Air Products and Chemicals
10:15 - 10:45
Thursday, 19 September 2019
T3.7 RESERVE: Controlling a Mixed Refrigerant Liquefaction Process to Improve Operations
Maximizing LNG production while minimizing power requirements are two key goals for LNG facilities. A patented enhanced control scheme has been developed and implemented that achieves these goals for mixed refrigerant liquefaction processes. This enhanced control scheme provides:
- independent control of both LNG production and LNG temperature
- stable turndown and turnup operation in response to demand changes due to loading and holding operations
- the ability to operate at maximum available power rather than fixed production, improving operation through diurnal fluctuations
Natural gas is liquefied and subcooled in the main cryogenic heat exchanger (MCHE). This is the “heart” of the liquefaction process. The temperature of the natural gas is lowered by over -120oC in the MCHE as it is converted to LNG. For large base load plants, the refrigeration to accomplish this is typically provided by a boiling mixed refrigerant exchanging heat with the natural gas in the MCHE. Properly and efficiently adjusting refrigerant conditions are critical to maximizing production while minimizing power requirements for the refrigeration circuit.
Automated adjustments to account for changes in operating conditions (e.g. while ship loading underway), feed composition, and ambient temperature significantly improve OPEX. The enhanced control scheme provides automated control to smoothly transition through these changes in a simple and efficient manner. It can be implemented on MCHEs in existing facilities as well as new facilities.
This paper will describe the development of the control scheme using dynamic simulation and discuss its successful implementation and current use in a baseload LNG plant.