Preheating High-Temperature Consolidation Vertical Furnace for Carbon-Containing Phosphate Ore Pellets

Abstract

The present invention discloses a preheating high-temperature consolidation vertical furnace for carbon-mixed phosphate ore pellets, which includes a vertical furnace body. A screening assembly is arranged in the inner cavity of the vertical furnace body, and the screening assembly divides the inner cavity of the vertical furnace body into an upper consolidation cavity and a lower ash discharge cavity. This high-temperature consolidation vertical furnace has the advantages of simple and compact structure, being able to achieve high-temperature consolidation and screening functions, and simplifying the process.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of phosphoric acid production, and particularly relates to a preheating and high-temperature consolidation vertical furnace for carbon-mixed phosphate ore pellets. Background Art

[0002] Kiln-process phosphoric acid is a process technology developed by Occidental Research Corporation (ORC) in the United States in the 1980s for directly using medium and low-grade phosphate rock and using a rotary kiln as a reactor to produce high-concentration phosphoric acid (referred to as the kiln-process phosphoric acid process, or KPA method). It makes carbonaceous pellets by mixing phosphate rock, silica, carbonaceous reducing agent and bentonite. The w(P2O5) of the pellets is 10% - 13, and n(CaO) / n(SiO2) is 0.26 - 0.55. When the high-temperature gas temperature in the reduction zone of the rotary kiln is about 1350°C, phosphorus vapor escapes from the pellets, oxidizes to P2O5, and at the same time releases heat to supply the reduction reaction. Gaseous P2O5 is hydrated to form phosphoric acid, and after cyclic absorption, concentrated phosphoric acid is obtained.

[0003] The greatest advantage of the kiln-process phosphoric acid is that it uses general production equipment and medium and low-grade phosphate rock to produce high-quality and high-concentration phosphoric acid. Compared with the electric furnace process phosphoric acid, the energy consumption is greatly reduced; compared with the wet-process phosphoric acid, it is not restricted by sulfur resources, does not produce phosphogypsum, has the characteristics of simple production process, less investment, environmental friendliness, high acid concentration and good quality of the product, and this process idea shows a good industrial application prospect.

[0004] In 1982, ORC Corporation conducted a pilot test on a Φ0.84m (inner diameter) × 9.14m rotary kiln pilot plant and carried out research on the mathematical model of the reduction of phosphate rock in a rotary kiln. However, they did not recognize the phosphorus loss caused by the reverse absorption of P2O5 in the process (i.e., the reaction of P2O5 in the gas phase with the phosphate rock powder on the surface of the pellets to produce phosphate, forming a white phosphorus-rich shell on the surface of the pellets), so the pilot test results were not satisfactory. How to effectively isolate the oxidation zone and the reduction zone in a rotary kiln, enable the reduction and oxidation reactions of phosphorus to be successfully completed simultaneously, make full use of the reaction heat, and at the same time avoid the occurrence of P2O5 reverse absorption to ensure the reduction rate of phosphorus has become the bottleneck restricting the rotary kiln process for phosphoric acid. Joseph A. Megy proposed some improved technical methods (see U.S. Pat. No. 4,351,809, 1982), using an inert gas as an isolation layer to prevent the pellets from contacting the kiln gas in the oxidizing atmosphere. The specific method is to drill many small holes in the rotary kiln body and continuously introduce inert gas from below the pellet layer to clean the reaction bed and prevent the carbon in the pellets from being oxidized. This method of protecting with inert gas has achieved certain results. However, due to the use of low-temperature consolidated pellets entering the kiln, the preheating section of the rotary kiln (the pellets from 200°C to 1200°C) is too long. Therefore, the amount of protective gas on the surface of the pellets entering the preheating section is very large, which not only has a high cost but also makes the structure and operation of the rotary kiln very complicated. Walter.C.Lapple adopted the method of covering the "free" coke particles on the pellet layer (see U.S. Pat. No. 3,241,917, 1996) to protect the carbon in the pellets from being oxidized. ORC Corporation used this method in the pilot test. Although the amount of "free" coke added was several times that of the pellets, during the rotation of the kiln body, the "free" coke separated from the pellets, and the protection effect was not obvious. None of the above measures have achieved satisfactory results, and so far, no industrial, large-scale or commercial application of the above KPA technology has been seen.

[0005] In view of the above problems, we (Changsha Research Institute of Mining and Metallurgy) have repeatedly studied and proposed a solution to overcome the above problems (see Chinese Patent Documents CN1026403C and CN1040199C), that is, to adopt a process for directly reducing phosphate rock with double-layer composite pellets to produce phosphoric acid (abbreviation: CDK rotary kiln process for phosphoric acid). The so-called double-layer composite pellets are formed by wrapping a carbon-containing coating layer on the outer surface of the phosphate rock carbon-containing pellets, just like wearing a layer of clothes. The carbon in this "clothes" reacts with external oxidizing substances to locally produce reducing atmospheres such as CO to separate the internal solid-phase reduction zone and the external gas-phase oxidation zone, avoiding the reverse absorption of P2O5. Pilot tests and semi-industrial tests have both proved that the double-layer composite pellets can solve the problem of effectively isolating the oxidation zone and the reduction zone in a rotary kiln.

[0006] However, our subsequent research found that using double-layer composite pellets to isolate the oxidation zone and the reduction zone comes at a high cost and causes a series of new technical problems. Its main defects are as follows:

[0007] 1) The problem of kiln ring formation caused by various factors makes it difficult for the rotary kiln to operate continuously and stably for a long period. For example:

[0008] a. The composite pellets are consolidated at a low temperature of about 200°C, resulting in low pellet strength and failure to remove harmful impurities (such as organic matter, sodium, potassium, etc.). During the long preheating section (200°C - 1200°C) of the rotary kiln, the pellets are worn and unevenly heated, causing them to burst, generating a large amount of powder. In addition, impurities in the pellets (such as K, Na, etc.) are also volatilized during this process. These powders and impurities react with P2O5 in the kiln gas to form low-melting phosphate compounds, which adhere to the kiln wall and accumulate continuously, causing ring formation.

[0009] b. A relatively large amount of carbon is incorporated into the pellet coating layer. It is difficult to control the uniform combustion of this kind of equipment in the rotary kiln, and local overheating is likely to occur, leading to high-temperature ring formation.

[0010] 2) The energy consumption and cost are relatively high, and the main reasons are as follows:

[0011] a. The carbon content in the pellet coating layer is relatively large. The combustion of this carbon in the kiln requires a large amount of air and generates a large amount of high-temperature waste gas that is discharged from the kiln tail. This not only results in extremely low thermal energy utilization efficiency of the carbon in this layer (only about 60% of the combustion heat of this part of the carbon is carried away by the high-temperature tail gas), but also brings a large amount of heat and kiln gas into the subsequent acid collection process. It is necessary to use cooling water to remove this part of the heat, which additionally increases the energy consumption and treatment cost.

[0012] b. Anthracite or coke with a relatively high cost is used for carbon addition in the pellets and the coating layer.

[0013] c. The coating layer also increases the consumption of coal and silica in the pellets, increases the slag volume, and increases the raw material cost and production cost.

[0014] d. The coating layer has low strength and is easily worn and lost, causing P2O5 to be reabsorbed into the surface layer of phosphate rock powder, reducing the P2O5 recovery rate.

[0015] If the problems of easy ring formation, high energy consumption and high cost existing in the above-mentioned CDK kiln method for phosphoric acid process are not solved, large-scale industrial production is difficult to achieve. Therefore, in order to improve the production efficiency of the existing kiln method for phosphoric acid process, reduce the production cost, and ensure the stable operation of the process, the existing kiln method for phosphoric acid process and key equipment still urgently need to be continuously improved by technical personnel in this field. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a preheating high-temperature consolidation vertical furnace for carbon-bearing phosphate ore pellets, which has a simple and compact structure, can achieve high-temperature consolidation and screening functions, and can simplify the process.

[0017] To solve the above technical problems, the present invention adopts the following technical solutions:

[0018] A preheating high-temperature consolidation vertical furnace for carbon-bearing phosphate ore pellets includes a vertical furnace body. A screening assembly is arranged in the inner cavity of the vertical furnace body, and the screening assembly divides the inner cavity of the vertical furnace body into an upper consolidation cavity and a lower ash discharge cavity.

[0019] As a further improvement of the above technical solution:

[0020] The top of the vertical furnace body is provided with a feed inlet and an air outlet communicating with the upper consolidation cavity; the lower part of the vertical furnace body is provided with a discharge outlet and an air inlet communicating with the upper consolidation cavity.

[0021] The inner wall of the upper consolidation cavity is provided with guiding protrusions for guiding the pellets onto the screening assembly.

[0022] The upper consolidation cavity forms a notch at the position below the guiding protrusions. The discharge outlet communicates with the bottom of the notch, and the air inlet communicates with the side of the notch.

[0023] The bottom of the vertical furnace body is provided with an ash discharge port communicating with the lower ash discharge cavity.

[0024] The screening assembly includes a support beam and a plurality of rod screens. The support beam is fixedly installed in the inner cavity of the vertical furnace body, and the rod screens are arranged on the support beam at uniform intervals.

[0025] The support beam is installed obliquely in the inner cavity of the vertical furnace body. The low end of the support beam is close to the discharge outlet and the air inlet, and the rod screens are arranged along the inclined surface of the support beam.

[0026] Partition plates are arranged between the two ends of adjacent rod screens inserted into the inner cavity of the vertical furnace body, and the partition plates are fixed by being inserted into the reserved holes of the vertical furnace body.

[0027] The vertical furnace body includes a shell, and refractory insulation bricks are laid inside the shell.

[0028] The vertical furnace body is arranged in a cylindrical structure, and a circular cavity is arranged in its inner cavity.

[0029] The vertical furnace body is arranged in a rectangular structure, and a rectangular cavity is arranged in its inner cavity.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] The preheating high-temperature consolidation vertical furnace for carbon-bearing phosphate ore pellets of the present invention includes a vertical furnace body. A screening assembly is arranged in the inner cavity of the vertical furnace body, and the screening assembly divides the inner cavity of the vertical furnace body into an upper consolidation cavity and a lower ash discharge cavity. When the vertical furnace body is in use, materials first enter the upper consolidation cavity for high-temperature consolidation, are screened by the screening assembly, the screened products are discharged from the lower ash discharge cavity, and the screened solid pellets are discharged from the upper consolidation cavity and enter the next process. Compared with the traditional structure, the present invention first uses a vertical furnace for high-temperature (600-1100°C) consolidation of carbon-bearing phosphate ore pellets, saving space and making the overall structure simpler and more compact; the inner cavity of the vertical furnace body is divided into an upper consolidation cavity and a lower ash discharge cavity by the screening assembly, integrating the two functions of high-temperature consolidation and screening, and the discharged materials can directly enter the external main reaction equipment (rotary kiln), simplifying the process of the kiln method phosphoric acid process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the schematic main sectional structure diagram of Embodiment 1 of the present invention.

[0033] Figure 2 is Figure 1 the A-A sectional structure diagram of

[0034] Figure 3 is Figure 1 the enlarged structure diagram at B of

[0035] Figure 4 is the structure diagram of Embodiment 2 of the present invention.

[0036] Each label in the figure represents:

[0037] 1. Vertical furnace body; 11. Shell; 12. Refractory insulation brick; 2. Screening assembly; 21. Support beam; 22. Rod screen; 23. Partition board; 3. Upper consolidation cavity; 31. Notch; 4. Lower ash discharge cavity; 5. Feed inlet; 6. Air outlet; 7. Discharge outlet; 8. Air inlet; 9. Guide projection; 10. Ash discharge port. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be further described in detail below with reference to the accompanying drawings of the specification and specific embodiments.

[0039] Embodiment 1:

[0040] As Figures 1 to 3As shown in the figure, the first embodiment of the preheating and high-temperature consolidation vertical furnace for carbon-bearing phosphate ore pellets of the present invention includes a vertical furnace body 1. A screening assembly 2 is arranged in the inner cavity of the vertical furnace body 1. The screening assembly 2 divides the inner cavity of the vertical furnace body 1 into an upper consolidation cavity 3 and a lower ash discharge cavity 4. When the vertical furnace body 1 is in use, the material first enters the upper consolidation cavity 3 for high-temperature consolidation, is screened by the screening assembly 2, the screened products are discharged from the lower ash discharge cavity 4, and the screened solid pellets are discharged from the upper consolidation cavity 3 and enter the next process. Compared with the traditional structure, the present invention first uses a vertical furnace for high-temperature (600 - 1100 °C) consolidation of carbon-bearing phosphate ore pellets, saving space and making the overall structure simpler and more compact; by dividing the inner cavity of the vertical furnace body 1 into an upper consolidation cavity 3 and a lower ash discharge cavity 4 through the screening assembly 2, the two functions of high-temperature consolidation and screening are integrated together, and the discharged material can directly enter the external main reaction equipment - rotary kiln, simplifying the process of the kiln method phosphoric acid process.

[0041] In this embodiment, the top of the vertical furnace body 1 is provided with a feed inlet 5 and an air outlet 6 that communicate with the upper consolidation cavity 3; a discharge outlet 7 and an air inlet 8 that communicate with the upper consolidation cavity 3 are provided below the vertical furnace body 1. In this structure, with air intake from the lower part, air outlet from the upper part, feeding from the lower part, and discharging from the lower part, the gas and solid phases are in full countercurrent contact in the furnace, and the gas flow is evenly distributed. Therefore, the solid pellets are evenly heated, and the temperature gradient distribution from top to bottom is reasonable, avoiding the bursting caused by uneven heating of the pellets. After consolidation, the pellets have high strength and good quality.

[0042] In this embodiment, a guiding protrusion 9 for guiding the pellets onto the screening assembly 2 is provided on the inner wall of the upper consolidation cavity 3. In this structure, the guiding protrusion 9 can guide all the pellets to pass through the screening assembly 2, screening out the broken materials, thereby ensuring the quality of the discharged pellets.

[0043] In this embodiment, a notch 31 is formed in the upper consolidation cavity 3 at a position below the guiding protrusion 9. The discharge outlet 7 communicates with the bottom of the notch 31, and the air inlet 8 communicates with the side of the notch 31. In this structure, in addition, both the air inlet 8 and the discharge outlet 7 are located at the notch 31 below the guiding protrusion 9, and the gas is more evenly distributed after passing through.

[0044] In this embodiment, an ash discharge port 10 that communicates with the lower ash discharge cavity 4 is provided at the bottom of the vertical furnace body 1. This ash discharge port 10 is used to discharge the broken materials.

[0045] In this embodiment, the screening assembly 2 includes a support beam 21 and multiple bar screens 22. The support beam 21 is fixedly installed in the inner cavity of the vertical furnace body 1, and the bar screens 22 are evenly spaced on the support beam 21. In this structure, the support beam 21 provides an installation basis for the bar screens 22, and the broken materials are screened out from the gaps between the bar screens 22 and fall into the lower ash discharge cavity 4 and are discharged from the ash discharge port 10.

[0046] In this embodiment, the support beam 21 is installed in an inclined manner in the inner cavity of the vertical furnace body 1. The low end of the support beam 21 is close to the discharge port 7 and the air inlet 8, and each rod sieve 22 is arranged along the inclined surface of the support beam 21. The inclination angle is 3 - 30°, specifically 20°. Such a setting enables the pellets to be quickly guided along the inclined surface to the discharge port 7, improving the efficiency.

[0047] In this embodiment, a partition plate 23 is provided between the two ends of adjacent rod sieves 22 inserted into the inner cavity of the vertical furnace body 1, and the partition plate 23 is fixed by being inserted into the reserved hole of the vertical furnace body 1. The setting of the partition plate 23 makes the distance between each rod sieve 22 reasonable and reliable, and the distance is set to 5 - 20 mm, specifically 10 mm.

[0048] In this embodiment, the vertical furnace body 1 includes a shell 11, and refractory insulation bricks 12 are laid inside the shell 11. The stability of the temperature inside the furnace is ensured by the refractory insulation bricks 12.

[0049] In this embodiment, the vertical furnace body 1 is set as a cylindrical structure, and a circular cavity is arranged in its inner cavity. Its structure is simple and reliable.

[0050] In this embodiment, the circular vertical furnace and its operating parameters are as follows: vertical furnace specification: φ3.6×4.4 m, flue gas temperature at the air inlet 8: 900 - 1000 °C, flue gas temperature at the outlet 6: 200 - 400 °C, pellet temperature at the air inlet 8: 200 °C, pellet temperature at the outlet 6: 900 - 1100 °C, pellet processing capacity: 30 t / h, and the empty tower gas velocity is 0.2 - 2 m / s.

[0051] Embodiment 2:

[0052] As Figure 4 shown, the second embodiment of the preheating and high-temperature consolidation vertical furnace for carbon-mixed phosphate ore pellets according to the present invention. This vertical furnace is basically the same as that in Embodiment 1, except that: in this embodiment, the vertical furnace body 1 is set as a rectangular structure, and a rectangular cavity is arranged in its inner cavity. Its structure is simple and reliable.

[0053] In this embodiment, the rectangular vertical furnace and its operating parameters are as follows: vertical furnace specification: 3×4.2×3.6 m, flue gas temperature at the air inlet 8: 900 - 1000 °C, flue gas temperature at the outlet 6: 200 - 400 °C, pellet temperature at the air inlet 8: 200 °C, pellet temperature at the outlet 6: 900 - 1100 °C, pellet processing capacity: 30 t / h, and the empty tower gas velocity is 0.2 - 2 m / s.

[0054] Although the present invention has been disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention, or modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A preheating and high-temperature consolidation vertical furnace for carbon-mixed phosphate ore pellets, characterized in that: It includes a vertical furnace body (1). A screening component (2) is arranged in the inner cavity of the vertical furnace body (1). The screening component (2) divides the inner cavity of the vertical furnace body (1) into an upper consolidation cavity (3) and a lower ash discharge cavity (4). A feed inlet (5) and an air outlet (6) communicating with the upper consolidation cavity (3) are arranged at the top of the vertical furnace body (1); a discharge outlet (7) and an air inlet (8) communicating with the upper consolidation cavity (3) are arranged below the vertical furnace body (1). Guide protrusions (9) for guiding pellets onto the screening component (2) are arranged on the inner wall of the upper consolidation cavity (3). A notch (31) is formed at the position below the guide protrusions (9) in the upper consolidation cavity (3). The discharge outlet (7) communicates with the bottom of the notch (31), and the air inlet (8) communicates with the side of the notch (31). A ash discharge port (10) communicating with the lower ash discharge cavity (4) is arranged at the bottom of the vertical furnace body (1).

2. The preheating high-temperature consolidation vertical furnace for carbon-matched phosphorite pellets according to claim 1, characterized in that: The screening component (2) includes a support beam (21) and multiple rod screens (22). The support beam (21) is fixedly installed in the inner cavity of the vertical furnace body (1), and the rod screens (22) are arranged on the support beam (21) at uniform intervals.

3. The preheating high-temperature consolidation vertical furnace for carbon-matched phosphorite pellets according to claim 2, characterized in that: The support beam (21) is installed obliquely in the inner cavity of the vertical furnace body (1). The lower end of the support beam (21) is close to the discharge outlet (7) and the air inlet (8), and the rod screens (22) are arranged along the inclined surface of the support beam (21).

4. The preheating and high-temperature consolidation vertical furnace for carbon-matched phosphate ore pellets according to claim 3, characterized in that: Partition plates (23) are arranged between the two ends of adjacent rod screens (22) inserted into the inner cavity of the vertical furnace body (1), and the partition plates (23) are fixed by being inserted into the reserved holes of the vertical furnace body (1).

5. The preheating high-temperature consolidation vertical furnace for carbon-matched phosphate ore pellets according to claim 1, characterized in that: The vertical furnace body (1) includes a housing (11), and refractory insulation bricks (12) are laid inside the housing (11).

6. The preheating high-temperature consolidation vertical furnace for carbon-matched phosphate ore pellets according to claim 1, wherein: The vertical furnace body (1) is set as a cylindrical structure, and a circular cavity is arranged in its inner cavity.

7. The preheating high-temperature consolidation vertical furnace for carbon-matched phosphorite pellets according to claim 1, wherein: The vertical furnace body (1) is set as a rectangular structure, and a rectangular cavity is arranged in its inner cavity.

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