Exergoeconomic Evaluation of an Integrated Nitrogen Rejection Unit with LNG and NGL Co-Production Processes Based on the MFC and Absorbtion Refrigeration Systems

Natural gas is associated with nitrogen and heavy compounds. These heavy components in the natural gas not only can feed downstream units, owing to the low temperature process, but may be formed solid as well. Heavy components separation is a necessity and can they produce useful products. All natural gases contain nitrogen which lower theirheating value. Removing nitrogen from natural gas at a concentration of more than 4% is essential. Integration of the natural gas liquids (NGL), liquefied natural gas (LNG) and nitrogen rejection unit processes is an effective procedure which can reduce the required refrigeration. A new mixed fluid cascade natural gas liquefaction process is assessed here through the exergy and exergoeconomic analysis methods. One of the vapor compression cycles is replaced with a water-ammonia absorption refrigeration cycle. The results include cost of exergy, exergoeconomic factor, exergy and exergy efficiency. Results of exergoeconomic analysis indicates that the maximum exergoeconomic factor, 89.49%, is related to the HX8 in the water-ammonia absorption refrigeration cycle and the minimum exergoeconomic factor, 0.0026%, is related to the HX2 in the liquefaction cycle. In this process, the fourthcompressor has the highest exergy destruction cost of (5750307$/hr) and HX8 in the absorption refrigeration cycle has the lowest exergy destruction cost of (2.033 $/hr). Due to the high value of fuel cost in compressor, their exergy destruction cost is much higher than other devices.