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Flare process control solution

29 March 2016

CyboSoft has developed a flare process control solution that is said to effectively control the flare vent gas heating value to meet the US EPA regulations. A flare control system has been running in a plant for over a year has achieved substantial economic benefits for the customer.

The US Environmental Protection Agency (EPA) is ramping up its enforcement actions to investigate illegal air emissions by industrial flares which makes it important for flare operators to install a real-time heating value sensor and control system to comply with the limits and have a record of compliance.

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 are able to 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 because there are large and varying time delays in the HV control loop; the HV process is nonlinear in different operating conditions; 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; the HV of each waste gas stream may change widely under operating condition changes; and 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 and 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 that it is the most cost-effective and robust control solution for flare processes," said Dr George Cheng, CEO at CyboSoft.


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