Interaction between design and control for heat-integrated recycle plants: Ternary system with two recycles

Abstract

This chapter describes the interaction between design and control for heat-integrated recycle plants. This chapter analyzes the trade-off between steady-state economics and dynamic controllability for heat-integrated recycle plants. The process consists of one reactor, two distillation columns and the two distillation columns are heat-integrated. Optimal trajectories for heat-integrated recycle plants with direct and indirect sequences are derived as the conversion varies. Provided with correct direction for heat-integration, at any given conversion, a flow sheet is established for both sequences. The results reveal that improved control can be achieved for well designed heat-integrated recycle plants. Most of the operating cost of the recycle plant comes from the energy cost in distillation columns. It is common to reduce the energy cost by heat-integration of these two columns. For the direct separation sequence, two configurations exist: direct sequence with forward heat-integration and direct sequence with backward heat-integration. Similarly, there are two possible configurations for the indirect separation sequence: indirect sequence with forward heat-integration and indirect sequence with backward heat-integration.