B. de Caprariis

Waste Gasification In An Up-draft Fixed-bedGasifier: Experimental Study AndModel Validation

Gasification has been identified as a key technology to enhance the environmental tolerability of low quality fuels such as waste and biomass. In this work the performances of a laboratory scale gasification process fed with waste are reported. Among the several technical choices, we selected the up-draft fixed-bed gasifier as an interesting solution for heat generation in small-scale applications, due to the characteristics of simple geometry and low cost. The experimental setup is composed by an up-draft gasifier followed by a reactor used as filter to remove the particulate and as second thermal and catalytic stage to convert the produced tar in lighter species. A literature model has been adapted to the case under study to analyse the influence of operative parameters such as oxidant flow rate (equivalent and air/steam ratio values) and gasification temperature of the process. The original literature model considers the species gas evolution along the axial coordinate only, and does not include time dependency. To make the model time dependent, the consumption time of the gasification fuel bed estimated from experimental tests was introduced. Since the oxidation zone is below the gasification one, the initial species concentrations were set as the species concentrations produced at the end of the oxidation zone, calculated with an atom mass balance considering a complete char combustion. Since the model concerns only the gasification, the up-draft process was split into two consecutive steps to allow direct comparison between experimental and simulated data: first the drying and pyrolysis processes and then the fixed bed gasification. The model was successfully validated with experimental data and then it was used to predict the operative parameters that determine the optimal syngas composition. The best syngas composition (35% Waste Management and the Environment VI 113 www.witpress.com, ISSN 1743-3541 (on-line) WIT Transactions on Ecology and The Environment, Vol 163,

BIOCRUDE PRODUCTION BY HYDROTHERMAL LIQUEFACTION OF OLIVE RESIDUE

Hydrothermal liquefaction (HTL) converts biomass into a crude bio-oil by thermally and hydrolytically decomposing the biomacromolecules into smaller compounds. The crude bio-oil, or biocrude, is an energy dense product that can potentially be used as a substitute for petroleum crudes. Liquefaction also produces gases, solids, and water-soluble compounds that can be converted to obtain valuable chemical species or can be used as energy vectors. The process is usually performed in water at 250°C–370°C and under pressures of 4–22 MPa: depending on the adopted pressure and temperature the process can be carried out in sub-critical or super-critical conditions. In the conditions reached in hydrothermal reactors, water changes its properties and acts as a catalyst for the biomass decomposition reactions. One of the main advantages of this process is that the energy expensive biomass-drying step, required in all the thermochemical processes, is not necessary, allowing the use of biomass with high moisture content such as microalgae or olive residue and grape mark. In this work, the feasibility of a hydrothermal process conducted under sub-critical conditions to obtain a bio-oil from the residue of olive oil production is investigated. The experimental tests were performed at 320°C and about 13 MPa, using a biomass to water weight ratio of 1:5. The influence of two different catalysts on the bio-oil yield and quality was investigated: CaO and a zeolite (faujasiteNa). CaO allows the increase of bio-oil yields, while the selected zeolite enhances the deoxygenation reactions, thus improving the bio-oil quality in terms of heating value.

The hydrothermal decomposition of biomass and waste to produce bio-oil

The hydrothermal decomposition of biomass is an alternative to the traditional pyrolysis processes to obtain liquid fuels with an increased energy density. Hydrothermal liquefaction is claimed to produce bio-oils with improved characteristics such as a reduced content of oxygen, avoiding at the same time the energy consuming biomass drying step necessary in the traditional thermochemical processes. However, at present the use of this technology is limited by the severe conditions needed and by the difficulties connected with the realization of a continuous process. In this work an innovative process, operating at atmospheric pressure and at moderate temperatures, is proposed, where water subcritical conditions are achieved locally by means of the energy released during cavitation. The process was tested on lab-scale on two biomass feeds obtaining a crude bio-oil with a composition very similar to that of fossil oil and greatly improved respect to those obtained in traditional pyrolysis processes.

Poultry Litter Valorization To Energy

Historically manure has found utilization as fertilizer in agriculture because it contributes to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, phosphorus and potassium. However, the current European Directive 91/676 reduces drastically the application of this material as fertilizer due to its high nitrate content. Therefore, identification of alternative eco-friendly disposal routes with potential financial benefits has become the need, and particularly promising is the energetic valorization of these biomasses. Poultry litter represents one of the more challenging bio-fuel feedstock for energy generation, being easy to handle and showing a composition that potentially assures a high energy content and the production of a byproduct (ash) with good fertilizing properties. In this paper an evaluation of the technical and economic feasibility of the energy conversion technologies usable to recover both the potential energy and fertilizer properties of poultry litter was provided. The focus was on the poultry farms of the North-East Italy, where more than half of the national poultry production is concentrated. The preliminary cost analysis suggests that actually energy production from poultry litter is economically viable in the case of large off-site plants only by means of anaerobic digestion, while in the case of small plants operating in situ for a mean holding capacity farm, utilization of gasification appears to be an option.

Experimental study and model validation of waste gasification in an up-draft fixed-bed gasifier

Gasification has been identified as a key technology to enhance the environmental tolerability of low quality fuels such as waste and biomass. In this work, the performances of a laboratory scale gasification process fed with waste are reported. Among the several technical choices, the up-draft fixed-bed gasifier was selected as an interesting solution for heat generation in small-scale applications, due to the characteristics of simple geometry and low cost. The experimental setup is composed of an up-draft gasifier followed by a reactor used as filter to remove the particulate and as second thermal and catalytic stage to convert the produced tar to lighter species. A literature model has been adapted to the case under study to analyse the influence of operative parameters such as oxidant flow rate (equivalent and air/steam ratio values) and gasification temperature of the process. The original literature model considers the species gas evolution along the axial coordinate only and does not include time dependency. To make the model time dependent, the consumption time of the gasification fuel bed estimated from experiments was introduced. Furthermore the modelling of the oxidation zone was introduced, adding the char combustion equation. Since the model concerns only the gasification, the up-draft process was split into two consecutive steps to allow direct comparison between experimental and simulated data: first the drying and pyrolysis processes and then the fixed bed gasification. During the pyrolysis, a second stage reactor for the tar reforming was included, allowing a tar reduction of about 85 %. The model was successfully validated with experimental data and then was used to predict the operative parameters that determine the optimal syngas composition. The best syngas composition (35% CO and 10% H2) was obtained with an equivalent ratio of 0.6 and a bed temperature of 1100 K.