Studies on the use of biomass focus on its effectiveness in producing efficient and clean energy production. Using two treatments, this research tested the joint combustion of coal and biomass in a circulating fluidized type boiler (CFBB). The parameters tested are divided into technical evaluations, namely the performance of the generator and the emissions produced. In contrast, the cost evaluation is an economic study of the co-firing method. The application of co-firing at both plants produces a good efficiency level, as indicated by the generator performance and emissions, as shown by a reduction in SO2 emissions by -33.8% in plant A. The co-firing method in plant A produces a higher heating value. In contrast, plant B produces a higher level of energy consumption. In the environmental aspect, co-firing in the two plants under review produces better emissions using the co-firing method. Plant B’s emission efficiency level is better than that of plant A. With a decrease in CO of 77% in plant A. In terms of economy, adding biomass in the co-firing method shows a reduction in costs in plant A by 0.35% and an increase in the expenses in plant B.