Most coal washeries produce a fine-coal tailings stream in their operation. It is desirable but difficult to recover this fine fraction product as it often contains a large amount of unwanted mineral matter. Most washeries regard this fraction of fine coal as uneconomic to recover and dispose of it into tailings ponds. The amount of coal discarded can vary between 5-30% of the mined product resulting in significant economic losses.

PRIOR ART Recovery of fine coal agglomerates from the discard stream of coal preparation plants is well-known technology. Two stages can be distinguished in oil agglomeration.

The first consists in mixing coal slurry with oil in order to induce selective agglomeration of coal grains while leaving the grains of mineral matter dispersed. In the second stage, the coal agglomerates are separated fi-om the mineral matter by screening, filtration or flotation.

The process of oil agglomeration was employed for coal beneficiation for the first time in 1921. It was not applied in industry, however, due to its high consumption of oil (up to 30%). Research on this was resumed in the 1950's. Based on oil agglomeration, processes known as Convertol, Olifloc and spherical agglomeration were developed. Special installations for this process were also designed. In Poland, a method of oil agglomeration known as"selective flocculation of minerals"was developed. On the basis of the studies carried out so far, it can be stated that the process of oil agglomeration is affecte by the following parameters : type and quantity of the oil (bridging liquid) added, mineral composition of the slurry, grain-size distribution of the slurry, pH of the medium, presence of solid particles in the slurry, slurry/bridging liquid mixing time, mixing intensity.

Whilst there have been a number of oil agglomeration processes employed in the recovery of fine coal tailings, to date each has proven to be uneconomic and commercially unviable particularly due to the over use, hence waste, of oil used in the recovery process. The excess was either wasted or recovered by costly recovery processes rendering the oil agglomeration process uneconomic overall.

Economic efficiency of the recovery process is generally dictated by use of a minimum but effective amount of oil ensuring that there is no waste or over use.

According to the known processes, higher cost oils such as diesel fuels were used but no attempts were made to efficiently control the amount of oil used in the processing.

The amount of oil required in the process is usually dictated by the concentration of solids in the coal/water/mineral slurry. Oil agglomeration was employed in the 930's using light oils but those caused the process to be expensive necessitating recovery of the oil for re-use, increasing the overall cost of the process.

In an article entitled"Oil Agglomeration and Selective Flocculation of Coal Slurries" by Zofia Blaschke a pilot plant for oil agglomeration was described. This article disclosed that in 1978, following pilot-plant investigations which had demonstrated the technical feasibility of the selective agglomeration process, a commercial-scale plant was constructed by the Broken Hill Proprietary Company Ltd. of Australia, at its John Darling Collier. The feed capacity of the plant was 5.5 tons per hour of dry solids. The process flow demonstrate the simplicity of the design.

The semi-commercial plant treated feed material in which the average feed ash ran at about 40%. Oil was added in the form of an emulsion produced by using an ultrasonic sound. This material when treated with oil at an addition rate of 7- 8% (dry feed basis) produced an agglomerated product of 79% ash at a yield representing 60% of the feed. The agglomerated product was amenable to handling and has been stockpiled for periods of 8 months without oxidation. The tailing ash was typically in the 80-85 % range and settled rapidly to produce an extremely clear supematant liquid in contrast to the feed material which settled slowly and left a stable grey layer in the supernatant liquid. This process did not however, include a system for the controlled feeding rate of oil emulsion determined by measurement of coal concentration in the coal/waste slurry.

Another known process was described in the same article known as the Aglofloat process which is an advanced spherical agglomeration and flotation process. In this process a first run-of-mine coal is crushed to pass 600 llm and slurried with re-cycled water. Crude oil is mixed with diesel fuel to form a bridging oil. The coal slurry and bridging oil are then combine in a high shear mixer where coal and oil form micro- <BR> <BR> agglomerates about 212 y in size. The micro-agglomerates are separated from coal mineral matter and refuse in a flotation cell, and then washed and separated from pyrite particles in a hydroseparator. The demineralised micro-agglomerates are transferred to a low shear mixer where more bridging oil is added and the micro- agglomerates are enlarged to about 850-335 pm. The refuse in the flotation and hydroseparator is removed and discarded as plant reject. The process is capable of beneficiating high-ash and high-sulphur bituminous coals. An Illinois No 6 coal with 39.5% ash and 4.19% total sulphur content was reduced to a product with 68% ash and 3.7% total sulphur, a pyritic sulphur removal of 77%, and combustibles recovery of 89%.

Another process known as the Bechtel spherical Agglomeration Process was described in the same article. This agglomeration process represented the first successful application of a spherical agglomeration process for coal. The process shown in figure 2 uses heptane selectively to agglomerate hydrophobic organic coal materials from an aqueous slurry of ultrafine (less than 20 urn) coal. A petroleum based asphalt binder is subsequently added toassist in cnlarging product agglomerates to more manageable 6.4111111 to 9.5mm spherical pellets. Hvdrophilic inorganic ash-forming and pyritic sulphur mincral matter is rcjcctcd. lcaving a virtuallx coal-frcc rcfusc. Thc agglomerated coal product is then strippcd of the heptane bridging liquid bs contact with steam. Steam stripping is used to recover the heptane because heptane and steam form an azeotrope which has a boiling point (79.20C) lover than either heptane or water atone (98'C and respectively).

Thosc plants wiihout tlotation gcncrallv disposc of the ultra fine material (less than 100 µm in size) as tailings to waste. In some cases this ultra fine waste contains up to 5 bv weight of relatively low ash coal of saleable quality. It is bclicvcd that this coal constitutes a loss of 8- I () million tonncs pcr annutn at current Australian coal industrv production ratcs.

Selective oil agglomeration involves the recovery of fine particles of coal (hydrophobic) from a minera ! matter (hydrophihc) rich liquid. The modern version of the process involves adding oil (usually in an emulsified state) to an agitated fine coal water sturry. The oil coats the surface of the individual coal particles. As the oil coated particles in the agitated slurry collide the particles coalesee by formation of pendular bridges of oil. The agglomerated coal particles can then bc separated from the mineral rich liquid by either screcning or by a flotation process. None of the above processes however, disclose the use of a control system which thequantityoftheagglomeratingagentusedintherecoverregulates process.

INVENTION The present invention in one form seeks to ameliorate the problems of the known processes cxamplcs of which arc described above by providing a process for the recovery of fine coat agglomerates utilising a system for accurately controlling delivery of an agglomerating agent such as an oil emulsion responsive to measurement of parameters of a coal/water/mineral sturry to prevent over use of and the need to recover that agent.

The invention according to that form further provides a method and the equipment required for maximising the economic recovery of finc-coal agglomcratcs bv using on-line monitoring <BR> <BR> <BR> <BR> <BR> devices and control loops. together with special recover/scparation screcns.<BR> <BR> <BR> <BR> <BR> <BR> <BR> <P>The present invention further provides an economic coal recovery process utitising an agglomerating agent such as low cost oils and a laser cut screen for separating the coal agglomerates and also comprising probes which monitor condition parameters of a coal/watcr/mincral slurry to thereby control the addition of those oils.

The invention further provides a nuclear monitoring system for determining the actual amount of coal in the coal/water/mineral sturry mixture and computer control of the agglomerating agent quantity required for recovery of fine coal from the mixture According to one embodiment a first probe will measure the total solids and a second probe the quantity of dirt. In a typical slurry there might be 20-30% solids and 70-80% is fine coal : alternativcly there might bc 2%-50% solids of which 5%-60%of said solids is mincral matter.

According to the process of the invention. all of thc agglomcrating agcnt will bc uscd. obviating the need for the added step of oil recovery as occurred in certain of the prior art processes.

In fact. thc oil consumption rate according to the process of the invention has been reduced to a level such that oil recover, is not necessary to achieve commercial viabilitv of the process.

Scicctivc oil agglomoration according to the present invention includes the following advantages over convcntional froth flotation for the economic recovery of fine coal: a) thickener underflow slurry as feed can bc used with solids concentration of 15-30% by weight compared to 5 - 10% for froth flotation; thus, volumetric feed rate to the plant is lower;thereforesignificantly b) no frothing reagent is required, consequently problems experimenced in convcntional plants with froth handling and overfrothing of watcr and magnctitc circuits arc eliminatcd: c) product dcwatcring according to the selective oil agglomcration process is relatively simple and does not require high cost vacuum filtration systems : d) coal recovery by oil agglomeration appears to bc lcss susceptible to oxidation or other variable surface characteristics of coal: c) tailings produced from the plant should not require rcthickening prior to disposa) : f) full process automation is possible with relatively simple field controls and minimal operator input required; g) the process of the invention is capable of very efficient recovery of sub-micron size coal particles, h) the fine coal recovery by oil agglomeration appears to be unaffected by the quantity of flocculant added to the thickener although longer term operation of plant will be required to verify this initial observation ; i) selectivity of the agglomeration process reduces the quantity of misplaced ultrafine mineral matter collecte in the product, thereby reducing agglomerate ash level.

In one broad form the present invention comprises ; a process for the separation of fine coal tailings from a coal/water/mineral slurry emanating from a coal preparation plant or tailings pond, the process comprising ; a first reservoir for receiving and holding a coal/water/mineral slurry discharged into said first reservoir from an infeed line ; a second reservoir for receiving and holding an emulsion comprising an oil, water and/or surfactant, a pump operably connected to said second reservoir ; wherein said first and second reservoirs are in communication with a mixing tank which receives said coal/water/mineral slurry from said first reservoir and said oil emulsion from said second reservoir ; a primary separator in communication with said mixing tank; and a vibrating screen separator in communication with said primary separator and/or the high shear mixing tank; the process further comprising ; control means in communication with at least one sensor in said first reservoir ; and said pump in communication with said second reservoir, said control means also in communication with said coal/water/mineral slurry infeed line, said control means controlling said pump responsive to a signal/s from said sensors indicating conditionparametcrs of the coal/watcr/mincral slurry thereby regulating the floN-%, of emulsion into said mixing tank from said second réservoir.

According to a preferred embodiment, the control means comprises a computer processor programmed to receive signals from said sensor/s which preferabiy comprise probes immersed in said coal/watcr/mineral slurry and which detect the concentration of coal fines whereupon said processor actuates the pump on said second reservoir responsive to data determined by said probes relating to the condition of the slurrv facilitate fccding into said mixing tank of a predetermined amount of cmulsion from said second réservoir. <BR> <BR> <BR> <BR> <BR> <P>According to onc embodiment. siurry from said first reservoir is delivered to a mixer by means of a pump or an overflow conduit.

In another broad form. the present invention comprises: a process for separation of fine coal from a coal/water/mineral sherry, the process comprising: <BR> <BR> <BR> <BR> <BR> an infeed fine which delivers a coal/water/minera slurry into a first reservoir :<BR> <BR> <BR> <BR> <BR> <BR> a second reservoir for receiving and holding an oil emulsion and including a dclivcrs pump<BR> <BR> <BR> <BR> <BR> in communication therewith : a mixing reservoir in/communication with said first and second reservoirs: control means including at least onc sensing probe in contact with said coal/water/mineral slurry for monitoring parameters of said coal/watcr/mincral slurry whilst in said infccd linc and/or in said first reservoir. and an interface linking said control means with said delivery pump: wherein. said control means controls the deHvcry of said oil emulsion via said pump to said mixing reservoir responsive to measurement of the parameters. including the concentration of fine coal. of the coal/water/mineral slurw in the first reservoir said process thereby obviating the need for oil recovery.

In a further broad form the present invention comprises: an oil agglomcration proccss for separation of fine coal from a coal/watcr/mincral siurry <BR> <BR> <BR> <BR> <BR> using an agglomerating agent such as an oil emulsion : characterised in that the process inciudcs computerised control mcanswhich controls the delivery of said oil émulsion from an oil émulsion holding tank to a fccd holding tank holding said coat/watcr/mincral s) urry : at a rate determined by measured parameters of said coal/ atcr/mincral slurry. therc6 prcvcnting ovcr use of said agent in said process and obviating the ncedfor agent recovery.

In another form the present invention comprises : an oil agglomeration process for the separation and recovery of fine coal agglomerates from a slurry, the process including : a slurry from which fine coal is to be recovered ; sensing means in direct or indirect communication with said slurry for detecting predetermined parameters relating to the condition of said slurry ; means in communication with the sensing means responsive to an instantaneous measured value or values of said condition parameters ; wherein said means responsive to said condition parameters controls/regulates the delivery of an agglomerating agent into the slurry at a rate or in a quantity determined by at least one of said condition parameters so as to minimise use of the agglomerating agent but maximise fine coal recovery for a predetermined quantity of the agent.

An oil agglomeration process for the recovery of fine coal agglomerates from a slurry, the process including: a slurry from which fine coal is to be recovered ; sensing means for detecting predetermined parameters relating to the condition of said slurry ; at least one signal processing assembly responsive to a reading of said parameters in direct of indirect communication with the sensing means and control means ; said signal processing assembly for controlling/regulating the delivery of an agglomerating agent into the slurry at a rate or in a quantity determined by said condition parameters so as to minimise use of the agglomerating agent but maximise fine coal recovery for a predetermined quantity of the agent.

A control system for regulating the coal slurry feed rate and solids concentration in an agglomeration process for the recovery of fine coal from said slurry the system comprising ; a central processor ; at least one remote sensor for measuring the condition parameters or ingredients of said coal/water/mineral slurry ; means linking said remote sensor/s to said central processor for transmission to said central processor of data measured by said at least one sensor; means connecting the central processor to a variable speed pump which regulates the delivery rate of an agglomerating agent to a coal slurry reservoir prior to a mixing tank.

A control system for regulating the delivery of an agglomerating agent into a coal/water/mineralslurry in an oil agglomeration process for the recovery of fine coal from said slurry ; the control system comprising ; a central processor ; at least one remote sensor for measuring the condition parameters or ingredients of said coal/water/mineral slurry ; means linking said remote sensor/s to said central processor for transmission to said central processor of data relating to the condition of said slurry measured by said at least one sensor ; means connecting the central processor to a variable speed pump which regulates the delivery of the agglomerating agent from an agent storage reservoir responsive to signals from the central processor which adjust the operation of the pump according to data relating to said condition parameters measured by said at least one sensor.

An assembly for controlling the delivery of an agglomerating agent to a slurry from which fine coal is to be recovered ; the assembly comprising ; at least one probe in contact with said slurry; a signal processing unit in communication with said at least one probe and which receives and processes data from said at least one probe relating to the condition of said slurry ; a programmable logic computer (PLC) in communication with and which receives said data from said processing unit; wherein said PLC monitors the density and flow of slurry delivered to said probes ; and wherein said PLC is in communication with a pump which is controlled by and operates in response to data received relating to said slurry ; wherein said pump is responsive to an input from said PLC thereby regulating delivery of the agglomerating agent to said slurry.

In another broad form the present invention comprises: a control system for regulating the <BR> <BR> <BR> <BR> <BR> dclivcrs of an oil emulsion into a coal/watcr/mincral slurw in an oil agglomeration process for the recovers of fine coal the system comprising ; a central processor: at least one remote sensor for measuring the condition and/or constitucnts of said coal/watcr/mincral slurry : means linking said remote scnsor/s to said central processor for transmission to said central processor of data measured by said at toast one sensor, means connecting the central <BR> <BR> <BR> <BR> <BR> processor to a variable speed pump which rcgulatcs the dclivcy of oil cnmlsion from an oil cmulsion/storagc reservoir responsive to signals from the central processor which adjust the operation of the pump according to data measured by said at least one sensor.

According to a preferred embodiment, the control means comprises a computcr proccssorand a programmable logic computer each instructed by software which processes data received from a first sensing probe or probes in an infeed line which dclivers the coal/watcr/mincral slurn and at least a second probe in a fccd holding tank for said coal/water/mineral slurry, wherein the programmable logic computer regulates the deliveryof the oil emulsion by actuating a variable drive delivery pump attached to or remote from said oil emulsion holding tank according to measured parameters of said coal/watcr/mincral slurr.

The measured parameters of the coal/water/mineral slurwvhich control thc activitv (speed) of the pump vill includc concentration of the coal fines and dirt.

According to a furthcr form of the invention there is providcd a mixing tank including at least one high shear agitator : substantiallS vcrtical baScsq an air distributor. an inlct and an outlct: wherein said baffles create an optimum level of turbulence to maximise contact between coal particles and oil droplets resulting in oil coating of the particles.

Preferably the high shear agitators have a geometry which facilitates a combination of axial and radial flow to allow optimum mixing within the tank whilst maintaining sufficient residence time and high shear to achieve coal-oil interaction. According to a further form the present invention comprises a filter for separating bulk liquid and mineras from coal having an aperture of between 200-50 um with open area between 10%-20%.

The present invention will now be described in more detail according to a preferred but non limiting embodiment and with reference to the accompanying illustrations wherein: Figure 1: shows schematic layout of a control assembly including probes linked to a signal processing computer and a PLC.

Figure 2: shows an analysis graph of Solids versus Time: Figure 3 : shows a schematic layout of a selective oil agglomeration coal recovery process according to a preferred embodiment of the invention ; Figure 4: ; shows a table of typical data produced by a run carried out on the pilot plant referred in figure 3 ; Figure 5: slows a summary of results from an oil agglomeration coal recovery plant.

Various prior art processes for fine coal recovery have previously been described including the Bechtel process. This process uses heptane selectively to agglomerate hydrophobic organic coal materials from an aqueous slurry of ultra fine {less thall 20y m) coal.

This system includes a recovery process for reuse of heptane mixed with the coal agglomerates in the agglomeration circuit. This arrangement does not however teach the controlled injection of an emulsion obviating the need for an oil recovery process to ensure economic viability. Such a system will now be described with reference to figure 1.

Referring to figure I there is shown a general schematic layout of a control assembly for use in controlling the recovery of fine coal from a slurry.

Control assembly I comprises an infeed pipe 2 which delivers a slurry containing water, fine coal and other mineral matter to a holding tank 3.

According to the example shown, tank 3 includes a receiving reservoir 4 and an overflow reservoir 5. Tank 3 includes a discharge assembly which comprises a delivery pipe 7 and control valve 8 which regulates delivery of the slurry to the agglomeration process.

Overflow reservoir 5 includes overflow pipe 9 which joins delivery pipe 7. Tank 3 has a wall 3a which is designed to maintain slurry level above the probe detecting areas. Control assembly I futher comprises probes 10 and 1 1 each sealed within a housing which are used to determine the ash content of the slurry. Probe 1 1 measures a density parameter of the slurry and probe 10 the mineral content. The probes allow on line determination of the ash of the slurry and subsequent continuous and instantaneous determinationof the coal content of the feed.

This in conjunction with mass flow determination allows mass flow of coal to be calculated and hence the approriate dosing pump flowrate of the agglomerating agent into the slurry. The probes are in communication with a personal computer based signal processing unit 12 which receives and processes data from the probes relating to condition parameters of the slurry.

Signal processing unit 12 is linked to a programmable logic computer (PLC) 13 which itself is in communication with a density guage 14 via interface 13a and flow meter 15 via interface 13b located in feed pipe 2.

An output of counts per second is sent to unit 12 (which could include a 486 chip processor or higher) whereupon its software determines the solids data for the slurry.

PLC 13 receives data regarding the slurry and responsive to condition parameters of the slurry operates pump 16 which is driven by variable speed drive motor 17 thereby controlling delivery of an agglomerating agent such as an oil emulsion in the agglomeration process for fine coal recovery. The agglomerating agent may also comprise oil only or a mixture of oil and water with additives to enhance dispersion of oil in water.

The oil must be capable of being finely dispersed in water and this is generally more difficult without surfactants in oils of increasing viscosity. Most mineral oils derived from the oil refining process would be suitable, typically ranging from light oils such as dieseline to heavy fuel oils such as fractionator bottoms and reprocessed waste mineral oils. Vegetable oils could also be used. Energy sources and receivers of the probes are sealed within a housing (not shown) immersed in the slurry.

According to one embodiment, probes used may be a Cs density probe and a 238Pu X-ray backscatter probe. Density probe 11 which provides a determination of solids and has a source that generates a gamma ray through the slurry to a receiver to determine the slurry density. Probe 10 uses a plutonium source to generate X-rays into the slurry and the X-ray back scatter is received to determine the slurry ash or mineral content.

The density is determined by passing the slurry across the path of the gamma ray and the mineral content is determined by generating X-rays through a window into the slurry and detecting back scatter from the slurry and also the intensity of Fe K shell X- rays excited in the slurry. Once the probes are calibrated they continuously and instantaneously monitor in that signals are continuously delivered to the signal processing unit for analysis.

Counts per second values obtained are sent to processing unit 12 for analysis and thus determination of ash content. An algorithm in the associated software determines oil or emulsion requirements based on coal content. The variable drive motol 17 is then instructed to allow supply of oil or emulsion by the dosing pump at a prescribed rate.

The accuracy of the probe processing depends upon measuring the same slurry at the same time i. e. close together.

In an alternative embodiment the probes may be installed in a feed box a feed tank or sampling loop. In a further embodiment, probes may be installed in a sampling loop on the Selective Oil Agglomeration Process (SOAP) reject stream to continuously measure the processrecovery rates.

The PLC interacting systems include in the associated software specifically designed algorithms to ; convert the density and mineral content probe signals to ash content of the slurry and then ; convert ash content to mass of carbonaceous material in the slurry and then ; determine the coal mass and flow rate which is then used to determine the required mass flow of agglomerating agent which as a consequence, signals the appropriate speed to run the agglomerating agent variable speed pump motor.

Referring to figure 2 there is shown a graph of Solids versus Time. The analyser probes provide an instantaneous readout of kilograms of coal, kilograms of mineral and kilograms of total solids. The data presented in the graph was collected over an 18 hour operating period of the SOAP plant in May 1998. The output from the probes is interpolated by a computer algorithm, which is used to control the on line addition of oil or an oil/water emulsion to a coal slurry. Oil pump rate responds via a variable frequency drive to the changes in coal content of the slurry, on a continuous basis, providing an accurately controlled correct addition to the slurry.

This is only possible by accurately monitoring the coal content continuously on line and interfacing this information with a computer controlled pump.

For safety reasons the probes are preferably installe in a large heavy guage steel containment vessel that is used as the slurry feed reservoir 3.

Calibration of the probes 10 and 1 I ailows the process to operate automatically. Solids and ash levels are determined according to prescribed equations with four unknowns to be determined. The equation for determining solids weight fraction (W) of the slurry independent of variable voidage is given by : W=a. In (1) +a2. In+a3/ls+a4. lFe/Is+a5 Where I is detected intensity is X-rays n is neutrons S isscattered X-rays Fe is X-rays.

Scripted values of a are constants.

In the present process as there is no neutron probe n need not be determined. The ash content of the slurry is calculated by the equation: Cash = {bl/ls + b2. IF/ls + b3 + [b4. In (1) + bS. In 18/W where the scripted values of b are constants and the first inner bracketed term is the ash sensitive term and the second inner bracketed term corrects for the effect of voidage on the scattered X-ray intensity.

The Fe content of the coal ash is given by : {(cl#IFe/1s+c2)+[c3#In(I)+c4#In]}/{w#Cash}CFe= where the scripted values of c are constants and the first inner bracketed term is the iron sensitive term.

Output signals from the density and X-ray probes are sent to the computer via two interfaced cards that control pulse height, pulse shape position and amplification.

There are a number of CRO test points and adjustable potentiometers on the two cards that are used to ensure that pulse heights and shapes are correct and that they are correctly positioned with respect to energy. Once the desired operating conditions have been entered into the on-line menu, on line analysis can be initiated by pressing R for RUN when it is highlighted. The computer can display such information as the maximum number of counts obtained for each peak over the preset counting period expressed as counts per second (cps).

Referring to figure 3 there is shown a general schematic layout of a process for recovery of fine coal agglomerates according to a preferred embodiment of the invention The process requires a source of slurry from which fine coal is to be extracted. The slurry is held in thickener tank 30 which includes slurry discharge line 31 in communication with pump 32 which itself is in communication with an infeed line 33 which terminates at feed holding tank 34. Infeed line 33 includes a flow meter (not shown) as previously described with reference to figure I and delivers a coal/water/mineral slurry into feed holding tank 34. Holding tank 34 includes a discharge or overflow 34a which takes any overflow to tailings sump 46. The coal water slurry inside feed holding tank 34 is delivered via feed pump 35 to a high shear mixer 38. Feed line 36 downstream of pump 35 includes in line mixer 37.

The process further comprises emulsion mixer 40 which receives a mixture of oil, water and surfactant to form an oil based emulsion. Emulsion mixer 40 further comprises feed line 41 terminating at pump 42. Pump 42 is joined on its downstream side delivery line 43 enabling communication between emulsion mixing tank 40 and high shear mixer 38. The process further comprises a signal processing computer 50 which is directly or indirectly linked to at least feed holding tank 34 via probes 54 & 55 referred to above thereby regulating flow of constituents through the system.

PLC Computer 50 includes an interface 57 and 58 allowing signal communication with a flow meter and density guage in feed line 33 as the coal/water/mineral slurry travels therealong. This enables the computer to meter the flow rate of the coal/water/mineral slurry which is infed into feed holding tank 34.

Computer 50 comprises interfaces 52 and 53 which terminate in probes 54 and 55 in contact with the coal/water/mineral slurry. Measuring gauges are used to measure the quantity of coal fines in the coal/water/mineral slurry in feed holding tank 34.

The state of the slurry is converted to a signal which inputs into the computer 50 which controls a loop to adjust the flow emanating from pump 42 via interface 56. In this way, the quantity and/or flow of emulsion delivered from tank 40 may be controlled so that an appropriate amount of emulsion to achieve maximum coal recovery without wastage is delivered to high shear mixer 38.

The probes used in this process are commercially available but have not previously been used in combination in the above described manner in fine coal recovery to effect controlled delivery of an oil emulsion. Pump 42 is preferably variable drive so that its speed can be adjusted according to the predetermined amount of oil required in high shear mixer 38 in response to readings received by computer 50.

The coal/water/mineral slurry and emulsion from emulsion mixing tank 40 are mixed in high shear mixing tank 38 by means of special agitator 38a including baffles (not shown). The coal/water/emulsion mixer is allowed to agglomerate whereupon the agglomerated fines gravitate into primary separator 39. Computer 50 is instructed by software which actuates the emulsion pump 42 to deliver the required dose of emulsion into the high shear mixer 38 as the coal/water/mineral slurry is continually infed. Flow of the coal/water/mineral slurry is monitored using a standard flow meter gauge located near the entry to the feed holding tank which is electronically linked to the computer 50. Preferably, the blend of emulsion/coal/water is mixed for several minutes. In an alternative embodiment, a second high shear mixing tank (not shown) which receives overflow from high shear mixer 38 can also be used to increase the residence time for high shear agitation Underflow from high shear mixing tank 38 is directed gravitationally into primary separator 39 which may either be a settling tank having no agitation or having a water washing cyclone or spirals. High shear mixer 38 further includes an overflow assembly allowill overflow from the high shear mixing tank 38 to be directed to laser-cut vibrating screen separator 39. Separator 39 is adapted with an overflow 39a which enables overflow from the primary separator to be directed to laser cut dewatering screen 45.

Underflows from both separator 39 and dewatering screen 45 are pumped into a tailings pond (not shown) via tailings pump 47 while the agglomerated coal fines or dewatered low ash coal agglomerates are directed to the product conveyor 48 where it is blended with a washery product.

The emulsion is preferably made up of water and oil with the addition of a small amount of surfactant sufficient to maintain a stable emulsion. The coal particle size can vary from 500 llm to sub micron size.

The dosage of emulsion is critical for the successful recovery of the maximum quantity of coal and as previously indicated is important for the overall economics of the process. If emulsion is used efficie1ltly operating costs can be reduced to a minimum. Furthermore, the process being computer controlled allows the system to operate without a hands on operator. Good coal agglomerates can only be formed with correct emulsion dosage and are required for high recoveries on the screen To achieve the correct dosage it is vital that the mass flow of coal to the plant is known and hence the need for on line monitoring gauges which provide information for the computer to actuate variable speed pump 42.

The mixing tank must have at least one high shear agitator, ánd vertical baSes to create maximum turbulence and hence giving greatest contact between coal particles and oil droplets resulting in oil coating of the particles. The tank must also have a quiet zone whereby the oil coating particle may be allowed to collide and grow in agglomerate size. The tank should also be fitted with an air distributor to promote agglomerate growth and to form a coal agglomerate floating mat. This floating mat of coal product should be able to overflow the mixing tank and report to the separating screen for dewatering. The mixing tank should also contain an outlet by which the underflow and/or the smaller agglomerates can pass into a primary separator for further treatment.

The high shear agitator/s must have a blade geometry such that a combination of axial and radial flow are created to allow good mixing within the body of the tank while maintaining sufficient residence time and high shear to achieve coal-oil interaction.

Re agitator diameter to tank diameter ratio (if cylindrical) should be in the range 1: 2 to 1 : 8 and have a power rating number between 0.5 and 10.

The mixing tank should have provisions for introduction of the nucleonic gauges and inlet lines for the coal/water/mineral slurry and emulsion. These two inlets should be in close proximity to each other or preferably mixed prior to entry into the tank.

The product from the overflow of the mixing tank and the primary separator requires dewatering via a screen or filter. While the coal product is agglomerated to larger sizes and floats on the mineral/water slurry, the mineral particles are still fine and can be sub-micron in size. To separate the bulk liquid from the coal it is necessary to use a fine screen with a maximum"open area". This has been achicvcd bx incorporating spccialle cut screens using lascr techniques. The screen should have an aperture of between 200-50 µm. with open arca between 20%- 10%. To aid separation these screens have been mounted in vibrating screen deck units and the laser cut screen specialty mounted to transfer the vibrations over the deck.Withoutthesespecialscreens.adequatescreen dewatering woutd not bc achieved. The cfficicncy of dcwatcring is based on forming good large agglomerates which float on the sturry surface. Blinding or blockages within the screen slots is not a problem using these screens as thcx havc minimal Icading cdgcs and arc cut from very thin stainless stccl sheets which ma bc surface hardened to overcome wear resistant Pilot studies have been performed using a pilot plant with capacity to handle up to 10 cubic mctrcs of slurrv pcr hour. Thc trial pilot plant was designcd as portable for rclocation to multiple test sites. The design of the pilot plant was initiaily madc up of thrcc modulcs cach with a specific dut !.

The first module prepares, stores and delivers oil emulsion at a controllcd rate depcnding upon fccd slurry density. flou rate and coal contents. The second module is involved in slurrsZ mixing, fine coal agglomcratc formation separation and dcwatcring processes and the third module is involved in bulk oil storage.

A pilot plant fully automated and provided with instrumentation and variable speed controls on pumps and mixers permit process variation while continuously measuring and recording operating parameters. The product gravitates to a collection bclt bciow thc structurc whilc the tailings stream is directed to a suitable disposal circuit. A tailings thickener underflow is provided as feed to the pilot plant. The fccd varies in solids conccntratioll during thc tcsting period in the range 10 - 25 % by weighjt and ash level in the range of 20-25 %. Combustible recovery from the pilot plant was found under normal 1 circumstances to bc in the range 75 90% while an oil loadings of 8 - 10% based on dry product tonnes was required. The product generated was low in ash (less than 10%). however the vibrating sieve bciid dewatering system generated relatively high moisture product. Figure 4 shows a summary oftypicai data derived from a mn of the pilot plant. Under normal operating circumstances and with a similar feed slurry, these results were found to be repeatable and representative of the response of coal from that particular seam. The data in figure 5 indicates a product yield of 72% at 8.1 % ash and a combustible recovery of 85.3% from a feed slurry containing 22.4% ash can be achieved using the oil agglomeration process.

When an operator requires the SOAP plant to start, a button on the operator interface screen in the washery control room is activated, and the plant operation sequence is automatically initiated.

An automatic valve opens and allows slurry from the tailings thickener disposa line to flow to the SOAP plant. A pump installed in the feed line controls feed to the plant, while slurry, excess to the plants requirements, is directed to the SOAP plant tailings sump. A constant flow of slurry feed and an automatically controlled quantity of oil is delivered to the high shear mixing process.

The speed of the fixed displacement oil dosing pump is controlled by an algorithm programmed into the PLC that takes into account the current operational parameters of flow rate to the process and oil loading, as well as slurry properties such as density and ash.

Agglomerated slurry overflows to a primary separator to which dilution water is added. The agglomerates tend to float. Some minerai rich liquid is removed from the underflow while the agglomerates and the remainder of the liquid flow to the dewatering screen. Product from the screen discharges onto a collection conveyor fitted with a weightometer that continuously monitors plant output. The conveyor carries the agglomeration process product to the main washery product conveyor where it is mixed with washery product. Tailings passing through the dewatering screen report to the tailings sump and combine with slurry, excess to the process capacity, is pumped away to the on site tailings disposa dam.

The operation is fully automatic from start up to shut down. The only routine operator involvement is to inspect the plant on a regulator basis and to report any problems for rectification. The operators can shut the plant down if an emergency condition arises.

Once again this can be achieved through a button on the operator interface or by an emergency stop at the plant.

The following results were achieved by another SOAP plant: -Total number of available operating days : 15 (including a 24 hour district stoppage and a 24 hour maintenance outage) -Total number of hours of plant operation for the period: 153 (availability 88%) -Total production: 845tonnes (average9.3% ash, 45.5% moisture and 31.52MJ/kg specific energy GAD) -Average oil consumption per tonne of coal produced (10% adjusted moisture basis) : 107 litres Further results in another trial indicated that a yield of 64% was achieved during the audit period. The oil consumption reported over the three week monitoring period indicated that an average of 107 litres of oil was required to recovery each saleable tonne of oil.

The high frequency screening process is, under norma ! operating circumstances, capable of producing a product higher than expected.

A number of methods of fixing the fine laser cut screen panels to the conventional high frequency have been trialed. The aim of these trials was to find a fixing method not only maximising the extent of agglomerate dewatering while maintaining process yield and throughput but also maximising screen iife.

Kcs factors in the success of the Selective Oil Agglomcration Process arc:-unique utilisation of the feed flow meter, densitometer, and ash gaugc to regulate emulsion dosing in accordance with the coal content of the slurry, not the total solids content. The influence of minera) matter content is thus discountcd.-Highlv efficient high shear mixing process that ensures oil consumption is minimise and all the emulsified oil fed to the process is effective in forming and growing agglomcrates : development of emutlsion chemistw that allows low value and waste oils to bc used in theprocess; adaption of laser cut fine aperture screen decks on a high frequency screen to dewater theagglomerated coal and separate the mineral matter from the agglomeratcs. berecognisedbypersonsskilledintheartthatnumerousvariationsan dmodificationItwill may be made to the invention as broadly described herein without departing from the overall spirit and scope of the invention