PROCESS FOR PRODUCING PROPPANTS

Abstract

The invention relates to a process for producing proppants, including 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 7 to 30 wt. %, producing a granular product from the mixture, and sintering the granular product.

Claims

1. A process 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 7 to 30 wt. %, producing a granular product from the mixture, and sintering the granular product.

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

3. The process according to claim 1, wherein the red mud has a second moisture content of at least 10 wt. %, preferably at least 15 wt. %.

4. The process according to claim 1, wherein the mixture contains 50 to 90 wt. %, preferably 60 to 75 wt. %, of red mud.

5. The process according to claim 1, wherein to adjust the first moisture content in the mixture, the second moisture content in the red mud is reduced by admixing fly ash to the red mud.

6. The process according to claim 1, wherein the second moisture content in the red mud is at most 30 wt. %.

7. The process according to claim 1, wherein the red mud has a pH of at least 10.

8. The process according to claim 1, wherein the fly ash has a third moisture content of at most 2 wt. %, preferably at most 1 wt. %.

9. The process according to claim 1, wherein the fly ash has a mean particle size D50 in the range of 1 to 15 μm.

10. The process according to claim 1, wherein the granular product is dried.

11. The process according to claim 1, wherein a predetermined grain fraction, preferably in a diameter range of 0.2 to 2.0 mm, is separated from the granular product by means of sieving.

12. The process according to claim 1, wherein the granular product is calcined at a temperature of 700° C. to 1.050° C. prior to sintering.

13. The process according to claim 1, wherein the granular product is sintered at a temperature in the range of 1.050° C. to 1.300° C.

14. The process according to claim 1, wherein the proppants are formed of spherical particles having an average diameter in the range of from 0.1 to 2.4 mm, preferably from 0.1 to 1.5 mm.

15. The process according to claim 1, wherein the proppants have a density greater than 1.0 g/cm.sup.3, preferably greater than 2.4 g/cm.sup.3.

Description

[0036] In the following, an embodiment of the invention is explained in more detail with reference to the drawings. It shows:

[0037] FIG. 1 a grain size distribution of sintered material,

[0038] FIG. 2 the sintered material,

[0039] FIG. 3 Cr leaching of the sintered material over time, and

[0040] FIG. 4 Na leaching of the sintered material over time.

[0041] Table 1 below shows chemical compositions of red mud used.

TABLE-US-00001 TABLE 1 Chemical composition of red mud SAMPLE Al.sub.2O.sub.3 SiO.sub.2 CaO Fe.sub.2O.sub.3 TiO.sub.2 SO.sub.3 P.sub.2O.sub.5 BaO SrO Mn.sub.3O.sub.4 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

[0042] The red mud has a second moisture content in the range of 22 to 26 wt. %. The average grain size D50 is about 1.7 μm.

[0043] Table 2 below shows chemical compositions of fly ashes used.

TABLE-US-00002 TABLE 2 Chemical composition of fly ash SAMPLE Al.sub.2O.sub.3 SiO.sub.2 CaO Fe.sub.2O.sub.3 MgO SO.sub.3 P.sub.2O.sub.5 K.sub.2O BaO TiO.sub.2 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

[0044] The fly ashes have a third moisture content of about 0.6 wt. %. An average grain diameter D50 of the fly ashes is about 4.1 μm.

[0045] To prepare the mixture of the red mud and fly ash, fly ash is stirred into the red mud until a first moisture content of the mixture is about 10 to 18 wt. %, preferably 11 to 16 wt. %.

[0046] Subsequently, the mixture is filled 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 by means of spray drying or in granulation pans, for example.

[0047] Table 3 below shows an example of a granulation protocol.

TABLE-US-00003 TABLE 3 Granulation protocol Mixing Settings method Water Step Rotor Vessel [ccf/cf] Process step additive [g] Time [s] 1 C 1 2 ccf Dry mix 0 60 2 C 1 2 ccf Water additive 0 15 3 C 2 2 ccf Water additive 360 60 4 C 2 2 ccf Micro granulation 0 120 5 B 2 2 ccf Micro ganulate 0 120 growth 6 A 2 2 ccf round granules 0 60 7 A 2 2 ccf Pulverization 0 60 8 A 1 2 ccf Finishing 0 60

[0048] Table 4 below describes the “Settings” in Table 3.

TABLE-US-00004 TABLE 4 Settings according to Table 3 Settings Granulation tool 1 diameter 0.136 m Granulation tool 2-diameter (pin type) 0.136 m Rotor A B C V-belt adjustment 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] Level 1 6.41 10.68 17.80 Level 2 12.82 21.36 35.60

[0049] According to the protocol (see Table 3), the mixture is first mixed in counter current flow (ccf) for 60 seconds to produce granular products. In steps 2 and 3, water is added. In step 4, the first micro granulation of the mixture takes place for a period of 120 seconds.

[0050] In step 5, growth of the grains of the microgranular product takes place. Step 5 is carried out until the grains have grown to the desired size.

[0051] In steps 6 to 8, the grains formed are rounded. In step 8, the surface of the grains is smoothed.

[0052] Advantageously, the granular product can be produced without the use of a binder.

[0053] The produced granular product has a fourth moisture content in the range of 7 to 11 wt. %.

[0054] In particular, for the production of proppants, the granular product is advantageously dried and then optionally screened, whereby a grain fraction in the range of 0.2 to 2.0 mm, preferably 0.2 to 1.0 mm, is separated.

[0055] For the separation of the aforementioned grain fraction, a vibrating screen with a screen combination of 30/50 mesh is expediently used. Of course, other grain fractions can also be separated. Suitable screen combinations are, for example, 16/30 mesh, 40/70 mesh, etc.

[0056] Subsequently, the granular product is first calcined, e.g. 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. Subsequently, 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.

[0057] The sintered material consists of spherical particles. For the production of proppants in particular, the sintered material can be classified again by means of sieving. Advantageously, a suitable grain fraction can be separated by means of a 30/50 mesh screen combination.

[0058] FIG. 1 shows the grain size distribution of a sintered material produced in this way. The sintered material is suitable for use as a proppant. An average grain diameter D50 of the proppants here is 0.66 mm.

[0059] FIG. 2 shows the proppants according to FIG. 1. A roundness of the proppants here is 0.8, their sphericity 0.9. The proppants 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 proppants is carried out according to the standard DIN EN ISO 13503-2 by Krumbein and Schloss.

[0060] FIGS. 3 and 4 show results of comparative leaching tests.

[0061] To perform the leaching tests, 25 grams of each sample was mixed with 500 ml of distilled water in a glass bottle. Samples were taken after 1 hour, 24 hours, 7 days and 28 days. About 12 ml of liquid was filtered, 10 ml of the filtered solution was taken and mixed with 3 drops of high purity 65% HNO.sub.3. The samples (leachates in FIG. 3 and FIG. 4) were then measured by ICP-MS, using a Thermo iCAP QcICP-MS.

[0062] 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 sintered material “RM/IF 60/40” has 60 wt. % red mud and 40 wt. % fly ash in the mixture. The other sintered materials “RM/IF 70/30 batch 1” and “RM/IF 70/30 batch 2” were produced from a mixture containing 70 wt. % of red mud and 30 wt. % of fly ash.

[0063] FIG. 3 shows that Cr is excellently bound in the sintered material. Even after a period of 600 hours, Cr is only leached from the sintered material in a concentration well below 10.0 ppb.

[0064] FIG. 4 shows that the sintered material releases about 100 times less Na than the red mud used.