Process for preparing water-soluble sulphur-based compound fertilizers

Abstract

The application discloses a kind of water-soluble sulphur-based compound fertilizer preparation method, belong to compound fertilizer technical field.The steps include as follows:(1) in reaction kettle, concentrated sulfuric acid and potassium chloride are reacted under heating condition, reaction temperature is 105-115 DEG C, reaction time is 25-45 minutes, slurry is sent to cooling kettle;(2) in cooling kettle, temperature is reduced to 40-60 DEG C, slurry is sent to mixed acid tank;(3) in mixed acid tank, add dilute phosphoric acid, potassium bisulfate solution and slurry, reaction temperature is 65-75 DEG C, slurry is sent to tubular reactor;(4) in tubular reactor, add ammonia, washing liquid and slurry, reaction temperature is 150-180 DEG C, slurry is sent to granulator;(5) in granulator, add alkaline compound fertilizer raw material, return material and slurry for granulation, granulation temperature is 80-95 DEG C, return material ratio is 1:1.5-2.0;(6) the granules obtained from granulator are cooled and screened to obtain product.

Description

Technical Field

[0001] This invention belongs to the field of compound fertilizer technology, and specifically relates to a method for preparing a water-soluble sulfur-based compound fertilizer. Background Technology

[0002] Compound fertilizers are chemical fertilizers containing two or more of the following nutrients: nitrogen, phosphorus, and potassium. They have advantages such as high nutrient content, fewer by-products, and good physical properties. They play a very important role in balancing fertilization, improving fertilizer utilization, and promoting high and stable crop yields.

[0003] like Figure 1 As shown, the existing compound fertilizer preparation method is as follows: concentrated sulfuric acid and potassium chloride react in a reactor to obtain potassium bisulfate, and the slurry is sent to a mixed acid tank; phosphoric acid is added to the mixed acid tank, and the slurry is sent to a tubular reactor; ammonia is introduced into the tubular reactor, and the main reaction is the reaction between phosphoric acid and ammonia, and the slurry is sent to a granulator; in the granulator, the slurry, return material, ammonia and urea (other raw materials can be added as needed) are granulated to obtain granules; the granules are dried, sieved, cooled and coated to obtain the product.

[0004] For example, patent application number CN201310344491.7 discloses a new process for producing compound fertilizer by spray granulation of amino acids, including batching, granulation, drying, cooling, sieving, metering, and finished product testing; batching involves mixing potassium chloride, monoammonium phosphate, and ammonium chloride raw materials evenly in a mixer; granulation involves coating the mixed raw materials into granules using a granulator. Before granulation, the mixed raw materials are sprayed with a slurry, and the steps are as follows: a) Prepare amino acids: Dilute 28% concentrated ammonia water to 20% dilute ammonia water with washing water in an ammonia water tank, pressurize it to 0.2-0.3 MPa using an ammonia water pump, meter it, and send it into a tubular reactor; pressurize 98% concentrated sulfuric acid to 0.2- After being metered at 0.3 MPa, the solution is fed into a tubular reactor. Dilute ammonia and sulfuric acid react in the tubular reactor for 50-60 seconds to generate a high-temperature amino acid solution. b. 47-52% urea and 1.8-2.2 times the amount of water are added to the amino acid solution by weight to form a viscous slurry. The viscous slurry is then sprayed directly and evenly onto the material layer in the granulator. The pH value of the material is controlled at 5.8-6.3. c. The water vapor and excess gas generated by the granulator are carried out by the exhaust fan, washed with water, and then discharged. Part of the recycled washing water is used as process water to dilute the concentrated ammonia, and the rest is recycled.

[0005] For example, patent application number CN202211418744.6 discloses a method for producing sulfur-containing compound fertilizer using low-quality phosphoric acid, including the following steps:

[0006] S1. Add elemental sulfur to low-quality phosphoric acid, with the mass of elemental sulfur accounting for 5-25% of the mass of low-quality phosphoric acid. Stir thoroughly at a temperature of 40-80℃ to obtain sulfur-containing phosphoric acid.

[0007] S2. The sulfur-containing phosphoric acid obtained in step S1 is fed into a first reactor, and ammonia gas is introduced to perform a neutralization reaction, so that the neutralization degree reaches 0.6-1.2, to obtain a sulfur-containing ammonium phosphate neutralization slurry.

[0008] S3. The sulfur-containing ammonium phosphate neutralization slurry in the first reactor is fed into a second reactor, and a potassium source and inorganic salts containing trace elements are added, the material temperature is controlled at 100-160℃, and a complex reaction is performed for 15-60 minutes, to obtain a powdery compound fertilizer product.

[0009] S4. The powdery compound fertilizer product obtained in step S3 is granulated, dried, screened, cooled and packaged to obtain the required sulfur-containing compound fertilizer product.

[0010] A compound fertilizer spraying granulation method is disclosed in patent application No. CN 200610043439.8, which is to generate potassium bisulfate solution by reacting potassium chloride with concentrated sulfuric acid, uniformly mix the potassium bisulfate solution with an aqueous solution of monoammonium phosphate, and then react with ammonia to generate neutralization slurry containing ammonium sulfate, potassium sulfate and diammonium phosphate, and then perform granulation, drying, cooling and screening processes to obtain the compound fertilizer.

[0011] The main component of the existing ternary compound fertilizer is ammonium phosphate, and for the compound fertilizer with ammonium sulfate as the main component, the process is optimized in the present patent; in addition, in the prior art, drying is generally required after granulation, and the energy consumption is high. SUMMARY

[0012] The embodiment of the present application provides a preparation method of water-soluble sulfur-based compound fertilizer, which is used for producing ternary compound fertilizer with low nutrient content, and has the advantages of good water solubility, good appearance and low chlorine content. The technical scheme is as follows:

[0013] The embodiment of the present application provides a preparation method of water-soluble sulfur-based compound fertilizer, which comprises the following steps:

[0014] (1) In a reactor, concentrated sulfuric acid and potassium chloride are reacted under heating, the reaction temperature is 105-115℃, the reaction time is 25-45 minutes, the slurry is sent to a cooling kettle, the molar ratio of concentrated sulfuric acid to potassium chloride is 6.6-8.4:1, and the sulfuric acid needs a large excess amount. In this step, since step (2) still has a high temperature, the potassium chloride can not be completely reacted in this step, but in order to ensure that hydrogen chloride can overflow from the slurry, the potassium chloride is reacted by more than 85% in this step.

[0015] (2) In the cooling kettle, the temperature is reduced to 40-60°C, and the slurry is sent to the mixed acid tank. This step requires the slurry to be cooled, and if it is cooled too much, a large amount of cooling water is required, which is not good for water balance. If the temperature is not reduced enough, the temperature in step (3) will be high, and boiling may occur.

[0016] (3) In the mixed acid tank, dilute phosphoric acid, potassium hydrogen sulfate solution and the slurry of step (2) are added, and the reaction temperature is 65-75°C. The slurry is sent to the tubular reactor. Among them, the molar ratio of potassium hydrogen sulfate to potassium chloride is 0.5-1.0:1, and the molar ratio of phosphoric acid to potassium chloride is 0.9-1.3:1.

[0017] (4) In the tubular reactor, ammonia gas, washing liquid and the slurry of step (3) are added, and the reaction temperature is 150-180°C. The slurry is sent to the granulator. Among them, the amount of washing liquid is controlled to keep the reaction temperature at 150-180°C and the density of the slurry after reaction less than 1.6 g / cm³, and the molar ratio of ammonia gas to potassium chloride is 8-11:1. The difference between this step and the prior art is that the prior art mainly reacts phosphoric acid with ammonia gas, and the reaction product is ammonium phosphate; this patent mainly reacts sulfuric acid with ammonia gas, and the reaction product is ammonium sulfate; the reaction heat of sulfuric acid and ammonia gas is larger than that of phosphoric acid and ammonia gas, and washing liquid needs to be added to control the temperature. In addition, ammonium sulfate has poor flowability, and washing liquid also needs to be used to increase the flowability (control the density). However, too much washing liquid may cause the granulated product to be wet, and drying is required to control the moisture. Through the applicant's experiments, when the reaction temperature is 150-180°C and the density of the slurry is less than 1.6 g / cm³, the slurry has good flowability, and after granulation, drying is not required, and the temperature entering the granulator will not be too high (too high will reduce the service life, especially the service life of the slurry nozzle).

[0018] (5) In the prilling machine, the basic compound fertilizer raw material, the return material and the slurry of step (4) are added to prilling, the prilling temperature is 80-95℃, the return material ratio (the mass ratio of the output to the secondary cooling structure to the output to the return material structure) is 1:1.5-2.0, and the amount of the basic compound fertilizer raw material (a small amount, 10-25% of the amount of the return material) needs to be controlled to control the pH of the product to be 3.6-4.2. Among them, the basic compound fertilizer raw material includes ammonium carbonate or ammonium bicarbonate, etc. The role of the basic compound fertilizer raw material has two aspects: one is to reduce the acidity of the product (the patent has a lot of excess sulfuric acid, and there may be free acid remaining in the product); the second is to reduce the adhesion of the product; the applicant found during the pilot test that if the basic compound fertilizer raw material is not added, the product is easy to stick to the equipment and pipeline, and regular maintenance is required. After adding the basic compound fertilizer raw material, especially ammonium bicarbonate, the product does not stick to the equipment and pipeline. The applicant found that if the prilling temperature is too high, the product is easy to powder, and the product size required by the compound particle cannot be obtained. The patent reduces the temperature during prilling by adding process water and increasing the amount of return material.

[0019] (6) The particles obtained from the prilling machine are cooled and screened to obtain the product, the return material of the screening is sent to the prilling machine, the prilling and cooling tail gas is sent to the tail gas treatment structure for treatment, and the washing liquid of the tail gas treatment structure is sent to the tubular reactor. In this embodiment, in order to increase the amount of return material, the range of the screen mesh size of the screening structure can be reduced, such as 1-4mm in the prior art, which can be designed as 3-4mm in this embodiment. The screening structure directly sends small particles to the prilling machine, and sends large particles to the prilling machine after being crushed.

[0020] Among them, the concentration of dilute phosphoric acid in this embodiment is 15-25wt% calculated as phosphorus pentoxide, the concentration of concentrated sulfuric acid is greater than 90wt%, and the concentration of potassium bisulfate solution is 20-33wt%. The patent has low requirements for raw materials, and low-concentration wet-process phosphoric acid can be used. The amount of wet-process phosphoric acid (with more impurities) used in the patent is small, and under the action of excess concentrated sulfuric acid, the product can be basically fully water-soluble.

[0021] Further, in this embodiment, the tail gas generated in steps (1) and (2) is treated by a graphite cooler and a falling film absorption tower to obtain hydrochloric acid (sold externally). The tail gas of the reaction kettle and the cooling kettle is sent to the graphite cooler for cooling, and the cooled tail gas is sent to the falling film absorption tower to prepare hydrochloric acid; both the cooling kettle and the graphite cooler are supplemented with clean water as cooling water, and the cooled water after heat exchange is sent to the cooling tower; the graphite cooler and the cooling tower form a circulating cooling system, and the cooled water after cooling in the cooling tower is sent to the falling film absorption tower and the tail gas treatment structure. Among them, the tail gas treatment structure in this embodiment includes multiple washing towers, the front washing tower uses dilute acid as the spray liquid to recover ammonia, and the rear washing tower uses the cooled water as the spray liquid to ensure the tail gas treatment effect.

[0022] Specifically, in step (6), the cooling process includes primary cooling and secondary cooling, the particles output by the granulator are subjected to primary cooling, screening and secondary cooling to obtain the product, the tail gas of the primary cooling is sent to a tail gas treatment structure, and the secondary cooling reduces the temperature of the product to below 40 DEG C. In step (6), due to the higher granulation temperature, although drying is not required, cooling is required. Specifically, the primary cooling adopts a fluidized bed cooler (air is introduced), which not only has good cooling effect, but also facilitates tail gas treatment; and the secondary cooling adopts a cooling cylinder.

[0023] Specifically, the basic compound fertilizer raw material in the embodiment is ammonium bicarbonate, and the amount of the ammonium bicarbonate needs to be controlled to make the pH of the product 3.8-4.2.

[0024] The preparation method of the water-soluble sulfur-based compound fertilizer provided by the application has the following advantages:

[0025] 1. After granulation, drying is not required, hot air is not required, energy consumption is reduced, and drying can be realized only by using the temperature of the material itself;

[0026] 2. The main component is ammonium sulfate, the ammonium sulfate is basically not hygroscopic, and no coating is required, thereby reducing the coating equipment;

[0027] 3. No filler is required, and the product is round;

[0028] 4. The product has good water solubility and is a fully water-soluble compound fertilizer; in the prior art, a large amount of wet-process phosphoric acid, a small amount of coating oil (or coating powder) and a filler (may not be required) are used, so that the product cannot be completely water-soluble;

[0029] 5. The product has low chlorine content, and can be used for crops or soil sensitive to chlorine content;

[0030] 6. Although the amount of returned material is large, the time in the reaction kettle is shortened, and a certain time can be reduced;

[0031] 7. The requirement for raw materials is low.

[0032] In addition, a large amount of concentrated sulfuric acid is excessively added before granulation in the patent, and the dilution of concentrated sulfuric acid releases heat, and the patent uses multiple means to control the reaction heat, including:

[0033] 1. A cooling kettle is arranged after the reaction kettle to cool the material;

[0034] 2. Potassium bisulfate solution (as the product of the previous step, which does not react at the acid mixing tank) is added at the acid mixing tank, the amount of slurry is increased to reduce the dilution heat of the added dilute phosphoric acid;

[0035] 3. Adding washing water (with lower density) at the tubular reactor can not only control the reaction heat release, but also facilitate the control of the density of the slurry, which is beneficial to the subsequent granulation process, and the elements recovered from the tail gas treatment are reused;

[0036] 4. The temperature at the granulator (the temperature of the slurry output from the tubular reactor is very high) is reduced by increasing the amount of returned material;

[0037] 5. The temperature of the product is reduced to below 40℃ by two cooling processes. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is the principle diagram of the existing ternary compound fertilizer production method;

[0039] Figure 2 is the principle diagram of the preparation method of the water-soluble sulfur-based compound fertilizer provided by the embodiment of the present application

[0040] Figure 3 is the flowchart of the preparation method of the water-soluble sulfur-based compound fertilizer provided by the embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings.

[0042] Referring to Figures 2-3 , the embodiment of the present application provides a preparation method of a water-soluble sulfur-based compound fertilizer, which comprises the following steps:

[0043] (1) In the reaction kettle, concentrated sulfuric acid and potassium chloride are reacted under heating conditions, the reaction temperature is 105-115℃, the reaction time is 25-45 minutes, the slurry is sent to the cooling kettle, the molar ratio of concentrated sulfuric acid to potassium chloride is 7.5:1, and the concentration of concentrated sulfuric acid is 98wt%.

[0044] (2) In the cooling kettle, the temperature is reduced to 40-60℃, and the slurry is sent to the mixed acid tank.

[0045] (3) In the mixed acid tank, dilute phosphoric acid, potassium hydrogen sulfate solution and the slurry of step (2) are added, the reaction temperature is 65-75℃, the slurry is sent to the tubular reactor, the molar ratio of potassium hydrogen sulfate to potassium chloride is 0.6:1, the molar ratio of phosphoric acid to potassium chloride is 1.2:1, the concentration of potassium hydrogen sulfate solution is 25wt%, and the concentration of dilute phosphoric acid is 20wt% in terms of phosphorus pentoxide.

[0046] (4) In the tube reactor, ammonia, washing liquid and the slurry of step (3) are added, the reaction temperature is 150-180℃, the slurry is sent to the granulator, the amount of washing liquid is controlled to make the reaction temperature 150-180℃ and the density of the slurry after reaction less than 1.6g / cm³, and the molar ratio of ammonia to potassium chloride is 10:1.

[0047] (5) In the granulator, ammonium bicarbonate (a small amount), return material and the slurry of step (4) are added for granulation, the granulation temperature is 80-95℃, the return material ratio is 1:2, and the amount of ammonium bicarbonate needs to be controlled to make the pH of the product 4.1.

[0048] (6) The output granules are cooled once, screened and cooled twice to obtain the product, the return material of screening is sent to the granulator, the tail gas of granulation and first cooling is sent to the tail gas treatment structure for treatment, the washing liquid of the tail gas treatment structure is sent to the tube reactor, and the product temperature is reduced to below 40℃ by the second cooling.

[0049] Further, the tail gas of the reaction kettle and the cooling kettle in the embodiment is sent to the graphite cooler for cooling, the cooled tail gas is sent to the falling film absorption tower to prepare hydrochloric acid, the cooling kettle and the graphite cooler are supplemented with clean water as cooling water, the cooled water after heat exchange is sent to the cooling tower, and the graphite cooler and the cooling tower form a circulating cooling system, and the cooled water after cooling in the cooling tower is sent to the falling film absorption tower and the tail gas treatment structure.

[0050] The patent is compared with the prior art (using the technical route shown in Figure 1 , a 15-15-15 ternary compound fertilizer), as shown in Tables 1 and 2:

[0051] Table 1

[0052]

[0053] As can be seen from Table 1, even if multiple means are used, the granulation temperature of the patent is still much higher than that of the prior art. In addition, at the mixed acid tank, the temperature will rise due to the heat release of dilution of sulfuric acid.

[0054] Table 2

[0055]

[0056] As can be seen from Table 2, the nutrient content of the patent is lower than that of the prior art, but the N content is similar. The product of the patent has the following advantages over the prior art: good water solubility, low chlorine content, no need for coating layer, and good product appearance (no coating layer, round).

[0057] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing water-soluble sulfur-based compound fertilizer, characterized in that, The method includes the following steps: (1) In a reaction vessel, concentrated sulfuric acid and potassium chloride react under heating conditions at a temperature of 105-115℃ for 25-45 minutes. The slurry is then sent to a cooling vessel. The molar ratio of concentrated sulfuric acid to potassium chloride is 6.6-8.4:

1. (2) In the cooling kettle, the temperature is reduced to 40-60℃, and the slurry is sent to the acid mixing tank; (3) In the mixed acid tank, add dilute phosphoric acid, potassium bisulfate solution and the slurry from step (2), the reaction temperature is 65-75℃, and the slurry is sent to the tubular reactor. The molar ratio of potassium bisulfate to potassium chloride is 0.5-1.0:1, and the molar ratio of phosphoric acid to potassium chloride is 0.9-1.3:

1. (4) In a tubular reactor, ammonia, washing liquid and slurry from step (3) are added. The reaction temperature is 150-180℃. The slurry is sent to a granulator. The amount of washing liquid should be controlled so that the reaction temperature is 150-180℃ and the density of the slurry after the reaction is less than 1.6 g / cm³. The molar ratio of ammonia to potassium chloride is 8-11:

1. (5) In the granulator, alkaline compound fertilizer raw materials, return material and slurry from step (4) are added for granulation. The granulation temperature is 80-95℃, the return material ratio is 1:1.5-2.0, and the amount of alkaline compound fertilizer raw materials needs to be controlled so that the pH of the product is 3.6-4.

2. The alkaline compound fertilizer raw materials include ammonium carbonate or ammonium bicarbonate. (6) The granules obtained from the granulator are cooled and screened to obtain the product. The screened return material is sent to the granulator. The granulation and cooling tail gas is sent to the tail gas treatment structure for treatment. The washing liquid of the tail gas treatment structure is sent to the tubular reactor. The concentration of the dilute phosphoric acid, calculated as phosphorus pentoxide, is 15-25 wt%, the concentration of the concentrated sulfuric acid is greater than 90 wt%, and the concentration of the potassium hydrogen sulfate solution is 20-33 wt%.

2. The method for preparing the water-soluble sulfur-based compound fertilizer according to claim 1, characterized in that, The exhaust gases from both the reaction vessel and the cooling vessel are fed into a graphite cooler for cooling. The cooled exhaust gases are then sent to a falling film absorption tower to prepare hydrochloric acid. Both the cooling vessel and the graphite cooler are replenished with clean water as cooling water, and the cooled water after heat exchange is sent to a cooling tower. The graphite cooler and the cooling tower form a circulating cooling system, and the cooled water after being cooled by the cooling tower is sent to the falling film absorption tower and the exhaust gas treatment structure.

3. The method for preparing the water-soluble sulfur-based compound fertilizer according to claim 1, characterized in that, In step (6), the cooling process includes primary cooling and secondary cooling. The granules output by the granulator are cooled, screened and cooled to obtain the product. The exhaust gas from the primary cooling is sent to the exhaust gas treatment structure, and the secondary cooling reduces the temperature of the product to below 40°C.

4. The method for preparing the water-soluble sulfur-based compound fertilizer according to claim 1, characterized in that, The alkaline compound fertilizer raw material is ammonium bicarbonate, and its dosage needs to be controlled so that the pH of the product is 3.8-4.2.

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