A method for firing red mud ceramsite and supplying waste heat steam

Abstract

The invention provides a method for firing red mud ceramsite and supplying waste heat steam, which belongs to the technical field of chemical production, and comprises the following steps: red mud meeting certain requirements of iron oxide and sodium oxide content is mixed with auxiliary materials and then granulated to obtain ceramsite green balls with a calorific value of 503-960 kcal / kg; the ceramsite green balls are placed in a roasting device for roasting, and hot air in a temperature range of 400-X°C is extracted at the same time to form waste heat and prepare steam, where X is 700-790°C; after roasting, a volume density of 890-1010 kg / m 3 The invention uses red mud as raw material, mixes auxiliary materials with certain calorific value, prepares high-strength ceramsite from ceramsite raw balls, and obtains and outputs flue gas with rich heat, which not only improves the utilization rate of energy, but also reduces the sintering cost of high-strength ceramsite and improves the mechanical properties of ceramsite.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, and in particular to a method for firing red mud ceramsite and supplying waste heat steam. Background Art

[0002] Red mud is a solid waste containing high alkalinity and harmful elements produced during the process of refining alumina from bauxite. In recent years, the environmental problems caused by the accumulation of red mud have become increasingly serious, and its harmless utilization is of great significance to the environment. Ceramic slag is a granular artificial lightweight aggregate. The raw materials can usually be prepared into ceramsite green balls and then obtained after roasting. It has a certain cylinder pressure strength and porosity. Ceramic slag is a kind of ceramic material. Since red mud has a high content of silicate components and meets the necessary conditions for the preparation of ceramic slag, the preparation of ceramic slag can be used as a large-scale disposal method for red mud.

[0003] Since red mud, a single raw material, cannot fully meet the component requirements for preparing expanded clay, it is necessary to add an appropriate amount of auxiliary materials to adjust the raw material composition. The reason for using auxiliary raw materials such as gangue, sludge, and coal slime is that the content of silicon oxide, calcium oxide, and aluminum oxide in the raw materials can be adjusted while increasing the calorific value to meet the component requirements for firing high-strength expanded clay.

[0004] In existing studies, ceramsite prepared using red mud as raw material has the characteristics of low strength and low density. In the study of the influence of preheating process on the firing characteristics and performance of red mud ceramsite, Light Metals, 2021(05):21-25, Wang Jina et al. prepared a bulk density of 731 kg / cm2 at a firing temperature of 1115 °C and a firing time of 15 min. 3 , porosity of 41.9%, 1h water absorption of 15.7%, and compressive strength of 1.63MPa lightweight red mud ceramsite. In the Journal of Guangxi University of Science and Technology, 2023, 34(04):25-31, in the preparation and performance research of red mud sound-absorbing ceramsite, Zhu Wanxu et al. prepared a lightweight red mud ceramsite with a cylinder compressive strength of 5.2MPa and a bulk density of 896kg / m 3 Red mud ceramsite. In Brick and Tile, 2013(01):54-55, in the preparation of red mud lightweight ceramsite, Ma Long et al. prepared a ceramsite with a bulk density of 574 kg / m at a sintering temperature of 1150 °C. 3 , cylinder pressure strength of 3.5MPa, water absorption rate of 8.6% ceramsite. These are lightweight red mud ceramsite, mainly used in functional building materials such as thermal insulation, heat insulation and lightweight. However, a single large-scale replacement of sand and gravel aggregate requires high-strength ceramsite, and lightweight ceramsite is no longer applicable.

[0005] The composition of most red muds limits the application of red mud in high-strength ceramsite. Among them, red mud with high iron and sodium content is not conducive to the firing of high-calorific value ceramsite. Because excessive iron content will cause pre-reduction to form low-valent low-melting point compounds, which will lead to problems such as adhesion and black heart at high temperatures, which is not conducive to industrial production decarbonization and the use of high calorific value raw materials. When the sodium content in red mud is too high, on the one hand, sodium ions are easy to evaporate in a high calorific value reducing atmosphere; on the other hand, the ceramsites are also easy to bond with each other, the sintering temperature is low, and there is limited room for improvement in mechanical properties, making it difficult to prepare high-strength ceramsite.

[0006] Another factor that limits the industrialization of red mud preparation into high-strength expanded clay is cost. The red mud processing methods in the prior art will result in a large amount of heat source waste, which increases production costs.

[0007] It can be seen that the high-strength expanded clay produced using red mud in the existing technology has poor mechanical strength, low bulk density, high energy waste rate in the production process, high production cost, and cannot achieve green production. Summary of the invention

[0008] The invention provides a method for firing red mud ceramsite and supplying waste heat steam, so as to solve the technical problems in the prior art that high-strength ceramsite produced by using red mud has poor mechanical strength, low bulk density, high energy waste rate in the production process and high production cost.

[0009] In order to solve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0010] A method for firing red mud ceramsite and supplying waste heat steam comprises the following steps:

[0011] S1. Mixing red mud with auxiliary materials and granulating them to obtain ceramsite green balls with a calorific value of 500-1000 kcal / kg, wherein the average mass percentage of silicon oxide in the auxiliary materials after deducting the burning loss is 48.7-56%;

[0012] S2, placing the ceramsite green balls in a roasting device, igniting and roasting, while extracting hot air in the temperature range of 400-X°C to form waste heat and prepare steam, controlling the temperature in the equipment to be less than 1000°C (no heat source is required at this stage), and above 1000°C, an external heat source is required to provide heat, and X is 700-790;

[0013] S3, calcination is completed, and the bulk density is 890-1010kg / m 3 And the cylinder pressure strength is greater than 7.5MPa high-strength expanded clay.

[0014] If the calorific value of expanded clay balls is too low, the temperature of self-combustion is low after ignition, the temperature of the hot air that can be extracted is low, the waste heat obtained is too little, and there is no value for secondary utilization; if the calorific value is too high, the calcination time is too long and the quality of expanded clay balls decreases.

[0015] Here, the calorific value of the ceramsite raw pellets is selected to be 503-960 kcal / kg, which is also beneficial to the mechanical strength of high-strength ceramsite. Specifically, when the calorific value of the ceramsite is too high (greater than 960 kcal / kg), the temperature rises too quickly and is difficult to control, which can easily cause the ceramsite to be overburned, and problems such as sticking into blocks and particle deformation occur, and the gas permeability is lost, resulting in sintering failure and unqualified finished products; it can also easily cause the surface of the ceramsite to heat up too quickly and densify too early, and there is too much residual carbon inside, making the black heart obvious, and the performance of ceramsite containing a large amount of residual carbon is poor. When the calorific value of the ceramsite is too low (less than 500 kcal / kg), most of the heat is provided to the heating process of the ceramsite itself, so that only very little heat can be used for output. Usually, the calorific value of the raw pellets needs to be around 300 kcal / kg to heat the ceramsite to about 1000°C, and the output of waste heat is small, and the waste heat utilization efficiency is poor.

[0016] Only the appropriate calorific value (503-960 kcal / kg) and the appropriate decarbonization combustion time (the residence time of the process from 600°C to 1000°C is 31-49 minutes) can ensure both high waste heat output and high sintering strength of ceramsite.

[0017] The addition of auxiliary materials can improve energy utilization efficiency. Auxiliary materials contain a certain amount of combustible substances, such as coal components and organic substances. After mixing them with red mud to prepare ceramsite, the combustibility of coal auxiliary materials can be utilized to increase the generated heat and energy utilization efficiency; since ceramsite raw balls have high calorific value and combustibility, the roasting time of ceramsite can be reduced and production efficiency can be improved. The abundant heat of ceramsite can also be output to form waste heat utilization, which not only achieves energy saving and carbon reduction, but also further reduces the cost of ceramsite. The combustible substances in the auxiliary materials burn and release heat during the roasting process, which promotes the combination of particles inside the ceramsite, forms a cross-linked structure, and promotes the improvement of the mechanical properties of the ceramsite.

[0018] After sintering reaction, silicon oxide in the auxiliary material can form mineral phases such as silicate. During the sintering process, the formation of these mineral phases can promote the crystallization of ceramsite green balls and the increase of grain size, which is beneficial to improve the mechanical strength of ceramsite.

[0019] Preferably, the mass percentage of iron oxide in the red mud in S1 is 4.5-6.5% and the mass percentage of sodium oxide is 10.61-13.44%.

[0020] Preferably, the mass percentage of iron oxide in the red mud in S1 is 26.7-31.5% and the mass percentage of sodium oxide is 5.8-7.1%.

[0021] Limit the content of iron oxide and sodium oxide in red mud to avoid technical problems such as adhesion and black core caused by inappropriate content of the two. Selecting appropriate sodium oxide and iron oxide components as solvents is very beneficial to reducing the sintering temperature of ceramics. When the content of solvent components such as sodium oxide or iron oxide is too low, the sintering temperature will be too high, thereby increasing energy consumption.

[0022] Preferably, the average calorific value of the auxiliary materials in S1 is 603-1908 kcal / kg.

[0023] Preferably, the auxiliary material in S1 is one or more of coal gangue, coal slime, steel slag, sewage sludge, cathode mud, carbon slag and tailings.

[0024] Preferably, the auxiliary material in S1 is a mixture of coal gangue and coal slime, and the mass ratio of the coal gangue to the coal slime is 5:1.

[0025] Preferably, the amount of auxiliary material added is 50-70% of the total mass of red mud and auxiliary material.

[0026] Preferably, the calcination temperature in S2 is 1000-1200°C, and the residence time during the process of heating from 600°C to 1000°C is 31-49 minutes.

[0027] Preferably, the pressure of the steam in S2 is 3-9.5 MPa, and the steam is used for the alumina evaporation crystallization process.

[0028] Preferably, the particle size of the high-strength ceramsite in S3 is 8-17 mm.

[0029] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0030] The present invention improves the utilization rate of energy and enhances the packing density of high-strength ceramsite by compounding ceramsite raw balls with a certain calorific value; at the same time, the content of silicon dioxide in the auxiliary materials is limited to ensure the improvement of the mechanical properties of the high-strength ceramsite; the high-strength ceramsite produced by the present invention; in the process of roasting, the excess hot air flow is timely recovered and reused in the process of its production process, thereby improving the utilization rate of secondary energy and effectively reducing the production cost of the high-strength ceramsite. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] The present embodiment provides a method for firing red mud ceramsite and supplying waste heat steam, which refers to mixing red mud with coal gangue and coal slime in a ratio of 4:5:1, and the auxiliary material is a mixture of coal gangue and coal slime, wherein the iron oxide content of the red mud is 4.5%, and the sodium oxide content is 13.44%; the aluminum oxide content of the auxiliary material in the coal gangue is 29.17% (excluding the loss on ignition), the silicon oxide content is 49.88%, and the calorific value of the coal gangue is 590kcal / kg; the silicon oxide content in the coal slime is 52.14% (excluding the loss on ignition), and the calorific value of the coal slime is 2979kcal / kg. The calorific value of the prepared ceramsite raw ball is 593kcal / kg, and the high-strength ceramsite is fired using a roasting machine, the roasting temperature is 1100℃, and the residence time during the temperature increase from 600℃ to 1000℃ is 42 minutes. The high-strength ceramsite has excellent performance, a particle size of 10mm, and a volume density of 970kg / m 3 , strength is 8.5MPa; during the roasting process, hot air in the temperature range of 400-785℃ is extracted. The hot air can be used to prepare steam through the waste heat boiler and return to the evaporation and crystallization process of the alumina plant. The steam pressure is 6.5MPa.

[0034] Example 2

[0035] This embodiment provides a method for firing red mud ceramsite and supplying waste heat steam, which refers to mixing red mud and coal gangue in a ratio of 3:7, and the auxiliary material is coal gangue, wherein the red mud has an iron oxide content of 4.7% and a sodium oxide content of 13.34%; the auxiliary material coal gangue has a silicon oxide content of 53.01% and a calorific value of 730kcal / kg. The calorific value of ceramsite raw balls is 511kcal / kg, and high-strength ceramsite is fired using a roasting machine, the roasting temperature is 1200℃, and the residence time at 600-1000℃ is 35 minutes. The high-strength ceramsite has excellent performance, a particle size of 8mm, and a volume density of 1010kg / m 3 The cylinder pressure strength is 9.3MPa; during the roasting process, hot air in the temperature range of 400-750℃ is extracted. The hot air can be used to prepare steam through the waste heat boiler and return to the evaporation and crystallization process of the alumina plant. The steam pressure is 8.5MPa.

[0036] Example 3

[0037] The present embodiment provides a method for firing red mud ceramsite and supplying waste heat steam, which refers to mixing red mud with coal gangue and sludge in a ratio of 3:4:3, and the auxiliary material is a mixture of coal gangue and sludge, wherein the red mud has an iron oxide content of 6.5% and a sodium oxide content of 10.61%; the auxiliary material coal gangue has a silicon oxide content of 49.88% and a calorific value of 590kcal / kg; the silicon oxide content in the sludge is 47.2%, and the calorific value of the sludge is 2386kcal / kg. The calorific value of ceramsite raw balls is 952kcal / kg. High-strength ceramsite is fired using a roasting machine, the roasting temperature is 1150°C, and the residence time at 600-1000°C is 49 minutes. The high-strength ceramsite has excellent performance, a particle size of 16mm, and a volume density of 910kg / m 3 , the strength is 8.1MPa; during the roasting process, hot air in the temperature range of 400-790℃ is extracted, and the hot air can be used to prepare steam through the waste heat boiler and return to the evaporation crystallization process of the alumina plant. The steam pressure is 8.5MPa.

[0038] Example 4

[0039] The present embodiment provides a method for firing red mud high-strength ceramsite and supplying waste heat steam, which refers to mixing red mud with slag and coal slime in a ratio of 5:3:2, and the auxiliary material is a mixture of slag and coal slime, wherein the red mud has an iron oxide content of 9.5% and a sodium oxide content of 10.61%; the auxiliary material slag has a silicon oxide content of 69.52%; the silicon oxide content in the coal slime is 52.14%, and the calorific value is 2979kcal / kg. The calorific value of ceramsite raw balls is 596kcal / kg. The high-strength ceramsite is fired in a roasting machine, the roasting temperature is 1160°C, and the residence time at 600-1000°C is 49 minutes. The high-strength ceramsite has excellent performance, a particle size of 12mm, and a volume density of 970kg / m 3 , with a strength of 7.9MPa; during the roasting process, hot air in the temperature range of 400-720℃ is extracted, and the hot air can be used to prepare steam through the waste heat boiler and return to the evaporation crystallization process of the alumina plant. The pressure of the steam is 6.5MPa.

[0040] Example 5

[0041] The present embodiment provides a method for firing red mud ceramsite and supplying waste heat steam, which refers to mixing red mud and coal gangue in a ratio of 4:6, and the auxiliary material is coal gangue, wherein the red mud has an iron oxide content of 26.7% and a sodium oxide content of 7.1%; the auxiliary material coal gangue has a silicon oxide content of 51.44% (excluding the loss on ignition), and a calorific value of 1005kcal / kg. The calorific value of ceramsite raw balls is 603kcal / kg. High-strength ceramsite is fired in a roasting machine, the roasting temperature is 1100℃, and the residence time at 600-1000℃ is 32 minutes. The high-strength ceramsite has excellent performance, a particle size of 12mm, and a volume density of 950kg / m 3, with a strength of 9.8MPa; during the roasting process, hot air in the temperature range of 400-730℃ is extracted, and the hot air can be used to prepare steam through the waste heat boiler and return to the evaporation and crystallization process of the alumina plant. The steam pressure is 8.5MPa.

[0042] Example 6

[0043] The present embodiment provides a method for firing red mud ceramsite and supplying waste heat steam, which refers to mixing red mud with sludge and tailings in a ratio of 50:40:10, and the auxiliary material is a mixture of sludge and tailings, wherein the red mud has an iron oxide content of 26.8% and a sodium oxide content of 7.0%; the auxiliary sludge has a silicon oxide content of 47.2%, and the calorific value of the sludge is 2386kcal / kg; the silicon oxide content of the tailings is 91.25% (excluding the burning loss), and the calorific value is 0. The calorific value of the ceramsite raw ball is 960kcal / kg, and the high-strength ceramsite is fired using a roasting machine, the roasting temperature is 1120°C, and the residence time at 600-1000°C is 48 minutes. The high-strength ceramsite has excellent performance, a particle size of 15mm, and a volume density of 890kg / m 3 , with a strength of 7.6MPa; during the roasting process, hot air in the temperature range of 400-700℃ is extracted, and the hot air can be used to prepare steam through the waste heat boiler and return to the evaporation and crystallization process of the alumina plant. The steam pressure is 8.5MPa.

[0044] Example 7

[0045] The present embodiment provides a method for firing red mud ceramsite and supplying waste heat steam, which is to mix red mud and coal gangue in a ratio of 50:50, and the auxiliary material is coal gangue, wherein the red mud has an iron oxide content of 31.5% and a sodium oxide content of 5.8%; the auxiliary material coal gangue has a silicon oxide content of 51.44% and a calorific value of 1005kcal / kg. The calorific value of ceramsite raw balls is 503kcal / kg, and high-strength ceramsite is fired using a roasting machine, the roasting temperature is 1200℃, and the residence time at 600-1000℃ is 31 minutes. The high-strength ceramsite has excellent performance, a particle size of 17mm, and a volume density of 970kg / m 3 , with a strength of 10.2MPa; during the roasting process, hot air in the temperature range of 400-720℃ is extracted, and the hot air can be used to prepare steam through the waste heat boiler and return to the evaporation and crystallization process of the alumina plant. The steam pressure is 8.5MPa.

[0046] Comparative Example 1

[0047] This comparative example is similar to Example 1, except that in this comparative example, the iron oxide content of the red mud is 36.5%, and the sodium oxide content is 7.5%. After roasting, the ceramsite is bonded to form a large block, a large amount of black core appears inside, the loss on ignition is greater than 5%, and it cannot be used as ceramsite. The hot air temperature is lower than 600°C, and the firing process fails.

[0048] Comparative Example 2

[0049] This comparative example is similar to Example 1, except that in this comparative example, the iron oxide content of the red mud is 4.5%, and the sodium oxide content is 7.3%. The bulk density of the ceramsite after firing is 950 kg / m 3 , the cylinder pressure strength is 4.8MPa; during the roasting process, hot air of 400-750℃ is extracted, the strength of the ceramsite is unqualified, and the firing of the ceramsite fails.

[0050] Comparative Example 3

[0051] This comparative example is similar to Example 1, except that the calorific value of the ceramsite green pellets in this comparative example is 400 kcal / kg. The high-strength ceramsite is fired in a roasting machine at a roasting temperature of 1180°C and a residence time of 31 minutes at 600-1000°C. The high-strength ceramsite has excellent performance, a particle size of 17 mm, and a bulk density of 970 kg / m 3 , the strength is 10.2MPa; during the roasting process, hot air at about 400℃ is extracted, and the hot air volume is small, so only a small amount of low-parameter saturated steam can be prepared, and the waste heat utilization efficiency is poor.

[0052] Comparative Example 4

[0053] This comparative example is similar to Example 1, except that the calorific value of the ceramsite green pellets in this comparative example is 1100 kcal / kg. The high-strength ceramsite was fired in a roasting machine at a roasting temperature of 1180°C and a residence time of 31 minutes at 600-1000°C. Some ceramsites were bonded into blocks, with black cores inside, and the loss on ignition was greater than 5%, which could not be used as qualified ceramsite. The strength was 3.3 MPa, which did not meet the relevant standards.

[0054] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for firing red mud ceramsite and supplying waste heat steam, characterized in that: The steps include: S1. Mixing red mud with auxiliary materials and granulating them to obtain ceramsite raw balls with a calorific value of 503-960 kcal / kg, wherein the average mass percentage of silicon oxide in the auxiliary materials after deducting the loss on burning is 48.7-56%, and the mass percentage of iron oxide in the red mud is 4.5-6.5% and the mass percentage of sodium oxide is 10.61-13.44% or the mass percentage of iron oxide is 26.7-31.5% and the mass percentage of sodium oxide is 5.8-7.1%; S2, placing the ceramsite green balls in a roasting device for roasting, while extracting hot air in the temperature range of 400-X°C to form waste heat and prepare steam, wherein X is 700-790, the roasting temperature is 1000-1200°C, and the residence time during the process of heating from 600°C to 1000°C is 31-49min; S3, calcination is completed, and the bulk density is 890-1010kg / m 3 And the cylinder pressure strength is greater than 7.5MPa high-strength expanded clay.

2. The method for firing red mud ceramsite and supplying waste heat steam according to claim 1, characterized in that: The average calorific value of the auxiliary materials in S1 is 603-1908 kcal / kg.

3. The method for firing red mud ceramsite and supplying waste heat steam according to claim 2, characterized in that: The auxiliary materials described in S1 are one or more of coal gangue, coal slime, steel slag, sewage sludge, cathode mud, carbon slag and tailings.

4. The method for firing red mud ceramsite and supplying waste heat steam according to claim 3, characterized in that: The auxiliary material in S1 is a mixture of coal gangue and coal slime, and the mass ratio of the coal gangue to the coal slime is 5:

1.

5. The method for firing red mud ceramsite and supplying waste heat steam according to claim 1, characterized in that: The amount of the auxiliary material added in S1 is 50-70% of the total mass of the red mud and the auxiliary material.

6. The method for firing red mud ceramsite and supplying waste heat steam according to claim 1, characterized in that: The pressure of the steam in S2 is 3-9.5 MPa.

7. The method for firing red mud ceramsite and supplying waste heat steam according to claim 1, characterized in that: The particle size of the high-strength ceramsite described in S3 is 8-17 mm.