EP4045474A1

EP4045474A1 - Process for producing proppants

Info

Publication number: EP4045474A1
Application number: EP20833906.9A
Authority: EP
Inventors: Natalia Schwamm; Ralph Enderle
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-01-31
Filing date: 2020-12-22
Publication date: 2022-08-24
Also published as: US20220411690A1; DE102020102489A1; US11905463B2; AU2020426186A1; BR112022010631A2; WO2021151597A1

Abstract

The invention relates to a method for producing proppants, comprising the following steps: providing red mud, providing fly ash, producing a mixture from the red mud and the fly ash so that the mixture has a first moisture content in the range of from 7 to 30 wt.%, producing a granular product from the mixture, and sintering the granular product.

Description

Process for the production of proppants

The invention relates to a method for the production of proppants and the use of red mud.

"Proppants" are ceramic support granules. Such Stützgra nulate z. B. used in crude oil or natural gas production to support cavities in the rock.

DE 16 71 229 A discloses a method for the production of porous ceramic's substances from red mud and fly ash. The porous ceramic materials have a density of at most 0.8 g / cm ³ . Their strength is at most 0.5 MPa. The known ceramic materials are not suitable for the use of proppants.

WO 2013/153 115 A2 discloses a method for wet-chemical separation of at least some of the iron-containing constituents from red mud.

From DE 21 50 677 a method for producing bricks from red mud is known. The bricks have a density of at most 0.95 g / cm ³ . Their compressive strength is at most 0.3 MPa. The known material is not suitable for use as proppants.

According to the prior art, a method for producing a free-flowing sintered material is also known from US Pat. No. 9,587,170 B2. The known material is used as proppant or proppant in the extraction of petroleum by means of fracking. According to the state of the art, fly ash, bauxite and clay are mixed to produce the sintered material. The mixture is granulated. The granulate is then coated with bauxite, then calcined and sintered. The known process requires the use of valuable raw materials. It is relatively complex.

The object of the invention is to provide a method for producing a free-flowing sintered material that can be carried out as simply and inexpensively as possible. The sintered material is said to be particularly suitable for use as a proppant.

This object is achieved by the features of claim 1.

Appropriate refinements of the invention result from the features of the dependent claims.

According to the invention, a method for producing a free-flowing sintered material or proppants with the following steps is proposed:

Provision of red mud,

Provision of fly ash,

Producing a mixture of the red mud and the fly ash, so that the mixture has a first moisture content in the range from 7 to 30% by weight,

Producing a granulate from the mixture, and

Sintering the granules.

The term "red mud" or "red mud" is understood to mean a bauxite residue which arises from the extraction of aluminum oxide from aluminum-containing ores, in particular bauxite. More than 95% of the aluminum produced worldwide oxides are manufactured using the Bayer process. About 1 to 1.5 tons of red mud are produced per ton of aluminum oxide.

Because of the caustic soda used in the Bayer process, the red mud has a pH value 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 threat to the environment.

The term "fly ash" is understood to mean a solid, disperse residue which arises during combustion in thermal power plants and / or waste incineration plants and is separated from the flue gas by means of dedusting devices. Fly ash usually has mean particle sizes in the range from 3 to 20 μm and a residual moisture content of less than 1% by weight.

The term “free-flowing material” is understood to mean a granular material whose grain size, grain size distribution and surface properties are formed in such a way that it is flowable. The flowability of a material can be determined with a device according to DIN EN ISO 6186. To do this, a predetermined amount of the free-flowing material is placed in a standardized funnel and the time it takes for the material to pass through the funnel is measured.

The method proposed according to the invention enables the production of a free-flowing sintered material using red mud and fly ash in a simple and inexpensive manner. The sintered material has a pH less than about 8.8. It is not harmful to the environment and is particularly suitable for use as a proppant. As a result, the method according to the invention, on the one hand, enables the disposal of highly toxic red mud and, on the other hand, inexpensive production, in particular of proppants.

According to a further advantageous embodiment, the first moisture content in the mixture is 10 to 21% by weight. Such a mixture can be granulated particularly well. 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 expediently a maximum of 30% by weight. A red mud with the aforementioned second moisture content is ideally suited for the production of the granules.

The mixture expediently contains 50 to 90% by weight, preferably 60 to 75% by weight, of red mud. With the proposed mixture, special proppants can be produced with a high strength.

According to a particularly advantageous embodiment, in order to set the first moisture content in the mixture, the second moisture content in the red mud is reduced by adding fly ash to the red mud. Using the aforementioned process step, a separate energy-intensive drying process for setting the first moisture content in the mixture can be dispensed with. This further increases the efficiency of the proposed method.

The red mud expediently has a pFI value of at least 10, preferably at least 11. I. E. the process enables the use of red mud without its pFI value first having to be reduced by neutralization. The proposed method is therefore simple and inexpensive.

According to a further embodiment, the fly ash has a third moisture content of at most 2% by weight, preferably at most 1% by weight. Customary fly ashes have the aforementioned third moisture contents. They can be used to make the mixture without changing the third moisture content beforehand. Fly ashes with an average particle size D50 in the range from 1 to 15 μm have proven to be expedient for producing the mixture. An addition of the like fly ash leads to a particularly strong sintered material.

The granulate is expediently dried, then a predetermined grain fraction, for example in a diameter range of 0.2 to 2.0 mm, is separated from the granulate by means of sieving. The remainder can in turn be used to manufacture the granulate.

In a further process step, the granulate is calcined at a temperature of 700 to 1050 ° C before sintering. The sintering of the granules is expediently carried out at a temperature in the range from 1050 ° to 1300 ° C. The step of calcining and sintering can take place in a rotary kiln with different heating zones.

The sintered material is expediently formed from spherical particles with a mean diameter of 0.1 to 2.4 mm, preferably 0.1 to 1.5 mm. Such a material is particularly suitable for use as a proppant. The sintered material is also suitable as an aggregate for building materials, in particular concrete, bricks, tiles, roof tiles and the like. In addition, the sintered material is particularly suitable as molding sand for making casting molds or as an aggregate for a molding sand.

The use of a mixture of red mud and fly ash for the production of proppants, molding sand, bricks, roof tiles, tiles or as an additive for building materials is also proposed. In particular for the production of bricks, roof tiles, tiles and the like, the production of granules is not required. - Because of the advantageous configurations of the mixture, reference is made to the above statements.

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

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

The density of the proppants produced is preferably from 1.0 to 3.8 g / cm ³ , in particular from 1.5 to 3.2 g / cm ³ , particularly preferably from 2 to 2.8 g / cm ³ .

An exemplary embodiment of the invention is explained in more detail below with reference to the drawings. Show it:

1 shows a grain size distribution of sintered material,

Fig. 2 the sintered material,

3 Cr leaching of the sintered material over time, and

Fig. 4 Na leaching of the sintered material over time.

Table 1 below shows the chemical compositions of the red sludge used.

Table 1: Chemical composition of red sludge The red mud has a second moisture content in the range from 22 to 26% by weight. The mean grain size D50 is about 1.7 gm.

Table 2 below shows the chemical compositions of the fly ash used.

Table 2: Chemical composition of fly ash

The fly ashes have a third moisture content of about 0.6% by weight. A mean grain diameter D50 of the fly ash is around 4.1 μm.

To freeze the mixture of the red mud and the fly ash, fly ash is stirred into the red mud until a first moisture content of the mixture is about 10 to 18% by weight, preferably 11 to 16% by weight.

The mixture is then poured into an Eirich R02 mixer. Of course, it is also possible to use other granulating mixers with a high shear field, similar to an Eirich mixer. It is also possible to granulate the mixture, for example by means of spray drying or in granulating pans.

The following table 3 gives an example of a protocol for granulation.

Table 3: Protocol for granulation

The following table 4 describes the "settings" in table 3. Table 4: Settings according to Table 3

According to the protocol (see Table 3), the mixture for producing granules is initially mixed for 60 seconds in countercurrent flow (= counter current flow (ccf)). In steps 2 and 3, water is added. In step 4, the mixture is first micro-granulated for a period of 120 seconds.

In step 5, the grains of the microgranulate grow. Step 5 is carried out until the grains have grown to the desired size. In steps 6 to 8, the formed grains are rounded. In step 8, the surface of the grains is smoothed.

The granules can advantageously be produced without the use of a binder.

The granules produced have a fourth moisture content in the range from 7 to 11% by weight.

In particular for the production of proppants, the granulate is advantageously dried and then optionally sieved, a grain fraction in the range from 0.2 to 2.0 mm, preferably 0.2 to 1.0 mm, being separated off.

A vibrating sieve with a sieve combination of 30/50 mesh is expediently used to separate the aforementioned grain fraction. Of course, other grain fractions can also be separated. Suitable sieve combinations are, for example, 16/30 mesh, 40/70 mesh and the like.

Subsequently, the granules z. B. in a rotary kiln initially at a temperature in the range of 750 to 850 ° C for a period of 5 to 30 Minu th, preferably 5 to 15 minutes, calcined. The calcined granulate is then sintered at a temperature in the range from 1100 to 1300 ° C. for a period of from 5 to 30 minutes, preferably from 5 to 15 minutes.

The sintered material consists of spherical particles. In particular for the manufacture of proppants, the sintered material can be classified again by means of sieves. For this purpose, a suitable grain fraction can advantageously be separated by means of a 30/50 mesh sieve combination.

Fig. 1 shows the grain size distribution of a sintered material produced in this way as. The sintered material is suitable for use as a proppant. A mean grain diameter D50 of the proppants is 0.66 mm here. FIG. 2 shows the proppants according to FIG. 1. A rounding of the proppants is 0.8 here, their sphericity 0.9. The proppants met the necessary requirements of a rounding of at least 0.6 and a sphericity of at least 0.6.

The roundness and sphericity of the proppants are determined according to the standard DIN EN ISO 13503-2 according to Krumbein and Schloss.

Figures 3 and 4 show results of comparative leaching experiments.

To carry out the leaching tests, 25 grams of a sample were mixed with 500 ml of distilled water in a glass bottle. The samples were taken after 1 hour, 24 hours, 7 days and 28 days. About 12 ml of liquid were filtered, 10 ml of the filtered solution were removed and 3 drops of high-purity 65% HNO3 were added. The samples (leachate in FIGS. 3 and 4) were then measured by means of ICP-MS, specifically by means of a Thermo iCAP QcICP-MS.

Figure 3 shows Cr leaching over time. Figure 4 shows Na leaching over time. For comparison, fly ash, red mud (bauxite remnant) and sand (sand) are given. The sintered material "RM / IF 60/40" has 60% by weight of red mud and 40% by weight of fly ash in the mixture. The other sintered materials "RM / IF 70/30 batch 1" and "RM / IF 70/30 batch 2" have been produced from a mixture which contained 70% by weight of red mud and 30% by weight of fly ash.

Fig. 3 shows that Cr is excellently bonded in the sintered material. Even after a period of 600 hours, Cr le is leached from the sintered material in a concentration of well below 10.0 ppb.

4 shows that the sintered material releases about 100 times less Na than the red mud used.

Claims

1. Process for the production of proppants with the following steps: Providing red mud,

Provision of fly ash,

Producing a granulate from the mixture, and

Sintering the granules.

2. The method of claim 1, wherein the first moisture content in the mixture is 10 to 21 wt.%.

3. The method according to any one of the preceding claims, wherein the red mud has a second moisture content of at least 10% by weight, preferably at least 15% by weight.

4. The method according to any one of the preceding claims, wherein the mixture contains 50 to 90% by weight, preferably 60 to 75% by weight, of red mud.

5. The method according to any one of the preceding claims, wherein for the setting len of the first moisture content in the mixture, the second moisture content in the red mud is reduced by adding fly ash to the red mud.

6. The method according to any one of the preceding claims, wherein the second moisture content in the red mud is at most 30% by weight.

7. The method according to any one of the preceding claims, wherein the red mud has a pH of at least 10.

8. The method according to any one of the preceding claims, wherein the fly ash has a third moisture content of at most 2% by weight, preferably at most 1% by weight.

9. The method according to any one of the preceding claims, wherein the fly ash has an average particle size D50 in the range from 1 to 15 μm.

10. The method according to any one of the preceding claims, wherein the granules are dried.

11. The method according to any one of the preceding claims, wherein a predetermined grain fraction, preferably in a diameter range of 0.2 to 2.0 mm, is separated from the granules by means of sieving.

12. The method according to any one of the preceding claims, wherein the granules are calcined at a temperature of 700 to 1050 ° C before sintering.

13. The method according to any one of the preceding claims, wherein the granules are sintered at a temperature in the range from 1050 ° to 1300 ° C.

14. The method according to any one of the preceding claims, wherein the proppants are formed from spherical particles with an average diameter in the range from 0.1 to 2.4 mm, preferably from 0.1 to 1.5 mm.

15. The method according to any one of the preceding claims, wherein the proppants have a density of more than 1.0 g / cm ³ , preferably more than 2.4 g / cm ³ .