Cryogenic liquefaction and separation of CO2 using nitrogen removal unit cold energy

The paper presents the separation of liquid CO2 from flue gases produced by oxy-fuel combustion using a cryogenic method. The outlet N-2 stream from a nitrogen removal unit (NRU) is utilized as the cold source of the condenser in the CO2 liquefaction system. Due to the low temperature of the expanded nitrogen, no external refrigeration cycle is required. This heat integration allows resource consumption to be reduced and economized. The influence of selected process parameters (flue gas composition and operating pressures) on CO2 recovery was analyzed. In this process, 83.07% of CO2 with 99.17% purity is captured. The required energy for separation of the liquefied carbon dioxide is 0.125 kWh/kg CO2 (449 kJ/kg CO2). Cryogenic CO2 capture is often considered as an unrealistic CO2 capture technology due to expected high cooling costs. So far, the required cold duty for CO2 separation was obtained by integration with processes of LNG regasification or/and cryogenic air separation. This paper shows that the addition of a CO2 liquefaction and separation module to the cryogenic nitrogen removal processes for natural gas allows a significant reduction of energy consumption. Denitrogenation of natural gas is poorly described in literature and this work provides a comprehensive description of a NRU double columns system. Newly developed CO2 separation unit offers an unique opportunity to produce liquid CO2 at moderate conditions. An integration of both cryogenic processes is technically and economically advantageous. A hybrid NRU-CO2 capture installation is an innovative concept with commercial potential. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.