Flare process control.

CyboSoft has developed a flare process control solution that can effectively control the flare vent gas heating value to meet EPA regulations. An MFA flare control system has been running in a plant for 1.5 years and achieved substantial economic benefits for the customer.

EPA is ramping up its enforcement actions to investigate illegal air emissions by industrial flares. Since EPA will want to see the flare net heating value data from the previous 5 years when they issue a Clean Air Act (CAA) section 114 letter, it is very important for all flare operators to install a real-time heating value sensor and control system to comply with the limits and save records.

CyboSoft CEO Dr. George Cheng said, "We have the technology, products, and experience in flare control and want to help the industry effectively control this complex and difficult process."

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 based on EPA 40CFR60.18 rules. 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. The MFA control system diagram illustrates a flare process and its key variables.

There are online calorimeters on the market that can determine the heating value or Wobbe-index of a gas in real-time. 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. On the other hand, model-based control can be costly to develop and maintain. CyboSoft's Model-Free Adaptive (MFA) control methods and products are well suited for this application and we are confident to say that it is the most cost-effective and robust control solution for flare processes," Dr. Cheng added.

• See the case study Model-Free Adaptive Control of Flare Heating Value Process here.

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