Out-kiln pre-decomposition system for sintering alumina clinker and application method of out-kiln pre-decomposition system

Abstract

The invention discloses an out-of-kiln pre-decomposition system for sintering alumina clinker and an application method.The out-of-kiln pre-decomposition system comprises a smoke chamber, a decomposition furnace, a cyclone cooler, a multi-stage cyclone preheater and a fan which are sequentially connected through pipelines, and the multi-stage cyclone preheater is further connected with the decomposition furnace through a pipeline; the cyclone cooler is further connected with the smoke chamber through a pipeline, and the fan is further connected with the cyclone cooler and the outside through pipelines. The multi-stage cyclone preheater and the decomposing furnace are utilized to complete complete pre-decomposition of the raw materials, low-temperature flue gas is utilized to reduce the temperature of the materials discharged from the decomposing furnace, and the problem that the high-temperature materials crust in the preheater and a smoke chamber is solved. The process is simple, the system is stable and reliable, the pre-decomposition outside the kiln of the raw materials can be fully completed, and good economic benefits and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to a raw material pre-decomposition system and its application method in the red mud alumina extraction process, and particularly to an external pre-decomposition system and its application method for sintered alumina clinker, belonging to the technical field of red mud sintered alumina clinker. Background Technology

[0002] Bayer process red mud is a highly alkaline industrial waste generated during alumina production. It is characterized by high alumina content (10%–30%), high water content (30%–60%), fine particles, and strong alkalinity (pH 10–13), making its comprehensive utilization challenging. Statistics show that approximately 0.8–1.8 tons of red mud are produced for every ton of alumina produced, with nearly 200 million tons of new red mud added globally each year. Bayer process red mud accounts for the majority of this, but its overall comprehensive utilization rate remains low.

[0003] In recent years, with the rise in alumina prices, the technology of recovering aluminum from red mud through sintering alumina clinker has received more attention. Although existing dry-process alumina clinker sintering processes use dry-based material batching and install two-stage preheaters at the kiln tail (with flue gas temperature controlled at 770–790℃) to preheat the materials using flue gas, the raw meal decomposition still relies heavily on heat after entering the kiln, resulting in a still high kiln heat load and limited energy efficiency improvement. While some improved processes have introduced external pre-decomposition technology, they mainly use cold raw meal to cool high-temperature materials to control the flue gas temperature, leading to insufficient decomposition of this portion of the raw meal.

[0004] In summary, there is still room for improvement in the efficiency of raw material predecomposition in existing processes, and there is an urgent need to develop a simple, efficient and reliable raw material predecomposition method. Summary of the Invention

[0005] Objectives of the Invention: One objective of this invention is to provide an external pre-decomposition system for Bayer process red mud sintered alumina clinker with suspension preheating and external decomposition. Another objective is to provide a method for external pre-decomposition of Bayer process red mud sintered alumina clinker using this system. This aims to address the problems of high energy consumption in the drying of raw slurry in existing wet processes and high heat load in the kiln decomposition of raw materials in dry preheater kiln sintering processes. By strengthening the raw material preheating and external decomposition processes, the heat utilization efficiency and raw material decomposition rate are improved, achieving high efficiency and energy saving in the production of Bayer process red mud sintered alumina clinker.

[0006] Technical solution: The present invention provides an external pre-decomposition system for sintered alumina clinker. The system includes a smoke chamber, a decomposition furnace, a cyclone cooler, a multi-stage cyclone preheater, and a fan connected in sequence by pipes. The multi-stage cyclone preheater is also connected to the decomposition furnace by pipes, the cyclone cooler is also connected to the smoke chamber by pipes, and the fan is also connected to the cyclone cooler and the outside environment by pipes.

[0007] Furthermore, the multi-stage cyclone preheater includes two or more cyclone tubes connected sequentially from top to bottom via pipes. The first-stage cyclone tube of the multi-stage cyclone preheater is connected to a blower via a pipe, and the last-stage cyclone tube of the multi-stage cyclone preheater is connected to the decomposition furnace and the cyclone cooler via pipes respectively.

[0008] Furthermore, when the multi-stage cyclone preheater is three-stage, it includes a first-stage cyclone, a second-stage cyclone, and a third-stage cyclone connected sequentially from top to bottom via pipes. The outlet of the first-stage cyclone is connected to a blower via a pipe, and the outlets of both the first-stage and third-stage cyclone are connected to the inlet of the second-stage cyclone via pipes. The outlet of the second-stage cyclone is connected to the inlet of the first-stage cyclone via a pipe. The outlet of the second-stage cyclone and the outlet of the cyclone cooler are both connected to the inlet of the third-stage cyclone via pipes, and the outlet of the third-stage cyclone is connected to the feed inlet of the decomposition furnace via a pipe.

[0009] Furthermore, the inlet of the cyclone cooler is connected to the outlet of the decomposition furnace and the outlet of the blower via pipes, and the outlet of the cyclone cooler is connected to the inlet of the smoke chamber via pipes.

[0010] This invention also includes an external pre-decomposition method for sintered alumina clinker, utilizing the external pre-decomposition system for sintered alumina clinker described in this invention, comprising the following steps:

[0011] (1) Raw material is fed into the first stage cyclone of the multi-stage cyclone preheater;

[0012] (2) After being preheated multiple times by the multi-stage cyclone preheater, the raw material enters the decomposition furnace. The temperature of the decomposition furnace is controlled so that the raw material can complete the full decomposition reaction in the decomposition furnace. After the heating and decomposition is completed, the material enters the cyclone cooler with the flue gas. After the flue gas preheats the raw material by the multi-stage cyclone preheater, it enters the fan from the air outlet of the first stage cyclone. The fan divides the flue gas into two paths: one path is introduced into the cyclone cooler to regulate the material temperature, and the other path is directly discharged to the outside.

[0013] (3) The low-temperature flue gas entering the cyclone cooler through the fan mixes with the high-temperature material and high-temperature flue gas from the decomposition furnace. After heat exchange, the flue gas enters the last stage cyclone of the multi-stage cyclone preheater as a heat source to preheat the raw material fed into the multi-stage cyclone preheater. The material enters the smoke chamber through the outlet of the cyclone cooler and is further heated by the kiln gas in the rotary kiln before entering the rotary kiln for calcination.

[0014] Further, in step (2), the raw material is preheated to 550-600℃ by a multi-stage cyclone preheater, and the temperature of the decomposition furnace is controlled at 850-900℃. The flue gas in the first stage cyclone of the multi-stage cyclone preheater is cooled to 180-230℃ before entering the blower. 30-60% of the flue gas at the blower outlet is controlled to enter the cyclone cooler, and 70-40% of the flue gas at the blower outlet is discharged outside the boundary. In step (3), the temperature of the high-temperature material and high-temperature flue gas entering the cyclone cooler from the decomposition furnace is 850-900℃. After heat exchange in the cyclone cooler, the flue gas temperature drops to 670-720℃, and the material temperature drops to 650-700℃ before entering the smoke chamber, where it is further heated to 750-800℃ under the action of the rotary kiln gas.

[0015] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0016] (1) By setting up a multi-stage cyclone preheater, the present invention improves the heat recovery efficiency of the system, which is conducive to reducing the heat consumption of the system;

[0017] (2) By setting up a decomposition furnace, the present invention improves the decomposition rate of raw materials entering the kiln, reduces the heat load inside the rotary kiln, which is conducive to improving the production capacity of the rotary kiln and reducing the system heat consumption.

[0018] (3) The present invention can flexibly adjust the proportion of low-temperature flue gas entering the cyclone cooler within the range of 30% to 60%, and achieve precise control of the temperature of the material entering the kiln by precisely adjusting the flue gas ratio, thus solving the industry technical problem of high-temperature materials easily forming scale and clogging in the flue chamber; at the same time, this control method can take into account multiple technical objectives such as high decomposition rate of material entering the kiln, low heat consumption of the system and high stability of operation, and achieve synergistic optimization of multiple technical indicators, breaking through the technical bottleneck of traditional processes that make it difficult to take into account both material temperature control and system energy efficiency.

[0019] (4) The method of the present invention is preferably made of red mud, limestone and soda ash as the main raw materials, and can be supplemented with dry base materials such as high-alumina coal gangue to prepare raw meal. The aim is to optimize the thermal process, improve the pre-decomposition rate of raw meal outside the kiln, and thus improve the overall process efficiency of Bayer process red mud sintering alumina clinker. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the pre-decomposition system outside the kiln for sintered alumina clinker in Example 1;

[0021] Among them, 1. Smoke chamber; 2. Decomposition furnace; 3. Cyclone cooler; 4. Multi-stage cyclone preheater; 5. Fan; C1. First-stage cyclone; C2. Second-stage cyclone; C3. Third-stage cyclone;

[0022] Figure 2 This is the raw material pre-decomposition system for sintered alumina clinker in Comparative Example 1;

[0023] Among them, 1. Smoke chamber; 2. Decomposition furnace; 3. Cyclone cooler; 4. Multi-stage cyclone preheater; 6. Material distribution valve; 7. Oxidation furnace; C1. First-stage cyclone; C2. Second-stage cyclone; C3. Third-stage cyclone. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Example 1

[0026] like Figure 1 As shown, the pre-decomposition system for sintered alumina clinker according to the present invention includes a smoke chamber 1, a decomposition furnace 2, a cyclone cooler 3, a multi-stage cyclone preheater 4, and a blower 5 connected in sequence by pipes. The multi-stage cyclone preheater 4 is also connected to the decomposition furnace 2 by pipes. The decomposition furnace 2 is connected to the cyclone cooler 3 by pipes. The cyclone cooler 3 is connected to the multi-stage cyclone preheater 4 and the smoke chamber 1 by pipes. The blower 5 is connected to the multi-stage cyclone preheater 4, the cyclone cooler 3, and the outside environment by pipes. The smoke chamber 1 is connected to the rotary kiln by pipes.

[0027] The multi-stage cyclone preheater 4 includes two or more cyclone tubes. This embodiment is a three-stage cyclone preheater, including a first-stage cyclone tube C1, a second-stage cyclone tube C2, and a third-stage cyclone tube C3 connected sequentially from top to bottom. The outlet of the first-stage cyclone tube C1 is connected to the fan 5 via a pipe. The outlets of both the first-stage cyclone tube C1 and the third-stage cyclone tube C3 are connected to the inlet of the second-stage cyclone tube C2 via pipes. The outlet of the second-stage cyclone tube C2 is connected to the inlet of the first-stage cyclone tube C1 via a pipe. The outlets of both the second-stage cyclone tube C2 and the cyclone cooler 3 are connected to the inlet of the third-stage cyclone tube C3 via pipes. The outlet of the third-stage cyclone tube C3 is connected to the feed inlet of the decomposition furnace 2 via a pipe. The inlet of the cyclone cooler 3 is connected to the outlet of the decomposition furnace 2 and the outlet of the fan 5 via pipes. The outlet of the cyclone cooler 3 is connected to the inlet of the smoke chamber 1 via pipes. Raw materials are fed into the first stage cyclone C1 of the multi-stage cyclone preheater 4. The outlet of the cyclone cooler 3 is connected to the inlet of the third stage cyclone C3 of the multi-stage cyclone preheater 4, used to preheat the raw materials fed into the first stage cyclone C1 of the multi-stage cyclone preheater 4 with hot flue gas. The outlet of the third stage cyclone C3 of the multi-stage cyclone preheater 4 is connected to the inlet of the decomposition furnace 2, used to send the preheated raw materials into the decomposition furnace 2 for calcination. The outlet of the decomposition furnace 2 is connected to the cyclone cooler 3, used to fully mix the reaction products with the flue gas blown into the cyclone cooler 3 by the blower 5 to achieve cooling, and then to complete gas-solid separation of the cooled gas-solid mixture. The blower 5 is used to control 30-60% of the flue gas from the outlet of the multi-stage cyclone preheater 4 to enter the cyclone cooler 3, and 70-40% of the flue gas to be discharged outside the boundary.

[0028] The method for pre-decomposition outside the kiln of sintered alumina clinker using the above-mentioned pre-decomposition system, as described in this invention, includes the following steps:

[0029] (1) Raw material is fed into the multi-stage cyclone preheater 4, first stage cyclone C1;

[0030] (2) The raw material is preheated to 550-600℃ by the multi-stage cyclone preheater 4 and then enters the decomposition furnace 2. The raw material stays at 850-900℃ for 6-10 s to complete the decomposition reaction. The reacted material enters the cyclone cooler 3 along with the flue gas. The low-temperature flue gas (180-230℃) from the first-stage cyclone C1 in the multi-stage cyclone preheater 4 enters the blower 5. 30-60% of the flue gas from the outlet of the blower 5 is controlled to enter the cyclone cooler 3, and 70-40% of the flue gas from the outlet of the blower 5 is discharged outside the boundary.

[0031] (3) The flue gas at 180-230°C in the cyclone cooler 3 is mixed with the high-temperature material and high-temperature flue gas at 850-900°C at the outlet of the decomposition furnace 2. After heat exchange, the material temperature drops to 650-700°C and the flue gas temperature drops to 670-720°C. The flue gas enters the third-stage cyclone C3 of the multi-stage cyclone preheater 4 as a heat source to preheat the raw material fed into the multi-stage cyclone preheater 4. The material enters the smoke chamber 1 through the outlet of the cyclone cooler 3. Under the action of the kiln gas in the rotary kiln, it is further heated to 750-800°C and then enters the rotary kiln for calcination.

[0032] Example 2

[0033] The system and method described in Example 1 are used, specifically as follows:

[0034] (1) Raw material is fed into the multi-stage cyclone preheater 4, first stage cyclone C1;

[0035] (2) After the raw material is preheated to 580°C by the multi-stage cyclone preheater 4, it enters the decomposition furnace 2. The raw material stays at 880°C for 8 seconds to complete the decomposition reaction. The reacted material enters the cyclone cooler 3 along with the flue gas. The low-temperature flue gas (210°C) from the first-stage cyclone C1 in the multi-stage cyclone preheater 4 enters the blower 5. 50% of the flue gas from the outlet of the blower 5 is controlled to enter the cyclone cooler 3, and 50% of the flue gas from the outlet of the blower 5 is discharged outside the boundary.

[0036] (3) The 210°C flue gas in the cyclone cooler 3 is mixed with the high-temperature material and high-temperature flue gas at the outlet of the decomposition furnace 2 at 880°C. After heat exchange, the material temperature drops to 680°C and the flue gas temperature drops to 700°C. The flue gas enters the third-stage cyclone C3 of the multi-stage cyclone preheater 4 as a heat source to preheat the raw material fed into the multi-stage cyclone preheater 4. The material enters the smoke chamber 1 through the outlet of the cyclone cooler 3. Under the action of the kiln gas in the rotary kiln, it is further heated to 780°C and then enters the rotary kiln for calcination.

[0037] In this embodiment, the heat required for raw material decomposition is obtained in the pre-decomposition system, and the decomposition rate of raw materials entering the kiln can reach 100%. Compared with a traditional 1500t / d kiln without a preheater, the rotary kiln output is increased by 120%, and the firing heat consumption is reduced by more than 65kcal / kg·cl.

[0038] Comparative Example 1

[0039] like Figure 2 As shown in the comparative example, a raw material pre-decomposition system for sintered alumina clinker is described, including a feed distribution valve 6 and a smoke chamber 1, a decomposition furnace 2, a cyclone cooler 3, a multi-stage cyclone preheater 4, and an oxidation furnace 7 connected in sequence by pipes. The cyclone cooler 3 is also connected to the smoke chamber 1 by pipes, and the multi-stage cyclone preheater 4 is also connected to the decomposition furnace 2 by pipes. The feed distribution valve 6 is connected to the feed inlet of the multi-stage cyclone preheater 4 and the inlet of the cyclone cooler 3 by pipes respectively.

[0040] The multi-stage cyclone preheater 4 is a three-stage cyclone preheater, comprising a first-stage cyclone C1, a second-stage cyclone C2, and a third-stage cyclone C3 connected sequentially from top to bottom. The discharge port of the first-stage cyclone C1 and the air outlet of the third-stage cyclone C3 are both connected to the inlet of the second-stage cyclone C2 via pipes. The discharge port of the second-stage cyclone C2 and the air outlet of the cyclone cooler 3 are both connected to the inlet of the third-stage cyclone C3 via pipes. The discharge port of the third-stage cyclone C3 is connected to the feed inlet of the decomposition furnace 2 via a pipe. The air outlet of the second-stage cyclone C2 and the distribution valve 6 are both connected to the inlet of the first-stage cyclone C1 via pipes. The air outlet of the first-stage cyclone C1 is connected to the inlet of the oxidizer 7. The outlet of the decomposition furnace 2 and the distribution valve 6 are both connected to the inlet of the cyclone cooler 3 via pipes. The discharge port of the cyclone cooler 3 is connected to the feed inlet of the smoke chamber 1 via a pipe.

[0041] Raw materials are fed into the first-stage cyclone C1 and cyclone cooler 3 of the multi-stage cyclone preheater 4 via the feed valve 6. 80-90% of the raw materials are fed into the first-stage cyclone C1, and 20-10% into the cyclone cooler 3, to meet the system's temperature control requirements. The outlet of the cyclone cooler 3 is connected to the inlet of the third-stage cyclone C3 of the multi-stage cyclone preheater 4, allowing hot flue gas to preheat the raw materials fed into the first-stage cyclone C1 via the feed valve 6. The outlet of the third-stage cyclone C3 is connected to the inlet of the decomposition furnace 2, allowing the preheated raw materials to be fed into the decomposition furnace 2 for calcination. The outlet of the decomposition furnace 2 is connected to the cyclone cooler 3, allowing the reaction products to be mixed and cooled with the raw materials fed into the cyclone cooler 3 via the feed valve 6, followed by gas-solid separation. The oxidizer 7 is used to burn and oxidize the reducing gas at the outlet of the multi-stage cyclone preheater 4, while increasing the flue gas temperature for drying the red mud raw material.

[0042] Pre-decomposition of Bayer process red mud sintered alumina clinker using the above-mentioned raw material pre-decomposition system:

[0043] (1) Raw material is fed through the feed valve 6. 85% of the raw material is fed into the first stage cyclone C1 of the multi-stage cyclone preheater 4, and the other 15% of the raw material is fed into the cyclone cooler 3.

[0044] (2) After the raw material is preheated to 580°C by the multi-stage cyclone preheater 4, it enters the decomposition furnace 2. The raw material stays at 880°C for 8 seconds to complete the reaction: calcium carbonate decomposes into calcium oxide and carbon dioxide. The reacted material enters the cyclone cooler 3 along with the flue gas. The low-temperature flue gas (200°C) from the first stage cyclone C1 in the multi-stage cyclone preheater 4 enters the oxidation furnace 7.

[0045] (3) The raw material in the cyclone cooler 3 is mixed with the high-temperature material and high-temperature flue gas at the outlet of the decomposition furnace 2 at 880°C. After heat exchange, the material temperature is reduced to 680°C and the flue gas temperature is reduced to 700°C. The flue gas enters the third cyclone cylinder C3 of the multi-stage cyclone preheater 4 as a heat source to preheat the raw material fed into the multi-stage cyclone preheater 4 through the material distribution valve 6. The material enters the smoke chamber 1 through the outlet of the cyclone cooler 3. Under the action of the kiln gas of the rotary kiln, it is further heated to 800°C and then enters the rotary kiln for calcination. The decomposition rate of the raw material entering the kiln exceeds 85%.

[0046] In this comparative example, the decomposition rate of raw materials entering the kiln was 85%. Compared with a traditional 1500t / d kiln without a preheater, the rotary kiln output increased by 100%, and the firing heat consumption decreased by more than 60kcal / kg·cl. Compared with the 100% precomposition rate of the external kiln precomposition system for sintering alumina clinker in Example 2, this is 15 percentage points lower, the rotary kiln output is 10% lower, and the firing heat consumption is 5kcal / kg·cl higher.

Claims

1. An external pre-decomposition system for sintered alumina clinker, characterized in that, The system includes a smoke chamber (1), a decomposition furnace (2), a cyclone cooler (3), a multi-stage cyclone preheater (4), and a fan (5) connected in sequence by pipes. The multi-stage cyclone preheater (4) is also connected to the decomposition furnace (2) by pipes, the cyclone cooler (3) is also connected to the smoke chamber (1) by pipes, and the fan (5) is also connected to the cyclone cooler (3) and the outside by pipes.

2. The pre-decomposition system for sintered alumina clinker outside the kiln according to claim 1, characterized in that, The multi-stage cyclone preheater (4) includes two or more cyclone tubes connected sequentially from top to bottom through pipes.

3. The pre-decomposition system for sintered alumina clinker outside the kiln according to claim 2, characterized in that, The first stage cyclone of the multi-stage cyclone preheater (4) is connected to the blower (5) through a pipe, and the last stage cyclone of the multi-stage cyclone preheater (4) is connected to the decomposition furnace (2) and the cyclone cooler (3) through pipes respectively.

4. The pre-decomposition system for sintered alumina clinker outside the kiln according to claim 3, characterized in that, When the multi-stage cyclone preheater (4) is three-stage, the multi-stage cyclone preheater (4) includes a first-stage cyclone, a second-stage cyclone, and a third-stage cyclone connected sequentially from top to bottom through pipes. The air outlet of the first-stage cyclone is connected to the blower (5) through a pipe. The discharge outlet of the first-stage cyclone and the air outlet of the third-stage cyclone are both connected to the inlet of the second-stage cyclone through pipes. The air outlet of the second-stage cyclone is connected to the inlet of the first-stage cyclone through a pipe. The discharge outlet of the second-stage cyclone and the air outlet of the cyclone cooler (3) are both connected to the inlet of the third-stage cyclone through pipes. The discharge outlet of the third-stage cyclone is connected to the feed inlet of the decomposition furnace (2) through a pipe.

5. The pre-decomposition system for sintered alumina clinker outside the kiln according to claim 4, characterized in that, The inlet of the cyclone cooler (3) is connected to the outlet of the decomposition furnace (2) and the outlet of the blower (5) through pipes, and the outlet of the cyclone cooler (3) is connected to the inlet of the smoke chamber (1) through pipes.

6. A method for pre-decomposition of sintered alumina clinker outside the kiln, characterized in that, The pre-decomposition system for sintered alumina clinker according to any one of claims 1-5 includes the following steps: (1) Raw material is fed into the first stage cyclone of the multi-stage cyclone preheater (4); (2) After being preheated multiple times by the multi-stage cyclone preheater (4), the raw material enters the decomposition furnace (2). The temperature of the decomposition furnace (2) is controlled so that the raw material can complete the full decomposition reaction in the decomposition furnace (2). After the heating and decomposition is completed, the material enters the cyclone cooler (3) with the flue gas. After the flue gas preheats the raw material by the multi-stage cyclone preheater (4), it enters the blower (5) from the air outlet of the first stage cyclone. The blower (5) delivers the flue gas in two ways: one way is introduced into the cyclone cooler (3) to regulate the material temperature, and the other way is directly discharged to the outside. (3) The low-temperature flue gas entering the cyclone cooler (3) through the fan (5) mixes with the high-temperature material and high-temperature flue gas from the decomposition furnace (2). After heat exchange, the flue gas enters the last stage cyclone of the multi-stage cyclone preheater (4) as a heat source to preheat the raw material fed into the multi-stage cyclone preheater (4). The material enters the smoke chamber (1) through the outlet of the cyclone cooler (3) and is further heated under the action of the kiln gas in the rotary kiln before entering the rotary kiln for calcination.

7. The pre-decomposition method outside the kiln for sintered alumina clinker according to claim 6, characterized in that, In step (2), the raw material is preheated to 550-600°C by the multi-stage cyclone preheater (4), and the temperature of the decomposition furnace (2) is controlled to be 850-900°C. The flue gas in the first stage cyclone of the multi-stage cyclone preheater (4) is cooled to 180-230°C and then enters the blower (5).

8. The pre-decomposition method for sintered alumina clinker outside the kiln according to claim 6, characterized in that, In step (2), 30-60% of the flue gas from the outlet of the control fan (5) enters the cyclone cooler (3), and 70-40% of the flue gas from the outlet of the control fan (5) is discharged outside the boundary.

9. The pre-decomposition method for sintered alumina clinker outside the kiln according to claim 6, characterized in that, In step (3), the temperature of the high-temperature material and high-temperature flue gas entering the cyclone cooler (3) from the decomposition furnace (2) is 850-900℃.

10. The pre-decomposition method for sintered alumina clinker outside the kiln according to claim 6, characterized in that, In step (3), after heat exchange by the cyclone cooler (3), the flue gas temperature drops to 670-720°C and the material temperature drops to 650-700°C before entering the flue gas chamber (1), where it is further heated to 750-800°C under the action of the rotary kiln gas.

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