Simulation and modification of an Ethane-Ethylene separation Unit using vapor recompression heat Pump: Energy, Exergy, and economic analyses

Abstract

This paper presents a comprehensive analysis involving simulation and thermo-economic evaluation of thermal integration technology, specifically the vapor recompression method, applied to an existing ethane-ethylene distillation process. The study commences with the simulation of the current process, revealing a favorable level of accuracy as evidenced by the strong agreement between simulation outcomes and real plant data. The energy analysis highlights key parameters, with consumption rates of 0.4 kg of refrigerant per kg of vapor in the condenser and 0.743 kg of heating fluid per kg of liquid in the reboiler. Moving to the economic analysis, the total investment cost for the existing process is estimated at 16,925,333 USD. However, a noteworthy concern is the high refrigerant consumption in the condenser, leading to elevated operational costs within ethylene production facilities. Consequently, this study focuses on reducing refrigerant consumption and enhancing the thermodynamic efficiency of the ethane-ethylene distillation column. Simulation results for the proposed process demonstrate an investment cost of 968,837 USD, marking a 5.72 % reduction compared to the current process. The optimization process, driven by sensitivity analysis, determines the optimal outlet fluid pressure for the compressor, setting it at 3730 kPa. Under this optimized condition, refrigerant consumption for condensing the overhead vapors within the distillation column drops by a significant 34.29 % compared to the base case. From an energy perspective, the optimal Mechanical Vapor Recompression method leads to a substantial reduction in utility consumption, decreasing the rate for feed separation from 3.92 kg of utilities per kg of feed to 1.52 kg of utilities per kg of feed. This represents an impressive improvement in process efficiency. The exergy analysis reveals that the Joule-Thomson valve is the primary contributor to total exergy loss. Notably, the reboiler and distillation column's condenser exhibit significantly reduced exergy losses, 33.77 % and 39.05 % lower, respectively, compared to the base case. This emphasizes the positive impact of the proposed optimization on exergy efficiency.