Simulation of SiO2/S coating deposition in a pilot plant set-up for coking inhibition

The anti-coking SiO2/S coating was prepared on the inner surface of HK40 alloy tube in a pilot plant set-up by atmospheric pressure chemical vapour deposition (APCVD). The coating deposition was simulated using the computational fluid dynamics code, Fluent. The reaction parameters of the surface reaction for SiO2 formation were determined based on the comparison between the experimental and the calculated values. Further, the influences of the inlet flow rate and mass concentration of source materials on the coating deposition rate were investigated. The simulated results showed that an increase of inlet flow rate led to the decrease of mass conversion of gas intermediates. The coating deposition rate along the reactor tube increased by 1-5 times as the inlet flow rate increased from 10 to 80 g min−1. The mass conversion rate of the gas intermediate, Si(OH)4, changed little at different inlet mass concentrations of source materials when the inlet flow rate was 30 g min−1, and it had an increase for sulphide intermediates. The coating deposition rate along the reactor tube increased by about 10 times with increasing the inlet mass concentration from 0.2% to 2%. In the conditions we studied, SiO2/S coating deposition was surface reaction rate limited. When the inlet flow rate was 30-40 g min−1 with the resource material concentration of 1-1.6%, the SiO2/S coating was about 15 μm at the tube outlet with the silicon-containing intermediate conversion rate of above 30% and a good uniformity of S along the reactor. This work provides a theoretical basis for optimisation of operational parameters of the anti-coking SiO2/S coating preparation in the pilot plant set-up.