Operating History of Arun Liquefied Natural Gas Plant
Authors: Oekon J.R. , Suyanto _ 
Published: December 2007

Introduction

The Arun liquefied natural gas (LNG) plant is located at Blang Lancang, North Aceh, Sumatra, Indonesia. It is about 15 km [9 miles] west of the port ofLhokseumawe and about 300 km [186 miles] northwest of the city of Medan. Theplant receives gas and unstabilized hydrocarbon condensate from the Arun fieldgas reservoir, which is about 30 km [19 miles] southeast of the plant. The gasand condensate are transported to the plant by pipeline (see Fig. 1 and Table1). Operation of the condensate recovery unit began in April 1977, and thethree LNG trains began producing LNG in Aug. 1978, Sept. 1978, and Feb. 1979.respectively. The original three-train plant now produces 34 000 m3/d [1.2million cu ft/D] LNG and 13 500 M3/d [85,000 B/D] condensate. Two additionalLNG trains began producing LNG in Oct. 1983 and Jan. 1984, respectively. All five trains produce a total of 55 000 m 3 /d [1.9 million cu ft/D] LNG and 18300 m'/d [ 1 15,000 B/D] condensate.

General Process Description

Figs. 2 and 3 illustrate the plant's processing system and the LNG trainflow scheme. Details of the major processing units follow.

Condensate Recovery Unit

The function of the condensate recovery unit is toremove liquid hydrocarbons from the gas as a stabilized condensate ready formarketing and to return the hydrocarbon gas to LNG producing units. The plantinlet streams are passed through the first-stage flash drum, which is operatedat 5378 kPa [780 psi] and 26 degrees C [78.8 degrees F]. Liquid from thefirst-stage flash drums is flashed at 2068 kPa [300 psi] in the second-stageflash drums. The liquid from second-stage flash drums is processed in areboiled stabilizer column at 1779 kPa 1258 psi] and heated to 260 degrees C[500 degrees F]. The stabilized psi] and heated to 260 degrees C [500 degreesF]. The stabilized condensate product is sent to storage ready for marketing. The separated vapor from the second-stage flash drums and the stabilizer columnis compressed through the feed gas booster compressor to 5378 kPa [780 psi] andcombined with the gas from the first-stage flash drums. The combined gas thenis routed to parallel-train gas treating and gas liquefaction units.

Gas Treating Unit

The gas first flows through mercury-removal vessels toreduce the mercury content from 300 mu g/std m3 [8–1 mu g/scf] to 0.1 mu g/stdM3 [2.7 × 10–3 mu g/scf] of gas. A sulfur-impregnated solid dessicant bed isused to remove mercury by adsorption and chemical reaction. A two-stageabsorption process uses potassium carbonate and diethanol amine to remove CO, and hydrogen sulfide (HS) from the gas stream. Each of the units was designedto process 319 000 std m 3 /h 1282 million scf/D] sour gas to produce 271 000std m3/h [240 million scf/D] sweet gas, not exceeding 100 PPM CO2 and 3.2 ppmHS, to feed the liquefaction unit. The gas flows through a packed column of hotpotassium carbonate absorber to remove CO, from the feed gas down to about 0.4%. The Las from the carbonate flows through a DEA absorber to remove CO, downto less than 100 ppm.

Gas Liquefaction Unit

The gas liquefaction unit receives sweet gas from thegas treating unit. Molsieve dryers are provided to remove moisture in the sweetgas down to 0.5 ppm maximum. The gas is cooled to - 10 degrees C [14 degrees F]and flows to the scrub tower, where the ethane and heavier hydrocarbons areremoved by fractionation. The bottom product is sent to the fractionation unit, which consists of a de-ethanizer, depropanizer, and debutanizer. The ethane andpropane production is for makeup to the multicomponent refrigerant (MCR)system. Excess product is injected to the liquefaction unit feed gas. Thebutane and heavier hydrocarbon production is injected to the condensate streamand sent to condensate storage. The overhead gas from the scrub tower flows tothe main heat exchanger (MHE), where the gas is liquefied by refrigeration. Theliquefied gas from the MHE is flashed through Joules-Thompson (JT) valves andfinally reaches - 159 degrees C [ –254.2 degrees F] in the product drum. Theflash from the product drum (about 10 % of inlet gas) is used for plant fuel. The LNG is sent to five storage tanks, each with 127 200-m3 [800,000-bbl]storage capacity. LNG loading transfer facilities include 11 LNG pumps. eachwith 2700-m3/h [16,982-bbl/hr] capacity.

Major Problems and Solutions

Amalgamation of Aluminum in the Cryogenic System. The Arun feed gas to theLNG train contains mercury up to about 300 g/std m3 [8.1 g/scf]. The originaldesign provided each processing train with a single bed of solid desiccantdesigned to remove all mercury from the gas. After operating about 1 year, freemercury was found in many places (e.g., the scrub tower bottom and LNG productpump). The liquid mercury can react with aluminum to form an amalgam.

JPT

P. 863