07 Alternative energy sources (bioconversion energy)

99102625 Experimental study of hydrogen kinetics from agrofndustrial byproduct: Optimal conditions for production and fuel cell feeding Perego, P. et al. Bioprocess Eng., 1998, 19, (3) 205-211. A study of hydrogen rich biogas production which contributes to create a system for biomass recovery, eliminates organic pollutants and produces energy with high efficiency without atmospheric emissions. The study, using batch reactors, is based on Escherichia coli and Enterabacter aerogenes strains. The aim is to verify optimal conditions of hydrogen production. This will lead to the realization of a reactor suitable to feed a stack of hydrogen fuel cells. These fuel cells are one of the best and cleanest systems of producing electrical energy. Different ways are considered to enhance the process performance, in terms of rate of hydrogen production, efficiency of hydrogen utilization and/or biosynthesis of valuable subproducts.

99102626 Greenhouse-gas emlssion mitigation from the use of agricultural residues: the case of ricehusk Bhattacharya, S. C. et al. Energy, 1999, 24, (l), 43-59. Greenhouse-gas emission mitigation has been estimated for the use of existing and mature biomass technologies. A general methodology has been developed to determine potential amounts of residues that can be made available for energy purposes and the resulting fossil-fuel replacement from utilization of these residues. The consequent reductions in CO*, CHd and NzO emissions in CO2 equivalents for a time horizon of 20 years, as well as costs of abatements, were calculated. Both traditional and improved energy uses are considered.

99102627 Hydropyrolysis of sugar cane bagasse: effect of sample configuration on bio-oil yields and structures from two bench-scale reactors Pindoria, R. V. et al. Fuel, 78, (l), 55-63. A wire-mesh reactor, with the capability of virtually eliminating secondary reactions, has been used as base-case in the study of product yields and structures from the pyrolysis and hydropyrolysis of a sample of sugar cane bagasse in a fixed-bed ‘hot-rod’ reactor. Results from the two reactors have been compared to determine how best to assess bench-scale data which might be used for eventual process development. Experiments have been carried out at 600°C at pressures up to 70 bar. Structural features of the bio-oils have been examined by size exclusion chromatography and FT- infrared spectroscopy. In both reactors the effect of increasing pressure was to reduce the bio-oil and total volatile yields; hydropyrolysis bio-oil yields were marginally higher than pyrolysis yields under equivalent operating conditions. About 5 to 6% bio-oil product is lost in the fixed-bed reactor, compared with the wire-mesh reactor, with consequent increase in recovered chars. Pressure and reactor bed depth appear to affect only the thermally more sensitive components of the bio-oils, and increasing pressure beyond 40 bar, or bed depth beyond the level reported, was found not to affect yields to an appreciable extent. Taken together, these data indicate that about one-third of the original biomass maybe converted to oil by direct pyrolysis. Size exclusion chromatograms and IT-infrared spectra of bio-oils from the hydropyrolysis experiments conducted at 1 and 70 bar suggest that oils from the hot-rod reactor experience a greater degree of secondary reactions than those from the wire-mesh reactor. Using tetrahydrofuran as eluent, the highest molecular masses were found to be around 1000 u in terms of polystyrene standards. However, comparison with size exclusion chromatograms using I-methyl-2-pyrrolidinone indicated partial loss of sample when operating in THF. The findings strongly suggest that THF is not a suitable eluent for the characterization of biomass-derived pyrolysis oils by size exclusion chromatography.

99102626 The influence of tars on hot gas filter performance in air blown gasification of coal and biomass Cahill, P. et al. High Temp. Gas Clean., (Pap. Int. Symp. Exhib. Gas Clean. High Temp.], 3, 1996, 782-793. Edited by Schmidt, E., Institut fur Mechanische Verfahrenstechnik und Mechanik der Universitaet Karlsruhe, Karlsruhe, Germany. Hot gas filtration forms a vital part of coal and biomass gasification combined cycle systems, and the systems based on ceramic candle filter elements have the greatest potential. Attempts have been made to improve the design and operation or control of hot gas filter units so that their availability is comparable to conventional low temperature dust removal systems. The Coal Technology Development Division (CTDD, formerly part of the Coal Research Establishment) and V’IT collaborated in an EEC Joule II Project to develop hot gas filtration for 400-600°C application for high pressure, air blown gasification. The study discusses the investigation of the effect of tar-related material on hot gas filter performance, which forms a part of this programme. The amount and nature of tars in fuel gas depend on the gasification process and the feedstock. Compared with some biomass fuels, tar concentrations were much lower for coal gasification. A laboratory and pilot scale study programme at VTT and CTDD found that tar materials can cause high pressure drop across the filters, which cannot be recovered using normal reverse pulse cleaning. Studies connect the cause of the high pressure drop to the cleaning properties of the filter cake rather than internal blinding of filter elements. From the results the way in which tar concentration and exposure time affects the filtration process can be determined.

99102629 Method and apparatus for treating biogas produced by anaerobic fermentations SITA S. A., Fr. Fr. Demande FR 2,758,740, (Cl. BOlD53114). 31 Jul 1998, Appl. 97/955, 29 Jan 1997, 12 pp. (In French) A method for the recovery of biogas produced from anaerobic fermentation is described. It involves compression of the fermented material at 1500 kPa followed by countercurrent washing and absorption of CO2 and HzS. The biogas is then dried using a molecular sieve. The purified biogas is compressed to 25,000 kPa and cooled for storage. The biogas produced can be used as a domestic fuel or automobile fuel.

99iO2630 Modeling the thermal decompositions of wood and leaves under a nitrogen atmosphere Liu, N. A. and Fan, W. C. Fire Mater., 1998, 22, (3) 103-108. Dynamic thermogravimetry was used to examine the thermal decomposi- tion of six different samples of wood and leaves in nitrogen. Two main weight loss processes occurred, the total weight loss at 500°C being over 95% in all six cases. Using the Doyle method, the two processes were found to correlate most clearly with the plot for the second-order equation in the form d-ytldt = k(l - 7)‘. Each of the weight loss processes was found to be controlled by two dominant reactions as the temperature increases. From this, the inference was that competing reactions occur during the overall temperature interval for all the six samples. By comparing the activation energies using this model with those by the method of Moll et al. and by comparing the experimental and theoretical thermogravimetric curves, the ‘second-order’ model was found to be able to acurately predict the weight loss processes of the samples. The ‘second-order’ kinetic model therefore appears to act much better than the conventionally adopted first- order model.

99lO2631 Potential of producing hydrogen and high Btu gas from steam gaslflcation of lignins Iqbal, M. et al. Proc. Intersoc. Energy Comers. Eng. Conf., [computer optical disk], 1998, 33, IECEC086/1-6. In this study the possibility of converting lignins, usually considered as a waste product from the pulp and paper industry, to hydrogen and high Btu gas by gasifying them with steam. Three lignins, Kraft- 1, Kraft-2 and Alcell. were gasified with steam in a fixed bed reactor in the temperature range 600-8Oo”C and with a steam flow rate of 10 g/h g of lignin. Lignin conversion was highest at 800°C with conversion being greatest in Kraft-1 and smallest in Alcell. The product gas consisted of Hz, CO, COz and CHI as well as Cz and C,+ hydrocarbons. It’s Btu value ranged between 450-850 Btu/ft’. The Hz content was fairly high, ranging between 30-50 mol% of the product gas mixture. The effect of steam flow rate was also studied under a fixed temperature of 800°C. It was observed that at high steam flow rates, the lignin conversion increased and the process resulted in high selectivity for CH4. The results of this study are compared with those of a previous study of steam gasification of biomass-derived chars.

99102632 A review of sorbent materials for fixed bed alkali getter systems in biomass gasifier combined cycle power generation applications Turn, S. Q. et al. J. Institute of Energy, 1998, LXXI, (489), 163-177. Gas phase alkali metal compounds contribute to fouling, slagging, corrosion and agglomeration problems in energy conversion facilities. One method of mitigation applicable at high temperature is to pass the gas stream through a fixed bed of sorbent or getter material that preferentially adsorbs alkali via physical adsorption or chemisorption. This paper reviews studies in which such materials, primarily alumina and silicate compounds, in inert and simulated combustor flue gas conditions were screened. Emathlite, diatomaceous earth, kaolinite and activated bauxite were identified as potential sorbents and were tested thermogravimetrically or in packed beds under various process conditions. Test experience with candidate sorbent materials in an environment representative of process conditions following a hot filter in a biomass integrated gasifier combined cycle system was found to be lacking.

99102633 Solar thermochemical conversion of biomass LCdC, J. Solar Energy, 1999, 65, (l), 3-13. The purpose of this paper is first to briefly describe the usual routes of biomass thermochemical conversion and then to discuss the possibility of using concentrated solar energy to provide the necessary heat for the processes. Gasification, fast and slow pyrolysis are more particularly described. They can be carried out for the preparation of a vast range of possible products that can be used as energy carriers and/or as a source of chemical commodities. The gasification processes are intended for the preparation of gas mixtures (CO, Hz, etc.) for chemical synthesis, heat or electricity generation. The fast pyrolysis formerly carried out for gas production (CO, H2, light hydrocarbons, etc.) is now mainly studied with the objective to produce liquids (bio-oils). Slow pyrolysis is in use for a long time for the preparation of solids (charcoal). The nature and quality of the products depend mainly on the experimental conditions of the process (temperature, heating rates, residence times, etc.). The possibility of a solar entry in the gasification and pyrolysis processes is then discussed. The technical and scientific benefits, as well as the difficulties, are underlined, showing the necessity to design new types of specific reactors. From a fundamental point of view the advantages are also underlined of using a concentrated radiation as a laboratory tool for studying the very fast

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07 Alternative energy sources (solar energy)

primary steps of biomass thermal decomposition as well as the possible existence of intermediate short life time species that are still not well known.

99102634 Synthesis and cetane improver performance of fatty acid glycol nltrates Suppes, G. J. et al. Fuel, 78, (l), 73-81. Triglycerides are renewable chemical feedstocks available from a variety of resources, including vegetable oils, tall oils and beef or pork fat. Chemical svnthesis methods, reaction conversions and performances of a series of organic acid glycol nitrates were investigated to evaluate the viability of converting triglycerides into nitrates for use as cetane improvers. Organic acid glycol nitrates were synthesized from five acids ranging from C6 to C,s to determine the impact of the acid’s carbon number and degree of saturation on performance as a cetane improver. Chemical synthesis included acid catalyzed esterification of organic acids with ethylene glycol followed by nitration of the terminal alcohol group to form fatty acid glycol nitrates. Fatty acid glycol nitrates with carbon numbers between eight and 14 exhibited the best performance - a balance between high carbon numbers and high nitrate group concentration. All the nitrates provided good cetane improving capabilities.

99102635 Thermochemical conversion research & develop ment activities in Canada Hogan, E. N. Prep. Symp. Am. Chem. Sot., Div. Fuel Gem., 1998,43, (3), 416-420. This paper presents a review of the research and development activities and strategies of the Canadian biomass thermochemical conversion programme, part of the CANMET Energy Technology Center (CETC). The pyrolysis technology area is focused on, and both the current status of research activities in Canada and the future research directions are examined. The major objective of this programme is the development of cost competitive technologies that convert biomass into gaseous and liquid fuels and chemicals to be used for process heat, electricity, alternate refinery feedstocks and value added products. The programme can be divided into the following main project areas: (1) assessment of the potential of thermochemical conversion systems to process new biomass and/or waste feedstocks; (2) process development and optimization of thermochemical conversion processes; (3) evaluation of the potential of producing value added chemicals from pyrolysis products and determination of end use industrial applications for these; (4) assessment of the commercial utilization of pyrolysis oils for heat and/or electricity production in boilers, diesel engines and gas turbines; and, (5) continued development and optimization of the production of high cetane diesel fuel from plant and vegetable oils.

::::636 Thermogravimetric study of the pyrolysis of waste

Reina, J. et al. Thermochim. Acta, 1998, 320, (l-2), 161-167. Using thermogravimetric analysis equipment, and a mixture of dynamic and isothermal techniques, a study of the pyrolysis of three different types of waste wood (forest wood, old furniture and used pallets) was conducted. Isothermal runs were carried out at low range (225-325°F) and high range (700-900°F). A high level of agreement was found between the kinetic parameters obtained using either dynamic or isothermal techniques. The chemical composition of each type of wood combined with the compounds added to the wood for each application, have an important fuction in determining the kinetic behaviour of their thermal decomposition.

Solar Energy

99102637 Accelerated degradation In amorphous silicon solar cells by a combination of current injection and light insolation Dasgupta, A. et al. Solar Energy Materials & Solar Cells, 1998,55, (4), 395- 402. A new degradation technique for amorphous silicon solar cells comprising of a combination of current injection and insolation has been developed. Compared to the conventional light degradation technique, current- induced degradation which involves forward biased current stress, results in a lower stabilized cell parameters including efficiency. This stabilized efficiency is, however, independent of the amount of current injected. The excess degradation is recovered under light illumination. The stabilized value of the conversion efficiency is within experimental error identical to that observed in long term, illumination only degradation. The method is fast, accurate and reliable. Its reliability has also been tested for single junction solar cells having intrinsic layers of different band gaps.

99102636 An analytical model for silicon MIS/IL solar cells to optimize cell parameters through thermal annealing ,4:4_lyd, A. K. et al. Solar Energy Materials & Solar Cells, 1998,55, (4),

A modei has been developed which simulates the effect oi cell parameters in order to optimize them by controlling the fabrication conditions, namely, annealing time and annealing temperature. Calculation of the efficiency as

a function of surface states density Di,, positive fixed oxide charge density Qf and mobile charge density Q,, that depend on annealing conditions are carried out. A compromise between Di, and Q,,, for different annealing temperatures for high performance cells has been investigated.

99lO2639 Application of concentrated solar radiation to high temperature detoxification and recycling processes of hazar- dous wastes Funken, K.-H. et al. Solar Energy, 1999, 65, (1). 25-31. In many cases, hazardous wastes are subject to thermal treatment at elevated temperatures. Some types of wastes do not have a sufficient calorific value to cover the heat demand of the high temperature process. For thermal treatment of, for example,. filter residues, dusts, sulfuric acid, aluminium dross, foundry sand or waste water, supplementary energy supply is needed. The specific energy demand ranges from 0.5 to 2.5 kWh/ kg (2-10 MJ/kg). An important aim of process optimization is the reduction of (fossil) energy consumption and exhaust gas flow. Concentrated solar energy promises advantages when applied to high energy consuming waste treatment processes with regard to substitute fossil or electric energy consumption, to reduce COZ emissions and exhaust gas flow. In parallel to conceptional studies, a solar-heated rotary kiln mini-plant has been designed and constructed for tests in the DLR solar furnace. The tests will give indications of boundary conditions for solar thermal treatment or conversion of selected hazardous materials.

99lO2640 Catalytic thermochemical reactor/receiver for solar reforming of natural gas: design and performance Anikeev, V. I. et al. Soluble Energy, 1998, 63, (2), 97-104. This paper discusses the advantages of converting concentrated solar energy thermochemically, using catalytic processes. It describes the design of a solar volumetric thermochemical reactor/receiver (TCRR) with catalytic absorber, the method for synthesizing catalytically activated ceramics, and the preparation of the catalytic absorber. The prototype TCRR was tested in the high flux solar furnace at the DAC, Cologne, using the carbon dioxide reforming of methane. The aim of the tests was to examine the main concept of the TCRR design and catalytic absorber, and to observe the influence of solar flux distribution, the reagent flows and their ratio on the productivity or conversion, attempting to determine the reagent’s conversion, depending on the focal point disposition with respect to the absorber. The efficiency of the thermochemical conversion was also analysed, and the chemical and total efficiencies of the carbon dioxide- methane conversion were calculated using the measured concentrations of the reaction products obtained in the experiment. The highest overall efficiency of 30% was achieved with the Ni-Cr catalytic absorber.

99iQ2641 Characterization of black nickel solar absorber coatings electroplated in a nickel chlorine aqueous solution Wlckelgrd, E. Solar Energy Materials & Solar Cells, 1998, 56, (I), 35-44. Black nickel coatings electroplated in a nickel- and sodium chlorine aqueous solution have been prepared and parameters in the process have been optimized to achieve optimal solar selectivity. The best result is a solar absorptance of 0.96 and a thermal emittance of 0.10. as also has been obtained previously for the same type of coating. Characterization by means of X-ray photo-electron spectroscopy (XPS), scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), Ruther- ford backscattering (RBS) and ‘H(“N, ay)“C nuclear resonance reaction (NRR) have contributed with new information about surface chemical composition, morphology and atomic composition in depth profile. These investigations reveal that the coating is porous and contains mainly metallic nickel at the substrate coating interface and mainly nickel hydroxide at the front surface. The stability of the coating has been tested regarding high- temperature and condensation at high humidity. It has been found that the solar absorptance changes initially, during the first hour of exposure at high temperature, but will then stabilize. Condensation causes a more severe attack on the coating by cracking it. This is contradictory to the results from previous tests at high temperature and humidity in which the black nickel coating was found to be resistant.

99102642 A cone concentrator for high-temperature solar cavity-receivers Hahm, T. et al. Solar Energy, 1999, 65, (l), 33-41. A cone concentrator combined with a solar cavity receiver is presented and its performance compared to a single cavity receiver. For both cases the available heat sink within the receiver is calculated. The cone concentrator suffers from a high amount of rejected rays if the exit aperture is made too small. A larger exit aperture on the other hand increases the thermal losses of the cavity. The optimum cone geometry therefore has to be found taking also into account a model of the cavity. Different operating temperatures and different values of absorption coefficients of the cavity walls are considered. A cone concentrator was built and tested at the solar furnace in Cologne. It transmits 97% of the rays entering the entrance aperture, which is in exact agreement with the theoretical predictions.

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