Energy analysis of a flue gas hydrate-based desalination system with liquefied natural gas cold energy

Abstract

A three-stage flue gas hydrate-based desalination system was designed using liquefied natural gas (LNG) cold energy. This system could increase the CO₂ amount-of-substance fraction in the flue gas from 17 % to 97 % and produce desalinated water with a desalting rate of approximately 95 %. Four system operating plans were simulated as follows: CO₂ + N₂ + seawater at 0.6 MPa, CO₂ + N₂ + seawater at 3 MPa, CO₂ + N₂ + tetra-n-butyl ammonium bromide (TBAB) + seawater at 0.6 MPa, and CO₂ + N₂ + tetrahydrofuran (THF) + seawater at 0.6 MPa. The energy consumption, LNG cold energy consumption, energy loss, and environmental friendliness were calculated and analyzed. The compression energy consumption was the highest contributor to the total energy consumption, and the highest percentage of total energy loss was heat exchange loss. Reducing the formation pressure in the first stage effectively reduced the total energy consumption, LNG cold energy consumption, and energy loss by 21.28 %, 24.41 %, and 23.99 %, respectively. Addition of TBAB/THF reduced the total energy consumption, LNG cold energy consumption, and energy loss by 18.45 %/17.88 %, 32.30 %/32.73 %, and 24.65 %/23.54 %, respectively. The CO₂ + N₂ + seawater operation at 0.6 MPa did not produce pollution. The CO₂ + N₂ + seawater operation at 3 MPa had the highest total energy consumption and LNG cold energy consumption. Operation with TBAB/THF had obvious advantages in terms of total energy consumption but suffered from the generation of pollution. Comprehensive analysis indicated that the CO₂ + N₂ + seawater operation at 0.6 MPa was the optimum system.