A process flow reformed metakaolin preparation system and preparation method

Abstract

The application discloses a process flow reengineering metakaolin preparation system and a preparation method thereof, which comprises a suspension preheating system, a preheating furnace, a modification furnace, a first cooling system and a second cooling system. The preheating furnace is directly connected with the modification furnace, the outlet of the modification furnace is connected with the inlet of a last-stage cyclone preheater, the material outlet of the last-stage cyclone preheater is connected with the material inlet of the first cooling system, the last-but-one-stage cyclone preheater is connected with the raw material feeding port of the modification furnace, the preheating furnace is not provided with a raw material feeding port, and the preheating furnace and the modification furnace are respectively provided with fuel feeding ports. The flue gas outlet of the suspension preheating system is connected with the flue gas inlet of the first cooling system, the flue gas outlet of the first cooling system is connected with the flue gas inlet of the preheating furnace, and the gas outlet of the second cooling system is connected with the combustion-supporting air inlet of the middle part of the modification furnace. The middle and lower parts of the preheating furnace and the modification furnace are the reduction zones, and the upper part of the modification furnace is the oxidation zone. The metakaolin prepared by the application can meet the requirements of color and activity index, and the system has low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of metakaolin preparation technology, and in particular to a metakaolin preparation system and method with redesigned process flow. Background Technology

[0002] Kaolin (Al₂O₃·2SiO₂·2H₂O, AS₂H₂) is a common mineral found in natural kaolin or kaolinite tailings. When heated in air, it undergoes several structural changes. At approximately 600℃, the layered structure of kaolin is destroyed due to the removal of hydroxyl groups, forming an amorphous transition phase—metakaolin (Al₂O₃·2SiO₂, AS₂). Metakaolin has an irregular molecular arrangement, exhibiting a thermodynamically metastable state. Under alkali activation, it possesses cementing properties and can react with calcium hydroxide (Ca(OH)₂) and water to produce volcanic ash-like hydration products similar to cement.

[0003] Leveraging the aforementioned characteristics, calcined kaolin containing kaolinite and structurally similar aluminosilicate minerals is used to prepare a composite material. This material is then combined with gypsum, silicate cement clinker, or limestone to produce calcined kaolin-based composite cement, which has become a research hotspot in the international cement and concrete industry in recent years. This type of cement, by using highly reactive calcined kaolin to replace clinker, can reduce the clinker content from 75% to 45%–50%, while maintaining the cement's 28-day compressive strength without decrease and increasing its flexural strength by more than 20%. This achieves the technical goals of low clinker coefficient, low carbon emissions, and high strength in cement production.

[0004] Since the preparation cost of calcined kaolin is lower than that of clinker, and the CO2 emissions during the preparation of calcined kaolin are also lower than those during the preparation of clinker, coupled with the wide availability of kaolin raw materials, the use of calcined kaolin in large quantities to replace clinker in the concrete and cement industries, thereby reducing the clinker content in cement, has a significant competitive advantage in the context of the active promotion of carbon emission reduction in the building concrete and cement industries.

[0005] Currently, existing methods for preparing calcined kaolin mainly include fixed-bed, semi-fixed-bed, and fluidized-bed methods. Among these, rotary kiln calcination is a commonly used method. However, rotary kiln calcination often suffers from high system heat consumption, easy over-burning and deactivation of the product, and difficulty in quality control. Furthermore, kaolin raw materials typically contain a certain amount of iron, mainly in the form of goethite, hematite, and siderite. During calcination, the iron phase undergoes a decomposition reaction, ultimately existing as red hematite, giving calcined kaolin a distinct red color. Directly using red calcined kaolin to prepare cement will affect the color of the finished cement product, easily leading the market to mistakenly believe it is inferior cement and affecting sales. Therefore, adopting reasonable process technology to produce highly active calcined kaolin with a color consistent with cement clinker at lower energy consumption and higher efficiency is crucial for the large-scale production and widespread application of calcined kaolin and calcined kaolin-limestone composite cement.

[0006] Therefore, based on market demand and the key technical challenges faced, it is of great practical significance to provide a metakaolin preparation system and method that fully considers the requirements of the cement concrete industry for color control and activity index control of calcined kaolin, while solving the problems of high energy consumption, small processing capacity and difficulty in controlling product quality in the calcined kaolin preparation system. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a metakaolin preparation system and method with process reengineering. This system can fully consider the control requirements of the cement concrete industry for the color and activity index of finished metakaolin products, and produce metakaolin that meets the color and activity index control requirements. At the same time, it solves the problems of high energy consumption, small processing capacity, and difficulty in controlling product quality in the metakaolin preparation system.

[0008] This invention is implemented as follows: a metakaolin preparation system with redesigned process flow includes a suspension preheating system, a calcination furnace system, a first cooling system, and a second cooling system. The calcination furnace system includes a preheating furnace and a modification furnace. The bottom of the preheating furnace is the flue gas inlet, and the top outlet of the preheating furnace is directly connected to the bottom inlet of the modification furnace. The top outlet of the modification furnace is connected to the inlet of the final-stage cyclone preheater of the suspension preheating system. The material outlet at the bottom of the final-stage cyclone preheater of the suspension preheating system is connected to the material inlet of the first cooling system. The discharge port of the penultimate-stage cyclone preheater of the suspension preheating system is connected to the raw material feeding port of the modification furnace. The preheating furnace does not have a raw material feeding port, but the preheating furnace and the modification furnace are each equipped with a fuel feeding port.

[0009] The top flue gas outlet of the suspension preheating system is connected to the flue gas inlet of the indirect heat exchanger, and the flue gas outlet of the indirect heat exchanger is connected to the flue gas inlet of the first cooling system. The first cooling system is used to rapidly cool the material to a temperature range of 300-350°C and below. The flue gas outlet of the first cooling system is connected to the flue gas inlet of the preheating furnace. The oxygen content in the top exhaust gas of the suspension preheating system is 1-3%. The material outlet of the first cooling system is connected to the material inlet of the second cooling system, and the gas outlet of the second cooling system is connected to the combustion air inlet in the middle of the modified furnace.

[0010] The lower part of the preheating furnace and the modification furnace is the reduction zone, and the upper part of the modification furnace is the oxidation zone.

[0011] Preferably, the modified furnace is composed of a modified furnace cone and a modified furnace column from bottom to top. The lower part of the modified furnace cone, the lower part of the modified furnace column, and the middle part of the modified furnace column are respectively provided with fuel feeding ports. The fuel feeding port in the middle part of the modified furnace column is located above the combustion air inlet of the modified furnace. The raw material feeding port is respectively provided above each fuel feeding port of the modified furnace.

[0012] Preferably, the preheating furnace and the modification furnace are arranged in layers along the height direction with multiple temperature measuring points for real-time monitoring of the temperature distribution inside the preheating furnace and the modification furnace. The temperature distribution inside the preheating furnace and the modification furnace is controlled within a reasonable range by adjusting the amount of fuel fed into the preheating furnace and the amount of raw material fed into the modification furnace and the amount of combustion air.

[0013] Preferably, the indirect heat exchanger is used to indirectly cool the flue gas discharged from the suspension preheating system to 80-120°C. The indirect heat exchanger has a cooling medium inlet and a flue gas outlet at the bottom and a flue gas inlet and a cooling medium outlet at the top, so that the flue gas and the cooling medium exchange heat in countercurrent. The cooling medium channel of the indirect heat exchanger is filled with cooling medium.

[0014] More preferably, the cooling medium of the indirect heat exchanger is cooling water, cooling oil, or other suitable cooling medium.

[0015] Preferably, flue gas circulation fans are respectively installed between the indirect heat exchanger and the first-stage cyclone preheater of the suspension preheating system, and between the indirect heat exchanger and the first cooling system.

[0016] Preferably, the gas outlet of the second cooling system is connected in sequence to the combustion air inlet in the middle of the modified furnace via a dust collector and a combustion air circulation fan.

[0017] Preferably, the second cooling system includes at least one cyclone cooler for cooling the material to below 100°C.

[0018] Preferably, the flue gas outlet of the suspension preheating system and the gas outlet of the second cooling system are also connected to a drying crusher or other waste heat utilization equipment.

[0019] The method for preparing metakaolin using the above system involves the following steps: raw materials are preheated by a suspension preheating system before entering a modification furnace. The decomposed material leaves the modification furnace and enters the final stage cyclone preheater of the suspension preheating system. The material separated by the final stage cyclone preheater enters the first cooling system. Flue gas discharged from the top of the suspension preheating system is cooled by an indirect heat exchanger and then enters the first cooling system to exchange heat with the material entering the first cooling system. The flue gas discharged from the first cooling system enters the preheating furnace. Gas discharged from the second cooling system enters the upper part of the modification furnace for combustion support. The amount of fuel, raw materials, and combustion air fed into the preheating furnace and modification furnace are adjusted to ensure incomplete combustion of fuel in the lower part of the preheating and modification furnaces, creating a reducing atmosphere, while the fuel in the upper part of the modification furnace is fully combusted, creating an oxidizing atmosphere. The first cooling system rapidly cools the material to a temperature range of 300-350°C or below, and then it enters the second cooling system, where it is cooled to below 100°C, resulting in metakaolin with controllable color.

[0020] Preferably, the calcination temperature in the preheating furnace and the lower part of the modification furnace is 600-800°C, and the calcination temperature in the upper part of the modification furnace is 700-900°C; the residence time of the flue gas in the calcination furnace system is 2-10 seconds.

[0021] Preferably, the excess air coefficient at the outlet of the modified furnace is 1.05 to 1.2.

[0022] Preferably, the cooling medium of the first cooling system is flue gas at a temperature of 80-120°C after being cooled by an indirect heat exchanger, and the oxygen content in the flue gas is 1-3%; the cooling medium of the second cooling system is room temperature air.

[0023] The specific principle of this invention is as follows:

[0024] The key to controlling the color of finished metakaolin is calcination control and cooling control. Calcination control requires strict control of the calcination atmosphere and temperature; cooling control requires comprehensive control of the cooling atmosphere and temperature. To control the color of the finished metakaolin, this invention controls the excess air coefficient at the outlet of the modification furnace during the decomposition of kaolin to form metakaolin. This ensures that the oxygen content in the flue gas at the outlet of the suspension preheating system is within a preferred range. Considering the ideal oxygen content of 1-3% in the flue gas at the outlet of the suspension preheating system, by controlling the fuel consumption in the preheating and modification furnaces, it is easy to achieve incomplete combustion of fuel in the lower part of the preheating and modification furnaces, forming a reducing atmosphere. This, in turn, reduces the Fe content in the kaolin raw material. 3+ Completely reduced to Fe 2+Simultaneously, by adding an appropriate amount of combustion air to the upper part of the modified furnace, the complete combustion of fuel and the full release of heat energy can be ensured. During the cooling process of high-temperature metakaolin, the cooling atmosphere and cooling temperature control need to be comprehensively considered. Detailed experimental studies have shown that if the cooling medium for metakaolin is an inert gas (such as N2) or low-oxygen flue gas (the oxygen concentration in the flue gas is preferably controlled at 1-3%), the Fe in the metakaolin prepared by reduction calcination will be reduced. 2+ It will not be oxidized to Fe again during the cooling process. 3+ Furthermore, experimental studies have verified that the Fe in metakaolin prepared by reduction calcination... 2+ It remains stable in the temperature range of 300-350℃ and below, and will not be re-oxidized to Fe even upon contact with ordinary air. 3+ Based on the aforementioned theoretical research, and considering that the oxygen concentration in the flue gas exiting the suspension preheating system can be controlled at 1-3%, making it an ideal cooling medium for achieving the first-stage rapid cooling of hot materials, this invention first fully cools the flue gas exiting the suspension preheating system, and then cools the hot materials entering the first cooling system. Detailed theoretical calculations show that the hot materials can be rapidly cooled to a temperature range of 300-350°C and below. The material after the first-stage rapid cooling enters the second cooling system, where it is cooled to approximately 100°C using ambient air.

[0025] The key to controlling the activity of the finished metakaolin product is the uniform control of the temperature field inside the modification furnace. This invention arranges a first burner in the preheating furnace, a second burner in the cone section of the modification furnace, a third burner in the lower part of the modification furnace, and a fourth burner in the middle of the modification furnace (more burners can be arranged according to the actual production process). By reasonably controlling the fuel quantity of each burner and the feed quantity at each feeding point, it is ensured that the temperature of each area in the calcining furnace is within the preferred calcining temperature of the calcining furnace. This achieves the full decomposition of kaolin to form metakaolin (i.e., avoiding "under-calcination"), while also preventing the crystallization and precipitation of metakaolin that loses its activity (i.e., avoiding "over-calcination"). This ensures that the activity index of the finished metakaolin product meets the requirements of subsequent production.

[0026] In the process, according to the material flow direction, kaolin raw materials undergo a raw material pretreatment process to obtain raw meal powder that meets production needs. The raw meal powder is fed into the suspension preheating system after gas-solid separation via a raw meal elevator and a feeding device or cyclone separator. The suspension preheating system includes multi-stage cyclone preheaters, a high-efficiency spreading device, and connecting pipes. The raw meal powder undergoes preheating and gas-solid separation within the cyclone preheaters. After multiple heat exchanges and gas-solid separations, the raw meal powder enters the modification furnace through the discharge pipe of the penultimate stage cyclone preheater in the suspension preheating system. The calcination furnace system includes a high-efficiency spreading device, a flue gas inlet pipe, a preheating furnace, a first burner arranged in the preheating furnace, a modification furnace, a second burner arranged in the cone section of the modification furnace, a third burner in the lower part of the modification furnace column, a fourth burner in the middle of the modification furnace column, and a flue gas outlet pipe. Multiple temperature measuring points are set up in layers along the height of the preheating furnace and the modification furnace to monitor the temperature distribution inside the preheating furnace and the modification furnace in real time. The temperature distribution inside the preheating furnace and the modification furnace is controlled within a reasonable range by adjusting the amount of fuel and material fed into them. A reasonable temperature distribution in the preheating furnace and the modification furnace ensures complete combustion of fuel and complete decomposition of kaolin, while preventing the kaolin from burning excessively. The activity index of the finished kaolin meets the requirements of subsequent production. In the calcination furnace system, fuel combustion releases a large amount of heat for the decomposition of kaolin. The decomposed hot material leaves the modification furnace and then undergoes gas-solid separation with the hot flue gas in the final stage cyclone preheater of the suspension preheating system before entering the first cooling system. The first cooling system includes one or more stages of cyclone coolers, a high-efficiency material spreading device, and connecting pipes. The hot material is cooled and undergoes gas-solid separation in the cyclone coolers of the first cooling system. The material cooled in the first cooling system then enters the second cooling system after gas-solid separation. The second cooling system includes one or more stages of cyclone coolers, a high-efficiency material spreading device, and connecting pipes. The material undergoes further cooling and gas-solid separation in the cyclone cooler of the second cooling system, and finally exits from the discharge pipe of the lowest-level cyclone cooler in the second cooling system, falling into the finished product zipper machine to obtain the desired finished product. In terms of gas flow, ambient temperature air enters the second cooling system, subsequently cooling the material entering the system. The air, having completed heat exchange, exits from the outlet of the highest-level cyclone cooler in the second cooling system, and then enters the dust collector to separate the metakaolin content from the air to the finished product zipper machine. The air exiting the dust collector is divided into two paths: the first path enters the modification furnace via the middle section for combustion support, and the second path enters the drying and crushing machine to dry the raw materials or for other forms of waste heat utilization. By rationally controlling the amount of fuel entering the preheating furnace and the amount of fuel and raw material in the lower part of the modification furnace, incomplete combustion of fuel in the preheating furnace and the lower part of the modification furnace creates a reducing atmosphere, thereby reducing the Fe content in the kaolin raw material. 3+ Completely reduced to Fe 2+By rationally controlling the amount of fuel, raw materials, and combustion air entering the upper part of the modified furnace, the complete combustion of fuel and full release of heat energy are ensured. The hot flue gas formed by the decomposition of kaolin then preheats and separates the raw material powder fed into the suspension preheating system multiple times, and finally leaves from the outlet of the top-level cyclone preheater of the suspension preheating system. It then splits into two paths: one path enters the indirect heat exchanger through the flue gas circulation fan. The indirect heat exchanger fully cools the flue gas by using cooling water, cooling oil, or other suitable cooling media. The fully cooled flue gas enters the first cooling system, which then cools the high-temperature materials entering the first cooling system. The cooled circulating flue gas leaves from the outlet of the top-level cyclone cooler of the first cooling system and then enters the preheating furnace; the second path enters the drying crusher to dry the raw materials or to utilize waste heat in other ways. After flue gas treatment, it is discharged into the atmosphere.

[0027] Compared with the prior art, the advantages and positive effects of this invention are:

[0028] 1. This invention takes into account that the O2 concentration in the flue gas outlet of the suspension preheating system is relatively easy to control at a low level of 1-3%, and uses an indirect heat exchanger to cool the circulating flue gas to a suitable temperature range, which is then used for primary quenching of high-temperature metakaolin, thus avoiding the presence of Fe in the metakaolin. 2+ It is re-oxidized to Fe upon contact with an oxygen-containing cooling medium. 3+ This leads to a loss of control over the color of the finished kaolin product; simultaneously, the circulating flue gas after heat exchange, due to its low O2 concentration, is more likely to form a localized reducing atmosphere in the lower part of the modification furnace, thereby reducing the Fe content in the kaolin raw material. 3+ Completely reduced to Fe 2+ That is, the circulating flue gas of this invention can be used simultaneously for the primary rapid cooling of high-temperature metakaolin and to significantly reduce the Fe content in the metakaolin from the source. 3+ The concentration effectively reduces the difficulty of color control in finished kaolin products.

[0029] 2. To prepare metakaolin with an activity index that meets subsequent requirements, this invention designs the calcination furnace system in two sections: a preheating furnace and a modification furnace. Since the decomposition reaction of kaolin is a strongly endothermic reaction, and considering the low temperature of the circulating flue gas entering the preheating furnace, this invention uses a preheating furnace that only feeds fuel, not raw materials, to react with the circulating flue gas. This preheats the circulating flue gas to a reasonable temperature range of 800–1000°C, facilitating subsequent fuel burnout and thorough decomposition of kaolin. Subsequently, the circulating flue gas enters the modification furnace, where fuel and raw materials are fed in at multiple points (or stages). Combustion air is introduced into the upper part of the modification furnace column, creating a uniform temperature distribution field within the furnace. This ensures thorough decomposition of kaolin to form metakaolin, while preventing crystallization and loss of activity.

[0030] 3. This invention sequentially comprises a first cooling system and a second cooling system, each with a clearly defined function. The first cooling system fully utilizes the low-oxygen flue gas from the outlet of the suspension preheating system to perform primary cooling of the metakaolin, thus preventing the Fe content in the metakaolin from being reduced. 2+ During the cooling process, it comes into contact with an oxygen-containing cooling medium (such as room temperature air) and is oxidized to Fe. 3+ Meanwhile, a well-designed low-oxygen flue gas volume can cool the metakaolin primary cooling system to a safe temperature range of 300-350℃ and below. The second cooling system fully utilizes ambient temperature air to cool the metakaolin secondary cooling system to around 100℃.

[0031] 4. The flue gas at the outlet of the suspension preheating system and the air at the outlet of the second cooling system of the present invention both take into account the full recovery and utilization of waste heat, which can effectively reduce system heat consumption and reduce production costs. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some specific embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a system flow diagram of the metakaolin preparation system with process reengineering provided in the embodiments of the present invention.

[0034] The system includes: 1. Suspension preheating system; 1-1. Cyclone preheater; 2. Calcination furnace system; 2-1. Preheating furnace; 2-2. Modification furnace; 3. First cooling system; 3-1. First cyclone cooler; 4. Second cooling system; 4-1. Second cyclone cooler; 4-2. Third cyclone cooler; 6. Indirect heat exchanger; 7. Dust collector. Detailed Implementation

[0035] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be noted that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Example

[0039] Please see Figure 1 This invention provides a metakaolin preparation system with redesigned process flow, including a suspension preheating system 1, a calcination furnace system 2, a first cooling system 3, and a second cooling system 4.

[0040] The suspension preheating system 1 includes a multi-stage cyclone preheater 1-1, a high-efficiency material spreading device, and connecting pipes, etc. The preferred number of stages for the cyclone preheater 1-1 in the suspension preheating system 1 is three to seven, used to preheat the raw materials. In this embodiment, the preferred number of stages for the cyclone preheater 1-1 in the suspension preheating system 1 is five, namely the first, second, third, fourth, and fifth cyclone preheaters. The calcining furnace system 2 includes a high-efficiency material spreading device, a flue gas inlet pipe, a preheating furnace 2-1, a first burner arranged in the preheating furnace 2-1, a modification furnace 2-2, a second burner arranged in the cone of the modification furnace 2-2, a third burner in the lower part of the column of the modification furnace 2-2, a fourth burner in the middle part of the column of the modification furnace 2-2, and a flue gas outlet pipe, etc. The preferred number of stages for the cyclone cooler in the first cooling system 3 is one to four. In this embodiment, a single-stage cyclone cooler is selected. The first cooling system 3 includes a first cyclone cooler 3-1, a high-efficiency material spreading device, and connecting pipes, etc. The preferred number of stages of the cyclone cooler in the second cooling system 4 is one to four. In this embodiment, a two-stage cyclone cooler is selected. The second cooling system 4 includes a second cyclone cooler 4-1, a third cyclone cooler 4-2, a high-efficiency material spreading device, and connecting pipes, etc.

[0041] The bottom of the preheating furnace 2-1 is the flue gas inlet. The top outlet of the preheating furnace 2-1 is directly connected to the bottom inlet of the modification furnace 2-2. The top outlet of the modification furnace 2-2 is connected to the inlet of the fifth cyclone preheater of the suspension preheating system 1. The material outlet at the bottom of the fifth cyclone preheater of the suspension preheating system 1 is connected to the material inlet of the first cyclone cooler 3-1 of the first cooling system 3. The discharge port of the fourth cyclone preheater of the suspension preheating system 1 is connected to the raw material feeding port of the modification furnace 2-2. The preheating furnace 2-1 is not equipped with a raw material feeding port. The preheating furnace 2-1 and the modification furnace 2-2 are respectively equipped with fuel feeding ports. The lower part of the preheating furnace 2-1 and the modification furnace 2-2 is a reduction zone, and the upper part of the modification furnace 2-2 is an oxidation zone. Specifically, the modified furnace 2-2 is composed of a modified furnace cone and a modified furnace column from bottom to top. Fuel feed ports are respectively provided in the lower part of the modified furnace cone, the lower part of the modified furnace column, and the middle part of the modified furnace column. The fuel feed port in the middle of the modified furnace column is located above the combustion air inlet of the modified furnace 2-2. Raw material feed ports are respectively provided above each fuel feed port of the modified furnace 2-2. Multiple temperature measuring points are arranged in layers along the height of the preheating furnace 2-1 and the modified furnace 2-2 for real-time monitoring of the temperature distribution within them. By adjusting the amount of fuel fed into the preheating furnace 2-1 and the amount of raw material fed into the modified furnace 2-2, as well as the combustion air volume, the temperature distribution within the preheating furnace 2-1 and the modified furnace 2-2 is controlled within a reasonable range.

[0042] The top flue gas outlet of the suspended preheating system 1 is connected to the flue gas inlet of the indirect heat exchanger 6. The indirect heat exchanger 6 is used to indirectly cool the flue gas discharged from the suspended preheating system 1 to 80-120°C. The indirect heat exchanger 6 has a cooling medium inlet and a flue gas outlet at its bottom, and a flue gas inlet and a cooling medium outlet at its top, allowing the flue gas and cooling medium to exchange heat in a counter-current manner. The cooling medium passage of the indirect heat exchanger 6 is filled with cooling medium. The cooling medium of the indirect heat exchanger 6 is cooling water, cooling oil, or other suitable cooling medium.

[0043] Considering that the oxygen content in the flue gas at the outlet of the suspension preheating system 1 can be controlled at 1-3%, it can be used to achieve primary rapid cooling of the hot material in the first cooling system 3. The flue gas outlet of the indirect heat exchanger 6 is connected to the flue gas inlet of the first cooling system 3. The first cooling system 3 is used to rapidly cool the material to a temperature range of 300-350℃ and below. The flue gas outlet of the first cooling system 3 is connected to the flue gas inlet of the preheating furnace 2-1, and the heat-exchanged flue gas is sent to the preheating furnace 2-1.

[0044] The material outlet of the first cooling system 3 is connected to the material inlet of the second cooling system 4. The cooling medium of the second cooling system 4 is ambient temperature air. The second cooling system 4 is used to cool the material to below 100°C. The gas outlet of the second cooling system 4 is connected to the combustion air inlet in the middle of the modified furnace 2-2 in sequence through the dust collector 7 and the combustion air circulation fan, and is used for combustion in the upper middle part of the modified furnace 2-2.

[0045] The flue gas outlet of the suspension preheating system 1 and the gas outlet of the second cooling system 4 are also connected to a drying crusher for drying raw materials, or connected to other waste heat utilization equipment for other forms of waste heat utilization. This fully considers waste heat recovery and utilization, which can effectively reduce system heat consumption and reduce production costs.

[0046] The specific method for preparing metakaolin using the above system is as follows:

[0047] After being preheated by the suspension preheating system 1, the raw material enters the modification furnace 2-2. The decomposed material leaves the modification furnace 2-2 and enters the final stage cyclone preheater 1-1 of the suspension preheating system 1. The material separated by the final stage cyclone preheater 1-1 enters the first cooling system 3. The flue gas with an oxygen content of 1-3% discharged from the top of the suspension preheating system 1 is cooled to 80-120℃ by the indirect heat exchanger 6 and then enters the first cooling system 3 to exchange heat with the material entering the first cooling system 3. The flue gas discharged from cooling system 3 enters preheating furnace 2-1, and the gas discharged from the second cooling system 4 enters the upper part of modification furnace 2-2 for combustion support. The amount of fuel fed into preheating furnace 2-1, the amount of raw material fed into modification furnace 2-2, and the amount of combustion air are adjusted to ensure incomplete combustion of fuel in the lower part of preheating furnace 2-1 and modification furnace 2-2, forming a reducing atmosphere. The calcination temperature in preheating furnace 2-1 and the lower part of modification furnace 2-2 is 600-800℃, reducing the Fe content in the raw materials. 3+ Reduced to Fe 2+ In the upper part of the modified furnace 2-2, the fuel is fully burned to form an oxidizing atmosphere. The calcination temperature in the upper part of the modified furnace 2-2 is 700-900℃, and the excess air coefficient at the outlet of the modified furnace 2-2 is 1.05-1.2, while ensuring that the kaolin is not burned. The first cooling system 3 rapidly cools the decomposed hot material (meta-kaolin) to a temperature range of 300-350℃ and below, so that the Fe in the meta-kaolin is reduced. 2+ During this cooling process, it will not be oxidized to Fe again. 3+The hot material is cooled and separated into gas and solid in the first cyclone cooler 3-1 of the first cooling system 3. After being cooled by the first cooling system 3, the material enters the second cooling system 4. The cooling medium of the second cooling system 4 is room temperature air. After being cooled to below 100°C by the second cooling system 4, the material is further cooled and separated into gas and solid in the third cyclone cooler 4-2 of the second cooling system 4. Finally, it leaves from the discharge pipe of the second cyclone cooler 4-1 and falls into the finished product zipper machine to obtain the finished product that meets the requirements.

[0048] In terms of material flow, kaolin raw materials undergo a pre-treatment process to obtain raw meal powder that meets production needs. The raw meal powder is fed into the suspension preheating system 1 via a raw meal elevator after gas-solid separation by a feeding device or cyclone separator. The raw meal powder undergoes preheating and gas-solid separation within the cyclone preheater 1-1. After multiple heat exchanges and gas-solid separations, the raw meal powder enters the modification furnace 2-2 through the discharge pipe of the fourth cyclone preheater 1-1 in the suspension preheating system 1. The calcination furnace system 2 includes a high-efficiency feeding device, a flue gas inlet pipe, a preheating furnace 2-1, a first burner arranged in the preheating furnace 2-1, a modification furnace 2-2, a second burner arranged in the cone section of the modification furnace 2-2, a third burner in the lower part of the modification furnace 2-2, a fourth burner in the middle of the modification furnace 2-2, and a flue gas outlet pipe, etc. Multiple temperature measuring points are set in layers along the height of preheating furnace 2-1 and modification furnace 2-2 to monitor the temperature distribution inside preheating furnace 2-1 and modification furnace 2-2 in real time. By adjusting the amount of fuel fed into preheating furnace 2-1 and the amount of fuel and material fed into modification furnace 2-2, the temperature distribution inside preheating furnace 2-1 and modification furnace 2-2 is controlled within a reasonable range. A reasonable temperature distribution inside preheating furnace 2-1 and modification furnace 2-2 can ensure complete combustion of fuel and complete decomposition of kaolin, while ensuring that the kaolin is not overburned, and the activity index of the finished kaolin meets the requirements of subsequent production. The combustion of fuel in calcining furnace system 2 releases a large amount of heat for the decomposition of kaolin. The decomposed hot material leaves modification furnace 2-2, and then enters the first cooling system 3 after gas-solid separation with hot flue gas in the fifth cyclone preheater 1-1 of suspension preheating system 1. Hot material is cooled and undergoes gas-solid separation in the cyclone cooler of the first cooling system 3. After gas-solid separation, the cooled material enters the second cooling system 4 through the discharge pipe of the first cyclone cooler 3-1. The material undergoes further cooling and gas-solid separation in the third cyclone cooler 4-2 of the second cooling system 4, and finally exits from the discharge pipe of the second cyclone cooler 4-1 of the second cooling system 4, falling into the finished product zipper machine to obtain the desired finished product.

[0049] In terms of gas flow, ambient temperature air enters the second cooling system 4, subsequently cooling the material entering the second cooling system 4. The air, having completed heat exchange, exits from the outlet of the third cyclone cooler 4-2 in the second cooling system 4, and then enters the dust collector 7 to separate the metakaolin products contained in the air to the finished product zipper. The air exiting the dust collector 7 is divided into two paths: the first path enters the upper part of the modification furnace 2-2 for combustion support, and the second path enters the drying and crushing machine to dry the raw materials or for other forms of waste heat utilization. By rationally controlling the amount of fuel entering the modification furnace 2-2, incomplete combustion of fuel in the preheating furnace 2-1 and the lower part of the modification furnace 2-2 creates a reducing atmosphere, thereby reducing the Fe in the kaolin raw material. 3+ Completely reduced to Fe 2+ By reasonably controlling the amount of combustion air entering the upper part of the modified furnace 2-2, the complete combustion of fuel and full release of heat energy are ensured. Subsequently, the raw material powder fed into the suspension preheating system 1 is preheated and separated into gas and solid multiple times. Finally, it leaves from the outlet of the first cyclone preheater 1-1 of the suspension preheating system 1 and is then divided into the following two paths: one path enters the indirect heat exchanger 6 through the circulating fan, and the circulating flue gas is fully cooled by using cooling water, cooling oil or other suitable cooling media. The fully cooled flue gas enters the first cooling system 3, and then cools the high-temperature material entering the first cooling system 3. The cooled circulating flue gas leaves from the outlet of the first cyclone cooler 3-1 of the first cooling system 3 and then enters the bottom of the preheating furnace 2-1; the second path enters the drying crusher to dry the raw material or to utilize waste heat in other forms. After flue gas treatment, it is discharged into the atmosphere.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A metakaolin preparation system with redesigned process flow, comprising a suspension preheating system, a calcination furnace system, a first cooling system, and a second cooling system, characterized in that: The calcination furnace system includes a preheating furnace and a modification furnace. The bottom of the preheating furnace is the flue gas inlet, and the top outlet of the preheating furnace is directly connected to the bottom inlet of the modification furnace. The top outlet of the modification furnace is connected to the inlet of the final stage cyclone preheater of the suspension preheating system. The material outlet at the bottom of the final stage cyclone preheater of the suspension preheating system is connected to the material inlet of the first cooling system. The discharge port of the penultimate stage cyclone preheater of the suspension preheating system is connected to the raw material feeding port of the modification furnace. The preheating furnace does not have a raw material feeding port, and both the preheating furnace and the modification furnace have fuel feeding ports. The top flue gas outlet of the suspension preheating system is connected to the flue gas inlet of the indirect heat exchanger, which is used to indirectly cool the flue gas discharged from the suspension preheating system to 80-120°C. The flue gas outlet of the indirect heat exchanger is connected to the flue gas inlet of the first cooling system, which is used to rapidly cool the material to a temperature range of 300-350°C and below. The flue gas outlet of the first cooling system is connected to the flue gas inlet of the preheating furnace. The oxygen content in the top flue gas discharged from the suspension preheating system is 1-3%. The material outlet of the first cooling system is connected to the material inlet of the second cooling system, and the gas outlet of the second cooling system is connected to the combustion air inlet in the middle of the modified furnace. The lower part of the preheating furnace and the modification furnace is a reduction zone where incomplete combustion of fuel creates a reducing atmosphere, thereby reducing the Fe in the kaolin raw material. 3+ Completely reduced to Fe 2+ ; The upper part of the modified furnace is an oxidation zone, which ensures complete combustion of fuel and full release of heat energy, so as to achieve full decomposition of kaolin to form metakaolin, while avoiding the crystallization and precipitation of metakaolin and loss of activity.

2. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, The modified furnace is composed of a modified furnace cone and a modified furnace column from bottom to top. Fuel feeding ports are respectively provided in the lower part of the modified furnace cone, the modified furnace column and the middle part of the modified furnace column. The fuel feeding port in the middle part of the modified furnace column is located above the combustion air inlet of the modified furnace. Raw material feeding ports are respectively provided above each fuel feeding port of the modified furnace.

3. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, The preheating furnace and the modification furnace are arranged in layers along the height direction with multiple temperature measuring points for real-time monitoring of the temperature distribution inside the preheating furnace and the modification furnace.

4. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, The indirect heat exchanger has a cooling medium inlet and a flue gas outlet at the bottom, and a flue gas inlet and a cooling medium outlet at the top, so that the flue gas and the cooling medium exchange heat in a countercurrent manner. The cooling medium is circulated in the cooling medium channel of the indirect heat exchanger.

5. The metakaolin preparation system with redesigned process flow according to claim 4, characterized in that, The cooling medium of the indirect heat exchanger is cooling water, cooling oil, or other suitable cooling medium.

6. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, A flue gas circulation fan is provided between the indirect heat exchanger and the first-stage cyclone preheater of the suspension preheating system, and between the indirect heat exchanger and the first cooling system.

7. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, The gas outlet of the second cooling system is connected in sequence to the combustion air inlet in the middle of the modified furnace via a dust collector and a combustion air circulation fan.

8. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, The second cooling system includes at least one cyclone cooler for cooling the material to below 100°C.

9. The metakaolin preparation system with redesigned process flow according to claim 1, characterized in that, The flue gas outlet of the suspension preheating system and the gas outlet of the second cooling system are also connected to a drying crusher or other waste heat utilization equipment.

10. A method for preparing metakaolin using the system described in any one of claims 1-9 for process reengineering, characterized in that, The method involves preheating raw materials in a suspension preheating system before they enter a modification furnace. The decomposed material leaves the modification furnace and enters the final stage cyclone preheater of the suspension preheating system. Material separated by the final stage cyclone preheater enters the first cooling system. Flue gas discharged from the top of the suspension preheating system is cooled by an indirect heat exchanger and then enters the first cooling system, exchanging heat with the material entering the first cooling system. Flue gas discharged from the first cooling system enters the preheating furnace, while gas discharged from the second cooling system enters the upper part of the modification furnace for combustion support. The amount of fuel, raw materials, and combustion air fed into the preheating furnace and modification furnace are adjusted to ensure incomplete combustion of fuel in the lower part of the preheating and modification furnaces, creating a reducing atmosphere, while the fuel in the upper part of the modification furnace is fully burned, creating an oxidizing atmosphere. The first cooling system rapidly cools the material to a temperature range of 300-350°C and below, after which it enters the second cooling system and is cooled to below 100°C, yielding metakaolin with controllable finished color.

11. The method for preparing metakaolin by process reengineering according to claim 10, characterized in that, The calcination temperature in the preheating furnace and the lower part of the modification furnace is 600-800℃, and the calcination temperature in the upper part of the modification furnace is 700-900℃; the excess air coefficient at the outlet of the modification furnace is 1.05-1.2; and the residence time of the flue gas in the calcination furnace system is 2-10 seconds.

12. The method for preparing metakaolin by process reengineering according to claim 10, characterized in that, The cooling medium of the first cooling system is flue gas at a temperature of 80-120°C after being cooled by an indirect heat exchanger, and the oxygen content in the flue gas is 1-3%; the cooling medium of the second cooling system is room temperature air.

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