If you want to buy a steam ejector system, it's best to call some vendors and tell them what you need it to do. I used to be a steam jet ejector designer, so please trust me when I say leave it to the experts. Steam ejectors work on very basic principles, but the final design is based ENTIRELY on proprietary emphirical data.
You see, ejector designers don't sit at a desk and design them from scratch using a given set of equations out of a text book. Well, with the nozzle they might. But beyond that it's almost an art based on past experience with certain geometries and conditions, knowing how to scale a proven design this way and that, and then maybe testing it to see if you were right. Some of the more reputable manufacturers have a 100 years of data under their belt. Here's a little inside tip: more than likely the exact size jet needed to meet your conditions had already been designed, installed, and rusted away to dirt decades ago for another client by a designer who retired and died before you were even born.
They are very simple devices, but their designs are highly emphirical and best left for experienced professionals working for reputable firms.