In our units We have had injection of antifoams with or without injector (QUILL) and what we founded based in our results obtained of the observations, that a good operations for that systems depend of the velocity of the fluid entering to the drum, the fluid that you use like Carrier (LCGO, HCGO, etc) and of the type of viscosity of the antifoam. This does not mean that this type of injector does not help us. but the difference that we saw was not much
About the criteria of the design speed for that system, there are pages in the previous forums where you can look for this topic (old discussions).
We used like injector a pipe of 1″of diameter (1 1/4″ tubingx 3/16″wall, Mat´l A-268-TP405) with some guide plate inside of the nozzle, This quill was mounted in a 4″ 300 # nozzle in the top, its length was of 1.5 meters
I´m sorry for my english, best Regards