Butane Gas Liquefaction Cycle Optimization Considering Compressor Technical Limitations

Natural gas is one of the cleanest sources of energy among all fossil fuel resources. The natural gas transfer from the extraction source to the consumption site often poses an expensive and challenging technical problem. In general for the transfer distances less than 4000 kilometers, pipe line is a suitable transfer method. But for longer distances, and places at sea or ocean, it is better to liquefy the natural gas and store it in reservoirs and transport it by ship. To liquefy the gas, its temperature needs to be reduced and considering the economic and safety limitations, the cooling process should be preferably carried out at atmospheric pressure. Therefore, refrigeration systems are required to do so. The required power for the refrigeration in liquefaction plants is notoriously high and contributes greatly in the cost of the final product, i.e. the liquefied natural gas. In this article, an industrial butane liquefaction unit is simplified and then simulated in the HYSYS software. After the validation of the HYSYS results, an optimization problem is defined and solved to minimize the power consumption of the refrigeration system. It is shown that the power consumption can be reduced about 31 percent in this particular case.