US20090172998A1

US20090172998A1 - System and method for refining carbonaceous material

Info

Publication number: US20090172998A1
Application number: US12/008,269
Authority: US
Inventors: Randall J. Harris; Damian Wales
Original assignee: Carbonxt Group Ltd
Current assignee: Carbonxt Group Ltd
Priority date: 2008-01-08
Filing date: 2008-01-08
Publication date: 2009-07-09
Also published as: WO2009089351A1; CA2711647A1; CN102159688A; JP2011509236A; EP2231837A1; AU2009204100B2; MX2010007402A; AU2009204100A1

Abstract

A system for refining carbonaceous material including a carbonaceous material feedstock unit including a first vibratory screen unit for sizing the carbonaceous material; a digestion unit including a digestion unit in communication with the carbonaceous material feedstock unit; and an acid feedstock unit in communication with the digestion unit for providing an acid mixture solution to the digestion unit including a source of H₂O; a source of HF; a source of H₂SiF₆, wherein the these compounds may be mixed together in ratios prior to being provided to the digestion unit; a separation unit in communication with the digestion unit for separating the digested carbonaceous material from the acid mixture solution; and a dryer unit in communication with the separation unit for drying the digested carbonaceous material and separating the carbonaceous material based on density.

Description

FIELD OF THE INVENTION

The field of the invention is directed to refining carbonaceous material and more specifically to refining coal and coal related materials.

BACKGROUND OF THE INVENTION

Coal includes many inorganic and organic impurities in its raw state, and these impurities create challenges to the processes that use coal. For example, coal is used primarily as a fuel to produce electricity and heat through combustion. However, burning coal may be more problematic than ever due to the increasing pressure by environmental regulators on utility owners/operators to reduce pollution. Retrofitting coal fired power plants with the latest pollutant scrubbers is extremely expensive.
In addition, coal may be used for a multitude of products from base products to consumer products. For example, coal may be used to make carbon black inks, activated carbon, tar, and the like. Nevertheless, due to its composition, it includes large numbers of macropores and micropores that may contain many impurities, which makes it difficult to remove impurities during the processing of these products. Generally, it is beneficial to treat raw coal to remove many of these impurities prior to using the coal in these various applications.
Processes are known that treat carbon to reduce the impurities, normally referred to as ash content. For example, it is known to use HF acid to remove contaminants from carbon. A problem with using just HF acid by itself is that it is a highly reactive compound, and thus reacts with essentially all of the contaminants. If the carbon contains calcium and magnesium species contaminants, then the HF acid produces insoluble CaF₂and MgF₂, which are then not easily removed. Also, some metal oxides contaminants are converted to metal fluorides, which may not be soluble in HF acid. Additionally, substantial amounts of HF acid are used in these digestions, which is an expensive component of the process.
In another example, U.S. Pat. No. 4,780,112 discloses treating carbon with a fluorine acid solution that consists of an aqueous solution of hydrofluorosilic acid (H₂SiF₄) and hydrogen fluoride or hydrofluoric acid (HF). Available metal oxides are converted to metal fluorides and/or metal fluorosilicates, which are dissolved in the aqueous solution and then separated from the carbon. The treated coal is then washed with H₂SiF₄to remove metal fluorides from the surface of the treated carbon and dried between a temperature of 70° C. and 140° C. The dried carbon is then heated between a temperature of 250° C. and 400° C. to remove the H₂SiF₄in the form of HF and SiF₄.
In another example, U.S. Pat. No. 4,804,390 discloses treating coal with HF and then washing the coal with H₂O to leach out impurities. This is followed by a second leaching step including treating the coal with an HCl acid solution, which is followed by another water wash. After each of these leaching steps, the acid solution is separated from the treated coal. Then the coal is heated between 20° C. to 100° C. under vacuum to remove any residual HCL, HF, and SiF₄.
In yet another example, U.S. Pub. Pat. App. No. 20060150474 discloses treating carbonaceous material with an aqueous solution of H₂SiF₆in the absence of HF wherein the sulfur-containing impurities react with the H₂SiF₆to form digestion products and then separating the digestion products from the treated carbonaceous material.

SUMMARY

In one embodiment, the present system and method for refining carbonaceous material (“system for refining carbonaceous material”) provides for improved digestion and lowered costs for such refining processes. The present system for refining carbonaceous material includes a carbonaceous material feedstock unit that acquires raw carbonaceous materials, such as coal, from a source that has been generally mechanically deconstructed. For example, the system for refining carbonaceous material may take a settling pond stream from a preparation plant that contains small coal fines 0-5 mm in size and efficiently produces carbonaceous material having a desirable size and water content without requiring expensive addition wetting steps as found in the prior art. The carbonaceous material feedstock unit processes the carbonaceous material to a diameter preferably less than 1 mm on a wet screening apparatus that washes and sizes the material. Then it may be fed to a gravity separation unit that mechanically separates the mechanically deconstructed carbonaceous material from heavy impurities or carbonaceous material that exceeds the desired threshold. The separated impurities are deposited into a hopper for removal and further processing or disposal, while the washed carbonaceous material exits the gravity separation unit and is deposited onto a vibratory dry screener to reduce the remaining water content of the washed and sized carbonaceous material to a desirable level for use in a later digestion unit. This washed carbonaceous material may be forwarded to a further drying process, using, for example, a microwave dryer to produce the carbonaceous material of a desirable moisture content, for example. The carbonaceous material feedstock unit may further include ultrasonic stimulation for improved sizing and wetting of the carbonaceous material. In addition, the partially dewatered carbonaceous material may then be sent to a centrifuge apparatus to further reduce the water content of the carbonaceous material to a desirable level for use in the later digestion unit. The present system for refining carbonaceous material may further include a moisture balance apparatus that may increase the moisture content of the washed and sized carbonaceous material.
The present system for refining carbonaceous material further includes a digestion unit that utilizes economical mixtures of acids containing fluorine for digesting and removing contaminants from the carbonaceous material. The system for refining carbonaceous material includes adding the carbonaceous material from the carbonaceous material feedstock unit into a digestion unit that contains at least one digestion vessel that contains an acid mixture solution of H₂SiF₄and HF acids and H₂O. The digestion vessel may include a mechanical agitator device to thoroughly mix the carbonaceous material with the acid mixture solution. The output of the digestion vessel includes at least one slurry of chemically treated or digested carbonaceous material. Generally, there is sufficient physical separation of the carbonaceous material within the digestion vessel to produce different layers of treated carbonaceous material. In one aspect, these different layers of carbonaceous material may be outputted as distinct slurries from the digestion vessel into different downstream vessels. The digestion unit may further include ultrasonic stimulation of the carbonaceous material during the digestion stage in a vessel at a frequency that creates cavitations with diameters approximately the same or smaller than those of the micropores of the carbonaceous material, thus creating a pumping or hydraulic action as the bubbles collapse inside the micropores of the carbonaceous material. This action causes the acid mixture solution at elevated temperatures into the micropores and macropores allowing it to come into physical contact with the inorganic compounds contained therein, thus greatly facilitating digestion. These ultrasonic stimulation sources may include novel square wave signals that generate the ultrasonic waves that create the desired sizes of cavitation bubbles. This ultrasonic action may provide for up to 100% digestion of the contaminants contained in the carbonaceous material for use in ultra-clean fuel operations and for commercially viable processes for producing such clean carbonaceous material. Further, the present system for refining carbonaceous material may reduce the digestion time, which increases productivity and improving the economic viability.
The system for refining carbonaceous material further separates the chemically digested carbonaceous material from the acid mixture solution and liquid waste products via a centrifuge, for example. The chemically digested carbonaceous material may be washed with hot water, which may be followed by a steam stripping process while in the centrifuge to remove as much as possible of the acid mixture solution and liquid waste products from the chemically treated carbonaceous material and to reduce the moisture content of the carbonaceous material. The solution of acid and liquid waste products is piped to recycling tanks to filter out the waste products, reclaim, and recharge the H₂SiF₆, which is then reused in the process. The dewatered chemically digested carbonaceous material exiting the centrifuge has a moisture content of preferably between 5% and 15%, and more preferably 5% and 10% and may be optionally dried further in a moderate temperature (<130° C.) dryer to reduce the moisture content without driving off all of the volatile components of the carbonaceous material.
The system for refining carbonaceous material provides a novel process for the acid digestion treatment and subsequent mechanical separation of the treated coal from the slurry to remove the metal impurities. The present system for refining carbonaceous material does not pressurize the digestion vessel, thus saving energy consumption in the process. Further, the present system for refining carbonaceous material does not wash or rinse the digested carbonaceous material structure with H₂SiF₆acid.
In one embodiment, the present system for refining carbonaceous material produces refined carbon that is more rapidly activated to produce activated carbon. Moreover, quality activated carbons were produced in less time that it takes to manufacture similar activated carbons from currently known processes. Additionally, carbonaceous material produced with the present system for refining carbonaceous material may allow the conventional power plants to meet the U.S. Environmental Protection Agency's emissions requirements without current post combustion treatment. Also, when particle sizes of the carbonaceous material are below 10 microns, the burn-off time is within 0.05 secs. The carbonaceous material with such characteristics produced by the present system for refining carbonaceous material performs like oil and approaches characteristics of natural gas when processed to approximately 1 micron. With the smaller combustion times experienced with the digested and sized carbonaceous material, residence time maybe even less than 0.05 seconds, combustion temperatures in a plant maybe more easily controlled.
In one embodiment, the present system for refining carbonaceous material may include a carbonaceous material feedstock unit including a first vibratory screen unit for sizing the carbonaceous material; a digestion unit including a first digestion unit in communication with the carbonaceous material feedstock unit; a second digestion unit in communication with the first digestion unit; and an acid feedstock unit in communication with the digestion unit for providing an acid mixture solution to the first digestion unit including a source of H₂O; a source of HF; a source of H₂SiF₆, wherein these compounds may be mixed together in ratios prior to being provided to the first digestion unit; a separation unit in communication with the digestion unit for separating the digested carbonaceous material from the acid mixture solution; and a dryer unit in communication with the separation unit for drying the digested carbonaceous material and separating the carbonaceous material based on density.
In another embodiment, the present system for refining carbonaceous material may include a carbonaceous material feedstock unit including a first vibratory screen unit for sizing the carbonaceous material; a digestion unit including a digestion unit in communication with the carbonaceous material feedstock unit; and an acid feedstock unit in communication with the digestion unit for providing an acid mixture solution to the first digestion unit including a source of H₂O, a source of HF; a source of H₂SiF₆, wherein the these compounds may be mixed together in ratios prior to being provided to the digestion unit; a separation unit in communication with the digestion unit for separating the digested carbonaceous material from the acid mixture solution; and a dryer unit in communication with the separation unit for drying the digested carbonaceous material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of a carbonaceous material feedstock unit according to an embodiment of the present invention;

FIG. 2 illustrates a schematic diagram of a microwave drying unit according to an embodiment of the present invention;

FIG. 3 illustrates a schematic diagram of a digestion unit according to an embodiment of the present invention;

FIG. 4 illustrates a schematic diagram of a fluidized bed dryer unit according to an embodiment of the present invention;

FIG. 5 illustrates a schematic diagram of a packaging and product unit according to an embodiment of the present invention;

FIG. 6 illustrates a schematic diagram of a vapor recovery unit according to an embodiment of the present invention;

FIG. 7 illustrates a schematic diagram of a feedstock storage unit according to an embodiment of the present invention

FIG. 8 illustrates a schematic diagram of an ultrasonic unit according to an embodiment of the present invention;

FIG. 9 illustrates a schematic diagram of an ultrasonic unit according to another embodiment of the present invention; and

FIG. 10 illustrates a flow diagram for an exemplary process for refining carbonaceous material according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings, like or similar elements are designated with identical reference numerals throughout the several views and figures thereof, and various depicted elements may not be drawn necessarily to scale.
The term “carbonaceous” means all materials that consist of substantial amounts of carbon. Without limitation the term includes coal, refined coal, activated carbon, carbon black carbon products, solid crude oil, coal tar pitch, carbon fibers, tar, carbon, coke, graphite, and other carbon structures.
The term “digested carbonaceous material” means a carbonaceous material that has been subject to a cleaning or digesting process as herein described. In one aspect, the term means chemically cleaning the carbonaceous material by digesting the minerals embedded within the carbonaceous material. This term may further mean a carbonaceous material that has been chemically cleaned and may be noted as “chemically cleaned carbonaceous material.”
The term “macropore” typically means pores having a diameter size of greater than 50 nm. The term “micropore” typically means pores having a diameter size of smaller than 50 nm. The term “product” means all materials that are made from refined carbonaceous material, including without limitation: plastics, fibers, solvents, pharmaceuticals, carbon black, inks, activated carbon, carbon, tar, specialty minerals, boiler fuels, additives, gas cleanup, and the like.
FIG. 1 illustrates an embodiment 100 of a carbonaceous material feedstock unit according to the present invention. In one embodiment, the carbonaceous material feedstock production unit 100 may be portable for relocating it at any location that produces a waste stream and/or settling pond stream containing carbonaceous material, such as preparation plants or washeries as is known to those skilled in the arts. Typically, a preparation plant is a plant that washes, sorts, sizes, cleans, and the like a source of carbonaceous material usually in proximity to a carbonaceous material mining operation, for example. Typically, these preparation plants produce smaller-sized carbonaceous material that are not processed further due to the cost of removing them from their carrier fluid stream, such as water. These smaller-sized carbonaceous particles required may be produced from washing the clays, carbonaceous material, and rocks off of the larger sized coal, which are generally separated out and discarded using various density related processes at a preparation plant. They are generally discarded because the size of the waste carbonaceous material is too small or not worth the expense to recover it from the preparation plant's process stream, thus this waste carbonaceous material flows with the waste water out to setting ponds where the waste carbonaceous material settles to the bottom of the settling pond and the waste water is later treated. In some instances, the percentage of carbonaceous material in these settling pond streams and/or settling ponds may be between 25%-75% of the entire settling pond depending on the age of the settling pond. In one aspect, the system for refining carbonaceous material may recover the carbonaceous material from a preparation plant's process stream, such as a settling pond stream. In another aspect, the system for refining carbonaceous material may recover the carbonaceous material from an impoundment, such as a settling pond.
The carbonaceous material feedstock production unit 100 may be moved or located nearby a carbonaceous material washery, carbonaceous material processing plant, coal preparation plant, coal mining plant, settling impoundment, settling pond, and the like where it is connected via pipe 102 to a waste stream of a preparation plant or settling pond stream material with water added that contains the smaller-sized carbonaceous material. The pipe 102 is connected to a vibratory screen unit 104 that separates the larger-sized carbonaceous material pieces from the smaller-sized carbonaceous material. In one aspect, the vibratory screen unit 104 includes a series of descending screens of decreasing screen size. The vibratory screen units 104 may include gravity and/or density separation apparatuses, such as teeter beds, waffle tables, jigs, pulsing water beds, steady flow beds, and the like. Thus, the larger-sized carbonaceous material pieces are screened out at the upper screens while the smaller-sized carbonaceous material falls through to the lower parts of the vibratory screen unit 104. In one aspect, one of the intermediate screens may contain the desired size of carbonaceous material. Offsite process water is supplied through pipe 106 to the vibratory screen unit 104 for improved washing and processing at the vibratory screen unit 104.
In one embodiment, the smaller-sized particles and larger-sized particles that exceed a desirable predetermined size of carbonaceous material are removed from the vibratory screen unit 104 via pipes 108 and 110 and may be returned to the preparation plant, for example. Offsite process water may also accompany the undesirable particles exiting the vibratory screen unit 104. For ease of use, the pipes 102, 106, 108, and 110 may be flexible hoses, tubes, pipes, and the like for ease of connecting the carbonaceous material feedstock production unit 100 to the preparation plant. The desirable sized particles exit the vibratory screen unit 104 and flow via pipe 112 to a density differential separator 114. In one embodiment, the density differential separator 114 separates higher-density particles from lower-density particles. Typically, the lower-density particles will contain the desired carbonaceous material particles that will be processed as further described. The higher-density particles typically contain the material and particles that may not be used by the system for refining carbonaceous material.
The desirable-sized particles exit the density differential separator 114 and flow via pipe 122 to another vibratory screen unit 120. In one aspect, the vibratory screen unit 120 may additionally wash the particles and may further dry the carbonaceous material particles that enter the vibratory screen unit 120. Any sized particles that are not of a desired size may exit the vibratory screen unit 120 via pipe 122 and be returned to the preparation plant, for example. The washed and sized carbonaceous material may further be dried by forced air from a dryer 124. In one embodiment, the water content is preferably from about 8% to about 40% w/w, and more preferably from about 12% to about 18% w/w. As described more fully below, carbonaceous material having such a water content may be ideal for the later digestion processes and may eliminate the necessity and cost of re-wetting dried carbonaceous material. This may further save energy that would otherwise be expended to wet completely dry carbonaceous material that is typically supplied to refining plants. In one aspect, the water content may be further reduced at a preparation plant by use of a microwave drying unit and/or centrifuge to lower the expense of transporting the carbonaceous material to an off-site refining plant. In this aspect, the water content of the carbonaceous material maybe approximately 7% w/w.
Once the carbonaceous material possesses water at a desired level, it may be transported by a conveyor or other appropriate device to an elevated height to be dropped into storage sacks, vessels, tanks, trucks, containers, and the like (storage containers 128). As described above, since the carbonaceous material feedstock production unit 100 may be movable or portable, the units described above may be mounted on a vehicle, such as a trailer 130. This enables the carbonaceous material feedstock production unit 100 to be moved from one site or preparation plant to another for supplying the later processes described herein with carbonaceous material of a desirable size and water or moisture content, while reducing the waste stream going to settling ponds, for example. In one embodiment, once the storage containers 128 are filled they may be loaded or moved to another vehicle (not shown) and may be transported to a microwave drying unit or digestion unit further described below. In one embodiment, the carbonaceous material feedstock production unit 100 may further include a centrifuge unit 132 for accepting a feed of carbonaceous material from the vibratory screen unit 120 for further reducing the moisture and/or water content of the carbonaceous material.
FIG. 2 illustrates an embodiment 200 of a microwave drying unit according to the present invention. In one embodiment, the system for refining carbonaceous material includes a microwave drying unit 200 and in another embodiment the system for refining carbonaceous material does not include a microwave drying unit 200. In this embodiment, storage containers 202 and 128 are emptied into a hopper 204 that feeds a conveyor 206 that passes through the microwave unit 208 for providing additional lowering of the water content of the carbonaceous material should it be desired. After exiting the microwave unit 208, the carbonaceous material may be transported via conveyor 212 to a hopper 214 for feeding to the next process unit. Hoppers 204 and 214 may be vibratory hoppers for unsettling clumped together carbonaceous material. In one embodiment, the microwave drying unit 200 may further include a centrifuge unit 216 for accepting a feed of carbonaceous material from the microwave unit 208 for further reducing the moisture and/or water content of the carbonaceous material. In another embodiment, additional centrifuge units may be used with the microwave unit 208, such as just before the microwave unit 208, for example
FIG. 3 illustrates an embodiment 300 of a digestion unit according to the present invention. Digestion unit 300 may include a conveyor 302 for transporting the cleaned and sized carbonaceous material to moisture balancing unit 346. The moisture balancing unit 346 may include a source of water and steam that controllably increases the moisture content of the cleaned and sized carbonaceous material. In cases where the moisture content of the carbonaceous material is reduced for transportation purposes, then the moisture balancing unit 346 may add moisture to the carbonaceous material. In one example, the moisture balancing unit 346 may produce carbonaceous material with a preferable moisture content of from about 7% to about 40% w/w, and more preferably a moisture content of from about 25% to about 35% w/w. After the moisture content has been adjusted or balanced in the moisture balancing unit 346, it may be fed to a conveyor 302, which transports the carbonaceous material to one or more digestion vessels 304, 308, and 310.
In one aspect, at the base of the conveyor 302 is a load cell 316 for weighing the carbonaceous material that enters the conveyor 302. Digestion unit 300 includes an acid mixture solution that is transported from an H₂SiF₆adjustment tank 712 (FIG. 7) via pipe 318. The acid mixture solution is fed into the digestion vessel 304, which includes a mixer 312 and a heater 314. The carbonaceous material is fed into the digestion vessel 304 and the digestion of the carbonaceous material is started. A valve 306 may be used to switch the carbonaceous material/acid mixture solution between the digestion vessels 304, 308, and 310. In one aspect, the digestion vessels 304, 308, and 310 may be gravity fed from one to another or pumped by pumps as described herein.
The carbonaceous material and acid mixture solution may then be fed into one of the digestion vessels 308 and 310 where the carbonaceous material is further digested. The digestion vessels 308 and 310 also include heaters 324 and 326, respectively, and mixers 322 and 326, respectively. The heaters 314, 324, and 326 are used to maintain the temperature of the digestion of the carbonaceous material in the digestion vessels 304, 308, and 310. The heaters may be steam fed heat exchangers as are commonly known in the art.
By having downstream digestion vessels 308 and 310, the carbonaceous material/acid solution mixture may be further digested while a new batch is being loaded into digestion vessel 304. Additionally, if a carbonaceous material/acid solution mixture is not in specification, it may be dumped to one of the digestion vessels 308 and 310 for further treating without holding up the digestion in the digestion vessel 304. Further, the carbonaceous material/acid mixture solution may be then moved or pumped to digestion vessel 310, which may be used to further the digestion of the carbonaceous material/acid mixture solution or may be used as a hold, stage, or surge vessel for feeding a centrifuge 328 via pipe 330, which may have a capacity or volume that is less than the digestion vessels 304, 308, and 310.
In one embodiment, the digestion vessels 304, 308, and 310 further include condensation loops or circuits 348 that may take any acid mixture solution that is vaporized in the digestion vessels 304, 308, and 310. The condensation circuits 348 may include condensation units, such as coolers, for condensing the vapor or gaseous acid mixture solution for storing in the present system for refining carbonaceous material. Separators, commonly known in the art, may further be used to separate the different components or compounds of the acid mixture solution. In another embodiment, catalyst beds may be used with the condensation circuits 348. In one aspect, the acid mixture solution may contain multiple acid compounds, such as HF and H₂SiF₆, that may be separated from each other by use of temperature controlled separators that separate the different compounds by temperature specific distillation. This separation may be controlled by controlling the temperature and ratio of the acid compounds within the separators. In addition, the metals digested out of the carbonaceous material may be precipitated at different pH levels and then filtered from the carbonaceous material/acid mixture solution.
In the above described embodiment, the present system for refining carbonaceous material may include multiple digestion vessels that are in series, one feeding the carbonaceous material/acid mixture solution to another downstream digestion vessel. In this embodiment, the carbonaceous material/acid mixture solution may be batched in a way to have a continuous flow downstream, which may be important for feeding a continuous centrifuge 328 via pipe 330, for example.
In another embodiment, the present system for refining carbonaceous material may include one digestion vessel by itself, such as digestion vessel 304. In this embodiment, no further downstream digestion vessels are fed the carbonaceous material/acid mixture solution and it is fed directly to a centrifuge 328, for example.
In yet another embodiment, the present system for refining carbonaceous material may include multiple digestion vessels that are in parallel that feed concurrently or simultaneously the carbonaceous material/acid mixture solution to the centrifuge 328, for example. In this embodiment, the digestion vessels 304, 308, and 310 are each individually fed the carbonaceous material/acid mixture solution from the conveyor 302.
Preferably, the acid mixture solution comprises HF and H₂SiF₆in a range of proportions. In one example, the HF is present in a range preferably from about 2% to about 20% w/w, and more preferably from about 5% to about 15% w/w. The H₂SiF₆is present in a range preferably from about 10% to about 58% w/w. Preferably, the HF is present in a range of from about 5% to about 12% w/w, and more preferably in the range of from about 8% to about 10% w/w and the H₂SiF₆is present in a range preferably from about 30% to about 38% w/w, and more preferably from about 22% to about 32% w/w. The balance of the mixture is water. So for example, an acid mixture solution that includes 10% HF and 35% H₂SiF₆will have a H₂O content of 55% taking into account the moisture of the carbonaceous material being fed into the digestion vessels, in one aspect. Preferably, the acid mixture solution includes these mixed portions of HF and H₂SiF₆prior to mixing them with the carbonaceous material
In another embodiment, a fluorine acid solution can be prepared from a solution of H₂SiF₆plus H₂O as the base acid to which anhydrous HF acid is added so that both of these reactive acids are in one solution. Some exemplary ranges of the acids are from about 5%-34% w/w H₂SiF₆, 32%-90% w/w H₂O, and 5%-34% w/w HF acid. In one aspect, a fluorine acid solution is prepared from a saturated solution of H₂SiF₆in water and adding gaseous anhydrous HF acid. In another embodiment, SiF₄maybe reacted with H₂O to form H₂SiF₆.
In one embodiment, the digestion vessels 304, 308, and 310 may be operated at temperatures of from about 10° C. to about 125° C. and at a pressure of from about 0 kPa to about 105 kPa. In another embodiment, the temperature of the digestion vessels 304, 308, and 310 maybe preferably in the range of from about 55° C. to about 85° C., and more preferably in the range of from about 70° C. to about 85° C.
In one embodiment, the carbonaceous material/acid mixture solution is agitated or stirred in the digestion vessels 304, 308, and 310 for preferably from about 20 to about 80 minutes, and more preferably from about 40 to about 60 minutes.
The digestion vessels 304, 308, and 310 may be made of a material that withstands the chemicals contained in them. For example, the digestion vessel 304 may be made from a blend of plastic and carbon fiber composites or any structural material lined with any material that is impervious to the corrosive effects of the acid used.
The treated carbonaceous material has a specific gravity lower than the carbonaceous material/acid mixture solution, thus the treated carbonaceous material may float to the top of the carbonaceous material/acid mixture solution in the digestion vessels 304, 308, and 310 when the mixers 312, 322, and 324 are turned off. Unreacted iron sulfide and other un-dissolved heavy metal salts whose specific gravities are greater than the acid mixture solution may fall to the bottom of the digestion vessels 304, 308, and 310 if the agitation is stopped by turning off the mixers 312, 322, and 324. In one embodiment, the specific gravity of certain carbonaceous material, such as coal, is approximately 1.3 and the acid mixture solution is approximately 1.2 when entering the digestion vessel. After digestion, the carbonaceous material then typically has a specific gravity of 1.1 and the specific gravity of acid solution is 1.2 entering the centrifuge 328. In addition, during the separation process, the treated carbonaceous material acts as a filter to the metal fluorides and/or metal fluorosilicates that are contained in the acid mixture solution.
In one embodiment, the pipe 330 is connected to a pump 332 that pumps the carbonaceous material/acid mixture solution to the centrifuge 328. Preferably, the pump 332 pumps the carbonaceous material/acid mixture solution without degrading the particle size. In one aspect, the pump 332 is a peristaltic pump.
In one aspect, the centrifuge 328 may include several different stages. For example, it may spin at a speed sufficient to remove the acid mixture solution from the carbonaceous material in a first stage. In a second stage, water supplied from a de-ionized water supply 336 and/or a rinse water supply 334 may be used in washing the carbonaceous material. Preferably, this rinse water may be applied to the carbonaceous material while it is being spun inside of the centrifuge 328. The water used in this cycle may be heated before it is input into the centrifuge 328. For example, the water may be in a temperature preferably from about 30° C. to about 100° C., and more preferably 75° C. to about 85° C. Then, the centrifuge 328 may remove this wash water where it can be recycled after being filtered through a filtration apparatus in this second stage. The rinse water that is removed from the centrifuge 328 is sent for recycling via pipe 342 as described below. In another embodiment, the wash water removed from the centrifuge 328 may be sprayed on the carbonaceous material prior to it entering the digestion vessels 304, 308, and 310 in the moisture balancing unit 346 as the moisture content of the incoming carbonaceous material is lower than desired prior to digestion as described herein. The filtration apparatus removes some of the metal fluorides and metal chlorides, which maybe sold to other markets, such as aluminum and steel plants.
Preferably, the third stage includes injecting steam into the centrifuge 328 during a spinning process. In one embodiment, the temperature within the centrifuge 328 is preferably from about 120° C. to about 400° C. and the quantity of steam that is applied to the carbonaceous material in the centrifuge 328 may be determined by several factors, including the size or carbonaceous material particles and the speed of drum inside the centrifuge 328 to prevent slumping of the carbonaceous material within the centrifuge 328. The steam helps in removing any residual fluorides. For example, the amount of steam applied to the carbonaceous material may be determined by the residual level of fluorine required in the finished carbonaceous material. For instance, an isotrope of HF, H₂SiF₆, and H₂O may vaporize preferably from about 105° C. to about 120° C. depending on the concentrations of the individual compounds. Thus, by providing steam into the centrifuge 328 the residual HF, H₂SiF₆, and H₂O are driven off of the carbonaceous material as a vapor and recovered later via pipe 342, for example, the steam process may also start the drying stage of the present system for refining carbonaceous material.
The centrifuge 328 may further include scrapers that remove the carbonaceous material from the centrifuge 328 by scraping the carbonaceous material as it is spinning inside the centrifuge 328. Thus, the carbonaceous material exits the centrifuge 328; the carbonaceous material is then moved to a hopper 344 via a conveyor. In one aspect, it may be important not to use any conveyance means that will degredate the carbonaceous material to prevent the creation of smaller undesirable fines. The moisture content of the carbonaceous material at this point may be from about 4% to about 12% w/w.
FIG. 4 illustrates an embodiment 400 of a drying unit according to the present invention. The drying unit 400 includes a dryer 402 that may further dry the carbonaceous material produced by the digestion unit 300. The carbonaceous material from the hopper 344 is fed into the dryer 402 where the carbonaceous material is subject to air flow of a desired velocity and temperature. After a residence time the carbonaceous material then exits the dryer 402 and is fed to a hopper 406 where it may be elevated above a final packaging and product unit 500 that may include a load cell or scale 504 for weighing the finished carbonaceous material that is placed in a storage container 502 as shown in FIG. 5, or sent to bulk storage, where the almost pure and dried carbonaceous material is ready for the next stage, fuel activation and the like.
In one embodiment, dryer 402 may be a fluidized bed that is generally a density dependent unit, like a teeter bed, that has air flowing from the bottom to the top of the fluidized bed dryer that pulls the lighter carbonaceous material out the top of the fluidized bed dryer for transfer to drum 410 by a cyclone 408. The carbonaceous material particles are suspended in the air flow based on their density and are dried further by this process. The medium-sized carbonaceous material particles that do not flow out the top of the fluidized bed dryer are recovered at the bottom of the fluidized bed dryer for transfer on conveyor 404. The fluidized bed dryer includes a weir that controls the height of carbonaceous material inside the fluidized bed dryer. Conveyor 404 may be a vacuum conveyor as is known in the art. In one aspect, the smaller-sized carbonaceous material particles that exit the top of the fluidized bed dryer may be approximately 200 microns or smaller. To control the separation of the particle sizes through the fluidized bed dryer, the air flow may be adjusted. A higher air flow through the fluidized bed dryer will produce larger-sized carbonaceous material particles exiting the top of the fluidized bed dryer, while a lower air flow will produce smaller-sized carbonaceous material particles exiting the top of the fluidized bed dryer. In addition, the smaller-sized carbonaceous material particles may be fed into storage container, such as sacks and the like.
In another embodiment, the dryer 402 may be a number of designs so long as there is air flow and carbonaceous material movement, the temperature of the dryer 402 may be preferably in the range from about 100° C. to about 160° C., more preferably from about 120° C. to about 140° C., the temperature may be high enough to drive off most of the moisture and some of the tars in order to liberate the residual fluorine to a level close to the inherent value of the original carbonaceous material.
FIG. 6 illustrates an embodiment 600 of a vapor recovery unit 600 according to the present invention. The process water produced by the system for refining carbonaceous material may be fed to a scrubber 602 where air is pulled through the scrubber 602 to remove any additional light volatile vapors from the process water. The air flow through the scrubber 602 is provided by blowers 608 which are fed to a stack 610. The stripped process water may be returned to the top of the scrubber 602 via pump 612. Additionally, the stripped process water may be fed to the moisture balancing unit 346 to be used as a feedstock for increasing the moisture content of the carbonaceous material within the moisture balancing unit 346.
FIG. 7 illustrates an embodiment 700 of a feedstock storage unit according to the present invention. The feedstock storage unit 700 includes a de-ionized water storage tank 702 for holding de-ionized water that is used in the system for refining carbonaceous material. For example, de-ionized water is fed from de-ionized water storage tank 702 to centrifuge 328 via pipe 704. Feedstock storage unit 700 further includes a HF storage tank 706 that feeds HF acid via pipe 708 to a HF adjustment tank 710 and a H₂SiF₆adjustment tank 712 may further include heaters to heat their respective acid mixture solutions after blending the acid mixture solution to a desirable strength. The H₂SiF₆adjustment tank 712 may further be fed H₂SiF₆in a more concentrated form that is stored in a H₂SiF₆storage tank 714. Once the desired strength of acid mixture solution is achieved, then it is piped via pipe 716 to digestion vessel 304 for mixing with carbonaceous material. In addition, HF adjustment tank 710 may feed a reduced strength of HF to the centrifuge 328 via pipe 718. Also, feedstock storage unit 700 may further include a rinse water collection tank 722 that contains rinse water collected from the system for refining carbonaceous material. This rinse water may be fed to centrifuge 328 via pipe 720. Additional vessels 724 and 728 may be used to contain caustic compounds, such as bases, for neutralizing any acid spills or reducing the strengths of the acids of the system for refining carbonaceous material Such bases may be fed to the digestion vessel 304 via pipe 726.
FIG. 8 illustrates an embodiment 800 of an ultrasonic unit according to the present invention. In one embodiment, the digestion vessels 304, 308, and 310 may include a pipe 802 that takes a stream of the carbonaceous material/acid mixture solution and pumps it through the pipe 802 through a source of ultrasonic waves 804 for improved penetration of the acid mixture solution into the micropores and macropores of the carbonaceous material. In one aspect, the source of ultrasonic waves 804 may be a water bath that is subject to a source of such ultrasonic waves, thus imparting the ultrasonic waves through the pipe 802 for improved penetration of the acid mixture solution. In one embodiment, the wave signals are square to improve such penetrating and digesting action.
FIG. 9 illustrates an embodiment 900 of an ultrasonic unit according to the present invention. In this embodiment, a source of ultrasonic waves 902 is placed upon the pipe 102 prior to entering the vibratory screen unit 104.
In one embodiment, the frequency of the source of ultrasonic waves 804 and 902 is from about 80 KHz to about 100 KHz. In one example, an opening of a macropore of carbonaceous material may be approximately 1 micron and it has been found that a frequency of 100 KHz source of ultrasonic waves 804 and 902 will cause the acid mixture solution to penetrate the macropore opening. Additionally, as the acid mixture solution is pumped into the macropores of the carbonaceous material, pressure is created within the macropore causing the acid mixture solution to be pumped out once the pressure becomes greater within the macropore than outside the macropore. This pumping action provides for improved penetration and digestion of contaminants of the carbonaceous material. The source of ultrasonic waves 804 and 902 may be generated by ultrasonic transducers as well known in the art. In one aspect, these transducers may be in contact or communication with a water bath, which transfers the wave action to the water, which then transfers the wave action to the pipe, and so on, to provide the pumping action to the micropore and macropores of the carbonaceous material. This reduces the need for mechanical agitation and provides for improved digestion times. The frequency of the source of ultrasonic waves 804 and 902 causes cavitations, cavitation bubbles, and/or cavity bubbles within the acid mixture solution such that they are the size or smaller than the typical openings of the macropores of the carbonaceous material. In general, the higher the frequency the smaller the cavitation bubbles. If the cavitation bubbles are too large, they may tend to pulverize the carbonaceous material to smaller sizes that may not be desirable to the process. In one embodiment, source of ultrasonic waves 804 and 902 are capable of producing power from about 250 watts to about 16,000 watts with a frequency of from about 10 KHz to about 50 KHz. The ultrasonication may be performed at an increased pressure over ambient pressure using a feed pump and adjustable back-pressure valve next to the pipe where it is desired to operate.
In addition to the aforementioned aspects and embodiments of the present system for refining carbonaceous material, the present invention further includes methods for refining carbonaceous material. FIG. 10 illustrates an embodiment 1000 of a method for refining carbonaceous material. In step 1002, an acid mixture solution is prepared by mixing HF, H₂O, and H₂SiF₆to a desired proportion. In this step, stored concentrated HF and H₂SiF₆may be individually pumped to individual vessels where the concentration of each is reduced with water or a base. Then, these reduced concentrations of the HF and H₂SiF₆may be combined into a vessel that then mixes and heats the mixture of HF, H₂SiF₆, and H₂O. In this step the exact amount of acid mixture solution is prepared for a specific amount of carbonaceous material to be digested.
In step 1004, the carbonaceous material is prepared by sizing a source of carbonaceous material, such as a preparation plant settling pond stream. This step further includes wetting the carbonaceous material with H₂O to a desired content, such as from about 8% to about 10% w/w. This step may further include the application of ultrasonic waves to the carbonaceous material during prior to or during the sizing operation.
In step 1006, the carbonaceous material and acid mixture solution are combined in a digestion vessel which is temperature and pressure controlled. This step may further include transferring the carbonaceous material/acid mixture solution to a second digestion vessel for additional digestion time. This step may further include transferring the carbonaceous material/acid mixture solution to a third digestion vessel for addition digestion time. This step may further include the application of ultrasonic waves to the digestion vessel or to a roundabout or circuit pipe that takes a stream of the carbonaceous material/acid mixture solution out of the digestion vessel and then later inputs it back into the digestion vessel after the application of ultrasonic waves for improved digestion.
In step 1008, the carbonaceous material/acid mixture solution is transferred to a centrifuge for removal of the acid mixture solution. This step may further include spraying rinse water into the centrifuge for washing any residual acid mixture solution from the carbonaceous material. This may be followed by additional centrifuging until the carbonaceous material has a desirable moisture content.
In step 1010, the carbonaceous material may be further dried and separated based on densities to achieve the size of desirable product for a particular application or order. This step may include applying an air flow in a vertical vessel such that the less dense carbonaceous material is removed from the top of the dryer while the more dense carbonaceous material is retained in the dryer for removal to a storage vessel, such as a sack In step 1012, the carbonaceous material is finished and weighed into final storage containers, such as sacks for their intended purpose. The process described herein is scale independent and can be used on a micro-scale, mesa-scale, and macro-scale.
There has been described a system for refining carbonaceous material. It should be understood that the particular embodiments described within this specification are for purposes of example and should not be construed to limit the invention. Further, it is evident that those skilled in the art may now make numerous uses and modifications of the specific embodiment described, without departing from the inventive concepts. For example, different temperatures, pressures, acid mixture solution compositions, and the like may be changed or altered to fit within the present system for refining carbonaceous material described herein or other without departing from the inventive concepts.

Claims

1. A system for refining carbonaceous material comprising:

a carbonaceous material feedstock unit comprising:

a first vibratory screen unit for sizing said carbonaceous material to a desired size; a density differential separation apparatus in communication with said first vibratory screen unit for producing a carbonaceous material of less than 5% mineral content;

a digestion unit in communication with said carbonaceous material feedstock unit;

an acid feedstock unit in communication with said digestion unit for providing an acid mixture solution to said first digestion unit comprising:

a source of H₂O;

a source of HF;

a source of H₂SiF₆, wherein said HF, H₂SiF₆, and H₂O may be mixed together in predetermined ratios to form said acid mixture solution prior to being provided to said first digestion unit;

a separation unit in communication with said digestion unit for separating the digested carbonaceous material from the acid mixture solution; and

a dryer unit in communication with said separation unit for drying the digested carbonaceous material and separating said carbonaceous material.

2. The system for refining carbonaceous material of claim 1 wherein said carbonaceous material feedstock unit comprises:

a feedstock supply from a settling pond stream from one of a carbonaceous material preparation plant and a carbonaceous material settling pond connected to said first vibratory screener.

3. The system for refining carbonaceous material of claim 1 wherein the carbonaceous material feedstock production unit is a portable unit.

4. The system for refining carbonaceous material of claim 1 wherein said digestion unit further includes:

a peristaltic pump located between said digestion unit and said separation unit for pump said carbonaceous material/acid mixture solution from said digestion unit to said separation unit with minimal particle degradation.

5. The system for refining carbonaceous material of claim 1 wherein said separation unit is a centrifuge.

6. The system for refining carbonaceous material of claim 1 wherein said separation unit further includes:

an H₂O rinse for rinsing any residual acid mixture solution from said digested carbonaceous material.

7. The system for refining carbonaceous material of claim 1 wherein said separation unit further includes:

a steam rinse for rinsing any residual acid mixture solution from said digested carbonaceous material.

8. The system for refining carbonaceous material of claim 1 further comprising:

a fluidized bed density dependent unit in communication with said separation unit for drying said digested carbonaceous material, wherein said drying process separates the digested carbonaceous material based on density of said digested carbonaceous material, and wherein said drying process and separating are controllable by the velocity of air flow through said fluidized bed density dependent unit.

9. The system for refining carbonaceous material of claim 8 further comprising:

a vacuum conveyor in communication in communication with said fluidized bed density dependent unit for transporting said dried digested carbonaceous material from said fluidized bed density dependent unit to a carbonaceous material finished product container.

10. The system for refining carbonaceous material of claim 1 wherein at least one of said carbonaceous material feedstock unit and said digestion unit further comprises:

an ultrasonic wave generator for producing ultrasonic waves of a size sufficient to cause cavitation bubbles having a diameter less than the average diameter of an opening of a macropore of said carbonaceous material.

11. A method for refining carbonaceous material comprising:

providing a digestion unit;

feeding an acid mixture solution consisting of a mixture of H₂O, HF, and H₂SiF₆into said digestion unit, wherein said HF, H₂SiF₆, and H₂O may be mixed together in predetermined ratios to form said acid mixture solution prior to being fed into said digestion unit;

feeding a supply of pre-wetted carbonaceous material into said digestion unit to form a carbonaceous material/acid mixture solution;

digesting said carbonaceous material to remove contaminants, wherein said contaminants are soluble in said acid mixture solution;

pumping said carbonaceous material/acid mixture solution from said digestion unit to a separation unit;

separating said digested carbonaceous material from said carbonaceous material/acid mixture solution; and

subjecting said digested carbonaceous material to a desired velocity of a heated air flow, wherein said desired velocity of heated air flow separates said digested carbonaceous material based on density of said carbonaceous material, and wherein said desired velocity of heated air flow further dries said digested carbonaceous material.

12. The method for refining carbonaceous material of claim 11 wherein said feeding a supply of pre-wetted carbonaceous material comprises:

receiving a feedstock supply of carbonaceous material from one of a carbonaceous material preparation plant and a carbonaceous material settling pond stream.

13. The method for refining carbonaceous material of claim 11 wherein said feeding said acid mixture solution further comprises:

heating said solution to a temperature of from about 55° C. to about 85° C.

14. The method for refining carbonaceous material of claim 11 wherein said providing a first digestion unit further comprises:

providing a second digestion unit in communication with said first digestion unit for transferring said carbonaceous material/acid mixture solution for additional digestion.

15. The method for refining carbonaceous material of claim 11 wherein said separating said digested carbonaceous material from said carbonaceous material/acid mixture solution further comprises:

removing said acid mixture solution from said carbonaceous material by subjecting said acid mixture solution to centrifugal forces.

16. The method for refining carbonaceous material of claim 15 wherein said removing said acid mixture solution further includes:

rinsing said carbonaceous material with a rinse water during said centrifugal forces.

17. The method for refining carbonaceous material of claim 15 wherein said removing said acid mixture solution further includes:

rinsing said carbonaceous material with steam during said centrifugal forces.

18. The method for refining carbonaceous material of claim 11 wherein at least one of said feeding a supply of pre-wetted carbonaceous material and digesting said carbonaceous material further comprises:

subjecting said carbonaceous material to an ultrasonic wave of a size sufficient to cause cavitation bubbles having a diameter less than the average diameter of an opening of a macropore of said carbonaceous material.

19. A system for refining carbonaceous material comprising:

means for providing a digestion unit;

means for feeding an acid mixture solution consisting of a mixture of H₂O, HF, and H₂SiF₆into said digestion unit, wherein said HF, H₂SiF₆, and H₂O may be mixed together in predetermined ratios to form said acid mixture solution prior to being fed into said first digestion unit;

means for feeding a supply of pre-wetted carbonaceous material into said first digestion unit to form a carbonaceous material/acid mixture solution;

means for digesting said carbonaceous material to remove contaminants, wherein said contaminants are soluble in said acid mixture solution;

means for pumping said carbonaceous material/acid mixture solution from said digestion unit to a separation unit;

means for separating said digested carbonaceous material from said acid mixture solution; and

means for subjecting said digested carbonaceous material to a desired velocity of heated air flow, wherein said desired velocity of heated air flow separates said digested carbonaceous material based on density of said carbonaceous material and wherein said desired velocity of heated air flow further dries said digested carbonaceous material.

20. The system for refining carbonaceous material of claim 19 wherein said means for feeding a supply of pre-wetted carbonaceous material comprises:

means for receiving a feedstock supply of carbonaceous material from a settling pond stream from a carbonaceous material preparation plant.

21. The system for refining carbonaceous material of claim 19 wherein said means for feeding said acid mixture solution further comprises:

means for heating said solution to a temperature of from about to about 55° C. to about 85° C.

22. The system for refining carbonaceous material of claim 19 wherein said means for providing a digestion unit further comprises:

means for providing a second digestion unit in communication with said digestion unit for transferring said carbonaceous material/acid mixture solution for additional digestion.

23. The system for refining carbonaceous material of claim 19 wherein said means for separating said digested carbonaceous material from said carbonaceous material/acid mixture solution further comprises:

means for removing said acid mixture solution from said carbonaceous material by subjecting said acid mixture solution to centrifugal forces.

24. The system for refining carbonaceous material of claim 23 wherein said means for removing said acid mixture solution further includes:

means for rinsing said carbonaceous material with steam during said centrifugal forces.

25. The system for refining carbonaceous material of claim 19 wherein at least one of said means for feeding a supply of pre-wetted carbonaceous material and means for digesting said carbonaceous further comprises:

means for subjecting said carbonaceous material to an ultrasonic wave of a size sufficient to cause cavitation bubbles having a diameter less than the average diameter of an opening of a macropore of said carbonaceous material.