Assessment of densified fuel quality parameters: A case study for wheat straw pellet

An investigation was conducted to examine the impact of additive mixing with wheat straw (WS) for pellet making. This study manufactured seven types of pellets with different additive combinations to evaluate pellet quality characteristics and their relationships. A laboratory-type hammer mill and a pellet mill were used for feedstock preparation and pellet production. Experimental investigations showed that the lignin content increased from 7.0% to 13.1%, which was a primary need for pelletization. Also, the heating value rose from 17.02 to 20.36 MJ/kg. However, the ash content also increased from 7.09% to 16.2%. Results showed that dimension (length and diameter), durability, and tensile strength increased significantly with additives while the fines content decreased. The fines content had an inverse relationship with durability and strength. Wheat straw (60%), together with 10% sawdust (SD), 10% corn starch (CS), 10% bentonite clay (BC), and 10% biochar (BiC), was optimal with good pellet performance (T7). In addition, both the T5 pellets (70% WS, 10% SD, 10% BiC, and 10% BC) and  the T6 pellets (70% WS, 10% SD, 10% BiC, and 10% CS) provide suitable quality according to EN plus 2015 standard requirements. The ash content of produced pellet was higher than the recommended value, which suggests that further research onto the alternative additive use for ash reduction is needed.