Abstract

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This study introduces a new method of methane pyrolysis in a rotary chemical reactor using wave rotor technology. The patented technology has been developed by New Wave Hydrogen, Inc. (New Wave H2 or NWH2) . The concept introduces an efficient method of hydrogen production driven by shock wave gasdyanmics, with no direct CO2 emissions and no water use. The New Wave Reformer is based on wave rotor designs where unsteady shock waves are generated within channels arrayed around a rotating drum. As in a typical wave rotor wave cycle, a sharp pressure increase occurs behind a reflected shock wave, resulting in a proportional increase in gas temperature. This temperature amplification can be used to initiate a thermal decomposition reaction in gaseous constituents. Past studies have proven that a wave reformer with onboard reactions can reform heavy hydrocarbon gases into lighter hydrocarbon products. The current NWH2 study explores how a wave rotor can employ pressurized natural gas as a driver gas for compression heating of a low-pressure hydrocarbon fuel inside the channels of a wave reformer, resulting in the decomposition of methane into hydrogen and carbon black. This study first reviews past efforts ranging from conceptual patents to experimental studies utilizing different wave cycles for rapid heating of gases in gas-phase chemical reactions. Examples of such reactions include the formation of acetylene from methane and the formation of nitric oxide from air. In ongoing research, the authors introduce a wave cycle that uses a dual-stage gas compression process designed to prolong reaction time within the channels, addressing a key factor in high methane-to-hydrogen conversion. The process has been modeled numerically using a customized version of the Tüchler-Copeland experimentally-validated quasi-one-dimensional CFD code. The computational results provide data used in the prediction of flow fields inside the channels and at the inflow/outflow ports of the reactor.

The article details a numerical investigation of methane pyrolysis inside a shock wave reformer using a quasi-2-dimensional (Q2D) Reynolds-Averaged Navier-Stokes (RANS) CFD model. This work is in support of the New Wave Hydrogen, Inc. (NWH2) proprietary technology development. To take account of the characteristics of the flow in the presence of shock waves, a simplified approach is proposed that captures the gas dynamics during partial opening with a lower computational cost suitable for the wave reformer design. The model is based on the three-dimensional, compressible, and unsteady Navier-Stokes equation coupled with k-ω - SST turbulence closure. Boundary conditions are implemented through a cell-centered approach with fictitious cells outside of the domain boundaries. The numerical results are compared with solutions from a quasi-one-dimensional (Q1D) unsteady model reported in literature. The simulations show a good agreement between the two different modelling approaches in terms of spatial distribution of the pressure gradient for one complete cycle. It is observed from the Q2D results that the entrance for each passage, especially upon opening of the high-pressure driver gas port, is a location of particular interest in the formation of the shock. The resulting acute pressure gradients induce loss inside the channel, decreasing the maximum temperature during a complete wave cycle by 15%, and consequently, reducing the methane pyrolysis process.

In this research, highly disturbed turbulent flow of distinct three-dimensional characteristics in a square duct with inclined or V-shaped ribs mounted on one wall is investigated using direct numerical simulation. The turbulence field is highly sensitive to not only the rib geometry but also the boundary layers developed over the side and top walls. In a cross-stream plane secondary flows appear as large longitudinal vortices in both inclined and V-shaped rib cases due to the confinement of four sidewalls of the square duct. However, owing to the difference in the pattern of cross-stream secondary flow motions, the flow physics is significantly different in these two ribbed duct cases. It is observed that the mean flow structures in the cross-stream directions are asymmetrical in the inclined rib case but symmetrical in the V-shaped rib case, causing substantial differences in the momentum transfer across the spanwise direction. The impacts of rib geometry on near-wall turbulence structures are investigated using vortex identifiers, joint probability density functions between the streamwise and vertical velocity fluctuations, statistical moments of different orders, spatial two-point autocorrelations and velocity spectra. It is found that near the leeward and windward rib faces, the mean inclination angle of turbulence structures in the V-shaped rib case is greater than that of the inclined rib case, which subsequently enhances momentum transport between the ribbed bottom wall and the smooth top wall.