Method for preparing ternary compound fertilizer with low energy consumption

Abstract

The invention discloses a method for preparing a ternary compound fertilizer with low energy consumption, and belongs to the technical field of compound fertilizers. Comprising the following steps: (1) reacting concentrated sulfuric acid and potassium chloride in a reaction kettle at 105-135 DEG C for 3-8 hours; (2) adding phosphoric acid into the acid mixing tank, and controlling the temperature to be 80-85 DEG C; the magnesium content of the phosphoric acid is 2.2-2.4 wt%; (3) feeding the slurry into a tubular reactor, introducing ammonia gas, and controlling the reaction temperature to be 145-150 DEG C and the reaction pressure to be 0.6-0.7 Mpa; (4) feeding the slurry to a flash tank for flash evaporation, and adding washing liquor to control the density of the slurry to be 1.55-1.58 g / cm < 3 >; (5) adding the returned material and the slurry into a granulation device, and controlling the granulation temperature to be 78-84 DEG C and the hot air temperature to be 650-700 DEG C; and (6) screening and cooling the granules obtained by the granulating device to obtain the compound fertilizer.

Description

Technical Field

[0001] The invention belongs to the technical field of compound fertilizers, and particularly relates to a method for preparing a ternary compound fertilizer with low energy consumption. Background Art

[0002] Compound fertilizer refers to a chemical fertilizer containing two or more nutrients including nitrogen, phosphorus and potassium. Compound fertilizer has the advantages of high nutrient content, few by-components and good physical properties. It plays a very important role in balanced fertilization, improving fertilizer utilization rate and promoting high and stable yields of crops.

[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 produce potassium bisulfate, and the slurry is sent to a mixing tank. Phosphoric acid is added to the mixing tank, and the slurry is then sent to a tubular reactor. Ammonia is introduced into the tubular reactor, and the primary reaction is between phosphoric acid and ammonia. The slurry is then sent to a granulation unit. In the granulation unit, the slurry, return material, and urea (other raw materials may or may not be added as needed) are granulated to produce granules. The granules are then dried, screened, cooled, and packaged to obtain the product. Granulation exhaust, drying exhaust, and cooling exhaust are sent to an exhaust gas treatment unit for treatment, and the washing liquid is sent to the tubular reactor for reuse.

[0004] For example, the patent with application number CN201910060089.3 discloses a new method for producing ammoniated sulfur-based compound fertilizer, which includes the following steps: mixing ammonium phosphate and water to make ammonium phosphate slurry, and adding the obtained mixture to a mixed acid tank; mixing sulfuric acid and potassium chloride and performing low-temperature conversion, adding water to the generated HCl to produce hydrochloric acid, and the generated potassium bisulfate enters the mixed acid tank; the slurry obtained after mixing the above materials in the mixed acid tank enters a tubular reactor, and ammonia is added to the tubular reactor. The material generated by the reaction of the slurry with ammonia in the tubular reactor is directly sprayed onto the granulation material bed, an ammonia shaft is provided in the granulation material bed, the ammonia shaft passes ammonia and water vapor into the granulation material bed, external supplementary solids are added to the granulation material bed, the product after granulation of the granulation material bed is dried, and after drying, it is screened, cooled, coated, and packaged in sequence, and the final finished product is directly shipped out.

[0005] For example, patent application number CN202010183294.1 discloses a process for producing sulfur-based high-nitrogen compound fertilizer, which includes the following steps: 1) Potassium chloride and sulfuric acid are converted into dechlorination in a reaction tank at low temperature.

[0006] 2) The hydrogen chloride gas produced in step 1 is reacted with potassium bisulfate, and hydrochloric acid is produced as a by-product after the hydrogen chloride gas is absorbed.

[0007] 3) The potassium bisulfate in step 2 is put into a mixed acid tank and phosphoric acid is added to form a mixed acid.

[0008] 4) The mixed acid in step 3 is neutralized with ammonia in a tubular reactor to form a finished slurry which enters a slurry tank.

[0009] 5) Urea and formaldehyde are put into a urea dissolving tank, heated and mixed, and then sent into a slurry tank for reaction and mixing.

[0010] 6) The total mixed slurry in step 6 is sent to a granulator for granulation, low-temperature drying, drying and granulation, and then screening and packaging to produce a compound fertilizer product.

[0011] All of the above processes require a drying process.

[0012] In addition, in the prior art, in order to reduce the drying process, a large amount of concentrated sulfuric acid is used. For example, patent application number CN202310907973.2 discloses a method for preparing a ternary compound fertilizer with low energy consumption, which includes the following steps: (1) In a reactor, concentrated sulfuric acid and potassium chloride react under heating conditions at a temperature of 105-115°C for 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.

[0013] (2) In the cooling kettle, the temperature is lowered to 40-60°C and the slurry is sent to the mixed acid tank.

[0014] (3) Add dilute phosphoric acid, potassium bisulfate solution and the slurry of step (2) into the mixed acid tank, the reaction temperature is 65-75°C, the slurry is sent to the tubular reactor, the molar ratio of the potassium bisulfate to potassium chloride is 0.5-1.0:1, and the molar ratio of the phosphoric acid to potassium chloride is 0.9-1.3:1.

[0015] (4) Ammonia, washing liquid and the slurry of step (3) are added to a tubular reactor, the reaction temperature is 150-180°C, and the slurry is sent to a granulator. The amount of the washing liquid is used to control the reaction temperature to be 150-180°C and the density of the slurry after the reaction to be less than 1.6 g / cm³. The molar ratio of ammonia to potassium chloride is 8-11:1.

[0016] (5) In a granulator, an alkaline compound fertilizer raw material, a return material, and the slurry of step (4) are added for granulation. The granulation temperature is 80-95° C., the return material ratio is 1:1.5-2.0, and the amount of the alkaline compound fertilizer raw material is required to control the pH of the product to 3.6-4.2. The alkaline compound fertilizer raw material includes ammonium carbonate or ammonium bicarbonate.

[0017] (6) The granules obtained by 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, and the washing liquid of the tail gas treatment structure is sent to the tubular reactor.

[0018] However, this method can only produce low-nutrient compound fertilizers, and the washing liquid will increase the burden on the tubular reactor (a key component that limits production), thereby reducing production. Summary of the Invention

[0019] To solve the aforementioned problems, the present invention provides a method for preparing a ternary compound fertilizer with low energy consumption, which does not require drying and reduces energy consumption. It does not require the washing liquid to be sent to a tubular reactor, thus ensuring the output. The technical solution is as follows: The embodiment of the present invention provides a method for preparing a ternary compound fertilizer with low energy consumption, the method comprising the following steps: (1) In a reactor 4, concentrated sulfuric acid and potassium chloride react at 105-135°C for 3-8 hours, and the slurry is sent to a mixed acid tank 5. The mass ratio of the concentrated sulfuric acid to potassium chloride is 0.72-0.78:1, and the concentration of the concentrated sulfuric acid is greater than 95wt%.

[0020] (2) Phosphoric acid is added to the mixed acid tank 5, the temperature is controlled at 80-85°C, and after being mixed evenly, it is sent to the mixed acid storage tank 7. The mass ratio of the phosphoric acid to potassium chloride is 5.0-5.4:1; the concentration of the phosphoric acid is 21-25wt% in terms of phosphorus pentoxide, the content of phosphogypsum is less than 1wt%, and the content of magnesium is 2.2-2.4wt%.

[0021] (3) The slurry in the mixed acid storage tank 7 is sent to the tubular reactor 9 and ammonia is introduced. The reaction temperature is 145-150°C, the reaction pressure is 0.6-0.7 MPa, and the mass ratio of ammonia to potassium chloride is 0.52-0.60:1.

[0022] (4) The slurry from step 3 is sent to the flash tank 10 for flash evaporation, and the washing liquid from the tail gas treatment device is added to control the density of the slurry after flash evaporation to 1.55-1.58 g / cm³; after the flash evaporation is completed, it is sent to the slurry storage tank 11 for temporary storage and the temperature is controlled to 80-100°C.

[0023] (5) In the granulation device, the return material and the slurry of step 4 are added, with or without urea. The granulation temperature is 78-84°C and the hot air temperature is 650-700°C.

[0024] (6) The granules obtained by the granulation device are screened and cooled to obtain compound fertilizer, the screened return material is sent to the granulation device, and the granulation and cooling tail gas is sent to the tail gas treatment device for treatment.

[0025] The density of the washing liquid from the tail gas treatment device is 1.45-1.50g / cm³.

[0026] Among them, the reactor 4 in the embodiment of the present invention is a cylindrical structure, and an overflow partition is provided in the middle to divide it into a primary reaction tank and a secondary reaction tank; the potassium chloride and sulfuric acid are continuously added to the primary reaction tank according to the ratio, and the reaction temperature of the primary reaction tank is 128-135°C; the reaction liquid overflows from the top of the overflow partition to the secondary reaction tank, and the reaction temperature of the secondary reaction tank is 105-110°C. The reaction liquid in the secondary reaction tank is intermittently discharged to the mixed acid tank 5 every 2-6 hours.

[0027] The tail gas from the flash tank 10 in the embodiment of the present invention is sent to a tail gas treatment device for treatment.

[0028] Among them, the exhaust gas treatment device in the embodiment of the present invention includes a venturi scrubber 13, a primary scrubber 14, a fan 15 and a secondary scrubber 16 connected in sequence from front to back, and the exhaust gas of the granulation device and the cooling device is sent to the venturi scrubber 13, and the venturi scrubber 13 and the primary scrubber 14 share a circulating scrubber; when the density of the washing liquid in the circulating scrubber is greater than 1.45g / cm³, the washing liquid is sent to the flash tank 10; the water supply of the secondary scrubber 16 is process water or clean water; when the density of the washing liquid in the secondary scrubber 16 is greater than 1.2g / cm³, it is sent to the primary scrubber 14 as water supply; the exhaust gas of the flash tank 10 is sent to the secondary scrubber 16.

[0029] Preferably, a demister is provided at the top of the secondary washing tower 16 in the embodiment of the present invention, an upper spray structure is provided at the upper part thereof, a lower spray structure is provided at the middle part thereof, a lower air inlet is provided at the lower part thereof, and an upper air inlet is provided at the upper part thereof; the upper spray structure and the lower spray structure are both connected to the bottom of the secondary washing tower 16 through a pipeline with a second circulation pump, the exhaust gas treated by the primary washing tower 14 is sent to the lower air inlet through the fan 15, and the exhaust gas from the flash tank 10 is sent to the upper air inlet.

[0030] The granulation device in the embodiment of the present invention is a spray granulator, and its height is greater than or equal to 20m.

[0031] In the embodiment of the present invention, in step 5, urea is not added, and the return ratio is 1:5.5-5.8.

[0032] The compound fertilizer prepared in the embodiment of the present invention has a particle size of 2-4 mm, a moisture content of less than 1.5%, a compressive strength greater than 32 N, and a total nutrient content greater than 45%. The technical solution provided by the embodiment of the present invention has the following beneficial effects: (1) Compared with existing technology, the production capacity is increased by about 6%.

[0033] (2) No drying process is required, and energy consumption is reduced by about 7% compared with the prior art. In this patent, due to the longer reaction time of step (1), the steam consumption is increased; however, the total energy consumption (including the energy consumption of steam) can also be reduced by about 3% compared with the prior art.

[0034] (3) Product parameters are: moisture content less than 1.5%, compressive strength greater than 32N (usually greater than 34N, excellent performance), total nutrient content greater than 45%, and chlorine content less than or equal to 1.8%.

[0035] (4) The granulation qualification rate is greater than 80%, which further guarantees the production capacity.

[0036] (5) The demagnesium process can be omitted or phosphate rock with a higher magnesium content can be used for production, which can reduce the production cost by 2-4%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the principle block diagram of the existing compound fertilizer production system; Figure 2 This is a principle block diagram of a method for preparing ternary compound fertilizer with low energy consumption provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the structure of a potassium chloride silo, a sulfuric acid storage tank, a phosphoric acid storage tank, a reactor, a mixed acid tank, a mixed acid storage tank, a tubular reactor, a flash tank and a slurry storage tank combination; Figure 4 It is a schematic diagram of the structure of the combination of venturi scrubber, primary scrubber, fan, secondary scrubber and chimney; Figure 5 The present invention provides a method for preparing a ternary compound fertilizer with low energy consumption.

[0038] In the figure, 1 is a potassium chloride silo, 2 is a sulfuric acid storage tank, 3 is a phosphoric acid storage tank, 4 is a reactor, 5 is a mixed acid tank, 6 is a first slurry pump, 7 is a mixed acid storage tank, 8 is a second slurry pump, 9 is a tubular reactor, 10 is a flash tank, 11 is a slurry storage tank, 12 is a third slurry pump, 13 is a venturi scrubber, 14 is a primary scrubber, 15 is a fan, 16 is a secondary scrubber, and 17 is a chimney. A hydrogen chloride tail gas, B ammonia, C from tail gas treatment device, D to granulation device, E granulation and cooling tail gas, F from flash tank, G process water or clean water, H to flash tank. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0040] Example 1 See also Figure 2-5Example 1 provides a method for preparing a ternary compound fertilizer with low energy consumption, the method comprising the following steps: (1) In reactor 4, concentrated sulfuric acid and potassium chloride react at 105-135°C for 3-8 hours (this patent has a longer reaction time), and the slurry is sent to mixed acid tank 5. The mass ratio of concentrated sulfuric acid to potassium chloride is 0.72-0.78:1, and the concentration of concentrated sulfuric acid is greater than 95wt%.

[0041] (2) Phosphoric acid is added to the mixed acid tank 5, the temperature is controlled to 80-85°C, and after uniform mixing, it is sent to the mixed acid storage tank 7. The mass ratio of phosphoric acid to potassium chloride is 5.0-5.4:1; the concentration of phosphoric acid is 21-25wt% in terms of phosphorus pentoxide, the phosphogypsum content is less than 1wt%, and the magnesium content is 2.2-2.4wt%. In the prior art, the lower the magnesium content, the better, preferably less than 1.5wt% to ensure the nutrient content. However, in this patent, in order to ensure the success rate of granulation and use higher temperature hot air, it is necessary to increase the magnesium content, which is contrary to the common sense in this field. Under normal circumstances, increasing the magnesium content will increase the viscosity of the slurry, making it inconvenient to process; however, the raw materials of this patent are simple and the viscosity is not high. The viscosity of the slurry itself is not high, so the increase in viscosity caused by the increase in magnesium content will not cause production difficulties (transportation and spraying). In this patent, due to the high magnesium content, in order to ensure the nutrient content, it is necessary to reduce the phosphogypsum content and chlorine content. According to this patent, when preparing wet-process phosphoric acid, the demagnesization process can be omitted or phosphate rock with a higher magnesium content can be used for production, thereby reducing the production cost by 2-4%.

[0042] (3) The slurry from the mixed acid storage tank 7 is sent to the tubular reactor 9 and ammonia is introduced. The reaction temperature is 145-150°C and the reaction pressure is 0.6-0.7 MPa. The mass ratio of ammonia to potassium chloride is 0.52-0.60:1.

[0043] (4) The slurry from step 3 is sent to the flash tank 10 for flash evaporation, and the washing liquid from the tail gas treatment device is added to control the density of the slurry after flash evaporation to 1.55-1.58 g / cm³. After the flash evaporation is completed, it is sent to the slurry storage tank 11 for temporary storage and the temperature is controlled to 80-100°C. The tail gas is sent to the tail gas treatment device for treatment. Among them, the density of the washing liquid from the tail gas treatment device is 1.45-1.50 g / cm³. In this patent, the slurry density is slightly higher than that of the prior art, and the spraying temperature is also slightly higher.

[0044] (5) In the granulation device, the return material and the slurry of step 4 are added, with or without urea, the return material ratio is 1:5.0-5.8, the granulation temperature is 78-84°C, and the hot air temperature is 650-700°C. The granulation device is a spray granulator, and its height is greater than or equal to 20m. In this patent, the spray temperature is about 5°C higher than that of the prior art, the hot air temperature is about 120°C higher than that of the prior art, and the height of the granulation device tower is about 5m higher than that of the prior art. In this patent, although the use of higher temperature hot air leads to increased energy consumption, the total energy consumption is reduced due to the reduction of the drying process.

[0045] In this patent, a thicker slurry is sprayed and the magnesium content in the slurry is increased, resulting in a good granulation effect and high strength of the particles. Due to the good granulation effect (fewer small particles) and high strength, coupled with the low moisture content of the particles themselves, the particles can withstand higher temperatures. By increasing the height of the granulation device and increasing the hot air temperature, drying can be achieved during granulation.

[0046] (6) The granules obtained by the granulation device are screened and cooled to obtain compound fertilizer, the screened return material is sent to the granulation device, and the granulation and cooling tail gas is sent to the tail gas treatment device for treatment.

[0047] The reactor 4 in the embodiment of the present invention is a cylindrical structure with an overflow baffle in the middle, dividing it into a primary and secondary reaction tanks. Potassium chloride and sulfuric acid are continuously added to the primary reaction tank according to the ratio, with the reaction temperature in the primary reaction tank being 128-135°C. The reaction liquid overflows from the top of the overflow baffle into the secondary reaction tank, with the reaction temperature in the secondary reaction tank being 105-110°C. The reaction liquid in the secondary reaction tank is intermittently discharged to the mixed acid tank 5 every 2-6 hours. In this patent, due to the high magnesium content, the chlorine content needs to be reduced to ensure nutrient content. The method of this patent can achieve a potassium chloride conversion rate greater than 95% in this step.

[0048] The exhaust gas treatment device in this embodiment of the present invention includes, in order from front to back, a Venturi scrubber 13, a primary scrubber 14, a fan 15, a secondary scrubber 16, and a chimney. The exhaust gas from the granulation unit and the cooling unit is fed to the Venturi scrubber 13. The Venturi scrubber 13 and the primary scrubber 14 share a circulating scrubber tank. When the density of the scrubbing liquid in the circulating scrubber tank exceeds 1.45 g / cm³ (a higher density can be used to ensure the density of the flash tank 10), the scrubbing liquid is fed to the flash tank 10. The secondary scrubber 16 is fed with process water or clean water. When the density of the scrubbing liquid in the secondary scrubber 16 exceeds 1.2 g / cm³, it is fed to the primary scrubber 14 as replenishment water. The exhaust gas from the flash tank 10 is fed to the secondary scrubber 16.

[0049] Among them, the compound fertilizer prepared in the embodiment of the present invention has a particle size of 2-4 mm, a moisture content of less than 1.5%, a compressive strength greater than 32N, a total nutrient content greater than 45%, and a chlorine content less than or equal to 1.8%. Example 2 See also Figure 3 Example 2 provides a low-energy method for preparing a ternary compound fertilizer. This method is substantially the same as Example 1, except that the secondary scrubber 16 in this embodiment of the present invention has a demister installed at the top, an upper spray structure installed at the upper portion, a lower spray structure installed at the middle portion, and a lower air inlet installed at the lower portion, with the upper portion being the upper air inlet. Both the upper and lower spray structures are connected to the bottom of the secondary scrubber 16 via a pipeline with a second circulation pump. Exhaust gas treated in the primary scrubber 14 is delivered to the lower air inlet via a blower 15, and exhaust gas from the flash tank 10 is delivered to the upper air inlet.

[0050] Example 3 Example 3 provides a method for preparing a ternary compound fertilizer with low energy consumption, which is basically the same as Example 1, except that: in step 5, no urea is added, and the return ratio is 1:5.5-5.8.

[0051] Example 4 See also Figure 3 Example 4 provides a method for preparing a ternary compound fertilizer with low energy consumption, the method comprising the following steps: (1) Potassium chloride and sulfuric acid are continuously added to the primary reaction tank according to a ratio, and the reaction temperature of the primary reaction tank is 132°C; the reaction liquid overflows from the top of the overflow baffle to the secondary reaction tank, and the reaction temperature of the secondary reaction tank is 105°C. The reaction liquid of the secondary reaction tank is intermittently discharged to the mixed acid tank 5 every 4 hours. Among them, the mass ratio of concentrated sulfuric acid to potassium chloride is 0.74:1, and the concentration of concentrated sulfuric acid is 98wt%.

[0052] (2) Phosphoric acid is added to the mixed acid tank 5, the temperature is controlled at 85°C, and the mixture is evenly mixed and then sent to the mixed acid storage tank 7. The mass ratio of phosphoric acid to potassium chloride is 5.2:1; the concentration of phosphoric acid is 22wt% in terms of phosphorus pentoxide, the content of phosphogypsum is 0.7wt%, and the content of magnesium is 2.3wt%.

[0053] (3) The slurry from the mixed acid storage tank 7 is sent to the tubular reactor 9 and ammonia gas is introduced. The reaction temperature is 145°C and the reaction pressure is 0.7 MPa. The mass ratio of ammonia gas to potassium chloride is 0.55:1.

[0054] (4) The slurry from step 3 is sent to a flash tank 10 for flash evaporation, and a wash solution from an exhaust gas treatment device is added to control the density of the slurry after flash evaporation to 1.56 g / cm³. After the flash evaporation is completed, the slurry is sent to a slurry storage tank 11 for temporary storage and the temperature is controlled at 90°C. The exhaust gas is sent to an exhaust gas treatment device for treatment. The density of the wash solution from the exhaust gas treatment device is 1.47 g / cm³.

[0055] (5) In the granulation device, the return material and the slurry of step 4 are added, the return material ratio is 1:5.7, the granulation temperature is 80°C, the hot air temperature is 660°C, and the height of the granulation device is 21m.

[0056] (6) The granules obtained by the granulation device are screened and cooled to obtain compound fertilizer, the screened return material is sent to the granulation device, and the granulation and cooling tail gas is sent to the tail gas treatment device for treatment.

[0057] The parameters of the obtained compound fertilizer are shown in Table 1: Table 1

[0058] In Table 1, the content represents the mass content; the qualified rate of granulation is the proportion of 2-4mm.

[0059] Operating the tubular reactor at maximum output, the daily output is approximately 524 tons, with a standard coal consumption of 0.064 tons per ton of compound fertilizer. By comparison, the existing technology produces approximately 494 tons per day, with a standard coal consumption of 0.069 tons per ton of compound fertilizer. This represents an approximately 6.1% increase in output and a 7.2% reduction in energy consumption. Assuming a selling price of 2,500 yuan per ton of compound fertilizer, the annual revenue increase is: 30 * 2,500 yuan * 330 days (based on a 330-day year) = 24.75 million yuan. The standard coal cost reduction is: 0.005 * 524 yuan * 950 yuan (standard coal price) * 330 yuan = 820,000 yuan.

[0060] The production conditions were verified and the magnesium content in phosphoric acid was controlled. The results are shown in Table 2: Table 2

[0061] As can be seen from Table 2, considering the moisture content (less than or equal to 1.5%), granulation qualification rate (greater than or equal to 80%) and compressive strength (greater than 31N), the magnesium content in phosphoric acid is 2.2-2.4wt%.

[0062] Comparative Example 1 is basically the same as Example 4, except that in step (4), no flash evaporation is performed, and the washing liquid is directly added and mixed.

[0063] Comparative Example 2 is basically the same as Example 4, except that: in step (5), the existing granulation conditions are adopted: the granulation temperature is 75°C, the hot air temperature is 550°C, and the height of the granulation device is 15m.

[0064] Comparative Example 3 is substantially the same as Example 4, except that in step (4), the density of the slurry after flash evaporation is controlled to be 1.52 g / cm³.

[0065] Comparative Example 4 is substantially the same as Example 4, except that in step (4), the density of the slurry after flash evaporation is controlled to be 1.60 g / cm³.

[0066] Comparative Example 5 is basically the same as Example 4, except that: the existing technology is used and the magnesium content in the phosphoric acid is 2.3 wt%.

[0067] Comparative Example 6 uses the existing technology (the magnesium content in the phosphoric acid is 1.6wt%), but the granulation conditions adopt the conditions of this patent: the granulation temperature is 80°C, the hot air temperature is 660°C, and the height of the granulation device is 21m.

[0068] The results are shown in Table 3: Table 3 .

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a ternary compound fertilizer with low energy consumption, characterized in that: The method comprises the following steps: (1) In a reactor (4), concentrated sulfuric acid and potassium chloride react at 105-135° C. for 3-8 hours, and the slurry is sent to a mixed acid tank (5). The mass ratio of the concentrated sulfuric acid to potassium chloride is 0.72-0.78:1, and the concentration of the concentrated sulfuric acid is greater than 95wt%; (2) Phosphoric acid is added to the mixed acid tank (5), the temperature is controlled at 80-85°C, the mixture is mixed evenly, and then the mixture is sent to the mixed acid storage tank (7). The mass ratio of the phosphoric acid to potassium chloride is 5.0-5.4:1; the concentration of the phosphoric acid is 21-25wt% in terms of phosphorus pentoxide, the content of phosphogypsum is less than 1wt%, and the content of magnesium is 2.2-2.4wt%; (3) sending the slurry from the mixed acid storage tank (7) to the tubular reactor (9) and introducing ammonia gas, the reaction temperature is 145-150°C, the reaction pressure is 0.6-0.7 MPa, and the mass ratio of ammonia gas to potassium chloride is 0.52-0.60:1; (4) sending the slurry from step (3) to a flash tank (10) for flash evaporation, and adding a wash solution from an exhaust gas treatment device to control the density of the slurry after flash evaporation to 1.55-1.58 g / cm³; after the flash evaporation is completed, sending the slurry to a slurry storage tank (11) for temporary storage and controlling the temperature to 80-100°C; (5) In a granulation device, the return material and the slurry of step (4) are added, with or without urea, the granulation temperature is 78-84°C, and the hot air temperature is 650-700°C; (6) The granules obtained by the granulation device are screened and cooled to obtain compound fertilizer, the screened return material is sent to the granulation device, and the granulation and cooling tail gas is sent to the tail gas treatment device for treatment.

2. The method for preparing ternary compound fertilizer with low energy consumption according to claim 1, wherein The density of the washing liquid from the exhaust gas treatment unit is 1.45-1.50 g / cm³.

3. The method for preparing ternary compound fertilizer with low energy consumption according to claim 1, wherein The reactor (4) is a cylindrical structure, with an overflow partition provided in the middle thereof to divide it into a primary reaction tank and a secondary reaction tank; the potassium chloride and sulfuric acid are continuously added to the primary reaction tank according to a ratio, and the reaction temperature of the primary reaction tank is 128-135° C.; the reaction liquid overflows from the top of the overflow partition to the secondary reaction tank, and the reaction temperature of the secondary reaction tank is 105-110° C. The reaction liquid in the secondary reaction tank is intermittently discharged to the mixed acid tank (5) every 2-6 hours.

4. The method for preparing ternary compound fertilizer with low energy consumption according to claim 1, wherein The tail gas from the flash tank (10) is sent to a tail gas treatment device for treatment.

5. The method for preparing ternary compound fertilizer with low energy consumption according to claim 4, characterized in that: The tail gas treatment device comprises a venturi scrubber (13), a primary scrubber (14), a fan (15) and a secondary scrubber (16) connected in sequence from front to back, the tail gas from the granulating device and the cooling device is sent to the venturi scrubber (13), and the venturi scrubber (13) and the primary scrubber (14) share a circulating scrubber; when the density of the washing liquid in the circulating scrubber is greater than 1.45 g / cm³, the washing liquid is sent to the flash tank (10); the water for replenishing the secondary scrubber (16) is process water or clean water; when the density of the washing liquid in the secondary scrubber (16) is greater than 1.2 g / cm³, it is sent to the primary scrubber (14) as replenishing water; the tail gas from the flash tank (10) is sent to the secondary scrubber (16).

6. The method for preparing ternary compound fertilizer with low energy consumption according to claim 5, characterized in that: The top of the secondary washing tower (16) is provided with a demister, the upper part of the secondary washing tower (16) is provided with an upper spray structure, the middle part of the secondary washing tower (16) is provided with a lower spray structure, the lower part of the secondary washing tower (16) is provided with a lower air inlet, and the upper part of the secondary washing tower (16) is provided with an upper air inlet; the upper spray structure and the lower spray structure are both connected to the bottom of the secondary washing tower (16) through a pipeline with a second circulation pump, the tail gas treated by the primary washing tower (14) is sent to the lower air inlet through a fan (15), and the tail gas of the flash tank (10) is sent to the upper air inlet.

7. The method for preparing ternary compound fertilizer with low energy consumption according to claim 1, characterized in that: The granulation device is a spray granulator, and its height is greater than or equal to 20m.

8. The method for preparing ternary compound fertilizer with low energy consumption according to claim 1, characterized in that: In step (5), no urea is added and the return ratio is 1:5.5-5.

8.

9. The method for preparing ternary compound fertilizer with low energy consumption according to claim 8, characterized in that: The prepared compound fertilizer has a particle size of 2-4 mm, a moisture content of less than 1.5%, a compressive strength of more than 32 N, and a total nutrient content of more than 45%.

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