Energy efficient polymers for gas-liquid heat exchangers

The compression process necessary for the liquefaction of natural gas on offshore platforms generates large amounts of heat, usually dissipated via sea water cooled plate heat exchangers. To date, the corrosive nature of sea water has mandated the use of metals, such as titanium, as heat exchanger materials, which are costly in terms of life cycle energy expenditure. This study investigates the potential of a commercially available, thermally conductive polymer material, filled with carbon fibers to enhance thermal conductivity by an order of magnitude or more. The thermofluid characteristics of a prototype polymer seawater-methane heat exchanger that could be used in the liquefaction of natural gas on offshore platforms are evaluated based on the total coefficient of performance (COP_T), which incorporates the energy required to manufacture a heat exchanger along with the pumping power expended over the lifetime of the heat exchanger, and compared with those of conventional heat exchangers made of metallic materials. The heat exchanger fabricated from a low energy, low thermal conductivity polymer is found to perform as well as, or better than, exchangers fabricated from conventional materials, over its full lifecycle. The analysis suggests that a COP_T nearly double that of aluminum, and more than ten times that of titanium, could be achieved. Of the total lifetime energy use, 70% occurs in manufacturing for a thermally enhanced polymer heat exchanger compared with 97% and 85% for titanium and aluminum heat exchangers, respectively. The study demonstrates the potential of thermally enhanced polymer heat exchangers over conventional ones in terms of thermal performance and life cycle energy expenditure.