Methods for producing sintered particles from a slurry of an alumina-containing raw material
View Patent ↗Methods for producing substantially round, spherical and sintered particles from a slurry of a calcined, uncalcined or partially calcined raw material having an alumina content of more than 55% by weight, and a mullite growth promoter in an amount of from about 2 to about 10% dry weight of the total solids in the slurry. Methods for using such substantially round, spherical and sintered particles in hydraulic fracturing operations.
1. A method for producing sintered particles comprising:
preparing a slurry having a solids content of from about 40 to about 60% by weight, and comprising water, a binder, a mullite growth promoter and a raw material having an alumina content in a range of from about 55 to about 80% by weight;
atomizing the slurry into droplets;
coating seeds comprising alumina with the droplets to form green particles; and
sintering at least a portion of the green particles at a temperature of from about 1000° C. to about 1600° C. for about 5 minutes to about 90 minutes, to form sintered particles having an alumina content of greater than about 55% by weight, an iron oxide content in a range of from about 2 to about 10% by weight, a specific gravity in a range of from about 2.70 g/cm 3 to about 3.50 g/cm 3 , and a bulk density in a range of from about 1.55 g/cm 3 to about 1.95 g/cm 3 .
2. The method of claim 1 wherein the mullite growth promoter comprises iron oxide present in the raw material in a range of from about 2 to about 10% by weight.
3. The method of claim 1 wherein the mullite growth promoter and raw material comprise the total solids in the slurry, and the mullite growth promoter comprises iron oxide added to the raw material in a range of from about 2 to about 10% by weight of the total solids in the slurry.
4. The method of claim 1 wherein the bulk density is from about 1.65 g/cm 3 to about 1.80 g/cm 3 .
5. The method of claim 1 further comprising adding to the slurry at least one of a pH-adjusting reagent, a dispersant and a defoamer before atomizing the slurry.
6. The method of claim 1 wherein atomizing the slurry comprises feeding the slurry to a fluidizer operable to atomize the slurry into droplets; and wherein the seeds are positioned in a particle bed in the fluidizer.
7. The method of claim 1 wherein the raw material comprises at least one of calcined kaolin, calcined bauxite, uncalcined kaolin and uncalcined bauxite.
8. The method of claim 1 further comprising drying the green particles before sintering.
9. The method of claim 1 wherein the slurry has an alumina content and the seeds have an alumina content, wherein the slurry alumina content is 10% less than the seed alumina content.
10. The method of claim 1 wherein the slurry has an alumina content and the seeds have an alumina content, wherein the slurry alumina content is 10% greater than the seed alumina content.
11. The method of claim 1 wherein the slurry has an alumina content from about 60 to about 70% by weight, and an iron oxide content from about 4 to about 10% by weight.
12. The method of claim 1 wherein the sintered particles have an alumina content from about 60 to about 70% by weight, and an iron oxide content from about 4 to about 10% by weight.