Class 2 (2nd Engineer) MEKG 📅 Jan 2017

Exam Question

With reference to the carriage and pumping of liquefied gas cargo:

(a) Sketch a suitable pumping system labeling the component parts

(b) State:

(i) Why submerged hydraulically driven pumps are not used; (ii) How overheating of pump drive shaft bearings is avoided;

Reference Answer

(a) A pumping system for liquefied gas cargo consists of a pump located at the bottom of each cargo tank. An electric motor, situated outside the deck hatch, drives the pump via a long shaft. The shaft housing also serves as a cargo riser, providing cooling and lubrication to the shaft guide bearings. An inducer improves the pump's suction characteristics. Guide vanes and diffuser vanes direct the flow and convert kinetic energy to pressure energy.
(b) (i) Submerged hydraulically driven pumps are unsuitable because the hydraulic oil may freeze at low cargo temperatures, suitable hydraulic fluids for these low temperatures are difficult to find, and leaks pose a risk of cargo contamination.
(ii) Overheating of the pump drive shaft bearings is prevented by using the shaft housing (which also acts as a cargo riser) to cool and lubricate the bearings.
(c) Fire and explosion risks in cargo tanks are mitigated by:

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