Numerical Modeling of Sublimation of Ammonium Carbamate Applied to Supply System of NOx Reductant

Abstract

Recently, ammonium carbamate (AC) has attracted attention as a substitute for urea, which is a commonly used reductant for NOx emitted from combustion engines. The AC exists as a solid at room temperature, and it is decomposed to NH3 and CO2 gases by heating. Therefore, adequate heat transfer is an essential issue in the design of AC pyrolysis reactor. In this study, a numerical model that describes the sublimation of AC was developed. For modeling, this study considered the three different calculation zones: solid-phase zone, gas-phase zone, and sublimation zone. Additionally, during the sublimation process, collapse of upper solid AC into the hollow space below by the effect of gravity is considered. As a result, it is presented that the modeling shows reasonable information about the AC sublimation in a reactor, such as temperatures in a reactor, pressure of reactor, and flow rate of sublimated gas. However, it is also found that accurate prediction of spatial temperature distribution is challenging because it is related to the accurate prediction of the internal shape of AC and its collapse in a reactor.