PROCESS FOR THE PRODUCTION OF PROPANTS

Abstract

PROCESS FOR THE PRODUCTION OF PROPANTS. The invention relates to a process for the production of propants, comprising the following steps: providing red mud; providing fly ash; producing a mixture of the red mud and fly ash, such that the mixture has an initial moisture content in the range of 7 to 30% by weight; producing a granular product from the mixture; and sintering the granular product.

Description

1 / 12 PROCESS FOR THE PRODUCTION OF PROPANTS

[001] The invention relates to a process for the production of propants and the use of red mud.

[002] Propants are granular ceramic support products. Such propants are used, for example, in oil and gas production to hold cavities in the rock.

[003] DE 16 71 229 A discloses a process for the production of porous ceramic materials from red mud and fly ash. The porous ceramic materials have a density of at most 0.8 g / cm3. Their strength is at most 0.5 MPa. Known ceramic materials are not suitable for use as proppants.

[004] WO 2013 / 153 115 A2 discloses a process for the wet chemical separation of at least a portion of the iron-containing constituents of red mud.

[005] DE 21 50 677 describes a process for the production of red mud bricks. The bricks have a density of at most 0.95 g / cm3. Their compressive strength is at most 0.3 MPa. The known material is not suitable for use as proppants.

[006] According to the prior art, a process for producing a free-flowing sintered material is also known from US 9,587,170 B2. The known material is used as a proppant in the extraction of crude oil by fracking. To produce the sintered material, the prior art mixes fly ash, bauxite, and clay. The mixture is granulated. The granular product is then coated with bauxite, subsequently calcined and sintered.

[007] The known process requires the use of Petition 870220047653, dated 05 / 31 / 2022, page 7 / 53 2 / 12 valuable raw materials. It is relatively expensive.

[008] The object of the invention is to provide a process for the production of a free-flowing sintered material, which can be carried out in the simplest and cheapest way possible. The sintered material should be suitable, in particular, for use as a proppant.

[009] This object is achieved through the resources of claim 1.

[0010] Useful embodiments of the invention are apparent from the features of the dependent claims.

[0011] According to the invention, a process for producing a free-flowing or proppant sintered material is proposed, and comprises the following steps: - to provide red mud; - to provide fly ash; - to produce a mixture of red mud and fly ash, so that the mixture has an initial moisture content in the range of 7 to 30% by weight; - to produce a granular product from a mixture; and - Sinter the granular product.

[0012] The term red mud refers to a bauxite residue, that is, produced during the extraction of aluminum oxide from aluminum ores, particularly bauxite. More than 95% of the world's aluminum oxide production is manufactured using the Bayer Process. This process produces approximately 1 to 1.5 metric tons of red mud per metric ton of alumina.

[0013] Because of the caustic soda used in Petition 870220047653, dated 05 / 31 / 2022, page 8 / 53 3 / 12 Due to the Bayer process, red mud has a pH of at least 11. In addition to iron oxide, red mud contains heavy metal oxides and heavy metal hydroxides. Overall, red mud poses a significant hazard to the environment.

[0014] The term fly ash is understood to be a solid and dispersed residue produced during combustion in thermal power plants and / or waste incineration facilities, and is separated from the combustion gases by means of dust removal devices. Fly ash generally has average particle sizes in the range of 3 to 20 µm and a residual moisture content of less than 1% by weight.

[0015] The term free-flowing material is understood to be a granular material whose grain size, grain size distribution, and surface properties are such that it is capable of flowing. The fluidity of a material can be determined with a device, in accordance with DIN EN ISO 6186. For this purpose, a specified quantity of the free-flowing material is placed in a standardized funnel, and the time taken for the material to pass through the funnel is measured.

[0016] The proposed process, in accordance with the invention, enables a free-flowing sintered material to be produced simply and cheaply using red mud and fly ash. The sintered material has a pH of less than about 8.8. It is not environmentally hazardous and is particularly suitable for use as a propant. As a result, the process according to the invention makes it possible, on the one hand, to dispose of highly toxic red mud and, on the other hand, to produce propants, particularly with Petition 870220047653, dated 05 / 31 / 2022, page 9 / 53 4 / 12 low cost.

[0017] According to an additional advantageous embodiment, the initial moisture content in the mixture is 10 to 21% by weight. Such a mixture can be granulated particularly well.

[0018] According to an advantageous embodiment, the red mud has a second moisture content of at least 10% by weight, preferably at least 15% by weight. The second moisture content in the red mud is conveniently at most 30% by weight. A red mud containing the aforementioned second moisture content is very suitable for the production of the granular product.

[0019] Ideally, the mixture contains 50 to 90% by weight, preferably 60 to 75% by weight, of red mud. The proposed mixture can be used, in particular, to produce propants with high strength.

[0020] According to a particularly advantageous embodiment, to adjust the first moisture content in the mixture, the second moisture content in the red mud is reduced by mixing fly ash into the red mud. By using the process step mentioned above, a separate drying step that consumes energy to adjust the first moisture content in the mixture can be omitted. This further increases the efficiency of the proposed process.

[0021] It is advisable that the red mud have a pH value of at least 10, preferably at least 11. That is, the process allows the use of red mud without first having to reduce its pH by neutralization. Thus, the proposed process is simple and inexpensive.

[0022] According to a further embodiment, fly ash has a third moisture content of, in Petition 870220047653, dated 05 / 31 / 2022, page 10 / 53 5 / 12 maximum 2% by weight, preferably a maximum of 1% by weight. Common fly ash has the third moisture content mentioned above. It can be used to prepare the mixture without prior modification of the third moisture content.

[0023] Fly ash with an average particle size D50 in the range of 1 to 15 µm proved suitable for the production of the mixture. The addition of such fly ash results in a particularly strong sintered material.

[0024] The granular product is properly dried, then a predetermined fraction of grains, for example, in a diameter range of 0.2 to 2.0 mm, is separated from the granular product by sieving. The remainder can be used again for the production of more granular product.

[0025] After another stage of the process, the granular product is calcined at a temperature of 700 °C to 1,050 °C before sintering. The sintering of the granular product is conveniently carried out at a temperature in the range of 1,050 °C to 1,300 °C. The calcination and sintering stage can be carried out in a rotary kiln with different heating zones.

[0026] The sintered material is conveniently formed from spherical particles with an average diameter of 0.1 to 2.4 mm, preferably 0.1 to 1.5 mm. This material is particularly suitable for use as a proppant. However, the sintered material is also suitable as an aggregate for construction materials, particularly concrete, bricks, tiles, roofing and the like. Additionally, the sintered material is also particularly suitable as molding sand for the production of foundry molds or as an aggregate for molding sand. Petition 870220047653, dated 05 / 31 / 2022, page 11 / 53 6 / 12

[0027] It is also proposed to use a mixture of red mud and fly ash for the production of proppants, molding sand, bricks, roofing, tiles or as aggregate for building materials. Particularly, for the production of bricks, roofing, tiles and the like, the production of a granular product is not necessary. Advantageous embodiments of the mixture have been referenced in the explanations above.

[0028] Surprisingly, highly toxic red mud with a pH of at least 11 is suitable as a raw material for the production of a free-flowing sintered material. The sintered material has a pH value in the range of 7 to 8.8. The metals contained in the red mud are bound to it as metal oxides. The sintered material is environmentally compatible.

[0029] The propants produced by the process according to the invention have a strength of at least 30 MPa, preferably at least 40 MPa, particularly and preferably at least 70 MPa. The process according to the invention can also be used to produce propants with a strength of at least 80 MPa. For the determination of the strength of the propants, reference is made to DIN EN ISO 13503-2.

[0030] The density of the propants produced is preferably from 1.0 to 3.8 g / cm3, particularly from 1.5 to 3.2 g / cm3, more preferably from 2 to 2.8 g / cm3.

[0031] Next, an embodiment of the invention is explained in more detail in relation to the figures. It shows: - in Fig. 1, a grain size distribution of the sintered material; - in Fig. 2, the sintered material; Petition 870220047653, dated 05 / 31 / 2022, page 12 / 53 7 / 12 - in Fig. 3, the leaching of Cr from the sintered material over time; and - in Fig. 4, leaching of Na from the sintered material over time.

[0032] Table 1 below shows the chemical compositions of the red mud used. SAMPLE Al2O3 SiO2 CaO Fe2O3 TiO2 SO3 P2O5 BaO SrO Mn3O4 Red mud #1 17.57 6.77 6.56 51.98 12.08 0.22 0.54 0.01 0.01 0.02 Red mud #2 15.13 5.48 6.31 53.55 13.20 0.20 0.53 0.03 0.01 0.04 Red mud #3 18.03 12.79 1.18 32.93 7.32 0.15 0.33 0.02 0.04 0.01 Table 1: Chemical composition of red mud

[0033] Red mud has a second moisture content in the range of 22 to 26% by weight. The average D50 grain size is about 1.7 µm.

[0034] Table 2 below shows the chemical compositions of the fly ash used. SAMPLE Al2O3 SiO2 CaO Fe2O3 MgO SO3 P2O5 K2O BaO TiO2 Fly ash_1 19.44 51.58 7.52 6.75 1.04 1.84 0.18 2.00 0.28 0.12 Fly ash_2 29.20 55.75 0.90 4.12 0.47 1.89 0.33 0.78 0.29 2.12 Fly ash_3 27.71 61.36 2.21 4.45 0.96 1.01 0.17 1.00 0.30 2.07 Table 2: Chemical composition of fly ash

[0035] Fly ash has a third moisture content of about 0.6% by weight. An average diameter of Petition 870220047653, dated 05 / 31 / 2022, p. 13 / 53 8 / 12 grain D50 of fly ash is approximately 4.1 µm.

[0036] To prepare a mixture of red mud and fly ash, the fly ash is mixed with the red mud until the initial moisture content of the mixture is about 10 to 18% by weight, preferably 11 to 16% by weight.

[0037] Next, the mixture is placed inside an Eirich R02 mixer. Of course, it is also possible to use other granulation mixers with a high shear field, similar to the Eirich mixer. It is also possible to granulate the mixture by spray drying or in granulation vessels, for example.

[0038] Table 3 below shows an example of a granulation protocol. Step Definitions Mixing Method [ccf / cf] Process Step Water Addition [g] Time [s] Rotor Container 1 C 1 2 ccf Dry Mix 0 60 2 C 1 2 ccf Water Addition 0 15 3 C 2 2 ccf Water Addition 360 60 4 C 2 2 ccf Microgranulation 0 120 5 B 2 2 ccf Microgranular Growth 0 120 6 A 2 2 ccf Rounded Granules 0 60 7 A 2 2 ccf Pulverization 0 60 8 A 1 2 ccf Finishing 0 60 Table 3: Granulation protocol

[0039] Table 4 below describes the Definitions in Table 3. Petition 870220047653, dated 05 / 31 / 2022, page 14 / 53 9 / 12 Definitions Granulation tool 1 - diameter 0.136 m Granulation tool 2 - diameter (pin type) 0.136 m Rotor Belt adjustment in VABC Rotation speed stage 1 [rpm] 900 1,500 2,500 Rotation speed stage 2 [rpm] 1,800 3,000 5,000 Peripheral speed [m / s] ABC Level 1 6.41 10.68 17.80 Level 2 12.82 21.36 35.60 Table 4: Definitions, according to Table 3

[0040] According to the protocol (see Table 3), the mixture is first mixed in countercurrent flow (ccf counter current flow) for 60 seconds to produce granular products. In steps 2 and 3, water is added. In step 4, the first microgranulation of the mixture occurs for a period of 120 seconds.

[0041] In step 5, the growth of the microgranular product grains occurs. Step 5 is carried out until the grains have grown to the desired size.

[0042] In steps 6 to 8, the formed grains are rounded. In step 8, the surface of the grains is smoothed.

[0043] Advantageously, the granular product can be produced without the use of a binder. Petition 870220047653, dated 05 / 31 / 2022, page 15 / 53 10 / 12

[0044] The granular product produced has a quarter moisture content in the range of 7 to 11% by weight.

[0045] In particular, for the production of propants, the granular product is advantageously dried and then optionally sieved, and a fraction of grains in the range of 0.2 to 2.0 mm, preferably 0.2 to 1.0 mm, is separated.

[0046] For the separation of the grain fraction mentioned above, a vibrating sieve with a 30 / 50 mesh combination is conveniently used. Of course, other grain fractions can also be separated. Suitable screen combinations are, for example, 16 / 30 mesh, 40 / 70 mesh, etc.

[0047] Next, the granular product is first calcined, for example, in a rotary kiln, at a temperature in the range of 750 °C to 850 °C for a period of 5 to 30 minutes, preferably 5 to 15 minutes. Then, the calcined granular product is sintered at a temperature in the range of 1,100 °C to 1,300 °C for a period of 5 to 30 minutes, preferably 5 to 15 minutes.

[0048] The sintered material consists of spherical particles. For the production of proppants in particular, the sintered material can be further classified by means of sieving. Advantageously, a suitable grain fraction can be separated by means of a combination of 30 / 50 mesh screen.

[0049] Fig. 1 shows the grain size distribution of a sintered material produced in this way. The sintered material is suitable for use as a propant. An average grain diameter D50 of the propants here is 0.66 mm.

[0050] Fig. 2 shows the propants according to Petition 870220047653, dated 05 / 31 / 2022, page 16 / 53 11 / 12 Fig. 1. The roundness of the propants here is 0.8, their sphericity is 0.9. The propants fulfilled the necessary requirements of a roundness of at least 0.6 and a sphericity of at least 0.6. The determination of the roundness and sphericity of the propants is carried out according to the Krumbein and Schloss DIN EN ISO 13503-2 standard.

[0051] Figs. 3 and 4 show comparative leaching test results.

[0052] To perform the leaching tests, 25 grams of each sample were mixed with 500 ml of distilled water in a glass bottle. Samples were taken after 1 hour, 24 hours, 7 days, and 28 days. Approximately 12 ml of liquid was filtered, 10 ml of the filtered solution was taken and mixed with 3 drops of 65% high-purity HNO3. The samples (leached in Figs. 3 and 4) were then measured by ICP-MS using a Thermo Scientific iCAP QcICP-MS.

[0053] Fig. 3 shows the leaching of Cr over time. Fig. 4 shows the leaching of Na over time. For comparison, fly ash, bauxite residue, and sand are shown. The RM / IF 60 / 40 sintered material has 60% by weight of red mud and 40% by weight of fly ash in a mixture. The other RM / IF 70 / 30 sintered materials, charge 1 and RM / IF 70 / 30 charge 2, were produced from a mixture containing 70% by weight of red mud and 30% by weight of fly ash.

[0054] Fig. 3 shows that Cr is bound excellently to the sintered material. Even after a period of 600 hours, Cr is only leached from the sintered material at a concentration well below 10.0 ppb.

[0055] Fig. 4 shows that the sintered material Petition 870220047653, dated 05 / 31 / 2022, page 17 / 53 12 / 12 releases about 100 times less Na than the red mud used. Petition 870220047653, dated 05 / 31 / 2022, page 18 / 53

Claims

1 / 2 CLAIMS 1. PROCESS FOR THE PRODUCTION OF PROPANTS, characterized by comprising the following steps: - providing red mud; - providing fly ash; - producing a mixture of the red mud and fly ash, such that the mixture has an initial moisture content in the range of 7 to 30% by weight; - producing a granular product from the mixture; - calcining the granular product at a temperature of 700°C to 1,050°C and then - sintering the calcined granular product at a temperature in the range of 1,050°C to 1,300°C.

2. PROCESS, according to claim 1, characterized in that the initial moisture content in the mixture is 10 to 21% by weight.

3. PROCESS, according to claim 1, characterized in that the red mud has a second moisture content of at least 10% by weight.

4. PROCESS, according to claim 3, characterized in that, to adjust the first moisture content in the mixture, the second moisture content in the red mud is reduced by mixing fly ash into the red mud.

5. PROCESS, according to claim 3, characterized in that the second moisture content in the red mud is at most 30% by weight.

6. PROCESS, according to claim 1, characterized in that the mixture contains 50 to 90% by weight.

7. PROCESS, according to claim 1, Petition 870240104704, dated 09 / 12 / 2024, page 7 / 16 2 / 2 characterized by the red mud having a pH of at least 10.

8. PROCESS, according to claim 1, characterized in that the fly ash has a third moisture content of, at most, 2% by weight, preferably, at most 1% by weight.

9. PROCESS, according to claim 1, characterized in that the fly ash has an average particle size D50 in the range of 1 to 15 µm.

10. PROCESS, according to claim 1, characterized in that the granular product is dry.

11. PROCESS, according to claim 1, characterized in that a predetermined grain fraction is separated from the granular product by means of sieving.

12. PROCESS, according to claim 1, characterized in that the propellants are formed of spherical particles with an average diameter in the range of 0.1 to 2.4 mm.

13. PROCESS, according to claim 1, characterized in that the propants have a density greater than 1.0 g / cm3.

14. PROCESS, according to claim 1, characterized in that the granular product is calcined at a temperature of 700°C to 1,050°C for 5 to 30 minutes, and then the calcined granular product is sintered at a temperature in the range of 1,050°C to 1,300°C. Petition 870240104704, dated 09 / 12 / 2024, page 8 / 16

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