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WO2025158164A1 - Two stage pellet drying - Google Patents

Two stage pellet drying

Info

Publication number
WO2025158164A1
WO2025158164A1 PCT/GB2025/050138 GB2025050138W WO2025158164A1 WO 2025158164 A1 WO2025158164 A1 WO 2025158164A1 GB 2025050138 W GB2025050138 W GB 2025050138W WO 2025158164 A1 WO2025158164 A1 WO 2025158164A1
Authority
WO
WIPO (PCT)
Prior art keywords
pellets
dryer
fraction
drying step
drying
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/GB2025/050138
Other languages
French (fr)
Inventor
Rudolph Johannes FOUCHEE
Wesley Robin GOUNDER
Garry LONSDALE
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Anglo American Woodsmith Ltd
Original Assignee
Anglo American Woodsmith Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Anglo American Woodsmith Ltd filed Critical Anglo American Woodsmith Ltd
Publication of WO2025158164A1 publication Critical patent/WO2025158164A1/en
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
    • C05D1/00—Fertilisers containing potassium
    • C05D1/04—Fertilisers containing potassium from minerals or volcanic rocks
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
    • C05D1/00—Fertilisers containing potassium
    • C05D1/005—Fertilisers containing potassium post-treatment
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
    • C05D3/00—Calcareous fertilisers
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
    • C05D5/00—Fertilisers containing magnesium
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
    • C05D9/00—Other inorganic fertilisers
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G5/00—Fertilisers characterised by their form
    • C05G5/10—Solid or semi-solid fertilisers, e.g. powders
    • C05G5/12—Granules or flakes
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G5/00—Fertilisers characterised by their form
    • C05G5/10—Solid or semi-solid fertilisers, e.g. powders
    • C05G5/14—Tablets, spikes, rods, blocks or balls
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B11/00—Machines or apparatus for drying solid materials or objects with movement which is non-progressive
    • F26B11/02—Machines or apparatus for drying solid materials or objects with movement which is non-progressive in moving drums or other mainly-closed receptacles
    • F26B11/04—Machines or apparatus for drying solid materials or objects with movement which is non-progressive in moving drums or other mainly-closed receptacles rotating about a horizontal or slightly-inclined axis
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
    • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
    • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
    • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
    • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
    • F26B3/092—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating
    • F26B3/0923—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating by mechanical means, e.g. vibrated plate, stirrer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
    • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
    • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
    • F26B3/092—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating
    • F26B3/0926—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating by pneumatic means, e.g. spouted beds
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/18—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact
    • F26B3/20—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact the heat source being a heated surface, e.g. a moving belt or conveyor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/28—Drying solid materials or objects by processes involving the application of heat by radiation, e.g. from the sun
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/32—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action
    • F26B3/34—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects
    • F26B3/347—Electromagnetic heating, e.g. induction heating or heating using microwave energy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
    • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
    • B07B13/00—Grading or sorting solid materials by dry methods, not otherwise provided for; Sorting articles otherwise than by indirectly controlled devices
    • B07B13/04—Grading or sorting solid materials by dry methods, not otherwise provided for; Sorting articles otherwise than by indirectly controlled devices according to size
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B2200/00—Drying processes and machines for solid materials characterised by the specific requirements of the drying good
    • F26B2200/08—Granular materials

Definitions

  • This invention relates to forming pelletised products, for example for use as fertiliser.
  • Evaporite minerals such as polyhalite, kieserite, dolomite and gypsum have the ability to provide nutrients, such as sulphur, potassium, calcium and magnesium to the soil, particularly when in a pelletised form.
  • a method for forming a pelletised evaporite mineral product comprising processing an evaporite mineral powder to form a quantity of pellets; a first drying step comprising drying the quantity of pellets using a first dryer configured to simultaneously agitate and dry the quantity of pellets; separating the quantity of pellets into an in-size fraction and at least one of an oversized fraction and an undersized fraction; and a second drying step comprising drying the in-size fraction of the quantity of pellets using a second dryer to form the pelletised evaporite mineral product.
  • the quantity of pellets may not be dried completely during the first drying step.
  • the first dryer may be configured to remove surface moisture from the quantity of pellets.
  • the in-size fraction of the quantity of pellets may be substantially completely dried during the second drying step.
  • the first drying step may remove between 0.5 and 2% of moisture from the quantity of pellets.
  • the second drying step may remove between 5 and 7% of moisture from the fraction of in-size pellets.
  • the in-size fraction may represent between 30% and 85% of the quantity of pellets.
  • the first drying step may have a shorter duration than the second drying step.
  • the first dryer may have a higher rate of energy consumption than the second dryer.
  • the first dryer may operate at a temperature higher than the temperature at which the second dryer operates.
  • the second dryer may operate at a temperature less than or equal to 150°C and the first dryer may operate a temperature greater than 150°C.
  • the first dryer may operate at a temperature of 450°C.
  • the second dryer may operate at a temperature of 115 °C.
  • the in-size fraction of the quantity of pellets may not have significantly varying positions on the drying surface.
  • the second drying step may comprise drying the in-size fraction of the quantity of pellets on a drying surface of the second dryer.
  • the first dryer may be configured to convey a first stream of gas onto the quantity of pellets.
  • the second dryer may be configured to convey a second stream of gas towards the drying surface and the pellets may rest on the drying surface during the second drying step.
  • the first dryer may be a rotary dryer, a fluidized bed or a Roto Louvre dryer.
  • the second dryer may be a belt dryer or an electromagnetic dryer.
  • the pelletised evaporite mineral may be one or more of polyhalite, halite, sylvite, carnallite, kainite, anhydrite, gypsum, kieserite, langbeinite, dolomite, calcite and magnesite.
  • the method may comprise pulverising an evaporite mineral feedstock to form the evaporite mineral powder.
  • Processing the evaporite mineral powder to form a quantity of pellets may comprise mixing the evaporite mineral power with a liquid and a binder to form a blend and processing the blend using the pelletiser to form the quantity of pellets.
  • Processing the blend using the pelletiser to form the quantity of pellets may comprise granulating the blend.
  • the method may comprise one or more of passing the in-size fraction of the quantity of pellets through a polishing screen; cooling the in-size fraction of the quantity of pellets; and coating the in-size fraction of the quantity of pellets to form the pelletised evaporite mineral product.
  • Separating the quantity of pellets into an in-size fraction and an oversized fraction may comprise passing the quantity of pellets through a screen having apertures of 4mm in diameter.
  • Separating the quantity of pellets into an in-size fraction and an undersized fraction may comprise passing the quantity of pellets through a screen having apertures of 2mm in diameter
  • Pellets of the in-size fraction of the quantity of pellets may have a diameter of between 2mm and 4mm.
  • a production facility for forming a pelletised evaporite mineral product
  • the production facility comprising processing apparatus configured to process an evaporite mineral powder to form a quantity of pellets; a first dryer configured to dry the quantity of pellets by simultaneously agitating and drying the quantity of pellets; a separator configured to separate the quantity of pellets into an in-size faction and at least one of an oversized faction and an undersized fraction; and a second dryer configured to dry the in-size faction of the quantity of pellets to form the pelletised evaporite mineral product.
  • the production facility may be configured such that the quantity of pellets are input to the first dryer; and the output of the first dryer is input to the separator.
  • the production facility may be configured such that the in-size fraction of the quantity of pellets are input to the second dryer.
  • Figure 1 illustrates a conventional method for forming a pelletised evaporite mineral product.
  • Figure 2 illustrates a method for forming a pelletised evaporite mineral product.
  • Figure 3 illustrates another method for forming a pelletised evaporite mineral product.
  • Figure 1 illustrates a known process 100 for forming a pelletised evaporite mineral product.
  • evaporite mineral powder 101 undergoes processing at 102.
  • the processing 102 may include a step of pelletising the powder.
  • the result of the processing 102 is evaporite mineral pellets 103.
  • the pellets 103 are input to a dryer 104 to be dried.
  • Dry pellets 105 are therefore output from the dryer 104.
  • the dry pellets 105 are passed through a separator 106 to separate the pellets having the desired size from other pellets of different sizes.
  • the separator may comprise one or more screens.
  • Pellets having a size within a desired range of sizes are referred to herein as the “in-size fraction” of pellets.
  • Pellets having a size larger than the desired range of sizes are referred to as an “oversized fraction”.
  • Pellets having a size smaller than the desired range of sizes are referred to as an “undersized fraction”.
  • the step of using the screen 106 may therefore involve separating the in-size fraction from at least one of an oversized fraction and an undersized fraction.
  • 107 denotes the in-size fraction of pellets that are output from the screen 106.
  • the in-size fraction of pellets 107 are used to form the pelletised evaporite mineral product.
  • pellets Due to the cohesive nature of the wet pellets 103, pellets have a tendency to cake or clump together during the drying process. It has been found that caking or clumping of pellets is minimised when a dryer is used which agitates the pellets as it dries them. Such dryers include rotary dryers and fluidized beds. However, dryers which are configured to simultaneously agitate and dry the pellets are highly energy intensive. There is therefore a need to develop a process which allows evaporite mineral pellets to be dried in a way which requires less energy.
  • the inventors of the present invention have developed a method for forming a pelletised evaporite mineral product in which the pellets are effectively dried in a manner which minimizes the method’s energy consumption.
  • Figure 2 illustrates an example of such a method and the apparatus used to execute the process 200.
  • evaporite mineral powder 201 undergoes processing.
  • the evaporite mineral powder 201 may have a size fraction of less than 2 mm.
  • the evaporite mineral powder 201 may have a size fraction of less than 1 .5 mm. More preferably, the evaporite mineral powder 201 may have a size fraction of less than 1 mm.
  • the grains of the evaporite mineral powder may be finer than 2 mm.
  • the grains of the evaporite mineral powder may be finer than 1.5 mm. More preferably the grains of evaporite mineral powder 201 may be finer than 1 mm.
  • the evaporite mineral powder 201 may comprise at least one of a size and a density falling within a predetermined in-form range.
  • the predetermined in-form range may comprise an upper limit of 1 mm to 2mm.
  • the processing may be performed by processing apparatus 202.
  • the processing may include a step of pelletising the powder.
  • the processing apparatus 202 may comprise a pelletiser.
  • the result of the processing by processing apparatus 202 is therefore a quantity of evaporite mineral pellets 203.
  • the output of the processing apparatus 202 is wet, substantially spherical pellets.
  • the quantity of wet pellets 203 are input to a dryer 204 to be dried.
  • the dryer 204 is configured to simultaneously agitate and dry the quantity of pellets.
  • to agitate the pellets means to cause the pellets to have significantly varying positions within the dryer whilst being dried.
  • the agitation causes the pellets to move around within the dryer 204 so that the position of the pellets varies significantly whilst inside the dryer relative to any surface that the pellets may contact.
  • the dryer 204 may be referred to herein as an “agitating dryer”.
  • the dryer may agitate the pellets during drying such that they do not rest on the surface. In other words, the dryer may cause the pellets to make intermittent contact with the drying surface whilst they are being dried.
  • the dryer 204 may comprise a housing and dry the quantity of pellets by conveying a stream of hot gas towards pellets positioned within the housing.
  • the gas may be air.
  • the dryer may agitate the pellets by rotating the housing in which the pellets are located such that the pellets are “tumbled” as the hot gas passes through the housing. In this example, the pellets are agitated such that they do not rest on the interior surface of the housing.
  • the pellets may make only intermittent contact with the interior surface of the housing.
  • the dryer 204 may be a rotary dryer. According to the example seen in figure 2, the dryer 204 is a rotary dryer and conveys hot gas through the housing of the dryer at a temperature of 450 °C.
  • the temperature of the hot gas conveyed through the dryer may be greater than 300 °C, or greater than 400 °C, greater than 500 °C, greater than 600 °C or greater than 700 °C .
  • the temperature of the hot gas may be between 300 °C and 600 °C, or between 300 °C and 500 °C or between 400°C and 600°C, or between 400 °C and 500 °C, or between 500 °C and 600 °C, or between 600 °C and 700 °C, or between 700 °C and 800 °C.
  • the temperature of the hot gas conveyed through the dryer may be as high as 800 °C.
  • the dryer 204 may comprise a housing and be configured to fluidize pellets within the housing.
  • the dryer may be configured to inject a stream of hot gas through a perforated bed in the housing at a velocity higher than the settling velocity applied to the pellets. In this way, the pellets are allowed to “float” on the injected air above the perforated bed while they are dried by the hot gas.
  • the injected stream of hot gas agitates the pellets within the housing.
  • the dryer 204 may be a fluidized bed.
  • the dryer 204 is a fluidized bed and conveys hot gas into the dryer housing at a temperature of 250 °C.
  • the dryer 204 may be a Roto Louvre dryer.
  • the dryer may dry the pellets using an energy source other than a hot gas.
  • the dryer may comprise visible light or infrared lamps.
  • the dryer may convey electromagnetic waves such as radio frequency waves and/or microwaves.
  • the dryer 204 may be an electromagnetic fluidized bed dryer.
  • the dryer may agitate the pellets using a different method than those described, for example, the dryer may comprise a surface on which the pellets rest and the surface is configured to shift back and forth whilst the pellets are dried so as to agitate the pellets.
  • the dryer may agitate the pellets by sequentially tipping the pellets onto a series of moving belts. The dryer may gently stir the pellets.
  • the dryer 204 performs a first drying step.
  • the first drying step partially dries the quantity of pellets.
  • the purpose of the first drying step is to remove surface moisture from the quantity of pellets.
  • the first drying step dries the outer surface of the pellets so that the pellets are no longer prone to sticking together.
  • the first drying step may completely dry the outer layer of each pellet.
  • the first drying step may remove between 0.5 and 2% of moisture from the quantity of pellets.
  • the first drying step removes 1 % of moisture from the quantity of pellets.
  • the first drying step may involve removing up to 4% of moisture from the quantity of pellets. In other words, the quantity of pellets are not dried completely during the first drying step.
  • the first dryer is configured to partially but not completely dry the pellets in the first drying step.
  • the pellets are dried to leave a wet core but a harder outer surface.
  • Partially dry pellets 205 are therefore output from the dryer 204.
  • the partially dried pellets 205 are then passed through at least one screen 206 to separate the pellets having the desired size from other pellets.
  • the first drying step is performed before the separating step. Due to the surface moisture having been removed from the pellets in the first drying step, the screen(s) 206 can effectively sort the quantity of pellets into different sizes without the pellets sticking to the screen. In other words, pellets which have a size that is less than the size of the apertures in the screen will pass through the screen without sticking to the screen.
  • Pellets having a size within a desired range of sizes is referred to herein as the “in-size fraction” of pellets.
  • Pellets having a size larger than the desired range of sizes are referred to as an “oversized fraction”.
  • Pellets having a size smaller than the desired range of sizes are referred to as an “undersized fraction”.
  • the step of using the screen(s) 206 therefore involves separating the in-size fraction from at least one of an oversized fraction or an undersized fraction. In other words, the separating step involves isolating the in-size fraction of the quantity of pellets.
  • the method may comprise separating the in-size fraction from an oversized fraction only.
  • the method may comprise separating the in-size fraction from an undersized fraction only.
  • the method may comprise separating the in-size fraction from an undersized fraction and an oversized fraction. According to an example in which the quantity of pellets is made up of undersized, oversized and in-size fractions, two separate screens are used to isolate the in-size fraction of pellets from the rest of the quantity of pellets.
  • pellets of the in-size fraction have a diameter between 2mm and 4mm.
  • Pellets of the undersized fraction therefore have a diameter of less than 2mm.
  • Pellets of the oversized fraction therefore have a diameter of more than 4mm.
  • the screening step 206 to isolate the in-size fraction of pellets may involve passing the quantity of pellets through a first screen having apertures of 4mm in diameter to remove the oversized fraction, and passing the remaining pellets through a second screen having apertures of 2mm in diameter to remove the undersized fraction.
  • the desired range of sizes may have a lower or higher upper bound and/or a lower or higher lower bound.
  • the size of an in-size pellet may be such that it has a diameter less than 5mm, less than 4mm, less than 3mm, less than 2mm or less than 1 mm.
  • the size of the pellet may be such that it has a diameter greater than 4mm, greater than 3mm, greater than 2mm, greater than 1 mm or greater than 0.5mm.
  • the volume of an in-size pellet may be less than 20mm 3 , less than 15mm 3 , less than 10mm 3 , less than 8mm 3 or less than 5mm 3 .
  • the volume of the pellet may be greater than 15mm 3 , greater than 10mm 3 , greater than 8mm 3 , greater than 5mm 3 or greater than 1 mm 3 . Other dimensions could be adopted.
  • 207 denotes the in-size fraction of the quantity of pellets that are output from the screen(s) 206.
  • the in-size fraction 207 are passed to a second dryer 208 to be dried.
  • dryer 208 is also configured to simultaneously agitate and dry the pellets.
  • the dryer 208 may be the same type of dryer as dryer 204. In the example seen in figure 2, both dryers are rotary dryers. Alternatively, as will be explained in more detail below, dryers 204 and 208 may be different types of dryers.
  • the second dryer 208 performs a second drying step in which the in-size fraction of the quantity of pellets are dried.
  • the separating step 206 is performed before the second drying step 208.
  • the first drying step 204 is therefore performed before the separating and second drying step.
  • the purpose of the second drying step is to substantially dry the in-size fraction of the quantity of pellets so that they may be used to form the evaporite pelletised product 209.
  • the evaporative pelletised product 209 is drier that the quantity of wet pellets 203.
  • the evaporite pelletised product 209 is drier than the partially dry pellets 205.
  • the second dryer may be configured to substantially completely dry the in-size fraction of pellets during the second drying step.
  • Performing the second drying step may remove between 5 and 7% of moisture from the fraction of in-size pellets.
  • the second drying step removes 6% of moisture from the quantity of pellets.
  • the second drying step may involve removing a higher or lower percentage of moisture such that the in-size pellets are substantially completely dried.
  • Substantially completely dry pellets may have a moisture content of less than 1 %, for example 0.2% or 0.5%.
  • the quantity of pellets are substantially completely dried during the second drying step. More moisture may be removed from the pellets in the second drying step than in the first drying step.
  • the second drying step may therefore have a longer duration than the first drying step. In other words, the first drying step has a shorter duration than the second drying step.
  • the quantity of pellets 203 output by the processing apparatus 202 have a moisture level of 7.5%.
  • the partially dried pellets 205 have a moisture level of 6.5% when they are screened by screen(s) 206.
  • the in-size fraction of the partially dried pellets 207 therefore have a moisture level of 6.5% upon entering the second dryer 208.
  • the second drying step is performed by the second dryer 208, the in-size fraction of substantially completely dry pellets 209 have a moisture level of 0.5% or lower.
  • 209 denotes the dried in-size fraction of pellets that are output from the dryer 208.
  • the dried in-size fraction of pellets are used to form the evaporite pelletised product.
  • Figure 2 illustrates a method used for forming a pelletised evaporite mineral product from an evaporite mineral powder.
  • the process of forming the product may additionally comprise pulverising an evaporite mineral feedstock to form the evaporite mineral powder.
  • the method may therefore involve a preliminary step of grinding a raw untreated evaporite mineral into powder using grinding apparatus. For example, using one or more of high pressure grinding rollers (HPGR), a ball mill (e.g. a continuous “Hardinge” ball mill), an attritor mill and an air classifier.
  • HPGR high pressure grinding rollers
  • ball mill e.g. a continuous “Hardinge” ball mill
  • an attritor mill e.g. a continuous “Hardinge” ball mill
  • an air classifier e.g. a continuous “Hardinge” ball mill
  • processing the evaporite mineral powder to form a quantity of pellets using processing apparatus 202 may involve a number of steps. Processing the evaporite mineral powder to form a quantity of pellets may comprise mixing the evaporite mineral power with a liquid and a binder to form a blend and processing the blend using a pelletiser to form the quantity of pellets. Processing the blend using the pelletiser to form the quantity of pellets may comprise granulating the blend.
  • water and a binder are added to the evaporite mineral powder.
  • the binder may be a starch-based binder such as starch itself or flour or an adhesive such as PVA.
  • Water may be added in the range of 5% to 10%, more preferably between 7% and 8%.
  • the amount of binder to be added will depend on the qualities of the binder. For typical binders, e.g. starch or flour, the amount added may be in the range of 0.5% to 4%.
  • the binder may be added directly to the evaporite mineral powder, or it may first be added to the water and then the water and binder combination may be added to the powder. According to further examples, other evaporite minerals and/or micronutrients may be added to the powder, binder, water combination.
  • the processing apparatus 202 may therefore include a mixer e.g. a ribbon blender, pin mixer or other high shear mixer.
  • a mixer e.g. a ribbon blender, pin mixer or other high shear mixer.
  • the powder/binder mixture is pelletised.
  • the processing apparatus 202 may therefore include a pelletiser e.g. a pan pelletiser.
  • a pelletiser e.g. a pan pelletiser.
  • the powder/binder mixture is passed to equipment that can both mix and pelletise.
  • An example of such equipment is an intensive mixer/granulator, e.g. as available from Maschinenfabrik Gustav Eirich GmbH & Co KG.
  • a pelletiser may be configured to expel processed material as it operates, allowing it to run continuously. Alternatively, the pelletiser may operate on a batch basis, with material being processed according to a defined programme and then expelled en masse. At completion of the pelletising process, the pellets (203) are expelled from the pelletiser.
  • processing the evaporite mineral powder to form a quantity of pellets may involve further steps.
  • the processing apparatus 202 may therefore include further devices.
  • the present method involves separating the partially dry insize fraction from at least one of the undersized and oversized fractions using screen(s) 206.
  • the undersized fraction may recirculated.
  • the undersized fraction may be returned to the processing apparatus 202.
  • the processing apparatus 202 includes a pelletiser, the undersized fraction of pellets may be returned to the pelletiser to be re-pelletised.
  • the oversized fraction may also be recirculated.
  • the oversized fraction may be returned to the processing apparatus 202.
  • Pellets of the oversized fraction may be recirculated to the grinding apparatus to be re-ground and then returned to the processing apparatus 202 to be pelletised.
  • the dried in-size fraction of pellets 209 form the pelletised evaporite mineral product.
  • the method for forming the pelletised evaporite mineral product may include further steps.
  • the method may comprise passing the in-size fraction of the quantity of pellets through a polishing screen.
  • the method may further comprise cooling the in-size fraction of the quantity of pellets.
  • the method may also comprise coating the in-size fraction of the quantity of pellets with a coating material to form the pelletised evaporite mineral product.
  • Coating the in-size fraction of the quantity of pellets may comprise feeding the pellets and the coating material into a mixer drum or a pan pelletiser and mixing the pellets with the coating material in order to coat the pellets with the coating material.
  • the in-size fraction of pellets may be packaged, for example in 600kg bags or 25kg sacks, or shipped loose for use or further processing elsewhere.
  • the pellets can be supplied for agricultural use. Eventually they can be spread on a field or other agricultural or horticultural substrate to act as a fertiliser.
  • the pellets may be used for purposes other than fertilisation.
  • the in-size fraction of the quantity of pellets may represent between 30% and 85% of the quantity of pellets.
  • the in-size fraction of the quantity of pellets may represent between 65% and 85% of the quantity of pellets.
  • the insize fraction of the quantity of pellets amount to 70% of the quantity of pellets.
  • the step of separating the quantity of pellets into an in-size fraction and at least one of an oversized fraction and undersized fraction may involve filtering out 30% of the quantity of pellets such that 70% of pellets (the in-size fraction) are passed to the second dryer 207 to be dried. It is therefore the case that more pellets are dried as part of the first drying step than as part of the second drying step.
  • pellets of the undersized and oversized fractions which are separated by screen(s) 206 may be recirculated and re-pelletised. There is therefore no benefit to drying pellets of the undersized or oversized fractions in the second drying step as the undersized/oversized pellets will be moistened again as they are re-pelletised and will need to be dried again after the re-pelletisation. Filtering the pellets to isolate in-size pellets using screen(s) 206 in between the first drying step performed by dryer 204 and the second drying step performed by dryer 207 therefore means that energy is not wasted by the second dryer due to drying undersized and/or oversized pellets.
  • the method of figure 2 therefore involves drying fewer pellets, for the production of a given volume of the pelletised evaporite mineral product, than the method seen in figure 1 in which dryer 104 dries pellets of all sizes (in-size, oversized and undersized). Therefore, in the method of figure 2, the amount of energy used by the process is reduced by not drying the oversized and undersized fractions of pellets in the second drying step. Accordingly, in order to produce a given volume of the pelletised evaporite mineral product, the total amount of energy consumed by the first dryer 204 and the second dryer 207 will be less than the amount of energy consumed by the dryer 104 of the prior art.
  • the method illustrated in figure 2 further addresses the problem of wet pellets getting stuck to screen during separation by implementing the first drying step to remove surface moisture from the pellets before the separating step is performed.
  • the ability of the first dryer to simultaneously agitate and dry the pellets is effective at minimising clumping of the pellets and prevents the pellets from getting stuck in the screen(s) during separation.
  • dryers which are configured to agitate while they dry such as rotary dryers, are highly energy intensive.
  • Rotary dryers dry their pellets by rotating the cylindrical housing in which the pellets are located such that the pellets are “tumbled”. Hot gas is conveyed through the cylindrical housing in a direction along the cylinder’s longitudinal axis and transfers heat to the pellets upon contact.
  • a significant portion of the hot gas passes straight through the housing without making much contact with the pellets inside. Heat transfer to the pellets in a rotary dryer can therefore be fairly inefficient.
  • the total amount of energy required to dry the pellets can thus further be reduced by using a second dryer which is not configured to agitate the pellets.
  • Figure 3 illustrates a variation on the previously described method for forming a pelletised evaporite mineral product. The method is similar to that previously described with respect to figure 2 and equivalent steps are illustrated as such. However, in figure 3, the second dryer 308 which performs the second drying step is not configured to agitate the pellets while it dries them. The second dryer 308 is a of a different type to the first dryer 204.
  • the second dryer 308 may comprise a drying surface on which the in-size fraction of pellets 207 may be placed.
  • the second dryer 308 may be configured to dry the pellets as they rest on the drying surface.
  • the second dryer may be configured to convey a stream of hot gas towards the drying surface.
  • the pellets may rest on the drying surface during the second drying step.
  • the dryer may dry the pellets using an energy source other than a hot gas, for example the dryer may comprise visible light or infrared lamps directed towards the drying surface.
  • the dryer may convey electromagnetic waves such as radio frequency waves and/or microwaves towards the drying surface.
  • the second dryer may be an electromagnetic dryer.
  • the second dryer may be an electromagnetic fluidized bed dryer.
  • the second dryer 308 is not configured to agitate the pellets as it dries them.
  • the pellets rest on the drying surface during the second drying step they are substantially stationary relative to the drying surface.
  • the fraction of in-size pellets do not have significantly varying positions on the drying surface. Instead, the pellets remain largely in the same area of the drying surface as they are carried by the surface Dryers which do not agitate the pellets as they dry them (non-agitating dryers) are less energy intensive than dryers which are configured to simultaneously agitate and dry the pellets.
  • the second dryer 308 is a belt dryer.
  • the belt dryer comprises a housing and a perforated belt.
  • the dryer is configured such that the perforated belt translates through the housing.
  • the perforated belt is the drying surface on which the in-size fraction of pellets rest.
  • the belt dryer 308 is configured to direct a stream of hot gas through the perforated belt such that the hot gas comes into contact with the pellets.
  • the belt dryer may comprise a source of hot gas located above the belt and be configured to direct a stream of gas towards the belt.
  • Non-agitating dryers such as belt dryers may operate at lower temperatures than agitating dryers such as fluidized beds or rotary dryers.
  • the first dryer may thus operate at a higher temperature than the temperature at which the second dryer operates.
  • the first dryer operating at a higher temperature than the temperature at which the second dryer operates may mean that the first dryer has a higher rate of transfer of energy to the pellets than the second dryer. In other words, the first dryer may create a greater heating effect than the second dryer.
  • the first dryer may transfer more heat to the pellets than the second dryer.
  • the first dryer may have a higher rate of heat transfer to the pellets than the second dryer.
  • the first dryer may be configured to increase the temperature of the pellets by a first temperature.
  • the second dryer may be configured to increase the temperature of the pellets by a second temperature.
  • the first temperature may be greater than the second temperature.
  • the first dryer may be configured to increase the temperature of the pellets to a first temperature.
  • the second dryer may be configured to increase the temperature of the pellets to a second temperature.
  • the first temperature may be greater than the second temperature.
  • the temperature at which the first dryer operates at may be higher than the temperature at which the second dryer operates by 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 335 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, or 685 °C.
  • the temperature at which the first dryer operates at may be higher than the temperature at which the second dryer operates at by 700 °C, 750 °C or 800 °C.
  • the first dryer may operate at a temperature of up to 800 °C.
  • the second dryer may operate at a temperature of up to 150 °C. According one example, the first dryer may operate at a temperature of 450 °C.
  • the second dryer may operate at a temperature of 115 °C.
  • both dyers 204 and 308 dry the pellets by conveying a stream of hot gas towards the pellets.
  • the first dryer conveys a first stream of gas onto the quantity of pellets and the second dryer conveys a second stream of gas onto the in-size fraction of the quantity of pellets.
  • the first stream of gas may have a temperature of 450 °C.
  • the second stream of gas may have a temperature of 115 °C.
  • the second dryer 308 energy is not required to deliberately agitate the pellets. Furthermore, in the second dryer 308, because the stream of gas is conveyed directly onto the pellets which rest on the drying surface, the heat transfer to the pellets in a belt dryer is more efficient than that of a rotary dryer. For example, in a belt dryer, less hot gas passes through the dryer without making contact with the pellets, than in a rotary. An agitating dryer may be more energy intensive than a non-agitating dryer. The first dryer may therefore have a higher rate of energy consumption than the second dryer.
  • the method of figure 3 therefore incorporates an initial first drying step using an agitating dryer to remove surface moisture from the pellets meaning that a separating step can be effectively implemented on the resulting partially dried pellets.
  • the method of figure 3 involves utilising a less energy- intensive dryer for a second drying step to remove the remaining moisture from only the in-size fraction of the pellets.
  • the method of figure 3 is less energy intensive than the method of the prior art of figure 1 due to the fact that only the in-size fraction of the quantity of pellets are dried as part of the second drying step. Furthermore, due to the implementation of a dryer which does not agitate the pellets as the second dryer 308, the method of figure 3 is less energy intensive than both the prior art method of figure 1 and the method of figure 2.
  • the advantages of the method of figure 3 with respect to the prior art method are twofold.
  • the total amount of energy consumed by the first dryer 204 and the second dryer 308 will be less than the amount of energy consumed by the dryer 104 of the prior art due to (1 ) the reduced number of pellets dried in the second drying step; and (2) the less energy-intensive dryer implemented used for the second drying step.
  • the methods described herein will primarily be implemented to create a pelletised polyhalite product. However, the methods could be applied equally to other evaporite minerals, for example, any one or more of halite, sylvite, carnallite, kainite, anhydrite, gypsum, kieserite, langbeinite, dolomite, calcite and magnesite.
  • the methods described herein may be performed by a production facility for forming a pelletised evaporite mineral product.
  • the production facility comprises processing apparatus 202, a first dryer 204, a separator 206 and a second dryer 208/308.
  • the processing apparatus may comprise a pelletiser.
  • the pelletiser may be a pan pelletiser.
  • the separator may comprise one or more screens.
  • the first and second dryers may be as previously described.
  • the processing apparatus is configured to process an evaporite mineral powder to form a quantity of pellets.
  • the facility is configured such that quantity of pellets are then input to the first dryer.
  • the first dryer is configured to dry the quantity of pellets by simultaneously agitating and drying the quantity of pellets.
  • the facility is configured such that the output of the first dryer is input to the separator.
  • the separator is configured to separate the quantity of pellets into an in-size faction and at least one of an oversized faction and an undersized fraction.
  • the facility is configured such that the in-size fraction of the quantity of pellets are input to the second dryer.
  • the second dryer is configured to dry the in-size faction of the quantity of pellets to form the pelletised evaporite mineral product.
  • the production facility may further comprise grinding apparatus.
  • the production facility may comprise one or more of high pressure grinding rollers (HPGR), a ball mill (e.g. a continuous “Hardinge” ball mill), an attritor mill and an air classifier.
  • HPGR high pressure grinding rollers
  • the production facility may be configured to form a pelletised evaporite mineral product from an evaporite mineral powder.
  • the production facility may be configured to pulverise an evaporite mineral feedstock to form the evaporite mineral powder.
  • the processing apparatus may also comprise a mixer e.g. a ribbon blender.
  • the production facility may be configured to mix the evaporite mineral power with a liquid and a binder to form a blend and process the blend using a pelletiser to form the quantity of pellets.
  • the processing apparatus of the production facility may comprise equipment that can both mix and pelletise.
  • An example of such equipment is an intensive mixer/granulator, e.g. as available from Maschinenfabrik Gustav Eirich GmbH & Co KG.
  • processing the evaporite mineral powder to form a quantity of pellets may involve further steps.
  • the processing apparatus of the production facility may therefore include further devices.
  • the undersized fraction may recirculated.
  • the production facility may be configured to return the undersized fraction to the processing apparatus.
  • the processing apparatus includes a pelletiser
  • the production facility may return the undersized fraction of pellets to the pelletiser to be re-pelletised.
  • the oversized fraction may also be recirculated.
  • the production facility may be configured to return the oversized fraction to the processing apparatus.
  • the production facility may be configured to recirculate the pellets of the oversized fraction to the grinding apparatus to be re-ground and then to the processing apparatus to be pelletised.
  • the production facility may include further devices for processing the output of the second dryer, the dried in-size fraction of pellets.
  • the production facility may include a polishing screen.
  • the production facility may include a mixer drum or a pan pelletiser in which the in-size pellets are coated with a coating material.
  • the production facility may include packaging apparatus for packaging the pelletised evaporite mineral product.

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Abstract

A method for forming a pelletised evaporite mineral product, the method comprising: processing an evaporite mineral powder to form a quantity of pellets; a first drying step comprising drying the quantity of pellets using a first dryer configured to simultaneously agitate and dry the quantity of pellets; separating the quantity of pellets into an in-size fraction and at least one of an oversized fraction and an undersized fraction; and a second drying step comprising drying the in-size fraction of the quantity of pellets using a second dryer to form the pelletised evaporite mineral product.

Description

TWO STAGE PELLET DRYING
TECHNICAL FIELD
This invention relates to forming pelletised products, for example for use as fertiliser.
BACKGROUND
It has been found to be advantageous to form evaporite minerals into pellets for use as fertiliser. Evaporite minerals, such as polyhalite, kieserite, dolomite and gypsum have the ability to provide nutrients, such as sulphur, potassium, calcium and magnesium to the soil, particularly when in a pelletised form.
A variety of techniques have been developed over recent years for forming raw untreated evaporite minerals into pellets. The process of pelletising the material commonly results in wet and often sticky pellets which need to be dried before they can be packaged and used by consumers.
The process of drying such evaporite mineral pellets has been found to be highly energy intensive. There is therefore a desire to develop a method for producing pelletised evaporite mineral products in which the drying stage consumes less energy.
SUMMARY OF THE INVENTION
According to a first aspect there is provided a method for forming a pelletised evaporite mineral product, the method comprising processing an evaporite mineral powder to form a quantity of pellets; a first drying step comprising drying the quantity of pellets using a first dryer configured to simultaneously agitate and dry the quantity of pellets; separating the quantity of pellets into an in-size fraction and at least one of an oversized fraction and an undersized fraction; and a second drying step comprising drying the in-size fraction of the quantity of pellets using a second dryer to form the pelletised evaporite mineral product.
The quantity of pellets may not be dried completely during the first drying step.
During the first drying step, the first dryer may be configured to remove surface moisture from the quantity of pellets. The in-size fraction of the quantity of pellets may be substantially completely dried during the second drying step.
The first drying step may remove between 0.5 and 2% of moisture from the quantity of pellets.
The second drying step may remove between 5 and 7% of moisture from the fraction of in-size pellets.
Fewer pellets may be dried in the first drying step than in the second drying step.
The in-size fraction may represent between 30% and 85% of the quantity of pellets.
The first drying step may have a shorter duration than the second drying step.
The first dryer may have a higher rate of energy consumption than the second dryer.
The first dryer may operate at a temperature higher than the temperature at which the second dryer operates.
The second dryer may operate at a temperature less than or equal to 150°C and the first dryer may operate a temperature greater than 150°C.
The first dryer may operate at a temperature of 450°C.
The second dryer may operate at a temperature of 115 °C.
In the second drying step, the in-size fraction of the quantity of pellets may not have significantly varying positions on the drying surface.
The second drying step may comprise drying the in-size fraction of the quantity of pellets on a drying surface of the second dryer.
The first dryer may be configured to convey a first stream of gas onto the quantity of pellets.
The second dryer may be configured to convey a second stream of gas towards the drying surface and the pellets may rest on the drying surface during the second drying step.
The first dryer may be a rotary dryer, a fluidized bed or a Roto Louvre dryer.
The second dryer may be a belt dryer or an electromagnetic dryer. The pelletised evaporite mineral may be one or more of polyhalite, halite, sylvite, carnallite, kainite, anhydrite, gypsum, kieserite, langbeinite, dolomite, calcite and magnesite.
The method may comprise pulverising an evaporite mineral feedstock to form the evaporite mineral powder.
Processing the evaporite mineral powder to form a quantity of pellets may comprise mixing the evaporite mineral power with a liquid and a binder to form a blend and processing the blend using the pelletiser to form the quantity of pellets.
Processing the blend using the pelletiser to form the quantity of pellets may comprise granulating the blend.
The method may comprise one or more of passing the in-size fraction of the quantity of pellets through a polishing screen; cooling the in-size fraction of the quantity of pellets; and coating the in-size fraction of the quantity of pellets to form the pelletised evaporite mineral product.
Separating the quantity of pellets into an in-size fraction and an oversized fraction may comprise passing the quantity of pellets through a screen having apertures of 4mm in diameter.
Separating the quantity of pellets into an in-size fraction and an undersized fraction may comprise passing the quantity of pellets through a screen having apertures of 2mm in diameter
Pellets of the in-size fraction of the quantity of pellets may have a diameter of between 2mm and 4mm.
According to a second aspect, there is provided a production facility for forming a pelletised evaporite mineral product, the production facility comprising processing apparatus configured to process an evaporite mineral powder to form a quantity of pellets; a first dryer configured to dry the quantity of pellets by simultaneously agitating and drying the quantity of pellets; a separator configured to separate the quantity of pellets into an in-size faction and at least one of an oversized faction and an undersized fraction; and a second dryer configured to dry the in-size faction of the quantity of pellets to form the pelletised evaporite mineral product.
The production facility may be configured such that the quantity of pellets are input to the first dryer; and the output of the first dryer is input to the separator.
The production facility may be configured such that the in-size fraction of the quantity of pellets are input to the second dryer.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a conventional method for forming a pelletised evaporite mineral product.
Figure 2 illustrates a method for forming a pelletised evaporite mineral product.
Figure 3 illustrates another method for forming a pelletised evaporite mineral product.
DETAILED DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a known process 100 for forming a pelletised evaporite mineral product.
As part of the process illustrated in figure 1 , evaporite mineral powder 101 undergoes processing at 102. The processing 102 may include a step of pelletising the powder. The result of the processing 102 is evaporite mineral pellets 103. As previously mentioned, when evaporite mineral pellets are created, they are commonly wet and sticky and therefore must be dried before being turned into a pelletised product ready for consumers. Therefore, according to the process seen in figure 1 , the pellets 103 are input to a dryer 104 to be dried.
Dry pellets 105 are therefore output from the dryer 104. In order to create a pelletised product that contains pellets of approximately similar sizes, for example within a desired range of sizes, the dry pellets 105 are passed through a separator 106 to separate the pellets having the desired size from other pellets of different sizes. The separator may comprise one or more screens. Pellets having a size within a desired range of sizes are referred to herein as the “in-size fraction” of pellets. Pellets having a size larger than the desired range of sizes are referred to as an “oversized fraction”. Pellets having a size smaller than the desired range of sizes are referred to as an “undersized fraction”. The step of using the screen 106 may therefore involve separating the in-size fraction from at least one of an oversized fraction and an undersized fraction. In figure 1 , 107 denotes the in-size fraction of pellets that are output from the screen 106. The in-size fraction of pellets 107 are used to form the pelletised evaporite mineral product.
Due to the cohesive nature of the wet pellets 103, pellets have a tendency to cake or clump together during the drying process. It has been found that caking or clumping of pellets is minimised when a dryer is used which agitates the pellets as it dries them. Such dryers include rotary dryers and fluidized beds. However, dryers which are configured to simultaneously agitate and dry the pellets are highly energy intensive. There is therefore a need to develop a process which allows evaporite mineral pellets to be dried in a way which requires less energy.
The inventors of the present invention have developed a method for forming a pelletised evaporite mineral product in which the pellets are effectively dried in a manner which minimizes the method’s energy consumption.
Figure 2 illustrates an example of such a method and the apparatus used to execute the process 200.
As part of the process illustrated in figure 2, evaporite mineral powder 201 undergoes processing.
The evaporite mineral powder 201 may have a size fraction of less than 2 mm. Preferably, the evaporite mineral powder 201 may have a size fraction of less than 1 .5 mm. More preferably, the evaporite mineral powder 201 may have a size fraction of less than 1 mm. The grains of the evaporite mineral powder may be finer than 2 mm. Preferably, the grains of the evaporite mineral powder may be finer than 1.5 mm. More preferably the grains of evaporite mineral powder 201 may be finer than 1 mm.
The evaporite mineral powder 201 may comprise at least one of a size and a density falling within a predetermined in-form range. The predetermined in-form range may comprise an upper limit of 1 mm to 2mm. The processing may be performed by processing apparatus 202. The processing may include a step of pelletising the powder. The processing apparatus 202 may comprise a pelletiser. The result of the processing by processing apparatus 202 is therefore a quantity of evaporite mineral pellets 203. The output of the processing apparatus 202 is wet, substantially spherical pellets. The quantity of wet pellets 203 are input to a dryer 204 to be dried.
The dryer 204 is configured to simultaneously agitate and dry the quantity of pellets. In the following description, to agitate the pellets means to cause the pellets to have significantly varying positions within the dryer whilst being dried. The agitation causes the pellets to move around within the dryer 204 so that the position of the pellets varies significantly whilst inside the dryer relative to any surface that the pellets may contact. The dryer 204 may be referred to herein as an “agitating dryer”. In an exemplary agitating dryer which has a drying surface on which the pellets may be placed before drying, the dryer may agitate the pellets during drying such that they do not rest on the surface. In other words, the dryer may cause the pellets to make intermittent contact with the drying surface whilst they are being dried. The dryer 204 may comprise a housing and dry the quantity of pellets by conveying a stream of hot gas towards pellets positioned within the housing. The gas may be air. The dryer may agitate the pellets by rotating the housing in which the pellets are located such that the pellets are “tumbled” as the hot gas passes through the housing. In this example, the pellets are agitated such that they do not rest on the interior surface of the housing. The pellets may make only intermittent contact with the interior surface of the housing. For example, the dryer 204 may be a rotary dryer. According to the example seen in figure 2, the dryer 204 is a rotary dryer and conveys hot gas through the housing of the dryer at a temperature of 450 °C. The temperature of the hot gas conveyed through the dryer may be greater than 300 °C, or greater than 400 °C, greater than 500 °C, greater than 600 °C or greater than 700 °C . The temperature of the hot gas may be between 300 °C and 600 °C, or between 300 °C and 500 °C or between 400°C and 600°C, or between 400 °C and 500 °C, or between 500 °C and 600 °C, or between 600 °C and 700 °C, or between 700 °C and 800 °C. The temperature of the hot gas conveyed through the dryer may be as high as 800 °C. According to an alternative example, the dryer 204 may comprise a housing and be configured to fluidize pellets within the housing. The dryer may be configured to inject a stream of hot gas through a perforated bed in the housing at a velocity higher than the settling velocity applied to the pellets. In this way, the pellets are allowed to “float” on the injected air above the perforated bed while they are dried by the hot gas. According to this example, the injected stream of hot gas agitates the pellets within the housing. For example, the dryer 204 may be a fluidized bed. According to one particular example, the dryer 204 is a fluidized bed and conveys hot gas into the dryer housing at a temperature of 250 °C. According to a further example, the dryer 204 may be a Roto Louvre dryer.
According to other examples, the dryer may dry the pellets using an energy source other than a hot gas. For example the dryer may comprise visible light or infrared lamps. The dryer may convey electromagnetic waves such as radio frequency waves and/or microwaves. For example, the dryer 204 may be an electromagnetic fluidized bed dryer. The dryer may agitate the pellets using a different method than those described, for example, the dryer may comprise a surface on which the pellets rest and the surface is configured to shift back and forth whilst the pellets are dried so as to agitate the pellets. The dryer may agitate the pellets by sequentially tipping the pellets onto a series of moving belts. The dryer may gently stir the pellets.
The dryer 204 performs a first drying step. The first drying step partially dries the quantity of pellets. The purpose of the first drying step is to remove surface moisture from the quantity of pellets. The first drying step dries the outer surface of the pellets so that the pellets are no longer prone to sticking together. The first drying step may completely dry the outer layer of each pellet. For example, the first drying step may remove between 0.5 and 2% of moisture from the quantity of pellets. According to one particular example, the first drying step removes 1 % of moisture from the quantity of pellets. According to other examples, the first drying step may involve removing up to 4% of moisture from the quantity of pellets. In other words, the quantity of pellets are not dried completely during the first drying step. The first dryer is configured to partially but not completely dry the pellets in the first drying step. The pellets are dried to leave a wet core but a harder outer surface. Partially dry pellets 205 are therefore output from the dryer 204. The partially dried pellets 205 are then passed through at least one screen 206 to separate the pellets having the desired size from other pellets. The first drying step is performed before the separating step. Due to the surface moisture having been removed from the pellets in the first drying step, the screen(s) 206 can effectively sort the quantity of pellets into different sizes without the pellets sticking to the screen. In other words, pellets which have a size that is less than the size of the apertures in the screen will pass through the screen without sticking to the screen. Pellets having a size within a desired range of sizes is referred to herein as the “in-size fraction” of pellets. Pellets having a size larger than the desired range of sizes are referred to as an “oversized fraction”. Pellets having a size smaller than the desired range of sizes are referred to as an “undersized fraction”. The step of using the screen(s) 206 therefore involves separating the in-size fraction from at least one of an oversized fraction or an undersized fraction. In other words, the separating step involves isolating the in-size fraction of the quantity of pellets.
The method may comprise separating the in-size fraction from an oversized fraction only. The method may comprise separating the in-size fraction from an undersized fraction only. The method may comprise separating the in-size fraction from an undersized fraction and an oversized fraction. According to an example in which the quantity of pellets is made up of undersized, oversized and in-size fractions, two separate screens are used to isolate the in-size fraction of pellets from the rest of the quantity of pellets.
According to one example, pellets of the in-size fraction have a diameter between 2mm and 4mm. Pellets of the undersized fraction therefore have a diameter of less than 2mm. Pellets of the oversized fraction therefore have a diameter of more than 4mm. Thus according to this example, the screening step 206 to isolate the in-size fraction of pellets may involve passing the quantity of pellets through a first screen having apertures of 4mm in diameter to remove the oversized fraction, and passing the remaining pellets through a second screen having apertures of 2mm in diameter to remove the undersized fraction. According to further examples, the desired range of sizes may have a lower or higher upper bound and/or a lower or higher lower bound.
The size of an in-size pellet may be such that it has a diameter less than 5mm, less than 4mm, less than 3mm, less than 2mm or less than 1 mm. The size of the pellet may be such that it has a diameter greater than 4mm, greater than 3mm, greater than 2mm, greater than 1 mm or greater than 0.5mm. The volume of an in-size pellet may be less than 20mm3, less than 15mm3, less than 10mm3, less than 8mm3 or less than 5mm3. The volume of the pellet may be greater than 15mm3, greater than 10mm3, greater than 8mm3, greater than 5mm3 or greater than 1 mm3. Other dimensions could be adopted.
In figure 2, 207 denotes the in-size fraction of the quantity of pellets that are output from the screen(s) 206. The in-size fraction 207 are passed to a second dryer 208 to be dried. In the example seen in figure 2, dryer 208 is also configured to simultaneously agitate and dry the pellets. The dryer 208 may be the same type of dryer as dryer 204. In the example seen in figure 2, both dryers are rotary dryers. Alternatively, as will be explained in more detail below, dryers 204 and 208 may be different types of dryers.
The second dryer 208 performs a second drying step in which the in-size fraction of the quantity of pellets are dried. The separating step 206 is performed before the second drying step 208. The first drying step 204 is therefore performed before the separating and second drying step. The purpose of the second drying step is to substantially dry the in-size fraction of the quantity of pellets so that they may be used to form the evaporite pelletised product 209. The evaporative pelletised product 209 is drier that the quantity of wet pellets 203. The evaporite pelletised product 209 is drier than the partially dry pellets 205. The second dryer may be configured to substantially completely dry the in-size fraction of pellets during the second drying step. Performing the second drying step may remove between 5 and 7% of moisture from the fraction of in-size pellets. According to one particular example, the second drying step removes 6% of moisture from the quantity of pellets. According to other examples, the second drying step may involve removing a higher or lower percentage of moisture such that the in-size pellets are substantially completely dried. Substantially completely dry pellets may have a moisture content of less than 1 %, for example 0.2% or 0.5%. The quantity of pellets are substantially completely dried during the second drying step. More moisture may be removed from the pellets in the second drying step than in the first drying step. The second drying step may therefore have a longer duration than the first drying step. In other words, the first drying step has a shorter duration than the second drying step.
According to one example, the quantity of pellets 203 output by the processing apparatus 202 have a moisture level of 7.5%. After the first drying step is performed by the first dryer 204, the partially dried pellets 205 have a moisture level of 6.5% when they are screened by screen(s) 206. The in-size fraction of the partially dried pellets 207 therefore have a moisture level of 6.5% upon entering the second dryer 208. After the second drying step is performed by the second dryer 208, the in-size fraction of substantially completely dry pellets 209 have a moisture level of 0.5% or lower.
In figure 2, 209 denotes the dried in-size fraction of pellets that are output from the dryer 208. The dried in-size fraction of pellets are used to form the evaporite pelletised product.
Figure 2 illustrates a method used for forming a pelletised evaporite mineral product from an evaporite mineral powder. The process of forming the product may additionally comprise pulverising an evaporite mineral feedstock to form the evaporite mineral powder. The method may therefore involve a preliminary step of grinding a raw untreated evaporite mineral into powder using grinding apparatus. For example, using one or more of high pressure grinding rollers (HPGR), a ball mill (e.g. a continuous “Hardinge” ball mill), an attritor mill and an air classifier.
Although not the focus of the present application, it is contemplated that processing the evaporite mineral powder to form a quantity of pellets using processing apparatus 202 may involve a number of steps. Processing the evaporite mineral powder to form a quantity of pellets may comprise mixing the evaporite mineral power with a liquid and a binder to form a blend and processing the blend using a pelletiser to form the quantity of pellets. Processing the blend using the pelletiser to form the quantity of pellets may comprise granulating the blend.
According to one example, in a first processing step, water and a binder are added to the evaporite mineral powder. In the description below, the additions of water and binder are specified by mass with reference to the mass of the powder to which they are added. The binder may be a starch-based binder such as starch itself or flour or an adhesive such as PVA. Water may be added in the range of 5% to 10%, more preferably between 7% and 8%. The amount of binder to be added will depend on the qualities of the binder. For typical binders, e.g. starch or flour, the amount added may be in the range of 0.5% to 4%. The binder may be added directly to the evaporite mineral powder, or it may first be added to the water and then the water and binder combination may be added to the powder. According to further examples, other evaporite minerals and/or micronutrients may be added to the powder, binder, water combination.
As part of a second processing step, the powder/binder mixture is mixed until homogeneous. The processing apparatus 202 may therefore include a mixer e.g. a ribbon blender, pin mixer or other high shear mixer.
As a third processing step, the powder/binder mixture is pelletised. The processing apparatus 202 may therefore include a pelletiser e.g. a pan pelletiser. According to one approach, which has been found to be efficient, the powder/binder mixture is passed to equipment that can both mix and pelletise. An example of such equipment is an intensive mixer/granulator, e.g. as available from Maschinenfabrik Gustav Eirich GmbH & Co KG. A pelletiser may be configured to expel processed material as it operates, allowing it to run continuously. Alternatively, the pelletiser may operate on a batch basis, with material being processed according to a defined programme and then expelled en masse. At completion of the pelletising process, the pellets (203) are expelled from the pelletiser.
According to other examples, processing the evaporite mineral powder to form a quantity of pellets may involve further steps. The processing apparatus 202 may therefore include further devices. As previously discussed, the present method involves separating the partially dry insize fraction from at least one of the undersized and oversized fractions using screen(s) 206. In an example in which the quantity of pellets includes an undersized fraction, the undersized fraction may recirculated. For example, the undersized fraction may be returned to the processing apparatus 202. For example, where the processing apparatus 202 includes a pelletiser, the undersized fraction of pellets may be returned to the pelletiser to be re-pelletised.
In an example in which the quantity of pellets includes an oversized fraction, the oversized fraction may also be recirculated. The oversized fraction may be returned to the processing apparatus 202. Pellets of the oversized fraction may be recirculated to the grinding apparatus to be re-ground and then returned to the processing apparatus 202 to be pelletised.
As mentioned, the dried in-size fraction of pellets 209 form the pelletised evaporite mineral product. The method for forming the pelletised evaporite mineral product may include further steps. For example, the method may comprise passing the in-size fraction of the quantity of pellets through a polishing screen. The method may further comprise cooling the in-size fraction of the quantity of pellets. The method may also comprise coating the in-size fraction of the quantity of pellets with a coating material to form the pelletised evaporite mineral product. Coating the in-size fraction of the quantity of pellets may comprise feeding the pellets and the coating material into a mixer drum or a pan pelletiser and mixing the pellets with the coating material in order to coat the pellets with the coating material.
Finally, the in-size fraction of pellets may be packaged, for example in 600kg bags or 25kg sacks, or shipped loose for use or further processing elsewhere. The pellets can be supplied for agricultural use. Eventually they can be spread on a field or other agricultural or horticultural substrate to act as a fertiliser. The pellets may be used for purposes other than fertilisation.
It will be appreciated that the method illustrated in figure 2 is advantageous with respect to the known method seen in figure 1 , as the overall quantity of pellets which are dried is reduced. The in-size fraction of the quantity of pellets may represent between 30% and 85% of the quantity of pellets. The in-size fraction of the quantity of pellets may represent between 65% and 85% of the quantity of pellets. According to one example, the insize fraction of the quantity of pellets amount to 70% of the quantity of pellets. In other words, in this example, the step of separating the quantity of pellets into an in-size fraction and at least one of an oversized fraction and undersized fraction may involve filtering out 30% of the quantity of pellets such that 70% of pellets (the in-size fraction) are passed to the second dryer 207 to be dried. It is therefore the case that more pellets are dried as part of the first drying step than as part of the second drying step.
As previously described, pellets of the undersized and oversized fractions which are separated by screen(s) 206 may be recirculated and re-pelletised. There is therefore no benefit to drying pellets of the undersized or oversized fractions in the second drying step as the undersized/oversized pellets will be moistened again as they are re-pelletised and will need to be dried again after the re-pelletisation. Filtering the pellets to isolate in-size pellets using screen(s) 206 in between the first drying step performed by dryer 204 and the second drying step performed by dryer 207 therefore means that energy is not wasted by the second dryer due to drying undersized and/or oversized pellets. The method of figure 2 therefore involves drying fewer pellets, for the production of a given volume of the pelletised evaporite mineral product, than the method seen in figure 1 in which dryer 104 dries pellets of all sizes (in-size, oversized and undersized). Therefore, in the method of figure 2, the amount of energy used by the process is reduced by not drying the oversized and undersized fractions of pellets in the second drying step. Accordingly, in order to produce a given volume of the pelletised evaporite mineral product, the total amount of energy consumed by the first dryer 204 and the second dryer 207 will be less than the amount of energy consumed by the dryer 104 of the prior art.
The method illustrated in figure 2 further addresses the problem of wet pellets getting stuck to screen during separation by implementing the first drying step to remove surface moisture from the pellets before the separating step is performed. As previously mentioned, the ability of the first dryer to simultaneously agitate and dry the pellets is effective at minimising clumping of the pellets and prevents the pellets from getting stuck in the screen(s) during separation. However, dryers which are configured to agitate while they dry, such as rotary dryers, are highly energy intensive. Rotary dryers dry their pellets by rotating the cylindrical housing in which the pellets are located such that the pellets are “tumbled”. Hot gas is conveyed through the cylindrical housing in a direction along the cylinder’s longitudinal axis and transfers heat to the pellets upon contact. However, a significant portion of the hot gas passes straight through the housing without making much contact with the pellets inside. Heat transfer to the pellets in a rotary dryer can therefore be fairly inefficient.
The total amount of energy required to dry the pellets can thus further be reduced by using a second dryer which is not configured to agitate the pellets.
Figure 3 illustrates a variation on the previously described method for forming a pelletised evaporite mineral product. The method is similar to that previously described with respect to figure 2 and equivalent steps are illustrated as such. However, in figure 3, the second dryer 308 which performs the second drying step is not configured to agitate the pellets while it dries them. The second dryer 308 is a of a different type to the first dryer 204.
According to this example, the second dryer 308 may comprise a drying surface on which the in-size fraction of pellets 207 may be placed. The second dryer 308 may be configured to dry the pellets as they rest on the drying surface. The second dryer may be configured to convey a stream of hot gas towards the drying surface. The pellets may rest on the drying surface during the second drying step. Alternatively, the dryer may dry the pellets using an energy source other than a hot gas, for example the dryer may comprise visible light or infrared lamps directed towards the drying surface. The dryer may convey electromagnetic waves such as radio frequency waves and/or microwaves towards the drying surface. The second dryer may be an electromagnetic dryer. The second dryer may be an electromagnetic fluidized bed dryer.
The second dryer 308 is not configured to agitate the pellets as it dries them. In other words, when the pellets rest on the drying surface during the second drying step they are substantially stationary relative to the drying surface. In other words, during the second drying step, the fraction of in-size pellets do not have significantly varying positions on the drying surface. Instead, the pellets remain largely in the same area of the drying surface as they are carried by the surface Dryers which do not agitate the pellets as they dry them (non-agitating dryers) are less energy intensive than dryers which are configured to simultaneously agitate and dry the pellets.
In the example seen in figure 3, the second dryer 308 is a belt dryer. The belt dryer comprises a housing and a perforated belt. The dryer is configured such that the perforated belt translates through the housing. In this example, the perforated belt is the drying surface on which the in-size fraction of pellets rest. The belt dryer 308 is configured to direct a stream of hot gas through the perforated belt such that the hot gas comes into contact with the pellets. According to another example, the belt dryer may comprise a source of hot gas located above the belt and be configured to direct a stream of gas towards the belt.
Non-agitating dryers such as belt dryers may operate at lower temperatures than agitating dryers such as fluidized beds or rotary dryers. The first dryer may thus operate at a higher temperature than the temperature at which the second dryer operates. The first dryer operating at a higher temperature than the temperature at which the second dryer operates may mean that the first dryer has a higher rate of transfer of energy to the pellets than the second dryer. In other words, the first dryer may create a greater heating effect than the second dryer. The first dryer may transfer more heat to the pellets than the second dryer. The first dryer may have a higher rate of heat transfer to the pellets than the second dryer. The first dryer may be configured to increase the temperature of the pellets by a first temperature. The second dryer may be configured to increase the temperature of the pellets by a second temperature. The first temperature may be greater than the second temperature. The first dryer may be configured to increase the temperature of the pellets to a first temperature. The second dryer may be configured to increase the temperature of the pellets to a second temperature. The first temperature may be greater than the second temperature. The temperature at which the first dryer operates at may be higher than the temperature at which the second dryer operates by 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 335 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, or 685 °C. The temperature at which the first dryer operates at may be higher than the temperature at which the second dryer operates at by 700 °C, 750 °C or 800 °C. The first dryer may operate at a temperature of up to 800 °C. The second dryer may operate at a temperature of up to 150 °C. According one example, the first dryer may operate at a temperature of 450 °C. The second dryer may operate at a temperature of 115 °C.
According to the example seen in figure 3 in which the second dryer 308 is a belt dryer and the first dryer 204 is a rotary dryer, both dyers 204 and 308 dry the pellets by conveying a stream of hot gas towards the pellets. In this example, the first dryer conveys a first stream of gas onto the quantity of pellets and the second dryer conveys a second stream of gas onto the in-size fraction of the quantity of pellets. The first stream of gas may have a temperature of 450 °C. The second stream of gas may have a temperature of 115 °C.
In the second dryer 308, energy is not required to deliberately agitate the pellets. Furthermore, in the second dryer 308, because the stream of gas is conveyed directly onto the pellets which rest on the drying surface, the heat transfer to the pellets in a belt dryer is more efficient than that of a rotary dryer. For example, in a belt dryer, less hot gas passes through the dryer without making contact with the pellets, than in a rotary. An agitating dryer may be more energy intensive than a non-agitating dryer. The first dryer may therefore have a higher rate of energy consumption than the second dryer.
As previously explained, due to clumping of the wet and sticky pellets leaving the pelletiser, it is not practicable to use a non-agitating dryer to dry pellets output by the pelletiser. The method of figure 3 therefore incorporates an initial first drying step using an agitating dryer to remove surface moisture from the pellets meaning that a separating step can be effectively implemented on the resulting partially dried pellets. After the separating step to isolate the in-size fraction of pellets, the method of figure 3 involves utilising a less energy- intensive dryer for a second drying step to remove the remaining moisture from only the in-size fraction of the pellets. For the reasons explained with respect to figure 2, the method of figure 3 is less energy intensive than the method of the prior art of figure 1 due to the fact that only the in-size fraction of the quantity of pellets are dried as part of the second drying step. Furthermore, due to the implementation of a dryer which does not agitate the pellets as the second dryer 308, the method of figure 3 is less energy intensive than both the prior art method of figure 1 and the method of figure 2.
The advantages of the method of figure 3 with respect to the prior art method are twofold. In order to produce a given volume of the pelletised evaporite mineral product, the total amount of energy consumed by the first dryer 204 and the second dryer 308 will be less than the amount of energy consumed by the dryer 104 of the prior art due to (1 ) the reduced number of pellets dried in the second drying step; and (2) the less energy-intensive dryer implemented used for the second drying step.
It is envisaged that the methods described herein will primarily be implemented to create a pelletised polyhalite product. However, the methods could be applied equally to other evaporite minerals, for example, any one or more of halite, sylvite, carnallite, kainite, anhydrite, gypsum, kieserite, langbeinite, dolomite, calcite and magnesite.
The methods described herein may be performed by a production facility for forming a pelletised evaporite mineral product. The production facility comprises processing apparatus 202, a first dryer 204, a separator 206 and a second dryer 208/308. The processing apparatus may comprise a pelletiser. The pelletiser may be a pan pelletiser. The separator may comprise one or more screens. The first and second dryers may be as previously described.
The processing apparatus is configured to process an evaporite mineral powder to form a quantity of pellets. The facility is configured such that quantity of pellets are then input to the first dryer. The first dryer is configured to dry the quantity of pellets by simultaneously agitating and drying the quantity of pellets. The facility is configured such that the output of the first dryer is input to the separator. The separator is configured to separate the quantity of pellets into an in-size faction and at least one of an oversized faction and an undersized fraction. The facility is configured such that the in-size fraction of the quantity of pellets are input to the second dryer. The second dryer is configured to dry the in-size faction of the quantity of pellets to form the pelletised evaporite mineral product. The production facility may further comprise grinding apparatus. For example, the production facility may comprise one or more of high pressure grinding rollers (HPGR), a ball mill (e.g. a continuous “Hardinge” ball mill), an attritor mill and an air classifier. The production facility may be configured to form a pelletised evaporite mineral product from an evaporite mineral powder. The production facility may be configured to pulverise an evaporite mineral feedstock to form the evaporite mineral powder.
The processing apparatus may also comprise a mixer e.g. a ribbon blender. The production facility may be configured to mix the evaporite mineral power with a liquid and a binder to form a blend and process the blend using a pelletiser to form the quantity of pellets.
According to one specific example, the processing apparatus of the production facility may comprise equipment that can both mix and pelletise. An example of such equipment is an intensive mixer/granulator, e.g. as available from Maschinenfabrik Gustav Eirich GmbH & Co KG.
According to other examples, processing the evaporite mineral powder to form a quantity of pellets may involve further steps. The processing apparatus of the production facility may therefore include further devices.
In an example in which the quantity of pellets includes an undersized fraction, after the separator separates the quantity of pellets into an in-size fraction and an undersized fraction, the undersized fraction may recirculated. For example, the production facility may be configured to return the undersized fraction to the processing apparatus. For example, where the processing apparatus includes a pelletiser, the production facility may return the undersized fraction of pellets to the pelletiser to be re-pelletised.
In an example in which the quantity of pellets includes an oversized fraction, the oversized fraction may also be recirculated. The production facility may be configured to return the oversized fraction to the processing apparatus. The production facility may be configured to recirculate the pellets of the oversized fraction to the grinding apparatus to be re-ground and then to the processing apparatus to be pelletised. The production facility may include further devices for processing the output of the second dryer, the dried in-size fraction of pellets. For example, the production facility may include a polishing screen. The production facility may include a mixer drum or a pan pelletiser in which the in-size pellets are coated with a coating material. Finally, the production facility may include packaging apparatus for packaging the pelletised evaporite mineral product.
The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1 . A method for forming a pelletised evaporite mineral product, the method comprising: processing an evaporite mineral powder to form a quantity of pellets; a first drying step comprising drying the quantity of pellets using a first dryer configured to simultaneously agitate and dry the quantity of pellets; separating the quantity of pellets into an in-size fraction and at least one of an oversized fraction and an undersized fraction; and a second drying step comprising drying the in-size fraction of the quantity of pellets using a second dryer to form the pelletised evaporite mineral product, wherein the first dryer operates at a temperature higher than the temperature at which the second dryer operates.
2. The method according to claim 1 , wherein the quantity of pellets are not dried completely during the first drying step.
3. The method according to claims 1 or 2, wherein, during the first drying step, the first dryer is configured to remove surface moisture from the quantity of pellets.
4. The method according to any preceding claim, wherein the in-size fraction of the quantity of pellets are substantially completely dried during the second drying step.
5. The method according to any preceding claim, wherein the first drying step removes between 0.5 and 2% of moisture from the quantity of pellets.
6. The method according to any preceding claim, wherein the second drying step removes between 5 and 7% of moisture from the fraction of in-size pellets.
7. The method according to any preceding claim, wherein fewer pellets are dried in the second drying step than in the first drying step.
8. The method according to any preceding claim, wherein the in-size fraction represent between 30% and 85% of the quantity of pellets.
9. The method according to any preceding claim, wherein the first drying step has a shorter duration than the second drying step
10. The method according to any preceding claim, wherein the first dryer has a higher rate of energy consumption than the second dryer.
11 . The method according to any preceding claim, wherein the second dryer operates at a temperature less than or equal to 150°C and the first dryer operates a temperature greater than 150°C.
12. The method according to any preceding claim, wherein the first dryer operates at a temperature of 450°C.
13. The method according to any preceding claim, wherein the second dryer operates at a temperature of 115 °C.
14. The method according to any preceding claim, wherein in the second drying step, the in-size fraction of the quantity of pellets do not have significantly varying positions on the drying surface.
15. The method according to any preceding claim, wherein the second drying step comprises drying the in-size fraction of the quantity of pellets on a drying surface of the second dryer.
16. The method according to any preceding claim, wherein the first dryer is configured to convey a first stream of gas onto the quantity of pellets.
17. The method according to claim 16, wherein the second dryer is configured to convey a second stream of gas towards the drying surface and the pellets rest on the drying surface during the second drying step.
18. The method according to any preceding claim, wherein the first dryer is a rotary dryer, a fluidized bed or a Roto Louvre dryer.
19. The method according to any preceding claim, wherein the second dryer is a belt dryer or an electromagnetic dryer.
20. The method according to any preceding claim, wherein the pelletised evaporite mineral is one or more of polyhalite, halite, sylvite, carnallite, kainite, anhydrite, gypsum, kieserite, langbeinite, dolomite, calcite and magnesite.
21. The method according to any preceding claim, wherein the method comprises pulverising an evaporite mineral feedstock to form the evaporite mineral powder.
22. The method according to any preceding claim, wherein processing the evaporite mineral powder to form a quantity of pellets comprises mixing the evaporite mineral power with a liquid and a binder to form a blend and processing the blend using the pelletiser to form the quantity of pellets.
23. The method according to claim 22, wherein processing the blend using the pelletiser to form the quantity of pellets comprises granulating the blend.
24. The method according to any preceding claim, wherein the method comprises one or more of: passing the in-size fraction of the quantity of pellets through a polishing screen; cooling the in-size fraction of the quantity of pellets; and coating the in-size fraction of the quantity of pellets to form the pelletised evaporite mineral product.
25. The method of any preceding claim, wherein separating the quantity of pellets into an in-size fraction and an oversized fraction comprises passing the quantity of pellets through a screen having apertures of 4mm in diameter.
26. The method of any preceding claim, wherein separating the quantity of pellets into an in-size fraction and an undersized fraction comprises passing the quantity of pellets through a screen having apertures of 2mm in diameter
27. The method of any preceding claim, wherein pellets of the in-size fraction of the quantity of pellets have a diameter of between 2mm and 4mm.
28. A production facility for forming a pelletised evaporite mineral product, the production facility comprising: processing apparatus configured to process an evaporite mineral powder to form a quantity of pellets; a first dryer configured to dry the quantity of pellets by simultaneously agitating and drying the quantity of pellets; a separator configured to separate the quantity of pellets into an in-size faction and at least one of an oversized faction and an undersized fraction; and a second dryer configured to dry the in-size fraction of the quantity of pellets to form the pelletised evaporite mineral product, wherein the first dryer operates at a temperature higher than the temperature at which the second dryer operates.
29. The production facility of claim 28, wherein the facility is configured such that: the quantity of pellets are input to the first dryer; and the output of the first dryer is input to the separator.
30. The production facility of claims 28 or 29, wherein the facility is configured such that the in-size fraction of the quantity of pellets are input to the second dryer.
PCT/GB2025/050138 2024-01-26 2025-01-24 Two stage pellet drying Pending WO2025158164A1 (en)

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