Supercritical water oxidation (SCWO) technology presents important environmental advantages for the treatment of industrial wastes and sludges. The homogeneous reaction that takes place between the oxidizable materials and oxygen, at temperatures and pressures above the critical point of the water (647.3 K and 22.12 MPa), is well known. Specific equations of state for water and aqueous mixtures, gases, and organics have been developed. The process is not having the expected industrial development. Some new plants have been closed by corrosion and operational problems related with high temperature, high pressure, and oxidative atmosphere inside of the equipments. To overcome these technical difficulties more research focused on solving operational problems is necessary. This article presents an overview of the technical aspects of the supercritical water oxidation process. Reactors design, construction materials, corrosion, salts precipitation problems, and industrial applications are discussed. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Supercritical water oxidation: A technical review

After more than three decades since its potential was first recognized, supercritical water oxidation (SCWO) remains an innovative and viable treatment technology for destruction of aqueous based organic wastes. An extensive data base of destruction efficiencies, corrosion data, and salt phase behavior has been developed over the years through the combined efforts of many investigators at both the fundamental research and commercial level. As a result, SCWO technology has been increasingly utilized in a variety of full-scale designs and applications, handling feeds as diverse as polychlorinated biphenyls (PCBs), sewage sludge, spent catalysts, and chemical weapons. This paper reviews the status of current full-scale commercial SCWO facilities around the world, focusing on the unique challenges and design strategies employed by different companies for corrosion and salt precipitation control in each application. A summary of past commercial SCWO activity as well as future plans among the current active SCWO companies is also included.

Supercritical water oxidation—Current status of full-scale commercial activity for waste destruction

Seabed Fluid Flow

Use of supercritical water (SCW) as a medium for oxidation reactions, conversion of organic materials to gaseous or liquid products, and for organic and inorganic synthesis processes, has been the subject of extensive research, development, and some commercial activity for over 25 years. A key aspect of the technology concerns the identification of materials, component designs, and operating techniques suitable for handling the moderately high temperatures and pressures and aggressive environments present in many SCW processes. Depending upon the particular application, or upon the particular location within a single process, the SCW process environment may be oxidizing, reducing, acidic, basic, nonionic, or highly ionic. Thus, it is difficult to find any one material or design that can withstand the effects of all feed types under all conditions. Nevertheless, several approaches have been developed to allow successful continuous processing with sufficient corrosion resistance for an acceptable period of time. The present paper reviews the experience to date for methods of corrosion control in the two most prevalent SCW processing applications: supercritical water oxidation (SCWO) and supercritical water gasification (SCWG).

Corrosion control methods in supercritical water oxidation and gasification processes

Water is a truly unique substance in many respects. It is the only chemical compound that naturally occurs in all three physical states (solid, liquid and vapor) under the thermodynamic conditions typical to the Earth’s surface. It plays the principal role in virtually any significant geological and biological processes on our planet. Its outstanding properties as a solvent and its general abundance almost everywhere on the Earth’s surface has made it also an integral part of many technological processes since the very beginning of the human civilization.

Aqueous fluids are crucial for the transport and enrichment of ore-forming constituents (Barnes 1997; Planetary Fluids 1990). Quantitative analysis of hydrothermal and metamorphic processes requires information on the physical-chemical, thermodynamic and transport properties of the fluid phases involved (Helgeson 1979, 1981; Sverjensky 1987; Eugster and Baumgartner 1987; Seward and Barnes 1997). These processes encompass a broad range of pressure and temperature conditions and, therefore, detailed understanding of the pressure and temperature dependencies of density, heat capacity, viscosity, diffusivities, and other related properties is necessary in order to develop realistic models of fluid behavior or fluid-mineral interactions.

Aqueous fluids under high-pressure, high-temperature conditions near and above the critical point of water ( P = 22.1 MPa and T = 647 K) are especially important in a variety of geochemical processes. Due to the large compressibility of supercritical fluid, small changes in pressure can produce very substantial changes in density, which, in turn, affect diffusivity, viscosity, dielectric, and solvation properties, thus dramatically influencing the kinetics and mechanisms of chemical reactions in water. Models of hydrothermal convection suggest that the near-critical conditions provide an optimal convective behavior due to unique combination of thermodynamic and transport properties in this region of the phase diagram of water (Norton 1984; Jupp and Schultz 2000 …

Molecular Simulations of Liquid and Supercritical Water: Thermodynamics, Structure, and Hydrogen Bonding

The supercritical water has some special characteristics that common water has no, and it can mix with oxygen with any ratio and offer solvent condition of SCWO reaction. It is a new research aspect to apply the SCWO technology on environmental protection. The technology has rapid development in recent years because of its many advantages such as low cost, good speed and high efficiency in disposing of wastes. The paper introduces the characteristics of supercritical water and the principles of SCWO, and reviews the applications of SCWO technique in treating poison organic wastes, downflow sludge and human metabolism, and point out the problems of SCWO during the research, and finally the application progresses in industry are introduced.

Liu Yong

Papers

Supercritical water oxidation technology