A comparative exergoeconomic analysis of two biomass and co-firing combined power plants

• Performances of external biomass combustion and co-firing combined cycles are evaluated using exergoeconomics.
• The unit cost of the product for the external biomass combustion cycle is lower than for the co-firing cycle.
• Energy and exergy efficiencies are maximized at particular pressure ratios.
• The combined co-firing cycle is found to be more efficient than the external biomass combustion cycle.

Biomass energy is a promising potential replacement for fossil fuels in future, because it is relatively abundant, clean and carbon dioxide neutral. Biomass can be converted using thermo-chemical and bio-chemical processes into solid, liquid and gas bio-fuels, which can then be used for generating heat and/or electricity. In the present work, the application of gasification for electricity production is investigated via energy, exergy and exergoeconomic analyses for two configurations: (1) externally fired biomass combined cycle, and (2) combined cycle with co-firing of biomass and natural gas. The second configuration is found to be more economic (on a large scale) as its relative cost difference and exergoeconomic factor are less than those for the first configuration. The results also indicate that the energy and exergy efficiencies of combined cycle with co-firing could be about 2% and 4% higher than those of the externally fired combined cycle, respectively. The energy and exergy efficiencies of both configurations are maximized at particular values of compressor pressure ratio, but higher pressure ratios lead to higher values of the total unit product cost in both configurations.