On-line remediation of high sulfur coal and control of coal-fired power plant feedstock

Abstract

With the system of the present invention, high sulfur content coal—a mixture of coal, sulfur compounds and ash (e.g., stone and slate)—is crushed, and a proportion of the higher density sulfur compounds and ash are separated from the lower density coal. The result of the separation process, the continuous supply of the separated coal mixture, is then continuously monitored for sulfur content. The system uses electronic controls to vary the proportion of sulfur compounds and ash which are separated out and removed from the coal mixture so as to maximize the economics of reducing the sulfur content, and of generating power. A centrifugal separator is used for continuously separating the relatively dense high sulfur content coal and ash from the coal mixture. This separator preferably has a substantially rotationally symmetric drum element which rotates about a horizontal central axis. The proportion of sulfur compounds and ash which are removed is controllable by controlling the particle size of the crushed coal mixture, controlling the speed of the separator and controlling the separator openings which allows the high-density material to emerge.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of application Ser. No. 09/550,560, filed Apr. 12, 2000, entitled “On-Line Remediation of High Sulfur Coal for Control of Power Plant Feed Stock At the Power Plant”, now U.S. Pat. No. 6,338,305.”

BACKGROUND OF THE INVENTION

[0002] This present invention relates to a method of removing sulfur from high sulfur coal just before it is burned at power plants in order to bring high sulfur coals into compliance levels of sulfur for electric power generation.

[0003] The burning of coal to generate power is regulated by the Environmental Protection Agency. Under current regulations coal having a sulfur content greater than 1.0% may not be burned at an electric power generating plant unless the plant is equipped with a scrubber large enough to remove much of the sulfur dioxide (SO2) from the exhaust, and even then the coal must not have more than 1.8 percent sulfur.

[0004] Sulfur in coal is mostly found combined with iron as FeS2 (also named pyrite) in the eastern part of the United States. There may, or may not, be free sulfur (sulfur in the pure state) in the coal. In all but a few cases removing a substantial part of the iron sulfide will lower the total sulfur level enough to bring the coal into compliance for generating electric power.

[0005] Further restrictions about fine particle sizes are imposed by the power plants as determined by the amount of coal fines that will pass through a ¼-inch screen opening. Typical requirements are: 1) all of the coal must pass through a 4-inch screen size (9 openings per square ft. of screen), and no more than 10 to 15 percent of the coal should pass through a ¼ inch screen size.

[0006] The reason for these restrictions is to limit the amount of small particles, and therefore the amount of moisture the coal will retain on the particle surfaces during shipment. This moisture will ultimately reach the firebox where a portion of the heat from burning the coal will be used to create steam in the firebox and rather than in the boiler.

[0007] Small particles have exponentially more surface for given weight of coal and therefore can retain much more moisture. This moisture can cause freezing during shipment and storage. If the fines are dry they can blow around and under the right conditions with a spark can explode during handling and shipping. Because of these hazards it is necessary that the removal of sulfur and other non-combustibles be done at or near to the power plant and the process protected from the weather until it is in the firebox.

[0008] In this way, crushing of the coal to small particle sizes will not add moisture from the weather and will create an opportunity for blending the cleaned coal with high sulfur coal to multiply the advantages of the process meeting environmental requirements.

[0009] Many methods have been developed to decrease the sulfur content of mined coal. Most of these methods are based on the difference in the density difference between coal and the impurities. Coal has a density ranging from 1.2 to 1.4 times the weight of water. Iron sulfide has a density of 5.0, pure sulfur 1.9, and rock and slate have densities ranging from 2.2 to 3.6. These methods use water to carry the particles through the separation process. The amount of separation is limited because of the moisture dilution of the energy available for making steam in the boiler.

[0010] Another process has shown some effectiveness in removing high-density compounds from coal by creating a fluidized bed of iron oxide with a density of about 4.0. In this process the coal floats to the surface in the fluidized bed and any iron oxide that clings to the coal is removed with strong magnets. But here again, to remove iron sulfide the coal must be crushed to a fine size—too fine to ship without gaining substantial amounts of moisture unless the industry is willing to pay extra for shipping in closed containers and store inside buildings or silos.

[0011] Miners do remove some iron sulfide at the mine. Over the years it has been noted that iron sulfide (pyrite) generally has formed in layers in the coal. If the coal is crushed using high-impact crusher some of the iron sulfide pops out of the coal as small nodules. If the sulfur content is above the limits the coal will be crushed to smaller size than required. All of the fines below a ¼-inch are then screened out. This way more iron sulfide is removed but much of the coal is thrown away. This practice makes it possible to sell the coal but it also creates another problem to store the hazardous fines that are potentially a fire hazard if stored in the open, and acid producing if stored in water.

SUMMARY OF THE INVENTION

[0012] The present invention provides an efficient system (method and apparatus) for removing sulfur from coal at the power plant by means of a continuous de-sulfuring process. With coordinated electronic controls the overall process can be controlled to produce economical feedstock and to maximize the economics for using high sulfur coals.

[0013] More particularly, the present invention comprises both a method and apparatus (“system”) for the reduction of the sulfur content of coal, for either blending with compliance, or non-compliance coal, or burning directly without being blended. With the system of present invention, the high sulfur content coal containing sulfur compounds, and perhaps pure sulfur, and non-combustibles such as stone and slate that can be separated from the lower density coal and removed.

[0014] The result of the separation process is that coal that otherwise could not meet environmental approval to be burned anywhere in the United States can now be used as continuous supply of “cleaned” coal for electric power generation. That this coal can have significant amounts sulfur removed to meet United States standards for burning in power plants. The system uses electronic controls to vary the mechanical operations to maximize the reduction of sulfur and ash content for continuously generating electrical power.

[0015] According to the invention, the coal is first crushed to a size and shape that best liberates the iron sulfide nodules. The crushed coal continuously flows from the crusher into a centrifugal separator, which is a horizontal cylinder with a slight taper enlarging in diameter as it extends away from the coal entrance. After about ⅔'s of the cylinder's length the diameter abruptly becomes smaller by about 25 percent in diameter and then continues to expand in diameter with another slight taper.

[0016] The cylinder's taper, the coal feed rate, and rotational speed, combined to determine the rate of coal flow through the centrifuge, are the main variables used to control the process. The separation of the heavy minerals, i.e. Iron sulfide, rock and perhaps pure sulfur, occurs in this first tapered cylinder with the heavier minerals building up against the inside wall. When the unwanted minerals reach a depth of a couple of inches, ports located around the largest diameter of the first tapered cylinder are opened for a brief period. The high-density minerals spin out of the centrifuge into a “catcher” ring that first slows their speed and then directs them into a container. The cleaned coal continues on into the last tapered cylinder where it leaves the end of the centrifuge into a catcher that directs it on to a conveyor belt that takes it to the firebox.

[0017] Hence, the present invention is directed to lowering the amount of sulfur and other contaminants from coal, using a separation and recovery process at the power plant that is electronically controlled and continuous, and whose end product is a lower cost feed stock for boiler fireboxes.

[0018] For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1, comprised of FIG. 1A and FIG. 1B, is a schematic diagram of the preferred embodiment of the apparatus and method (system) according to the present invention.

[0020] FIG. 2 is a perspective view of one side of a centrifugal separator which may be used in the system of FIG. 1.

[0021] FIG. 3 is a perspective view of the opposite side of the centrifugal separator of FIG. 2.

[0022] FIG. 4 is a side elevational view of the centrifugal separator of FIG. 2.

[0023] FIG. 5 is a transverse cross-sectional view of the centrifugal separator of FIG. 2 taken along the line A-A of FIG. 4.

[0024] FIG. 6 is a longitudinal cross-sectional view of the centrifugal separator of FIG. 2 taken along the line B-B of FIG. 5.

[0025] FIG. 7 is a representational diagram of a device for closing circumferential outlet openings in the centrifugal separator of FIG. 2.

[0026] FIG. 8, comprised of FIG. 8A and FIG. 8B, are cutaway views showing details of the device of FIG. 7.

[0027] FIG. 9 is a cross-sectional view of the centrifugal separator of FIG. 2 taken along the line C-C of FIG. 6.

[0028] FIG. 10, comprised of FIG. 10A and FIG. 10B, are cross-sectional diagrams showing the various air lines within the spokes of the separator of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The preferred embodiments of the present invention will now be described with reference to FIGS. 1-10 of the drawings. Identical elements in the various figures are designated with the same reference numerals.

General Description of the Apparatus and the Functions of the Components

[0030] FIG. 1 is the schematic diagram of the preferred embodiment of the apparatus according to the present invention. A conveyor belt 1 deposits as-shipped high sulfur raw coal 2 into the cage mill crusher 3 and into the rotating cage bars 10 (not shown) powered by an electric motor 11. The crushed coal exits at 21 onto a conveyor 23 to drop through an enclosed chute 24 into a separator 25.

[0031] Along this route are a water spray nozzle 4 and an automatically controlled valve 5 for the time it is used to prevent dust in the air that might cause an explosion. There is also a sampling device (not shown) of the type produced by TEMA Systems that removes a uniform sample of coal from the conveyor belt after the coal has been crushed. This sample can be analyzed in two or three minutes and the results automatically supplied to a computer control system 8. Faster Systems are also available commercially.

[0032] The coal at power plants is typically analyzed every day or every eight hours because the power plant generally uses only one coal supplier at a time. This would guide the initial settings for the crusher and the separator but a more timely and sophisticated analysis method is required to respond faster for better control of the separator's operating settings.

[0033] The separator 25 is rotated about a horizontal axis by an electric motor 15. The speed of this motor, and thus the rotational speed of the separator, is controlled by the electronic control device 8.

[0034] Since a proportion of the particles of the dense high sulfur compounds and ash are separated out and removed from the particles of less dense coal, the percentage of high sulfur compounds and ash forming compounds in the separated coal mixture is reduced.

[0035] This separated coal mixture, with any water, leaves the separator at a second outlet 28 and is directed to a conveyor belt 29. This separated coal mixture may contain more fines than would be safe in a coal reclaiming process at a mine, as the fines are not intended for shipment or storage, but the coal mixture with the fines can be immediately used as feedstock if the system is located at a power plant.

[0036] The separated coal mixture on the conveyor 29 is analyzed for sulfur content by known means 30, such as x-ray spectrometer, x-ray fluorescence, or x-ray diffraction devices. When using x-ray fluorescence, the level of sulfur may be determined indirectly by measuring the high molecular weight of iron in the iron sulfites. Sensor means 30 are connected to the electronic control means 8 for continuous monitoring of the sulfur level, and the percentage volume lost in this sulfur reduction process. Based on the actual sulfur levels, the electronic control means 8 can adjust the coal input rate and/or the water spray and/or the crusher speed and/or the particle screen to adjust particle size and/or the separator speed and/or the high density outlet openings of the separator to permit more or less high density sulfur compounds and ash to emerge from the separator.

[0037] Although FIG. 1 illustrates a centrifugal separator, other alternative means for separating may be used, such as a number of smaller cyclone separators.

[0038] From the conveyor belt 29 the separated coal mixture (and any water) are directed to a conveying means 32, preferably with scoop-like appendages 33, to transport the coal mixture to drier feed means, such as chute 34, of a centrifugal drier 35. Most of the flowable water traveling with the coal mixture is eliminated before entry into the drier, such as by draining through the apertured conveyor belt 29 or apertured conveying means 32. All water may be directed to a drain 36 and, if desired, may be recycled and reused in the system. Any water extracted through the spin dryer 35 may also be supplied to the drain 36, and added to the water to be recycled. The drier outlet 37 leads to means, such as conveyor 38, for supplying the feedstock to a power plant or to a transport or storage facility.

[0039] Finally, the separated coal mixture is analyzed by known means 40, such as those described in the U.S. Pat. No. 4,817,021, for continuously determining the moisture content of the coal mixture to keep it within the acceptable parameters for feedstock. For example, the monitoring device may use an AC signal generator connected across two electrodes remote from the coal mixture, but generating an AC field passing through the coal, and a measuring device to detect the AC impedance, radio frequency loss or dielectric loss, for deriving the moisture content of the coal mixture. The means 40 are connected to the electronic control 8 which adjusts the water inflow by means of the valve 5 and adjusts the speed of the centrifugal drier by controlling the drier motor 39.

[0040] When the coal mixture leaves the drier it may be conveyed to the power plant's existing crushers where it is reduced to a fine powder that is blown into the firebox. The coal mixture may also be combined with low sulfur coal from the plant's Compliance coal stockpile. The precise blend can be determined by sulfur and moisture content of the mix and economic factors.

[0041] This system uses many known types of equipment except for the centrifugal separator which will be described below.

[0042] The entire apparatus should be placed in, or near to, a power plant to produce lower sulfur coal for storage or for a continuous supply of feed stock for the power plant. The required services are:

[0043] 1) To be near or on the inside of the power plant, sheltered from weather and excessive moisture;

[0044] 2) Electric power, 440 or 220 volts, three phase;

[0045] 3) A source of water to mist over the coal if dust becomes a problem and to deal with any potential fire threat in the building not related to electrical apparatus;

[0046] 4) Weather protected means of conveying the clean coal to the fireboxes; and

[0047] 5) A dry storage area for the non-combustibles removed from the coal, which can in some circumstances, ignite any attached combustibles caused by the chemical reaction of water with iron sulfide.

[0048] The apparatus depicted in FIGS. 1A and 1B operates continuously to remove sulfur and other non-combustibles, such as rock, slate, and sand, from a supply of high sulfur coal having varying sulfur content. The coal will have been analyzed before it arrives at the crusher. For most types of coal, the “Cage Mill” type crusher is preferred because the high impact of the cage bars on relatively small particles tends to break out the iron sulfide nodules and produces a uniform size of coal with only a small percentage of fines and dust.

[0049] This uniform particle size makes centrifugal separation much more effective for most coals. The cage mill crusher also tends to produce rounded corners on the particles, which enhance the separation process.

[0050] Cage mills are built with 2, 4 or 6 sets of cages. Each set of cage bars rotates in the opposite direction from its neighboring cages such that the particles are batted back and forth until they are small enough to pass through the cages and the screen openings at the bottom of the crusher. The present system will typically use 4 cages. Other types of crushers can be used but the first choice is the cage mill. One of the key variables of the process is the consistent average size and a minimum of fines and the rounding of the particles. There is a wide range of size settings available with the cage mill. The size can be varied by changing the speed of rotation of the cages and by changing the size of the openings in the bottom exit screen.

[0051] The amount of coal supplied by the conveyor 1 is controlled by means of a variable speed motor 6 on the conveyor drive, controlled in turn by the computer control device 8.

[0052] The crushed coal and impurities are passed down chute 21 to a belt lifting conveyor 22 with scoop-like appendages 23, transferring it to a chute 24, that carries it into the inlet of the centrifugal separator 25. The crushed coal should be dropped from a height that allows it to gain enough speed from the fall to help it approach the speed of rotation near the entrance to have the coal enter traveling in the direction of rotation of the centrifuge.

[0053] In the rotating centrifugal separator, the high-density particles FeS2 (4 times more dense than coal), rock (2 to 3 times heavier), slate (1.5 to 2.2 times heavier), and even pure sulfur (1.3 times heavier than coal) push aside the lighter density coal and build up on the inside of the rotating cylinder. As the coal and heavy particles move toward the larger diameter end they are removed through controllable ports 26. The sharp reduction in diameter of the second cone restricts any further advance of the high-density particles but allows the coal to advance to the end of the body of the centrifuge and exit through the catcher 28. The catcher slows the coal particles and directs them onto the conveyor belt taking them to the firebox.

[0054] The high-density compounds that collect against the inner wall of the centrifuge (see FIG. 6) build to an ever thickening layer until the exit ports 26 are opened to discharge the unwanted high-density materials. The ports are opened for only a few seconds to prevent coal from escaping. Removing 2 percent of sulfur (by weight) as iron sulfide means removing 5.26 percent of the total weight because of the iron content. But because of the much higher density of iron sulfide, the volume of the iron sulfide is less than 2 percent of the total volume of the coal Therefore, the volume extracted from the coal is about 1.5 percent.

Description of the Centrifuge as Shown in FIG. 6

[0055] The goal of bringing high sulfur coal into Government compliance can be accomplished generally by removing half, or slightly more, of the iron sulfide. Removing any part of the other non-combustibles is a small bonus for the power plants. The iron sulfide recovered can often be sold to chemical companies for use in making sulfuric acid.

[0056] The cleaned coal on the conveyor 29 is analyzed for sulfur, iron and ash content using known sensor means 30 such as an x-ray spectrometer. If it can't be done on the conveyor belt, for reasons of exposing radiation, an automatic sampler will remove a representative sample and have it analyzed off of the conveyor in a small booth with radiation protection walls. The results will be sent automatically to the computer control 8. Sensor 30 readings are connected to the electronic control 8 for continuous monitoring of the sulfur level.

[0057] Based on measured sulfur levels, the computer control system 8 can: (1) adjust the speed of centrifuge rotation, (2) adjust the coal input rate, (3) open and close the exit ports of the centrifuge for removal of non-combustible matter, (4) turn the air injection on and off and adjust the air injection into the coal inside the centrifuge, (5) turn on the water misting valve at the first reading of explosion conditions because of coal dust, and (6) respond to coal feed rate needs of the power station.

[0058] Considering FIG. 6, which shows the centrifugal separator in a longitudinal cross-section through the axis of rotation, coal enters from the right through a spiral tube into the opening at 56. The coal, illustrated as the darker particles, and the high-density (unwanted) materials, illustrated as the lighter particles, all enter mixed together.

[0059] The coal progresses to the middle cone where the abrupt narrowing in the diameter causes the coal to build up until it can overflow into cone 58. This batch of coal allows time for the separation process to take place. The high-density particles begin to push aside the lower density coal until a thick layer of high-density material forms at the larger diameter end of the cone. It is then that the ports 26 are opened with the slide valves 62 with rods 80 powered by air pressure supplied through the center shaft 64, and the spokes 66 and 67, which are airfoil shaped, to the cap rings 70 around the centrifuge. These caps strengthen the main body where it is stressed the greatest. The caps also house the air cylinders 80 (FIG. 7) that open and close the ports. The ports will be closed most of the time because there is only 1.5 to 2.5 of the volume that will exit through these parts and the centrifugal force will send a large volume through the ports in very little time. The computer 8 controls the opening and closing of the ports.

[0060] The clean coal progresses through the narrow restriction of the middle cone 58 and out the end 58 into a “catcher” that slows the velocity, muffles the sound and directs the coal onto the conveyor belt that takes it to the firebox.

[0061] The high-density particles exit in much the same way through a catcher 74 and into a container to be sold for chemical content value. The container is on a roller conveyor that automatically replaces the full container with an empty one when the built-in scale (not shown) reaches a set weight.

[0062] In operation, the separator works by distinguishing and separating particles by density. In the case of removing iron sulfide from coal, the density of coal is 1.35 compared to iron sulfide at 5.0—almost 4 times heavier. With pure sulfur compared with the coal, the sulfur has a density of 1.9—less than a third heavier.

[0063] The ideal separation might be envisioned as between dried peas and steel ball bearings. Both types of particles are round and the higher peas can be easily rolled out of the way of the steel balls. However, if there is a significant amount of sand in the mix, it becomes almost impossible to separate anything. This is why the crushing is so important and the amount of fines needs to be limited.

[0064] Most of the time iron sulfide is found in nodules about the size of a BB for a BB gun. Sometimes they are smaller and shaped differently, but they are almost always either round or football shaped. Now we can compare separating BB's and grains of rice with the coal meaning that the coal must be of a size that will first liberate the high-density particles and that will allow easy operation.

[0065] The coal particles are about the size and shape of small grains of rice mixed with smaller, nearly round iron sulfide nuggets spinning around the first tapered cone 50 with a centrifugal force that can be many times greater than the force gravity. Too much force can “freeze” all of the particles in place so that no separation takes place. There should be just enough centrifugal force in the mix of particles for the separation to take place smoothly.

[0066] This is where use of the cage mill crusher helps greatly. Because coal has formed in layers over millions of years, it tends to crush into cube shaped particles after coming through the first two layers of bars in a cage mill crusher. The next two sets of bars in the cage mill tend to knock the corners off of the cubes such that the particle shape approaches that of a sphere. In the ideal situation, both the high-density particles and the low-density coal are in small spheres. That is fluidity at its best.

[0067] There are three elements in the design of the centrifuge that can be used to help improve this fluidity for the coal particles.

[0068] 1) An inside lining 68 of the centrifuge is preferably made of Ultra High Molecular Weight (UHMW) plastic that is very wear resistant and very slippery. This is the plastic that is used in place of ice to make skating rinks inside shopping centers.

[0069] 2) A sudden increase in diameter, or a step, may be provided on the inner wall of the centrifuge (not shown in FIG. 6). This may be done at two or three places about a third of the way from the coal entrance 56 of the centrifuge to the exit ports 26. These “steps”, if provided, cause all the particles to behave like small cascading waterfalls in an otherwise calm river. The “drop-off” should be small—approximately ¼ to ¾ of an inch each—but even this small drop would help increase the fluidity of the particles, especially if the coal had more than the usual amount of fines from the cage crusher.

[0070] 3) About half way between the entrance 56 and the exit ports 26, there can be a series of small holes in the supporting arms 66, 67 or in the wall of the centrifuge where short blasts of compressed air help the separation. The air pressure should be strong enough to lift the coal off of the wall but not strong enough to lift the iron sulfide. The pressure level is coordinated with the rotational speed and is controlled by the computer 8. The source of the air pressure source would come through the spokes 66, 67, the same way the air travels for opening and closing the ports through the center shaft 64. However, this air would have a separate line than the supply of air for opening the ports. Activation and switching on and off the air vents will be controlled by the computer 8 once it is determined the process is effective for a type of coal.

[0071] Again, considering FIG. 6, which shows the separator in longitudinal cross-section, it is seen that the centrifuge comprises a substantially rotationally symmetric drum element 50 having two ends 52 and 54, respectively. The first end 52 has an inlet 56 at the center thereof for the incoming coal mixture (particulate coal with sulfur compounds and ash). The opposite end 54 has a central outlet 58 for the separated coal mixture. The drum is tapered with increasing radius in the direction from the first end 52 toward the second end 54. Second outlet openings 26 are provided on the drum element at the point of greatest radius. These openings allow the discharge of the high-density unwanted material; i.e., the particulate sulfur compounds and ash forming compounds.

[0072] The openings or ports 26 can be opened and closed by means of valve elements 62 which are further illustrated in FIGS. 7 and 8. These valve elements comprise a valve member 63 which is moveable back and forth to cover and uncover the respective opening 26. The valve member 63 is actuated by a piston (not shown) within an air cylinder 80. Compressed air is alternately applied to one end or the other of the air cylinder 80, via tubes 96 and 98, to drive the piston back and forth.

[0073] The drum element 50 is supported and rotated about a horizontal central axis by a shaft 64 and six airfoil shaped axial support arms or “spokes” 66 and 67. The shaft 64 is rotated by a variable speed motor 15 (FIG. 1) that is controlled by the electronic control device 8.

[0074] The drum element 50 as well as the shaft 64 and the spokes 66, 67 are made of structural steel. However, the drum is lined on the inside with a layer 68 of an ultra high molecular weight polymer which is highly wear resistant and which forms an extremely “slippery” surface.

[0075] The opening 58 at the outlet end of the drum element 54 discharges into a hood-like collector 28 which guides the discharge coal downward to the conveyor 29 (FIG. 1). Similarly, the openings 26 discharge into a surrounding hood-like enclosure 74, which guides the high-density unwanted material into a separate receptacle or container 27. When this container is almost full, all the outlet openings 26 are temporarily closed and an empty container 27 is rolled into position under the enclosure 74 on a roller conveyor 78.

[0076] As mentioned above, the centrifuge drum element 50 is lined with the ultra high molecular weight polymer. This unique material layer 68 has a much better wear resistance than most steels and is even slippery enough and rugged enough to ice skate upon in the summer. This layer improves the ability of the various high-density particles to reach the wall because it makes it easier for them to move (slide) the lighter coal particles out of the way.

[0077] The separation process may also be augmented by incorporating into the separator air nozzles near the wall of the drum element 50 which stir the particles by blowing air through the bed of coal. The air is preferably of sufficient pressure and volume to lift the coal against the centrifugal force but not so strong as to lift the high-density materials. This feature also greatly adds to the fluidity of the particle bed.

[0078] FIGS. 10A and 10B illustrate how air is supplied to the nozzles 90 on each set of spokes 66 and 67. In particular, air is introduced into a longitudinal opening 92 in the shaft 64 and allowed to branch out through the spokes 66 and 67, respectively, to the air nozzles 90.

[0079] As explained above, the ports or openings 26 for the high-density material are covered and uncovered by the valves 62 powered by air cylinders 80. A separate compressed air line 94 passes through the drive shaft 64 and extends radially into all six of the axial spokes 66, 67. The radial lines lead to the air cylinders 80 for all twelve openings: two per spoke. These small cylinders 80 are enclosed under the support bands 70 arranged around the midsection of the centrifuge. The air is directed within the support bands 70 to the respective air lines 96 and 98 that open into the opposite ends of each cylinder. Thus, each spoke 66 and 67 has two air lines embedded in it—one for opening and one for closing the valve element 63. With normal “shop” air pressure applied to the air line 94, the small cylinders 80 can produce over 700 pounds of push or pull. Alternatively, mechanical (“hydraulic”) or electrical methods may be used to open and close the ports 26.

[0080] The operation of the pneumatic cylinders 80 is controlled by the electronic control device 8. Valves arranged in the air lines 96 and 98 and situated within the support bands 70 control the application of the air to the cylinders 80.

[0081] Control signals from the control device 8 are passed to these valves via electric lines (not shown) which are fed through a commutator on the shaft 64. The timing of the opening and the duration of the open cycle for the exit ports 26 is controlled in this manner to adjust the proportion of the sulfur compounds and ash which are removed from the coal mixture.

Materials Used in the Centrifuge

[0082] The body of the centrifuge, the outer shell, uses 321 stainless steel, which is one of the better stainless steels for welding and corrosion resistance. This is available at any steel sales organization handling stainless.

[0083] The spokes, which receive high stresses, are preferably made from IN 718, a jet engine material available from any producer, or distributor, of jet engine alloys. It is one of the strongest and widest used materials in jet engines and can be welded to stainless steel.

[0084] The chutes, conveyors and slides should be made from 316 stainless, a steel that has good strength and superb resistance to corrosion.

[0085] The UHMW Plastic for the lining of the Centrifuge can be purchased in sheet form at any commercial plastic's supplier. It is held in place mechanically by friction or clamping, or by a suitable adhesive.

[0086] The present invention is not to be considered limited in scope by the specific embodiments described above, as these embodiments are intended only to be illustrative of particular aspects of the invention. Modifications of the above-described embodiments and modes for carrying out the invention that are obvious to those skilled in the coal fired generation of power, or power generators, or coal mining and refining, are intended to be within the scope of the following claims.

Claims

1. A method of removing high sulfur compounds, ash, and pure sulfur from high sulfur coal to meet environmental standards and to recover sulfur, said method comprising the steps of:

a) crushing the coal in a way to provide uniform particle size with limiting fines, and liberate the sulfur compounds from the coal;

b) separating out a significant portion of the sulfur compounds and ash from the coal to provide clean coal for power generation;

c) determining the sulfur content of the cleaned coal; and

d) controlling the proportion of dense high-sulfur compounds and ash remaining to produce most economic, environmentally acceptable continuous supply of feedstock coal for use in a electric power generating plant.

2. The method of claim 1, wherein the size of the crushed particles is controlled to minimize the sulfur content in the separated coal.

3. The method of claim 1, wherein the maximum size of the crushed particles are controlled by the selecting one of the plurality of mesh size screens through which the particles must pass.

4. The method of claim 1, wherein the crushing step is carried out with a cage mill crusher having rotatable cage mill cages and an exit screen.

5. The method of claim 1 further comprising the step of controlling the speed of rotation of the cage mill cages and cage mill exit screen size to produce the size and shape of particles that will produce optimum separation of the sulfur compounds from the coal.

6. The method of claim 1, wherein the separating step is carried out by means of a centrifuge separator, and wherein a portion of high density sulfur compounds and ash are remove from the coal by using the best combination of speed of rotation and coal feed rate.

7. The method of claim 1, wherein the sulfur content of the cleaned coal is determined by a method selected from the group consisting of x-ray spectroscopy, x-ray fluorescence, x-ray diffraction, and digital analyses of the reflected color spectrum from a flash of intense light.

8. The method of claim 1, further comprising the steps of monitoring the water moisture content of the separated coal mixture and reducing the amount of moisture in the separated coal mixture when the moisture content exceeds a permissible level for feedstock to a power plant.

9. The method of claim 8, further comprising the step of adding water to the high-sulfur content coal mixture prior to crushing.

10. The method of claim 9, further comprising the step of controlling the amount of water added in dependence upon the moisture content of the separated coal mixture.

11. The method of claim 8, wherein the moisture content is monitored by means of a gamma ray field passing through the separated coal mixture.

12. The method of claim 11, wherein the moisture content is monitored by means of a gamma ray back scattering source and a gamma ray detector arranged to detect the gamma rays passing through the separated coal mixture.

13. The method of claim 8, further comprising the step of drying the separated coal mixture prior to monitoring its moisture content.

14. The method of claim 1, further comprising the step of continuously supplying the separated coal mixture to a firebox of a power plant.

15. A method for continuously removing sulfur compounds and non-combustibles from a continuous supply of high sulfur raw coal, prepared for immediate use as feedstock at a power generating plant, said method comprising the steps of:

a) crushing the high sulfur content raw coal mixture to produce particles of dense high-sulfur compounds, ash forming compounds, and particles of less dense coal;

b) removing a proportion of the particles of dense high-sulfur compounds and non-combustible compounds that produce ash by separating these from the particles of the less dense coal to reduce the total sulfur content to bring the remaining coal into compliance with environmental laws;

c) determining the sulfur content of the cleaned coal; and

d) automatically adjusting the particle size of the high-sulfur content coal mixture in dependence upon the sulfur content of the separated coal mixture.

16. Apparatus for cleaning a continuous supply of high sulfur raw coal comprising coal, high sulfur compounds and ash forming materials so as to maximize the economics of generating electric power therefrom, said apparatus comprising in combination:

a) means for crushing high-sulfur raw coal supplied to the power plant;

b) means for separating and removing the high sulfur compounds and minerals that form ash when heated from particles of less dense coal to reduce the sulfur-dioxide and ash in the exhaust from the burning of the cleaned coal;

c) means for determining the sulfur content of the separated coal mixture; and

d) means, responsive to the sulfur content determining process, for controlling the proportion of dense high-sulfur and ash-forming compounds which are separated and removed from the coal to produce the most economic, legally acceptable, continuous supply of coal for use in a power plant.

17. The apparatus of claim 16, wherein the separating means comprises a rotating centrifugal separator having an inlet for continuous receipt of particles of coal, an outlet for removing the cleaned less dense coal, and a series of small outlets for discharging the relative dense sulfur and ash forming compounds.

18. The apparatus of claim 16, wherein the separating means comprises a rotating centrifugal separator and wherein the proportion of high density sulfur and ash forming compounds which are separated out is controlled by adjusting at least one of (1) the size of the particles produced by the crusher (2), the rotational speed of the centrifuge and (3) the feed rate of the coal going into the separator.

19. The apparatus of claim 18, wherein the separator includes a series of outlets for removing the particles of high-density sulfur and ash forming compounds, said apparatus further comprising the means for controlling the opening and closing of the outlets for removing the high density sulfur and ash forming compounds.

20. A centrifuge separator apparatus for continuously separating sulfur and ash forming compounds from a continuous supply of raw coal after crushing it to produce optimum size and shape particles for separation, said apparatus comprising, in combination:

a) a rotating symmetrical tapered cylinder having a horizontal central axis and two ends, a first end being slightly smaller than the other end having an entrance for all product being processed, and a second having an outlet at the center thereof;

b) means for supporting said cylinder for rotation about said cylinder's central horizontal axis;

c) means for rotating said cylinder about the central axis;

d) means for continuously supplying coal in particulate form to the entrance of said cylinder;

e) means for receiving coal in particulate form from the exit of the cylinder; and

f) means for receiving the non-coal particles from a series of exit ports around the tapered cylinder at the point of greatest diameter.

21. A centrifugal separator apparatus for continuously separating sulfur compounds and ash from a continuous supply of high sulfur content coal in particulate form, said separator apparatus comprising, in combination:

a) a substantially rotationally symmetric drum element having a horizontal central axis and two ends, a first end having a first inlet at the center thereof and a second end having a first outlet at the center thereof;

b) means for supporting said drum element for rotation about said central axis;

c) drive means for rotating said drum element about said central axis;

d) means for continuously supplying coal in particulate form to said first inlet of said drum element;

e) means for continuously receiving coal in particulate form from said first outlet of said drum element;

wherein said drum element further includes at least one second outlet, arranged at a greater radial distance from said central axis than said first outlet, for preferentially discharging sulfur compounds and ash having a higher density relative to coal.

22. The separator apparatus of claim 21, wherein said drum element is tapered with increasing radius in the direction from said first end toward said second end, and wherein said at least one second outlet is arranged adjacent said second end at a position on said drum element having greater distance from the central axis than the radius of said first outlet.

23. The separator apparatus of claim 22, further comprising valve means for controlling the opening and closing of said at least one second outlet.

24. The separator apparatus of claim 21, wherein said drum element includes a steel outer casing and an inner layer formed of an ultra high molecular weight polymer.

25. The separator apparatus of claim 21, wherein the drum element has an inner surface, said inner surface including a plurality of ridges extending longitudinally, substantially parallel to said horizontal central axis, for tumbling the particulate material in said separator.

26. The separator apparatus of claim 25, wherein the inner surface has a saw-tooth shape in profile.

27. The separator apparatus of claim 21, wherein said means for supporting said drum element include a shaft disposed on said central axis and a plurality of spokes, extending from said shaft to said drum element.

28. The separator apparatus of claim 27, wherein said drive means include a variable speed electric motor, coupled to said shaft, for rotating said shaft, said spokes and said drum element.

29. The separator apparatus of claim 27, further comprising air jet means for introducing compressed air into the interior of said drum element to aerate the particulate material therein.

30. The separator apparatus of claim 29, wherein said air jet means include air passages within said shaft and said spokes.

31. The separator apparatus of claim 23, wherein said means for supporting said drum element include a shaft disposed on said central axis and a plurality of spokes, extending from said shaft to said drum element, wherein said valve means include a valve element and a pneumatic cylinder for moving said valve element with respect to said at least one second outlet, and wherein said shaft and spokes include air openings for delivering compressed air to said pneumatic cylinder.