6 - Tanker and gas carrier cargo pumps and systems

Abstract

Crude oil is delivered to refineries in large crude oil carriers, which may carry more than one grade. Refinery products are transported in smaller tankers, which may be used for a variety of cargoes. Before the advent of large tankers, reciprocating pumps were commonly installed for cargo discharge and tank draining. Centrifugal cargo pumps with a double-entry impeller have replaced reciprocating pumps in modem oil tankers. Control equipment is available for managing the loading and discharge of oil tankers, and instrumentation is used to monitor the state of the cargo. The risk of explosion or fire within the cargo tanks, pump rooms and other enclosed areas of an oil tanker are high because of hydrocarbon gases or vapors, which make explosive mixtures. Inert gas is delivered to the cargo tanks of crude oil tankers before the loading commences to purge the air content, and to maintain a slightly higher-than-atmospheric pressure and so exclude air during operations in cargo pumps. The antipollution regulations divide bulk liquid chemical cargoes into four categories (A, B, C, and D) and gives a general direction for discharge and tank washing. Each of these categories has been described in this chapter.