GB897925A - Method of dehydrating gypsum - Google Patents

Abstract

<PICT:0897925/III/1> <PICT:0897925/III/2> In the dehydration of gypsum to the hemihydrate in a sealable indirectly heated vessel which is alternately sealed for at least 3 minutes and then vented until the desired dehydration has occured, a minimum positive gauge pressure is maintained in the vessel until the dehydration is completed. The temperature is maintained below 330 DEG F. during the alternate venting and sealing but finally when the dehydrating chamber is sealed the temperature rises to 330 DEG F. whilst the pressure remains below that previously attained. Venting is generally effected at 30 to 40 p.s.i.g. The minimum gauge pressure is generally from 4 to 6 p.s.i.g. and the temperature on venting should not drop below 212 DEG F. The apparatus employed is the same as that disclosed in Specifications 866,126, 897,923 and 897,924. As shown in Figs. 1 and 2, a drum 7 is supported by and rotated with an axial pipe 21 which rests on rollers 5 carried by support 2. Inside the drum the tube 21 carries a concertina-like arrangement of annular dished members 26 peripherally joined to form a series of chambers communicating with the interior of pipe 21 through perforations 25. A gas burner 22 delivers a blast of hot combustion products into pipe 21 from the left-hand side and these gases pass through perforations 25 into the chambers 33 formed by the annular dished members 26. The chambers 33 communicate with tubes 8 (Fig. 2) formed in the walls 7 of the container, by means of pipes 30. Tubes 8 are provided with exhaust passages 31 having a terminal elbow whereby the hot combustion gases from chamber 33 pass through connections 30 into tube 8 and out through exhaust 31 in contact with the exterior of the drum 6. Gypsum is fed to the drum through removable closures such as 11 and the steam formed by dehydration is vented through valves 13. As shown in Fig. 2 the valves 13 are operated by a lever 16 which abuts a valve-operating cam 19 which is manually adjustable so as to release steam pressure as desired when the drum rotates.