Feeding device and process and feeding system which utilize the feeding device
Feeding device for feeding burned lime to a reaction vessel for causticizing a soda liquor to caustic soda. The feeding device, in its upper part, comprises an inlet for a slurry of the burned lime and the soda liquor for formation of said slurry inside said feeding device. The system further comprises a tall and slender feed vessel having a lower part having an outlet defined therein for the slurry. The outlet, via a pump, is operatively connected to the reaction vessel. The process and the feeding system utilize the feeding device, in which process the slurry is created of the burned lime and a first part of the soda liquor, a second part being preheated before addition to the slurry, whereafter slaking and causticizing reactions are completed under elevated temperature and pressure.
1. A process for reacting a soda liquor being at a first temperature with a burned lime for production of caustic soda, comprising:
(a) dividing the soda liquor, being at the first temperature, into a first part and a second part and forming a slurry of the burned lime and the first part of the soda liquor and allowing the slurry a retention time of 10–150 seconds in a feed vessel and reacting the burned lime with the first part of the soda liquor to increase the temperature of the reacted slurry to a second temperature as a result of an exothermic slaking reaction therebetween, the second temperature being higher than the first temperature;
(b) preheating the second part of the soda liquor from the first temperature to a third temperature, the third temperature being higher than the first temperature;
(c) combining the reacted slurry from step (a) and the preheated second part of the soda liquor of step (b) prior to conveying the reacted slurry and the second part of the soda liquor to a reactor; and
(d) maintaining the combined reacted slurry and the second part of the soda liquor at an pressure and at a fourth elevated temperature in the reactor for completion of the reaction between the slurry of the burned lime and the soda liquor to yield caustic soda and lime mud, the fourth temperature being higher than the first temperature.
2. The process according to claim 1 wherein the method further comprises filling the feed vessel with a sufficient amount of the combined slurry and the soda liquor to provide a hydrostatic pressure that is sufficiently high to prevent boiling due to an exothermic reaction between the burned lime and the soda liquor.
3. The process according to claim 1 wherein the elevated pressure is at least 1.1 bar and at the fourth temperature is 100–160° C.
4. The process according to claim 1 wherein the elevated pressure is at least 1.5 bar and the fourth temperature is 100–160° C.
5. The process according to claim 1 wherein the elevated pressure is at least 2 bar and the fourth temperature is 100–160° C.
6. The process according to claim 3 wherein the fourth temperature is between 110–150° C.
7. The process according to claim 3 wherein the fourth temperature is between 120–140° C.
8. The process according to claim 1 wherein the method further comprises maintaining the combined slurry and the soda liquor at the elevated pressure and at the fourth temperature for 1–60 minutes.
9. The process according to claim 1 wherein the method further comprises maintaining the combined slurry and the soda liquor at the elevated pressure and at the fourth temperature for 10–40 minutes.
10. The process according to claim 1 wherein the method further comprises a retention time in step (a) that is 20–120 seconds.
11. The process according to claim 1 wherein the method further comprises a retention time in step (a) that is 30–60 seconds.
12. The process according to claim 1 wherein the first part of the soda liquor constitutes about ⅓ to ½ of an entire amount of the soda liquor and wherein the second part of the soda liquor constitutes about ½ to ⅔ of the entire amount of soda liquor.
13. The process according to claim 1 wherein the second part of the soda liquor is preheated to the third temperature that is about 5–10° C. below the fourth temperature.
14. The process according to claim 13 wherein the method further comprises preheating the second part of the soda liquor by indirect heat exchanging against a caustic soda that is produced in the process.
15. The process according to claim 1 wherein the method further comprises allowing coarse, unreacted, burned lime to settle and thereafter discharging the burned lime.
16. The process according to claim 1 wherein the method further comprises filtering the lime mud and a caustic soda under the pressure and the temperature to separate the caustic soda from the lime mud.