Investigation of thermochemical conversion of biomass in supercritical water using a batch reactor (original) (raw)
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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.
Supercritical Water Gasification of Biomass: A Literature and Technology Overview
Energies, 2015
The supercritical water gasification process is an alternative to both conventional gasification as well as anaerobic digestion as it does not require drying and the process takes place at much shorter residence times; a few minutes at most. The drastic changes in the thermo-physical properties of water from the liquid state to the supercritical state make it a promising technology for the efficient conversion of wet biomass into a product gas that after upgrading can be used as substitute natural gas. The earliest research goes back as far as the 1970s and since then, supercritical water has been the subject of many research works in the field of thermochemical conversion of wet biomass. This article reviews the state of the art of the supercritical water gasification technology starting from the thermophysical properties of water and the chemistry of reactions to the process challenges of such a biomass based supercritical water gasification process plant.
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.
Supercritical Water Gasification of Biomass for Hydrogen Production: Variable of the Process
Food and Public Health, 2015
Waste biomass has various origins, such as agricultural crops, food waste, animal waste, municipal solid waste, and has the potential to be converted into energy and applied in biorefineries, thus contributing with lignocellulosic material. The emerging technology "Supercritical Water Gasification" has a great potential for recycling biomass for the production of synthesis gas with a higher percentage of hydrogen. The supercritical water gasification (SCWG) does not require drying; thus, the problem of drying is largely avoided by the SCWG and can be used for biomass with high percentage of humidity. The conversion efficiency of the SCWG is generally higher when compared with conventional technologies. This paper reviews known and emerging key supercritical water properties that influence the SCWG of biomass (viscosity, density, dielectric constant and ionic product), the advantages of the SCWG with respect to conventional gasification, the economic viability of the process, and the kinetics of the biomass in the process, this review describes the factors that influence the process (temperature, pressure, residence time, concentration, effect of the catalyst, effect of the reactor geometry, reactor design, heating rate of the biomass particle and type of biomass). Finally, this article concludes that the technology "supercritical water gasification" has great potential for a cleaner biogas production, with a high percentage of hydrogen, by different types of biomass, thus reducing the pollution and CO 2 emissions.
Supercritical water gasification of biomass for H2 production: Process design
Bioresource Technology, 2012
Waste biomass has various origins, such as agricultural crops, food waste, animal waste, municipal solid waste, and has the potential to be converted into energy and applied in biorefineries, thus contributing with lignocellulosic material. The emerging technology "Supercritical Water Gasification" has a great potential for recycling biomass for the production of synthesis gas with a higher percentage of hydrogen. The supercritical water gasification (SCWG) does not require drying; thus, the problem of drying is largely avoided by the SCWG and can be used for biomass with high percentage of humidity. The conversion efficiency of the SCWG is generally higher when compared with conventional technologies. This paper reviews known and emerging key supercritical water properties that influence the SCWG of biomass (viscosity, density, dielectric constant and ionic product), the advantages of the SCWG with respect to conventional gasification, the economic viability of the process, and the kinetics of the biomass in the process, this review describes the factors that influence the process (temperature, pressure, residence time, concentration, effect of the catalyst, effect of the reactor geometry, reactor design, heating rate of the biomass particle and type of biomass). Finally, this article concludes that the technology "supercritical water gasification" has great potential for a cleaner biogas production, with a high percentage of hydrogen, by different types of biomass, thus reducing the pollution and CO 2 emissions.
Iranica Journal of Energy & Environment, 2012
The aim of this study was to investigate the feasibility of hydrogen production from sugarcane bagasse by supercritical water gasification (SCWG) at low temperature and in presence of alkali catalyst. Experiments were carried out in a batch autoclave reactor at 400 °C and 9% solid content. Effect of reaction time and alkali catalyst on gas yield, gas composition, carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) were investigated. Influence of reaction time on gas yield and composition as well as on CGE was found to be insignificant. Extending the reaction time even up to 4 h could not cause an attractive conversion of bagasse. In the presence of catalysts (K CO , KHCO , NaHCO and NaOH), sugarcane 2 3 3 3 bagasse was partially gasified in SCW and hydrogen-rich gas containing CO as the main carbon compound 2 was produced. Among the implemented catalysts, KCO was identified to be the most effective for 2 3 improvement of HGE. Use of the catalyst under our experimental conditions, the maximum HGE of 19% was achieved; however the highest CGE occurred with KHCO. Results showed that feed to catalyst ratio of 2 was 3 high enough to reach the greatest possible gasification of hydrogen at 400 °C and 45 min. More CGE and HGE would be possible only by increasing the temperature, pressure and/or reaction time.
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...
Journal of Supercritical Fluids, 2012
This article presents a system model for the process of gasification of biomass model compounds in supercritical water. Supercritical water gasification of wet biomass (water content of 70 wt% or more) has as the main advantage that conversion may take place without the costly drying step. The thermodynamic model is generated in ASPEN 12.1 under the assumption of chemical equilibrium and using model compounds to represent the organics in the wet biomass. The research focuses on predicting the influence of several parameters on the thermal efficiency of the process. One of the important parameters under investigation is the heat exchanger effectiveness. The possibility of tailoring the product gases and in situ CO 2 capturing using water are also modeled and described. (J.A.M. Withag).