Anti-Surge Methods for the Base Load LNG Plant Propane Compressor

The propane compressor represents a significant capital investment and operating expense of a LNG plant, and is an essential component in providing revenue streams of the plant. Therefore, operation and protection of the propane compressor are critical issues in the plant design and operation.

The propane compressor can operate under a wide range of conditions over the plant life cycle, especially during transient operations such as start-up, shutdown, restart and load variation. When the process condition changes, there is risk of surge where the compressor operates below its minimum stable flow, resulting in vibration and damage to the compressor and its components. Therefore, the propane compressor is required to have an anti-surge system for protection against surge.

The main difference between these methods is how the recycle stream is cooled. Different licensors/technology providers may provide different methods. This paper will summarize

• All the anti-surge methods which were used on some of the existing LNG plants. The LNG plants should be in operation or under the EPC stage, with the size varying from less than 3 to over 7 MMTPA. The driver should include GE's Frame 5, Frame 6, Frame 7, Frame 9 and the total motor driven case.
• Assessment and comparison of technical and economical benefits for different anti-surge methods,
• Indicating the advantages and disadvantages under the start-up, normal operation and trip scenarios.
• Assessment of any technical risk of using each method.