GB2121433A

GB2121433A - Converting a carbonaceous material into an improved feedstock

Info

Publication number: GB2121433A
Application number: GB08217958A
Authority: GB
Inventors: Leonard Messer
Original assignee: American Minechem Corp
Current assignee: American Minechem Corp
Priority date: 1982-05-14
Filing date: 1982-06-21
Publication date: 1983-12-21
Also published as: ZA826525B; AU560491B2; JPS58206689A; GB2121433B; DE3224957A1; AU8510882A

Abstract

An improved method of converting a solid carbonaceous material into an improved feedstock comprising the steps of dispersing a mixture of carbonaceous and noncarbonaceous fine particles in a suspension liquid to form a first slurry; adding to the first slurry a hydrocarbon liquid that is lyophobic to the suspension liquid and the noncarbonaceous fine particles and lyophilic to the carbonaceous fine particles to form a mixture; agitating the mixture to preferentially agglomerate the carbonaceous fine particles into discrete carbonaceous agglomerates while said noncarbonaceous fine particles remain substantially unagglomerated in the mixture, said discrete agglomerates having a substantially uniform ash content of less than about 12% by weight, and being substantially inert to atmospheric oxidation for a substantial period time; and separating the discrete carbonaceous agglomerates from the mixture, the improvement comprising, in combination with the above steps, comminuting the discrete carbonaceous agglomerates to reduce their particle size.

Description

SPECIFICATION A method for converting a carbonaceous material into an improved feedstock Field of the invention The present invention relates to the recovery of carbonaceous materials, especially coal, from an unusable source and preparing a product suitable for conversion to a superior energy source or a high quality supply of fuel for a combustion, gasification or liquifaction system.

Background of the invention There has been and is a steady demand for coal. In recent years, the consumption of coal has been rising steadily. A record amount of coal, over 800 million tons, was produced in 1980, and there are sufficient reserves to supply the United States with energy in the form of heat or fuels derived from coal for hundreds of years. Over 80 percent of the coal produced was consumed in power plants for generation of electricity in excess of 2 trillion kilowatt-hours. The balance of the coal was consumed in the production of coke, the generation of industrial steam and other varied uses.

Systems for the conversion of coal are wellknown as are the specifications for the coal being supplied to such systems. Most systems are designed for fuels having a particular composition, particularly with respect to the ash and moisture content, and in some cases the sulfur content where pollution control requirements must be met.

Coal is a combustible, natural product that is derived from plant remains deposited centuries ago that has undergone various stages of metamorphasis. The present state of coal is the result of geological and environmental history, forestfires, floods and like events. The end product is a heterogeneous mass that resembles everything from wood to graphite.

Coal is generally classified as anthracite, bituminous and subbituminous coals and lignites.

Peat, although closer to wood in composition, can be a source of carbonaceous material for conversion. Also included within the scope of carbon sources are chars and cokes similar in composition to the anthracite coals, although the chars and cokes are formed during short term heating processes. Carbon content of the coals described above vary from about 45 to 98 percent by weight on a moisture and ash free basis.

Low grade materials such as lignites and peats are sometimes considered unsatisfactory for conversion processes because of their low calorific value and high ash and moisture contents. Utilization has generally been limited to regional areas where transportation is not a factor. If these materials can be upgraded by some economicai means, then these low grade fuels can be more competitive with the bituminous and higher quality coals. Further, even though coal is a plentiful resource, many of the reserves are unsuitable for economical conversion to energy directly or via a synthetic fuel in accordance with known conversion processes.

There is a steady demand for natural gas and the gaseous products than can be made from petroleum. Some natural gas is imported into the United States because national production cannot keep up with the demand. Even where natural gas is available via pipelines or underground storage, additional quantities are needed occasionally to meet peak demans that can occur on short notice.

These additional supplies can be produced by the pyrolysis of liquid hydrocarbons.

Another important use for gaseous fuels is to supply clean heat for processing where ash or soot released during combustion would discolor the product or interfere with operation of the equipment.

Processes for the conversion of coal to gaseous products are numerous and are described in the literature. For example, commercially available processes are manufactured by companies such as Lurgi, Woodell-Duckham, Kerpley, Koppers, Winkler and Combustion Engineering to name a few. However, all of these gasification processes have physical and chemical limitations. Furthermore, they all depend on the same basic equation that depicts the reaction of carbon with steam to make a low or medium Btu gas. Gasification occurs at high temperatures, on the order of about 1 0000C.

Several other reactions can occur between the reactants and products as the steam flows through the reactor(s), thus yielding a product of varying composition.

Separation of the unreacted solids from these coal conversion processes is accomplished by cyclones, scrubbers and precipitators which are expensive to build and costly to operate. Besides the expenditure of energy, the separation and disposal operations result in a loss of heat from the system.

Known processes for the conversion of coal to liquid products are also described in the patent and technical literature. Like the gasification systems, liquifaction involves the heating of coal to between about 3500 and 600"C in the presence of hydrogen or a hydrogen donor. After reaction, the waste solids are separated by centrifuging or filtration, slow steps that can limit the speed of the process. Cooling of these residues resuits in a heat loss from the system and is a function of the quantity of ash and other impurities.

Certain impurities in the coal have been identified as undesirable pollutants if they are released as stable oxides during combustion, most notably sulfur oxides, nitrogen oxides and metal oxides. Some of the metal oxides are volatile, and in a high temperature system, they can be found in the stack gases. These volatile oxides include oxides of arsenic, beryllium, cadmium, lead, selenium and mercury. Present and future environmental controls could limit the use of coals containing such impurities.

The present invention substantially reduces, eliminates and avoids the disadvantages of previous coal conversion systems. It reduces or eliminates the energy required for removal of environmental contaminants. A low ash/impurity feed to the coal conversion systems vastly improves process efficiency. Application of the subject process makes available coal and related materials recovered from sources that were previously discarded as waste because of their large quantity of impurities. The present invention provides a product of improved quality that can be produced from coal deposits previously considered unacceptable for conversion by current technology.Moreover, application of agglomeration techniques and controlled preparation of the feed material in accordance with the present invention vastly improves the conversion of carbonaceous materials, even those that exist in presently uneconomical concentrations.

Summary of the invention The present invention provides a simple method of converting coal-containing streams into a concentrated feed stream of constant composition suitable for conversion in subsequent coal conversion processes, such as combustion, liquifaction and gasification. The prepared coal stream is of unique purity and quality and may be designed for a specific application.

A mixture of carbonaceous and noncarbonaceous fine particles, preferably ash and coal, are first dispersed in a suspension liquid such as water, to fqrm a slurry. The fine particles are formed preferably by comminuting coal from a mine in a grinder, mill or similar device.

Alternatively, the fine particles may be contained in the waste stream from a coal washing or preparation plant, in a settling pond associated with a coal washery, or other fine carbonaceous source, such as the slurry coming from a gas scrubber in a coke plant and containing coke breeze. Similarly, any stream containing carbonaceous material that may be agglomerated by the technology described herein comes within the purview of the invention.

Added to the slurry is a hydrocarbon agglomerating liquid, lyophobic to both the suspension liquid and to the non-carbonaceous fine particles, and lyophilic to the carbonaceous fine particles. The mixture of slurry and agglomerating liquid is then agitated to agglomerate preferentially the carbonaceous fine particles into discrete agglomerates, while leaving the non-carbonaceous fine particles substantially unagglomerated in the mixture. Thereafter, the agglomerated carbonaceous particles are separated from the mixture.

The chemical and physical properties of the discrete agglomerates are substantially uniform throughout and are substantially constant for a long period of time. The size and packing (density) of the agglomerates have substantial uniformity and the size can be controlled by the composition and percentage of the agglomerating liquid and the degree and duration of the agitation. The ash content is uniformly low, generally less than about 4 to 12 percent, preferably 4 to 6.5 percent by weight. The moisture content of the discrete carbonaceous agglomerates is uniformly distributed throughout and is typically from about 7 to 20 percent by weight.The agglomerating liquid coats the carbonaceous particles that make up the discrete agglomerates, thus making the agglomerates substantially unreactive to atmospheric oxygen such that the chemical and physical properties of the agglomerates remain constant for substantial periods of time.

After separation of the discrete carbonaceous agglomerates from the slurry, they are passed through a mixer/blender where the discrete carbonaceous agglomerates, a coal-in-oil or coalin-water mixture, are comminuted prior to further processing. The mixer/blender can be of the paddle-, pugmill- or similar type of blender. The discrete carbonaceous agglomerates thus prepared are controlled in composition so that they are suitable for subsequent conversion processes including combustion, hydrogenation, alkylation or gasification. The feed materials are low in ash and moisture (except for the water content of the coal-in-water combustion mixture).

At the mixer/blender, additives can be incorporated so that the prepared feedstock contains components such as catalysts, recycle oils, recycled solids and in the case of combustion, smoke depressants, combustion enhancers and the like.

The products formed from the discrete carbonaceous agglomerates will vary depending on the subsequent conversion process applied. In the case of liquifaction, the product can range from a heavy fuel oil to a light gasoline; in the case of gasification, the product can be a mixture of carbon monoxide, hydrogen and in some processes a hydrocarbon byproduct; and in the case of combustion, the product can be heat transferred to a steam boiler and flue gas. In any case, the product has unique properties resulting from the unique purity and uniform and constant chemical and physical properties of the discrete carbonaceous agglomerates. More specifically, the yields are higher per weight of feedstock owing to its uniformly controlled size, low ash content, low moisture content, reduced oxidation and controlled composition of the discrete carbonaceous agglomerates. Also the product streams have a noticeably reduced content of non-carbonaceous solids resulting in (1) reduced contamination by sulfur, lead, beryllium, cadmium and other impurities that are generally associated with coal and (2) greater recovery of liquid products, where formed, since less solids are present to absorb oils requiring pyrolysis or extraction reactions for their recovery or gasification. Moreover, beneficiation of the coal by the use of the hydrocarbon agglomerating liquids increases the calorific value of the products formed in the coal conversion processes known in the prior art.

Other details, objects and advantages of the present invention will be apparent from the following description of the presently preferred methods of practicing and making the invention.

Brief description of the drawings Figure 1 is a schematic drawing of a method for the combustion of discrete carbonaceous agglomerates into energy of combustion in accordance with the present invention.

Figure 2 is a schematic drawing of a method for the conversion of discrete carbonaceous agglomerates into a liquid in accordance with the present invention.

Figure 3 is a schematic drawing of a method for converting discrete carbonaceous agglomerates into a gas in accordance with the present invention.

Detailed description of the invention Referring to Figure 1, particulate carbonaceous material 11 in the form of finely divided dry solids from a source such as coal or a coke dust collector is stored until ready for processing in a storage and mixing container 12.

The particulate carbonaceous material preferably comprises a mixture of carbonaceous and non-carbonaceous fine particles that are preferably less than 590 micrometers in diameter (28 mesh Tyler). As used herein "carbonaceous material" is defined to include any raw material containing carbon which, when divided into fine particles, contains fine particles of both carbonaceous and non-carbonaceous materials.

Most desirably, the carbonaceous material is an anthracite or lower rank coal such that the carbonaceous fine particles are coal, and the noncarbonaceous fine particles are ash. As used herein, ash is defined to include small particles of materials such as clay, slate, sand, metal oxides and other impurities that generally appear as "ash" rather than gaseous products upon complete burning of coal.

Alternatively, the carbonaceous material can come from a settling/storage pond discharge or coal washery discharge 10 where the coal is already suspended in water. The waste stream from a conventional coal washer or the slurry from a settling/storage pond 10 typically has a relatively low solids content of about 5 to 1 5 percent by weight in water. The waste stream 10 may be combined with fine particles having a higher carbon content already in the storage vessel 12.

Mixing of the raw material streams 11 and 12 should yield a slurry entering the agglomerator 1 5 preferably with a solids concentration of about 5 to 40 weight percent solids and more typically about 20 to 25 weight percent solids, of coal and ash fine particles, and a suspension liquid content of about 60 to 95, preferably 75 to 80, weight percent. The carbonaceous and noncarbonaceous particles may already be sufficiently small so that they are discretely separated from each other and suspended in the slurry. Suspension of the particles is maintained by agitation of the agglomerator contents. If the fine material in vessel 12 is dry, a suspension liquid preferably water, 1 9 may optionally be added to provide the slurry.

Before or after entering the agglomerator 15, the stream to be processed is mixed with an agglomerating liquid 13. The agglomerating liquid 13 is generally a hydrocarbon with an initial boiling point above about 650C, and most preferably higher than about 1 500C, and is added in amounts of up to about 20 weight percent of the solids. Further, the agglomerating liquid 13 is preferably a light, liquid hydrocarbon being liquid below about 800C and preferably below about 400C and most preferably below about 200C.

Light liquid hydrocarbons as used herein are hydrocarbons which have boiling ranges, as determined by a standard method such as ASTM D 86, from room temperature to about 2500C. Intermediate range hydrocarbons are those of somewhat higher boiling ranges but still liquid at room temperature. Typically, materials such as kerosene, fuel oil and iubricating oils fall into this intermediate range. Heavy hydrocarbons are generally those that have melting points around room temperature and can be liquified by heating. These heavy hydrocarbons are differentiated from hydrocarbon solids such as coke that has no rational melting point or coals that may fuse momentarily and then become a char or coke. Some crude petroleum oils contain the full range of materials, i.e. from light hydrocarbons to heavy hydrocarbon, asphaltic components.Separation by distillation or extraction can usually produce the three fractions described above.

The agglomerating liquid is lyophobic to both the suspension liquid, preferably water, and to the non-carbonaceous fine particles, and lyophilic to the carbonaceous fine particles thereby wetting the surface thereof. As used herein, "lyophobic" describes a liquid with substantially no affinity, i.e.

wetting ability between the components involved; in this instance, between a hydrocarbon liquid and water or ash particles. As used herein, "Iyophilic" describes a marked affinity (wettability) between the component involved; in this instance, between the selected hydrocarbon liquid and the fine coal particles suspended in water.

Agglomerating liquid 13 is preferably a hydrocarbon liquid that can be utilized or converted along with the agglomerated, concentrated coal particles. Materials particularly suitable as an agglomerating liquid are light hydrocarbon liquids. Specifically suitable are light oil, light fuel oil, and kerosene. Also suitable are creosote, filtered anthracene oil, hydrogenated anthracene oil, lubricating oil such as light SAE 20 oil, and chlorinated biphenyls. Heavy hydrocarbons liquids such as crude petroleum, shale oil and or coal tar are not preferred. Heavy hydrocarbons typically contain molecular groups that are lyophilic to the non-carbonaceous fine particles as well as the carbonaceous fine particles and, therefore, do not provide the degree of separation of carbonaceous fine particles from non-carbonaceous fine particles desired.

Furthermore, heavy hydrocarbon liquids often must be heated to provide sufficient fluidity in the agglomerator 1 5.

The selected agglomerating liquid 1 3 is added in measured amounts to control the agglomeration of the carbonaceous particles.

Preferably, agglomerating liquid 1 3 is added in amounts of from about 2 to 10 percent by weight of the total solids, and most desirably, from about 3 and 7 percent by weight of the total solids in agglomerator 1 5. Greater amounts, up to and exceeding about 30 percent, may be utilized in some instances. However, lesser or greater amounts are not preferred because lesser amounts do not provide sufficient agglomeration and binding of the coal particles, while on the other hand, excess amounts waste valuable hydrocarbons and may result in an amalgam.

The mixture of agglomerating liquid and carbonaceous feed slurry are mixed and agitated in the agglomerator 1 5 which may be one or more vessels provided with a turbine or impeller type stirrer 20 and with or without recirculation 21. Preferably however, the agglomerator 15 apparatus is a tank equipped with a motor-driven, high shear impeller 20 extending to the bottom portion of the tank.

During agitation of the feed streams in the agglomerator 15, the carbonaceous fine particles are wetted preferentially by agglomerating liquid 13, which is preferably immiscible in water, and are agglomerated into coarser particles. The size of the agglomerated particles is determined primarily by the composition and percentage of the agglomerating liquid 13 added to the incoming slurry and the mixing conditions. For the preferred percentage of agglomerating liquid, about 2 to 10 weight percent of the solids feed, the discrete carbonaceous agglomerates have a size typically of about 1 to 2 millimeters. With a given agglomerating liquid, the time required for developing a discrete carbonaceous agglomerate of a given size is generally a function of the degree of agitation, shorter agglomerating times for a given size requiring a higher agitation speed.

The degree of and the duration of agitation in agglomerator 1 5 also controls the size and packing (density) of the discrete agglomerates.

Suitable duration times may be about one minute to about one hour.

The carbonaceous agglomerates containing oil with a specific gravity of less than about one gram per cubic centimeter (the specific gravity of water is nominally 1 gm/cc but is in effect slightly higher when ash particles are suspended therein) tend to be less dense than the suspension liquid and fioat to the top of the mixture. The discrete agglomerates and some of the suspension slurry are removed from agglomerator 1 5 and transported to a separator 1 6 where the discrete carbonaceous agglomerates are separated from the suspension liquid containing unagglomerated, non-carbonaceous fine particles. Preferably, separator 1 6 is a sieve bend or similar device having an appropriate mesh size, for example, a Dutch State Mines sieve bend with a 100 or 200 mesh Tyler screen.Alternatively, other types of commercially available separators, including an elutriator, a cyclone and a spiral separator may be utilized. Further, the separated, discrete carbonaceous agglomerates 22 may be suspended in a float-sink tank wherein the agglomerates tend to float to the surface and are skimmed off by a rotating paddle through an overflow, while the water and unagglomerated non-carbonaceous fine particles, which tend to sink, are removed from the bottom of the floatsink tank as a slurry containing the noncarbonaceous fine particles and substantially free of carbonaceous fine particles and agglomerating liquid.

A water spray may be used to flush fine particles of non-agglomerated matter from the surface of the discrete carbonaceous agglomerates as they pass through separator 1 6.

The water and non-carbonaceous particles pass to an exit conduit 1 7 for discharge, and recovery of water for recirculation to upstream processing.

The discharge stream is substantially free of carbonaceous fine particles and agglomerating liquid.

The resulting discrete carbonaceous agglomerates have a low ash and impurities content, a uniform size and density and a low and uniform moisture content. Typically, the content of impurities of non-carbonaceous material, preferably ash, occluded in the discrete carbonaceous agglomerate is less than about 4 to 1 2 percent, preferably 4 to 6.5 percent. The discrete carbonaceous agglomerates are of uniform size and density and within a narrow range as determined by the conditions of formation. Typically, the moisture content is uniformly distributed and is in the range of from about 7 to 20 percent. Consistent size and composition of the discrete carbonaceous agglomerates permits subsequent conversion steps to proceed predictably and efficiently.

The discrete carbonaceous agglomerates 22 from separator 1 6 are next conducted to mixer/blender 1 8 where further treatment to the discrete carbonaceous agglomerates takes place.

The mixer/blender includes the ribbon, pugmill or paddle mill type blender wherein the agglomerates may be mixed with a carrier liquid 24 to form a second slurry that transports the agglomerates to the combustion system. The carrier liquid can be water or a hydrocarbon liquid, such as a fuel oil that is fluid at room temperature or a heavier type liquid such as Bunker C oil that requires heat to make it flow. Concentrations of discrete agglomerates in the range of about 30 to 75 percent solids may be used. Preferably, concentrations of discrete agglomerates in the range of about 30 to 60 percent are utilized. At this stage via line 23, smoke inhibitors, stabilizers, promoters or other materials that may be applied to enhance combustion or to keep the agglomerates in suspension during transport and storage may be added.

The mixer/blender 1 8 provides several unique functions in addition to the improvements already made in the agglomeration step. The agglomeration system provides agglomerates that are low in water and non-carbonaceous matter such as ash. This advantage increases the throughput of carbonaceous matter in the conversion system and reduces the slow and costly steps of separation and removal after the converters. Conversely, the equipment size can be reduced to accomplish the same conversion of carbonaceous material. The absence of ash can also reduce or eliminate erosion problems in high velocity sections and during pressure let-down operations.The mixer/blender 1 8 functions to comminute the discrete carbonaceous agglomerates and regenerate them to the size of the fine particles of carbonaceous material that enter the process of the invention. These carbonaceous fine particles had been agglomerated so that they could be isolated from the water and ash in the separator 1 6. However, in slurry systems, fine particles react more quickly than larger particles because there is more surface exposed, and contact with additives and/or reactants is also increased. This characteristic also serves to improve the throughput and efficiency of the conversion system. Yet another improvement resulting from the particle size reduction is the ability to use pump valves similar to those used for pumping clean liquids.Large particles may tend to prevent valve parts from seating properly to prevent backflow. Preferably, the discrete carbonaceous agglomerates are reduced to a particle size of no greater than about 70%--200 mesh in mixer/blender 18.

The comminuted discrete carbonaceous agglomerates are suitable for use as the feed in subsequent coal conversion processes. In Figure 1, the product is used as a feed for combustion to generate energy. Combustion is the burning of carbonaceous material in the presence of air, generally for the release of heat, wherein the energy produced is generally used for the production of steam which in turn performs useful work. The combustion reaction is basically C+O2CO2 with a heat release of about 94 kilocalories (KCal) per Mole or 14,500 Btu per Lb.

Bituminous coal involves a more complex reaction in that it contains, in varying quantities, components other than carbon, such as hydrogen, oxygen, nitrogen and sulfur. It may also contain significant quantities of ash and moisture which contribute little to the heat produced. In fact, these materials are a burden on the combustion process in terms of the costs of ash handling and recovery and in terms of the energy required for the heating and evaporation of water and for the heating of ash particles.

The amount of heat released can be estimated from the coal composition by using the classic Dulong formula:

wherein Hc is the gross heat of combustion, Btu per Ib, and wherein: C is the weight percent of carbon, H is the weight percent of hydrogen, O is the weight percent of oxygen, S is the weight percent of sulfur.

Thus, the reactions that generate heat, in addition to the carbon reaction described above, are: 2 H2+O2e2 H2O 29,150 Cal/gram H2 S+O2eSO2 2,220 Cal/gram S The heat released by combustion is usually converted to steam that can be used to generate electric power or for process steam such as is used in the gasification reactions discussed below.

A large number of furnace designs are available, based on different methods for efficiently bringing coal into contact with the oxygen in air. Such designs include stokers, fixed beds, fluidized beds, atomizers and pulverized fuel. The preferred embodiments of this application are associated with suspension firing wherein the coal is transported to the combustion chamber as a prepared suspension of coal-in-oil or coal-in-water. Efficient dispersion of the coal in the fire box improves combustion, and the low values of moisture and/or ash increase the efficiency of the overall system.

In the process of Figure 1, prepared coal-in-oil or coal-in-water 'slurries are transported from a mixer-blender 1 8 to a buffer tank 50 where the slurry is stored prior to transport via conduit 57 to the burners 52 as a combustion fuel source for the furnace 58. Primary air for combustion or steam for atomization 51 may be added to the slurry stream before the slurry enters the burners.

Hot flue gases containing small amounts of ash particles may pass through the heat exchangers 53 for the recovery of energy as preheat for incoming air and water streams. The cooled gas stream may then pass through an electrostatic precipitator, bag house or other apparatus 55 for the removal of entrained fly ash particles before being discharged to the atmosphere via conduit 54. The agglomeration process of the invention leaves the flue gas stream with only a negligible amount of fly ash and, therefore, the fly ash removal system 55 may be bypassed via conduit 57' if desired. It is also possible that some of the ash might remain in the furnace and fall to the bottom of the combustion chamber. If such ash remains, it may be removed through a discharge port 56.

The calorific value of the slurry of comminuted discrete carbonaceous agglomerates entering the combustion chamber is dependent upon the calorific value of the carbonaceous agglomerate 22 in the slurry. Inclusion of the agglomerating hydrocarbon liquid in the agglomerates 22 and the hydrocarbon carrier liquid 24 beneficiates the calorific value of this coal-in-oil or coal-in-water mixture. The quality of this coal-in-oil or coal-inwater mixture is further improved in that the comminuted discrete carbonaceous agglomerates 22 are protected from partial oxidation of the carbonaceous particles by exposure to air in that agglomerating liquid 13 coats the individual carbonaceous particles and protects them from oxidation prior to combustion or other postconversion processes.Partial oxidation of the discrete carbonaceous agglomerates destroys the uniformity of their chemical and physical properties thereby affecting the efficiency of the combustion process and the heat liberated in the combustion chamber.

The discrete agglomerates of the present invention are resistant to changes in their chemical and physical composition caused by oxidation and can be stored for substantial periods, if necessary, without appreciable oxidation. Moreover, the prepared coal-in-oil or coal-in-water slurry requires no special storage facilities such as the use of an inert gas blanket over the material.

Figures 2 and 3 are illustrative of alternative embodiments of the present invention in which the discrete carbonaceous agglomerates 22 are produced in the same manner as described above with respect to Figure 1. Accordingly, the same reference numerals have been applied to like units and components of Figures 2 and 3. However, in Figures 2 and 3, the comminuted discrete carbonaceous agglomerates from mixer/blender 1 8 are converted to different products by subsequent, alternative, coal conversion steps.

A variety of alternative embodiments for the further conversion of the discrete carbonaceous agglomerates 22 may be used with the present invention. These alternative embodiments comprise various downstream process stages designed for the optimum conversion of the discrete carbonaceous agglomerates 22 to a fluid product.

In the process of Figure 2, comminuted discrete carbonaceous agglomerates are converted to a fluid product by a liquifaction process. The comminuted discrete carbonaceous agglorherntes may be mixed with a carrier liquid 23 and, if desired, an appropriate catalyst 24 that can accelerate the hydrogenation reaction in the liquifaction process. The catalyst may be a natural material such as the ash from the coal or a prepared complex of active metallic components.

In a donor solvent embodiment of the liquifaction process, no catalyst is added to the incoming slurry stream containing the discrete agglomerates, but rather hydrogen transfer occurs through the reaction of hydroaromatic compounds with the solubilized coal. In the process of Figure 2, the oil supplied to the mixer/blender 18 can be a partially hydrogenated oil or a reactive hydroaromatic oil from a vessel that converts part of the product oil to a donor solvent. Since the ash and moisture content of the carbonaceous agglomerates is substantially uniform, the addition of oil and catalyst can be at a constant rate. Accordingly existing liquifaction processes can be modified and new processes designed without regard to the physical and chemical properties of a particular source of carbonaceous feed material such as a particular deposit of coal.

Steps for the preliminary preparation of the discrete carbonaceous agglomerates can be accomplished by known methods similar to the ones described for the combustion embodiment of Figure 1 that provide a constant composition feed 22 to the mixer/blender 1 8 where further preparation of the discrete carbonaceous agglomerates takes place. As before, the mixer/blender can be of the ribbon, pugmill or paddle type wherein the agglomerates are mixed with a carrier liquid 23, such as an oil or water.

The carrier liquid oil can be a recycle oil being returned to the reactor 43 for additional hydrogenation, a partially hydrogenated oil that is a mixture of hydroaromatic and aromatic materials, a tar oil or any other hydrocarbon suitable to transport the coal particles to the liquifaction reaction system.

At this stage, a catalyst 24 that is selected for the specific hydrogenation process being applied may optionally be added. Such a catalyst accelerates the reaction rate and can be selected from any of a wide variety of materials. Suitable catalysts include simple catalysts for the hydrogenation of coal and coal-in-oil slurries, such as iron oxide and iron sulfide. Concentrations of the catalyst are preferably in the order of from about 1 to 1 0 percent by weight of the coal.

Preferably, the concentration is from about 3 to 7 percent by weight of the discrete carbonaceous agglomerates.

More active catalysts such as cobalt molybdate may also be used, but may require more sophisticated preparation methods. The cobalt and molybdenum can originate as their water soiuble salts and by proper formulation precipitate a cobalt oxide-molybdenum oxide complex.

Molybdenum catalysts added to the hydrogenation system can usually be added in low concentrations, sometimes only a fraction of one percent, depending on the operating conditions. Hydrogenation systems have been successfully employed using only 0.01% of molybdenum based on the weight of coal (i.a, discrete carbonaceous agglomerates).

When catalysts are added to these coal-oil mixtures, mixing is important so as to provide an intimate contact between the catalyst and the surface of the coal. Mixer/blender 1 8 provides the necessary mixing of the components.

Coal hydrogenation reactions are generally carried out at pressures of about 2000 to 4000 psi and a temperature of about 8500F.

Suspending the comminuted discrete carbonaceous agglomerates in a slurry permits it to be pumped by pump 40 to the system pressure. The concentrations of coal in the slurry may be between about 10 and 75 percent, preferably between about 30 and 50 percent by weight. Before entering the preheater 42, some or all of the hydrogen 41 needed for the hydrogenation reaction can be added to the slurry. In some systems, part of the hydrogen can be added directly to the hydrogenation reactor 43 to provide control of the exothermic hydrogenation reaction. Residence time in the preheater and in the reactor can be improtant operating parameters and will vary depending on the discrete carbonaceous agglomerate composition and the catalyst used.Thus, it is important that the discrete carbonaceous agglomerates entering the mixer/blender 1 8 have uniform composition and uniform physical properties. It is generally preferable that the ash content and the moisture content be reduced to the lowest practical value.

The liquid products from the reactor 43 may go first to a high pressure receiver 44 where undissolved gases 46 are separated from the liquid product. The liquids next may pass to a low pressure receiver 45 where most of the remaining gases 47 may be separated from the liquid product. The essentially gas-free, liquid product goes next to a solids separator 49. Devices such as centrifuges, filters, cyclones may be applied to achieve the physical separation of the solids and liquids. Alternatively, solids separation may be achieved by distillation, steam stripping or extraction. Some of the resulting product oil 48 may be returned to the hydrogenation system as a carrier liquid 23 used to transport the comminuted discrete carbonaceous agglomerates to the high pressure reaction system.

In one embodiment of the hydrogenation process, some of the solids 50 may be recycled to the mixer/blender 18 because of their catalytic activity. Generally, however, the solids 50 from solids separator 49 will be sent to a gasifier 60 or a pyrolysis unit. These units can recover some of the heavy oil intermingled with solids 50 or can make hydrogen needed for the coal hydrogenation reaction.For the production of hydrogen, steam 61 reacts with the heavy oil intermingled with the solids 50 to form synthesis gas 63, carbon monoxide and hydrogen, according to the empirical equation: CH2+nH2O--- (CO)n+3n H2 Carbon monoxide (CO) in the synthesis gas is reacted with steam in a shift reactor 64 to form carbon dioxide (CO2) according to the equation: CO+H20--- C02+H2 The carbon dioxide (CO2) may be removed by any of several commercially available processes to yield essentially pure hydrogen. Alternatively, the carbon monoxide and hydrogen may be separated by cryogenic means whereby the carbon monoxide is liquified at low temperatures leaving hydrogen as the gas product.

The fact that the oil agglomeration process according to the invention reduces the amount of ash entering the hydrogenation reactor 43 minimizes the solids burden entering the gasifier 60. If insufficient heavy oil is intermingled with solids 50 for the formation of hydrogen 66, some coal can be used to supplement the feed to the gasifier. Coal is a much less costly raw material than residue from the hydrogenation process.

Figure 3 illustrates a further embodiment of the present invention in which the comminuted discrete carbonaceous agglomerates are prepared in mixer/blender 18 for injection into a gasifier 73.

A major problem in the prior art when operating a gasifier at elevated pressures is to compress the coal stream from atmospheric pressure to some eievated pressure in the reactor. The use of lock hoppers 71 to achieve the necessary pressurization is wasteful of gas used for pressurization. Accordingly, the mixer/blender 1 8 provides a means to add oil and tars 83 recovered from the gasifier 73 to be recycled as carrier liquid 24 to transport the comminuted discrete carbonaceous agglomerates to the gasifier 73.

In this further embodiment, discrete agglomerates of carbonaceous material, nominally coal, 22, low in ash and moisture content are prepared as hereinbefore described.

These agglomerates of constant chemical and physical properties go to a mixer/blender 1 8 where comminution of the discrete carbonaceous agglomerates takes place. Additional coal 21 from a preparation plant may be added at mixer/blender 1 8 if its properties are consistent with the desired gasifier feed composition. Water may also be added at mixer/blender 1 8 if water is to be the carrier liquid 24. Otherwise, oil of controlled composition can be added at the same point to modify or supplement the mixture oil 83 being recycled from the gasifier section as the carrier liquid 24.Additives such as alkaline salts that act as a catalyst during the gasification process can also optionally be added to mixer/blender 1 8. A typical catalyst is an alkali, such as a sodium or potassium salt, that is known to increase the gasification rate.

The coal stream from mixer/blender 1 8 is pumped by pump 20 from ambient pressure to that pressure necessary to inject the prepared coal stream into the gasifier 73 having a flame temperature of about 33000 to 35000F. Air or oxygen 74 and steam 75 are added to the gasifier 73. Oxygen is added to assist the combustion of part of the incoming coal slurry. Gasification takes place at high temperatures between the steam and the carbon in the coal and the hydrocarbon oil. The gasifier is of a type that can process the coal particles of the size generated in the mixer/blender 1 8. Typical gasifiers would be the Texaco and the Koppers-Totzek systems.

The total product from gasifier 73 next goes to a clean-up unit 78 wherein a series of reactions take place. The produced gas is cooled to processing condition by water and solvent wash 76. A clean synthesis gas 77, carbon monoxide and hydrogen (medium Btu gas), is the product gas if oxygen 74 is used as the combustion gas. If air is used, the product is a low Btu gas, i.e., synthesis gas diluted with nitrogen from the air.

Water, tar, light oils and solids leave clean-up unit 78 and are introduced into a separator unit 79.

The separator unit 79, like the cleanup unit 78, can be a series of vessels to carry out the necessary processing steps to yield the desired products. Solvent recycle 80 typically can be methanol as used in the weil-known Rectisol process or a potassium carbonate solution as used in the well-known Benfield process, both used for the removal of carbon dioxide and other contaminants from the raw gasifier product.

Product oil 81 can be an oil fraction from the pyrolysis of the coal stream from mixer/blender 18 or carrier liquid 24. This product oil may be suitable as a fuel oil, a chemical raw material or feedstock for a refining operation.

Ash 82 is the entrained solids carried from the gasifier to the recovery units 78, 79. In some systems, most of the ash is recovered as slag 84 in the bottom of the gasifier 73. The amount of ash recovered at this point in the process is a function of the ash fusion temperature and the gasifier temperature. More importantly, however, is the control of the ash content entering the gasification system as determined by the oil agglomeration process and the blending of components to be introduced into the gasifier.

Many other processes and schemes can be described which make use of carefully comminuted discrete carbonaceous agglomerates to produce specific products efficiently and in optimum yields.

Advantageously, the present invention is totally compatable with the efficient transportation of prepared carbonaceous material.

Thus, when final conversion of the carbonaceous material is performed at a location remote from the source of carbonaceous material, discrete carbonaceous agglomerates 22 are readily transported to the conversion site. Preferably, carbonaceous agglomerates 22 are transported in comminuted form in a liquid slurry. Alternatively, carbonaceous agglomerates 22 can be shipped in conventional transportation, such as railroad tank cars and river barges.

In accordance with the foregoing description, a method for the conversion of a carbonaceous material to an improved feedstock has been described in which non-carbonaceous particles are removed from the carbonaceous material prior to subsequent conversion processes, such as combustion, liquifaction or gasification, the remaining discrete carbonaceous agglomerates comminuted, and the composition of the comminuted discrete carbonaceous agglomerates adjusted to its optimum composition. The efficiency and economy of the final conversion steps are thereby improved since significantly less non-carbonaceous material remains to be separated from the product by relatively difficult and expensive purification and clarification procedures.Furthermore, the disclosed method for conversion of carbonaceous material improves the rate of conversion of the carbonaceous material into a final product because the carbonaceous agglomerates deveioped in the process have an improved composition that is substantially uniform in its chemical and physical properties and because less non-carbonaceous material is processed through the final conversion step where removal of the non-carbonaceous material is relatively slow, difficult and expensive.

Also, the disclosed method is completely compatible with systems in which the conversion step is performed at a location which is remote from the source of the carbonaceous material since the prepared agglomerates are readily transportable, preferably as a liquid slurry that is pumped through pipelines.

Although the invention has been described in detail in the foregoing for the purpose of iilustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the

Claims

claims. Claims

1. A method of converting a solid carbonaceous material into an improved feedstock comprising the steps of: A. dispersing a mixture of carbonaceous and non-carbonaceous fine particles in a suspension liquid to form a first slurry; B. adding to the first slurry a hydrocarbon liquid that is lyophobic to the suspension liquid and the non-carbonaceous fine particles and lyophilic to the carbonaceous fine particles to form a mixture:: C. agitating the mixture preferentially to agglomerate carbonaceous fine particles into discrete carbonaceous agglomerates while said non-carbonaceous fine particles remain substantially unagglomerated in the mixture, said discrete agglomerates having a substantially uniform ash content of less than about 12% by weight and being substantially inert to atmospheric oxidation for a substantial period of time; D. separating the discrete carbonaceous agglomerates from the mixture; and E. comminuting the discrete carbonaceous agglomerates to reduce the particles size of the discrete carbonaceous agglomerates.

2. The method of Claim 1, wherein the discrete carbonaceous agglomerates are dispersed in a carrier liquid to form a second slurry prior to, during or subsequent to comminution.

3. The method of Claim 2, wherein the discrete carbonaceous agglomerates are present in the second slurry in from about 30 to 75% by weight.

4. The method of Claim 1 comprising the further step of mixing the discrete carbonaceous agglomerates with sufficient quantities of an additive to enhance the properties of the discrete carbonaceous agglomerates, said mixing being prior to, during or subsequent to comminution.

5. The method of Claim 4, wherein the additive is selected from the group consisting of stabilizers, smoke inhibitors, catalysts, combustion enhancers, recycle oils and recycle solids.

6. The method of Claim 1, wherein the suspension liquid is present in the first slurry in from about 30 to 95% by weight.

7. The method of Claim 1, wherein the suspension liquid is water.

8. The method of Claim 1, wherein the hydrocarbon liquid added to the first slurry is present in the mixture in from about 2 to 10% by weight of the combined weight of the carbonaceous and non-carbonaceous fine particles.

9. The method of Claim 1 comprising the further step of heating the comminuted discrete carbonaceous agglomerates to produce a product selected from the group consisting of energy of combustion, a liquid product and a gaseous product

10. The method of Claim 1, wherein the discrete carbonaceous agglomerates are comminuted to a particle size of no greater than about 70%--200 mesh.

11. In a method of converting a solid carbonaceous material into an improved feedstock comprising the steps of dispersing a mixture of carbonaceous and non-carbonaceous fine particles in a suspension liquid to form a first slurry; adding to the first slurry a hydrocarbon liquid that is lyophobic to the suspension liquid and the non-carbonaceous fine particles and lyophilic to the carbonaceous fine particles to form a mixture; agitating the mixture preferentially to agglomerate carbonaceous fine particles into discrete carbonaceous agglomerates while said non-carbonaceous fine particles remain substantially unagglomerated in the mixture, said discrete agglomerates having a substantially uniform ash content of less than about 12 ,ó by weight and being substantially inert to atmospheric oxidation for a substantial period of time; and separating the discrete carbonaceous agglomerates from the mixture, the improvement comprising in combination with the above steps: comminuting the discrete carbonaceous agglomerates to reduce the particle size of the discrete carbonaceous agglomerates.

12. The method of Claim 11, wherein the discrete carbonaceous agglomerates are dispersed in a carrier liquid to form a second slurry prior to, during or subsequent to comminution.

13. The method of Claim 12, wherein the discrete carbonaceous agglomerates are present in the second slurry in from about 30 to 75% by weight.

14. The method of Claim 11, wherein the discrete carbonaceous agglomerates are comminuted to a particle size of no greater than about 70%--200 mesh.

1 5. A method of converting a solid carbonaceous material into a feedstock, substantially as hereinbefore described with reference to the drawings.

16. A feedstock obtained by a method according to any of claims 1 to 15.