Method and system for preparing expanding agent and co-producing sulfuric acid by decomposing phosphogypsum

Abstract

The invention discloses a method and a system for preparing an expanding agent and co-producing sulfuric acid by decomposing ardealite, and relates to the technical field of solid waste utilization and concrete admixtures. The method comprises the following steps: mixing ardealite, aluminum slag and fly ash according to a mass ratio of (67-77): (19-27): (4-6), and grinding to obtain a raw material; calcining the raw material at 1250-1350 DEG C for 60-120 minutes to obtain clinker, and collecting SO2-containing flue gas generated by calcining; mixing the clinker, phosphogypsum, limestone and fly ash according to a mass ratio of (60-85): (10-20): (5-10): (5-10), and grinding to obtain an expanding agent; and preparing sulfuric acid by using the SO2-containing flue gas in the step S2. According to the method, mineral components in the raw materials are regulated and controlled, the mode that decomposition of phosphogypsum is promoted under the calcining condition is combined, additional reducing agents do not need to be added, the production cost is reduced, and the process difficulty is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical fields of solid waste utilization and concrete admixture, and particularly relates to a method and system for preparing expansive agent and co-producing sulfuric acid by decomposing phosphogypsum. BACKGROUND

[0002] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the general background of the application and does not necessarily constitute an admission by the patent applicant(s) that this information constitutes prior art nor that this information is entirely accurate.

[0003] Phosphogypsum is a large amount of solid waste produced in the process of preparing phosphoric acid by wet method, and its output ratio is as high as 4.0-6.0 tons per ton of phosphoric acid. Long-term stacking not only occupies land resources, but also causes complex environmental risks to the surrounding soil, water (permeation pollution) and atmosphere (dust diffusion) due to the presence of soluble phosphorus, fluorine and heavy metal impurities.

[0004] Expansive agent is a key admixture for inhibiting the shrinkage and cracking of concrete, and can be divided into calcium sulphoaluminate, calcium oxide and composite (calcium sulphoaluminate-calcium oxide) according to the expansion source. Among them, the calcium sulphoaluminate expansive agent generates ettringite (3CaO·Al2O3·3CaSO4·32H2O) through hydration reaction, and the volume expansion generated by the crystal growth of ettringite can accurately compensate the hardening shrinkage of concrete, thereby significantly reducing the cracking risk of the structure. The traditional process uses natural gypsum (providing CaSO4) and limestone (providing CaO) as raw materials, but the content of calcium sulfate dihydrate (CaSO4·2H2O) in phosphogypsum is >90%, which has the potential to replace natural gypsum. If the resource utilization of phosphogypsum can be realized, not only the pressure of solid waste disposal can be relieved, but also the production cost of expansive agent can be reduced.

[0005] When phosphogypsum is used to replace natural gypsum, due to the high decomposition temperature and low decomposition efficiency of phosphogypsum itself, reducing substances such as coke and high-sulfur coal are often used as reducing agents in the traditional method to make phosphogypsum decompose, which not only leads to the need to control the mixing amount and reaction atmosphere of the reducing agent in the rotary kiln calcination stage, but also causes problems such as unstable decomposition of phosphogypsum, high production energy consumption, serious kiln ring formation and unstable product quality. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method and system for preparing expansive agent and co-producing sulfuric acid by decomposing phosphogypsum, which promotes the decomposition of phosphogypsum by adjusting the components such as Al2O3, Fe2O3 and SiO2 in the raw materials and combining with the calcination conditions, and produces expansive agent with low production cost and stable performance while co-producing sulfuric acid.

[0007] In order to achieve the above-mentioned purpose, the present application is realized by the following technical solutions: The first aspect of the present application provides a method for preparing an expansive agent and co-producing sulfuric acid from phosphogypsum decomposition, comprising the following steps: S1, mixing phosphogypsum, aluminum slag and fly ash according to a mass ratio of (67-77):(19-27):(4-6), and then grinding to obtain raw materials; S2, calcining the raw materials at 1250-1350 DEG C for 60-120 min to obtain clinker, and collecting SO2-containing flue gas generated during calcination; S3, mixing the clinker, phosphogypsum, limestone and fly ash according to a mass ratio of (60-85):(10-20):(5-10):(5-10), and then grinding to obtain an expansive agent; S4, using the SO2-containing flue gas in S2 to prepare sulfuric acid.

[0008] The second aspect of the present application provides a system for preparing an expansive agent and co-producing sulfuric acid from phosphogypsum decomposition, comprising: a proportioning device, a raw material mill, a rotary kiln, a clinker storage, a clinker proportioning device and a clinker mill connected in sequence; the flue gas outlet of the rotary kiln is connected in sequence to a flue gas washing and adsorption device, a converter and an absorption tower.

[0009] The beneficial effects of the present application are as follows: 1. In the present application, by adjusting the components of Al2O3, Fe2O3 and SiO2 in the raw materials, the minerals formed among Al2O3, Fe2O3 and SiO2 promote the decomposition process of phosphogypsum, and the decomposition of phosphogypsum is completed by combining with the calcination conditions, so that the minerals of the clinker are normally formed, and the SO2 flue gas generated can be used for co-production of sulfuric acid. Compared with the method of adding reducing agents such as coke and high-sulfur coal, by adjusting the components of minerals (including Al2O3, Fe2O3 and SiO2) in the raw materials and combining with the calcination conditions to promote the decomposition of phosphogypsum, no additional reducing agent is needed, which reduces the production cost. In addition, it is not necessary to strictly control the amount of reducing agent and the reaction atmosphere, which reduces the process difficulty, makes the calcination process easier to operate, stabilizes the production process, and avoids problems such as serious kiln ring and unstable product quality.

[0010] 2. In the raw material preparation and clinker calcination process of the present application, no limestone is used to provide calcium source, which means that CO2 generated by the decomposition of limestone can be avoided, and the carbon emission in the process is reduced. Although limestone is added in S3, according to the life cycle assessment theory, the carbon emission per unit production of expansive agent and co-production of sulfuric acid is reduced by 18.36% compared with the carbon emission of separate production of expansive agent and sulfuric acid. It can also alleviate the problems of phosphogypsum accumulation and depletion of natural mineral resources, and has high environmental value. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments of the application, and their

[0012] The distances between the parts or the sizes in the figures are exaggerated to show the parts and the sizes clearly.

[0013] Figure 1 is a schematic diagram of a system for preparing an expansive agent and co-producing sulfuric acid by coupling decomposition of phosphogypsum in Example 1. DETAILED DESCRIPTION

[0014] The application will be further described below with reference to the drawings and examples.

[0015] The application provides one or more embodiments of a method for preparing an expansive agent and co-producing sulfuric acid by decomposing phosphogypsum, comprising the following steps: S1, mixing phosphogypsum, aluminum slag and fly ash according to a mass ratio of (67-77):(19-27):(4-6), and grinding to obtain raw materials; S2, calcining the raw materials at 1250-1350°C for 60-120 min to obtain clinker, and collecting SO2-containing flue gas generated during calcination; S3, mixing the clinker, phosphogypsum, limestone and fly ash according to a mass ratio of (60-85):(10-20):(5-10):(5-10), and grinding to obtain an expansive agent; S4, preparing sulfuric acid using the SO2-containing flue gas in S2.

[0016] The aluminum slag is a byproduct generated during aluminum smelting and forming, and contains metal aluminum, aluminum oxide, SiO2, Fe2O3 and MgO and other impurities.

[0017] Fly ash is fine ash collected from flue gas after coal combustion. Fly ash is the main solid waste discharged by coal-fired power plants, and the main oxides are SiO2, Al2O3, FeO, Fe2O3, CaO, TiO2, etc.

[0018] In the above process, Al2O3, Fe2O3 and SiO2 in the aluminum slag and fly ash form target minerals with CaSO4, which can strengthen the decomposition of phosphogypsum. Combined with the set calcination conditions, the decomposition of phosphogypsum is strengthened, the decomposition rate and desulfurization rate of phosphogypsum can be maintained at a high level, and no additional reducing agent such as coke or high-sulfur coal is needed during the calcination process, which reduces the cost and makes the production process easier to operate. In S1 and S3 steps, phosphogypsum is added respectively. In S1, the phosphogypsum serves as a raw material to provide CaSO4 and CaO for the formation of calcium sulfoaluminate, and in S3, the phosphogypsum serves to extend the setting time and reduce the reaction rate.

[0019] Optionally, in S1, the ground raw meal is sieved through a 180-mesh sieve, and the mass percentage of coarse particles (particle size ≥ 80 μm) remaining on the sieve is not more than 30%, so that the obtained raw meal meets the calcination conditions.

[0020] Optionally, in S1, the ground raw meal is homogenized for standby use; the homogenization is carried out in a homogenization library, which is used to adjust the component ratio of the raw meal, the main components of which are calcium sulphoaluminate and dicalcium silicate, and the proportion of calcium sulphoaluminate is more than 70%, and the proportion of calcium sulphoaluminate can be floated between 70% and 90% according to different proportions.

[0021] Optionally, in S2, the calcination equipment is a rotary kiln.

[0022] Optionally, in S3, the clinker, phosphogypsum, limestone and fly ash are mixed and ground according to a mass ratio of (62-64):(16-18):10:10 to obtain the expansion agent.

[0023] Optionally, in S3, the ground raw meal is sieved through a 180-mesh sieve, and the mass percentage of coarse particles (particle size ≥ 80 μm) remaining on the sieve is not more than 10% to meet the product requirements of the expansion agent.

[0024] Optionally, in S4, the SO2-containing flue gas is treated by removing impurities and catalytic conversion to produce sulfuric acid products; the method for preparing sulfuric acid products from SO2-containing flue gas is a conventional technical means in the art, such as contact method for preparing sulfuric acid.

[0025] The one or more embodiments provided by the application provide a system for preparing expansion agent and co-producing sulfuric acid from phosphogypsum, which comprises: sequentially connected proportioning device, raw material mill, rotary kiln, clinker storage, clinker proportioning device and clinker mill; the flue gas outlet of the rotary kiln is sequentially connected with a flue gas washing and adsorption device, a converter and an absorption tower.

[0026] In each component of the above system, the proportioning device is used to mix phosphogypsum, aluminum slag and fly ash according to a mass ratio of (67-77):(19-27):(4-6); the raw material mill is used to grind the material output by the proportioning device to a 0.08 mm sieve residue of not more than 30%; the rotary kiln is used to calcine the raw meal at 1250-1350℃ for 60-120 min to obtain clinker; the clinker storage is used to cool and store the clinker, the clinker proportioning device is used to mix clinker, phosphogypsum, limestone and fly ash according to a mass ratio of (60-85):(10-20):(5-10):(5-10); and the clinker mill is used to grind the material output by the clinker proportioning device to a 0.08 mm square hole sieve residue of 10%.

[0027] Optionally, a raw material mill and a rotary kiln are sequentially provided with a raw material homogenizing bin and a cyclone preheater; the raw material homogenizing bin is used for homogenizing raw materials, and the cyclone preheater is used for preheating the raw materials to 500-600 ℃, which functions to dry and preheat the raw materials.

[0028] Optionally, the clinker mill leads to an expanding agent product bin; the product bin is used for storing the prepared expanding agent.

[0029] Optionally, the flue gas washing and adsorption device comprises a dynamic wave scrubber, a packed tower, an electric demister and a drying tower which are sequentially communicated; the dynamic wave scrubber is used for removing dust, fluorine and arsenic and the like impurities in the flue gas, the packed tower is used for further removing dust, fluorine and arsenic and the like impurities in the flue gas, the electric demister is used for removing acid mist in the flue gas, and the drying tower is used for absorbing water in the flue gas.

[0030] Optionally, a heat exchanger is arranged between the flue gas washing and adsorption device and the converter, which is used for preheating the gas to be transported into the converter and recovering heat.

[0031] Optionally, the absorption tower comprises an intermediate absorption tower, a final absorption tower and a tail gas absorption tower which are sequentially communicated; the intermediate absorption tower is used for preliminarily absorbing SO3 to generate concentrated sulfuric acid, the final absorption tower is used for deeply absorbing residual SO3 to improve the conversion rate, and the tail gas absorption tower is used for treating trace SO2 in the tail gas to meet the discharge standard. SO3

[0032] Embodiment 1 A method for preparing expanding agent and co-producing sulfuric acid by decomposing phosphogypsum, comprising the steps of: S1, the pre-dried phosphogypsum, aluminum slag and fly ash are proportioned, wherein the mass percentage of each component is: phosphogypsum 72.07%, aluminum slag 22.52%, fly ash 5.41%, and the three materials are mixed and ground to a sieve residue of 0.08 mm ≤30% to obtain raw materials; the chemical composition analysis of the phosphogypsum, aluminum slag and fly ash used in this embodiment is shown in Table 1.

[0033] Table 1 Chemical element composition of different industrial solid wastes (wt. %)

[0034] S2, the raw materials are calcined after being preheated to 500 ℃, the calcination temperature is 1250 ℃, the calcination time is 120 min, and the expanding agent clinker is obtained after the calcination is completed; the chemical composition analysis of the expanding agent clinker after cooling is measured and shown in Table 2.

[0035] Table 2 Chemical composition of clinker (wt. %)

[0036] ​S3, the obtained expansion agent clinker, phosphogypsum, fly ash and limestone are mixed, wherein the mass percentage of each component is: expansion agent clinker 65%, phosphogypsum 20%, fly ash 10%, limestone 5%, and the four materials are ground to 0.08mm square hole screen residue of about 10% after mixing.

[0037] The reference cement specified in GB 8076 "Concrete Admixture" is mixed with 10wt% of the expansion agent obtained in this example, and the performance is detected according to GB / T 23439-2009 "Concrete Expanding Agent". The results are shown in Table 3.

[0038] Table 3 Performance table of expansion agent of Example 1

[0039] S4, the SO2-containing flue gas discharged in S3 is used to obtain sulfuric acid product by contact method.

[0040] Example 2 A method for preparing expansion agent and co-producing sulfuric acid by decomposing phosphogypsum, which is different from Example 1: In S1, the mass percentages of pre-dried phosphogypsum, aluminum slag and fly ash are: phosphogypsum 70.75%, aluminum slag 23.58%, fly ash 5.66%; In S2, the calcination temperature is 1275℃, and the calcination time is 100min; In S3, the expansion agent clinker, phosphogypsum, fly ash and limestone are mixed, wherein the mass percentage of each component is: expansion agent clinker 70%, phosphogypsum 15%, fly ash 7.5%, limestone 7.5%.

[0041] The requirements of each raw material and other steps in the preparation method are the same as those in Example 1.

[0042] The performance of the expansion agent obtained in this example is detected, and the results are shown in Table 4.

[0043] Table 4 Performance table of expansion agent of Example 2

[0044] Example 3 A method for preparing expansion agent and co-producing sulfuric acid by decomposing phosphogypsum, which is different from Example 1: In S1, the mass percentages of pre-dried phosphogypsum, aluminum slag and fly ash are: phosphogypsum 67.71%, aluminum slag 26.04%, fly ash 6.25%; In S2, the calcination temperature is 1300℃, and the calcination time is 80min; In S3, the expanding agent clinker, phosphogypsum, fly ash and limestone are mixed, wherein the mass percentage of each component is: expanding agent clinker 75%, phosphogypsum 10%, fly ash 5%, and limestone 10%.

[0045] The requirements of each raw material and other steps in the preparation method are the same as those in Example 1.

[0046] The expanding agent obtained in this example is subjected to performance detection, and the results are shown in Table 5.

[0047] Table 5 Performance table of the expanding agent of Example 3

[0048] Example 4 A method for preparing expanding agent and co-producing sulfuric acid by decomposing phosphogypsum, which is different from Example 1 in that: In S1, the mass percentages of pre-dried phosphogypsum, aluminum slag and fly ash are: phosphogypsum 74.38%, aluminum slag 20.66%, and fly ash 4.96%; In S2, the calcination temperature is 1325℃, and the calcination time is 70min; In S3, the expanding agent clinker, phosphogypsum, fly ash and limestone are mixed, wherein the mass percentage of each component is: expanding agent clinker 70%, phosphogypsum 10%, fly ash 10%, and limestone 10%.

[0049] The requirements of each raw material and other steps in the preparation method are the same as those in Example 1.

[0050] The expanding agent obtained in this example is subjected to performance detection, and the results are shown in Table 6.

[0051] Table 6 Performance table of the expanding agent of Example 4

[0052] Example 5 A method for preparing expanding agent and co-producing sulfuric acid by decomposing phosphogypsum, which is different from Example 1 in that: In S1, the mass percentages of pre-dried phosphogypsum, aluminum slag and fly ash are: phosphogypsum 76.34%, aluminum slag 19.08%, and fly ash 4.58%; In S2, the calcination temperature is 1350℃, and the calcination time is 60min; In S3, the expanding agent clinker, phosphogypsum, fly ash and limestone are mixed, wherein the mass percentage of each component is: expanding agent clinker 63%, phosphogypsum 17%, fly ash 10%, and limestone 10%.

[0053] The requirements of each raw material and other steps in the preparation method are the same as those in Example 1.

[0054] The performance of the expansion agent obtained in the present example was detected, and the results are shown in Table 7.

[0055] Table 7 Performance table of the expansion agent of Example 5

[0056] Example 9 A system for implementing the method of preparing expansion agent and co-producing sulfuric acid from phosphogypsum described in Examples 1-8, as shown in the figure, comprises, in sequence, a batching device, a raw material mill, a rotary kiln, a clinker bin, a clinker batching device, and a clinker mill; the flue gas outlet of the rotary kiln is sequentially connected to a flue gas washing and adsorption device, a converter, and an absorption tower. Figure 1

[0057] The batching device is used to mix phosphogypsum, aluminum slag, and fly ash according to the mass ratio set in the example; the raw material mill is used to grind the material output by the batching device to the particle size set in the example; the rotary kiln is used to calcine the raw meal according to the calcination method set in the example to obtain clinker; the clinker bin is used to cool and store the clinker, and the clinker batching device is used to mix the clinker, phosphogypsum, and limestone according to the mass ratio set in the example; the clinker mill is used to grind the material output by the clinker batching device to the particle size set in the example.

[0058] A raw material bin and a dryer are sequentially arranged in the upstream direction of the batching device; the dryer is used to dry the phosphogypsum, aluminum slag, and fly ash to a set dryness, and the raw material bin is used to store the raw materials and maintain the dry state of the raw materials.

[0059] A raw meal homogenization bin and a cyclone preheater are sequentially arranged between the raw material mill and the rotary kiln; the raw meal homogenization bin is used to homogenize the raw meal, and the cyclone preheater is used to preheat the raw meal.

[0060] A preheating zone, a decomposition zone, a sintering zone, and a cooling zone are sequentially arranged in the rotary kiln, which is used to calcine the raw meal into clinker according to the set calcination method.

[0061] A clinker cooling device is arranged between the rotary kiln and the clinker bin, which is used to cool the clinker to facilitate the storage of the clinker and the batching of the expansion agent raw materials.

[0062] The clinker mill leads to an expansion agent product bin; the product bin is used to store the prepared expansion agent.

[0063] The flue gas washing and adsorption device comprises, in sequence, a dynamic wave scrubber, a packed tower, an electric precipitator, and a drying tower; the dynamic wave scrubber is used to remove dust, fluorine, arsenic, and other impurities in the flue gas, the packed tower is used to further remove dust, fluorine, arsenic, and other impurities in the flue gas, the electric precipitator is used to remove acid mist in the flue gas, and the drying tower is used to absorb water in the flue gas.

[0064] ​A heat exchanger is provided between the flue gas scrubbing adsorption device and the converter for preheating the gas into the converter and recovering heat.

[0065] The absorption tower comprises an intermediate absorption tower, a final absorption tower and a tail gas absorption tower which are sequentially communicated; the intermediate absorption tower is used for preliminarily absorbing SO3 to generate concentrated sulfuric acid, the final absorption tower is used for deeply absorbing residual SO3 to improve the conversion rate, and the tail gas absorption tower is used for treating trace SO2 in tail gas to achieve standard emission.

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum, characterized in that: The following steps are involved: S1. Phosphogypsum, aluminum slag and fly ash are mixed in a mass ratio of (67-77): (19-27): (4-6) and then ground to obtain raw meal; S2. calcining the raw material at 1250-1350°C for 60-120 minutes to obtain clinker, and collecting the SO2-containing flue gas generated during the calcination; S3, mixing and grinding the clinker, phosphogypsum, limestone and fly ash in a mass ratio of (60-90): (10-20): (5-10): (5-10) to obtain an expansion agent; S4: Utilize the SO2-containing flue gas in S2 to prepare sulfuric acid.

2. The method for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In S1, the raw material is ground to a 0.08 mm sieve residue of ≤30%; the ground raw material is homogenized and set aside.

3. The method for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In S2, the calcining equipment adopts a rotary kiln.

4. The method for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In S3, clinker, phosphogypsum, limestone and fly ash are mixed and ground in a mass ratio of (62-64): (16-18): 10: 10 to obtain an expansion agent.

5. The method for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, wherein in S3, the powder is ground to a residue of 10% on a 0.08 mm square mesh sieve.

6. The method for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In S4, the SO2-containing flue gas is subjected to impurity removal and catalytic conversion treatment to produce sulfuric acid products.

7. A system for preparing an expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to any one of claims 1 to 6, characterized in that: It includes a batching device, a raw material mill, a rotary kiln, a clinker storage, a clinker batching device and a clinker mill which are connected in sequence; the flue gas outlet of the rotary kiln is connected in sequence to a flue gas washing and adsorption device, a converter and an absorption tower.

8. The system for preparing expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 7, characterized in that: A raw material homogenization tank and a cyclone preheater are sequentially arranged between the raw material mill and the rotary kiln; The clinker mill leads to the expansion agent product warehouse; the product warehouse is used to store the prepared expansion agent.

9. The system for preparing expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 7, characterized in that: The flue gas scrubbing and adsorption device comprises a power wave scrubber, a packing tower, an electric demister and a drying tower which are connected in sequence; Alternatively, a heat exchanger is provided between the flue gas scrubbing adsorption device and the converter.

10. The system for preparing expansion agent and co-producing sulfuric acid by decomposing phosphogypsum according to claim 7, characterized in that: The absorption tower includes an intermediate absorption tower, a final absorption tower and a tail gas absorption tower which are connected in sequence.

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