Silicon-based antifoams (PDMS) is routinely injected in the top of coker drums to reduce foam height. However, it has been claimed by some refiners that injecting the antifoam directly with the vacuum residue in the feed line, before entering in the drum, is more effective, with a fast response and a lower dosage required.
Has anybody experience with this kind of injection? If so, which is the optimum injection point and which are the issues that must be taken into account?