Dimensionamento de uma coluna de absorção para processamento de gás natural

Abstract

Cryogenic technologies for separations are widely used in natural gas processing. Among the traditional technologies, such as turbo-expansion, refrigerated lean oil absorption presents a high recovery capacity with a lower cost. Aiming to analyse the operational conditions and the sizing of an absorber column for this technology, a study was conducted in the commercial software Aspen Plus. To ensure a trustworthy modelling and simulation, a thermodynamic analysis of the models used to predict the particles interactions was performed. Among the tested models, Peng-Robinson was chosen. The column sizing was done for different solvent flowrates and different gas compositions, resulting in a column of 14 theorical stages, with a diameter of 1.3 m and a 7.0 m high. A solvent flowrate of 30 Nm²/h was selected to process a total natural gas flowrate of 1.42 MNm³/day. Both streams were cooled down until –20 ºC before feeding the column. The process had 67.0% of propane recovery, producing a sales gas with 90.4% methane, 7.1% ethane, 1.4% propane, and an inert content near 1%. After a sensitivity analysis, the column diameter was increased to 1.4 m, allowing the utilization of the equipment in a larger operational range. It was analysed the influence of the cooling temperature of the feed streams in the sales gas. Furthermore, it was evaluated the use of the sized equipment for processing of distinct natural gas compositions. Finally, a comparative study was done between the operation conditions needed to produce a natural gas with composition according to the commercialization range, and the conditions needed to produce a natural gas with low content of heavy hydrocarbons, specified for the use in ANG (adsorbed natural gas) technology.