Process controller having improved surge capacity control and related methodology

A non-linear level controller (NLLC) for controlling surge capacity in a processing system comprising at least one vessel receiving an inlet flow of a fluid comprising liquid subject to variation and supplying an outlet flow to at least one downstream processing unit, comprising:

• a CPU running stored executable software implementing the following steps:
• computing a first parameter relating to a difference between a current inventory in said vessel and a prevailing inventory limit for said vessel and a second parameter relating to a difference between said current inventory and an inventory set point;
• and comparing an unforced time to reduce said first parameter by a first percentage (T*) in a first time T1;
• a plurality of inputs coupled to said CPU operable for receiving process information comprising fluid comprising liquid information during a process run by said processing unit, and
• a plurality outputs driven by said CPU for sending control signals to control said inlet flow or said outlet flow based on said first parameter if T*≦T1 and based on said second parameter if T*>T1.

A processing system, comprising

• equipment for performing actions to process fluid comprising liquids in said processing system, said system comprising at least a first vessel, said first vessel having a capacity and an inlet for receiving an inlet flow of said fluid comprising liquid and an outlet for supplying an outlet flow to at least one downstream unit, and
• a non-linear level controller (NLLC) for controlling surge capacity in said system coupled to a flow controller, said flow controller coupled to a control valve operable to control said inlet flow to or said outlet flow from said vessel, said NLLC comprising:
• a CPU running stored executable software implementing the following steps:
• computing a first parameter relating to a difference between a current inventory in said vessel and a prevailing inventory limit for said vessel and a second parameter relating to a difference between said current inventory and an inventory set point;
• and comparing an unforced time to reduce said first parameter by a first percentage (T*) in a first time T1;
• a plurality of inputs coupled to said CPU operable for receiving process information comprising fluid comprising liquid information during a process run by said processing unit, and
• a plurality outputs driven by said CPU for sending control signals to control said inlet flow or said outlet flow based on said first parameter if T*≦T1 and based on said second parameter if T*>T1.