Flare Process: Most refinery and chemical plants operate flares to burn off waste gas. The vent gas heating value of a flare must be monitored and controlled based on EPA 40CFR60.18 rules.
Flare Control Challenges: (1) There are large and varying time delays in the HV control loop; (2) The HV process is nonlinear in different operating conditions; (3) Multiple waste gas streams in a plant are sent to the flare stack, where stream flows can vary widely causing big disturbances to the heating value; (4) The HV of each waste gas stream may change widely under operating condition changes; and (5) Nitrogen is often used as purge gas to keep positive pressure in the vent pipe, making the process more complex.
MFA Flare Control System: The flare vent gas consists of waste gas from multiple streams and purge gas. Its heating value is measured with an online calorimeter. CyboCon MFA control software is installed in a PC interfacing to a DCS through OPC. A special Anti-delay Feedforward MFA controller controls the heating value in real-time by manipulating natural gas flow. The trends show a typical condition where the waste gas flow (gray) swings causing heating value to change while MFA takes quick control actions (red) to assure HV is in control.
Case History: An MFA flare control system has been running in a petrochemical plant in Texas for 2 years. Due to its robust control performance in varying operating conditions, the customer is able to lower the heating value setpoint from 400 to 350 Btu/scf to reduce natural gas consumption and still meet the EPA’s 300 Btu/scf low limit. The control system achieved substantial economic benefits for the customer.
Solution: CyboSoft is working with leading companies in the industry to offer a complete solution that the customer wants. CyboSoft can provide: (1) consulting service and design support, (2) MFA flare control solution implemented in CyboCon MFA control software, (3) CyboLink interface software to a specific DCS or PLC, (4) on-site control system commissioning and training, and (5) annual support services.
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