Overview
ABSTRACT
The regulations relating to aqueous effluents impose lower and lower thresholds concerning the discharge composition. The remedial action for effluent treatment must be more efficient, simpler, less expensive, but also more environmentally friendly. The wet oxidation procedure is fully consistent with this approach. This procedure would be feasible for the treatment of effluents that are problematic in terms of their low biodegradability and intermediate contents (between 1 and 20%). Wet oxidation is performed at a temperature comprised between 150 and 325°C for a wide range of total pressure (air or oxygen). This article presents the principle operation of the various types of reactors, as well as the constraints inherent to the procedure.
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Read the articleAUTHORS
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Olivier BOUTIN: Doctorate in Process Engineering - Engineer from the École nationale supérieure des industries chimiques - Senior Lecturer, Paul Cézanne University, Aix-Marseille - Director of the Ecotechnologies and Clean Processes master's program - Researcher at the Modélisation, Mécanique et Procédés Propres laboratory, UMR CNRS 6181.
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Jean-Henry FERRASSE: Doctorate in energy systems - Senior Lecturer, Paul Cézanne University, Aix-Marseille - Researcher at the Modélisation, Mécanique et Procédés Propres laboratory, UMR CNRS 6181.
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Sébastien LEFEVRE: Doctorate in Process Engineering - R&D Process Engineer (A3i)
INTRODUCTION
Regulations on aqueous effluents, imposed by various regulations (ICPE, European laws on water and air), require compliance with increasingly drastic thresholds on the composition of discharges. Effluent decontamination processes must therefore be more efficient.
Aqueous industrial effluents are mainly made up of organic molecules synthesized by the chemical industry and sludge from wastewater treatment plants. In addition to the simplicity and low cost of treatment, which represent major economic criteria for industrialists, current environmental and societal challenges are emphasizing the need to develop "green" processes, i.e. those that respect the environment. One such process, using pressurized water under sub-critical conditions, is wet oxidation (WVO). The effluents targeted in the long term are specific effluents with low biodegradability rates, often posing treatment problems. Let's take a look at the different wastewater treatment processes: for concentrations below 1% by mass, the most commonly used process is biological (biodegradability permitting). For concentrations in excess of 20%, incineration or co-incineration may be considered. For effluents of intermediate content, particularly for waters with a high chemical oxygen demand (between 20 and 200 g.L- 1 ), the OVH process can be considered. This process involves oxidation at a temperature of between 150 and 325°C over a wide range of total pressures (air or oxygen) from 2 to 30 MPa. In all cases, the process operates under sub-critical water temperature conditions. The low temperatures, compared with other thermochemical processes, limit the formation of toxic compounds in the gas phase (dioxins, NO x ...). Residence time in the reactor ranges from a few minutes to several hours. Oxidation yields are in the order of 70-95%. The reaction may or may not be catalyzed.
The OVH process uses pressurized water, and its properties will be presented. The operating principle of the process will be explained, with particular emphasis on thermodynamic and kinetic aspects (gas/liquid transfer and chemistry). The different types of reactor and the constraints inherent in the process will be explained. Given the pressure and temperature conditions involved, aspects of energy recovery and optimization will also be discussed. Finally, a number of industrial realizations will be detailed.
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Wet oxidation processes
Bibliography
Websites
LINNHOFF Marc, Introduction to Pinch Technology, 1998 http://www.linnhoffmarch.com .
Regulations
Directive no. 91/271 of 05/21/91 concerning urban waste water treatment.
Patents
Waste Disposal, Zimpro, USPTO 2665249, 1950.
Device for treating waste water by wet oxidation, Toshiba, JP1307494, 1989.
Process for wet oxidation treatment of organic pollutants in wastewater, Bayer, EP0738238 (A1), 1996.
Shaft reactor for wet oxidation of sewage at high temperature and pressure, Mannesmann, DE19614766, 1997.
Process...
Directory
Association Innovation fluides supercritiques IFS http://wikini.supercriticalfluid.org
Association International Society for Advancement of Supercritical Fluids ISASF http://isasf.net/
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