Quench-converter ammonia synthesis loop

The multi-bed quench converter BASF first installed in 1942, which displaced the tube-cooled converters before it, running inside a complete 200 bar synthesis loop. Ammonia synthesis is equilibrium-limited and exothermic, so the catalyst wants to run hot for rate and cool for equilibrium, and no single adiabatic bed can do both. The quench converter's answer is mechanical: split the loop gas, send 55% through the interchanger into bed 1 and inject the other 45% as cold shots between the beds, so each bed heats up adiabatically and each quench pulls it back down. What it computes: the sawtooth, 673 -> 766 K in bed 1, quenched to 689 K and out at 760 K, quenched to 712 K and out at 766 K; 12.5 mol% ammonia at the converter exit, in the 12-18% band real quench converters deliver, at 20.9% nitrogen conversion per pass; 44.6 mol/s of 97.8% liquid ammonia off the 250 K separator; and argon and methane held at 3.3% and 4.2% in the loop by a 3% purge, with the recycle closed by a Wegstein tear. The acid test is the counterfactual: one adiabatic bed producing that same 12.51 mol% ammonia exit ends at 834.7 K -- 562 C, past the sintering limit of promoted-magnetite catalyst -- while the three-bed quench converter delivers the identical duty with a 766 K (493 C) peak. Honesty notes: (1) each bed is a specified-conversion adiabatic reactor, so the model computes the THERMAL consequence of a given quench split faithfully but does not predict the conversion itself -- the equilibrium ceiling that motivates the design is an input to the story here, not an output of it, and a kinetic or equilibrium bed model is the next increment; (2) the feed/effluent interchanger is represented by two specified-temperature heaters rather than a coupled exchanger, so its area and approach are not checked; (3) no catalyst kinetics, bed pressure drop, or converter sizing; (4) the 2.2% dissolved hydrogen, nitrogen and argon in the liquid ammonia is a real separator result, not an artifact -- a plant recovers it in a letdown flash that is not modeled here; (5) this is the converter class BASF pioneered, not a reproduction of a specific BASF converter. Closed loop balances of this kind are what an acceptance test under VDI 2048 reconciles plant measurements against.