A method and system for preparing calcium aluminate powder from primary aluminum ash

Abstract

The present invention relates to a method and system for preparing calcium aluminate powder from primary aluminum ash in the field of calcium aluminate preparation, and the method comprises the following steps: 1) extracting aluminum from primary aluminum ash to obtain raw aluminum ash; 2) mixing and grinding the raw aluminum ash with raw gypsum to obtain raw material; 3) heating the raw material to a defluorination temperature for defluorination, and then heating it to a reaction temperature after defluorination to calcine calcium aluminate to obtain clinker; the defluorination temperature is not higher than 1000°C; the reaction temperature is not lower than 1400°C; 4) the clinker is crushed and ground to obtain calcium aluminate powder. The present invention can shorten the production process of preparing calcium aluminate powder for water purifier raw material from primary aluminum ash, reduce costs, and improve production efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium aluminate preparation, and particularly relates to a method and a system for preparing calcium aluminate powder from primary aluminum ash. Background Art

[0002] When using aluminum ash to prepare calcium aluminate powder as a raw material for water purifiers, it is necessary to focus on the defluorination, denitrification and heavy metal removal of the aluminum ash. Since the calcination temperature of calcium aluminate is as high as 1400°C, high-temperature denitrification and heavy metal removal can be achieved. However, the raw materials for the preparation of calcium aluminate contain limestone, which decomposes into calcium oxide at high temperature. If aluminum ash is directly mixed with limestone to prepare calcium aluminate, the fluorine in the aluminum ash will combine with calcium oxide under high temperature conditions to form high-temperature stable calcium fluoride, so defluorination cannot be completed.

[0003] Some of the technologies that have been made public for recovering aluminum ash and producing calcium aluminate are mostly used in cement building materials and have no strict requirements on fluorine content.

[0004] In the prior art, when using aluminum ash to prepare calcium aluminate powder used as a raw material for water purifiers, the aluminum ash is generally subjected to two-stage ball milling to screen out the metallic aluminum, and then a defluorinating agent is added for calcination. During the calcination process, the aluminum ash is defluorinated, denitrified and heavy metals are removed to obtain a high-aluminum inorganic material, which is then mixed with limestone and calcined to prepare calcium aluminate powder.

[0005] The above process involves the preparation of intermediate products, high-aluminum inorganic materials, which requires two high-temperature calcinations and cooling. The process is long, energy-intensive, increases production costs, and has low efficiency. Summary of the invention

[0006] The technical problem to be solved by the present invention is to shorten the process of preparing calcium aluminate powder from aluminum ash and improve production efficiency. The technical solution adopted is:

[0007] A method for preparing calcium aluminate powder from primary aluminum ash comprises the following steps:

[0008] 1) The primary aluminum ash is subjected to aluminum extraction to obtain raw aluminum ash;

[0009] 2) Raw materials aluminum ash and raw gypsum are mixed and ground to obtain raw material;

[0010] 3) The raw material is first heated to the defluorination temperature for defluorination, and then heated to the reaction temperature for calcium aluminate calcination to obtain clinker; the defluorination temperature is not higher than 1000°C; the reaction temperature is not lower than 1400°C;

[0011] 4) The clinker is crushed and ground to obtain calcium aluminate powder.

[0012] In this scheme, raw gypsum is selected to replace limestone to react with aluminum ash to prepare calcium aluminate powder, thereby shortening the production process of preparing calcium aluminate powder from aluminum ash, reducing costs and improving production efficiency.

[0013] Limestone begins to decompose at 800°C and decomposes rapidly at 900°C. When it is mixed with aluminum ash and calcined, the calcium oxide and fluorine generated combine to form stable calcium fluoride.

[0014] The properties of gypsum are relatively stable, and the decomposition starting temperature is above 1200°C. Therefore, the defluorination and decomposition of gypsum can be carried out in stages to avoid the combination of calcium oxide generated after the decomposition of gypsum with fluorine.

[0015] In the prior art, the defluorination of aluminum ash requires the addition of about 10% of a defluorinating agent. The defluorinating agent is generally selected from aluminum tailings with bound water. The principle is that the bound water generates water vapor under heating conditions, and the water vapor reacts with fluoride salts to generate gaseous hydrogen fluoride and volatilizes. The defluorination efficiency is related to the amount of defluorinating agent added, the defluorination temperature and the defluorination time. When the amount of defluorinating agent added is large, defluorination can be achieved at a lower temperature.

[0016] In this scheme, raw gypsum is selected as the raw material. Raw gypsum itself contains crystal water and can act as a defluorinating agent. Moreover, the addition amount of raw gypsum as the raw material is large, which can improve the defluorination efficiency and is also conducive to the staged defluorination and gypsum decomposition.

[0017] Specifically, the mass ratio of aluminum ash to raw gypsum in step 2) is 1-2: 1. The specific ratio of aluminum ash to raw gypsum is determined according to the equivalent of Al2O3 and CaO.

[0018] In a specific improvement of the present invention, in step 3), defluorination and calcium aluminate calcination are carried out in separate heating areas in sequence; after the raw material is defluorinated, coal powder is added and mixed to carry out calcium aluminate calcination.

[0019] Under reducing conditions, such as when mixed with coal powder, the decomposition starting temperature of gypsum can be reduced to below 1000°C. In the improved scheme, defluorination and calcium aluminate sintering are carried out separately, and coal powder can be mixed in after defluorination is completed to improve the decomposition efficiency of gypsum and facilitate the sintering of calcium aluminate.

[0020] In the present invention, the tail gas from the calcination of calcium aluminate in step 3) is used to prepare sulfuric acid. The calcination stage includes the decomposition of gypsum, and the product of the gypsum decomposition contains a large amount of sulfur dioxide, which can be introduced into the sulfuric acid production system to convert sulfur dioxide into sulfur trioxide through catalytic oxidation, and produce sulfuric acid as a by-product.

[0021] The present invention provides a system for preparing calcium aluminate powder from primary aluminum ash, which is used to implement the method of the present invention, and includes a raw material processing section and a firing section. The raw material processing section includes a grinding mechanism, and the grinding mechanism is provided with a raw aluminum ash inlet, a raw gypsum inlet and a raw material outlet. The firing section includes a rotary kiln, and the raw material outlet is connected to the rotary kiln feed port. The raw material processing section may also include aluminum extraction equipment for primary aluminum ash and crushing and grinding equipment for raw gypsum. The aluminum extraction of primary aluminum ash may adopt multi-stage ball milling and screening to separate and recover metallic aluminum in the primary aluminum ash. The treated raw aluminum ash and raw gypsum enter the grinding mechanism together for mixing to produce raw material. The grinding mechanism may adopt a ball mill or a roller mill.

[0022] In view of an improved method in the present invention, the system of the present invention also proposes corresponding improvements, wherein a pre-decomposition furnace is provided in the firing section, the raw material outlet is first connected to the pre-decomposition furnace, and the pre-decomposition furnace is then connected to the feed port of the rotary kiln; the feed port of the rotary kiln is also provided with a coal powder inlet. Accordingly, the defluorination of the raw material is carried out in the pre-decomposition furnace, and the decomposition of gypsum and the firing of calcium aluminate are carried out in the rotary kiln.

[0023] Different from the improved system, specifically, the firing section does not have a pre-decomposition furnace, and the rotary kiln uses gaseous or liquid fuel. When the pre-decomposition furnace is not set, the defluorination of the raw meal and the firing of calcium aluminate are both carried out in the rotary kiln. In order to achieve the staged defluorination and firing of calcium aluminate, it is necessary to avoid the premature decomposition of gypsum. When solid fuels, such as coal powder, are used as the fuel of the rotary kiln, the combustion speed is slow, and the coal powder that does not have time to be completely burned will be mixed into the raw meal, promoting the premature decomposition of gypsum. When the decomposition of gypsum and the defluorination of the raw meal are carried out simultaneously, calcium fluoride may be generated and affect the defluorination. Therefore, when the pre-decomposition furnace is not set, the rotary kiln uses gaseous or liquid fuel combustion to provide heat, such as natural gas, coal gas or heavy oil.

[0024] When the pre-calcining furnace is not set, the decomposition of gypsum occurs in the high temperature section of the rotary kiln, which may affect the burning of calcium aluminate. To address this problem, a first measuring point is set in front of the secondary air duct of the rotary kiln; the first measuring point is used to detect the sulfur dioxide concentration at the front end of the blast port of the secondary air duct in the rotary kiln; when the sulfur dioxide concentration at the first measuring point exceeds the threshold, the air intake of the secondary air duct is increased. Increasing the air intake of the secondary air duct can increase the temperature of the calcining zone near the kiln head, accelerate the decomposition of gypsum, and facilitate the burning of calcium aluminate.

[0025] Furthermore, in order to improve the segmented control effect of defluorination and firing in the rotary kiln, a second measuring point is set in front of the tertiary air duct of the rotary kiln. The second measuring point is used to detect the concentration of hydrogen fluoride at the front end of the blast port of the tertiary air duct in the rotary kiln. When the concentration of hydrogen fluoride at the second measuring point exceeds the threshold, the air intake of the tertiary air duct is increased. Increasing the air intake of the tertiary air duct can increase the temperature of the heating zone near the kiln tail and accelerate the defluorination of the raw material.

[0026] Specifically, a gas concentration detection mechanism is set at the first measuring point and the second measuring point, and the gas concentration detection mechanism includes a sampling air duct, the sampling air duct is provided with a sampling port, a draft fan and a detection chamber, and the sampling port is set at the front end of the blower port of the secondary air duct or the tertiary air duct; the sampling air duct is connected to a radiator, and the radiator is set at the air inlet of the secondary air duct or the tertiary air duct.

[0027] The present invention uses raw gypsum and aluminum ash to react to prepare calcium aluminate powder, and the raw gypsum can also play a defluorination role without adding an external defluorination agent. The present invention can use aluminum ash to prepare calcium aluminate powder for water purifier raw materials, and compared with the prior art, the process flow can be shortened, the cost can be reduced, and the production efficiency can be improved. In addition, the present invention can also produce sulfuric acid as a by-product when preparing calcium aluminate powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0029] Figure 1 It is a schematic diagram of the process of preparing calcium aluminate powder from primary aluminum ash in Example 2.

[0030] Figure 2 It is a schematic diagram of the process of preparing calcium aluminate powder from primary aluminum ash in Example 3.

[0031] Figure 3 This is a schematic diagram of the positions of the first measuring point and the second measuring point in Example 3.

[0032] Figure 4 It is a schematic diagram of the gas concentration detection mechanism of Example 3.

[0033] Figure 5 It is a schematic diagram of the location of the sampling port in Example 3. DETAILED DESCRIPTION

[0034] The present invention is described clearly below in conjunction with the drawings and specific embodiments in the embodiments of the present invention. The description herein is only used to explain the present invention, but is not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work, any modifications, equivalent substitutions, improvements, etc., should be included in the protection scope of the present invention.

[0035] The method for preparing calcium aluminate powder from primary aluminum ash comprises the following steps:

[0036] 1) The primary aluminum ash is subjected to aluminum extraction to obtain raw aluminum ash;

[0037] 2) Raw materials aluminum ash and raw gypsum are mixed and ground to obtain raw material;

[0038] 3) The raw material is first heated to the defluorination temperature for defluorination, and then heated to the reaction temperature for calcium aluminate calcination to obtain clinker; the defluorination temperature is not higher than 1000°C; the reaction temperature is not lower than 1400°C;

[0039] 4) The clinker is crushed and ground to obtain calcium aluminate powder.

[0040] The defluorination efficiency in the defluorination stage in step 3) is related to the amount of defluorination agent added, the heating temperature and the heating time.

[0041] At a temperature of 1000°C, there is an obvious relationship between the defluorination rate and the amount of defluorination agent added:

[0042] Defluorination agent addition amount 10％ 20％ 30％ 40％ 50％ Defluorination rate 42％ 45％ 48％ 52％ 65％

[0043] In the prior art, aluminum tailings are added as a defluorinating agent. Considering the heat utilization efficiency, the amount of the defluorinating agent added is controlled below 10%, the temperature is controlled at 1100°C, and the defluorinating rate reaches 66%.

[0044] In this scheme, the raw gypsum in the raw material also acts as a defluorinating agent. According to the ratio of aluminum ash to raw gypsum of 1:1, the heating time is 50 minutes, and the relationship between the defluorination rate and temperature is as follows:

[0045] temperature 600℃ 700℃ 800℃ 900℃ 1000℃ Defluorination rate 42％ 45％ 48％ 58％ 62％

[0046] Select 1000℃ as the defluorination temperature, and the relationship between the defluorination rate and time is as follows:

[0047] time 20min 30min 40min 50min 60min Defluorination rate 32％ 43％ 55％ 62％ 63％

[0048] The sintering temperature of calcium aluminate is above 1400℃. At 1450℃, the relationship between the dissolution rate of calcium aluminate powder and the ratio of aluminum ash and raw gypsum is as follows:

[0049] Ratio 1:1 1.3:1 1.6:1 1.8:1 2.0:1 Dissolution rate 82％ 87％ 92％ 94％ 94％

[0050] The mass ratio of aluminum ash to raw gypsum was selected to be 1:1.8, and the raw aluminum ash powder and raw gypsum powder were mixed, and the temperature was first raised to 1000°C in a laboratory muffle furnace, and kept warm for 50 minutes, and then raised to 1450°C, and kept warm for 30 minutes, and the sintered product was tested for indicators. Three groups of comparative examples were set for comparison, and by comparison, the defluorination effect of Example 1 was the best.

[0051]

[0052]

[0053] Example 2

[0054] The system for preparing calcium aluminate powder from primary aluminum ash in this embodiment is as follows: Figure 1As shown, it includes an aluminum ash ball mill, an aluminum ash screening machine, a raw aluminum ash storage bin, a mixing ball mill, a raw gypsum crusher, a raw gypsum ball mill, a raw gypsum storage bin, a raw material storage bin, a pre-calcining furnace, a rotary kiln, a pulverized coal ball mill, a pulverized coal storage bin, a cooling kiln, a clinker crusher, a clinker ball mill, and a finished product storage bin. The feed port at the end of the rotary kiln is connected to the raw material storage bin, and a pulverized coal inlet is also provided at the feed port.

[0055] After two rounds of ball milling and screening, most of the metallic aluminum is separated from the primary aluminum ash to obtain raw aluminum ash; raw gypsum is crushed and ball milled to obtain raw gypsum powder. The raw aluminum ash and raw gypsum powder are ground and mixed in a mixing ball mill to obtain raw material. The raw material first enters the pre-decomposition furnace, and the temperature is controlled at 900-1000°C for defluorination. Then it is added to the rotary kiln through the feed port at the end of the rotary kiln, and coal powder is added along the feed port. In the rotary kiln, the temperature of the calcination zone is controlled at above 1400°C, and the gypsum is decomposed to generate calcium oxide. At the same time, the aluminum nitride in the aluminum ash is oxidized at high temperature to generate aluminum oxide and nitrogen, completing denitrification. Aluminum oxide and calcium oxide undergo mineralization reaction under high temperature conditions to generate calcium aluminate. At the same time, under high temperature conditions above 1400°C, most of the heavy metals in the aluminum ash are volatilized and removed in the form of chlorides. The tail gas of the pre-decomposition furnace can be treated by water washing and alkali washing. After sedimentation, dust removal and water spraying, the tail gas from the rotary kiln can enter the sulfuric acid production system to recover the sulfur dioxide in the tail gas to produce sulfuric acid.

[0056] The sintered calcium aluminate enters a cooling kiln for cooling, and then is crushed and ball-milled to obtain the finished calcium aluminate powder.

[0057] Example 3

[0058] The system for preparing calcium aluminate powder from primary aluminum ash in this embodiment is as follows: Figure 2 As shown, it includes an aluminum ash ball mill, an aluminum ash screening machine, a raw aluminum ash storage bin, a mixing ball mill, a raw gypsum crusher, a raw gypsum ball mill, a raw gypsum storage bin, a raw material storage bin, a rotary kiln, a cooling kiln, a clinker crusher, a clinker ball mill, and a finished product storage bin. This embodiment does not have a pre-calcining furnace, and defluorination and sintering are both carried out in the rotary kiln. The rotary kiln uses natural gas for heating.

[0059] Traditional rotary kiln systems generally only monitor the flame temperature in the calcining zone, and the temperature zone control is unreliable. For example, when the temperature rise zone is short, the defluorination reaction may continue to the high temperature zone. The temperature zone distribution can be controlled by setting thermocouples in the kiln body. This embodiment provides another solution to adjust and control the temperature distribution in the kiln by monitoring the target gas concentration in the kiln.

[0060] like Figure 3The first measuring point 2 and the second measuring point 3 are set on the kiln body of the rotary kiln. The first measuring point 2 is used to detect the sulfur dioxide concentration at the front end of the blast port of the secondary air duct 4 in the rotary kiln, and the second measuring point 3 is used to detect the hydrogen fluoride concentration at the front end of the blast port of the tertiary air duct 5 in the rotary kiln. In the present invention, the front end refers to the end close to the kiln head 1. The first measuring point and the second measuring point are set with gas concentration detection mechanisms. Figure 4 The gas concentration detection mechanism includes a sampling air duct, which is provided with a sampling port 6, an induced draft fan 10 and a detection chamber 8. Figure 5 The sampling port 6 is arranged at the front end of the tuyere 7 of the secondary or tertiary tuyere, and the sampling tuyere connected to the sampling port is buried in the casting material of the tuyere. Under the negative pressure at the kiln tail of the rotary kiln, the air flow in the kiln flows to the kiln tail. The sampling port is arranged at the front end of the tuyere to avoid the influence of the tuyere on the sampling air flow.

[0061] The sampling air duct is connected to a radiator 9, which is arranged at the air inlet of the secondary air duct or the tertiary air duct. The gas introduced into the sampling air duct is cooled by air cooling to reach a suitable temperature for entering the detection chamber. A corresponding hydrogen fluoride concentration sensor or sulfur dioxide concentration sensor is arranged in the detection chamber.

Claims

1. A method for preparing calcium aluminate powder from primary aluminum ash, characterized in that: The following steps are involved: 1) The primary aluminum ash is extracted to obtain raw aluminum ash; 2) Raw materials aluminum ash and raw gypsum are mixed and ground to obtain raw material; 3) The raw material is first heated to the defluorination temperature for defluorination, and then heated to the reaction temperature for calcium aluminate calcination to obtain clinker; the defluorination temperature is not higher than 1000℃; the reaction temperature is not lower than 1400℃; 4) After the clinker is crushed and ground, calcium aluminate powder is obtained; The system used includes a raw material processing section and a firing section. The raw material processing section includes a grinding mechanism, which is provided with a raw material aluminum ash inlet, a raw gypsum inlet and a raw material outlet. The firing section includes a rotary kiln, and the raw material outlet is connected to the rotary kiln feed port. The firing section does not have a pre-calcining furnace, and the rotary kiln uses gaseous or liquid fuel. Alternatively, the firing section is provided with a pre-decomposition furnace, the raw meal outlet is first connected to the pre-decomposition furnace, and the pre-decomposition furnace is then connected to the rotary kiln feed port; the rotary kiln feed port is also provided with a coal powder inlet; in step 3), defluorination and calcium aluminate firing are carried out in sequence in independent heating areas respectively; after the raw meal defluorination is completed, coal powder is added and mixed to carry out calcium aluminate firing.

2. The method for preparing calcium aluminate powder from primary aluminum ash according to claim 1, characterized in that: The mass ratio of aluminum ash to raw gypsum in step 2) is 1-2:

1.

3. The method for preparing calcium aluminate powder from primary aluminum ash according to claim 1, characterized in that: In step 3), the tail gas from the calcination of calcium aluminate is used to prepare sulfuric acid.

4. The method for preparing calcium aluminate powder from primary aluminum ash according to claim 1, characterized in that: A first measuring point is set in front of the secondary air duct of the rotary kiln; the first measuring point is used to detect the sulfur dioxide concentration at the front end of the tuyere of the secondary air duct in the rotary kiln; when the sulfur dioxide concentration at the first measuring point exceeds a threshold value, the air intake of the secondary air duct is increased.

5. The method for preparing calcium aluminate powder from primary aluminum ash according to claim 1, characterized in that: A second measuring point is set in front of the tertiary air duct of the rotary kiln, and the second measuring point is used to detect the hydrogen fluoride concentration at the front end of the tuyere of the tertiary air duct in the rotary kiln; when the hydrogen fluoride concentration at the second measuring point exceeds a threshold value, the air intake of the tertiary air duct is increased.

6. The method for preparing calcium aluminate powder from primary aluminum ash according to claim 1, characterized in that: A gas concentration detection mechanism is set at the first measuring point and the second measuring point. The gas concentration detection mechanism includes a sampling air duct. The sampling air duct is provided with a sampling port, an induced draft fan and a detection chamber. The sampling port is set at the front end of the blower port of the secondary air duct or the tertiary air duct; the sampling air duct is connected to a radiator, and the radiator is set at the air inlet of the secondary air duct or the tertiary air duct.

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