Analysis of the Interactions between Moisture Evaporation and Exothermic Pyrolysis of Hazelnut Shells

Abstract

Packed-bed experiments are conducted to examine the effects of moisture evaporation on the global exothermicity of hazelnut shell pyrolysis. Percentages typically reached from ambient conditioning (9–12 wt %, dry basis) do not modify the features of the pyrolytic runaway, with respect to bone-dry samples, apart from the obvious temporal delay. In fact, consequent to moderate external heating, moisture evaporation and solid decomposition take place sequentially. Instead, higher moisture contents lower the display of the reaction exothermicity, owing to the simultaneous occurrence of the two processes at different spatial positions. The interaction between the two is also highly dependent upon the thermal severity of the external heating. Finally, induced humidification by wetting small-sized particles (versus steaming), applied to achieve moisture contents above those of ambient conditioning, modifies the sample chemical properties, thus giving only a qualitative valence to the measurements.

Role of the Potassium Chemical State in the Global Exothermicity of Wood Pyrolysis

“…As an example, these features can be well observed from the temporal profiles of the bed temperature recorded at various radial positions for raw wood and wood loaded with various contents of potassium acetate reported in Figure (Figure S3 provides a comparison for the same radial position). Moreover, from the qualitative point of view, the center bed heating dynamics still reproduce the same trends observed for various lignocellulosic fuels. − Two peaks separated by a valley in the temporal profile of the heating rate are observed. These, according to the corresponding temperatures, can be associated with the main pseudocomponent decomposition (Figure ).…”

“…Extensive experimental investigation − carried out for lignocellulosic fuels in the packed-bed configuration of this study clearly demonstrates that the main contribution in the exothermicity of the pyrolysis process originates from secondary reaction activity. The influence of char on the extent of secondary reactions has been examined in a number of studies.…”

“…The bench-scale pyrolysis experiments are conducted for a 16 g sample mass, consisting of 5 mm sized particles, by means of a cylindrical packed bed (40 mm diameter and length) instantaneously and uniformly heated along the lateral surface, as already described in detail elsewhere − and whose main features are summarized with the aid of a schematic in the Supporting Information. The thermal field (five thermocouples positioned at the median section starting from r = 0 mm (center) to 1.9 mm (subsurface)) and the yields of the lumped product classes and the gas composition are measured.…”

“…In this study, packed-bed pyrolysis experiments are carried with wood particles impregnated with variable percentages of potassium compounds (KOH, KCl, KC 2 H 3 O 2 , and K 2 CO 3 ) providing measurements of the thermal field, so as to evaluate the induced modification in the global exothermicity of the conversion process and the yields of the lumped classes of products. The reactor configuration consists of a cylindrical bed, uniformly heated along the lateral surface, which has been shown to be very effective for a clear display of the global thermal character of the reaction − and permits us to identify the conditions of pyrolytic runaway. This is the fast and uncontrolled conversion of the entire bed with very high temperature overshoots, with respect to the programmed value.…”

Impact of Wood Moisture in Charcoal Production and Quality

“…Furthermore, the carbonization of wood with such characteristics slows the furnace heating rate. The moisture evaporation rate depends on the heating rate of the pyrolysis, if this process is carried out with a low heating rate, the wood external surface degradation occurs, while water evaporation is still under way in the internal zones (Di Blasi et al, 2016). These simultaneous reactions can cause an increase in the pressure inside the cells, thus causing a rupture of the parenchyma cells of wood (Zeng et al, 2017).…”