GB2154604A - Process for producing a coal-water mixture - Google Patents

Abstract

A process for producing a coal-water mixture includes classifying the coal in an aqueous coal feedstock to form first and second coal feed streams each comprised of differently-classified coal particles, determining the distribution of coal particles in each coal feed stream and mixing appropriate proportions of the streams together, possibly in the presence of a dispersing agent, to form a coal-water mixture of a predetermined make-up. The product is comprised of at least 65% by weight coal particles, preferably 70%. The coal content may be increased and flow properties of the mixture improved by removing a minus 2-micron particle fraction (which is predominantly clay) from feedstock and mixing a minus 2-micron fraction of clean coal particles with the first and second feed streams. Feed stock coal may be rendered dilatant (eg by treatment with ozone). The process is readily operable under microprocessor control.

Description

SPECIFICATION Process for producing a coal-water mixture This invention relates to a process to produce a coal-water mixture comprised of coal particles in an aqueous liquid medium. More particularly, the present invention relates to a process for producing a coal-water mixture from feedstock formed of coal particles which can be ground, freshly-mined coal or coal salvaged from silt ponds or other sources after processing to remove clay, shale, pyrite and other minerals wherein the feed-stock is classified and/or treated to impart dilatancy to the coal particles and two or more feed streams comprised of differently-sized, e.g., classified, coal particles in a liquid medium are mixed together with a dispersing agent to form a coal-water mixture having at least 65% by weight coal particles.

One characteristic of the coal recovered from silt ponds is a substantial variation to the coal particle size distribution in a flow stream on a day-to-day basis and possibly on an hour-to-hour basis. A substantial variation of the particle size distribution of ultrafine sizes of freshly-mined coal can be expected when preparing feedstock for a process to form a coal-water mixture. The problem of variations to the particle size distribution of the feedstock exists in all currently-known methods for wet and dry grinding of coal.

In a paper entitled Rheology of High Solids Coal Water Mixture by D.R. Dinger, J.E. Funk, Jr. and J.E. Funk, Sr., 4th International Symposium on Coal Slurry Combustion, May 10-12, 1984, there is described the "rheological properties of a coalwater mixture having 98.5% coal particles at 50 mesh or less depending on the particle-packing efficiency which minimizes interstitial porosity. An equation for optimum particle-packing efficiency is derived and an algorithm developed calculating the porosity of real particle distributions. The calculated porosity was checked by pressure filtration and measurement of porosity. The specific surface area is also calculated by an algorithm. The data provides a family of particle size distributions which produce exceptional rheological properties provided that a surfactant addition is effective for dispersing the coal particles.It was found that monospheres, regardless of their size will usually pack to an average orthorhombic array of about 60% by volume. In order to shear, the structure must open or dilate to a cubic array where the porosity increases from 40% to about 48%. It was found that to prevent dilatancy, or interparticle collisions in shear, the system must be diluted so that the interparticle spacing is at least IPS - (2 < )D, where IPS is the interparticle spacing and D is the particle size.

The problem arises, however, as to the manner by which a coal-water mixture can be produced comprising at least, for example, 65% by weight coal particles and preferably 70% and up to about 82% by weight coal particles on an hourly and a day-to-day basis for reliable use. At about 65% by weight coal particles, a coal-water mixture requires the use of additional fuel such as a combustible gas when used in a power plant. However, the coal-water mixture can be economically utilized. It is, however, far more economical to provide a coal-water mixture with a coal-particle concentration of at least 70% by weight coal particles. Above 82% by weight coal particles, mechanical problems can be expected to impede delivery of the coalwater mixture by piping networks, pumps and valves.

Feedstock for a coal-water mixture is usually an aqueous coal slurry at about 20% to 40% by weight coal particles. The slurry must be dewatered to an extent sufficient to form a flowable coal-water mixture with at least 65% by weight coal and rheological properties, particularly viscosity that will not impede flow in pipelines at normal ambient temperatures, e.g., 0OC to 35"C. It has been discovered that dilatancy of coal particles can be effectively utilized for dewatering a mass of coal particles derived from an aqueous coal slurry. It has also been discovered that dilatancy can be imparted to coal particles by increasing the ratio of surface area to mass whereby a dispersing agent in a subsequently-formed coal-water mixture functions in a surprising and far superior manner to enhance the flow characteristics of the mixture.The feedstock for the coal-water mixture can be made dilatant also by removing a clay constituent that is hydrophobic and prevents dilatancy.

It is, therefore, an object of the present invention to provide a process for controlling the coal-particle concentration and optimizing the coal-particle distribution in a coal-water mixture.

More particularly, according to the present invention, there is provided a process for producing a coal-water mixture wherein the steps include forming at least first and second coal feed streams comprised of differently-classified sizes of coal particles and an aqueous liquid medium, and mixing together a portion of each stream in the presence of a dispersing and stabilizing agent to form a coal-water mixture comprising at least 65% by weight coal particles.

Preferably, the aqueous coal slurry is comprised of granular coal feedstock which is greater than 50% by weight of an aqueous liquid medium and the slurry is treated to impart dilatency to coal of the coal feed streams. The aqueous liquid medium of the slurry is less than 50% by weight of the granular coal feedstock. Usually, it will be necessary to extract fluid medium from one or more of the coal feed streams so that effective proportions of coal particles from each stream can be mixed together with a controlled quantity of liquid medium to achieve the coal-water mixture comprised of the desired percent coal particles. Separate surge vessels are used to maintain a continuous supply of the first and second coal feed streams and to control the flow of at least one of the coal feed streams in relation to the delivery of the other feed stream.The coal feed streams are first combined in a mixer where liquid medium can be added for blending of the mixture in the presence of a dispersing agent and/or a stabilizing agent to maintain a uniform dispersion of coal particles in the liquid medium.

Preferably, the coal of an aqueous coal slurry is made dilatent by increasing the ratio of surface area to mass of coal particles through treatment with a oxidant, such as ozone. The coal particles will display hydrophobic properties and clay particles will continue to display a hydrophilic property.

If clay is allowed to remain in the coal-water mixture, the effectiveness of a dispersing agent is reduced. Clay particles are a contaminant in the coalwater mixture and by removing the clay particles from the coal particles before forming the coalwater mixture, the coal particles also become dilatant. A further discovery forming part of the present invention in its preferred form is that a minus 2-micron fraction when removed from the coal particles of the aqueous coal slurry is effective for the removal of clay and effectively contributes to the dilatancy of the coal particles. The minus 2-micron fraction, particularly when using coal from silt ponds, comprise essentially only clay with some pyrite and a small amount of carbon.A minus 2micron fraction of cleaned coal, such as anthracite or bituminous, is preferably added to one of the aforesaid dilatant coal feed streams for improving flow characteristics and increasing the carbon content of the resulting coal-water mixture. Before adding a minus 2-micron fraction of coal particles, preferably to a feed stream which is comprised of the smaller coal particles, the dilatant coal particles of the feed stream are treated to reduce the moisture content. Advantageously, the moisture content is reduced by introducing the feed stream into a container at the lower end of an upwardly-inclined dewatering device. The device includes a stepped bottom plate with perforated risers that is supported to extend upwardly and connected to a drive mechanism for vibrating the bottom plate.

The dilatant coal particles advance along the plate from riser-to-riser while aqueous medium drains from the mass of coal particles retained by the risers. The dilatancy of the coal particles greatly enhances the coal-liquid separation process. Liquid can flow from a discharge opening such as can be provided by a water-discharge weir in the container at the lower end portion of the bottom plate.

These features and advantages of the present invention as well as others will be more fully understood when the following description is read in light of the accompanying drawings, in which: Figure 1 is a diagrammatic flow sheet of a practical installation for producing a coal-water mixture according to the present invention; Figure 2 is an elevational view of a preferred form of a dewatering device for use in the process of the present invention; and Figure 3 is a diagrammatic flow sheet of a further installation for producing a coal-water mixture according to the present invention.

Feedstock conducted by line 10 for the process of the present invention may be freshly-mined coal or coal salvaged from silt ponds or other suitable sources. The feedstock is processed by conventional state-of-the-art means. Sulfur and clay may be removed from the feedstock before use in the present process. If desired, batching of the feedstock may be carried out in a suitable vessel. The feedstock can be an aqueous coal slurry and delivered by line 10 to a vessel 11. In this embodiment, the feedstock is preferably at ambient temperature but can be supplied at an elevated temperature in the range of 140"F to 180OF. At an elevated temperature, the viscosity of the slurry is lower and the moisture content can be more easily controlled.

Also, a slurry which is warm can be more thoroughly mixed with the chemicals selected to form a stabilizing agent and a dispersing agent. Some of these chemicals have a liquidus temperature at about 140"F. The process of the present invention is particularly useful to form and deliver a coalwater mixture for use at a remote site at ambient temperature. The coal slurry in line 10 is preferably formed by a mixture of bituminous coal particles 150 and 0 microns and water. The aqueous slurry preferably at about 20%, usually not in excess of 40%, by weight coal particles is treated with ozone in vessel 11. The ozone is fed by line 12 into the vessel to increase the ratio of the surface area to a mass. This treatment renders the coal of the slurry dilatant.The oxidizing action of the ozone on the surface of the coal particles causes pockmarks resembling the dimpled configuration of a golf ball.

The treatment with ozone renders the coal dilatant.

Impurities in the aqueous coal slurry in vessel 11, if present, are most clay with some pyrite that comprises a minus 2-micron size fraction. The minus 2-micron fraction will also include some, e.g., 7% by weight, carbon which is an insignificant carbon loss. It is to be understood that the coal slurry in vessel 11 can be treated with other agents to achieve dilatancy. If bituminous, the coal particles have a specific gravity of between 1.26 and 1.40.

The treated slurry in vessel 11 is delivered by a line 13 to a classifier 14 which is operated to deliver, in line 15, a first aqueous coal fraction comprised of coal particles greater than 30 microns.

Preferably, the first aqueous coal fraction is a 44 micron by 150 micron coal particle fraction and a small amount of liquid medium, e.g., 16% by weight of the fraction. Usually, this first fraction will have flow characteristics of a semi-fluid slurry, e.g., wet cake, and not a liquid. The lower size limit to the particles forming the first fraction is preferably at 44 microns but can be larger, e.g., 50 to 60 microns. The upper size limit to the coal particles of this fraction can be as large as 200 to 300 microns; however particles of 150 microns or less are preferred. Line 15 is connected to deliver the first fraction of coal particles to a surge vessel 16. A minus 30-micron fraction, preferably the minus 44 micron, from classifier 14 is delivered by a line 17 to a classifier 18. Classifier 18 is operated to effect a sharp separation at 2 microns. The minus 2-micron fraction from classifier 18 is delivered by line 19 to other apparatus for processing or disposal because this fraction contains a substantial amount of ash and, therefore, is not suitable to form part of a coal-water mixture. The remaining 30 micron by 2 micron fraction of coal particles, preferably 44 by 2 micron fraction, from classifier 18 constitutes the second fraction of coal particles and is conveyed by line 21 for delivery to a surge vessel 22.

This second fraction will usually have the characteristic of a flowable viscous slurry and, therefore, a dwatering device 23, described in greater detail hereinafter, is placed in line 21 to reduce the aqueous liquid component of the second fraction down to 30% or less by weight of the fraction, and thereby increasing the concentration of coal particles in the second feed stream. The extracted aqueous liquid medium is discarded from the dewatering device by line 24. The liquid conducted by line 24 may be returned to vessel 11 for reuse to form additional quantities of the coal slurry.

Lines 15 and 21 are provided with particle-concentration monitors 25 and 26, respectively, which deliver electrical signals in lines 25A and 26A to a microprocessor 27. The monitors 25 and 26 are well known in the art, per se, and may be a sonic, a nuclear or a product-sampling type of monitor.

The surge vessels 16 and 22 are used to deliver feed streams having a substantially uniform particle distribution in each feed stream. The discharge flow of the first aqueous coal fraction from surge vessel 16 is delivered to a flow controller 28 which may be a valve, but preferably a flow-assisting conveyor or a proportioning flow controller driven by a variable speed motor which forms a control element 29. The discharge flow of the second aqueous coal fraction from surge vessel 22 is delivered to a flow controller 31 which also can be a valve, but preferably a flow-assisting conveyor or a proportioning flow controller driven by a variable speed motor which forms a control element 32.

The control elements 29 and 32 respond to separate electrical signals delivered from the microprocessor 27 on the basis of a program which utilizes the electrical signals from the monitor 25 and 26 and correspond to the concentration of coal particles in each of the first and second feed streams.

The program also utilizes electrical signals fed to the microprocessor from volume-measuring or weighing devices 33 and 34 that form part of separate delivery systems for the feed streams issuing from flow controllers 28 and 31, respectively. After weighing, the separate feed streams are combined in a mixer 35 to form a coal-water mixture. The dewatering device 23 is operated to increase the coal particle concentration in the second fraction to the extent that when this fraction is combined with the first fraction, the supply stream has a desired or greater than desired final particle concentration of the coal-water mixture. According to the present invention, the coal-water mixture is comprised of at least 65% by weight coal particles and up to about 82% by weight coal particles.The dewatering device 23 is operated by a drive which can be controlled by an electrical signal from the microprocessor to assume that the combined quantities of aqueous media in the two fractions do not exceed the desired content of aqueous media in the coal-water mixture. It will usually be necessary to control extraction of the aqueous medium by the dewatering device to compensate for quantities of aqueous media that form part of a surfactant such as a stabilizing agent and/or dispersing agent that is added to each of the first and second feed stream. Preferably, a water-soluble dispersing agent is added to the vessel forming the mixer containing quantities of each feed stream.

The dispersing agent can be selected from the group consisting of lignosulfonate, condensed polynuclear hydrocarbons or alkoxylated amine. Preferbly, the dispersing agent is a water-soluble ethoxylated, propoxylated or ethoxylated-propoxylated composition, which is mixed with the feed streams in mixer 35 to prevent physical separation of the coal particles in the coal-water mixture. The coal particles in the coal-water mixture are compacted in the liquid medium which is delivered by line 36 to a storage tank or site for final usage such as a blast furnace, boiler or the like.

The preferred dispersing agent will eliminate the need for a stabilizing agent; however, a stabilizing agent can be selected from the group consisting of attapulgite clay, branched macromolecules containing active carbonyl and hydroxyl groups. To control the supply of a surfactant, e.g., dispersing agent, an electrical signal is delivered from the microprocessor in line 37 to a controller 38, e.g., a valve or pump, for controlling the delivery of the surfactant from a tank 39 to the mixer 35. However, it is preferred to use tank 39 for supplying the preferred dispersing agent. An electrical signal is also provided by the microprocessor in line 41 for controlling a valve 42 in an aqueous fluid medium supply line 43 extending to the mixer 35. Fluid medium is added to the mixture in the mixer to adjust the density of coal particles in the final coal-water mixture to the desired extent.The combined feed streams, absent a surfactant and additional aqueous fluid medium from line 43 will typically comprise 20% to 25% by weight aqueous medium which is increased to the desired extend by the addition of a dispersing agent, preferably in an aqueous medium, and aqueous medium to produce a coal-water mixture having about 70% by weight solids.

While the foregoing description of the invention utilizes a two-stage classification, proportioning and blending of coal particles, it will now be apparent to those skilled in the art that three or more stages of classification can be used to produce a coal-water mixture. It is important to determine and control the distribution of coal particles within each size fraction, particularly the smaller size particles for subsequent mixing together of each fraction of coal particles. In this way, one can control the particle size distribution and, in turn, the density of the coal particles in the coal-water mixture derived from the princess.

As will be explained in greater detail hereinafter, the dilatant property of the coal particles forming the second feed stream greatly enhances the removal of the aqueous medium from the feed stream through the use of the dewatering device 23. However, to assure a desired carbon content in the final coal-water mixture and optimize the particle packing, particularly by the use of smaller coal particles to fill inner spaces in the coal-water mixture, it is desired to introduce a minus 2-micron coal fraction to replace the minus 2-micron fraction that was discarded in line 19. The replacement fraction should, of course, comprise essentially only coal particles which can be derived by both processing of a small subflow from one of the first or second feed stream in a ball mill.The feed stream which is selected to provide the subflow of the ball mill can vary from time-to-time based on an oversupply of one particular coal fraction due to an ever-changing coal particle size distribution forming the feed-stock. Thus, for example, should a feedstock throughout a period of time contain an overabundant supply of coal particles within the size range of 44 by 150 microns, then the first feed stream is selected to form the subflow to the ball mill. Thereafter, should the feedstock contain an overabundant supply of coal particles within the size range of 2 by 44 microns, then the second feed stream will be selected to form the subflow to the ball mill. Depending upon the source of the feedstock, a continuing over-abundant supply of 2 by 44 micron coal particles is likely to occur.To avoid depleting of the 44 by 150 micron coal particle fraction, a ball mill is used to reduce an oversize coal fraction of a separate supply of coal is used to produce make-up quantities of the insufficient coal particle fraction. Make-up quantities of a coal particle fraction are treated to impart dilatancy as described hereinbefore. Make-up quantities for the first coal particle fraction are delivered to the surge-holding vessel 22 by line 45.

In Figure 1, a subflow of the first feed stream in line 15 is delivered by line 46 through a three-way valve 47 to a header pipe 48 extending to a ball mill 49. A subflow of the second feed stream in line 21 is directed by line 51 to valve 47 which can be positioned to deliver a partial flow of the second fraction to header pipe 48 and thence to ball mill 49. A minus 2-micron coal fraction derived through the operation of the ball mill is fed by line 52 from a surge-holding vessel 53.A signal is delivered from valve 47 based on the position thereof to provide a signal to the microprocessor whereby a partial subflow in lines 46 and 51, which occurs after the particle concentration monitors 25 and 26, respectively, insures that the quantity of coal particles in the partial flows from the first or second feed stream, occurring at a fixed rate, will update the storage of information in the microprocessor to accurately indicate the quantity and partial distribution size in each of the surge-holding vessels 16, 22 and 53. This insures that the quantity of the minus 2-micron coal fraction in surge-holding vessel 53 is controlled so that this particle size fraction does not exceed an overabundant supply of about 5% or less by dry weight of a minus 2-micron coal fraction for the coal-water mixture.

Instead of deriving a subflow from either the first or second feed stream for subdividing the coal particles to form a minus 2-micron coal particle fraction, it is preferred to use a supply of coal particles, particularly anthracite coal, having a spe cific gravity of between 1.54 and 1.80 and feeding this supply of coal particles to ball mill 49 to form a minus 2-micron coal fraction which is separately introduced into surge vessel 53 in quantities sufficient to form a 5% dry weight component to the coal forming the coal-water mixture. The discharge flow of the minus 2-micron coal fraction from surge-holding vessel 53 is delivered by line 52 to a flow controller 54 which may be a valve but preferably a flow-assisting conveyor or proportioning flow controller driven by a variable speed motor which forms a control element 55.The program of the microprocessor 27 utilizes an electrical signal fed thereto from a volume-measuring or weighting device 56. After weighing, the minus 2-micron coal fraction is fed by line 57 to the mixer 35. In the final coal-water mixture, the plus 2-micron coal particles add significantly to the viscosity characteristic of the ooal-water mixture. Specifically, the viscosity is generally increased over a temperature range of between 0 C and 35"C by the addition of the minus 2-micron coal particle fraction since these particles facilitate shear between larger coal particles due to the "pockmarking" on the surface of the coal particles.The very favourable viscosity characteristics was discovered by laboratory tests which sow that an unozonized 150 by 4 micron coal-water mixture exhibited a viscosity of 4000 centipoise; whereas a coal-water mixture comprised of 150 by 2 micron coal particles which were treated with ozone, exhibited a viscosity of 2000 centipoise. The viscosity using ozonized coal particles of the coal-water mixture at 3"C was less than 900 centipoise. In view of this discovery, it is desirable to cool the coal-water mixture while mixing occurs in mixer 35. For this purpose, a watercoolant jacket 58 is arranged to withdraw heat from the mixture in the vessel during the process by the use of a motor-driven mixer 59.The mixer 35 is supported on a base by load cells 61 which provide electrical signals corresponding to the weight of the material in the mixer and are fed by line 62 to the microprocessor. The microprocessor also receives an electrical signal in line 63 from a volume-measuring device 64 such as a sonar or nuclear detector. The favourable viscosity property of the coal-water mixture is attributed to the increase in the ratio of surface area to mass characteirstic of the coal particles. The flow properties of the coal-water mixture produced according to the present invention are improved further by the addition of a minus 2-micron fraction of coal particles. This enables an increase in the carbon content of the coal-water mixture as well as improving the shear in the presence of a dispersing agent.

Turning now, to Figure 2 of the drawings, there is illustrated a preferred form of dewatering device to reduce the aqueous medium content of the second feed stream down to at least 30% or less by weight of the coal particles. Line 21 is preferably arranged vertically to discharge the second fraction below a water-pool level identified by reference numeral 70. The water-pool level is contained within peripheral side walls 71 that extend around the outer edge of a stepped plate 72 having perfo rated risers 73 arranged transversely of the plate with respect to the length thereof.The side walls 71 and bottom plate 72 form a container that is inclined 0 to 30 to the horizontal by support columns 74 that are angularly arranged and constructed with an effective length to bring about the angular arrangement of the stepped plate with respect to a support base 75. Preferably, the members 74 are supported at each of their opposite ends by hinge pins so that a drive 76 supported by the base and coupled to the stepped plate 72 can vibrate the plate at a selected frequency. Because the coal particles comprising the second fraction are dilatant, the vibratory action imparted to the stepped plate quickly forces entrained water to the surface of the second fraction within the dewatering device.A pool of water will overlie the condensed solids and a discharge weir identified by reference numeral 77 is provided for removal of excess aqueous medium from the dewatering device. As apparent from Figure 2, the weir is situated in the back wall of the dewatering device. The dewatering of the coal slurry continues throughout the time while the coal particles are advanced along the length of the pan from riser-to-riser. The length of the pan is selected commensurate with the desired extent to which the moisture content of the second fraction is to be reduced. While the dewatering device illustrated in Figure 2 is useful for removing water from granular feedstock, per se, it is particularly useful for the dewatering process to reduce the residual moisture to a desired extent for the second feed stream in the production of the coai-water mixture.A minus 100-mesh centrifuge cake of coal particles having a moisture content of 50% may be reduced to a moisture content of 28% through the use of the dewatering device shown in Figure 2.

The submerged feed to the dewatering device produces a smooth laminar movement zone of the coal cake without turbulence.

In the embodiment of Figure 3, feedstock comprising an aqueous coal slurry as described previously, is delivered, preferably at an elevated temperature in the range of 140"F to 1800F by line 110 to a classifier 112. A coal slurry at ambient temperature can be used; however at an elevated temperature, the viscosity of the slurry is lower and the moisture content can be used; however at an elevated temperature, the viscosity of the slurry is lower and the moisture content can be more easily controlled. Also, a slurry which is warm can be more thoroughly mixed with the chemicals selected to form a stabilizing agent and a dispersing agent.Some of these chemicals have a liquidus temperature of about 140"F. Classifier 112 is operated to deliver, in line 114, a first aqueous coal fraction comprised of coal particles greater than 30 microns and a small amount of liquid medium.

Usually, the first fraction will have flow characteristics of a semi-fluid slurry, e.g., wet cake, and not a liquid. The lower size limit to the particles forming the first fraction is preferably at 30 microns but can be larger, e.g., 50 to 60 microns. The upper size limit to the coal particles of this fraction can be as large as 200 to 300 microns; however particles of 150 microns or less are preferred. Line 114 is connected to deliver the first fraction of coal particles to a surge vessel 116. The minus 30 micron fraction from classifier 112 is delivered by line 118 to a classifier 120. Classifier 120 is operated to effect a sharp separation at 2 microns.The minus 2-micron fraction from classifier 120 is delivered by line 122 to other apparatus for processing or disposal when this fraction contains a substantial amount of ash and, therefore, is not suitable to form part of a coal-water mixture. The remaining 30 micron by 2 micron fraction of coal particles from classifier 120 constitutes the second fraction of coal particles and is delivered by line 124 to a surge vessel 126. This second fraction will usually have the characteristic of a flowable liquid slurry having low viscosity and, therefore, an in-line dewatering device 127 is placed in line 124 to increase the concentration of coal particles in the second feed stream by extracting liquid medium which is discharged from the process by line 127A.

The lines 114 and 124 are provided with particleconcentration monitors 128 and 130, respectively, which deliver electrical signals in lines 128A and 130A in a microprocessor 132. The monitors 128 and 130 are well known in the art, per se, and may be a sonic, a nuclear or a product-sampling type of monitor.

The surge vessels are used to deliver feed streams having a substantially uniform particle distribution in each feed stream. The discharge flow of the first aqueous coal fraction from surge vessel 116 is delivered to a flow controller 134 which may be a valve, but preferably a flow-assisting conveyor or a positive displacement pump driven by a variable speed motor which forms a control element 135. The discharge flow of the second aqueous coal fraction from surge vessel 126 is delivered to a flow controller 136 which also can be a valve, but preferably a flow-assisting conveyor or a positive displacement pump driven by a variable speed motor which forms a control element 137.

The control elements 135 and 137 respond to separate electrical signals derived from the microprocessor 132 on the basis of a program which utilizes the electrical signals from the monitors and correspond to the concentration of coal particles in each of the first and second feed streams. The program also utilizes electrical signals fed to the microprocessor from volume-measuring or weighing devices 138 and 139 that form part of separate delivery systems for the feed streams issuing from flow controllers 134 and 136, respectively. After weighing, the separate feed streams are combined in a mixer 140 to form a supply stream. The dewatering apparatus 127 is operated to increase the coal particle concentration in the second fraction to the extent that when this fraction is combined with the first fraction, the supply stream has a desired or greater than desired final particle concentration of the coal-water mixture. The final coal-water mixture is comprised of at least 65% by weight coal particles and up to about 82% by weight coal particles. The dewatering apparatus 127 is controlled by an electrical signal from the microprocessor to ad just the combined quantities of aqueous media in the supply stream. It will usually be necessary to control extraction of the aqueous medium by the dewatering apparatus to compensate for quantities of aqueous media that form part of a stabilizing agent that is added to each of the first and second feed streams.

Electrical signals are delivered from the microprocess in lines 141 and 142 to controllers 143 and 144, e.g., valves or pumps, for controlling the delivery of a dispersing agent from tank 145 to mixers 146 and 147. These mixers can be static, in-line mixers provided in lines 114 and 124, respectively, downstream of the monitors 128 and 130. The dispersing agent can be selected from the group consisting of lignosulfonate, condensed polynuclear hydrocarbons and alkoxylated amine. The dispersing agent is mixed with the feed stream in a blender 148 to prevent separation of the coal particles. The coal particles in the coal-water mixture are compacted in the liquid medium which is delivered by line 149 to a storage tank or site for final usage such as a blast furnace, boiler or the like.

The stabilizing agent can be selected from the group consisting of attapulgite clay, branched macromolecules containing active carbonyl and hydroxyl groups. An electrical signal is delivered from the microprocessor in line 150 to a controller 151, e.g., a valve or pump, for controlling the delivery of the stabilizing agent from a tank 152 to the blender 148. An electrical signal is also provided by the microprocessor in line 153 for controlling a valve 154 in a supply fluid medium supply line 155 extending to the blender 148. Fluid medium is added to the mixture in the blender to adjust the density of coal particles in the final coal-water mixture to the desired extent.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Claims (33)

1. In a process for producing a coal-water mixture, the steps including: providing an aqueous coal slurry comprised of granular coal feedstock which is greater than 50% by weight of an aqueous liquid medium, forming at least first and second coal feed streams each comprised of a different size classification of said granular coal feedstock in an aqueous liquid medium, and mixing together selected amounts of said first and second coal feed streams in the presence of a dispersing agent to form a coal-water mixture comprised of at least 65% by weight coal particles.

2. The process according to claim 1 wherein said granular feedstock comprises less than 50% by weight aqueous liquid medium.

3. The process according to claim 1 wherein said step of forming includes removing a minus 2micron particle fraction from the coal feedstock.

4. The process according to claim 1 wherein said step of forming includes discarding a minus 2micron particle fraction from the coal feedstock.

5. The process according to claim 2 wherein the first and second coal streams are dilatant.

6. The process according to claim 5 wherein said step of forming includes increasing the ratio of surface area to mass of coal particles comprising the coal feedstock.

7. The process according to claim 5 wherein said step of forming further includes removing a minus 2-micron particle fraction from the coal feedstock.

8. The process according to claim 1 wherein said step of forming includes contacting particles of the coal feedstock with an oxidizing agent to increase the ratio of surface area to mass of coal particles.

9. The process according to claim 8 wherein said step of forming the coal feedstock further includes removing a minus 2-micron particle fraction.

10. The process according to claim 1 wherein said step of forming includes forming depressed areas in the surfaces of coal particles of the coal feedstock.

11. The process according to claim 10 wherein the ratio of surface area to mass of coal particles is increased by about 5% to 7%.

12. The process according to claim 3 including the further step of providing 2 micron or less granular coal particles and supplying a controlled portion of said 2 microns or less granular coal particles for said step of mixing.

13. The process according to claim 1 wherein said step of forming at least first and second coal feed streams includes forming said first coal feed stream by processing said coal feedstock in a first classifier, forming said second coal feed stream by processing a residual coal feed stream from said first classifier in a second classifier while discarding a minus 2-micron particle fraction from the second classifier, and dewatering the second coal feed stream.

14. The process according to claim 13 wherein said step of dewatering includes feeding said second stream on the lower end of an upwardly-inclined stepped plate having transversely-extending attachments, and vibration of said stepped plate to advance said second fraction upwardly from attachment-to-attachment to separate aqueous medium from the second stream.

15. The process according to claim 14 wherein said step of dewatering further includes arranging said upwardly-inclined stepped plate at an angle of the horizontal of between 0c and 3 .

16. In a process for producing a coal-water mixture, the steps including: providing an aqueous coal slurry comprised of granular coal feedstock which is greater than 50% by weight of an aqueous liquid medium, forming at least first and second dilatant coal feed streams each comprised of a different size classification of said granular coal feedstock in an aqueous liquid medium which is less than 50% by weight of the granular coal feedstock, combining selected amounts of first and second dilatant coal feed streams, and mixing the combined amounts of dilatant coal feed streams with a dispersing agent in effective quantities to form a coal-water mixture having a viscosity that gradually increases throughout a temperature range of 00C to 35"C, said coal-water mixture being comprised of at least 65% by weight coal particles.

17. The process for producing a coal-water mixture according to claim 1 including the further step of determining the concentration of the coal particles in the aqueous liquid medium forming each of said coal feed streams.

18. The process according to claim 1 including the further step of collecting each of said first and second coal feed streams in separate surge vessels to deliver separate feed streams having substantially uniform particle distrib ution for said step of mixing.

19. The process according to claim 18 including the further step of controlling the flow of at least one of said coal feed streams from the separate surge vessels.

20. The process according to claim 19 wherein said step of mixing includes combining said feed streams and thereafter adjusting the quantity of aqueous fluid medium in the mixture of the combined feed streams in a mixer together with said dispersing and stabilizing agents to form a coalwater mixture having a desired amount of aqueous medium.

21. The process according to claim 20 including the further step of adding a dispersing agent to each feed stream before said step of mixing and adding a controlled amount of a stabilizing agent in a mixer for forming a coal-water mixture.

22. The process according to claim 1 wherein said step of forming further includes forming said first stream of coal particles having a size greater than 30 microns.

23. The process according to claim 22 wherein said step of forming further includes forming said second stream of coal particles ranging in size of at least 2 microns and up to about 30 microns.

24. The process according to claim 23 wherein said step of determining includes separately weighing unit amounts of each of said coal feed streams to produce corresponding electrical signals, and using said electrical signals for controlling the amounts of each feed stream for said step of mixing.

25. A process for separating a slurry comprised of a fluid medium fraction and a dilatant granular material fraction, said process including the steps of: introducing said slurry onto the lower end of an upwardly-inclined stepped plate, driving the fluid medium fraction toward the top of the slurry at the lower end of the stepped plate, and advancing the dilatant granular material fraction upwardly along the plate from the fluid medium at the top of the slurry.

26. The process according to claim 25 including the further step of arranging said upwardly-inclined stepped plate at an angle to the horizontal of between 0 and 3 .

27. The process according to claim 25 including the further step of arranging transversely-extending attachments along the length of said upwarldyinclined stepped plate to retain quantities of the dilatant granular material fraction while advanced upwardly from attachment-to-attachment along said plate.

28. The process according to claim 27 wherein said attachments include openings to drain fluid material from granular material retained on the stepped plate by the attachments.

29. The process according to claim 25 including the further step of controlling the level of fluid medium retained on the said upwardly-inclined stepped plate.

30. The process according to claim 25 wherein said step of driving tie fluid medium fraction includes vibrating said stepped plate.

31. The process according to claim 25 wherein said step of advancing the dilatant material in- cludes vibrating said stepped plate.

32. A process for separating a slurry comprised of a fluid medium fraction and a dilatant granular material fraction, said process including the steps of: introducing said slurry into a container, driving the fluid medium fraction toward the top of the slurry by vibrating the container to densify the granular material fraction, and withdrawing fluid medium from the top of the densified granular material fraction.

33. A process of producing a coal-water mixture, substantially as herein described with reference to the accompanying drawings.