*1.4. Objectives*

The overall goal of the project is to develop and demonstrate a state-of-the-art biomass merchandising and processing depot to identify and reduce sources of variation along the supply chain of two high-impact biomass species (i.e., pine and switchgrass), and to develop practices that manage biomass variability to deliver a consistent feedstock optimized for performance in a specific conversion-technology platform [5]. One way to manage the moisture and particle size variability is to densify the biomass. Many refineries are not ready to densify biomass, and the cost is a prohibitive factor. In this paper, new pelleting concepts, such as high-moisture pelleting, were tested on woody and herbaceous biomass blends, and the ability of this technology to efficiently manage the moisture in the blends was demonstrated.

Most of the pelleting work completed by earlier researchers has been focused on either woody or herbaceous biomass feedstocks. In addition, most of the reported literature on pelleting has been on the single pellet press. Harun and Afzal [45] worked on pelleting of agricultural and woody biomass blends in a single pellet press. These authors studied the effect of blending spruce and pine with reed canary grass, timothy hay, and switchgrass. Tumuluru et al. [9] and Harun and Afzal [45] indicated that pelleting agricultural biomass alone does not result in good pellet quality in terms of durability, which could be due to low lignin content in the agricultural biomass. In addition, low lignin content in the agricultural biomass results in higher energy consumption during the pelleting process.

The data on the pelleting blends of woody and herbaceous biomass at high moisture content (≥ 20%, w.b.) in a continuous flat die pellet mill are not available. Experimental data on how high moisture content, the compression (L/D) ratio in the pellet die, and the blend ratio of pine and switchgrass impact pellet quality and energy consumption of the pelleting process are also not available. The present study aims to understand the pelleting characteristics of pine + switchgrass blends at high moisture contents. The specific objectives of the present study are to: (1) understand how the L/D ratio in the pellet die in a flat die pellet mill and blend moisture content in the range of 20–30% (w.b.) impact the quality of pellets produced using the blends of 2-inch top pine residue + switchgrass at different ratios (i.e., 25:75; 50:50; and 75:25); (2) develop response surface models and surface plots to understand

the interactive effect of process variables on pellet quality and the specific energy consumption (SEC) of the process; and (3) optimize the response surface models to identify the process conditions that can minimize the pellet moisture content and maximize bulk density and the durability of blend pellets.
