The boiler concept for combustion of large soya straw bales

In one of the largest agricultural companies in Serbia, with over 2000 ha of soya plantations, there are 4000 t/year of baled soya straw produced. Soya straw biomass is planned to be used as a renewable energy source for heating the greenhouses, with 5 ha in area. Therefore, efforts have been made to develop a technology for utilizing large bales of soya straw for energy production. In the first phase, a demo energy production facility-furnace was developed and built. The facility had been tested in order to examine the quality of combustion of large soya straw bales. Since experimental results of testing of this facility have proved to be very satisfactory, in the second phase of the development, a hot water boiler of similar characteristics (burning soya straw bales, with dimensions 0.7×1.2×2.7 m³) has been designed.     

Experimental investigation on the influence of different grades of wood chips on screw feeding performance

Although basic investigations on wood chip material properties haven been carried out, only few studies deal with transport of wood chips, despite the fact that significant problems are commonly observed when feeding biomass in industrial applications. Within the work presented, basic bulk material properties were measured and experiments carried out with a system consisting of a hopper, agitator and a screw conveyor. The aim of this study was to investigate how three different wood chip grades and two blends of wood chips influence typical design parameters, such as mass flow and driving torque, of a biomass feeding system. The measured basic bulk properties are in good overall agreement with the literature. However, discrepancies were discovered between two standardized methods for determination of the bulk density. The results for the driving torque, mass flow and mass-related energy consumption showed that different grades of wood chips can alter these values considerably. Between two wood chip grades, a twice as high torque was recorded, while a third grade could not be fed due to jamming. One of the major findings of this study is that mixing a rather small amount of a high-fine content grade with the non-feedable grade of wood chips resulted in a blend which inhibited jamming during the screw feeding process.     

Characteristics of syngas from co-gasification of polyethylene and woodchips

Gasification of polyethylene (PE) and woodchips (WC) mixtures have been investigated in a semi-batch reactor, using high temperature steam as the gasifying agent. The reactor temperature was maintained at 900 °C. The ratio of PE–WC was varied from 0% to 100% in 20% intervals. Characteristics of syngas were evaluated based on the yield of syngas, hydrogen, energy, ethylene, total hydrocarbons and apparent thermal efficiency of the process. Results show that properties of syngas evolved during gasification of PE–WC blends cannot be determined from the weighted average syngas properties obtained from separate gasification of WC and PE. Superior results in terms of syngas yield, hydrogen yield, total hydrocarbons yield, energy yield and apparent thermal efficiency from PE–WC blends were obtained as compared to expected weighed average yields from gasification of individual components. Results confirm synergistic interaction between PE and WC during high temperature steam gasification of these mixtures. These results also provide the importance of mixing two or more compounds on the performance of stream gasification of wastes.     

Comparing hybrid Populus clones for SRF across northern Italy after two biennial rotations: Survival, growth and yield

Short rotation forest (SRF) plantations of hybrid poplars are attractive for Italian farmers due to the availability of public grants and the potential for producing wood chips for energy production. Growth and dendromass yield of new clones for SRF were evaluated after two biennial rotations within a network of experimental fields established in 2003 on three sites of low (Bigarello), medium (Vinovo) and high soil quality (Mira), across northern Italy. Soil preparation, planting density (5900 trees ha⁻¹), weed control, tree water status and mechanical harvesting were homogeneous across the sites. Nitrogen fertilization was applied only in Mira (300 kg N ha⁻¹).In all sites, survival was high for almost all clones, and stem density increased dramatically, with a decrease of stem dimensions, after the first coppicing. In Bigarello, with limiting soil conditions, there was no significant difference among clone biennial yields, which varied from 10.3 (first rotation) to 14.2 (second rotation) Mg ha⁻¹ in dry matter (dm). In the medium and high quality sites of Vinovo and Mira, there was a significant difference in clone yields, with the new clones performing better than control clones (I-214 and Lux). In Mira, mean biennial yield increased from 30.2 to 40.3 Mg dm ha⁻¹ from the first to second cycle.Preliminary results of new clones on medium and high soil quality need to be further confirmed throughout further coppicing cycles; on a marginal soil, even by using the new clones, poplar SRF is not an advisable option.     

Design of chemical composition and optimum working conditions for trivalent black chromium electroplating bath used for solar thermal collectors

Black chromium is one of the selective surfaces which are commonly used in solar thermal systems. The aim of this research was to design an electroplating bath, using chromium trivalent ions instead of its hexavalent ions because of its toxicity, for black chromium coating to produce a good metallurgical and light properties at low cost and reproducibility. The effect of the additives was investigated and a coating with an absorption coefficient of 0.96 was prepared. The bath contained inexpensive constituents such as chromium sulfate, cobalt chloride, sodium fluoride, sodium hypophosphite and sodium dihydrogen phosphate and did not need any pH control. Thermal resistance, corrosion resistance and adhesion of the coatings as well as throwing power of the bath were investigated. The effect of bright Ni as an undercoat before black chromium electroplating was also investigated. SEM and XRD techniques were employed to characterize the surface microstructure and chemical composition. Spectroscopy was also used to measure absorptance of the coatings.     

Energy and CO2 analysis of poplar and maize crops for biomass production in north Italy

The rising price of fossil fuel and the increasing environmental concern encourage the use of biomasses as energy sources. Aim of this study was to compare two poplar SRC and vSRC (6 and 3 years rotation cycle) with an annual crop (maize), used for biomass production in north Italy.The average of the biomass production was 13.9 Mg DM ha⁻¹ per year for the SRC and vSRC poplar and 19.2 Mg DM ha⁻¹ for the maize.The energy consumption for the poplar cultivations was about 15 GJ ha⁻¹ per year, which represented only the 6% of the energy biomass product (about 257 GJ ha⁻¹ per year).The input value of the maize was higher (26.8 GJ ha⁻¹ per year). In this case, the input value was about the 7% of the energy content in the biomass product (about 370 GJ ha⁻¹ per year).During the vSRC cultivation an amount of 8090 kg CO₂ eq ha⁻¹ was emitted, 6420 kg CO₂ eq ha⁻¹ for the SRC and 26,370 kg CO₂ eq ha⁻¹ for the maize.Compared to the maize, the poplar SRC (or vSRC) crops are interesting from an energetic point of view, while maize requires less manpower, but it has major problems related to the landscape biodiversity.     

Energy value as a factor of agroforestry wood species selectivity in Akinyele and Ido local government areas of Oyo State, Nigeria

Wood usage for cooking and heating is still very relevant in most developing countries especially those of sub-Saharan Africa and many parts of Asia. Therefore, sustainable means of generating it for this and other purposes are necessary bearing in mind the influence of indigenous knowledge/users' perspective on any production method regarding success and sustenance. In conformity with this view, questionnaires were administered on 240 respondents in 8 rural communities of Akinyele and Ido Local Government Areas (LGAs) of Oyo State, Nigeria, to elicit information on species that can be used as fuelwood, preferred by the respondents for incorporation into and/or retention in agroforestry plots, out of which 179 (i.e. 75% of the total number of questionnaires administered) were successfully retrieved for statistical analyses. Twelve woody species namely: Annona senegalensis, Anogeissus leiocarpus, Bridelia ferruginea, Daniellia oliveri, Detarium microcarpum, Gardenia ternifolia, Hymenocardia acida, Lophira lanceolata, Parkia biglobosa, Terminalia avicennioides, Triplochiton scleroxylon and Vitellaria paradoxa were prioritized on the basis of respondents' preference using a ranking pattern. Friedman chi-square analysis showed that there was no significant difference (p < 0.05) in the ranking pattern of the respondents from the two LGAs. The mean net calorific values (NCV) of the 12 species were found to be 17.71, 18.63, 18.04, 16.03, 17.67, 18.46, 19.00, 21.68, 19.63, 18.25, 14.65, and 19.47 MJ kg⁻¹ respectively. The result of a two-way analysis of variance indicated a significant variation (p < 0.05) in NCV data for all the species pooled together but not for each species except for D. oliveri with a follow-up test using Fisher's Least Significant Difference. The Pearson's moment correlation analysis gave positive coefficient values (r = 0.868 and 0.874, p < 0.05) between NCV and the cumulative ranking values in Akinyele and Ido LGAs respectively. There was also a coefficient value of 0.873 (p < 0.05) between the cumulative ranking values in the two LGAs. In line with the outcome of this study, it was therefore recommended that native intelligence/indigenous knowledge and/or users' perspective should be part of the criteria for selecting potential fuelwood species for incorporation into and/or retention in agroforestry systems in this and other areas with similar characteristics.     

Household level domestic fuel consumption and forest resource in relation to agroforestry adoption: Evidence against need-based approach

The need-based approach (assuming that higher consumption of tree products would motivate farmers to adopt agroforestry) has led to uneven success, in many cases failure, of many agroforestry projects. Current study investigated the association between fuelwood and forest resource use, and agroforestry adoption based on a survey of 401 households in the Indian Western Himalaya. Data on household domestic fuel utilisation and forest resource use were collected using a questionnaire in personal interviews. Agroforestry adoption increased significantly with increase in distance of nearest State forest from the house, distance travelled to collect fuelwood, and consumption of cattle dung, crop residues, charcoal, kerosene and liquid petroleum gas as domestic fuels by the household. Agroforestry adoption was also significantly higher in households with non-forest than those with State forests as primary source of fuelwood and timber. The proportion of adopters decreased significantly with increase in quantity of fuelwood used for domestic consumption, frequency of collection from State forests, total domestic energy consumption, fuelwood dependency, timber consumption and availability of timber through rights of households on State forests. Logistic regression analysis revealed that none of the factors related to need (quantity of fuelwood and timber used) appeared in the model but primary source of fuelwood, distance travelled to collect fuelwood and availability of timber through rights on the State forests appeared as important factors. This implies that need of the tree products is not a necessary condition to motivate farmers to adopt agroforestry, rather, it is accessibility of tree products which influence agroforestry adoption.     

Biohydrogen production from poplar leaves pretreated by different methods using anaerobic mixed bacteria

Leaves are one of the main by-products of forestry. In this study, batch experiments were carried out to convert poplar leaves pretreated by different methods into hydrogen using anaerobic mixed bacteria at 35 °C. The effects of acid (HCl), alkaline (NaOH) and enzymatic (Viscozyme L, a mixture of arabanase, cellulase, β-glucanase, hemicellulase and xylanase) pretreatments on the saccharification of poplar leaves were studied. Furthermore, the effects of acid and enzymatic pretreatment on hydrogen production, together with their corresponding degradation efficiencies for the total reducing sugar (TRS) and metabolites were compared. A maximum cumulative hydrogen yield of 44.92 mL/g-dry poplar leaves was achieved from substrate pretreated with 2% Vicozyme L, which was approximately 3-fold greater than that in raw substrate and 1.34-fold greater than that from substrate pretreated with 4% HCl. The results show that enzymatic pretreatment is an effective method for enhancing the hydrogen yield from poplar leaves.     

The effect of inaccurate volume calibrations on hydrogen uptake measured by the Sieverts method

The Sieverts technique is a popular method of measuring the uptake of gas on a sample and is an important tool for the characterisation of hydrogen uptake by potential hydrogen storage materials. An analysis of the consequences of errors in the calibration of volumes in this technique has been made using hydrogen absorption on an AB₂ alloy as an example. Trends in the error in the uptake as a function of errors in the volumes have been explained in terms of the equations for uptake. Significant advantages are found for calibration techniques for which the ratio of volumes is an intrinsic measurement.     

Optical properties of black nickel selective surface by conversion coating process

Optical properties of nickel black selective surfaces, prepared by a conversion coating process, on zincated aluminium alloy surfaces are studied in relation to the processing parameters. It is possible to obtain nickel black surfaces with solar absorptances ranging from 0.95 to 0.97 and thermal emittances ranging from 0.2 to 0.4. The coatings are stable up to 200°C but show degradation under humid conditions. Surface studies indicate that the optical properties may be explicable by the structure of these nickel films.     

Land use change to bioenergy: A meta-analysis of soil carbon and GHG emissions

A systematic review and meta-analysis were used to assess the current state of knowledge and quantify the effects of land use change (LUC) to second generation (2G), non-food bioenergy crops on soil organic carbon (SOC) and greenhouse gas (GHG) emissions of relevance to temperate zone agriculture. Following analysis from 138 original studies, transitions from arable to short rotation coppice (SRC, poplar or willow) or perennial grasses (mostly Miscanthus or switchgrass) resulted in increased SOC (+5.0 ± 7.8% and +25.7 ± 6.7% respectively). Transitions from grassland to SRC were broadly neutral (+3.7 ± 14.6%), whilst grassland to perennial grass transitions and forest to SRC both showed a decrease in SOC (−10.9 ± 4.3% and −11.4 ± 23.4% respectively). There were insufficient paired data to conduct a strict meta-analysis for GHG emissions but summary figures of general trends in GHGs from 188 original studies revealed increased and decreased soil CO₂ emissions following transition from forests and arable to perennial grasses. We demonstrate that significant knowledge gaps exist surrounding the effects of land use change to bioenergy on greenhouse gas balance, particularly for CH₄. There is also large uncertainty in quantifying transitions from grasslands and transitions to short rotation forestry. A striking finding of this review is the lack of empirical studies that are available to validate modelled data. Given that models are extensively use in the development of bioenergy LCA and sustainability criteria, this is an area where further long-term data sets are required.     

Storage dynamics and fuel quality of poplar chips

Poplar cultivation for wood/timber production has a growth production cycle of about 10–15 years. Usually the stem is separated from the crown and used to produce material of different kind such as veneer, pallets, panels, etc. For wood industries, crowns generally represent waste material to be disposed of, causing economic and time losses. It is generally believed that the costs of managing crown biomass are higher than the potential incomes obtainable. Nonetheless, it is worthwhile investigating the possibility of using these byproducts as energy source and evaluating their value as a fuel. However, storing such residues presents several problems connected with spontaneous microbial degradation.The aim of this work was to evaluate the storage effects on chipped biomass deriving from the crown and stem wood of poplar and how they affect fuel quality and dry matter losses.A storage trial was carried out with three piles of stem wood chips and three of crown chips coming from a 15 year old poplar plantation. The piles were stored outdoors for six months under the same climatic conditions.The effect of storage on fuel quality was evaluated with respect to moisture content, gross and net calorific values, chemical composition, ash content, and bulk density.The variation of temperatures inside each pile due to heat development was continuously monitored and showed different trends between piles depending on source material. Results showed that chips from crown material had better storage properties and exhibited lower decay than chips from stem wood.