Performance analysis of a novel marine engine waste heat recovery system for combined power and cooling generation

The maritime industry’s pursuit of energy efficiency and emission reduction requires advanced waste heat recovery (WHR) systems. Shipping accounts for about 3 % of global greenhouse gas emissions, and marine engines release more than 50 % of fuel energy as exhaust heat. Although many studies have examined the Organic Rankine Cycle (ORC) and CO₂ cycles separately, integrated systems that combine power generation with cooling are still underdeveloped. This paper introduces a new combined power and cooling generation (CPCG) system that integrates multiple ORCs to use exhaust waste heat in marine applications, allowing concurrent electricity and refrigeration production with improved overall performance. A detailed thermodynamic model is created using Aspen HYSYS to simulate and optimize the system under real marine operating conditions. System performance is evaluated based on net power output, refrigeration capacity, the coefficient of performance (COP) of the refrigeration cycle, and energy/exergy efficiencies. Different working fluids, including synthetic refrigerants (R245fa, R1233zd(E), R1234yf, R1336mzz-Z) and hydrocarbons (n-butane, n-octane, toluene), are compared. Results show notable improvements, with a maximum net power output of 11.8 MW, a refrigeration capacity of 3.9 MW, a COP of 4.2, and energy and exergy efficiencies of 72.5 and 96 %, respectively. Under optimal conditions, energy efficiency reaches 76.07 %, with a COP of 5.2. Among the ORC working fluids studied, R-1233zd(E) is identified as the most sustainable and environmentally friendly, achieving 77 % energy efficiency. N-butane and other hydrocarbons achieve slightly higher efficiencies of 79 %, but they pose significant safety risks due to flammability. R-245fa is considered environmentally unsustainable. Although NOVEC-649 demonstrates high efficiency, its discontinuation limits its future relevance.