Advantages of Submersible Motor Pumps in Deep-Sea Mining
Authors: Kuntz G. 
Published: December 2007

This paper discusses the application of submersible pumps with water-filled motors in deep-sea technology. A detailed description is given of the pumping system and the submersible motor pump which succeeded in delivering pumping system and the submersible motor pump which succeeded in delivering about 1,000 tons (907 Mg) of manganese nodules out of a depth of 16,404 ft. (5000 m).

Introduction

The submersible motor pump (SMP) owes its development to the demand for a pumping set capable of operating fully immersed in the liquid pumped with complete reliability and capable of pumped with complete reliability and capable of operating without any facility of easy accesse.g, for maintenance purposes.An important aspect in favor of the development of the SMP is the basic physical fact that the suction head of a pump operating in open circuit is limited by the barometric pressure. Because of these considerations, the principal fields of application of the SMP are (1) the winning of groundwater out of deep wells and (2) the drainage of mines because of the floodability of the SMP. During the last two decades, several entirely new fields of application have been found for the SMP in offshore and onshore technology:the pumping of hydrocarbons stored in underground caverns andvarious applications on drilling rigs and production platforms-e.g., as trim and ballast pumps, firelighting pumps (because of their readiness for instant start-up at all times), cooling water pumps, and bilge pumps.

SMP's made headline news in deep-sea technology at the beginning of 1978. After direct handling of about 1,000 tons (907 Mg) of manganese nodules out of a depth of more than 16,404 ft (5000 m), the most surprising feature was the almost total absence of abrasive wear in the pump. Before discussing this sensational development in greater detail, we will give a brief description of the design and construction of the SMP.

Description of the Design and Construction of the SMP

The main feature of the SMP is its slim outline which enables it to be installed in narrow and deep boreholes. Fig. 1 illustrates two SMP's in cross section, with the motor depicted in shortened form. Because of the relatively small diameter of the pump, in most cases it is necessary to provide a large number of stages (impellers and diffusers) to attain the required total head.Fig. 2 illustrates a double-entry SMP with its associated driver. In this case, the hydraulic axial thrust is balanced almost entirely, and the thrust bearing arranged at the bottom of the motor is required only to absorb the rotor weights. The submersible motor is coupled rigidly to the pump.There are three different basic types of motors in existence today.

Oil-Filled Submersible Motors. It is necessary for this type of motor to be fitted with a completely reliable and leakproof shaft seal. The dissipation of the waste heat generated by the motor (as a result of the relatively low thermal conductivity of oils) and thermal expansion present problems which require correspondingly expensive solutions. In addition, oil has the disadvantage of a higher fluid friction than water, but on the other hand it permits the use of antifriction bearings.

JPT

P. 2241