Effect of the exposure time in coke making atmosphere on the microstructure and properties of a refractory castable used in the petrochemical industry

Refractory castables used in Fluidized Catalytic Cracking Units (FCCU) are said to deteriorate due coke formation during the production of light hydrocarbons, causing a shortening in the operating time of the reactor. Consequently, a significant financial loss for the petrochemical will occur. Several studies have been carried out, but none of them showed clearly how much is the contribution of the coke for the concrete final deterioration. It still remains the doubt if the coke is the responsible for the damage observed macroscopically in a FCCU's riser. In this way, this work aimed to study the effect of the time in a coke making atmosphere on an anti-erosive class-C refractory castable, seeking for microstructural changes or on physical properties that indicate degradation mechanisms and give support to the understanding of the phenomenon. Samples of an industrial refractory castable used in petrochemical units were prepared and subjected to a forced coke making process in a simulation reactor. The temperature and the heating rate were kept constant at 540 deg C and 50 deg C/h, respectively. The values of 10, 60, 120, 240 and 480 h were used for the time of exposition to the propene gas. The microstructure of the samples was characterized through optical and scanning electron microscopy and its mineralogical phases through X-ray diffraction. Complementary analyses were necessary to a better understanding of the phenomenon. The results show that the surface and the microstructure are gradually impregnated by coke, which fills up pores, microcracks and cracks. Evidences of microcracking around the coke filled pores were not found. However, many aggregates present some type of deterioration related to the time of exposition to propene. Those damages are not necessarily caused by coke directly (author)