Environment-friendly and continuously industrialized production of calcium oxide expanded clinker and preparation method thereof

Abstract

This invention discloses an environmentally friendly, continuously industrially produced expanded calcium oxide clinker and its preparation method. The expanded calcium oxide clinker of this invention is prepared by high-temperature rapid calcination at 1400℃-1500℃ in a rotary kiln using raw meal powder obtained from limestone, smithsonite, and fluorite. This invention utilizes the characteristic that Zn2+ produced during the calcination and decomposition of smithsonite has a higher oxygen-removing capacity than Ca2+, and with the assistance of fluorine mineralization, produces expanded calcium oxide clinker with low viscosity in the calcined liquid phase and no sulfur-aluminum components. Combined with the high-temperature rapid calcination process in a rotary kiln, continuous industrial production of expanded calcium oxide clinker is achieved in a rotary kiln. This invention effectively avoids the occurrence of environmental monitoring failures caused by excessive SO2 emission concentration at the kiln tail due to SO3 volatilization during the expanded clinker calcination process, and greatly promotes the green, environmentally friendly, and sustainable development of the expanded clinker industry.

Description

Technical Field

[0001] This invention relates to the field of industrial production and preparation technology of expanded clinker, specifically to an environmentally friendly, continuously industrially produced calcium oxide expanded clinker and its preparation method. Background Technology

[0002] With the rapid development of ready-mixed concrete technology in my country, the shrinkage rate of concrete has increased from 0.04-0.06% to 0.06-0.08%, significantly increasing the risk of structural cracking. Shrinkage cracking in concrete has become a major problem plaguing contemporary cement concrete engineering, and related research has become a focus of international concrete materials research. Utilizing the volume expansion of expansive components during hydration to compensate for the shrinkage of cement-based materials is one of the effective measures to inhibit concrete shrinkage cracking. Calcium oxide expansive agents, with their advantages of low hydration water requirement, low wet curing requirements, and high expansion efficiency, have become the main direction of current research on concrete crack-resistant materials.

[0003] Calcium oxide, as an expanded clinker, was first invented and widely used in Japan. Denka Kogyo Co., Ltd. of Japan uses limestone, gypsum, and bauxite as raw materials, mixes them in a certain proportion to form raw meal, and then melts and calcines them in an electric furnace to produce expanded clinker. The calcined expanded clinker is then ground into an expanding agent product of a specified fineness. This expanding agent has excellent performance, but the production process is difficult and costly. Domestic manufacturers often use quicklime, calcium sulfoaluminate, and calcium sulfate composites to prepare expanding agents. However, after years of market application, it has been found that minerals with the same chemical composition, without calcination, have very low activity as expanding agents and cannot compare with the performance of Japanese expanding agents. Only by calcining to form expanded clinker can the expanding performance of the expanding agent be significantly improved. Therefore, as the core material of expanding agent products, the industrial production process of expanded clinker has become a hot research topic in the expanding agent industry.

[0004] Chinese patent CN101333083A discloses a high-performance expansive cement clinker and a series of expansive agents prepared from it. The clinker is made by grinding limestone, bauxite, gypsum, and iron powder into raw meal powder, which is then calcined at 1250℃-1400℃ in a rotary kiln, tunnel kiln, or roller kiln. However, in the industrial production of expansive clinker using this method, the large amount of gypsum introduced in the batching process leads to high viscosity of the calcined liquid phase during decomposition and recrystallization at high temperatures. This easily forms a sintering ring in the rotary kiln, and the released SO3 can easily cause excessive SO2 emissions at the kiln tail, resulting in failure to meet environmental monitoring standards and affecting the continuity of expansive clinker production in the rotary kiln.

[0005] Chinese patent CN103130437A discloses an expanded clinker containing gypsum and calcium oxide molten inclusions, a concrete expansion agent, and its preparation method and application. The method uses limestone, gypsum, alumina, and / or aluminum sulfate as raw materials, which are ground into raw meal powder and then calcined at 1300℃-1500℃ in a rotary kiln. When this method is used for industrial production of expanded clinker, the batching scheme, while ensuring the Ca / S ratio, introduces a large amount of sulfur-aluminum components. On the one hand, this easily generates anhydrous calcium sulfoaluminate; on the other hand, it lowers the liquid phase temperature of the clinker, which is beneficial for the calcination and molten inclusion of calcium oxide. However, the SO3 produced by the decomposition of sulfur-containing components during calcination is easily volatilized, escapes, and re-condenses, causing the formation of a sulfur-rich ring in the rotary kiln and excessive SO2 emission concentration at the kiln tail, affecting the continuity of expanded clinker calcination and production efficiency.

[0006] Chinese patent CN103496867A discloses a calcium sulfoaluminate or calcium sulfoaluminate-calcium oxide concrete expansion agent, its preparation method, and its application. The method involves calcining raw materials limestone, gypsum, bauxite, and quicklime in a rotary kiln at a temperature of 1250℃-1450℃ for 10-30 minutes. After calcination, the calcined material is ground to a specific surface area of ​​150-400 m². 2 / kg, yielding calcium sulfoaluminate or calcium sulfoaluminate-calcium oxide type fully clinker concrete expansive agent. However, this method of producing expansive agents also suffers from high liquid phase viscosity, easy ring formation, and excessive SO2 emission concentration, leading to ring formation inside the kiln and failure to meet environmental protection online monitoring standards at the kiln tail, interrupting the continuous production of the rotary kiln, forcing kiln shutdown, and affecting production efficiency.

[0007] Due to limitations imposed by its feedstock formulation and the influence of the eutectic points of its three main oxide components (CaO, SO3, and Al2O3) in the ternary phase diagram, expanded calcium oxide clinker exhibits a large liquid phase content and a narrow sintering temperature range for liquid phase generation during calcination. High temperatures lead to flow during burning, while low temperatures result in raw material leakage, making the calcination process extremely difficult to control. Continuous industrial production in rotary kilns using conventional processes is simply impossible, primarily because technical challenges such as material ring formation and melt flow during calcination cannot be resolved. This is why Japan uses electric furnace melting and calcination processes to produce this expanded clinker. However, electric furnace melting and calcination processes suffer from high power consumption and low output, significantly increasing production costs and hindering market adoption. Furthermore, with increasingly stringent environmental regulations, rotary kiln online monitoring systems have higher requirements for SO2 emission concentrations, posing a greater challenge to the green and environmentally friendly production of expanded calcium oxide clinker with gypsum as the main raw material. How to reduce the amount of sintering liquid phase and SO3 emission during the calcination process of calcium oxide expanded clinker, and achieve environmentally friendly, continuous, and industrially stable production of calcium oxide expanded clinker in rotary kilns, is a key factor related to whether calcium oxide expanded clinker can be applied and promoted on a large scale nationwide. Summary of the Invention

[0008] To address the shortcomings of traditional expanded clinker production in rotary kilns, such as the easy volatilization and recondensation of SO3 during industrial production, leading to severe ring formation within the kiln, difficulties in continuous production, and excessive SO2 emissions at the kiln tail, this invention eliminates the use of gypsum, bauxite, and other sulfur-aluminum phase raw materials commonly used in conventional calcium oxide expanded clinker production. Instead, it fully utilizes Zn... 2+ The strong oxygen-removing ability, combined with the CaF2 mineralization process, promotes the formation of f-CaO and sintering to achieve density, resulting in an environmentally friendly, continuously industrially produced expanded calcium oxide clinker.

[0009] Another objective of this invention is to provide an environmentally friendly and continuously industrially producible method for preparing expanded calcium oxide clinker. By utilizing existing cement clinker rotary kiln production lines and processes, and adjusting the types of raw materials and some firing parameters, expanded calcium oxide clinker that meets environmental emission and quality requirements can be continuously and industrially produced.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] An environmentally friendly, continuously industrially produced calcium oxide expanded clinker is prepared by mixing and grinding limestone as the main raw material, smithsonite as the regulating material, and fluorite as the mineralizing material. The raw meal powder obtained by mixing and grinding the above three materials in a certain proportion is then subjected to high-temperature rapid calcination at 1400℃-1500℃ in a rotary kiln to obtain calcium oxide expanded clinker.

[0012] The above three materials, by weight, are as follows:

[0013] 85-90 parts limestone

[0014] Zinc ore, 6-14 parts

[0015] 1-4 parts fluorite;

[0016] The limestone contains ≥95wt% CaCO3;

[0017] The ZnCO3 content in the smithsonite is ≥70wt%;

[0018] The fluorite contains ≥80wt% CaF2.

[0019] The present invention also provides a method for preparing the above-mentioned expanded calcium oxide clinker, comprising the following steps:

[0020] S1. Mix the following components by weight: 85-90 parts limestone, 6-14 parts smithsonite, and 1-4 parts fluorite to obtain a mixture.

[0021] S2. Grind the above mixture together until the specific surface area is 250m².2 / kg~300m 2 / kg, and the residue on an 80μm square hole sieve is no more than 10%, to obtain the raw meal powder used for producing calcium oxide expanded clinker;

[0022] S3. Feed the above raw meal powder into the rotary kiln through an automatic conveying and metering device. By adjusting the burner position and fuel consumption, maintain the temperature of the rotary kiln calcination zone at 1400℃-1500℃ to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln.

[0023] S4. The expanded clinker, after being rapidly calcined at high temperature in the rotary kiln, is discharged from the kiln head of the rotary kiln and enters a single-cylinder cooler with lifting plates for cooling.

[0024] S5. Grind the cooled calcined clinker powder from step S4 into clinker powder with a residue of ≤10% on a 0.08mm sieve to obtain the calcium oxide expanded clinker of the present invention.

[0025] Furthermore, the rotary kiln used in the industrial production equipment for calcium oxide expanded clinker is a rotary kiln with a five-stage preheater, preferably with a kiln diameter of 2.5m-3.2m.

[0026] Furthermore, the rotary kiln speed is 2.0 rpm to 2.5 rpm.

[0027] Furthermore, the vertical weight control index for expanded clinker sampled at the kiln head cooler outlet in step S4 is 1600g / L-1700g / L. Sampling and testing the vertical weight of clinker particles at the cooler outlet can help understand the quality stability of the calcined clinker.

[0028] Furthermore, the fuel used in step S3 is low-sulfur petroleum coke, which has a high calorific value and produces less volatile SO3 during combustion.

[0029] Furthermore, the SO2 emission concentration at the kiln tail of the present invention is ≤50mg / Nm³. 3 .

[0030] This invention abandons the traditional formula for expanded calcium oxide clinker, which uses limestone as the main raw material and gypsum, bauxite, and iron powder as auxiliary materials, and fully utilizes Zn. 2+ The oxygen abstraction coefficient (0.331) is greater than that of Ca. 2+ The novel approach incorporates a high oxygen abstraction coefficient (0.201) and a Zn-rich substrate. 2+ Using smithsonite as a calcium oxide sintering promoter, and with the assistance of high-quality mineralized component CaF2, a novel feedstock formulation for sulfur-free aluminum-iron phase calcium oxide expanded clinker was developed.

[0031] In this invention, since the raw material formula eliminates commonly used sulfur, aluminum and iron phase components such as gypsum, bauxite and iron powder, the mineral composition of the expanded clinker is mainly free calcium oxide, supplemented by some calcium zinc solid solution dissolved in the calcium oxide lattice. There is no anhydrous calcium sulfoaluminate mineral formation, which is beneficial to controlling the hydration rate, expansion development process and expansion efficiency of calcium oxide expanded clinker in cement concrete.

[0032] This invention utilizes the mineral composition characteristics of smithsonite and combines these characteristics with the performance of calcium oxide expanded clinker. By forming a limited solid solution between the highly active ZnO generated during the calcination and decomposition of smithsonite and the f-CaO generated during the decomposition of limestone, the f-CaO lattice distortion and sintering density are promoted, making it easy to control and ensure the lattice size and content of the effective expanded component, free calcium oxide (f-CaO), in the expanded clinker.

[0033] In this invention, the raw material formula contains no gypsum component, which significantly reduces the risk of SO2 emission concentration exceeding the standard due to the volatilization and escape of SO3 generated during the calcination and decomposition of gypsum in the rotary kiln. It solves the problem that the SO2 emission concentration of calcium oxide expanded clinker in the industrial production process on the rotary kiln cannot meet the requirements of environmental protection online monitoring and control, and realizes the green, environmentally friendly and sustainable production of calcium oxide expanded clinker.

[0034] This invention employs a sulfur-free feedstock scheme, resulting in almost no SO3 generation during the calcination process in the rotary kiln. There is also no phenomenon of SO3 volatilization and re-condensation to regenerate sulfate minerals, thus preventing the formation of solid sulfur rings in the rotary kiln and improving the continuity of calcium oxide expanded clinker calcination production in the rotary kiln.

[0035] This invention uses petroleum coke with low sulfur content and high calorific value as fuel and adopts a high-speed kiln firing process for high-temperature rapid firing, which reduces the residence time of expanded clinker in the rotary kiln and makes it less likely for the calcined liquid phase to agglomerate. This solves the problem of poor firing continuity caused by the adhesion of the liquid phase in conventional expanded clinker, and realizes the continuous industrial stable production of calcium oxide expanded clinker in the rotary kiln, reducing the heat consumption of expanded clinker firing.

[0036] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0037] (1) This invention uses a sulfur-free aluminum phase raw material formulation scheme such as limestone, smithsonite and fluorite to prepare calcium oxide expanded clinker, thereby reducing the amount of SO3 generated and SO2 emitted at the kiln tail during the calcination process in the rotary kiln from the source of raw materials. This solves the problem that the SO2 emission concentration at the kiln tail of calcium oxide expanded clinker in the industrial production process of rotary kiln cannot meet the requirements of environmental protection online monitoring and control, and realizes the green and environmentally friendly production of calcium oxide expanded clinker.

[0038] (2) This invention innovatively introduces Zn-rich...2+ Zinc ore is used as a calcium oxide sintering promoter, Zn 2+ By occupying Ca 2+ The formation of a limited solid solution at the junction sites promotes calcium oxide lattice distortion and sintering density, while controlling the amount of liquid phase in the entire batching scheme. Combined with the high-temperature and fast-firing production process of the rotary kiln, it reduces the residence time of calcium oxide expanded clinker in the rotary kiln, making it less likely for the calcined liquid phase to agglomerate into rings. This solves the problem of poor firing continuity caused by the adhesion of the liquid phase in conventional expanded clinker, and realizes the continuous industrial and stable production of calcium oxide expanded clinker in the rotary kiln.

[0039] (3) This invention achieves low SO3 generation and SO2 emissions at the kiln tail during the calcination of calcium oxide expanded clinker in a rotary kiln through the combined control of raw material batching scheme and clinker calcination process. It also reduces the production of calcium oxide expanded clinker in a green, environmentally friendly, sustainable and stable manner in a rotary kiln. Compared with the traditional production technology of calcining expanded clinker in a rotary kiln and shutting down the kiln for three days and running for four days, this invention significantly extends the production continuity of the rotary kiln, ensures the quality stability of the calcined expanded clinker, effectively reduces the heat consumption of expanded clinker calcination, saves the production cost of expanded clinker, and improves the market competitiveness of expanded clinker. Detailed Implementation

[0040] The technical features of the environmentally friendly, continuously industrially produced expanded calcium oxide clinker and its preparation method described in this invention are further illustrated below with specific embodiments. The limestone, smithsonite, and fluorite used in the following embodiments of this invention are all sourced from factory mines.

[0041] An environmentally friendly, continuously industrially produced calcium oxide expanded clinker is prepared by using limestone as the main raw material, smithsonite as the regulating material, and fluorite as the mineralizing material. The raw meal powder is made from 85-90 parts by weight of limestone, 6-14 parts by weight of smithsonite, and 1-4 parts by weight of fluorite, and is then rapidly calcined at 1400℃-1500℃ in a rotary kiln.

[0042] This invention also provides an environmentally friendly and continuously industrially produced method for preparing expanded calcium oxide clinker. Preferably, a rotary kiln with a five-stage preheater is used as the industrial production equipment, with a preferred kiln diameter of 2.5m-3.2m. The preferred fuel is petroleum coke with high calorific value and low sulfur content. The preferred rotary kiln operation process is high-temperature rapid firing, with a preferred kiln speed of 2.0-2.5 rpm. The calcination temperature in the rotary kiln firing zone is controlled between 1400℃ and 1500℃. The vertical weight of the expanded clinker exiting the kiln is controlled at 1600-1700 g / L.

[0043] The embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. The embodiments will help to understand the present invention, but the protection scope of the present invention is not limited to the following embodiments.

[0044] Example 1

[0045] Example 1 of the present invention: Calcium oxide expanded clinker is composed of the following raw materials in parts by weight:

[0046] 90 parts limestone

[0047] 6 portions of zirconia

[0048] 4 parts fluorite;

[0049] The industrial production method of calcium oxide expanded clinker in this embodiment, using a rotary kiln with a diameter of 3.0 meters and a five-stage preheater, includes the following steps: First, 90 parts limestone, 6 parts smithsonite, and 4 parts fluorite are mixed in proportion and then ground together to a specific surface area of ​​250 m². 2 / kg; then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1400℃-1500℃ and the kiln speed is adjusted to be stable at 2.0 rpm to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. The calcined expanded clinker is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1600 g / L. Finally, the cooled calcined clinker powder is ground into clinker powder with ≤10% residue on a 0.08mm sieve, which is the calcium oxide expanded clinker.

[0050] Example 2

[0051] Example 2 of the present invention: Calcium oxide expanded clinker is composed of the following raw materials in parts by weight:

[0052] 88 portions of limestone

[0053] 9 portions of smithsonite

[0054] 3 parts fluorite;

[0055] The industrial production method of calcium oxide expanded clinker in this embodiment, using a rotary kiln with a diameter of 3.0 meters and a five-stage preheater, includes the following steps: First, 88 parts of limestone, 9 parts of smithsonite, and 3 parts of fluorite are mixed in a certain proportion and then ground together to achieve a specific surface area of ​​280 m². 2 / kg; then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1400℃-1500℃ and the kiln speed is adjusted to be stable at 2.2 rpm to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. The expanded clinker after calcination is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1650 g / L. Finally, the cooled calcined clinker powder is ground into clinker powder with ≤10% residue on a 0.08mm sieve, which is the calcium oxide expanded clinker.

[0056] Example 3

[0057] Example 3 of the present invention: Calcium oxide expanded clinker is composed of the following raw materials in parts by weight:

[0058] 86 portions of limestone

[0059] 12 portions of smithsonite

[0060] 2 parts fluorite;

[0061] This embodiment describes an industrial-scale production method for calcium oxide expanded clinker using a 3.0-meter diameter rotary kiln with a five-stage preheater. The method includes the following steps: First, 86 parts limestone, 12 parts smithsonite, and 2 parts fluorite are mixed in a specific ratio and then ground together to a powder with a specific surface area of ​​300 m². 2 / kg; then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1400℃-1500℃ and the kiln speed is adjusted to be stable at 2.4 rpm to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. The calcined expanded clinker is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1680 g / L. Finally, the cooled calcined clinker powder is ground into 0.08 mm clinker powder with a sieve residue of ≤10%, which is the calcium oxide expanded clinker.

[0062] Example 4

[0063] Example 4 of the present invention: Calcium oxide expanded clinker is composed of the following raw materials in parts by weight:

[0064] 85 parts limestone

[0065] 14 portions of smithsonite

[0066] 1 part fluorite;

[0067] This embodiment describes an industrial-scale production method for calcium oxide expanded clinker in a 3.0-meter diameter rotary kiln with a five-stage preheater. The method includes the following steps: First, 85 parts limestone, 14 parts smithsonite, and 1 part fluorite are mixed in a specific ratio and then ground together to a powder with a specific surface area of ​​300 m². 2 / kg; then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1400℃-1500℃ and the kiln speed is adjusted to be stable at 2.5 rpm to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. The calcined expanded clinker is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1700 g / L. Finally, the cooled calcined clinker powder is ground into 0.08 mm clinker powder with a sieve residue of ≤10%, which is the calcium oxide expanded clinker.

[0068] Comparative Example 1

[0069] The limestone used is the same as that used in Example 1, except that an equal amount of anhydrite is used instead of smithsonite, and an equal amount of bauxite is used instead of fluorite. As in Example 1, industrial production is also carried out on a rotary kiln with a kiln diameter of 3.0 meters and a five-stage preheater.

[0070] The production process is as follows: First, 90 parts by weight of limestone, 6 parts by weight of anhydrite, and 4 parts by weight of bauxite are mixed in a certain proportion and then sent to a common mill with a specific surface area of ​​250 m². 2 / kg, and then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1400℃-1500℃, and the kiln speed is adjusted to be stable at 2.0 rpm to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. The expanded clinker after calcination is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1200g / L. Finally, the cooled calcined clinker powder is ground into clinker powder with ≤10% residue on a 0.08mm sieve, which is the comparative clinker 1 prepared by the same calcination process as in Example 1 of this invention.

[0071] Comparative Example 2

[0072] The raw materials and calcination process used in Comparative Example 1 are basically the same, the only difference being the composition of the raw material formula.

[0073] The production process is as follows: First, 70 parts limestone, 24 parts anhydrite, and 6 parts bauxite are mixed according to a specific weight ratio and then sent to a common mill with a specific surface area of ​​250 m². 2 / kg, and then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1400℃-1500℃, and the kiln speed is adjusted to be stable at 2.0 rpm to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. The expanded clinker after calcination is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1550g / L. Finally, the cooled calcined clinker powder is ground into clinker powder with ≤10% residue on a 0.08mm sieve, thus preparing comparative clinker 2, which has a basically the same calcination process as Example 1 of this invention but with significant differences in raw materials and batching scheme.

[0074] Comparative Example 3

[0075] The raw materials and raw meal formula used in Example 1 are basically the same, the only difference being the rotary kiln calcination process.

[0076] The production process is as follows: First, 90 parts limestone, 6 parts smithsonite, and 4 parts fluorite are mixed in a certain proportion and then sent to a common mill with a specific surface area of ​​250m². 2 / kg; then the raw meal powder is fed into the feed port of the five-stage preheater through an automatic conveying and metering device. After being fully preheated, it enters the rotary kiln from the kiln tail for high-temperature calcination. The burner position and fuel consumption are controlled at the kiln head to keep the temperature of the rotary kiln calcination zone at 1250℃-1350℃ and the kiln speed is adjusted to be stable at 1.3 rpm to ensure that the raw meal powder is slowly calcined at low temperature in the rotary kiln. The expanded clinker after calcination is discharged from the kiln head and enters the cooler for cooling. The vertical weight of the expanded clinker is measured at the outlet of the cooler to be 1250g / L. Finally, the cooled calcined clinker powder is ground into clinker powder with ≤10% residue on a 0.08mm sieve. This is the comparative clinker 3, which is basically the same as the raw materials and batching scheme of Example 1 of this invention, but with a large difference in calcination process.

[0077] Performance testing

[0078] A rotary kiln with a preheater and a diameter of 3.0 meters was used as the industrial production kiln. The comparative analysis of the various embodiments and comparative examples in the rotary kiln firing process is shown in Table 1.

[0079] Table 1. Performance Comparison Analysis of Each Example and Comparative Example in Industrial Production Process on Rotary Kiln

[0080]

[0081] As shown in Table 1, when Examples 1-4 were industrialized in a 3.0-meter diameter rotary kiln with a preheater, a high-temperature, rapid-firing process was adopted, resulting in a low viscosity of the fired liquid phase. Only a certain thickness of kiln skin was formed inside the rotary kiln, with no obvious ring formation. This thick kiln skin provided good protection for the refractory bricks in the calcination zone, significantly extending their service life. As a result, continuous production time after ignition and heating could reach approximately 180 days. The rotary kiln was generally only stopped during normal maintenance shutdowns. Furthermore, the produced expanded clinker particles had a density of 1600 g / L to 1700 g / L per liter, exhibiting good sintering compactness. According to data from the environmental online monitoring system, the SO2 emission concentration at the kiln tail during the industrialized production process in the rotary kiln of this invention was 26 mg / Nm³. 3 -40mg / Nm 3 The concentrations are significantly lower than the standard limits (SO2 emission concentration at kiln tail ≤ 200 mg / Nm³). 3 This achieves ultra-low environmental emissions;

[0082] Compared to Comparative Example 1, which was prepared using the same calcination process as Example 1, Comparative Example 1 had a lower clinker calcinability due to its higher limestone content and lower content of auxiliary components such as gypsum and bauxite in the feedstock. Even under high-temperature calcination at 1400℃-1500℃, raw material leakage still occurred, resulting in a lower clinker density at the cooler outlet, a looser structure, and poorer sintering compactness. Furthermore, the calcination decomposition, volatilization, escape, and re-condensation of gypsum in the feedstock formed two recrystallization sulfur-fixing rings in the rotary kiln, affecting kiln ventilation and SO2 emission concentration at the kiln tail. Consequently, the continuous firing time could only last for 35 days, and the SO2 emission concentration at the kiln tail reached as high as 260 mg / Nm³. 3 It fails to meet environmental monitoring requirements;

[0083] Comparative Example 2 used the same raw materials and calcination process as Comparative Example 1. The only difference was that, in order to improve the calcinability of the clinker, the amount of limestone was reduced according to the traditional calcium oxide expanded clinker batching scheme, while the amount of gypsum and bauxite was significantly increased. Under high-temperature calcination of 1400℃-1500℃, the rotary kiln operated stably on the first day, and the produced expanded clinker particles had a vertical weight of up to 1550 g / L, exhibiting good sintering density. However, due to the high calcination temperature in the kiln, the amount of liquid phase in the clinker increased, and the decomposition, volatilization, and recrystallization of gypsum increased. On the second day, sintering rings began to form in the calcination zone of the rotary kiln. The sintering rings developed rapidly, adhering to the calcination zone and could not be effectively treated without stopping the kiln. By the third day, the sintering rings had begun to affect the ventilation in the kiln, and the SO2 emission concentration at the kiln tail increased significantly, reaching as high as 350 mg / Nm³. 3By the fourth day, the sintering ring had severely hindered the entry of raw material powder at the kiln tail, forcing the kiln to be shut down. Only after the kiln temperature cooled to room temperature could personnel be organized to enter the rotary kiln to clean the sintering ring before the kiln could be restarted to resume the industrial production of calcium oxide expanded clinker. This process was repeated, resulting in serious environmental violations, high heat consumption, high labor intensity for workers, and poor production continuity.

[0084] Comparative Example 3 used the same raw materials and batching scheme as Example 1, the only difference being the calcination process in the rotary kiln. Due to the use of a low-temperature, slow-calcination process with low calcination temperature and low rotary kiln speed, the expanded clinker remained in the rotary kiln for a longer time. Although the amount of calcined liquid phase was not large, adhesion and ring formation, as well as raw material leakage, still occurred. The clinker at the cooler outlet had a low vertical density, a loose structure, and poor sintering compactness. As the calcination time continued, two liquid phase adhesion rings formed in the rotary kiln, affecting kiln ventilation and SO2 emission concentration at the kiln tail. This resulted in a calcination continuity of only 50 days, with a high SO2 emission concentration at the kiln tail reaching 210 mg / Nm³. 3 It cannot meet environmental monitoring requirements.

[0085] As can be seen, the embodiments of the present invention can achieve environmentally friendly and continuous industrial production of calcium oxide expanded clinker through the combined control of the batching scheme and the firing process.

[0086] Application Examples

[0087] Using the reference cement specified in GB8076 and referring to the provisions of GB / T23439-2017 "Concrete Expansion Agents", the expanded clinker prepared in the examples and comparative examples was mixed with cement at 10% internal admixture to conduct a restricted expansion test on the mortar. The results are shown in Table 2. As can be seen from the results in Table 2, the expansion efficiency of the expanded clinker samples prepared in the examples of this invention is not only significantly greater than that of the expanded clinker samples prepared in Comparative Examples 1 and 3 (which have poor sintering density), but also significantly greater than that of the expanded clinker sample prepared in Comparative Example 2 (which has good sintering density). Furthermore, it far exceeds the national standard control requirements for concrete expansion agents, demonstrating excellent expansion effects.

[0088] Table 2 Comparative analysis of the restricted expansion rate of expanded clinker mortar prepared in the examples and comparative examples.

[0089] Example 1 0.269 0.172 Example 2 0.274 0.181 Example 3 0.258 0.160 Example 4 0.255 0.162 Comparative Example 1 0.057 -0.021 Comparative Example 2 0.198 0.102 Comparative Example 3 0.066 -0.010 GB / T23439-2017 Type II Index Values ≥0.050 ≥-0.010

Claims

1. An environmentally friendly, continuously industrially produced expanded calcium oxide clinker, characterized in that, Calcium oxide expanded clinker is prepared by grinding raw meal powder obtained from limestone as the main raw material, smithsonite as the conditioning material, and fluorite as the mineralizing material, and then firing the powder at a high temperature of 1400℃-1500℃ in a rotary kiln. The above three materials, by weight, are as follows: 85-90 parts limestone Zinc ore, 6-14 parts 1-4 parts fluorite; The limestone contains ≥95wt% CaCO3; The ZnCO3 content in the smithsonite is ≥70wt%; The fluorite contains ≥80wt% CaF2.

2. A method for preparing the calcium oxide expanded clinker according to claim 1, characterized in that, Includes the following steps: S1. Mix the following components by weight: 85-90 parts limestone, 6-14 parts smithsonite, and 1-4 parts fluorite to obtain a mixture. S2. Grind the above mixture together until the specific surface area is 250m². 2 / kg~300m 2 / kg, and the residue on an 80μm square hole sieve is no more than 10%, to obtain raw meal powder for the production of calcium oxide expanded clinker; S3. Feed the above raw meal powder into the rotary kiln through an automatic conveying and metering device. By adjusting the burner position and fuel consumption, maintain the temperature of the rotary kiln calcination zone at 1400℃-1500℃ to ensure that the raw meal powder is calcined at high temperature and quickly in the rotary kiln. S4. The expanded clinker, after being rapidly calcined at high temperature in the rotary kiln, is discharged from the kiln head of the rotary kiln and enters a single-cylinder cooler with lifting plates for cooling. S5. Grind the cooled calcined clinker powder from step S4 into clinker powder with a residue of ≤10% on a 0.08mm sieve to obtain the calcium oxide expanded clinker.

3. The preparation method according to claim 2, characterized in that, The rotary kiln used in the industrial production equipment for calcium oxide expanded clinker is a rotary kiln with a five-stage preheater, and the diameter of the rotary kiln is 2.5m-3.2m.

4. The preparation method according to claim 2, characterized in that, The rotary kiln speed is 2.0 rpm to 2.5 rpm.

5. The preparation method according to claim 2, characterized in that, In step S4, the controlled index for the vertical weight of expanded clinker sampled at the kiln head cooler outlet is 1600g / L-1700g / L.

6. The preparation method according to claim 2, characterized in that, The fuel used in step S3 is low-sulfur petroleum coke.

7. The preparation method according to claim 2, characterized in that, SO2 emission concentration at kiln tail ≤50mg / Nm 3 .

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