Investigation of competitive tar reforming using activated char as catalyst

Syngas tar removal is one of the biggest challenges for the gasification of biomass as a clean energy source. Efforts to understand the reforming mechanism of tar compounds have been continuous during the last decades. Kinetic studies often employ a single tar species, neglecting possible interactions between different tar compounds. On the other hand, char, a by-product from biomass gasification, presents opportunities to catalyze tar reforming. In this work, reforming experiments were conducted in a fixed-bed reactor using syngas with a known mixture of benzene (C6H6), toluene (C7H8) and naphthalene (C10H8). Hardwood char and an in-situ CO2-activated hardwood char were used as catalysts. The activated hardwood char exhibited the best reforming capabilities by converting 44% and 90% of the tars at 750 and 850°C, respectively, compared to 24% and 87% tar conversion obtained with the regular hardwood char at 750 and 850°C, respectively. From the experiments, a reduced mechanism model was proposed. This mechanism was used in computational simulations for analysis of the reaction kinetics, including possible catalyst selectivity. It was found that under a range of conditions, the benzene degradation is slower than its formation rate from toluene and naphthalene decomposition. This leads to increases in the benzene fraction at temperatures around 700°C. If the naphthalene and toluene concentrations are sufficient, benzene will accumulate even at high temperatures (around 800°C) regardless of residence times. It can be concluded that when benzene, toluene and naphthalene are present together, char favors the heterogeneous reforming of toluene and naphthalene, with benzene following an homogeneous reforming pathway

Simulazioni Numeriche e Fenomenologie di Flussi Tridimensionali in un Aerospike Lineare

Vincenzo Ciampi, Bernardo Favini, Annalisa Fregolen

Three Dimensional Features of Clustered Plug Nozzle Flows

The plug nozzle is one of the concepts proposed to improve the overall performance of large liquid rocket engines for launcher first stages. One of the aspects to be investigated is the three dimensional flow field generated by partitioning of the primary nozzle in modules. Three configurations with different size of the gap between two adjacent primary nozzles are selected and numerically simulated. Specific three-dimensional flow structures that take place on the plug are identified comparing the numerical solutions. The relationship between these structure and the skin friction distribution along the plug surface is also investigated. Finally, a performance analysis of the selected test cases based on the thrust coefficient evaluation is presented

RANS Analysis of Merging Supersonic Streamwise Vortices for Enhanced Mixing in Scramjet Combustors

Streamwise vortices are studied as a mixing enhancer for scramjet combustors due to their insensitivity to compressibility relative to spanwise structures. A specific merging interaction between supersonic corotating vortices has been shown in experiments to sustain turbulence production against decay. In this paper this interaction is investigated numerically to determine how well it can be replicated with a RANS approach, and the effect of increasing the Mach number. The shape and rotation of the merging vortices appears similar to experimental results. The decay of vorticity follows a similar trend to experimental results, however the vorticity was higher in the RANS results. At higher Mach numbers the merging process appears to be pushed further down the domain