A multi-unit model for the biorefinery supply chain focusing on capacity planning for the processing units

Biomass to biofuel conversion is carried out using complex technologies, which are often capacity restricted. Although these restrictions are used to satisfy the design limitations of the processing units, they often lead to the selection of suboptimal choices for technologies to fulfil the demand. This article proposes a distributed multi-unit mixed integer linear programming model for a biorefinery supply chain capable of utilizing multiple technologies for each biomass. A single-unit superstructure from the literature is improved to accommodate decisions related to multiple technological choices for different biomass and extended to a multi-unit model by allowing the installation of more than one process unit of the selected technology. This study incorporates the investment and operational costs for processing facilities to demonstrate the long-term cost analysis of the supply chain. The efficacy of the proposed model is demonstrated in a distributed biorefinery case study involving industrial units known as secondary processing facilities, which fulfil their biofuel demand using onsite production and external processing facilities. The objective is to obtain an optimal production plan by minimizing the total cost while satisfying the demands of all users and other resource constraints. The optimal solution of the multi-unit model has reduced the total cost by 1.31%, compared to the single-unit model. A rigorous solution analysis of the single and multi-unit models is performed to validate the proposed model.