Stochastic state-space temperature regulation of biochar production. Part I: Theoretical development

BACKGROUND: The concept of a designer biochar that targets the improvement of a specific soil property imposes the need for production processes to generate biochars with both high consistency and quality. These important production parameters can be affected by variations in process temperature that must be taken into account when controlling the pyrolysis of agricultural residues such as manures and other feedstocks. RESULTS: A novel stochastic state-space temperature regulator was developed to accurately match biochar batch production to a defined temperature input schedule. This was accomplished by describing the system's state-space with five temperature variables - four directly measured and one change in temperature. Relationships were derived between the observed state and the desired, controlled state. When testing the unit at two different temperatures, the actual pyrolytic temperature was within 3 degrees C of the control with no overshoot. CONCLUSION: This state-space regulator simultaneously controlled the indirect heat source and sample temperature by employing difficult-to-measure variables such as temperature stability in the description of the pyrolysis system's state-space. These attributes make a state-space controller an optimum control scheme for the production of a predictable, repeatable designer biochar. Published 2011 by John Wiley & Sons, Ltd.