An alkali lime sintering process for extracting alumina from fly ash

Abstract

The present application relates to a kind of alkali lime sintering process for extracting alumina from fly ash, comprising the following steps: 1) dry raw material includes by weight parts: fly ash 35-45 parts, limestone 20-35 parts, soda 20-40 parts;Starch is mixed with lye, and heated to 80-85 DEG C;The weight of starch is 3%-5% of dry raw material;2) the dry raw material is mixed, and it is put into lye containing starch and mixed again;Ball is made on disc balling machine, when the particle size of ball reaches about 10, stop adding lye, and add fly ash on the surface of ball;When the particle size is about 12, stop adding fly ash, and get green ball;3) drying, sintering to get clinker.The advantages are: using widely sourced starch, can form biomass carbon after entering high temperature, can reduce sulfate in ball, reduce alkali consumption, and there is no residue after sintering, no effect on the following process.Clinker strength reaches more than 500 N / individual ball.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fly ash recycling, and particularly relates to an alkali lime sintering process for extracting alumina from fly ash. BACKGROUND

[0002] Fly ash is a product after coal is burned as fuel, and is mainly from power plants. Coal is ground into coal powder below 100 μm in power plants, and is sprayed into a combustion furnace for suspension combustion to produce high-temperature flue gas mixed with a large amount of combustion residues. After dust removal, fly ash is obtained. The composition of fly ash is different with different fuel coals, and mainly includes silicon dioxide, aluminum oxide, iron oxide, calcium oxide and completely burned carbon. In addition, it also contains a small amount of K, P, S, Mg and other compounds, and some trace elements. Most power plants in China use bituminous coal as fuel, and the content of calcium oxide in fly ash is low, and the content of aluminum oxide is generally high.

[0003] At present, the utilization of fly ash is still in the initial stage, and the utilization rate of fly ash is not high. Moreover, the utilization level of fly ash in China is not balanced, and the utilization rate in some areas has reached more than 50%, but in Inner Mongolia Autonomous Region and Hainan, the utilization rate is less than 5%. With the increasing demand for electricity, a large amount of fly ash will be produced every year, and if the fly ash cannot be well utilized, it will cause environmental pollution.

[0004] Fly ash often contains a large amount of metal aluminum, and when the content of aluminum oxide is more than 25%, aluminum oxide can be recovered therefrom. The commonly used method is alkali lime sintering method, and has been put into production. The process includes raw material batching and sintering, dissolution of clinker, desilication of crude liquid, carbonation decomposition, and calcination of aluminum hydroxide. After batching and sintering, the aluminum in fly ash is converted into sodium aluminate, which is dissolved by dilute alkali solution to obtain sodium aluminate solution. After purification, aluminum hydroxide is obtained after carbonation, and the remaining mother liquor can be recycled. The main alkali lime sintering equipment at present is a rotary kiln, which is divided into a drying zone, a preheating zone, a decomposition zone, a sintering zone and a cooling zone. However, as a sintering equipment, the rotary kiln is easy to form a liquid phase in the sintering process, which causes the rotary kiln to be ringed, directly affecting the normal production. In addition, Na2SO4 is easy to accumulate on the equipment, increasing the alkali consumption.

[0005] In order to effectively utilize fly ash resources and reduce environmental pollution, domestic scientific research institutions and research institutions have also carried out a lot of research on the comprehensive utilization of fly ash. For example: patent application number CN202210408872.6 discloses a method for producing alumina from fly ash and recycling auxiliary materials, which adopts mineral processing technology and hydrometallurgy technology to produce alumina; patent application number: CN201610083890.6 discloses a method for producing alumina from high-aluminum fly ash, limestone is added to fly ash, soda ash and lye for batching, granulated by a roller granulator, and then sintered on a sintering machine, and the clinker powder is added to the adjusting liquid for dissolution. The efficient comprehensive utilization of fly ash is realized, and different specifications of calcium silicate by-products can be produced by controlling the batching formula, sintering conditions and dealkalization conditions; patent application number: CN201610083295.2 discloses a method for producing alumina from high-aluminum fly ash, which adds limestone to fly ash, soda ash and lye for batching, and uses a disc balling machine to make pellets, and the finished pellets are sintered into sintered pellets after drying, drying, preheating, sintering and cooling. The method realizes the efficient comprehensive utilization of fly ash and can produce calcium silicate by-products of different specifications. However, the burst temperature of the fly ash pellets used in this method is very low, and the pellets must be dried at a low temperature (100-130℃), the heating time is relatively long, and the use of belt sintering machine sintering is easy to cause the bonding between the pellets and the grate bars.

[0006] At present, there are still some limitations in the comprehensive utilization of fly ash. The sintering process has special requirements for raw materials or special requirements for sintering equipment, so it still needs a lot of work to realize the sintering of fly ash with soda lime. SUMMARY

[0007] The purpose of the present application is to provide an alkali lime sintering process for extracting alumina from fly ash, which can extract alumina from fly ash and realize the recycling of fly ash. The widely available starch is used to improve the index of green balls, and the biomass carbon formed at high temperature is used to reduce the alkali consumption. It can reduce the occurrence of equipment scaling and ensure the normal operation of the equipment.

[0008] To achieve the above purpose, the present application realizes the following technical scheme:

[0009] An alkali lime sintering process for extracting alumina from fly ash, comprising the following steps:

[0010] 1) Raw material preparation

[0011] The dry raw materials include, by weight: fly ash 35-45 parts, limestone 20-35 parts, soda ash 20-40 parts;

[0012] The starch is mixed with alkali liquor and heated to 80-85 DEG C; the alkali liquor has a concentration of 100-520 g / L of Na2O; the weight of the starch is 3-5% of the dry raw materials, and the weight of the alkali liquor is 7.0-7.5% of the dry raw materials;

[0013] 2) batching into balls

[0014] The dry raw materials are mixed and put into the alkali liquor containing starch and mixed again; the balling is carried out on a disc balling machine, when the ball size reaches 10±0.5 mm, the addition of alkali liquor is stopped, and the fly ash is added on the surface of the balls to form a fly ash layer on the surface of the balls;

[0015] When the size is 12±0.5 mm, the addition of fly ash is stopped, and the balls are continuously rolled for 2±0.5 min and then taken out to obtain green balls;

[0016] 3) drying

[0017] The green balls are taken out and dried at 450-600 DEG C, with a wind speed of 1.5±0.2 m / s and a material layer thickness of 150±5 mm; after drying for 4-5 min, sintering is started;

[0018] 4) sintering

[0019] The temperature is increased to 1250-1300 DEG C, and sintering is carried out for 30-35 min to obtain clinker.

[0020] The starch contains more than 90% of -200 mesh starch by weight.

[0021] The ratio of the amount of the alkali liquor containing starch added in the mixing to the amount of the alkali liquor added in the disc balling machine in step 2) is (8.5-9.5):(0.5-1.5).

[0022] The green balls have a drop strength of ≥5.0 times per ball, a green ball compression strength of ≥12.0 N per ball, and a burst temperature of 500 DEG C or above.

[0023] The dry balls after drying in step 3) have a strength of ≥500 N per ball.

[0024] The roasting equipment used in step 4) is one of a shaft furnace, a belt roasting machine and a rotary kiln.

[0025] The clinker in step 4) is dissolved with alkali liquor, and the dissolution rate of alumina in the fly ash is above 85%.

[0026] The starch is corn starch or potato starch.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. The application uses widely available starch, which is gelatinized by alkali liquor, can significantly improve the index of green ball, and the green ball will not be damaged after falling 5 times / 0.5m, the compressive strength is more than 12N / ball, and the burst temperature is more than 550℃.

[0029] 2. The starch added in the application can form biomass carbon after entering high temperature, can reduce sulfate in the pellet, reduce alkali consumption, and there is no residue after sintering, which has no effect on the subsequent process.

[0030] 3. The dry ball strength of the application after drying is more than 500N / ball.

[0031] 4. In the application, the dry ball does not adhere to each other during sintering, and is not easy to produce fouling phenomenon, which can be used in belt machine, shaft furnace, rotary kiln and other production equipment, does not affect the normal production of equipment, and does not increase the alkali consumption.

[0032] 5. In the application, the dry ball strength is high, and the starch inside forms biomass carbon, which can also improve the internal temperature of the pellet during combustion, and shorten the preheating time.

[0033] 6. Due to the addition of starch binder, the porosity of the product is increased, and the dissolution rate of the finished product is more than 85%. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is the process flow chart of the application. DETAILED DESCRIPTION

[0035] The application will be described in detail below in conjunction with the drawings of the specification, but it should be pointed out that the implementation of the application is not limited to the following embodiments.

[0036] See Figure 1 An alkali lime sintering process for extracting alumina from fly ash, the raw materials are: fly ash, limestone, solid sodium carbonate is industrial chemical pure. The fineness of corn starch is more than 90% of -200 mesh. The alkali liquor is the alkali liquor with a concentration of 100-500g / L, which is recycled on site. 3%-5% of corn starch is added to the alkali liquor, heated and gelatinized, and then balling is carried out on the disc balling machine. The main chemical components and particle size composition of fly ash and limestone are shown in Table 1 and Table 2.

[0037] Table 1 Chemical composition test results of solid raw materials

[0038]

[0039] Table 2 Test results of raw material particle size composition

[0040]

[0041] Example 1

[0042] The soda lime sintering process for extracting alumina from fly ash includes the following steps:

[0043] 1) Raw material preparation

[0044] The dry raw material consists of the following components by weight percentage:

[0045] Fly ash 35%, limestone 25%, soda ash 40%.

[0046] The alkali concentration is Na2O 100 g / L, and 4% of the dry raw material weight of corn starch is added to the alkali solution, the weight of the alkali solution is 7.2% of the dry raw material, heated to 80°C for standby.

[0047] 2) Balling

[0048] Mix the dry raw material and add the alkali solution containing corn starch and mix again. And on the disc balling machine, balling is carried out. When the pellet size reaches 10±0.5mm, stop adding alkali solution, and continue to add fly ash on the surface of the pellets. Make the fly ash layer on the surface of the pellets, when the particle size is 12±0.5mm, stop adding fly ash, let the pellets roll for a certain time and take out, get green balls.

[0049] 3) Drying

[0050] Take out the green balls and dry at 500°C, air speed 1.5m / s, bed thickness 150mm (bed refers to the thickness of the green ball accumulation), after drying, increase to 1280°C in 4-5min.

[0051] 4) Sintering

[0052] The sintering temperature is relatively high, at 1280°C, sintering for 30min, sintering is completed.

[0053] 5) Leaching

[0054] The raw material is leached with alkali solution, the leaching rate of alumina is 81%.

[0055] Example 2

[0056] The soda lime sintering process for extracting alumina from fly ash includes the following steps:

[0057] 1) Raw material preparation

[0058] The dry raw material consists of the following components by weight percentage:

[0059] Fly ash 40%, limestone 35%, soda ash 25%.

[0060] The alkali solution concentration is 510 g / L Na₂O. 4% (by weight of the dry raw material) of corn starch is added to the alkali solution and heated to 80°C. The weight of the alkali solution is 7.1%–7.4% of the dry raw material.

[0061] 2) Ingredients are mixed and formed into balls.

[0062] The dry raw materials are mixed evenly, and then an alkaline solution containing corn starch is added and mixed again. The mixture is then pelletized on a disc pelletizer. When the pellet size reaches 10±0.5 mm, the addition of alkaline solution is stopped, and fly ash is added to the surface of the pellets. This forms a fly ash layer on the surface of the pellets. When the particle size reaches 12±0.5 mm, the addition of fly ash is stopped, and the pellets are allowed to roll for a certain period of time before being removed to obtain green pellets.

[0063] 3) Drying

[0064] The green balls are taken out and dried at 600℃ with a wind speed of 1.5m / s and a material layer thickness of 150mm. After drying, the temperature is raised to 1250℃ in 4-5 minutes.

[0065] 4) Sintering

[0066] The sintering temperature is relatively high, and sintering is completed at 1250℃ for 30 minutes.

[0067] 5) Dissolution

[0068] The clinker was leached with an alkaline solution, and the alumina leaching rate was 85%.

[0069] Example 3

[0070] The quicklime sintering process for extracting alumina from fly ash includes the following steps:

[0071] 1) Raw material preparation

[0072] The dry raw material consists of the following components by weight percentage:

[0073] Fly ash 45%, limestone 30%, soda ash 25%.

[0074] The alkali solution concentration is 320 g / L Na₂O. 4% (by weight of the dry raw material) of corn starch is added to the alkali solution and heated to 80°C. The alkali solution should be 7.2%–7.3% of the dry raw material weight.

[0075] 2) Ingredients are mixed and formed into balls.

[0076] The dry raw materials are mixed, and the alkali solution containing corn starch is added and mixed again, and then balling is performed on a disc balling machine. When the balling particle size reaches 10 ± 0.5 mm, the addition of alkali solution is stopped, and the fly ash is continuously added on the surface of the balling. The fly ash layer is formed on the surface of the balling, and when the particle size is 12 ± 0.5 mm, the addition of fly ash is stopped, and the balling is rolled for a certain time to obtain the green ball.

[0077] 3) Drying

[0078] The green ball is dried at 550°C, the wind speed is 1.5 m / s, the material layer thickness is 150 mm, and after drying for 4-5 min, it is raised to 1280°C.

[0079] 4) Sintering

[0080] The sintering temperature is relatively high, and the sintering is performed at 1280°C for 30 min, and the sintering is completed.

[0081] 5) Dissolution

[0082] The raw material is dissolved in alkali solution, and the dissolution rate of aluminum oxide is 83%.

[0083] Example 4

[0084] The soda lime sintering process for extracting aluminum oxide from fly ash includes the following steps:

[0085] 1) Raw material preparation

[0086] The dry raw materials are composed of the following components by weight percentage:

[0087] Fly ash 40%, limestone 30%, and soda ash 30%.

[0088] The alkali solution has a concentration of Na2O 370 g / L, and 4% of the weight of the dry raw material corn starch is added to the alkali solution and heated to 80°C for standby. The weight of the alkali solution is 7.2%-7.5% of the weight of the dry raw material.

[0089] 2) Proportioning and balling

[0090] The dry raw materials are mixed, and the alkali solution containing corn starch is added and mixed again, and then balling is performed on a disc balling machine. When the balling particle size reaches 10 ± 0.5 mm, the addition of alkali solution is stopped, and the fly ash is continuously added on the surface of the balling. The fly ash layer is formed on the surface of the balling, and when the particle size is 12 ± 0.5 mm, the addition of fly ash is stopped, and the balling is rolled for a certain time to obtain the green ball.

[0091] 3) Drying

[0092] The green ball is dried at 500°C, the wind speed is 1.5 m / s, the material layer thickness is 150 mm, and after drying for 4-5 min, it is raised to 1250°C.

[0093] 4) Sintering

[0094] Sintering temperature is relatively high, at 1250℃, sintering 30min, sintering is completed.

[0095] 5) Dissolution

[0096] The base solution is dissolved in the material, and the dissolution rate of alumina is 86%.

Claims

1. A quicklime sintering process for extracting alumina from fly ash, characterized in that, Includes the following steps: 1) Raw material preparation The dry raw materials include, by weight: 35-45 parts fly ash, 20-35 parts limestone, and 20-40 parts soda ash; Starch is mixed with alkaline solution and heated to 80-85℃; the concentration of alkaline solution is 100-520 g / L of Na2O; the weight of starch is 3%-5% of the dry raw material, and the weight of alkaline solution is 7.0%-7.5% of the dry raw material. 2) Ingredients are mixed and formed into balls. Mix the dry raw materials evenly, add the starch-containing alkaline solution and mix again; pelletize on a disc pelletizer, and when the pellet size reaches 10±0.5mm, stop adding alkaline solution and add fly ash to the surface of the pellets to form a fly ash layer on the surface of the pellets. When the particle size is 12±0.5mm, stop adding fly ash, and take out the pellets after rolling for another 2±0.5min to obtain green pellets; The green pellets have a drop strength of ≥5.0 drops / pellet, a compressive strength of ≥12.0 N / pellet, and a bursting temperature of ≥500℃; 3) Drying Take out the green pellets and dry them at 450-600℃ with an air velocity of 1.5±0.2m / s and a material layer thickness of 150±5mm. After drying, sintering begins 4-5 minutes later. The strength of the dried pellets is ≥500N / pellet. 4) Sintering The temperature is raised to 1250-1300℃ and sintered for 30-35 minutes to obtain clinker.

2. The soda lime sintering process for extracting alumina from fly ash according to claim 1, characterized in that, The starch comprises more than 90% by weight of -200 mesh starch.

3. The soda lime sintering process for extracting alumina from fly ash according to claim 1, characterized in that, The ratio of the amount of starch-containing alkaline solution added during mixing to the amount added in the disc pelletizer in step 2) is (8.5-9.5):(0.5-1.5).

4. The soda lime sintering process for extracting alumina from fly ash according to claim 1, characterized in that, The roasting equipment used in step 4) is one of the following: vertical furnace, belt roaster, or rotary kiln.

5. The soda lime sintering process for extracting alumina from fly ash according to claim 1, characterized in that, In step 4), the clinker is dissolved in alkaline solution, and the alumina dissolution rate in fly ash is over 85%.

6. The soda lime sintering process for extracting alumina from fly ash according to claim 1, characterized in that, The starch mentioned is corn starch or potato starch.

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