Aeration system and method

1. A system for introducing gas into a slurry disposed in a tank, said system comprising:

an impeller disposed in the tank for agitating the slurry, and

a stationary lance disposed on an outflow side of the impeller, the lance including (i) a conduit through which the gas passes, the conduit having an outlet formed therein that is generally directed away from the impeller, and (ii) at least one vane coupled to the conduit.

2. The system of claim 1 wherein the lance is spaced apart from the impeller.

3. The system of claim 1 wherein the at least one vane is a single, approximately planar blade.

4. The system of claim 1 wherein the at least one vane converts at least a portion of a swirling flow from the impeller into longitudinal flow.

5. The system of claim 1 wherein the at least one vane is a pair of vanes disposed on opposing sides of the lance, a first one of the pair of vanes is pitched relative to a second one of the pair of vanes such that the vanes have an orientation opposing the direction of swirling flow of the impeller.

6. The system of claim 5 wherein the vanes convert a portion of the swirling flow into longitudinal flow.

7. The system of claim 5 wherein the vanes are approximately planar.

8. The system of claim 5 wherein each vane is relatively thin at a leading edge and a trailing edge and is relatively thick therebetween.

9. The system of claim 1 wherein the conduit includes a main supply pipe, an elbow, and an outlet portion, and the gas outlet is disposed in the outlet portion.

10. The system of claim 9 wherein the outlet portion is approximately parallel to an impeller axis of rotation.

11. The system of claim 10 wherein the impeller axis of rotation is pitched approximately 10° to approximately 15° below horizontal.

12. The system of claim 9 wherein the direction of the gas outlet is substantially horizontal.

13. The system of claim 9 wherein the elbow has an inside radius equal to or greater the internal diameter of the main supply pipe.

14. The system of claim 9 wherein the vane has a length about two to about four times the internal diameter of the main supply pipe.

15. The system of claim 14 wherein the vane length is about twice the pipe internal diameter.

16. The system of claim 14 wherein the vane has a width about three to about five times the pipe internal diameter.

17. The system of claim 16 wherein the width is approximately four times the pipe internal diameter.

18. The system of claim 9 wherein a centerline of the outlet portion is offset from an impeller axis of rotation by a distance R that is approximately 25% to 100% of the impeller diameter.

19. The system of claim 18 wherein the distance R is approximately 35% to approximately 45% of the impeller diameter.

20. The system of claim 18 wherein the distance R is approximately 38% of the impeller diameter.

21. The system of claim 18 wherein the main supply pipe is spaced apart from the impeller by approximately one third to approximately two thirds the impeller diameter.

22. The system of claim 18 wherein the main supply pipe is spaced apart from the impeller by approximately one-half the impeller diameter D.

23. The system of claim 9 wherein the at least one vane is connected to the horizontal portion of the conduit.

24. The system of claim 23 wherein the main supply pipe is a downcomer that is approximately vertical.

25. The system of claim 1 wherein the conduit includes an approximately horizontal portion, said portion terminating to form the gas outlet.

26. The system of claim 1 wherein the gas lance outlet is offset from a longitudinal center line of the agitator.

27. The system of claim 1 wherein the slurry comprises calcium sulfite in a flue gas desulfurization process.