Exergy analysis and thermodynamic optimization of a bioenergy with carbon capture and storage gas power plant using Monte Carlo simulation of sewage sludge composition

• High exergy destruction in the combustion chamber is revealed. • Optimum ejector vacuum pressure found through sensitivity analysis. • Sewage sludge composition modeled with Monte Carlo simulation. • Simulated gas power plant tests different fuel compositions. • Methane fraction in syngas correlates positively with plant exergy efficiency. An exergy analysis is performed on the negative CO 2 emission gas power plant (nCO 2 PP), which integrates the fuel preparation, power generation and carbon capture process sections. The cycle is modeled in Aspen Plus coupled with REFPROP, combining deterministic and Monte Carlo stochastic approaches, the latter being a novelty in this work. In all cases studied, the simulations maintain the complex thermodynamic relationships. Exergy losses with areas of potential improvement are identified, while Monte Carlo simulation in Python generates sewage sludge composition, improving cycle realism. In the deterministic approach, the exergies are calculated for a single sewage sludge composition under ambient air conditions with relative humidity of 40 %, 50 % (base case) and 60 % and CO 2 air concentration of 375 ppm, 417 ppm (base case) and 1000 ppm, representing a worst case scenario of CO 2 increase until the year 2100. For the deterministic base case nCO 2 PP, the largest exergy losses are observed in the wet combustion chamber (127 kW, 62 % efficiency), gasification process (43 kW, 89 % efficiency), and water condensation in the gas scrubber (43 kW, 87 % efficiency), while the nCO 2 PP exergy efficiency, related to the chemical exergy of the sewage sludge, is 33.3 %. Sensitivity analysis on turbine vacuum and spray-ejector condenser suction pressure results in an increase of the nCO 2 PP efficiency by 0.3 % to 33.6 %. Monte Carlo results are incorporated into the Aspen Plus model after the base case optimization. These yield in a range of nCO 2 PP exergy efficiencies from 33.6 % to 39.7 % with a mean of 37.5 %.