Superstructure optimization of thermal conversion based poultry litter valorization process

The optimal design and synthesis of the poultry litter valorization process is addressed in this paper. A superstructure, which consists of seven processing sections, is proposed for treating poultry litter. Nine thermal conversion technologies, five oil upgrading units, three hydrogen production options and two power generation alternatives are considered. Based on the proposed superstructure, a mixed integer nonlinear fractional programming (MINLFP)model is developed to maximize the return on investment (ROI)of waste valorization process. The solution strategies, including piecewise linear approximation and parametric reformulation, are employed to convert the original MINLFP problem into a computationally tractable mixed integer linear program. The results indicate that, at the production scale of 150 kt/yr, the fast pyrolysis based pathway has the highest value of ROI, followed by HTL, gasification and slow pyrolysis based pathways. A sensitivity analysis also shows that the diesel selling price causes the largest impact on the ROI of the fast pyrolysis, gasification and HTL based pathways, because selling diesel product contributes to a large proportion of total revenue. However, since the major product of slow pyrolysis based pathway is biochar, this pathway is more sensitive to the selling price of fertilizer. © 2019 Elsevier Ltd