Development of CO2 Tolerant LNG Production System
Authors: Lee JungHan , Jung Jeheon , Kim Kyeongmin 
Published: April 2012

During LNG liquefaction, CO2 component in natural gas has to be removedcompletely to prevent icing and plugging in the system. The CO2 removal systemmay be the most important part in gas treatment system. Acceptable CO2 level oftypical 50 ppm in feed gas is very stringent and hard to meet. H2O in feed gasis relatively easily removed by molecular sieve type dehydration system. However, CO2 removal system requires complicated amine contactor andregeneration system with substantial heat source. Especially in floatingenvironment operation, reducing CO2 level could be the most critical part ofthe FLNG availability, consequently, continuation of LNG liquefaction operationin severe weather condition may be determined by the CO2 removal capability, whereas the cryogenic liquefaction part may affect production performance only.DSME has developed highly efficient and CO2 tolerant LNG liquefaction systemcalled " Cluster LNG" with increased pressure liquefaction and associatedcontainment system. The developed system accepts approximately 1% of CO2 forthe liquefaction and related systems. The CO2 tolerant characteristics of theliquefaction process will provide multifold safety margin against CO2 problemsin cryogenic systems and valves. Moreover, when CO2 level is less than 1%, theCO2 removal system may be eliminated from the liquefaction plant. Extensiveverification tests of different CO2 contents in the developed process have beencarried out, and found that experimental results are well coincident withtheoretical expectations. In addition, CO2 removal system and related testshave been carried out. From the experiment, possibility of CO2 removal system(CO2 2 ~ 5%) other than traditional amine base system has been investigated andnew concept CO2 removal system is being developed. The non-conventional CO2removal system, which includes icing and solid removal with hydro-cyclone, isbeing tested in a bench scale pilot plant. The new CO2 removal system combinedwith increased pressure liquefaction process will bring competitiveness innatural gas liquefaction. The developed system may accelerate monetization ofstranded gas fields with low unit liquefaction and gas treatment cost.

1. Backgrounds

Lowering final delivery price to end-users would be important for businesssurvival in energy industry. To cope with the fundamental task, finding moreeconomic ways to transport gas from production sites to consumers have beenendeavored for many years. Among them, LNG is one of the efficient methods forlong distance and large volume gas transportation. But for the production ofLNG, stringent gas treatment, highly expensive liquefaction, transportation, and regasification systems have to be adequately prepared, which ultimatelyaffects the final gas delivery cost.

In order to produce LNG, CO2 level in feed gas has to be removed, typicallyless than 50 ppm, to prevent ice formation during liquefaction. However, theCO2 removal to such low level is necessary only for liquefaction interimpurpose considered that most of the gas consumers such as gas engines andboilers tolerate certain percentages of CO2, at least up to pipeline gasquality, in the feed gas. With the reason, if CO2 tolerant LNG productionsystem is developed, it would be equally acceptable.