Eco-efficient marine power system with cooled air ventilation by waste LNG cold energy for reefer holds in an ultra-large container ship

Abstract

This study investigates dissipated heat removal from the internal cargo holds of an ultra-large container ship utilizing an LNG waste cold source. The reefer containers in the cargo hold dissipate heat to maintain certain freight conditions. While the extracted air from the atmosphere absorbs cold energy during LNG vaporization, it prevents a temperature increase inside the cargo holds by supplying cooled air. Herein, the marine power system is an electric propulsion type with a combined gas turbine electric and steam system. The cooled-airflow-ventilation system linked to the power system is evaluated regarding energy and exergy flows and greenhouse gas emissions. Cooled-airflow-ventilation performs efficiently as its coefficient-of-performance becomes twice that of atmospheric-airflow-ventilation when the reefer container box temperature is above zero and heat dissipation is high. Moreover, cooled-airflow-ventilation reduces the maximum-continuous-rating and improves the exergy efficiency. LNG waste cold source utilization benefits the response to the enforced regulation of ship greenhouse gas emissions. However, a high atmospheric temperature makes dissipated heat removal difficult. Consequently, cold energy cannot be provided to all cargo holds. The lower the box temperature is; the more cargo holds that can utilize cold energy.