Wall‐resolved large eddy simulation of turbulent flows in helically ribbed steam cracker reactors

Helically ribbed coils are commonly applied in steam cracking furnaces. To fully understand the impact of these ribbed wall modifications on the local heat transfer and associated pressure drop throughout the reactor, detailed experimental, and numerical studies have been performed. Experimental data based on stereo-particle image velocimetry (S-PIV) and liquid crystal thermography have been used to validate the numerical results from wall-resolved large eddy simulations using OpenFOAM. The validation shows an excellent agreement in terms of mean and fluctuating velocities, pressure drop, and heat transfer behavior in a discontinuously ribbed tube. Compared with the pressure drop in a continuously ribbed tube, an approximately 40% lower pressure drop is obtained with a discontinuously ribbed tube, at the cost of a slightly decreased heat transfer enhancement. This makes the discontinuously ribbed tube design particularly interesting for steam cracking applications. The results also show that the nonuniform heat transfer at the wall is inherently linked to the flow reattachment and recirculation zones caused by the rib. Finally, the validated numerical model was used to study comparable designs and propose novel helical rib designs. Based on the results of the study, enlarging the trailing edge of the conventional ribbed geometry will improve the thermal enhancement performance, and is therefore found most promising for steam cracking reactor design

Sustainable innovations in steam cracking : CO2 neutral olefin production

Steam cracking of hydrocarbons is and will continue to be the main industrial process to produce light olefins in the coming decades. In state of the art steam cracking plants more than 90% of the CO2 emissions can be directly related to the high energy consumption of the endothermic conversion in the cracking furnaces. Steam cracking accounts for a global emission of more than to 300 million tonnes of CO(2)per annum. Enhancing heat transfer in the radiation section, using green energy and reducing coke formation are key to substantially reduce CO2 emissions. Heat transfer can be increased by implementing three-dimensional (3D) coil technologies such as swirled and dimpled tubes. These reactor technologies also reduces coke formation because of the lower wall temperatures that are consequently obtained. Advanced manufacturing techniques and better computational abilities have opened the door to novel and improved 3D reactor technologies that are designed to increase the heat transfer while minimizing the pressure drop penalty. At the same time applying high emissivity coatings on the furnace refractory and reactor tubes can further reduce CO2 emissions. Substantial fuel savings can also be obtained by a novel furnace design, where the heat recovery scheme is substantially modified. Combining all these technologies could result in reducing emissions by 30%. Shifting completely to green electricity, which is practically infeasible today, is another alternative but the technologies that would potentially allow this are still in their infancy. These new technologies, combined with advanced process innovations and CO2 capture, will help the industry to meet future emissions targets

Dimples in turbulent pipe flows : experimental aero-thermal investigation

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