Heat transfer of supercritical mixtures of water, ethanol and nitrogen in a bluff body annular flow

Supercritical water oxidation for the treatment and utilization of organic wastes: Factor effects, reaction enhancement, and novel process

Supercritical water oxidation (SCWO) has been regarded as a new and efficient technology for the harmless treatment and energy utilization of organic wastes, resulting in the quickly homogeneous oxidation between organics and oxidizers and the former being wholly degraded into small environment-friendly green molecules such as H2O and N2 and inorganic salts. This paper systematically analyzed the influencing behavior and mechanisms of the reaction factors, such as temperature, pressure, residence time, oxidant type, oxidation coefficient, and the concentration and pH values of the raw material, on the treatment effect of organic wastes. For most organic wastes, the SCWO conditions at 550 °C with a residence time of 1min and an oxidation coefficient of 100% can meet the removal rate of more than 99%. To further enhance the degradation rate of organics, the principles, implementation cases, and related equipment components of general enhancement technologies of supercritical water oxidation were discussed, such as fractional oxygen injection, auxiliary fuel co-oxidation, and hydrothermal flame-assisted degradation. This paper proposes a novel supercritical flame-assisted oxidation process in which the reactor performs preheating, corrosion protection, and desalination functions. The use of additive-enhanced oxidation, segmented oxidation, and supercritical hydrothermal flame-assisted oxidation has achieved good results in the complicated treatment process of brutal degradation of organic matter.

Hydrothermal flames for subaquatic, terrestrial and extraterrestrial applications

Hydrothermal flames are formed in supercritical water in the presence of a fuel and an oxidant (usually air or oxygen). Integrating hydrothermal flames as the heat source for supercritical water oxidation helps to minimize the reaction time (to milliseconds), improve the reaction kinetics and reduce the chances of corrosion and reactor plugging. This review outlines state-of-the-art research on hydrothermal flames including the impacts of process parameters on flame ignition. The ignition and sustainability of hydrothermal flames are dependent on several factors such as the type of fuel and its concentration, type of oxidant (air and oxygen) as well as the temperatures and flow rate of the feed and oxidant. The article describes some novel applications of hydrothermal flames for clean energy production, geothermal energy recovery, deep well spallation, wastewater treatment, degradation of recalcitrant nitrogen-containing compounds and heavy oil upgrading. Finally, the challenges and future perspectives of hydrothermal flame applications are discussed. This review also highlights some technical considerations relating to hydrothermal flames such as the choice of organic solvent and its characteristics, preheating, ignition mechanism, flame stability and propagation, advanced reactor configurations, mixing with subcritical and supercritical components, recirculation zones, cooling mechanisms, corrosion and salt precipitation.

Review on an Advanced Combustion Technology: Supercritical Hydrothermal Combustion

Supercritical hydrothermal combustion, a new and promising homogeneous combustion technology with a wide range of application scenarios and broad development prospects, provides creative ideas and means for the enhanced degradation of organic wastes, hydrothermal spallation drilling, thermal recovery of heavy oil, etc. This technology is elaborated upon in five parts: (1) introducing the main devices including semi-batch reactor and continuous reactor to study the hydrothermal flame in accordance with research institutions, (2) presenting the research status of related numerical simulation from the angles of reaction kinetics and flow-reaction, (3) summarizing the characteristics of hydrothermal flame and combustion by five key parameters, (4) dividing up ignition process and explaining ignition mechanism from the perspectives of critical physical properties of water and heat transfer and mixing conditions, (5) discussing and forecasting its industrial applications including hydrothermal spallation drilling, the thermal recovery of heavy oil, the clean conversion and utilization of coal-based fuel, and the harmless treatment of pollutants. By and large, this paper analyzed in detail everything from experimental equipment to industrial applications, from combustion characteristics to ignition mechanisms, and from summary conclusions to prospect prediction. In the end, herein is summarized a couple of existing paramount scientific and technical obstacles in hydrothermal combustion. Further significant studies in the future should include excellent reactors, advanced monitoring techniques, and powerful computational fluid dynamics.

Ignition of hydrothermal flames

The operating parameters influence the ignition and stability of premixed and diffusion limited hydrothermal flames in continuous and semi-continuous modes.