CFD simulation of a transpiring‐wall SCWO reactor: Formation and optimization of the water film

Abstract

A two-dimensional axisymmetric computational fluid dynamics model of a transpiring wall reactor for supercritical water oxidation was developed using the commercial software Fluent 6.3. Numerical model was validated by comparisons with experimental temperature profiles and product properties (total organic carbon and CO). Compared with the transpiration intensity, the transpiring water temperature was found to have a more significant influence on the reaction zone. An assumption that an ideal corrosion and salt deposition inhibitive water film can be formed when the temperature of the inner surface of the porous tube is less than 3748C was made. It was observed that lowering transpiring water temperature is conducive to the formation of the water film at the expense of feed degradation. The appropriate mass flux ratio between the total transpiring flow and the core flow was determined at 0.05 based on the formation of the water film and feed degradation.

Characteristics analysis of water film in transpiring wall reactor

“…Furthermore, some process parameters were optimized based on the temperature profiles and gas-liquid products in a transpiring wall reactor SCWO pilot plant by Zhang et al [20]. Some calculated models of TWRs are also proposed to simulate and improve the performance of the reactor [1,12,[21][22][23][24]. Bermejo et al [22] established a simplified model of a TWR and studied the effects of transpiring water temperature, flow rate and composition of the oxidant on the reactor performance such as the temperature and composition contours, flow path lines and effluent compositions using the commercial software Fluent 6.3.…”

“…Bermejo et al [22] established a simplified model of a TWR and studied the effects of transpiring water temperature, flow rate and composition of the oxidant on the reactor performance such as the temperature and composition contours, flow path lines and effluent compositions using the commercial software Fluent 6.3. Zhang et al [24] also presented a numerical model of TWR for SCWO and discussed the effect of the transpiration intensity and the transpiring water temperature on the temperature profile and TOC removal rate in the reactor. Moreover, the temperature of water film was optimized by controlling the inner surface temperature of the porous tube less than 374°C.…”

Effects of structural parameters on water film properties of transpiring wall reactor

“…transpiring-wall SCWO reactors. 14,[16][17][18][19] Hence, the RNG k-ε model was selected as the turbulence model for turbulence calculation in this work.…”

“…Transpiring wall porosity (β) is one of the vital structural parameters affecting the flow resistance of transpiration water. 16,27 Internal resistance coefficient (η) and permeability (ζ) are two significant factors to characterize the flow resistance above, 28 and can be obtained via the Darcy's law 22 and basic formulas of fluid flow. Internal resistance coefficient and permeabilities at various porosities conditions can be seen in Table 2.…”

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

“…Segal et al proposed an analytical model for a jet breakup in subcritical and supercritical medium accounting for the effect of the critical phase transition on surface tension. Zhang et al , evaluated the mixing enhancement of jets in a supercritical environment as a function of jet velocity and temperature in an inverted transpiring-wall reactor. Moussière et al , studied the effect of turbulence on oxidation rate and heat release.…”