Flare Design: Sonic tips with variable exit area

Image courtesy of Zeeco, Inc.® – all rights reserved.

Summary

Sonic tips are designed to discharge the flare gas at sonic velocities. The most conventional technology is the multi-arm design, with fixed or variable exit areas.

Variable exit tips allow greater flexibility in dictating the velocity of gas, and therefore mixing with air for low emission combustion. However, additional moving parts adds complexity to the flare design.

How it Works

• The multi-arm design allows to route the gas to a number of smaller diameter burner nozzles in order to achieve high velocities, increase mixing with combustion air, improve combustion efficiency and reduce soot and smoke formation at high flow rates.
• Multi-arm with variable slot flare tips have been developed to achieve sonic velocities over the entire operating range and maintain a good combustion efficiency at any flow rate thus providing smokeless operation.
• Multi-arm with variable slot flare tips are fitted with a spring mechanism in each arm connected to a moving part that allows the exit area of the flare tip to change depending on the supply pressure and flow rate of the gas.

• A high pressure guy-supported flare with a capacity of 120 MMSCFD was installed in a large capacity electric powered compressor station located in the greater Permian Basin area.
• The flare tip consists of high pressure multi-jet tips. Each arm of the tip incorporates a self-actuated variable exit area assembly that opens as necessary relative to internal pressure. This ensures operation at high exit velocities over a wide range of flow rates.
• 80 psig pressure is maintained upstream of the flare tip. Since the flare tip operates at high pressure, it does not require additional assist media (steam or air) even at low flow rates.
• Based on the performance of multi-jet tips in the facility, this type of tip provides smokeless operation with 98% destruction efficiency over a large range of operation.