US3850739A

US3850739A - Retorting oil shale with special pellets and precoking stage

Info

Publication number: US3850739A
Application number: US00410099A
Authority: US
Inventors: D Wunderlich; J Skinner
Original assignee: Atlantic Richfield Co
Current assignee: Atlantic Richfield Co
Priority date: 1972-11-20
Filing date: 1973-10-26
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

Hot special heat-carrying pellets are continuously cycled to a retort zone to mix with and continuously retort fresh crushed oil shale, thereby producing carbonaceous products and spent shale. The main source of heat for retorting is derived from controlled burning of a coke-like carbon-containing deposition which is deposited on the pellets as they are cycled in the process. At least a portion of the pellets are coked to some extent by cracking or stabilizing oil products in a thermal precoking zone. Some of the pellets from the precoking zone may be cycled to the retort zone. The amount of preretort coking provides flexible regulation over the total deposition formed on the pellets during the process especially that portion of the deposition formed during the retorting of oil shale and over product quality. After retorting, the pellets passed to the retort zone are separated from substantially all of the spent shale smaller than the pellets prior to combustion of the carbon deposition on the pellets. The pellets from the precoking zone and from the retorting zone are passed or lifted to a pellet deposition burning zone where the deposition is burned. The special pellets are characterized primarily by their effective surface area, size, and quantity relative to the oil shale. The process stresses improvement in the quality of the liquid oil products and at the same time greater useful recovery of the carbonaceous matter in oil shale.

Description

United States Patent 1191 Wunderlich et al.

[ Nov. 26, 1974 RETORTING OIL SHALE WITH SPECIAL Primary Examiner-C. Davis PELLETS AND PRECOKING STAGE [75] Inventors: Donald K. Wunderlich; James L. [57] ABSTRACT Skinner, both of Richardson, Tex. Hot special heat-carrying pellets are continuously cycled to a retort zone to mix with and continuously re- [73] Assxgnee' Atlanuc Rldlf'eld Company L08 tort fresh crushed oil shale, thereby producing carbo- Angeles, Calif. I

naceous products and spent shale. The mam source of [22] Filed: Oct. 26, 1973 heat for retorting is derived from controlled burning of a coke-like carbon-containing deposition which is [2]] Appl' 410099 deposited on the pellets as they are cycled in the pro- Related US. Application Data cess. At least a portion of the pellets are coked to [63] Continuation-impart" of Ser. No. 308,136, Nov. 20, some extent by Frackmg or Stablhzing Oil products in a 1972, abando ed, which i a c ii q f thermal precoklng zone. Some of the pellets from the Ser. No. 304,074, Nov. 6, 1972, abandoned, which is precoking zone may be cycled to the retort zone. The a continuation-in-part of Ser. No. 284,288, Aug. 28, amount of preretort coking provides flexible regula- 1972.11bafld9nedtion over the total deposition formed on the pellets during the process especially that portion of the depo- U-S- Cl. sition formed during the retorting of hale and over [51] Int. Cl C10b 53/06 product lit After retorting, the pellets passed to Fleld of Search t t l the retort ane are separated from substantially all of the spent shale smaller than the pellets prior to com- References Clled bustion of the carbon deposition on the pellets. The UNITED STATES PATENTS pellets from the precoking zone and from the retorting 3.008.894 1 1 I196] Culbertson 208/11 Zone are Passed Or lifted to a P deposition burning 3,013,343 1 19 2 Ncvens 203 1 zone where the deposition is burned. The special pel- 3.020.227 2/1962 Nevens et al. 208/11 lets are characterized primarily by their effective sur- 3,058,903 10/1962 Otis 208/11 face area, size, and quantity relative to the oil shale. 3251836 5/1966 Crawfordw 208/11 The process stresses improvement in the quality of the ggz a liquid oil products and at the same time greater useful u-aman I 1 1803.022 4/1974 AbduLRahman lllllllllllllllll H 208/ recovery of the carbonaceous matter in Oll shale.

50 Claims, 2 Drawing Figures FLUE GAS h I TION DE os BURNING n- 57COMBUSTION GAS 20m:

HOT A53 67 SPECIAL PELLETS ,65 69 'x THERMALLY CRACKED PRODUCTS 1 PRODUCTS PRECOKING j ZONE 73 5 PRODUCTS 71 /l 31 SHALE RETORT paooucrs A2 FEED ZONE AND PELLET SPENT SHALE SEPARATION K 47 1a ZONE 2| PELLET LIFTING PELLETS PATENTE W 3,850,739

SHEET 10F 2 FLUE GAS PELLET DEPOS'T'ON COMBUSTION GAS BURNING ZONE HOT 67 SPECIAL PELLETS 69 v THERMALLY CRACKED PRQDUCTS.

33 r I PRODUCTS PRECOKING v C ZONE 49 PRODUCTS 3|/ SHALE l7 I l2 FEED S I S PRODUCTS AND PELLET SPENT SHALE 47 ggglRATlON Y 2| 4 l PELLETS a F l G. l

RETORTING OIL SHALE WITH SPECIAL PELLETS AND PRECOKING STAGE CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 308,136, filed Nov. 20, 1972, entitled Retorting Oil Shale with Special Pellets and Precoking Stage, now adandoned, which was a continuation-in-part of copending application Ser. No. 304,074, filed Nov. 6, 1972, entitled Retorting of Oil Shale with Special Pellets and Supplemental Deposition," which is a continuation-in-part of copending application Ser. No. 284,288, filed Aug. 28, 1972, entitled Retorting of Oil Shale with Special Pellets, both now abandoned. All of these applications have been filed by the same inventors as this application and are owned by a common assignee.

BACKGROUND OF THE INVENTION This invention relates to a process for retorting of the solid carbonaceous organic matter in crushed oil shale. In the process, special heat-carrying pellets are cycled to a thermal precoking stage, or to a retorting stage zone, or to both stages.

As a preliminary stage in the production of petroleum oils and gases, the solid carbonaceous organic solid matter or kerogen in oil shale is pyrolyzed or retorted. In an overall commercial operation, the retort products are processed in additional stages, for example, solids separation, condensation, fractionation, coking, hydrogenation, and the like, depending on the types of marketable products being produced. Many processes have been suggested for the retorting stage of a commercial operation. The term retorting denotes. thermal conversion of kerogen or organic matter to oil vapors and gas thereby leaving solid particulate spent shale and includes separation of the oil vapors and gas from the spent shale. The spent shale contains residual carbonaceous organic matter and matrix mineral matter.

Frequently, the yields of various processes are compared with Fischer Assay yields. For a description of the FischerAssay refer to Method of Assaying Oil Shale by a Modified Fischer Retort by E. Stanfield and I. C. Frost, R. I. 4477, June 1949, US. Department of Interior.

When the kerogen is retorted, a normally gaseous fraction, a normally liquefiable vaporous fraction, and a combustible organic residue are formed. The product distribution between gas, liquid, and residue is important and relates to the distribution of the various boiling point fractions in the liquid product. It is highly desirable to obtain a liquid product that is directly adaptable to prerefining and avoids or lessens the amount of residue or 975F plus fraction that must be subjected to In addition, the kerogen content of the oil shale inherently or naturally fluctuates between rich and lean, and many processes are not sufficiently flexible to control product distribution when the kerogen content varies.

Some advances to more flexible and efficient control over the products of retorting and of other variables have been made by using solid heat-carrying bodies which exhibit good heat transfer properties and supply the heat needed for retorting with a reduction in process problems. In such processes, the heatcarrying bodies and the oil shale feedstock are intermixed thereby retorting oil vapors, gases, and combustible residue from the feedstock. The heat-carrying bodies are usually heated in a separate heating zone by burning combustible fuel material, such as heavy resid or natural gas. But in general, this method of heating necessitates additional equipment and creates additional handling problems.

Others have proposed cycling the partially spent shale and supplying some of the heat by burning the residual carbonaceous organic matter or solid organic char developed in the retort zone, or cycling catalyst particles and supplying some of the heat by burning carbon deposited on the catalyst (for example, US. Pat. No. 3,281,349). In this latter process, the surface area of the catalyst particles is not specified. Some types of catalyst particles frequently have high surface areas which result in loss of valuable liquid product and excessive gaseous product, excessive residue, excessive heating of the catalyst during burning, loss of valuable heat values, higher oxygen demands, and other disadvantages.

In addition, a large amount of fine (e.g. minus 14 US. Standard Sieve size) spent shale is usually present during burning and reheating. This spent shale contains organic carbon and increases oxygen demands, causes loss of useful heat values, and adversely enlarges the size of equipment. Fine materials also interfere with control of the burning and other stages of the process and create many other problems especially when the entrained spent shale is smaller than other heatcarrying bodies. Moreover, the presence of appreciable amounts of fine spent shale severely limits the type of equipment which can be used for burning the residue. Generally, burning relatively large particles in the presence of fine material requires the use of lift pipes. If air is used as the lift gas, this form of burning could entail a large excess of oxygen which could rapidly burn the organic matter and create disadvantages in the process of this invention.

Copending application Ser. No. 410,200 filed Oct. 26, 1973, which is a continuation-in-part of application Ser. No. 284,288, whichis incorporated herein, provides a process for retorting oil shale using special pellets in a way which regulates the amount of combustible organic carbon deposition formed on the pellets during retorting of oil shale and improves the recovery of useful components and liquid product distribution.

The process relies on the interrelation between the surface area of the pellets and other conditions and variables; however, additional regulation and flexibility are desired primarily because it has been found that the retorting stage of the process requires constant control and adjustment and altering one variable affects other variables and results and because it is desirable at times to produce higher gravity or upgraded products and/or to supply more sensible heat and deposition to the pellets. Additional process flexibility and regulation is re quired, for example, when the retorting stage of the process is operated under conditions such that the amount of deposition formed on the pellets during retorting is not sufficient to reheat the pellets. Such conditions could arise when a vein of lean oil shale is encountered and the design and size of the retorting equipment are such that it would be undesirable or inefficient to adjust operation to the lean shale. There are other similar occurrences or objectives which arise during the retorting of shale. For example, a rich vein of oil shale is also likely to be encountered. When such occurrence takes place or when objectives change or fluctuate, more process flexiblity and regulation are advantageous. Briefly, therefore, a principle object of this invention is to provide greater flexibility and adaptability to a retorting process of the type disclosed in copending application Ser. No. 410,200.

SUMMARY OF THE INVENTION In a retorting process, crushed carbonaceous solid organic matter is retorted to gas, oil vapor, and combustible residue with special heat-carrying pellets in a manner which emphasizes greater utility of all three re tort products and greater useful recovery of the residue that is normally formed when oils are retorted, cracked or vaporized. Greater useful recovery of this residue reduces the need for liquid fuels and residue treating processes thereby increasing the ultimate yield of the liquid oil products in a commercial syncrude operation. The process cycles special hot heat-carrying pellets in a way which produces a carbon-containing deposition on the pellets and renders the deposition useful as a fuel for heating the pellets. In the process some or all of this deposition is burned in a pellet deposition burning zone to heat and reheat the pellets. Some of this deposition is formed on the pellets during a precoking or thermal cracking or stabilization stage in which at least a portion of the vaporous, or condensed, or condensed and fractionated retort products are cracked or stabilized in the presence of at least a portion of the pellets to deposit a coke-like deposition on the pellets thus exposed. This thermal precoking stage is carried out after the pellets have been reheated by combustion of the deposition on the pellets. But the thermal cracking stage is carried out before the precoke pellets, if any, are fed to the retort zone where the solid organic matter in oil shale is retorted. Since a portion of the deposition is formed on the pellets in the precoking zone, the effective surface area of the pellets passed to the retorting zone may be altered by passing some or all of the precoked pellets to the retorting zone. Consequently, the deposition formed on the precoked pellets passed to the retorting zone either reduces the amount of deposition formed on the pellets in the retort or adds to the amount of deposition formed in the retort, thereby increasing the total amount of deposition formed on the pellets. The amount of deposition formed on the pellets during the retorting stage of the process is preferably less than 1.5 per cent by weight per pass through the retort. The pellet precoking or prethermal cracking stage thereby provides greater regulation and greater flexibility and adaptability to the retorting process. As a side advantage, the retorting process provides a way to upgrade or stabilize products by thermal cracking or stabilization and at the same time place the coke that is normally formed during thermal cracking in a better position to be used as fuel for reheating the pellets to retort oil shale. The pellet precoking or prethermal cracking or stabilization stage is itself flexible and adaptable since the operator has the choice of subjecting any part of the retort products to such prethermal cracking or stabilization conditions, or of passing any part of the pellets through the prethermal cracking or stabilization stage. A preferred feed for the precoking zone is oil out boiling between 100F and 700F. The quantities of pellets or products, or both, so treated may be varied to coact with changes in other variables especially the organic content of the raw shale and the desired product yields. Further, since the precoking stage is carried out while the pellets are hottest, sensible heat requirements for such thermal cracking or stabilization are better controlled and more flexible; moreover, the temperature of the pellets entering the retorting stage of the process is under better control in the event that the pellet deposition burning zone is not adequately controlled. Still further advantages are available in that the burning of the deposition and the cycling of the pellets tends to reduce the effective surface area of the pellets. The rate of change in surface area is not constant and tends to approach an asymptotic or equilibrium value which is established by the nature of the pellets and the process conditions. The flexibility provided by the precoking stage can be used to compensate for such changes in surface area or to provide more uniform operating conditions for the retort zone.

The special pellets are comprised of particulate or divided solid heat carriers whose physical properties and characteristics, especially surface area, size, shape, temperature, and amount, coact with other variables to control the amount of organicdeposition formed on the pellets during the process, especially during the retorting stage, and to accomplish the other objectives and advantages of the process.

In the process, mined oil shale which contains solid carbonaceous organic matter and other mineral matter and which has been crushed and may have been preheated is retorted in a retort zone with the special hot heat-carrying pellets at a temperature and in an amount sufficient to provide at least 50 per cent of the sensible heat required to retort the oil shale. Retorting oil shale produces gas and oil products, which are recovered, and particulate spent shale. Retorting also tends to deposit a carbon-containing deposition on the special pellets.

After retorting the oil shale, at least per cent of the total spent shale and at least per cent of the spent shale smaller than the pellets are separated from the pellets prior to burning deposition on the pellets. One way to accomplish this separation is to first screen large spent shale and agglomerates from the pellets and thereafter subject the pellets and remaining spent shale to gas elutriation with a noncombustion supporting gas. A way to enhance the degree of total separation is to control the sphericity factor of the pellets to at least 0.9, or to crush the raw oil shale to a smaller than normal size, that is, to minus 6 US. Sieve Series size.

After separation of the spent shale, the pellets from the retorting zone which have a combustible deposition deposited thereon along with any pellets passed directly from the precoking zone are passed to a pellet deposition burning zone where at least a portion of the deposition is burned to heat the pellets. Thereafter, at least a portion of the heated pellets and at least a portion of the oil products are passed to a precoking zone where the heat in the pellets causes partial thermal sta bilization and cracking of oil products from the retort and causes deposition of a combustible coke-like deposition on the pellets. The precoked pellets are then either passed to the retort zone or directly back to the pellet deposition burning zone.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a schematic flow-sheet of the process of this invention; and

FIG. 2 is a partly schematical, partly diagrammatical flow illustration of a system for carrying out a preferred sequence of the process of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION A process for retorting crushed oil shale containing carbonaceous organic matter and other mineral matter is described in general terms having reference to FIG. 1 and in more particular terms having reference to FIG. 2. I Raw or fresh oil shale which has been mined and pulverized, crushed or ground for the most part to a predetermined maximum size for handling in a retort system by any suitable particle diminution process is fed directly from a crusher or from a hopper or accumulator by way of shale inlet line 11 into retort zone 13. At the same time, special heatcarrying pellets substantially hotter than the shale feed are fed by gravity or other mechanical means to the retort zone by way of pellet inlet pipe 15. The pellets and shale feedstock could be fed to the retort zone by way of a common retort zone inlet.

Crushing of the raw mined shale expedites more uniform contact and heat transfer between the shale feedstock and hot pellets. In normal practice, the degree of crushing is simply dictated by an economic balance be tween the cost of crushing and the advantages to be gained by crushing when retorting the kerogen from the shaleQGenerally the shale feedstock is crushed to about inch and no particular care is taken to produce or restrict production of finer material. In this process, crushing has a special purpose and aids in a preburn separation step. In one embodiment, for reasons which will be hereinafter shown and despite the added costs and standard practice, the mined shale is crushed to a substantially finer size wherein at least 95 per cent by weight of the crushed oil shale will pass through a U.S. Sieve Series size 6 screen.

The crushed oil shale may or may not be preheated by direct or indirect heat from any source including indirect heat exchange with pellets or flue gases generated during this retorting process. If the shale feedstock is preheated, the temperature of the feedstock will not exceed 600F. The shale feedstock will usually be fed by way of a metered weight controller system, for reasons hereinafter made apparent, and which may include a preheat and/or gas lift system. The preferred system for preheating the raw shale is to lift the shale in lift pipes with the hot flue gases generated in the combustion phase of the process.

The hot special heat-carrying pellets are especially characterized by having a principal size during use of between approximately 0.055 and 0.5 inch, and preferably between 0.055 and 0.375 inch, and a surface area during use of between 10 and 150 square meters per gram. The surface area is the average effective surface area of the pellets as they enter the pyrolysis zone. The surface area may be determined by the conventional nitrogen absorption method. In one embodiment of the process of this invention, the surface area of the pellets on a gram basis is between 10 and 100 square meters. The importance of surface area is hereinafter discussed in detail. The heatcarrying pellets are at a temperature ranging between l,000F and 1400F which is about 100F to 500F higher than the designed retort temperature within the retort zone. The most favorable practical temperature range depends on "the process variables and more particularly on the specific advantages and characteristics of this process. The quantity of pellet heat carriers is controlled to coact with other variables so that the pellet-to-shale feedstock ratio on a weight basis is between 1 and 3. This ratio is, moreover, such that the sensible heat in the pellets is sufficient to provide at least per cent of the heat required to heat the shale feedstock from its retort zone feed temperature to the designed retort temperature. The feedstock feed temperature is the temperature of the oil shale after preheating, that is the temperature of the shale upon entry into the retort. The average retort temperature ranges between about 850F and l,200F depending on the nature of the shale feedstock, the pellet-to-shale ratio, the type of product distribution desired, heat losses, and the like.

The relative mass and size of the pellets are selected in a manner hereinafter set forth which facilitates separation of the pellets from spent shale, controls the amount of combustible deposition deposited on the pellets, optimizes other facets of the retorting process, and makes allowance for wear or size reduction of the pellets as they are cycled and recycled through the retorting process.

The term pellets refers to subdivided or particulate bodies. A majority of the bodies have the characteristics and properties herein required and which are composed of the same or dissimilar materials having the specified surface area and strength and of irregular shape, cylindrical shape, approximately oval or spherifrom other solids produced in the process as hereinafter set forth. The sphericity factor is the external or geometric surface area of a sphere having the same volume as the pellet divided by the extemal'surface area of the pellet.

The pellets are made up of materials, such as alumina or silica alumina, which are not consumed in the process and which are subdivided or particulate matter having significantly high internal surface area but not excessively high. The pellets are sufficiently wear or breakage resistant and heat resistant to maintain enough of their physical characteristics under the conditions employed in the'process to satisfy the requirements herein set forth, to affect retorting of the oil shale, and to permit controlled burning of a carboncontaining deposition formed on the pellets during the process. More specifically, the pellets do not disintegrate or decompose, melt or fuse, or undergo excessive surface area reduction at the temperatures encountered during such burning and the thermal stresses inherent in the process. The pellets will, of course, undergo some gradual wear or size reduction.

As will be shown, the size of the pellets is related to the other process variables and to the preburn spent shale separation step of this process. The original or fresh pellets are generally comprised of particulate sensible heat carriers in a size range between about 0.1 inch and 0.5 inch, and preferably between 0.1 and 0.375 inch, and are for the most part maintained during use at a plus 14 US. Sieve Series Screen size, that is, approximately 0.055 inch or greater. Finer pellet grain sizes are undesirable in the process of this invention.

Suitable pellet materials are also found in cracking catalyst; however, the retorting process of this invention is not to be considered as relying on active catalytic sites. Many catalysts have surface areas far in excess of the maximum surface area of 150 square meters per gram provided in this process. For example, some silica alumina catalyst may have a surface area ranging between 180 and 700 square meters per gram. As will hereinafter be discussed and as indicated by the trend shown in TABLE 1, high surface areas tend to cause too much carbon-containing deposition being deposited in the retort zone.

Active catalytic sites tend to have effects similar to excessively high surface areas. As a result, in this process, although cracking catalysts may be used, it is preferred that the pellets bear no added active acid cracking catalyst sites or the like when the pellets are added to the retorting zone. What is preferred are pellets that have the size and surface area limitations herein set forth. Of course, the retorting phase of this process and the subsequent deposition combustion phase could be conducted with a catalyst with some loss of flexibility in such a manner as to kill or limit active catalyst sites and limit or destroy excessive available pellet surface area; but it is preferred that the pellets not bear such sites and have or rapidly develop the prescribed surface area range naturally. Thus, the pellets could be comprised of particulate or subdivided matter, for example, catalyst particles, composed or manufactured of materials which can be treated to reduce their surface area and which are of appropriate size, but which originally had a surface area in excess of 150 square meters per gram, and which have been treated to reduce the effective surface area to less than 150 square meters per gram. An originally high surface area can be permanently reduced by methods similar to the way that catalyst particles lose their effective surface area as they age when used in catalytic cracking or hyrogenation units, or by subjecting the particles to rapid or prolonged aging at temperatures and fluid pressures sufficient to reduce the surface area of the particles. A preferred way to cause this reduction in surface area is to subject the particles to temperatures above 1,400F and in the presence of steam at pressures between 0.5 and 7 atmospheres until the surface area is reduced to the desired level. By way of illustration, it has previously been reported in accelerated aging experiments that by subjecting a silica-alumina catalyst to one atmosphere of steam for one hour at 1,585F the surface area was reduced from about 180 square meters per gram to about 95 square meters per gram, and in a similar experiment at 1,432F the surface area was reduced from about 400 square meters per gram to about square meters per gram. The high surface area particulate matter thus treated may originally have been comprised of high surface area particles with active acid catalytic sites. In such case, the particles could also be treated to deactivate their active acid catalytic sites by subjecting them to conditions and chemicals known to poison or kill such active acid catalytic sites, for example, by treatment with sodium bicarbonate, sodium hyroxide, or sodium carbonate.

The retort zone is any sort of retort which causes intimate contact or mixing of the crushed oil shale and pellets. The preferred retort is any sort of horizontal or inclined retorting drum that causes the oil shale and pellets to undergo a tumbling action. This sort of retort is herein referred to as a rotating retort zone. This type of retort zone is quite flexible over a wide range of conditions and has the advantages of causing rapid solidto-solid heat exchange between the pellets and shale feedstock thereby flashing and pyrolyzing the oil and gas vapors from the shale in a way which allows the vapors to separate from the solids without passing up through a long bed of solids and which minimizes dilution of the product vapors by extraneous undesirable retorting gases; of allowing for a high shale throughput rate at high yields for a given retort volume; of providing for greater control over residence time; of aiding in preventing overcoking and agglomeration of the pellets and shale; of facilitating formation of a more uniform controlled amount of combustible carbon-containing deposition on the surface area of the pellets; and of causing flow of the pellets and shale through the retort zone in a manner which aids in eventual separation of the pellets from the spent shale. The amount of deposition deposited on the pellets during the retorting stage of the process is an important feature and will be discussed later in more detail. The retorting process is carried out in concurrent or parallel flow fashion with the hot pellets and the raw shale feedstock being fed into the same end of the retort. The retort zone may be maintained under any pressure which does not hamper efficient operation of the retort, interfere with production of valuable retort vapors, or cause excessive deposition of residue on the pellets. Generally, pressurization of the pyrolysis or retort zone causes considerable difficulties, especially if a rotating retort zone is used. The pressure employed is, therefore, generally the autogenous pressure.

In the retort zone, the hotter pellets and cooler crushed shale feedstock are admixed and intimately contacted almost immediately upon being charged into the retort zone. The shale particles are rapidly heated by sensible heat transfer from the pellets to the shale. Any water in the shale is distilled and the kerogen or carbonaceous matter in the shale is decomposed, distilled, and cracked into gaseous and condensable oil fractions, thereby forming a valuable vaporous effluent including gas, oil vapors, and superheated steam. Pyrolysis and vaporization of the carbonaceous matter in the oil shale leaves a particulate spent shale in the form of the spent mineral matrix matter of the oil shale and relatively small amount of unvaporized or coked organic carbon-containing material.

As the aforementioned vaporous effluents are formed, a combustible carbon-containing deposition or residue will be formed or deposited on the pellets if the effective surface area of the pellets has not already been covered with all of the deposition that it can sustain. The variables and stages of this process as herein set forth are related in a manner which controls the total amount of combustible deposition thus deposited during the retort stage of the process and the amount deposited during a preretort coking or thermal cracking stage of the process. The total amount of deposition formed or deposited on the pellets upon one passage through the process is sufficient upon combustion to provide at least 50 per cent of the heat required to re heat the pellets. The amount of combustible deposition deposited on the pellets during the retorting stage is on an average less than 1.5 per cent by weight of the pellets and the preferred range is between 0.8 and 1.5 per cent. Basically, these controls are critical in two respects. First, the total amount of deposition on the pellet is important since, as will hereinafter be shown, this deposition is burned in a controlled manner to generate a major portion of the heat necessary for heating the pellets to carry out the retorting phase of the process. Second, the total amount of deposition affects the relative yields of gas and condensable or final liquefied products. This in turn affects the distribution of various boiling point fractions in the liquefied products. The total amount of combustible deposition deposited is basically regulated in this process by a precoking product cracking or stabilization stage as hereinafter described and by the amount of deposition deposited on the pellets in the oil shale retorting stage, which deposits are determined by the interrelation of several variables, such as pellet-to-shale ratio, pellet size and surface area, the percentage of the pellets passed through both the precoking zone and the retort zone, the amount and types of products cracked or stabilized relative to the percentage of pellets passed through both the precoking zone and the retort zone, temperatures in the precoking zone and in the retort zone, the outlet temperatures of the precoking cracking stage and the retort zone, and thetype of retort zone. Additional control over both the total amount of deposition deposited on the pellets may be obtained by residence time and throughput rate of the precoking zone and in the retort zone, partial or complete combustion of the deposition, controlled deposition combustion'time' or amount of oxidizing gas used during burning, the noncatalytic characteristics of the pellets, and the size of the pores at the surface of the pellets. As can be readily seen by this description of the process, the degree of regulation or control provided by a single variable is never independent and the flexibility of regulation varies with the type of variable.

The pellet surface area is considered one of the most important variables. The effect of pellet surface area is illustrated by the test results set forth in TABLES l, 2, and 3. The effect of pellet surface area on the amount of carbon-containing deposition formed on pellets and on distribution of carbon deposition between the pellets and spent shale without the precoking thermal stabilization or cracking stage is illustrated in TABLE 1. The effect of pellet surface area on liquid product distribution when a modified Fischer retort was used is i1- lustrated in TABLE 2. The effect of pellet-toshale ratio and, therefore, total surface area of the pellets is illustrated in TABLE 3. The total surface area is determined by the surface area per gram of pellets and the total pellet weight which in turn is controlled by the pellet-to-shale ratio and shale throughput rate. The results illustrated in these. tables lead to several conclusions. First, if the surface area exceeds square meters per gram, too much deposition may be produced on the pellets during the retorting stage of the process when the pellet-to-shale ratios specified herein are used. This in turn indicates an undesirable or excessive shift toward gaseous products in the retort zone. In this process, the total amount of deposition formed on the pellets during the retorting stage may also be partially altered by passing pellets from the thermal precoking stage to the retort zone.

If the surface area of the pellets is less than 10 square meters per gram, either too little total deposition will be formed or the burning of the deposition will not be sufficient to provide a major portion of the heat required to heat the pellets to the desired temperature and to carry out the retorting phase of this process. This would necessitate the use of supplementary fuels and as indicated previously, this has significant disadvantages to the objects of this process.

TABLE 1 EFFECT OF PELLET SURFACE AREA ON CARBON DEPOSITION PELLET AREA WT. PERCENTAGE OF CARBON ON ON PELLETS RESIDUAL SHALE No Pellets 4.30

TABLE 2 EFFECT OF PELLET SURFACE AREA ON LIQUID PRODUCT DISTRIBUTION PRODUCT NO PELL ET AREA BOILING RANGE PELLETS 47m /g 96mlg 150 400F 12% 27% 34% 400 700F 37% 46% 48% 700 900F 32% 22% 14% 900F 19% 5'7: 47:

Pellet Shale Ratio 211 TABLE 3 EFFECT OF PELLET SHALE RATIO ON LIQUID PRODUCT DISTRIBUTION PRODUCT NO PEILLET SHALE RATIO BOILING RANGE PELLETS 1:! 1.5:] 2:1

150 400F 14% 25% 30% 34% 400 700F 38% 45% 47'?! 48% 700 900F 31% 22% 17% 14% 900F 17% 8% 6% 4% by the preretorting or precoking thermal cracking or stabilization stage of this process. In other words, the total effective surface area is not only determined by the original surface area of the pellets and the amount of pellets, but also by the amount of coke or deposition formed on the pellets in the thermal cracking or stabilization stage prior to feeding some or all precoked pellets to the retort zone. As a result, the operator has additional leeway when selecting the pellet-to-shale ratio and the original surface area of the pellets. All variables considered, it has been concluded that an original pellet surface area between and 150 square meters per gram is acceptable with the range of 10 to 100 being preferred and that operating with a pellet-to-shale ratio between 0.5 and 3.5 is feasible with a ratio between I and 3 being preferred.

The mixture of pellets and shale moves through the retort zone toward retort exit 17 and the gaseous and vaporous effluents containing the desired hydrocarbon values separate from the mixture. Since there is no need to use carrier, fluidizing or retorting gases in the retort zone, the gaseous and vaporous effluents are able to leave the retort essentially undiluted by extraneous fluids except for any water or steam vapor added to prevent or retard carbonization, or to sweep product vapors from the solids, or for other reasons to the retort or effluent collection chamber. In a rotating retort system, the mixture movement is continuous and is aided by the action or design of the retort and by continuous withdrawing of pellets and spent shale from the exit end of the retort zone. If a rotating retort zone is used, caking or coking together of the heat-carrying pellets or spent shale will be kept low. Moreover, a rotating type of retort zone is especially suited to varying the residence time, that is, the length of time that the shale and pellets remain in the retort zone by allowing variations in pellet-to-shale ratio and volume of shale throughput. As previously indicated, greater than normal leeway in control over these variables is especially advantageous to regulation of the amount of deposition deposited on the pellets during the retorting stage of the process. The residence time for the pellets required to effect retorting and deposition of the pellet deposition is on the order of about 3 to about minutes with residence times of less than 12 minutes for the pellets being preferred. The shale residence time depends on its flow or movement characteristics and since the shale is not uniform in size and shape, the shale residence time varies.

The mixture of pellets and spent shale exits from retort zone 13 at a temperature between 800 and 1,050F by way of retort exit 17 into separation zone 19 for separation of the vapor, pellets, and spent shale. The separation zone may be any sort of exiting and separation system accomplishing the functions hereinafter mentioned and may be comprised of any number of units of equipment for separating and recovering one or more of these three classes of retort zone effluents either simultaneously, or in combination, or individually. In the process of this invention, it is critical that at least 75 per cent of the total spent shale be separated from the pellets in the separation zone to eventually be collected in separation zone exit line 21. In addition, at least 95 per cent of the spent shale smaller than the pellets, that is, smaller than 0.055 inch, are separated. As shown in FIG. 2, the retort zone mixture is first passed through revolving screen or trommel 23 which has openings or apertures sized to pass the pellets and spent shale of the same or smaller size than the pellets. The trommel extends into product recovery chamber 25. In the trommel, the gaseous and vaporous products separate from the mixture of pellets and spent shale and, at the same time, at least a portion of the larger spent shale particles or agglomerates are separated from the pellets and spent shale. Most of the spent shale and the pellets flow through the openings in trommel 23 and drop to the bottom of recovery chamber 25 to exit via retort exit line 27. Any spent shale or agglomerates too large to pass through the openings in the trommel pass outward through exit 29. The product vapors and gases resulting from retorting the oil shale collect overhead in recovery chamber 25 and rapidly pass to overhead retort products line 31 at an exit temperature between about 750 and 1,050F where the product vapors may or may not be divided into two streams either before or after the vapors are subjected either in their vaporous or condensed or partially condensed state to hot dust separation (not shown) and/or fractionation or partial fractionation (not shown), and/or other stages (not shown) of the overall operation. The hot dust separation may be interior or exterior, or both, of recovery chamber 25 and the dust thus collected may be combined and handled with other spent shale. I-Iot dust or fines separation may be accomplished by hot gas cyclones, quenching and washing, agglomeration with sludge or a separately condensed heavy product fraction, centrifuging, filtration, or the like. Partial fractionation may be accomplished by condensing only a high boiling fraction of the vapors, e.g. 900F+ materials.

Regardless of whether any such additional processing step is taken, at least a part of the product oil collected in overhead line 31 is eventually passed through precoker feed line 33 to thermal precoking zone 35 which will be hereinafter described. For simplicitys sake, feed line 33 is shown directly connected through a metering valve and cracker feed pump 37 to overhead line 31 in a way which allows all or a part of the product to be fed to thermal cracking unit 35.

As mentioned previously, the gases are not diluted by other gases and are, therefore, readily used in the overall shale operation. Some gas may be needed for supplementary fuel and some for production in the usual manner of hydrogen if hydrogenation is used in the overall shale operation. The optimum amount of gas production is just enough to satisfy these requirements as this process stresses the liquid oil products produced in the overall shale operation.

The spent shale and pellets in recovery chamber 25 are discharged via exit line 27 at a temperature between about 750 and 1,050F where these particulate solids are passed or conducted by gravity or other means of conveyance to gas elutriation system 39 which is a part of separation zone 19. In the elutriation system, a major portion, and more preferably substantially all, of the remaining spent shale is separated from the pellets. It is essential that elutriation be accomplished in a way which retains the desired amount of combustible deposition on the pellets; consequently, the elutriating gas fed by line 41 is a noncombustion supporting gas. By conducting the process with pellets in the size range between 0.055 and 0.5 inch, and preferably between 0.055 and 0.375 inch, at least percent of the total spent shale may be separated by action of the trommel and subsequent gas elutriation at a velocity of between 18 and 25 feet per second if most of the raw shale feedstock was crushed to one-half inch. Based on an average of six sieve analyses of the spent shale produced by retorting of minus three-fourths inch shale feedstock in a rotating retort using ceramic onehalf inch balls, about 16 per cent by weight (analyses range 8 to 27 percent) of the spent shale is retained on a US. Sieve Series size 14 screen which is in a size range similar to the pellets. Gas elutriation with irregular or cylindrical shaped pellets only separates about 2.0 to 4.0 per cent of this portion of the spent shale from the pellets. Therefore, on an average between 12 and 13 per cent of the spent shale is difficult to separate by screening and elutriation depending on whether the pellets cover the entire size range of this part of the spent shale. As mentioned previously, retention of more than 25 per cent of the spent shale interferes with proper operation of the pellet deposition burning zone even if most of the spent shale entering the burning zone is originally in the same size range as the pellets. Upon combustion, this spent shale would disintegrate further to fine ashand cause erratic operation of the combustion zone. In addition, some allowance is made for spent shale and ash buildup as the pellets are cycled and recycled through the process.

Since the spent shale having a size similar to the pellets is difficult to elutriate while the spent shale smaller than the pellets is readily separated by elutriation, and practically complete, it is desirable to alter the characteristics of the spent shale or of the pellets to accomplish a greater degree of separation while holding heat losses in the pellets to a reasonable level. One way to accomplish this objective is to crush at least 95 per cent by weight of the shale feedstock to a minus 6 screen size. This results in a separation of at least 95 per cent by weight of the total spent shale from the pellets and the trommel may also be eliminated. As mentioned previously, crushing to this size is costly and normally not done; however, in view of the fact that in this invention it is essential that the bulk of the spent shale be separated from the pellets prior to reheating of the pellets, the cost of additional'crushing may be justified. Another way to accomplish the objective of this separation prior to reheating the pellets has been discovered. It has been found that if the pellets are essentially spherical, that is, have a sphericity factor of at least 0.9, the efficiency of separation by gas elutriation is greatly increased when the raw shale is crushed to a minus three-fourths size. Spherical pellets have improved flow properties over the spent shale and for a given screen size particle exhibit greater weight per particle. Gas elutriation with spherical pellets will separate about 97 per cent or more of the spent shale retained on a US. Sieve Series size 14 screen and will provide almost complete separation of the smaller spent shale. Thus, if spherical pellets are used, gas elutriation will separate at least 95 per cent of the spent shale in the separation zone. As mentioned previously, therefore, the preferred shape of the pellets is spherical, that is, the preferred pellet should have a sphericity factor of at least 0.9.

The separated spent shale is carried out of the elutriating chamber overhead through line 43. The spent shale is collected and may be combined and handled with other spent shale for eventual compaction and waste disposal or sale for use in manufacturing other products.

The separated pellets with their combustible deposi tion are then passed from the separation zone to a pellet deposition burning zone via pellet return line to pellet lifting system 47 where the pellets are lifted preferably to an elevation which allows gravity feed to retort zone 13 by way of lift line 49 to pellet deposition burning zone 51, which as ShOWfll in FIG. 2 has surge hopper 53 for collecting the lifted pellets and leveling out fluctuations and from which the pellets fall into pel let deposition burning zone 55. While any conveying and lifting system holding heat losses to a reasonable value may be used, it is preferred as shown in FIG. 2 that the pellet lifting system be a pneumatic conveying system which will operate in the conventional manner to lift the pellets to the pellet deposition burning zone. The lift gas enters the lift system via line 56 at a velocity between 25 and 70 feet per second and the lift time is,

.therefore, very short. As a result, air may be used as the lift gas without causing uncontrolled combustion of the deposition on the pellets and the detrimental effects attendant to such uncontrolled burning.

As mentioned previously, the pellets bear a combustible deposition which was absorbed or deposited during the process. This combustible deposition is burned in combustion or pellet deposition burning zone 55 to provide at least per cent of more of the heat re quired to reheat the pellets to the temperature required to effect retorting of the shale. The combustible deposition is burned in a manner similar to the way that cracking catalysts particles are regenerated and which is controlled to avoid excessive heating of the pellets which would excessively reduce the effective surface area of the pellets to less than 10 square meters per gram.- A progressive bed burner with a gas flow of about 1 to 2 feet per second is preferred. A combustible supporting gas, for example air, a mixture of air and fuel gas generated in the process, flue gas with the desired amount of free oxygen, is blown into the pellet deposition buming zone at a temperature at which the deposition on the pellets is ignited by way of combustion gas inlet 57 which lllFIGyZ includes a blower. Steam may also be used to controlbuming provided that the steam does not excessively reduce the surface area of the pellets. The combustion supporting gas may be preheated in heaters 59 by burning some of the gases produced in the process to reheat the pellets t0 the minimum ignition temperature. The quantity of combustion supporting gas, e.g., about 10 to 15 pounds of air perv pound of deposition, affects the total amount of deposition burned and the heat generated by such burning and in turn the temperature of the pellets. The bulk density of the pellets is about 40 to 50 pounds per cubic foot and the specific heat of the pellets varies between about 0.2 and 0.3 British Thermal Units per pound per degree Farenheit. The gross heating value of the carhon-containing deposition is estimated to be about 15,000 to 18,000 BTU per lb. The amount of carbon dioxide and carbon monoxide produced. in the flue gases created by burning the pellet deposition indicate the amount of combustion supporting gas required or used and the amount of carbon-containing deposition not burned. Generally. it is desirable to attempt to free the pellets of deposition. In any case, at least 50 per cent of the deposition is burned. The unburned deposition stays with the pellets and affects to some degree the total amount of combustible deposition deposited in the next cycle. It should be noted that this type of controlled burning does not selectively burn the same amount of deposition from every pellet. Other factors taken into consideration during burning of the pellet deposition are the pellet porosity, density, and size, the burner chamber size and pellet bed size, residence burning time, the desired temperature for the pellets, heat losses and inputs, the pellet and shale feed rates to the retort zone and the like. The residence burning time will usually be rather long and up to about to minutes. Combustion of the deposition should be controlled in a manner which does not heat the pellets to above 1,400F. The hot flue gases generated in the pellet deposition burning zone may be removed by burning zone exit line 61 and used to preheat cool raw shale feedstock or for heat transfer to any other phase or part of the shale operation. For example, this stream could be fed to a carbon monoxide boiler and the heat available from the boiler could be used for processing product vapors or to drive turbines. Of course, additional fuel material or gases may be used to supplement burning of the pellet deposition if this is necessary, but it is to be understood that the pellet deposition supplies the major portion of the sensible heat required for retorting the shale and that the variables are set to accomplish this objective along with the other advantages and objectives of this process.

A continuous stream of hot pellets having a temperature above 1,000F and not exceeding 1,400F is thereby produced. The hot pellets pass through the pellet deposition burning zone exit line 63 either by gravity and/0r mechanical means. As previously indicated, the rate of passage of the pellets from the combustion zone will be metered or controlled in conventional manners to eventually provide the optimum pellet-tooil shale feedstock ratio to the retort zone. The optimum ratio is governed by the pellet properties, the amount of deposition on the pellets as they enter the retort zone, the organic content of the raw oil shale, and the other process variables as previously described.

As previously mentioned, at least a portion of the hot pellets and retort oil products are passed or fed to precoking zone 35 which may consist of one or more cracking units. When the oil products contact the hot pellets, some of the oil is thermally stabilized and cracked to upgrade the oil and the resulting coke-like deposition is deposited as useful fuel material for heating the pellets. The amount of stabilization, cracking, and deposition is primarily dependent on the temperature in the precoking zone; on the surface area of the pellets; the pellet-to-oil ratio; on the nature of the oil products passed to the precoking zone; and on the space velocity and pellet holding time. For practical reasons, once a system has been placed in operation, the results of the precoking zone are adjusted by the oil product feed rate, the pellet rate, the temperature, or any combination thereof. Since the pellets have just exited from the pellet deposition burning zone, the temperature may be varied over a wide range. The pellet holding time can be changed by altering pellet feed rate or by varying the total pellet charge in the precoking zone. The total pellet charge can be varied by adding or removing cracking units or by decreasing the pellet charge to each unit. The oil feed rate can, of course, be changed at will. The pellet feed rate can be varied, but

there is less leeway for change unless the holding time is changed or unless the holding time is changed and pellets are removed from the cycle. It is usually uneconomical to attempt to change the nature of the oil feed, the pellet surface area. and the like. Originally, the nature of the oil feed can be preset by fractionating the retort zone oil products; but generally, once a fractionating unit is in operation, it is undesirable to attempt to change the nature of the oil feed by changing the fractionating unit. The preretort thermal cracking zone. therefore, provides flexibility and adaptability in regulating the total amount of deposition formed on the pcllets during the process by controlling and/or adding to the deposition formed on the pellets during the retorting stage of the process. This in turn allows more leeway in operation of the retort zone.

Accordingly, as illustrated in the drawings, the hot pellets in line 63 can either pass by way of precoker feed line 65 to precoker zone 35 or bypass the precoking stage by way of bypass line 67 directly to pellet inlet pipe 15. Ofcourse, it is to be understood that the pellet deposition burning zone could be comprised of more than one zone which could be operated under different conditions or which could exit by way of separate lines which could in turn be used as separate feed lines to precoking zone 35 or as separate cracking zone bypass lines.

The hot pellets from the pellet deposition burning zone are available for entry into the precoking or thermal cracking zone at any temperature up to the exit temperature of the pellet deposition burning zone. The temperature may, therefore, be selected to thermally stabilize or crack a portion of the oil products which are fed into precoking zone 35 by way of precoker feed line 33 and which are passed in the usual reactor manner over and into contact with a bed of pellets fed to the unit. The oil products passed to the supplemental deposition zone may if desired be preheated by indirect heat exchange located either outside or inside the precoking zone. Generally, it is best to preheat the oil products if the products are substantially cooler than the pellets. For example, the oil products may have been derived from a fractionating unit.

It has been discovered that a preferred oil feed for the precoking zone is the portion of the retort zone products within the boiling point between lO0F and 700F. Higher boiling point feeds tend to create problems, and reduce flexibility and reliability of use of the supplemental deposition as a control over the overall retorting process. An oil feed has a boiling point range between 100F and 700F if at least per cent of the feed has a boiling point within this range. Narrower oil cuts within this range may be selected.

As mentioned previously, it is highly desirable that the precoking zone be operated under conditions such that the oil products fed to the zone undergo significant thermal stabilization and some thermal cracking so that the deposition formed in the supplemental deposition zone will be comprised essentially of coke-like products. This limits product losses for fuel on the pellets to coke-like residues and at the same time provides additional stabilization and upgrading of the selected products. Oil feed with above-mentioned preferred boiling point range are especially useful for this purpose.

As mentioned previously, the chief factors affecting the amount of stabilization and cracking of the feed and the amount ofcombustible deposition deposited on the precoker pellets are the properties of the products fed to the unit, the space velocity, the pellet holding time in the precoking unit, the rate of feed and effective surface area of the pellets, and the average temperature in-the cracking or precoking zone. Under thermal cracking or thermal stabilization conditions, therefore, the space velocity may be varied to control the amount of combustible deposition formed on the pellets passed to the precoking zone and on the degree of cracking and stabilization of the oil products treated. The space velocity is herein defined as the ratio of the pounds of oil products passed to the precoking zone per hour to the pounds of pellets in the precoking zone. As shown in TABLE 4, when a composite naphtha oil fraction from a ball type of oil shale retort with a selected boiling range between 100F and 700F was thermally treated at 900F, small incremental changes in space velocities from 2.5 to 0.25 and lower cause a substantial change in the amount of carbon deposited on the pellets passed to the precoking zone. With less desirable higher boiling oil feeds, even lower space velocities must be used.

TABLE 4 position burning zone when the combustible deposition on the pellets is burned.

EXAMPLE A retort train operating at a poundsof-pellets to pounds-of-shale ratio of 2:1 and charging pellets with an effective surface area of 46 square meters per gram processes 458.3 tons per hour of raw oil shale. Hot pellets exit a pellet deposition burning zone at 1,300F and at a rate of 1,904,533 pounds per hour. The hot pellets are divided into two streams with 1,833,333 pounds per hour of pellets at an average temperature of about 1,300F entering a retort zone and with 71,200 pounds per hour at about 1,300F being passed to one or more precoking units containing a total pellet charge of 35,600 pounds. Raw oil shale preheated to 450F is fed to the retort at the rate of 916,667 pounds per hour with the hot pellets. The hot pellets provide the heat necessary to retort the preheated oil shale. A combustible deposition of 1.24 weight per cent is deposited on the pellets in the retort. The pellets and processed shale exit the retort zone into a separation zone where about THERMAL TREATMENT OF COMPOSITE NAPHTHA AT 900F Endpoint of the Treated Product Maleic Carbon Deposit Space Velocity and Cumulative Wt. Percent Anhydride On Pellets Treated No. Feed/hr/No. Pellets'" 4 Boiling Below Endpoint Numher" Wt. Percent" 200F 300F 400F 500F Pellet Holding time was 30 minutes. Values are approximate values. Values for 0.25 Space Velocity are extrapolated values.

As illustrated by TABLE 4, the cumalative weight per cent at different endpoint boiling points of the cracked, stabilized product from the illustrative precoking zone shows that as .the space velocity is decreased the oil fraction undergoes a greater degree of cracking and stabilization. The maleic anhydride number is a standard test used to indicate conjugate diolefins which in turn is an indicator of the degree of stabilization of the thermally treated product. Since the ma-' Ieic anhydride number is the milligrams reacted per gram of feed, a decrease in maleic anhydride number indicates a greater degree of stabilization. As the space velocity decreases the product treated in the precoking zone is made more stable. t

As a result. the oil product feed is thermally stabilized or cracked producing coke or residue on the pellets and an upgraded product which passes to cracking zone product line 69. The precoked pellets, which may have been swept or stripped of products, are passed by gravity or other means through precoker exit line 71 to either pellet inlet line 15 and into pyrolysis zone 13m to bypass the retort zone via bypass line 73 to pellet return line 45 where they are carried to pellet deposition burning zone SI. The amount of combustible deposition deposited on the pellets duringthe precoking or thermal stabilization stage should be less than five per cent by weight of the pellets passed through the supplemental deposition zone. This avoids overheating of the treated pellets and localized hot spots in the pellet de- 98 per cent of the processed shale is separated from the pellets. The pellets exit the separation zone at a temperature of about 900F. For illustration purposes, a rough naphtha oil having a simulated gas chromatographic true boiling point distillation showing 35' cumulative weight per cent at 350F, 68 cumulative weight per cent at 500F, and 94 cumulative weight per cent at 600F is available for use as an oil feed to the precoking unit. The hot pellets passed to the precoking zone are cooled to 900F, and the rough :naphtha feed passed to the precoking zone is preheated to 900F by indirect heat exchange or any other means so that the precoking zone temperature is about 900F. The pellet holding time is about 0.5 hour. In one instance, 32,667 pounds per hour of rough naphtha is fed to the precoking zone. The space velocity is 0.92, and 2.72 per cent combustible fuel than would have been generated if all- .of the pellets had been passed through the retort zone without the precoking stage. In another instance, only 8,900 pounds per hour of rough naphtha is fed to the precoking zone. The space velocity is 0.25, and 0.78 per cent'by weight of combustible deposition is deposited on the pellets passed through the precoking zone. The rough naphtha feed is partially thermally stabilized and cracked with an estimated reduction maleic anhydride number of from about 21.7 to about 4.5. If the precoked pellets are combined with the pellets going to the retort zone, the precoking stage will generate about 550 pounds per hour of additional combustible deposition for use as fuel for heating the pellets. If the precoked pellets bypass the retort zone, the total amount of fuel will be about 330 pounds per hour less than would have been formed if all of the pellets had been passed through the retort zone without the precoking stage.

Although the retorting process is carried out in a manner to hold loss of pellets to a minimum, some pellets will be lost in the process and a relatively small quantity of pellets may be added continuously to maintain the pellet quantity.

The foregoing description of the conditions and variables under which the cracking or precoking stage and the retorting stage can be conducted illustrates how the precoking or pretort thermal cracking coacts with the retorting stage to accomplish the advantages and objec* tives herein set forth.

Reasonable variations and modifications are practical within the scope of this disclosure without departing from the spirit and scope of the claims of this invention. For example, while the disclosure of this process and the variables have been limited to oil shale, the process concepts lend themselves readily to retorting any solid organic carbonaceous material containing hydrocarbon values which can be recovered by thermal vaporization of the solid carbonaceous material, such as, for example, coal, peat, and tar sands. By way of further example, while only a single train of units and stages have been described, it is to be understood that any stage or zone could be comprised of more than one stage or zone, each of which could be operated under different conditions to provide the overall combined effect set forth.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for retorting of crushed oil shale containing carbonaceous organic matter and mineral matter wherein pellets have been heated in a burning zone to a burning zone exit temperature of between 1,000F and 1,400F mainly by a combustion of a combustible carbon-containing deposition on said pellets, and wherein oil shale is retorted in a retort zone to gas and oil products, and solid particulate spent shale by contacting said oil shale with a sufficient amount of said heated pellets passed to said retort zone to provide at least 50 per cent of the heat required to vaporize a major portion of the carbonaceous matter from said oil shale and to heat said crushed oil shale from its retort zone inlet temperature to a retort zone outlet temperature of between 800F and l,l50F, and wherein said gas and oil products are separated and recovered, the improvement comprising passing at least a portion of said heated pellets from said heating zone to a thermal precoking zone and at the same time passing at least a portion of said oil products to said thermal precoking zone into contact with said pellets in said thermal precoking zone to effect some thermal stabilization and cracking of said oil products and to at least partially deposit a combustible coke-like deposition on the pellets passed to said thermal precoking zone, and thereafter eventually passing the pellets with said combustible coke-like deposition deposited thereon from said thermal precoking zone to said burning zone.

2. The method according to claim 1 wherein said pellets are comprised of particulate solid heat carriers in a size range between approximately about 0.055 inch and 0.5 inch and have a surface area of between 10 and 150 square meters per gram of pellets, and the amount of said heated pellets passed to said retort zone is such that the ratio of said heated pellets to said crushed oil shale in said retort zone on a weight basis is between one and three, and wherein at least percent by weight of the total of said spent shale and at least percent by weight of the portion of said spent shale that is smaller in size than said heated pellets is separated in a separation zone from said heated pellets after retorting of said oil shale but prior to said heating of said pellets by combustion of said deposition on said pellets.

3. The method according to claim 1 wherein the particulate solid heat carriers are in a size range between approximately about 0.055 inch and 0.375 inch.

4. The method according to claim 1 wherein at least a portion of the pellets from said thermal precoking zone is passed through said retort zone prior to eventually being passed to said burning zone.

5. The method according to claim 4 wherein said pellets are comprised of particulate solid heat carriers in a size range between approximately about 0.055 inch and 0.5 inch and have a surface area of between 10 and 150 square meters per gram of pellets, and the amount of said heated pellets passed to said retort zone is such that the ratio of said heated pellets to said crushed oil shale in said retort zone on a weight basis is between one and three, and wherein at least 75 percent by weight of the total of said spent shale and at least 95 percent by weight of the portion of said spent shale that is smaller in size than said heated pellets is separated in a separation zone from said heated pellets after retorting of said oil shale but prior to said heating of said pellets by combustion of said deposition on said pellets.

6. The method according to claim 1 wherein the particulate solid heat carriers are 'in a size range between approximately about 0.055 inch and 0.375 inch.

7. The method according to claim 1 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

8. The method according to claim 1 wherein the oil products passed to said thermal precoking zone have a boiling point range between F and 700F.

9. A method for retorting of crushed oil shale containing carbonaceous organic matter and mineral matter comprising a. feeding crushed oil shale and pellets to a retort zone, said pellets being comprised chiefly of particulate heat carriers being in a size range between 0.5 inch and approximately 0.055 inch and having a surface area of between 10 and square meters per gram of pellets, said pellets being at a retort zone inlet temperature between l,000F and 1,400F and in a quantity such that the ratio of said heat-carrying pellets to said crushed oil shale entering said retort zone on a weight basis is between 1 and 3, said ratio also beingsuch that the sensible heat in said pellets is sufficient to provide at least 50 per cent of the heat required to heat said crushed oil shale from its retort zone feed tempera ture to a retort zone outlet temperature of between 800F and 1,150F;

b. retorting in said retort zone gas and oil products from said crushed oil shale, thereby forming particulate spent shale;

c. causing said pellets and said spent shale to pass from said retort zone to a particle separation zone and separating from said pellets at least 75 per cent by weight of the total spent shale and at least 95 per cent by weight of the portion of said spent shale that is smaller in size than said pellets, prior to heating said pellets in a pellet deposition burning zone;

d. recovering said gas and oil products generated by retorting said crushed oil shale;

e. passing said pellets from said separation zone to a pellet deposition burning zone; f. heating said pellets in said pellet deposition burning zone to an outlet temperature of between 1,000F and 1,400F by burning a combustible carboncontaining deposition on said pellets with a combustion supporting gas;

g. passing at least a portion of said pellets from said pellet deposition burning zone to a thermal precoking zone and at the same time passing at least a portion of said oil products to said thermal precoking zone into contact with the pellets in said thermal precoking zone to effect partial thermal stabilization and cracking of said oil products and to at least partially deposit a combustible coke-like deposition on the pellets in said thermal precoking zone; and

h. thereafter eventually passing the pellets from said thermal precoking zone with said deposited cokelike deposition thereon to said pellet deposition burning zone.

10. The method according to claim 9 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

11. The method according to claim 9 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100F and 700F.

12. The method according to claim 9 wherein a combustible carbon-containing deposition is deposited on said pellets in said retort zone, the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets passed through said retort zone.

13. The method according to claim 9 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately 0.055 inch.

14. The method according to claim 9 wherein at least a portion of the pellets from said thermal precoking zone is passed through said retort zone prior to eventually being passed to said pellet deposition burning zone.

15. The method according to claim 14 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 percent by weight of the pellets passed through said thermal precoking zone.

16. The method according to claim 14 wherein the oil products passed to said thermal precoking zone have a boiling point range between l00F and 700F.

17. The method according to claim 9 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately 0.055 inch.

18. The method according to claim 9 wherein the separation of step (c) is comprised of first passing said pellets and said spent shale through apertures in a trommel to screen out at least a portion of the spent shale and any agglomerates larger than said pellets, and thereafter subjecting the remaining pellets and spent shale to gas elutriation with a noncombustible supporting gas to effect further separation of the spent shale from the pellets.

19. The method according to claim 18 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 percent by weight of the pellets passed through said thermal precoking zone.

20. The method according to claim 18 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100F and 700F.

21. The method according to claim 18 wherein a combustible carbon-containing deposition is deposited on said pellets in said retort zone, the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets passed through said retort zone.

22. The method according to claim 18 wherein at 24. The method according to claim 22 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100F and 700F.

25. The method according to claim 9 wherein the pellets have a sphericity factor of at least 0.9 and at least percent by weight of the total spent shale is separated from said pellets in step (c).

26. The method according to claim 25 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately 0.055 inch.

27. The method according to claim 25 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

28. The method according to claim 25 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100F and 700F.

29. The method according to claim 25 wherein a combustible carbon-containing deposition is deposited on said pellets in said retort zone, the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 per cent by weight of said pellets passed through said retort zone.

30. The method according to claim 25 wherein at least a portion of the pellets from said thermal precoking zone is passed through said retort zone prior to eventually being passed to said pellet deposition burning zone.

31. The method according to claim 30 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than per cent by weight of the pellets passed through said thermal precoking zone.

32. The method according to claim 30 wherein the oil products passed to said thennal precoking zone have a boiling point range between 100F and 700F.

33. The method according to claim 9 wherein at least 95 percent by weight of the crushed oil shale of step (a) has been crushed to a size to pass through a U.S. Sieve Series size 6 screen and at least 95 percent by weight of the total spent shale is separated from said pellets in step (c).

34. The method according to claim 33 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

35. The method according to claim 33 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100F and 700F.

36. The method according to claim 33 wherein a combustible carbon-containing deposition is deposited on said pellets in said retort zone, the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 per cent by weight of said pellets passed through said retort zone.

37. The method according to claim 33 wherein at least a portion of the pellets from said thermal precoking zone is passed through said retort zone prior to eventually being passed to said pellet deposition burning zone.

38. The method according to claim 37 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

39. The method according to claim 37 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100F and 700F.

40. The method according to claim 9 wherein said pellets have a surface area of between 10 and 100 square meters per gram of pellets.

41. The method according to claim 40 wherein the particulate heat carriers are in a size range between 0.375 inch and 0.055 inch.

42. The method according to claim 40 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

43. The method according to claim 40 wherein the oil products passed to said thermal precoking zone have a boiling point range between l00F and 700F.

44. The method according to claim 40 wherein a combustible carbon-containing deposition is deposited on said pellets in said retort zone, the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 per cent by weight of said pellets passed through said retort zone.

45. The method according to claim 40 wherein at least a portion of the pellets from said thermal precoking zone is passed through said retort zone prior to eventually being passed to said pellet deposition burning zone.

46. The method according to claim 45 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

47. The method according to claim 45 wherein the oil products passed to said thennal precoking zone have a boiling point range between 100F and 700F.

48. The method according to claim 40 wherein the separation of step (c) is comprised of first passing said pellets and said spent shale through apertures in a trommel to screen out at least a portion of the spent shale and any agglomerates larger than said pellets, and thereafter subjecting the remaining pellets and spent shale to gas elutriation with a non-combustion gas to effect further separation of the spent shale from the pellets.

49. The method according to claim 40 wherein the pellets have a sphericity factor of at least 0.9 and at least per cent by weight of the total spent shale is separated from said pellets in step (c).

50. The method according to claim 40 wherein at least 95 per cent by weight of the crushed oil shale of step (a) has been crushed to a size to pass through a U.S. Sieve Series size 6 screen and at least 95 per cent by weight of the total spent shale is separated from said pellets in step (c).

Claims

1. IN A METHOD FOR RETORTING OF CRUSHED OIL SHALE CONTAINING CARBONACEOUS ORGANIC MATTER AND MINERAL MATTER C WHEREIN PELLETS HAVE BEEN HEATED IN A BURNING ZONE TO A BURNING ZONE EXIT TEMPERATURE OF BETWEEN, 1,000*F AND 1,400*F MAINLY BY A COMBUSTION OF A COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID PELLETS, AND WHEREIN OIL SHALE IS RETORTED IN A RETORT ZONE TO GAS AND OIL PRODUCTS AND SOLID PARTICULATE SPENT SHALE BY CONTACTING SAID OIL SHALE WITH A SUFFICIENT AMOUNT OF SAID HEATED PELLETS PASSED TO SAID RETORT ZONE TO PROVIDE AT LEAST 50 PER CENT OF THE HEAT REQUIRED TO VAPORIZE A MAJOR PORTION OF THE CARBONACEOUS MATTER FROM SAID OIL SHALE AND TO HEAT SAID CRUSHED OIL SHALE FROM ITS RETORT ZONE INLET TEMPERATURE TO A RETORT ZONE OUTLET TEMPERATURE OF BETWEEN 800*F AND 1,150*F, AND WHEREIN SAID GAS AND OIL PRODUCTS ARE SEPARATED AND RECOVERED, THE IMPROVEMENT COMPRISING PASSING AT LEAST A PORTION OF SAID HEATED PELLETS FROM SAID HEATING ZONE TO A THERMAL PRECOKING ZONE AND AT THE SAME TIME PASSING AT LEAST A PORTION OF SAID OIL PRODUCTS TO SAID THERMAL PRECOKING ZONE INTO CONTACT WITH

2. The method according to claim 1 wherein said pellets are comprised of particulate solid heat carriers in a size range between approximately about 0.055 inch and 0.5 inch and have a surface area of between 10 and 150 square meters per gram of pellets, and the amount of said heated pellets passed to said retort zone is such that the ratio of said heated pellets to said crushed oil shale in said retort zone on a weight basis is between one and three, and wherein at least 75 percent by weight of the total of said spent shale and at least 95 percent by weight of the portion of said spent shale that is smaller in size than said heated pellets is separated in a separation zone from said heated pellets after retorting of said oil shale but prior to said heating of said pellets by combustion of said deposition on said pellets.

6. The method according to claim 1 wherein the particulate solid heat carriers are in a size range between approximately about 0.055 inch and 0.375 inch.

8. The method according to claim 1 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

9. A method for retorting of crushed oil shale containing carbonaceous organic matter and mineral matter comprising a. feeding crushed oil shale and pellets to a retort zone, said pellets being comprised chiefly of particulate heat carriers being in a size range between 0.5 inch and approximately 0.055 inch and having a surface area of between 10 and 150 square meters per gram of pellets, said pellets being at a retort zone inlet temperature between 1,000*F and 1,400*F and in a quantity such that the ratio of said heat-carrying pellets to said crushed oil shale entering said retort zone on a weight basis is between 1 and 3, said ratio also being such that the sensible heat in said pellets is sufficient to provide at least 50 per cent of the heat required to heat said crushed oil shale from its retort zone feed temperature to a retort zone outlet temperature of between 800*F and 1,150*F; b. retorting in said retort zone gas and oil products from said crushed oil shale, thereby forming particulate spent shale; c. causing said pellets and said spent shale to pass from said retort zone to a particle separation zone and separating from said pellets at least 75 per cent by weight of the total spent shale and at least 95 per cent by weight of the portion of said spent shale that is smaller in size than said pellets, prior to heating said pellets in a pellet deposition burning zone; d. recovering said gas and oil products generated by retorting said crushed oil shale; e. passing said pellets from said separation zone to a pellet deposition burning zone; f. heating said pellets in said pellet deposition burning zone to an outlet temperature of between 1,000*F and 1,400*F by burning a combustible carbon-containing deposition on said pellets with a combustion supporting gas; g. passing at least a portion of said pellets from said pellet deposition burning zone to a thermal precoking zone and at the same time passing at least a portion of said oil products to said thermal precoking zone into contact with the pellets in said thermal precoking zone to effect partial thermal stabilization and cracking of said oil products and to at least partially deposit a combustible coke-like deposition on the pellets in said thermal precoking zone; and h. thereafter eventually passing the pellets from said thermal precoking zone with said deposited coke-like deposition thereon to said pellet deposition burning zone.

11. The method according to claim 9 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

16. The method according to claim 14 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

20. The method according to claim 18 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

22. The method according to claim 18 wherein at least a portion of the pellets from said thermal precoking zone is passed through said retort zone prior to eventually being passed to said pellet deposition burning zone.

23. The method according to claim 22 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 percent by weight of the pellets passed through said thermal precoking zone.

24. The method according to claim 22 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

25. The method according to claim 9 wherein the pellets have a sphericity factor of at least 0.9 and at least 95 percent by weight of the total spent shale is separated from said pellets in step (c).

28. The method according to claim 25 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

31. The method according to claim 30 wherein the average amount of said combustible coke-like deposition formed on the pellets in said thermal precoking zone is on said average less than 5 per cent by weight of the pellets passed through said thermal precoking zone.

32. The method according to claim 30 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

35. The method according to claim 33 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

39. The method according to claim 37 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

43. The method according to claim 40 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

47. The method according to claim 45 wherein the oil products passed to said thermal precoking zone have a boiling point range between 100*F and 700*F.

49. The method according to claim 40 wherein the pellets have a sphericity factor of at least 0.9 and at least 95 per cent by weight of the total spent shale is separated from said pellets in step (c).