Risk-based shutdown management of LNG units

Global demand for natural gas may double by 2030, with Liquefied Natural Gas (LNG) growing perhaps fivefold - driven by continued cost reduction. Propane Pre-cooled Mixed Refrigerant (PPMR) of Air Products and Chemicals Inc. (APCI) currently holds 78% of the liquefaction plants on the market. Since the PPMR process has the largest production capacity, its operational reliability needs to be high as any failure may result in catastrophic consequences. Therefore, operational reliability has a key importance in LNG plants. To achieve an acceptable reliability, usually, a constant interval of a preventive maintenance method is used. The limitation of such a method is that the shutdown strategy is not optimum. This study focuses on determining a risk-based shutdown management strategy for APCI plants with capacity of 4.5 million tons per annum. To achieve the minimum risk for the expected life of an LNG plant, a combination of preventive maintenance, active redundancy and standby redundancy is considered. Results of this study reveal that such a combination can significantly reduce the operational risk. This combination improves the plant reliability and maintains it above a minimum operational reliability.