Numerical study on premixed hydrothermal combustion in tube reactor

Abstract

Premixed hydrothermal combustion of ethanol was numerically studied as a fundamental research to develop an energy conversion system utilising biomass and low quality oil. A simulation code available for oxidation of water solution mixture under sub/super critical conditions was developed. Lee-Kesler equation was selected as the equation of state. Chemical species of ethanol, oxygen, carbon dioxide and water, were considered as reactants and products of complete reaction. Mixing laws by Chung et al. and Wilke et al. were used for transport properties and that of Plöcker et al. was used for thermal properties and Lee-Kesler equation of state.Behaviours of ethanol oxidation under sub/super critical conditions were numerically simulated. For the reaction rate, we selected Schanzenbächer et al.'s expression obtained by the experiment under supercritical condition. Effects of preheat temperature, heat loss and flow velocity were examined by simulation. The differences of preheat temperatures led to the differences of temperature increase T around critical point because of the specific heat peak at the critical point. Larger flow velocity caused slower increase of ethanol conversion and temperature increase. Changes of reaction rate for different flow velocities showed that larger flow velocity caused thicker reaction zone and higher reaction peak than that for smaller one because of the fluid advection. From the calculation with different heat losses (different heat transfer rate coefficients α), twostep temperature decrease appeared for larger heat loss (α = 2.5 × 10 4 W·m −2 ·K −1 ) while monotonous temperature decrease appeared for smaller heat loss (α = 2.5×10 3 W·m −2 ·K −1 ).

Supercritical Water Oxidation Using Hydrothermal Flames at Microscale as a Potential Solution for Organic Waste Treatment in Space Applications – a Practical Demonstration and Numerical Study

“…k and ωk denote species mass fraction, diffusion velocity, and rate of formation/consumption of k th species, respectively. In the current work, we assume Fick's law of diffusion as given in [42] which…”

“…The diffusion coefficient in Eq. ( 2) representing the Fick's diffusion coefficient is given by the following expression [42]:…”

“…k denoting reaction coefficients and W k is the species molar mass. In the current work, we consider a single step irreversible reaction for the oxidation of ethanol (which also acts like a fuel) described in [42],…”

Review on an Advanced Combustion Technology: Supercritical Hydrothermal Combustion

“…Koido et al numerically studied the laminar premixed hydrothermal flame of ethanol in one-dimensional tube flow [91]. After weighing the pros and cons of some EoS and overall reaction kinetic models, they selected the EoS of Lee-Kesler et al and the ethanol overall reaction kinetic model of Schanzenbacher et al [92] based on experimental fitting data.…”

Kinetics of Ethanol Oxidation in High-Pressure Steam

“…They reported the estimation of capacity for ethanol oxidation in subcritical water as a heat source. At the same time, Hirosaka (10) and Koido (11) have worked on the numerical simulation of the behaviour of reactive flow in the reactor. These studies have been implemented with a single step reaction rate of reactants considering decomposition of ethanol into acetic acid.…”