SCWO OF SALT-CONTAINING ARTIFICIAL WASTEWATER USING A TRANSPIRING-WALL REACTOR

摘要

Supercritical Water Oxidation (SCWO) is a high-pressure high-temperature process for the destruction of toxic, hazardous and/or non-biodegradable aqueous organic waste. SCWO is carried out at conditions above the critical point of pure water (T_c=374°C and p_c=221 bar). As a result of the complete miscibility of organic substrates and gases in supercritical water (SCW), high reaction rates and conversions close to unity can be achieved. The thermophysical properties of water near and above its critical point change significantly compared to ambient conditions. Water, which is polar in the liquid state, is much less polar in its critical state and becomes a good solvent to non-polar compounds and gases such as oxygen, nitrogen or carbon dioxide [1-3]. The lack of interfacial mass transfer resistances in such a single-phase mixture (under salt-free conditions) combined with high reaction temperatures, leads to short residence times and small reactor volumes (i.e., high space-time yields). Corrosion of reaction vessels and process equipment when employing SCW combined with reactive ions such as Cl~-, F~-, (H_3O)~+ and oxygen is one of the major challenges that the use of this technology needs to address [4-9]. Besides corrosion, the problem of equipment plugging due to precipitation of salt particles in SCW is the most severe problem that SCWO processes face nowadays [6]. The solubility of inorganic salts in SCW decreases sharply when exceeding the critical point of water [10-12]. Agglomerates of precipitated salts formed during operation adhere to reactor walls and change flow and heat transfer conditions across the reactor walls.