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SOLVENT CONVERSION OF THE GAS PURIFICATION SYSTEM AT THE BADAK NGL PLANT

RÜDIGER WELKER AND VOLKER SCHUDA BASF

Alemania

Presented at Venezuelan Gas Processors Association (AVPG)

XIV International Gas Convention May 10-12, 2000

Caracas, Venezuela

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AVPG, XIV Convención de Gas, Caracas, Mayo 10 al 12, 2000. Página 2

SOLVENT CONVERSION OF THE GAS PURIFICATION SYSTEM AT THE BADAK NGL PLANT

ABSTRACT PT Badak operate the world´s largest natural gas liquefaction plant in Kalimantan, Indonesia. The acid

gas removal process was originally employing Monoethanolamine [MEA] which has been encountered

with stress corrosion cracking. In the context of a capacity increase in 1989, MEA was replaced by a

formulated Methyldiethanolamine solution. The hopes placed in this solvent conversion, however,

have proven to be unfounded as the plant still suffered from severe corrosion: failures of major

equipment and the pipework caused numerous extra shutdowns and adversely effected plant safety.

Considering high on-stream times essential to economic production, a second conversion project is

being carried out between 1997 and 1999, comprising the solution swap in a total of eight acid gas

removal units to BASF aMDEA solvent. This paper will provide a detailed consideration of the solvent

conversion. The operational experiences gained with aMDEA and the previous solvent will be

compared, featuring results from solvent analyses, equipment inspection and plant reliability studies.

Plant records prove the complete eradication of earlier corrosion and scaling problems. Solvent

circulation rates have been reduced by 30 %, providing energy savings and operational freedom. The

selection of BASF aMDEA solvent has thus made a substantial contribution to both the reliability and

the economy of the Badak NGL plant.

Rüdiger Welker Volker Schuda

BASF Fax: +49 – 621 – 60 – 41398

Copyright BASF AG Ludwigshafen / Germany

January 2000

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1. INTRODUCTION In 1977 PT. Badak, a subsidiary of the Indonesian states oil & gas company Pertamina, started

production of LNG with two trains, each of 800,000 t/yr capacity. During the period 1982 to 1999, six

further trains were constructed. At the end of 1999, PT. Badak was operating the world’s largest

natural gas liquefaction plant, with an annual capacity of about 21 millions tons of LNG, one million

tons LPG Propane & Butane and one million tons of hydrocarbon condensate; the 9th train is presently

being designed.

2. PROCESS HISTORY OF THE ACID GAS REMOVAL UNIT AT PT. BADAK The PT. Badak LNG facilities utilize an amine based natural gas purification process in order to

achieve the specification of less than 50 ppm CO2 in the treated gas. The acid gas removal unit of all

trains comprises a single stage absorber, a high pressure flash-vessel and a stripper regenerator.

Both columns are equipped with bubble cap trays, the heat exchangers are either shell and tube or

plate and frame types. Fin-fan air coolers are used for most of the cooling duty of the lean amine

solvent.

Fig. 1: Process Flow Diagram of the Acid Gas Removal Unit at PT. Badak

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2.1 First solvent swap from MEA to a formulated MDEA

The original solvent in the trains A – D right from start -up was MonoEthanolAmine (MEA). Despite the

addition of corrosion inhibitors, major equipment was subject to severe corrosion and scale formation,

whichin turn caused foaming and solvent carry-over. Many leaks were caused by stress corrosion

cracking as a result of primary amine attack.

In the context of a capacity increase commencing 1990, a formulated MDEA solvent system replaced

the MEA solution consecutively in Trains A-D. The newer Trains E-G were directly commissioned with

this alternative solvent.

Understandably, the corrosivity of the solvent was investigated extensively. Following the swap,

solvent analyses showed no untoward heavy metal content in the solution for about two months.

Thereafter, a low concentration of heavy metals was observed and subsequently a steep increase of

the iron content in the solution took place.

Fig. 2: Increasing iron content during the operation of the former formulated MDEA-solvent

The iron content reached a level of 700 ppmw, representing an oversaturated solution, followed by a

slight reduction to about 250 ppmw as a result of precipitation of iron carbonate complexes. This

coincided with a considerable accumulation of heat stable salts. At this time, the formulated MDEA

became corrosive and abrasive. The operating conditions approached an equilibrium state of

continuous equipment corrosion on the one hand, and scaling of material surfaces with deposit layers

on the other hand. This required excessive defoamer dosage rates, which in turn enhanced the

formation of scale.

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Fig. 3: Scaling of tubes: The hot end bundles of the exchangers exhibited considerable scaling on

both the shellside (lean amine) but most severe on the tubeside (rich amine) causing

excessive pressure drop across the bundles.

Fig. 4: Example of two tubes of above shown heat exchanger

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All major equipment as well as large sections of the pipework were subject to severe corrosion attack.

The corrosion problems led to several unplanned shutdowns, and the need to repair or replace the

corroded equipment. This happened not only in the old trains A to D, but also in the new ones E, F

and G, which were never operated with the MEA solvent and which utilize much more stainless steel

equipment.

Fig. 5: Window patching in order to repair the flash drum

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Fig. 6: Leaking heat exchanger tube sheets after operating the former solvent for one year

The tubes of the lean solution air cooler also exhibited severe thinning and a great number leaked.

This proves the corrosive/abrasive nature of the former solvent as CO2 pitting corrosion attack can be

ruled out for a fully regenerated lean solution.

PT. Badak pursued a cost intensive reengineering option to overcome the corrosion problem, and

initiated a “material upgrade” program. Sections of the rich and lean solution piping were replaced by

stainless steel in order to cope with the erosion corrosion attack, in particular of elbows, flanges,

reducers/expanders. Heat exchanger bundles were upgraded from S.S. series 304 to series 316. The

regenerator columns of trains F, G and H were completely constructed from stainless steel. Plant

reengineering, however, was not successful, as Fig. 7 depicts the increase of the Chromium ion

content indicating corrosion of stainless steel material.

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Fig. 7: Increasing chromium -ion content in the former formulated solvent

The hopes placed in this first solvent change to a formulated MDEA proved to be unfounded, as the

unit still suffered from leaks due to corrosion and severe scaling, causing production losses and high

maintenance costs. Every remedy that PT. Badak tried to improve the plant operation was merely

“curing the symptoms”. Consequently a new approach to tackle the problems was sought.

3. SOLVENT SWAP In 1995 BASF proposed to PT. Badak the solvent conversion in the existing units to aMDEA. Two

years later, after a profound evaluation, PT. Badak decided to carry out a field test in one train. The

decision was mainly based on the records of over 100 aMDEA reference plants, many of which were

converted to solve operational problems with the former solution, and not a single aMDEA plant ever

being converted to another solvent.

The older Train C was chosen for the trial: A straight solvent swap without any plant modifications was

carried out in October 1997. In a rapid turnaround, the previous solvent was drained off, the unit

cleaned, filled with aMDEA-solution and re-started.

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3.1 Cleaning Procedure

The corroded equipment surfaces were washed off with a water jet. Corrosion cavities were then

hollow-ground and coated with an epoxy protection layer. The trays and the column base of the

absorber and stripper were covered with metal dust and residues and had to be cleaned with a

vacuum cleaner.

The heat exchanger tube bundles were removed and cleaned with a high pressure water jet. The

tubing at the hot end in the solvent heat exchangers was mostly replaced as the firm deposit layer

inside the tubes could not be removed. The outer surface of the tubes was covered with a greyish-

brown layer (mainly FeCO3) after cleaning, which could partly be removed.

The system was then flushed by circulating caustic solution, especially for the removal of grease,

corrosion and decomposition products, rust or other residues to minimize the impact of the operational

history on the aMDEA performance.

Afterwards, the whole unit was filled with condensate, heated up to about 90 °C and circulated for 6

hours. This procedure was repeated once more, with samples being taken to check for the absence of

residual suspensed particles in filtration tests. The condensate analysis after 6 hours circulation

showed no foam activity, no suspended particles and the samples had a clear colouration.

The aMDEA-premix was introduced into the system and diluted with water to an amine concentration

of 40 wt%. The solvent circulation was started and afterwards the feed gas throughput stepwise

increased until 110% of the former capacity was reached within 3 days. The CO2-slip was less than

10 ppmv at a 30% lower solvent circulation rate. That means an easy access to a capacity increase of

the existing unit or, in turn for a new plant, a more compact design with reduced CAPEX & OPEX.

4. BENEFITS OF THE SOLVENT SWAP TO aMDEA The swap to BASF aMDEA solvent in the world’s largest LNG plant may be the fastest solvent change

which has ever been carried out. Within two years the former solvent was exchanged in all 7 existing

trains while the 8th train was commissioned with aMDEA in October 1999.

PT. Badak carried out the conversion project completely and rapidly, because the improvements were

noticeable, even before a visual equipment inspection proved the eradication of corrosion and scaling.

The experience of about 2 years of operating aMDEA at PT. Badak can be summarized as follows:

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Benefits of the Solvent Swap

- no corrosion damage; iron content in the solution less than 10 ppmw; corrosion

rate measured from coupons lower than 0.1 mm per year.

- plant reliability increased by more than 10%

- solvent make-up 47 % lower

- steam consumption 20 % lower

- solvent circulation rate 30 % lower

Fig. 8: Benefits of the solvent swap

5. CONCLUSION PT. Badak declared the conversion to BASF’s aMDEA

® solvent a full success, as the plant reliability

was considerably increased while the maintenance costs decreased drastically. Earlier corrosion,

scaling and associated operational problems encountered with the former solvent were completely

eradicated which also contributes to plant safety.

This example shows the immense potential available in existing facilities to improve their profitability

and competitiveness, and the easy access of its utilization - i.e. just a straight solvent swap.

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