Methods for calcining gypsum

Patent metadata

Field	Value
Publication number	US-2025326654-A1
Application number	US-202318871159-A
Country	US
Kind code	A1
Filing date	Jun 23, 2023
Priority date	Jul 15, 2022
Publication date	Oct 23, 2025
Grant date	—

Abstract

A method for calcining gypsum includes subjecting a composition including gypsum dihydrate to a predetermined vacuum. The method further includes maintaining the composition under the at least partial vacuum at a calcining temperature for a predetermined calcining time. The calcining temperature may be in a range from 60° C. to 125° C., or in a range from 65° C. to 85° C. The vacuum may be in a range from 25 mbar to 50 mbar. The predetermined calcining time may be in a range from 3 hours to 10 hours. The maintaining is effective to at least partially remove water of crystallization from the gypsum dihydrate to convert the composition to a product including gypsum hemihydrate.

First claim

1 . A method for calcining gypsum, the method comprising: subjecting a composition comprising gypsum dihydrate to a predetermined vacuum; and maintaining the composition under the predetermined vacuum at a calcining temperature for a predetermined calcining time, wherein the calcining temperature is in a range from 60° C. to 125° C., and wherein the maintaining is effective to at least partially remove water of crystallization from the gypsum dihydrate to convert the composition to a product comprising gypsum hemihydrate,
wherein the composition comprises at least 83% of gypsum dihydrate by weight when the composition is initially subjected to the predetermined vacuum.

2 . (canceled)

3 . The method of claim 1 , wherein the calcining temperature is in a range from 60° C. to 100° C.

4 . The method of claim 3 , wherein the calcining temperature is in a range from 65° C. to 85° C.

5 . (canceled)

6 . (canceled)

7 . The method of claim 1 , further comprising heating the composition to the calcining temperature, wherein the heating is initiated before the subjecting the composition to the predetermined vacuum.

8 . The method of claim 1 , further comprising heating the composition to the calcining temperature, wherein the heating is initiated during or after the subjecting the composition to the predetermined vacuum.

9 . The method of claim 1 , wherein the calcining temperature is a first calcining temperature, wherein the predetermined calcining time is a first predetermined calcining time, and wherein the method further comprises maintaining the composition under the predetermined vacuum at a second calcining temperature for a predetermined second calcining time, wherein the second calcining temperature is greater than the first calcining temperature and less than 125° C.

10 . (canceled)

11 . The method of claim 1 , wherein the predetermined vacuum is in a range selected from the group consisting of:
(a) pressures less than atmospheric (1013.2 mbar at sea level) and greater than 1 mbar; (b) 5 to 200 mbar; (c) 10 to 100 mbar; and (d) 25 mbar to 50 mbar.

12 . The method of claim 1 , wherein the predetermined vacuum is a first predetermined vacuum, and wherein the method further comprises maintaining the composition under a second predetermined vacuum deeper than the first predetermined vacuum.

13 . (canceled)

14 . (canceled)

15 . The method of claim 1 , wherein the predetermined calcining time is at least 5 hours.

16 . (canceled)

17 . (canceled)

18 . (canceled)

19 . (canceled)

20 . The method of claim 1 , wherein the composition consists of the gypsum dihydrate comprising the water of crystallization.

21 . (canceled)

22 . The method of claim 1 , wherein the gypsum hemihydrate consists of alpha gypsum hemihydrate.

23 . The method of claim 1 , wherein the gypsum hemihydrate consists of beta gypsum hemihydrate.

24 . The method of claim 1 , wherein the product has a compressive strength of at least 2700 psi.

25 . The method of claim 1 , wherein the product has a compressive strength of at least 3000 psi.

26 . (canceled)

27 . The method of claim 1 , wherein the product has a moisture content of less than 6% by weight.

28 . A method for calcining gypsum, the method comprising: subjecting a composition comprising gypsum dihydrate to a vacuum of from 25 mbar to 50 mbar; and maintaining the composition under the vacuum at a calcining temperature of from 65° to 85° C. for a predetermined calcining time of from 3 hours to 10 hours, wherein the maintaining is effective to at least partially remove water of crystallization from the gypsum dihydrate to convert the composition to a product comprising gypsum hemihydrate.

29 . The method of claim 28 , wherein the product consists of beta gypsum hemihydrate.

30 . The method of claim 28 , wherein the product has a compressive strength of at least 3000 psi.

31 . The method of claim 1 , where the composition comprises up to 10% moisture.

32 . A method for calcining gypsum, the method comprising: subjecting a composition comprising gypsum dihydrate to a vacuum of from 25 mbar to 50 mbar; and maintaining the composition under the vacuum at a calcining temperature of from 65° to 85° C. for a predetermined calcining time, wherein the maintaining is effective to at least partially remove water of crystallization from the gypsum dihydrate to convert the composition to a product comprising gypsum hemihydrate.

Assignees

• Georgia Pacific Gypsum Llc

Inventors

• Carpenter Randy B
• Causey Ronald W
• Plummer Jennifer L

Classifications

• C01P2006/90

  Other properties not specified above · CPC title

• C01P2006/82

  water content · CPC title

• C01F11/466 Primary

  Conversion of one form of calcium sulfate to another · CPC title

• C04B11/02 Primary

  Methods and apparatus for} dehydrating gypsum {(for other purposes than cement manufacture C01F11/466) · CPC title