Papers by Keyword: Salt Deposition

Abstract: Supercritical water oxidation (SCWO) has a promising future for treating high concentration and bio-refractory organic wastewaters. However, the reactor plugging problem induced by salt deposition has hindered its extensive commercial application. In this work, we used a continuous-flow experiment plant to systematically examine the influences of the pressure, temperature, running time, initial concentration and flow rate on the deposition properties of Na₂CO₃ under supercritical water conditions. Two parameters including the deposition ratio (R) and the deposition rate (V) were defined to evaluate the deposition extent of Na₂CO₃ in the reactor. The results showed that the pressure and temperature had remarkable influences on the R and V of 1 wt% Na₂CO₃, and their increase would make R and V reduce. The running time had slight effect on the varieties of R and V. Both R and V would rise with the initial Na₂CO₃ concentration increasing. However, V had a reverse change tendency compared with R as the flow rate rose. The R and V of 1 wt% Na₂CO₃ with the flow rate of 0.65 L/h at 550 °C and 25 MPa were higher than 80% and 64 μm/h, respectively. This meant a high reactor plugging risk under the long-time run conditions. Moreover, NaOH was not suitable as the alkali neutralizer of the SCWO process at the low velocity condition in the reactor.

Abstract: The surface alloying of Si into SUS304 austenitic stainless steel was carried out by a halide-activated pack-cementation method. By this treatment, the silicon diffusion layer containing about 13 at.% Si was formed. The high temperature corrosion resistance of this specimen was evaluated under the continuous deposition of salt. The result of the corrosion test showed that the oxidation mass gain of the siliconized stainless steel was lower than that of non-treated stainless steel. It was found from the observation of the cross-section of the specimen after the corrosion test that a thin scale was formed on the silicon diffusion layer and silicon oxide was formed as an inner layer of the scale. A mechanism of the oxidation suppression for the siliconized steel under the continuous deposition of salt was investigated by the oxidation test of pure silicon, iron, chromium or nickel powder mixed with equimolar NaCl-KCl. As a result, it was found that the high corrosion resistance of the siliconized steel was attributable to the fact that the silicon oxide formed on the silicon diffusion layer was inert to the chemical reaction with the NaCl-KCl salt.