Calcium aluminate powder production from aluminous ash

Abstract

The present application relates to a kind of calcining control method for preparing calcium aluminate from aluminium ash, and the method comprises the following steps: judging the aluminum content index of secondary aluminium ash, classifying secondary aluminium ash according to the aluminum content index, obtaining raw material aluminium ash by matching different types of secondary aluminium ash, and controlling the aluminum content index of raw material aluminium ash.The method can solve the technical problems of normal operation affected by ring formation in the tail of rotary kiln and low firing rate of calcium aluminate caused by material caking when preparing calcium aluminate from aluminium ash.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of calcium aluminate powder preparation, and particularly relates to a calcination control method for preparing calcium aluminate powder from aluminum ash. BACKGROUND

[0002] Primary aluminum ash generated in the process of aluminum smelting and processing contains more than 20% of metallic aluminum. After most of the metallic aluminum in the primary aluminum ash is extracted, secondary aluminum ash is formed. The secondary aluminum ash contains fluorine, nitrogen and heavy metals, and belongs to hazardous solid waste, which is difficult to handle. At present, the technology of preparing calcium aluminate powder from aluminum ash has been put into practical use. The high-temperature condition during the sintering of the calcium aluminate powder can realize the defluorination, denitrification and heavy metal removal of the aluminum ash, so that the aluminum ash can meet the recycling requirements.

[0003] In the process of preparing calcium aluminate powder from aluminum ash, the secondary aluminum ash formed after the extraction of metallic aluminum from the primary aluminum ash is mixed with limestone and ground to obtain raw material. The raw material is calcined at high temperature in a rotary kiln to obtain clinker. Since about 5-10% of metallic aluminum still exists in the secondary aluminum ash, the melting point of the metallic aluminum is 660 DEG C. If the metallic aluminum is not burned in time, liquid phase is formed when the temperature is higher than the melting point. Firstly, the rotary kiln tail is prone to peeling and ring forming, which affects the normal operation of the rotary kiln. Secondly, the material is bonded into blocks, which affects the material flow and heat transfer, and leads to low sintering rate of the calcium aluminate and the decrease of the product dissolution rate index. SUMMARY

[0004] The purpose of the application is to solve the technical problem that the metallic aluminum in the aluminum ash affects the calcination process control of the calcium aluminate. One technical idea of the application is to control the metallic aluminum content in the raw material aluminum ash within a standard range and to control the fluctuation of the aluminum content to correspondingly reduce the control difficulty of the calcination process. The technical scheme adopted is as follows.

[0005] A calcination control method for preparing calcium aluminate powder from aluminum ash, comprising the following steps: judging the aluminum content index of the secondary aluminum ash, classifying the secondary aluminum ash according to the aluminum content index, mixing the secondary aluminum ash of different classes to obtain raw material aluminum ash, and controlling the aluminum content index of the raw material aluminum ash.

[0006] The judgment of the aluminum content index of the secondary aluminum ash can be achieved by sampling the secondary aluminum ash and directly detecting the aluminum content in the secondary aluminum ash, such as using the EDTA titration method. However, this method has low detection efficiency and poor timeliness. Moreover, when the metallic aluminum in the aluminum ash is unevenly distributed, the method may not truly and accurately reflect the overall aluminum content of the secondary aluminum ash due to the limitation of the sampling point.

[0007] An improved scheme, the aluminum content index judgment method of secondary aluminum ash is that weighing mechanisms are respectively arranged at the aluminum ash outlet and the aluminum sheet outlet of the screening device after the primary aluminum ash is ball milled, the weight m1 of the aluminum ash at the aluminum ash outlet and the weight m2 of the aluminum sheet at the aluminum sheet outlet are weighed, the ratio m2 / m1 of the aluminum sheet weight and the aluminum ash weight in a period is calculated, and the m2 / m1 is taken as the aluminum content index of the secondary aluminum ash.

[0008] When the aluminum ash is ball milled, the granular metallic aluminum is rolled into aluminum sheets on one hand, and the apparent size is larger than that of the powdery aluminum ash, so the aluminum sheets can be separated by screening. On the other hand, due to the crushing effect of the ball milling, part of the aluminum sheets are crushed into smaller particles, and when the particles are smaller than the screen mesh diameter, the aluminum sheets are mixed into the aluminum ash and cannot be separated. When the ball milling process parameters are fixed, the crushing effect on the metallic aluminum is also relatively fixed. When the content of the metallic aluminum is high, the amount of the aluminum sheets rolled increases, and at the same time, the amount of the aluminum sheets crushed into small particles also increases, so the amount of the metallic aluminum screened out can reflect the amount of the metallic aluminum entering the raw aluminum ash.

[0009] The scheme does not directly take the amount of the metallic aluminum screened out as the judgment index, but takes the ratio of the amount of the metallic aluminum screened out to the amount of the aluminum ash screened out as the index, which is considered that the material flow is not stable during screening, and the ratio is more accurate.

[0010] Further, the m2 / m1 of the raw aluminum ash is controlled to be not higher than 0.3. When the m2 / m1 is higher than 0.3, the content of the aluminum in the raw aluminum ash is too high, the calcination process control is difficult, and the skin peeling and the material caking in the kiln are easily caused.

[0011] Another technical idea of the present application is that in the process control of the rotary kiln, how to promote the metallic aluminum in the aluminum ash to burn completely in time is focused on. The conditions for the combustion of a substance are temperature and oxygen. In the rotary kiln, the metallic aluminum in the aluminum ash needs to be controlled to burn completely at the tertiary air, so the temperature and the oxygen supplement amount at this stage need to be ensured.

[0012] According to the principle, an improved scheme of the present application is that the tail gas temperature t1 of the rotary kiln is monitored, when t1 is lower than the control range, the tertiary air amount is first increased by a small amplitude, when t1 is fed back to rise, the tertiary air amount is gradually increased to t1 to rise to the control range; when t1 is fed back to decrease, the tertiary air amount is returned to the original value, and the negative pressure of the rotary kiln is increased by a small amplitude, when t1 is fed back to rise, the negative pressure is gradually increased to t1 to rise to the control range.

[0013] Specifically, the control range of t1 is 900-1000℃. Since the heat of the metallic aluminum is high, when the metallic aluminum burns near the tail end of the rotary kiln, heat is released, and the tail gas temperature of the rotary kiln will rise. When bauxite and limestone are used as raw materials for calcination, the tail gas temperature of the rotary kiln is generally controlled at 800-900℃, so in the present scheme, the control range of the tail gas temperature of the rotary kiln is increased to 900-1000℃.

[0014] According to the second technical idea of the application, the following improvements focus on improving the air mixing effect during the combustion of metal aluminum, and the scheme is to improve the structure of the tuyere of the tertiary air pipe. Specifically, a secondary air pipe is arranged at the tuyere of the tertiary air pipe of the rotary kiln, the secondary air pipe is communicated with the main air pipe, the opening of the secondary air pipe is arranged at the side of the tuyere, the opening of the secondary air pipe faces the head end of the kiln, and the opening of the secondary air pipe faces away from the rotary direction of the rotary kiln, and the height of the opening of the secondary air pipe from the bottom of the tuyere is less than the thickness of the material layer in the rotary kiln.

[0015] The opening height of the conventional tuyere structure is greater than the thickness of the material layer, so that the material is prevented from flowing back into the air pipe along the opening during the rotation of the rotary kiln, and air pipe blockage is caused. In the traditional process, the raw material does not contain combustible materials, and the tertiary air supply is mainly used for combustion support of the combustible materials in the flue gas, and the air mixing of the material layer does not need to be considered.

[0016] The powdered metal aluminum is extremely easy to burn when it is completely exposed to air due to the large surface area. However, when aluminum ash is used as raw material, the metal aluminum powder in the aluminum ash is mixed in the material and has a small air contact surface, and cannot burn in time, and forms a liquid phase when the temperature is higher than the melting point, causing the material to stick together.

[0017] The scheme sets the secondary air pipe at the tuyere of the tertiary air pipe, and sets the opening position of the secondary air pipe below the material layer height, so that the mixing effect of the material layer and air can be increased, the combustion of the metal aluminum in the material layer is supported, and the timely combustion of the metal aluminum is facilitated.

[0018] Considering that the opening of the secondary air pipe needs to avoid material backflow, the opening is arranged on the side of the tuyere that faces away from the material flow. Moreover, the air pipe at the opening end is inclined to the bottom of the tuyere.

[0019] Specifically, the angle between the axis of the opening end of the secondary air pipe and the longitudinal section of the tuyere is 50-60°, and the angle between the axis of the opening end of the secondary air pipe and the cross section of the tuyere is 70-80°.

[0020] Specifically, the main air pipe is provided with a tapered closing portion at the connection with the secondary air pipe. The tapered closing portion can form a high pressure at the connection, so as to ensure the air inlet amount of the secondary air pipe.

[0021] Specifically, the connection of the secondary air pipe and the main air pipe is located outside the kiln body of the rotary kiln, the secondary air pipe is provided with a valve at the connection, a dust concentration sensor is arranged at the kiln tail flue of the rotary kiln, and when the measurement value of the dust concentration sensor is higher than the control range, the opening degree of the valve of the secondary air pipe is reduced. The arrangement of the secondary air pipe can cause the material layer in the kiln to be stirred, and dust is generated. Too much dust can affect the yield of the material, and increase the load of the tail gas treatment. By detecting the dust concentration at the kiln tail to control the air inlet amount of the secondary air pipe, the influence degree of the dust can be controlled.

[0022] In the application, the aluminum content refers to the content of metal aluminum.

[0023] The method can solve the technical problems of the ring formation in the tail of the rotary kiln, the low sintering rate of calcium aluminate caused by the material caking and the normal operation. BRIEF DESCRIPTION OF DRAWINGS

[0024] The application will be further described below in connection with the drawings and examples.

[0025] Figure 1 is a top view schematic diagram of the tuyere of the tertiary air pipe in Example 3.

[0026] Figure 2 is a schematic diagram of the A-A cross section of the tuyere structure.

[0027] Figure 3 is a schematic diagram of the A-A cross section of another tuyere structure. DETAILED DESCRIPTION

[0028] The application will be further described below in connection with the drawings and examples in the embodiments of the application, and the description herein is only used to explain the application, but not as a limitation on the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor, any modification, equivalent replacement, improvement, etc. should be included in the protection scope of the application.

[0029] Example 1

[0030] A method for preparing calcium aluminate powder from aluminum ash, comprising the following steps: judging the aluminum content index of secondary aluminum ash, classifying the secondary aluminum ash according to the aluminum content index, and obtaining raw aluminum ash by matching different types of secondary aluminum ash, and controlling the aluminum content index of the raw aluminum ash.

[0031] The method for judging the aluminum content index of secondary aluminum ash is that a weighing mechanism is arranged at the aluminum ash outlet and the aluminum sheet outlet of the screening equipment after the ball milling of the primary aluminum ash, the weight m1 of the aluminum ash at the aluminum ash outlet and the weight m2 of the aluminum sheet at the aluminum sheet outlet are weighed, the ratio m2 / m1 of the aluminum sheet weight and the aluminum ash weight in a period is calculated, and m2 / m1 is taken as the aluminum content index of the secondary aluminum ash.

[0032] After the primary aluminum ash is ground by the ball mill, the roller screen is generally used for screening, the aluminum sheet after calendering is separated and conveyed away from the aluminum sheet outlet, and the secondary aluminum ash is conveyed away along the aluminum ash outlet. In this embodiment, a belt scale can be arranged at the belt conveyor at the aluminum ash outlet and the aluminum sheet outlet as the weighing mechanism to monitor the weight of the screened aluminum ash and the weight of the aluminum sheet in real time. The statistical period can be divided according to different incoming batches. As shown in the following table:

[0033]

[0034]

[0035] It can be seen that this indicator can accurately reflect the metallic aluminum content in secondary aluminum ash. The m2 / m1 ratio of the secondary aluminum ash after aluminum extraction in the third batch is greater than 0.3, and the aluminum content is higher than 7%, making calcination control difficult. Mixing the third batch with the second batch of secondary aluminum ash at a ratio of 1:2 can control the m2 / m1 ratio to within 0.3.

[0036] Example 2

[0037] The method in this embodiment can be implemented alone or in combination with Embodiment 1. When the aluminum content of the raw material aluminum ash is high, the influence of metallic aluminum is significant, making calcination control difficult. The control method in this embodiment is as follows: monitor the flue gas temperature t1 at the kiln tail of the rotary kiln. When t1 is below the control range, first slightly increase the tertiary air volume. If feedback indicates t1 is rising, gradually increase the tertiary air volume until t1 reaches the control range. If feedback indicates t1 is falling, adjust the tertiary air volume back to its original value, then slightly increase the rotary kiln negative pressure. If feedback indicates t1 is rising, gradually increase the negative pressure until t1 reaches the control range. The control range for t1 is 900–1000℃.

[0038] The tertiary air volume is controlled by the frequency of the tertiary air fan inverter. For example, when t1 is 850℃, if the tertiary air fan frequency is increased from 15Hz to 16Hz, and the t1 feedback temperature increases, the tertiary air fan frequency is gradually increased to 20Hz, eventually raising t1 to 950℃. If, after increasing the tertiary air fan frequency, the t1 feedback temperature decreases instead, the tertiary air fan frequency is adjusted back to 15Hz, and the kiln tail negative pressure is increased from -55Pa to -57Pa. When the feedback t1 increases, the negative pressure is gradually increased to -60Pa, eventually raising t1 to 920℃.

[0039] Example 3

[0040] The solution in this embodiment can be combined with Embodiment 1 or 2, or it can be implemented alone. This solution improves the structure of the tuyeres in the rotary kiln to enhance the oxygen supply to the material bed. For example... Figure 1 Specifically, an auxiliary air duct 2 is installed at the air nozzle 1 of the tertiary air duct of the rotary kiln, and the auxiliary air duct 2 is connected to the main air duct 3; the opening of the auxiliary air duct is located on the side of the air nozzle; the opening of the auxiliary air duct faces the kiln head end and is away from the rotation direction of the rotary kiln. When the rotary kiln rotates, the opening of the auxiliary air duct is away from the material flow direction; the height of the opening of the auxiliary air duct from the bottom of the air nozzle is less than the thickness of the material layer inside the rotary kiln.

[0041] The angle between the axis of the secondary duct opening and the longitudinal section of the air nozzle is 50–60°, and the angle between the axis of the secondary duct opening and the cross-section of the air nozzle is 70–80°. For example... Figure 2 As shown in Figure 3, the angle between the axis of the secondary duct opening and the longitudinal section of the nozzle is 57°, and the angle between the axis of the secondary duct opening and the cross section of the nozzle is 75°.

[0042] The main air pipe is provided with a tapered neck 4 at the joint with the auxiliary air pipe. The auxiliary air pipe 2 is connected to the tapered neck.

[0043] As Figure 3 The joint of the auxiliary air pipe with the main air pipe is located outside the kiln body of the rotary kiln. The auxiliary air pipe is provided with a valve 5 at the joint. The dust concentration sensor is arranged in the kiln tail flue of the rotary kiln. When the measured value of the dust concentration sensor is higher than the control range, the valve opening of the auxiliary air pipe is reduced.

[0044] Compared with the calcination process control before the improvement. Before the improvement, the rotary kiln tail part has many ring forming times, needs to stop the kiln to burn the ring, and the product sampling analysis dissolution rate index is 92-93%. After the improvement, the rotary kiln ring forming times are reduced, and the product dissolution rate index is improved to 95%.

Claims

1. A method for controlling the calcination of calcium aluminate powder prepared from aluminum ash, characterized in that, Includes the following steps: The aluminum content of the secondary aluminum ash is determined, and the secondary aluminum ash is classified according to the aluminum content. Different types of secondary aluminum ash are mixed to obtain raw material aluminum ash, and the aluminum content of the raw material aluminum ash is controlled. The method for judging the aluminum content index of secondary aluminum ash is as follows: weighing mechanisms are set at the aluminum ash outlet and aluminum sheet outlet of the screening equipment after primary aluminum ash ball milling. The weight of aluminum ash at the aluminum ash outlet (m1) and the weight of aluminum sheet at the aluminum sheet outlet (m2) are weighed. The ratio of aluminum sheet weight to aluminum ash weight (m2 / m1) within one cycle is calculated, and m2 / m1 is used as the aluminum content index of secondary aluminum ash. Monitor the kiln tail flue gas temperature t1 of the rotary kiln. When t1 is lower than the control range, first slightly increase the tertiary air volume. When the feedback t1 increases, gradually increase the tertiary air volume until the temperature of t1 rises to the control range. When the feedback t1 decreases, adjust the tertiary air volume back to the original value, and then slightly increase the rotary kiln negative pressure. When the feedback t1 increases, gradually increase the negative pressure until the temperature of t1 rises to the control range. A secondary air duct is installed at the air nozzle of the tertiary air duct of the rotary kiln, and the secondary air duct is connected to the main air duct; the opening of the secondary air duct is located on the side of the air nozzle; the opening of the secondary air duct faces the kiln head end and is away from the rotation direction of the rotary kiln. The distance between the opening of the secondary air duct and the bottom of the air nozzle is less than the thickness of the material layer inside the rotary kiln.

2. The method for controlling the calcination of calcium aluminate powder prepared from aluminum ash according to claim 1, characterized in that: The ratio of m2 / m1 of the raw material aluminum ash should be controlled to be no higher than 0.

3.

3. The method for controlling the calcination of calcium aluminate powder prepared from aluminum ash according to claim 1, characterized in that: The control range of t1 is 900~1000℃.

4. The method for controlling the calcination of calcium aluminate powder prepared from aluminum ash according to claim 1, characterized in that: The angle between the axis of the secondary air duct opening and the longitudinal section of the air nozzle is 50-60°, and the angle between the axis of the secondary air duct opening and the cross section of the air nozzle is 70-80°. The opening is inclined towards the bottom of the air nozzle.

5. The method for controlling the calcination of calcium aluminate powder prepared from aluminum ash according to claim 1, characterized in that: The main air duct is provided with a tapered end at the connection between it and the secondary air duct.

6. The method for controlling the calcination of calcium aluminate powder prepared from aluminum ash according to claim 1, characterized in that: The connection between the auxiliary air duct and the main air duct is located outside the rotary kiln body. A valve is installed along the connection of the auxiliary air duct. A dust concentration sensor is installed in the kiln tail flue of the rotary kiln. When the measured value of the dust concentration sensor is higher than the control range, the valve opening of the auxiliary air duct is reduced.

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