Data from: Role of ambient pressure in self-heating torrefaction of dairy cattle manure

This paper describes the role of ambient pressure in self-heating
torrefaction of livestock manure. We explored the initiating temperatures
required to cause self-heating of wet dairy cattle manure at different
ambient pressures (0.1, 0.4, 0.7, and 1.0 MPa). Then, we conducted
proximate, elemental, and calorific analyses of biochar torrefied at 210,
250, and 290 °C. The results showed that self-heating was induced at 155
°C or higher for 0.1 MPa and at 115 °C or lower for 0.4 MPa or higher. The
decrease of the initiating temperature at elevated pressure was due not
only to more oxygen, but also to the retention of moisture that can
promote chemical oxidation of manure. Biochar yields decreased with
increasing torrefaction temperature and pressure, and the yield difference
at 0.1 and 1.0 MPa was more substantial at lower temperatures: a 29.8,
16.4, and 9.4% difference at 210, 250, and 290 °C, respectively. Proximate
and elemental analyses showed that elevated pressure promotes
devolatilization, deoxygenation, and coalification compared to atmospheric
pressure; its impact, however, was less at higher temperatures as the
torrefaction temperature became more dominant. Calorific analysis revealed
that elevated pressure can increase the higher heating value (HHV) on a
dry and ash-free basis at 210 °C because of the increase in carbon
content, but its impact is limited at 250 and 290 °C. Meanwhile, the HHV
on a dry basis exhibited the opposite trend due primarily to an
enlargement of ash content. The present study revealed that ambient
pressure considerably affects the initiating temperature of self-heating
and the chemical properties of biochar at a low torrefaction temperature.