CO2 gasification of chars prepared from wood and forest residue

The CO2 gasification of chars prepared from Norway spruce and its forest residue was investigated in a thermogravimetric analyzer (TGA) at slow heating rates. The volatile content of the samples was negligible; hence the gasification reaction step could be studied alone, without the disturbance of the devolatilization reactions. Six TGA experiments were carried out for each sample with three different temperature programs in 60 and 100% CO2. Linear, modulated, and constant-reaction rate (CRR) temperature programs were employed to increase the information content available for the modeling. The temperatures at half of the mass loss were lower in the CRR experiments than in the other experiments by around 120 degrees C. A relatively simple, well-known reaction kinetic equation described the experiments. The dependence on the reacted fraction as well as the dependence on the CO2, concentration were described by power functions (n-order reactions). The evaluations were also carried out by assuming a function of the reacted fraction that can mimic the various random pore/random capillary models. These attempts, however, did not result in an improved fit quality. Nearly identical activation energy values were obtained for the chars made from wood and forest residues (221 and 218 kJ/mol, respectively). Nevertheless, the forest residue char was more reactive; the temperatures at half of the mass loss showed 20-34 degrees C differences between the two chars at 10 degrees C/min heating rates. The assumption of a common activation energy, E, and a common reaction order, v, on the CO2, concentration for the two chars had only a negligible effect on the fit quality

Out of the wave: The meaning of suffering and relief from suffering as described in autobiographies by survivors of the 2004 Indian Ocean tsunami

The aim of this study was to explore the meaning of suffering and relief from suffering as described in autobiographies by tourists who experienced the tsunami on 26 December 2004 and lost loved ones. A lifeworld approach, inspired by the French philosopher Merleau-Ponty's phenomenology of perception, was chosen for the theoretical framework. This catastrophe totally changed the survivors' world within a moment. In this new world, there were three main phases: the power of remaining focused, a life of despair, and the unbearable becoming bearable. Life turns into a matter of making the unbearable bearable. Such challenging experiences are discussed in terms of the philosophy of Weil, Jaspers, and Merleau-Ponty. The survivors of the tsunami catastrophe were facing a boundary situation and “le malheur,” the unthinkable misfortune. Even at this lowest level of misfortune, joy is possible to experience. This is part of the survivors' ambivalent experiences of their lifeworld. In this world of the uttermost despair there are also rays of hope, joy, and new life possibilities

Kinetic Behavior of Torrefied Biomass in an Oxidative Environment

The combustion of four torrefied wood samples and their feedstocks (birch and spruce) was studied at slow heating programs, under well-defined conditions by thermogravimetry (TGA). Particularly low sample masses were employed to avoid the self-heating of the samples due to the huge reaction heat of the combustion. Linear, modulated and constant-reaction rate (CRR) temperature programs were employed in the TGA experiments in gas flows of 5 and 20% O2. In this way the kinetics was based on a wide range of experimental conditions. The ratio of the highest and lowest peak maxima was around 50 in the experiments used for the kinetic evaluation. A recent kinetic model of Várhegyi et al. [Energy & Fuels 2012, 26, 1323-1335] was employed with modifications. This model consists of two devolatilization reactions and a successive char burn-off reaction. The cellulose decomposition in the presence of oxygen has a self-accelerating (autocatalytic) kinetics. The decomposition of the non-cellulosic parts of the biomass was described by a distributed activation model. The char burn-off was approximated by power-law (n-order) kinetics. Each of these reactions has its own dependence on the oxygen concentration that was expressed by power-law kinetics, too. The complexity of the applied model reflects the complexity of the studied materials. The model contained 15 unknown parameters for a given biomass. Part of these parameters could be assumed common for the six samples without a substantial worsening of the fit quality. This approach increased the average experimental information for an unknown parameter by a factor of 2 and revealed the similarities in the behavior of the different samples

Commodity fuels from biomass through pretreatment and torrefaction: effects of mineral content on torrefied fuel characteristics and quality

Torrefaction of biomass is rapidly gaining popularity as a viable pretreatment for use with co-combustion with coal or with other thermochemical conversion processes. This work explores the effects of combining pretreatment washing techniques using water, ammonium acetate, and hydrochloric acid. Four biomasses were studied, short-rotation coppiced willow, eucalyptus, Miscanthus, and wheat straw, all in chipped or chopped form. The resultant fuels, after the pretreatments, were characterized for ultimate analysis, proximate analysis, heating value, and pyrolysis behavior (via thermogravimetric analysis), and mass and energy yields in a fixed-bed torrefier were measured. The ease of removal of certain metals, Na, K, Mg, and Ca, as well as PO43?, SO42?, and Cl? was assessed by ion chromatography on the leachates from the water washing, and influences on fouling behavior were predicted. Fuel ashes (both prior to and after torrefaction) were also assessed in the ash fusion test, a probe for slagging behavior. Water washing resulted in a high removal of alkali metal ions and chloride, particularly for the herbaceous biomass, where up to 92% of sodium and 62% of potassium were removed, together with up to 100% of the chloride. There was a general trend of higher concentrations of water-soluble species for the herbaceous biomass compared to the woody biomass, although there were a few exceptions, such as phosphate. As a consequence of water washing, the alkali indices (an index for fouling) decreased markedly. Because the ash composition changes as a result of the different washing procedures, the ash melting behavior also changes, and hemisphere temperatures (oxidizing conditions) were seen to increase substantially, by approximately 400 °C for wheat straw to 1500 °C and 290 °C for Miscanthus to 1490 °C. Different pretreatment methods also influenced the progress of torrefaction. After all washings, the fuels became less reactive to thermal degradation, and therefore, mass (and energy yields) increased during a fixed torrefaction operation. This could be explained through measurement of the pyrolysis kinetics; removal of key catalytic metal species (such as Na and K, in particular) by washing results in slower reaction rates. Water washing was seen as the most beneficial pretreatment, because it produced the most marked improvement in the torrefied fuel in terms of its ash fusion test behavior. Torrefaction of biomass is rapidly gaining popularity as a viable pretreatment for use with co-combustion with coal or with other thermochemical conversion processes. This work explores the effects of combining pretreatment washing techniques using water, ammonium acetate, and hydrochloric acid. Four biomasses were studied, short-rotation coppiced willow, eucalyptus, Miscanthus, and wheat straw, all in chipped or chopped form. The resultant fuels, after the pretreatments, were characterized for ultimate analysis, proximate analysis, heating value, and pyrolysis behavior (via thermogravimetric analysis), and mass and energy yields in a fixed-bed torrefier were measured. The ease of removal of certain metals, Na, K, Mg, and Ca, as well as PO43?, SO42?, and Cl? was assessed by ion chromatography on the leachates from the water washing, and influences on fouling behavior were predicted. Fuel ashes (both prior to and after torrefaction) were also assessed in the ash fusion test, a probe for slagging behavior. Water washing resulted in a high removal of alkali metal ions and chloride, particularly for the herbaceous biomass, where up to 92% of sodium and 62% of potassium were removed, together with up to 100% of the chloride. There was a general trend of higher concentrations of water-soluble species for the herbaceous biomass compared to the woody biomass, although there were a few exceptions, such as phosphate. As a consequence of water washing, the alkali indices (an index for fouling) decreased markedly. Because the ash composition changes as a result of the different washing procedures, the ash melting behavior also changes, and hemisphere temperatures (oxidizing conditions) were seen to increase substantially, by approximately 400 °C for wheat straw to 1500 °C and 290 °C for Miscanthus to 1490 °C. Different pretreatment methods also influenced the progress of torrefaction. After all washings, the fuels became less reactive to thermal degradation, and therefore, mass (and energy yields) increased during a fixed torrefaction operation. This could be explained through measurement of the pyrolysis kinetics; removal of key catalytic metal species (such as Na and K, in particular) by washing results in slower reaction rates. Water washing was seen as the most beneficial pretreatment, because it produced the most marked improvement in the torrefied fuel in terms of its ash fusion test behavior