Classifications

• • C—CHEMISTRY; METALLURGY
  • C05—FERTILISERS; MANUFACTURE THEREOF
  • C05B—PHOSPHATIC FERTILISERS
  • C05B1/00—Superphosphates, i.e. fertilisers produced by reacting rock or bone phosphates with sulfuric or phosphoric acid in such amounts and concentrations as to yield solid products directly
  • C05B1/04—Double-superphosphate; Triple-superphosphate; Other fertilisers based essentially on monocalcium phosphate
• • C—CHEMISTRY; METALLURGY
  • C05—FERTILISERS; MANUFACTURE THEREOF
  • C05C—NITROGENOUS FERTILISERS
  • C05C1/00—Ammonium nitrate fertilisers
• • C—CHEMISTRY; METALLURGY
  • C05—FERTILISERS; MANUFACTURE THEREOF
  • C05B—PHOSPHATIC FERTILISERS
  • C05B11/00—Fertilisers produced by wet-treating or leaching raw materials either with acids in such amounts and concentrations as to yield solutions followed by neutralisation, or with alkaline lyes
  • C05B11/04—Fertilisers produced by wet-treating or leaching raw materials either with acids in such amounts and concentrations as to yield solutions followed by neutralisation, or with alkaline lyes using mineral acid
  • C05B11/08—Fertilisers produced by wet-treating or leaching raw materials either with acids in such amounts and concentrations as to yield solutions followed by neutralisation, or with alkaline lyes using mineral acid using sulfuric acid
• • C—CHEMISTRY; METALLURGY
  • C05—FERTILISERS; MANUFACTURE THEREOF
  • C05B—PHOSPHATIC FERTILISERS
  • C05B7/00—Fertilisers based essentially on alkali or ammonium orthophosphates
• • 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
  • C05G1/00—Mixtures of fertilisers belonging individually to different subclasses of C05

Definitions

• NPK-fertilizer ( "azophoska” , “nitroammophoska” ) is a complex fertilizer possessing high economic efficiency and intended for use in growing different crops and in almost any soil.
• NPK type is characterized by mass fractions of nitrogen, phosphorus and potassium in a fertilizer.
• the present invention relates to preparation of granulated NPK-fertilizers from phosphate salt containing up to 99% fluorapatite, in particular said phosphate salt is a mixture of CaHP0 4 x nH 2 0 (dicalcium phosphate) and Ca 5 (P0 4 ) 3 F (fluorapatite), where n is 0 to 2, fluorapatite Ca5(P0 4 )3F content in phosphate salt is 27% to 99%, wherein the method allows to use various potassium and ammonium salts as sources of nutrients in the fertilizer.
• phosphate salt is a mixture of CaHP0 4 x nH 2 0 (dicalcium phosphate) and Ca 5 (P0 4 ) 3 F (fluorapatite), where n is 0 to 2, fluorapatite Ca5(P0 4 )3F content in phosphate salt is 27% to 99%, wherein the method allows to use various potassium and ammonium salts
• the invention also relates to a continuous method for the preparation a granulated NPK-fertilizer from said phosphate salt consisting largely of fluorapatite.
• the potassium salts are used, which are raw materials available on the market, in particular potassium sulfate K 2 S0 4 .
• As a nitrogen source ammonium nitrate NH 4 N0 3 is used.
• RU 2216526 discloses a method for obtaining a NPK-fertilizer with adjustable N:P 2 0 5 :K 2 0 ratio, said method comprising acid decomposition of phosphate raw material with nitric acid, adding nitrogen-containing component, neutralization with ammonia, mixing NP-slurry with potassium chloride or sulfate, granulation and drying of the target product.
• Patents RU 2439039 and RU 2223933 also disclose the methods of phosphate rock decomposition with nitric acid accompanied by neutralizing slurry with ammonia and adding potassium salts.
• Drawbacks of these methods are: the use of expensive and scarce component, i.e. nitric acid, as the acid, unsatisfactory consumer properties of granules due to their low strength and hydrochloric acid release during storage in case of using potassium chloride as a raw material.
• Product evaporation stage to attain residual moisture results in additional energy consumption, while the use of ammonia to neutralize the residual acid results in reduction of soluble phosphorus salts content in the product.
• Patent RU 2107055 discloses method for the preparation of complex fertilizers by decomposition of phosphate rocks with a mixture of phosphoric and sulfuric acids with neutralization of the mixture with alkaline potassium salt such as potassium carbonate, followed by neutralization with ammonia.
• the drawback of this method is the use of extraction phosphoric acid, which is an expensive product, the production thereof is accompanied by generation of a large amount of waste, namely phosphogypsum, also a lot of water is introduced into the system together with phosphoric acid, which necessitates evaporation stage to obtain the final product.
• the use of ammonia to neutralize the mixture reduces soluble phosphorus portion to less than 60%.
• Chinese patent CN 1113900 (1994) discloses producing of a fertilizer containing nitrogen and phosphorus, wherein the fertilizer is produced from phosphate rock and nitric acid, and the resulting product is Ca(H 2 P0 4 ) 2 , which is crystallized; NHH 2 P0 4 is obtained by mixing the ammonium nitrate with the mother liquor, and bubbling of the obtained mother liquor with ammonia yields CaHP0 4 .
• the drawback of this method may include: the presence of evaporation stage in the method, in the product phosphorus is not in a water-soluble form of dicalcium phosphate, and the method of potassium introduction into fertilizer is not disclosed.
• Patent GB 662079 discloses production of fertilizers containing soluble phosphorus salts based on the slurry resulting from decomposition of natural phosphates, DCP (dicalcium phosphate) or TCP (tricalcium phosphate) .
• Phosphates are decomposed by sulfuric acid treatment, then the mixture is exposed to nitric acid to yield MAP and calcium nitrate.
• the product is stabilized by adding ammonium sulfate, whereby gypsum and ammonium nitrate are formed from calcium nitrate. Additional quantity of added ammonium sulphate has a favorable effect on the fertilizer, as double salt of ammonium sulfate with two ammonium nitrate molecules is formed.
• Patent CN 1220236 discloses a method which comprises mixing of the hydrated lime with one or both substances: powdered Ca 3 (P0 4 )2 and CaHP0 4 , adding phosphoric acid with a concentration of 62% to 85% under stirring at 80°C for 20 to 60 seconds to give MCP (monocalcium phosphate) , followed by curing for 8-100 hours, natural drying and grinding to yield the product.
• MCP monocalcium phosphate
• H3P0 4 /Ca 3 (P0 4 ) 2 or H 3 P0 4 /CaHP0 4 ratios are identical (7 to 16): 100.
• the powdered Ca(H 2 P0 4 )2 reacts with powdered Ca(OH) 2 to give CaHP0 4 and Ca (OH) 2 /Ca (H 2 P0 4 ) 2 ratio is (10 to 22):100.
• the drawbacks of this method include the use of hydrated lime, the production of which requires additional energy, the method is periodic (there is a product maturing stage) .
• MCP Another methods for producing MCP are the methods of apatites decomposition with phosphoric acid.
• Apatite reaction with phosphoric acid Apatite reaction with phosphoric acid:
• the method, method and forms of the main products vary depending on which acids: HC1, HN0 3 , H 2 S0 4 and acid mixture are used as a starting material.
• Citride CN 1305946 discloses obtaining monocalcium phosphate (MCP) from phosphorite .
• This method includes reaction of phosphorite and sulfuric acid at temperatures ranging from 70°C to 95°C for 2-8 hours; filtration to obtain 10% to 30% phosphoric acid; adding CaC0 3 to phosphoric acid and removal of impurities; neutralization with Ca(OH) 2 and filtering; adding CaHP0 4 and CaO; and spray-drying to obtain Ca(H 2 P0 4 ) 2 and a product with a high phosphorus content (core of calcium salts of phosphoric acid, 19-22% phosphorus).
• a disadvantage of this method is that one of the method stages is the production of an aqueous phosphoric acid solution, therefore, the need of water evaporation leads to additional costs associated with carrying out the method.
• the purified solution reacts with calcium hydroxide suspension to yield crystals suspension in DCP, which are then separated by decantation.
• the resulting crystals are then reacted with acid ammonium sulfate to give monoammonium phosphate solution, and insoluble crystals of calcium sulfate dihydrate are separated by filtration.
• concentrated hydrochloric acid and ammonia are added to DCP suspension. Filtration yields a solution with MCP concentration of more than 48%.
• the drawbacks include: technological complexity of carrying out the method, the use of numerous reagents, product losses in precipitate during filtration and decantation, and also obtaining MCP in the form of a solution that complicates its further processing .
• Mexican patent MX NL0500002 discloses method for the preparation ofmonocalcium phosphate MCP, sodium phosphate, potassium and MAP, where phosphate rock, sulfuric acid, calcium oxide, ammonium sulphate or potassium sulphate are used as starting materials.
• the important part is the method for producing phosphate salts, which are prepared by reacting DCP (dicalcium phosphate) with appropriate acid sulphates of the corresponding (magnesium, ammonium, potassium) salts.
• DCP diicalcium phosphate
• appropriate acid sulphates of the corresponding (magnesium, ammonium, potassium) salts Upon gypsum filtration, the resulting MAP or other salts are concentrated in an evaporator and crystallized.
• the disadvantage of the method is the stage of salts solution preparation and gypsum filtration, which leads to additional costs associated with product solidification by evaporation.
• Using natural phosphate rock for decomposition results in a large quantities of waste — phosphogypsum.
• MCP monocalcium phosphate
• H3PO4 reaction of calcium containing compounds, such as lime milk
• Another method includes preparation of calcium orthophosphate Ca 3 (P0 4 )2 f known as calcium phosphate, by treating a mixture of calcium sulphate and phosphoric acid with sulfuric acid or by reaction of sulfuric acid with calcium sulfate and monocalcium phosphate Ca(H2P0 4 )2 mixture.
• the NPK preparation is mainly carried out by decomposition of natural phosphates with acids.
• the state of the art comprises a method of preparation of a material which is simple superphosphate (SSP) or triple superphosphate (TSP) , by reaction of phosphates with sulfuric or phosphoric acid.
• a soluble portion consists primarily of calcium monophosphate, and the insoluble part is a gypsum in case of SSP (and other insoluble impurities in addition to those contained in the gypsum) .
• feedstock is granulated in drum granulators with the addition of a small amount of alkali (e.g. ammonia) .
• Free phosphoric acid content which is up to 5% in the powdered superphosphate, is reduced by 1-2% due to neutralization in the method of granulation.
• a water soluble portion is reduced reaching the level of 60% in such methods .
• the present invention is aimed to develop a novel type of complex NPK-fertilizer having high water solubility of P2O5.
• NPK-fertilizer using K 2 S0 4 as a potassium source and ammonium nitrate as a nitrogen source in the presence of MCP (monocalcium phosphate) and gypsum.
• the final product comprises anhydrous fine gypsum (calcium sulfate) providing access (for plants) to such element as sulfur, which is necessary and which is present in the target fertilizer introduced into the soil.
• anhydrous fine gypsum calcium sulfate
• the present invention provides improvement of NPK-fertilizer properties, while a method for its production can improve the strength of granules, allows to solve the problem associated with plasticity of granulated complex fertilizers and thereby enhance consumer properties of NPK-fertilizers .
• the present invention provides complex nitrogen-phosphorus-potassium fertilizer (NPK) comprising ammonium nitrate, anhydrous calcium sulfate, potassium dihydrogen phosphate, wherein the mass fraction of total nitrogen is from 13-15%, mass fraction of total phosphates, in terms of P 2 0 5 , is from 9-10%, mass fraction of potassium, in terms of K 2 0, is from 13-15%.
• NPK nitrogen-phosphorus-potassium fertilizer
• the method for the preparation of a complex NPK-fertilizer from a solid phosphate salt includes decomposing of said solid phosphate salt with sulfuric acid according to semi-dry method, adding potassium sulfate as a potassium source, ammonium nitrate as a nitrogen source, preparing NPK slurry, and granulating and drying the final product.
• This solid phosphate salt is a mixture of fluorapatiteCa 5 (PO4) 3 F and dicalcium phosphate CaHP0 4 x nH 2 0, where n is 0 to 2, with fluorapatite Ca 5 (P0 4 ) 3 F content from 27% to 99%.
• the technical result of practicing this method is that water soluble form of P 2 0 5 reaches 98%. In other words, the phosphorus contained in the fertilizer is 98% water soluble.
• An important point of resolving the technical problem is the fact that practicing said technological method results in obtaining MCP (monocalcium phosphate) by reaction in the form of monohydrate (i.e., it remained stable) .
• MCP monocalcium phosphate
• the temperature during dicalcium phosphate decomposition should not exceed 120 °C. At this temperature dehydration begins.
• An important aspect of the claimed method realization is adding potassium sulfate to MCP at one of the method stages, which provides substantially anhydrous gypsum in certain method conditions. Namely, reaction of MCP with potassium sulfate at the temperature not lower than 120°C provides substantially anhydrous gypsum.
• the conditions of the proposed method namely that the temperature of the slurry obtained after preparing MCP and feeding to the reactor should not be less than 120 °C, allow to avoid the formation of gypsum hemihydrate (which is highly undesirable for the resulting fertilizer) .
• Technological conditions for obtaining anhydrous gypsum in fine-dispersed form further ensure availability of essential fertilizer element, sulfur, upon fertilizer application in the soil .
• the important aspect is that the method for producing involves the use of MCP in monohydrate form at the temperature not exceeding 120 °C, which in turn avoids degradation of MCP to dicalcium phosphate and phosphoric acid.
• MCP monocalcium phosphate
• DCP dicalcium phosphate
• DCP as a starting material, is not a pure substance but rather a mixture, where, along with DCP, at least fluorapatite is present.
• reaction enthalpy refers to the following general equation:
• DCP is commonly referred to as "brushite", which is dicalcium phosphate dihydrate.
• brushite dicalcium phosphate dihydrate.
• DCP is shown in anhydrous form.
• the resulting gypsum is in the form of anhydride and the reaction is exothermic.
• the reaction 1— MCP formation— proceeds in two stages :
• sulfuric acid reacts with fluorapatite .
• phosphates decomposition reaction occurs in two stages; in practice the second stage is slower and proceeds not quite up to the end:
• MCP water-soluble phosphorus
• the reaction proceeds in a saturated ammonium nitrate solution, which contains small amount of water at a high temperature.
• the system has molar excess of potassium sulphate; no free MCP remains in the system.
• the resulting gypsum is in anhydrous form at ambient temperature .
• NPK product prepared using DCP, sulfuric acid, ammonium nitrate and potassium sulphate mainly comprises the following components:
• the technological method for producing the claimed NPK-fertilizer according to the invention comprises the following steps:
• phosphate salt in particular the mixture of DCP and fluorapatite
• MCP monocalcium phosphate
• the method is carried out in a fluidized bed mixer for optimum contact of the particles during the reaction. Conducting the reaction in a fluidized bed avoids dehydration of MCP monohydrate. After reaction in the mixer, ending of the reaction and waste gases release occurs in the maturing unit.
• a further scheme of the method is as follows: in the first reactor: MCP (monocalcium phosphate) reacts with ammonium nitrate to give ammonium monophosphate. Ammonium nitrate is dosed in the form of melt or granules through the dosing device; in the second reactor: potassium sulphate is fed through the dosing device, such potassium sulphate being fine enough for complete reaction to occur; the third reactor in the cascade is a maturing unit used prior to product granulation.
• MCP monocalcium phosphate
• Ammonium nitrate is dosed in the form of melt or granules through the dosing device
• potassium sulphate is fed through the dosing device, such potassium sulphate being fine enough for complete reaction to occur
• the third reactor in the cascade is a maturing unit used prior to product granulation.
• a slurry is fed to granulation step, which is carried out in the granulator of suitable design by agglomeration and layering in a fluidized bed. Returns are input to the front part of the granulator. Drying is carried out with hot air. After carrying out the following operations: screening, crushing, cooling, surface treatment with anti-caking additive, the finished product suitable for storage and transportation is obtained .
• Waste gases containing dust of products and raw materials used in the production as well as gases released during production are captured in wet scrubbers with the addition of neutralizing agents into absorbent.
• the main object of the present invention is the production of NPK-fertilizer using K 2 S0 4 as a potassium source and ammonium nitrate as a nitrogen source in the presence of MCP and gypsum. Due to strict requirements concerning P2O5 water solubility it is necessary to have essentially all the phosphorus feedstock in the form of MCP or other salt of phosphoric acid, which would provide water-solubility. MCP should remain stable in order to prevent its conversion to DCP and phosphoric acid.
• calcium phosphates only acid calcium phosphate, monocalcium phosphate (MCP), in the form of anhydrous salt Ca(H 2 P0 4 ) 2 or monohydrate Ca(H 2 P0 4 )2 x H 2 0 is water soluble.
• Middle calcium phosphate, dicalcium phosphate (DCP) is not water soluble and is found in the dihydrate form CaHP0 4 x 2H 2 0 or in the form of anhydrous salt CaHP0 4 .
• tricalcium phosphate Ca 3 (P0 4 ) 2 is insoluble in water.
• the whole proposed NPK production method can be divided into 2 main stages: the method of producing a water-soluble phosphate salt and the method of producing complex fertilizers from this salt .
• the production of complex NPK fertilizer consists of two main methods: wet (NPK slurry production) and dry (granulation, milling, screening and cooling of the finished product) methods.
• Fig. 1 is a diagram of wet method to give NPK slurry using potassium sulfate K 2 S0 4 as a potassium source in the product.
• the phosphate salt being a mixture of calcium phosphates with fluorapatite (stream 1) together with sulfuric acid (stream 2) are fed into the flow device (unit A) , which is a mixer with fast rotating blades and reaction mass maturing unit. Sulfuric acid is dosed in equimolar ratio to the phosphate salt.
• the method results in the following chemical reactions in the reaction mass in unit A:
• H 2 S0 4 + 2CaHP0 4 + H 2 0 Ca(H 2 P0 4 ) 2 + CaS0 4 (1)
• Reactions 1 and 2 are exothermic, especially the reaction 2.
• the technical solution for removing heat of reaction is a complex one: reactor is equipped with a water jacket and also part of the heat is removed from the system with exhaust gases and part of the heat is removed with water vapor. To ensure the removal of vapor and gases mixing unit A is operated under vacuum. Heat removal system parameters must be adjusted so that the temperature of the reaction mixture does not exceed 120°C.
• the reaction mixture is fed into maturing unit, being a part of unit A, which is a device with a stirrer.
• the following methods take place in the maturing unit: completion of the reaction methods; final removal of gases from the reaction mixture; averaging of the chemical and physical properties of the reaction mass.
• the first slurry reactor (unit B) The first slurry reactor (unit B) :
• the main agent of the method in the reactor is ammonium nitrate. It is supplied in granulated form. Two approaches can be used to input it into the system:
• ammonium nitrate Prior to inputting to the system ammonium nitrate is melted in a separate reactor to give melt, then aqueous solution containing 93-97% ammonium nitrate at about 158°C is dosed into the first slurry reactor.
• Ammonium nitrate is input into the system in the form of granules, which are dosed into the first slurry reactor using a dosing device.
• Ammonium nitrate in the form of granules or melt (stream 5) is fed to reactor unit B, depending on the product composition MCP monohydrate (along with formed gypsum) is fed and water in the form of vapor (stream 4) is added in the needed quantity.
• the reactor mixture is maintained at a temperature not exceeding 160°C.
• the heat is transferred by steam jacket and direct steam. No chemical methods take place in the reactor, the mixing gives homogeneous slurry in the saturated ammonium nitrate solution.
• MCP is partly dissolved and some part remains insoluble, gypsum remains anhydrous, it does not dissolve in the system.
• Slurry from the second reactor is fed via the overflow to the third reactor (unit D) .
• This reactor acts as a compensator for this product prior to granulation.
• the temperature is maintained in the range of 125°C to 145°C.
• Hydrogen fluoride is captured in unit F.
• the stream of vapor and low pressure gases from the mixer (stream 3) is fed to the absorption column, where hydrogen fluoride is captured using the main solution (slurry of calcium carbonate or calcium hydroxide, alkali metals hydroxides solutions) .
• the end product, metal fluorides is washed and, according to the application, is either recycled or dried and packaged and then sent to a warehouse.
• Such NPK product prepared using phosphate salt, sulfuric acid, ammonium nitrate and potassium sulphate mainly comprises the following components:
• Slurry at the temperature 125°C to 145°C flows by gravity from the third reactor to the granulator of paddle mixer type. Returns are input to its front part.
• Distributor distributes slurry in the material within the granulator.
• Granulation is carried out by agglomeration and layering in a fluidized bed, which is created by blades mounted on two shafts.
• Steam with pressure 0,3 to 0,4 MPa may be fed to granulator to adjust the optimal operating conditions of the granulator (temperature, humidity) according to the quality of the combined fertilizer produced.
• the resulting complex nitrogen-phosphorus-potassium fertilizer contains ammonium nitrate, anhydrous calcium sulfate, potassium dihydrogen phosphate, wherein mass fraction of total nitrogen is from 13-15%, mass fraction of total phosphates, in terms of P2O5, is from 9-10%, mass fraction of potassium, in terms of K 2 0, is from 13-15%.
• the production of the above NPK based on solid phosphate salt being a mixture of fluorapatite Ca 5 (PO 4 ) 3 F and dicalcium phosphate CaHP0 4 x nH 2 0, where n is 0 to 2, with fluorapatite Ca 5 (P0 4 ) 3 F content from 27% to 99%, allows the use of potassium sulfate and ammonium nitrate.
• phosphate salt As raw material phosphate salt is used, said salt is obtained by decomposition of phosphoric rock with hydrochloric acid, separating the insoluble precipitate, followed by precipitation of solid phosphate salt using calcium carbonate slurry.
• the rock from Keysik deposits was used for the production of the phosphate salt: Substance Unit Content
• the method gives a mixture of fluorapatiteCa 5 ( P0 4 ) 3 F and dicalcium phosphate CaHP0 4 nH 2 0, where n is 0 to 2, which is used in further production method of NPK composition:
• Fluorine contained in the phosphate salt and obtained by decomposition of phosphate rock with hydrochloric acid is present in the mixture in the form of fluorapatite, which is confirmed by analytical control of the samples.
• Phosphate salt containing 27% fluorapatite is further used for NPK production, namely:
• the stage of decomposition of said solid phosphate salt with sulfuric acid is carried out at the temperature 115°C using semi-dry method, where decomposition takes place with low water content.
• This necessary condition is due to the selection of equimolar ratios in the system to maintain stability of CP in monohydrate form. More specifically, to a phosphate salt [100 kg/h] in the mixer with fluidized bed 98% sulfuric acid [38 kg/h] is fed in the equimolar ratio.
• the method is conducted under vacuum for better removal of released gases, mainly hydrogen fluoride.
• the reaction mass is fed through maturing unit into the cascade of reactors with stirrer. Gas, mainly hydrogen fluoride, is supplied to the absorption step.
• the method is carried out at a temperature not exceeding 120 °C.
• ammonium nitrate [106 kg/h] is fed, the method is carried out at 125°C, potassium sulfate [161 kg/h] is fed into the second rector.
• the resulting complex nitrogen-phosphorus-potassium fertilizer contains ammonium nitrate, anhydrous calcium sulfate, potassium dihydrogen phosphate, wherein mass fraction of total nitrogen is from 13-15%, mass fraction of total phosphates, in terms of P2O5, is from 9-10%, mass fraction of potassium, in terms of K 2 0, is from 13-15%.
• the production of the above NPK based on solid phosphate salt being a mixture of fluorapatite Ca 5 (PO4) 3F and dicalcium phosphate CaHP0 4 x nH 2 0, where n is 0 to 2, with fluorapatite Ca 5 (P0 4 )3F content from 27% to 99%, allows the use of potassium sulfate and ammonium nitrate.
• the method gives a mixture of fluorapatiteCa 5 (P0 4 ) 3 F and dicalcium phosphate CaHP0 4 x nH 2 0, where n is 0 to 2, which is used in further production method of NPK composition:
• Fluorine contained in the phosphate salt and obtained by decomposition of phosphate rock with hydrochloric acid is present in the mixture in the form of fluorapatite, which is confirmed by analytical control of the samples.
• Phosphate salt containing 99% fluorapatite is further used for NPK production, namely:
• the stage of decomposition of said solid phosphate salt with sulfuric acid is carried out at the temperature 115°C using semi-dry method, where decomposition takes place with low water content.
• This necessary condition is due to the selection of equimolar ratios in the system to maintain stability of MCP in monohydrate form. More specifically, to a phosphate salt [100 kg/h] in the mixer with fluidized bed 98% sulfuric acid [38 kg/h] is fed in the equimolar ratio.
• the method is conducted under vacuum for better removal of released gases, mainly hydrogen fluoride.
• the reaction mass is fed through maturing unit into the cascade of reactors with stirrer. Gas, mainly hydrogen fluoride, is supplied to the absorption step.
• the method is carried out at a temperature not exceeding 120 °C.
• ammonium nitrate [106 kg/h] is fed, the method is carried out at 125°C, potassium sulfate [161 kg/h] is fed into the second rector.
• the production of the above NPK based on solid phosphate salt being a mixture of fluorapatite Ca 5 (P0 ) 3 F and dicalcium phosphate CaHP0 4 x nH 2 0, where n is 0 to 2, with fluorapatite Ca 5 (P0 4 ) 3 F content from 27% to 99%, allows the use of potassium sulfate and ammonium nitrate.
• NPK nitrogen-phosphorus-potassium fertilizer

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