Simulation of a Concentric-Tube Reactor for Supercritical Water Oxidation

Abstract

To further enhance the development of the supercritical water oxidation (SCWO) process, a concentric-tube reactor model has been developed. Because of the heat generation and transfer processes within the reactor, both reaction kinetics and heat transfer rate factors are incorporated in the model. The simulation model treats the reactor as a number of segments, and each segment is assumed to be isothermal.The model was validated by pilot-plant tests involving the destruction of acetic acid, phenol, and n-cctanol. These tests were conducted in a pilot-scale SCWO facility that is equipped with a 6.1-meter long concentric-tube reactor and capable of treating waste water at a rate of 150 liter per hour. All simulation results, using pseudo-first-order kinetic models, agreed favorably with the pilot-plant data. The simulated reactor temperature profiles agreed well with the measured profiles.The supercritical water oxidation process (SCWO) is an environmentally attractive method for the safe and economical treatment of toxic organic waste waters and sludges. The SCWO process is capable of destroying undesirable organic compounds, converting the waste into non-noxious materials, accomplishing this task within an essentially enclosed environment. The key unit in the SCWO process is the reactor that generally operates at temperatures and pressures ranging from 400°C to 650°C and 25 MPa to 35 MPa, respectively. The exothermic heat can be sufficient to sustain the reaction. It has also been demonstrated that byproducts such as reusable water, heat, and usable inorganic substances can be produced by the SCWO process.After more than a decade of research and development, the process is now poised for potential wide-spread application (1), especially with the first commercial unit in operation.To further enhance the development of the SCWO process for industrial-scale applications, it is necessary to understand the reactor performance and develop reliable 1

Supercritical water oxidation: A technical review

“…With the scaling of the processes and the interest in the heat integration, 4,22,23 models taking into account mass and energy balances 24,25,26 were developed. To obtain accurate results of this kind of models, precise values of densities, enthalpies, and heat capacities are needed, for both water and aqueous mixtures.…”

Supercritical water oxidation with hydrothermal flame as internal heat source: Efficient and clean energy production from waste

“…Anikeev et al [20] RKS -Bermejo et al [26] VTPR IM (NIST) a Chen et al [27] Pure water Pure water Donatini et al [15] PSRK -Dutournié et al [28] Pure water Pure water Lavric et al [6] PR PR Leybros et al [29] IM (VTPR) a IM (VTPR) a Lieball [18] IM (VTPR) a IM (VTPR) a Moussière et al [30] Ideal Mixing Ideal Mixing Moussière et al [31] IM (NIST) a IM (NIST) a Narayanan et al [32] IM (VTPR) a IM (VTPR) a Oh et al [33] IM (SR-Polar, NIST) a , b IM (SR-Polar, NIST) a , b Queiroz et al [34] VTPR PR Queiroz et al [35] VTPR PR Sierra-Pallares et al [36] VTPR VTPR Vielcazals et al [37] Pure water Pure water Zhou et al [38] IM (NIST) a IM (NIST) a Zhou et al [39] SUPERTRAPP SUPERTRAPP a IM stands for ideal mixture. The property of each pure component is calculated by the method inside parenthesis.…”

“…Bermejo et al [26] IM (NIST) a IM (NIST) a -Chen et al [27] Pure water Pure water Pure water Dutournié et al [28] Pure water Pure water -Leybros et al [29] Ideal mixing Ideal mixing -Lieball [18] IM ( combustion of natural gas. The pressure dependencies, relevant for the SCWO conditions were included as well as the collision efficiency of water, when appropriate, using literature values.…”

“…Increasing complexity, models that include simple flow patterns (plug flow or perfect mixing) can give more information about the behavior of particular reactors (e.g. [19,27,[106][107][108]). Models like those need a kinetic model for the reaction and also good predictions of densities.…”

“…On the other hand, in presence of a flame, the high temperatures make the reaction rate much higher than the mixing rate, leading to the concept of "mixed is burnt", where the mixing controls the combustion and a correct mixing model is needed [110]. [27] Plug flow Premixed Arrhenius Donatini et al [15] Plug flow Premixed -a Dutournié et al [28] CFD Premixed Arrhenius Lavric et al [6] Plug flow Premixed Arrhenius Leybros et al [29] CFD Premixed Eddy dissipation Lieball [18] CFD Non-premixed Arrhenius/Eddy dissipation Moussière et al [30] CFD Premixed Eddy dissipation Moussière et al [31] CFD Premixed Eddy dissipation Narayanan et al [32] CFD Non-premixed Eddy dissipation Oh et al [33] CFD Non-premixed Arrhenius/Eddy dissipation Queiroz et al [34] PFR/CSTR Premixed Arrhenius Queiroz et al [35] CFD Premixed Arrhenius Sierra-Pallares et al [36] CFD Non-premixed Eddy dissipation Vielcazals et al [37] Plug flow Premixed b Arrhenius Zhou et al [38] CFD Premixed Eddy dissipation Zhou et al [39] CFD Non-premixed Arrhenius a Assumes total conversion regardless of kinetic model. b It is actually a partially premixed system due the multiple injection of oxygen, but the mixing process is not accounted.…”