Experimental and numerical simulation verification of depositional characteristics of NH4Cl particles under variable conditions

Abstract

ABSTRACT The primary cause of U-tube heat exchanger leakage and perforation is attributed to the deposition and corrosion of NH4Cl within the condensing pipeline located at the summit of the crude oil distillation tower. This paper aims to investigate the deposition law of NH4Cl in U-shaped tubes under variable operating conditions and the impact of diverse factors on the deposition features of NH4Cl. To achieve this objective, the study establishes appropriate experimental equipment, designs a 4-factor and 4-level orthogonal experimental table, and manipulates the variables of particle incidence velocity (v), relative humidity (RH), particle size (d), and temperature (T). The experimental results of each group are recorded and analyzed. The observed experimental data reveals that under the operational parameters of Group H (v: 7 m/s, RH: 50%, d: 0.7 mm, T: 140°C), particle accumulation peaks at the elbow outlet, resulting in a substantial volume ratio of 17.14%. Conversely, Group M (v: 10 m/s, RH: 1%, d: 0.1 mm, T: 140°C) demonstrated the minimal particle deposition in the angular sector between 30° − 60° of the elbow, yielding a minimal volume ratio of 0.22%. Further scrutiny suggests that environmental humidity and incident flow velocities significantly influence particle deposition, whilst ambient temperature and particle size exert less substantial effects. A multivariate linear deposition equation between NH4Cl deposition and v, RH, d, T was derived through linear regression, yielding an Rc2 of 0.913, indicating a high level of concordance. A mathematical model was constructed, incorporating computational fluid dynamics (CFD), to simulate and analyze the flow characteristics of ammonium chloride particles in U-shaped tube bundles, which was subsequently validated with the experimental results obtained, the comparison results showed a good degree of coincidence, with an error of 4.41%.