Simulation and optimization of temperature control and industrial design of hydrogen production of biomass via microwaves

Hydrogen production of biomass via microwaves is an efficient, rapid, and environmentally friendly chemical engineering technology. Lignin is the only renewable aromatic hydrocarbon resource in the nature, and thus, the lignin-based forest biomass, which has the advantages of low sulfur, is a good raw material for hydrogen production. However, the microwave hot spot effect restricts the industrial application of hydrogen production by microwave. In this study, the reactor was carried out based on the penetration depth of biomass under different microwave frequencies was designed by modeling. Orthogonal design simulation, CFD, and HYSYS were used to obtain the distribution of temperature field with different microwave power density, the radius of biomass particles, bulk density, and the coefficient of variation. Based on the results, the optimal microwave power density was 30 W·g^–1, the optimal radius of biomass particles was 4 mm, and the optimal bulk density was 800 kg·m^–3, at which a favorable uniform temperature field was achieved, and its coefficient of variation was only 0.009, less than the standard value of 0.01. Then, to reduce energy consumption and improve product economy, the Computational Fluid Dynamics (CFD) method was used to analyze the cloud image of hydrogen production with different height to diameter ratio of the reactor. It was found that when the height to diameter ratio of the reactor was 2.0, the hydrogen-flow could not only fully contact with the falling materials, but also achieve thermal energy circulation by using its own high temperature. Finally, the industrial process of hydrogen production of biomass via microwave was added into HYSYS, and the operating parameters of the maximum hydrogen yield of the 10000-ton industrial device were simulated and optimized. In the reforming reaction, by adding steam in the mid-piece and the end-piece, the production yield of hydrogen can be maximized and the temperature of the reactor can be maintained continuously after the heat energy of hydrogen was recovered. Under the conditions optimized, when the mid-piece and end-piece fluxes of steam were 290 and 1230 m³·h^–1, respectively, a favorable hydrogen production of biomass was achieved. The output of hydrogen, the mole fraction and the yield of hydrogen production were 922.98 m³·h^–1, 0.4781 and 82.49%, respectively. Moreover, the hydrogen product can reach the high standard of 6.592 g hydrogen/ 100 g biomass, which was far superior to the industry level.