Dynamics and products of potato crop residue conversion under a pyrolytic runaway regime - Influences of feedstock variability

Potato, ranked third among food crops, gives rise to huge amounts of plant residues largely unutilized owing to the presence of toxic compounds. The fundamentals of the pyrolytic runaway of these residues are investigated for a packed bed heated at a temperature of 570 K. The feedstock variability (five samples of different harvest year and cultivar), corresponding to variable average plant ageing, causes remarkable differences in the characteristic times (values between 6 and 42 s), heating rates (maxima between 5 and 155 K/s) and temperature overshoots (maxima between 220 and 410 K) of the runaway. On the other hand, the total gas and char yields are approximately the same (60–63 wt%), in consequence of the always fast and severe self-heating, also leading to evenly distributed and intense melting phenomena. The very high potassium contents (about 5–8 wt%) and a cellular structure with low porosity are the chief properties responsible for the significant exothermicity, resulting in intrinsically fast, in-situ catalyzed pyrolysis. The enhancement in the thermal severity of the pyrolytic runaway with longer plant ageing can be attributed to higher cellulose/starch contents, producing larger amounts of more reactive vapors, and thicker stem walls, confirming the key role of secondary reactions for the process.