Numerical modelling of char formation during glucose gasification in supercritical water (original) (raw)
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Gasification of biomass in supercritical water
2002
Conversion in hot compressed water (e.g. 600C and 300 bar) is considered to be a promising technique to treat very wet biomass or waste streams. In this chapter, a new experimental method is described that can be used to screen the operating window in a safe, cheap, and quick manner (one measurement takes about 5 min). Small sealed quartz capillaries (i.d. = 1 mm) filled with biomass or model compounds in water are heated rapidly in a fluidized bed to the desired reaction temperature. The reaction pressure can be controlled accurately by the initial amount of solution in the capillary. After a certain contact time, the capillaries are lifted out of the fluidized bed, rapidly quenched, and destroyed to collect the produced gases for GC analysis. Results of measurements for formic acid and glucose solutions have shown that the technique is reliable enough for screening purposes including trend detection. For conversions above 30%, three identical measurements are sufficient to produce...
Bioresource Technology, 2011
A new continuous supercritical water gasification reactor was designed to investigate glucose gasification in supercritical water at high temperatures and low residence times. A 2 3 full factorial experiment was performed to determine the effects of feed concentration, temperature, and residence time on glucose gasification. The temperature levels (750°C and 800°C) were higher than ever used, while the residence times (4 and 6.5 s) were shorter than ever used in previous supercritical water gasification studies. The reactor proved capable of attaining higher gasification rates than previously shown with high efficiencies and yields. In addition, the glucose gasification reaction was modeled by estimating activation energy and reaction order of glucose gasification in supercritical water.
Supercritical water gasification of biomass: Thermodynamic constraints
Bioresource Technology, 2011
In the present work, the supercritical water gasification (SCWG) of biomass is analyzed with a view to outlining the possible thermodynamic constraints that must be taken into account to develop this new process. In particular, issues concerning the formation of solid carbon and the process heat duty are discussed. The analysis is conducted by means of a two-phase non-stoichiometric thermodynamic model, based on Gibbs free energy minimization. Results show that char formation at equilibrium only occurs at high biomass concentrations, with a strong dependence on biomass composition. As regards the process heat duty, SCWG is mostly endothermic when biomass concentration is low, although a very small amount of oxidizing agent is able to make the process exothermic, with only a small loss in the heating value of the syngas produced.
Industrial & Engineering Chemistry Research, 2004
To understand the influence of experimental conditions on the chemistry of biomass degradation in supercritical water, the effect of heating rate and of different catalysts (1 wt % of Raney nickel and 0.5 wt % K 2 CO 3 ) on the product distribution during hydropyrolysis of glucose is investigated. Glucose in aqueous solution (5 wt %) is selected as a model compound for cellulosic biomass. The heating rates are 1 or 3 K/min up to 500°C, and then, the reactor is kept at this temperature for 1 h. Despite the long reaction time of 1 h at 500°C, the presence of catalysts has an significant influence on intermediates of glucose gasification such as phenols or furfurals. The influence of catalyst and the heating rate on these intermediates and the product yields points to the assumption that the chemical processes during heating have a drastic effect on the results of the gasification process at 500°C.
Influence of phenol on glucose degradation during supercritical water gasification
The Journal of Supercritical Fluids, 2010
Biomass is an ideal candidate for renewable energies and to decrease CO 2 emissions. Super Critical Water Gasification (SCWG) is a recent way of treatment still in development for wet biomass. Above its critical point water has particular properties and is able to convert wet biomass into gas, hydrogen particularly. In order to propose a general scheme of the SCWG for lignocellulosic biomass, the interactions between lignin and cellulose must be highlighted. Lignocellulosic biomass could be modelled with phenol (lignin) and glucose (cellulose). In a continuous reactor, the gasification efficiency of solutions containing phenol, glucose or the two compounds are realized in presence of an alkaline catalyser. The comparison of global parameter, such as Total Organic Carbon (TOC), the composition of liquid (glucose, phenol…), the volume and composition of gas phase (H 2 , CO 2 , CH 4 …) showed that a small quantity of phenol in a glucose solution decreased dramatically the conversion efficiency of glucose.
Biomass gasification in supercritical water: Part 1. Effect of the nature of biomass
Fuel, 2007
In this study, biomass feedstocks, including lignocellulosic materials and the tannery wastes, were gasified in supercritical water. Gasification experiments were performed in a batch autoclave at 500°C. The amount of gases, the gas compositions and the amount of water soluble compounds from gasification were determined. The hydrogen yields ranging between 4.05 and 4.65 mol H 2 /kg biomass have been obtained. The results showed that the yields and composition of gases depend also on the organic materials other than cellulose and lignin in lignocellulosic material. In addition to this, it was concluded that the kind of lignin may also have an effect on gasification products. In the case of tannery wastes, the type of tannen agent used in leather production considerably effected the gasification results.
Thermodynamic Analysis of the Supercritical Water Gasification of Biomass
Biofuels and Biorefineries, 2014
In the present work the Gibbs free energy minimization, using a non-linear programming formulation and an approximation in the gas fugacities, was used to calculate the equilibrium composition for supercritical water gasification of methanol, ethanol, glycerol, glucose and cellulose. The proposed formulation mathematically ensures finding the global optimal solution with no need of an initial estimate and the numerical results are close to the ones calculated using non-ideal gas formulation. Therefore, the proposed approach is reliable and easy to use, without numerical difficulties, such as an undesirable local minimum. The model predictions show a good agreement with the experimental studies in all cases studied in this work.
Industrial & Engineering Chemistry Research, 2015
With the shift in interest towards renewable energy, hydrogen as an alternative gaseous fuel seems to attract much attention. Waste biomass is an ideal option for the synthesis of biofuels due to its abundance and no net CO 2 emissions. Hydrogen can be produced through supercritical water gasifi cation of waste biomass. Hydrogen is an attractive energy carrier which can be used as a direct fuel or in fuel cells to generate electricity and in other energy-producing processes. Gasifi cation of biomass in supercritical water can be performed for hydrogen generation in both batch and continuous modes with/ without the application of catalysts. In spite of the progress made in various gasifi cation technologies, diamond anvil cells and fl uidized beds as the new-generation batch and continuous reactors, respectively, are not fully recognized. The current review is focused on understanding the design, application and limitations of these two new reactor confi gurations to help motivate their wide-scale utilization. The review also discusses the potential of diamond anvil cells in studying the involved chemical reactions, thermodynamics, and phase behavior of biomass components during gasifi cation. Nonetheless, the caliber of fl uidized beds in continuously gasifying biomass for hydrogen production in supercritical water is also documented.
Investigation of thermochemical conversion of biomass in supercritical water using a batch reactor
Fuel, 2011
This study focused on gasification of biomass and a biomass model compound. Data are presented that show the presence of supercritical water enhances gasification efficiency, as it participates as both a solvent and a reactant. It is established that biomass gasification efficiencies are in the same range for all types of biomass. The thermodynamic changes of state are functions of elemental composition, not biomass species. The oxidation state of carbon atom of biomass is a key variable in determining the changes in enthalpy during both conventional combustion and supercritical water gasification. The oxidation state of the feed (together with the reaction conditions that influence the degree to which water participates as a reactant) also determines the vapor product composition.