Numerical and experimental investigation into clogging phenomenon in vaporizer coil of methanol steam reformers

Following long-term continuous operation, the outlet regions of the vaporizer coils in methanol steam reformers become clogged as the result of particle deposition. The resulting reduction in the cross-sectional area of the coil impedes the outlet flow of the vaporized gas and may cause serious operational problems, including a reduced hydrogen production efficiency, power surging, and even system shutdown. Accordingly, the present study performs numerical simulations to investigate the clogging phenomenon in the vaporizer coil of a methanol steam reformer operated on five different fuels, namely methanol-water fuels with molar ratios of 75%:25%, 62%:38%, and 50%:50%, respectively, pure methanol fuel, and pure ethanol. For each fuel, the simulations investigate the velocity field distribution within the coil, the clogging formation in the outlet region of the coil, and the particle penetration probability. The results show that of the five fuels, the pure methanol fuel (with the lowest dynamic viscosity coefficient (5.008.10(-4)N.s . m(-2)) has the highest flow velocity at the coil outlet (10.2 m s(-1)). By contrast, the pure ethanol fuel (with the highest dynamic viscosity coefficient (1.074.10(-3)N. s.m(-2)) has the lowest exit velocity (8.17 m s(-1)). For each fuel, the flow velocity within the coil remains approximately constant and a clogging effect is observed at the coil outlet. The severity of the clogging effect increases with a decreasing outlet velocity. Thus, the particle penetration probability has a maximum value of 71.88% for the pure methanol fuel and a minimum value of 70.958% for the pure ethanol fuel. The validity of the simulation results is confirmed by comparing the clogging results for the methanol-water fuel with a molar ratio of 62%:38% with the experimental observations. It is shown that a good qualitative agreement exists between the two sets of results for both the thickness of the deposited layer and the positions of the main clog formations. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.