Various Rankine cycle architectures for single fluids and other improved versions operating with ammonia/water mixture are presented in this paper. Untapped heat resources and their potential for ...driving organic Rankine cycles are outlined. The nature – state and temperature of the heat source significantly influences the choice of the type of organic Rankine cycle machine. The temperature appears as a critical parameter during the selection process. Modules differ from one another from technology, size and cost viewpoints. The investment cost of an ORC project includes machine, engineering, system integration, capital costs, etc. and is closely linked to the application.
Chemical reactivity of heat-treated wood Nguila Inari, G; Petrissans, M; Gerardin, P
Wood science and technology,
02/2007, Letnik:
41, Številka:
2
Journal Article
Recenzirano
Chemical reactivity of heat-treated wood was compared with that of untreated wood. For this purpose, heat-treated pine or beech sawdust was reacted with different carboxylic acid anhydrides in ...pyridine or with phenyl isocyanate in dimethyl formamide. Compared to controls, weight gains obtained with heat-treated sawdust are smaller showing a lower chemical reactivity. FTIR analyses of lignin and holocellulose fractions, isolated after acidic hydrolysis of polysaccharides or delignification with sodium chlorite, indicate that both components are involved in the reactions. Compared to lignin, holocellulose exhibits important infrared absorptions of about 1,730 cm-¹, characteristic of ester or urethane linkages formed. Lower reactivity of heat-treated sawdust is explained by the decrease in free reactive hydroxyl groups in holocellulose due to the thermal degradation of hemicelluloses, considered more reactive than cellulose.
Torrefaction is a thermal treatment step in a temperature range of 210–240 °C, which aims to improve the dimensional stability and durability of wood. The mass loss kinetics for torrefaction of wood ...samples was studied using equipment specially conceived to measure mass losses during thermal treatment. Laboratory experiments were performed under nitrogen for heating rates of 0.1, 0.25, 1, and 2 °C min
−1
. A mathematical model for the kinetics of the thermodegradation process was used and validated. Measurements of temperature distribution and anhydrous mass loss were performed on dry sample of poplar wood during torrefaction in an inert atmosphere for different temperatures. The mathematical formulation describing the simultaneous heat and mass transfers requires coupled nonlinear partial differential equations. These unsteady-state mathematical model equations were solved numerically by the commercial package FEMLAB for the temperature under different treatment conditions. A detailed discussion of the computational model and the solution algorithm is given below. Once the validity of different assumptions of the model had been analyzed, the experimental results were compared with those calculated by the model. Acceptable agreement was achieved.
Wettability of Heat-Treated Wood Pétrissans, M.; Gérardin, P.; bakali, I. El ...
Holzforschung,
01/2003, Letnik:
57, Številka:
3
Journal Article
Recenzirano
The aim of this work was to study the wettability and chemical composition of heat-treated wood. Heat treatment was performed at 240°C under inert atmosphere on four European wood species (pine, ...spruce, beech and poplar). Contact angle measurements before and after treatment indicated a significant increase in wood hydrophobicity. Advancing contact angles of a water drop were in all cases systematically higher for heat-treated than for untreated wood. Chemical modifications of wood after heat treatment were investigated using FTIR and 13C NMR analysis. FTIR spectra indicated little structural change which could be attributed either to carbon-carbon double bond formation or to adsorbed water. NMR spectra also revealed little chemical change except for the degree of cellulose crystallinity which was considerably higher in heat-treated wood and could explain the higher contact angles.
In this study, heat treatment was carried out in a relatively low temperature (230 degrees C). Mass loss kinetics was studied using equipment, specially conceived to measure sample's mass during the ...thermal treatment. Laboratory experiments were performed for heating rates of 1 degrees C min(-1). Mathematical model for kinetics of pyrolysis process was used and validated. During the pyrolysis of dry wood samples under inert atmosphere, measurements of temperature distribution and dynamic weight loss were performed. Five different wood species Fagus sylvatica (Beech), Populus nigra (Poplar), Fraxinus excelsior (Ash), Pinus sylvestris (Pine) and Abies pectinata (Silver Fir) were investigated. The unsteady-state mathematical model equations were solved numerically using the commercial package Femlab 2.0. A detailed discussion of the computational model and the solution algorithm is given. The validity of different model assumptions was analyzed. Experimental results were compared with those calculated by the model. Acceptable agreement was achieved.
Wood heat treatment is an attractive alternative to improve decay resistance of wood species with low natural durability. However, this improvement of durability is realized at the expense of the ...mechanical resistance. Decay resistance and mechanical properties are strongly correlated to thermal degradation of wood cells wall components. Mass loss resulting from this degradation is a good indicator of treatment intensity and final treated wood properties. However, the introduction of a fast and accurate system for measuring this mass loss on an industrial scale is very difficult. Nowadays, many studies are conducted on the determination of control parameters which could be correlated with the treatment conditions and final heat treated wood quality such as decay resistance. The aim of this study is to investigate the relations between kinetics of temperature used during thermal treatment process representing heat treatment intensity, mass losses due to thermal degradation and conferred properties to heat treated wood. It might appear that relative area of treatment temperature curves is a good indicator of treatment intensity. Heat treatment with different treatment conditions (temperature-time) have been performed under vacuum, on four wood species (one hardwood and three softwoods) in order to obtain thermal degradation mass loses of 8, 10 and 12%. For each experiment, relative areas corresponding to temperature kinetics, mass loss, decay resistance and mechanical properties have been determined. Results highlight the statement that the temperature curves' area constitutes a good indicator in the prediction of needed treatment intensity, to obtain required wood durability and mechanical properties such as bending resistance and Brinell hardness.
Last decades, wood was promoted as building material. Wood heat treatment by mild pyrolysis has been reported to improve biological durability and dimensional stability of the material and ...constitutes an attractive `` non biocidal `` alternative to classical preservation treatments. Previous studies have shown that conferred properties strongly depend on the heat treatment intensity. A quality control marker based on mass loss has been developed. For several years, the increased development of Tunisian wood industry provides a significant capacity of wood production and transformation. Forests in Tunisia consist essentially of coniferous species Aleppo pine (Pinus halepensis), Radiata pine (Pinus radiata), Maritime pine (Pinus pinaster), Stone pine (Pinus pinea), characterised by a weak natural durability. Improved durability and fungal resistance should allow the use of Tunisian species in the wood industry. Import limitation of European species and the use of local species allow the conservation of economic value added in the country and improve the economic balance. For this reason, several Tunisian softwood species (Aleppo pine, Radiata pine and Maritime pine) have been heat-treated under vacuum atmosphere at 230 degrees C to obtain a thermal degradation with mass losses of approximately 8, 10 and 12%. The oven device allows recording the dynamic Mass Loss (ML) during the treatment and following the thermodegradation kinetic. The chemical composition of the studied wood samples was determined before and after heat treatment. For each wood species and treatment intensity, wood chemical and mechanical analyses were performed by measuring O/C ratio, bending and hardness tests. Afterward, tests of decay resistance were performed according to the EN 113 Standard, with different fungal attacks (Poria Placenta, Coriolus Versicolor) at 22 degrees C and 70% of humidity for 16 weeks. Results were related to the mass loss. Furthermore, intensity of thermal degradation was evaluated by TD-GC-MS. Treated and untreated wood samples were maintained during 15 minutes at 230 degrees C under nitrogen in the thermodesorption tube in order to analyse and compare resulting from the wood thermodegradation volatile compounds.
Contact angles, measured by Wilelhmy technique, during beech heat treatment by mild pyrolysis under inert atmosphere, indicated a significant increase of wood hydrophobicity for a temperature between ...130 and 160
°C. This behaviour, generally reported for higher temperatures, has been investigated in terms of chemical modifications and molecular organization of wood biopolymers to understand the reasons of these hydrophobic properties. Different experiments indicate that degradation reactions and extractives generation are not the origin of these properties.
13C MAS NMR and FTIR analysis suggest that wettability modification during heat treatment could be explained by a modification of conformational arrangement of wood biopolymers due to loss of residual water or more probably to plasticisation of lignin.
Chemical composition of Norway spruce and pine, two softwood species, has been investigated by X-ray Photoelectron Spectroscopy (XPS). Contrary to results previously obtained with beech wood, which ...allow to obtain information on bulk chemical composition from surface composition analysis, XPS analysis appears to be unsuitable for the characterisation of Norway spruce and pine wood chemical composition. Indeed, chemical compositions calculated from XPS data differ strongly from those obtained from microanalyses which are in good agreement with theoretical composition described in the literature. XPS analysis of both the softwood surfaces indicated high carbon contents explained by migration of lipophilic extractives to the surface under the influence of the vacuum necessary for XPS analysis. Nonvolatile extractives contained in wood were extracted and deposited on glass plates and analysed. Survey and detailed C1s spectra indicated similar signals to those recorded on wood surfaces. This phenomenon was not observed when samples had been previously extracted before analysis. These results strongly evidenced that extractives present in both species are able to migrate through resin canals from the bulk of the sample to the surface when put into ultra high vacuum. XPS presents, therefore, some limits in the case of the analysis of softwood species containing extractives able to migrate to the surface during analysis. This behaviour, difficult to control, could lead to erroneous interpretations due to extractives enrichment of the surface under the effect of vacuum.
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