Two-stage pellet drying

Abstract

A method of forming a pelleted 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, the first dryer configured for simultaneous agitation and drying of the quantity of pellets; separating the quantity of pellets into a moderate size fraction and at least one of an oversized size fraction and an undersized size fraction; and a second drying step comprising drying the moderate size fraction of the quantity of pellets using a second dryer to form the pelleted evaporite mineral product.

Description

Technical Field

[0001] This invention relates to products that are formed into pellets, for example, for use as fertilizers. Background Technology

[0002] It has been found that forming evaporite minerals into pellets for use as fertilizer is advantageous. Evaporite minerals, such as carnallite, kieserite, dolomite, and gypsum, have the ability to provide nutrients such as sulfur, potassium, calcium, and magnesium to the soil, especially when they are in pellet form.

[0003] In recent years, various technologies have been developed for forming untreated coarse evaporite minerals into pellets. Methods of pelletizing materials typically produce moist and often sticky pellets that need to be dried before they can be packaged and used by consumers.

[0004] The methods for drying these evaporite mineral pellets have been found to be highly energy-intensive. Therefore, it is desirable to develop a method for producing pelletized evaporite mineral products in which the drying stage consumes less energy. Summary of the Invention

[0005] According to a first aspect, a method for forming a pelletized evaporite mineral product is provided, the method comprising: processing evaporite mineral powder to form a quantity of pellets; a first drying step, the 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 at least one of an in-size fraction and an oversized fraction and an undersized fraction; and a second drying step, the second drying step comprising drying the in-size fraction of the quantity of pellets using a second dryer to form the pelletized evaporite mineral product.

[0006] During the first drying step, a certain amount of pellets may not be completely dried.

[0007] During the first drying step, the first dryer may be configured to remove surface moisture from the stated amount of pellets.

[0008] During the second drying step, the appropriate size fraction of the pellets can be dried substantially completely.

[0009] The first drying step can remove 0.5% to 2% of the moisture from the given amount of pellets.

[0010] The second drying step can remove 5% to 7% of the moisture from the medium-sized fraction of the pellets.

[0011] Fewer pellets can be dried in the first drying step compared to the second drying step.

[0012] The appropriate size fraction can account for 30% to 85% of the total amount of pellets.

[0013] The first drying step can have a shorter duration than the second drying step.

[0014] The first dryer can have a higher energy consumption rate than the second dryer.

[0015] The first dryer can operate at a higher temperature than the second dryer.

[0016] The second dryer can operate at a temperature of less than or equal to 150°C, and the first dryer can operate at a temperature greater than 150°C.

[0017] The first dryer can operate at a temperature of 450°C.

[0018] The second dryer can operate at a temperature of 115°C.

[0019] In the second drying step, the position of the appropriate size fraction of the certain amount of pellets on the drying surface may not change significantly.

[0020] The second drying step may include drying the appropriate size fraction of the given amount of pellets on the drying surface of the second dryer.

[0021] The first dryer can be configured to deliver a first airflow onto the given amount of pellets.

[0022] The second dryer can be configured to deliver a second airflow to the drying surface, and the pellets can remain on the drying surface during the second drying step.

[0023] The first dryer can be a rotary dryer, a fluidized bed dryer, or a Roto Louvre dryer.

[0024] The second dryer can be a belt dryer or an electromagnetic dryer.

[0025] Granular evaporite minerals can be one or more of the following: carnallite, rock salt, potash, carnallite, kainite, anhydrite, gypsum, magnesium sulfate, anhydrous potassium magnesium alum, dolomite, calcite, and magnesite.

[0026] The method may include crushing evaporite mineral raw materials to form evaporite mineral powder.

[0027] The process of processing evaporite mineral powder to form a certain amount of pellets may include mixing evaporite mineral powder with liquid and binder to form a blend, and processing the blend using a granulator to form a certain amount of pellets.

[0028] The process of using a granulator to process blends to form a certain amount of pellets may include pelletizing the blends.

[0029] The method may include one or more of the following steps: passing a certain amount of pellets of appropriate size fraction through a polishing screen; cooling the certain amount of pellets of appropriate size fraction; and coating the certain amount of pellets of appropriate size fraction to form the pelletized evaporite mineral product.

[0030] The process of separating the given amount of pellets into medium-sized and oversized fractions may include passing the given amount of pellets through a sieve with holes having a diameter of 4 mm.

[0031] The process of separating the given amount of pellets into medium-sized fractions and excessively small-sized fractions may include passing the given amount of pellets through a sieve with holes having a diameter of 2 mm.

[0032] The pellets of the appropriate size grade of the specified amount of pellets can have a diameter of 2 mm to 4 mm.

[0033] According to a second aspect, a production facility for forming pelletized evaporite mineral products is provided, the production facility comprising: a processing device configured to process evaporite mineral powder to form a certain amount of pellets; a first dryer configured to dry the certain amount of pellets by simultaneously stirring and drying the certain amount of pellets; a separator configured to separate the certain amount of pellets into at least one of a moderate-size fraction and an oversized fraction and an undersized fraction; and a second dryer configured to dry the moderate-size fraction of the certain amount of pellets to form the pelletized evaporite mineral product.

[0034] The production facility can be configured to: input a certain amount of pellets into the first dryer; and input the output of the first dryer into a separator.

[0035] The production facility can be configured to input a certain amount of pellets of appropriate size into a second dryer. Attached Figure Description

[0036] Figure 1 A conventional method for forming pelletized evaporite mineral products is shown.

[0037] Figure 2A method for forming pelletized evaporite mineral products is shown.

[0038] Figure 3 This demonstrates another method for forming pelletized evaporite mineral products. Detailed Implementation

[0039] Figure 1 A known process 100 for forming pelletized evaporite mineral products is shown.

[0040] As Figure 1 As part of the process shown, evaporite mineral powder 101 is processed at 102. Processing 102 may include a step of pelletizing the powder. The result of processing 102 is evaporite mineral pellets 103. As mentioned earlier, when evaporite mineral pellets are produced, they are typically wet and sticky, and therefore must be dried before becoming a pelletized product ready for consumers. Therefore, according to Figure 1 The method shown involves feeding pellets 103 into dryer 104 for drying.

[0041] Therefore, dried pellets 105 are output from dryer 104. To produce a pelletized product comprising pellets of approximately similar sizes (e.g., within the desired size range), the dried pellets 105 are passed through separator 106 to separate pellets of the desired size from other pellets of different sizes. The separator may include one or more screens. Pellets with sizes within the desired size range are referred herein to as a “moderate size fraction” of pellets. Pellets with sizes larger than the desired size range are referred to as an “oversized size fraction”. Pellets with sizes smaller than the desired size range are referred to as an “undersized size fraction”. Therefore, the step of using screen 106 may include separating the moderate size fraction from at least one of the oversized and undersized size fractions. Figure 1 In this context, 107 represents the moderate size fraction of the pellets output from screen 106. The moderate size fraction of pellets 107 is used to form pelletized evaporite mineral products.

[0042] Due to the adhesive properties of wet pellets 103, the pellets tend to clump or agglomerate during drying. It has been found that pellet clumping or agglomeration is minimized when using a dryer that agitates the pellets during drying. Such dryers include rotary dryers and fluidized beds. However, configuring a dryer for simultaneously agitating and drying pellets is highly energy-intensive. Therefore, there is a need to develop a method that enables the drying of evaporite mineral pellets in a manner requiring less energy.

[0043] The inventors of this invention have developed a method for forming pelletized evaporite mineral products, wherein the pellets are dried efficiently in a manner that minimizes the energy consumption of the method.

[0044] Figure 2 An example of the method and apparatus for implementing process 200 is shown.

[0045] As Figure 2 As part of the process shown, evaporite mineral powder 201 undergoes processing.

[0046] The evaporite mineral powder 201 can have a size fraction of less than 2 mm. Preferably, the evaporite mineral powder 201 can have a size fraction of less than 1.5 mm. More preferably, the evaporite mineral powder 201 can have a size fraction of less than 1 mm. The particles of the evaporite mineral powder can be finer than 2 mm. Preferably, the particles of the evaporite mineral powder can be finer than 1.5 mm. More preferably, the particles of the evaporite mineral powder 201 can be finer than 1 mm.

[0047] The evaporite mineral powder 201 may include at least one of a size and density falling within a predetermined form range. The predetermined form range may include an upper limit of 1 mm to 2 mm.

[0048] This processing can be performed by processing device 202. The processing may include the step of granulating the powder. Processing device 202 may include a granulator. Therefore, the result of processing by processing device 202 is a certain amount of evaporite mineral pellets 203. The output of processing device 202 is wet, substantially spherical pellets. A certain amount of wet pellets 203 is fed into dryer 204 for drying.

[0049] Dryer 204 is configured to simultaneously agitate and dry the stated quantity of pellets. In the following description, agitating the pellets means causing a significant change in the position of the pellets within the dryer while they are being dried. Agitation causes the pellets to move around within dryer 204, resulting in a significant change in the position of the pellets relative to any surface they may come into contact with within the dryer. Dryer 204 may be referred to herein as an "agglomerated dryer." In an exemplary agitated dryer with a drying surface (on which the pellets may be placed before drying), the dryer may agitate the pellets during drying so that they do not remain on the surface. In other words, the dryer may allow the pellets to intermittently contact the drying surface while they are being dried. Dryer 204 may include a housing and dry the stated quantity of pellets by supplying a hot gas stream to the pellets located within the housing. The gas may be air. The dryer may agitate the pellets located within the housing by rotating the housing, such that the pellets are "tumbled" as the hot gas passes through the housing. In this example, the pellets are agitated so that they do not remain on the inner surface of the housing. The pellets may only intermittently contact the inner surface of the housing. For example, dryer 204 can be a rotary dryer. According to... Figure 2In the example shown, dryer 204 is a rotary dryer, and hot gas is conveyed through the dryer housing at a temperature of 450°C. The temperature of the hot gas conveyed through the dryer can 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 can be 300°C to 600°C, or 300°C to 500°C, or 400°C to 600°C, or 400°C to 500°C, or 500°C to 600°C, or 600°C to 700°C, or 700°C to 800°C. The temperature of the hot gas conveyed through the dryer can be as high as 800°C.

[0050] According to an alternative example, dryer 204 may include a housing and be configured to fluidize the pellets within the housing. The dryer may be configured to inject a hot gas flow through a porous bed in the housing at a velocity higher than the settling velocity applied to the pellets. In this way, as the pellets are dried by the hot gas, they are able to “float” on the injected air above the porous bed. According to this example, the injected hot gas flow agitates the pellets within the housing. For example, dryer 204 may be a fluidized bed. According to a specific example, dryer 204 is a fluidized bed and delivers hot gas into the dryer housing at a temperature of 250°C. According to another example, dryer 204 may be a Roto Louvre dryer.

[0051] According to other examples, the dryer can use an energy source other than hot gas to dry the pellets. For example, the dryer may include visible light or infrared lamps. The dryer may deliver electromagnetic waves, such as radio frequency waves and / or microwaves. For example, dryer 204 may be an electromagnetic fluidized bed dryer. The dryer may use methods different from those described to agitate the pellets; for example, the dryer may include a surface on which the pellets remain, and this surface is configured to move back and forth while the pellets are being dried to agitate them. The dryer may agitate the pellets by successively tilting them onto a series of moving belts. The dryer may gently agitate the pellets.

[0052] Dryer 204 performs a first drying step. The first drying step partially dries the given quantity of pellets. The purpose of the first drying step is to remove surface moisture from the given quantity of pellets. The first drying step dries the outer surface of the pellets so that the pellets no longer easily stick together. The first drying step can completely dry the outer layer of each pellet. For example, the first drying step can remove 0.5% to 2% moisture from the given quantity of pellets. According to one specific example, the first drying step removes 1% moisture from the given quantity of pellets. According to other examples, the first drying step may include removing up to 4% moisture from the given quantity of pellets. In other words, the given quantity of pellets is not completely dried 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 the outer surface is harder.

[0053] Therefore, partially dried pellets 205 are output from dryer 204. The partially dried pellets 205 are then passed through at least one sieve 206 to separate pellets of the desired size from other pellets. The first drying step is performed before the separation step. Since surface moisture has been removed from the pellets in the first drying step, the sieve 206 can effectively classify the quantity of pellets into different sizes without causing the pellets to stick to the sieve. In other words, pellets smaller than the size of the holes in the sieve will pass through the sieve without sticking. Pellets within the desired size range are referred to herein as the “moderate size fraction” of the pellets. Pellets larger than the desired size range are referred to as the “oversized size fraction”. Pellets smaller than the desired size range are referred to as the “undersized size fraction”. Therefore, the step using sieve 206 includes separating the moderate size fraction from at least one of the oversized and undersized size fractions. In other words, the separation step includes separating a quantity of moderate size fractions of pellets.

[0054] This method may include separating only the medium-sized fraction from the oversized fraction. This method may include separating only the medium-sized fraction from the undersized fraction. This method may include separating the medium-sized fraction from both the undersized and oversized fractions. In an example where a certain amount of pellets consists of undersized, oversized, and medium-sized fractions, two separate sieves are used to separate the medium-sized fractions of the pellets from the remainder of the certain amount of pellets.

[0055] According to one example, the pellets in the medium-size fraction have a diameter of 2 mm to 4 mm. Therefore, the pellets in the excessively small-size fraction have a diameter of less than 2 mm. Therefore, the pellets in the excessively large-size fraction have a diameter of greater than 4 mm. Therefore, according to this example, the sieving step 206 for separating the medium-size fraction of the pellets may include passing a certain amount of pellets through a first sieve with holes of 4 mm in diameter to remove the excessively large-size fraction, and passing the remaining pellets through a second sieve with holes of 2 mm in diameter to remove the excessively small-size fraction. According to other examples, the desired size range may have a lower or higher upper limit and / or a lower or higher lower limit.

[0056] Medium-sized pellets can be sized such that their diameter is less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, or less than 1 mm. Pellet sizes can be sized such that their diameter is greater than 4 mm, greater than 3 mm, greater than 2 mm, greater than 1 mm, or greater than 0.5 mm. The volume of medium-sized pellets can be less than 20 mm². 3 Less than 15 mm 3 Less than 10 mm 3 Less than 8 mm 3 or less than 5 mm 3 The volume of the pellets can be greater than 15 mm. 3 Greater than 10 mm 3 Greater than 8 mm 3 Greater than 5 mm 3 or greater than 1 mm 3 Other sizes are also available.

[0057] exist Figure 2 In this context, 207 represents a suitable size fraction of pellets output from screen 206. This suitable size fraction 207 is then conveyed to a second dryer 208 for drying. Figure 2 In the example shown, dryer 208 is also configured for simultaneously stirring and drying pellets. Dryer 208 can be the same type of dryer as dryer 204. Figure 2 In the example shown, both dryers are rotary dryers. Alternatively, as will be explained in more detail below, dryers 204 and 208 can be different types of dryers.

[0058] The second dryer 208 performs a second drying step in which a certain amount of the pellet's intermediate size fraction is dried. The separation step 206 is performed prior to the second drying step 208. Therefore, the first drying step 204 is performed prior to the separation and second drying steps. The purpose of the second drying step is to substantially dry a certain amount of the pellet's intermediate size fraction so that they can form evaporite pelletizing product 209. The evaporite pelletizing product 209 is drier than the stated amount of wet pellets 203. The evaporite pelletizing product 209 is drier than partially dried pellets 205. The second dryer can be configured to substantially completely dry the pellet's intermediate size fraction during the second drying step. Performing the second drying step can remove 5% to 7% of the moisture from the pellet's intermediate size fraction. According to one specific example, the second drying step removes 6% of the moisture from a certain amount of pellets. According to other examples, the second drying step may include removing a higher or lower percentage of moisture, such that the intermediate-sized pellets are substantially completely dry. The moisture content of essentially completely dried pellets can be less than 1%, for example, 0.2% or 0.5%. During the second drying step, a certain amount of pellets is essentially completely dried. Compared to the first drying step, more moisture can be removed from the pellets in the second drying step. Therefore, the second drying step can 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.

[0059] According to one example, a certain amount of pellets 203 output from processing device 202 has a moisture content of 7.5%. After a first drying step in first dryer 204, the partially dried pellets 205 have a moisture content of 6.5% when sieved through screen 206. Therefore, the intermediate size fraction 207 of the partially dried pellets has a moisture content of 6.5% when entering second dryer 208. After a second drying step in second dryer 208, the intermediate size fraction 209 of the substantially completely dried pellets has a moisture content of less than 0.5%.

[0060] exist Figure 2 In the diagram, 209 represents the medium-size fraction of the dried pellets output from dryer 208. The medium-size fraction of the dried pellets forms evaporite pelletizing products.

[0061] Figure 2 A method for forming granulated evaporite mineral products from evaporite mineral powder is shown. The method of forming the product may further include pulverizing the evaporite mineral raw material to form evaporite mineral powder. Therefore, the method may include a preliminary step of grinding coarse, unprocessed evaporite mineral into powder using a grinding apparatus. For example, one or more of a high-pressure grinding roller (HPGR), a ball mill (e.g., a continuous "Hardinge" ball mill), a vertical mill, and an air classifier may be used.

[0062] Although not the focus of this application, it is conceivable that the process of processing evaporite mineral powder using processing apparatus 202 to form a certain amount of pellets may include multiple steps. The process of processing evaporite mineral powder to form a certain amount of pellets may include mixing the evaporite mineral powder with a liquid and a binder to form a blend, and processing the blend using a granulator to form a certain amount of pellets. The process of processing the blend using a granulator to form a certain amount of pellets may include pelletizing the blend.

[0063] According to one example, in a first processing step, water and a binder are added to the evaporite mineral powder. In the following description, the amounts of water and binder added are specified as percentages relative 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 a binder (e.g., PVA). The amount of water added may be 5% to 10%, more preferably 7% to 8%. The amount of binder added will depend on the mass of the binder. For general binders, such as starch or flour, the amount added may be 0.5% to 4%. The binder may be added directly to the evaporite mineral powder; or it may be added to water first, and then the combination of water and binder may be added to the powder. According to other examples, other evaporite minerals and / or micronutrients may be added to the combination of powder, binder, and water.

[0064] As part of the second processing step, the powder / binder mixture is mixed until homogeneous. Therefore, the processing apparatus 202 may include a mixer, such as a ribbon blender, a pin mixer, or other high-shear mixer.

[0065] As a third processing step, the powder / binder mixture is pelletized. Therefore, processing apparatus 202 may include a pelletizer, such as a pan pelletizer. According to a method found to be effective, the powder / binder mixture is fed into a device that can both mix and pelletize. An example of such device is a high-intensity mixer / granulator, for example, available from Maschinenfabrik Gustav Eirich GmbH & Co KG. The pelletizer can be configured to discharge the processed material during its operation, thus enabling continuous operation. Alternatively, the pelletizer can operate in batches, processing the material according to a prescribed procedure and then discharging it all. Upon completion of the pelletizing process, pellets (203) are discharged from the pelletizer.

[0066] According to other examples, the process of processing evaporite mineral powder to form a certain amount of pellets may include other steps. Therefore, processing apparatus 202 may include other equipment.

[0067] As described above, this method includes using sieve 206 to separate a portion of dried, moderately sized fractions from at least one of oversized and oversized fractions. In instances where a quantity of pellets includes oversized fractions, the oversized fractions can be recycled. For example, the oversized fractions can be returned to processing apparatus 202. For example, in cases where processing apparatus 202 includes a granulator, the oversized fractions of the pellets can be returned to the granulator for re-granulation.

[0068] In instances where the stated quantity of pellets includes oversized fractions, the oversized fractions can also be recycled. The oversized portions can be returned to the processing unit 202. The oversized pellets can be recycled to the grinding unit for re-grinding, and then returned to the processing unit 202 for pelletizing.

[0069] As described above, the dried, moderate-sized fractions of pellets 209 form a pelletized evaporite mineral product. The method for forming a pelletized evaporite mineral product may include other steps. For example, the method may include passing a quantity of moderate-sized pellets through a polishing screen. The method may also include cooling a quantity of moderate-sized pellets. The method may further include coating a quantity of moderate-sized pellets with a coating to form a pelletized evaporite mineral product. Coating a quantity of pellet size fractions may include feeding the pellets and coating into a mixer drum or disc granulator and mixing the pellets with the coating to coat the pellets with the coating.

[0070] Finally, the pellets can be packaged into appropriately sized bags, such as 600 kg or 25 kg bags, or transported loosely for use elsewhere or further processing. The pellets can be used for agricultural purposes. Ultimately, they can be dispersed in fields or other agricultural or horticultural substrates as fertilizer. The pellets can also be used for purposes other than fertilization.

[0071] It should be understood that Figure 2 The method shown is relative to Figure 1 The known method shown is advantageous because the total amount of dried pellets is reduced.

[0072] A certain amount of pellets may have a suitable size fraction accounting for 30% to 85% of the total number of pellets. Alternatively, a certain amount of pellets may have a suitable size fraction accounting for 65% to 85% of the total number of pellets. According to one example, a certain amount of pellets may have a suitable size fraction accounting for 70% of the total number of pellets. In other words, in this example, the step of separating a certain amount of pellets into at least one of a suitable size fraction and an oversized and undersized size fraction may include filtering out 30% of the pellets, such that 70% of the pellets (the suitable size fraction) are conveyed to the second dryer 207 for drying. Therefore, in this case, the number of pellets dried in the first drying step is greater than the number of pellets dried in the second drying step.

[0073] As mentioned earlier, the undersized and oversized pellets separated by screen 206 can be recycled and re-spheronized. Therefore, drying the undersized or oversized pellets in the second drying step is not beneficial, as these pellets will be re-wetted during re-spheronization and will require further drying afterward. Therefore, using screen 206 to filter the pellets between the first drying step by dryer 204 and the second drying step by dryer 207 to separate the medium-sized pellets means that energy is not wasted in the second dryer due to drying undersized and / or oversized pellets. Thus, for the production of a given volume of granulated evaporite mineral product, compared to drying all sizes (medium, oversized, and undersized) of pellets in dryer 104, the energy expenditure is significantly reduced. Figure 1 The method shown, Figure 2 The method requires fewer dried pellets. Therefore, in Figure 2 In this method, since the excessively large and small size fractions of the pellets are not dried in the second drying step, the energy used in the process is reduced. Therefore, in order to produce a given volume of pelletized evaporite mineral product, the total energy consumed by the first dryer 204 and the second dryer 207 will be less than the energy consumed by the prior art dryer 104.

[0074] Figure 2 The method shown further addresses the problem of wet pellets sticking to the screen during separation by implementing a first drying step to remove surface moisture from the pellets before the separation step.

[0075] As mentioned earlier, the ability of the first dryer to simultaneously agitate and dry the pellets effectively minimizes pellet agglomeration and prevents pellets from sticking to the screen during separation. However, configuring a dryer for agitation during drying (e.g., a rotary dryer) is highly energy-intensive. A rotary dryer dries the pellets by rotating a cylindrical shell, causing it to "tumble." Hot gas is introduced into the cylindrical shell along its longitudinal axis and transfers heat to the pellets upon contact. However, a significant portion of the hot gas passes directly through the shell without sufficient contact with the internal pellets. Therefore, heat transfer to the pellets in a rotary dryer can be quite inefficient.

[0076] Therefore, by using a second dryer that is not configured for stirring the pellets, the total energy required for drying the pellets can be further reduced.

[0077] Figure 3 A variation of the previously described method for forming granulated evaporite mineral products is shown. This method is similar to the previously mentioned method. Figure 2 The method described is also shown, along with equivalent steps. However, in Figure 3 In this process, the second dryer 308, which performs the second drying step, is not configured to stir the pellets while they are being dried. The second dryer 308 is of a different type from the first dryer 204.

[0078] According to this example, the second dryer 308 may include a drying surface on which a suitable size fraction 207 of the pellets may be placed. The second dryer 308 may be configured to dry the pellets while they remain on the drying surface. The second dryer may be configured to deliver a hot gas flow toward the drying surface. During the second drying step, the pellets may remain on the drying surface. Alternatively, the dryer may use an energy source other than hot gas to dry the pellets; for example, the dryer may include visible light or infrared lamps directed toward the drying surface. The dryer may deliver electromagnetic waves, such as radio frequency waves and / or microwaves, to the drying surface. The second dryer may be an electromagnetic dryer. The second dryer may be an electromagnetic fluidized bed dryer.

[0079] The second dryer 308 is not configured to agitate the pellets during drying. In other words, when the pellets remain on the drying surface during the second drying step, they are essentially stationary relative to the drying surface. In other words, the position of the appropriate size fraction of the pellets on the drying surface does not change significantly during the second drying step. Instead, the particles remain largely within the same area of ​​the drying surface as they are conveyed along the surface. A dryer that does not agitate the pellets during drying (a non-agitated dryer) consumes less energy compared to a dryer configured to simultaneously agitate and dry the pellets.

[0080] exist Figure 3In the example shown, the second dryer 308 is a belt dryer. The belt dryer includes 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 a drying surface on which the pellets of moderate size are placed. The belt dryer 308 is configured to guide a hot gas flow through the perforated belt, such that the hot gas contacts the pellets. According to another example, the belt dryer may include a hot gas source located above the perforated belt and is configured to guide the airflow toward the perforated belt.

[0081] Non-stirred dryers (such as belt dryers) can operate at lower temperatures than stirred dryers (such as fluidized bed or rotary dryers). Therefore, the first dryer can operate at a higher temperature than the second dryer. Operating the first dryer at a higher temperature may mean that the first dryer transfers energy to the pellets at a higher rate than the second dryer. In other words, the first dryer can produce a greater heating effect than the second dryer. The first dryer can transfer more heat to the pellets compared to the second dryer. The rate of heat transfer from the first dryer to the pellets can be higher than the second dryer. The first dryer can be configured to raise the temperature of the pellets to a first temperature. The second dryer can be configured to raise the temperature of the pellets to a second temperature. The first temperature can be greater than the second temperature. The operating temperature of the first dryer can be 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 higher than that of the second dryer. The operating temperature of the first dryer can be 700°C, 750°C, or 800°C higher than that of the second dryer. The first dryer can operate at temperatures up to 800°C. The second dryer can operate at temperatures up to 150°C. According to one example, the first dryer can operate at 450°C. The second dryer can operate at 115°C.

[0082] according to Figure 3 In the example shown, the second dryer 308 is a belt dryer, and the first dryer 204 is a rotary dryer. Both dryers 204 and 308 dry the pellets by supplying hot air streams to them. In this example, the first dryer supplies a first air stream to a quantity of pellets, and the second dryer supplies a second air stream to a suitable size fraction of the quantity of pellets. The first air stream can have a temperature of 450°C. The second air stream can have a temperature of 115°C.

[0083] In the second dryer 308, no energy is required to intentionally agitate the pellets. Furthermore, in the second dryer 308, because the airflow is directly delivered to the pellets resting on the drying surface, the heat transfer efficiency to the pellets is higher in a belt dryer than in a rotary dryer. For example, in a belt dryer, less hot gas passes through the dryer without contacting the particles than in a rotary dryer. Agitated dryers may consume more energy than non-agitated dryers. Therefore, the energy consumption rate of the first dryer may be higher than that of the second dryer.

[0084] As mentioned earlier, due to the clumping of moist and viscous pellets leaving the granulator, it is not feasible to use a non-stirred dryer to dry the pellets output from the granulator. Therefore, Figure 3 The method incorporates an initial first drying step using a stirred dryer to remove surface moisture from the pellets, meaning that a separation step can be effectively performed on the resulting partially dried pellets. Following this separation step, which separates the pellets into appropriate size fractions, Figure 3 The method involves using a low-energy dryer for a second drying step to remove excess moisture only from the moderate-sized fraction of the pellets.

[0085] Reference Figure 2 The reasons stated above Figure 3 The method is more Figure 1 The existing technology consumes less energy because only a certain amount of the moderate-size fraction of the pellets is dried in the second drying step. Furthermore, since a dryer without stirring the pellets is used as the second dryer 308, therefore… Figure 3 The method is more Figure 1 Existing technical methods and Figure 2 The methods used all have lower energy consumption.

[0086] Figure 3 The method has two advantages over existing methods. To produce a given volume of pelletized evaporite mineral product, the total energy consumed by the first dryer 204 and the second dryer 308 will be less than that consumed by the existing dryer 104, because: (1) the number of pellets dried in the second drying step is reduced; and (2) a lower energy-consuming dryer is used for the second drying step.

[0087] It is conceivable that the method described herein will primarily be used to produce granulated heterohalite products. However, this method can also be applied to any one or more of other evaporite minerals, such as rock salt, potash, carnallite, potassium magnesia, anhydrite, gypsum, magnesium sulfate, anhydrous potassium magnesia, dolomite, calcite, and magnesite.

[0088] The method described herein can be carried out in a production facility that forms granulated evaporite mineral products. The production facility includes a processing unit 202, a first dryer 204, a separator 206, and a second dryer 208 / 308. The processing unit may include a granulator. The granulator may be a disc granulator. The separator may include one or more screens. The first and second dryers may be as described above.

[0089] The processing apparatus is configured to process evaporite mineral powder to form a certain amount of pellets. The facility is configured such that the certain amount of pellets is subsequently fed into a first dryer. The first dryer is configured to dry the certain amount of pellets by simultaneously agitating and drying them. The facility is configured to feed the output of the first dryer into a separator. The separator is configured to separate the certain amount of pellets into at least one of a suitable size fraction and an oversized and undersized fraction. The facility is configured to feed the suitable size fraction of the certain amount of pellets into a second dryer. The second dryer is configured to dry the suitable size fraction of the certain amount of pellets to form a pelletized evaporite mineral product. The production facility may also include a grinding device. For example, the production facility may include one or more of a high-pressure grinding roller (HPGR), a ball mill (e.g., a continuous "Hardinge" ball mill), a vertical mill, and an air classifier. The production facility may be configured to form a pelletized evaporite mineral product from the evaporite mineral powder. The production facility may be configured to pulverize the evaporite mineral raw material to form evaporite mineral powder.

[0090] The processing apparatus may also include a mixer, such as a screw mixer. The production facility may be configured to mix evaporite mineral powder with liquid and binder to form a blend, and to process the blend using a granulator to form a certain amount of pellets.

[0091] According to a specific example, the processing equipment in a production facility may include equipment capable of both mixing and pelletizing. An example of such equipment is a high-intensity mixer / granulator, for instance, available from Maschinenfabrik Gustav Eirich GmbH & Co KG.

[0092] According to other examples, the process of processing evaporite mineral powder to form a certain amount of pellets may include other steps. Therefore, the processing equipment of the production facility may include other equipment.

[0093] In instances where a given quantity of pellets includes undersized fractions, the undersized fractions can be recycled after a separator separates the pellets into oversized and undersized fractions. For example, the production facility can be configured to return the undersized fractions to the processing unit. For instance, if the processing unit includes a granulator, the production facility can return a portion of the undersized pellets to the granulator for re-granulation.

[0094] In instances where a certain amount of pellets includes oversized fractions, the oversized fractions can also be recycled. The production facility can be configured to return the oversized portions to the processing unit. The production facility can also be configured to recycle the oversized fractions of the pellets to a grinding unit for re-grinding, and subsequently to the processing unit for pelletizing.

[0095] The production facility may include other equipment for processing the output of the second dryer, i.e., a suitable size fraction of the dried pellets. For example, the production facility may include a polishing sieve. The production facility may include a mixing drum or disc granulator in which suitable-sized pellets are coated with a coating. Finally, the production facility may include packaging equipment for packaging the pelletized evaporite mineral products.

[0096] The applicant hereby separately discloses each individual feature described herein, as well as any combination of two or more such features, provided that such features or combinations can be implemented based on the entire specification in accordance with common general knowledge of those skilled in the art, regardless of whether such features or combinations of features solve any problem disclosed herein, and without limiting the scope of the claims. The applicant notes that various aspects of the invention may be constituted by any such individual feature or combination of features. In view of the foregoing description, it will be apparent to those skilled in the art that various modifications can be made within the scope of the invention.

Claims

1. A method for forming pelletized evaporite mineral products, the method comprising: Process evaporite mineral powder to form a certain amount of pellets; A first drying step includes drying the quantity of pellets using a first dryer configured to simultaneously stir and dry the quantity of pellets. The specified amount of pellets is separated into at least one of the following: a moderate size fraction, an excessively large size fraction, and an excessively small size fraction; as well as The second drying step includes drying the medium-sized fractions of the given amount of pellets using a second dryer to form the pelletized evaporite mineral product, wherein the first dryer operates at a higher temperature than the second dryer.

2. The method as described in claim 1, wherein, During the first drying step, a certain amount of pellets were not completely dried.

3. The method as described in claim 1 or 2, wherein, During the first drying step, the first dryer is configured to remove surface moisture from the given amount of pellets.

4. The method as described in any of the preceding claims, wherein, During the second drying step, the appropriate size fraction of the pellets is dried substantially completely.

5. The method as described in any one of the preceding claims, wherein, The first drying step removes 0.5% to 2% moisture from the given amount of pellets.

6. The method as described in any of the preceding claims, wherein, The second drying step removes 5% to 7% of the moisture from the moderate-size fraction of the pellets.

7. The method as described in any of the preceding claims, wherein, The number of pellets dried in the second drying step is less than the number of pellets dried in the first drying step.

8. The method as described in any of the preceding claims, wherein, The appropriate size fraction accounts for 30% to 85% of the total amount of pellets.

9. The method as described in any of the preceding claims, wherein, The first drying step has a shorter duration than the second drying step.

10. The method as described in any of the preceding claims, wherein, The first dryer has a higher energy consumption rate than the second dryer.

11. The method as described in any of the preceding claims, wherein, The second dryer operates at a temperature less than or equal to 150°C, and the first dryer operates at a temperature greater than 150°C.

12. The method as described in any of the preceding claims, wherein, The first dryer operates at a temperature of 450°C.

13. The method as described in any of the preceding claims, wherein, The second dryer operates at a temperature of 115°C.

14. The method as described in any of the preceding claims, wherein, In the second drying step, the position of the appropriate size fraction of the certain amount of pellets on the drying surface does not change significantly.

15. The method as described in any of the preceding claims, wherein, The second drying step includes drying the appropriate size fraction of the given amount of pellets on the drying surface of the second dryer.

16. The method as described in any of the preceding claims, wherein, The first dryer is configured to deliver a first airflow onto the specified amount of pellets.

17. The method of claim 16, wherein, The second dryer is configured to deliver a second airflow to the drying surface, and the pellets remain on the drying surface during the second drying step.

18. The method as described in any of the preceding claims, wherein, The first dryer is a rotary dryer, a fluidized bed dryer, or a Roto Louvre dryer.

19. The method as described in any of the preceding claims, wherein, The second dryer is a belt dryer or an electromagnetic dryer.

20. The method as described in any of the preceding claims, wherein, The pelletized evaporite minerals are one or more of the following: carnallite, rock salt, potassium salt, carnallite, potassium magnesia, anhydrite, gypsum, magnesium sulfate, anhydrous potassium magnesia, dolomite, calcite, and magnesite.

21. The method as described in any of the preceding claims, wherein, The method includes crushing evaporite mineral raw materials to form evaporite mineral powder.

22. The method as described in any of the preceding claims, wherein, The process of processing evaporite mineral powder to form a certain amount of pellets includes mixing the evaporite mineral powder with a liquid and a binder to form a blend, and processing the blend using a granulator to form the certain amount of pellets.

23. The method of claim 22, wherein, The process of processing the blend using a granulator to form the given amount of pellets includes pelletizing the blend.

24. The method as described in any of the preceding claims, wherein, The method includes one or more of the following steps: The appropriate size fraction of the specified amount of pellets is passed through a polishing screen; Cooling the appropriate size fraction of the given amount of pellets; and A certain amount of pellets of appropriate size fractions are coated to form the pelletized evaporite mineral product.

25. The method as described in any of the preceding claims, wherein, The process of separating the given amount of pellets into medium-sized and oversized fractions includes passing the given amount of pellets through a sieve with holes having a diameter of 4 mm.

26. The method as described in any of the preceding claims, wherein, The process of separating the given amount of pellets into medium-sized fractions and excessively small-sized fractions includes passing the given amount of pellets through a sieve with holes having a diameter of 2 mm.

27. The method as described in any of the preceding claims, wherein, The pellets of the appropriate size fraction of the specified amount have a diameter of 2 mm to 4 mm.

28. A production facility for forming pelletized evaporite mineral products, the production facility comprising: A processing device configured to process evaporite mineral powder to form a certain amount of pellets; A first dryer is configured to dry the quantity of pellets by simultaneously stirring and drying the quantity of pellets. A separator configured to separate the quantity of pellets into at least one of a moderate-size fraction and an oversized fraction and an undersized fraction. as well as A second dryer is configured to dry a certain amount of pellets of moderate size fractions to form the pelletized evaporite mineral product, wherein the first dryer operates at a higher temperature than the second dryer.

29. The production facility as claimed in claim 28, wherein, The facility is configured as follows: The specified amount of pellets is fed into the first dryer; and The output of the first dryer is fed into the separator.

30. The production facility as described in claim 28 or 29, wherein, The facility is configured to input a certain amount of pellets of appropriate size fractions into the second dryer.

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