Simulation of VOC Emission During Loading Operations in a Crude Oil Tanker

Abstract

“Volatile Organic Compounds” (VOCs) are known to contribute significantly to environmental pollution. Crude oil loading operations in a marine oil tanker produces a significant quantity of hydrocarbon (HC) vapours in the surrounding atmosphere. A large percentage of these HC vapour emission consists of ‘Volatile Organic Compounds’ (VOCs). This VOC emission has not been previously analysed in detail to understand health and environmental impact. The scope of the study reported in this paper demonstrates the use of chemical processing simulation software (Aspen HYSYS ®) to model and identify significant VOCs in this HC vapour emission during crude oil loading operations. The objective is to determine the detailed variation in the volume and the composition of the HC vapour emission and hence, VOCs, as the level in a ship's tank rises while being filled and the influence of crude oil temperature and pressure in the filled tank has on the extent of VOC emission. Total VOC emission per tonne of crude oil is calculated and compared with other similar field measurements. The analysis identifies the concentration of toxic VOCs in the hydrocarbon emission, as well as the liquid fraction lost in the loading operation. The simulation data is analysed for crude oil temperature between 10°C to 45°C and tank level from empty to 90% full. The resulting information is useful to assess the environmental and health impact and efficiency of the current crude oil loading operations. Potential to recover the monetary loss by increasing tank pressure and installation of the 'VOC Recovery Unit' is analysed.