(138g) A Step Change in LNG Operations through Advanced Process Control

Shell Global Solutions has been implementing and supporting Advanced Process Control (APC) projects in several LNG plants worldwide, including ones in Oman, Brunei, Malaysia, Nigeria, Indonesia and Australia. This presentation focuses on work carried out with some of the LNG producers. APC is a model based predictive tool that enables automatic online control of a total unit or LNG train. Within the oil and gas industry APC was firstly applied in refining but over the past decade, also has become widely recognized as a value-adding technology in LNG processing.

The production process in LNG plants is sensitive to a wide range of disturbances, notably, the variations in the air ambient temperature and feed conditions / composition. APC technology reacts constantly, and very quickly, by making automatically countless small changes to the process parameters. With such tight control, a process may be operated closer to its limits. In fact, APC continuously pushes the process against its constraints while keeping at the same time a proper distance of the safeguarding (trip) and relief settings which leads to financial rewards.

APC in LNG processing has been applied to a variety of units. Results noted are: ? 1 to 3% higher throughput, ? Higher efficiency, ? More LPG or NGL, ? Less flaring. APC stabilizes plant operations resulting in less upsets and higher plant availability. Also, operations between various shifts become more consistent. APC is flexible to different objectives e.g. under certain conditions LNG production is maximized where under other conditions efficiency is maximized.

The levels of benefits achieved depend on local conditions such as cooling-system type, compressor driver type and product prices. Gas-turbine-driven sites tend to enjoy higher benefits because of the strong impact of air ambient temperature on gas-turbine efficiency.

APC covers one whole LNG train including: ? liquefaction sections (main cryogenic heat exchangers [MCHE] and refrigerant loops) ? fractionators ? scrubber columns ? stabilisers

The paper covers recent developments to in the area of APC. Some case studies where the fuel gas balance is optimized and overall efficiency is further enhanced are described.