Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/16/2011
Publication Date: 1/5/2012
Citation: Cantrell, K.B., Martin, J.H. 2012. Stochastic state-space temperature regulation of biochar production Part II: Application to manure processing via pyrolysis. Journal of the Science of Food and Agriculture. 92:490-495. Interpretive Summary: State-of-the-art control systems will be needed in pyrolysis production processes that will generate biochars with specific soil improving qualities. A new control system was developed for a non-continuous, laboratory-scale biochar production unit that accurately matched the desired pyrolysis input temperature to the actual biochar temperature. This control system was evaluated three times at 350°C and three times 700°C for its ability to generate biochar from swine manure with consistent composition, carbon structures, and combustion profile. When comparing biochars to the parent feedstock, the control system generated a 350°C with lower variation in carbon, hydrogen, nitrogen, and sulfur composition. For each temperature, the carbon structures across the three replications were near similar. These findings suggested the controller had the ability to pyrolyzed a feedstock and generate a consistent biochar.
Technical Abstract: 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°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.