Wet air oxidation for the treatment of solid wastes generated on autarkic sites

International audienceIndustrial effluents have variable compositions depending on the industry: refineries, pharmaceuticals, distilleries, food processing, paper mill… The most widespread treatment of effluents containing organic pollutants is the biological way, but microorganisms are unsuitable in the case of refractory or toxic products. Legislations regulate more and more severely the management of these wastes and favor the development of alternative processes allowing to treat effectively particular pollutions, as in pre-treatment before a biological process or for a complete degradation of organic matters in carbon dioxide and in water. Other technologies are under research and development, as for instance Wet Air Oxidation (WAO), especially for wastewaters that contains high chemical oxygen demand

Wet air oxidation for the treatment of solid wastes generated on autarkic sites

International audienceIndustrial effluents have variable compositions depending on the industry: refineries, pharmaceuticals, distilleries, food processing, paper mill… The most widespread treatment of effluents containing organic pollutants is the biological way, but microorganisms are unsuitable in the case of refractory or toxic products. Legislations regulate more and more severely the management of these wastes and favor the development of alternative processes allowing to treat effectively particular pollutions, as in pre-treatment before a biological process or for a complete degradation of organic matters in carbon dioxide and in water. Other technologies are under research and development, as for instance Wet Air Oxidation (WAO), especially for wastewaters that contains high chemical oxygen demand

Energetic optimization of wet air oxidation process using experimental design coupled with process simulation

International audienceWet air oxidation process (WAO) is used for wastewater treatment, especially when it contains high chemical oxygen demand. With non-catalytic processes, temperatures between 200 and 350 °C and pressures between 15 and 30 MPa are generally applied. A method, based on the coupling of simulations and experimental design, is used to compare and optimize two reactors (adiabatic and isotherm), their volume being equal and fixed. The interest of an experimental design approach is to plan simulation and to present results in immediate response surface. Four parameters have been selected; temperature, pressure, chemical oxygen demand, air ratio. After achieving the 25 simulations of the “numerical design”, mass and energy balances were analysed through two energetic values integrated as the design responses: exergetic efficiency and minimum heat required by the process for the functioning. The surface response methodology determines which are the most influencing parameters on design responses. It also shows that temperature of reaction and air ratio are the most influencing parameters. At least elements to calculate the cost of the plant, for both reactors are given. Both reactors allow to get complete degradation of pollutants, but strategy of investment and control are opposite

Wet air oxidation for the treatment of solid wastes generated on autarkic sites

International audienceIndustrial effluents have variable compositions depending on the industry: refineries, pharmaceuticals, distilleries, food processing, paper mill… The most widespread treatment of effluents containing organic pollutants is the biological way, but microorganisms are unsuitable in the case of refractory or toxic products. Legislations regulate more and more severely the management of these wastes and favor the development of alternative processes allowing to treat effectively particular pollutions, as in pre-treatment before a biological process or for a complete degradation of organic matters in carbon dioxide and in water. Other technologies are under research and development, as for instance Wet Air Oxidation (WAO), especially for wastewaters that contains high chemical oxygen demand

Thermodynamic and kinetic study of phenol degradation by a non-catalytic wet air oxidation process

International audienceThis work is dedicated to an accurate evaluation of thermodynamic and kinetics aspects of phenol degradation using wet air oxidation process. Phenol is a well known polluting molecule and therefore it is important having data of its behaviour during this process. A view cell is used for the experimental study, with an internal volume of 150 mL, able to reach pressures up to 30 MPa and temperatures up to 350 °C. Concerning the thermodynamic phase equilibria, experimental and modelling results are obtained for different binary systems (water/nitrogen, water/air) and ternary system (water/nitrogen/phenol). The best model is the Predictive Soave Redlich Kwong one. This information is necessary to predict the composition of the gas phase during the process. It is also important for an implementation in a process simulation. The second part is dedicated to kinetics evaluation of the degradation of phenol. Different compounds have been detected using GC coupled with a MS. A kinetic scheme is deduced, taking into account the evolution of phenol, hydroquinones, catechol, resorcinol and acetic acid. The kinetic parameters are calculated for this scheme. These data are important to evaluate the evolution of the concentration of the different polluting molecules during the process. A simplified kinetic scheme, which can be easily implemented in a process simulation, is also determined for the direct degradation of phenol into H2O and CO2. The Arrhenius law data obtained for the phenol disappearance are the following: k = 1.8 × 106 ± 3.9 × 105 M−1 s−1 (pre-exponential factor) and Ea = 77 ± 8 kJ mol−1 (activation energy)

Gas hold up in bubble column at high pressure and high temperature

International audienceGas holdup of water/nitrogen, water-phenol/nitrogen and water-phenol/air systems was successfully measured by a method based on the use of a differential pressure sensor installed on a bubble column reactor, in a wide domain of temperature (from 100 to 300 degrees C) and pressure (from 10 to 30 MPa). These experimental conditions are little or no explored in literature. Results show a predominant influence of the superficial gas velocity, the evaporation of the liquid phase, the ratio of the gas volume flowrate on the liquid volume flowrate and the phenol concentration. Pressure and chemical reaction have little effect on gas holdup. The temperature has an effect in the case of phenol solutions. The different correlations and parameters influence determined in this work are very helpful for the design of gas liquid contactors (for instance bubble column) at high pressure and high temperature

Bubble rising velocity and bubble size distribution in columns at high pressure and temperature: From lab scale experiments to design parameters

International audienceThe design of bubble column for industrial applications is well known under near ambient pressure and temperature conditions, contrary to high pressure and temperature conditions. Accurate data on the evolution and behaviour of the bubbles is proposed as a basis for the evaluation of the surface area developed in the column and further design of such reactor. Two columns are used for the experiments: a small column (8 mL) with a total visualisation of the flow, and a bigger one (1 L), necessary for the scale up. Main results show that the influence of pressure and temperature are significant on the behaviour of bubbles and bubble size distribution and must be characterized and considered for the design of the columns in such conditions. The results allow the determination of two correlations: one for the bubble diameter and the other one for the bubble rise velocity, considering different parameters, and especially the superficial gas velocity in saturated conditions. These correlations are a basis to determine mass transfer correlations for the design of bubble column at high pressure and temperature conditions. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved

Process optimisation using the combination of simulation and experimental design approach: Application to wet air oxidation

International audienceThis study develops a coupling of energetic and experimental design approaches on a given configuration of wet air oxidation process (WAO), applied for wastewater containing a hard chemical oxygen demand (phenol for instance). Taking into account thermodynamic principles and process simulation, the calculation of minimum heat required by the process, exergetic efficiency and work balance is presented. Five parameters are considered: pressure (20–30 MPa); temperature (200–300 °C); chemical oxygen demand (23–143 g l−1); air ratio (1.2–2) and temperature of exiting steam utilities (160–200 °C). Using the surface response method, it appears that initial chemical oxygen demand and temperature are the two parameters that mainly influence the result. With the modelling, good conditions for the functioning of the presented process are the following: pressure of 19.4 MPa, temperature of 283 °C, chemical oxygen demand of 54.9 g l−1, air ratio of 1.7 and vapour temperature of 183 °C