Reducing Weight, Footprint, and Capital Cost of Sulphate Removal Units Using Modified Membranes

Abstract

Membrane suppliers manufacture RO (Reverse Osmosis) and NF (Nano Filtration) in spiral wound elements, being 8" the most common element size. The spiral wound element was developed in 1970 to package RO and NF material into compact, efficient, and usable unit. Over the last decades, optimization of the manufacturing processes such as robotic glue lines and automated rolling of the elements, provided incremental improvements in the ability to pack more active membrane area in the same limited available volume defined by the length and diameter of the 8" element; but as the technology became mature, the room for further packing improvements vanished and spiral element configuration has reached an optimal plateau. Available membranes in the market have mainly been optimized up to two standard offerings: a) the higher surface of 440 ft2 per element using thinner feed spacer of 26-mil, or b) the thicker feed spacer of 34-mil having 400 ft2 per element. System designers decide on either of the optimizations depending on the feedwater and pretreatment quality, being the high surface of 440 ft2 elements reserved for "good" feedwaters. This optimal plateau drove the market at least over the last decade where all new models launched offer improvements in either rejection, permeability, fouling resistant or robustness. However, all these new products have not varied in packing density that remained unchanged. Thanks to innovation in materials science, a new generation of RO and NF elements has been developed using unique New Thin-membrane technology. This unique technology allows for significative improvement in the packing density, offering the possibility of taking advantage of the combination of both forementioned optimizations in the same membrane element, that is the high active surface area of 440 ft2 and the 34-mil feed spacer. Alternatively, the technology allows to keep the thinner 26-mil feed spacer but boosting the active membrane area up to 510 ft2 per membrane element. This new technology has already been marketed and since 2020, several systems have been in service with the new generation elements. In this paper we discuss the advantages of using the new generation elements as experienced in the replacement of older generation elements used for Sulphate Removal in FPSOs in Brazil and other regions.