COMPARISON OF BASELOAD LIQUEFACTION …

1 1 COMPARISON OF BASELOADLIQUEFACTION PROCESSESCOMPARAISON DES PROCEDES DE LIQUEFACTIONDES USINES DE GRANDE VinkR. Klein NagelvoortShell International Oil Products, box 451, 2501 CMThe Hague, The NetherlandsABSTRACTThis paper summarises a recent COMPARISON of five BASELOAD LNG processes . Therange of technology encompasses the Propane/MR process, a Cascade process, a versionof the Dual Mixed Refrigerant process, a simple Single Mixed Refrigerant process and apre-cooled Nitrogen expansion process. Each process was assessed on the basis of specificcosts, specific power and fuel efficiency for a nominal 2 train LIQUEFACTION conclusions are: The Propane/MR process appears to be the best choice within the premises of thiscomparison study, viz.

2 Large capacity LNG trains, employing air cooling in a tropicalclimate. Other promising processes are the Dual Mixed Refrigerant process and theSingle Mixed refrigerant process. The Cascade process appears to be relatively expensive, partly disadvantaged as it is bythe study premises. Under colder conditions (arctic, water cooling), the costs andpower requirements come closer to the Propane/MR process. The pre-cooled Nitrogen Expansion process is not an economic choice for a largeonshore application. It may be an alternative for smaller scale offshore article r sume une r cente comparaison de cinq proc d s GNL de base.

3 Lagamme de technologies inclut le proc d propane/R frig rant M lang (RM), unproc d cascade, une version du proc d r frig rant double m lang , un proc d r frig rant unique m lang et un proc d expansion d azote pr -r froidi. Chaqueproc d a fait l objet d une valuation bas e sure les co ts sp cifiques, l nergie sp cifiqueet la rentabilit de carburant pour une usine de liqu faction de 2 cha nes 2 Les conclusions sont: Le proc d propane/RM s est r v l la meilleure alternative dans le cadre de l tudecomparative, c est-a-dire des cha nes de GNL de grande capacit , employant lerefroidissement par air sous un climat tropical.

4 Les autres proc d s prometteurs sont leproc d r frig rant double m lang et le proc d r frig rant unique m lang . Le proc d cascade se r v le relativement co teux, en partie d savantag comme telpar le cadre de l tude. Dans les conditions plus froides (zone arctiques,refroidissement par eau), les co ts et les besoins en nergie se rapprochent de ceux deproc d propane/RM. Le proc d expansion d azote pr -r froidi n est pas une alternative conomique pourune grande installation c ti re mais il peut l tre pour des installations offshore dedimensions plus 3 COMPARISON OF BASELOADLIQUEFACTION PROCESSESINTRODUCTIONThe LIQUEFACTION unit accounts for approximately 50 % of the total capital costs of 1-2billion US$ for a BASELOAD LNG plant.

5 The type of LIQUEFACTION process, in combinationwith the rotating equipment and ambient cooling system, affects the capacity andavailability of the entire LNG system so it is essential that the best process is world of BASELOAD LNG processes is dominated by the propane pre-cooled/mixedrefrigerant (C3/MR) process, introduced by Air Products and Chemicals, Inc. in the earlyseventies. Nearly 95 % of the word wide LNG production capacity is based on thisprocess in various forms, employing steam turbines, and gas turbines as compressordrivers and water and air cooling for heat rejection.

6 Over the years APCI was able toenlarge its spoolwound main cryogenic heat exchanger and to adopt the C3/MR processfor a wide range of conditions. Shell has further advanced the C3/MR process by theintroduction of large gas turbines/compressors, liquid expanders, air cooling, new gasscrubbing and Nitrogen rejection systems, etc., thus improving the competitiveness of theprocess. Unit sizes up to 4 MTPA are now recent upsurge in the LNG industry stimulates new developments and a revival ofold LNG processes , especially for use in smaller schemes, on floaters, concrete gravitystructures, barges, etc.

7 For instance, with the development of the Atlantic LNG project thePhillips optimised Cascade process has received renewed interest. Pritchard has alsoimproved the power efficiency of its Single Mixed Refrigerant (SMR) based PRICO process and now proposes it for applications onshore and offshore. A new developmentoriginating from LNG peak shaving is the Compact LNG or CLNG process developed byBHP Petroleum and Linde AG of Germany for an offshore application (Bayu-Undan in theTimor Sea). The CLNG process is based on a pre-cooled (chilled water) nitrogenrefrigeration system and it utilises a Linde spoolwound heat is therefore timely that a COMPARISON is conducted to assess the latest FOR COMPARISONA like-for-like COMPARISON of the different process is difficult to achieve in practicebecause the technical content is not available in the public domain.

8 Shell has thereforeconducted a comprehensive study comparing an optimised C3/MR process with the bestof four alternative processes , starting from basics and using the same conditions likecooling medium, feedgas, standards and cost basis. The processes are: The Propane/Mixed Refrigerant process The Cascade process A version of the Dual Mixed Refrigerant (DMR) 4 A version of the Single Mixed Refrigerant (SMR) process The pre-cooled Nitrogen Expansion is realised that for each of these processes several options exist in the configurationof the process that will influence the capacity and overall attractiveness.

9 This variationwithin a process results from the hardware selected and the particular gas turbine driversand cryogenic heat study focused on large LIQUEFACTION units with a capacity in the range of 3-4 MTPA, installed onshore in a tropical location. For each process an optimum capacity hasbeen assessed within this capacity range. Air cooling is used for heat rejection, minimisingpre-investments for water cooling differences in capacity, refrigerant make-up, power consumption, etc. of thevarious LIQUEFACTION units are also reflected in the fractionation and utility requirements.

10 Itwas therefore decided to extend the scope of the study to include all process facilities andrelated utilities in a combined LIQUEFACTION package. Each package consists of 2 completeLNG trains with a common fractionation/refrigerant make-up unit and utilities likeelectrical power, process heat, etc. Such a LIQUEFACTION package can be added to anexisting LNG plant or form the heart of a new LNG consistency of COMPARISON the LNG trains have a similar pre-treating line-up, aSulfinol (Shell licence) unit for acid gas removal, molecular sieve dryers, a mercuryremoval bed and a simple scrubbing system for removal of heavy hydrocarbons.