A new torrefaction system employing spontaneous self-heating of livestock manure under elevated pressure

This report describes a new oxidative torrefaction method employing spontaneous self-heating of feed-stock as a means of overcoming practical difficulties in converting livestock manure to biochar. We examined the initiating temperature required to induce self-heating of wet dairy cattle manure under 1.0 MPa pressure and conducted elemental and calorific analyses of the solid products prepared at 200, 250, and 300C°. Self-heating was initiated with oxidation below 100C°, and the lower limit of the initiation temperature was between 85 and 90C°. Comparing processes performed at 0.1 and 1.0 MPa, the higher pressure promoted self-heating by both preventing heat loss due to moisture evaporation occurring at approximately 100C° and supplying oxygen to the high-moisture feedstock. In addition, as drying occurred at 160-170C° during the process, the system did not require pre- or post-drying. Although the heating values of the solid products decreased due to high ash content, the elemental composition of the products was altered to that of peat-like (200C°) and lignite-like (250 and 300C°) materials. Cessation of self-heating of the manure is recommended at approximately 250C° to avoid severe decomposition at higher temperatures. Overall, these results demonstrated the utility of the proposed method for converting wet manure into dried biochar through self-heating as well as potential applications in manure management systems. © 2019 The Authors. Published by Elsevier Ltd.