CN116902935A - A kind of composite pellet suitable for kiln phosphoric acid rotary kiln process and its preparation method - Google Patents

Abstract

The application discloses a composite pellet suitable for a kiln-method phosphoric acid rotary kiln process and a preparation method thereof, wherein the composite pellet is of a core-shell structure with an outer shell coating an inner sphere, the inner sphere comprises an inner sphere material and a binder, and the outer shell comprises an outer shell material and a binder; the inner ball material comprises phosphate ore, carbonaceous reducing agent and regulator, and the addition amount of the binder in the inner ball is 1-15% of the mass of the inner ball material; the shell material comprises phosphate ore, a carbonaceous reducing agent and a regulator, wherein the addition amount of the binder in the shell is 1-15% of the mass of the shell material; the inner ball and the outer shell are compounded into a core-shell structure through an adhesive. The impurity problem caused by non-similar substances and the problem that the non-similar substances are difficult to bond with each other to obtain the high-strength composite pellets can be avoided on one hand only by changing the content composition of the substances in the inner and outer pellets without changing the composition of the substances in the inner and outer pellets.

Description

A kind of composite pellet suitable for kiln phosphoric acid rotary kiln process and its preparation method

Technical field

The present invention mainly relates to the technical field of phosphoric acid production, and in particular to a composite pellet formula and preparation method suitable for the kiln-based phosphoric acid rotary kiln process.

Background technique

In the 1960s, Lapple and others in the United States first proposed a new process for producing phosphoric acid using a rotary kiln. Based on their research results, Occidental Petroleum Corporation (ORC) in the United States carried out semi-industrial experiments in the 1980s, forming the kiln phosphoric acid process. The prototype is referred to as the kiln phosphoric acid process or KPA method. This process is to carry out the reduction of phosphate rock and the oxidation of yellow phosphorus in the same rotary kiln. Since the heat released by the oxidation of yellow phosphorus and carbon is higher than the heat absorption of phosphate rock reduction, the energy consumption of phosphate rock reduction is greatly reduced. At the same time, this process can also process low-grade phosphate rock.

At present, there are two raw material formulas for kiln-process phosphoric acid. One is a high-calcium formula (CaO/SiO ₂ molar ratio 2 to 8). This formula is more suitable for the characteristics of China's phosphate rocks. The amount of silica added is small, and the P content of the kiln raw materials is _{The 2O5 content} is high and the output per unit volume is large. However, the reduction temperature required for this formula is as high as 1450°C, making production difficult to achieve. The second is a high silicon formula (CaO/SiO ₂ molar ratio 0.2~0.5). This formula has a low reduction temperature of only 1300~1350°C and a high phosphorus volatilization rate. It has always been the focus of research, and semi-industrial tests have also been carried out. However, this formula usually requires the addition of a large amount of silica, resulting in a low P ₂ O ₅ content in the kiln and a reduction in unit volume output. In addition, the rotary kiln can easily form rings composed of Si and P as the main elements, resulting in the kiln phosphoric acid process being unable to Stable and long-term operation has not been achieved yet.

Solving the problem of easy ring formation in the kiln phosphoric acid process is the key to realizing the industrial application of the kiln phosphoric acid process. To this end, many improvement measures have been proposed, including: high-temperature consolidation pretreatment, improved rotary kiln method, composite pellet process, catalyst reduction method, etc.

The high-temperature consolidation pretreatment method can be seen in Chinese patent CN112320775A, which discloses a rotary kiln phosphoric acid production system and production method with high-temperature consolidation and preheating outside the kiln. Most of the impurities in the pellets are removed in advance through preheating and high-temperature consolidation outside the kiln. , which solves the ring formation problem in the rotary kiln caused by various factors caused by low-temperature consolidation pellets entering the kiln. However, the additional high-temperature consolidation process will inevitably increase the energy consumption of the overall process.

The improved rotary kiln method can be seen in Chinese patent CN104211032A, which discloses an improved kiln-based phosphoric acid process using a reduced phosphate rock rotary kiln and a method to solve the problem of ringing at the end of the kiln. Specifically, the kiln flue gas does not occur when entering the exit flue. A large offset will prevent centrifugal physical sedimentation at the end of the kiln, causing the metaphosphoric acid in the kiln gas to directly enter the hydration tower along with the flue gas from the kiln. However, this process only alleviates the ring formation problem of the rotary kiln, but cannot fundamentally avoid the ring formation problem of the rotary kiln.

The catalyst reduction method is disclosed in Chinese patent CN101850953A, which discloses a method for reducing the reaction temperature and accelerating the reaction temperature of the kiln-process high-calcium phosphate formula. In the present invention, a mineral activator is added to the kiln-process high-calcium phosphate formula at a rate of 0.5%-12% by weight of the total material. , the calcium oxide content of the kiln-process high calcium phosphate formula is reduced by about 3 times the amount of silica, and the reaction temperature is reduced from 1450°C-1520°C to 1260°C-1350°C. In any case, the activators they added were fluoride salts, phosphoric acid, chloride, sulfur, sulfide, sulfuric acid, sulfate and other substances. This introduced other impurity elements into the phosphate rock, making it impossible to meet the conventional process in subsequent phosphoric acid products. impurities; it will also cause the reduced slag to become hazardous solid waste, making it difficult to safely dispose of it.

For the composite pellet process, see Chinese patent CN104211028A, which discloses the composite pellet raw material and its forming method for the kiln phosphoric acid process. It adopts a core-shell structure in which the outer shell covers the inner ball. The inner ball is composed of inner ball material and binder. , the outer shell is composed of wrapping material and binder. The inner ball material is mainly composed of carbonaceous reducing agent powder, phosphate powder and silica powder. The wrapping material is mainly composed of carbonaceous reducing agent powder and silica powder. The inner ball and the outer shell are bonded by The agents are compounded into a core-shell structure. However, on the one hand, this process simply wraps P-free silica powder, which significantly reduces the P grade of the entire pellet and reduces the process efficiency; it also does not take into account the low softening temperature of SiO ₂ and cannot completely solve the problem of rotation under test conditions. Kiln ring problem. In addition, the composite pellet process can also be seen in the Chinese patent application CN104531984A, which discloses a preparation method of cold-solidified pellets suitable for the kiln-type phosphoric acid rotary kiln process. It also uses silica powder as a package and also has the above problems.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings and defects mentioned in the above background technology, and provide a method that consumes less auxiliary raw materials, has more stable quality, has higher strength, has a higher grade of raw material P ₂ O ₅ entering the furnace and can effectively suppress The formula of the reaction material balls formed by the rotary kiln ring and its preparation method are used to solve the problem that the current kiln phosphoric acid process cannot stabilize the long-term industrial operation.

In order to solve the above technical problems, the technical solutions proposed by the present invention are:

A composite pellet suitable for kiln phosphoric acid rotary kiln technology. The composite pellet is a core-shell structure with an outer shell covering an inner ball. The inner ball includes an inner ball material and a binder. The outer shell includes an outer shell material. and binder; the inner ball material includes phosphate rock, carbonaceous reducing agent and regulator, and the amount of binder added in the inner ball is 1%-15% of the mass of the inner ball material; the outer shell material includes phosphorus Ore, carbonaceous reducing agent and regulator, the amount of binder added in the outer shell is 1%-15% of the mass of the outer shell material; the inner ball and the outer shell are combined into a core-shell structure through the binder.

The above-mentioned composite pellet formula suitable for the kiln-method phosphoric acid rotary kiln process not only takes into account the key indicators CaO and SiO ₂ content in the traditional formula, but more importantly, is based on our understanding of the P ₂ O involved in the reduction of phosphate rock non-melting systems. ₅ -CaO-MgO-SiO ₂ -Al ₂ O ₃ -F multi-component system phase transformation rules and the latest results of the research on phosphorus reduction/fluorine volatilization behavior. The Mg and Al content in the formula and the migration behavior of fluorine are also considered. On this basis, a new composite pellet formula for the kiln phosphoric acid process is creatively proposed, which can effectively solve the problem of easy ring formation in traditional high-silicon batching rotary kilns, and avoid The problem that the reduction temperature required for high-calcium ingredients is too high.

Preferably, the carbonaceous reducing agent powder includes one or more of anthracite, bituminous coal, coke or petroleum coke.

Preferably, the binder is one of sodium carboxymethyl starch, bentonite, sodium humate solution, asphalt, ammonium humate, water glass, sulfite pulp waste liquid, syrup or lignosulfonate. or more.

Preferably, the regulator contains one or more of Ca, Si, Al or Mg elements.

Preferably, the adjuster includes one or more of quartz stone, river sand, dolomite, limestone, alumina, magnesium oxide or magnesium carbonate.

Preferably, the inner ball material includes CaO, SiO ₂ , MgO and Al ₂ O ₃ , and the molar ratio of CaO/SiO ₂ in the inner ball material is controlled between 0.35 and 2.0, and (MgO+Al ₂ O ₃ ) accounts for 2 to 15% of the total mass of the inner pellet. The amount of carbonaceous reducing agent powder measured in terms of effective carbon is 6 times the amount of phosphate rock powder measured in terms of P ₂ O ₅ ~8 times.

Preferably, the shell material includes CaO, SiO ₂ , MgO and Al ₂ O ₃ , the molar ratio of CaO/SiO ₂ in the shell material is controlled between 2.0-7.0, and the total (MgO+Al ₂ O ₃ ) The mass accounts for 10 to 50% of the total shell material mass. The amount of carbonaceous reducing agent powder measured in terms of effective carbon is 7 to 9 times the amount of phosphate rock powder measured in terms of P ₂ O ₅ .

This application adjusts different formula ratios of inner ball material and outer ball material (or shell material) internally and externally. The molar ratio of CaO/SiO ₂ in the inner ball material formula is controlled between 0.35 and 2.0, and (MgO+Al ₂ O ₃ ) accounts for 2 to 15% of the total mass of the inner ball material. On the one hand, it ensures a very high reduction volatilization rate of P in the inner ball. On the other hand, it promotes as much F as possible to volatilize to the outer shell in the form of SiF ₄ , adjust the physical and chemical properties of the shell. The outer shell formula can fully absorb part of the SiF ₄ volatilized by the inner ball. Together with the control of the molar ratio of CaO/SiO ₂ and the total mass percentage of (MgO + Al ₂ O ₃ ), the melting temperature of the outer shell ball is higher than 1300. ℃, it is not easy to melt under the process conditions of the rotary kiln, thus effectively suppressing the problem of easy loop formation in the rotary kiln. In addition, by only changing the material content ratio of the inner and outer pellets without changing the material composition of the inner and outer pellets, the structural strength of the entire pellet can be effectively solved. On the other hand, other impurities will not be introduced, which will lead to the occurrence of undesired phosphoric acid in the later stage. Anticipate impurity components.

Preferably, the mass percentage of P in the composite pellets is ≥15%.

Under the same technical concept, this application also provides a preparation method of composite pellets suitable for the kiln-based phosphoric acid rotary kiln process, which includes the following steps:

(1) Nucleation: Mix the carbonaceous reducing agent, phosphate rock and regulator, add a binder, mix thoroughly and then pelletize; during pelletizing, add the adhesive in the form of drops and/or mist. The additional amount of binder is 1%-15% of the mass of the mixture, and the inner ball is obtained after the balling is completed;

(2) Preparation of shell material: Mix carbonaceous reducing agent, phosphate rock and regulator, add binder at the same time, mix thoroughly to obtain shell material;

(3) Composite molding: Screen the inner ball obtained in step (1) and send it to the pelletizing machine. At the same time, add the outer shell material obtained in step (2) to the pelletizing machine; during the wrapping process, The binder is added in the form of drops and/or mist application, and the added amount is 1%-15% of the mass of the mixture, and the wrapping process is completed to obtain composite green balls;

(4) Drying and solidification: The composite green balls obtained after step (3) are dried and solidified, and finally formed into composite pellets.

Preferably, the drying temperature of the pellets in step (4) is ≤600°C, and the drying time is ≤600 min.

Preferably, the drying in step (4) is divided into three drying sections: low temperature, medium temperature and high temperature. The low temperature is 100°C-200°C, the middle temperature is 150°C-250°C, and the high temperature is 200°C-350°C.

Preferably, in the drying and consolidation step, the composite green balls are fed into a dryer, and the dryer used is a scale dryer. The scale dryer is divided into three types: low temperature, medium and high temperature along the transportation direction of the composite green balls. A drying section; the low-temperature drying section introduces low-temperature hot air at 100°C-200°C to exhaust from top to bottom or blow from bottom to top, so that the low-temperature hot air passes vertically through the material layer and flows through the composite green balls. Drying; the low-temperature heat content is the exhaust gas discharged from the high-temperature hot air outlet of the high-temperature drying section; the medium-temperature hot air 150°C-250°C introduced into the medium-temperature drying section is from top to bottom Exhaust air or blow from bottom to top, so that the medium-temperature hot air passes vertically through the material layer, and the composite green balls are cross-flow dried; the high-temperature hot air of 200°C-350°C is introduced into the high-temperature drying section. Exhaust air from top to bottom or blast air from bottom to top, so that high-temperature hot air passes vertically through the material layer, and the composite green balls are cross-flow dried.

Compared with the prior art, the beneficial effects of the present invention are:

(1) Fully consider the influence of fluorine, aluminum, magnesium and other elements in phosphate rock, regulator and carbonaceous reduction powder on the physical and chemical properties of pellets and phosphorus reduction volatilization behavior, effectively reducing the quality requirements of phosphate rock powder and expanding This reduces the source of raw materials and improves the applicability of the process.

(2) By only changing the material content and composition of the inner and outer pellets without changing the material composition of the inner and outer pellets, on the one hand, it can avoid the problem of impurities introduced by non-similar substances and the difficulty of non-similar substances bonding to each other to obtain high-strength composite pellets. question.

(3) The inner and outer layers of the composite pellets are mainly composed of phosphate rock powder and work together to form a pellet with a higher P content in the total pellet, effectively avoiding excessive reduction in the P grade of the pellets caused during the preparation process of the composite pellets. question.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be described more comprehensively and in detail below with reference to preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used below have the same meanings as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased in the market or prepared by existing methods.

Example 1

This method will be further described below with reference to the examples, but this does not limit the scope of the present invention.

This embodiment provides a composite pellet formula and preparation method suitable for the kiln-method phosphoric acid rotary kiln process. The composite pellet has a core-shell structure with an outer shell covering an inner ball. The inner ball is mainly composed of inner ball material and a binder. , the outer shell is mainly composed of outer shell material and binder; the inner ball material is composed of phosphate rock powder, carbonaceous reducing agent powder and adjuster powder. The amount of binder added in the inner ball is 6% of the mass of the inner ball material; the outer shell The material is also composed of phosphate rock powder, carbonaceous reducing agent powder and regulator. The amount of binder added in the outer shell is 8% of the mass of the outer shell material; the inner ball and the outer shell are combined into a core-shell structure through the binder.

In the composite pellet in this embodiment, the carbonaceous reducing agent powder is coke powder, the binder is sodium humate solution, and the adjusting agent is river sand, limestone and alumina powder. The molar ratio of CaO/SiO ₂ in the inner ball is controlled at 0.38 and the total mass percentage of (MgO + Al ₂ O ₃ ) is 4%. The amount of carbonaceous reducing agent powder measured in terms of effective carbon is P ₂ O ₅ measurements of phosphate rock powder are 7 times the amount of material. The molar ratio of CaO/SiO ₂ in the shell material is controlled at 2.6 and the total mass percentage of (MgO+Al ₂ O ₃ ) is 25%. The amount of carbonaceous reducing agent powder measured in terms of effective carbon is P ₂ O ₅ Measure 9 times the amount of phosphate rock powder. The mass percentage of P in the composite pellets is 18%.

The above-mentioned composite pellet forming method in this embodiment specifically includes the following steps:

(1) To prepare the inner ball, add the carbonaceous reducing agent powder, phosphate rock powder and adjuster into a powerful mixer or grinder according to the stated proportion requirements, and at the same time add the binder according to the stated amount to fully The mixed mixture enters the mixing bin and is sent to the pelletizing machine through the metering and feeding equipment for pelletizing. During pelletizing, the binder is added in the form of drops and/or mist. The additional amount It is 1%-15% of the mass of the mixture, and the inner ball is obtained after the balling is completed;

(2) Preparation of shell material: Add carbonaceous reducing agent powder, phosphate rock powder and adjuster into a powerful mixer or grinder according to the stated proportion requirements, and at the same time add binder according to the stated amount to fully After mixing, the shell material is obtained and sent to the shell silo;

(3) Forming of composite green balls: The inner balls obtained in step (1) are subjected to double-layer roller screening, and the inner balls that meet the particle size required by the process are screened out and sent to another pelletizing machine for wrapping. , and at the same time, the outer shell material obtained in step (2) is passed into the pelletizing machine (the electronic feeding device is set in proportion to the inner pellet material). The binder is added in the form of mist application, and the added amount is 1%-15% of the mass of the mixture, and the wrapping process is completed to obtain composite green balls;

(4) Drying and consolidation: Send the composite green balls obtained after step (3) into a dryer for drying and consolidation. The dryer used is a scale dryer. The scale dryer is along the conveying direction of the composite green balls. It is divided into three drying sections: low temperature, medium temperature and high temperature; the low temperature drying section is passed into the low temperature hot air of 100℃-200℃ to exhaust from top to bottom or blow from bottom to top, so that the low temperature hot air passes vertically through the material layer , and carry out cross-flow drying of composite green balls; the low-temperature heat content is the waste gas discharged from the high-temperature hot air outlet of the high-temperature drying section; the medium-temperature hot air introduced into the medium-temperature drying section is 150°C-250°C The medium-temperature hot air is exhausted from top to bottom or blown from bottom to top, so that the medium-temperature hot air passes vertically through the material layer, and the composite green balls are cross-flow dried; the high-temperature hot air introduced into the high-temperature drying section The high-temperature hot air at 200℃-350℃ is exhausted from top to bottom or blown from bottom to top, so that the high-temperature hot air passes vertically through the material layer and cross-flow dries the composite green balls. The composite pellets are finally formed with a compressive strength of ≥250KN/piece and a drop strength of ≥20 times/1 meter, which can fully meet the requirements of the kiln phosphoric acid process.

Claims (10)

1. The composite pellet is characterized in that the composite pellet is of a core-shell structure with an outer shell coating an inner sphere, the inner sphere comprises an inner sphere material and a binder, and the outer shell comprises an outer shell material and a binder; the inner ball material comprises phosphate ore, carbonaceous reducing agent and regulator, and the addition amount of the binder in the inner ball is 1-15% of the mass of the inner ball material; the shell material comprises phosphate ore, a carbonaceous reducing agent and a regulator, wherein the addition amount of the binder in the shell is 1-15% of the mass of the shell material; the inner ball and the outer shell are compounded into a core-shell structure through an adhesive.

2. The composite pellet suitable for kiln phosphoric acid rotary kiln process of claim 1, wherein the carbonaceous reductant powder comprises one or more of anthracite, bituminous coal, coke, or petroleum coke.

3. The composite pellet suitable for kiln process phosphoric acid rotary kiln process according to claim 1, wherein the binder is one or more of sodium carboxymethyl starch, bentonite, sodium humate solution, asphalt, ammonium humate, water glass, sulfite pulp waste liquor, syrup or lignin sulfonate.

4. The composite pellet suitable for kiln phosphoric acid rotary kiln process of claim 1, wherein the modifier contains one or more of Ca, si, al or Mg elements.

5. The composite pellet suitable for kiln phosphoric acid rotary kiln process of claim 4, wherein the modifier comprises one or more of quartz, river sand, dolomite, limestone, alumina, magnesia, or magnesium carbonate.

6. The composite pellet suitable for kiln phosphoric acid rotary kiln process according to claim 1, wherein the inner pellet comprises CaO, siO ₂ MgO and Al ₂ O ₃ CaO/SiO in the inner ball ₂ The molar ratio of (MgO+Al) is controlled to be between 0.35 and 2.0 ₂ O ₃ ) The total mass of the carbon reducing agent powder accounts for 2-15 percent of the total internal pellet mass, and the mass of the carbon reducing agent powder measured by effective carbon is expressed as P ₂ O ₅ The amount of the material of the phosphate rock powder is 6 to 8 times of the amount of the material of the phosphate rock powder.

7. The composite pellet suitable for kiln phosphoric acid rotary kiln process according to claim 1, wherein the outer shell material comprises CaO, siO ₂ MgO and Al ₂ O ₃ CaO/SiO in the shell material ₂ Is controlled to be between 2.0 and 7.0 and (MgO+Al) ₂ O ₃ ) The total mass accounts for 10-50 percent of the total shell material mass, and the mass of the carbonaceous reducing agent powder measured by effective carbon is expressed as P ₂ O ₅ And 7-9 times of the amount of the material of the phosphate rock powder.

8. The composite pellet suitable for the kiln process phosphoric acid rotary kiln process according to claim 1, wherein the mass percentage of P in the composite pellet is more than or equal to 15%.

9. A method for preparing composite pellets suitable for kiln process phosphoric acid rotary kiln process according to any of claims 1-8, characterized by comprising the steps of:

(1) And (3) core making: mixing a carbonaceous reducing agent, phosphate ore and a regulator, adding a binder, fully and uniformly mixing, and pelletizing; the adhesive is added in a drop-shaped and/or mist-shaped application form during pelletizing, the adding amount is 1-15% of the mass of the mixture, and an inner pellet is obtained after pelletizing is completed;

(2) And (3) shell material preparation: mixing a carbonaceous reducing agent, phosphate ore and a regulator, adding a binder, and fully and uniformly mixing to obtain a shell material;

(3) And (3) composite forming: screening the inner spheres obtained in the step (1), feeding the inner spheres into a pelletizer, and simultaneously adding the outer shell material obtained in the step (2) into the pelletizer; in the wrapping treatment process, the adhesive is supplemented in a drop-shaped and/or mist-shaped application form, the supplement amount is 1-15% of the mass of the mixture, and the composite green pellets are obtained after the wrapping treatment;

(4) Drying and solidifying: and (3) drying and concreting the composite green pellets obtained in the step (3), wherein the pellet drying temperature is less than or equal to 600 ℃, the pellet drying time is less than or equal to 600 minutes, and finally forming to obtain the composite pellets.

10. The method for preparing composite pellets suitable for kiln process phosphoric acid rotary kiln process according to claim 9, wherein the drying in the step (4) is divided into three drying sections of low temperature, medium temperature and high temperature, wherein the low temperature is 100-200 ℃, the medium temperature is 150-250 ℃, and the high temperature is 200-350 ℃.