Simulation of Flared Gases Combustion Inside a Double-Wall Thermal Chimney Using Computational Fluid Dynamics

In most refineries and petrochemicals in the Middle East, flare gases are sent to the environment without using their thermal energy. The present research aimed to design a double-walled thermal chimney to generate electricity from the energy of the combustion gases. The design includes a two-wall chimney, combustion chamber, canopy, and flare. A ring-type flare was placed under the canopy. Fresh air enters the combustion chamber (under the canopy). Hot combustion gases heat it. Then, all the gases find their way to the chimney. Fuel includes air and methane, which enters the combustion chamber with a mass flow rate of 414.72 kg/day and a molar ratio of 2:1 at 303 K. The daily consumption of methane is 138.24 kg. The effects of the canopy angle, fuel flow rate, chimney height, wall distance, and fire burner on electricity production were investigated using commercial CFD software. Results showed as the distance between the two walls increases, the temperature, velocity, and electric power change non-monotonic. Changing the canopy angle from 7  to 25  increased the throat density to 0.805 kg/m3 and decreased the outlet temperature to 423 K. The velocity and electric power both showed non-monotonic behavior. Additionally, increasing the chimney height led to an increase in outlet velocity to 19.80 m/s, density to 0.829 kg/m3, and electric power to 2.368 kW/day. In contrast, the outlet temperature decreased to 378 K. Also, increasing the burner’s distance from the chimney’s central line resulted in non-monotonic behavior. The velocity at the throat reached up to 30.182 m/s, while the temperature of the throat increased significantly to 995 K. Finally, for the current design, the maximum electric power available was 3.568 Kw/day.