Retort System For Oil Shales And The Like

Abstract

In apparatus for retorting oil shale, oil sands and similar materials wherein finely divided solids residue is used as a heat carrier and is heated in a vertical pneumatic conveyor-burner, mixed with fresh finely divided solid feed, product distillation vapors are removed from the mixture, and the solid distillation residue is returned to the conveyor-burner, the improvement whereby the propellant gas is introduced axially to the bottom of the conveyor-burner and the cool heat carrier is introduced thereinto from a concentric annular chamber thereabout through slits or openings in the propellant gas conduit by means of a flow of a control gas. Other specific improvements of portions of the retorting apparatus and solids circulating system are examplified and claimed, especially a screw conveyor-mixer retorting chamber.

Description

PRIOR ART

Portions of the retorting system of this invention are similar to apparatus disclosed in U.S. Pat. Nos. 2,788,314; 3,056,248 and 2,983,653.

PREAMBLE

Recently there has been an intensification of efforts to dry-distill solid hydrocarbonaceous materials such as bituminous coals, oil shales, oil sands and the like to produced oils, which may be further converted by hydrogenation and conventional refining to products similar to natural petroleum products, e.g. gasoline. Such efforts are being carried on particularly in countries that do not have a cheap and adequate supply of petroleum, but do have large, easily workable deposits of coal, oil shale, or oil sand. In order for an "artificial petroleum" of this kind to be able to compete with natural petroleum, the content of bitumen or oil in the starting material must be relatively high, and if possible should be at least 8 percent, and preferably more than 10 percent. The starting material should also be able to be mined at moderate investment and operating costs.

The distillation apparatus used for this purpose should desirably be able to handle quite large quantities of material in a single unit. It should yield a high quantity of liquid oil with little gas, and the apparatus should make the distillation vapors available for further processing free from admixture with combustion gases or large amounts of recycled higher distillation gases. The expenditure of heat and the power requirements of the distillation process must be low.

Shaft furnaces or retort furnaces are not suitable for a distillation of such hydrocarbonaceous material, because the residence time of the distillate vapors in such units is usually too long and accordingly the formation of gas and residual coke is too great. Shaft furnaces operating with scavenging or stripping gas heating or by internal combustion are not suitable either, because they, require that the starting material be in lumps, and because the distillate vapors produced in them are diluted by the scavenging gas or combustion gas.

Neither can the known methods for the dry distillation of a finely granular starting material in one-stage or multi-stage fluidized beds be used, because the distillate vapors are diluted by the fluidizing gas. If the fluidizing gas is produced by the partial combustion of the starting material or by the admixture of hot flue gases, the distillation gas then contains nitrogen. This necessitates a considerable enlargement of the condensation apparatus and diminishes the value of the distillation gas by making it unusable directly as a pipeline (e.g. public utility) gas, as a source of hydrogen for hydrogenating, or as a synthesis gas.

It is known to carry out the dry distillation of bituminous and petroliferous materials by means of circulating heat carriers. Ceramic balls or steel balls are used as the heat carriers, whose heat is transferred to the material to be distilled by direct mixing and contact therewith, as in a rotating tube. This procedure has been known for some time, but it has not been widely used because the heating and transport of the heat carrier balls through the heater and the rotating tube or kiln is complicated and expensive.

The use of finely divided heat carrying agents offers important advantages, especially if the solid residue from the distillation of the finely granular starting material can be used as the heat carrier. Processes and apparatus are known which heat finely granular heat carriers in a pneumatic conveyor or in a fluidized bed.

Processes and apparatus are also know in which the heat carrier and the raw hydrocarbonacous material are mixed by feeding them together into a shaft retort, thereby heating the starting material and distilling it. The vapors and gases that are released support the fluidization and the mixing together of the heat carriers and the raw material. But this method of effecting mixing in a shaft furnace is not satisfactory when the quantities of raw material and heat carrier to be processed are great. This retorting method also causes increased formation of coke and gas, thereby resulting in considerable losses in the yield of recoverable oils.

The heating of very large quantities of circulating finely granular heat carriers in a fluidized bed requires a large capital investment and frequently results in unsafe operation. Heating in a pneumatic conveyor is therefore to be preferred.

THIS INVENTION

The invention is directed to an apparatus for the dry distillation of bituminous or petroleum-containing materials such as coal, lignite, oil shale, oil sand or the like in a finely granular state and the winning of a distillate therefrom. The material to be distilled is heated by means of being thoroughly mechanically mixed with a circulating, finely divided heat carrier which is thereafter separated from the distillation vapors along with the solid distillation residue, heated in a pneumatic conveyor, and returned to the distillation apparatus.

The requirements for a high oil yield with a low formation of coke and gas, a rapid and uniform heating of the starting material and a rapid removal of the distillate vapors from the distillation zone are effectively met by this invention.

The apparatus according to this invention consists of a vertical pneumatic conveying and heating unit for the particulate heat carrier to the bottom end of which a free-oxygen containing gaseous propellant is fed axially as through a venturi tube and finely granular thermal carrier is introduced thereinto from a concentric annular chamber thereabout through slits by means of a flow of a control gas.

A separator at the upper end of the conveyor is divided by a wall extending downward from the top into a separating chamber and a secondary chamber containing the discharge for the propelling gas and products of combustion, and a bottom solids collecting chamber that is common to both.

A distillation chamber is connected at its input end to the heat carrier discharged from the separator. It also receives the raw material or feed that is to be distilled. At its discharge end, one conduit carries away the hot mixture of thermal carrier and fresh solid distillation residue and another conduit carries away the distillate vapors. The distillation chamber has a screw conveyor or the like to force and mix the solids along the length thereof.

An intermediate reservoir or hopper is connected at one end to the distillation chamber and at the other end to the annular chamber at the bottom of the conveyor.

A dust gas separator is used to remove fines from the distillation vapors after which they are condensed in a product recovery system in which the vapors are condensed by spraying them with previously separated and cooled condensate.

Another dust separator cleans the products of combustion discharged from the conveyor-separator and the gas is then utilized in heat exchange to heat the incoming propellant gas and/or in a waste heat boiler.

The particulate solids removed from the process are cooled, preferably with water, in a solids cooler.

The finely divided solid distillation residue which serves as the heat carrier is carried and simultaneously heated in a vertical pneumatic conveying and heating unit and then is separated from the combustion gases by free fall and inertial ejection in a separating chamber, and delivered to a mechanical mixer in the distillation chamber. In the mixer the thermal carrier, heated to 700.degree. C., for example, is combined with the finely granulated starting material that is to be distilled, e.g., coal, oil shale, oil sand or the like, and blended intensely therewith within seconds. A very rapid transfer of heat from the thermal carrier to the finely granulated starting material takes place. This heat quickly brings the starting material to the desired distillation temperature, usually between 450.degree. and 650.degree. C., breaks down the bitumen, and/or drives out in vapor form the oils contained in or developing from the raw material, together with water vapor formed from the moisture and from chemically bound water. The formation of light cracked gases while this is taking place is extremely slight.

The mixture of thermal carrier and fresh distillation residue flows from the distillation chamber into an intermediate reservoir or hopper for the after-distillation of the feed material and for the driving of hydrocarbon vapors from the interstices and pores of the solids as by the injection of water vapor returned light distillation gases into the mixture. The solids are then fed back into the bottom part of the pneumatic conveying and heating unit, thereby completing the cycle of the thermal carrier through the heating and distillation steps.

The apparatus of this invention permits an effective and simple distillation of finely granulated oil-bearing materials, the condensation of the distillation vapors, and a good recovery of heat from the waste gas from the heating of the thermal carrier. The distillation vapors from the mixer-distilling chamber are processed in a cooling system providing for several stages of contact of the distillate vapors with their own cooled condensate, while the cooling of gases from the heater-conveyor is performed in an air preheater and/or a waste-heat boiler.

The specific investment costs of large units embodying this invention are low. The consumption of heat and power by such units is also low.

THE DRAWINGS

FIG. 1 is a flow diagram of an installation according to the invention;

FIG. 2 is a sectional view in elevation of the distillation chamber taken along the axis thereof and showing in particular the mixer-screw conveyors;

FIG. 3 is a sectional view of the distillation chamber taken perpendicular to the axis thereof; and

FIG. 4 is a horizontal sectional view of the conveyor-solids separator in one alternative embodiment of this invention.

DESCRIPTION

FIG. 1, is the vertical pneumatic conveying and heating unit, 2 is the conveyor-separator for the separation of the thermal carrier from the combustion gases, 3 is the mechanical mixer-distillation chamber and 4 is the intermediate reservoir when the solids are finally stripped of hydrocarbon gases.

Separator 2 and the retort-mixer 3 are connected by the feed line 5, which in its lower portion has a closing and flow regulating slide valve 17, thereby permitting a dense, gas-blocking accumulation of solids in line 5 above the valve. In like manner, the intermediate reservoir 4 and the conveyor-burner unit 1 are connected by a feed line 7, which has a closing and flow regulating slide valve 25 in its lower portion, thus also creating a dense, gas-blocking accumulation of the solids above the valve 25. These blocking accumulations in the lines 5 and 7 separate the retort-mixer 3 and the intermediate reservoir 4, in which the distillate vapors and a gas of high heat value flow, from the bottom portion of the conveyor-burner unit 1 in which there is air, and from the separator 2 in which combustion gases are flowing.

The combination conveyor and heating unit 1 is constricted in its bottom portion where the mixture enters through slits or openings 9 into the conveying tube 1 which is constricted into venture at its entrance at the openings 9. Propellant air, which is preferably preheated is introduced from the bottom by conduit 10 from which it flows upward, taking with it the mixture flowing in through the openings 9, burning the carbon contained in or attached to the mixture and thereby heating the mixture to the desired temperature of, for example, 700.degree. C. If the mixture should not contain enough carbon to heat it sufficiently, additional fuel is introduced into the propellant air through line 65 and nozzle 66, in the form, for example, of gas, waste oil or coat dust in a proportioned amount.

The combustion takes place very rapidly and the heat that is released is immediately transferred to a great extent to the solids of the mixture. Overheating or great temperature differences between the combustion gases and the solids does not occur. This rapid temperature eqalization also makes it possible to preheat the propellant gas to a high temperature, so that excess air can be reduced to a minimum. The rate of flow of air and the rate of flow of any fuel that may be added are adjusted so that no more than the required heating of the mixture is achieved in the conveying unit 1.

Conveying unit 1 is generally 20 to 40 m. long and it is desirable that it flare from the bottom to the top, either at a constant rate or in a step-wise manner. In the bottom part the velocity of the air or combustion gases must be higher, e.g., 30 to 40 m./sec., in order to accelerate the mixture and in the upper part the velocity can drop to 15 to 25 m./sec.

The solids from reservoir 4 and feed line 7 run from the annular chamber 11 surrounding the conveyor unit 1 to the openings 9 in the latter. It is desirable for each opening or slit to receive a controlled feed of secondary propellant-control air through the nozzle 53 to drive the mixture in as well as control, by its rate of flow, the amount of mixture which it injects. In this manner the mixture is introduced around the entire periphery of the conveyor unit and charges it evenly, which is especially important where the diameter of the conveyor is great, e.g., 1 meter or more. Since the rate of flow of the propellant air is individually adjustable at each slit, the recirculated material can be introduced in relatively greater amounts at the individual slits, if this becomes necessary.

It is very important to separate the conveyed and hot solids from the propellant gas in such a manner as to prevent abrasion of the apparatus walls and the formation of any large amount of fine debris. This requirement is met by the arrangement of the conveyor-separator 2. The vertical conveyor unit empties into a greatly expanded separating chamber 13 of unit 2, which has from 5 to 20 times, and preferably 7 to 12 times the cross-sectional area of the conveyor. The velocity of the propellant gases drops greatly in this chamber. The flow of gas is obliged to pass around a vertical partition wall 12 which extends downward from the cover, so that the solids are ejected from it because of the abrupt change in direction. The gas thus separated flows upwardly through the adjacent chamber 14 of unit 2 to an outlet 60.

Separator 2 is designed in its lower portion so as to serve simultaneously as a collecting reservoir or hopper 15 for the hot solids. Hopper 15 communicates with both the large separating chamber 13 and with the smaller adjacent chamber 14. Chamber 14 can be made larger or smaller by varying the position of the partition 12. This may be important because the upward velocity of the hot combustion gases in chamber 14 is determined by the cross section of this chamber. This upward velocity, in turn, is what determines the amount of the finely divided solids that are separated or fall out into hopper 15.

The distance between the cover of the separating chamber 13 and the top edge of the vertical conveyor 1 amounts, according to the invention, to from 3 to 10 m., and preferably 5 to 7 m. At this distance practically no wear is observed in the cover of the separator. The separator is preferably provided with a wear-resistant ceramic lining.

A cyclone separator can be used instead of the separator 2, to the bottom of which a collecting hopper can be connected. In this case the upper end of the conveyor is turned 90.degree. to the horizontal and connected to the cyclone separator.

A narrow feed line 5 runs from the lower portion or collecting hopper 15 to the input of the mechanical mixer-retort 3. In the lower portion of line 5 is a slide valve 17 by which control can be exercised over the amount of heated solids that are continuously fed to the mixing mechanism. Valve 17 provides for the formation of dense accumulation of the solids above the valve. To accommodate thermal expansion, it is desirable for feed line which is preferably ceramically lined to have an expansion joint 16 above valve 17 which joint can also be equipped with a feed line 18 for an auxiliary gas, such as water vapor.

The finely granular feed to be distilled, e.g. tar, sand, oil shale, or asphalt is fed from the hopper 19 through line 20 into the distillation chamber 3, in which it is rapidly and energetically mixed with hot solids from conduit 5. Within a few seconds the finely granular raw material is raised by rapid heat transfer to a prescribed temperature between 450.degree. and 650.degree. C., so that the bitumen is decomposed and the oils are released in vapor form by dry distillation. At the same time the moisture and the chemically bonded water in the solid feed are released in vapor form. In addition, a small amount of distillation gas develops, amounting to about 5 to 100 standard cubic meters, and usually to 10 to 40 standard cubic meters per ton of starting material.

The mixer-retort 3 is illustrated in longitudinal section in FIG. 2 and in cross section in FIG. 3. It has two shafts 21 which rotate in the same direction, each bearing two vanes 22. The vanes of the two shafts are 90.degree. out of phase and interplay with one another and carry the material being mixed around the two shafts. This circulation is produced by the fact that one vane of the mixing shaft strips the material being mixed from the other mixing shaft, carries it around the shaft in its own area of movement, and yields it back to the other mixing shaft. In the stripping action the space filled with the material being mixed constantly changes its form, the material in the marginal portions being pushed to the interior and the material in the inner portions being pushed to the margin.

The vanes 22 are preferably mounted on the shafts in a spiral or worm manner and thus also advance the mixture forward, axially along the shafts. The spiral shape of the vanes also promotes a more uniform stressing of the mixing shafts and of the transmission that drives them. The forward movement of the mixture can be aided by tilting the mixing shafts downward from the horizontal by 5.degree. to 45.degree., preferably 20.degree. to 30.degree.. The interplay of the vanes of the two shafts produces a mutual cleaning of the shafts on all but a lens-shaped cross section around the two vanes of each shaft. If deposits in this lens-shaped cross section cause trouble, the vanes themselves can be bent or curved accordingly. The vanes of the two shafts additionally clean the mixer housing in the areas of their movements.

The vanes 22 are best welded directly onto the mixing shafts 21. It is advantageous to avoid making them continuous so as to prevent damage by thermal expansion. The vanes are therefore interrupted by by gaps of 1 to 10 mm., preferably 2 to 5 mm., at intervals of 100 to 500 mm., preferably 150 to 300 mm. Continuous vanes can also be interrupted by notches extending nearly to the welding seam and can be made more elastic. The vanes and mixing shafts are exposed to only slight wear, and can be made of ordinary steel or from a material of slightly higher wear resistance. It is important, however, to equip the edges of the vanes with a highly wear resistant deposit as by welding material, or to make them of hard steel inserts that are replaceable and can be fastened on by screws, clamping or welding.

Distillation chamber 3 has to handle material with an average temperature of 450.degree. to 650.degree. C., and only in exceptional cases does it come in contact with heated solids of a temperature of up to 750.degree. C. To cool shafts 21, it is desirable to use hollow shafts to which a coolant is fed through a pipe extending all the way to the end of the bore in the hollow shaft, returning it through a bore around the infeed pipe. Water is normally used as the coolant. To keep the heat loss because of the cooling of the mixer shafts to a minimum, circulating oil can be used having a temperature around 200.degree. to 250.degree. C., or some what similar coolant suitable for high temperatures can be used. It is best to leave the other parts of the mixer uncooled.

The mixer shafts 21 equipped with the spiral vanes 22 advantageously have short spiral sections 54 at the inlet, so as to positively feed the solids. The spiral sections 54 and the vanes 22 of the mixer shafts 21 are connected to one another by transitional pieces of appropriate shape. The raw feed can also be blown in together with returned light distillation gases. These gases can also be used for the purpose of more rapidly removing the vapors and gases formed in the mixer.

The housing 55 of the mixer 3 is preferably insulated and equipped with a masonry lining in the bottom part and in the side parts, and is given an external covering of metal plate welded to form a hermetic seal. The cover is also preferably insulated. The cover plate, however, can also be welded on without inside insulation, or it can be at least partially attached by screws, so as to be easily removed for inspection of the interior of the mixing mechanism. The cover plate as illustrated is externally insulated.

Between the area of movement of the mixer shafts 21 and the cover plate, a free gas collecting chamber 56 is left so as to permit a more ready passage of the vapors and gases formed in the mixer. This chamber 56 is enlarged at the outlet end of the retort 3 to form a dome 50 to draw off the vapors and gases to the condensation apparatus. This suppresses the entrainment of dust into the condensation apparatus. Chamber 56 is advantageously constructed in such a manner that the velocity of the vapors and gases does not exceed 10 m./sec., if possible, while it can increase to 20 m./sec. and more in the pipe 51 leading to the condensation or product recovery apparatus. The velocity in chamber 56 must also not be too low, because a long residence time of the vapors favors secondary reaction, particularly of the high-boiling hydrocarbons. Distillation gas fed back into mixture-retort 3 supports the rapid removal of the vapors and gases and suppresses secondary reactions.

The mechanical mixer-retort 3 with the two mixer shafts 21 revolving in the same direction permits the rapid and intense mixing of the solids even at high throughput, and permits distillation within a few seconds when large amounts of finely granular heat carrier. The abrupt heating achieved prevents the extensive decomposition of the oil vapors and makes possible an optimum yield of liquid hydrocarbons from the starting material.

Pneumatic mixing systems have proved impractical at high flow rates because large amounts of steam or returned distillation gases are required for the pneumatic propulsion. This places an unnecessary burden on the condensation apparatus. Mechanical mixers of other kinds do not mix rapidly or intensely enough, and they excessively comminute the material and are not self-cleaning.

The present invention, however, is not necessarily directed to the use of a mixer having 2 mixer shafts revolving in the same direction, and in some cases simpler mixers using vertical mixer shafts can be used.

The starting material is substantially completely distilled in the distillation chamber 3 and, still mixed with the heat carrier, it flows down through line 23 at the end of the mixer into an intermediate hopper 4, where the mixture accumulates, the transfer of heat from the heat carriers to the starting material is completed, and the distillation of the starting material is completed.

The solids are continuously drawn from hopper 4 through conduit 7 to the annular chamber 11 of the vertical conveyor-burner 1. In the bottom part of the conduit 7 there is provided a slide valve 25 with which the rate of flow of the mixture into the annular chamber 11 is controlled. Valve 25 brings about the formation of a dense accumulation of the solids above the valve and up into the intermediate hopper 4.

The intermediate hopper 4 tapers towards conduit 7. In this tapered portion it is desirable to install a diffuser 26, in the form, for example, of a tubular ring with outlet orifices, so that steam or returned light distillation gas can be fed through line 27 and distributed by means of the diffuser 26 into the solids. The steam or gas introduced in this manner drives hydrocarbon vapors out of the interstices and pores of the solids. According to the invention, the time of stay of the solids in the intermediate hopper for post-distillation, the driving out of hydrocarbon vapors and the compensation of certain irregularities that may occur in the circulation of the solids is about 0.5 to 5 minutes, preferably 1 to 2 minutes. The size of the free gas space in hopper 4 is desirably at lease equivalent to a possible detention time of the solids of 1 to 2 minutes, to permit accumulation thereof in case of a process interruption. Hence, the hydrocarbon vapors would normally flow only slowly through the free gas space in the intermediate hopper, and could be decomposed by secondary reactions. Consequently it is desirable to introduce steam or distillation gas in such a quantity that the detention time of the hydrocarbon vapors in the free gas space of the intermediate hopper does not exceed 1 to 2 seconds.

The hydrocarbonaceous feed material has a particle size of less than 6 mm., and preferably less than 4 mm. If the grains decrepitate easily, a feed grain size of up to 2 mm. can be used. The maximum particle size is determined by the requirement of performing the distillation all the way to the center of the grains during the short time of stay in mixer-retort 3, so as to achieve a high yield of oils.

The solid residue remaining after the distillation of the starting material is preferably used as the heat carrier. Depending on the starting material, the size of the grains of this residue remains approximately equal to the particle size of the starting material, or it may shrink or swell slightly. In many cases, it may tend to crumble.

The residue that serves as the heat carrier preferably has a particle size greater than 0.2 mm., so that the separation in separator 2 can be effected readily with only small quantities of inder dust being carried into the condensation apparatus by the vapors and gases. The recirculation of the heat carriers produces a constant attrition creating dust, most of which is carried out of the circulating system with the combustion gases.

A rather large amount of particulate solid residue is freshly formed continuously by the distillation process, and this is removed from the circulation system as by conduit 61 connected to intermediate hopper 4. At this point, however, there is a portion of freshly distilled residue which has not yet passed through the conveying and heating unit 1 and has therefore a carbon content. To enable the solids residue to be free of carbon when brought into contace with the air, excess residue can be removed by line 28 from hopper 15 of the separator through a cooler 43 to the dump.

The vapors and gases liberated in the distillation are collected at the discharge end of the mixer-retort 3 in the enlarged gas dome 50, to which the vapors and gases formed in the intermediate hopper 4 are also passed, and from there they are fed through conduit 51 to a dry dust gas separator 29. The gas separator 29 is preferably in the form of one or more cyclone separators in parallel or series. The dust that is removed is fed through line 30 into the bottom portion of the intermediate hopper 4 or into line 7, and thence to the conveyor-burner.

The vapors and gases flow from dust gas separator 29 through conduit 68 into a cooling or product recovery system 69, in which they are scrubbed and cooled by means of cooled condensate. This treatment is best performed in a plurality of stages, three for example. In the first stage 30, the heavy oil condensed is used for the cooling of the vapors and gases. The heavy oil practically completely absorbs from the vapors and gases any dust that has not been eliminated by the dry dust separator. The recirculated oil can be cooled in a heat exchanger 31 by water, air or the like, or the cooling can also be brought about by the production of low-pressure steam. If the utilization of the waste heat is not considered important, one simple solution is to spray water into the scrubber 30 and evaporate it. The amount of water is then so proportioned and the temperature of the vapors and gases so adjusted that as much heavy oil condenses in the scrubber as is necessary to keep the heavy oil with its dust content satisfactorily fluid and pumpable. The vapors and gases are in this case cooled to a temperature between 200.degree. and 300.degree. C. The temperature can, however, be reduced still further in order to make more oil condense and to obtain a more greatly diluted heavy oil.

In the second stage of the cooling system, in the scrubber 33, the gases and vapors are cooled by recirculated medium oil to such an extent that the oil vapors condense substantially, but no water vapor precipitates. This is the case when the temperature of the vapors and gases at the discharge of scrubber 33 is slightly above 100.degree. C. The circulating medium oil is recooled for this purpose in a heat exchanger 34 by water, air or the like. The injection and evaporation of water is impractical in scrubber 33, because it is difficult to completely vaporize the water at the low temperatures and thus keep the circulating oil free of water. The excess medium oil taken from the circulation is practically free of dust and water and can be used directly for further processing or can be delivered to the storage tank.

In an additional stage of the cooling system 69, the scrubber-cooler 35, the remaining mixture of gases and vapors is chilled to about 30.degree. C. by sprinkling with their own condensate and water. This recirculated water is best cooled by air in a first cooler 59 and indirectly in a second cooler 62. The condensed light oils and the gasoline are separated from the process water in a separating tank 36. In this cooling stage the light oils, gasoline and water vapor condense. At this point an indirect cooler with cooling surfaces can also be used. The distillation gas which is saturated with water vapor and gasoline vapors at the cooling temperature, is left behind. The gasoline vapors still contained therein can be recovered by scrubbing with light oil, by compression of the gases and then cooling them, or also by intense cooling. A portion of the light distillation gas is fed back as scaventing gas to the mechanical mixer 3 and the intermediate hopper 4.

The light distillation gases have a high content of C.sub.1 to C.sub.3 hydrocarbons, and furthermore contain hydrogen, carbon monoxide and often carbon dioxide, too. They have a high heat value and are practically free of nitrogen. They can be sold as a public utility gas or can be processed to yield synthesis gas or hydrogen.

The combustion gases which have heated and driven the circulating heat carrier upward in the conveyor-burner unit 1 and have been separated from the carriers in the separator 2 pass from the chamber 14 through conduit 60 into a cyclone 37 in which the entrained dust is substantially separated from the gases. This dust can be fed back through line 38 into the feed line 5 or directly to the mechanical mixer-retort 3. Preferably, this dust is ejected from the process, e.g., through conduit 39, in order to keep the percentage of dust in the circulating solids low.

It is desirable to connect to cyclone 37 an air preheater 40 and a waste heat boiler 41 with a steam collector 64 for the production of steam, so as to utilize the waste heat from the waste gases. In some cases it might be better to place the waste heat boiler 41 first and the air preheater 40 second in the waste gas line.

In air preheater 40 air is compressed in blower 63, that is needed for the conveyor-burner 1 and is preheated. It is advantageous to design the air preheater 40 and the waste heat boiler 41 in such a manner that the heat of the waste gases is substantially utilized, but the temperature should not be lowered below the dewpoint if the gases contain sulfor dioxide.

After the heat of the waste gases has been utilized, dust must be thoroughly removed from them before they can be passed through a smokestack into the open air. A mechanical or electrical dust remover 42 or a conbination of both can be used. This dust remover can also be connected to a wet scrubber if the circumstances require it. Since the apparatus according to the invention is used in large units of high output and consequently very large amounts of waste gases have to be released into the atmosphere, their content of fine dust must be very low. This can only be achieved in may cases by an electrical fine cleaning in the final stage. Wet scrubbing is involved when the waste gases are rich in SO.sub.2 and the SO.sub.2 is to be recovered.

The dust drawn from cyclone 37 through conduit 39 and from the dust removers 42 through pipe 67 has to be cooled and moistened so that it can be handled, transported and dumped without creating a nuisance by producing great clouds of dust. All of the solid residue that is to be dumped can be introduced into cooler 43. The cooling and moistening of the hot residue is performed preferably in a mixer 43 which, like mixer 3, contains two mixer shafts rotating in the same direction and equipped with spirally curved vanes. At the point where the dust is fed in, a line 44 is connected which carries water, preferably condensate produced in the process. By the spraying in and evaporation of the water the dust is cooled to a temperature below 100.degree. C. and can be brought to a moisture content either of 24 - 4 percent, for example, or as high as 10 to 20 percent, if desired.

If the apparatus according to the invention is used for the distillation of coals, large quantities of coke are produced in addition to tar. This coke is used as the circulating heat carrier and is consumed in small quantity to supply the fuel requirement in the conveying and heating unit 1. The large mass of the coke ejected from the circuit can be burned in a power plant or, if it is possible and profitable, it can be used as a sintering fuel, as a leaning material in coking works, or as a tar-free reducing fuel in dust form. This residue coke can also be briquetted and the briquettes can be treated to serve for house heating purposes or as blast-furnace coke. In the distillation of coal, experience dictates the maintenance of a temperature between 550.degree. and 650.degree. C. at the discharge of the mixer-retort 3 and in the intermediate hopper 4 in order to obtain a maximum yield of tar. Experience shows that this yield amounts to about 100 to 170 percent, depending on the type of coal, of the tar content that can be detected in the starting coal by the low-temperature carbonization analysis according to Fischer and Schrader. The apparatus is suitable for use both with coking and with non-coking coals.

Oil shale has an oil content of 2 to better than 30 percent by weight, depending on its source. Oil shales of different types and origins can be processed in the apparatus according to the invention. Experience shows, however, that the oil content should not be less than 8 percent, and preferably not less than 10 percent, in order to make it sufficiently profitable to work. In detail, profitability depends on the cose of decomposing the oil shale, the region in which the oil shale is located, and the price of natural petroleum at the point of use of the shale oil. A special economic advantage is had when the oil-shale residue can be used in whole or in part for special purposes and does not have to be simply wasted by dumping it. Depending on the composition of the residue, it can be used as a hydraulic binder, as raw material for the manufacture of cement, for the production of bricks, or for the recovery of aluminum oxide, uranium oxide or the like.

Oil shale having an oil content of more than 20 percent is often plastic by nature, or becomes plastic upon passing through a certain temperature range. The apparatus according to the invention can be operated without any trouble even with oil shales that behave plastically in the cold or hot state.

The oil yield from oil shale differs according to its character. In comparison with the oil production that can be achieved in the Fischer analysis, yields between 95 and 110 percent by weight are achieved in the apparatus according to the invention.

Oil sands are often hard to work, because they may become plastic even at temperatures of around 20.degree. C. and tend to cake up. By the use of appropriate mechanical crushers, especially toothed roller mills, a crushing to under 10 mm. can be achieved. If the broken material has an undesirable tendency to cake up before its introduction into the mechanical mixer-retort 3, it is advantageous to add finely granular residue from the distillation of the oil sand to the crushed material immediately after it is crushed, thus keeping it from sticking together. Often the oil sand has a tendency to stick undesirably to the walls of the crushers and transporting means. This sticking can be completely prevented if the walls are heated by low-pressure steam or the like.

In oil sand, the oil is present in petroleum form. The same is the case with oil shale. In the case of distillation in the apparatus according to the invention, an oil yield of 95 percent of the oil content determinable by extraction can be achieved if the proper distillation temperature is maintained and the residence time of the oil vapors in the hot part of the apparatus is kept short. By using a somewhat higher distillation temperature, the character of the overall oil production can be improved, with a lower overall yield.

The apparatus according to the invention can be made in large units of high output capable of distilling 200 to 400 metric tons per hour of coal, oil shale, oil sand or the like. If a total oil yield of 10 percent by weight is assumed, 20 to 40 metric tons of oils can be produced per hour in one unit, corresponding to 160,000 to 320,000 tons of oil per year. The inside diameter of the conveying and heating unit 1 should not be much greater than 1,500 mm., on the basis of past experience. For high throughputs, therefore, 2 to 4 conveying units can be connected in parallel to one sifter 2. FIG. 4 indicates how, in an apparatus having a plurality of parallel conveying units, the separating chamber 13 of the sifter 2 is subdivided by cross partitions 44, so that if one conveying unit fails it will not be packed full by the others that are in operation.

The capacity of the mechanical mixer-retort 3 is also limited. In the case of a temperature difference of 100.degree. - 150.degree. C. between the hot heat carrier flowing into the distillation chamber 3 and the solids emerging from the intermediate hopper 4, the amount of circulating solids that is required is normally 4 to 8 times the weight of the starting material that has to be distilled. Consequently the distillation of 200 to 400 tons of starting material per hour requires 800 to 3,200 tons of circulating solids per hour. The mixing together of these great quantities is advantageously divided among a plurality, preferably two to four mixer-retorts 3, which are disposed and operated in parallel underneath a common separator 2. Whether to associate a separate intermediate hopper with each mixer-retort 3 must be decided from case to case. FIG. 4 is a top view of a cross section through the apparatus 2 with the openings of three parallel conveying and heating units 1 in the separating chamber 13 equipped with the partition and the two cross-partitions 44. Two mixers 3 and one intermediate hopper 4 underneath the apparatus 2 are indicated by broken lines.

Claims

What is claimed is:

1. In an apparatus for the dry distillation of finely divided solid hydrocarbonaceous material by admixing therewith in a distillation retort a hot finely divided heat carrier taken from the solid distillation residue of said dry distillation, which heat carrier is thereafter separated from the vaporous distillation product and conveyed pneumatically, separated from the conveying gas and after reheating is recycled to said distillation retort, said apparatus comprising

a. said distillation retort having an elongated casing with a feed end portion and a discharge end portion, and a pair of rotating worms in said elongated casing,

b. a feed conduit for said hydrocarbonaceous material and

c. a separator containing said hot heat carrier connected to the feed end of said distillation retort,

d. a product recovery and cooling system adapted to receive vaporous distillation product,

e. an intermediate hopper adapted to receive solid distillation residue connected to the discharge end of said distillation retort, and

f. a vertical pneumatic conveyor connecting said intermediate hopper and said separator, the improvement comprising

I. inlet conduit means for introducing a free oxygen containing propellant gas upwardly through the lower end of said vertical pneumatic conveyor to burn at least a part of the carbonaceous material in said carrier material to heat it by combustion, and a concentric annular chamber about said inlet conduit means adapted to receive said carrier material to be heated from said intermediate hopper, said inlet conduit means having openings communicating with said annular chamber, and controlled gas introduction means communicating with said openings so as to regulate the amount of said heat carrier material passing therethrough,

Ii. a first separator to receive the hot carrier material from the upper end of said vertical pneumatic conveyor comprising in its upper portion two chambers separated by a downwardly directed wall, one of said chambers communicating directly with the upper discharge end of said vertical pneumatic conveyor, the other chamber having an outlet for gaseous combustion products, a solids reservoir in the lower portion common to said upper two chambers to collect hot heat carrier material, and a discharge conduit connecting said reservoir and the inlet of said distillation retort,

Iii. a second separator to receive gaseous combustion products from said first separator to separate entrained dust therefrom,

Iv. indirect heat exchange means connected to said second separator, to transfer heat from said hot gaseous combustion products to said free oxygen containing propellant gas for introduction to said lower end of the vertical pneumatic conveyor, and

V. conduit means adapted to remove solid distillation residues from said two separators and said intermediate hopper connected to a mixing device for cooling and quenching with water said solid distillation residues for disposal.

2. The apparatus of claim 1 wherein said first separator has a cross-sectional area in the range of 5 to 20 times the average cross-section of said vertical pneumatic conveyor and the distance from the discharge end of said conveyor to the top of said first separator in the range of 3 to 10 m.

3. The apparatus of claim 1 wherein at least two of said conveyors operate in parallel and commonly discharge into said first separator.

4. The apparatus of claim 1 including valve means in said solids discharge conduit from said first separator and in said conduit between said intermediate hopper and said annular chamber, said valve means permitting the build-up of solids in the conduits and said intermediate hopper.

5. The apparatus of claim 1 wherein said product recovery and cooling system comprises three scrubbers adapted to progressively cool said distillation vapors by contact in each with cooled liquid condensate.

6. The apparatus of claim 1, wherein said mixing device for water quenching the discharged solids is connected to said product recovery and cooling system so as to receive condensed water therefrom.

7. The apparatus of claim 1, including a dust gas separator connected to said distillation chamber and to the intermediate hopper so as to receive distillation vapors from said distillation chamber and to discharge dust recovered therefrom to the intermediate hopper.