Exergoeconomic analysis and optimization of the Allam cycle with liquefied natural gas cold exergy utilization

Abstract

The Allam cycle is a promising oxy-fuel combustion power cycle with high electrical efficiency and near-zero carbon dioxide emissions. In this paper, the thermodynamic and exergoeconomic analyses are performed for a novel combined power and cooling oxy-fuel power cycle, which combines the Allam cycle with liquefied natural gas regasification process. Parametric study is conducted to investigate the effects of key cycle variables on the electrical and exergy efficiencies and total product unit cost of the proposed cycle. Multi-objective optimization is carried out to maximize the exergy efficiency and minimize the total product unit cost. The results show that Condenser 2 has the highest exergy destruction of 22.81 MW, followed by the combustor (22.72 MW). The combustor, Condenser 2 and gas turbine are the three most important components from exergoeconomic aspects. The introduction of adiabatic compression heat of the bypass stream has a positive impact on the system performance, especially when the outlet temperature of the combustor is low. The optimization results indicate that the exergy efficiency and the total product unit cost cannot reach the optimal values at the same time. The highest exergy efficiency of 50.31% and the lowest total product unit cost of 16.654 $/GJ are obtained respectively with different sets of cycle variables. In addition, the electrical efficiency of the optimized proposed cycle is up to around 65.7%, about 11 percentage points higher than that of the Allam cycle.