E.G. Koukios

Aessessment of biomass potential for power production: a GIS based method

Abstract A method is presented, which estimates the potential for power production from agriculture residues. A GIS decision support system (DSS) has been developed, which implements the method and provides the tools to identify the geographic distribution of the economically exploited biomass potential. The procedure introduces a four level analysis to determine the theoretical, available, technological and economically exploitable potential. The DSS handles all possible restrictions and candidate power plants are identified using an iterative procedure that locates bioenergy units and establishes the needed cultivated area for biomass collection. Electricity production cost is used as a criterion in the identification of the sites of economically exploited biomass potential. The island of Crete is used as an example of the decision-making analysis. A significant biomass potential exists that could be economically and competitively harvested. The main parameters that affect the location and number of bioenergy conversion facilities are plant capacity and spatial distribution of the available biomass potential.

STRUCTURE AND COMPOSITION OF SWEET SORGHUM STALK COMPONENTS

Abstract Stem bark and pith of sweet sorghum were analyzed with reference to their sucrose, simple reducing sugars, cellulose, hemicelluloses, lignin and associated phenolic acids contents. Moreover, lignin monomeric units (guaiacyl and syringyl) engaged in non-condensed structures were characterized by thioacidolysis, whereas cell wall associated phenolic acids ( p- coumaric and ferulic acids) were estimated by alkaline hydrolysis at 170°C. The results obtained showed that bark and pith are heterogeneous as far as their chemical composition and the structure of their chemical components are concerned. In particular, the pith content in water soluble sugars is twice as high compared with the one in the bark, whereas bark is enriched in lignocellulosic fibres. Bark lignin is twice as important in content and less condensed in structure compared to pith lignin. p- Coumaric acid is the predominant p- hydroxycinnamic acid associated to the cell walls, whereas ferulic acid is present in significant quantities.

Physicochemical upgrading of agroresidues as feedstocks for energy production via thermochemical conversion methods

Abstract Ash-related problems including deposition, slagging, fouling, sintering, and agglomeration, caused during the operation of biomass gasifiers and combustors using various agroresidues, e.g., wheat straw, olive residue, corn cobs, as feedstocks constitute the limiting factor for a broad use of this kind of biomass materials for energy production via thermochemical conversion methods. Ash content minimization and simultaneous removal of a number of so-called troublesome elements, e.g., potassium, sodium, chlorine, sulfur, from the ash fraction of these materials were performed by two different pretreatment techniques, fractionation and leaching. Fractionation appeared to remove in all cases a large amount of the materials inherent ash fraction but resulted in a deterioration of the quality of the remaining ash. On the other hand, leaching resulted in both removal of a large portion of the materials inorganic fraction and an improvement of the quality of the remaining ash by removing to a large extent the so-called troublesome elements causing problems during the thermochemical conversion of biomass. Furthermore, ash thermal behavior of various untreated and pretreated samples using sintering tests performed in a laboratory muffle furnace in combination with SEM-EDX elemental analyses of the thermally treated ash samples was studied. In most cases, the results from the thermal treatment technique appeared to be in good agreement with the results obtained from the ash elemental analyses of the tested samples.

An alternative approach to the bioconversion of sweet sorghum carbohydrates to ethanol

The ethanol fermentation of juice and press cake, resulting from the squeezing of sweet sorghum stalks at high pressure, was investigated. The juice was fermented by Saccharomyces cerevisiae and yielded 4.8 g ethanol per 100 g of fresh stalks. The press cake was fermented directly to ethanol by a mixed culture of Fusarium oxysporum and Saccharomyces cerevisiae and yielded 5.1 g ethanol per 100 g of fresh stalks. An overall ethanol concentration and yield of 5.6% (w/v) and 9.9 g of ethanol per 100 g of fresh stalks respectively was obtained. Based on soluble carbohydrates, the ethanol yield from press cake was doubled while the overall theoretical yield was enhanced by 20.7% due to the bioconversion of a significant portion of cell wall polysaccharides to ethanol. The process was found promising for further investigation.

Effect of leaching on the ash behavior of wheat straw and olive residue during fluidized bed combustion

Abstract Fluidized bed combustion has been proven to be an attractive method for the conversion of agroresidues to energy offering economical and environmental benefits. The low melting point ash of agroresidues cause a number of problems e.g., sintering, agglomeration, deposition, etc., which consist the main obstacles for economical and viable application of this conversion method. Leaching that is considered to be a low cost pretreatment technique for the elimination of ash related problems in biomass boilers studied here. The produced results clearly demonstrate that leaching could help significantly to reduce the ash related problems caused during the operation of fluidized bed combustors with biomass.

Bioethanol from sweet sorghum: Simultaneous saccharification and fermentation of carbohydrates by a mixed microbial culture

Sweet sorghum carbohydrates were simultaneously saccharified and fermented to ethanol by a mixed culture of Fusarium oxysporum and Saccharomyces cerevisiae in a bioreactor. Fusarium oxysporum was grown aerobically for the production of the enzymes necessary for the saccharification of sorghum cellulose and hemicellulose. Saccharomyces cerevisiae, together with F. oxysporum, converted the soluble sugars to ethanol. Three batches of sorghum were used, harvested at different periods of the year. The optimum yield of bioconversion and ethanol concentration was 5·2–8·4 g ethanol/100 g of fresh sorghum and 3·5–4·9% (w/v), respectively, depending on the composition of sorghum stalks. In all experiments, the ethanol yield exceeded the theoretical, based on soluble sugars, by 20·0–32·1% due to bioconversion of polysaccharides to ethanol.

Fermentative hydrogen production from pretreated biomass: A comparative study

The aim of this work was to evaluate the potential of employing biomass resources from different origin as feedstocks for fermentative hydrogen production. Mild-acid pretreated and hydrolysed barley straw (BS) and corn stalk (CS), hydrolysed barley grains (BG) and corn grains (CG), and sugar beet extract (SB) were comparatively evaluated for fermentative hydrogen production. Pretreatments and/or enzymatic hydrolysis led to 27, 37, 56, 74 and 45 g soluble sugars/100 g dry BS, CS, BG, CG and SB, respectively. A rapid test was applied to evaluate the fermentability of the hydrolysates and SB extract. The thermophilic bacterium Caldicellulosiruptor saccharolyticus showed high hydrogen production on hydrolysates of mild-acid pretreated BS, hydrolysates of BG and CG, and SB extract. Mild-acid pretreated CS showed limited fermentability, which was partially due to inhibitory products released in the hydrolysates, implying the need for the employment of a milder pretreatment method. The difference in the fermentability of BS and CS is in strong contrast to the similarity of the composition of these two feedstocks. The importance of performing fermentability tests to determine the suitability of a feedstock for hydrogen production was confirmed.

Solar systems diffusion in local markets

Abstract This paper reports on a study of the driving forces and barriers of the spectacular diffusion of solar energy use for domestic hot-water production in Greece. Through the various kinds of questionnaires used in this work, the main diffusion actors have been requested to grade the various diffusion factors identified by desk and preliminary field research. Households identify a number of economic (available family income), technical (new technologies), political (new incentives), and socio-cultural (sensitivity in energy matters) factors as dominant. According to the solar industry, advertising, distribution and quality control standards have to be added to the list of critical factors. Technical experts contribute with identifying, besides R&D, public awareness on energy matters. Solar collector diffusion, despite the fact that it has followed a market-driven mechanism, was revealed to be a multi-actor, multi-dimensional and multi-parametric phenomenon. Presently, the phenomenon is constrained by the available family income, with technology-related factors, i.e., research, and standardization quality control, playing increasing roles.

Agglomeration problems during fluidized bed gasification of olive-oil residue: evaluation of fractionation and leaching as pre-treatments☆

The effect of two pre-treatment techniques leaching and fractionation on the agglomeration problems observed during the gasification of the olive-oil residue material in a fluidized bed reactor was studied. The obtained results proved to be very positive in the case of leaching showing a substantial decrease of the agglomeration phenomena in the bed during the gasification tests compared with the results from the tests with the un-treated material. On the other hand, fractionation appeared to increase the ash reactivity leading to a dramatic increase of the agglomeration problems during the gasification process.

Two-stage acid-catalyzed fractionation of lignocellulosic biomass in aqueous ethanol systems at low temperatures

Abstract Wheat straw was fractionated into cellulosic fibres, hemicellulose sugars and solid lignin oligomers through a two-stage, acid-catalyzed process. During the first stage, raw material was treated with dilute H2SO4 (0·5–2·5 n ) at reflux temperature (99·5 ± 1·0°C) for 10–60 min. Subsequently, delignification was conducted with H2SO4 (2 n ) in aqueous ethanol (62·5–87·5% EtOH v/v) at reflux temperature (81·0 ± 2·0°C) for 90 min. Selective hydrolysis of about 50% of the straw hemicelluloses (w/w on original straw hemicelluloses), converted to water-soluble oligo- and monosaccharides (first stage), followed by delignification in 87·5% v/v EtOH (second stage), led to optimal component fractionation efficiency with negligible cellulose loss (less than 2% w/w on original straw cellulose) and high lignin removal (more than 70% w/w on original straw lignin). By this two-stage process, high overall fibre yields (more than 60% on original raw material) and good pulp mechanical properties were achieved.