Thermo-economic evaluation of cogeneration plants based on municipal solid waste gasification in the Brazilian scenario

Municipal Solid Waste (MSW) management is currently a worldwide challenge, which strongly emerges in highly populated countries, where landfilling is still the dominating option. The present work provides an energetic and thermo-economic evaluation of electric and cooling power cogeneration plants based on MSW energy recovery through gasification, in the Brazilian context. After the physical and chemical characterization of the available MSW, a Bubbling Fluidized Bed (BFB) gasifier is modeled and simulated using the software Aspen Plus 8 ®, in order to estimate the syngas composition. A thermodynamic equilibrium model with a Quasi-Equilibrium Temperature (QET) approach is adopted for simulating the gasification process; a sensitivity analysis is performed to verify the effect of the “steam-to-solid waste” (or “steam-to-feed”, S/F) ratio on Cold Gas Efficiency (CGE) of gasifier, Lower Heating Value (LHV) of syngas and Exergy Efficiency. Syngas energy recovery occurs by combustion coupled with a Rankine steam cycle in a cogeneration plant, which is simulated using a range of representative thermal input according to the pro-capita daily MSW generation. The electric power is produced through an extraction-condensation steam turbine, while the low-pressure steam is used in absorption chillers for chilled water production. Finally, a thermo-economic analysis is carried out in order to allocate the cost of the products using exergy-based cost partition criteria. Results show that the medium range of installable power is the most economically convenient, corresponding to thermal inputs between 30 and 150 MWth, being the major costs linked to the gasification section. The high cost of absorption chiller equipment strongly influences the chilled water unit cost, which results almost three times higher than the electricity one.