Experimental techniques to determine salt formation and deposition in supercritical water oxidation reactors

Conference · Mon Aug 01 04:00:00 EDT 1994

OSTI ID:10173804

Chan, J P.C.; LaJeunesse, C A; Rice, S F

Supercritical Water Oxidation (SCWO) is an emerging technology for destroying aqueous organic waste. Feed material, containing organic waste at concentrations typically less than 10 wt % in water, is pressurized and heated to conditions above water`s critical point where the ability of water to dissolve hydrocarbons and other organic chemicals is greatly enhanced. An oxidizer, is then added to the feed. Given adequate residence time and reaction temperature, the SCWO process rapidly produces innocuous combustion products. Organic carbon and nitrogen in the feed emerge as CO{sub 2} and N{sub 2}; metals, heteroatoms, and halides appear in the effluent as inorganic salts and acids. The oxidation of organic material containing heteroatoms, such as sulfur or phosphorous, forms acid anions. In the presence of metal ions, salts are formed and precipitate out of the supercritical fluid. In a tubular configured reactor, these salts agglomerate, adhere to the reactor wall, and eventually interfere by causing a flow restriction in the reactor leading to an increase in pressure. This rapid precipitation is due to an extreme drop in salt solubility that occurs as the feed stream becomes supercritical. To design a system that can accommodate the formation of these salts, it is important to understand the deposition process quantitatively. A phenomenological model is developed in this paper to predict the time that reactor pressure begins to rise as a function of the fluid axial temperature profile and effective solubility curve. The experimental techniques used to generate effective solubility curves for one salt of interest, Na{sub 2}SO{sub 4}, are described, and data is generated for comparison. Good correlation between the model and experiment is shown. An operational technique is also discussed that allows the deposited salt to be redissolved in a single phase and removed from the affected portion of the reactor. This technique is demonstrated experimentally.

• Research Organization: Sandia National Labs., Livermore, CA (United States)
• Sponsoring Organization: Department of Defense, Washington, DC (United States)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 10173804
• Report Number(s): SAND--94-8554C; CONF-9411106--1; ON: DE94016617
• Country of Publication: United States
• Language: English

Related Subjects

052001
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
320305
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES
CHEMICAL REACTORS
CORROSION
DEPOSITION
INDUSTRIAL WASTE MANAGEMENT
ORGANIC WASTES
OXIDATION
SALTS
SODIUM SULFATES
SUPERCRITICAL STATE
WASTE PROCESSING
WATER