Numerical study of reaction enhancement in hydrogen oxidation reactor with supercritical water medium by twisted oval structure

Abstract

The oxidation of hydrogen in supercritical water supplies heat for the supercritical water gasification technology and is an essential part of the system. The mild release of heat in a limited space is a significant challenge. In the present study, a twisted oval structure was used to enhance the mixing inside the reactor, avoiding excessive local temperature and promoting heat transfer to the outside. A numerical model was developed to investigate hydrogen oxidation in supercritical H2O / CO2 mixtures. The effects of different inlet and structure parameters, including temperature, velocity, components, twisted pitch length, and aspect ratio, were evaluated. The steady-state simulation found that the circular structure allowed high-temperature fluids to cluster significantly around the nozzle and axis, resulting in excessive local temperatures. In contrast, the twisted oval structure stabilized the axial temperature faster while enabling more uniform temperature distribution in the radial direction. The maximum radial temperature difference and radial temperature variance were reduced by an average of 52.18% and 81.31%, respectively. Furthermore, the unreacted hydrogen escaping from the reactor at high flow rates was also avoided due to the enhanced radial mixing by the secondary flow in the twisted oval structure. The transient-state simulation showed that the twisted oval structure could stabilize the temperature distribution rapidly during reactor start-up, which might support further scale-up for the reactor.