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 300 degrees C. Self-heating was initiated with oxidation below 100 degrees C, and the lower limit of the initiation temperature was between 85 and 90 degrees C. 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 100 degrees C and supplying oxygen to the high-moisture feedstock. In addition, as drying occurred at 160-170 degrees C 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 (200 degrees C) and lignite-like (250 and 300 degrees C) materials. Cessation of self-heating of the manure is recommended at approximately 250 degrees C 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. (C) 2018 Elsevier Ltd. All rights reserved.