The CO 2 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% CO 2 . 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 °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 CO 2 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 °C differences between the two chars at 10 °C/min heating rates. The assumption of a common activation energy, E, and a common reaction order, ν, on the CO 2 concentration for the two chars had only a negligible effect on the fit quality.

No abstract

The evaporation of pyrolysis oil was studied at varying heating rates (∼1–106°C/min) with surrounding temperatures up to 850°C. A total product distribution (gas, vapor, and char) was measured using two atomizers with different droplet sizes. It was shown that with very high heating rates (∼106°C/min) the amount of char was significantly lowered (∼8%, carbon basis) compared to the maximum amount, which was produced at low heating rates using a TGA (∼30%, carbon basis; heating rate 1°C/min). The char formation takes place in the 100–350°C liquid temperature range due to polymerization reactions of compounds in the pyrolysis oil. All pyrolysis oil fractions (whole oil, pyrolytic lignin, glucose and aqueous rich/lean phase) showed charring behavior. The pyrolysis oil chars age when subjected to elevated temperatures (≥700°C), show similar reactivity toward combustion and steam gasification compared with chars produced during fast pyrolysis of solid biomass. However, the structure is totally different where the pyrolysis oil char is very light and fluffy. To use the produced char in conversion processes (energy or syngas production), it will have to be anchored to a carrier. © 2010 American Institute of Chemical Engineers AIChE J, 2010

No abstract

In the present work, experimental and computational fluid dynamics (CFD) approaches were proposed and applied to assess rapid devolatilization behaviors of four types of biomass (forest residue, torrefied forest residue, Norwegian spruce, and torrefied Norwegian spruce). Biomass particles were subjected to devolatilization experiments at 1073 and 1473 K in a drop-tube reactor. Torrefaction was found to have consistent effects on the size reduction of studied biomass. In addition, similar behaviors of char fragmentation were observed for tested torrefied biomass after rapid devolatilization at 1473 K. Mass loss during devolatilization of biomass was highly dependent on heating condition. Both rates and extents of devolatilization of biomass were increased at elevated temperatures and heating rates. In comparison with raw feedstock, high char yields were realized with the torrefied biomass after devolatilization experiments. Evolution of elemental composition of studied biomass was found to be insensitive to tested conditions. However, organic composition of char was strongly affected by elemental composition of fuel, thus also influenced by torrefaction. CFD simulation showed that sizes of fuel particles had decisive effects on residence time of them in the reactor, especially particles with diameter larger than 355 μm. Particle temperature, in contrast, depended on both particle diameter and particle density. A modified two-competing-rates devolatilization model was also presented in the present work. On the basis of experimental data, one optimal set of kinetic parameters was obtained following a proposed procedure. The model predicted well the mass loss of all tested fuel and the evolution of each organic element in char at all operation conditions.

In the work reported here, both forest residue (FR) and torrefied forest residue (TFR) were devolatilized in a drop tube reactor at 1473 K at a heating rate greater than 10 4 K/s. The physical properties of parent fuel particles and their corresponding char particles were examined by using a scanning electron microscope and a granulometer. After the same milling and sieving process, the TFR particles had a smaller size and smaller aspect ratio than the FR particles. The char particles consisted of two types of particles with different sizes and morphologies: a small particle mode (presumably char fragments) and a large particle mode. The volume fraction of char fragments in the TFR char was considerably less than for the FR char. Both types of char were converted in a drop tube reactor under oxidation and gasification conditions at 1473 and 1573 K, respectively. The total organic mass loss and release of individual organic elements during char conversion were determined using a tracer method. Calcium, manganese, barium, and magnesium were found to be suitable for use as tracers. The fractional carbon conversion rate of TFR char was found to be slower than that of FR char under both oxidation and gasification conditions. The fractional release rate of hydrogen was much higher than that of total organic mass loss, while the corresponding oxygen release was lower for both types of char and for different reactive environments.

No abstract

This article presents a detailed techno-economic analysis, under Norwegian conditions, for the production of biocrude from woody biomass via high temperature entrained flow gasification and Fischer−Tropsch (FT) synthesis with integrated coproduction of heat and electricity. Biomass pretreatment based on both conventional drying and torrefaction processes are considered as options. Maximum calculated efficiency of biocrude at lower and upper bound CO conversions of 40% and 80% at the gasifier operating conditions of lambda value 0.2 and temperature 1300°C are 27% and 44%, respectively. Under these conditions, maximum thermal and net electrical efficiency are 55% and 15.5%, respectively. The economic viability of the biocrude production for plant capacities in the range of 150−600 MW thermal input has been evaluated as a function of the type of biomass pretreatment, gasification operating conditions, and the heat to electricity production ratios. Results from the economic analysis show that coproduction of biocrude combined with 100% heat production for district heating gives the lowest biocrude cost under Norwegian conditions, with large variations as the electricity to heat production ratio increases.