AF comes on 12.5k cSt all the way up to 1M cSt. Their are benefits and costs to each level in terms of effectiveness, cost, and Si carryover. It depends on your injection practices, feed foam tendency, and Si carryover + bed protection downstream to reach an optimism decision.
Other chemicals include blowdown demulsifiers, APS for ovhd corrosion, and various antifoulants for HX and heaters. There are other niche applications of chemicals but they are one off’s.
RE Cyanides, water wash is effective for piping but H2 blistering in the ovhd drum can persist and should be inspected for during TAR or online (diffusion testing).