Modeling of a Porous Reactor for Supercritical Water Oxidation by a Residence Time Distribution Study

Abstract

Supercritical water oxidation (SCWO) performances are limited by salt precipitation and corrosion when it comes to treating real wastes. A porous reactor has been developed to overcome these problems. It consists of a concentric double-wall reactor in which the corrosive reactants are maintained inside an alumina porous tube, whereas pressure resistance is ensured by a stainless steel external vessel. Hydrodynamics in the reactor is thought to be rather complex. Thus, a residence time distribution study was performed to investigate the flow pattern. The experiments were carried out in supercritical carbon dioxide for experimental consideration. According to the experimental results, the axially dispersed-plug-flow model as well as the tanks in the series model can be used to describe the tubular reacting zone when there is no radial flow through the porous barrier. The whole reactor can then be considered as a cascade of equal ideally mixed tanks with a stage radial feed. This proposed hydrodynamic model was validated by the experiments of ethanol oxidation in supercritical water. Our model enables us to estimate and optimize the conversion of a waste if its oxidation kinetics is known.

Supercritical Water Gasification of Municipal Sludge: A Novel Approach to Waste Treatment and Energy Recovery

“…Most commercial and industrial applications require that engineering designs and materials overcome corrosion and plugging problems and that systems operate on a continuous duty cycle (Azadi et al, 2011;Elliott, 2008;Guo et al, 2007). Some common, SCW-reactor considerations are presented here, while extensive and detailed reviews can be found elsewhere (Bermejo et al, 2005a(Bermejo et al, , 2005b(Bermejo et al, , 2009Calzavara et al, 2004;Fauvel et al, 2003Fauvel et al, , 2005Lieball et al, 2001;Machida et al, 2011;Marrone & Hong, 2009;Mitton et al, 2000;Peter, 2004;Tan et al, 2011;Veriansyah et al, 2009;Wellig et al, 2005;Yoshida & Matsumura, 2009). …”

Operating characteristics of a transpiring-wall SCWO reactor with a hydrothermal flame as internal heat source

“…Reports [57][58][59], Crooker et al [60] (and literature cited in Ref. [60]), Abeln et al [61,62], Fauvel et al [63]), yet the use of a separate hydrothermal flame as an internal heat source is novel in SCWO reactors. Table 1.…”

Modelling residence time distribution in chemical reactors: A novel generalised n-laminar model

“…However, little information is available about RTD curves in reactors working at supercritical conditions, so far. Fauvel et al [11] estimated that such a study is difficult to perform in such conditions because of the compressibility of near critical and supercritical fluids. They concluded that this is possibly the reason of the lack of reported RTD experiments in supercritical fluids.…”

“…RTD theory requires a constant-volume flow rate in the reactor and that is difficult to achieve when dealing with compressible gases. In addition to this, in some cases like supercritical water, the extreme pressure and temperature conditions (over 22.1 MPa and 374.1 • C) causes damage to most of the detectors and cannot be easily measured directly [11].…”

“…Fauvel et al have applied three different convection models presented by Levenspiel [13] to study the RTD curves obtained in a porous reactor for supercritical water oxidation [11]. They found that the 'axially dispersed-plug flow model' and 'tanks in series model' could be used to adequately describe their reactor.…”