Analysis and optimization of a cogeneration system based on biomass combustion

The paper deals with analysis and optimization of the performance of the combustion process in a biomass furnace at a biomass cogeneration plant. For the purpose a thermodynamic model for the biomass burning process in a grate furnace was developed. The mathematical model describes both, the thermal decomposition of the fuel on the grate as well as gas phase combustion in the secondary zone. The presented approach is based on energy equations for each individual step of the biomass combustion process.Measurement results from a biomass-fired cogeneration plant were used to validate the model. Comparison between simulation and measurement results shows good agreement. The model predicts accurately the temperature profiles in the combustion chamber.The presented approach is suitable for model based analysis and optimization of control strategies. The developed model was used to optimize the performance of the recirculation system of the combustion appliance. The simulation based analysis showed, that the flow rate of the recirculated exhaust fumes can be significantly reduced which results in energy savings of 17% of the auxiliary electrical power demand.     

Biomass gasification cogeneration – A review of state of the art technology and near future perspectives

Biomass is a renewable resource from which a broad variety of commodities can be produced. However, the resource is scarce and must be used with care to avoid depleting future stock possibilities. Flexibility and efficiency in production are key characteristics for biomass conversion technologies in future energy systems. Thermal gasification of biomass is proved throughout this article to be both highly flexible and efficient if used optimally. Cogeneration processes with production of heat-and-power, heat-power-and-fuel or heat-power-and-fertilizer are described and compared. The following gasification platforms are included in the assessment: The Harboøre up draft gasifier with gas engine, the Güssing FICFB gasifier with gas engine or PDU, the LT-CFB gasifier with steam cycle and nutrient recycling and finally the TwoStage down draft gasifier with gas engine, micro gas turbine (MGT), SOFC, SOFC/MGT or catalytic fuel synthesis.     

A genetic algorithm for the two-dimensional knapsack problem with rectangular pieces

Given a set of rectangular pieces and a rectangular container, the two-dimensional knapsack problem (2D-KP) consists of orthogonally packing a subset of the pieces within the container such that the sum of the values of the packed pieces is maximized. If the value of a piece is given by its area, the objective is to maximize the covered area of the container. A genetic algorithm (GA) is proposed addressing the guillotine case of the 2D-KP as well as the non-guillotine case. Moreover, an orientation constraint may optionally be taken into account and the given piece set may be constrained or unconstrained. The GA is subjected to an extensive test using well-known benchmark instances. Compared with recently published methods, the GA yields competitive results.     

Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells

We describe a method to fill thin films of nanoporous TiO₂ with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO₂/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.     

Changes in volatile composition during fruit development and ripening of ‘Alphonso’ mango

BACKGROUND: Volatile blends of five developing and five ripening stages of mango (Mangifera indica L. cv. Alphonso) were investigated along with those of flowers and leaves. Raw and ripe fruits of cv. Sabja were also used for comparison. RESULTS: A total of 55 volatiles belonging to various chemical classes such as aldehydes, alcohols, mono‐ and sesquiterpene hydrocarbons, lactones and furanones were identified. In all Alphonso tissues monoterpenes quantitatively dominated, with 57–99% contribution; in particular, (Z)‐ocimene was found in the highest amount. Ripeness was characterized by the de novo appearance of lactones and furanones in the blend of monoterpenes. Sabja was distinguished by the abundance of monoterpene hydrocarbons in the raw fruit, and that of sesquiterpene hydrocarbons and their derivatives in the ripe stage. CONCLUSION: Various stages of the Alphonso fruit during transition from flower to ripe fruit are characterized by unique volatile signatures that are distinguished from each other by the qualitative and quantitative appearance of different volatile compounds. Thus volatiles can be highly informative markers while studying the development and ripening of mango. Copyright © 2009 Society of Chemical Industry     

Pathways and pitfalls of implementing the use of woodfuels in Germany's bioenergy sector

The paper presents an empirical study on the use of woody biomass for energy supply in Germany and the federal state of Brandenburg. It aims to explain the role forestry enterprises have for bioenergy provision in this area. The ‘Institutions of Sustainability’ framework is used as an analytical tool to investigate the role of private and public actors in these transactions, respectively, in the governance structures they are subject to. Empirical evidence was gathered by in-depth interviews with actors from forestry and bioenergy practice. Triggered by favorable governance structures, i.e. strong support by national and regional policies, rising prices for fossil energy sources, and co-operation of committed individuals and groups, a new bioenergy industry has been successfully established. However, the forestry sector has so far been just a marginal fuel supplier for this industry. The study identifies pitfalls impeding a broad implementation of wood-energy supply in forestry: not cost-covering prices offered by the bioenergy sector, lacking market transparency and security of supply, lacking mobilization of forest wood, and a preference among forest managers to sell products to the wood-processing industry. In terms of the Institutions of Sustainability the properties of transactions (asset specificities, uncertainties, separability), characteristics of actors (values, rationality) and governance structures (long-term contractual obligations elsewhere) are decisive in explaining the current form of transaction.     

Microstructure Development of Oxycarbide Composites during Active-Filler-Controlled Polymer Pyrolysis

The microstructure development of a ceramic composite material fabricated by active-filler-controlled polymer pyrolysis (AFCOP) was investigated. During heating of a polysiloxane precursor mixed with titanium powder in argon atmosphere up to 1400°C, thermally induced decomposition of the polymer phase is combined with simultaneous carburization of the transition metal filler. Precipitation of nanocrystalline titanium carbide at the filler particle surface starts above 400°C, and larger, faceted carbide particles have growth above 800°C. A skeleton of turbostratic carbon is formed above 800°C in the polymer-derived silicon oxycarbide matrix from which b-silicon carbide and cristobalite crystallize above 1000°C. A pronounced reduction in linear shrinkage involved in polymer–ceramic conversion is observed. The shrinkage reduction ranges from more than 25% for the filler-free precursor to less than 10% in the presence of 30 vol% of the titanium filler. Thus, active-filler-controlled pyrolysis offers the possibility of controlling shrinkage and porosity formation during polymer–ceramic conversion in order to fabricate bulk components from organometallic polymer precursor systems.     

Electrochemical machining of refractory materials

The feasibility of the electrochemical machining (ECM) of pure TiC, ZrC, TiB₂ and ZrB₂ has been established. In addition, the ECM behaviour of a cemented TiC/10% Ni composite has been investigated and compared to that of its components, TiC and nickel. ECM was carried out in 2M KNO₃ and in 3 M NaCl at applied voltages of 10–31 V and current densities of 15–115 A cm^–2. Post-ECM surface studies on the TiC/Ni composite showed preferential dissolution of the TiC phase during machining.Nomenclature E ₀ thermodynamic equilibrium potential (V) - F Faraday's constant (96 500 Coul mol^–1) - toolpiece feed rate (cm s^–1 or mm min^–1) - I current (A) - i current density (A cm^–2) - k electrolyte conductivity (^–1 cm^–1) - l interelectrode gap (mm) - mass removal rate (g s^–1 or g min^–1) - M formula weight (g mol^–1) - Q electrolyte flow rate (l min^–1) - t electrolyte temperature (°C) - V applied voltage (V) - V _IR ohmic drop through electrolyte (V) - z apparent valence of dissolution (eq mol^–1) - _i overvoltages (V) - density of refractory materials (g cm^–3)     

Electron transfer capacities and reaction kinetics of peat dissolved organic matter

Information about electron-transfer reactions of dissolved organic matter (DOM) is lacking. We determined electron acceptor and donor capacities (EAC and EDC) of a peat humic acid and an untreated peat DOM by electrochemical reduction and reduction with metallic Zn and H2S (EAC), and by oxidation with complexed ferric iron (EDC) at pH 6.5. DOC concentrations (10-100 mg L(-1)) and pH values (4.5-8) were varied in selected experiments. EAC reached up to 6.2 mequiv x (g C)(-1) and EDC reached up to 1.52 mequiv-(g C)(-1). EDC decreased with pH and conversion of chelated to colloidal iron, and the electron-transfer capacity (ETC) was controlled by the redox potential Eh of the reactant (ETC = 1.016x Eh - 0.138; R(2) = 0.87; p = 0.05). The kinetics could be adequately described by pseudo first-order rate laws, one or two DOM pools, and time constants ranging from 2.1 x 10(-3) d-1 to 1.9 x 10(-2) d(-1) for the fast pool. Reactions were completed after 24-160 h depending on the redox couple applied. The results indicate that DOM may act as a redox buffer over electrochemical potentials ranging from -0.9 to +1.0 V.