A review on pyrolysis and coking of liquid hydrocarbons in heated pipe

Pyrolysis coking of hydrocarbon fuels in heated pipe has attracted extensive attention in regenerative cooling technology, ethylene cracking industry and combustion engine. The reactor geometry, feedstock types, and product detection and characterization mean of concern are abstracted from engineering practice. Liquid hydrocarbon produces small molecules of alkanes, alkenes and aromatics by gas phase pyrolysis, then transforms into coke through chemical vapor deposition. Due to the extremely low partial pressure of carbon on coke surface, the process from hydrocarbon gas to solid coke was modeled into a pseudo-homogeneous process. In order to realize the dynamic simulation of the coking process, researchers found the characteristic time of gas-phase reaction was much shorter than that of the surface reaction. Therefore, the corresponding coking kinetics model was built based on the specific experimental coking mode and was widely used in the multi-physical field coupling CFD calculation. This study demonstrates that the dynamic evolution of coke morphology plays a pivotal role in governing transient variations of coking rates. Therefore, capturing the instantaneous evolution of coke morphology could serve as a novel approach to constructing unsteady-state coking model. The in-situ carbon protective layer is formed to shield catalytic sites and precursors, addressing the challenges of poor adhesion between coatings and substrates, as well as the tendency of coatings to delamination. Moreover, coke-removal coatings that catalyze carbon conversion and enable online de-coking show significant potential for development. Additionally, the introduction of functional additives—such as O2, CO2, syngas, ammonia, alcohols, and furans—represents an emerging direction for suppressing coke formation.