Recovering a caustic solution via calcium carbonate crystal aggregates
Techniques for growing crystalline calcium carbonate solids such that the crystalline calcium carbonate solids include a volume of 0.0005 mm 3 to 5 mm 3 , include a slaker to react quicklime (CaO) and a low carbonate content fluid to yield a slurry of primarily slaked lime (Ca(OH) 2 ); a fluidized-bed reactive crystallizer that encloses a solid bed mass and includes an input for a slurry of primarily slaked lime, an input for an alkaline solution and carbonate, and an output for crystalline calcium carbonate solids that include particles and an alkaline carbonate solution; a dewatering apparatus that includes an input coupled to the crystallizer and an output to discharge a plurality of separate streams that each include a portion of the crystalline calcium carbonate solids and alkaline carbonate solution; and a seed transfer apparatus to deliver seed material into the crystallizer to maintain a consistent mass of seed material.
1. A method for growing calcium carbonate solids, the method comprising:
introducing a slurry of primarily slaked lime that comprises between 2 wt % and 40 wt % calcium hydroxide at a loading rate between 20 kg-Ca/m 2 /h and 30 kg-Ca/m 2 /h into a fluidized-bed reactive crystallizer that comprises a bed of solid particles;
introducing an alkaline carbonate solution that comprises hydroxide and carbonate into the fluidized-bed reactive crystallizer that comprises the bed of solid particles;
flowing the slurry of primarily slaked lime and the alkaline carbonate solution through the fluidized-bed reactive crystallizer to fluidize the bed of solid particles;
reacting at least a portion of the slurry of primarily slaked lime and the alkaline carbonate solution to precipitate calcium carbonate and deposit a portion of precipitated calcium carbonate onto the bed of solid particles; and
discharging a portion of the bed of solid particles and the alkaline carbonate solution from the fluidized-bed reactive crystallizer, the portion of the bed of solid particles comprising a portion of mature pellets of calcium carbonate.
2. The method of claim 1 , wherein introducing the slurry of primarily slaked lime includes injecting the slurry of primarily slaked lime directly into the bed of solid particles with at least one injection device.
3. The method of claim 2 , wherein injecting the slurry of primarily slaked lime with the at least one injection device includes injecting the slurry through a horizontal cross-sectional area of the bed of solid particles.
4. The method of claim 2 , wherein injecting the slurry of primarily slaked lime with at least one injection device includes injecting the slurry with one or more lances or nozzles that extends into the fluidized-bed reactive crystallizer at a particular angle.
5. The method of claim 4 , wherein each of the one or more lances includes a set of branches that angularly extend from a main trunk.
6. The method of claim 1 , further comprising:
extracting the portion of mature pellets of calcium carbonate discharged from the fluidized-bed reactive crystallizer;
grinding the portion of mature pellets of calcium carbonate into a seed material; and
delivering at least a portion of the seed material to the fluidized-bed reactive crystallizer.
7. The method of claim 1 , further comprising:
obtaining a portion of pellets from a wastewater treatment process or a water softening process;
grinding the portion of pellets into a seed material; and
delivering at least a portion of the seed material to the fluidized-bed reactive crystallizer.
8. The method of claim 1 , wherein flowing the slurry of primarily slaked lime and the alkaline carbonate solution through the fluidized-bed reactive crystallizer includes introducing the slurry of primarily slaked lime and the alkaline carbonate solution at a calcium to carbonate molar ratio in a range of 1.1:1 to 30:1.
9. The method of claim 1 , wherein:
introducing the slurry of primarily slaked lime into the fluidized-bed reactive crystallizer includes introducing the slurry of primarily slaked lime into the fluidized-bed reactive crystallizer at an influent flow rate, the method further comprising:
recirculating a portion of the alkaline carbonate solution at a recirculation flow rate, a ratio of the recirculation flow rate to the influent flow rate being between 19:1 and 50:1.
10. The method of claim 1 , further comprising:
separating the portion of the mature pellets of calcium carbonate from the portion of the bed of solid particles and from at least a portion of the alkaline carbonate solution; and
yielding a washed mature pellets stream comprising less than 15 wt % moisture content.
11. The method of claim 1 , wherein flowing the slurry of primarily slaked lime and the alkaline carbonate solution through the fluidized-bed reactive crystallizer to fluidize the bed of solid particles includes fluidizing the bed of solid particles at a fluidization velocity range between 60 m/h and 120 m/h.
12. The method of claim 1 , wherein flowing the slurry of primarily slaked lime and the alkaline carbonate solution through the fluidized-bed reactive crystallizer to fluidize the bed of solid particles includes fluidizing the bed of solid particles at a fluidization velocity range between 80 m/h and 100 m/h.
13. The method of claim 1 , wherein introducing the slurry of primarily slaked lime and introducing the alkaline carbonate solution into the fluidized-bed reactive crystallizer includes introducing the slurry of primarily slaked lime together with the alkaline carbonate solution into the fluidized-bed reactive crystallizer.
14. The method of claim 1 , wherein the portion of mature pellets of calcium carbonate includes mature pellets of calcium carbonate each having a diameter between 0.1 mm and 0.4 mm.
15. A system for growing calcium carbonate solids in the presence of an alkaline carbonate solution, the system comprising:
a slaker configured to yield a slurry of primarily slaked lime that comprises between 2 wt % and 40 wt % calcium hydroxide; and
a fluidized-bed reactive crystallizer fluidly coupled to the slaker and configured to enclose a bed of solid particles, the fluidized-bed reactive crystallizer configured to:
receive the slurry of primarily slaked lime at a loading rate between 20 kg-Ca/m 2 /h and 30 kg-Ca/m 2 /h and receive the alkaline carbonate solution comprising hydroxide and carbonate; and
discharge the alkaline carbonate solution and discharge a portion of the bed of solid particles, the portion of the bed of solid particles comprising a portion of mature pellets of calcium carbonate.
16. The system of claim 15 , further comprising at least one injection device configured to introduce the slurry of primarily slaked lime directly into the bed of solid particles.
17. The system of claim 16 , wherein the at least one injection device is configured to inject the slurry of primarily slaked lime through a horizontal cross-sectional area of the bed of solid particles.
18. The system of claim 16 , wherein the at least one injection device comprises at least one lance or nozzle that extends into the fluidized-bed reactive crystallizer at an angle.
19. The system of claim 18 , wherein the at least one injection device comprises the at least one lance, and the at least one lance includes a main trunk and a plurality of branches that angularly extend from the main trunk within the fluidized-bed reactive crystallizer.
20. The system of claim 15 , further comprising:
a grinding system configured to extract the portion of mature pellets of calcium carbonate discharged from the fluidized-bed reactive crystallizer and to grind the portion of mature pellets of calcium carbonate into a seed material; and
a seed transfer apparatus configured to deliver the seed material into the fluidized-bed reactive crystallizer.
21. The system of claim 15 , further comprising:
a grinding system configured to obtain a portion of pellets from a wastewater treatment process or a water softening process and to grind the portion of pellets into a seed material; and
a seed transfer apparatus configured to deliver the seed material into the fluidized-bed reactive crystallizer.
22. The system of claim 15 , wherein the fluidized-bed reactive crystallizer is configured to receive the slurry of primarily slaked lime and the alkaline carbonate solution at a calcium to carbonate molar ratio in a range of 1.1:1 to 30:1.
23. The system of claim 15 , wherein:
the fluidized-bed reactive crystallizer is configured to receive the slurry of primarily slaked lime at an influent flow rate, the fluidized-bed reactive crystallizer configured to recirculate a portion of the alkaline carbonate solution at a recirculation flow rate; and
a ratio of the recirculation flow rate over the influent flow rate ranges from 19:1 to 50:1.
24. The system of claim 15 , further comprising a separation and washing station fluidly coupled to the fluidized-bed reactive crystallizer, the separation and washing station configured to wash the portion of mature pellets of calcium carbonate, and to yield a washed mature pellets stream comprising less than 15 wt % moisture content.
25. The system of claim 15 , further comprising a control system communicably coupled to at least one of the slaker or the fluidized-bed reactive crystallizer, the control system configured to perform operations comprising:
operating one or more pumps that is fluidly coupled to the fluidized-bed reactive crystallizer to flow the alkaline carbonate solution to fluidize the bed of solid particles.
26. The system of claim 25 , wherein the control system is configured to perform operations comprising operating the one or more pumps to fluidize the bed of solid particles at a fluidization velocity range between at least one of:
60 meter per hour (m/h) and 120 m/h; or
80 m/h and 100 m/h.
27. The system of claim 15 , wherein the fluidized-bed reactive crystallizer is configured to receive the slurry of primarily slaked lime together with the alkaline carbonate solution.
28. The method of claim 1 , wherein the portion of mature pellets of calcium carbonate includes calcium carbonate crystal aggregates.