Deposition properties of sodium carbonate in supercritical water in a continuous-flow tubular reactor

摘要

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 Na_2CO_3 under supercritical water conditions. Two parameters including the deposition ratio (R) and the deposition rate (V) were defined to evaluate the deposition extent of Na_2CO_3 in the reactor. The results showed that the pressure and temperature had remarkable influences on the R and V of 1 wt% Na_2CO_3, 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 Na_2CO_3 concentration increasing. However, V had a reverse change tendency compared with R as the flow rate rose. The R and V of 1 wt% Na_2CO_3 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.