dual mixed refrigerant process

Natural gas liquefaction processes require a lot of investment and operation costs and are part of the energy consuming industries. In this research, parameters such as refrigerant component, inlet and outlet pressure to compressors were optimized in dual mixed refrigerant system to reduce operating costs. The optimized system was then evaluated by exergy to obtain the amount of exergy loss in various components of the system, , Exergy efficiency of the entire cycle was obtained 41/63%, finding illustrate the highest exergy losses were in compressors, heat exchangers, after coolers and throttle valves, respectively. The reason is the high exergy loss in the compressors due to their low polytrophic efficiency. In the analysis of exergy it was found that the exergy loss in the main cycle heat exchanger is 4% higher than that of the pre-cooling cycle heat exchanger, reason is the high temperature difference in the input and output of the currents in the converter. Choosing the right heat exchanger can help reduce investment costs. For this purpose, analysis of the effect of the size of the heat exchanger on the specific power consumption was carried out, results showed that changes in the size of the heat exchanger near the optimum point on the power consumption of the cycle are low and increases with the distance from the optimum point of this effect. However, the main cycle curve will have a greater impact on the power consumption of the cycle due to its lower slope.

In this article, the leakage of the refrigerant in a two stage liquefaction system with multi component refrigerant is studied. Leakage is occurred due to various factors, including the existence of cavity in high pressure area and affects the performance of the process. Due to the absence of a specific method to handle leakage of refrigerant an innovative method is performed and validated by comparing experimental data. The results show the leakage at high-pressure points, causes a little reduction of specific work, but the product (liquefied natural gas) is significantly reduced. Additionally, it is shown that leakage increases the risk of temperature interference in heat exchangers, which should cause malfunctions in system operation.

In this study, the double stage mixed refrigerant LNG system is investigated, which is known for having the highest efficiency among the liquefaction cycles. The main purpose is to evaluate the performance double stage mixed refrigerant LNG system of point of view effect of variations the environmental and operating conditions of feed that has not been previously discussed. Such as variable environmental conditions during liquefaction processes, temperature, pressure and feed gas composition are. To view the response of the DMR liquefaction system to these changes, system which has been designed and implemented, was selected as the base case.The Results show that with decreasing temperature and increasing pressure feed natural gas, as an advantage, specific shaft work decreases and since in this case, minimum approach temperature in heat exchangers only slightly reduced than the allowed amount 3°C therefore with accepting a safety factor less (to insignificant amount) than the optimal case, can be used of this available advantage. Also, with increasing temperature and decreasing pressure of feed natural gas, while increasing the specific shaft work as well as temperature cross occurs in heat exchangers and means to from entering of the feed natural gas in the area prevented with special controls. Also, any changes in mole fraction of natural gas components make temperature cross in heat exchangers. And due to the change of the natural gas components mole percent, during the life of the well, should over time, the refrigerant composition in the cycle is optimized regarding to new conditions.