US3597347A - Process for retorting carbonaceous material - Google Patents

Abstract

AN IMPROVED PROCESS FOR RETORTING CARBONACEOUS MATERIAL, SUCH AS OIK SHALE, WHERE THE HET OF PYROLYSIS IS SUPPLIED BY MIXING HOT SPENT SHALE ASH WITH RAW SHALE FEED SHALE PARTICLWS LOSE THEIR STRENGTH PROGRESSIVELY ABOVE ABOUT 500*F. SO CRUSHING OF THE FEED TO MINUM 1/8 INCH SIZE DOES NOT TAKE PLACE UNTIL AFTER MIXING OR RETORTING. COLD SHALE FEED FINES ARE ADDED TO THE MIXED HOT SHALE ASH AND LARGER SHALE FEED BEFORE RETORTING.

Description

Aug. 3, 1971 R. 'r. ELLINGTON, JR 3,597,347

PROCESS FOR RETORTING CARBONACEOUS MATERIAL Filed Dec. 6, 1968 TO PRODUCT 8 I6 RECOVERY l7 km WASTE l2 4-- AIR INVEN'IFOR REX T. ELLINGTON,JR.

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ATI'UHNEYH United States Patent 3,597,347 PROCESS FOR RETORTING CARBONACEOUS MATERIAL Rex. T. Ellington, Jr., Tulsa, Okla, assiguor to The Oil Shale Corporation, New York, NX. Filed Dec. 6, 1968, Ser. No. 781,769 Int. Cl. Cb 53/06 US. Cl. 208-11 9 Claims ABSTRACT OF THE DISCLOSURE An improved process for retorting carbonaceous material, such as oil shale, where the heat of pyrolysis is supplied by mixing hot spent shale ash with raw shale feed. Shale particles lose their strength progressively above about 500 P. so crushing of the feed to minum /3 inch size does not take place until after mixing or retorting. Cold shale feed fines are added to the mixed hot shale ash and larger shale feed before retorting.

This invention relates to the removal of volatile material from solid carbonaceous material. More particularly, this invention relates to an improved process for the recovery of volatile material, such as combustible gases, liquid motor fuels, and various grades of oil, from solid carbonaceous material, such as oil shale, tar sand, coal, lignite and the like.

Many techniques have been employed for thebeneficiation of solid carbonaceous material. For example, oil shale has been retorted in batch-type tfixed bed operations, rotating drums, chain grate kilns, moving bed retorts and fluidized beds.

One of the processes of recent interest is the sandcracking process. In operation, spent shale ash preheated to about 1200 F. is mixed with cold raw shale feed that has been previously crushed to minus inch size. The spent shale ash thus provides the heat of pyrolysis. After mixing, the shale ash and feed are discharged into a retorting vessel. The size of the vessel and the rate of withdrawal of spent shale ash are in such relationship that the shale feed has adequate time to absorb heat from the shale ash and to be fully retorted before it is discharged from the retort vessel. Air is introduced into the solid efiiuent discharged from the retorting vessel and the air-entrained efiluent is passed into a lift-tube combustor where the carbon content of the spent shale is burned off to heat the air and the shale ash to the desired temperature. At the top of the lift pipe, part of the entrained shale ash is knocked out and dropped in the retention bin to provide heat for retorting. The remainder is carried off with the hot combustion products, through a waste heat boiler and/ or any other heat recovery means and then through a cyclone where the ash is separated from the cooled combustion products and sent to disposal. The gaseous retort products are withdrawn from the top of the retort vessel and transferred to a hot-dust separator where the entrapped waste dust is removed. The thuspurified gaseous retort products are then conventionally treated to remove oil and other products.

While this process, as outlined above, offers oil yields of at least 90% Fischer Assay, it also presents problems. The raw oil shale feed must be crushed from a size of 1 inch or more to the minum A2. inch size to give optimum operation of the lift-tube combustor. Also. there is the possibility that the burned off shale ash will absorb shale oil vapors in the retorting drum and thus carry part of the yield from new shale out to the combustor, thus reducing the yield in the recovery system.

It is an object of this invention to provide an improved process for retorting carbonaceous materials, particularly oil shale, where the heat of pyrolysis is supplied by hot spent shale ash wherein the prior crushing of the raw shale feed is made easier or some stages of crushing eliminated. It is a further object of this invention to provide an improved process for retorting carbonaceous materials, particularly oil shale, wherein the heat of pyrolysis is supplied by mixing the feed with a heatcarrying solid and the retort yield is maximized by controlling the retort atmosphere and other process variables.

These objects and other advantages are achieved by mixing shale ash of a temperature of about l000 to 1500 F. preferably 1200 to 1400 F. with cold raw oil shale feed fines and larger feed of a size of about minus 1.5 inch to minus 1 inch down to /8 inch, the larger feed preferably being preheated to about 500 to 550 F., transferring the mix to a retort vessel wherein the atmosphere is maintained non-combustion supporting (an atmosphere of natural gas or processed retort gas containing 10 vol. percent CO is preferred), retorting otf volatile material at a preferred retort temperature of about 800 to 950 R, such as oil, with the heat of pyrolysis supplied by the hot spent shale ash, crushing the shale mixture at temperature above about 500 F. to essentially minus inch size, preferably minus inch size, passing the spent shale through a lift-tube combustor by the addition of air where the carbon content of the spent shale is burned off to heat the air and shale ash to the desired temperatures, and recycling part of the heated spent shale back to the mixer for mixing with raw feed oil shale.

It has been found that oil shale commences to lose crushing strength above about 500 F. and is very friable by the time it reaches retort temperature and is retorted. As a consequence, crushing of the oil shale above about 500 F. is much easier and requires less extensive crushing apparatus to achieve the fineness normally sought in the low tempearture crushing. Retorting for the oil can be done with the large pieces nearly as easily as with the finer particles normally used. However, finer particles are desirable for flow through the lift-tube combustor under the action of air. The crusher can thus be placed in the process anywhere the shale is at a temperature of over 500 F. and before the lift-tube combustor. It may thus be placed at the outlet of the mixer, or, if residence time in the mixer is not sufficient to raise the raw shale temperature to above 500 F. and larger particles in the retort vessel do not affect yield, at the outlet of the retort vessel.

The figure is a schematic diagram of the process of my invention.

Referring to the figure, raw shale feed 1 of a size of about minus 1.5 inch to minus 1 inch is fed into the raw shale preheater 2 where the feed 1 is preheated to a temperature range of about 500 to 550 F. The preheater is heated by heat taken from the ash and flue gas taken from the retort vessel as described below. The preheated raw shale feed 3 is then transferred to a mixer 4, Which can be any conventional mixing apparatus such as a screw mixer, where it is mixed with hot shale ash 5 from the retention drum 6, described below, and fine-size, i.e., minus 4 inch, raw shale feed 7. The fine-size raw shale feed 7 is preferably separated from the larger raw shale feed 1 before the latter is preheated. The mixed shales 8 are then transferred to the retorting vessel 9. If the mixed shales 8 are discharged at a. temperature of 500 F. or higher, a crusher 10 can be used between the mixer 4 and retort vessel 9 to crush the shale pieces to a size sufiicient to be transferred by air to the retention drum 6, i.e., essentially minus A inch size, preferably minus inch size. If the discharge temperature at the mixer 4 is not 5 00 F. or above or if it is desired to omit 3 any further fine-size pieces that may carry away the oil vapor, the crusher may be inserted intermediate the discharge side of the retort vessel 9 and the liftpipe 11, as indicated in the figure at 12.

The feed shale is retorted in retort vessel 9 with the heat of pyrolysis supplied by the hot shale ash 5. The retorting is carried out at a temperature range of about 500 to 1500 F., preferably 800 to 950 F. The charge of mixed sh ales 8 is preferably maintained during retorting in a non-combustion supporting atmosphere as taught in copending application Serial Number 781,901 filed of even date herewith. The atmosphere may be pure natural gas or a gas of similar composition but optimum results are achieved using an atmosphere of natural gas containing up to 20 volume percent carbon dioxide, preferably 10 volume percent. Processed and recycled retort gas can also be employed as the atmosphere. This surrounding atmosphere is injected into the retort vessel 9 at inlet 13. Compositional control can be achieved through conventional means such as an on-line chromatograph (not shown) and gas mixing. The gaseous efiluent 14 from the reactor vessel containing the retorted oil is taken off the top of the retort vessel 9 and transferred to a hot dust separator 15 through conventional piping. The dust-removed gas 16 is transferred to a conventional product recovery system 17 (not shown). The dust 18 removed in the separator is disposed of.

If extra insurance is needed against condensation in transfer piping or hot cyclones used to remove shale ash or shale dust from the retort vapor, extra gas of the same composition as surrounding the particles or recycled processed retort gas and preferably preheated can be fed above the bed in the retort vessel 9 as indicated at 31 to lower the dew point of the vapor stream leaving the retort.

The solid oil-depleted shale mixture 19 is removed from the retort vessel 9, passed through the optional crusher 12, as explained above, and is transferred into the lift-pipe combustor 11 by the injection of air 20. As the solid-air mixture 21 passes up the lift-pipe combustor 11, the carbon in the oil-depleted shale is burned off, raising the temperature of both the shale and the air. At the top of the lift-pipe 11 is a retention drum 6 into which the combusted shale ash is transferred. Part of this hot shale ash 22 is recycled into the mixer 4 as explained above for heat transfer to the raw shale feeds 3 and 7. The balance of the hot shale as 22 and the flue gas combustion products from lift pipe 11 are transferred into the heat exchanger 23, such as a waste heat boiler. The cooled ash-gas mixture 24 is then further transferred to cyclone 25 where the shale ash and the flue gas are separated. The flue gas 26 is then transferred into raw shale preheater 2 for direct or indirect heat exchange with the large-size raw shale feed 1. After this exchange, the flue gas is vented into a stack as generally indicated at 27. The shale ash 28 from cyclone 25 is transferred to shale ash cooler 29 from whence it is disposed of as generally indicated at 30.

In another form of the invention the non-combustion supporting atmosphere 13 is used with special advantage. When all the material is finely crushed (as to minus Ms inch) or the crusher 10 is inserted after the mixing vessel 4, the rate of injection can be controlled so that the bed in the retort vessel 9 is swept at a low rate to educt retorting products and obtain yield improvement. Injection can be controlled at a higher rate to expand the bed and reduce the residence time of the retorting products in vessel 9, or at still higher rates to fluidize the upper part or all of the bed to minimize residence time of retorting products in the vessel. Such injection also serves to achieve the dew point reduction mentioned for over-bed injection above.

The following example further illustrates the invention.

4 EXAMPLE Raw shale feed of minus 1.5 in. size and at a temperature of about 60 F. is fed to a raw shale preheater where it is preheated to a temperature of about 520 F. The preheated raw shale is transferred to a mixing vessel where it is mixed with hot shale ash at a temperature of about 1250" F. After one to three minutes residence time, the mixed shale ash and feed are discharged into a retort vessel maintained under an atmosphere of processed retort gas containing at least CH Shale oil is retorted from the feed with the heat of pyrolysis being suppliedby the hot shale ash. After three to ten minutes residence time, the shale ash and shale coke at equal temperatures of about 875 F. are discharged into a crusher which crushes the mix to essentially minus A3 inch size. The crushed particles at a temperature of about 900 F. are transferred into a lift-tube combustor by the injection of air. The carbon in the shale coke is burned off in the combustor. At the top of the lift-tube combustor, the shale ash is transferred to a retention drum at a temperature of about 1250 F. Part of this shale ash is recycled back to the mixing vessel for retorting. Part is transferred to a heat-exchanger unit where steam can be generated by heat exchange with the hot shale ash. The shale ash is then transferred to a cyclone where the shale ash and flue gas are separated. The hot flue gas is then transferred tofthe raw shale preheater where it preheats the raw shale feed by direct or indirect heat exchange. The shale ash is transferred to a spent shale ash cooler from whence it is disposed of.

Table I shows the flow rates of materials in the example.

' TABLE I Stream Flow rate In: (lbs/hr.) Raw shale feed 916,667 Fluidizing gas 62,861 Combustion air 355,347

Total 1,334,875

Out: '4 Retort vessel eflluent vapors 231,318 Spent shale ash to disposal 690,069 Flue gas 413,488

Total 1,334,875

Internal:

Preheated raw shale 916,667 Raw shale/ spent shale ash mixture (retort feed) 2,223,741 Retort vessel effluent solids 2,055,284 Crusher product 2,055,284 Combustion lift tube eflluent 2,410,631 Spent shale ash to retort 1,307,074 Flue gas plus spent shale ash 1,103,557 Flue gas to raw shale preheat 413,488 Flue gas to stack 413,488

What I claim is:

1. A process for the recovery of volatile material from solid carbonaceous material wherein raw feed of the solid carbonaceous material is mixed with hot ash of processed carbonaceous material, the raw feed-hot ash mixture is transferred to a retort vessel, the volatile material being retorted from the raw feed in the retort vessel with the heat of pyrolysis being supplied by the heat of the hot ash, the resulting spent mixture then being discharged from the retort vessel, mixed with air and transferred to a lift-tube combustor wherein at least part of the carbon of the spent mixture is burned off to form hot ash and flue gases, the hot ash at the end of the lift-tube combustor being transferred to a retention bin and thereafter part of the hot ash is then mixed with raw feed to provide the heat of pyrolysis and the volatile material; one of said mixtures of the group of raw feed-hot ash mixture and spent mixture being crushed to a smaller particle size at a temperature above 500 F. prior to transference of the spent mixture to the lift-tube combustor.

2. The process of claim 1 wherein the solid carbonaceous material is oil shape and the voltile material contains oil.

3. The process of claim 1 wherein the raw feed-hot ash mixture is crushed after mixing and before entering the retort vessel.

4. The process of claim 1 wherein the spent mixture is crushed after being discharged from the retort vessel and before entering the lift-tube combustor.

5. The process of claim 3 wherein the raw feed of the raw feed-hot ash mixture before crushing consists essentially of particles of minus 1.5 inch to about /8 inch size.

6. The process of claim 5 wherein the raw feed of the raw feed-hot ash mixture after crushing consists essentially of particles of minus /1 inch size.

7. The process of claim 5 wherein the raw feed of the raw feed-hot ash mixture after crushing consists essentially of particles of minus inch size.

8. The process of claim 2 wherein a non-combustion gas is present in the retort vessel and is one of the group consisting of natural gas, processed recycled retort gas, a gas of similar composition to natural gas, and natural gas or processed recycled retort gas containing up to about 20 volume percent carbon dioxide.

9. The process of claim 8 wherein the non-combustion supporting gas is natural gas or processed recycled retort gas containing about 10 volume percent carbon dioxide.

References Cited UNITED STATES PATENTS 2 656,308 10/1953 Pettyjohn 201-7 3,167,494 1/1965 Crawford 208-11 3,346,481 10/1967 Johnsen 20811 3,361,644 1/1968 Deering 208-11 CURTIS R. DAVIS, Primary Examiner U.S. c1. X.R. 201-7, 12, 20

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