
The low-rank coal is increasing every year but still slightly exploited by the industry, due to it being caused by the low-calorie value of the low-rank coal waste. Therefore, the mixture of other biomass is expected to raise the calorie value. This approach could potentially make the low-rank coal more economically viable for use in various industries, especially as a source of energy. Additionally, further research and development in this area could lead to more efficient and sustainable energy production methods. The study uses the Central Composite Design with ratio of low-rank coal waste and palm kernel shells of 40%: 60%, 60%: 40%, and 80%: 20% and variations of the glue starch (5 to 7%), which have been optimized and validated using the Response Surface Method approach. The results of the study showed volatile matter, fixed carbon, and calorie values of 61.43% to 71.69%, 16.56% to 26.98%, and 5190.44 to 6330.40 kcal/g, respectively. The results also demonstrated that the glue with 6% variation showed the highest fixed carbon content and calorie value in comparison to the other variations. The optimum of concentration of low-rank coal and palm kernel shell for co-firing of 80: 20% with 5% glue addition resulting in a volatile matter, fixed carbon, calorie value, flame capacity, flammability, of 54.41%, 33.39%, 6192.123 kcal/g, 14.12 min, and 0.052 g/min, respectively. The validation process also met the requirements for SNI 01-6235-2000 and SNI 8675-2018. Overall, the study concluded that the co-firing of low-rank coal waste and palm kernel shell with glue starch can result in an optimized fuel mixture with high performance characteristics. These findings are significant for industries looking to improve their energy efficiency and reduce emissions.