Daniele Castello

Supercritical water gasification of biomass: Thermodynamic constraints.

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.

Agro-industrial waste to solid biofuel through hydrothermal carbonization

In this paper, the use of grape marc for energy purposes was investigated. Grape marc is a residual lignocellulosic by-product from the winery industry, which is present in every world region where vine-making is addressed. Among the others, hydrothermal carbonization was chosen as a promising alternative thermochemical process, suitable for the treatment of this high moisture substrate. Through a 50 mL experimental apparatus, hydrothermal carbonization tests were performed at several temperatures (namely: 180, 220 and 250 °C) and residence times (1, 3, 8 h). Analyses on both the solid and the gaseous phases obtained downstream of the process were performed. In particular, solid and gas yields versus the process operational conditions were studied and the obtained hydrochar was evaluated in terms of calorific value, elemental analysis, and thermal stability. Data testify that hydrochar form grape marc presents interesting values of HHV (in the range 19.8-24.1 MJ/kg) and physical-chemical characteristics which make hydrochar exploitable as a solid biofuel. In the meanwhile, the amount of gases produced is very small, if compared to other thermochemical processes. This represents an interesting result when considering environmental issues. Statistical analysis of data allows to affirm that, in the chosen range of operational conditions, the process is influenced more by temperature than residence time. These preliminary results support the option of upgrading grape marc toward its energetic valorisation through hydrothermal carbonization.

Supercritical water gasification of biomass for H2 production: Process design

The supercritical water gasification (SCWG) of biomass for H(2) production is analyzed in terms of process development and energetic self-sustainability. The conceptual design of a plant is proposed and the SCWG process involving several substrates (glycerol, microalgae, sewage sludge, grape marc, phenol) is simulated by means of AspenPlus™. The influence of various parameters - biomass concentration and typology, reaction pressure and temperature - is analyzed. The process accounts for the possibility of exploiting the mechanical energy of compressed syngas (later burned to sustain the SCWG reaction) through expansion in turbines, while purified H(2) is fed to fuel cells. Results show that the SCWG reaction can be energetically self-sustained if minimum feed biomass concentrations of 15-25% are adopted. Interestingly, the H(2) yields are found to be maximal at similar feed concentrations. Finally, an energy balance is performed showing that the whole process could provide a net power of about 150 kW(e)/(1000 kg(feed)/h).

Hydrothermal carbonization of off-specification compost: A byproduct of the organic municipal solid waste treatment

The possibility to apply the hydrothermal carbonization (HTC) process to off-specification compost (EWC 19.05.03) at present landfilled was investigated in this work. The aim was to produce a carbonaceous solid fuel for energy valorization, with the perspective of using HTC as a complementary technology to common organic waste treatments. Thus, samples of EWC 19.05.03 produced by a composting plant were processed through HTC in a batch reactor. Analytical activities allowed to characterize the HTC products and their yields. The hydrochar was characterized in terms of heating value, thermal stability and C, H, O, N, S and ash content. The liquid phase was characterized in terms of total organic carbon and mineral content. The composition of the gas phase was measured. Results show that the produced hydrochar has a great potentiality for use as solid fuel.

Supercritical Water Gasification of Glucose/phenol Mixtures as Model Compounds for Ligno-cellulosic Biomass

Supercritical Water Gasification of Glucose/Phenol Mixtures as Model Compounds for Ligno-Cellulosic Biomass Daniele Castello*, Andrea Kruse, Luca Fiori Department of Civil, Environmental and Mechanical Engineering, University of Trento, via Mesiano 77 – 38123 Trento, Italy Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz, 1 – 76344 Eggenstein-Leopoldshafen, Germany Institute of Agricultural Engineering, Conversion Technology and Life Cycle Assessment of Renewable Resources, University of Hohenheim, Garbenstrasse 9 – 70599 Stuttgart, Germany daniele.castello@ing.unitn.it

Thermodynamic Analysis of the Supercritical Water Gasification of Biomass

Thermodynamic equilibrium modeling is important in order to understand which are the expected yields and the energy needs of the supercritical water gasification (SCWG) process. A thermodynamic equilibrium model allows calculating which is the system composition at equilibrium. Equilibrium composition can allow calculating, with good approximation, the overall process yields, especially when high temperatures and/or catalysts are used. In this Chapter, the current state of the art in the field of thermodynamic equilibrium modeling of SCWG is reviewed. The most common modeling approaches are presented, highlighting their advantages and disadvantages. Then, the practical implementation of a non-stoichiometric thermodynamic equilibrium model, based on Gibbs energy minimization, is performed. Finally, it is shown how thermodynamic modeling can be used to build a process model for SCWG, which is a fundamental tool to evaluate the process energy sustainability and its practical feasibility.