Abstract
Low-grade coal, such as sub-bituminous, is characterized by low calorific value. In this context, combining coal (C) with coconut shell (CS) biomass can upgrade the quality. Therefore, this study aims to analyze the effect of feed ratio and carbonization temperature on improving the biobriquette quality. The processes included preparation, carbonization at 300°C and 400°C, variation in feed ratios, mixing, molding, and drying. Evaluation was conducted for proximate composition, calorific value, combustion rate, and thermal stability characteristics using Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA). The results showed that the biobriquette with 100CS contained 100% CS carbonized at 400°C. Furthermore, it had the best quality, with 5.05% moisture content, 1.83% ash content, 36.11% volatile matter, 57.01% fixed carbon, and a calorific value of 6,075 cal/g. These values met the Indonesian Ministry of Energy Regulation No. 47 of 2006. TGA–DTA analysis showed a total mass loss of 98–99% up to approximately 800°C, featuring the best thermal stability. Based on observation, 100% coconut shell (100CS) provided the best quality. This did not imply that hybrid composition was ineffective. For combustion performance tests, the highest combustion rate was recorded in a mixture of 50C: 50CS, namely 0.3005 g / min. The addition of coal to biomass briquettes aimed to improve combustion performance, specifically through increasing the combustion rate. This suggested that the briquettes are easier to ignite (easy ignition), and heat is generated more quickly. In conclusion, the mixture of coal and coconut shell is suitable for applications that require fast heating, such as cooking activities.