Anaerobic digestion of industrial hemp-Effect of harvest time on methane energy yield per hectare

There is a worldwide emphasis to increase the share of renewable transportation fuels. When using agricultural land for production of renewable transportation fuels, the energy output per hectare for different crops and transportation fuels is a crucial factor. In this study, the gross methane energy yield per hectare from anaerobic digestion of industrial hemp (Cannabis sativa L.), was determined at four different harvest times between July and October in Southern Sweden, a cold climate region. The biomass yield was determined for three years and the methane yield was determined for two years through the biochemical methane potential test. The highest biomass yield, 16 tonnes dry matter per hectare on an average, and the highest methane energy yield per hectare was achieved when the hemp was harvested in September or October, with an average gross methane energy yield of 136 ± 24 GJ per hectare. There was no significant difference in the specific methane yield between the harvest times; the average being 234 ± 35 m³ per tonne volatile solids. Biogas from hemp turned out to be a high yielding alternative to the currently dominating renewable transportation fuels produced from crops grown in Sweden: ethanol from wheat and biodiesel from rapeseed.     

Impact of genotype, harvest time and chemical composition on the methane yield of winter rye for biogas production

Rye (Secale cereale L.) is an ideal crop for the agricultural biogas production in regions with less fertile and sandy soils. Maximum methane yield per hectare is the main aim of the farmer. Objectives were to establish differences by the Hohenheim Biogas Test among (1) 25 genotypes (experiment 1) and (2) three harvest dates (early heading, early and late milk ripening) and three plant fractions (ears, leaves and stems, stubbles) for four genotypes including an analysis of their nutrient composition (experiment 2). Significant (P < 0.05) genotypic variation was found for dry matter yield, specific gas yield and methane yield among the 25 genotypes, but no differences for methane content and specific methane yield. Broad ranges were achieved for dry matter yield (0% water content) and methane yield amounting to 2.9 t ha⁻¹ and 840 m³ ha^-1 respectively, combined with moderate to high heritabilities (0.71-0.98). Both traits were highly correlated (r = 0.95, P < 0.01). Compared to population and forage rye, hybrid rye achieved significantly higher methane yields. The latest harvest date at late milk ripening resulted in the highest dry matter yield on a whole plant level with an average of 16.0 t ha⁻¹. Accordingly, methane yield was reaching a mean of 4424 m³ ha^-1 and a maximum of 4812 m³ ha^-1. No correlations between content of crude nutrients or cell-wall fractions and specific gas or methane yield were evident neither for the plant fractions nor for the whole plant. In conclusion, harvesting at late milk ripening was clearly superior in dry matter and methane yields although specific methane yield was higher at early heading. A selection for maximum dry matter yield in rye breeding should indirectly improve also methane yield.     

Compositional changes in industrial hemp biomass (Cannabis sativa L.) induced by electron beam irradiation Pretreatment

The effects of electron beam irradiation on chemical decomposition of industrial hemp biomass were evaluated at doses of 150, 300, and 450 kGy. The quantity of decomposed components was indirectly estimated by measuring changes in alkaline extraction. The more severe degradation of structural components induced by higher irradiation doses resulted in larger amounts of alkaline extract. Carbohydrate compositional analysis using ¹H-NMR spectroscopy was applied to quantitatively investigate changes in the polysaccharides of the industrial hemp. The xylose peak intensity in the NMR spectra decreased with increasing electron irradiation dose, indicating that xylan was more sensitive to electron beam irradiation than cellulose.     

Fuel utilization and fuel sensitivity of solid oxide fuel cells

Fuel utilization and fuel sensitivity are two important process variables widely used in operation of SOFC cells, stacks, and generators. To illustrate the technical values, the definitions of these two variables as well as practical examples are particularly given in this paper. It is explicitly shown that the oxygen-leakage has a substantial effect on the actual fuel utilization, fuel sensitivity and V-I characteristics. An underestimation of the leakage flux could potentially results in overly consuming fuel and oxidizing Ni-based anode. A fuel sensitivity model is also proposed to help extract the leakage flux information from a fuel sensitivity curve. Finally, the “bending-over” phenomenon observed in the low-current range of a V-I curve measured at constant fuel-utilization is quantitatively coupled with leakage flux.     

Evaluation of biomass and thermal energy utilization efficiency of oilseed Brassica (Brassica juncea) under altered microenvironments

Changes in within-canopy microenvironments may significantly influence the physiological response pattern of the crop eventually influencing biomass, seed yield and their heat utilization behavior. Therefore, energy use efficiency in oilseed crop Brassica juncea was evaluated to have better understanding of impact of microenvironments on plant characteristics. Linear and non-linear regression analysis showed significant and positive response of Brassica towards time variable leaf area index (LAI), dry biomass accumulation and their heat utilization efficiencies. Linear and third order polynomial regression models indicated 81 and 94% variation in LAI and dry biomass production respectively as a function of time (t) while about 85-93% variation in thermal energy use efficiency (THUE) was observed which might be due to differential thermal heat accumulation at its various phenological stages. Its quantification was done with second order regression equations using accumulated thermal heat (TI) (R² = 0.93∗∗) and solar energy (PTI) (R² = 0.85∗∗). THUE was predicted as 0.1616 × LAI - 0.0294; R² = 0.74∗∗ using TI and 0.0179 × LAI - 0.0044; R² = 0.75∗∗ using PTI and 0.0378 + 0.0012 × (DM) -3E-07 × (DM)²; R² = 0.97∗∗ using TI and 0.0042 + 0.0001 × (DM)−3E-08 × (DM)²; R² = 0.96∗∗ using PTI. The significant changes in seed yield heat use efficiency of the order 80-87% were attributed to differential thermal energy utilization capacities. We conclude that the prediction models developed from this study could be used in predicting energy use efficiency in other related species of oilseed Brassica.     

A novel microbial fuel cell stack for continuous production of clean energy

Production of sustainable and clean energy through oxidation of biodegradable materials was carried out in a novel stack of microbial fuel cells (MFCs). Saccharomyces cerevisiae as an active biocatalyst was used for power generation. The novel stack of MFCs consist of four units was fabricated and operated in continuous mode. Pure glucose as substrate was used with concentration of 30 g l⁻¹ along with 200 μmol l⁻¹ of natural red (NR) as a mediator in the anode and 400 μmol l⁻¹ of potassium permanganate as oxidizing agent in the cathode. Polarimetry technique was employed to analyze the single cell as well as stack electrical performance. Performance of the MFCs stack was evaluated with respect to amount of electricity generation. Maximum current and power generation in the stack of MFC were 6447 mA.m⁻² and 2003 mW.m⁻², respectively. Columbic efficiency of 22 percent was achieved at parallel connection. At the end of process, image of the outer surface of graphite electrode was taken by Atomic Force Microscope at magnification of 5000. The high electrical performance of MFCs was attributed to the uniform growth of microorganism on the graphite surface which was confirmed by the obtained images.     

Conceptual design and modelling of the Steam-Iron process and fuel cell integrated system

The Steam-Iron process, based on the redox reaction of iron oxides (Fe₃O₄ + 4H₂ ↔ 3Fe + 4H₂O), is an interesting alternative to other methods of storing and generating pure hydrogen. In order to evaluate the ability of the Steam-Iron process to supply hydrogen to a solid oxide fuel cell (SOFC), a mathematical model for the oxidation process in a fixed bed reactor has been developed and is used to estimate the behaviour of the reactor under various operating conditions (e.g. amount of iron, steam flow rate, temperature). As a result of the simulations, information is provided for the preliminary design of the reactor and the selection of optimal reaction conditions. Furthermore, we have shown that the Steam-Iron reactor can be successfully integrated with an SOFC, and two system options have been explored to determine the overall system efficiency.     

Environmental impacts and energy demand of rapeseed as an energy crop in Chile under different fertilization and tillage practices

The implementation of energy crops in Chile is an option that requires prior environmental studies within the framework of a sustainable national policy of energy security. The aim of this study is to assess the environmental performance of rapeseed crop (Brassica napus L.) in Chile in view of its potential use for the production of biodiesel. Using Life Cycle Assessment (LCA), the study quantifies the energy demand and the environmental impacts associated with the main tillage systems of Chilean rapeseed production on a national level: conventional tillage and zero tillage, and with four mineral fertilisation trials on a local level (combination of N, P and K rates). In the inventory, the agricultural inputs are obtained from national sources; international databases processes are partially adapted to Chilean conditions. For the impact assessment, the CML 2 baseline 2001 method is applied. The results indicate that the two tillage systems present similar energy demand and environmental impacts profile, with the exception of the categories photochemical ozone creation and freshwater aquatic ecotoxicity. In both systems, the use of mineral fertilisers has the greatest energy demand, with a contribution of over 75%, and the greatest environmental impacts. In contrast, fungicides and seeds have a minimum contribution, all together, less than 3%. The results of LCA of fertilisation trials show that higher fertilisation rates require an increase in seed yield to compensate additional impacts and to be environmentally favourable.     

Surface texture, chemistry and adsorption properties of acid blue 9 of hemp (Cannabis sativa L.) bast-based activated carbon fibers prepared by phosphoric acid activation

Hemp (Cannabis sativa L.) bast was used to prepare activated carbon fibers by phosphoric acid activation at 400-600 °C. The pyrolysis process, textural and chemical properties for the samples were investigated by means of TG/DTA, SEM, cryogenic N₂ adsorption, FTIR and XPS. Dye adsorption on the resultant sample was also measured. The textural properties of the activated carbon fibers were found to be strongly dependent on the activation temperature. Activated carbon fibers exhibited narrow pore size distributions with maxima in the micropore and small mesopore regions. BET surface area, total pore volume, micropore volume and mesopore volume increased with the increase of activation temperature up to 450 °C and then decreased with further heating, and a sample with maximum surface area of 1142 m² g⁻¹ and total pore volume of 0.67 cm³ g⁻¹ was obtained. Phosphoric acid facilitated the conservation of porous structure, led to the creation of tremendous porosity, and resulted in various P-containing functional structures on the surface and in the bulk phase of the resultant samples. The adsorption of acid blue 9 on the sample could be favorably described by Langmuir isotherm, and the adsorption kinetics was found to be well fitted by the intraparticle diffusion model.     

Synthesis and characterization of platinum nanoparticles on in situ grown carbon nanotubes based carbon paper for proton exchange membrane fuel cell cathode

Multi-walled carbon nanotubes (MWCNTs) based micro-porous layer on the carbon paper substrates was prepared by in situ growth in a chemical vapor deposition setup. Platinum nanoparticles were deposited on in situ grown MWCNTs/carbon paper by a wet chemistry route at <100 °C. The in situ MWCNTs/carbon paper was initially surface modified by silane derivative to incorporate sulfonic acid–silicate intermediate groups which act as anchors for metal ions. Platinum nanoparticles deposition on the in situ MWCNTs/carbon paper was carried out by reducing platinum (II) acetylacetonate precursor using glacial acetic acid. High resolution TEM images showed that the platinum particles are homogeneously distributed on the outer surface of MWCNTs with a size range of 1–2 nm. The Pt/MWCNTs/carbon paper electrode with a loading of 0.3 and 0.5 mg Pt cm⁻² was evaluated in proton exchange membrane single cell fuel cell using H₂/O₂. The single cells exhibited a peak power density of 600 and 800 mW cm⁻² with catalyst loadings of 0.3 and 0.5 mg Pt cm⁻², respectively with H₂/O₂ at 80 °C, using Nafion-212 electrolyte. In order to understand the intrinsically higher fuel cell performance, the electrochemically active surface area was estimated by the cyclic voltammetry of the Pt/MWCNTs/carbon paper.     

Efficiency model for photovoltaic modules and demonstration of its application to energy yield estimation

A new method has been proposed [W. Durisch, K.H. Lam, J. Close, Behaviour of a copper indium gallium diselenide module under real operating conditions, in: Proceedings of the World Renewable Energy Congress VII, Pergamon Press, Oxford, Elsevier, Amsterdam, 2002, ISBN 0-08-044079-7] for the calculation of the annual yield of photovoltaic (PV) modules at selected sites, using site-specific meteorological data. These yields are indispensable for calculating the expected cost of electricity generation for different modules, thus allowing the type of module to be selected with the highest yield-to-cost ratio for a specific installation site. The efficiency model developed and used for calculating the yields takes three independent variables into account: cell temperature, solar irradiance and relative air mass. Open parameters of the model for a selected module are obtained from current/voltage (I/V) characteristics, measured outdoors at Paul Scherrer Institute's test facility under real operating conditions. From the model, cell and module efficiencies can be calculated under all relevant operating conditions. Yield calculations were performed for five commercial modules (BP Solar BP 585 F, Kyocera LA361K54S, Uni-Solar UPM-US-30, Siemens CIS ST40 and Wuerth WS11003) for a sunny site in Jordan (Al Qawairah) for which reliable measured meteorological data are available. These represent mono-crystalline, poly-crystalline and amorphous silicon as well as with copper–indium-diselenide, CuInSe₂ PV modules. The annual yield for these modules will be presented and discussed.     

Slow expansion and low yields of willow short rotation coppice in Sweden; implications for future strategies

About 16 000 ha of commercial willow Short Rotation Coppice (SRC) fields for production of biomass for energy were planted in the early 1990s in Sweden. The cultivated with SRC area has remained almost stable and was slightly decreased during the last years despite the incentives and predictions for drastic increases. Similar incentives and predictions in other countries have been lately launched. The bioenergy produced in the planted SRC areas in Sweden has been lower than anticipated, partly due to the lower than expected biomass yields and the termination of some willow SRC plantations. Explanations for the low yields are depicted based on analyzing the results of a survey where 175 willow SRC growers participated. Lower biomass yields are attributed to: (i) the low input in management activities; (ii) the choice of land for the willow SRC plantation; (iii) and the level of personal involvement of the farmer. Understanding the reasons to earlier years’ performance of willow SRC is important for development of better performing systems in the future, in Sweden as well as in other countries.     

Preparation and electrochemical properties of strontium doped Pr2NiO4 cathode materials for intermediate-temperature solid oxide fuel cells

Pr_2−xSr_xNiO₄ (PSNO, x = 0.3, 0.5 and 0.8) cathode materials for intermediate-temperature solid oxide fuel cell (IT-SOFC) were synthesized by a glycine-nitrate process using Pr₆O₁₁, Ni(NO₃)₂·6H₂O and SrCO₃ powders as raw materials. Phase structure of the synthesized powders was characterized by X-ray diffraction analysis (XRD). Microstructure of the sintered PSNO samples was observed and thermal expansion coefficient (TEC) and electrical conductivity were investigated. Electrochemical impedance spectroscopy (EIS) measurement of the PSNO materials on Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte was carried out, and single cells based on the PSNO cathodes were also assembled and their performances were tested. The results show that the synthesized PSNO powders have pure K₂NiF₄-type structure and the PSNO materials are chemically stable with Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte. The sintered PSNO samples have porous and fine microstructure with pore size smaller than 1 μm. Average thermal expansion coefficient of the PSNO materials is about 12–13 × 10⁻⁶ K⁻¹ at 200–800 °C and the electrical conductivity is in the range of 70–120 Scm⁻¹ at 800 °C. Area specific resistance (ASR) of the Pr_2−xSr_xNiO₄ materials on SCO electrolyte is 0.407 Ωcm², 0.126 Ωcm² and 0.112 Ωcm² for x = 0.3, 0.5 and 0.8 at 800 °C, respectively. Maximum open circuit voltage (OCV) and power density of the single NiO-SCO/SCO/PSNO cells are 0.75 V and 298 mWcm⁻² at 700 °C, respectively, which indicates that Pr_2−xSr_xNiO₄ may be a potential cathode material for IT-SOFC.     

Theoretical models for effective electrical and electrochemical properties of nano-particle infiltrated electrode of solid oxide fuel cell

Single- and binary-phase nano-particle infiltrated electrodes (SIE and BIE) have been actively studied experimentally. To properly understand the experimental results and the benefits of SIE and BIE designs, new models for electrical conductivities of BIE and TPB lengths of SIE and BIE are proposed here. The models agree with experiments on the variation of conductivity with LSM loading. SIE and BIE may provide adequate electronic conductivity at low loading of conducting material. The theoretical effective properties are further used in multi-physics modeling and the obtained I–V curves also agree with the experiments. Quantitative comparisons of the ionic conductivities of SIE, BIE and conventional composite electrode (CE) are made. BIE possesses the longest TPB length and SIE may also yield a TPB length that is one order of magnitude larger than that of CE. The new theory allows for in-depth analysis and design optimization of BIE and SIE for improved performance.     

Effect of pruning history on growth and dry mass partitioning of jatropha on a plantation site in Madagascar

While technical aspects of oil processing of seeds of jatropha are under intensive investigation, comparably little is known about the performance of jatropha in the field. We investigated the effects of water availability (rainfed versus irrigated) and pruning-induced differences in plant stature on growth, biomass partitioning, and canopy size at a plantation site in Madagascar in 2010. Plants of different pruning types differed in trunk height (43 versus 29 cm) and primary branches total length (171 versus 310 cm). The two pruning types had effects on dry mass formation and leaf area projection (LAP) during the vegetation period. Trees which had a shorter trunk and longer lateral branches produced more biomass and had a higher LAP. Total dry mass formation varied from 489 to 912 g m⁻² and LAP from 3.26 to 7.37. Total aboveground biomass increased from 2.3 ± 0.5 to 4.89 ± 1.4 kg tree⁻¹ and from 4.6 ± 1.8 to 8.9 ± 1.0 kg tree⁻¹ for the pruning types with shorter and longer lateral branches, respectively. Growth of twigs and leaves was positively correlated with total length of branches. Relative dry mass allocation to branches, twigs and leaves, length of twigs per cm of branches and specific leaf area (13.57 ± 0.72 m² kg⁻¹) were not affected by pruning and water supply. Trees with shorter branches had higher LAD. Results indicate that pruning type should be considered as a management tool to optimize biomass production. Detailed studies on effects of canopy size and shape on radiation interception and growth are required to improve the productivity of jatropha.     

Synthesis and performance of Sr1.5LaxMnO4 as cathode materials for intermediate temperature solid oxide fuel cell

A-site non-stoichiometric materials Sr_1.5La_xMnO₄ (x = 0.35, 0.40, 0.45) are prepared via solid state reaction. The structure of these materials is determined to be tetragonal. Both the lattice volume and the thermal expansion coefficient reduce with the decrease of lanthanum content. On the contrary, the conductivity increases and the maximum value of 13.9 S cm⁻¹ is found for Sr_1.5La_0.35MnO₄ at 750 °C in air. AC impedance spectroscopy and DC polarization measurements are used to study the electrode performance. The optimum composition of Sr_1.5La_0.35MnO₄ results in 0.25 Ω cm² area specific resistance (ASR) at 750 °C in air. The oxygen partial pressure measurement indicates that the charge transfer process is the rate-limiting step of the electrode reactions.     

Preparation and characterization of Pr1−xSrxFeO3 cathode material for intermediate temperature solid oxide fuel cells

A kind of cathode material of Pr_1−xSr_x FeO₃ (x = 0–0.5) for intermediate temperature solid oxide fuel cells (IT-SOFCs) was prepared by the coprecipitation method. Crystal structure, thermal expansion, electrical conductivity and electrochemical performance of the Pr_1−xSr_xFeO₃ perovskite oxide cathodes were studied by different methods. The results revealed that Pr_l−xSr_xFeO₃ exhibited similar orthorhombic structure from x = 0.1 to 0.3 and took cubic structure when x = 0.4–0.5. The unit cell volume decreased and the thermal expansion coefficient (TEC) of the materials increased as the strontium content increased. When 0 < x ≤ 0.3, the samples exhibited good thermal expansion compatibility with YSZ electrolyte. The electrical conductivity increased with the increasing of doped strontium content. When x = 0.3–0.5, the electrical conductivities were higher than 100 S cm⁻¹. The conductivity of Pr_0.8Sr_0.2FeO₃ was 78 S cm⁻¹ at 800 °C. Compared with the La_0.8Sr_0.2MnO₃ cathode, Pr_0.8Sr_0.2FeO₃ showed higher polarization current density and lower polarization resistance (0.2038 Ω cm²). The value of I₀ for Pr_0.8Sr_0.2FeO₃ at 800 °C is 123.6 mA cm⁻². It is higher than that of La_0.8Sr_0.2MnO₃. Therefore, Pr_1−xSr_xFeO₃ can be considered as a candidate cathode material for IT-SOFCs.     

Direct utilization of methanol on impregnated Ni/YSZ and Ni-Zr0.35Ce0.65O2/YSZ anodes for solid oxide fuel cells

Some of the limits on fuel cell development include the issues of hydrogen availability and storage. Methanol has many advantages as an alternative fuel for fuel cells but depending on the anode composition, the formation of carbon may be a problem. In this paper, the direct utilization of methanol in solid oxide fuel cells with impregnated Ni/YSZ and Ni-Zr_0.35Ce_0.65O_2−δ (ZDC)/YSZ anodes was investigated at 1073 K. Performance and stability of these anodes, as measured by steady-state polarization and electrochemical impedance spectroscopy, were improved by the presence of ZDC; although, the deposition of carbon, as detected by scanning electron microscopy and temperature-programmed oxidation analysis, was not entirely avoided. The impact of the carbon, however, was different depending on the anode. That is, carbon formation caused the delamination of impregnated Ni/YSZ anodes, while the structural integrity of Ni-ZDC/YSZ anodes was maintained and the cell performance was not negatively impacted. Increasing the fuel utilization decreased coking, as predicted by equilibrium calculations.     

Lifecycle assessment of the economic, environmental and energy performance of Jatropha curcas L. biodiesel in China

Due to issues relating to the sustainability of biofuel production, second generation biofuel has attracted much attention. As a promising feedstock of second generation biodiesel, Jatropha curcas L. (JCL) is being massively planted on marginal land in China, but its viability as a biofuel source has not been systematically assessed. This paper performed a lifecycle assessment of the economic, environmental and energy (3E) performance of the JCL biodiesel, assuming JCL oil is either used for direct blending with diesel or further processed into JCL methyl ester (JME). The results show that, at the current technical levels, the production of JCL biodiesel is financially infeasible, but has positive environmental and energy performance. Despite the additional cost incurred in the transesterification process, the net present value of JME is slightly higher than that of JCL oil when a part of the cost is allocated to the co-product, i.e., glycerin. As compared with that of diesel, the production and consumption of per liter JCL oil and JME can reduce 7.34 kg and 8.04 kg CO₂ equivalent, respectively. The energy balances of both JCL oil and JME are 1.57 and 1.47, respectively, in terms of the ratio of the heat value of biodiesel and that of energy input. The main factors affecting the 3E performance of JCL biodiesel are seed yield, co-product output, and farm energy input.     

PrBa0.5Sr0.5Co2O5+x as cathode material based on LSGM and GDC electrolyte for intermediate-temperature solid oxide fuel cells

PrBa_0.5Sr_0.5Co₂O_5+x (PBSC) oxides have been evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ce_0.9Gd_0.1O_1.95 (GDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolytes. XRD results show that PBSC cathode is chemically compatible with the intermediate-temperature electrolyte materials GDC and LSGM. The maximum electrical conductivity is 1522 S cm⁻¹ at 100 °C and its value is higher than 581 S cm⁻¹ over the whole temperature range investigated. Microstructures show that the contact between PBSC and LSGM is better than that between PBSC and GDC. The area-specific resistances (ASRs) of PBSC cathode on GDC and LSGM electrolytes are 0.048 and 0.027 Ωcm² at 800 °C, respectively. The electrolyte-supported (thickness of electrolyte is 300 μm) fuel cells generate good performance with the maximum power densities of 617 mW cm⁻² on GDC electrolyte and 1021 mW cm⁻² on LSGM electrolyte at 800 °C. All results demonstrate that PBSC oxide is a very promising cathode material for application in IT-SOFCs and this cathode based on LSGM electrolyte obtained better performance than on GDC electrolyte.