Method for producing low-iron low-silicon high-quality chromium oxide green based on electromagnetic rotary kiln

Abstract

The invention relates to a method for producing low-iron low-silicon high-quality chromium oxide green based on an electromagnetic rotary kiln, which comprises the following steps: continuously or batch-wise feeding raw materials into the electromagnetic rotary kiln, controlling the temperature in the kiln body to be 400-1100 DEG C by adjusting the current and frequency of a coil in sections, and dividing the treatment process of the materials in the kiln into a preheating section, a high-temperature reaction section, a heat preservation section and a cooling section; and staying the materials in the kiln for 3 hours, heating and calcining through heat radiation and heat conduction to generate chromium oxide green, and crushing to obtain a low-iron low-silicon high-purity chromium oxide green product. In the final product, the content of Cr2O3 can reach 99.5% or above, the content of Fe2O3 is smaller than or equal to 0.01%, the content of SiO2 is smaller than or equal to 0.1%, and the content of S is smaller than or equal to 0.003%, all indexes meet high-end application requirements, the process is accurate in control, energy-saving and environment-friendly, the structure of the rotary furnace is simplified, and the maintenance cost is low.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical engineering and high-end pigment preparation technology, and in particular to a method for producing low-iron, low-silicon, high-quality chromium oxide green based on an electromagnetic rotary kiln. Background Technology

[0002] Chromium oxide green (Cr2O3) is an important green inorganic pigment widely used in coatings, ceramics, building materials, and refractory materials due to its excellent weather resistance, chemical corrosion resistance, and high-temperature stability. For high-end applications, such as special ceramic glazes, military camouflage coatings, advanced plastics, and artistic pigments, extremely high purity is required for chromium oxide green, especially strict control of impurities such as sulfur (S), iron (Fe), and silicon (Si). Iron impurities can darken or yellow the color, while silicon impurities can affect its dispersibility and glaze smoothness.

[0003] Currently, the mainstream industrial method for producing chromium oxide green is the calcination method, which uses chromium anhydride (CrO3) as raw material and carries out a thermal decomposition reaction in a high-temperature rotary kiln. However, traditional rotary kilns mostly use gas or oil for heating from the kiln opening, and are made of carbon steel with refractory bricks lining the interior. This calcination method has the following inherent drawbacks: 1) Severe contamination by impurities: Impurities from fuel combustion and the erosion of the refractory kiln lining by high-temperature materials introduce impurities such as sulfur, iron, silicon, and aluminum. These impurities will mix into the product at high temperatures and are difficult to remove, making it difficult for the product purity to meet the requirements of high-end products.

[0004] 2) Poor temperature control accuracy: The temperature gradually decreases from the heating end (which is also the feeding end) to the discharge end. The flame heating temperature fluctuates greatly and has a large thermal inertia, making it difficult to achieve precise constant temperature control, which affects the reaction efficiency and the stability of the product's crystal form and color.

[0005] 3) Low thermal efficiency and high energy consumption: A large amount of heat is lost through the kiln body and carried away by the exhaust gas, resulting in low energy utilization, usually only 30%-50%.

[0006] Therefore, developing a method for preparing high-purity chromium oxide green that can fundamentally avoid the introduction of impurities, achieve precise temperature control, and is environmentally friendly has become a pressing technical problem to be solved in this field. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for producing high-quality chromium oxide green with low iron and low silicon based on an electromagnetic rotary kiln, so as to achieve the purpose of improving product purity, precise temperature control and environmental friendliness.

[0008] To address the above problems, the present invention provides a method for producing high-quality, low-iron, low-silicon chromium oxide green based on an electromagnetic rotary kiln, comprising: (1) Chromium anhydride and corresponding additives are selected as raw materials; (2) The raw materials are continuously or in batches fed into the electromagnetic rotary kiln. The kiln body of the electromagnetic rotary kiln is made of special stainless steel and has no refractory material inside. The outer periphery of the cylinder is wrapped with medium-frequency or high-frequency induction coils with heat preservation measures. The coils are arranged in multiple sections. (3) By adjusting the current and frequency of the coil in segments, the temperature inside the kiln is controlled at 400-1100℃, with a temperature fluctuation range of ±1-5℃, and the material processing process inside the kiln is divided into a preheating section, a high-temperature reaction section, a heat preservation section, and a cooling section. (4) The material stays in the kiln for 3 hours and is heated and calcined by thermal radiation and thermal conduction to generate chromium oxide green. After being crushed, a high-purity chromium oxide green product with low iron and low silicon is obtained, wherein Fe2O3≤0.01% and SiO2≤0.1%.

[0009] Preferably, the temperature of the preheating section is 800-850℃, the temperature of the high-temperature reaction section is 1050-1080℃, the temperature of the heat preservation section is 1000-1030℃, and the temperature of the cooling section is 450℃.

[0010] Preferably, the electromagnetic rotary kiln has a comprehensive thermal efficiency of 60%-75%, and the heating process does not produce CO2 or SO2. X NO X Emissions of greenhouse gases and dust.

[0011] Preferably, the high-purity chromium oxide green product has a Cr2O3 content ≥99.5% and an S content ≤0.003%.

[0012] Compared with the prior art, the present invention has the following advantages: 1. Extremely high product purity: The use of electromagnetic induction non-contact heating completely isolates the product from impurities such as iron and silicon caused by fuel ash and kiln lining erosion, ensuring high product purity from the source; segmented and precise temperature control helps to obtain high-quality products with stable composition and consistent crystal form. In the final product, the Cr2O3 content can reach more than 99.5%, Fe2O3≤0.01%, SiO2≤0.1%, and S content≤0.003%, all of which meet the requirements of high-end applications.

[0013] 2. Precise process control: Electromagnetic heating has a fast response speed and temperature control accuracy of ±5℃. The temperature field inside the kiln is uniform, which is conducive to obtaining high-quality products with complete crystal form, uniform particle size and stable color.

[0014] 3. Energy saving and environmental protection: The overall thermal efficiency of electromagnetic rotary kilns can typically reach 60%-75% or more, far exceeding that of traditional gas / oil kilns; preheating loss is small, eliminating the need for lengthy preheating of refractory linings like in combustion kilns; the kiln body heats up directly after startup, resulting in rapid temperature rise; zero emissions, as the heating process does not produce CO2 or SO2 generated by fuel combustion. X NO X It emits greenhouse gases and harmful gases, and has no dust emissions, making it environmentally friendly.

[0015] 4. Simplified structure and low maintenance cost: It eliminates the need for complex combustion systems (such as burners, fuel pipelines, combustion fans, etc.), large flue gas treatment systems (such as desulfurization towers), and high-temperature chimneys. The cylinder structure is relatively simple, with fewer points of failure, reducing maintenance workload and costs.

[0016] 5. High safety: There is no risk of flammable or explosive fuel leakage or explosion. The coil is typically water-cooled, resulting in a low surface temperature and reducing the risk of burns. Uniform heating is achieved throughout the entire circumference of the cylinder, preventing localized high temperatures from eroding the kiln lining, ensuring even heating and a long service life. Detailed Implementation

[0017] The core principle of an electromagnetic rotary kiln (also known as an induction heating rotary kiln) is electromagnetic induction and eddy current effect. Its structural characteristics are as follows: 1. A medium-frequency or high-frequency induction coil made of copper tube is wound around the outer shell of the rotary kiln. The coil is insulated to prevent heat loss. 2. The kiln body is made of special stainless steel that responds well to alternating magnetic fields. There are no refractory materials inside, which can prevent impurities such as silicon, iron, and aluminum from contaminating the products from the source. 3. When a medium-frequency or high-frequency alternating current is passed through the coil, a strong and rapidly changing alternating magnetic field will be generated inside and around the coil. Due to the resistance of the cylinder material, when the powerful eddy current flows inside the cylinder, the electrical energy is quickly converted into heat energy, causing the cylinder itself to heat up rapidly. 4. The metal cylinder, which is in a high-temperature state, transfers heat to the material tumbling inside through both thermal radiation and thermal conduction, thereby heating and calcining the material.

[0018] Example 1: A method for producing high-quality, low-iron, low-silicon chromium oxide green using an electromagnetic rotary kiln includes: continuously feeding 1 ton of chromium anhydride (CrO3) into the electromagnetic rotary kiln via a screw weighing system. The kiln's preheating section temperature is set to 800℃, the high-temperature reaction section temperature to 1050℃, the holding section temperature to 1000℃, and the cooling section temperature to 450℃. The material's residence time in the kiln is 3 hours. During rotation and heating, the chromium anhydride reacts to produce chromium oxide green (Cr2O3). The material is then pulverized to obtain a high-quality, low-sulfur, low-iron, and low-silicon chromium oxide green product.

[0019] Testing revealed that the product contains 99.5% Cr2O3, 0.003% S, 0.008% Fe, and 0.004% Si, all of which meet the requirements for high-end applications.

[0020] Example 2: A method for producing high-quality, low-iron, low-silicon chromium oxide green using an electromagnetic rotary kiln includes: continuously feeding 1 ton of chromium anhydride (CrO3) into the electromagnetic rotary kiln via a screw weighing system. The kiln's preheating section temperature is set to 850℃, the high-temperature reaction section temperature to 1050℃, the holding section temperature to 1000℃, and the cooling section temperature to 450℃. The material's residence time in the kiln is 3 hours. During rotation and heating, the chromium anhydride reacts to produce chromium oxide green (Cr2O3). The material is then pulverized to obtain a high-quality, low-sulfur, low-iron, and low-silicon chromium oxide green product.

[0021] Testing revealed that the product contains 99.55% Cr2O3, 0.003% S, 0.0075% Fe, and 0.0035% Si, all of which meet the requirements for high-end applications.

[0022] Example 3: A method for producing high-quality, low-iron, low-silicon chromium oxide green using an electromagnetic rotary kiln includes: continuously feeding 1 ton of chromium anhydride (CrO3) into the electromagnetic rotary kiln via a screw weighing system. The kiln's preheating section temperature is set to 850℃, the high-temperature reaction section temperature to 1080℃, the holding section temperature to 1000℃, and the cooling section temperature to 450℃. The material's residence time within the kiln is 3 hours. During rotation and heating, the chromium anhydride reacts to produce chromium oxide green (Cr2O3). The material is then pulverized to obtain a high-quality, low-sulfur, low-iron, and low-silicon chromium oxide green product.

[0023] Testing revealed that the product contains 99.7% Cr2O3, 0.0025% S, 0.007% Fe, and 0.004% Si, all of which meet the requirements for high-end applications.

[0024] Example 4: A method for producing high-quality, low-iron, low-silicon chromium oxide green using an electromagnetic rotary kiln includes: continuously feeding 1 ton of chromium anhydride (CrO3) into the electromagnetic rotary kiln via a screw weighing system. The kiln's preheating section temperature is set to 850℃, the high-temperature reaction section temperature to 1080℃, the holding section temperature to 1030℃, and the cooling section temperature to 450℃. The material's residence time in the kiln is 3 hours. During rotation and heating, the chromium anhydride reacts to produce chromium oxide green (Cr2O3). The material is then pulverized to obtain a high-quality, low-sulfur, low-iron, and low-silicon chromium oxide green product.

[0025] Testing revealed that the product contains 99.8% Cr2O3, 0.002% S, 0.006% Fe, and 0.003% Si, all of which meet the requirements for high-end applications.

[0026] Comparative example (traditional gas-fired rotary kiln): A method for producing high-quality, low-iron, low-silicon chromium oxide green using a traditional gas-fired rotary kiln includes: calcining the same raw material formula in a natural gas-heated rotary kiln at 1020-1100℃ for 3 hours, followed by the same subsequent processing. The resulting product, upon testing, has an S content of 0.007-0.010%, an Fe content of 0.01-0.05%, and a Si content of 0.007-0.012%, and its color is noticeably dark yellow, failing to meet high-end standards.

[0027] The technical solution provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for producing high-quality, low-iron, low-silicon chromium oxide green based on an electromagnetic rotary kiln, characterized in that, include: (1) Chromium anhydride and corresponding additives are selected as raw materials; (2) The raw materials are continuously or in batches fed into the electromagnetic rotary kiln. The kiln body of the electromagnetic rotary kiln is made of special stainless steel and has no refractory material inside. The outer periphery of the cylinder is wrapped with medium-frequency or high-frequency induction coils with heat preservation measures. The coils are arranged in multiple sections. (3) By adjusting the current and frequency of the coil in segments, the temperature inside the kiln is controlled at 400-1100℃, with a temperature fluctuation range of ±1-5℃, and the material processing process inside the kiln is divided into a preheating section, a high-temperature reaction section, a heat preservation section, and a cooling section. (4) The material stays in the kiln for 3 hours and is heated and calcined by thermal radiation and thermal conduction to generate chromium oxide green. After being crushed, a high-purity chromium oxide green product with low iron and low silicon is obtained, wherein Fe2O3≤0.01% and SiO2≤0.1%.

2. The method for producing low-iron, low-silicon chromium oxide green based on an electromagnetic rotary kiln as described in claim 1, characterized in that: The preheating section temperature is 800-850℃, the high-temperature reaction section temperature is 1050-1080℃, the heat preservation section temperature is 1000-1030℃, and the cooling section temperature is 450℃.

3. The method for producing low-iron, low-silicon chromium oxide green based on an electromagnetic rotary kiln as described in claim 1, characterized in that: The electromagnetic rotary kiln has a comprehensive thermal efficiency of 60%-75%, and the heating process does not produce CO2 or SO2. X NO X Emissions of greenhouse gases and dust.

4. The method for producing low-iron, low-silicon chromium oxide green based on an electromagnetic rotary kiln as described in claim 1, characterized in that: The high-purity chromium oxide green product contains ≥99.5% Cr2O3 and ≤0.003% S.