• Energy Research

A new simplified approach based on equilibrium modeling is proposed in this work to describe the correlations among syngas species experimentally observed in a pilot scale downdraft biomass gasifier operated with different feedstocks (biomass pellets and vine prunings). The modeling approach is based on experimental evidence on the presence of devolatilization products in the syngas and fluctuations of syngas composition during stationary operation, accounted for by introducing two empirical parameters, a by-pass index and a permeability index. The simplified model correctly reproduces the correlations among the main syngas species (including methane and ethylene) resulting from experimental data of pilot tests with different feedstocks and under a wide range of operating conditions.

Abstract A pilot-scale trial of oil and biodiesel production from high-oleic sunflower was performed in Tuscany (central Italy). An experimental investigation was carried out to evaluate the field performance and the product properties and yields of two high-oleic hybrids (PR64 H31 and PR65 H41). The processing facility, a pilot plant with a limited production capacity located in the proximity of the production field, included a platform for oil production and transesterification. The oil yields of the two high-oleic varieties were around 35% with respect to seed weight. The sunflower seed oils obtained fulfilled most of the quality requirements for the use of vegetable oils as engine fuels. The production of biodiesel was carried out in the transesterification unit. However, the production and the direct use of the sunflower seed oil seemed to be a more suitable option than its conversion to biodiesel, especially at a small scale like that considered in this study. The possible exploitation of seed pressing co-product (sunflower cake) as solid biofuel was assessed. The relatively high calorific value (21 MJ kg −1 ) and the low moisture content ( −1 and 68.7 and 59.6 GJ ha −1 were obtained for oil and cake, respectively. Based on these data, different scenarios of fuel and energy production in the rural context of Tuscany were hypothesized.

Biomass fuels represent a renewable energy source, they are CO2 neutral fuels, and their use reduces the consumption of fossil fuels and limits the emissions of SOx, NOx, and heavy metals. They are...

This work presents a pilot-scale investigation aimed at assessing the feasibility and reliability of biomass pellet gasification. Wood sawdust and sunflower seeds pellets were tested in a 200 kW downdraft gasifier operating with air as gasifying agent. The gasification of pelletized biomass led to rather high and unstable pressure drops, reducing the gasifier productivity and stability. Furthermore the generation of fine residues compromised the operation of wet ash removal systems. On the other hand, good syngas compositions (H(2) 17.2%, N(2) 46.0%, CH(4) 2.5%, CO 21.2%, CO(2) 12.6%, and C(2)H(4) 0.4%), specific gas production (2.2-2.4 N m(3) kg(-1)) and cold gas efficiency (67.7-70.0%) were achieved. For these reasons pelletized biomass should be considered only as complementary fuel in co-gasification with other feedstock.

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.

Biomass gasification couples the high power efficiency with the possibility of valuably using the byproducts heat and biochar. The use of agricultural wastes instead of woody feedstock extends the seasonal availability of biomasses. The downdraft type is the most used reactor but has narrow ranges of feedstock specifications (above all on moisture and particle size distribution), so tests on a demonstrative scale are conducted to prove the versatility of the gasifier. Measurements on pressure drops, syngas flow rate and composition are studied to assess the feasibility of such operations with corn cobs. Material and energy balances, and performance indexes are compared for the four tests carried out under different biomass loads (66-85 kg/h). A good operability of the plant and interesting results are obtained (gas specific production of 2 m3/kg, gas heating value 5.6-5.8 MJ/m3, cold gas efficiency in the range 66-68%, potential net power efficiency 21.1-21.6%).

The heat of pyrolysis of beech and spruce wood was investigated by means of a differential scanning calorimeter. Wide variations were found for the heat of the primary pyrolysis process, depending on the initial sample weight and on the conditions used in the measurements. However, reporting the heat of the primary pyrolysis process versus the final char yield resulted in a linear correlation. This strong dependency of the heat of wood pyrolysis on the final char yield, that is in turn highly sensitive to the experimental conditions, can explain the uncertainty of the data for the heat of wood pyrolysis reported in the literature. A possible explanation for the variability of the heat of wood pyrolysis depending on the final char yield seems to be an exothermic primary char formation process competing with an endothermic volatile formation process.

A possible cause of the wide differences present in the literature values for the calorimetric measurements of the pyrolysis heat of biomass was analyzed. The apparent specific heat of char from pyrolysis of beech wood was investigated by means of a differential scanning calorimeter (DSC). The objective was to find out the influence of the use of a lid on the crucible on the experimental results. In a first experimental series, the crucible containing the sample and the empty reference crucible were closed by a pierced lid. In a second experimental series, the crucible containing the sample and the reference crucible were used without a lid. Results of experiments within the same series showed excellent agreement, but the results of the first series were completely different with respect to those of the second series. A possible explanation for these differences are the different emissivities of the crucible material (aluminium) and char. During experiments without a lid a different radiative heat exchange occurs between the two crucibles and the opposite wall of the DSC measurement cell. In order to confirm the effect of heat radiation inside the DSC measuring cell, additional experiments with aluminium oxide and graphite were carried out.

Bio-oils were produced from bench-scale slow-pyrolysis of three different biomass samples (corn stalks, poplar and switchgrass). Experimental protocols were developed and applied in order to screen their chemical composition. Several hazardous compounds were detected in the bio-oil samples analysed, including phenols, furans and polycyclic aromatic hydrocarbons. A procedure was outlined and applied to the assessment of toxicological and carcinogenic hazards of the bio-oils. The following hazardous properties were considered: acute toxicity; ecotoxicity; chronic toxicity; carcinogenicity. Parameters related to these properties were quantified for each component identified in the bio-oils and overall values were estimated for the bio-oils. The hazard screening carried out for the three bio-oils considered suggested that: (i) hazards to human health could be associated with chronic exposures to the bio-oils; (ii) acute toxic effects on humans and eco-toxic effects on aquatic ecosystems could also be possible in the case of loss of containment; and (iii) bio-oils may present a marginal potential carcinogenicity. The approach outlined allows the collection of screening information on the potential hazards posed by the bio-oils. This can be particularly useful when limited time and analytical resources reduce the possibility to obtain detailed specific experimental data.