(642f) LPG and Ethane Combined Refrigeration Cycle and Offloading Process

As the operation on a process gas facility usually leads to the necessity of storage at low temperatures (e.g: storage of LPG and NGL at refrigerated tanks), the need of cooling utilities is a constant on process gas industry. Currently, the duty required for the cooling process on a plant is achieved by the utilization of a refrigeration cycle (common used utilities are: ethane and propane), those cycles are composed by four steps: compression, condensation of the compressed gas, isenthalpic expansion of the liquid (or isentropic when turbo-expander is applicable), and finally the evaporation of the fluid removing the required energy from the process system. However, as a process plant usually has more than one product that must be refrigerated before the storage, the usage of a refrigeration cycle with an utility may lead to a very large and expensive cycle, or even to the utilization of a cycle for each product, thus resulting in an economically unviable process. Therefore, it is needed to search for an alternative solution that is more economically attractive. A possible solution for this problem is to use one of the products in the refrigeration cycle, to provide the cooling requirement for the other products, and also for the product used on the cycle. As the cooling fluid needs to be stored, this refrigeration process is labelled as an open cycle, which means that the cooling fluid is meant to leave the process at some point on the cycle. This paper studies the applicability and the benefits of this process on a Gas processing plant, which produces Petrochemical ethane, Natural Gas (NG) and Liquefied Petroleum Gas (LPG). The LPG should be stored liquid at atmospheric pressure (which leads to a temperature of -40 °C), and the ethane should be stored liquid at 10 barg. It was used the ethane on an open refrigerated cycle, in order to achieve the storage requirement for both the LPG and the Petrochemical ethane.