Optimizing an intensive energetically integrated cryogenic process

M. SOLEDAD DÍAZ; JUAN I. LAIGLECIA; MARIELA A. RODRIGUEZ; PATRCIA M. HOCH

Santiago

Conferencia; The International Conference on Continuous Optimization; 2010

We perform dynamic optimization of an integrated turboexpansion natural gas processing plant. Cryogenic countercurrent heat exchangers with partial condensation have been modeled through dynamic mass, energy and momentum balances in both phases, and thermodynamics with the SRK equation of state. The dcmethanizer model includes path constraints on C02 solubility in the upper stages. Dynarnic separation vessels and static turboexpander Dynarnic separation vessels and static turboexpander models have been included. The DAE optimizatian problem has been transformcd into a large NLP applying orthogonal collocation over finite clemcnts in time. An IP method with rSQP techniques is used. Optimization variables are top pressure in the demethanizer and a bypass fractian in heat exchangers. The objective is to maximize ethane recovery, when changing to a different operating mode or when step and ramp changes are introduced in feed flowratc. Numcrical results provide optimal temporal and spatial profiles and have been compared to plant data, with good agreement.