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ABSTRACT. Wastes from brewery, industrial coffee roasting and fiberboard furniture were investigated.Thermogravimetric experiments were carried out with different types of temperature programs. Three models were proposed describing equally well the behavior of the samples. One of the models consisted of three partial reactions with distributed activation energies (DAEM). In this case 12 parameters were sufficient to describe the behavior of a sample in the whole range of observations. The other two models were mathematically simpler, but contained higher numbers of adjustable parameters. The reliability of the models was tested in three ways: (i) the models provided good fit for all experiments; (ii) the evaluation of a narrower subset of the experiments resulted in approximately the same parameters as the evaluation of the whole series of experiments; (iii) the models allowed accurate extrapolations to higher heating rates.

Nitrogen release is a little known aspect of pyrolysis of biomass. In this study on thermally thick samples of three biomass residues with high N-content, the NO x precursors NH 3 and HCN were measured with a Fourier transform infrared (FTIR) analyzer at different heating rates (low and high) and temperatures (400-900 °C). The feedstocks investigated have been given scarce or no attention. At a high heating rate, (1) NH 3 is the main N-compound with increasing yield with increasing temperature until reaching a plateau at 825-900 °C at a conversion level of 31-38%; (2) HCN release is increasing sharply with temperature to reach a conversion of 9-18%; (3) the (HCN + NH 3 ) conversion levels of all samples are close; (4) N-selectivity is affected by temperature and particle size; (5) release patterns and thermal behaviors of N and C are different and influence of fuel properties (intrinsic and physical) may be inferred; (6) the intricate structure of biomass indicates that decomposition paths may include (N-compounds + non-N-compounds) reactions. At a low heating rate, (1) NH 3 is the main N-compound; (2) HCN and NH 3 release are significantly different for the various fuels (7.9-19.2%) and fuel properties (intrinsic and physical) might be of importance; (3) the release pattern of N is affected by fuel properties.

Elevated pressure secures the highest fixed-carbon yields of charcoal from corncob. Operating at a pressure of 0.8 MPa, a flash-carbonization reactor realizes fixed-carbon yields that range from 70 to 85% of the theoretical thermochemical equilibrium value from Waimanalo corncob. The fixed-carbon yield is reduced to a range from 68 to 75% of the theoretical value when whole Waimanalo corncobs are carbonized under nitrogen at atmospheric pressure in an electrically heated muffle furnace. The lowest fixed-carbon yields are obtained by the standard proximate analysis procedure for biomass feedstocks; this yield falls in a range from 49 to 54% of the theoretical value. A round-robin study of corncob charcoal and fixed-carbon yields involving three different thermogravimetric analyzers (TGAs) revealed the impact of vapor-phase reactions on the formation of charcoal. Deep crucibles that limit the egress of volatiles from the pyrolyzing solid greatly enhance charcoal and fixed-carbon yields. Likewise, capped crucibles with pinholes increase the charcoal and fixed-carbon yields compared to values obtained from open crucibles. Large corncob particles offer much higher yields than small particles. These findings show that secondary reactions involving vapor-phase species (or nascent vapor-phase species) are at least as influential as primary reactions in the formation of charcoal. Our results offer considerable guidance to industry for its development of efficient biomass carbonization technologies. Size reduction handling of biomass (e.g., tub grinders and chippers), which can be a necessity in the field, significantly reduces the fixed-carbon yield of charcoal. Fluidized-bed and transport reactors, which require small particles and minimize the interaction of pyrolytic volatiles with solid charcoal, cannot realize high yields of charcoal from biomass. When a high yield of corncob charcoal is desired, whole corncobs should be carbonized at elevated pressure. Under these circumstances, carbonization is both efficient and quick.

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The prosperity of Silicon Valley is built upon a foundation of wood charcoal that is the preferred reductant for the manufacture of pure silicon from quartz. Because ordinary pyrolysis processes offer low yields of charcoal from wood, the production of silicon makes heavy demands on the forest resource. The goal of this paper is to identify process conditions that improve the yield of charcoal from wood. To realize this goal, we first calculate the theoretical fixed-carbon yield of charcoal by use of the elemental composition of the wood feedstock. Next, we examine the influence of particle size, sample size, and pressure on experimental values of the fixed-carbon yields of the charcoal products and compare these values with the calculated theoretical limiting values. The carbonization by thermogravimetric analysis of small samples of small particles of wood in open crucibles delivers the lowest fixed-carbon yields, closely followed by standard proximate analysis procedures that employ a closed crucible and realize somewhat improved yields. The fixed-carbon yields (as determined by thermogravimetry) improve as the sample size increases and as the particle size increases. Further gains are realized when pyrolysis occurs in a closed crucible that hinders the egress of volatiles. At atmospheric pressure, high fixed-carbon yields are obtained from 30 mm wood cubes heated in a closed retort under nitrogen within a muffle furnace. The highest fixed-carbon yields are realized at elevated pressure by the flash carbonization process. Even at elevated pressure, gains are realized when large particles are carbonized. These findings reveal the key role that secondary reactions, involving the interaction of vapor-phase pyrolysis species with the solid substrate, play in the formation of charcoal. Models of biomass pyrolysis, which do not account for the impacts of sample size, particle size, and pressure on the interactions of volatiles with the solid substrate, cannot predict the yield of charcoal from biomass. These findings also offer important practical guidance to industry. Size reduction of wood feedstocks is not only energy and capital intensive; size reduction also reduces the yield of charcoal and exacerbates demands made on the forest resource.