• Energy Research

Abstract This paper investigates the syngas production in a hybrid filtration reactor composed of aleatory waste tires particles and alumina spheres. Parameters as reaction wave temperature, propagation rate and gaseous and solid emissions products were measured as a function of gasifier agents (air and steam) and natural gas presence. Hydrogen and carbon monoxide concentrations in the reaction products were determined by gas chromatography and solid emissions by X-ray spectrometry. Downstream reaction zone propagation was observed in all experiments yielding high reaction temperature (1,100–1,500 K) responsible of: (1) generating H2 and CO as main products of the process for different gasifier agents and natural gas presence, and (2) decreased solid particles emissions in comparison with temperatures below 1,100 K. X-ray spectrometry with total reflection was able to detect peaks of Zn and Fe, thought to originate from waste tires particles as well as from reactoŕs insulation material. It was detected that pure air had the best performance as a gasifier agent.

Abstract This paper investigates temperature profiles and heat fluxes in a packed bed heated by radiation that simulates solar energy flux. For this purpose, the discrete element method (DEM) was used along a heat transfer model (conduction and radiation mechanism). Short-range model is proposed for considering thermal radiation in a discrete elements system, which represents an easy-to-implement and low-computational-cost alternative. As results of the simulations, thermal profiles through the packed bed were obtained, as well as the accompanying heat flux. Experiments were performed in a packed bed of inert ceramic particles (alumina spheres). A radiant porous burner was placed at the bottom of the packed bed to simulate an imposed concentrated solar heat flux. Numerical results show good agreement with experimental data. In addition, the thermal profiles, obtained by the heat transfer model in DEM, were compared with the results obtained by discretizing the conservation of energy equation of the solid phase using finite differences, showing a correlation between the power and temperatures reached. It is concluded that the radiation model proposed provides the basis to continue with the study of granular materials at high temperature, where radiation is the dominant mechanism.

Abstract The characteristics of combustion and the flame stabilization within a two-layer porous media burner were investigated experimentally in the present study. Lean propane-air mixtures were used with the equivalence ratio values ϕ in the range between 0.1 and 0.5 and the flow rate Q of the mixture in the range between 10 and 45 l/min. It was experimented with three porous ceramics: reticulated foam alumina, honeycomb foam alumina and SiC foam. The axial temperature distribution, reaction zone, maximum temperature, CO and NOx emissions, and combustion wave propagation rate were analyzed. The experimental results showed that, in the three ceramics studied, the combustion wave propagation rate increases with increased inlet velocity and decreased equivalence ratio of premixed gases. Result of the analysis of the information obtained, a porous burner with flame stabilized between two porous ceramics was built that works permanently with the equivalence ratio ϕ = 0.5 and the flow rate of the mixture in the range between 20 and 35 l/min. The honeycomb foam was placed on top of the burner and the reticulated foam on the bottom. The combustion temperatures were in the range between 1160 and 1380 K, where a higher flow rate resulted in higher temperatures. The CO and NOX emissions did not exceed a few ppm showing that combustion was almost complete.

Abstract Conditions for flame stabilization in a porous media combustor formed by two beds of different sizes of alumina balls were studied. Premixed combustion of lean methane–air mixtures were used as variables. Measurements performed included temperature profiles and chemical products compositions. Stabilized flames were observed in the range of volumetric flow rate from 7.01 l/min to 19.00 l/min at equivalence ratio of ϕ = 0.6 and ϕ = 0.7. Low pollutants emissions were found in the entire operation range.

Abstract Numerical model for heavy fuel oil and air mixtures combustion is presented to simulate the behavior of the fuel in an inert porous medium reactor for hydrogen production. Three-zone combustion of oil and petroleum cokes separated by temperature ranges starting from ambient temperature to 560 K, from 560 K to 673 K, and above 673 K, is presented. Hydrogen production is achieved using water gas shift equilibrium reaction on the combustion products at different temperatures. Results show a high enthalpy contribution due to coke combustion formed in the low temperature oxidation reaction, being the most important reaction in relation to its zone size. Simulations increasing filtration velocity (from 0.05 to 0.9 m/s) has a favorable effect on the maximum temperature and the combustion front velocity. The effect of the simplified combustion model lowers computational time, with acceptable results for temperature as well as hydrogen production in contrast to laboratory tests and other software simulation such as COMSOL Multiphysics.

Abstract Valorisation of plastic waste or forest-agroindustrial residues poses an opportunity to reduce landfilling and to obtain value-added products simultaneously. Through thermal partial oxidation, hydrocarbon fuels can be gasified and converted into syngas. Particularly, hybrid porous media reactors allow gasifying low-grade fuels in an efficient eco-friendly way. In this work, the natural gas-supported gasification of polyethylene and wood mixtures in a porous bed reactor is studied. The reactor is designed and built to operate in semi-continuous mode. The temperature evolution, the reaction wave propagation rate, and the resulting concentration of the main gas species (H2, CO, CH4, CO2, NOx, and UHC) were measured for different polyethylene and wood mixtures, keeping an optimum natural gas-to-air ratio of 0.8. The influence of the gasification conditions on the reaction pathways and the process development is analysed by sampling the system in two representative moments. The maximum syngas production was 23.86 vol%, which was obtained when loading only 100% polyethylene, while the maximum energy return on investment of 49% was registered for the highest biomass fraction in mixture. The semi-continuous operation design was validated based on the thermal behaviour and the combustion wave displacement. This experimental work shows promising results in the search for solutions to gasify solid wastes in continuous mode.