Control Strategies for Natural Gas Liquids Recovery Plants

Nowadays the improvements on the extraction methods of natural gas has increased the availability of natural gas liquids (NGL), which represent a valuable source of energy and industrial feedstock. Several process schemes have been developed in the past for an economical, safe and efficient recovery of these components including the conventional, cold residue recycle (CRR), and gas subcooled process (GSP), each comprising a range of competing advantages. In the present work, the control problem of the NGL extraction in a CRR process scheme is addressed aiming to achieve a recovery of at least 84% of ethane while maintaining low the level of methane impurity in the bottom of the demethanizer. Considering the high cost of composition analyzers, different temperature control structures are assessed. The temperature direct control and cascade control are proposed to improve the rejection of the disturbances. The operability of these NGL recovery technologies is evaluated under typical disturbances.