DCCD™ - A New Dual Column Cryogenic Distillation Technology for Natural Gas Sweetening: The Operations of a Laboratory Scale Pilot Plant

Abstract

This work presents the highlights of the results obtained from the operations of a laboratory-scale pilot plant, designed for the demonstration of an innovative gas sweetening technology. The theory behind the process, based on a dual-pressure cryogenic distillation, will be described and checked against the experimental results from the plant. Experimental test runs with different feed gas compositions have been carried out: mixtures with a variable content of CH4, CO2, C2 and C3 have been tested. The design of the distillation columns of the laboratory-scale experimental plant allowed to process feed gas with a CO2 content up to 50 mol%, while C2 and C3 content has been limited to few percentages, aiming to reproduce the situation of a lean gas composition. Data from the plant have been used to cross-check predictions of commercial process simulators (e.g. Aspen HYSYS® V10). The experimental results obtained from the laboratory-scale pilot plant allowed to successfully demonstrate the theoretical concept underlying the new dual-pressure cryogenic distillation technology. Adjusting the operating conditions of the pilot plant has allowed to treat gas mixtures with different contents of CH4, CO2, C2 and C3, and to study the effect of the operational parameters on the system. The presence of heavier hydrocarbons proved to be beneficial in avoiding solid CO2 formation, in accordance with available literature. The comparison between experimental data and predictions by commercial process simulators allowed to gather more information on the relevant thermodynamic framework, improving the overall degree of confidence in the models to be used during the design phase. The increasing natural gas demand challenges the industry to find new solutions for the profitable exploitation of natural gas fields with a higher than ever CO2 and H2S content. In this scenario, cryogenic distillation represents a cost-effective alternative to traditional sweetening technologies. The concept of the new technology has been demonstrated through the operations of a laboratory scale pilot plant, confirming its capability to produce sweet gas while avoiding CO2 solidification.