Characterization of the deposition and transport of magnetite particles in supercritical water

Characteristics, mechanisms and measurement methods of dissolution and deposition of inorganic salts in sub-/supercritical water

The efficient and harmless treatment of hypersaline organic wastes has become an urgent environmental problem. Compared to traditional thermochemical methods, supercritical water oxidation has been proven to be an efficient organic waste treatment technology due to the advantages of low cost, high degradation rate, no secondary pollutants, etc. However, the solubilities of inorganic salts drop rapidly near the critical point of water, and some sticky salts form easily agglomerates and then adhere to internal surfaces of reactor and pipeline, causing plugging and inhibition of heat transfer. Hence, the characteristics, mechanisms and measurement methods of the dissolution and deposition of inorganic salts in sub-/supercritical water are summarized and analyzed systematically and comprehensively in this work, intending to provide a valuable guide for salt deposition prevention and subsequent research directions. Firstly, a new classification form of inorganic salt is put forward based on melting point. The phase equilibriums of brine systems are then analyzed in detail. Six theories concerning dissolution mechanisms are discussed deeply and various measurement methods of salt solubility are also supplemented. Furthermore, salt deposition characteristics and related measurement technologies are summarized. Notably, a new idea "hydrothermal molten salt" system is reviewed which may provide a solution for salt deposition in sub/supercritical water. Finally, an outlook for the follow-up researches is prospected and some suggestions are proposed.

Study on the Movement and Deposition of Particles in Supercritical Water Natural Circulation Based on Grey Correlation Theory

The movement and deposition of particles that occur during their natural circulation in supercritical water exercise an important impact on the safe and stable operation of a supercritical water reactor (SCWR). When supercritical water flows in pipelines, a large number of corrosive particles may be generated due to pipeline corrosion or the purity of the fluid itself. The presence of particulate matter affects the heat transfer efficiency of the pipeline, increasing flow resistance and easily promoting heat transfer deterioration. ANSYS-CFX numerical analysis software was used to simulate the natural circulation loop of supercritical water, and micron particles were added in the initial flow field. The effects of heating power, particle concentration and particle diameter on particle deposition were obtained. Through this analysis, it can be concluded that the heating of the pipeline has a certain inhibitory effect on the deposition of particles. The rise in both initial particle concentration and particle diameter serve to reinforce the deposition of particles in the heating section. Depending on the degree of influence, the contributory parameters to particle deposition include particle diameter, particle concentration and heating power in turn.