Cooling effects of different molten salts and tube diameters on the performance of chemical reactors using butadiene synthesis as a case study

Abstract

Many industrial applications adopt solar salt as the go-to heat transfer fluid for both cooling and thermal storage systems. However, the high melting temperature of this salt makes it economically unattractive. Hence, in this study, the investigation of 12 different molten salts was carried out to provide the right decision basis for selecting suitable salts for both cooling and thermal storage applications. In light of this, we developed a computational fluid dynamics (CFD) model to simulate butadiene synthesis via the oxidative dehydrogenation of butene in a single tube reactor equipped with a cooling jacket. The CFD model was validated against experimental results with an average error of 3.5%. Parametric studies involving the different salts indicated that low melting point salts resulted in high heat removal efficiencies but reduced the overall conversion, yield, and selectivity of the reactor due to the lower reaction temperatures. Thermophysical properties such as specific heat capacities were found to have no significant impact on the cooling efficiency of the reactor. An economic evaluation of the salts based on their heating costs indicated that salts of LiNaKCsCaNO3 and NaKCaNO3 are most suitable, especially for thermal storage systems where only latent heat of fusion is required. However, in cases where further heating of the salt is needed, higher melting point salts (such as solar salt) proved to be much more economical. Investigation of the effect of different tube diameters on the cooling performance of the reactor indicated that reactors having a diameter to length ratio between 32 and 58 provide sufficient cooling and high conversion.