(140i) Prediction of Thermal Cracking of Hydrocarbon Feedstocks in Feed System of Syngas Reformers

Syngas is typically produced by steam reforming of hydrocarbons (HC). The reformer which is the heart of this process consists of the radiant section containing the catalyst tubes and the convection section for waste heat recovery. The mixed feed (steam plus hydrocarbon) is preheated in the convection section and the preheated mixed feed is sent to the catalyst tubes through crossover piping. Undesired cracking reactions can take place either in the convection coil or the crossover piping. The cracking reactions which take place in the crossover piping are adiabatic cracking reactions and those that occur in the mixed feed preheat coil, are non-adiabatic.

The extent of both the non-adiabatic cracking reaction in the convection section and adiabatic cracking reaction in the adiabatic zone depend on the hydrocarbon feed type, steam/carbon ratio, mixed feed inlet temperature, mixed feed inlet pressure, and mixed feed residence time in the adiabatic zone, etc.

The objectives of this study are to explore the parameters which will affect the undesired cracking of reformer feedstocks in the mixed feed preheater coil and the crossover piping.

Reformer feedstocks used in the study are naphtha, butane fractions and liquefied natural gas (LNG). The paper will study the effect of reformer feed temperature and pressure, feed residence time in the crossover volume, mixed feed preheater geometry, as well as steam/carbon molar ratio on cracking potential. The ranges of these parameters used in the study are 460 - 590 oC (reformer inlet temperature), 23.7 ? 31.7 kg/cm2-g (reformer inlet pressure), 0 ? 8 seconds (residence time in the crossover volume) and 3.0 -3.5 (steam/carbon molar ratio).

The cracking kinetics have been simulated using Technip's proprietary SPYRO® program which is widely used by the industry for prediction of hydrocarbon cracking.