DYNAMIC OPTIMIZATION OF INTENSIVE ENERGETICALLY INTEGRATED CRYOGENIC PROCESSES

JUAN I. LAIGLECIA; MARIELA RODRIGUEZ; PATRICIA HOCH; MARIA SOLEDAD DIAZ

Santiago de Chile

Congreso; ICCOPT2010, International Conference on Continuous Optimization; 2010

Universidad de Chile

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 demethanizer model includes path constraints on CO2 solubility in the upper stages. Dynamic separation vessels and static turboexpander models have been included. The DAE optimization problem has been transformed into a large NLP applying orthogonal collocation over finite elements in time. An IP method with rSQP techniques is used. Optimization variables are top pressure in the demethanizer and a bypass fraction 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 flowrate. Numerical results provide optimal temporal and spatial profiles and have been compared to plant data, with good agreement.