MXPA00012814A - A process for the preparation of compound fertilizer granules - Google Patents

Abstract

The invention relates to a process for the preparation of compound fertilizer granules containing at least two of the plant nutrients nitrogen, phosphorus and potassium, said process comprising the steps of:providing a solid feed material comprising at least one solid fertilizer raw material and optionally recycle material, feeding the feed material or a part thereof into a melter for melting a desired portion thereof and keeping said portion in molten state, feeding the molten or partly molten material and optionally other desired solid raw materials to a granulator to obtain a granulated product, and cooling and optionally screening the granulated product to obtain dry compound fertilizer granules having a desired size distribution, provided that no water or aqueous liquid is introduced into the process.

Description

A PROCESS FOR THE PREPARATION OF COMPOSITE FERTILIZER GRANULES The present invention relates to a process for the preparation of composite fertilizer granules by using solid granulation. The term "compound fertilizer" is defined and used with several different meanings; It contains at least two of the plant nutrients of nitrogen, phosphorus, and potassium. Compound fertilizers are produced chemically or by mixing. They will be in the form of granules, platelets, nuggets, or crystals and they will be flowing. Compound fertilizers are frequently manufactured and used because they are convenient for producing, transporting, storing and applying and because they meet regional or local nutrient requirements, especially the needs of the fundamental nutrient. In addition to containing different proportions of primary nutrients (N + P2O5 + K2), compound fertilizers may contain certain secondary and micronutrients specific to the needs of crops in particular agroclimatic regions. Granulated fertilizers have several advantages over powders, particularly in reducing the amount of dust, improving flow uniformity when fertilizers are applied and segregation when they are mixed. In the classification of the granulation methods, the physical properties of the materials to be granulated will be used. According to the density of the materials, the following three groups can be distinguished: granulation of solids, granulation of mixtures or fusions and granulation of fluids simultaneously with the reaction, by which the product is formed. The basic processes to manufacture compound fertilizers are: steam / water granulation, chemical granulation or granulation of complex or mixture, granulation or drop formation, granulation of compaction and mixing or dry bonding. The main mechanisms responsible for the initial formation of fertilizer granule and subsequent growth are agglomeration and accumulation. The known and widely applied compound fertilizer granulation methods are reported, for example, in "Fertilizer Manual", Kluwer Academic Publishers, 1 998, p. 434-451 and "Studies of Granulation of Compound Fertilizers Containing Urea: A Literature Review", G.C. Hicks, National Fertilizer Development Center; Bull Y-108, 15 pp., 1976. Accumulation is a process in which the layer on layer of a fluid material is applied to a solid particle causing it to grow in size; for example, the granulation processes of the mixture type used to produce DAP, MAP, TSP, and some nitrophosphate compounds are accumulation type of granulation processes. The agglomeration or granulation of solid particles is a classic method for granulating fertilizers, for example NPK products. In most agglomeration-type NPK formulations, 50-75% of the raw materials are fed as solid particles.

The raw materials (premixed) are fed to a granulator where the agglomeration begins. In the granulator steam and / or water or other liquid is added to provide enough liquid to increase the granulation. In the same processes, a small amount of ammonia can also be added to promote granulation and improve product quality by increasing CHR (critical relative humidity) and reducing acidity. The solid particles are combined and bonded together by a combination of cementing and mechanical entanglement. A number of industrial scale processes to manufacture compound fertilizers are developed and applied. In the steam / water granulation process, steam and / or water or other purifying liquid is added to the granulator to provide sufficient liquid phase and plasticity to cause the dried raw materials to agglomerate into the granules of required product size. The use of urea as a source of N for fertilizers of different types and grades has been established. Solid urea with a very high biuret content (0, 8-2.0% by weight) is mainly used for direct application to fertilizer and weak aqueous urea solutions with low biuret (max 0.3% by weight) are used as foliage sprays. The use of urea in the manufacture of compound (granular) fertilizers based on, for example, superphosphate or ammonium phosphate has also been established. Conventional wet granulation is not an adequate method to produce formulations containing urea, particularly when potassium chloride is also present, because the product is very hygroscopic and therefore difficult and expensive to dry. In the chemical granulation together with a large quantity of solid raw materials, water, steam, purifying liquid, and / or ammonia and acid are fed to the granulator; the granules are formed mainly by agglomeration but in some processes the formation of granules can occur by accumulation, too. The formation or granulation of drop, granulation of compaction, mixing or dry bonding, etc. , they are also very widely applied to produce different granular fertilizer formulations. Because water or humidity always occurs in the most traditional granulation processes, drying is a mandatory, difficult and expensive step in the processes and causes the need for a separate dryer construction. To solve granulation problems, different processes are developed that depend on the degree of drying fertilizer and product quality. A granulation process is described by Doshi, S.R. in the article "Fusion blend", Fertilizer Research Vol. 30 (1): p.87-97, 1991. Water (or steam) has been used to agglomerate solids in either powder, granulated or pip form but no other liquids such as ammonia, phosphoric acid, or nitric acid are understood in the process described; still drying is essential. Some water or moisture is also included in the process. The process is related to the humidity of material and temperature. For example, for most agglomeration type NPK fertilizers it is shown that a liquid phase of approximately 300 kg / t of product is optimal. Patent publication GB 1, 189,398 (Sumitomo) describes a process for producing an NK fertilizer, which process comprises spraying a liquid mixture of urea, potassium chloride, gypsum and 1 -1 0 wt.% Of water into the solid material in a granulator Drying was not used. However, the amount of water added in the process is high enough to maintain the urea in the dissolved state and the final product has a high water content of 1-2% by weight. Patent publication EU 4,138,750 (TVA) describes a process for the production of phosphoric acid, sulfuric acid, dehydrated ammonia and urea fertilizers, where a specially designed tube crossing reactor is used to produce a homogeneous melt or blend of low moisture content of phosphoric acid, sulfuric acid and dehydrated ammonia. The tube crossover reactor eliminates the need for a preneutralizer and in addition, due to the low moisture content of mixing or melting, the dryer is removed. The heat of the neutralization reaction dries the material in the tube crossing reactor. Due to water / moisture content of raw materials and products, process problems and product quality, such as hygroscopicity and increased plasticity, will often occur when fertilizers are granulated using steam / water and chemical granulation processes; particularly when, for example, SSP, TSP and / or urea is present in the product. The hygroscopicity and the operations of drying, purification and trituration complicated of plasticity, and in addition, the storage properties of those compound fertilizers are often lower than those of fertilizers that do not contain these substances. The present invention is developed to solve the problems of granulation, product quality, and storage etc. , in the manufacture of compound fertilizers. The present invention relates to a process for the preparation of compound fertilizers such as NPK, NK, etc. , where the solid raw materials are mixed in a mixer and fed to a granulator, where the hot air is also fed. The raw materials are granulated without the aid of water or any other liquid such as ammonia, phosphoric acid or sulfuric acid. In this way, granulation is a true process of solid granulation. Because no water or any other liquid is added, there is no need to dry the granulated product. In addition, the physical quality of the product is also good. Particularly, the process of the present invention has great advantages to known granulation methods, which require higher temperatures in the drying phase.

Particularly, it is important and difficult to control the humidity and drying temperature, the high temperature can cause the melting of the granulated material and it will adhere to the internal walls and slats of the dryer near the discharge terminal. The optimum values for humidity and temperature vary mainly from product to product. Thus, the present invention provides a process for the preparation of compound fertilizer granules containing at least two of the plant nutrients of nitrogen, phosphate and potassium, said process comprising the steps of: providing a solid feed material comprising less a solid fertilizer feedstock and optionally recyclable material, feeds the feedstock or a portion thereof into a merger to fuse a desired portion thereof and maintain said portion in a fused state. feeding the fused or partially fused material and optionally other desired solid raw materials to a granulator to obtain a granulated product, and cooling and optionally purifying the granulated product to obtain the dried compost granules having a desired size distribution, noting that No water liquid or water is introduced in the process. The melting of the feed material or a part of it in the melter can be done by introducing hot air into the melter. The melting can also be effected by other means, for example, by heaters. According to a preferred embodiment of the invention the process is carried out continuously, and the fused portion of the feedstock is kept constant during the process by controlling the flow velocity of the feedstock and the temperature of the hot air introduced into the feedstock. merger The optimum proportion of the fused feed material is dependent on the degree of the fertilizer wanted and the raw materials used. The optimum proportion of the fused material can for example be about 10-40% by weight, preferably about 10-25% by weight, more preferably about 1-2-20% by weight, depending on the degree. When the fusion is carried out by the aid of hot air, a suitable temperature of the hot air introduced in the fusioner is between 200 and 550 ° C. At the outlet of the fusioner hot air has a temperature of approximately 90 ° C to 1 20 ° C. Suitably, the temperature of the fused or partially fused feedstock leaving the melter is between 70 ° C and 1 35 ° C, preferably between 70 ° C and 1 10 ° C. The process of the invention can be carried out either by introducing all the individual components of the raw materials into the merger or by introducing one or some of the individual components of the raw materials into the merger and the rest of the components in the merger. pelletizer The material to be fed into the melter and / or granulator can be preheated. This is preferred in view of the process temperature control. The material can be adequately preheated to a temperature in the range of about 80 ° C to approximately 1 1 0 ° C. The granulation temperature may vary depending on the formula of the fertilizer. The granulation temperature is preferably between about 75 ° C and about 1 25 ° C, more preferably between about 80 ° C and about 125 ° C. The temperature of the cooled granulated product to be purified is typically between about 40 ° C and 60 ° C. Typical raw materials of solid fertilizers, which may be used in the present invention are for example, urea, diammonia phosphate (DAP), K2SO4 (SOP), monoammonium phosphate (MAP), mineral phosphate, potassium chloride (MOP ie, KCl), simple superphosphate (SSP), triple superphosphate (TSP), ammonia sulfate (AS) and ammonia chloride (AC). Preferably, the fertilizer raw materials comprise urea, especially urea seeds, and at least one other fertilizer raw material. Additionally, manganese sulfate and / or one or more trace elements, ie micronutrients, such as boron, can be added.

In addition bentonite, calcite, calcium oxide, calcium sulfate (dehydrated or hemihydrate), dolomite and / or sand and / or any other conventionally used filler can be added. According to the present invention all solid raw materials (solid fertilizer raw materials and optionally recyclable material, micronutrients and fillers) can be introduced into the melter. However, it is also possible to introduce a part of the solid raw materials in the melter and the rest of the solid raw materials in the granulator. In a preferred embodiment, the process of the invention comprises the step of purifying the granulated product to obtain dried composite compost granules having a size of 2 to 5 mm. The sub-size material (<2 mm) and the extra-large material (> 5 mm) obtained in the depuration can be recycled as said recyclable material. Optionally the extra-large material can be ground after debugging before being recirculated. The temperature of the recyclable material of the scrub is typically about 60 ° C or less. The merger and granulator can be separate units but the merger and granulator can also be part of the same equipment. This invention has advantages over traditional granulation methods of prior art technology because the raw materials are granulated without the aid of any water or any other liquid such as ammonia, phosphoric acid or sulfuric acid. Because no other liquid or water is added, there is no need to dry the product. This makes the granulation operation simpler and the investment costs less expensive because no separate equipment is needed for drying. The final product will have a low water content (0.2-0.6% by weight) that originates from the raw materials. No additional drying is required. The water content of the products produced by traditional methods is usually approximately 1-2% by weight, causing the problems of application and agglomeration already mentioned. The invention is illustrated in and by the following examples. Additionally, the strength of the granules of the product obtained in the following examples were checked after 3 months of storage, and the strength was invariable. Example 1 Bench scale process for solid granulation. Formulas (kg / t) GRADE Raw material 1 5-1 5-1 5 1 5-1 5-1 5 1 7-1 7-17 DAP + SSP MAP + MAP sand + NH4CI Urea 249 255 204 MAP (Lithuania 1 1 -50) - 300 340 DAP (Pernis 17-45 21 0 SSP (Lithuania 1 9%) 287 NH4CI (N 26%) - 1 53 KCl (K2O 60%) 250 250 284 Sand - 175 The mixture of the solid raw materials was fed to the bench scale pelletizer, urea was added as pellets, the melting of the mixture occurred with hot air at the beginning of the granulator, granulation was carried out in the granulator and Partially in the cooler The results and process conditions are shown in Table 1. Table 1 GRADE 15-15-1 5 15-15-1 5 1 7-17-1 7 DAP + SSP MAP + MAP sand + NH4CI Process Conditions: Feeding + recyclable kg / h 8.3 1 0.1 1 1 .9 Proportion of recyclable 0.2 0.2 0.2 Air heater -temperature ° C 336 316 322 -bar of pressure 1 .8 1 .8 1 .8 Temperature of product Output of granulator ° C 97 92 97 Exit of cooler 30 32 35 Granulation Good Very good Good Product properties: H2O (KF)% 0.25 0.15 0.28 N% 1 5.2 16.1 18.2 P2O5 total% 1 5.9 15.0 17.1 K2O% 15.8 16.7 18.5 Granule strength N 52 40 50 Deterioration% 0 0.2 0.7 Billing% 37 32 45 CRH% 34 35 43 Absorption mixture 80% RH 2 h% 2.8 2.7 3.2 4 h% 5.7 5.5 6.2 6 h% 8.8 8.3 9.1 Grade 1 5-1 5-1 5 was granulated better when MAP + sand was contained than DAP + SSP. The grade 1 7-1 7-17 containing ammonium chloride was well granulated as well. The ammonia chloride reacted partially with urea and urea formed • NH CI. The nutrient content of each product was good. The physical properties of the products were good; the products were very dry. Example 2 Bench scale process for solid granulation. GRADE NK 1 6-0-31 2A 2B Formula 16-0-31 1 6-0-31 Fill Filler CaSO4 Bentonite Hemihydrate Kg / t Kg / t Urea (nuggets) 348 348 KCl (white) 51 7 51 7 Bentonite 1 25 _ CaSO4 * 0.5H2O - 1 25 (as dry matter) The mixture of solid raw materials was fed with the recyclable to the bench scale granulator. The fusion occurred with hot air at the beginning of the granulator. The granulation has been carried out in the granulator and partially in the cooler. The products were coated with Esso coating oil 2 kg / t + talc 3 kg / t. Very good and good granulation was obtained with good product quality. However, the high air humidity during the process caused some immediate increase in the water content of the final product. The results and conditions of the testing process - '"• * of the product are shown in Table 2. Table 2 GRADE NK 16-0-31 2A 2B 16-0-31 16-0-31 Fill Filler CaSO Bentonite Hemihydrate Feeding + recyclable kg / h 9.0 9.0 Proportion of recyclable 0.7 0.4 Air heater -temperature ° C 294 238 -pressure rod 1.6 1.6 Fert temperature ° C Granulator output 104 88 Cooler outlet 28 27 Granulation Very good Good Product properties: Chemical analysis Water (KF)% 0.77 0.78 Urea-N% 16.6 1 6.8 N% 1 6.6 1 6.8 K2O% 31 .8 30.9 S% 0.51 3.0 pH% 7.3 5.6 Physical Properties Granule strength N 27 41 Deterioration% 1 .3 1 .1 Weight in volume kg / l 0.77 0.80 Fluidity kg / min 4.83 4.80 Billing% 52 45 CRH% 40 38 Moisture Absorption 80% RH 2 h% 2.9 2.7 4 h% 5.0 4.5 6 h% 7.0 6.8 Example 3 Bench scale process for solid granulation. GRADE 18-1 2-6 + 1 .5MgO Kg / t Urea (nuggets) 1 72 KCl (white) 1 00 Phosphate Kodvor 1 55 DAP (Pernis) 17-45 143 AS (Leuna) 366 MgSO 53 The mixture of raw materials solid was fed with the recyclable to the bench scale granulator. The fusion occurred with hot air at the beginning of the granulator. The granulation has been carried out in the granulator and partially in the cooler. The products were coated with Esso coating oil 2 kg / t + talc 3 kg / t. Very good granulation was obtained with good product quality. The results and process conditions of the product tests are shown in Table 3. Table 3 GRADE 18-1 2-6 + 1 .5MgO Feeding + recyclable kg / h 9.0 Proportion of recyclable 0.6 Air heater -temperature ° C 233 -pressure bar 1 .6 Fe ° ° C temperature Granulator output 98 Cooler output 28 Granulation Good Product properties: Chemical analysis Water (KF)% 0.36 Urea-N% 8.5 NH4-N% 9.7 N% 1 8.2 P2O5 - Total% 1 1 .3 P2O5 - NAC% 6.0 (53%) P2O5 - WS% 5.5 (49% K2O% 8.4 Mg% 1 .3 S% 1 0.8 PH 5.8 Physical Properties Granule strength N 41 Deterioration% 0.6 Weight in volume kg / l 0.84 Fluidity kg / min 4.88 Billing% 59 CRH% 40 Moisture absorption 80% RH 2 h 3.3 4 h% 5.2 6 h Example 4 Bench scale process for solid granulation. GRADE 12-12-17 + 2 MgO + 0.5 B2O3 Kg / t Urea (crushed) 264 Phosphate Morocco 270 TSP (P2O5 45%) 89 KCl (white) 284 MgSO4 64 Colemanite 6 The mixture of solid raw materials was preheated to approximately 1 00 ° C in the feed screw of the granulator. The fusion occurred with hot air in the granulation cylinder. The granulation has been carried out in the granulator and partly in the cooling cylinder. The products were coated with SK Fert FW5 AG 2 kg / t + talc 3 kg / t. Very good and good granulation was obtained with good product quality. The results and process conditions of the product tests are shown in Table 4. Table 4 GRADE 12-12-1 7 + 2 MgO + 0.5 B2O3 Feeding + recyclable kg / h 5.3 Proportion of recyclable 0.6 Granulation temperature ° C Approximately 1 20 Coolant air 27 Granulation Good Pipeline properties: Chemical analyzes Water (KF)% 0.35 Urea-N% 12.4 P2O5 - Total% 12.2 P2O5 - NAC% 6.0 (49%) P2O5 - ws% 2.8 (23%) K2O% 18.8 Mg% 1 .5 B % 750 pH 4.8 Physical Properties Granule strength N 40 Deterioration% 0.1 Weight in volume Kg / l 0.82 Fluidity Kg / min 5.4 CRH% 23 Absorption of humidity 80% RH 2 h% 3.2 4 h% 5.5 6 h 8.0 Example 5 Bench scale process for solid granulation. GRADE 1 2-6-24 Kg / t Urea (crushed) 264 SSP (P2O5 20%) 100 Phosphate Morocco 1 30 KCl (white) 400 Colemanite 6 Bentonite 80 The mixture of solid raw materials was preheated to approximately 1000 ° C in the advance screw of the granulator. The fusion occurred with hot air in the granulation cylinder. The granulation has been carried out in the granulator and partly in the cooling cylinder. The products were coated with SK Fert FW5 AG 2 kg / t + talc 3 kg / t. Very good and good granulation was obtained with good product quality. The results and process conditions of the product tests are shown in Table 5. Table 5 GRADE 12-6-24 Feeding + recyclable kg / h 5.1 Proportion of recyclable 0.84 Granulating temperature ° C Approximately 120 Cooler air 28 Granulation Very good Product properties: Chemical analysis Water (KF)% 0.27 Urea-N% 1 3. 1 P2O5 - Total% 6.0 P2O5 - NAC% 2.9 (4.8%) P2O5 - WS% 0.84 (14%) K2O% 25.8 B% 850 PH 6.1 Physical Properties Granule strength N 39 Deterioration% 0. 1 Weight in volume kg / l 0.84 Fluidity kg / min 5.6 CRH% 15 Moisture absorption 80% RH 2 h% 2.1 4 h% 4.1 6 h 6.0 Example 6 GRADE 15-15-15 Urea (crushed) 285 kg / t Fused Urea 1 00% DAP 1 17 kg / t Yunnan mineral phosphate 330 kg / t MOP 225 kg / t Bentonite 6 kg / t The urea was fused in a separate reactor and mixed with the other raw materials preheated to 90 ° C. The temperature at the beginning of the granulation was 1 10.4 ° C at the end of the granulation of 1 03.2 ° C. The duration of the granulation step was 4 minutes.

Product properties: H2O (KF) 0.09 Granule strength N 34.5 Very good granulation was obtained. Example 7 Bench scale process for solid granulation. GRADE 15-15-15 Urea (46%) 276 kg / t DAP (17-45) 142 kg / t Mineral phosphate 270 kg / t (P2O5 32%) K2SO4 300 kg / t (K2O 50%) The mixture of solid and recyclable raw materials was preheated at approximately 100 ° C with IR in the lead screw of such cylinder. The outer wall of the granulation cylinder was heated with IR as well. The urea was previously ground. A small amount of hot air was used in the urea melt in the granulation cylinder. The drying cylinder worked as a cooler. The products were coated with SK Fert FW5 AG 2 kg / t + 3 kg / t.

Processing Conditions: Feeding and recyclable kg / h 5.07 Proportion of recyclable 0.75 Recyclable heater ° C 1 79 Granulation cylinder x Exterior 268 x Interior 1 17 Air to cylinder 287 Air to cooler 24 Cooler air 28 Good granulation Properties of the product: H2O (KF)% 0.09 N 1 5.5 P2O5 - Total 1 5.4 K2O 16.1 S% 6.6 Resistance of 9 loo N 30 Deterioration% 0.4 Fracturing% 28 CRH% 18 80% RH 2 h% 2.6 4 h% 4.8 6 h% 6.6 SOP based 15-15-1 5 well granulated.

Claims (18)

1. CLAIMS 1. A process for the preparation of composite fertilizer granules containing at least two of the plant nutrients of nitrogen, phosphorus and potassium, said process comprises the steps of: Providing a solid feed material comprising at least one solid fertilizer raw material and optionally recyclable material, Feeding the feedstock or a part thereof in a merger to fuse a desired portion thereof and maintaining said portion in a melting state, Feeding the partially fused material and optionally other desired solid feedstocks to a granulator to obtain a granulated product, and Cool and optionally purify the granulated product to obtain dry compost granules having a desired size distribution, noting that no aqueous liquid or water is introduced into the process. 2. A process according to claim 1, characterized in that the process is carried out continuously, and the fused portion of the feedstock is kept constant during the process by controlling the flow rate of the feedstock and the temperature of the melter. 3. A process according to claim 1 or 2, characterized in that the temperature of the partially fused feed material is between 70 ° C and 1 35 ° C. 4. A process according to any of claims 1 -3, characterized in that the melting is effected by introducing hot air into said melter. 5. A process according to claim 4, characterized in that the temperature of the hot air introduced into the melter is between 200 ° C and 550 ° C. 6. A process according to any of claims 1-5, characterized in that from 10 to 40% by weight of the feedstock is fused in the melter. A process according to any of claims 1-6, characterized in that said solid feed material to be fed into the melter comprises all the individual components of the raw materials. A process according to any of claims 1-6, characterized in that said solid feed material to be fed into the melter comprises one or more of the individual components of the raw materials, and the rest of the components is fed to the pelletizer. A process according to any of claims 1 - 8, characterized in that said solid feed material to be fed into the melter is preheated. 1 0. A process according to any of claims 1-9, characterized in that the solid raw material to be fed into the granulator is preheated. eleven . A process according to claim 9 or 1 0, characterized in that the material is preheated to a temperature in the range of 80 ° C to 1 1 0 ° C.
2. 2. A process according to claim 1, characterized in that the granulation temperature is in the range of 75 ° C to 125 ° C, preferably 80 ° C to 1 25 ° C. A process according to any of claims 1 - 12, characterized in that the fertilizer raw materials are selected from the group consisting of urea, diammonia phosphate (DAP), K2SO4 (SOP), monoammonium phosphate (MAP), potassium chloride (MOP), mineral phosphate, simple superphosphate (SSP), triple superphosphate (TSP), ammonia sulfate (AS) and ammonia chloride (AC). A process according to claim 13, characterized in that the fertilizer raw materials comprise urea and at least one other said fertilizer raw material. 5. A process according to claim 1, wherein additionally at least the material selected from the group consisting of manganese sulfate and micronutrients is introduced into the process. 16. A process according to any of claims 1 - 15, characterized in that in addition to at least the filler selected from the group consisting of bentonite, calcite, calcium oxide, anhydrous calcium sulfate, calcium sulfate hemihydrate, dolomite, and sand, is introduced into the process. 17. A process according to claim 1, characterized in that the sub-size material and the extra-large material obtained in the purification were recycled as said recyclable material, said extra-large material optionally being ground after debugging. 18. A process according to any of claims 1-17, characterized in that the moisture content of the compound of dry fertilizer granules is below 0.6% by weight, preferably below 0.3% by weight.