Deposition Properties of Sodium Carbonate in Supercritical Water in a Continuous-Flow Tubular Reactor

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.