Improvements in Nitrogen rejection Unit Performance with Changing Gas Compositions
Presented at the Annual Conference, Warsaw September 2005.
By Katarzyna CHolast & Andrzej Kociemba, KRIO, Odolanow, Harry Isalski Tractebel Gas Engineering and John Heath, Ebara International.
The KRIO Nitrogen Rejection Plant in Odolanów, Poland was constructed in the 1970s to upgrade a lean natural gas to pipeline specification and to produce liquid helium for sale. This plant has seen changes to the gas feed composition which necessitated modifications to it in order to continue economic performance and to reduce methane emissions. Several studies were undertaken to examine options for modifications that would satisfy environmental needs and changing market requirements. Whilst the feed gas became richer in methane, the needs to retain plant flexibility became more important.The paper describes the history of the plant, the changes that have occurred over its years of operation, the decisions taken to implement the modifications and the final configuration of the cryogenic part of the process. The paper also covers the initial start-up trials, the results and the final acceptance test data. The paper discusses the operational aspects of the facility and the benefits in having the main modifications in the selected locations.The paper describes the use of Variable Frequency Drive (VFD) of liquid methane pumps to improve cold production in the process as the first modification. Also covered is the subsequent installation of LNG expanders, now an important part of every new LNG liquefaction plant, where expansion of methane-rich, sub-cooled liquid enters the two-phase region. The paper reports the successful operational experience of two such turbine Expanders implemented in the nitrogen rejection unit revamps in order to improve their performance. The implementation of these 2-phase expanders heralds a new chapter in the use of expanders in the LNG and general cryogenic industry. This paper also serves to update the audience with results of a further years' operation of these turbines.
