(94c) Processes for High C2 Recovery from LNG –Part III: Simar Applied to Gas Processing

Expander technology has played an important role in the gas processing industry since the 1970's. This is particularly true in ethane (C2) recovery applications because the expander is an efficient way of generating refrigeration in low temperature regions. There are hundreds of patents in the open domain describing different processes with various claims. Just the quantity itself makes process selection anything but a straightforward task.

In our previous works on high C2 recovery from liquefied natural gas (LNG), a procedural definition of System Intrinsic Maximum Recovery (SIMAR) was provided. It has been demonstrated that without any constraints in the refrigeration supply, the maximum C2 recovery is capped by the physical configuration of the system, which includes an expander, sub-cooler, demethanizer (DeC1) column, and reflux streams.

This work extends SIMAR to gas processing where the supply of refrigeration is finite. The total compression work includes both residue gas compression and external refrigeration. The impacts on SIMAR by inlet gas pressure, composition, and the number of side-boilers of DeC1 are discussed. Also, installing heat pumps in the system is addressed separately because heat pumps change temperature distributions in the system.

It is shown that the total compression work is fairly independent of deviations from SIMAR operations. Therefore, given the conditions of an inlet gas, SIMAR serves as an expedient tool to establish the relations between C2 recovery and total compression work. Afterwards, the exact provision of external refrigeration can be determined based on other factors, such as economics.