Measurements and modeling of deposition rates from a near supercritical aqueous sodium sulfate solution to a heated cylinder
Toxic organic wastes and mixed wastes, composed of toxic organic compounds and radioactive elements, are a major environmental management problem. Supercritical water oxidation (SCWO) shows promise for effective remediation of these wastes by destroying their organic constituents and, when necessary, concentrating their radioactive ingredients in forms suited to safe disposal. In the Supercritical Water oxidation process, organic compounds containing heteroatoms such as S, Cl or P are oxidized to the corresponding acid. In order to avoid corrosion, bases are therefore often injected into the reactor. The salts that are formed upon neutralization (sulfates, chlorides, phosphates, etc.) have low solubility in SCW and consequently precipitate as solid phases. These salts can form agglomerates and coat internal surfaces, leading to plugging of transport lines and inhibition of heat transfer. The purpose of this study is to develop an understanding of salt deposition kinetics and nucleation phenomena in SCWO reactors. The authors provide experimental deposition rate data from a sodium sulfate-containing SCW stream to a heated cylinder and develop a predictive model which is buttressed by these data. They also discuss how the deposition rate is linked to the nucleation mechanism and what type of nucleation is most important in the experiments. For the experiments, the test section is a six-port chamber which is fashioned from a 1.91 cm (3/4 in.) diameter Swagelok cross. One port was used to mount a 5.08 mm diameter internally heated cylinder into the center of the chamber and the remaining ports provided fluid cross flow, visual observation capability and instrumentation access. Aqueous sodium sulfate solutions of 4 wt% salt concentration were pumped at about 250 bar through preheaters that brought the solution to a temperature close to that at which precipitation occurs. The heated cylinder raised the nearby solution above this temperature, thus limiting deposition almost exclusively to the heated cylinder. The rate of deposition was observed to be of order 0.1 gm/minute. Natural convection dominated transport at the conditions investigated and the observed deposition rates indicate that all the salt nucleated heterogeneously at the salt layer-solution interface.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (US)
- Sponsoring Organization:
- National Institute of Standards and Technology
- OSTI ID:
- 20014385
- Resource Relation:
- Conference: 32nd National Heat Transfer Conference, Baltimore, MD (US), 08/08/1997--08/12/1997; Other Information: PBD: 1997; Related Information: In: ASME proceedings of the 32nd national heat transfer conference (HTD-Vol. 350). Volume 12: Fundamental experiment techniques in heat transfer; Thermal hydraulics of advanced nuclear reactors; Heat and mass transfer in supercritical liquid systems; Heat transfer in energy conversion; Heat transfer equipment; Heat transfer in gas turbine systems, by Beasley, D.E.; Hassan, Y.A.; Cheung, F.B.; Yang, B.; Presser, C.; Olsen, D.A.; Tong, W.; Phelan, P.; Swanson, L.W.; McEligot, D.W.; Bogard, D.G. [eds.], 261 pages.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Experimental techniques to determine salt formation and deposition in supercritical water oxidation reactors
Oxidation and hydrolysis of acetic acid and methylene chloride in supercritical water as a means of remediation