I thinked a lot about that cascade for few days, thanks NoL and Tom for conversations

So, I will change I stage compressor with II stage compressor, so compressor with the highest capacity will be placed on stage II (we wanna super low HX temperature).

Third stage will be autocascading Methane with R290, I will try to get good condenser for it. I will play with captubes too and tune I stage for super high load, it should hold at least -35*C@full load (II and III stage with III stage loaded), it will be enough for ethylene to condense properly.

We will spend some more money, but I think that that unit is worth it. If everything will go ok, it will be one of the strongest cascades in the world, won`t be ?

Still waiting for Symphy