Methodology of exergy-based economic analysis incorporating safety investment cost for comparative evaluation in process plant design

This study proposes a new methodology of exergy-based economic analysis incorporating safety investment cost (SIC) for the comparative evaluation of process design alternatives for plants in terms of efficiency and economics while considering safety. Exergy-based economic analysis is employed to synthetically evaluate the design factors within the same framework. The SIC is estimated as the cost required to ensure the safety of the design by reducing accident risks to a level that is ‘as low as reasonably practicable’ (ALARP), which presents a rational approach to converting the risks associated with design alternatives into monetary values for economic analysis. The proposed method is applied to select the optimal working fluid in the Rankine cycle used in the recovery of both waste heat from a gas turbine and cold energy from liquefied natural gas (LNG) of the regasification process. The Rankine cycle, using ammonia, propane, and carbon dioxide as the working fluid, produces electric power of 11.7 MW, 8.9 MW, and 7.4 MW with specific exergy costs of 45.0 $/GJ, 61.9 $/GJ, and 77.8 $/GJ, respectively. Ammonia can be selected as the best alternative. The results are limited to quantitative risk assessment that does not consider domino effect and environmental damage. •Exergy-based economic analysis incorporating safety investment cost is proposed.•The method evaluates the design in terms of efficiency and economics while considering safety.•The SIC is used to convert the risks into monetary values considering the ALARP principle.•The accident risks associated with the design alternatives are quantitatively assessed.•The proposed methodology is demonstrated using the case of the Rankine cycle.