Balance En Reactores Frios

J. of Supercritical Fluids 31 (2004) 41–55

Cool wall reactor for supercritical water oxidation Modelling and operation results
M.J. Cocero∗ , J.L. Mart´nez ı
Departamento de Ingenier´a Qu´mica, Universidad de Valladolid, 47011-Valladolid, Spain ı ı Received 17 October 2002; received in revised form 18 July 2003; accepted 30 September 2003

Abstract This work presents an innovative designand modelling of a supercritical water oxidation (SCWO) reactor capable of operating effectively under industrial requirements. The cool wall reactor has a reaction chamber where the reaction occurs and a pressure vessel, which support pressure but not oxidant atmosphere. The pressurised feed-stream flows down and cool the reaction chamber so reactor temperatures up to 800 ◦ C are possible forpressure vessel temperatures of 400 ◦ C. The reactor allows to carry out total degradation of the pollutant (over 99.9 wt.% in TOC removal) and has been design to maximise the heat recovery from the reaction effluents, and therefore, is able to operate in almost autothermal conditions with flowrates between 25 and 65 kg/h of polluted water. The proposed design has been tested in pilot scale withoutstanding results to degrade organic pollutants. A mathematical model has been implemented to show the advantages of applying an indirect kinetic pathway: the results of the simulation agree with the experimental data, and show that the use of low temperatures in the reactor enhances the formation of stable reaction intermediates (acetic acid and methanol) which reduces the total removal efficiency ofthe reactor. Result are shown for oxidation of isopropyl alcohol (5.3–8 wt.% ) and 0.5 wt.% of dimethylsulfoside (DMSO) using both air and pure oxygen as oxidant agents. © 2003 Elsevier B.V. All rights reserved.
Keywords: Reactor design; Supercritical water oxidation (SCWO); Reactor modelling; Reaction stable intermediates

1. Introduction Supercritical water oxidation (SCWO) has extensivelydemonstrated to be one of the most effective methods to purify complex industrial wastes. The physical–chemical properties of SC water induce a drastically increase in the kinetic of degradation of organic and inorganic compounds. The reaction pro∗ Corresponding author. Tel.: +34-983-423174; fax: +34-983-423166. E-mail address: mjcocero@iq.cie.uva.es (M.J. Cocero).

ceeds in a homogeneous phasewithout interface mass transfer limitations. Reaction efficiency over 99.9% can be easily reached with residence times lower than 1 min. At this conditions organic compounds are destroyed rapidly with high conversions into CO2 and H2 O. The SCWO system is capable of operating as a treating facility achieving a complete destruction of organic compounds [1,2]. The SCWO process requires extremetemperature and pressure conditions at the same time, which enhance corrosions of most materials [3]. Two types of corrosion are presented in this kind of processes:

0896-8446/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2003.09.023

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M.J. Cocero, J.L. Mart´nez / J. of Supercritical Fluids 31 (2004) 41–55 ı

Nomenclature A Ai C Cp d DMSO Ea Fi HR K IPA m Minc ODE o.d. R ri ρ S SS SCWO T tr TOC U v Xi z Orthogonal collocation matrix Arrhenius kinetic constant (s−1 ) Concentration (mol/dm3 ) Heat capacity (J/kg ◦ C) Diameter (m) Dimethylsulfoside Preexponential factor (J/mol) Molar flowrate (mol/s) Reaction enthalpy (J/mol) Kinetic constant (s−1 ) Isopropyl alcohol Mass flowrate (kg/s) Molecular mass (kg/mol) Number of carbon atoms Ordinarydifferential equation External diameter Gas constant (8.314 J/mol K−1 ) Reaction kinetic (mol/dm3 s−1 ) Density (kg/m3 ) Free transversal surface (m2 ) Stainless Steel Supercritical water oxidation Temperature (◦ C) Residence time (s) Total organic carbon (ppm) Heat transfer coefficient (W/m2 ◦ C) Volumetric flowrate (m3 /s) Conversion Length of reactor (m)

Subscripts and superscripts A pollutant B fuel C...