Model-Free Adaptive Control for Flares and Wastewater - 4C Conference 5455

Model-Free Adaptive Control for Flares and Wastewater

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Most refinery and chemical plants operate flares to burn off waste gas for operational and safety reasons. The vent gas heating value of a flare must be monitored and controlled to meet EPA regulations. For steam-assisted or air-assisted flares, the net heating value of the gas being combusted must be 300 Btu/scf or greater. When the waste gas heating value is below this limit, supplemental gas, such as natural gas, must be added to assure sufficient combustion and minimal emission.

There are online calorimeters on the market for heating value measurement. However, adding a heating value (HV) control loop can be a challenging task due to the following reasons: (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. The flare process is difficult to control using conventional PID controllers. Model-based control can be costly to develop and maintain due to the complexity and uncertainties of the flare process.

In this training class, we will show the behavior of a typical flare process by running a real-time flare heating value process model. We will compare the control performance of different control methods by running control simulations. Lastly, we will present the results of a flare heating value control system using Model-Free Adaptive (MFA) control technology in a petrochemical plant.

In the Q&A session, we can discuss: (1) new EPA regulations relating to steam or air over-assisting problems, which are commonly seen in refineries where vent gas may have high heating values, and (2) implementation of MFA control systems for your specific applications.

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