In thread number 124-84220 on Jan 17, 2004, I posted a method that will work. It has worked in actual practice, but the applications were for low pressure steam (15 Psig range) How you design it is up to you. Surely with 300 PSIG steam, there is a lower pressure you can drop a small amount down to in order to get a superheated point to control at. You can do the thermodynamics to calculate the water flow needed, etc. The beauty of your application, is that it is sloppy wet by definition, and just about any old type of desuperheater should do the trick. I am leaning toward a venturi type. Better have some good long runs of straight length after the DSH, though.