PROCESS FOR DRYING AND PASSIVATING COAL

Technical Field

A process for irreversibly drying and passivating coal in which coal is contacted in a fluidized bed with a fluidizing gas that contains from 5 to 15 volume percent of oxygen at a partial pressure of from about 2 to 6 pounds per square inch while being subjected to a temperature of from about 575 to about 620 degrees Fahrenheit for less than about 10 minutes. Background Art

Several United States patents have issued to the applicant for drying coal in a fluidized bed reactor. These include United States patents 5,830,246 ("Process for processing coal"), 5,830,247("Process for processing coal"), 5,858,035 ("Process for processing coal"), 5 ,904,741 ("Process for processing coal"), and 6,162,265 ("Process for processing coal"). The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

With increasing energy demands, and increasing energy production costs, there is a need for efficient production methods for upgrading low rank or "wet" coal products to consumable energy products. Many researchers have devoted significant resources to developing these processes and technologies.

The coal industry has faced excessive transportation costs for these moisture-laden low- rank coal products. However, while drying coal to a low moisture content prior to shipment offers significant advantages in terms of reduced transportation costs, it renders the coal subject to spontaneous combustion during shipment and storage. Significant inflagration and explosion hazards are created, exposing workers and emergency responders to dangerous conditions.

The problem of spontaneous combustion of coal has been well known for more than half a century. Sub-bituminous, bituminous, lignite, brown coal and coal char can spontaneously combust by chemical reactions between the coal, moisture and oxygen present in the air. This reaction can occur when water combining with other components in the coal generate a sufficient amount of heat to raise the temperature of the coal to the ignition point. Additionally, noncarbonaceous or unsaturated carbon compound materials present in the coal may oxidize upon exposure to air, which, in turn, generates a sufficient amount of heat for the coal to reach ignition temperature.

Applicant has patented several different processes that, at least in certain preferred embodiments thereof, require the use of mineral oil to coat coal prior to the time the coal is dried. By way of illustration, United States patent 5,830,246, the entire disclosure of which is

hereby incorporated by reference into this specification, provides a process for preparing an irreversibly dried coal comprising the step of "...(d)feeding to said reactor from about 0.5 to about 3.0 weight percent... of mineral oil..."(see claim 1. at column 6 of such patent). This patent, in claim 16 thereof, also describes a coal-liquid slurry containing from about 60 to about 82 weight percent of coal that has a combined oxygen content of from about 10 to about 20 weight percent and contains from about 5 to about 70 weight percent of colloidal coal particles.

The coal used in the process of United States patent 5,830,246 preferably contains at least 10 weight percent of ash (see claim 3 of such patent). After such coal has been dried in a fluidized bed reactor, it preferably is deashed by froth flotation (see column 5, lines 17-26 of the patent) and/or other suitable means and then mixed with liquid and other reagents (see lines 27-56 of column) in order to produce a slurry.

A similar process for the preparation of an irreversibly dried coal is described in United States patent 5,830,247, the entire disclosure of which is also hereby incorporated by reference into this specification. The process described in this patent also requires the step of "...(e)feeding to said second fluidized bed reactor from about 0.5 to about 3.0 weight percent...of mineral oil..." (see claim 1 at column 10 of such patent). In the example presented in such patent (see lines 10 et seq. of column 9 of the patent), 50 pounds of Wyodak coal obtained from the Montana Power Corporation mine in Colestrip, Montana was used. It is disclosed (at lines 47 to 50 of column 3 of this patent) that this coal contains at least about 10 weight percent of ash.

In the process of United States patent 5,830,247, after coated coal has been heated to a temperature "...of from about 480 to about 600 degrees Fahrenheit for from about 1 to about 5 minutes..." (see lines 42 to 46 of column 10 of the such patent), it preferably is quickly quenched within about 5 seconds to reduce its temperature to ambient. As is disclosed at lines 17 to 23 of column 8 of such patent, "The mixture of materials from lines 82 and 84 is passed via line 68 to quench 70, wherein it is contacted with water which is introduced into quencher 70 via line 72. It is preferred that the water be at ambient temperature, and it is preferred that it be introduced at a rate sufficient to reduce the temperature of the coal particles within about 5 seconds to ambient temperature."

The processes of United States patents 5,830,246 and 5,830,247 require the use of mineral oil. Although the use of such mineral oil confers many advantages, it is somewhat expensive. Thus, it is desirable to be able to produce an irreversibly dried coal by a process that does not require the introduction of a mineral oil reagent into a reactor. It is an object of this invention to provide such a process.

Disclosure of the invention

In accordance with this invention, there is provided a process for preparing an irreversibly dried coal that, in one embodiment, utilizes as a starting material a coal with an ash content of less than about 8 weight percent and a sulfur content of less than about 1 weight percent. In this embodiment, one can either utilize a raw coal with these properties and/or beneficiate a raw coal until it has these properties; or one can use a coal that has higher levels of ash and/or sulfur.

The raw coal used in process of the instant invention is preferably disposed in a fluidized bed with a density of from about 10 to about 40 pounds per cubic foot. A fluidizing gas is passed through the bed and the coal at a flow rate of from about 7 to about 25 feet per second while the bed and the coal are subjected to a temperature of from about 575 to about 620 degrees Fahrenheit for less than about 10 minutes; the fluidizing gas preferably contains from about 5 to about 15 volume percent of oxygen at a partial pressure of from about 2 to about 6 pounds per square inch.

After the dried coal has been subjected to such temperature of from about 575 to about 620 degrees Fahrenheit for less than about 10 minutes, it is cooled from such temperature to a temperature of from about 200 to about 300 degrees Fahrenheit in a period of from about 10 to about 120 seconds, preferably by quenching the coal with water.

After the temperature of the dried coal has been reduced to such temperature of from about 200 to about 300 degrees Fahrenheit, it is preferably cooled to a temperature of less than about 100 degrees Fahrenheit a period of from about 10 seconds to about 60 minutes.

The irreversibly dried coal made by this process can then be advantageously utilized to make a coal-liquid slurry. Brief description of the drawings

The invention will be described by reference to the specification and the drawings, in which like numerals refer to like elements, and in which:

Figure 1 is a flow diagram of one preferred process of the invention;

Figure 2 is a schematic diagram of one preferred fluidized bed reactor assembly; and

Figure 3 is a schematic diagram of a process for controlling the partial pressure of oxygen in the fluidizing gas used in the process of the invention. Best Mode for Carrying Out the Invention

In accordance with one embodiment of this invention, there is provided a process for the passivation of coal in which dried coal material is disposed in a fluidized bed with fluidized

combustion gases containing less than about 15 weight percent oxygen until the moisture content of said coal material is from about 0.01 to about 1% water by weight.

In one aspect of this embodiment, the residence time of the coal in the fluidized bed is about 4 to about 7 minutes. The process preferably takes place at a temperature from about 575 to about 620 degrees Fahrenheit. The pressure used in such process may be atmospheric pressure to about 1000 psig, although it is preferred to use a pressure of from about atmospheric pressure to about 20 pounds per square inch.

This process of this embodiment is particularly beneficial for passivating finely divided particles of lower rank coals with greater surface area and greater tendency to spontaneously ignite. The coal may include, but is not limited to coal, low-rank coal, dried coal, peat, char, or other porous solid fuel. Preferably, the carbonaceous material is bituminous, sub-bituminous or lignitic coal or char. The carbonaceous material may contain from about 0.1 weight percent to about 65 weight percent of moisture.

The process of this embodiment of the invention can be effectuated either in a batch-wise manner in a fluidized bed in which conditions are changed successively, or continuously, in which the material is mechanically moved through successive drying steps, such as by a moving belt or screw conveyor. A continuous drying procedure is preferred for large capacity commercial drying applications for coal or lignite, such as those exceeding about 500 tons per day.

The process of this invention is especially advantageous for drying and passivating coals containing from about 15 to about 40 weight percent of moisture. Thus, and referring to Column 1 of United States patent 5,830,246 (see lines 7 et seq.), "Many coals contain up to about 30 weight percent of moisture. This moisture not only does not add to the fuel value of the coal, but also is relatively expensive to transport."

In one embodiment, the coal used in the process of this specification is similar in some respects to the coal used in the process of United States patent 5,830,246. Thus, and referring again to United States patent 5,830,246 (see Column 2), "It is preferred that the coal used in the process of FIG. 1 contain from about 5 to about 30 weight percent of moisture and, more preferably, from about 10 to about 30 weight percent of moisture." However, in the instant case, the coal used may often contain up to about 40 weight percent of water.

As is also disclosed in column 2 of United States patent 5,830,246, "...the moisture content of coal may be determined by conventional means in accordance with standard A.S.T.M. testing procedures. Means for determining the moisture content of coal are well known in the art; see, e.g., United States patents 5,527,365 (irreversible drying of carbonaceous

fuels), 5,503,646, 5,411,560 (production of binderless pellets from low rank coal), 5,396,260, 5,361,513 (apparatus for drying and briquetting coal), 5,327,717, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification."

In one preferred embodiment, the coal used in the process of this invention contains from about 10 to about 25 percent of combined oxygen. The combined oxygen content of certain coals, and means for determining them, are described in column 2 of United States patent 5,830,246, wherein it is disclosed that "It is also preferred that the coal used in the process of FIG. 1 contain from about 10 to about 20 weight of combined oxygen, in the form, e.g., of carboxyl groups, carbonyl groups, and hydroxyl groups. As used in this specification, the term "combined oxygen" means oxygen which is chemically bound to carbon atoms in the coal. See, e.g., H.H. Lowry, editor, "Chemistry of Coal Utilization" (John Wiley and Sons, Inc., New York, N.Y., 1963)....The combined oxygen content of such coal may be determined, e.g., by standard analytical techniques; see, e.g., United States patents 5,444,733, 5,171,474, 5,050,310, 4,852,384 (combined oxygen analyzer), 3,424,573, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification."

In one embodiment, the coal used in the process of the instant invention contains less than about 8 weight percent of ash. In one aspect of this embodiment, described in Figure 1, one starts with a coal containing from about 10 to about 25 weight percent of ash and thereafter reduces the ash content of the coal. Referring to Figure 1, and to the process 100 depicted therein, in step 102 one preferably deashes and/or desulfurizes the high-moisture coal.

Referring again to Figure 1, and to step 102, in such step a coal with an ash content of less than about 8 weight percent preferably is produced. In one aspect of this embodiment, the ash content of the coal produced is less than about 7 weight percent. In another aspect of this embodiment, the ash content of the coal produced is less than about 6 weight percent. In yet another aspect of this embodiment, the ash content of the coal produced is less than about 5 weight percent.

As is disclosed in United States patent 5,830,247 (see column 3), ash is the inorganic residue left in the coal after the ignition of combustible substances. Reference maybe had, e.g., to United States patents 5,534,137 (high ash coal), 5,521,132 (raw coal fly ash), 4,795,037 (high ash coal), 4,575,418 (removal of ash from coal), 4,486,894 (method and apparatus for sensing the ash content of coal), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

Referring to Figure 1, and to the preferred process 100 depicted therein, one may determine the ash content of the high-ash coal in an ash analyzer by conventional means. Thus, by way of illustration and not limitation, one may use the bulk material analyzer described in United States patent 4,582,992, the entire disclosure of which is hereby incorporated by reference into this specification. As is disclosed in such patent, "Bulk material analyzers are used to measure the elemental content of bulk material. Such analyzers have been developed primarily to measure the quantitative content of materials, such as ash, in batches of coal, but also are useful for measuring the elemental content of the bulk materials. Such development is described in the following publications: Stewart and Hall, "On Line Monitoring of Major Ash Elements in Coal Conversion Process," Reprint 789671, October 1978, 13th Intersociety Energy Conversion Engineering Conference, Society of Automotive Engineer, Inc. Warrendale, Pa., pp 586-591; Cekorich et al "Development of an Elemental Analyzer for Coal, Oil and Similar Bulk Streams— A Status Report," 1979 Symposium on Instrumentation and Control Fossil Energy Processes, Aug. 20, 1979, Denver, Colo., pp 297-313; Yeager "R & D Status Report, Coal Combustion Systems Division," EPRI journal; June 1981, pp 32-24; Cooper, "Progress in On-Line Coal Quality Measurement," CQ, January 1984, pp 16-23; and NOLA 1 Data Sheet, "Neutron Activation Analysis for Industrial Process Control, Model NA 79," Texas Nuclear Division of Ramsey Engineering Company, Austin, Tex."

United States patent 4,582,992 also discloses that: "Bulk material analyzers typically are used at the bulk material processing or utilizing facilities. Knowledge of the elemental content is important to determining those operating parameters which will provide optimum material processing. For example, coal analysis enables knowledgeable blending of batches of coal having excessive ash and sulfur content with batches of a coal having lower contents of ash and sulfur."

When the coal used contains less than about 8 percent ash, it may be used without being subjected to deashing. If, however, it contains more than about 8 percent of ash, in one embodiment it preferably is deashed in step 102. One may effectuate such deashing by conventional means. Thus, e.g., one may use one or more of the processes or devices described in United States patents 4,119,523 (processes for the production of deashed coal), 4,227,994 (operation of a coal deashing process), 4,396,396 (deashing of coal by the oil agglomeration process), 4,437,861 (coal deashing process), 4,762,526 (process for deashing coal), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

In one embodiment, the high-ash coal may be cleaned by froth flotation in order to deash it. Froth flotation cleaning of coal is well known and is described, e.g., in United States patents 5,379,902, 4,820,406, 4,770,767, 4,701,257, 4,676,804, 4,632,750, 4,532,032, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

Referring again to Figure 1, and to step 102, the coal used in one embodiment of the process of this invention preferably contains less than 1 weight percent of sulfur. In one aspect of this embodiment, the coal used in such process preferably contains less than about 0.5 weight percent of sulfur. In another aspect of this embodiment, the coal used in such process preferably contains less than about 0.4 weight percent of sulfur.

The sulfur content of the candidate coal may be analyzed by conventional means such as, e.g., the bulk materials analyzer described elsewhere in this specification. If the candidate coal contains more than about 1 weight percent of sulfur, it preferably is desulfurized in step 102 until it contains less than about 1 weight percent of sulfur.

One may use any of the conventional processes for desulfurizing coal. Reference may be had, e.g., to United States patents 3,886,048 (desulfurization of coal), 3,909,211 (coal desulfurization process), 3,909,213 (desulfurization of coal), 3,988,120 (method of desulfurizing coal), 4,076,607 (process for coal desulfurization), 4,081,250 (coal desulfurization process), 4,118,200 (process for desulfurizing coal), 4,146,367 (coal desulfurization), 4,232,034 (desulfurization of coal), 4,297,108 (desulfurization of coal), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

In one preferred embodiment, there is utilized a desulfurization unit that operates magnetically by attracting and removing ferromagnetic particles such as, e.g., pyritic sulfur. One may use any of the magnetic separators known to those skilled in the art such as, e.g., those disclosed in United States patents 4,946,470, 5,520,288, 5,543,041, 5,607,575, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

In one embodiment, it is preferred that the coal used in the instant process contain from about 5 to about 30 weight percent of moisture and, more preferably, from about 10 to about 30 weight percent of moisture. As is disclosed, e.g., in column 2 of United States patent 5,830,246, the moisture content of coal may be determined by conventional means (such as, e.g., the "analyzer 102" depicted in Figure 1 of this case) in accordance with standard A.S.T.M. testing procedures. Means for determining the moisture content of coal are well known; reference may

be had, e.g., to United States patents 5,527,365 (irreversible drying of carbonaceous fuels), 5,503,646, 5,411,560 (production of binderless pellets from low rank coal), 5,396,260, 5,361,513 (apparatus for drying and briquetting coal), 5,327,717, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

In one embodiment, the raw coal used in the process of this invention preferably contains from about 10 to about 20 weight percent of combined oxygen, and the dried coal produced by such process also preferably contains from about 10 to about 20 weight percent of combined oxygen; such combined oxygen may be in the form, e.g., of carboxyl groups, carbonyl groups, hydroxyl groups, etc. As used in this specification, the term "combined oxygen" means oxygen which is chemically bound to carbon atoms in the coal. Reference may be had, e.g., to H.H. Lowry, editor, "Chemistry of Coal Utilization" (John Wiley and Sons, Inc., New York, New York, 1963).

As is disclosed, e.g., in column 2 of United States patent 5,830,246, the combined oxygen content of coal may be determined by standard analytical techniques such as, e.g., those disclosed in United States patents 5,444,733, 5,171,474, 5,050,310, 4,852,384 (combined oxygen analyzer), 3,424,573, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

Referring again to Figure 1, the coal used in step 102 may be, e.g., lignite coal, subbitiminous coal, bituminous coal, etc. These coals are described, e.g., in applicant's United States patent 5,145,489, the entire disclosure of which is hereby incorporated by reference into this specification.

In one embodiment, the coal used in step 101 is preferably 2" x 0" and, more preferably, 2" x 1/4" or smaller. As is known, 2" x 1/4" coal has all of its particles within the range of from about 0.25 inches to about 2.0 inches. Crushed coal conventionally has a 2" x 0" particle size distribution.

Referring again to Figure 1, and in the preferred embodiment depicted therein, after the coal has been deashed and/or desulfurized in step 102, it is fed to a fluidized bed reactor (not shown in Figure 1, but see Figure 2) by conventional means such as, e.g., a coal feeder. One such coal feeder 202 is illustrated in Figure 2.

Figure 2 is a schematic of preferred apparatus 200 that may be used in the process of the invention. In the preferred device depicted in Figure 2, the apparatus 200 is comprised of a coal feeder assembly 202.

Referring again to Figure 2, the feeder assembly 202 can be any coal feeder commonly used in the art. Thus, e.g., feeder assembly 202 may be one or more of the coal feeders described in United States patents 4,071,151 (vibratory high pressure coal feeder with helical ramp), 4,149,228, 4,140,228 (dry piston coal feeder), 4,142,86S (rotary piston coal feeder), 4,341,530, 4,353,427 (gravimetric coal feeder), 4,430,963, 4,497,122 (rotary coal feeder), 5,030,054 (mechanical/pneumatic coal feeder), 5,265,744, and the like. The entire disclosure o: each of these United States patents is hereby incorporated by reference into this specification.

In one embodiment, a star feeder is used as part of feeder assembly 202. A star feeder iϊ a metering device which may be operated by a controller and which controls the rate of coal removal from a hopper. Reference may be had, e.g., to United States patent 5,568,896, the entire disclosure of which is hereby incorporated by reference into this specification.

Referring again to Figure 2, and to the preferred embodiment depicted therein, it will be seen that feeder assembly 202 is preferably comprised of a hopper 204 and a star feeder 206. A controller (not shown) preferably controls the rate of coal removal from the hopper 204. Coal is fed from feeder assembly 202 via line 208 to a fluidized bed 210 disposed within a fluidized bed reactor 212.

Referring again to Figure 2, a fluidized bed 210 is provided within reactor vessel 212, The fluidized bed 210 is comprised of a bed of fluidized coal particles, and it preferably has a density of from about 10 to about 40 pounds per cubic foot and, more preferably, from about 15 to about 40 pounds per cubic foot. In one embodiment, the density of the fluidized bed 210 is from about 20 to about 40 pounds per cubic foot. In another embodiment, the density of fluidized bed 210 is from about 20 to about 30 pounds per cubic foot.

Fluidized bed 210 may be provided by any of the means well known to those skilled in the art. Reference may be had, e.g., to United States patents 4,324,544 (drying coal by partial combustion in a fluidized bed), 4,495,710 (stabilizing particulate low rank coal in a fluidized bed), 4 571,174 (drying particulate low rank coal in a fluidized bed), 5,087,269 (drying fine coal in a fluidized bed), 5,145,489, 5,197,398 (separation of pyrite from coal in a fluidized bed), 5,546,875 (heat treatment of coal in a fluidized bed reactor), 5,547,549, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

Referring again to Figure 2, and in the preferred embodiment depicted therein, fluidized bed 210 is preferably maintained at a temperature of from about 575 to about 620 degrees Fahrenheit. Various means may be used to maintain the fluidized bed at this temperature. Thus, e.g., one may use an internal or external heat exchanger (not shown). Reference may be

had, e.g., to United States patents 5,426,932, 5,442,919, 5,471,955, 5,477,850, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

In one embodiment, the fluidized bed 210 is maintained at a temperature of from about 585 to about 615 degrees Fahrenheit. In another embodiment, the fluidized bed 210 is maintained at a temperature of from about 590 to about 610 degrees Fahrenheit.

By way of illustration and not limitation, one may use the temperature control means described in applicant's United States patent 6,162,265, the entire disclosure of which is hereby incorporated by reference into this specification. Thus, e.g., in section (c).. of claim 1 of this patent, there is described the step of "...feeding to said first fluidized bed liquid phase water, inert gas, and air and subjecting said coal in said first fluidized bed to a temperature of from about 480 to about 600 degrees Fahrenheit for from about 1 to about 5 minutes...."

One may also use inert gas in the process depicted in Figure 2, and it may be introduced into fluidized bed 210 via line 214. Preheated air may be introduced into the bed 210 via line 216, and the relative flow rates of the t\γo gaseous components may be varied in order to control the temperature within the bed 210. The temperature within the bed 210 may be monitored by a sensor 218, such as thermocouple 218, which is operatively connected to a controller (not shown in Figure 2, but see Figure 3). Alternatively, or additionally, a mixture of inert gas and incoming air may be introduced via lines 214 and/or 216.

Referring to Figure 1, and in step 106 thereof, the incoming air may be treated to modify its temperature and/or its moisture content. The goal is to control the properties of the fluidizing gas (which may contain, e.g., a mixture of air and inert gas) in order to moderate the exothermic reactions occurring in fluidized bed 210 so that the coal in such bed 210 is subjected to a temperature within the range of from about 575 to about 620 degrees Fahrenheit.

In applicant's United States patent 6,162,265, the entire disclosure of which is hereby incorporated by reference into this specification, it is disclosed that "The fluidized bed 210 is preferably maintained at a temperature of from about 480 to about 600 degrees Fahrenheit, and most preferably at from about 550 to about 600 degrees Fahrenheit. When the reaction temperature is too low, i.e., less than about 480 degrees Fahrenheit, the reaction rate is extremely slow. When the reaction rate is too high, i.e., greater than 600 degrees Fahrenheit, decomposition of the coal starts to occur and produces undesirable product with relative low volatility. It is difficult, however, to maintain the reaction temperature at less than about 600 degrees Fahrenheit because many of the reactions which occur within fluidized bed 21 are exothermic. In applicants' process, liquid water may be used to both maintain the desired

temperature while not adversely affecting the degree of dehydration in the coal product produced."

Without wishing to be bound to any particular theory, applicant believes that some of the exothermic reactions occurring in fluidized bed 210 involve the reaction of oxygen with one or more hydrocarbons to produce carbon dioxide and water. Changing the concentration of oxygen in the fluidized bed 210, and/or the concentration of water, affects both the reaction rates of the exothermic reactions and the amount of heat produced.

In the preferred process 300 depicted in Figure 3, liquid water is used to moderate the temperature in fluidized bed reactor 212. Referring to Figure 3, and in the preferred embodiment depicted therein, it will be seen that a pump 326 pumps water from a water reservoir 328 via lines 330 and 332. The water fed via lines 330 and 332 is preferably in the liquid phase and at ambient temperature, although temperatures higher and lower than ambient also may be used.

In the embodiment depicted in Figure 3, it is preferred to control the temperature within the fluidized bed reactor 212 by controlling the extent to which and the rate at which exothermic reactions and endothermic reactions occur in the system. Without wishing to be bound to any particular theory, applicant believes that the conversion of water from a liquid state to a gaseous state is endothermic. By comparison, applicant also believes that oxidation of many of the carbonaceous materials in the coal involves exothermic reactions. By varying the feed rate of the coal and/or of the oxygen-containing gas and/or of the inert gas and/or of water, one may vary the balance between the exothermic and endothermic reactions.

Referring again to Figure 3, a sensor 218 is disposed in fluidized bed 210. When it is determined that the fluidized bed temperature is higher than desired (i.e., in excess of about 600 degrees Fahrenheit), a valve 334 is opened, pump 326 is actuated, and a sufficient amount of water is introduced into reactor 212 to maintain the temperature within the desired range. As will be apparent to those skilled in the art, conventional control and feedback means can be used to insure that the temperature within bed 210 is always within the desired range of from about 575 to about 620 degrees Fahrenheit.

In the preferred embodiment illustrated in Figure 3, the water is shown entering fluidized bed 210 only at point 333 and 335. As will be apparent to those skilled in the art, in other embodiments the water may be introduced at a multiplicity of points within the fluidized bed 210 to improve the efficiency of its temperature regulation.

In addition to using water to moderate the temperature in fluidized bed 210, one may also advantageously feed a fluidizing gas that is comprised of a mixture of inert gas and air to

control the amount of oxygen within the fluidized bed reactor 12. The inert gas used may be produced from the off-gas from cyclone 218.

Figure 3 shows one means of generating such an inert gas. Referring to Figure 3, off gas from cyclone 218 (also see Figure 2) is preferably passed via line 302 to baghouse 304, in which coal fines and other fine particles are collected. These particles may be blended back with the desired product, or disposed of as waste, or used in other processes.

One may use, as cyclone 218, any of the cyclones conventionally used in fluidized bed reactors for separating solids from gas. Thus, e.g., one may use as cyclone 218 the cyclones described in United States patents 5,174,799 (cyclone separator for a fluidized bed reactor), 5,562,884, 5,612,003 (fluidized bed with cyclone), 5,625,119, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

Referring again to Figure 3, and in the preferred process depicted therein, the exhaust gas from baghouse 304 is preferably passed via line 306 to heat exchanger 308. In the embodiment depicted, water maybe fed via line 310 into heat exchanger 308; this water, e.g., may be pumped via a line (not shown) from pump 326. Condensed water may be removed from heat exchanger 308 via line 312. The dried gas from heat exchanger 308 is removed via line 314, and it may be fed via such line 314 into gas mixer 316.

Referring again to Figure 3, a portion of the off gas from cyclone 218 (see Figure 2) may be fed via line 318 to heat exchanger 320. Incoming air may be fed via line 322 to heat exchanger 320, and it is preheated to a temperature controlled by controller 324 which is operatively connected to heat exchanger 320, gas mixer 316, heat exchanger 308, and thermocouple 218, as well as other components of the system. For the sake of simplicity of representation, not all of the links between such controller 324 and such other components are shown.

Referring again to Figure 3, and to a preferred embodiment depicted therein, preheated incoming air from heat exchanger 320 is mixed with the inert gas from heat exchanger 308 in gas mixer 316 in ratios determined by controller 324. The mixture of heated incoming air and inert gas is then fed via line 326 to fluidized bed 210 in order to help control the temperature within such fluidized bed 210 within the desired range of from about 590 to about 610 degrees Fahrenheit.

The temperature control system described hereinabove is very similar to the temperature control system described in United States patent 6,1621,265, the entire disclosure of which is hereby incorporated by reference into this specification. As is disclosed at lines 46 to 60 of

column 8 of such patent, "The fluidized bed 210 is preferably maintained at a temperature of from about 480 to about 600 degrees Fahrenheit, and most preferably at from about 550 to about 600 degrees Fahrenheit...It is difficult, however, to maintain the reaction temperature at less than about 600 degrees Fahrenheit because many of the reactions which occur within fluidized bed 21 are exothermic. In applicant's process, liquid water may be used to both maintain the desired temperature while not adversely affecting the degree of dehydration in the coal product produced."

A similar system may be used in the process depicted in Figure 3. Liquid water may be fed via line 328 into pump 330 and thence via line 332 into fluidized bed 210. The water from pump 330 maybe also used in the quenching step of the process of this invention, which is discussed elsewhere in this specification.

Referring again to Figure 1, in step 106 of the process depicted the incoming air may be treated. The incoming air is preferably introduced into fluidized bed reactor 212 at a flow velocity (bulk gas velocity) of from about 7 to about 25 feet per second. In one preferred embodiment, the incoming air is introduced at a flow velocity of from about 15 to about 25 feet per second. As will be apparent to those skilled in the art, the flow velocity of the incoming air will preferably be the same as the flow velocity of the fiuidizing gas. Thus, e.g., when the flow velocity of the incoming air is from about 7 to about 25 feet per second, and when the fiuidizing gas is comprised of a mixture of incoming air and inert gas, the flow velocity of the fiuidizing gas will be substantially identical, from about 7 to about 25 feet per second in the embodiment discussed.

In one preferred embodiment, the flow velocity of the fiuidizing gas is less than about 10 feet per second. In one aspect of this embodiment, the flow velocity of the fiuidizing gas is from about 8 to about 10 feet per second. In another embodiment, such flow velocity of the fiuidizing gas is from about 15 to about 25 feet per second.

Referring to Figure 1, in step 106 of the process the incoming air may be treated to modify its temperature. In another embodiment, the incoming air may be cooled. By such means, one can directly (by temperature) affect the temperature within the fluidized bed 210.

One may indirectly affect the temperature within the fluidized bed 210 by modifying the composition of the incoming air so that it affects the reaction rates of the exothermic reactions occurring in such bed. Thus, e.g., by diminishing the amount of oxygen in the incoming air, one can slow down such reaction rates and, thus, limit the amount of heat produced by the exothermic reactions.

Thus, referring to Figure 3, incoming air may be introduced via line 340 and mixed, e.g., with a "gaseous oxygen getter" such as, e.g., carbon monoxide introduced via line 342. The incoming air, and/or the mixture of incoming air and carbon monoxide, may be fed via line 344 to pump/compressor 346 wherein the properties of the air may be further modified. Thereafter, the air so modified may be fed via line 348 to humidifϊer/dehumidifϊer 350, wherein the moisture content of the air may be adjusted, as appropriate. Thereafter the air so modified may be fed via line 352 to gas mixer 316.

Referring again to Figure 1, the off-gas may be similarly treated in step 108 to adjust its water content and/or its oxygen content and/or other of its properties, and it may thereafter mixed in step 110 with the incoming air (modified or unmodified) to produce a fluidizing gas that, in step 112, is fed via line 216 to the fluidized bed reactor 212.

Referring again to Figure 1, and to step 112 of the process, the fluidizing gas preferably contains from about 5 to about 15 percent by volume of oxygen, wherein the partial pressure of oxygen in such fluidizing gas is from about 0.2 to about 5 pounds per square inch. In one aspect of this embodiment, the partial pressure of oxygen in the fluidizing gas is from about 1 to about 5 pounds per square inch. In another aspect of this embodiment, the partial pressure of oxygen in the fluidizing gas is from about 2 to about 5 pounds per square inch. In yet another aspect of this embodiment, the partial pressure of oxygen in the fluidizing gas is from about 3 to about 5 pounds per square inch. In yet another aspect of this embodiment, the partial pressure of oxygen in the fluidizing gas is from about 4 to about 5 pounds per square inch.

As is known to those skilled in the art, the partial pressure of a gas is the pressure that would be exerted by one component of a mixture of gases if it were present alone in a container. Reference may be had, e.g., to United States patents 3,805,590 (oxygen partial pressure sensor), 3,881,152 (method and device for measuring oxygen partial pressure), 4,173,975 (magnetic means for determining partial pressure of oxygen), 4,269,684 (apparatus for oxygen partial pressure measurement), 4,384,934 (means for determining the partial pressure of oxygen in an atmosphere), 4,414,531 (partial pressure of oxygen sensor), 4,592,825 (probe for measuring oxygen partial pressure in a gas atmosphere), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

In one preferred embodiment, the fluidizing gas contains from about 5 to about 10 volume percent of oxygen.

Referring again to Figure 1, in step 104, the aforementioned fluidizing gas as well as the deashed and desulfurized coal is fed to the fluidized bed reactor 212. The fluidizing gas is

preferably heated, and it is preferably introduced into the fluidized bed 210 at a sufficient flow rate to fluidize the bed of coal particles. The gas is heated sufficiently to heat the coal particles to a temperature preferably in the range of about 575 to 620 ⁰ F. and, more preferably, from about 590 to 610 ⁰ F .The pressure within the vessel 613 is essentially atmospheric, but one may utilize a slight positive pressure if desired.

The fluidizing gas is an oxygenated gas, and it preferably comprises from about 6 volume percent to about 15 volume percent oxygen. In another embodiment, the oxygenated gas comprises 7 to 10 volume percent oxygen.

In one embodiment, illustrated in step 106 of Figure 1, the incoming air is heated with a propane flame to a temperature of from about 450 to about 650 degrees Fahrenheit; in one aspect of this embodiment, such incoming air is heated with such flame during the start-up process only (about the first half hour), and the heating with such flame is discontinued thereafter. In another embodiment, a heat exchanger may be used to heat the atmospheric air.

Referring again to Figure 2, a fluidized bed 210 is established in reactor 212. One may establish such a fluidized bed by conventional means such as, e.g., the means disclosed in United States patent 6,162,265, at column 4 thereof. Referring to such column 4, it is disclosed that "... a fluidized bed 14 is provided in a reactor vessel 10. The fluidized bed 14 is comprised of a bed of fluidized coal particles, and it preferably has a density of from about 20 to about 40 pounds per cubic foot. In one embodiment, the density of the fluidized bed 20 is from about 20 to about 30 pounds per cubic foot. The fluidized bed density is the density of the bed while its materials are in the fluid state and does not refer to the particulate density of the materials in the bed Fluidized bed 14 may be provided by any of the means well known to those skilled in the art. Reference maybe had, e.g., to applicant's U.S. Pat. Nos. 5,145,489, 5,547,549, 5,546,875 (heat treatment of coal in a fluidized bed reactor), U.S. Pat. No. 5,197,398 (separation of pyrite from coal in a fluidized bed), U.S. Pat. No. 5,087,269 (drying fine coal in a fluidized bed), U.S. Pat. No. 4,571,174 (drying particulate low rank coal in a fluidized bed), U.S. Pat. No. 4,495,710 (stabilizing particulate low rank coal in a fluidized bed), U.S. Pat. No. 4,324,544 (drying coal by partial combustion in a fluidized bed), and the like." In the process of this instant invention, air is fed into the fluidized bed to heat the fluidized bed and to maintain the bed at the desired density.

In one preferred embodiment, the air flow into the fiuidized bed is from about 5 to about 8 feet per second. .

The fluidized bed reactor 212 is preferably a cylindrical reactor. In one preferred embodiment, the fluidized bed 210 is heated. One may heat the fluidized bed 210 by

conventional means such as, e.g., an internal or external heat exchanger (not shown). See, e.g., United States patents 5,537,941, 5,471,955, 5,442,919, 5,477,850, 5,462,932, and the like, the entire disclosure of each of which is hereby incorporated by reference into this specification. In one aspect of this embodiment, the heated fluidizing gas is preferably at a temperature of from about 480 to about 600 degrees Fahrenheit and, more preferably, at a temperature of from about 525 to about 575 degrees Fahrenheit.

Referring again to Figure 2, and in the preferred embodiment depicted therein, coal "fines" are removed from the reaction mass disposed within the fluidized bed 210 The finer coal portions (i.e., those with a particle size less than about 400 microns) are entrained from the top 220 of the fluidized bed to the cyclone 218 via line 222. The coarser component of the entrained stream will preferably be cooled in a cooler (not shown), as are the coarser components from cyclone 218.

Referring again to Figure 3, in reactor 212, water is removed from the coal fed via line 104. The raw coal fed via line 208 preferably contains from about 15 to about 40 weight percent of water. By comparison, the coal withdrawn via line 224 contains from about 40 to about 60 percent less water. Put another way, the ratio of the water concentration in the raw coal divided by the water concentration in the dry coal is at from about 1.6 to about 2.5.

In one embodiment, the water removed from the coal within the reactor 212 is passed together with flue gas and fines to cyclone 218 and thereafter to a condenser (not shown) wherein it is removed. The gas passing from the condenser (not shown) is preferably substantially dry, containing less than about 5 weight percent of water. Thereafter, this dry gas is mixed with the air in line mixer and thence fed into the fluidized bed 210

Referring again to Figure 3, the raw coal from feeder assembly 202 is maintained in reactor 212 for a time sufficient to remove from about 40 to about 60 weight percent of the water in the raw coal. Generally, such "residence time" is preferably less than about 10 minutes and, more preferably, less than about 5 minutes.

In one embodiment, such residence time is from about 0.7 to about 5.0 minutes. In another embodiment, such residence time is from about 1 to about 5 minutes. In another embodiment, the residence time is from about 5 to about 7 minutes. In another embodiment, the residence time is less than about 4 minutes.

The dried coal may be discharged, e.g., from line 224; the water content of such coal is preferably less than about 1 weight percent. In one aspect of this embodiment, the fluidized bed reactor is comprised of a moving bed (not shown) on which the coal is disposed.

In one embodiment, the fluidized bed reactor has a height often feet and a diameter of three feet. It is to be understood that any size fluid bed reactor may be used with this process. In one aspect of this embodiment, partially dried coal material is conveyed into a moving bed of hot coal at a temperature in the range from about 590 to 610 ⁰ F at a rate sufficient to maintain partial combustion of the coal at atmospheric pressure. In one aspect of this embodiment, pyrophoric partially dried coal is charged from a hopper 204 into the bottom of a fluidized bed reactor 210 via a screw feeder at a rate of from about one to about four thousand pounds per hour. It is to be understood that the rate may vary and be optimized according to the fluid bed reactor size and type used in carrying out the process of this invention. In one embodiment, it is desirable that the partially dried coal be fed to the reaction vessel at a rate of three thousand pounds per hour. In another embodiment, it is desirable that the partially dried coal be fed to the reaction vessel at a rate of three hundred pounds per hour.

Referring again to Figure 2, a star feeder 206, as described elsewhere in this specification, may be used to charge (feed) the coal material to the reactor. Alternatively, any of the commercially available blending apparatus may be employed in the process, including but not limited to, a rotating drum or belt conveyor. Alternatively, in another embodiment, any appropriate feeder known to one skilled in the art may be used to charge the coal into the reaction vessel.

In some aspects of this invention, such partially dried coal or char material may have been dried by a pyrolysis process. In some aspects of this invention, such partially dried coal or char material may have been dried in an inert environment. In other aspects, such partially dried coal has been dried by a process described elsewhere in this specification.

In some embodiments, the coal used may be lignitic, bituminous or sub-bituminous crushed coal with a particle size of no larger than about 2 inches by one-quarter inch. In another embodiment, 1" by 0" size particles may be used. Preferably, the carbonaceous material may contain from about 0.01 weight percent to about 20 weight percent of moisture, and more preferably may contain from about 1 weight percent to about 15 weight percent of moisture.

This process is particularly advantageous for use with fine coal particulates since they have greater surface area and this more easily oxidize and spontaneously combust. Other coal types and particle sizes described elsewhere in this specification may be used in other embodiments. Optionally, the coal particles may be preheated prior to being charged into the reaction vessel. Heating may be accomplished by any conventional means known to those skilled in the art.

The coal drying process of the invention can readily be carried out in an apparatus comprising a moving bed, such as a fluidized bed of coal to which the partially dried coal material is fed under the conditions described elsewhere in this specification. For example, a fluidized bed reactor is operated with fluidizing gas made by blending air and recycled off-gas to maintain an oxygen level of about 6% to about 15% by volume and regulating the temperature of the bed at 590 to 610 ⁰ F by introduction of partially dried coal. The pressure may be atmospheric pressure to about 1000 psig. In this manner, the product coal has been partially oxidized and is extremely stable to spontaneous combustion. After the initial start-up, this process can be operated so that little or no external source of heat is required, advantageously using in-situ generated thermal energy.

A fluidized bed reactor as described elsewhere in this specification may be used as the type of reaction vessel. Alternatively, in another embodiment, any appropriate reaction vessel known to one skilled in the art may be used as a reaction vessel.

In step 106 of process 100 (see Figure 1), the heat generated by the combustion is absorbed by the partially dried coal material being fed into the system and is effective for drying the coal material to the desired level of 0.01-1.0%. A two-stage quenching process

Referring to Figure 1 , and in step 108, after the coal has been subjected to a temperature of from about 590 to about 610 degrees Fahrenheit for less than about 10 minutes, in step 108 it is quickly quenched, i.e., its temperature is quickly reduced from a temperature of from about 590 to about 610 degrees Fahrenheit to a temperature of from about 200 to about 300 degrees Fahrenheit in less than about 120 seconds. In one aspect of this embodiment, the temperature of the coal is reduced from a temperature of from about 590 to about 610 degrees Fahrenheit to a temperature of from about 215 to about 300 degrees Fahrenheit in less than about 120 seconds. In another aspect of this embodiment, the temperature of the coal is reduced from a temperature of from about 590 to about 610 degrees Fahrenheit to a temperature of from about 215 to about 250 degrees Fahrenheit in less than about 120 seconds.

In one embodiment, the coal is cooled from its temperature of from about 590 to about 610 degrees Fahrenheit to a temperature in the range of from about 200 to about 250 degrees Fahrenheit in less than about 60 seconds and, more preferably, in less than about 30 seconds. In one aspect of this embodiment, the coal is cooled from its temperature of from 590 to 610 degrees Fahrenheit to a temperature in the range of from about 200 to about 250 degrees Fahrenheit in less than about 15 seconds.

Referring to Figure 3, one can quickly quench the coal from its temperature of from about 590 to about 610 degrees Fahrenheit by spraying water onto the fluidized coal particles. This act vaporizes the water, but it does not cause the coal to reabsorb the water. The water used, which is preferably at ambient temperature, does not wet the coal; unlike certain prior art processes, an insufficient amount of water is used to submerge the coal.

Referring to Figure 3, sensor 218 measures the temperature of the fluidized bed 210. When such temperature exceeds 610 degrees Fahrenheit, or when one is quickly quenching the coal from its temperature of from 590 to 610 degrees Fahrenheit, controller 324 opens valve 334 and causes a sufficient amount of water from receptacle 328 to flow into the fluidized bed 210 to reduce the temperature of the coal to the desired temperature within the desired time.

Alternatively, or additionally, one may use a system similar to that which is described in United States patent 5,830,247, the entire disclosure of which is hereby incorporated by reference into this specification. As is disclosed at lines 17-23 of Column 8 of this patent, "The mixture of materials from lines 82 and 84 is passed via line 68 to quench 70, wherein it is contacted with water which is introduced into quencher 70 via line 72. Referring to Figure 3, one may withdraw material from line 368 to quencher 370 and contact it with water introduced via line 372. The difference between the process of this patent application and United States patent 5,830,247 is that, in the latter patent, the water is "...introduced at a rate sufficient to reduce the temperature of the coal particles within about 5 seconds to ambient temperature...," whereas in the process of the instant case a lesser amount of water is used to reduce the temperature of the coal particles within no less than about 15 seconds to a temperature within the range of from about 200 to about 300 degrees Fahrenheit. If the rate of temperature decrease is too great, the controller 324 will decrease the amount of water introduced into the system.

Referring again to Figure 1, and to step 108 thereof, once the coal has been cooled to a temperature within the desired range between 200 and 300 degrees Fahrenheit, the temperature of such coal is then reduced to a temperature of less than about 100 degrees Fahrenheit in a period of less than about 60 minutes and, more preferably, in less than about 30 minutes. It is preferred to reduce the temperature of the coal to less than about 100 degrees Fahrenheit is less than about 15 minutes, more preferably less than about 10 minutes, and even more preferably in less than about 5 minutes.

The temperature of the coal can be reduced to less than 100 degrees Fahrenheit by conventional means. Thus, by way of illustration and not limitation, one may dispose the dry coal at a temperature of from about 200 to about 300 degrees Fahrenheit in a heat exchanger (such as, e.g., heat exchanger 320) and, preferably, an air solids heat exchanger.

It is preferred to dry and cool the hot coal with flowing air. The hot coal, at a temperature of, e.g., 215 to 250 degrees Fahrenheit, is preferably moved by a coal conveyor to a heat exchanger. One may use any of the coal conveyors known to those skilled in the art such as, e.g., the conveyor described in United States patent 4,766,992 (coal conveyor construction), the entire disclosure of which is hereby incorporated by reference into this specification. In one aspect of this embodiment, the coal conveyor is a metallic coal conveyor. Properties of the coal produced by the process of the invention

In one embodiment, the dried coal produced by the process of this invention is comprised of at least 38 weight percent of volatile matter, dry basis. In one aspect of this embodiment, the dry coal is comprised of at least about 39 weight percent of volatile matter.

In one embodiment, the dried coal produced by the process of this invention has a heating value of at least about 12,000 British Thermal Units (BTUs) per pound and, more preferably, at least about 12,500 BTU's per pounds. In one aspect of this embodiment, the dried coal has a heating value of at least about 12,800 BTU's per pounds.

In one embodiment, the dried coal produced by the process of this invention contains at least bout 70 weight percent of carbon and, more preferably, at least about 71 weight percent of carbon.

In one embodiment, the dried coal produced by the process of this invention has a combined oxygen content of from about 10 to about 20 weight percent. In one aspect of this embodiment, the combined oxygen content is at least about 14 weight percent.

In one embodiment, the residence time of the coal in the reactor 212 is from about 4 to about 7 minutes. A particularly significant feature of the process of the invention is that most of all of the energy for drying the coal is generated in situ and, thus, a highly efficient, economical process results and produces a very passivated coal product with less than 1 % water content.

The drying method of this invention can be accomplished either in (a) batch-wise manner such as in a fluidized bed in which conditions are changed successively, or (b) continuously by mechanically moving the material through drying steps, such as by a moving belt or screw conveyor. A continuous drying procedure is preferred for large capacity commercial drying applications for coal or lignite, such as those exceeding about 500 tons per day.

Without wishing to be bound by any particular theory, applicants believe that, if the temperature to which the coal is subjected is substantially below 575 degrees Fahrenheit, the coal so dried tends to reabsorb an unacceptable amount of water upon standing. It is also

believed that, if the temperature is substantially higher than 620 degrees, the coal thus produced has lower volatility and unacceptable heating values.

In the process of the invention, it is preferred to maintain the fluidized bed 210 at a density of from about 15 to about 50 pounds for cubic foot and, more preferably, at a density of from about 20 to about 40 pounds per cubic foot.

Without wishing to be bound to any particular theory, applicants believe that the oxygen in the fluidizing gas used preferentially reacts with volatile elements in the coal being dried to deprive such coal of such elements and render such coal less likely to spontaneously combust.

In one embodiment, the total pressure of the system illustrated in Figures 1, 2, and 3 is from about 15 to about 30 psi. Preparation of a coal -liquid slurry with the dried coal of this invention

In one preferred embodiment, and referring to Figure 1 (and to step 112 thereof), a coal- liquid slurry may advantageously be produced with the dried and passivated coal produced by the process of this invention. Such a slurry may be produced by the processes described in United States patents 5,830,246 and 5,904,741, the entire disclosure of which is hereby incorporated by reference into this specification.

Referring to Figure 2 of the instant case, and to the preferred embodiment depicted therein, fines from cyclone 218 may be fed via line 219 to mixer/blender device 221. Applicants believe that the coal particles entrained from the top of the fluidized bed to the cyclone 218 have a relatively fine particle size distribution, whereas the particles fed to such mixer/blender device 221 from the bottom of the fluidized bed (via line 224) have a relatively coarse particle size distribution. The use of these two coal streams is merely illustrative; it should be understood that coal particles from other portions of the fluidized bed reactor (or even from other sources) may be blended in mixer/blender device 221. Such external sources of coal particles may be fed, e.g., via line 223.

Referring again to Figure 2, the coal(s) fed into device 221 preferably are blended in ratios sufficient to achieve a desired particle size distribution. In one preferred embodiment, the blending occurs in such a manner to approach or achieve the particle size distribution disclosed in U.S. Pat. No. 4,282,006; the entire disclosure of this patent is hereby incorporated by reference into this specification. If the nature of the coal fractions in lines 219, 223, and 224 are not suitable for making such particle size distribution, one or both of these streams may be further ground as disclosed in such patent.

Referring again to Figure 2, and in one preferred embodiment, after the coal segments have been blended in blender 221 they then may be passed via line 224 to cleaner 46 wherein

they can be beneficiated in a conventional manner such as, e.g., by froth flotation. Froth flotation cleaning of coal is well known; see, e.g., U.S. Pat. Nos. 5,379,902, 4,820,406, 4,770,767, 4,701,257, 4,676,804, 4,632,750, 4,532,032, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification.

Cleaned coal from cleaner 226 may be passed via line 228 to slurry preparation tank 230 and/or unbeneficiated coal from mixer blender 221 may be passed via line 232 to slurry preparation tank 230. In either case, it is preferred to treat said coal and/or combine it with additional reagents such as, e.g., water, dispersing agent(s), etc. (which may be added, e.g., via line 234) in order to obtain a slurry with specified properties.

One of the desired specified properties is that the slurry be comprised of from about 60 to about 82 weight percent of coal, from about 18 to about 40 weight percent of carrier liquid (such as, e.g., water), and from about 0.1 to about 4.0 weight percent, by weight of dry coal, of dispersing agent.

Another of the desired specified properties is that the slurry consist have a specific surface area of from about 0.8 to about 4.0 square meters per cubic centimeter and an interstitial porosity of less than 20 volume percent.

Yet another of the desired specified properties is that the slurry have a particle size distribution such that from about 5 to about 70 weight percent of the particles of coal in the slurry are of colloidal size, being smaller than about 3 microns.

One may prepare a slurry with these desired properties by the method disclosed in U.S. Pat. No.4,477,259. The entire disclosure of this patent is hereby incorporated by reference into this specification.