Thermal and Hydraulic Effects of Coke Deposit in Hydrocarbon Pyrolysis Process

Fuel pyrolysis can be of benefit for regenerative cooling techniques, due to its endothermic effect in ensuring the thermal resistance of hypersonic vehicles and structures. Among pyrolysis species production, there is that of coke formation. A numerical code is used in this paper to investigate the related phenomena, based on two experiments using titanium and stainless steel reactors, which present different pyrolysis rates under similar operating conditions. The absence of effect of the reactor’s physical properties on the pyrolysis is demonstrated. The thermal insulationeffectbycokedepositisprovedtohaveanegligibleimpactonthesystem.Thecloggingofthereactorfound experimentally is confirmed numerically at the same time. The carbon deposit thickness reaches the value of the reactor’s inner radius: 2.175 mm. The corresponding reduction of flow cross section modifies the Reynolds number, the residence time (decreased by a factor of 4) and the absorbed energy (reduction by a factor of 3). This last point is responsibleforthediscrepanciesobservedexperimentally.Thecokestickstothestainlesssteelreactorandnottothe titaniumreactor.Consequently,pyrolysis islowerforthe stainlesssteelcasethanforthe titaniumcaseunder similar furnace-temperature setups.

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