Plant-wide control of coupled distillation columns with partial condensers

Common natural gas processing provides a specific example of this alternative control system. Natural gas commonly includes high concentrations of CO2 that must be removed prior to pipeline or LNG distribution. The existence of a minimum-boiling temperature azeotrope between ethane, virtually always present in natural gas, and carbon dioxide complicates the separation of CO2 from the hydrocarbons. This separation commonly employs extractive distillation with high-molecular-weight hydrocarbons. Our recent paper Ebrahimzadeh et al. (2016) discusses in detail the steady-state economic design of a new extractive distillation strategy for the CO2-ethane azeotrope separation with three columns. This strategy shows a 5% reduction in capital and 15% reduction in operating costs when compared to optimized versions of the conventional process. The new strategy also produces CO2 in a liquid rather than a vapor phase, which simplifies transport, storage, and handling. Two columns of the proposed design use partial condensers and are the focus of this investigation.