OTEC Advanced Composite Cold Water Pipe


A. Miller and M. Ascari – Technical Report submitted to DOE EERE Wind & Water Power Program, September, 2011

Abstract

Ocean Thermal Energy Conversion can exploit natural temperature gradients in the oceans to generate usable forms of energy (for example, cost-competitive baseload electricity in tropical regions such as Hawaii) free from fossil fuel consumption and global warming emissions.The No.1 acknowledged challenge of constructing an OTEC plant is the Cold Water Pipe (CWP), which draws cold water from 1000m depths up to the surface, to serve as the coolant for the OTEC Rankine cycle. For a commercial-scale plant, the CWP is on the order of 10m in diameter.This report describes work done by LMSSC developing the CWP for LM MS2 New Ventures emerging OTEC business. The work started in early 2008 deciding on the minimum-cost CWP architecture, materials, and fabrication process. In order to eliminate what in previous OTEC work had been a very large assembly/deployment risk, we took the innovative approach of building an integral CWP directly from theOTEC platform and down into the water. During the latter half of 2008, we proceeded to a successful small-scale Proof-of-Principles validation of the new fabrication process, at the Engineering Development Lab in Sunnyvale. During 2009-10, under the Cooperative Agreement with the US Dept. of Energy, we have now successfully validated key elements of the process and apparatus at a 4m diameter scale suitable for a future OTEC Pilot Plant. The validations include: (1) Assembly of sandwich core rings from pre-pultruded hollow ‘planks,’ holding final dimensions accurately; (2) Machine-based dispensing of overlapping strips of thick fiberglass fabric to form the lengthwise-continuous face sheets, holding accurate overlap dimensions; (3) Initial testing of the fabric architecture, showing that the overlap splices develop adequate mechanical strength (work done under a parallel US Naval Facilities Command program); and (4) Successful resin infusion/cure of 4m diameter workpieces, obtaining full wet-out and a non-discernable knitline between successive stepwise infusions.

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