(140a) Ensuring Operability and Controllability of a Natural Gas Plant Using Dynamic Simulation

The natural gas industry has seen tremendous growth in recent years. Several new facilities to liquefy and export natural gas are under construction or have been started up recently. Some of these LNG facilities also have provisions to utilize the gas supply for domestic use. The reliable operation of these plants is important to ensure a steady supply of natural gas for domestic consumers. The analysis and enhancement of operability of a gas plant for domestic sales is discussed here.

Dynamic simulation was used to evaluate the operational response of an export gas plant for a range of transient upset scenarios. A high fidelity simulation model of the facility was built using actual equipment and piping information.  The scenarios studied included the sudden shutdown of the sales gas export compression system, ramp-down and ramp-up of plant capacity, sudden changes in inlet composition, and loss of inlet pressure. These cases were used to assess the response of pressure and flow controllers, to identify any operational concerns or abnormal flow conditions, and to analyze the plant’s ability to maintain the delivery pressure and specifications of the domestic sales gas.

When the export compressor is unexpectedly shut down, the loss of forward flow can result in significant disruptions in systems upstream of the compressor. Of particular concern is the buildup of pressure than can eventually lead to flaring or equipment damage. The results of the shutdown simulations demonstrated the potential for pressure build-up and flaring as well as the impact that the timing of the compressor start-up sequence can have on the severity and duration of flaring. In addition to the compressor shutdown scenarios, cases assessing the impact that variations in the feed flow rate, feed pressure, and feed compositions can have on the operability of the plant were investigated. The results of the transition simulations demonstrated that the rate of change in feed conditions can significantly impact the operation of the plant. The simulations were also used to identify specific controllers that were most significantly impacted by the transitions and to determine potential options for minimizing disruptions in plant operation.