Abstract
On the technology utilizing supercritical water, it is a severe problem that the inorganic salts deposition caused by the decrease of the dielectric constant of supercritical water. Depending on the kind and concentration of salt, operation temperature and pressure, inorganic salts will cause the blockade in the process pipes during a short operation time. If the chlorinated organic compounds are decomposed by supercritical water oxidation (SCWO : 600°C, 25MPa), HCl is generated as the result of the decomposition reaction. This HCl is neutralized by an alkali solution and transformed to an inorganic salt. We have found the salt passage characteristics (the extent of salt entrained by the reactor effluent) varies with the kind of alkali under the supercritical water condition. If a NaOH solution is used as a neutral agent, HCl is transformed to NaCl. If a KOH is used, it is KCl is formed. The solubility of NaCl and KCl are almost same values (100mg/L) under the conditions of 500°C and 23MPa. When a NaCl solution having a concentration of 10,000mg/L was supplied to a straight pipe (4.5mmID×455mmL) at the flow velocities of 5.5∼176 cm/s in the supercritical water under these conditions, the NaCl solution caused blockade by salt deposition in a short operation time. On the other hand, when a KCl or a CaCl2 solution (100,000mg/L) was supplied under condition of 600°C and 25MPa, these salts were completely recovered in the effluent without deposition for 4 hr operation time. These results indicate that solubility of a salt does not necessarily reflect its passage characteristic. In this paper we present some experimental results about the passage characteristics of inorganic salts.
