Comparison of methods for determining composition and energy content

A reli­able and low-main­te­nance alter­na­tive to con­ven­tion­al gas chro­matog­ra­phy (GC) evap­o­ra­tor sys­tems are ana­lyt­i­cal sys­tems based on Raman spec­troscopy, which are used in cus­tody trans­fer trans­ac­tions to mea­sure the com­po­si­tion and ener­gy con­tent of liq­ue­fied nat­ur­al gas. This is the con­clu­sion of a study con­duct­ed over sev­er­al years by the Euro­pean Gas Research Group (GERG) com­par­ing dif­fer­ent meth­ods. GERG rep­re­sents 33 mem­ber com­pa­nies and orga­ni­za­tions from 15 countries. 

“Raman spec­troscopy is just becom­ing of increas­ing inter­est world­wide when it comes to deter­min­ing the com­po­si­tion of LNG. As an ana­lyt­i­cal tech­nique, Raman is robust, effi­cient and at the same time eco­nom­i­cal. When it comes to crit­i­cal, cus­tody trans­fer trans­ac­tions, com­pa­nies can rely on our Raman instru­ments to ensure that their LNG mea­sure­ments are cor­rect and accu­rate. At the same time, main­te­nance require­ments are sig­nif­i­cant­ly reduced.” 

- John Schnake, Man­ag­ing Direc­tor and Cor­po­rate Direc­tor Process Analyzer

Contributing to the global energy transition

Glob­al efforts to reduce green­house gas emis­sions are ensur­ing that demand for liq­ue­fied nat­ur­al gas is grow­ing rapid­ly because large vol­umes of nat­ur­al gas can be trans­port­ed around the world so effi­cient­ly. In the process chain, the cus­tody trans­fer in sea and land trans­porta­tion is always a crit­i­cal step. At each of the con­trac­tu­al­ly defined han­dover points, fast and reli­able mea­sure­ment of the com­po­si­tion of liq­ue­fied nat­ur­al gas is cru­cial. Even the small­est dif­fer­ences in calorif­ic val­ue can change the val­ue of a car­go by a few hun­dred thou­sand euros. 

Certified and validated LNG data 

The goal of the eval­u­a­tion project was to val­i­date the per­for­mance of Raman tech­nol­o­gy in reli­ably, cor­rect­ly, and accu­rate­ly deter­min­ing the com­po­si­tion of LNG, as need­ed to cal­cu­late ener­gy con­tent dur­ing cus­tody trans­fer. As part of the mul­ti-year study, wide-rang­ing inves­ti­ga­tions were con­duct­ed at a trans­fer facil­i­ty at Fluxys LNG in Zee­brugge, Bel­gium, dur­ing base-load operation. 

Appro­pri­ate ref­er­ence sam­ples were pro­vid­ed to ensure that the data met the metro­log­i­cal require­ments for LNG appli­ca­tions. EffecTech, a lead­ing provider of inspec­tion, cal­i­bra­tion and test­ing ser­vices, was respon­si­ble for this. In each case, the mea­sure­ments were car­ried out direct­ly in the liq­uid phase. The Endress+Hauser Raman sys­tem used con­sist­ed of an Rxn-41 cryo­genic Raman probe con­nect­ed via fiber optics to a Raman ana­lyz­er opti­mized for LNG.

Reliable Raman measurements with lower operating costs 

The study report, enti­tled “Raman method for deter­mi­na­tion and mea­sure­ment of LNG com­po­si­tion,” which has since been pub­lished, con­cludes that Raman analy­sis sys­tems from Endress+Hauser offer com­pa­ra­ble mea­sure­ment uncer­tain­ty to tra­di­tion­al gas chro­matog­ra­phy-evap­o­ra­tor sys­tems, but with sig­nif­i­cant­ly low­er oper­at­ing costs and low­er tech­ni­cal exper­tise require­ments. Not only did the Raman sys­tem reduce the com­plex­i­ty of the LNG mon­i­tor­ing sys­tem, sta­bi­liza­tion times after sys­tem start­up were much shorter. 

In addi­tion, repeata­bil­i­ty was bet­ter, response to process changes was faster, and the sys­tem required no main­te­nance through­out the assess­ment peri­od. Sys­tem uptime exceed­ed 99%. These results show how valu­able the use of Endress+Hauser’s Raman mea­sure­ment tech­nol­o­gy can be, for field instal­la­tions at LNG base­load, satel­lite, and peak shav­ing sites, or for LNG load­ing sta­tions for tankers or gas tankers. 

“The results pre­sent­ed in the GERG study clear­ly demon­strate the val­ue of our Raman analy­sis port­fo­lio when it comes to cus­tody trans­fer of LNG. We are very pleased about this,” explains John Schnake. “We can offer fast and reli­able liq­uid phase mea­sure­ments at these impor­tant points in the LNG process chain. Our Raman sys­tems thus play an impor­tant role in the glob­al ener­gy tran­si­tion that is just pick­ing up speed.”