High-recycle ammonia loop (equation-oriented)

A tight, high-recycle ammonia synthesis loop built to show why a modern simulator solves recycles the way legacy sequential-modular tools can't. Fresh syngas (N2 + 3H2, with argon inert) mixes with a large recycle, reacts to only ~10% per pass, chills so ammonia condenses out as product, and the unreacted gas recycles — a recycle-to-fresh ratio of ~5:1, with argon building up until a small purge balances it. Run this in Equation-Oriented mode (Solver menu > Mode > Equation-oriented). In the default sequential-modular mode the solver tears the recycle and iterates Wegstein ~78 times to close the loop; the equation-oriented solver instead makes every inter-unit stream a global unknown and closes all ~35 of them in one simultaneous Newton solve — the same simultaneous approach AVEVA SimCentral / gPROMS / IDAES use, and the reason tightly coupled recycles that crawl (or stall) in sequential-modular converge cleanly here. Honesty note: the ammonia-formation Keq is illustrative (chosen for a realistic ~10% per-pass conversion and ~5:1 recycle), not a fitted plant value; both solver modes reach the same converged answer — the point is the path, not the result.