Experimental and theoretical study of the influence of pressure on SCWO

It is well known that pressure is an important parameter in the SCWO process, because it produces changes in the phase behavior and thermodynamics properties of the system. The influence of pressure on the oxidation efficiency of feeds containing isopropyl alcohol as fuel and acetic acid as waste was studied in an autothermal adiabatic transpiring wall reactor at pilot-plant scale, at pressures from 13 to 25 Mpa, and temperatures from 600 to 750 degrees C. It was found that reaction temperature decreased between 40 and 100 degrees C, when pressure was lowered, and, subsequently TOC removal decreased. At higher-temperatures, the decreasing of TOC removal due to pressure difference was reduced. The process was simulated at different pressures using a mathematical model previously developed for the reactor. The Anderko-Pitzer EoS, especially developed for aqueous systems at high-temperatures and pressures, was used to have accurate values of the heat capacities of the reaction mixture. It was found that having into account only the effect of pressure in the thermodynamical properties and in the concentration of the reagents, the experimental results could not be explained. Thus, the influence of the pressure in the reaction rate equation had to be considered. Results were qualitatively reproduced considering the reaction rate constant variable with pressure, using a constant volume of activation of -1400 cm(3)/mol. (c) 2006 American Institute of Chemical Engineers AIChE J, 52: 3958-3966, 2006.