Design and Simulation of Natural Gas Liquid Recovery Process from Rich Natural Gas

Abstract

Natural gas plays a growing role in the energy mix by displacing coal due to its relative economic and/or environmental advantages A process of natural gas liquid (NGL) recovery utilizing internally generated energy to achieve energy efficiency was designed. The process utilizes heat generated from the compressor end of the turbo-expander to provide heat energy required to maintain the appropriate operating conditions at the intermediate and bottom sections of the demethanizer column, rather than utilizing dedicated steam generators that requires additional construction, installation, operations and maintenance cost. Simultaneously, the temperature of the hot residue gas is also dropped to the required range for export, rather than utilizing dedicated process gas coolers. The various unit operations such as heat exchangers, liquid separators, Joules Thompson Valve coefficient, demethanizer column, reflux condenser, and bottom reboiler were designed, and cost evaluation performed for each unit, while models were solved using MatLab software. The quality and composition of NGL and residue gas produced are consistent with industrial process plant data. In addition, condenser and reboiler showed that the heat removed from the condenser is 3.180.5kW and 1.65m 2 area was exchanged, while the heat for the reboiler is 474.5kW at 47.25m 2 exchanged area. Also, the temperature profile of the demethanizer column is not uniform as lower temperature is required for the rectifying section (cryogenic absorption). Thus, temperature of -90 o C to – 95 o C favours the production of sales gas as the top product stream, while a temperature range of 30 o C to 36 o C at the bottom favours the recovery of NGL product as the bottom stream. The height and diameter of demethanizer column for distillation and absorption sections are 28m and 1.55m and 7.24m and 3m respectively.