional view of a preferred embodiment of the combustion device of this invention.
Referring to Figure l, fresh crushed oil shale enters retort 2 via conduit 4 where it is mixed with the hot heat carrier material tburned shale) entering the retort through conduit 6. The mixture of hot burned shale and fresh shale moves downward in the retort 2 through a series of dispersing elements 8, lO and 12 which prevent substantial vertical bachmixing of the solidsO A substantially oxygen free stripping gas enters retort 2 through gas inlet 14 creating a countercurrent gas flow through the retort in opposition to the downward moving bed of shaleO Gas from the gas inlet 14, product vapors, and pneumatically entrained fine particles of shale move upward and leave the retort via conduit 160 The gas and .. .
5~S9 product vapors are separated from the entrained fines in cyclone 18;
the gaseous material exits by conduit 20 and the fines are carried away .- by conduit 22.
The coarse material containing particles of both burned oil shale and pyrolyzed oil shale leaves the bottom of retort 2 via solids conduit 24 and is conveyed to the combustor 26. Air entering the combustor via air conduit 28 is mixed with the coarse particles of shale, and the residual carbonaceous material present in the pyrolyzed material is ignitedO In this particular processs&heme, the fine particulate oil shale . 10 material separated by cyclone 18 enters the combustor as a separate feedstream from the coarse particulate material from the retort. The advantages of this scheme will be discussed in detail later. The fine material carried by conduit 22 is pneumatically entrained by air from conduit 30 and enters the combustor at the bottomO Following combustion of the carbonaceous residue, the coarse particles of burned shale and fine particles of burned shale are separated in the top part of the combustor, The coarse particles of burned shale leave the combustor via common conduit 320 Hot burned shale serving as heat carrier material is recycled to the retort via conduit 6 while excess burned shale is drswn off through outlet 34~ Flue gases and entrained fines leave the combustor via conduit 36 and are carried to cyclone 380 Fines are disposed of through conduit 40. Flue gases are carried off via conduit 42 for venting or recycling as stripping gasO
Turning to Pigure 2, a combustion device suitable for use in the retorting process described above is illustratedO Fine particles of shale separated from the product vapors and stripping gas enter the engaging ~P65Z59 chamber 104 at the bottom of the combustor via conduit 1020 Air enters chamber 106 by way of air line 108. The fine particles of shale are entrained by the air stream and carried upward through the fine shale preburner 110 where they are ignited and partially burnedO The burning fines exit the open upper end 112 of the fine shale preburner 110 and enter the main liftpipe engaging area 114 for the main combustion liftpipe Pyrolyzed shale from the bottom of the retort enters the main liftpipe engaging area 114 via conduit 1180 This feed may contain some fine particles but will consist mostly of coarser grained shale particles of a large enough size to not be entrained by the stripping gas passing through the retortO Shale entering via conduit 118 along with fine shale from the preburner 110 are entrained in additional air entering through air conduit 120. Both coarse and fine particles are carried upward by the gas stream and burned in the main combustion liftpipe 116.
The burned particles of oil shale enter the enlarged disengaging chamber 122 of the combustor which serves as a coarse solids disengaging area.
The coarse particles of burned shale settle out in collection zone 124 while the burned fines and flue gases leave the combustor via outlet 126, Coarse particles of burned shale for recycling to the retort or for disposal are removed via outlet 1280 An alternate embodiment for a combustor which may be used in carrying out this process is shown in Figure 3O In this design the fine shale enters the vertical fine preburner 202 via conduit 204. Air enters the preburner and entrains the fines by way of a venturi throat 206~ The burning fines enter plenum chamber 208 where they are mixed with .,.~ .
~. ~65'~59 secondary air entering via conduit 210. The bulk of the retorted oil shale enters the combustor through conduit 212 and is mixed in the engager 214 with the fines entering from the plenum chamber. The velocity of the primary and secondary air is sufficient to entrain both the coarse and fine particles which are carried up the main liftpipe combustor 216 where the coarse material is burnedO An adjustable seat 218 controls the size of opening ;220 between the engager and the main liftpipe combustor 216~ Tertiary air may be introduced as needed via conduit 222 to maintain sufficient velocity to prevent choking of the liftpipe, iOeO, collapse of the solids due to insufficient velocity to maintain entrainment, or to introduce additional oxygen for combustion. The burned shale and flue gas leave the combustor via outlet 224 and pass to a solids disengaging zone (not shown).
A particularly preferred way of operating the process which is the subject of this invention is by inclusion of a preburner for the coarse shale to partially burn the carbonaceous residue therein prior to mixing with the fine shale in the second dilute phase combustion zone.
Such an embodiment is shown in Figure 4.
As shown in Figure 4, fine particles of shale from the retort are carried to the combustor by fine shale inlet line 102. Air entering air inlet 104 is distributed around the open end 106 of fine shale liftpipe 108 by air plenum 110. The pneumatically entrained fines are ignited and carried upward through fine shale liftpipe 108. The burning fines exit the open upper end 112 of the fine shale liftpipe 108 and enter the liftpipe engaging area 114 for the main combustion liftpipe 116.
Coarse shale from the retort enters the annular coarse shale i9 preburning area 118 via inlet 1200 A fluidized bed of coarse shale is supported by perforated plate 122 and burned with a fluidizing gas containing a substoichiometric amount of oxygen introduced via inlet 124. Coarse particles from the fluidized bed in the preburner 118 spill over into the liftpipe engaging area 114 of the main combustion liftpipe where they, along with fine shale from fine shale liftpipe 108, are ~ entrained in a gas stream containing excess oxygen entering through primary air inlet 126. Both coarse and fine particles are carried upward by the gas stream and burned in the main combustion liftpipe 116.
The burned particles of oil shale enter the enlarged upper zone 128 of the combustion device which serves as a coarse solids disengaging area~
The coarse particles Gf burned shale settle out in collection zone 130 while the burned fines and flue gases leave the combustion device via outlet 132. Coarse particles of burned shale for recycling to the retort are drawn off Yia outlet 1340 Excess burned coarse shale is removed via outlet 136 for disposalO
As used herein, the phrase "fine particles of burned shale"
refers to particles of a size unsuitable for recycling as heat transfer material. Usually particles smaller than aboui 100 mesh size tTyler standard) are not suitable for use in the retorting process. Therefore, particles below this range are preferably removed with the flue gas as entrained fines. The separation of the fine and coarse particles is inherent in the design of the upper disengaging area of the combustion deviceO By exclusion "coarse particles of burned shale" refer to particles larger than about 100 mesh size. It should be understood that the terms fine and coarse are relative terms, the size of which may vary ' ` ~652~9 somewhat depending on the exact details of the process scheme. Thus in process schemes where particles smaller than 100 mesh may be tolerated, the term fine may include particles of a smaller diameter. Likewise, under other circumstances particles of a larger minimum mesh size may be required and the definition of "fine" may be adjusted accordingly.
In carrying out the process that is part of this invention the fine particles of retorted oil shale are preferably burned in the fine shale liftpipe with a substoichiometric amount of oxygen, iOe., insuffic-ient oxygen to allow complete combustion of the char. An air to fuel ratio in the range of from about 0O2 to about 0O9 would be suitable for operation This is to prevent excessive carbonate decomposition.
Usually temperatures in both the fine shale liftpipe and the coarse preburner are kept below about 1500F.
To insure entrainment of the fine particles in the fine shale liftpipe a minimum gas velocity of about 4 to 6 feet per second is required to prevent choking, i.eO, collapse of the solids in the pneumatic pipeO Preferably the velocity of the entraining gas is in the range of from about lO feet per second to about 20 feet per secondO In the preferred embodiment of this invention the fine particles have a residence time of about 105 to 2 seconds in the fine shale liftpipe which results in about 25% of the carbonaceous residue being burned in that zone (air/fuel mole ratio = o25)~
The coarse preburner is also operated in the substoichiometric mode and is usually designed to contain a bed of burning coarse material fluidized by a flow of gas from below.
The flow of gas through the main combustion liftpipe must be ~ ~5259 sufficient to entrain both the fine and the coarse particles of shale.
Usually a gas velocity in the range of from about 50 feet per second to about 150 feet per second is employed, with a preferred range of from about 80 feet per second to about 100 feet per second. It should be noted the velocity of the gas in the main combustion liftpipe is usually higher than that in the fine shale liftpipe to insure entrainment of particles entering from the coarse preburner. Combustion in the main liftpipe is carried out with at least a stoichiometric amount of oxygen present, and usually an excess of oxygen is employed. In the preferred embodiment of this invention the velocity of the gas in the main combustion liftpipe is greater than that in the fine shale liftpipeO
The combustion device and process described herein has the advantage of minimizing the height of the liftpipe required to completely burn the particles of retorted oil shaleO By preburning the coarse and fine shale in separate zones taking advantage of the relative sizes of both feeds, the total residence time required for combustion is satisfied in a shorter liftpipeO
Although the process of this invention is most advantageously used in an oil retorting process using recycled burned shale as the heat transfer material, the invention should not be limited to that retorting method. One skilled in the art can easily devise schemes by which other types of heat transfer material, such as for example ceramic compositions, sand, alumina, iron, steel or the like, are employed. In such an instance the heat transfer material may be simply mixed with the coarse shale feedstream to the combustor~ Even in processes using spent shale as the principal heat transfer material, it is often necessary to add supplemental ~ -12-~6~'~59 heat transfer material to the systems. Likewise, it is possible to devise other embodiments of the invention which could utilize the hot flue gas in retorting the raw oil shale or even use the combustor to heat water to produce steam.
In addition, if the carbonaceous residue in the pyrolyzed solids is insufficient to provide the necessary heat for maintaining the temperature in the reactor vessel at pyrolyzing levels, a supplemental fuel, such as granular coal or oil, may be added to the solids entering the combustor. Such a mode of operation may be necessary when the carbon-containing solid is of a low grade or where large amounts of supplemental heat carrier material are employed, thus lowering the percent of carbonaceous residue present in the feedO
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for burning pyrolyzed solids containing a carbonaceous residue to provide heat for the pyrolysis of a particulate carbon-containing solid, wherein said pyrolyzed solids contain both a fine fraction and a coarse fraction and at least part of said fine fraction is contained in a separate feedstream from the coarse fraction of the pyrolyzed solids, said process comprising:
(a) burning at least part of the carbonaceous residue in the fine fraction contained in said separate feedstream in a dilute phase preburner by entraining the fine fraction in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the particles in the fine fraction;
(b) mixing the entrained, partially burned fine fraction from the preburner with the remainder of the pyrolyzed solids in a second entraining gas stream having a velocity greater than the terminal velocity of the coarse and fine fractions; and (c) burning the unburned carbonaceous residue in the fine and coarse fractions in a second dilute phase combustion zone through which the second entraining gas and entrained solids are directed, said second dilute phase combustion zone containing sufficient oxygen to burn all of the unburned carbonaceous residue in the fine and coarse fractions.
(a) burning at least part of the carbonaceous residue in the fine fraction contained in said separate feedstream in a dilute phase preburner by entraining the fine fraction in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the particles in the fine fraction;
(b) mixing the entrained, partially burned fine fraction from the preburner with the remainder of the pyrolyzed solids in a second entraining gas stream having a velocity greater than the terminal velocity of the coarse and fine fractions; and (c) burning the unburned carbonaceous residue in the fine and coarse fractions in a second dilute phase combustion zone through which the second entraining gas and entrained solids are directed, said second dilute phase combustion zone containing sufficient oxygen to burn all of the unburned carbonaceous residue in the fine and coarse fractions.
2. The process of Claim 1 wherein the fine fraction of pyrolyzed solids is partially burned in the preburner with a substoichiometric amount of oxygen.
3. The process of Claim 1 including the additional step of separating a fine fraction of ash from a coarse fraction of ash, said ash being formed by the combustion of the pyrolyzed carbon-containing solids.
4. The process of Claim 3 wherein the coarse fraction of ash is recycled as heat carrier material.
5. The process of Claim 1 wherein the carbon-containing solid is oil shale.
6. The process of Claim 5 wherein the temperature of the fine fraction in the preburner does not exceed 1500°F.
7. The process of Claim 5 wherein the air to fuel ratio in the preburner is in the range of from about 0.2 to about 0.9.
8. The process of Claim 1 wherein a supplemental fuel is added to the pyrolyzed solids before entry into the combustion zone.
9. In a process for retorting oil shale using a heat transfer material heated by burning retorted oil shale containing residual carbonaceous material, wherein said retorted oil shale contains both fine and coarse grained material and at least part of said fine grained material is contained in a separate feedstream from the coarse grained material, an improved process for burning the oil shale comprising:
(a) burning at least part of the residual carbonaceous material in the fine grained material present in said separate feedstream in a fine preburner by entraining said fine particles in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the fine particles, (b) burning part of the carbonaceous residue in the coarse grained material in a coarse preburner containing less than a stoichiometric amount of oxygen;
(c) mixing the entrained partially burned fine grained material from the fine preburner and the partially burned coarse grained material from the coarse preburner in a second entraining gas stream having a velocity greater than the terminal velocity of the mixture of fine and coarse particles and containing at least a stoichiometric amount of oxygen; and (d) burning the carbonaceous residue remaining in the entrained fine and coarse grained material in a vertical combustion zone through which the second entraining gas is directed.
(a) burning at least part of the residual carbonaceous material in the fine grained material present in said separate feedstream in a fine preburner by entraining said fine particles in a first entraining gas stream containing oxygen and having a velocity greater than the terminal velocity of the fine particles, (b) burning part of the carbonaceous residue in the coarse grained material in a coarse preburner containing less than a stoichiometric amount of oxygen;
(c) mixing the entrained partially burned fine grained material from the fine preburner and the partially burned coarse grained material from the coarse preburner in a second entraining gas stream having a velocity greater than the terminal velocity of the mixture of fine and coarse particles and containing at least a stoichiometric amount of oxygen; and (d) burning the carbonaceous residue remaining in the entrained fine and coarse grained material in a vertical combustion zone through which the second entraining gas is directed.
10. The process of Claim 9 wherein the fine grained material is partially burned in the fine preburner with a substoichiometric amount of oxygen.
11. The process of Claim 9 wherein the temperature of the material burned in the coarse preburner and the fine preburner does not exceed 1500°F.
12. The process of Claim 9 wherein the coarse grained material in the coarse preburner is contained in a fluidized bed.
13. The process of Claim 9 wherein the velocity of the entraining gas in the fine preburner is less than the velocity of the gas stream in the vertical combustion zone.
14. The process of Claim 13 wherein the velocity of the gas stream in the vertical combustion zone is in the range of from about 80 feet per second to about 150 feet per second and the velocity of the entraining gas in the fine preburner is in the range of from about 10 feet per second to about 20 feet per second.
15. The process of Claim 9 wherein burned oil shale is used as heat transfer material.
16. A combustion device for burning particulate retorted oil shale separated into a fine particulate feedstream and a coarse particulate feedstream which comprises:
(a) a generally vertical main combustion chamber having an upper zone closed at the top, a middle zone, and a lower zone open at the bottom, said lower zone having means for pneumatically entraining solids entering said lower zone, said middle zone being an elongate tubular zone adapted for the combustion of entrained particulate solids, said upper zone being adapted for the disengagement of entrained coarse particles and for the collection and removal of the disengaged coarse particles, said upper zone further having an outlet for the removal of combustion gases and fine entrained particles;
(b) a generally vertical tubular fine solids combustion chamber adapted for burning pneumatically entrained fine solids, said fine solids combustion chamber having an open upper end communicating with the lower zone of the main combustion chamber, said fine solids combustion chamber further having a lower end having an inlet for the introduction of the fine particulate feedstream and means for pneumatically entraining the fine particulate material and conveying it the length of the fine solids combustion chamber; and (c) a coarse solids preburning chamber having an inlet for the introduction of the coarse particulate feedstream, means for fluidizing a burning bed of the coarse particulate material, and means for communication with the lower zone of the main combustion chamber.
(a) a generally vertical main combustion chamber having an upper zone closed at the top, a middle zone, and a lower zone open at the bottom, said lower zone having means for pneumatically entraining solids entering said lower zone, said middle zone being an elongate tubular zone adapted for the combustion of entrained particulate solids, said upper zone being adapted for the disengagement of entrained coarse particles and for the collection and removal of the disengaged coarse particles, said upper zone further having an outlet for the removal of combustion gases and fine entrained particles;
(b) a generally vertical tubular fine solids combustion chamber adapted for burning pneumatically entrained fine solids, said fine solids combustion chamber having an open upper end communicating with the lower zone of the main combustion chamber, said fine solids combustion chamber further having a lower end having an inlet for the introduction of the fine particulate feedstream and means for pneumatically entraining the fine particulate material and conveying it the length of the fine solids combustion chamber; and (c) a coarse solids preburning chamber having an inlet for the introduction of the coarse particulate feedstream, means for fluidizing a burning bed of the coarse particulate material, and means for communication with the lower zone of the main combustion chamber.
17. The combustion device of Claim 16 wherein the coarse solids preburning chamber forms an annulus around the lower zone of the main combustion chamber.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/246,555 US4336126A (en) | 1981-03-23 | 1981-03-23 | Process for burning retorted oil shale and improved combustor |
| US246,555 | 1981-03-23 | ||
| US06/267,137 US4336127A (en) | 1981-05-26 | 1981-05-26 | Staged burning of retorted carbon-containing solids |
| US267,137 | 1981-05-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165259A true CA1165259A (en) | 1984-04-10 |
Family
ID=26938070
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000399028A Expired CA1165259A (en) | 1981-03-23 | 1982-03-22 | Staged burning of retorted carbon-containing solids |
Country Status (10)
| Country | Link |
|---|---|
| AU (1) | AU550189B2 (en) |
| BR (1) | BR8201574A (en) |
| CA (1) | CA1165259A (en) |
| DE (1) | DE3210635A1 (en) |
| FR (1) | FR2502168B1 (en) |
| GB (1) | GB2095391B (en) |
| IL (1) | IL64906A (en) |
| MA (1) | MA19414A1 (en) |
| NL (1) | NL8201017A (en) |
| SE (1) | SE8201800L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102008021629B4 (en) | 2008-04-25 | 2017-09-14 | Technische Werke Ludwigshafen Ag | Apparatus for the production of raw materials, fuels and fuels from organic substances |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4293401A (en) * | 1980-02-21 | 1981-10-06 | Chevron Research Company | Shale retorting with supplemental combustion fuel |
-
1982
- 1982-02-01 IL IL64906A patent/IL64906A/en unknown
- 1982-02-10 AU AU80355/82A patent/AU550189B2/en not_active Ceased
- 1982-03-11 NL NL8201017A patent/NL8201017A/en not_active Application Discontinuation
- 1982-03-12 GB GB8207278A patent/GB2095391B/en not_active Expired
- 1982-03-15 MA MA19619A patent/MA19414A1/en unknown
- 1982-03-15 FR FR8204328A patent/FR2502168B1/en not_active Expired
- 1982-03-22 CA CA000399028A patent/CA1165259A/en not_active Expired
- 1982-03-22 BR BR8201574A patent/BR8201574A/en not_active IP Right Cessation
- 1982-03-22 SE SE8201800A patent/SE8201800L/en not_active Application Discontinuation
- 1982-03-23 DE DE19823210635 patent/DE3210635A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| SE8201800L (en) | 1982-09-24 |
| NL8201017A (en) | 1982-10-18 |
| AU550189B2 (en) | 1986-03-06 |
| FR2502168B1 (en) | 1986-05-02 |
| BR8201574A (en) | 1983-02-08 |
| DE3210635A1 (en) | 1982-10-28 |
| GB2095391B (en) | 1984-08-22 |
| AU8035582A (en) | 1982-09-30 |
| MA19414A1 (en) | 1982-10-01 |
| IL64906A (en) | 1984-10-31 |
| IL64906A0 (en) | 1982-04-30 |
| GB2095391A (en) | 1982-09-29 |
| FR2502168A1 (en) | 1982-09-24 |
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