Development of a bi-equilibrium model for biomass gasification in a downdraft bed reactor.
This work proposes a simple and accurate tool for predicting the main parameters of biomass gasification (syngas composition, heating value, flow rate), suitable for process study and system analysis. A multizonal model based on non-stoichiometric equilibrium models and a repartition factor, simulating the bypass of pyrolysis products through the oxidant zone, was developed. The results of tests with different feedstocks (corn cobs, wood pellets, rice husks and vine pruning) in a demonstrative downdraft gasifier (350kW) were used for validation. The average discrepancy between model and experimental results was up to 8 times less than the one with the simple equilibrium model. The repartition factor was successfully related to the operating conditions and characteristics of the biomass to simulate different conditions of the gasifier (variation in potentiality, densification and mixing of feedstock) and analyze the model sensitivity.
Study of the equilibrium of air-blown gasification of biomass to coal evolution fuels
Abstract A non-stoichiometric equilibrium model based on the minimization of the Gibbs free energy was used to study the isothermal and adiabatic air-blown gasification of solid fuels on a carbonization curve from fossil (hard/brown coals, peat) to renewable (green biomasses and cellulose) fuels, including torrefied biofuels. The maps of syngas composition, heating value and process efficiency were provided as functions of equivalent ratio (oxygen-to-fuel ratio) in the range 0–0.6, temperature in 500–2000 K, and a fuel parameter, which allowed different cases to be quantitatively compared. The effect of fuel moisture, unconverted carbon and conditions to limit the tar formation was also studied. Cold gas efficiency >0.75 can be achieved for coals at high temperature, using entrained beds (which give low unconverted carbon), and improved by moisture/added steam. The bigger efficiency of green biomasses is only potential, as the practical limits (high temperature required to limit tar formation, moisture content and unconverted carbon in small gasifiers) strongly reduce the gasification performance. Torrefied biomasses (and plastics having an intermediate fuel parameter between coals and green biomasses) can attain high efficiency also in real conditions. The results shown in this work can be useful to evaluate the most promising feedstock (depending on its composition and possible pre-treatment/upgrading), define the operating conditions for maximizing the syngas heating value or the global efficiency, assess the techno-economic-environmental feasibility of a gasification-based system.
Fortune and Responsibility in Calderón's La gran Cenobia
La gran Cenobia deals with the war between Queen Zenobia of Palmyra and the Emperor Aurelian. Calderón de la Barca draws most of his information from historical sources; the dramatist, however, changes history and adapts it to his own dramatic purpose. The theme of Fortune gives unity to the play. Aureliano is portrayed as a tyrant who, to prove his independence from Fortune, behaves tyrannically, causing his eventual downfall. Cenobia believes that Fortune controls her life, but does not acknowledge that her own actions contribute to her misfortune. The analysis concludes that Fortune, as depicted in this play, is not an omnipotent and blind force, but what one has forged with his or her own actions coupled with the actions of others and circumstance.