US3032477A

US3032477A - Fluidized carbonization

Info

Publication number: US3032477A
Application number: US787874A
Authority: US
Inventors: Marvin F Nathan
Original assignee: MW Kellogg Co
Current assignee: MW Kellogg Co
Priority date: 1959-01-20
Filing date: 1959-01-20
Publication date: 1962-05-01
Anticipated expiration: 1979-05-01

Description

May 1, 1962 HOPPER \f FEED DRYER & PREHEATER COAL HEATER CARBONIZER STEA M M. F. NATHAN FLUIDIZED CARBONIZATION Filed Jan. 20, 1959 CHAR INVENTOR.

MARVIN F. NATHAN BY zm. 001M;

MIS

ATTORNEYS United States Patent tion of Delaware Filed Jan. 20, 1959, Ser. No. 787,874 4 Claims. (Cl. 202-27) This invention relates to an improved process for the carbonization of carbonaceous materials such as coal, lignite, shale, asphalt, etc. More particularly it relates to an improved carbonization process wherein a carbonaceous material is pretreated with oxygen prior to carbonization and the heat required for carbonization is supplied from the combustion of a portion of the carbonaceous material with oxygen.

This application is a continuation in part of my copending application Serial No. 488,034, filed February 14, 1955, now forfeited, and my copending application Serial No. 585,354, filed May 16, 1956, and now Patent No. 2,933,822, dated April 26, 1960, which in turn is a continuation in part of my application Serial No. 517,472, filed June 23, 1955, and now Patent No. 2,775,551, dated December 25, 1956.

The treatment of carbonaceous solids to form valuable liquid, gaseous and solid products is well known in the art. An example of one process frequently employed entails the treatment of solids, such as coal at elevated temperatures whereby volatile materials are released from the solids and a valuable solid product is formed. This process is usually called carbonization. It has been the practice in the past to carry out carbonization in both non-fluid and fluid systems, however, the present invention is concerned with a carbonization process of the fluid type wherein the various steps are performed with a finely divided feed material which is maintained in a high turbulent state of agitation by the passage therethrough of a fiuidizing medium.

One of the major problems encountered in handling fluidized carbonaceous materials results from the tendency of the carbonaceous particles when elevated in temperature to pass through a so-called plastic state wherein the particles become soft and malleable and tend to adhere together. This change in the physical characteristics of the carbonaceous material usually takes place at an elevated temperature, for example, in the case of coal, between a temperature of about 700 F. and about 800 F. Several methods have been suggested for combating this problem. One of the more successful procedures comprises contacting the carbonaceous particles prior to carbonization with a limited amount of oxygen whereby the physical characteristics of the particles are altered to provide a fluidized mass of solids which resist agglomeration. The actual mechanism by which this result is brought about is not clearly understood, however, according to one theory, the oxygen reacts with the surface of the carbonaceous particles to convert a portion of the solid and/ or volatile components of the carbonaceous material to a hard shell, thereby case hardening the solid particles. This treatment does not prevent the carbonaceous material from passing through the plastic state, however, it does reduce the sticking tendency of the carbonaceous particles during this phase and provides an operable fluid process.

After the pretreating operation is completed, the carbonaceous particles are passed into a carbonization zone wherein they are further elevated in temperature for the removal of volatile tar components and the production of a residue char product. As used herein, the term tar comprises any volatile organic compounds released from the carbonaceous material in the 3,032,477 Patented May 1, 1962 ice carbonization process, either liquid or vapor and either cracked or uncracked; and the term char comprises any solids remaining after carbonization of the carbonaceous material. The heat required in the carbonization zone may be obtained from one or more of several sources, for example it may be supplied from an inert gas such as fuel gas heated to a high temperature, it may be supplied from the burning of a combustible gas such as a fuel gas mixed with oxygen, it may be supplied from the combustion of oxygen or an oxygen containing gas with a portion of: the pretreated carbonaceous material etc. Of the available heat sources, the latter is to be preferred for various reasons and the invention disclosed herein is directed to processes wherein this method of supplying heat is employed.

It has been customary in the past to carry out pretreating and carbonization of carbonaceous materials in separate vessels. Since oxygen is used in the carbonization zone as well as in the pretreating zone, it has also been the practice to introduce pretreated solids and oxygen together into the carbonization zone. Usually air in quantity to supply the required oxygen is used for fluidizing and transporting the pretreated solids between the two zones. This manner of moving the pretreated solids while effective, results in a consumption of tar compounds by burning thereby reducing the amount of tar produced in the process. disclosed herein to provide a process without this draw: back.

In carrying out the carbonization process of the invention herein the heat required for pretreating and carbonization is provided by the combustion of a portion of the carbonaceous material. The amount of oxygen required in the process per pound of carbonaceous material is established by the temperatures maintained in the pretreating and carbonizing zones. In order to obtain maximum product yields it is desirable that the proportion of the total oxygen consumed in the pretreating step be limited to the minimum required to provide a process wherein particle agglomeration is held to a minimum. If an excessive amount of oxygen is used in the pretreating zone, valuable tar components are consumed and the tar yield is correspondingly reduced. If insufiicient pretreatment oxygen is used, the carbonaceous particles may adhere and the process may become inoperable. The pretreatment temperature is also important in determining the operability of the fluidized carbonaceous solids system; it is preferred to carry out the pretreating step at an elevated temperature. At the temperatures normally used all of the heat required in the pretreating zone cannot be supplied by burning carbonaceous material therein and at the same time provide optimum pretreating. It is, therefore, necessary to provide an additional large quantity of heat from another source, usually by preheating the carbonaceous solids in a conventional manner, such as for example by indirect heat exchange with a hot fluid. The further amount of heat required to raise the carbonaceous material from pretreating temperature to the carbonizing temperature and to carry out the carbonization process is then supplied by oxygen introduced in the carbonization zone. The problem of controlling the temperature in the pretreating zone particularly downward fluctuations thereof is important in maintaining operability.

It is an object of this invention to provide an improved process for the pretreating and carbonization of carbonaceous materials.

It is another object of this invention to increase the yield of volatile materials resulting from the carbonization of carbonaceous materials.

Still another object of this invention is to provide an improved method of controlling the temperature in the- It is proposed by the invention pretreating zone in a process for the combined pretreating and carbonization of carbonaceous materials.

These and other objects of the invention will become more apparent from the following detailed description and discussion.

The above objects are achieved by carrying out pretreating and carbonization in such a manner that partially oxidized pretreated carbonaceous material is passed from a pretreating zone immediately into a carbonization zone and is therein heated to carbonizing temperature without further contacting oxygen. The invention comprises preheating finely subdivided carbonaceous material, pretreating the carbonaceous material with oxygen in a dense phase bed at an elevated temperature, carbonizing carbonaceous material in a similar dense phase bed at a higher temperature in the presence of oxygen whereby volatile materials are released from the carbonaceous material and a solid char residue is produced and admixing pretreated carbonaceous material with char in the carbonization zone in a region of low oxygen concentration whereby the pretreated carbonaceous material is heated and is stripped of volatile materials by contact with hot combustion gases.

In another aspect of the invention, the temperature in the pretreating zone is controlled by introducing therein a small variable quantity of hot char from the carbonizing zone.

It is within the scope of this invention to treat various carbonaceous materials, including coals, shales, lignites, asphalts, oil sands, etc. The invention is particularly exemplified, however, by its application to the treatment of coal, and further discussion of the invention is directed to the use of this material. It is not intended, however, that this particular application should limit the scope of the invention in any way.

In carrying out the invention, finely subdivided coal which has been dried and preheated to between about 100 F. and about 650 F. is introduced into a pretreating zone wherein it is partially burned with oxygen to provide the case hardening effect. The temperature at which the pretreatment step is carried out may vary over a range between about 600 F. and about 825 F., more usually the range of temperature between about 650 F. and about 800 F. is preferred. The pretreatment is carried out in a conventional dense phas bed wherein the coal is maintained in a turbulent fluid state by passage therethrough of a gasiform medium. Adequate turbulence to maintain the dense phase bed is provided by maintaining a linear gas velocity therein between about 0.5 and about 5 feet per second, or more usually between about 0.75 and about 3 feet per second. Under normal operating conditions the density of the dense phase bed varies between about and about 40 pounds per cubic foot. Generally, a portion or all of the fluidizing medium is supplied in conjunction with the oxygen required for pretreating, for example by diluting the oxygen with air, by using air alone or by diluting air or oxygen with steam or other inert gas. It is within the scope of the invention to supply the pretreatment oxygen to the pretreating zone in a gaseous stream of varying oxygen content. The amount of oxygen required for pretreating is usually between about 0.02 and about 0.08 pound per pound of the fresh coal feed. To provide suflicient time for the pretreating combustion reactions to take place, the rate of introduction of coal to the pretreating zone is controlled to allow an average residence time therein of the coal particles of between about 10 and about 60 minutes. The pressure used in the pretreating may vary from as low as atmospheric pressure to several hundred pounds per square inch, usually it is preferred to operate near atmospheric pressure.

Both the pretreating and carbonization steps are car-.

ried out in conventional fluid beds which are maintained by passing a fluidizing medium through finely subdivided particles of coal. The'amount of vapor and solids introduced into these beds per unit of time is important in determining both the volume of the beds and the degree of solids turbulence therein. It is desirable in carrying out these processing steps, as in other fluid processes, to maintain solids beds of relatively constant size having a sufficient flow of fluidizing medium therethrough to provide adequate turbulence of the fluidized solids. Thus, control of vapor and solid flow rates to the fluid beds is of utmost importance. In carrying out the pretreating of finely subdivided coal particles in such a solids bed, it has been found that the amount of oxygen that combines with coal at a given temperature is dependent on the size distribution of the coal particles, that is on the amount of coal surface presented to the oxygen. If the coal particles increase in size the coal surface is decreased and the amount of oxygen consumed is also decreased. On the other hand, when the coal particles decrease in size the reverse is true. conventionally, coal particle size distribution on a commercial scale is provided by mechanical crushing and grinding. Any variation in the operation of the equipment employed for this purpose, which is not uncommon, usually means a change in the size distribution of the coal produced. As previously mentioned, if the coal particle size suddenly increases the amount of oxygen consumed in the pretreater will decrease and the temperature therein will also decrease. The obvious solution which springs to mind in such an event is to introduce more oxygen into the pretreating zone. This has the elfect of increasing the concentration of oxygen in the pretreating zone whereby the combustion reaction rate is accelerated and the temperature may be brought back to its former level. Unfortunately, however, introduction of more oxygen into this zone requires decreasing the quantity of air introduced into the carbonization zone unless the temperature in the latter zone is also increased. Obviously, an increase in carbonization temperature is undesirable from the viewpoint of uniformity of operation and product yields. Furthermore, withdrawal of oxygen from the carbonization zone decreases the vapor velocity in this zone and affects the degree of turbulence and size of the dense phase bed maintained therein, both of which are equally undesirable. Similarly, increasing the oxygen to the pretreating zone increases the turbulence and vapor velocity in this zone which may also have a detrimental effect. Still another disadvantage of increasing the amount of oxygen entering the pretreating zone lies in the fact that only a portion of the additional oxygen is consumed in the pretreatment and the remainder along with the unreacted portion of the original oxygen passes from the pretreating zone into the carbonization zone. Here it is consumed at least in part by reactions which involve tar rather than the non-volatile portion of the coal.

In the method of this invention it has been found that the problem of temperature decrease due to changes in the size distribution of the fresh coal feed is substantially eliminated and effective temperature control obtained in the pretreating zone by recycling a small, variable quantity of hot char from the carbonization zone to the pretreating zone. Not only is this method of temperature control simple in operation, but it is without the defects attendant with attempts to control the temperature by varying the oxygen to carbon ratio. The amount of char required for cfiective temperature control may vary at any instant from as low as zero to about /2 pound per hour per pound of coal present in the pretreating zone; however, more usually the quantity of char required to compensate for temperature upsets is relatively low, that is between 0.01 and about 0.2 pound per hour per pound of coal present in the pretreating zone. The recycle char flow rate may be controlled manually or more usually by the installation of a temperature controller in the recycle line. Itis contemplated that a small amount of char will be recycled continuously when using this method of temperature control in order to prevent plugging of the recycle line. The amount of heat introduced into the pretreating zone in this continuous char stream, however, is verysmall compared to the total heat required in thepretreating zone, usually not more than about 5 percent thereof.

During normal operation a major portion, more usually at least 90 percent of the oxygen introduced into the pretreating zone is consumed therein. Because of this, the problem of increasing pretreating temperature due to a decrease in the average particle size of the coal is not nearly as critical as temperature movement in the opposite direction. The unconsumed oxygen even if totally reacted can raise the pretreating temperature only a few degrees. The major reason for temperature control is to prevent excessive drops in temperature which may affect the operability of the process. On the other hand, increases in pretreating temperature will rarely, if ever, have any detrimental effect on operability, although increased temperature may lower the yield of tar products. Other operating changes besides particle size may affect the temperature in the pretreating zone, for example there may be a temporary variation in the rate of introduction of fresh coal into this zone. It is within the scope of this invention to provide a degree of temperature control by the aforedescribed method immaterial of the causes of temperature variation, however, the proposed mode of operation is directed primarily to eliminating the problem resulting from recurrent variations in feed coal particle size.

As previously mentioned, prior methods of pretreating coal before carbonization have included the portion of the oxygen required in the carbonization zone in the fluidizing medium during passage of the pretreated coal particles from the pretreator to the carbonizer, more usually through a transfer line. It has been found that this method of operation does not provide the highest tar yield. The reason or reasons for this are not clearly understood but are believed to be related to the time during which tar vapors and oxygen are in contact. In order to obtain an effective coal pretreatment, it is necessary to provide an average coal particle residence time in the pretreating zone of several minutes. Since oxygen is introduced into the pretreating zone continuously, the solids in this zone, are, of necessity, in contact with oxygen for substantially this period of time. On the other hand, gases entering and released in the pretreating zone reside therein for only a few seconds, more usually about 5 and about 20 seconds and subsequently pass from this zone. Thus, tar vapors released from the coal in the pretreating zone are in contact with oxygen for a very short period of time compared to the time of oxygen-solids contact. When the pretreated coal and effluent gases from the pretreating zone containing oxygen are passed to a carbonization zone through a transfer line, the total time of contact between the tar vapors and oxygen is substantially increased, by as much as 100 percent or more depending on the length of the transfer line and the velocity of the gases therein. The additional few seconds of contact time between the coal particles and oxygen provided by use of the transfer line is, however, insignificant. If it is assumed that oxygen shows equal preference for tar and coal it is obvious that the combustion of tar is increased by use of a processing method which includes the use of a transfer line with oxygen in the transferring medium.

In the method of this invention, pretreated solids are passed directly from the pretreating zone into the carbonizing zone without the use of a transfer line, thus minimizing contact between the tar vapors and oxygen. Oxygen required in the carbonization zone is introduced into this zone separately from the pretreated solids. The direct passage of solids between the two zones is provided by using contiguous openly communicating zones, more specifically by using a single vessel which contains both zones, separated by appropriate means. A further improvement over previous practice is obtained by introducing the pretreated solids into a portion of the carbonizing zone wherein the concentration of oxygen is low. Since the tar materials distilled from the coal during carbonization vary in composition and comprise numerous organic compounds of widely varying boiling points, only a portion of these compounds is removed from the coal during the pretreating step, and by far the larger amount of tar is distilled from the coal in the higher temperature carbonization zone. The proposed separate introduction of pretreated coal and oxygen into the carbonization zone is effective in reducing the consumption of tar already vaporized, however, unless the pretreated coal is maintained free from contact with oxygen in this zone for a period of time sufficient for the remaining tars to be distilled, a substantial portion of these volatile components may also be consumed. Thus, in addition to passing the pretreated solids directly from the pretreating zone to the carbonization zone, it is further desirable to introduce these solids into a region of the latter zone which is free or relatively free of oxygen, whereby remaining tar materials are distilled therefrom and removed from the carbonization zone before the pretreated coal enters the region of combustion. In the method of this invention, this is accomplished by introducing combustion oxygen into a dense phase bed of char in the carbonization zone in the lower portion thereof whereby the oxygen is substantially consumed before the fluidizing and combustion gases pass into the upper portion of the bed. The pretreated coal is introduced into the top portion of the same dense phase bed below the surface thereof, is heated by contact with the hot char and is stripped of volatile material by fiuidization and combustion gases in a relatively oxygen free atmosphere. The total gases from both zones then enter the dilute phase above the carbonization dense phase bed and are passed from the system. Although the effective removal of volatile components may be attributed to a combination of heating and stripping it is probable that the primary separating force is provided by the heat in the carbonized coal or char.

In addition to the advantages mentioned, the proposed method of operation eliminates another defect of previous carbonization processes. Because of the relatively low temperatures used in pretreating, it is difficult to provide for complete consumption of the oxygen introduced into the pretreating zone for this purpose. As a result, the effluent gases from this zone usually contain some oxygen. In normal operations, for example the amount of oxygen break through may be as high as 10 to 15 percent of the total introduced. When pretreating is carried out in a conventional manner in separate vessels in a conventional dense phase bed, unconsumed pretreatment oxygen passes into the dilute phase of the pretreating zone and reacts therein with tar vapors released from the coal. In the method of this invention, there is no dilute solids phase in the pretreating zone and oxygen which is not consumed in this zone passes into a dense phase bed of char in the carbonization zone along with the combustion gases and pretreated coal. Here the oxygen has at least an equal chance to react with solids rather than tar, thus effectively increasing the tar yield.

The depth of solids bed required in the carbonization zone to successfully carry out the invention depends on several factors, including the velocity of the fluidizing medium therein, the degree of turbulence in the fluidized bed, the temperature at which carbonization is carried out and the diameter of the bed. In general, a bed of the depth normally maintained in commercial catalyst cracking processes is adequate, deeper beds may be used to assure the complete absence of tar-oxygen contact. The depth of bed maintained in the pretreating zone is less critical, here too the degree of oxygen consumption is an important factor in determining bed depth. Usually in either zone a bed of between about 10 feet and about 40 feet in depth is maintained, if desired, more shallow beds and beds up to feet in depth may be used. It is not necessary that the beds be of equal depth.

As previously described, one aspect of the invention comprises passing effiuent gases from the pretreating zone through the dense solids bed in the carbonization zone whereby unreacted oxygen is contacted with hot char solids. The residence time required to complete the oxygen reaction is provided by maintaining a head of dense solids above the outlet from the pretreating zone. Usually a very short period of time is required, namely between about and about 30 seconds which is provided by holding a solids head between about 5 and about 40 feet.

The carbonization of coal may be carried out over a wide range of temperatures, usually between about 700 F. and about 2400 F., the preferred thermal rangeis largely determined by the type of liquid product desired. For example, when it is preferred to distill a minimum of cracked or volatile constituents the temperature is held to a minimum of about 800 F. and not more than about 1300 F., more usually the low temperature carbonization is carried out between about 825 F and about 1l00 F. The type of coal to be carbonized is of importance in establishing the operating temperature. In the method of this invention, the carbonization step is carried out in a dense phase bed similar to that used for the pretreating portion of the process, and provided in a similar manner, while the pretreatment step is carried out entirely in the dense phase, the carbonization zone contains a dense phase bed superposed by a disperse or dilute phase which may have a solids concentration as low as 0.001 pound per cubic foot. Gases from both zones pass into this dilute phase for preliminary rough separation of vapors and solids. Further solids separation is provided by conventional means, such as for example, cyclones.

Substantially all of the distillable constituents of the coal are removed at the aforementioned carbonization temperatures within a very short period of time, that is between 0.25 and about minutes. To prevent agglom eration of the coal particles in the carbonizing zone, it is preferred to maintain a substantial ratio of char to fresh feed therein. This dilution of the fresh pretreated coal makes it necessary to substantially increase the coal residence time in order to provide a reasonable size carbonization zone. At the usual char to fresh feed ratio maintained in the carbonization zone, that is between about 5 pounds per pound and about 50 pounds per pound, the residence time is between about 2 minutes and about 200 minutes, or more usually between about 20 minutes and about 100 minutes. Carbonization may be carried out over a wide range of pressures, usually between about atmospheric and about 500 p.s.i.g., preferably not over about 100 p.s.i.g. Similar processing considerations are important and similar operating conditions are required when carbonizing feed materials other than coal. The conditions appropriate for each specific feed material are well known to those skilled in the art and therefore do not need repeating here.

In carrying out fluidized carbonization of carbonaceous materials, it has been found that several process steps are necessary in order to provide a workable operation and assure a maximum yield of desirable vapor, liquid and solid products. More usually the first step in the carbonization process concerns the proper preparation of the raw feed material. This involves proper selection and sizing of the carbonaceous solids to provide a readily fluidizible feed and proper handling of the solids to maintain the fluid system.

One of the problems frequently encountered when handling carbonaceous materials such as coal in a fluidized system results from the tendency of the finely divided solids to agglomerate because of water condensed thereon. Most coals coming from a treating plant, for example, have a relatively high surface or free water content, usually between about 2 and about percent by weight, or higher. This moisture may cause packing or bridging in process equipment of restricted cross section, such as, for example in feed hoppers, standpipes, etc.

This moisture may be removed in various conventional ways but it is preferred in accordance with this invention to achieve the aforementioned desired results by introducing finely divided solids wet with a liquid material into a dense phase fluidized bed containing similar solids having a lower liquid content, said bed being maintained at a temperature below the boiling point of the wetting material. The solids of lower liquid content are provided by introducing to said bed dry solids fluidized with gaseous material condensable at the temperature in the dense phase bed. Fluidization of the dense phase bed is provided by the introduction thereto of a non-condensable gas. The amount of said gas is controlled to provide a solids bed of high density and low fluidizing gas velocity whereby entrainment of solids from said bed is held to a minimum.

In a narrower aspect of the invention the wetting material is water and the solids of lower liquid content are provided by introducing to said bed dry solids fluidized with steam and a non-condensable gas, the quantity and composition of this fluidizing material being such that the fluid bed is maintained without entrainment of any substantial amount of solids therefrom.

In still another aspect of the invention wet finely divided solids are passed downwardly from a non-fluid feed zone through a confined zone to a dense phase bed of dry solids. During said passage solids from the dense phase bed fluidized with gaseous wetting material and non-condensable gas are introduced to the confined zone in with cient quantity to fluidize the descending wet solids and provide the desired moisture content thereof.

In carrying out a preferred embodiment of the invention, wet coal ground to a suitable size, usually between about 10 mesh and 5 microns, is introduced into an elevated feed hopper in a non-fluidized condition. Within the hopper there is maintained a dense phase fluidized bed of coal having a lower average moisture content and a higher temperature than the wet feed coal. Wet coal entering the hopper commingles with the solids in this bed and is quickly elevated in temperature and distributed through the bed. The resulting mixture is readily maintained in a fluidized state. In a separate drier and preheater vessel there is provided a second dense phase bed of dry coal at a temperature substantially higher than the solids in the hopper. The average moisture content of the coal in the feed hopper is maintained below the level of the wet coal feed by circulating dry solids from the second phase bed to the hopper and by returning an equal amount of solids plus the fresh feed from the hopper to the dry coal bed. The amount of solids circulated varies depending primarily on the water content and fluidization properties of the wet coal, usually a dry coal circulation rate between about 1 and about 3 pounds per pound of wet feed coal is employed.

The mixing of wet and dry solids is performed in as small a vessel as possible and preferably without the installation of cyclones or other expensive solids recovery apparatus. Thus a system is provided in which the wet and dry solids are mixed in a turbulent solids bed characterized by its high density and low fluidizing gas velocity. The result is a minimum of solids entrainment in the effluent gases. To maintain the solids in the feed hopper in a fluidized state, a small amount of non-condensable gas, such as, for example air or flue gas is introduced into this vessel. The amount of such gas is regulated to provide a velocity in the solids bed of between about 0.25 and about 0.5 foot per second, which provides a solids density therein between about 40 and about 30 pounds per cubic feet. When operating under these conditions solids entrainment from the dense phase is negligible. Usually the loss of solids in the fluidizing gas does not amount to more than about 0.02 percent by weight of the fresh feed and more usually between about 0.01 and about 0.001 percent thereof.

The temperature in the feed hopper is prevented from exceeding the boiling point of water since any substantial amount of vaporization in the feed hopper would result in increased gas velocities and excessive entrainment of solids from the bed. It is preferred to operate the hopper at essentially atmospheric pressure, accordingly, the temperature therein is maintained between about 100 and about 200 F. Due to the turbulent nature of the fluid bed in the feed hopper only a very short solids residence time is provided in this vessel, usually between about /2 and about 5 minutes. It is preferred to place the feed hopper above and support it on the drier and preheater. This presents a problem, however. To provide the required dry coal recycle, it becomes necessary to entrain coal from the drying zone in a fluidizing medium and pass the mixture upwardly from the drying zone into the feed hopper. The amount of fluidizing medium required to accomplish this, more usually between about 0.001 and about 0.05 pound per pound of dry coal circulated is much greater than the quantity of vapor which can be handled in the feed hopper without excessive solids entrainment. One method of overcoming this difiiculty is to use a mixed fluidizing gas containing primarily steam and only sufficient air to maintain the partially dried solids in the feed hopper in a fluidized condition. The major portion of the steam in the fluidizing gas immediately condenses upon entering the feed hopper solids bed and is distributed throughout the coal particles. The small amount of fluidizing air used and the uncondensed steam pass through the dense phase bed into a dilute phase and from there to the atmosphere. Since additional water is introduced into the feed hopper in this method of operation, it is necessary to circulate more dry coal to this vessel, however, the amount of Water introduced as fluidizing steam is still very small, usually less than about percent of the water present in the wet feed coal.

Operation in the manner previously described provides a mixture of wet and dry coal which is readily fluidized and which may be subjected to further treatment without danger of agglomeration or equipment plugging. Due to the low velocity of the fluidizing gases in the feed hopper no solids recovery system is required and it is not necessary to seal the conveying system which supplies wet feed coal to the feed hopper.

In carrying out the drying operation which follows the predrying treatment, the mixture of wet and dry coal from the feed hopper is introduced to the drying zone wherein it is commingled with dry heated coal in sufiicient quantity to elevate the entire mass to a temperature suitable to effect the removal of water. The dry coal is then passed through a heater, where it is further elevated in temperature by indirect heat exchange with a hot fluid and then into a second zone. The higher temperature coal in the second zone serves as the source of the coal commingled with the wet coal feed, and in addition, provides preheated coal for the next phase of the carbonization process. The entire drying and preheating step is conveniently conducted in a fluid system with both the low and high temperature zones containing a dense phase bed of fluidized coal. Adequate turbulence to maintain each dense phase bed is provided by maintaining a linear gas velocity therein between about 0.5 and about 5 feet per second, or more usually between about 0.75 and about 3 feet per second. Under normal operating conditions the density of the beds thus provided varies between about 10 and about 40 pounds per cubic foot. The temperatures in the two zones will vary. Usually the first zone is operated at a temperature between about 220 F. and about 325 F., and the second zone is preferably maintained at a temperature of between about 350" F. and about 600 F. Fluidization of the solids in the low temperature zone is partially provided by moisture released from the coal and may be augmented by the introduction into this zone of air or an inert gas such as, for example flue gas, steam, etc. The coal in the high temperature or preheating zone is maintained in a fluid state by the introduction of a similar gasifying medium. It is necessary to circulate a sufficient amount of coal from the low temperature zone through the heater to the high temperature zone and back to the low temperature zone to provide both the sensible heat acquired by the dry solids and the heat of vaporization of the water released therefrom. When operating in accordance with the zonal temperature ranges given, the amount of coal circulated relative to the raw coal feed rate is between about 2 and about 5 pounds per pound.

The heat transfer surface required for drying and preheating the coal is preferably provided by a conventional shell and tube heat exchanger with the solids passed through the tubes in indirect heat exchange with a hot fluid passed through the exchanger shell. The heat required to dry the coal is provided by a fluid heating medium which may be a petroleum oil or vapor, or mixtures thereof, or other liquid or vapor material which is easily transported and can withstand relatively high temperatures. The temperature at which the heating medium is employed varies with the temperature maintained in the drying zone and with the heat transfer characteristics of the heating medium. Usually, it is preferred to introduce the heating medium at a temperature between about 350 F. and about 1000 F. More usually a surface area between about 0.02 and about 0.30 square foot per pound of fresh coal feed per hour is sufficient to provide the desired drying and preheat.

In order to more clearly describe the invention and provide a better understanding thereof, reference is bad to the following drawings of which:

FIG. 1 is a diagrammatic illustration in cross section of process equipment used in carrying out a preferred embodiment of the invention comprising a unitary coal carbonization system which includes a feed hopper, dryer, preheater, pretreater, carbonizer, char hopper and associated lines and heat exchange equipment.

FIG. 2 is a diagrammatic illustration of pretreating and carbonization zones suitable for carrying out the preferred embodiment of the invention, and

FIG. 3 is a View similar to that of FIG. 2 showing a somewhat modified system for carrying out the preferred embodiment of the invention.

Referring to FIG. 1, coal at a temperature of about 60 F. having a particle size distribution between about 10 mesh and about 5 microns and containing about 8 percent water is introduced from a feed means through conduit 11 into feed hopper 10 in a non-fluidized condition. Within vessel 10, which is at atmospheric pressure, there is maintained a conventional dense phase fluid bed of coal particles 12 having a temperature of about F. and containing on the average about 3.3 percent water. Above the dense phase is a dilute phase 13 of very low solids concentration through which the gases leaving the dense bed pass prior to release through conduit 14. The wet solids entering the dense phase bed 12 are quickly raised in temperature to the level of the solids contained therein and due to the turbulent nature of the bed are mixed and dispersed throughout the hopper.

Support for the feed hopper 10 is provided by a subjacent drier and preheater vessel 15. Within this vessel there is maintained a dense highly turbulent bed 16 of dry coal particles at a temperature of about 270 F. The upper portion of this bed occupies the entire cross section of the drier vessel 15; however, in the lower portion the dry coal is confined within an annular space lying between the walls of the vessel 15 and a cylindrical elongated conduit 17 extending upwardly through the bottom of the drier. 18 in which there is maintained a higher temperature dense bed of coal particles which overflow continuously into the lower temperature dry solids bed 16. Above the dense bed of dry and preheated coal is a dilute phase 19 of low solids concentration. Water vapors released from the coal pass upwardly through this space into a Within conduit 17 lies a preheating zone- 1 l cyclone from which separated solids are returned to the dense phase of dry coal, and from which the vapors leave the drier through conduit 21.

To provide the lower solids water content required in bed 12, dry coal from bed 16 is passed upwardly through conduit 22 into the feed hopper 1% The motive force necessary to transfer this solids stream is supplied by steam introduced into the bottom of riser 22 through conduit 23. Upon entering the feed hopper, the major portion of the fluidizing steam is quickly condensed and distributed throughout the solids bed 12. To provide solids turbulence in bed 12 and maintain the coal therein in a fluid state, a small amount of non-condensable gas in this specific illustration air, is introduced either through conduit 24 or through conduit 23 or both. Taking into account the amount of water introduced to the feed hopper as fluidizing steam, a solids circulation rate of about 2 pounds per pound of wet coal feed is required to provide the desired temperature and solids water content. The flow of solids between

beds

16 and 12 takes place through the standpipe 25 which is controlled by a slide valve 26 or other conventional means.

The fluidizing mixture of air and steam passes through the dense phase bed at a very low velocity, about 0.2 foot per second, providing thereby a bed density of about 35 pounds per cubic foot. Although the velocity of the fluidizing gas is sufiicient to maintain solids turbulence, it is not great enough to entrain any substantial amount of solids from the dense phase. As a result, it becomes unnecessary to provide for solids recovery from said gases.

To obtain the heat required in the drying zone, a stream of dry coal is removed therefrom through conduit 27, entrained in fluidizing steam, and passed to coal heater 28 wherein the temperature of the coal is increased to about 480 F. From the heater the hot coal is passed through line 29 into conduit 17 from whence it eventually overflows to the drying zone. In order to maintain the desired temperature in the drying zone, it is necessary to overflow about 2 pounds of solids from conduit 14 per pound of Wet coal introduced into the unit. Thus the solids circulation rate through the coal heater 28 is about 3 pounds of coal per pound of wet feed. The heat required in the combined drying and preheating operation is supplied by passing the circulating solids stream in indirect heat exchange with a cat cracker decanted oil having an API gravity of about 15. This material is introduced to heater 28 through conduit 30 at a temperature of about 680 F. and exits therefrom through conduit 32 at a temperature of about 400 F. The foregoing method in addition to effecting the removal of moisture from the coal provides a ready means of adding the amount of preheat required before pretreating the coal.

Although the hot coal leaving heater 28 enters zone 18 in a fluidized condition, it may be desirable to introduce additional gases, such as for example steam through conduit 33. The amount of fluidizing gases passed through each zone is controlled to provide a velocity therein of about 1.2 feet per second, thereby maintaining a solids density in each bed of about 25 pounds per cubic foot.

The combined drying and preheating vessel 15 forms a part of a single unitary vessel structure superposed above a carbonization vessel 34 which contains within its lower portion a pretreating zone 35. Passage of solids from the preheating zone 18 to the pretreating zone 35 is effected by flowing them downwardly through a standpipe 36 enclosed within the carbonizer vessel. Inasmuch as the standpipe passes through the carbonizer before it reaches the pretreating zone, it is exposed to the high temperatures in the former zone and it may be desirable to provide some form of insulation to protect this conduit. The rate of flow of solids from the preheating zone 18 to the pretreating zone 35 is controlled to maintain a more or less constant level in vessel 15 by a conventional plug valve 37 in contact with the bottom terminus of the standpipe 36. The pretreating zone 35 is separated in part from the carbonization zone 38 by a vertical baifle 39 attached at the bottom and sides to the inner wall of the carbon'izer vessel 34. The bottom portion of the pretreating zone contains a distribution grid 40 for distributing fluidizing gases throughout the pretreating zone. The pretreating zone opens upwardly into the carbonizing zone 38 and is separated therefrom by a grid 49 through which pretreated solids and vapors pass from the former to the latter zone.

The pretreating operation involves contacting the coal particles with a controlled amount of oxygen, viz., about 0.0 4 pound per pound of preheated coal whereby the coal particles are partially oxidized. In this manner, the physical characteristics of the particles are altered so as to nullify their tendency to adhere to each other as they are elevated in temperature and pass through the so-called plastic stage. The effectiveness of the pretreating step is dependent not only on the extent to which the coal particles are oxidized, but is also a function of the pretreatment temperature, which is substantially increased over the preheating temperature, that is to about 725 F. The heat required to elevate the coal to this temperature may be supplied entirely from the heat of combustion of the coal. In carrying out the pretreating step, oxygen is introduced through conduit 41 and is distributed in the lower portion of the pretreating zone through grid 40. The oxygen may be supplied in a relatively pure state; however, more usually, it is preferred to use air so as to supply the additional gases necessary to maintain the solids in a fluidized state. Additional gases for example, steam, flue gas, etc., may be introduced through conduit 41 for fiuidization purposes.

Coal entering the pretreating zone commingles with the solids contained therein and is partially oxidized and rapidly increased in temperature to that of the dense phase bed. In this process about 4 percent by weight of the preheated coal is reacted with the oxygen and converted to combustion products. The resulting mixture of pretreated coal and combustion gases, along with any portion of unconsumed oxygen, passes upwardly through the pretreating zone and through grid 49 into the carbonization zone 38. Within this zone there is maintained a dense phase turbulent bed of solid char particles at a substantially higher temperature, that is about 950 F. Inasmuch as the pretreating zone is entirely beneath the top level of the solids in the carbonization zone, the grid 49 serves the dual purpose of distributing the solids and gases leaving the pretreating zone and at the same time prevents passage of solids from the carbonization zone tov the pretreating zone. By use of this separating means, it is possible to maintain two contiguous, yet distinct and separate dense phase beds of solids at quite difierent temperatures.

The preheated coal from zone 18 contains a large number of organic tar compounds varying widely in molecular structure and boiling point. The increase in temperature in the pretreating zone 35 releases a portion of the lower boiling of these volatile compounds which pass upwardly into the carbonization zone 38 along with the pretreated solids and other gases. Upon entering the latter zone the pretreated solids are quickly elevated to the temperature prevailing therein and large additional amounts of volatile components are released from the coal. The total time required in the two zones to carry out the process of tar removal is of short duration, however, in order to prevent solids from agglomerating and thereby assure an operable fluid process, it is desirable to maintain a large excess of pretreated solids in the pretreating zone and a similar excess of carbonized solids or char in the carbonization zone. This is effectively provided by sizing the pretreating and carbonization zones to allow an average particle residence therein of about 25 minutes and about 60 minutes, respectively. The

pretreated solids bed is maintained in a higher turbulent state by controlling the flow of vapors therethrough to provide a gas velocity of about 1.2 feet per second and a solids density of about 25 pounds per cubic foot. Usually, this is effected by varying the oxygen rate through conduit 41, however, if necessary an extraneous gas (not shown) is admitted to zone 35. The degree of turbulence and density of the solids in zone 38 is regulated in a similar manner.

The heat required for carbonizing the coal feed is also supplied by burning a portion of this material. For this purpose, about 0.03 pound of oxygen per pound of pretreated coal feed is introduced into the carbonization zone 38. In this operation also the oxygen is supplied as air. Since one of the important features in optimizing liquid product yield is minimum contact between oxygen and volatile tar constituents, the oxygen required for carboniza-tion is introduced into the bottom of the carbonization zone through conduit '42 which is at a point remote from the area of introduction of pretreated coal. Oxidation and combustion of the carbonized coal particles proceeeds rapidly and is substantially completed before the carbonizer fiuidizing and combustion gases reach the elevation at which the pretreated coal is present in quantity. The heat released by the combustion reactions is quickly transmitted throughout the dense char bed providing a hot turbulent mass into which lower temperature pretreated solids are introduced. The transfer of heat from the char particles to the pretreated solids in turn is equally swift and these solids reach the general char bed temperature level within a very short period of time. The process of devolatilization also proceeds at a fast rate and, by the time the pretreated solids reach the zone of combustion, they are substantially free of volatile tars.

By reason of the location of withdrawal conduit 43, char product from the main upper portion of the carbonization solids bed is forced to flow downwardly through the space provided between bafiie 39 and the wall of the carbonizer vessel 34. Hot combustion and fluidizing gases flow upwardly through the same space countercurrent to the descending char and provide a stripping action which assists in the removal of tar compounds from the char. The removal of volatile components from the coal in the carbonization zone, therefore, is effected in two ways, i.e., by elevating the pretreated coal particles to the carbonization temperature and by passing these particles downwardly countercurrent to ascending combustion and fluidizing gases before withdrawing them from the carbonization zone.

The final products of the carbonization process comprise a mixture of tar vapors, steam and combustion gases, and carbonaceous char solids. Distribution of these products, based on the unconverted Wet coal feed, is approximately 8 percent steam, 14 percent tar compounds and 78 percent char. The remainder of the coal is converted to combustion products to supply the process heat requirements. The gaseous products pass from the dense phase bed of char 44 upwardly into a dilute phase 45 and from there through a cyclone separator 46 and conduit 47. Solids recovered in the cyclone are returned to the dense char bed below the surface thereof. Char solids product are removed from the bottom of the carbonizer 34 through conduit 43, are picked up by a stream of fluidizing steam and are passed to cooling and storage equipment.

Referring to FIG. 2, wherein is diagrammatically illustrated pretreating and carbonization zones suitable for carrying out the preferred embodiment of the invention, the coal carbonization process is carried out in a vertical cylindrical vessel 50 internally divided into an annular carbonizing zone 51 and a cylindrical pretreating zone 52, centrally disposed therein. In each of the two zones there is maintained a dense phase fluidized bed of finely subdivided particles of coal. The pretreatment zone is entirely dense phase, however, above the carbonizer dense phase bed there is a dilute phase zone 53 of low solids concentration.

Suitable lines

54, 55, 56, 57 and 59 are provided for the introduction and removal of gases and solids, and a conduit transfer means is provided for the movement of char from the carbonizing zone to the pretreating zone. The vessel of FIG. 3 is similar to that just described except that the separate carbonization and pretreating zones are provided by a vertical transverse plate 60 sealed to each wall and the bottom of vessel 50, the vessel of FIGURE 3 shows a somewhat modified system for carrying out the preferred embodiment of the invention.

A finely subdivided bituminous coal having a particle size distribution between about 10 and about 400 mesh is introduced through conduit 61 into conduit 54 after being preheated to about 550 F. The coal is preferably dried and preheated as disclosed heretofore in connection with the method carried on in the apparatus of FIG. 1, although other modes of drying and preheating the coal which provide a coal of the same characteristics at the same final temperature, may be employed if desired. The entire volume of the pretreating zone is maintained in a dense turbulent state by the passage therethrough of a fluidizing medium, in this particular instance the fluidizing air and gaseous combustion products resulting from the reaction of coal with the oxygen in the air. Entering the dense phase bed the oxygen in the air reacts with and partially oxidizes the coal to provide a case hardening effect and thereby nullify the tendency of the coal particles to adhere when passing through the plastic state. As a result of the combustion reaction, the solids are further elevated in temperature to about 725 F. and a portion of the volatile tar components contained therein is released. In order to provide an optimum amount of case hardening, the amount of oxygen introduced into the pretreating zone is regulated to provide an oxygen to feed ratio of about 0.04 pound of oxygen per pound of coal. It is also necessary for effective pretreatment that the coal particles be held at the aforementioned temperature for an extended period of time, namely about 35 minutes. This is accomplished by appropriately regulating the flow of coal into the pretreating zone 52.

Surrounding the pretreating zone 52 and contiguous thereto is carbonizing zone 51 which also contains a dense phase bed of finely subdivided particles of coal having an upper level above the top of the pretreating zone 52. This bed is maintained at a temperature of about 925 F. by introducing a stream of combustion air into the carbonization zone through conduits 55. In order to confine the zone of combustion, the air is introduced into the bottom portion of the fluidized bed whereby the combustion reactions are substantially completed before the gases pass into the upper portion of said bed. To maintain the desired bed temperature, air is introduced at a rate sufficient to provide a ratio of about 0.03 pound of oxygen per pound of pretreated coal entering the bed. The bed is appropriately sized relative to the rate of entry thereto of pretreated coal to provide a char to fresh feed ratio therein of about 20 pounds per pound, this being sufficient to prevent agglomeration and provide an operable process. Under these conditions of operation, the residence time of the coal in the carbonization zone is about 30 minutes.

In carrying out the carbonization process, pretreated coal from zone 52. passes continuously into the higher temperature bed of coal and char particles in the carbonization zone. In order to prevent back mixing, the exit from the pretreating zone is restricted in size to provide a relatively high solids-vapor velocity therethrough. The pretreated coal entering the carbonization zone is quickly increased in temperature so that volatile tar components are released therefrom. The pretreated coal particles are also subjected to the stripping action of hot combustion gases on their Way to the dilute phase zone 53. This combined action is sufiicient to remove the remaining volatile components from the pretreated coal before it enters the lower region of the carbonization zone, wherein combustion reactions are taking place so that the air introduced into the carbonization zone consumes a maximum of char and a minimum of volatile tar components. The gases leaving the pretreating zone 52 combine with the gases from the carbonization zone 55 and the combined vapors pass upward and out of the dense phase char bed into a dilute phase zone 53 of low solids concentration. In this zone there is provided a conventional cyclone 63 for the removal of entrained solids which are returned to the carbonization dense phase bed. The efliuent pretreatment and carbonization gases are passed from the system through conduit 56 for further processing, as required. Residue char solids are removed from the carbonization zone through conduit 57 also for further processing (not shown).

About percent of the oxygen admitted to the pretreating zone 52 is unreacted therein and passes into the dense char bed 51 in the carbonization zone. To provide sufficient time in the latter zone for consumption of the oxygen before the gases enter the disperse phase 53 a head of char about feet in depth is maintained above the outlet from the pretreating zone. The portion of the char bed below the pretreater outlet also measures about 15 feet in depth, thus providing a carbonization bed having a total depth of about 30 feet. In this specific illustration the pretreating bed is substantially shallower than the carbonization bed being about 15 feet in depth.

Commercial scale crushing and grinding equipment is limited in its degree in size reproducibility, thus, there is a certain amount of variation in the size of the coal particles introduced into the pretreating zone. In order to compensate for temperature changes due to coal particle size variation a small controlled amount of hot char is recycled to the pretreating zone through

conduits

59 and 62. The amount of char recycled at any particular time may vary over a Wide range, however, usually the char rate does not exceed about 0.2 pound per pound of coal in the pretreating zone. It is desirable, in order to prevent plugging of the recycle system to pass a small amount of char therethrough continuously. This mode of operation also assures more positive temperature control by making it possible to withdraw heat from the pretreating zone should the temperature increase. The driving force required to convey char between the two zones is provided by superheated steam introduced through conduit 62.

It may be found more desirable for temperature control in the pretreating zone to provide an internal char recycle system as shown in FIG. 3. In the method therein disclosed, hot char from the carbonization zone is picked up by superheated steam supplied through line 64, passed upwardly through conduit 65 into a pot 66 and then downwardly through conduit 67 into the pretreating zone. This method of operation is advantageous from the viewpoint of thermal efiiciency inasmuch as it minimizes heat losses. The amount of char so recycled is, of course, the same with both types of installation, and preheating, pretreating and carbonization steps are carried out in the same manner as previously described for the operation illustrated by FIG. 2. The char recirculation disclosed above in connection with the methods described in connection with the apparatus of FIGS. 2 and 3, to provide temperature control so that compensation may be made for temperature variations in the pretreating zone by reasonof variations in particle size of the coal supplied, may also be employed. in the method described in connection with the apparatus of FIG. 1. For this purpose, see FIG. 1, a line 67 connects the char outlet line 43 to the bottom region of the pretreating zone 35 while a branch line 68 is provided through which steam enters the line 67 for propelling the char into the pretreating zone 35.

5 The following data are presentedto illustrate a typical commercial carbonization operation based on the processing arrangement of FIG. 1.

Example Flow: Lb./hr.

Wet coal- 10 to 5 micron 450,000 Water content 35,000 Dry coal 415,000 Coal circulation through feed hopper 1,250,000 Char product 345,000 Carbonizer volatile product 60,000 Solids content 1,000 Gases leaving feed hopper- Steam 350 Air 200 Solids 5 Pretreater air 80,000 Carbonizer air 50,000 Char recycle (for pretreater temperature control 25,000 Feed coal heater Coal circulation rate 1,250,000 Heating fiuid15 API hydrocarbon oil 1,550,000

Temperatures: F. Wet coal 60 Feed hopper Drying zone 270 Preheating zone 480 Pretreating zone 725 Carbonization zone 950 Feed coal heater- Coal in 270 Coal out 480 Heating fluid in 500 Heating fluid out 400 Pressures: P.s.i.g. Feed hopper 0 Drying zone 3.8 Preheating zone 6.0 Pretreating zone (top) 11.0 Carbonization zone (disperse phase) 8.0

Average residence time of coal in: Minutes Feed hopper 0 Pretreating zone 60 Carbonization zone 30 Gas velocity in: Ft./sec. Feed hopper 0.3 Drying zone 2.0 Preheating zone 2.5 Pretreating zone 1.0 Carbonization zone 1.5

Density of solids in: Lb./ cu. ft. Feed hopper 36 Drying zone 25 Preheating zone 25 Pretreating zone 22 Carbonization zone 18 A typical applicationof the embodiment of the invention as disclosed in connection with the apparatus of FIGS. 1 and 2, on a commercial scale is illustrated by the following data.

17 Example Flows: Lb./hr. Raw coalto 400 mesh 400,000 Char product 340,000 Volatile product 51,000 Pretreater air 81,000 Carbonizer air 47,500 Char recycle (for temperature control) 25,000

Temperatures: F. Raw coal 60 Preheated coal 500 Pretreating zon 725 Carbonization zone 925 Pressures: P.s.i.g. Pretreating zone (top) l1 Carbonization zone (disperse phase) 8 Average residence time of coal in: Minutes Pretreating zone 40 Carbonization zone 30 Miscellaneous:

Gas velocity in pretreating zone ft./sec 1.0 Gas velocity in carbonization zone ft./sec- 1.5 Carbonization bed density lb./cu. ft 18 Pretreating bed density lb./cu. ft 22 carbonization bed depth ft 30 Pretreating bed depth ft In the above disclosure, FIGS. 1, 2 and 3, exemplify preferred embodiments of the invention; however, it is not intended that they be construed in a limiting sense as other processing schemes and variations and modifications are also within the scope of this invention.

Having thus described my invention by reference to a specific example thereof, it is understood that no undue limitations or restrictions are to be imposed by reason thereof, but that the scope of the invention is defined by the appended claims.

I claim:

1. A unitary process for the treatment of carbonaceous solids to remove therefrom volatile constituents which comprises heating and drying the solids in a finely subdivided state in a drying zone in a dense phase fluidized bed, further heating the dry solids in a preheating zone in a second dense phase bed, passing dry heated solids from the preheating zone as a confined stream through an adjacent carbonization zone to a pretreating zone wherein there is maintained at an elevated temperature above the temperature in the heating zone a third dense phase bed of finely subdivided pretreated solids, said pretreating zone being enclosed within the carbonization zone and openly communicating therewith, introducing oxygen into the pretreated solids bed and partially burning heated solids introduced thereto, maintaining within the carbonization zone a dense phase bed of finely subdivided char at a temperature above the temperature in the pretreating zone, passing pretreated solids and combustion gases directly into the enclosing carbonization zone beneath the level of said dense phase bed of char as a confined stream having a forward velocity sufiicient to prevent backmixing and passage of the char from said bed of char into said pretreating zone, vaporizing from the pretreated solids volatile tar constituents whereby said carbonaceous solids are converted to char, introducing additional oxygen into the lower portion of the char solids bed to burn a portion of the devolatilized char and thereat completely consuming the additional oxygen to provide the heat required to elevate the pretreated solids to the carbonization temperature and vaporize the volatile components therefrom, said pretreated solids and combustion gases being introduced into said dense phase bed of char at a point remote from the region of consumption of said additional oxygen so that the pretreated carbonaceous particles are heated by the hot char and are stripped of volatile components by substantially oxygen-free hot fluidizing gases, recovering combustion gases and volatile tar components from a dilute phase above the dense char bed, and removing product char from said bed.

2. The process of claim 1 in which temperature variations in the pretreating zone are compensated for by recycling a small, variable quantity of hot char from the carbonization zone to tthe pretreating zone, the amount of heat continuously supplied thereby being small in comparison with the total heat required for pretreating.

3. A unitary process for the treatment of carbonaceous solids to remove therefrom volatile constituents which comprises progressing a stream of subdivided carbonaceous solids through a drying and preheating zone to remove wetting liquid therefrom and to raise the temperature thereof to a preheating temperature substantially above the boiling point of the wetting liquid, maintaining a dense phase bed of preheated subdivided solids in a pretreating zone contiguous to a carbonization zone which extends above the upper end of said pretreating zone and is in open communication with said upper end,

-introducing a stream of preheated subdivided solids into said bed in said pretreating zone, introducing oxygen into said bed in said pretreating zone to partly burn preheated solids to raise the temperature in said pretreating zone to a pretreating temperature substantially higher than said preheating temperature, maintaining a dense phase bed of subdivided carbonaceous solids in said carbonization zone at a temperature above the temperature in said pretreating zone, said bed in said carbonization zone having a level substantially above said upper end, passing pretreated solids and combustion gases directly from said pretreating zone as a dense phase and at a high velocity into said bed in said carbonization zone and below the level of said bed in said carbonization bed to penetrate said bed in said carbonization zone and to widely disperse its gas and solids burden therein, vaporizing from the pretreated solids volatile tar constituents whereby said carbonaceous solids are converted to char, introducing additional oxygen into said bed in said carbonization zone to burn char thereat to provide all the heat required to elevate said pretreated solids to the carbonization temperature and to vaporize volatile tar components therefrom, recovering combustion gases and volatile tar components from a dilute phase above said bed in said carbonization zone, and removing the char product from said bed at a point below said upper end.

4. A unitary process for the treatment of carbonaceous solids to remove therefrom volatile constituents which comprises progessing a stream of subdivided carbonaceous solids through a drying and preheating zone to remove wetting liquid therefrom and to raise the temperature thereof to a preheating temperature substantially above the boiling point of the wetting liquid, maintaining a dense phase bed of preheated su'bidivided solids in a pretreating zone at least partly enclosed within a carbonization zone which extends above the upper end of said pretreating zone and is in open communication with said upper end, introducing a stream of preheated subing a dense phase bed of preheated subdivided s lids in troducing oxygen into said bed in said pretreating zone to partly burn preheated solids to raise the temperature in said pretreating zone to a pretreating temperature substantially higher than said preheating temperature, maintaining a dense phase bed of subdivided carbonaceous solids in said carbonization zone at a temperature above the temperature in said pretreating zone, said bed in said carbonization zone having a level substantially above said upper end, passing pretreated solids and combustion gases directly from said .pretreating zone into said bed in the enclosing carbonization zone as a dense high velocity stream which penetrates into said 'bed in the carbonization zone and widely disperses its gas and solids burden therein, vaporizing from the pretreated solids volatile tar constituents whereby said carbonaceous 1% 2Q solids are converted to char, introducing additional oxyand removing the char product'from said bed at a point gen into said bed in said carbonization zone and below b l id upper the upper end of said pretreating zone to burn char thereat to provide all the heat required to elevate said preeferences Qited in the file of this patent treated solids to the carbonization temperature and to 5 UNITED'STATES PATENTS aporizevolatile tar components therefrom, recovering combustion gases and volatile tar components from a 2582712 Howard 1952 dilute phase above said bed in said carbonization zone, 2775551 Nathan at 1956

Claims

1. A UNITARY PROCESS FOR THE TREATMENT OF CARBONACEOUS SOLIDS TO REMOVE THEREFROM VOLATILE CONSTITUENTS WHICH COMPRISES HEATING AND DRYING THE SOLIDS IN A FINELY SUBDIVIDED STATE IN A DRYING ZONE IN A DENSE PHASE FLUIDIZED BED, FURTHER HEATING THE DRY SOLIDS IN A PREHEATING ZONE IN A SECOND DENSE PHASE BED, PASSING DRY HEATED SOLIDS FROM THE PREHEATING ZONE AS A CONFINED STREAM THROUGH AN ADJACENT CARBONIZATION ZONE TO A PRETREATING ZONE WHEREIN THERE IS MAINTAINED AT AN ELEVATED TEMPERATURE ABOVE THE TEMPERATURE IN THE HEATING ZONE A THIRD DENSE PHASE BED OF FINELY SUBDIVIDED PRETREATED SOLIDS, SAID PRETREATING ZONE BEING ENCLOSED WITHIN THE CARBONIZATION ZONE AND OPENLY COMMUNICATING THEREWITH, INTRODUCING OXYGEN INTO THE PRETREATED SOLIDS BED AND PARTIALLY BURNING HEATED SOLIDS INTRODUCED THERETO, MAINTAINING WITHIN THE CARBONIZATION ZONE A DENSE PHASE BED OF FINELY SUBDIVIDED CHAR AT A TEMPERATURE ABOVE THE TEMPERATURE IN THE PRETREATING ZONE, PASSING PRETREATED SOLIDS AND COMBUSTION GASES DIRECTLY INTO THE ENCLOSING CARBONIZATION ZONE BENEATH THE LEVEL OF SAID DENSE PHASE BED OF CHAR AS A CONFINED STREAM HAVING A FORWARD VELOCITY SUFFICIENT TO PREVENT BACKMIXING AND PASSAGE OF THE CHAR FROM SAID BED OF CHAR INTO SAID PRETREATING ZONE, VAPORIZING FROM THE PRETREATED SOLIDS VOLATILE TAR CONSTITUENTS WHEREBY SAID CARBONACEOUS SOLIDS ARE CONVERTED TO CHAR, INTRODUCING ADDITIONAL OXYGEN INTO THE LOWER PORTION OF THE CHAR SOLIDS BED TO BURN A PORTION OF THE DEVOLATILIZED CHAR AND THEREAT COMPLETELY CONSUMING THE ADDITIONAL OXYGEN TO PROVIDE THE HEAT REQUIRED TO ELEVATE THE PRETREATED SOLIDS TO THE CARBONIZATION TEMPERATURE AND VAPORIZE THE VOLATILE COMPONENTS THEREFROM, SAID PRETREATED SOLIDS AND COMBUSTION GASES BEING INTRODUCED INTO SAID DENSE PHASE BED OF CHAR AT A POINT REMOTE FROM THE REGION OF CONSUMPTION OF SAID ADDITIONAL OXYGEN SO THAT THE PRETREATED CARBONACEOUS PARTICLES ARE HEATED BY THE HOT CHAR AND ARE STRIPPED OF VOLATILE COMPONENTS BY SUBSTANTIALLY OXYGEN-FREE HOT FLUIDIZING GASES, RECOVERING COMBUSTION GASES AND VOLATILE TAR COMPONENTS FROM A DILUTE PHASE ABOVE THE DENSE CHAR BED, AND REMOVING PRODUCT CHAR FROM SAID BED.