Design of cascade refrigerant process utilizing CO2 and NH3 to remove volatile organic compounds

Abstract

Volatile Organic Compounds (VOC) are organic substances that evaporate from crude oil. About 0.08-0.15 % of the crude oil loaded into the ship is released as VOCs, which indicates that 50-200 tons of VOC are generated per loading. The recovery of VOCs generated by crude oil loading is essential to avoid any environmental issues. In this study, we developed the VOCs recovery process based on the selective condensation of VOCs. The process was modeled using Aspen HYSYS V10, and economic evaluation methods including CAPEX, OPEX, and benefits obtained by utilizing VOCs were conducted to analyze the economic effect of increasing the condensation temperature. Moreover, this system was optimized to increase the efficiency of the refrigerant cycle at a pre-determined condensation temperature based on an economic evaluation. We investigated carbon dioxide and ammonia, which is eco-friendly and can be used in ammonia-powered ships with on-board CCS system, to replace propylene refrigerant. COP (Coefficient of Performance) was optimized when modifying the design of the refrigerant process such as mixed refrigerant and cascade refrigeration. As a result, using a cascade refrigerant system with carbon dioxide and ammonia exhibits a higher process efficiency than that of the existing propylene refrigerant. Using the proposed cascade refrigerant system using carbon dioxide and ammonia will enable a more efficient and eco-friendly operation of the VOC recovery system