CONTROLLED PRODUCTION AND RECOVERY OF FINE-COAL AGGLOMERATES

Abstract: An oil agglomeration process for the separation and recovery of fine coal agglomerates from a slurry, the process including: a source of 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 thereby obviating the need for recovery of said agent.

Description: CONTROLLED PRODUCTION AND RECOVERY OF FINF-C AI AGGLOMERATES BACKGROUND The present invention relates to a process for recovery of fine coal agglomerates and more particularly relates to a process for recovery of such agglomerates utilising a control system including means to monitor the concentration of fine coal in a coal/water/mineral slurry to facilitate controlled delivery of an optimum quantity of an agglomeration agent such as an oil based emulsion used in the recovery process thereby preventing over use of the agent and obviating the need for agglomeration agent recovery as a result of its over use. 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 from the mineral matter by screening, filtration or flotation. The process of oil agglomeration was employed for coal beneficiatio 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 affected 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 1930'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 Colliery 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 supematant 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 μm 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 combined in a high shear mixer where coal and oil form micro- agglomerates about 212 μm 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 μm 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 6 8% 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 μm) coal A petroleum based asphalt binder is subsequently added toassist in enlarging product agglomerates to more manageable 6 4mm to 9 5mm spherical pellets H\ drophilic inorganic ash-forming and pyritic sulphur mineral matter is rejected, leaving a virtualh coal-free refuse The agglomerated coal product is then stripped of the heptane bridging liquid b\ contact with steam Steam stripping is used to recover the heptane because heptane and steam form an azcotrope which has a boiling point (79 20C) lower than either heptane or watci alone (98'C and lOO'C. respective.) ) Those plants without flotation gcncralh dispose of th ultia fine matcπal (less than 100 μm in size) as tailings to waste In some cases this ultra fine waste contains up to 50% weight rclativch low ash coal of saleable quahtv It is believed that this coal constitutes a loss of 8- 10 million tonnes per annum at current Australian coal industtΛ production rates Selective oil agglomeration involves the recover) of fine particles of coal (h\ drophobic) from a mineral matter (h) drophilic) rich liquid The modern version of the pioccss involves adding oil (usualh in an emulsified state) to an agitated fine coal water slu The oil coats the surface of the individual coal particles As the oil coated particles in the agitated slum collide the particles coalesce b\ formation of pendular bridges of oil The agglomerated coal particles can then be separated from the mineral rich liquid b\ cither screening or b\ a flotation process None of the above processes however, disclose the use of a control s\stcm which accuratch regulates the quantity of the agglomerating agent used in the recover) process INVENTION The present invention in one form seeks to ameliorate the problems of the know n processes examples of which arc described above providing a process for the ιeco\ eπ of fine coal agglomerates utilising a s\stcm for accuratch controlling deliver) of an agglomerating agent such as an oil emulsion responsive to measurement of parameters of a coal/water/mincial slum to prevent over use of and the need to recover that agent The l cntion according to that form further piovides a method and the equipment required for maximising the economic of fine-coal agglomerates using on-line monitoring devices and control loops, together with special recover) /separation screens The present invention further piovides an economic coal recovers process utilising 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/w ater/mincral slum to thercb) control the addition of those oils The invention further a nuclear monitoring s\ stem for determining the actual amount of coal in the coal/water/mineral slum mixture and computer control of the agglomerating agent quantιt\ required for rccoveπ, of fine coal from the mixture According to one embodiment a first probe will measure the total solids and a second piobc the quantity of dirt In a t\pιcal slum there might be 20-30% solids and 70-80% is fine coal, alternative!) there might be 2%-50% solids of which 5%-60%of said solids is mineral matter According to the process of the invention, all of the agglomerating agent ill be used, obviating the need for the added step of oil recover)' as occurred in certain of the prior art processes In fact, the oil consumption rate according to the process of the invention has been leduced to a level such that oil recover)' is not nccessarv to achieve commercial viabiht) of the process Selective oil agglomeration according to the present invention includes the following advantages over com entional froth flotation for the economic recover) of fine coal a) thickener underflow slum as feed can be used with solids concentration of 15-30% weight compared to 5 - 10% for froth flotation, thus, volumetric feed rate to the plant is therefore significant!) lower. b) no frothing reagent is required, consequcnth problems experienced in conventional plants with froth handling and overfrothing of watei and magnetite ciicuits aie eliminated. c) product dew teπng according to the selective oil agglomeration piocess is relative!) simple and does not require high cost vacuum filtration s) stems. d) coal recover) b\ oil agglomeration appears to be less susceptible to oxidation oi othei variable surface characteristics of coal. c) tailings produced from the plant should not requπe rcthickening prior to disposal 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 collected 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 conditionparameters of the coal/water/mineial slum thereb) regulating the flow of emulsion into said mixing tank from said second reservoir According to a preferred embodiment, the control means comprises a computer processor programmed to receive signals from said sensor/s which preferabh comprise probes immersed in said coal/water/mincral slum and which detect the concentration of coal fines whereupon said processor actuates the pump on said second reservoir responsive to data determined bv said piobes relating to the condition of the slum facilitate feeding into said mixing tank of a predetermined amount of emulsion from said second rcscn oir According to one embodiment, slurn from said first reservoir is delucred to a mixci b) 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 slurn . the process comprising an infeed line which delivers a coal/water/mincral slurn into a fust lescivou . a second reservoir for icceiung and holding an oil emulsion and including a deliver) pump m communication therewith. a mixing reservoir in/communication with said first and second reservoirs, control means including at least one sensing probe in contact with said coal/watcr/mmcial slum foi monitoring parameters of said coal/water/mincral slum whilst in said infeed line and/or in said first reservoir. and an interface linking said control means with said deliver) pump wherein said control means controls the deliver) of said oil emulsion via said pump to said mixing rcseivoir responsive to measurement of the parameters, including the concentration of fine coal of the coal/watcr/mineral slur in the first reservoir said pioccss thercb * s obviating the need for oil recover) In a further broad form the present invention comprises. an oil agglomeration process for separation of fine coal from a coal/watcr/mmeral slum using an agglomerating agent such as an oil emulsion characteiised in that the process includes computerised control mcanswhich controls the deliver) of said oil emulsion from an oil emulsion holding tank to a feed holding tank holding said coal/water/mincral slurn at a rate determined by measured parameters of said coal/w atcr/mincral slum, thereb) preventing over use of said agent in said process and obviating the ncedfor agent recover) 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 piobe i elating 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 sv stem for regulating the deliver) of an oil emulsion into a coal/water/mincral slurn in an oil agglomeration process for the recover) of fine coal the s\ stctn comprising, a central processor. at least one remote sensor for measuring the condition and/oi constituents of said coal/water/mincral slum . means linking said remote sensor/s to said central processor foi transmission to said cential processor of data measured b\ said at least one sensor, means connecting the central processor to a variable speed pump which regulates the dclivcn of oil emulsion fio an oil emulsion storage rcsen'oir responsive to signals from the central processor which ad)ust the operation of the pump according to data measured by said at least one sensoi According to a preferred embodiment, the control means comprises a computer processorand a programmable logic computer each instructed b) software which processes data recen ed from a first sensing probe or probes in an infeed line which delivers the coal/water/mincral slurn and at least a second piobe in a feed holding tank foi said coal/w atei /mineral shu . whcicin the programmable logic computer regulates the deliver) of the oil emulsion b) actuating a variable drive deliver) pump attached to or remote from said oil emulsion holding tank according to measured parameters of said coal/water/mincral slurn The measured parameters of the coal/w ater/mmeral slurn which control the actnit) (speed) of the pump will include concentration of the coal fines and dirt According to a further form of the invention there is provided a mixing tank including at least one high shear agitator. substantial!) vertical baffles, an air distributor, an inlet and an outlet. 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 minerals from coal having an aperture of between 200 - 50 μm 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 shows 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 than 20μ 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 1 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 1 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 1 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 1 1 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 14 SUBSTITUTE SHEET -(Rule 26) 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 motor 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 installed in a large heavy guage steel containment vessel that is used as the slurry feed reservoir 3 Calibration of the probes 10 and 1 1 allows 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 + a4.1 Fe / Is + a5 Where 1 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/Is + b2 . IF/ls + b3 + [b4 • ln( I ) + b5 . In ] ) / 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 CFe = { ( cl . I Fe / ls + c2 ) + [ c3 . In (I ) + c4 . In ] } / { w . Cash} 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 3 1 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 1 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 allowing 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. SUBSTΓTUTE SHEET (Rule 26) 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 μm 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 efficiently 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, and vertical baffles 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 achieved b\ incorporating spcciall) cut screens using laser techniques The screen should have an aperture of between 200-50 μm with open area between 20% - 10% To aid separation these screens c been mounted in vibrating screen deck units and the laser cut screen special!)' mounted to transfer the vibrations over the whole screen deck Without these special screens, adequate dewatering would not be achieved The efficienc) of dew tering is based on forming good large agglomerates which float on the slurn surface Blinding or blockages ithin the scieen slots is not a problem using these screens as the) have minimal leading edges and are cut from λ'cn thin stainless steel sheets which be surface hardened to overcome wcai resistant Pilot studies have been perfoimed using a pilot plant with capacit) to handle up to 10 cubic metres of slurn per hour The trial pilot plant was designed as portable for relocation to multiple test sites The design of the pilot plant was initially made up of three modules each with a specific dut) The first module prepares, stores and delivers oil emulsion at a controlled rate depending upon feed slurr) density, flow rate and coal contents The second module is involved in slurn' mixing, fine coal agglomerate formation separation and dewatering processes and the third module is involved in bulk oil storage A pilot plant full) automated and provided with instrumentation and variable speed controls on pumps and mixers permit process variation while continuoush measuring and recording operating parameters The product gravitates to a collection belt below the structure while the tailings stream is directed to a suitable disposal circuit A tailings thickener underflow is provided as feed to the pilot plant The feed vanes in solids concentration during the testing period in the range 10 - 25 % b) weight and ash level in the range of 20 - 25 % Combustible recover) from the pilot plant was found under normal circumstances to be in the lange 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 1 %). however the vibrating sieve bend dewatering system generated relativeh high moisture product Figure 4 shows a summar) of h ical data derived from a mn of the pilot plant Under nonnal 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 inteiface 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 disposal 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 mineral 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 combined with slurry, excess to the process capacity, is pumped away to the on site tailings disposal 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 3 1 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 recover}' each saleable tonne of oil The high frequency screening process is, under normal 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 life Ke) factors in the success of the Sclectne Oil Agglomeration Process are - unique utilisation of the feed flow ctei. densitomctcr. and ash gauge to icgulate emulsion dosing in accordance with the coal content of the slurry, not the total solids content The influence of mineral matter content is thus discounted - Highh efficient high shear mixing pioccss that ensures oil consumption is minimised and all the emulsified oil fed to the process is effective in forming and growing agglomerates, development of emulsion chcmistn that allows low value and waste oils to be used in thepiocess. adaption of laser cut fine apeituic scieen decks on a high frcqucnc) screen to dewater thcagglomcrated coal and separate the mineral matter from the agglomerates It will be lecognised peisons skilled in the art that numerous λaπations and modifications may be made to the invention as broadly described herein without departing from the overall spirit and scope of the invention

Claims: The claims defining the invention are as follows: 1 An oil agglomeration process for the separation and recovery of fine coal agglomerates from a slurry, the process including: a source of 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. 2. A process according to claim 1 wherein said means responsive to said condition parameters includes at least one signal processing assembly and an interface between said sensing means and said processing assembly for transfering said condition parameters to said processing assembly for processing. 3 An oil agglomeration process for the recovery of fine coal agglomerates from a slurry, the process including: a source of 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 or 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 4. A process according to claims 2 or 3 wherein the sensing means comprises at least one probe including at least one sensor/receiver for detecting and receiving said condition parameters of said slurry 5. A process according to claim 4, wherein said at least one probe is/are at least partially immersed in said slurry for detecting said parameters 6. A process according to claim 5 wherein there are two probes which instantaneouslydet ermine the ash content of the slurry 7. A process according to claim 6 wherein a first of said two probes is a density probe and the second a mineral content probe 8 A process according to claim 7 wherein the signal processing assembly includes a personal computer based processing unit in communiacation with said probes and a programmable logic computer (PLC) responsive to said processing unit and in communication with said source of slurry 9. A process according to claim 8 wherein the PLC is in communication with a density guage and flow meter on a feed pipe providing said source of slurry 10. A process according to claim 9 wherein the PLC is in communication with a pump actuated by a variable speed drive responsive to changes in measured condition parameters of said slurry processed by said computer based processing unit. 11. A process according to claim 10 wherein the agglomerating agent is mixed with the slurry in either a slurry reservoir or in a separate high shear mixing tank 12 A process according to claim 1 1 wherein said slurry comprises at least a coal/oil/water blend. 13. A process according to claim 12 wherein said agg,omerating agent is an oil in water dispersion emulsion, oil only or a mixture of oil and water together with additives to facilitate dispersion of oil in water 14. A process according to claim 13 wherein the emulsion comprises a selected oil and water, or a selected water and a surfactant 15. A process according to claim 14 wherein the condition parameters of the slurry are instantaneously and continuously measured by the probe/s and include coal grains content, kg of non coal mineral matter, kg of total solids grain size, pH of slurry and oil mixture and mixing intensity 16. A process according to claim 15 wherein the first probe detects total quantity of solids and the second probe detects mineral concentration 17 A process according to claim 16 wherein a slurry typically comprises 2% - 50% solids of which 5% - 60% of said solids is mineral matter 18 A process according to claim 17 wherein said probes are located in or adjacent a feed line which delivers the slurry to or in a reservoir prior to delivery of said slurry to a mixing tank 19. A process according to claim 18 wherein parameters measured by said probes are processed by a computer program which activates said pump to control the on line addition to said slurry of oil or oil/water emulsion 20. A process according to claim 19 wherein said pump is responsive to changes in coal content of said slurry 21. A process according to claim 20 further comprising a primary separator in communication with said reservoir or mixing tank, wherein said separator may comprise a cyclone, settling tank, floatation cell or a centrifuge 22. A process according to claim 21 further comprising a primary dewatering device in communication with the primary separator or said reservoir or said mixing tank 23. A process according to claim 22 wherein the high shear mixer includes a high shear agitator 24. A process according to claim 23 wherein the delivery of the oil agglomerating agent is automatic. 25. A process for the separation and recovery of fine coal tailings from a coal/water/mineral slurry emanating from a coal preparation plant or tailings pond utilising controlled delivery of a pre-selected admixture, the process comprising, a source of coal/water/mineral slurry delivered to a first reservoir via a slurry infeed line, a second reservoir for receiving and holding an admixture a pump in communication with 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 admixture 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 mixing tank; the process further comprising; control means in communication with at least one sensor in contact with said slurry for detecting condition parameters of said slurry; and a pump in communication with said second reservoir and responsive to said condition parameters, wherein, said control means controlling said pump is responsive to a signal or signals from said sensors indicating the parameters of the coal/water/mineral slurry thereby regulating the flow of admixture into said mixing tank from said second reservoir. 26. A process for separation of fine coal from a coal/water/mineral slurry, the process comprising: an infeed line which delivers a coal/ water/mineral slurry into a first reservoir; a second reservoir for receiving and holding an admixture and including a delivery pump in communication therewith; a mixing reservoir in communication with said first and second reservoirs; control means including at least one sensing probe in contact with said coal/water/mineral slurry for monitoring condition parameters of said coal/water/mineral slurry whilst in said infeed line and/or in said first reservoir, and an interface linking said control means with said delivery pump, wherein, said control means controls the delivery of said admixture via said pump to said mixing reservoir responsive to measurement of said condition parameters, including the concentration of fine coal in the coal/water/mineral slurry in the first reservoir 27. An oil agglomeration process for separation of fine coal from a coal/water/mineral slurry using an admixture, characterised in that the process includes computerised control means which controls the delivery of said admixture from a holding tank to a tank holding said coal/water/mineral slurry at a rate determined by measured condition parameters of said coal/water/mineral slurry, thereby controlling the use of admixture in said process 28. A process according to any one or more of claims 23 - 25 wherein the admixture comprises an agglomerating agent 29. A process according to claim 26 wherein the agglomerating agent comprises and oil in water dispersion emulsion, oil and water together with additives to facilitate dispersion of oil in water 30. A process according to claim 29 wherein the delivery of the agglomerating agent is automatic 31. A control system for regulating the delivery of an admixture into a coal/water/mineral slurry in an oil 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 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 admixture from an admixture 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 32. 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 processorof data measured by said at least one sensor, means connecting the central processor to a variable speed pump which regulates the delivery rate and solids concentration from a coal slurry feed line to a coal slurry reservoir prior to a mixing tank or to said mixing tank or after said mixing tank 3. An assembly for controling 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 data received by said slurry, wherein said pump is responsive to an input from said PLC thereby regulating the delivery of the agglomerating agent to said slurry 34. A high shear mixer for use in an oil agglomeration process hereinbefore described wherein the mixer includes a high shear agitator and baffles with a blade geometry for axial and radial flow ratios and which maximise turbulance 35. A mixer according to claim 34 wherein the agitator diameter to tank diameter ratio ( if cylindrical) is within the range 1 2 to 1 8 and with a power rating number between 0 5 and 10

Inventors: DONNELLY JAMES CLINTON, HOARE IAN CLARENCE, WAUGH ALLAN BRUCE, DONNELLY, JAMES, CLINTON, HOARE, IAN, CLARENCE, WAUGH, ALLAN, BRUCE
Applicants: DONNELLY JAMES CLINTON, HOARE IAN CLARENCE, SELECTIVE OIL AGGLOMERATION PR, WAUGH ALLAN BRUCE, DONNELLY, JAMES, CLINTON, HOARE, IAN, CLARENCE, SELECTIVE OIL AGGLOMERATION PROCESS PTY. LTD., WAUGH, ALLAN, BRUCE
Application year: 1998
Main classification: B03D3
IPC codes: B01D21