ABSTRACT:

An underwater mining system with a crawler based mining machine and a flexible riser system has been conceptualised for manganese nodule mining. The flexible riser system with a single positive displacement pump mounted on the mining machine is different from the rigid riser concepts of the seventies where multiple pumps are mounted at different levels along the riser. The system has been tested for mining operations at 410 metres water depth. Four tests were carried out on this system in the Indian seas. The paper discusses the flexible riser concept, details of the tests carried out and results obtained. Specific details of pumping and maneuverability tests carried out are discussed. Based on results from the tests enhancements proposed for future deep sea mining systems are also discussed

INTRODUCTION

Deep sea mining of minerals like manganese nodules has been one of the challenging tasks facing ocean engineering. The nodules occur in the ocean floor at 5000 to 6000 metres depth. The mining machine / vehicle has to move on the ocean floor of very low bearing strength of the order of 50 g/cm2, encounter gradients and obstacles, and selectively mine nodules with minimum environmental disturbance. The entire system must be capable of being deployed and retrieved easily and be reliable, as underwater maintenance will almost be impossible. Most of the existing deep sea mining concepts are based on the tests carried out by various consortia active in the seventies (Chung, Whitney and Loden 1980; Brink and Chung, 1981; Chung, 1996). The systems had either a self propelled nodule collector (Chung 1996) or a towed collector (Heine and Sung, 1978) which collects and pumps nodules from the ocean floor to the lifting system, either directly or through an intermediate storage buffer unit.

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