Pinch analysis approach to optimal planning of biochar-based carbon management networks

Abstract

Biochar offers a potentially scalable option for achieving negative carbon emissions. The photosynthetic fixation of atmospheric carbon into biomass, followed by carbonization of plant biomass into stable biochar which is then added to soil, results in a reversal of the normal flow of carbon from man-made systems. In addition, these systems can provide economic benefits, such as enhancement of soil quality for agriculture, or co-production of valuable goods (e.g., energy and chemicals) along with biochar. However, the amount of biochar that can be added to agricultural land without causing adverse effects is limited by impurities such as salts, heavy metals and dioxins, which can cause a decline in soil quality. Thus, allocation of biochar from different sources (i.e., pyrolysis plants) to different sinks (i.e., farms or plantations) can be framed as a source-sink optimizations problem. In process integration literature, such problems have been solved via mathematical programming, pinch analysis or allied techniques such as process graphs. In this work, a pinch analysis approach for planning biochar-based carbon management networks is proposed. This methodology provides an alternative or complementary approach that facilitates decision-making and interpretation through visually oriented graphical displays. A case study is solved to illustrate how system-wide carbon sequestration can be maximized, while still satisfying soil impurity limits.