Exergy analysis of combined simultaneous Liquid Natural Gas vaporization and Adsorbed Natural Gas cooling

The liquefaction process of Natural Gas (NG) involves high energy consumption. Although this energy expenditure is partly offset by benefits in LNG transportation there is a need of improving the balance of the LNG process chain. Nowadays the cost of liquefaction of LNG oscillates between 0.45 and 0.55 kW h/kg when the thermodynamic minimum is 0.30 kW h/kg (assuming the composition is 100% methane). The proximity of these numbers means that the possibility of improving the liquefaction process is very limited. A different approach to the problem allows LNG as a source of exergy which can be utilized by combining LNG gasification with other processes to be considered. Such solutions can help optimize the economical balance of the overall LNG process chain. The paper proposes a novel idea of coupling the LNG regasification with the filling process of Adsorbed Natural Gas (ANG) tanks. Latent heat of LNG vaporization is directly used for the precooling of the ANG adsorption bed. This enables gas compressors to be avoided and improves the competitiveness of the ANG storage method which is an alternative to Compressed Natural Gas (CNG) storage and distribution. Exergy analysis presented in the article allows the proposed idea and conventional methods of Natural Gas regasification to be compared.